@article {pmid38534866, year = {2024}, author = {Gan, W and Zuo, Z and Zhuang, J and Bie, D and Xiang, J}, title = {Aerodynamic/Hydrodynamic Investigation of Water Cross-Over for a Bionic Unmanned Aquatic-Aerial Amphibious Vehicle.}, journal = {Biomimetics (Basel, Switzerland)}, volume = {9}, number = {3}, pages = {}, doi = {10.3390/biomimetics9030181}, pmid = {38534866}, issn = {2313-7673}, support = {U2141249, 11902018, and U2141252//National Natural Science Foundation of China/ ; }, abstract = {An aerodynamic/hydrodynamic investigation of water cross-over is performed for a bionic unmanned aquatic-aerial amphibious vehicle (bionic UAAV). According to flying fish features and UAAV flight requirements of water cross-over, the bionic conceptual design of crossing over water is described and planned in multiple stages and modes of motion. A solution procedure for the numerical simulation method, based on a modified SST turbulence model and the VOF model, is expressed, and a verification study is presented using a typical case. Longitudinal-lateral numerical simulation analysis investigates the cruise performance underwater and in the air. The numerical simulation and principal experiment verification are conducted for crossing over water and water surface acceleration. The results indicate that the bionic UAAV has an excellent aerodynamic/hydrodynamic performance and variant configuration to adapt to water cross-over. The bionic UAAV has good water and air navigation stability, and the cruise flying lift-drag ratio is greater than 15 at a low Reynolds number. Its pitching moment has the phenomenon of a "water mound" forming and breaking at the water cross-over process. The present method and the bionic variant configuration provide a feasible water cross-over design and analysis strategy for bionic UAAVs.}, } @article {pmid38518328, year = {2024}, author = {Zapata, F and Angriman, S and Ferran, A and Cobelli, P and Obligado, M and Mininni, PD}, title = {Turbulence Unsteadiness Drives Extreme Clustering.}, journal = {Physical review letters}, volume = {132}, number = {10}, pages = {104005}, doi = {10.1103/PhysRevLett.132.104005}, pmid = {38518328}, issn = {1079-7114}, abstract = {We show that the unsteadiness of turbulence has a drastic effect on turbulence parameters and in particle cluster formation. To this end we use direct numerical simulations of particle laden flows with a steady forcing that generates an unsteady large-scale flow. Particle clustering correlates with the instantaneous Taylor-based flow Reynolds number, and anticorrelates with its instantaneous turbulent energy dissipation constant. A dimensional argument for these correlations is presented. In natural flows, unsteadiness can result in extreme particle clustering, which is stronger than the clustering expected from averaged inertial turbulence effects.}, } @article {pmid38518311, year = {2024}, author = {Bandak, D and Mailybaev, AA and Eyink, GL and Goldenfeld, N}, title = {Spontaneous Stochasticity Amplifies Even Thermal Noise to the Largest Scales of Turbulence in a Few Eddy Turnover Times.}, journal = {Physical review letters}, volume = {132}, number = {10}, pages = {104002}, doi = {10.1103/PhysRevLett.132.104002}, pmid = {38518311}, issn = {1079-7114}, abstract = {How predictable are turbulent flows? Here, we use theoretical estimates and shell model simulations to argue that Eulerian spontaneous stochasticity, a manifestation of the nonuniqueness of the solutions to the Euler equation that is conjectured to occur in Navier-Stokes turbulence at high Reynolds numbers, leads to universal statistics at finite times, not just at infinite time as for standard chaos. These universal statistics are predictable, even though individual flow realizations are not. Any small-scale noise vanishing slowly enough with increasing Reynolds number can trigger spontaneous stochasticity, and here we show that thermal noise alone, in the absence of any larger disturbances, would suffice. If confirmed for Navier-Stokes turbulence, our findings would imply that intrinsic stochasticity of turbulent fluid motions at all scales can be triggered even by unavoidable molecular noise, with implications for modeling in engineering, climate, astrophysics, and cosmology.}, } @article {pmid38516562, year = {2023}, author = {Marschik, C and Roland, W}, title = {Correction factors for the drag and pressure flows of power-law fluids through rectangular ducts.}, journal = {Polymer engineering and science}, volume = {63}, number = {7}, pages = {2043-2058}, doi = {10.1002/pen.26344}, pmid = {38516562}, issn = {1548-2634}, abstract = {There are many industrial examples of low Reynolds number non-Newtonian flows through rectangular ducts in polymer processing. They occur in all types of manufacturing processes in which raw polymeric materials are converted into products, ranging from screw extrusion to shaping operations in dies and molds. In addition, they are found in numerous rheological measurement systems. The literature provides various mathematical formulations for non-Newtonian flows through rectangular ducts, but-if not simplified further-their solution usually requires use of numerical techniques. Removing the need for these time-consuming techniques, we present novel analytical correction factors for the drag and pressure flows of power-law fluids in rectangular flow channels. We approximated numerical results for a fully developed flow under isothermal conditions using symbolic regression based on genetic programming. The correction factors can be applied to the analytical theory that describes the flow of power-law fluids between parallel plates to include effects of the side walls in the prediction of flow rate and viscous dissipation.}, } @article {pmid38509923, year = {2024}, author = {Iqra, T and Nadeem, S and Ghazwani, HA and Duraihem, FZ and Alzabut, J}, title = {Instability analysis for MHD boundary layer flow of nanofluid over a rotating disk with anisotropic and isotropic roughness.}, journal = {Heliyon}, volume = {10}, number = {6}, pages = {e26779}, pmid = {38509923}, issn = {2405-8440}, abstract = {The study focuses on the instability of local linear convective flow in an incompressible boundary layer caused by a rough rotating disk in a steady MHD flow of viscous nanofluid. Miklavčič and Wang's (Miklavčič and Wang, 2004) [9] MW roughness model are utilized in the presence of MHD of Cu-water nanofluid with enforcement of axial flows. This study will investigate the instability characteristics with the MHD boundary layer flow of nanofluid over a rotating disk and incorporate the effects of axial flow with anisotropic and isotropic surface roughness. The resulting ordinary differential equations (ODEs) are obtained by using von Kàrmàn (Kármán, 1921) [3] similarity transformation on partial differential equations (PDEs). Subsequently, numerical solutions are obtained using the shooting method, specifically the Runge-Kutta technique. Steady-flow profiles for MHD and volume fractions of nanoparticles are analyzed by the partial-slip conditions with surface roughness. Convective instability for stationary modes and neutral stability curves are also obtained and investigated by the formulation of linear stability equations with the MHD of nanofluid. Linear convective growth rates are utilized to analyze the stability of magnetic fields and nanoparticles and to confirm the outcomes of this analysis. Stationary disturbances are also considered in the energy analysis. The investigation indicates the correlation between instability modes Type I and Type II, in the presence of MHD, nanoparticles, and the growth rates of the critical Reynolds number. An integral energy equation enhances comprehension of the fundamental physical mechanisms. The factors contributing to convective instability in the system are clarified using this approach.}, } @article {pmid38509193, year = {2024}, author = {Rehman, N and Mahmood, R and Majeed, AH and Khan, I and Mohamed, A}, title = {Multigrid simulations of non-Newtonian fluid flow and heat transfer in a ventilated square cavity with mixed convection and baffles.}, journal = {Scientific reports}, volume = {14}, number = {1}, pages = {6694}, pmid = {38509193}, issn = {2045-2322}, abstract = {The impact of baffles on a convective heat transfer of a non-Newtonian fluid is experimentally studied within a square cavity. The non-Newtonian fluid is pumped into the cavity through the inlet and subsequently departs from the cavity via the outlet. Given the inherent non-linearity of the model, a numerical technique has been selected as the method for obtaining the outcomes. Primarily, the governing equations within the two-dimensional domain have been discretized using the finite element method. For approximating velocity and pressure, we have employed the reliable P 2 - P 1 finite element pair, while for temperature, we have opted for the quadratic basis. To enhance convergence speed and accuracy, we employ the powerful multigrid approach. This study investigates how key parameters like Richardson number (Ri), Reynolds number (Re), and baffle gap b g influence heat transfer within a cavity comprising a non-Newtonian fluid. The baffle gap (b g) has been systematically altered within the range of 0.2-0.6, and for this research, three distinct power law indices have been selected namely: 0.5, 1.0, and 1.5. The primary outcomes of the investigation are illustrated through velocity profiles, streamlines, and isotherm visualizations. Furthermore, the study includes the computation of the Nu avg (average Nusselt number) across a range of parameter values. As the Richardson number (Ri) increases, Nu avg also rises, indicating that an increase in Ri results in augmented average heat transfer. Making the space between the baffles wider makes heat flow more intense. This, in turn, heats up more fluid within the cavity.}, } @article {pmid38502909, year = {2024}, author = {Cao, Y and Liu, X and Zhang, L and Wu, Y and You, C and Li, H and Duan, H and Huang, J and Lv, P}, title = {Water Impalement Resistance and Drag Reduction of the Superhydrophobic Surface with Hydrophilic Strips.}, journal = {ACS applied materials & interfaces}, volume = {}, number = {}, pages = {}, doi = {10.1021/acsami.3c18905}, pmid = {38502909}, issn = {1944-8252}, abstract = {Superhydrophobic surfaces (SHS) offer versatile applications by trapping an air layer within microstructures, while water jet impact can destabilize this air layer and deactivate the functions of the SHS. The current work presents for the first time that introducing parallel hydrophilic strips to SHS (SHS-s) can simultaneously improve both water impalement resistance and drag reduction (DR). Compared with SHS, SHS-s demonstrates a 125% increase in the enduring time against the impact of water jet with velocity of 11.9 m/s and a 97% improvement in DR at a Reynolds number of 1.4 × 10[4]. The key mechanism lies in the enhanced stability of the air layer due to air confinement by the adjacent three-phase contact lines. These lines not only impede air drainage through the surface microstructures during water jet impact, entrapping the air layer to resist water impalement, but also prevent air floating up due to buoyancy in Taylor-Couette flow, ensuring an even spread of the air layer all over the rotor, boosting DR. Moreover, failure modes of SHS under water jet impact are revealed to be related to air layer decay and surface structure destruction. This mass-producible structured surface holds the potential for widespread use in DR for hulls, autonomous underwater vehicles, and submarines.}, } @article {pmid38501605, year = {2024}, author = {Mattusch, AM and Schaldach, G and Bartsch, J and Thommes, M}, title = {Intrinsic dissolution rate modeling for the pharmacopoeia apparatus rotating disk compared to flow channel method.}, journal = {Pharmaceutical development and technology}, volume = {}, number = {}, pages = {1-10}, doi = {10.1080/10837450.2024.2329115}, pmid = {38501605}, issn = {1097-9867}, abstract = {For a solid understanding of drug characteristics, in vitro measurement of the intrinsic dissolution rate is important. Hydrodynamics are often emphasized as the decisive parameter influencing the dissolution. In this study, experiments and computational fluid dynamic (CFD) simulations showed that the mixing behavior in the rotating disc apparatus causes an inhomogeneous flow field and a systematic error in the calculation of the intrinsic dissolution rate. This error is affected by both the experimental time and the velocity. Due to the rotational movement around the tablet center, commonly utilized in pharmacopeia methods, a broad variance is present with regard to the impact of fluid velocity on individual particles of the specimen surface. As this is significantly reduced in the case of uniform overflow, the flow channel is recommended for investigating the dissolution behavior. It is shown that rotating disc measurements can be compared with flow channel measurements after adjusting the measured data for the rotating disc based on a proposed, representative Reynolds number and a suggested apparatus-dependent correction factor. Additionally, modeling the apparatus-independent intrinsic dissolution rate for different temperatures in the rotating disc apparatus is possible using the adapted Levich's equation.}, } @article {pmid38493264, year = {2024}, author = {Mwapinga, A}, title = {Mathematical formulation and computation of the dynamics of blood flow, heat and mass transfer during MRI scanning.}, journal = {Scientific reports}, volume = {14}, number = {1}, pages = {6364}, pmid = {38493264}, issn = {2045-2322}, abstract = {Computational modeling of arterial blood flow, heat and mass transfer during MRI scanning is studied. The flow is assumed to be unsteady, in-compressible, and asymmetric. Mathematical formulation considers the presence of stenosis, joule heating viscous dissipation and chemical reaction. The explicit finite difference scheme is used to numerically solve the model equations. The MATLAB software was used to plot the graphical results. The study reveals that, during MRI scanning, both radial and axial velocities diminish with increase in the strength of magnetic fields. Besides, the study found that, Eckert number and Hartman number enhance the blood's temperature and the same, diminishes with increase in Prandtl and Reynolds numbers. Concentration profile is observed to decline with increase in chemical reaction parameter, Schmidt number and Reynolds number. Soret number on the other hand, is observed to positively influence the concentration.}, } @article {pmid38467620, year = {2024}, author = {Labonte, D and Bishop, PJ and Dick, TJM and Clemente, CJ}, title = {Dynamic similarity and the peculiar allometry of maximum running speed.}, journal = {Nature communications}, volume = {15}, number = {1}, pages = {2181}, pmid = {38467620}, issn = {2041-1723}, support = {851705//EC | EU Framework Programme for Research and Innovation H2020 | H2020 Priority Excellent Science | H2020 European Research Council (H2020 Excellent Science - European Research Council)/ ; RGY0073/2020//Human Frontier Science Program (HFSP)/ ; }, abstract = {Animal performance fundamentally influences behaviour, ecology, and evolution. It typically varies monotonously with size. A notable exception is maximum running speed; the fastest animals are of intermediate size. Here we show that this peculiar allometry results from the competition between two musculoskeletal constraints: the kinetic energy capacity, which dominates in small animals, and the work capacity, which reigns supreme in large animals. The ratio of both capacities defines the physiological similarity index Γ, a dimensionless number akin to the Reynolds number in fluid mechanics. The scaling of Γ indicates a transition from a dominance of muscle forces to a dominance of inertial forces as animals grow in size; its magnitude defines conditions of "dynamic similarity" that enable comparison and estimates of locomotor performance across extant and extinct animals; and the physical parameters that define it highlight opportunities for adaptations in musculoskeletal "design" that depart from the eternal null hypothesis of geometric similarity. The physiological similarity index challenges the Froude number as prevailing dynamic similarity condition, reveals that the differential growth of muscle and weight forces central to classic scaling theory is of secondary importance for the majority of terrestrial animals, and suggests avenues for comparative analyses of locomotor systems.}, } @article {pmid38464493, year = {2024}, author = {Golmirzaee, N and Wood, DH}, title = {Some effects of domain size and boundary conditions on the accuracy of airfoil simulations.}, journal = {Advances in aerodynamics}, volume = {6}, number = {1}, pages = {7}, pmid = {38464493}, issn = {2524-6992}, abstract = {This paper investigates a specific case of one of the most popular fluid dynamic simulations, the incompressible flow around an airfoil (NACA 0012 here) at a high Reynolds number (6×106). OpenFOAM software was used to study the effect of domain size and four common choices of boundary conditions on airfoil lift, drag, surface friction, and pressure. We also examine the relation between boundary conditions and the velocity, pressure, and vorticity distributions throughout the domain. In addition to the common boundary conditions, we implement the "point vortex" boundary condition that was introduced many years ago but is now rarely used. We also applied the point vortex condition for the outlet pressure instead of using the traditional Neumann condition. With the airfoil generating significant lift at incidence angles of 5∘,10∘, and 14∘, we confirm a previous finding that the boundary conditions combine with domain size to produce an induced (pressure) drag. The change in the pressure drag with domain size is significant for the commonly-used boundary conditions but is much smaller for the point vortex alternative. The point vortex boundary condition increases the execution time, but this is more than offset by the reduction in domain size needed to achieve a specified accuracy in the lift and drag. This study also estimates the error in total drag and lift due to domain size and shows it can be almost eliminated using the point vortex boundary condition. We also used the impulse form of the momentum equations to study the relation between drag and lift and spurious vorticity, which is generated as a result of using non-exact boundary conditions. These equations reveal that the spurious vorticity throughout the domain is associated with cancelling circulation around the domain boundaries.}, } @article {pmid38463765, year = {2024}, author = {Uddin, MN and Hoque, KE and Billah, MM}, title = {The impact of multiple stenosis and aneurysms on arterial diseases: A cardiovascular study.}, journal = {Heliyon}, volume = {10}, number = {5}, pages = {e26889}, pmid = {38463765}, issn = {2405-8440}, abstract = {The comparative effect of serial stenosis and aneurysms arteries on blood flow is examined to identify atherosclerotic diseases. The finite element approach has been used to solve the continuity, momentum, and Oldroyd-B partial differential equations to analyze the blood flow. Newtonian and non-Newtonian both cases are taken for the viscoelastic response of blood. In this study, the impact of multiple stenotic and aneurysmal arteries on blood flow have been studied to determine the severity of atherosclerosis diseases through the analysis of blood behavior. The novel aspect of the study is its assessment of the severity of atherosclerotic disorders for the occurrence of serial stenosis and aneurysm simultaneously in the blood vessel wall in each of the four cases. The maximum abnormal arterial blood flow effect is found for the presence of serial stenoses compared to aneurysms which refers to the severity of atherosclerosis. At the hub of stenosis, the blood velocity magnitude and wall shear stress (WSS) are higher, whereas the arterial wall normal gradient values are lower. For all cases, the contrary results are observed at the hub of the aneurysmal model. The blood flow has been affected significantly by the increases in Reynolds number for both models. The influence of stenotic and aneurysmal arteries on blood flow is graphically illustrated in terms of the velocity profile, pressure distribution, and WSS. Medical experts may use this study's findings to assess the severity of cardiovascular diseases.}, } @article {pmid38457940, year = {2024}, author = {Wang, Z and Xu, P and Ren, Z and Yu, L and Zuo, Z and Liu, S}, title = {Dynamics of cavitation bubbles in viscous liquids in a tube during a transient process.}, journal = {Ultrasonics sonochemistry}, volume = {104}, number = {}, pages = {106840}, doi = {10.1016/j.ultsonch.2024.106840}, pmid = {38457940}, issn = {1873-2828}, abstract = {We experimentally, numerically, and theoretically investigate the dynamics of cavitation bubbles in viscous liquids in a tube during a transient process. In experiments, cavitation bubbles are generated by a modified tube-arrest setup, and the bubble evolution is captured with high-speed imaging. Numerical simulations using OpenFOAM are employed to validate our quasi-one-dimensional theoretical model, which effectively characterizes the bubble dynamics. We find that cavitation onset is minimally affected by the liquid viscosity. However, once cavitation occurs, various aspects of bubble dynamics, such as the maximum bubble length, bubble lifetime, collapse time, and collapse speed, are closely related to the liquid viscosity. We further establish that normalized bubble dynamics are solely determined by the combination of the Reynolds number and the Euler number. Moreover, we also propose a new dimensionless number, Ca2, to predict the maximum bubble length, a critical factor in determining the occurrence of liquid column separation.}, } @article {pmid38445957, year = {2024}, author = {Hu, X and Chen, W and Lin, J and Nie, D and Zhu, Z and Lin, P}, title = {The motion of micro-swimmers over a cavity in a micro-channel.}, journal = {Soft matter}, volume = {}, number = {}, pages = {}, doi = {10.1039/d3sm01589k}, pmid = {38445957}, issn = {1744-6848}, abstract = {This article combines the lattice Boltzmann method (LBM) with the squirmer model to investigate the motion of micro-swimmers in a channel-cavity system. The study analyses various influential factors, including the value of the squirmer-type factor (β), the swimming Reynolds number (Rep), the size of the cavity, initial position and particle size on the movement of micro-swimmers within the channel-cavity system. We simultaneously studied three types of squirmer models, Puller (β > 0), Pusher (β < 0), and Neutral (β = 0) swimmers. The findings reveal that the motion of micro-swimmers is determined by the value of β and Rep, which can be classified into six distinct motion modes. For Puller and Pusher, when the β value is constant, an increase in Rep will lead to transition in the motion mode. Moreover, the appropriate depth of cavity within the channel-cavity system plays a crucial role in capturing and separating Neutral swimmers. This study, for the first time, explores the effect of complex channel-cavity systems on the behaviour of micro-swimmers and highlights their separation and capture ability. These findings offer novel insights for the design and enhancement of micro-channel structures in achieving efficient separation and capture of micro-swimmers.}, } @article {pmid38434303, year = {2024}, author = {Wannapop, R and Jearsiripongkul, T and Jiamjiroch, K}, title = {Adaptive urban drinking water supply model using the effect of node elevation and head loss formula: A case study.}, journal = {Heliyon}, volume = {10}, number = {5}, pages = {e26181}, pmid = {38434303}, issn = {2405-8440}, abstract = {Along with population growth and health improvement, water demand due to urbanization is increasing and creating a need to develop a strategy for handling water supply networks (WSNs). In the last decade, software modeling of WSNs has been developed to evaluate the state of networks in terms of pressure control, leakage analysis, and overall demand determination. In the case of very complex and extremely large networks, it is very difficult to manage the water supply. Metropolitan Waterworks Authority (MWA) in Thailand has to supply drinking water to the three densely populated cities; Bangkok, Nonthaburi, and Samut Prakan, that cover an area of 2944.05 km[2]. Hence, MWA has developed a main pipe model using EPANET software as a managing tool. This tool can offer a good solution for the water supply, but there is approximately a 14 percent error, mainly due to not having the elevation data of the pipe network. The current research is based on demand and pressure modeling analysis with utilizing two important parameters, node elevations, and head loss. The first trial model was an initial revision of the node elevation based on a road surface map. It was found that the model with elevation data could offer a better solution and was 3.95% more accurate than the existing model. The result was significantly improved, but another error, which may have been caused by using an inappropriate head loss model, was found. As the introduced model is based on the Hazen-William model, it cannot offer an accurate solution for all Reynolds number ranges. Even though Darcy-Weisbach is more complex to use, it could provide a better solution. The results indicate the Darcy-Weisbach model produces results that are 8.65% more accurate than the Hazen-William model.}, } @article {pmid38430250, year = {2024}, author = {Pandey, SK and Prajapati, A}, title = {An analytical and comparative study of swallowing in a tumor-infected oesophagus: a mathematical model.}, journal = {Journal of mathematical biology}, volume = {88}, number = {3}, pages = {37}, pmid = {38430250}, issn = {1432-1416}, abstract = {This study discusses non-steady effects encountered in peristaltic flows in oesophagus. The purpose of this communication is to evolve a mechanism to diagnose tumor in an oesophagus mathematically. The tumor is modelled by generic bump function of certain height and width. The method of solution follows long wavelength and low-Reynolds number approximations for unsteady flow, while integrations have been performed numerically in order to plot graphs, which reveal various characteristics of the flow. The goal is to assess how pressure varies across the tumor's width. The spatial, as well as temporal, dependence of pressure has been studied in the laboratory frame of reference. The pressure distribution for tumor-infected oesophagus is compared with that of normal oesophagus. An intensified pressure is obtained in the presence of tumor. The interruption while swallowing through benign oesophageal tumor is confirmed by an abrupt pressure rise across the tumor's width. Tumor position also plays a significant role whether it is at contraction or relaxation of walls. Additionally, wall-shear-stress, volumetric flow rate and streamlines have also been described and compared with that without tumor growth. The expressions corresponding to all the physical quantities are computed numerically. Further, this model may also be implemented to the two-dimensional channel flow for an industrial application.}, } @article {pmid38427109, year = {2024}, author = {Zidi, K and Texier, BD and Gauthier, G and Seguin, A}, title = {Viscosimetric squeeze flow of suspensions.}, journal = {The European physical journal. E, Soft matter}, volume = {47}, number = {3}, pages = {17}, pmid = {38427109}, issn = {1292-895X}, support = {ANR-10-LABX-0039-PALM//Laboratoire d'excellence Physique Atomes Lumière Matière/ ; }, abstract = {The rheology of particle suspensions has been extensively explored in the case of a simple shear flow, but less in other flow configurations which are also important in practice. Here we investigate the behavior of a suspension in a squeeze flow, which we revisit using local pressure measurements to deduce the effective viscosity. The flow is generated by approaching a moving disk to a fixed wall at constant velocity in the low Reynolds number limit. We measure the evolution of the pressure field at the wall and deduce the effective viscosity from the radial pressure drop. After validation of our device using a Newtonian fluid, we measure the effective viscosity of a suspension for different squeezing speeds and volume fractions of particles. We find results in agreement with the Maron-Pierce law, an empirical expression for the viscosity of suspensions that was established for simple shear flows. We prove that this method to determine viscosity remains valid in the limit of large gap width. This makes it possible to study the rheology of suspensions within this limit and therefore suspensions composed of large particles, in contrast to Couette flow cells which require small gaps.}, } @article {pmid38413619, year = {2024}, author = {Elmhedy, Y and Abd-Alla, AM and Abo-Dahab, SM and Alharbi, FM and Abdelhafez, MA}, title = {Influence of inclined magnetic field and heat transfer on the peristaltic flow of Rabinowitsch fluid model in an inclined channel.}, journal = {Scientific reports}, volume = {14}, number = {1}, pages = {4735}, pmid = {38413619}, issn = {2045-2322}, abstract = {The recent study is focused on discussion of heat transfer and magnetic field results of peristaltic flow of Rabinowitsch fluid model in an Inclined Channel. In this piece of research, peristalsis's fundamental problem with heat transfer in the presence of a magnetic field is checked. An incompressible Rabinowitsch fluid is present in an inclined channel, which is considered as the reference for this research. The solutions are devised with the assumptions of long wavelength and low Reynolds number approximations. The resulting equations are then solved exactly by implementing various command of MATHEMATICA subject to relevant boundary conditions. Results are discussed for various flow quantities like temperature, velocity, tangential stress, pressure gradient and rise, and friction force. Computational simulations are performed to determine the flow quantities. This investigation goes beyond mere calculations and examines particle motion to gain deeper insights into flow quantities. Furthermore, this investigates how magnetic field and heat transfer parameters influence these peristaltic flow phenomena. The outcomes of important parameters were plotted and scrutinized. There is amultitude of medical implementations derived from the current consideration, such as the depiction of the gastric juice motion in the small intestine when an endoscope is inserted through it.}, } @article {pmid38407396, year = {2024}, author = {Chand, K and Rosenberger, H and Sanderse, B}, title = {A pressure-free long-time stable reduced-order model for two-dimensional Rayleigh-Bénard convection.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {34}, number = {2}, pages = {}, doi = {10.1063/5.0168857}, pmid = {38407396}, issn = {1089-7682}, abstract = {The present work presents a stable proper orthogonal decomposition (POD)-Galerkin based reduced-order model (ROM) for two-dimensional Rayleigh-Bénard convection in a square geometry for three Rayleigh numbers: 104 (steady state), 3×105 (periodic), and 6×106 (chaotic). Stability is obtained through a particular (staggered-grid) full-order model (FOM) discretization that leads to a ROM that is pressure-free and has skew-symmetric (energy-conserving) convective terms. This yields long-time stable solutions without requiring stabilizing mechanisms, even outside the training data range. The ROM's stability is validated for the different test cases by investigating the Nusselt and Reynolds number time series and the mean and variance of the vertical temperature profile. In general, these quantities converge to the FOM when increasing the number of modes, and turn out to be a good measure of accuracy. However, for the chaotic case, convergence with increasing numbers of modes is relatively difficult and a high number of modes is required to resolve the low-energy structures that are important for the global dynamics.}, } @article {pmid38381133, year = {2024}, author = {Chang, R and Davydov, A and Jaroenlak, P and Budaitis, B and Ekiert, DC and Bhabha, G and Prakash, M}, title = {Energetics of the mokicrosporidian polar tube invasion machinery.}, journal = {eLife}, volume = {12}, number = {}, pages = {}, doi = {10.7554/eLife.86638}, pmid = {38381133}, issn = {2050-084X}, support = {HHMI Faculty fellowship/HHMI/Howard Hughes Medical Institute/United States ; R35GM128777/GM/NIGMS NIH HHS/United States ; }, abstract = {Microsporidia are eukaryotic, obligate intracellular parasites that infect a wide range of hosts, leading to health and economic burdens worldwide. Microsporidia use an unusual invasion organelle called the polar tube (PT), which is ejected from a dormant spore at ultra-fast speeds, to infect host cells. The mechanics of PT ejection are impressive. Anncaliia algerae microsporidia spores (3-4 μm in size) shoot out a 100-nm-wide PT at a speed of 300 μm/s, creating a shear rate of 3000 s[-1]. The infectious cargo, which contains two nuclei, is shot through this narrow tube for a distance of ∼60-140 μm (Jaroenlak et al, 2020) and into the host cell. Considering the large hydraulic resistance in an extremely thin tube and the low-Reynolds-number nature of the process, it is not known how microsporidia can achieve this ultrafast event. In this study, we use Serial Block-Face Scanning Electron Microscopy to capture 3-dimensional snapshots of A. algerae spores in different states of the PT ejection process. Grounded in these data, we propose a theoretical framework starting with a systematic exploration of possible topological connectivity amongst organelles, and assess the energy requirements of the resulting models. We perform PT firing experiments in media of varying viscosity, and use the results to rank our proposed hypotheses based on their predicted energy requirement. We also present a possible mechanism for cargo translocation, and quantitatively compare our predictions to experimental observations. Our study provides a comprehensive biophysical analysis of the energy dissipation of microsporidian infection process and demonstrates the extreme limits of cellular hydraulics.}, } @article {pmid38378438, year = {2024}, author = {Qiao, S and Cai, C and Pan, C and Liu, Y and Zhang, Q}, title = {Study on the Performance of a Surface with Coupled Wettability Difference and Convex-Stripe Array for Improved Air Layer Stability.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {}, number = {}, pages = {}, doi = {10.1021/acs.langmuir.3c03929}, pmid = {38378438}, issn = {1520-5827}, abstract = {The existence of an air layer reduces friction drag on superhydrophobic surfaces. Therefore, improving the air layer stability of superhydrophobic surfaces holds immense significance in reducing both energy consumption and environmental pollution caused by friction drag. Based on the properties of mathematical discretization and the contact angle hysteresis generated by the wettability difference, a surface coupled with a wettability difference treatment and a convex-stripe array is developed by laser engraving and fluorine modification, and its performance in improving the air layer stability is experimentally studied in a von Kármán swirling flow field. The results show that the destabilization of the air layer is mainly caused by the Kelvin-Helmholtz instability, which is triggered by the density difference between gas and liquid, as well as the tangential velocity difference between gas and liquid. When the air layer is relatively thin, tangential wave destabilization occurs, whereas for larger thicknesses, the destabilization mode is coupled wave destabilization. The maximum Reynolds number that keeps the air layer fully covering the surface of the rotating disk (with drag reduction performance) during the disk rotation process is defined as the critical Reynolds number (Rec), which is 1.62 × 10[5] for the uniform superhydrophobic surface and 3.24 × 10[5] for the superhydrophobic surface with a convex stripe on the outermost ring (SCSSP). Individual treatments of wettability difference and a convex-stripe array on the SCSSP further improve the air layer stability, but Rec remains at 3.24 × 10[5]. Finally, the coupling of the wettability difference treatment with a convex-stripe array significantly improves the air layer stability, resulting in an increase of Rec to 4.05 × 10[5], and the drag reduction rate stably maintained around 30%.}, } @article {pmid38377615, year = {2024}, author = {Dunt, T and Heck, KS and Lyons, K and Murphy, CT and Cal, RB and Franck, JA}, title = {Wavelength-induced shedding frequency modulation of seal whisker inspired cylinders.}, journal = {Bioinspiration & biomimetics}, volume = {}, number = {}, pages = {}, doi = {10.1088/1748-3190/ad2b04}, pmid = {38377615}, issn = {1748-3190}, abstract = {The spanwise undulated cylinder geometry inspired by seal whiskers has been shown to alter shedding frequency and reduce fluid forces significantly compared to smooth cylindrical geometry. Undulation wavelength is systematically investigated in order to explore its effect on unsteady lift force and shedding frequency. Prior research has parameterized the whisker-inspired geometry and demonstrated the relevance of geometric variations on force reduction properties. Among the geometric parameters, undulation wavelength was identified as a significant contributor to forcing changes. To analyze the effect of undulation wavelength, a thorough investigation isolating changes in wavelength is performed to expand upon previous research that parameterized whisker-inspired geometry and the relevance of geometric variations on the force reduction properties. A set of five whisker-inspired models of varying wavelength are computationally simulated at a Reynolds number of 250 and compared with an equivalent aspect ratio smooth elliptical cylinder. Above a critical nondimensional value, the undulation wavelength reduces the amplitude and frequency of vortex shedding accompanied by a reduction in oscillating lift force. Frequency shedding is tied to the creation of wavelength-dependent vortex structures which vary across the whisker span. These vortices produce distinct shedding modes in which the frequency and phase of downstream structures interact to decrease the oscillating lift forces on the whisker model with particular effectiveness around the wavelength values typically found in nature. The culmination of the these location-based modes produces a complex and spanwise dependent lift frequency spectra at those wavelengths exhibiting maximum force reduction. Understanding the mechanisms of unsteady force reduction and the application of this geometry to vibration tuning and passive flow control for vortex-induced vibration (VIV) reduction.}, } @article {pmid38366478, year = {2024}, author = {Zhou, H and Blackman, EG}, title = {Helical dynamo growth and saturation at modest versus extreme magnetic Reynolds numbers.}, journal = {Physical review. E}, volume = {109}, number = {1-2}, pages = {015206}, doi = {10.1103/PhysRevE.109.015206}, pmid = {38366478}, issn = {2470-0053}, abstract = {Understanding magnetic field growth in astrophysical objects is a persistent challenge. In stars and galaxies, turbulent flows with net kinetic helicity are believed to be responsible for driving large-scale magnetic fields. However, numerical simulations have demonstrated that such helical dynamos in closed volumes saturate at lower magnetic field strengths when increasing the magnetic Reynolds number Rm. This would imply that helical large-scale dynamos cannot be efficient in astrophysical bodies without the help of helicity outflows such as stellar winds. But do these implications actually apply for very large Rm? Here we tackle the long-standing question of how much helical large-scale dynamo growth occurs independent of Rm in a closed volume. We analyze data from numerical simulations with a new method that tracks resistive versus nonresistive drivers of helical field growth. We identify a presaturation regime when the large-scale field grows at a rate independent of Rm, but to an Rm-dependent magnitude. The latter Rm dependence is due to a dominant resistive contribution, but whose fractional contribution to the large-scale magnetic energy decreases with increasing Rm. We argue that the resistive contribution would become negligible at large Rm and an Rm-independent dynamical contribution would dominate if the current helicity spectrum in the inertial range is steeper than k^{0} . As such helicity spectra are plausible, this renews optimism for the relevance of closed dynamos. Our work pinpoints how modest Rm simulations can cause misapprehension of the Rm→∞ behavior.}, } @article {pmid38361591, year = {2024}, author = {Chen, Y and Chong, KL and Liu, H and Verzicco, R and Lohse, D}, title = {Buoyancy-driven attraction of active droplets.}, journal = {Journal of fluid mechanics}, volume = {980}, number = {}, pages = {}, doi = {10.1017/jfm.2024.18}, pmid = {38361591}, issn = {0022-1120}, abstract = {For dissolving active oil droplets in an ambient liquid, it is generally assumed that the Marangoni effect results in repulsive interactions, while the buoyancy effects caused by the density difference between the droplets, diffusing product and the ambient fluid are usually neglected. However, it has been observed in recent experiments that active droplets can form clusters due to buoyancy-driven convection (Krüger et al. Eur. Phys. J. E, vol. 39, 2016, pp. 1-9). In this study, we numerically analyze the buoyancy effect, in addition to the propulsion caused by Marangoni flow (with its strength characterized by Péclet number Pe). The buoyancy effects have their origin in (i) the density difference between the droplet and the ambient liquid, which is characterized by Galileo number Ga, and (ii) the density difference between the diffusing product (i.e. filled micelles) and the ambient liquid, which can be quantified by a solutal Rayleigh number Ra. We analyze how the attracting and repulsing behaviour of neighbouring droplets depends on the control parameters Pe, Ga, and Ra. We find that while the Marangoni effect leads to the well-known repulsion between the interacting droplets, the buoyancy effect of the reaction product leads to buoyancy-driven attraction. At sufficiently large Ra, even collisions between the droplets can take place. Our study on the effect of Ga further shows that with increasing Ga, the collision becomes delayed. Moreover, we derive that the attracting velocity of the droplets, which is characterized by a Reynolds number Red, is proportional to Ra[1/4]/(ℓ/R), where ℓ/R is the distance between the neighbouring droplets normalized by the droplet radius. Finally, we numerically obtain the repulsive velocity of the droplets, characterized by a Reynolds number Rerep, which is proportional to PeRa[-0.38]. The balance of attractive and repulsive effect leads to Pe ~ Ra[0.63], which agrees well with the transition curve between the regimes with and without collision.}, } @article {pmid38359059, year = {2024}, author = {Xi, Y and Meng, F}, title = {Numerical study on flow and heat transfer characteristics of rectangular mini-channel of interpolated double S turbulators.}, journal = {PloS one}, volume = {19}, number = {2}, pages = {e0297678}, doi = {10.1371/journal.pone.0297678}, pmid = {38359059}, issn = {1932-6203}, abstract = {In this study, we propose a new type of small-channel plug-in, the double S turbulators, for passive heat transfer enhancement to improve the flow and heat transfer performance of the fluid in the channel. In the range of Reynolds number 254.51~2545.09, under constant wall temperature heating conditions, the effects of interpolated double S turbulators with different long axial radii (1mm, 1.5mm, 2mm) on the average Nusselt number, pressure drop, total thermal resistance and field synergy number in the rectangular mini-channel were studied. The simulation results show that compared with the smooth rectangular mini-channel, after interpolating double S turbulators with different long axial radii (1mm, 1.5mm, 2mm), the average Nusselt number increased by 81.74%~101.74%, 71.29%~94.06%, 67.16%~88.48%, the total thermal resistance decreased by 45.1%~50.72%, 41.72%~48.74%, 40.28%~47.2%, and the number of field synergies increased by 85.58%~111.65%, 74.1%~102.6%, 69.64%~96.12%. At present, there are few studies on the boundary condition of constant wall temperature, and this paper supplements the research on this aspect. At the same time, the heat transfer performance of the rectangular mini-channel of the interpolated double S turbulators is stronger than that of the ordinary smooth rectangular mini-channel, which not only provides a new idea for the manufacture of micro heat dissipation equipment, but also improves the heat transfer performance of micro heat dissipation equipment and improves its work efficiency. According to the simulation data, the prediction formula of average Nusselt number and pressure drop was established by nonlinear regression method, which can be used to predict the flow and heat transfer characteristics of the rectangular mini-channel of the interpolated double S turbulators.}, } @article {pmid38352662, year = {2024}, author = {Gnanasekaran, M and Satheesh, A}, title = {Numerical analysis of turbulent flow characteristics with the influence of speed ratio in a double-sided cavity.}, journal = {MethodsX}, volume = {12}, number = {}, pages = {102594}, pmid = {38352662}, issn = {2215-0161}, abstract = {The present study numerically investigates the two-dimensional steady incompressible turbulent flow characteristics in an enclosed cavity. The finite volume method (FVM) is used to discretize the governing equations, and k-ε turbulence models are adopted to predict the flow characteristics. The turbulent flow behavior is studied by varying the speed ratio (0.05 ≤ S ≤ 1.0), aspect ratio (0.5 ≤ K ≤ 2.0), and Reynolds number (1 × 10[4] ≤ Re ≤ 2 × 10[5]). The flow characteristics are analyzed using stream function (ψ), Reynolds stresses (u'v'), and turbulent quantities. Results show the Reynolds number and speed ratio significantly influence the formation of vortices over the selected range of operating parameters. With the speed ratio, the turbulent kinetic energy reduces considerably by increasing the Reynolds number and aspect ratio. Similarly, for S = 0.05 and K = 0.5, the turbulent kinetic energy and dissipation rate are decreased by 89.16% and 42.28%, respectively. When Re is increased from 1 × 10[4] to 2 × 10[5], the turbulent viscosity increases by 92.10%. By comparing the results, average turbulent quantities are decreased by increasing the flow parameters.•Turbulent flow behavior is investigated by using the FVM near-wall treatment approach.One of the unique parameters called speed ratio is emphasized.•Contours of turbulence kinetic energy, dissipation, and viscosity are examined.•The average intensity of turbulent quantities is decreased by increasing the speed ratio.}, } @article {pmid38336842, year = {2024}, author = {Kim, SJ and Kos, Ž and Um, E and Jeong, J}, title = {Symmetrically pulsating bubbles swim in an anisotropic fluid by nematodynamics.}, journal = {Nature communications}, volume = {15}, number = {1}, pages = {1220}, pmid = {38336842}, issn = {2041-1723}, abstract = {Swimming in low-Reynolds-number fluids requires the breaking of time-reversal symmetry and centrosymmetry. Microswimmers, often with asymmetric shapes, exhibit nonreciprocal motions or exploit nonequilibrium processes to propel. The role of the surrounding fluid has also attracted attention because viscoelastic, non-Newtonian, and anisotropic properties of fluids matter in propulsion efficiency and navigation. Here, we experimentally demonstrate that anisotropic fluids, nematic liquid crystals (NLC), can make a pulsating spherical bubble swim despite its centrosymmetric shape and time-symmetric motion. The NLC breaks the centrosymmetry by a deformed nematic director field with a topological defect accompanying the bubble. The nematodynamics renders the nonreciprocity in the pulsation-induced fluid flow. We also report speed enhancement by confinement and the propulsion of another symmetry-broken bubble dressed by a bent disclination. Our experiments and theory propose another possible mechanism of moving bodies in complex fluids by spatiotemporal symmetry breaking.}, } @article {pmid38335533, year = {2024}, author = {Wang, Z and Liu, X and Guo, Y and Tong, B and Zhang, G and Liu, K and Jiao, Y}, title = {Armored Superhydrophobic Surfaces with Excellent Drag Reduction in Complex Environmental Conditions.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {}, number = {}, pages = {}, doi = {10.1021/acs.langmuir.3c03544}, pmid = {38335533}, issn = {1520-5827}, abstract = {Superhydrophobic surfaces (SHSs) have possibilities for achieving significantly reduced solid-liquid frictional drag in the marine sector due to their excellent water-repelling properties. Although the stability of SHSs plays a key role in drag reduction, little consideration was given to the effect of extreme environments on the ability of SHSs to achieve drag reduction underwater, particularly when subjected to acidic conditions. Here, we propose interconnected microstructures to protect superhydrophobic coatings with the aim of enhancing the stability of SHSs in extreme environments. The stability of armored SHSs (ASHSs) was demonstrated by the contact angle and bounce time of droplets on superhydrophobic surfaces treated by various methods, resulting in an ASHS surface with excellent stability under extreme environmental conditions. Additionally, inspired by microstructures protecting superhydrophobic nanomaterials from frictional wear, the armored superhydrophobic spheres (ASSPs) were designed to explain from theoretical and experimental perspectives why ASSPs can achieve sustainable drag reduction and demonstrate that the ASSPs can achieve drag reduction of over 90.4% at a Reynolds number of 6.25 × 10[4] by conducting water entry experiments on spheres treated in various solutions. These studies promote a fundamental understanding of what drives the application of SHSs under extreme environmental conditions and provide practical strategies to maximize frictional drag reduction.}, } @article {pmid38335336, year = {2024}, author = {Wang, K and Sprinkle, B and Zuo, M and Ristroph, L}, title = {Centrifugal Flows Drive Reverse Rotation of Feynman's Sprinkler.}, journal = {Physical review letters}, volume = {132}, number = {4}, pages = {044003}, doi = {10.1103/PhysRevLett.132.044003}, pmid = {38335336}, issn = {1079-7114}, abstract = {The issue of reversibility in hydromechanical sprinklers that auto-rotate while ejecting fluid from S-shaped tubes raises fundamental questions that remain unresolved. Here, we report on precision experiments that reveal robust and persistent reverse rotation under suction and a model that accounts for the observed motions. We implement an ultralow friction bearing in an apparatus that allows for free rotation under ejection and suction for a range of flow rates and arbitrarily long times. Flow measurements reveal a rocketlike mechanism shared by the reverse and forward modes that involves angular momentum flux, whose subtle manifestation in the reverse case stems from centrifugal effects for flows in curved conduits. These findings answer Feynman's long-standing question by providing quantitatively accurate explanations of both modes, and they suggest further inquiries into flux-based force generation and the roles of geometry and Reynolds number.}, } @article {pmid38322951, year = {2024}, author = {Mishra, NK and Sharma, P and Sharma, BK and Almohsen, B and Pérez, LM}, title = {Electroosmotic MHD ternary hybrid Jeffery nanofluid flow through a ciliated vertical channel with gyrotactic microorganisms: Entropy generation optimization.}, journal = {Heliyon}, volume = {10}, number = {3}, pages = {e25102}, doi = {10.1016/j.heliyon.2024.e25102}, pmid = {38322951}, issn = {2405-8440}, abstract = {In this study, the computational analysis of entropy generation optimization for synthetic cilia regulated ternary hybrid Jeffery nanofluid (Ag-Au-TiO2/PVA) flow through a peristaltic vertical channel with swimming motile Gyrotactic microorganisms is investigated. Understanding the intricate interaction of multiple physical phenomena in biomedical applications is essential for optimizing entropy generation and advancing microfluidic systems. The characteristics of nanofluid are explored for the electroosmotic MHD fluid flow in the presence of thermophoresis and Brownian motion, viscous dissipation, Ohmic heating and chemical reaction. Using the appropriate transformations, a set of ordinary differential equations are created from the governing partial differential equations. The resulting ODEs are numerically solved using the shooting technique using BVP5C in MATLAB after applying the long-wavelength and low Reynolds number approximation. The velocity, temperature, concentration, electroosmosis, and microorganism density profiles are analyzed graphically for different emerging parameters. Graphical investigation of engineering interest quantities like heat transfer rate, mass transfer rate, skin friction coefficient, and entropy generation optimization are also presented. It is observed that the rate of mass transfer increases for increasing thermophoretic parameter, while reverse effect is noted for Brownian motion parameter, Schmidt number, and chemical reaction number. The outcomes of present study can be pertinent in studying Cilia properties of respiratory tract, reproductive system, and brain ventricles.}, } @article {pmid38322945, year = {2024}, author = {Selimefendigil, F and Ghachem, K and Albalawi, H and AlShammari, BM and Labidi, T and Kolsi, L}, title = {Magneto-convection of nanofluid flow over multiple rotating cylinders in a confined space with elastic walls and ventilated ports.}, journal = {Heliyon}, volume = {10}, number = {3}, pages = {e25101}, doi = {10.1016/j.heliyon.2024.e25101}, pmid = {38322945}, issn = {2405-8440}, abstract = {In this study, convective heat transfer for nanofluid flow over multiple rotating cylinder in a confined space is analyzed under magnetic field while enclosure has one inlet and one outlet port. Three identical circular cylinder are used and the two walls of the cavity are considered to be elastic. The coupled fluid-structure interaction and magneto-convection problem is solved by finite element method. Impacts of rotational Reynolds number (Rew between -100 and 100), Hartmann number (Ha between 0 and 50), cylinder size (R between 0.001H and 0.11H) and Cauchy number (Ca between 10-8 and 10-3) on the flow and thermal performance features are explored. The flow field and recirculation inside the cavity are significantly affected by the activation of rotation and magnetic field. The vortices are suppressed by increasing the strength of magnetic field and thermal performance is improved. Thermal performance of 56.6% is achieved by activation of magnetic field at the highest strength with rotations of the circular cylinders. When rotations are active, heat transfer rate is reduced while up to 40% reduction is obtained without magnetic field. Cylinder size has the highest impact on the overall thermal performance improvement while up to 132% enhancements are achieved. The contribution of elastic walls on the thermal performance is slight while less than 5% improvements in the average heat transfer is obtained. An optimization study leads to 12.7% higher thermal performance improvements as compared to best case of parametric computational fluid dynamics simulation results while the optimum values of (Rew, Ha, R) is obtained as (-80.66, 50, 0.11H).}, } @article {pmid38321050, year = {2024}, author = {Massaro, D and Karp, M and Jansson, N and Markidis, S and Schlatter, P}, title = {Direct numerical simulation of the turbulent flow around a Flettner rotor.}, journal = {Scientific reports}, volume = {14}, number = {1}, pages = {3004}, pmid = {38321050}, issn = {2045-2322}, abstract = {The three-dimensional turbulent flow around a Flettner rotor, i.e. an engine-driven rotating cylinder in an atmospheric boundary layer, is studied via direct numerical simulations (DNS) for three different rotation speeds ([Formula: see text]). This technology offers a sustainable alternative mainly for marine propulsion, underscoring the critical importance of comprehending the characteristics of such flow. In this study, we evaluate the aerodynamic loads produced by the rotor of height h, with a specific focus on the changes in lift and drag force along the vertical axis of the cylinder. Correspondingly, we observe that vortex shedding is inhibited at the highest [Formula: see text] values investigated. However, in the case of intermediate [Formula: see text], vortices continue to be shed in the upper section of the cylinder ([Formula: see text]). As the cylinder begins to rotate, a large-scale motion becomes apparent on the high-pressure side, close to the bottom wall. We offer both a qualitative and quantitative description of this motion, outlining its impact on the wake deflection. This finding is significant as it influences the rotor wake to an extent of approximately one hundred diameters downstream. In practical applications, this phenomenon could influence the performance of subsequent boats and have an impact on the cylinder drag, affecting its fuel consumption. This fundamental study, which investigates a limited yet significant (for DNS) Reynolds number and explores various spinning ratios, provides valuable insights into the complex flow around a Flettner rotor. The simulations were performed using a modern GPU-based spectral element method, leveraging the power of modern supercomputers towards fundamental engineering problems.}, } @article {pmid38305052, year = {2024}, author = {Mandujano, F and Vázquez-Luis, E}, title = {Chaotic vortex-induced rotation of an elliptical cylinder.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {34}, number = {2}, pages = {}, doi = {10.1063/5.0170987}, pmid = {38305052}, issn = {1089-7682}, abstract = {Non-linear oscillations of an elliptical cylinder, which can rotate about an axis that passes through its symmetry axle due to a torsional spring and hydrodynamic torque produced by the flow of a Newtonian fluid, were analyzed in terms of a single parameter that compares vortex shedding frequency with the torsional spring's natural frequency. The governing equations for the flow coupled with a rigid body with one degree of freedom were solved numerically using the lattice-Boltzmann method. The Reynolds number used was Re=200, which, in the absence of torsional spring, produces chaotic oscillations of the elliptical cylinder. When the torsional spring is included, we identified three branches separated by transition regions when stiffness of the restorative torque changes, as in the case of vortex-induced vibrations. However, in this case, several regions presenting chaotic dynamics were identified. Two regions with stable limit cycles were found when both torques synchronized and when stiffness of the torsional spring is big enough so that the ellipse's oscillation is small.}, } @article {pmid38302543, year = {2024}, author = {Ashkani, A and Jafari, A and Ghomsheh, MJ and Dumas, N and Funfschilling, D}, title = {Enhancing particle focusing: a comparative experimental study of modified square wave and square wave microchannels in lift and Dean vortex regimes.}, journal = {Scientific reports}, volume = {14}, number = {1}, pages = {2679}, pmid = {38302543}, issn = {2045-2322}, abstract = {Serpentine microchannels are known for their effective particle focusing through Dean flow-induced rotational effects, which are used in compact designs for size-dependent focusing in medical diagnostics. This study explores square serpentine microchannels, a geometry that has recently gained prominence in inertial microfluidics, and presents a modification of square wave microchannels for improved particle separation and focusing. The proposed modification incorporates an additional U-shaped unit to convert the square wave microchannel into a non-axisymmetric structure, which enhances the Dean flow and consequently increases the Dean drag force. Extensive experiments were conducted covering a wide range of Reynolds numbers and particle sizes (2.45 µm to 12 µm). The particle concentration capability and streak position dynamics of the two structures were compared in detail. The results indicate that the modified square-wave microchannel exhibits efficient particle separation in the lower part of the Dean vortex-dominated regime. With increasing Reynolds number, the particles are successively focused into two streaks in the lift force-dominated regime and into a single streak in the Dean vortex-dominated regime, in this modified square wave geometry. These streaks have a low standard deviation around a mean value. In the Dean vortex-dominated regime, the location of the particle stream is highly dependent on the particle size, which allows good particle separation. Particle focusing occurs at lower Reynolds numbers in both the lift-dominated and lift/Dean drag-dominated regions than in the square wave microchannel. The innovative serpentine channel is particularly useful for the Dean drag-dominated regime and introduces a unique asymmetry that affects the particle focusing dynamics. The proposed device offers significant advantages in terms of efficiency, parallelization, footprint, and throughput over existing geometries.}, } @article {pmid38298735, year = {2024}, author = {Xia, Y and Lyu, S}, title = {Direct numerical simulation of contaminant removal in presence of underfloor air distribution system.}, journal = {Heliyon}, volume = {10}, number = {2}, pages = {e24331}, doi = {10.1016/j.heliyon.2024.e24331}, pmid = {38298735}, issn = {2405-8440}, abstract = {Indoor contaminant removal over 0.5 ≤ FrT ≤ 5.0, 0.5 ≤ N ≤ 5.0, and 50 ≤ Re ≤ 500 was investigated numerically, wherein FrT refers to the Froude number, N refers to the buoyancy ratio, and Re refers to the Reynolds number. As demonstrated, the ventilation effectiveness increased with increasing contaminant source intensity and air supply intensity at a constant air temperature, indicating that increase the fresh air can effectively eliminate contaminants in this case. At high air supply temperatures, the heat retention time and contaminant transport was extremely short, and the fresh air induced by strong natural convection floating lift was rapidly discharged. Additioanlly, the air supply intensity had significant effects on contaminant removal. Quantification of the ventilation effectiveness under the combined effects of air supply intensity, air supply temperature and contaminant source intensity was determined based on the results of direct numerical simulations.}, } @article {pmid38298636, year = {2024}, author = {Almutairi, DK}, title = {Mathematical modelling and heat transfer observations for Jeffrey nanofluid with applications of extended Fourier theory and temperature dependent thermal conductivity.}, journal = {Heliyon}, volume = {10}, number = {2}, pages = {e24353}, doi = {10.1016/j.heliyon.2024.e24353}, pmid = {38298636}, issn = {2405-8440}, abstract = {The suspension of non-Newtonian materials with nanoparticles is important to enhance the thermal phenomenon in various engineering and industrial processes. The versatile research in nanomaterials provide different applications in thermal processes, heat exchangers, thermoelectric devices, HVAC systems, energy processes etc. Following to such novel motivations in mind, current research endorsed the enhancement in heat transfer due to suspension of Jeffrey nanofluid comprising the variable thermal conductivity. The cause of flow is associated to two disks attaining fixed distance. The modified developed relations for Fourier's hypothesis are utilized to model the problem. The flow problem is modeled with appliance of fundamental novel laws. By applying suitable transformations, corresponding differential equations are renovated into dimensionless forms which are solved with applications of analytic homotopic algorithm. The behavior of temperature and velocity due to various parameters is discussed. The numerical calculations have been done for wall shear force and Nusselt number. The results show that the velocity profile boosted due to variation of stretching ratio constant. The enhancement in heat transfer is observed due to Reynolds number. Moreover, the increasing observations for wall shear force in upper and lower disk surfaces are obtained against larger material parameter. The simulated results may find applications in improving heat transfer phenomenon, manufacturing systems, recovery processes, cooling systems, chemical phenomenon, fuel cells etc.}, } @article {pmid38298373, year = {2024}, author = {Gande, VV and Podupu, PKR and Berry, B and Nere, NK and Pushpavanam, S and Singh, MR}, title = {Engineering advancements in microfluidic systems for enhanced mixing at low Reynolds numbers.}, journal = {Biomicrofluidics}, volume = {18}, number = {1}, pages = {011502}, doi = {10.1063/5.0178939}, pmid = {38298373}, issn = {1932-1058}, abstract = {Mixing within micro- and millichannels is a pivotal element across various applications, ranging from chemical synthesis to biomedical diagnostics and environmental monitoring. The inherent low Reynolds number flow in these channels often results in a parabolic velocity profile, leading to a broad residence time distribution. Achieving efficient mixing at such small scales presents unique challenges and opportunities. This review encompasses various techniques and strategies to evaluate and enhance mixing efficiency in these confined environments. It explores the significance of mixing in micro- and millichannels, highlighting its relevance for enhanced reaction kinetics, homogeneity in mixed fluids, and analytical accuracy. We discuss various mixing methodologies that have been employed to get a narrower residence time distribution. The role of channel geometry, flow conditions, and mixing mechanisms in influencing the mixing performance are also discussed. Various emerging technologies and advancements in microfluidic devices and tools specifically designed to enhance mixing efficiency are highlighted. We emphasize the potential applications of micro- and millichannels in fields of nanoparticle synthesis, which can be utilized for biological applications. Additionally, the prospects of machine learning and artificial intelligence are offered toward incorporating better mixing to achieve precise control over nanoparticle synthesis, ultimately enhancing the potential for applications in these miniature fluidic systems.}, } @article {pmid38295375, year = {2024}, author = {Shi, Q and Wu, J and Chen, H and Xu, X and Yang, YB and Ding, M}, title = {Inertial migration of polymer micelles in a square microchannel.}, journal = {Soft matter}, volume = {}, number = {}, pages = {}, doi = {10.1039/d3sm01304a}, pmid = {38295375}, issn = {1744-6848}, abstract = {Using a hybrid simulation approach that combines a lattice-Boltzmann method for fluid flow and a molecular dynamics model for polymers, we investigate the inertial migration of star-like and crew-cut polymer micelles in a square microchannel. It is found that they exhibit two types of equilibrium positions, which shift further away from the center of the microchannel when the Reynolds number (Re) increases, as can be observed for soft particles. What differs from the behaviors of soft particles is that here, the blockage ratio is no longer the decisive factor. When the sizes are the same, the star-like micelles are always relatively closer to the microchannel wall as they gradually transition from spherical to disc-like with the increase of Re. In comparison, the crew-cut micelles are only transformed into an ellipsoid. Conversely, when the hydrophobic core sizes are the same, the equilibrium position of the star-like micelles becomes closer to that of the crew-cut micelles. Our results demonstrate that for polymer micelles with a core-shell structure, the equilibrium position is no longer solely determined by their overall dimensions but depends on the core and shell's specific dimensions, especially the hydrophobic core size. This finding opens up a new approach for achieving the separation of micelles in inertial migration.}, } @article {pmid38284759, year = {2024}, author = {Maar, K and Shavit, U and Andersen, A and Kiørboe, T}, title = {The fluid dynamics of barnacle feeding.}, journal = {The Journal of experimental biology}, volume = {}, number = {}, pages = {}, doi = {10.1242/jeb.246541}, pmid = {38284759}, issn = {1477-9145}, abstract = {Sessile barnacles feed by sweeping their basket-like cirral fan through the water, intercepting suspended prey. A primary component of the diet of adult barnacles is copepods that are sensitive to fluid disturbances and capable of escaping. How do barnacles manage to capture copepods despite the fluid disturbances they generate? We examined this question by describing the feeding current architecture of 1 cm sized Balanus crenatus using particle image velocimetry, and by studying the trajectories of captured copepods and the escapes of evading copepods. We find that barnacles produce a feeding current that arrives both from behind and the sides of the barnacle. The flow from the sides represents quiescent corridors of low fluid deformation and uninterrupted by the beating cirral fan. Potential prey arriving from behind are likely to encounter the cirral fan and, hence, capture here is highly unlikely. Accordingly, most captured copepods arrived through the quiet corridors, while most copepods arriving from behind managed to escape. Thus, it is the unique feeding flow architecture that allows feeding on evasive prey. We used the Landau-Squire jet as a simple model of the feeding current. For the Reynolds number of our experiments, the model reproduces the main features of the feeding current, including the lateral feeding corridors. Furthermore, the model suggests that smaller barnacle specimens, operating at lower Reynolds numbers, will produce a fore-and-aft symmetric feeding current without the lateral corridors. This suggests an ontogenetic diet shift from non-evasive prey to inclusion of evasive prey as the barnacle grows.}, } @article {pmid38282920, year = {2023}, author = {Abbas, N and Mustafa, Z and Abodayeh, K and Shatnawi, TAM and Shatanawi, W}, title = {Darcy resistant of Soret and Dufour impact of radiative induced magnetic field sutterby fluid flow over stretching cylinder.}, journal = {Heliyon}, volume = {9}, number = {12}, pages = {e22503}, doi = {10.1016/j.heliyon.2023.e22503}, pmid = {38282920}, issn = {2405-8440}, abstract = {The incompressible two-dimensional steady flow of Sutterby fluid over a stretching cylinder is taken into account. The magnetic Reynolds number is not deliberated low in the present analysis. Radiation and variable thermal conductivity are considered to debate the impact on the cylindrical surface. The Dufour and Soret impacts are considered on the cylinder. The mathematical model is settled by employing boundary layer approximations in the form of differential equations. The system of differential equations becomes dimensionless using suitable transformations. The dimensionless nonlinear differential equations are solved through a numerical scheme(bvp4c technique). The flow parameters of physical effects on the velocity, temperature, heat transfer rate, and friction between surface and liquid are presented in tabular as well as graphical form. The velocity function declined by improving the values of the Sponginess parameter. The fluid temperature is reduced by increment in curvature parameter.}, } @article {pmid38276832, year = {2023}, author = {Chang, L and Zhao, G and Buren, M and Sun, Y and Jian, Y}, title = {Alternating Current Electroosmotic Flow of Maxwell Fluid in a Parallel Plate Microchannel with Sinusoidal Roughness.}, journal = {Micromachines}, volume = {15}, number = {1}, pages = {}, doi = {10.3390/mi15010004}, pmid = {38276832}, issn = {2072-666X}, support = {Nos. 12162003, 11862018, 12262026//the National Natural Science Foundation of China/ ; Grant Nos. 2022LHMS01001, 2021MS01007//the Natural Science Foundation of the Inner Mongolia Autonomous Region of China/ ; No. NMGIRT2323//Innovative Research Team in the Universities of Inner Mongolia Autonomous Region/ ; No. NCYWT23035//Basic Research funds for Universities Directly under the Autonomous Region/ ; Grant No. NJZY23054//the Research Program of Science and Technology in the Universities of Inner Mongolia Autonomous Region/ ; }, abstract = {The EOF of a viscoelastic Maxwell fluid driven by an alternating pressure gradient and electric field in a parallel plate microchannel with sinusoidal roughness has been investigated within the Debye-Hückel approximation based on boundary perturbation expansion and separation of variables. Perturbation solutions were obtained for the potential distribution, the velocity and the mean velocity, and the relation between the mean velocity and the roughness. There are significant differences in the velocity amplitudes of the Newtonian and Maxwell fluids. It is shown here that the velocity distribution of the viscoelastic fluid is significantly affected by the roughness of the walls, which leads to the appearance of fluctuations in the fluid. Also, the velocity is strongly dependent on the phase difference θ of the roughness of the upper and lower plates. As the oscillation Reynolds number ReΩ increases, the velocity profile and the average velocity um(t) of AC EOF oscillate rapidly but the velocity amplitude decreases. The Deborah number De plays a similar role to ReΩ, which makes the AC EOF velocity profile more likely to oscillate. Meanwhile, phase lag χ (representing the phase difference between the electric field and the mean velocity) decreases when G and θ are increased. However, for larger λ (e.g., λ > 3), it almost has no phase lag χ.}, } @article {pmid38267645, year = {2024}, author = {Salman, M and Liu, J and Chauhan, R and Souby, MM and Kim, SC}, title = {A MATLAB simulation-based analytical study of energy, exergy, and cost benefits in jet-impinged protrusion-roughened double pass solar air collector.}, journal = {Environmental science and pollution research international}, volume = {}, number = {}, pages = {}, pmid = {38267645}, issn = {1614-7499}, support = {2019R1A5A8080290//National Research Foundation of Korea/ ; }, abstract = {This study analyzes the performance and cost-effectiveness of a protrusion-roughened jet-impinged double-pass solar air collector (PRJDPSAC) within a Reynolds number (Re) range of 2500 to 22,500. Examining jet slot parameters, i.e., the jet height ratio (Hjp/Dhd = 0.11-0.44), stream-wise pitch ratio (Xjp/Dhd = 0.44-1.32), and span-wise pitch ratio (Yjp/Dhd = 0.44-1.32), the model demonstrates enhanced energy conversion, minimizes losses, improves efficiency, and brings positive economic impact, making it a promising solution for diverse applications including drying processes, livestock facilities, remote accommodations, and HVAC system pre-heating. The examination incorporates advanced MATLAB simulations to assess energy-exergy performance and cost viability. At lower Re values, both energy ([Formula: see text]) and exergy ([Formula: see text]) efficiencies increase uniformly; however, stabilization and decline occur at higher Re values. The maximum [Formula: see text] for the PRJDPSAC is 4.38% under a temperature rise parameter of 60 × 10[-3] Km[2]/W for obtaining optimum values of Xjp/Dhd = 1.32, Hjp/Dhd = 0.22, and Yjp/Dhd = 1.32, which is 31% higher than that of the smooth double-pass solar air collector (DPSAC). Economic benefits are significant for PRJDPSAC within mair (0.01-0.07 kg/s), but above 0.07 kg/s, the DPSAC becomes more cost-effective. Integrating simulation and experimental data, the study highlights MATLAB's effectiveness for solar energy system analysis and optimization, reinforcing the practicality of the proposed collector design.}, } @article {pmid38265427, year = {2024}, author = {Wu, Y and Wang, F and Zheng, S and Nestler, B}, title = {Evolution dynamics of thin liquid structures investigated using a phase-field model.}, journal = {Soft matter}, volume = {}, number = {}, pages = {}, doi = {10.1039/d3sm01553j}, pmid = {38265427}, issn = {1744-6848}, abstract = {Liquid structures of thin-films and torus droplets are omnipresent in daily lives. The morphological evolution of liquid structures suspending in another immiscible fluid and sitting on a solid substrate is investigated by using three-dimensional (3D) phase-field (PF) simulations. Here, we address the evolution dynamics by scrutinizing the interplay of surface energy, kinetic energy, and viscous dissipation, which is characterized by Reynolds number Re and Weber number We. We observe special droplet breakup phenomena by varying Re and We. In addition, we gain the essential physical insights into controlling the droplet formation resulting from the morphological evolution of the liquid structures by characterizing the top and side profiles under different circumstances. We find that the shape evolution of the liquid structures is intimately related to the initial shape, Re, We as well as the intrinsic wettability of the substrate. Furthermore, it is revealed that the evolution dynamics are determined by the competition between the coalescence phenomenology and the hydrodynamic instability of the liquid structures. For the coalescence phenomenology, the liquid structure merges onto itself, while the hydrodynamic instability leads to the breakup of the liquid structure. Last but not least, we investigate the influence of wall relaxation on the breakup outcome of torus droplets on substrates with different contact angles. We shed light on how the key parameters including the initial shape, Re, We, wettability, and wall relaxation influence the droplet dynamics and droplet formation. These findings are anticipated to contribute insights into droplet-based systems, potentially impacting areas like ink-jet printing, drug delivery systems, and microfluidic devices, where the interplay of surface energy, kinetic energy, and viscous dissipation plays a crucial role.}, } @article {pmid38264707, year = {2024}, author = {Jeon, H and Lee, SH and Shin, J and Song, K and Ahn, N and Park, J}, title = {Elasto-inertial microfluidic separation of microspheres with submicron resolution at high-throughput.}, journal = {Microsystems & nanoengineering}, volume = {10}, number = {}, pages = {15}, pmid = {38264707}, issn = {2055-7434}, abstract = {Elasto-inertial microfluidic separation offers many advantages including high throughput and separation resolution. Even though the separation efficiency highly depends on precise control of the flow conditions, no concrete guidelines have been reported yet in elasto-inertial microfluidics. Here, we propose a dimensionless analysis for precise estimation of the microsphere behaviors across the interface of Newtonian and viscoelastic fluids. Reynolds number, modified Weissenberg number, and modified elastic number are used to investigate the balance between inertial and elastic lift forces. Based on the findings, we introduce a new dimensionless number defined as the width of the Newtonian fluid stream divided by microsphere diameter. The proposed dimensionless analysis allows us to predict whether the microspheres migrate across the co-flow interface. The theoretical estimation is found to be in good agreement with the experimental results using 2.1- and 3.2-μm-diameter polystyrene microspheres in a co-flow of water and polyethylene oxide solution. Based on the theoretical estimation, we also realize submicron separation of the microspheres with 2.1 and 2.5 μm in diameter at high throughput, high purity (>95%), and high recovery rate (>97%). The applicability of the proposed method was validated by separation of platelets from similar-sized Escherichia coli (E.coli).}, } @article {pmid38248619, year = {2024}, author = {Macías, MM and García-Ortiz, JH and Oliveira, TF and Brasil Junior, ACP}, title = {Numerical Investigation of Dimensionless Parameters in Carangiform Fish Swimming Hydrodynamics.}, journal = {Biomimetics (Basel, Switzerland)}, volume = {9}, number = {1}, pages = {}, doi = {10.3390/biomimetics9010045}, pmid = {38248619}, issn = {2313-7673}, abstract = {Research into how fish and other aquatic organisms propel themselves offers valuable natural references for enhancing technology related to underwater devices like vehicles, propellers, and biomimetic robotics. Additionally, such research provides insights into fish evolution and ecological dynamics. This work carried out a numerical investigation of the most relevant dimensionless parameters in a fish swimming environment (Reynolds Re, Strouhal St, and Slip numbers) to provide valuable knowledge in terms of biomechanics behavior. Thus, a three-dimensional numerical study of the fish-like lambari, a BCF swimmer with carangiform kinematics, was conducted using the URANS approach with the k-ω-SST transition turbulence closure model in the OpenFOAM software. In this study, we initially reported the equilibrium Strouhal number, which is represented by St∗, and its dependence on the Reynolds number, denoted as Re. This was performed following a power-law relationship of St∝Re(-α). We also conducted a comprehensive analysis of the hydrodynamic forces and the effect of body undulation in fish on the production of swimming drag and thrust. Additionally, we computed propulsive and quasi-propulsive efficiencies, as well as examined the influence of the Reynolds number and Slip number on fish performance. Finally, we performed a vortex dynamics analysis, in which different wake configurations were revealed under variations of the dimensionless parameters St, Re, and Slip. Furthermore, we explored the relationship between the generation of a leading-edge vortex via the caudal fin and the peak thrust production within the motion cycle.}, } @article {pmid38243509, year = {2023}, author = {Xiong, J and Liu, X and Feng, H and Huang, H}, title = {Inertial migration of spherical and oblate particles in a triangular microchannel.}, journal = {Physical review. E}, volume = {108}, number = {6-2}, pages = {065105}, doi = {10.1103/PhysRevE.108.065105}, pmid = {38243509}, issn = {2470-0053}, abstract = {The. inertial migration of both spherical and oblate particles within an equilateral triangular channel is studied numerically. Our study primarily focuses on the effects of fluid inertia, quantified by the Reynolds number (Re) and particle size (β). Our observations reveal two distinct equilibrium positions: the corner equilibrium position (CEP) is situated along the angle bisector near the corner, while the face equilibrium position (FEP) is located on a segment of the line perpendicular from the triangle's center to one of its sides. Spherical particles with varying initial positions predominantly reach the FEP. For oblate particles initially positioned along the angle bisector with a specific orientation, meaning the particle's evolution axis is inside the plane bisecting the angle, they will migrate along the angle bisector to reach the CEP while rotating in the tumbling mode. Conversely, for particles with different initial orientations and positions, they will employ the log-rolling mode to reach the FEP. Notably, we identify a dual-stage particle migration process to the FEP, with trajectories converging to an equilibrium manifold, which bears a resemblance to the cross section of the channel. To further illustrate the transition between FEP and CEP under general initial conditions, except for those along the angle bisector, we construct a phase diagram in the (Re, β) parameter space. This transition is often triggered by the size of larger particles (as the FEP cannot accommodate them) or the influence of inertia for smaller particles. For the FEP, especially for medium- or small-size particles, we notice an initial outward movement of the FEP from the center of the cross section as Re increases, followed by a return towards the center. This behavior results from the interplay of three forces acting on the particle. This research holds potential implications for the design of microfluidic devices, offering insights into the behavior of particles within equilateral triangular channels.}, } @article {pmid38243467, year = {2023}, author = {Wang, S and Wang, J and Deng, J}, title = {Effect of layer thickness for the bounce of a particle settling through a density transition layer.}, journal = {Physical review. E}, volume = {108}, number = {6-2}, pages = {065108}, doi = {10.1103/PhysRevE.108.065108}, pmid = {38243467}, issn = {2470-0053}, abstract = {We study numerically a spherical particle settling through a density transition layer at moderate Reynolds numbers Re_{u} =69∼259 for the upper fluid. We investigate how the transition layer thickness affects the particle's bouncing behavior as it crosses the interface. The previous intuitive understanding was that the bounce occurs when the relative thickness of the transition layer, L/D, which is characterized by the ratio of the layer thickness L to the particle diameter D, is small. Indeed, we report no bounce phenomenon for very thick interfaces, i.e., L/D>10 in the current parametric range. However, we argue that the bounce can also be inhibited when L/D is too small. Upon a fixed upper layer Reynolds number Re_{u} =207 with varying L/D, we examine the flow evolution of these cases. We propose that this inhibition is attributed to two mechanisms. First, as the interface thickness decreases, the detachment of the attached lighter fluid from the upper layer occurs more rapidly, resulting in a faster decrease in buoyancy. Second, in the case of a very thin interface (L/D=0.5-3.0), the residual light fluid accumulates and undergoes a secondary detachment, separating from the particle at an angle relative to the central axis. This secondary detachment reduces the drag force and effectively prevents the particle from experiencing a rebound motion.}, } @article {pmid38237184, year = {2024}, author = {Liu, T and Deng, H and He, F and Wu, Y and Wu, Z and Wan, F and Chen, T and Xu, W and Song, Y and Guo, X}, title = {Synthesizing high performance LNMO cathode materials with porous structure by manipulating Reynolds number in a microreactor.}, journal = {Nanotechnology}, volume = {}, number = {}, pages = {}, doi = {10.1088/1361-6528/ad2017}, pmid = {38237184}, issn = {1361-6528}, abstract = {The demand for Lithium-ion batteries (LIBs) has significantly grown in the last decade due to their extensive use electric vehicles (EVs). To further advance the commercialization of LIBs for various applications, there is a pressing need to develop electrode materials with enhanced performance. The porous microsphere morphology LiNixMn2-xO4 (LNMO) is considered to be an effective material with both high energy density and excellent rate performance. Nevertheless, LNMO synthesis technology still has problem such as long reaction time, high energy consumption and environmental pollution. Herein, LNMO microsphere was successfully synthesized with short precursors reaction time (18 seconds) at 40oC without using chelating agent by microreaction technology combined solid-state lithiation. The optimized LNMO cathode shows microsphere (~8μm) morphology stacked by nano primary particles, with abundant mesoporous and fully exposed low-energy plane. The electrochemical analysis indicates that the optimized LNMO cathode demonstrates 97.33% capacity retention even after 200 cycles at 1C. Additionally, the material shows a highly satisfactory discharge capacity of 92.3 mAh·g-1 at 10C. Overall, microreaction technology is anticipated to offer a novel approach in the synthesis of LNMO cathode materials with excellent performance.}, } @article {pmid38233489, year = {2024}, author = {Ashraf, H and Siddique, I and Siddiqa, A and Tawfiq, FMO and Tchier, F and Zulqarnain, RM and Rehman, HU and Bhatti, S and Rehman, A}, title = {Analysis of two layered peristaltic-ciliary transport of Jeffrey fluid and in vitro preimplantation embryo development.}, journal = {Scientific reports}, volume = {14}, number = {1}, pages = {1469}, pmid = {38233489}, issn = {2045-2322}, abstract = {The analysis of peristaltic-ciliary transport in the human female fallopian tube, specifically in relation to the growing embryo, is a matter of considerable physiological importance. This paper proposes a biomechanical model that incorporates a finite permeable tube consisting of two layers, where the Jeffrey fluid model characterizes the viscoelastic properties of the growing embryo and continuously secreting fluid. Jeffrey fluid entering with some negative pressure gradient forms the core fluid layer while continuously secreting Jeffrey fluid forms the peripheral fluid layer. The resulting partial differential equations are solved for closed-form solutions after employing the assumption of long wavelength. The analysis delineated that increasing the constant secretion velocity, Darcy number, and Reynolds number leads to a decrease in the appropriate residue time of the core fluid layer and a reduction in the size of the secreting fluid bolus in the peripheral fluid layer. Eventually, the boluses completely disappear when the constant secretion velocity exceeds 3.0 Progesterone ([Formula: see text]) and estradiol ([Formula: see text]) directly regulate the transportation of the growing embryo, while luteinizing hormone (LH) and follicle-stimulating hormone (FSH), prolactin, anti-mullerian hormone (AMH), and thyroid-stimulating hormone (TSH) have an indirect effects. Based on the number and size of blastomeres, the percentage of fragmentation, and the presence of multinucleated blastomeres two groups were formed in an in vitro experiment. Out of 50 patients, 26 (76.5%) were pregnant in a group of the good quality embryos, and only 8 (23.5%) were in a group of the bad quality embryos. The transport of growing embryo in the human fallopian tube and preimplantation development of human embryos in in vitro are constraint by baseline hormones FSH, LH, prolactin, [Formula: see text], AMH, and TSH.}, } @article {pmid38233420, year = {2024}, author = {Akbar, NS and Rafiq, M and Muhammad, T and Alghamdi, M}, title = {Microbic flow analysis of nano fluid with chemical reaction in microchannel with flexural walls under the effects of thermophoretic diffusion.}, journal = {Scientific reports}, volume = {14}, number = {1}, pages = {1474}, pmid = {38233420}, issn = {2045-2322}, abstract = {The current investigation examines the peristaltic flow, in curved conduit, having complaint boundaries for nanofluid. The effects of curvature are taken into account when developing the governing equations for the nano fluid model for curved channels. Nonlinear & coupled differential equations are then simplified by incorporating the long wavelength assumption along with smaller Reynolds number. The homotopy perturbation approach is used to analytically solve the reduced coupled differential equations. The entropy generation can be estimated through examining the contributions of heat and fluid viscosities. The results of velocity, temperature, concentration, entropy number, and stream functions have been plotted graphically in order to discuss the physical attributes of the essential quantities. Increase in fluid velocity within the curved conduit is noticed for higher values of thermophoresis parameter and Brownian motion parameter further entropy generation number is boosted by increasing values of Grashof number.}, } @article {pmid38213601, year = {2023}, author = {Allehiany, FM and Riaz, A and Shoukat, S and Alhamzi, G and Mahmoud, EE}, title = {Three dimensional study for entropy optimization in nanofluid flow through a compliant curved duct: A drug delivery and therapy application.}, journal = {Heliyon}, volume = {9}, number = {12}, pages = {e22255}, pmid = {38213601}, issn = {2405-8440}, abstract = {This research explores the three-dimensional characteristics of nanofluid dynamics within curved ducts, in contrast to earlier studies that mainly focus on two-dimensional flow. By using this ground-breaking method, we can capture a more accurate depiction of fluid behavior that complies with the intricate duct design. In this study, we investigate the three dimensional flow and entropic analysis of peristaltic nanofluid flows in a flexible curved duct, comparing the effects of silver and copper nanoparticles. To obtain accurate results, we assume physical constraints such as long wavelength and low Reynolds number and used a perturbation technique through NDSolve commands for finding exact solutions of the obtained differential equations. A comprehensive error analysis is provided through residual error table and figures to estimate a suitable range of the physical factors. Our findings indicate that the velocity of the nanofluid is directly proportional to the elasticity of the walls, while the mass per unit volume inversely affects velocity. We show that reducing the aspect ratio of the duct rectangular section can decrease entropy generation by raising magnitudes of damping force exerted by to the flexible walls of the enclosure. Additionally, using a larger height of the channel than the breadth can reduce stream boluses. The practical implications of this study extend beyond turbines and endoscopy to biomedical processes such as drug delivery and microfluidic systems.}, } @article {pmid38212397, year = {2024}, author = {Uttieri, M and Svetlichny, L}, title = {Escape performance in the cyclopoid copepod Oithona davisae.}, journal = {Scientific reports}, volume = {14}, number = {1}, pages = {1078}, pmid = {38212397}, issn = {2045-2322}, support = {CN00000033//Ministero dell'Università e della Ricerca/ ; }, abstract = {Escaping a predator is one of the keys to success for any living creature. The performance of adults (males, females, and ovigerous females) of the cyclopoid copepod Oithona davisae exposed to an electrical stimulus is analysed as a function of temperature by measuring characteristic parameters associated with the escape movement (distance covered, duration of the appendage movement, mean and maximum escape speeds, Reynolds number). In addition, as a proxy for the efficiency of the motion, the Strouhal number was calculated. The escape performance showed temperature-dependent relationships within each adult state, as well as differences between sexes; additionally, changes owing to the presence of the egg sac were recorded in females. In a broader perspective, the results collected reveal the occurrence of different behavioural adaptations in males and females, adding to the comprehension of the mechanisms by which O. davisae interacts with its environment and shedding new light on the in situ population dynamics of this species.}, } @article {pmid38198675, year = {2024}, author = {Banerjee, A and Pavithran, I and Sujith, RI}, title = {Early warnings of tipping in a non-autonomous turbulent reactive flow system: Efficacy, reliability, and warning times.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {34}, number = {1}, pages = {}, doi = {10.1063/5.0160918}, pmid = {38198675}, issn = {1089-7682}, abstract = {Real-world complex systems such as the earth's climate, ecosystems, stock markets, and combustion engines are prone to dynamical transitions from one state to another, with catastrophic consequences. State variables of such systems often exhibit aperiodic fluctuations, either chaotic or stochastic in nature. Often, the parameters describing a system vary with time, showing time dependency. Constrained by these effects, it becomes difficult to be warned of an impending critical transition, as such effects contaminate the precursory signals of the transition. Therefore, a need for efficient and reliable early-warning signals (EWSs) in such complex systems is in pressing demand. Motivated by this fact, in the present work, we analyze various EWSs in the context of a non-autonomous turbulent thermoacoustic system. In particular, we investigate the efficacy of different EWS in forecasting the onset of thermoacoustic instability (TAI) and their reliability with respect to the rate of change of the control parameter. This is the first experimental study of tipping points in a non-autonomous turbulent thermoacoustic system. We consider the Reynolds number (Re) as the control parameter, which is varied linearly with time at finite rates. The considered EWSs are derived from critical slowing down, spectral properties, and fractal characteristics of the system variables. The state of TAI is associated with large amplitude acoustic pressure oscillations that could lead thermoacoustic systems to break down. We consider acoustic pressure fluctuations as a potential system variable to perform the analysis. Our analysis shows that irrespective of the rate of variation of the control parameter, the Hurst exponent and variance of autocorrelation coefficients warn of an impending transition well in advance and are more reliable than other EWS measures. Additionally, we show the variation in the warning time to an impending TAI with rates of change of the control parameter. We also investigate the variation in amplitudes of the most significant modes of acoustic pressure oscillations with the Hurst exponent. Such variations lead to scaling laws that could be significant in prediction and devising control actions to mitigate TAI.}, } @article {pmid38191806, year = {2024}, author = {Faisal, S and Barbour, M and Seibel, EJ and Aliseda, A}, title = {Hemodynamics of Saline Flushing in Endoscopic Imaging of Partially Occluded Coronary Arteries.}, journal = {Cardiovascular engineering and technology}, volume = {}, number = {}, pages = {}, pmid = {38191806}, issn = {1869-4098}, support = {1R43HL139323-01/GF/NIH HHS/United States ; GCR 2120774//National Science Foundation/ ; }, abstract = {PURPOSE: Intravascular endoscopy can aid in the diagnosis of coronary atherosclerosis by providing direct color images of coronary plaques. The procedure requires a blood-free optical path between the catheter and plaque, and achieving clearance safely remains an engineering challenge. In this study, we investigate the hemodynamics of saline flushing in partially occluded coronary arteries to advance the development of intravascular forward-imaging catheters that do not require balloon occlusion.

METHODS: In-vitro experiments and CFD simulations are used to quantify the influence of plaque size, catheter stand-off distance, saline injection flowrate, and injection orientation on the time required to achieve blood clearance.

RESULTS: Experiments and simulation of saline injection from a dual-lumen catheter demonstrated that flushing times increase both as injection flow rate (Reynolds number) decreases and as the catheter moves distally away from the plaque. CFD simulations demonstrated that successful flushing was achieved regardless of lumen axial orientation in a 95% occluded artery. Flushing time was also found to increase as plaque size decreases for a set injection flowrate, and a lower limit for injection flowrate was found to exist for each plaques size, below which clearance was not achieved. For the three occlusion sizes investigated (90, 95, 97% by area), successful occlusion was achieved in less than 1.2 s. Investigation of the pressure fields developed during injection, highlight that rapid clearance can be achieved while keeping the arterial overpressure to < 1 mmHg.

CONCLUSIONS: A dual lumen saline injection catheter was shown to produce clearance safely and effectively in models of partially occluded coronary arteries. Clearance was achieved across a range of engineering and clinical parameters without the use of a balloon occlusion, providing development guideposts for a fluid injection system in forward-imaging coronary endoscopes.}, } @article {pmid38181350, year = {2023}, author = {Inubushi, M and Saiki, Y and Kobayashi, MU and Goto, S}, title = {Characterizing Small-Scale Dynamics of Navier-Stokes Turbulence with Transverse Lyapunov Exponents: A Data Assimilation Approach.}, journal = {Physical review letters}, volume = {131}, number = {25}, pages = {254001}, doi = {10.1103/PhysRevLett.131.254001}, pmid = {38181350}, issn = {1079-7114}, abstract = {Data assimilation (DA) of turbulence, which involves reconstructing small-scale turbulent structures based on observational data from large-scale ones, is crucial not only for practical forecasting but also for gaining a deeper understanding of turbulent dynamics. We propose a theoretical framework for DA of turbulence based on the transverse Lyapunov exponents (TLEs) in synchronization theory. Through stability analysis using TLEs, we identify a critical length scale as a key condition for DA; turbulent dynamics smaller than this scale are synchronized with larger-scale turbulent dynamics. Furthermore, considering recent findings for the maximal Lyapunov exponent and its relation with the TLEs, we clarify the Reynolds number dependence of the critical length scale.}, } @article {pmid38177658, year = {2024}, author = {Akbar, NS and Rafiq, M and Muhammad, T and Alghamdi, M}, title = {Electro osmotically interactive biological study of thermally stratified micropolar nanofluid flow for Copper and Silver nanoparticles in a microchannel.}, journal = {Scientific reports}, volume = {14}, number = {1}, pages = {518}, pmid = {38177658}, issn = {2045-2322}, abstract = {A novel mathematical analysis is established that summits the key features of peristaltic propulsion for a non-Newtonian micropolar fluid with the electroosmosis and heat transfer enhancement using nanoparticles. In such physiological models, the channel have a symmetric configuration in accordance with the biological problem. Being mindful of this fact, we have disclosed an integrated analysis on symmetric channel that incorporates major physiological applications. The creeping flow inference is reviewed to model this realistic problem. Flow equations are model using cartesian coordinates and simplified using long wave length and low Reynolds number approximation. Nonlinear linear couple equations are solving numerically. We have studied the variation in the properties of nanofluid developed by two different types of nanoparticles (i.e. Cu and Ag nanoparticles). Graphical illustrations are unveiled to highlight the physical aspects of nanoparticles and flow parameters. The exploration demonstrates that the micro-rotation of the nano-liquid elements enhances the thermal conductivity of the fluid movement. The effect of micropolar fluid parameters on mean flow and pressure variables is also presented.}, } @article {pmid38177235, year = {2024}, author = {Chinnasamy, P and Sivajothi, R and Sathish, S and Abbas, M and Jeyakrishnan, V and Goel, R and Alqahtani, MS and Loganathan, K}, title = {Peristaltic transport of Sutterby nanofluid flow in an inclined tapered channel with an artificial neural network model and biomedical engineering application.}, journal = {Scientific reports}, volume = {14}, number = {1}, pages = {555}, pmid = {38177235}, issn = {2045-2322}, support = {R.G.P.2/453/44//Deanship of Scientific Research, King Khalid University/ ; R.G.P.2/453/44//Deanship of Scientific Research, King Khalid University/ ; }, abstract = {Modern energy systems are finding new applications for magnetohydrodynamic rheological bio-inspired pumping systems. The incorporation of the electrically conductive qualities of flowing liquids into the biological geometries, rheological behavior, and propulsion processes of these systems was a significant effort. Additional enhancements to transport properties are possible with the use of nanofluids. Due to their several applications in physiology and industry, including urine dynamics, chyme migration in the gastrointestinal system, and the hemodynamics of tiny blood arteries. Peristaltic processes also move spermatozoa in the human reproductive system and embryos in the uterus. The present research examines heat transport in a two-dimensional deformable channel containing magnetic viscoelastic nanofluids by considering all of these factors concurrently, which is vulnerable to peristaltic waves and hall current under ion slip and other situations. Nanofluid rheology makes use of the Sutterby fluid model, while nanoscale effects are modeled using the Buongiorno model. The current study introduces an innovative numerical computing solver utilizing a Multilayer Perceptron feed-forward back-propagation artificial neural network (ANN) with the Levenberg-Marquardt algorithm. Data were collected for testing, certifying, and training the ANN model. In order to make the dimensional PDEs dimensionless, the non-similar variables are employed and calculated by the Homotopy perturbation technique. The effects of developing parameters such as Sutterby fluid parameter, Froude number, thermophoresis, ion-slip parameter, Brownian motion, radiation, Eckert number, and Hall parameter on velocity, temperature, and concentration are demonstrated. The machine learning model chooses data, builds and trains a network, and subsequently assesses its performance using the mean square error metric. Current results declare that the improving Reynolds number tends to increase the pressure rise. Improving the Hall parameter is shown to result in a decrease in velocity. When raising a fluid's parameter, the temperature profile rises.}, } @article {pmid38167620, year = {2024}, author = {Heronimczak, M and Mrowiec, A and Rząsa, M and Koszela, K}, title = {Measurements of the flow of a liquid-solid mixture/suspension through a segmented orifice.}, journal = {Scientific reports}, volume = {14}, number = {1}, pages = {269}, pmid = {38167620}, issn = {2045-2322}, abstract = {The paper attempts to solve the metrological problem that occurs when measuring the intensity of a flowing fluid with suspended solids with densities greater and less than the density of the fluid. The issue of the possibility of self-cleaning of a prototype variant of a segmented orifice from floating solid particles forming mixture/suspensions is discussed. For spherical particles of solids calculations have been made to allow for determining a borderline between their floating and entrainment by the flow, based on dimensionless numbers: Archimedes number and Reynolds number. Experimental tests and CFD simulations were conducted with a variable flow determined by Reynolds number for comparable segmental orifices with orifice module m = 0.102. Flow characteristics were plotted. Based on the results obtained from numerical simulations, positive influence of the inclination of skew segmental orifice downflow plane was presented. The results obtained from the study are a guideline for planning further studies to expand the knowledge of segmented orifices with inclined inflow plane.}, } @article {pmid38164243, year = {2024}, author = {Jubaer, H and Thomas, M and Farkas, D and Kolanjiyil, AV and Momin, MAM and Hindle, M and Longest, W}, title = {Development of an effective two-equation turbulence modeling approach for simulating aerosol deposition across a range of turbulence levels.}, journal = {Journal of aerosol science}, volume = {175}, number = {}, pages = {106262}, doi = {10.1016/j.jaerosci.2023.106262}, pmid = {38164243}, issn = {0021-8502}, abstract = {Pharmaceutical aerosol systems present a significant challenge to computational fluid dynamics (CFD) modeling based on the need to capture multiple levels of turbulence, frequent transition between laminar and turbulent flows, anisotropic turbulent particle dispersion, and near-wall particle transport phenomena often within geometrically complex systems over multiple time scales. Two-equation turbulence models, such as the k-ω family of approximations, offer a computationally efficient solution approach, but are known to require the use of near-wall (NW) corrections and eddy interaction model (EIM) modifications for accurate predictions of aerosol deposition. The objective of this study was to develop an efficient and effective two-equation turbulence modeling approach that enables accurate predictions of pharmaceutical aerosol deposition across a range of turbulence levels. Key systems considered were the traditional aerosol deposition benchmark cases of a 90-degree bend (Re=6,000) and a vertical straight section of pipe (Re=10,000), as well as a highly complex case of direct-to-infant (D2I) nose-to-lung pharmaceutical aerosol delivery from an air-jet dry powder inhaler (DPI) including a patient interface and infant nasal geometry through mid-trachea (500
OBJECTIVE: In this review, we seek to provide a much-needed bridge between the technical and medical aspects of microfluidic sperm selection. Here, we provide an up-to-date list on microfluidic sperm selection procedures and its application in assisted reproductive technology laboratories.

SEARCH METHOD: A literature search was performed in Web of Science, PubMed, and Scopus to select papers reporting microfluidic sperm selection using the keywords: microfluidic sperm selection, self-motility, non-motile sperm selection, boundary following, rheotaxis, chemotaxis, and thermotaxis. Papers published before March 31, 2023 were selected.

OUTCOMES: Our results show that most studies have used motility-based properties for sperm selection. However, microfluidic platforms are ripe for making use of other properties such as chemotaxis and especially rheotaxis. We have identified that low throughput is one of the major hurdles to current microfluidic sperm selection chips, which can be solved via parallelization.

CONCLUSION: Future work needs to be performed on numerical simulation of the microfluidics chip prior to fabrication as well as relevant clinical assessment after the selection procedure. This would require a close collaboration and understanding among engineers, biologists, and medical professionals. It is interesting that in spite of two decades of microfluidics sperm selection, numerical simulation and clinical studies are lagging behind. It is expected that microfluidic sperm selection platforms will play a major role in the development of fully integrated start-to-finish assisted reproductive technology systems.}, } @article {pmid38144068, year = {2023}, author = {Liu, L and Meng, Z and Zhang, Y and Sun, Y}, title = {Simulation of High-Viscosity Generalized Newtonian Fluid Flows in the Mixing Section of a Screw Extruder Using the Lattice Boltzmann Model.}, journal = {ACS omega}, volume = {8}, number = {50}, pages = {47991-48018}, pmid = {38144068}, issn = {2470-1343}, abstract = {The mixing quality of polymer melts in the mixing section of a single-screw extruder and an injection molding machine has considerable effects on the properties of the molded products. Therefore, the study of the flow field of polymer melts in the mixing section is of great importance. The lattice Boltzmann method (LBM) exhibits unique advantages in simulating non-Newtonian fluids. Many researchers have used LBM to study the flow of medium- and low-viscosity fluids. In their studies, the Reynolds number of fluid flows is generally moderate. However, polymer melts are typical high-viscosity fluids, and their flow Reynolds number is generally very small. The single-relaxation-time lattice Boltzmann method (SRT-LBM) has been used previously to study the flow field of power law fluids in the mixing section. Herein, the flow field of high-viscosity generalized Newtonian fluids in the mixing section of a single-screw extruder is studied using SRT-LBM, the two-relaxation-time lattice Boltzmann method (TRT-LBM), and the multiple-relaxation-time lattice Boltzmann method (MRT-LBM). Through comparison, TRT-LBM has been found to exhibit obvious advantages regarding stability, calculation accuracy, calculation efficiency, and selection of simulation parameters. The TRT-LBM is more suitable for studying high-viscosity generalized Newtonian fluids than SRT-LBM and MRT-LBM. SRT-LBM has low computational efficiency when simulating high-viscosity generalized Newtonian fluids, and instability is easily caused when the fluid has a yield stress. For MRT-LBM, only by studying the relaxation parameters can its advantages be fully utilized. However, optimizing the accuracy and stability of the MRT-LBM via parameter research and linear stability analysis is difficult. For non-Newtonian fluids, it is difficult to optimize the relaxation parameters to make the MRT-LBM more stable and accurate than the TRT-LBM. It is difficult for the MRT-LBM to realize its potential when simulating high-viscosity generalized Newtonian fluids. In addition, we studied the flow pattern in the cross section of the screw channel and compared it to the results reported in previous studies.}, } @article {pmid38132896, year = {2023}, author = {Qiao, Z and Pan, Y and Tang, Y and Cao, Y and Si, F}, title = {Numerical Simulation of Membrane Separation Characteristics of Supercritical Carbon Dioxide and Water.}, journal = {Membranes}, volume = {13}, number = {12}, pages = {}, doi = {10.3390/membranes13120892}, pmid = {38132896}, issn = {2077-0375}, abstract = {To solve the problem of water carryover in the supercritical CO2 separation and mining process in the CO2 plume geothermal system, a three-dimensional shell-tube hollow fiber membrane absorption separator is designed in this study. A coupled species transport model, a porous medium model, and an absorption mathematical model are established, and the flow field and separation characteristics in the circular and flat tubes are analyzed using numerical simulation. The results show that the membrane separation efficiency increases with an increase in the flatness and membrane tube length. When the inlet velocity of the mixture is 0.1 m/s, the separation efficiency can reach 75.92%. Selecting a smaller flow Reynolds number and a more significant membrane tube flatness will reduce the water mass fraction at the outlet. When adding baffles of different shapes to the membrane tube, the mixture fluid in the membrane tube meanders forward and flows in the shape of "Z" under the blocking effect of the arcuate baffles. With an increase in the number of arcuate baffles in the membrane tube, the membrane separation efficiency of the separator increases continuously. The mixture fluid flows in the membrane tube with the built-in torsional baffles in a spiral manner, and the separation efficiency of the membrane separator increases with a torsion ratio reduction in the membrane tube.}, } @article {pmid38118145, year = {2023}, author = {L'Estimé, M and Schindler, M and Shahidzadeh, N and Bonn, D}, title = {Droplet Size Distribution in Emulsions.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {}, number = {}, pages = {}, doi = {10.1021/acs.langmuir.3c02463}, pmid = {38118145}, issn = {1520-5827}, abstract = {The droplet size in emulsions is known to affect the rheological properties and plays a crucial role in many applications of emulsions. Despite its importance, the underlying mechanisms governing droplet size in emulsification remain poorly understood. We investigate the average drop size and size distribution upon emulsification with a high-shear mixer for model oil-in-water emulsions stabilized by a surfactant. The size distribution is found to be a log-normal distribution resulting from the repetitive random breakup of drops. High-shear emulsification, the usual way of making emulsions, is therefore found to be very different from turbulent emulsification given by the Kolmogorov-Hinze theory, for which power-law distributions of the drop size are expected. In agreement with this, the mean droplet size does not follow a scaling with the Reynolds number of the emulsification flow but rather a capillary number scaling based on the viscosity of the continuous phase.}, } @article {pmid38117193, year = {2023}, author = {Tang, Y and Li, G and Wu, J and Wang, G and He, Y and Wei, J}, title = {Charging characteristics of long distance accumulator for underwater electro-hydraulic control system.}, journal = {The Review of scientific instruments}, volume = {94}, number = {12}, pages = {}, doi = {10.1063/5.0168419}, pmid = {38117193}, issn = {1089-7623}, abstract = {Long distance accumulators are widely used in underwater electro-hydraulic control systems. However, as the working depth increases, the underwater umbilical cable becomes longer. The actual physical properties of the gas in the accumulator change. These factors affect the charging characteristics of the accumulator. To address the above issues, a simulation model of the charging of the long distance accumulator under real operating conditions is developed. Among them, the real properties of the gas inside the accumulator were calculated using the Redlich-Kwong-Soave method. The coefficient of friction within the umbilical cable is based on the Reynolds number and relative roughness. The simulation data were compared with the experimental results in the South China Sea to verify the accuracy of the simulation model. The effects of key factors on the charging characteristics of the long distance accumulators were also analyzed. The results show that the simulation results are in good agreement with the experimental results. The law of accumulator charging was analyzed: the greater the pressure of the gas source, the smaller the accumulator charging time; the greater the working water depth, the shorter the accumulator charging time. The research provides guidance for the design of long distance accumulators.}, } @article {pmid38011727, year = {2023}, author = {Bao, H and Song, B and Ma, D and Xue, D}, title = {Aerodynamic performance of flapping wing with alula under different kinematics of complex flapping motion.}, journal = {Bioinspiration & biomimetics}, volume = {19}, number = {1}, pages = {}, doi = {10.1088/1748-3190/ad0ffd}, pmid = {38011727}, issn = {1748-3190}, abstract = {The flight of birds is a remarkable feat, and their remarkable ability to fly derives from complex multi-degree-of-freedom flapping motions and small-scale feather structures that have evolved over millions of years. One of these feather structures is the alula, which can enhance the birds' flight performance at low speeds and large angles of attack. Previous studies on the alula have focused on the steady state. This undoubtedly ignores the unsteady effect caused by complex flapping motion, which is also the most important characteristic of avian flight. Therefore, this paper carries out a study on the effect of different motion modes and motion parameters on the aerodynamic mechanism of the alula. Previous studies found the dominate effect in the lift enhancement is influenced by Reynolds number, stall condition and geometric parameters. After coupling complex flapping motion, aerodynamic characteristics of the flapping wing are greatly influenced by different motion patterns and parameters. For pure plunge motion, both the slot effect and the vortex generator effect of the alula dominate the lift enhancement; while for plunge-twist and plunge-sweep motion, the vortex generator dominates more. At a low plunge amplitude, a low twist amplitude and a low sweep amplitude, the deflection of the alula has a good lift enhancement compared with the baseline wing. Increasing these amplitudes attenuates both the slot effect and the vortex generator effect. The alula can enhance the lift by 10.4% at the plunge amplitude of 25 deg (for pure plunge motion), by 7.9% at the plunge amplitude of 25 deg and twist amplitude of 10 deg (for plunge-twist motion), by 3.3% at the plunge amplitude of 25 deg and sweep amplitude of 15 deg (for plunge-sweep motion). Meanwhile, at a large sweep phase angle, the alula has a better lift enhancement. Increasing the phase angle enhances the vortex generator effect of the alula, and it has an optimal lift enhancement effect of 11% at the phase angle of 180 deg.}, } @article {pmid38089999, year = {2023}, author = {Shuvo, MS and Mahmud, MJ and Saha, S}, title = {Multi-scaling analysis of turbulent boundary layers over an isothermally heated flat plate with zero pressure gradient.}, journal = {Heliyon}, volume = {9}, number = {12}, pages = {e22721}, doi = {10.1016/j.heliyon.2023.e22721}, pmid = {38089999}, issn = {2405-8440}, abstract = {A meticulous investigation into turbulent boundary layers over an isothermally heated flat plate with zero pressure gradient has been conducted. Eight distinct turbulence models, including algebraic yPlus, standard k-ω, standard k-ε, length-velocity, Spalart-Allmaras, low Reynolds number k-ε, shear stress transport, and v[2]-f turbulence models, are carefully chosen for numerical simulation alongside thermal energy and Reynolds-Averaged Navier-Stokes equations. A comparative analysis has determined that the Spalart-Allmaras model exhibits remarkable agreement with the results from direct numerical simulation, making it a reliable tool for predicting turbulent heat transfer and fluid flow, particularly at higher Prandtl and Reynolds numbers. Subsequently, a multi-scale investigation employs a comprehensive four-layer structure scheme and encompasses various momentum thickness Reynolds numbers of 1432, 2522, and 4000, and Prandtl numbers of 0.71, 2, and 5. The subsequent investigation reveals the governing non-dimensional numbers' substantial impact on the distribution and magnitude of mean thermal and flow characteristics. Notably, the scaling of mean thermal and momentum fields discloses the existence of a meso or intermediate layer characterized by a logarithmic nature unique to itself. The multi-scaling analysis of the flow field demonstrates greater conformity with the selected scaling variables primarily relying on the Reynolds number. Furthermore, the scaling of the energy field yields compelling outcomes within the inner and intermediate layers. However, according to the four-layer theory, minor discrepancies are observed in the outer layer when using the current scaling.}, } @article {pmid38083455, year = {2023}, author = {Akram, MM and Nazila Hosseini, S and Levesque, J and Shi, W and Gosselin, B}, title = {A fully-flexible and thermally adjustable implantable neural probe with a U-turn polyester microchannel.}, journal = {Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual International Conference}, volume = {2023}, number = {}, pages = {1-4}, doi = {10.1109/EMBC40787.2023.10340838}, pmid = {38083455}, issn = {2694-0604}, abstract = {This work presents a fully flexible implantable neural probe fabricated with Polydimethylsiloxane (PDMS) and including a thermally-tunable stiffness microchannel filled with Polyester. The probe includes an optimized microfluidics mixer for drug delivery. Polyester, which is solid at room temperature and has a low melting point close to body temperature, is used to decrease the stiffness of the probe after insertion, after getting in contact with tissues. We designed a U-turn microchannel inside the PDMS neural probe and filled it up with melted polyester. The microchannel has a cross-section of 30 μm × 5 μm and a length of 14.7 mm. The following probe dimensions were chosen after extensive simulation: thickness = 20 μm, width = 300 μm, and length = 7 mm. These values yield a buckling force above 1 mN, which is sufficient for proper insertion into the brain tissues. Simulation results show that the microfluidics mixer with a cross-section of 90 μm × 5 μm and a length of 7 mm has optimum performance for the desired flow rate and quantity of drug to deliver. The pressure drop inside the microfluidic channel is less than 0.43 kPa, which is appropriate for PDMS-PDMS bonding, whereas the Reynolds number is near 1.91k in the laminar regime. No leakage or bubble occurred during the experimental validation, which suggests an appropriate pressure and a laminar flow in the channel.}, } @article {pmid38076113, year = {2023}, author = {Srivathsan, B and G, T and Ram, KV and R, H}, title = {Multiphase simulation of sustainable nanoenhanced ionic liquid coolants for improved thermal performance in Ti-6Al-4V alloy drilling.}, journal = {Heliyon}, volume = {9}, number = {12}, pages = {e23020}, pmid = {38076113}, issn = {2405-8440}, abstract = {Extensive research has been conducted by the manufacturing industry to enhance the efficiency of drilling processes by focusing on the utilization of nanoenhanced cutting fluids that possess excellent heat conductivity. Due to their eco-friendliness and adaptability of physical and chemical properties, ionic fluids offer enormous potential for application as cutting fluids. This study investigates the computational fluid dynamics analysis of the heat transfer performance of various ionanofluid pairs dispersed with nanoparticles as cutting fluids in the drilling process using Ansys Fluent software. For this purpose, 1-Hexyl-3-methyl-imidazolium-tetrafluoroborate is considered the ionic fluid, and its thermal behavior is examined by dispersing it with nanoparticles of copper, silver, and multiwalled carbon nanotubes (MWCNT) at different particle volume fractions and Reynolds numbers. The workpiece is composed of an alloy of titanium Ti-6Al-4V, while the drill bit is made of tungsten carbide-cobalt. It is observed that the ionic nanocoolant mist emanates from the spray tip and moves towards the drill bit-workpiece interface. Initially, the coolant's velocity is greatest close to the orifice, and as time passes, it approaches the drilling space. The data indicates that the spraying velocity of the coolant augments over time and that it disperses heat at the tool-chip interface. The results help us validate the flow and interaction of ionanocoolant with the drilling zone. With a rise in the volume fraction of added nanoparticles and Reynolds number, the results indicated a significant decrease in the drilling temperature. With a higher particle volume fraction, the MWCNT-ionic coolant combination decreases the drilling temperature of pure ionic liquid by 25.64 %. The copper, silver, and MWCNT ionanofluids enhance the average heat transfer coefficient of pure ionic coolant by 35.14 %, 47.42 %, and 62.75 %, respectively. In addition, MWCNT nanocoolants demonstrated improved thermal performance and heat removal rate in comparison to copper and silver ionanocoolants.}, } @article {pmid38071256, year = {2023}, author = {Ahmadi Azar, A and Jalili, B and Jalili, P and Domiri Ganji, D}, title = {Investigating the effect of structural changes of two stretching disks on the dynamics of the MHD model.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {21833}, pmid = {38071256}, issn = {2045-2322}, abstract = {The purpose of this theoretical study is to explore the behavior of an electrically conducting micropolar fluid when subjected to a uniform magnetic field along the vertical axis between two stretching disks as the structure of the problem changes. In this context, structural changes refer to alterations in the distance between the two discs or the stretching rate of the two discs. The governing equations of this problem are a set of nonlinear coupled partial differential equations, which are transformed into a nonlinear coupled ordinary differential equation set by a similarity transformation. The transformation results in four dimensionless quantities and their derivatives that appear in the equations. Nine dimensionless parameters are derived via similarity variables, including stretching Reynolds number, magnetic parameter, radiation parameter, Prandtl number, Eckert number, Schmidt number, and three micropolar parameters. Previous similarity solutions focused on analyzing the effect of changes in each parameter on the four dimensionless quantities. However, this type of analysis is mainly mathematical and does not provide practical results. This study's primary novelty is to redefine the magnetic parameter, Eckert number, stretching Reynolds number, and two micropolar parameters to analyze physical parameters that depend on the stretching rate of the two discs or the distance between them. The semi-analytical hybrid analytical and numerical method (HAN-method) is used to solve the equations. The results demonstrate that structural changes affect all five quantities of radial velocity, axial velocity, microrotation, temperature, and concentration. The study's most significant finding is that an increase in the stretching rate of the two disks causes a sharp increase in temperature and Nusselt number. Conversely, increasing the distance between the two disks causes a sharp decrease in micro-rotation and wall couple stress. They were compared to a previous study in a specific case to validate the results' accuracy.}, } @article {pmid38059033, year = {2023}, author = {Alqarni, MM and Memon, AA and Memon, MA and Mahmoud, EE and Fenta, A}, title = {Numerical investigation of heat transfer and fluid flow characteristics of ternary nanofluids through convergent and divergent channels.}, journal = {Nanoscale advances}, volume = {5}, number = {24}, pages = {6897-6912}, pmid = {38059033}, issn = {2516-0230}, abstract = {The characteristics of nanomaterials have garnered significant attention in recent research on natural and forced convection. This study focuses on the forced convection characteristics of ternary nanofluids within convergent and divergent channels. The ternary nanofluid comprises titanium oxide (TiO2), zinc oxide (ZnO), and silver suspended in water, which serves as the base fluid. Using COMSOL Multiphysics 6.0, a reliable software for finite element analysis, numerical simulations were conducted for steady and incompressible two-dimensional flow. Reynolds numbers varying from 100 to 800 were employed to investigate forced convection. Additionally, we explored aspect ratios (channel height divided by the height of the convergent or divergent section) of -0.4, -0.2, 0, 0.2, and 0.4. Our findings revealed that only at aspect ratio a = 0.4 did the average outlet temperature increase as the Reynolds number rose, while other aspect ratios exhibited decreasing average temperatures with declining Reynolds numbers. Moreover, as the Reynolds number increased from 100 to 800 and the total volume fraction of the ternary nanofluids ranged from 0.003 to 0.15, there was a significant 100% enhancement in the average Nusselt number. For clarity, this article briefly presents essential information, such as the study's numerical nature, fluid properties (constant-property fluid), and the methodology (COMSOL Multiphysics 6.0, finite element analysis). Key conclusions are highlighted to enable readers to grasp the main outcomes at a glance. These details are also adequately covered in the manuscript to facilitate a comprehensive understanding of the research. The utilization of this emerging phenomenon holds immense potential in various applications, ranging from the development of highly efficient heat exchangers to the optimization of thermal energy systems. This phenomenon can be harnessed in scenarios in which effective cost management in thermal production is a critical consideration.}, } @article {pmid38046301, year = {2023}, author = {Wang, Q and Pang, Z and Tian, C and Chen, J}, title = {New Design Method of a Supersonic Steam Injection Nozzle and Its Numerical Simulation Verification.}, journal = {ACS omega}, volume = {8}, number = {47}, pages = {44485-44496}, pmid = {38046301}, issn = {2470-1343}, abstract = {Steam huff-n-puff in horizontal wells often had limitations, such as uneven steam injection and low reservoir utilization. To improve steam injection efficiency, a new method for designing a supersonic nozzle was proposed based on the principles of aerodynamics and thermodynamics. The nozzle featured a tapering section, a throat, and a diverging section. The best geometric shape of the tapering section was the Witoszynski curve. A set of nozzle size designs were established, and the size parameters were optimized. The results showed that the nozzle could inject steam into the formation at supersonic speed and it had the characteristics of constant flow rate and uniform development of the steam chamber. According to the steam Reynolds number and the good aggregation distribution characteristics of the size design model, three sequential nozzles of 3.0, 5.0, and 6.5 mm were formed based on the throat. When the throat diameter was 5.0 mm, the tapering length was 4.3 mm, the diverging length was 5.5 mm, the throat length was 3.0 mm, the inlet diameter was 9.8 mm, and the outlet diameter was 6.2 mm. Numerical simulations indicated that the pressure drop loss during steam huff-n-puff injection in horizontal wells was within 10%. It was of great significance to establish the nozzle size design model of the steam injection effect of horizontal wells.}, } @article {pmid38042993, year = {2023}, author = {Liu, X and Zhao, Z and Xu, S and Zhang, J and Zhou, Y and He, Y and Yamaguchi, T and Ouyang, H and Tanaka, T and Chen, MK and Shi, S and Qi, F and Tsai, DP}, title = {Meta-Lens Particle Image Velocimetry.}, journal = {Advanced materials (Deerfield Beach, Fla.)}, volume = {}, number = {}, pages = {e2310134}, doi = {10.1002/adma.202310134}, pmid = {38042993}, issn = {1521-4095}, abstract = {Fluid flow behavior is visualized through particle image velocimetry (PIV) for understanding and studying experimental fluid dynamics. However, traditional PIV methods require multiple cameras and conventional lens systems for image acquisition to resolve multi-dimensional velocity fields. In turn, it introduces complexity to the entire system. Meta-lenses are advanced flat optical devices composed of artificial nanoantenna arrays. It can manipulate the wavefront of light with advantages of ultrathin, compact, and no spherical aberration. Meta-lenses offer novel functionalities and promise to replace traditional optical imaging systems. Here, we propose a binocular meta-lens PIV technique, where a pair of GaN meta-lenses are fabricated on one substrate and integrated with a CMOS sensor to form a compact binocular PIV system. The meta-lens weigh only 116 mg, much lighter than commercial lenses. The three-dimensional velocity field can be obtained by the binocular disparity and particle image displacement information of fluid flow. The measurement error of vortex-ring diameter is about 1.25% experimentally validated via a Reynolds-number 2000 vortex-ring. This work demonstrates a new development trend for the PIV technique for rejuvenating traditional flow diagnostic tools towards a more compact, easy-to-deploy technique. It enables further miniaturization and low-power systems for portable, field-use, and space-constrained PIV applications. This article is protected by copyright. All rights reserved.}, } @article {pmid38039459, year = {2023}, author = {Buaria, D and Sreenivasan, KR}, title = {Saturation and Multifractality of Lagrangian and Eulerian Scaling Exponents in Three-Dimensional Turbulence.}, journal = {Physical review letters}, volume = {131}, number = {20}, pages = {204001}, doi = {10.1103/PhysRevLett.131.204001}, pmid = {38039459}, issn = {1079-7114}, abstract = {Inertial-range scaling exponents for both Lagrangian and Eulerian structure functions are obtained from direct numerical simulations of isotropic turbulence in triply periodic domains at Taylor-scale Reynolds number up to 1300. We reaffirm that transverse Eulerian scaling exponents saturate at ≈2.1 for moment orders p≥10, significantly differing from the longitudinal exponents (which are predicted to saturate at ≈7.3 for p≥30 from a recent theory). The Lagrangian scaling exponents likewise saturate at ≈2 for p≥8. The saturation of Lagrangian exponents and transverse Eulerian exponents is related by the same multifractal spectrum by utilizing the well-known frozen hypothesis to relate spatial and temporal scales. Furthermore, this spectrum is different from the known spectra for Eulerian longitudinal exponents, suggesting that Lagrangian intermittency is characterized solely by transverse Eulerian intermittency. We discuss possible implications of this outlook when extending multifractal predictions to the dissipation range, especially for Lagrangian acceleration.}, } @article {pmid38036626, year = {2023}, author = {Abd-Alla, AM and Abo-Dahab, SM and Salah, DM and Bayones, FS and Abdelhafez, MA}, title = {Magneto-hydrodynamic peristaltic flow of a Jeffery fluid in the presence of heat transfer through a porous medium in an asymmetric channel.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {21088}, pmid = {38036626}, issn = {2045-2322}, abstract = {In the present paper, the effects of magnetic field and heat transfer on the peristaltic flow of a Jeffery fluid through a porous medium in an asymmetric channel have been studied. The governing non-linear partial differential equations representing the flow model are transmuted into linear ones by employing the appropriate non-dimensional parameters under the assumption of long wavelength and low Reynolds number. Exact solutions are presented for the stream function, pressure gradient, and temperature. The frictional force and pressure rise are both computed using numerical integration. Using MATLAB R2023a software, a parametric analysis is performed, and the resulting data is represented graphically. For all physical quantities considered, numerical calculations were made and represented graphically. Trapping phenomena are discussed graphically. The obtained results can be applied to enhance pumping systems in engineering and gastrointestinal functions. This analysis permits body fluids such as blood and lymph to easily move inside the arteries and veins, allowing oxygen supply, waste elimination, and other necessary elements.}, } @article {pmid38036570, year = {2023}, author = {Ahmad, S and Ali, K and Castellanos, HG and Aryanfar, Y and Rashid, FL and Hendy, AS and Deifalla, A and Ragab, AE and Khan, M and Gomaa, HG}, title = {Complex dynamics of induced vortex formation and thermal-fluid coupling in tri-hybrid nanofluid under localized magnetic field: a novel study.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {21140}, pmid = {38036570}, issn = {2045-2322}, support = {RSPD2023R711//King Saud University/ ; }, abstract = {Hybrid nanofluids offer higher stability, synergistic effects, and better heat transfer compared to simple nanofluids. Their higher thermal conductivity, lower viscosity, and interaction with magnetic fields make them ideal for various applications, including materials science, transportation, medical technology, energy, and fundamental physics. The governing partial differential equations are numerically solved by employing a finite volume approach, and the effects of various parameters on the nanofluid flow and thermal characteristics are systematically examined from the simulations based on a self-developed MATLAB code. The parameters included magnetic field strength, the Reynolds number, the nanoparticle volume fraction, and the number and position of the strips in which the magnetic field is localized. It has been noted that the magnetized field induces the spinning of the tri-hybrid nanoparticles, which generates the intricate structure of vortices in the flow. The local skin friction (CfRe) and the Nusselt number (Nu) increase significantly when the magnetic field is intensified. Moreover, adding more nanoparticles in the flow enhances both Nu and CfRe, but with different effects for different nanoparticles. Silver (Ag) shows the highest increase in both Nu (52%) and CfRe (110%), indicating strong thermal-fluid coupling. Alumina (Al2O3) and Titanium Dioxide (TiO2) show lower increases in both Nu (43% and 34%) and CfRe (14% and 10%), indicating weaker coupling in the flow. Finally, compared with the localized one, the uniform magnetic field has a minor effect on the flow and temperature distributions.}, } @article {pmid38034878, year = {2023}, author = {Han, J and Lee, H}, title = {Control Volume Analysis of the Infusion Rate in Cephalic and Median Cubital Veins Based on Infusion Bag Height and Peripheral Venous Catheter Inner Diameter: Application of Bernoulli's Equation and Consideration of Frictional Forces.}, journal = {Journal of multidisciplinary healthcare}, volume = {16}, number = {}, pages = {3609-3618}, doi = {10.2147/JMDH.S409050}, pmid = {38034878}, issn = {1178-2390}, abstract = {PURPOSE: This pilot study aimed to provide basic data on intravenous infusion nursing by analyzing the infusion rate in the cephalic and median cubital veins depending on the height of the infusion bag and inner diameter of the peripheral venous catheter (PVC).

METHODS: While infusing 0.9% normal saline at 22 °C (room temperature) into elbow cephalic and median cubital veins, the infusion rate may be controlled by adjusting the fluid height and PVC diameter. To assess the validity of the laminar flow assumption, the study estimated the Reynolds number (Re) using the velocity obtained by applying Bernoulli's equation considering the friction coefficient.

RESULTS: At a constant fluid height, the infusion rate increased with increasing PVC diameter. At a constant PVC diameter, the infusion rate increased with increasing fluid height. In a comparison between the cephalic and median cubital veins at constant fluid height and PVC diameter, the solution was infused at a higher rate into the cephalic vein, which was under lower venous pressure.

CONCLUSION: The analysis of the infusion rate according to fluid height and PVC diameter provided basic data on intravenous infusion nursing. The results are expected to provide evidence for the standardization of intravenous infusion nursing.}, } @article {pmid38027788, year = {2023}, author = {Jamil, DF and Uddin, S and Kazi, M and Roslan, R and Gorji, MR and Kamalrulzaman Md Akhir, M}, title = {MHD blood flow effects of Casson fluid with Caputo-Fabrizio fractional derivatives through an inclined blood vessels with thermal radiation.}, journal = {Heliyon}, volume = {9}, number = {11}, pages = {e21780}, doi = {10.1016/j.heliyon.2023.e21780}, pmid = {38027788}, issn = {2405-8440}, abstract = {This study investigates a fractional-order time derivative model of non-Newtonian magnetic blood flow in the presence of thermal radiation and body acceleration through an inclined artery. The blood flow is formulated using the Casson fluid model under the control of a uniformly distributed magnetic field and an oscillating pressure gradient. Caputo-Fabrizio's fractional derivative mathematical model was used, along with Laplace transform and the finite Hankel transform technique. Analytical expressions were obtained for the velocity of blood flow, magnetic particle distribution, and temperature profile. These distributions are presented graphically using Mathcad software. The results show that the velocity increases with the time, Reynolds number and Casson fluid parameters, and diminishes when Hartmann number increases. Moreover, fractional parameters, radiation values, and metabolic heat source play an essential role in controlling the blood temperature. More precisely, these results are beneficial for the diagnosis and treatment of certain medical issues.}, } @article {pmid38027752, year = {2023}, author = {Alklaibi, AM and Chandra Mouli, KVV and Syam Sundar, L}, title = {Experimental and support vector machine predictions of entropy generations and exergy efficiency of Fe3O4-SiO2/Water hybrid nanofluid in a plate heat exchanger.}, journal = {Heliyon}, volume = {9}, number = {11}, pages = {e21730}, doi = {10.1016/j.heliyon.2023.e21730}, pmid = {38027752}, issn = {2405-8440}, abstract = {Several experiments of Fe3O4-SiO2/water hybrid nanofluids with volumetric concentrations ranging from 0.2 % to 1.0 % circulating in the cold-side of a plate heat exchanger at flow rates ranging from 0.05 kg/s to 0.1166 kg/s are performed. Under these ranges of flow rates and volumetric concentrations, the flow of Fe3O4-SiO2/water hybrid nanofluids remains laminar. The results of these experiments are predicted with support vector machine (SVM) algorithm to determine hybrid nanofluid entropy generation thermal, entropy generation frictional, and efficiency of exergy. Fe3O4-SiO2 nanomaterials was synthesized with reduction of chemicals and insitu development techniques, with XRD, FTIR and VSM instruments, characterizations were done. The SVM model gives large precision predictions of the measured data with correlations coefficients of 0.9944, 0.99798, and 0.99428 for frictional entropy generation, thermal entropy generation and exergy efficiency. At a flow rate of 0.1166 kg/s in the cold-side of PHE, the exergy efficiency is found to be 77.96 % for water (Reynolds number of 935.4) and with 1.0 vol% of Fe3O4-SiO2/water hybrid nanofluid in the cold-side of PHE, the efficiency is increased to 82.97 %, respectively. Under similar conditions of 0.1166 kg/s of flow circulation and 1.0 % vol. concentration of hybrid nanofluid, the thermal entropy generation is dropped off to 18.37 %, but the frictional entropy generation is increased by 20.97 %, compared to water, with the results that the total entropy generation drops off by 15.91 %, compared to water data. Preliminary curve-fitting correlations have been developed for the frictional entropy generation, thermal entropy generation, and exergy efficiency.}, } @article {pmid38005406, year = {2023}, author = {Krauter, N and Stefani, F}, title = {Simultaneous Measurement of Flow Velocity and Electrical Conductivity of a Liquid Metal Using an Eddy Current Flow Meter in Combination with a Look-Up-Table Method.}, journal = {Sensors (Basel, Switzerland)}, volume = {23}, number = {22}, pages = {}, doi = {10.3390/s23229018}, pmid = {38005406}, issn = {1424-8220}, support = {787544/ERC_/European Research Council/International ; }, abstract = {The Eddy Current Flow Meter (ECFM) is a commonly employed inductive sensor for assessing the local flow rate or flow velocity of liquid metals with temperatures up to 700 ∘C. One limitation of the ECFM lies in its dependency on the magnetic Reynolds number for measured voltage signals. These signals are influenced not only by the flow velocity but also by the electrical conductivity of the liquid metal. In scenarios where temperature fluctuations are significant, leading to corresponding variations in electrical conductivity, it becomes imperative to calibrate the ECFM while concurrently monitoring temperature to discern the respective impacts of flow velocity and electrical conductivity on the acquired signals. This paper introduces a novel approach that enables the concurrent measurement of electrical conductivity and flow velocity, even in the absence of precise knowledge of the liquid metal's conductivity or temperature. This method employs a Look-Up-Table methodology. The feasibility of this measurement technique is substantiated through numerical simulations and further validated through experiments conducted on the liquid metal alloy GaInSn at room temperature.}, } @article {pmid38004897, year = {2023}, author = {Borbas, SW and Shen, K and Ji, C and Viallat, A and Helfer, E and Peng, Z}, title = {Transit Time Theory for a Droplet Passing through a Slit in Pressure-Driven Low Reynolds Number Flows.}, journal = {Micromachines}, volume = {14}, number = {11}, pages = {}, doi = {10.3390/mi14112040}, pmid = {38004897}, issn = {2072-666X}, support = {DMS 1951526//National Science Foundation/ ; 1948347//National Science Foundation/ ; IIP-1841473//National Science Foundation/ ; PHY2210366//National Science Foundation/ ; }, abstract = {Soft objects squeezing through small apertures are crucial for many in vivo and in vitro processes. Red blood cell transit time through splenic inter-endothelial slits (IESs) plays a crucial role in blood filtration and disease progression, while droplet velocity through constrictions in microfluidic devices is important for effective manipulation and separation processes. As these transit phenomena are not well understood, we sought to establish analytical and numerical solutions of viscous droplet transit through a rectangular slit. This study extends from our former theory of a circular pore because a rectangular slit is more realistic in many physiological and engineering applications. Here, we derived the ordinary differential equations (ODEs) of a droplet passing through a slit by combining planar Poiseuille flow, the Young-Laplace equations, and modifying them to consider the lubrication layer between the droplet and the slit wall. Compared to the pore case, we used the Roscoe solution instead of the Sampson one to account for the flow entering and exiting a rectangular slit. When the surface tension and lubrication layer were negligible, we derived the closed-form solutions of transit time. When the surface tension and lubrication layer were finite, the ODEs were solved numerically to study the impact of various parameters on the transit time. With our solutions, we identified the impact of prescribed pressure drop, slit dimensions, and droplet parameters such as surface tension, viscosity, and volume on transit time. In addition, we also considered the effect of pressure drop and surface tension near critical values. For this study, critical surface tension for a given pressure drop describes the threshold droplet surface tension that prevents transit, and critical pressure for a given surface tension describes the threshold pressure drop that prevents transit. Our solutions demonstrate that there is a linear relationship between pressure and the reciprocal of the transit time (referred to as inverse transit time), as well as a linear relationship between viscosity and transit time. Additionally, when the droplet size increases with respect to the slit dimensions, there is a corresponding increase in transit time. Most notably, we emphasize the initial antagonistic effect of surface tension which resists droplet passage but at the same time decreases the lubrication layer, thus facilitating passage. Our results provide quantitative calculations for understanding cells passing through slit-like constrictions and designing droplet microfluidic experiments.}, } @article {pmid37964837, year = {2023}, author = {Rahman, MT and Habib, K and Quader, MN and Aslfattahi, N and Kadirgama, K and Das, L}, title = {Effect of porous density of twisted tape inserts on heat transfer performance inside a closed conduit.}, journal = {Heliyon}, volume = {9}, number = {11}, pages = {e21206}, doi = {10.1016/j.heliyon.2023.e21206}, pmid = {37964837}, issn = {2405-8440}, abstract = {This study examines the impact of varying the porosity density of twisted tape inserts (TTI) on the temperature distribution, fluid velocities, heat transfer coefficients (HTC), Nusselt numbers (Nu), turbulent kinetic energy (TKE), and performance from 5000 to 12500 Reynolds numbers (Re). The entire process involved the design of TTIs and double pipe heat exchangers using SolidWorks. Subsequently, a three-dimensional fluid flow model was employed to solve equations related to energy mass, energy, and momentum within the ANSYS Fluent interfaces. The findings highlight the noteworthy impact of high porosity TTIs, which consistently reduce temperature spans, increase fluid velocities, and greatly HTC and Nu when compared to low porosity TTI, typical TTI, and plain tubes. Furthermore, high porosity TTI significantly increases TKE, indicating increased fluid turbulence and higher heat transfer efficiency, especially at Re = 12500. The assessment of PEC emphasizes the superiority of high porosity TTI, demonstrating their significant performance increase potential of over 6.44 % over low porosity TTI and a staggering 62.5 % above typical TTI. In conclusion, high porosity TTI emerges as a potential solution for improving heat transfer efficiency and overall system performance in a variety of industrial applications, promising enhanced energy efficiency and superior performance.}, } @article {pmid37963561, year = {2023}, author = {Htet, PH and Lauga, E}, title = {Cortex-driven cytoplasmic flows in elongated cells: fluid mechanics and application to nuclear transport in Drosophila embryos.}, journal = {Journal of the Royal Society, Interface}, volume = {20}, number = {208}, pages = {20230428}, doi = {10.1098/rsif.2023.0428}, pmid = {37963561}, issn = {1742-5662}, abstract = {The Drosophila melanogaster embryo, an elongated multi-nucleated cell, is a classical model system for eukaryotic development and morphogenesis. Recent work has shown that bulk cytoplasmic flows, driven by cortical contractions along the walls of the embryo, enable the uniform spreading of nuclei along the anterior-posterior axis necessary for proper embryonic development. Here, we propose two mathematical models to characterize cytoplasmic flows driven by tangential cortical contractions in elongated cells. Assuming Newtonian fluid flow at low Reynolds number in a spheroidal cell, we first compute the flow field exactly, thereby bypassing the need for numerical computations. We then apply our results to recent experiments on nuclear transport in cell cycles 4-6 of Drosophila embryo development. By fitting the cortical contractions in our model to measurements, we reveal that experimental cortical flows enable near-optimal axial spreading of nuclei. A second mathematical approach, applicable to general elongated cell geometries, exploits a long-wavelength approximation to produce an even simpler solution, with errors below [Formula: see text] compared with the full model. An application of this long-wavelength result to transport leads to fully analytical solutions for the nuclear concentration that capture the essential physics of the system, including optimal axial spreading of nuclei.}, } @article {pmid37957450, year = {2023}, author = {Bureau, L and Coupier, G and Salez, T}, title = {Lift at low Reynolds number.}, journal = {The European physical journal. E, Soft matter}, volume = {46}, number = {11}, pages = {111}, pmid = {37957450}, issn = {1292-895X}, support = {101039103/ERC_/European Research Council/International ; }, abstract = {Lift forces are widespread in hydrodynamics. These are typically observed for big and fast objects and are often associated with a combination of fluid inertia (i.e. large Reynolds numbers) and specific symmetry-breaking mechanisms. In contrast, the properties of viscosity-dominated (i.e. low Reynolds numbers) flows make it more difficult for such lift forces to emerge. However, the inclusion of boundary effects qualitatively changes this picture. Indeed, in the context of soft and biological matter, recent studies have revealed the emergence of novel lift forces generated by boundary softness, flow gradients and/or surface charges. The aim of the present review is to gather and analyse this corpus of literature, in order to identify and unify the questioning within the associated communities, and pave the way towards future research.}, } @article {pmid37952804, year = {2023}, author = {Lordifard, P and Shariatpanahi, SP and Khajeh, K and Saboury, AA and Goliaei, B}, title = {Frequency dependence of ultrasonic effects on the kinetics of hen egg white lysozyme fibrillation.}, journal = {International journal of biological macromolecules}, volume = {}, number = {}, pages = {127871}, doi = {10.1016/j.ijbiomac.2023.127871}, pmid = {37952804}, issn = {1879-0003}, abstract = {Our study aimed to investigate the effects of ultrasound on the fibrillation kinetics of HEWL (hen egg white lysozyme) and its physicochemical properties. Ultrasound, a mechanical wave, can induce conformational changes in proteins. To achieve this, we developed an ultrasound exposure system and used various biophysical techniques, including ThT fluorescence spectroscopy, ATR-FTIR, Far-UV CD spectrophotometry, Fluorescence microscopy, UV-spectroscopy, and seeding experiments. Our results revealed that higher frequencies significantly accelerated the fibrillation of lysozyme by unfolding the native protein and promoting the fibrillation process, thereby reducing the lag time. We observed a change in the secondary structure of the sonicated protein change to the β-structure, but there was no difference in the Tm of native and sonicated proteins. Furthermore, we found that higher ultrasound frequencies had a greater seeding effect. We propose that the effect of frequency can be explained by the impact of the Reynolds number, and for the Megahertz frequency range, we are almost at the transition regime of turbulence. Our results suggest that laminar flows may not induce any significant change in the fibrillation kinetics, while turbulent flows may affect the process.}, } @article {pmid37942161, year = {2023}, author = {Abdalkarem, AAM and Ansaf, R and Muzammil, WK and Ibrahim, A and Harun, Z and Fazlizan, A}, title = {Preliminary assessment of the NACA0021 trailing edge wedge for wind turbine application.}, journal = {Heliyon}, volume = {9}, number = {11}, pages = {e21193}, pmid = {37942161}, issn = {2405-8440}, abstract = {The airfoil blade is the primary component of a wind turbine, and its aerodynamic properties play a crucial role in determining the energy conversion efficiency of these blades. Many researchers have proposed different airfoil modifications intending to enhance the aerodynamic characteristics and limit the unsteady interaction with the atmospheric boundary layer. This study evaluates the benefits of mounting wedge tails (WTs) on the trailing edge of an airfoil. The aerodynamic characteristics of a 2-D, steady-state NACA 0021 airfoil featuring the wedge tails (WT) and fish wedge tails (FWT) were studied computationally by employing the shear stress transport (SST) k-ω turbulence model. Different WT and FWT configurations were studied at various wedge length (L) to wedge height (H) ratios, L/H, at the airfoil's trailing edge. The effects of different L/H ratios, including L/H > 1, L/H = 1, and L/H < 1, were considered in the present study to determine the optimal configuration to achieve the maximum glide ratio, CL/CD at the Reynolds number of 180,000. The findings indicate that the performance of the NACA 0021 airfoil was notably affected by the height of the tail; however, the length had only a minor impact when L/H was less than 1. The mounted FWT resulted in significant enhancements to both the lift and glide ratio of the airfoil. Specifically, the lift ratio experienced an increase of over 41 % compared to the clean airfoil, while the glide ratio increased by more than 31 %. These improvements were observed at an ideal height and length of 2.5 % and 1 % of the airfoil, respectively. Moreover, the mounted FWT performed better than the Gurney flap using the same configurations.}, } @article {pmid37939394, year = {2023}, author = {Fercak, O and Lyons, K and Murphy, CT and Kamensky, K and Cal, RB and Franck, JA}, title = {Multicolor dye-based flow structure visualization for seal-whisker geometry characterized by computer vision.}, journal = {Bioinspiration & biomimetics}, volume = {}, number = {}, pages = {}, doi = {10.1088/1748-3190/ad0aa8}, pmid = {37939394}, issn = {1748-3190}, abstract = {Pinniped vibrissae possess a unique and complex three-dimensional topography, which has beneficial fluid flow characteristics such as substantial reductions in drag, lift, and vortex induced vibration. To understand and leverage these effects, the downstream vortex dynamics must be studied. Dye visualization is a traditional qualitative method of capturing these downstream effects, specifically in comparative biological investigations where complex equipment can be prohibitive. High-fidelity numerical simulations or experimental particle image velocimetry (PIV) are commonplace for quantitative high-resolution flow measurements, but are computationally expensive, require costly equipment, and can have limited measurement windows. This study establishes a method for extracting quantitative data from standard dye visualization experiments on seal whisker geometries by leveraging novel but intuitive computer vision techniques, which maintain simplicity and an advantageous large experimental viewing window while automating the extraction of vortex frequency, position, and advection. Results are compared to direct numerical simulation (DNS) data for comparable geometries. Power spectra and Strouhal numbers show consistent behavior between methods for a Reynolds number of 500, with minima at the canonical geometry wavelength of 3.43 and a peak frequency of 0.2 for a Reynolds number of 250. The vortex tracking reveals a clear increase in velocity from roll-up to 3.5 whisker diameters downstream, with a strong overlap with the DNS data but shows steady results beyond the limited DNS window. This investigation provides insight into a valuable bio-inspired engineering model while advancing an analytical methodology that can readily be applied to a broad range of comparative biological studies.}, } @article {pmid37927848, year = {2023}, author = {Gjerde, IG and Rognes, ME and Sánchez, AL}, title = {The directional flow generated by peristalsis in perivascular networks-Theoretical and numerical reduced-order descriptions.}, journal = {Journal of applied physics}, volume = {134}, number = {17}, pages = {174701}, pmid = {37927848}, issn = {0021-8979}, abstract = {Directional fluid flow in perivascular spaces surrounding cerebral arteries is hypothesized to play a key role in brain solute transport and clearance. While various drivers for a pulsatile flow, such as cardiac or respiratory pulsations, are well quantified, the question remains as to which mechanisms could induce a directional flow within physiological regimes. To address this question, we develop theoretical and numerical reduced-order models to quantify the directional (net) flow induceable by peristaltic pumping in periarterial networks. Each periarterial element is modeled as a slender annular space bounded internally by a circular tube supporting a periodic traveling (peristaltic) wave. Under reasonable assumptions of a small Reynolds number flow, small radii, and small-amplitude peristaltic waves, we use lubrication theory and regular perturbation methods to derive theoretical expressions for the directional net flow and pressure distribution in the perivascular network. The reduced model is used to derive closed-form analytical expressions for the net flow for simple network configurations of interest, including single elements, two elements in tandem, and a three element bifurcation, with results compared with numerical predictions. In particular, we provide a computable theoretical estimate of the net flow induced by peristaltic motion in perivascular networks as a function of physiological parameters, notably, wave length, frequency, amplitude, and perivascular dimensions. Quantifying the maximal net flow for specific physiological regimes, we find that vasomotion may induce net pial periarterial flow velocities on the order of a few to tens of μm/s and that sleep-related changes in vasomotion pulsatility may drive a threefold flow increase.}, } @article {pmid37920481, year = {2023}, author = {Vakilabadi, KA and Ghafari, HR and Ghassemi, H}, title = {Experimental and numerical investigation on a trimaran airwake, geometry modification.}, journal = {Heliyon}, volume = {9}, number = {11}, pages = {e21144}, doi = {10.1016/j.heliyon.2023.e21144}, pmid = {37920481}, issn = {2405-8440}, abstract = {The aerodynamic interaction between a helicopter and a trimaran ship's flight deck can be complex and have an impact on handling quality and performance, especially in turbulent conditions. This article presents research on the flight deck geometry of a trimaran vessel without the presence of a helicopter. Both Particle Image Velocimetry (PIV) and computational fluid dynamics (CFD) were used to analyze the effect of wind velocity on air pressure in the flight deck region. The study proposed and evaluated different geometries of the top structure at several air velocities to minimize pressure differences. The results of the numerical simulation were validated by experimental measurements using PIV, which showed that the effect of the Reynolds number on the non-dimensional pressure near the top structure is negligible except for the biggest Reynolds number (Re = 50e6), while at x/L = 0.5 the significant difference can be seen, however, the same result found for Re = 38e6 and 50e6. At the farthest distance (x/L = 1), the pressure difference for different Reynolds numbers case studies is negligible. Among the various geometries assessed, the maximum non-dimensional pressure differences along the lines show the highest value occurs for the base geometry (A) while geometries C and F show lower values, which have chamfering along the middle and side horizontal edges at a 45-degree angle and chamfering along all vertical and horizontal edges at a 30-degree angle.}, } @article {pmid37918090, year = {2023}, author = {Zhou, ZL and Zhu, LF and Li, TX and Wu, LH and Guan, M and Ma, ZK and Liu, YH and Qin, J and Gao, BL}, title = {Sub-satisfactory stenting recanalization of severe vascular stenosis of the posterior circulation can significantly improve cerebral hemodynamic perfusion.}, journal = {European journal of radiology}, volume = {169}, number = {}, pages = {111135}, doi = {10.1016/j.ejrad.2023.111135}, pmid = {37918090}, issn = {1872-7727}, abstract = {PURPOSE: To investigate the effect of sub-satisfactory stenting recanalization of severe vascular stenosis of the posterior circulation on cerebral hemodynamic perfusion.

MATERIALS AND METHODS: Patients with severe vascular stenosis of the posterior circulation who had undergone three-dimensional cerebral angiography before and after stenting were retrospectively enrolled. Computational fluid dynamic (CFD) analysis of hemodynamic parameters at the stenosis, perforating branch, and normal arterial segments proximal and distal to the stenosis were performed.

RESULTS: Sixty-two patients with basilar artery stenosis aged 60.9 ± 9.6 years were enrolled, and stent angioplasty resulted in the reduction of stenosis degree from 85.3 ± 7.2% before to 18.6 ± 6.4% after stenting. After stenting, at the proximal normal artery, the total pressures had significantly (P < 0.05) decreased, whereas all the other parameters (WSS, cell Reynolds number, velocity, vorticity, turbulence intensity, turbulence kinetic energy and dissipation rate) had significantly (P < 0.05) increased. At the stenosis, all hemodynamic parameters had significantly decreased. At the stenosis perforating branch, the WSS, cell Reynolds number, velocity, and vorticity were all significantly decreased, and the total pressure, turbulence intensity, kinetic energy, and dissipation rate were all significantly increased. At the distal normal artery, the total flow pressure (perfusion pressure) and velocity were both significantly (P < 0.05) increased, and the total pressure, WSS, cell Reynolds number, vorticity, turbulence intensity, kinetic energy, and dissipation rate were all significantly (P < 0.05) decreased. The hemodynamic parameters after stenting were closer to those after virtual stenosis repair at all measurements.

CONCLUSION: Sub-satisfactory recanalization has significantly restored the stenosis and improved the hemodynamic parameters near the stenosis and at the root of the perforating branch, thus significantly improving the cerebral perfusion, similar to the changes of hemodynamic status and cerebral perfusion after virtual removal of the vascular stenosis. This may indicate the good effect of sub-satisfactory stenting recanalization of the vascular stenosis at the posterior circulation.}, } @article {pmid37914697, year = {2023}, author = {Javaherchian, J and Moosavi, A and Tabatabaei, SA}, title = {Numerical analysis of pressure drop reduction of bubbly flows through hydrophobic microgrooved channels.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {18861}, pmid = {37914697}, issn = {2045-2322}, abstract = {Due to the high performance of hydrophobic surfaces in pressure drop reduction, they have been proposed for various applications. However, despite the extensive uses of two-phase flows in many industries, the effect of hydrophobic surfaces on the pressure drop reduction of two-phase flows has not been well understood yet. Thus, in the present study, by implementing the phase-field and finite element methods, the bubbly flows as an example of two-phase flows are considered for examining the effect of hydrophobic microgrooved microchannels on the pressure drop reduction of these regimes in the laminar state. We found out that hydrophobic microgrooved surfaces not only can be efficient in the bubbly flow but also can even cause a maximum pressure drop reduction of up to 70%, which is almost 3.5 times higher than in single-phase flow. We also studied the influence of each parameter, such as bubbles volume or length, Reynolds number, capillary number, and their combination on this phenomenon. The pressure drop reduction grows by increasing the volume of the bubbles but decreases by increasing the flow velocity or the surface tension coefficient. The combination of these parameters demonstrated different results in some circumstances.}, } @article {pmid37909299, year = {2023}, author = {Zhao, W and Shang, X and Zhang, B and Yuan, D and Nguyen, BTT and Wu, W and Zhang, JB and Peng, N and Liu, AQ and Duan, F and Chin, LK}, title = {Squeezed state in the hydrodynamic focusing regime for Escherichia coli bacteria detection.}, journal = {Lab on a chip}, volume = {}, number = {}, pages = {}, doi = {10.1039/d3lc00434a}, pmid = {37909299}, issn = {1473-0189}, abstract = {Flow cytometry is an essential technique in single particle analysis and cell sorting for further downstream diagnosis, exhibiting high-throughput and multiplexing capabilities for many biological and biomedical applications. Although many hydrodynamic focusing-based microfluidic cytometers have been demonstrated with reduced size and cost to adapt to point-of-care settings, the operating conditions are not characterized systematically. This study presents the flow transition process in the hydrodynamic focusing mechanism when the flow rate or the Reynolds number increases. The characteristics of flow fields and mass transport were studied under various operating conditions, including flow rates and microchannel heights. A transition from the squeezed focusing state to the over-squeezed anti-focusing state in the hydrodynamic focusing regime was observed when the Reynolds number increased above 30. Parametric studies illustrated that the focusing width increased with the Reynolds number but decreased with the microchannel height in the over-squeezed state. The microfluidic cytometric analyses using microbeads and E. coli show that the recovery rate was maintained by limiting the Reynolds number to 30. The detailed analysis of the flow transition will provide new insight into microfluidic cytometric analyses with a broad range of applications in food safety, water monitoring and healthcare sectors.}, } @article {pmid37906645, year = {2023}, author = {Zöttl, A and Tesser, F and Matsunaga, D and Laurent, J and du Roure, O and Lindner, A}, title = {Asymmetric bistability of chiral particle orientation in viscous shear flows.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {120}, number = {45}, pages = {e2310939120}, doi = {10.1073/pnas.2310939120}, pmid = {37906645}, issn = {1091-6490}, support = {682367//European Commission (EC)/ ; M 2458-N36//Austrian Science Fund (FWF)/ ; ANR-10- EQPX-34//Agence Nationale de la Recherche (ANR)/ ; 21H05879//MEXT | Japan Society for the Promotion of Science (JSPS)/ ; JPMJPR21OA//MEXT | JST | Precursory Research for Embryonic Science and Technology (PRESTO)/ ; }, abstract = {The migration of helical particles in viscous shear flows plays a crucial role in chiral particle sorting. Attaching a nonchiral head to a helical particle leads to a rheotactic torque inducing particle reorientation. This phenomenon is responsible for bacterial rheotaxis observed for flagellated bacteria as Escherichia coli in shear flows. Here, we use a high-resolution microprinting technique to fabricate microparticles with controlled and tunable chiral shape consisting of a spherical head and helical tails of various pitch and handedness. By observing the fully time-resolved dynamics of these microparticles in microfluidic channel flow, we gain valuable insights into chirality-induced orientation dynamics. Our experimental model system allows us to examine the effects of particle elongation, chirality, and head heaviness for different flow rates on the orientation dynamics, while minimizing the influence of Brownian noise. Through our model experiments, we demonstrate the existence of asymmetric bistability of the particle orientation perpendicular to the flow direction. We quantitatively explain the particle equilibrium orientations as a function of particle properties, initial conditions and flow rates, as well as the time-dependence of the reorientation dynamics through a theoretical model. The model parameters are determined using boundary element simulations, and excellent agreement with experiments is obtained without any adjustable parameters. Our findings lead to a better understanding of chiral particle transport and bacterial rheotaxis and might allow the development of targeted delivery applications.}, } @article {pmid37898603, year = {2023}, author = {Jalili, B and Shateri, A and Akgül, A and Bariq, A and Asadi, Z and Jalili, P and Ganji, DD}, title = {An investigation into a semi-porous channel's forced convection of nano fluid in the presence of a magnetic field as a result of heat radiation.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {18505}, pmid = {37898603}, issn = {2045-2322}, abstract = {This study investigates the impact of heat radiation on magnetically-induced forced convection of nanofluid in a semi-porous channel. The research employs Akbari-Ganji's and Homotopy perturbation methods to analyze the effects of multiple parameters, including Hartmann number, Reynolds number, Eckert number, radiation parameter, and suction parameter, on the flow and heat transfer characteristics. The results demonstrate that increasing Reynolds number, suction, and radiation parameters increases temperature gradient, providing valuable insights into improving heat transfer in semi-porous channels. The study validates the proposed methods by comparing the results with those obtained from other established methods in the literature. The main focus of this work is to understand the behavior of nanofluids in semi-porous channels under the influence of magnetic fields and heat radiation, which is essential for various industrial and engineering applications. The future direction of this research includes exploring the effects of different nanoparticle shapes and materials on heat transfer performance and investigating the influence of other parameters, such as buoyancy forces and variable properties, on the flow and heat transfer characteristics. The findings of this study are expected to contribute to the development of more efficient thermal management systems in the future.}, } @article {pmid37893255, year = {2023}, author = {Zhao, H and Ma, H and Yan, X and Yu, H and Xiao, Y and Xiao, X and Liu, H}, title = {Investigation of Hydrothermal Performance in Micro-Channel Heat Sink with Periodic Rectangular Fins.}, journal = {Micromachines}, volume = {14}, number = {10}, pages = {}, doi = {10.3390/mi14101818}, pmid = {37893255}, issn = {2072-666X}, abstract = {The micro-channel heat sink (MCHS) is an excellent choice due to its exceptional cooling capabilities, surpassing those of its competitors. In this research paper, a computational fluid dynamics analysis was performed to investigate the laminar flow and heat transfer characteristics of five different configurations of a variable geometry rectangular fin. The study utilized a water-cooled smooth MCHS as the basis. The results indicate that the micro-channel heat sink with a variable geometry rectangular fin has better heat dissipation capacity than a straight-type micro-channel heat sink, but at the same time, it has larger pressure loss. Based on the analysis of various rectangular fin shapes and Reynolds numbers in this study, the micro-channel heat sink with rectangular fins exhibits Nusselt numbers and friction factors that are 1.40-2.02 and 2.64-4.33 times higher, respectively, compared to the smooth heat sink. This significant improvement in performance results in performance evaluation criteria ranging from 1.23-1.95. Further, it is found that at a relatively small Reynolds number, the micro-channel heat sink with a variable geometry rectangular fin has obvious advantages in terms of overall cooling performance. Meanwhile, this advantage will decrease when the Reynolds number is relatively large.}, } @article {pmid37886753, year = {2023}, author = {Vaferi, K and Vajdi, M and Nekahi, S and Heydari, A and Sadegh Moghanlou, F and Nami, H and Jafarzadeh, H}, title = {Thermo-hydraulic performance optimization of a disk-shaped microchannel heat sink applying computational fluid dynamics, artificial neural network, and response surface methodology.}, journal = {Heliyon}, volume = {9}, number = {10}, pages = {e21031}, pmid = {37886753}, issn = {2405-8440}, abstract = {The current research focuses on optimizing the Nusselt number (Nu) and pressure drop (ΔP) in a bionic fractal heat sink. The artificial neural network (ANN) and response surface methodology (RSM) were used to model the thermos-hydraulic behavior of the MCHS. The aspect ratios of t/b (cavities' upper side to bottom side ratio) and h/b (cavities' height to bottom side ratio), as well as the Reynolds number, were set as the independent variables in both ANN and RSM models. After finding the optimum state for the copper-made MCHS (containing the optimum design of the cavities along with the best applied velocity), different materials were tested and compared with the base case (heat sink made of copper). The obtained results indicated that both ANN and RSM models (with determination coefficient of 99.9 %) could exactly anticipate heat transfer and ΔP to a large extent. To achieve the optimal design of the microchannel heat sink (MCHS) with the objective of maximizing Nu and minimizing ΔP, the efficiency index of the device was evaluated. The analysis revealed that the highest efficiency index (1.070 by RSM and 1.067 by ANN methods) was attained when the aspect ratios were t/b = 0.2, h/b = 0.2, and the Reynolds number was 1000. Next, the effect of the different materials on heat sink performance was investigated, and it was observed that by reducing the thermal conductivity, the thermal resistance of the heat sink increased and its overall performance decreased.}, } @article {pmid37849125, year = {2023}, author = {Paludan, MV and Biviano, MD and Jensen, KH}, title = {Elastohydrodynamic autoregulation in soft overlapping channels.}, journal = {Physical review. E}, volume = {108}, number = {3-2}, pages = {035106}, doi = {10.1103/PhysRevE.108.035106}, pmid = {37849125}, issn = {2470-0053}, abstract = {Controlling fluid flow from an unsteady source is a challenging problem that is relevant in both living and man-made systems. Animals have evolved various autoregulatory mechanisms to maintain homeostasis in vital organs. This keeps the influx of nutrients essentially constant and independent of the perfusion pressure. Up to this point, the autoregulation processes have primarily been ascribed to active mechanisms that regulate vessel size, thereby adjusting the hydraulic conductance in response to, e.g., sensing of wall shear stress. We propose an alternative elastohydrodynamic mechanism based on contacting soft vessels. Inspired by Starling's resistor, we combine experiments and theory to study the flow of a viscous liquid through a self-intersecting soft conduit. In the overlapping region, the pressure difference between the two channel segments can cause one pipe segment to dilate while the other is compressed. If the tissue is sufficiently soft, this mode of fluid-structure interactions can lead to flow autoregulation. Our experimental observations compare well to a predictive model based on low-Reynolds-number fluid flow and linear elasticity. Implications for conduit arrangement and passive autoregulation in organs and limbs are discussed.}, } @article {pmid37850032, year = {2021}, author = {Xing, Y and Burdsall, AC and Owens, A and Magnuson, M and Harper, WF}, title = {The effect of mixing and free-floating carrier media on bioaerosol release from wastewater: a multiscale investigation with Bacillus globigii.}, journal = {Environmental science : water research & technology}, volume = {7}, number = {}, pages = {}, pmid = {37850032}, issn = {2053-1400}, abstract = {Aeration tanks in wastewater treatment plants (WWTPs) are significant sources of bioaerosols, which contain microbial contaminants and can travel miles from the site of origin, risking the health of operators and the general public. One potential mitigation strategy is to apply free-floating carrier media (FFCM) to suppress bioaerosol emission. This article presents a multiscale study on the effects of mixing and FFCM on bioaerosol release using Bacillus globigii spores in well-defined liquid media. Bioaerosol release, defined as percentage of spores aerosolized during a 30 minute sampling period, ranged from 6.09 × 10[-7]% to 0.057%, depending upon the mixing mode and intensity. Bioaerosol release increased with the intensity of aeration (rotating speed in mechanical agitation and aeration rate in diffused aeration). A surface layer of polystyrene beads reduced bioaerosol released by >92% in the bench-scale studies and >74% in the pilot-scale study. This study discovered strong correlations (R[2] > 0.82) between bioaerosol release and superficial gas velocity, Froude number, and volumetric gas flow per unit liquid volume per minute. The Reynolds number was found to be poorly correlated with bioaerosol release (R[2] < 0.5). This study is a significant step toward the development of predictive models for full scale systems.}, } @article {pmid37848600, year = {2023}, author = {Maruai, NM and Ali, MSM and Zaki, SA and Ardila-Rey, JA and Ishak, IA}, title = {The influence of different downstream plate length towards the flow-induced vibration on a square cylinder.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {17681}, pmid = {37848600}, issn = {2045-2322}, support = {PY/2021/00886//Universiti Teknologi Malaysia/ ; PY/2021/00886//Universiti Teknologi Malaysia/ ; PY/2021/00886//Universiti Teknologi Malaysia/ ; Agencia Nacional de Investigación y Desarrollo (ANID)//FONDECYT Regular 1230135/ ; }, abstract = {The investigations of flow-induced vibration have been around for decades to solve many engineering problems related to structural element. In a hindsight of advancing technology of microelectronics devices, the implementation of flow-induced vibration for energy harvesting is intrigued. The influence of downstream flat plate to flow-induced vibration experienced by a square cylinder is discussed in this study to surpass the limitation of wind energy due to geographical constraints and climate change. The mechanism of flow-induced vibration experienced by a square cylinder with downstream flat plate is numerically simulated based on the unsteady Reynolds Navier-Stokes (URANS) flow field. The Reynolds number, Re assigned in this study is ranging between [Formula: see text]-[Formula: see text] and the mass damping ratio designated for the square cylinder is [Formula: see text] = 2.48. The influence of three different flat plate lengths [Formula: see text], 1 and 3 is examined. Each case of different flat plate is explored for gap separation between the square cylinder and the plate in the range [Formula: see text]. Based on the numerical findings, the configuration of cylinder-flat plate with length [Formula: see text] has shown the highest potential to harvest high energy at comparatively low reduced velocity.}, } @article {pmid37822907, year = {2023}, author = {Akram, M and Memon, AA and Memon, MA and Obalalu, AM and Khan, U}, title = {Investigation of a two-dimensional photovoltaic thermal system using hybrid nanofluids and a rotating cylinder.}, journal = {Nanoscale advances}, volume = {5}, number = {20}, pages = {5529-5542}, pmid = {37822907}, issn = {2516-0230}, abstract = {This article focuses on a numerical investigation aimed at enhancing the electrical performance of a two-dimensional photovoltaic thermal system (PV/T) through the application of cooling using hybrid nanofluids. The hybrid nanofluids consist of titanium oxide and silver nanoparticles suspended in water, while the PV/T system is based on polycrystalline silicon, copper, and a flow channel with a rotating cylinder. PV/T devices generate electricity from sunlight, but their performance degrades over time due to the heat generated by solar radiation. Therefore, nanofluids can be circulated through the bottom flow channel to cool the device. This study utilizes 2D incompressible Navier-Stokes equations to control fluid flow and energy equations to manage energy distribution. The COMSOL 6.0 finite element software is employed for comprehensive modeling and simulation. To enhance the performance of the PV/T system, a parametric study is conducted by varying the Reynolds number (ranging from 100 to 1000), cylinder rotational speed (varying from 0.01 to 0.2 m s[-1]), and silver volume fraction (ranging from 0.01 to 0.2). The results show that increasing the Reynolds number and the volume fraction of silver leads to a reduction in the maximum temperature of the cell. The maximum temperature of the cell also decreases with the rotational speed of the cylinder but only for high Reynolds numbers. By applying the present model, the cell's efficiency is improved by 5.93%.}, } @article {pmid37822766, year = {2023}, author = {Sutton, GP and Szczecinski, NS and Quinn, RD and Chiel, HJ}, title = {Phase shift between joint rotation and actuation reflects dominant forces and predicts muscle activation patterns.}, journal = {PNAS nexus}, volume = {2}, number = {10}, pages = {pgad298}, pmid = {37822766}, issn = {2752-6542}, abstract = {During behavior, the work done by actuators on the body can be resisted by the body's inertia, elastic forces, gravity, or viscosity. The dominant forces that resist actuation have major consequences on the control of that behavior. In the literature, features and actuation of locomotion, for example, have been successfully predicted by nondimensional numbers (e.g. Froude number and Reynolds number) that generally express the ratio between two of these forces (gravitational, inertial, elastic, and viscous). However, animals of different sizes or motions at different speeds may not share the same dominant forces within a behavior, making ratios of just two of these forces less useful. Thus, for a broad comparison of behavior across many orders of magnitude of limb length and cycle period, a dimensionless number that includes gravitational, inertial, elastic, and viscous forces is needed. This study proposes a nondimensional number that relates these four forces: the phase shift (ϕ) between the displacement of the limb and the actuator force that moves it. Using allometric scaling laws, ϕ for terrestrial walking is expressed as a function of the limb length and the cycle period at which the limb steps. Scale-dependent values of ϕ are used to explain and predict the electromyographic (EMG) patterns employed by different animals as they walk.}, } @article {pmid37821662, year = {2023}, author = {Saparbayeva, N and Balakin, BV}, title = {CFD-DEM model of plugging in flow with cohesive particles.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {17188}, pmid = {37821662}, issn = {2045-2322}, support = {300286//Norges Forskningsråd/ ; }, abstract = {Plugging in flows with cohesive particles is crucial in many industrial and real-life applications such as hemodynamics, water distribution, and petroleum flow assurance. Although probabilistic models for plugging risk estimation are presented in the literature, multiple details of the process remain unclear. In this paper, we present a CFD-DEM model of plugging validated against several experimental benchmarks. Using the simulations, we consider the process of plugging in a slurry of ice in decane, focusing on inter-particle collisions and plugging dynamics. We conduct a parametric study altering the Reynolds number (3000...9000), particle concentration (1.6...7.3%), and surface energy (21...541 mJ/m[Formula: see text]). We note the process possesses complex non-linear behaviour for the cases where particle-wall adhesion reduces by more than 20% relative to inter-particle cohesion. Finally, we demonstrate how the simulation results match the flow maps based on the third-party experiments.}, } @article {pmid37810730, year = {2023}, author = {Sun, T and Liu, H and Yan, T and Zhang, Y}, title = {Numerical Study on Enhanced Heat Transfer of Downhole Slotted-Type Heaters for In Situ Oil Shale Exploitation.}, journal = {ACS omega}, volume = {8}, number = {39}, pages = {36043-36052}, pmid = {37810730}, issn = {2470-1343}, abstract = {In order to improve the flow state of the heater shell side and enhance the performance evaluation of the heater, this paper proposes a perforated plate-type heater model. Based on Fluent, numerical studies are conducted on the heat transfer performance and shell-side fluid flow characteristics of a perforated plate-type heater. The variations of the heat transfer factor Nu, friction factor f, and evaluation parameter Nu/f[1/3] are analyzed for different helix angles β and ratios of the long and short semiaxes of the circular holes on the heating plate under different Reynolds numbers Re. The results reveal that under the same shell-side Reynolds number Re, the heat transfer factor Nu shows an increasing trend with the increase in the proportion of the helix angle β. The heat transfer factor Nu for the heating plate with the hole shape ratio a/b = 1 does not exhibit significant improvement compared to hole shape ratios a/b = 0.8 and a/b = 0.6, but it increases by 4.87 to 7.07% compared to the hole shape ratio a/b = 0.4 in the perforated plate-type heater. On the other hand, the friction factor f decreases as the helix angle β and the ratio of hole shapes on the heating plate increase. The lowest friction factor f is observed for the helix angle β of 25° and the hole shape ratio a/b = 1 in the perforated plate-type heater. When the helix angle β is 25° and the hole shape ratio is a/b = 1, the evaluation parameter Nu/f[1/3] reaches its highest value, indicating the optimal overall performance of the perforated plate-type heater.}, } @article {pmid37809404, year = {2023}, author = {Hosseinzadeh, K and Roshani, M and Attar, MA and Ganji, DD and Shafii, MB}, title = {Heat transfer study and optimization of nanofluid triangular cavity with a pentagonal barrier by finite element approach and RSM.}, journal = {Heliyon}, volume = {9}, number = {9}, pages = {e20193}, pmid = {37809404}, issn = {2405-8440}, abstract = {Nowadays, several engineering applications and academic investigations have demonstrated the significance of heat transfers in general and mixed convection heat transfer (MCHT) in particular in cavities containing obstacles. This study's main goal is to analyze the MCHT of a nanofluid in a triangular cavity with a pentagonal barrier using magneto hydrodynamics (MHD). The cavity's-oriented walls are continuous cold temperature, whereas the bottom wall of the triangle and all pentagonal obstacle walls are kept at a constant high temperature. For solving governing equations, we utilized the Galerkin's finite element approach. Four dimensionless factors, Richardson number (0.01 ≤ Ri ≤ 5), Reynolds number (10 ≤ Re ≤ 50), Buoyancy ratio (0.01 ≤ Br ≤ 10) and Hartmann number (0 ≤ Ha ≤20) are examined for their effects on streamlines, isotherms, concentration, velocity, and the Nusselt number. Also, with the help of Taguchi method and Response Surface Method (RSM) the optimization of the studied dimensionless parameters has been done. The optimum values of Ri, Re, Ha and Br are obtained 4.95, 30.49,18.35 and 0.05 respectively. Ultimately, a correlation has been extracted for obtaining the optimum average Nusselt number (Nu) in mentioned cavity.}, } @article {pmid37809384, year = {2023}, author = {Rasul, MG and Ahmed, S and Sattar, MA and Jahirul, MI}, title = {Hydrodynamic performance assessment of photocatalytic reactor with baffles and roughness in the flow path: A modelling approach with experimental validation.}, journal = {Heliyon}, volume = {9}, number = {9}, pages = {e19623}, pmid = {37809384}, issn = {2405-8440}, abstract = {Purification of wastewater is essential for human being as well as for the flora and fauna, and sustainable environment. Photocatalytic reactor with TiO2 coated layer can be used to degrade the pollutants but without proper pollutant mass transfer in the reactive surface, photocatalytic reactor decreases its effectiveness. The baffles and rough surface in the flow path can improve the fluid mixing to enhance pollutant mass transfer to improve the reactor's performance. In this study, a computational fluid dynamics (CFD) model has been developed to investigate the effect of four top baffles and three rough surfaces (semi-circular, triangle, and rectangle) on pressure drops, mass transfer and the hydrodynamic performance of the reactor. The experimental investigation was carried out using Formic Acid (FA) as pollutant in feed water for model validation. The simulated result varies only within 5% with the experimental data of FA concentration versus feed flow rate and fluid velocity. The model was run at fluid velocity of 0.15 m/s and 0.5 m/s (Reynolds number of 2150 (laminar flow) and 7500 (turbulent flow), respectively. The simulation result shows that the addition of baffles and roughness on the reactive surfaces increases the turbulent kinetic energy (minimum increase 8%) and consequently increases the mass transfer (maximum increase 37%) of the pollutant. The highest wall shear was observed to be 40 Pa when both square and triangular elements were used as roughness elements at turbulent flow condition. The results also shows that the highest pressure-drop of 8 kPa was found when the square roughness element was used at turbulent flow condition. Overall, the photocatalytic reactor performance is significantly enhanced by the application of combined baffles and roughness elements in the reactive surface.}, } @article {pmid37807009, year = {2023}, author = {Allehiany, FM and Memon, AA and Memon, MA and Fenta, A}, title = {Maximizing electrical output and reducing heat-related losses in photovoltaic thermal systems with a thorough examination of flow channel integration and nanofluid cooling.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {16961}, pmid = {37807009}, issn = {2045-2322}, abstract = {In recent years, global energy demand has surged, emphasizing the need for nations to enhance energy resources. The photovoltaic thermal (PV/T) system, capable of generating electrical energy from sunlight, is a promising renewable energy solution. However, it faces the challenge of overheating, which reduces efficiency. To address this, we introduce a flow channel within the PV/T system, allowing coolant circulation to improve electrical efficiency. Within this study, we explore into the workings of a PV/T system configuration, featuring a polycrystalline silicon panel atop a copper absorber panel. This innovative setup incorporates a rectangular flow channel, enhanced with a centrally positioned rotating circular cylinder, designed to augment flow velocity. This arrangement presents a forced convection scenario, where heat transfer primarily occurs through conduction in the uppermost two layers, while the flow channel beneath experiences forced convection. To capture this complex phenomenon, we accurately address the two-dimensional Navier-Stokes and energy equations, employing simulations conducted via COMSOL 6.0 software, renowned for its utilization of the finite element method. To optimize heat dissipation and efficiency, we introduce a hybrid nanofluid comprised of titanium oxide and silver nanoparticles dispersed in water, circulating through the flow channel. Various critical parameters come under scrutiny, including the Reynolds number, explored across the range of 100-1000, the volume fractions of both nanoparticle types, systematically tested within the range of 0.001-0.05, and the controlled speed of the circular cylinder, maintained within the range of 0.1-0.25 m/s. It was found that incorporating silver nanoparticles as a suspended component is more effective in enhancing PV/T efficiency than the addition of titanium oxide. Additionally, maintaining the volume fraction of titanium oxide between 4 and 5% yields improved efficiency, provided that the cylinder rotates at a higher speed. It was observed that cell efficiency can be regulated by adjusting four parameters, such as the Reynolds number, cylinder rotation speed, and the volume fraction of both nanoparticles.}, } @article {pmid37798525, year = {2023}, author = {Zhang, B and Liu, G and Li, Y and Lin, Z}, title = {Experimental study on the seepage mutation of natural karst collapse pillar (KCP) fillings over mass outflow.}, journal = {Environmental science and pollution research international}, volume = {}, number = {}, pages = {}, pmid = {37798525}, issn = {1614-7499}, support = {41807209//Natural Science Foundation of China/ ; }, abstract = {Conduction between the unique geological formation karst collapse pillar (KCP) and the fractures caused by mining in the coal seam floor can lead to catastrophic water inrush disasters in many coalmines in Northern China. It is widely recognized that seepage mutation induced by the migration/loss of KCP fillings (highly broken rocks filling the fractured rocks) happens during occurrence of the KCP-related water inrush. However, roles of fluid path (mining-induced fracture) scale and KCP filling porosity in seepage mutation evolution remain unclear. Here, we conducted seepage tests on natural KCP fillings containing rock particles of different sizes. The filling specimens were deformed to different porosities from 14 to 26% through axial compression, and small to large fluid paths were simulated by seepage plates with distinct pore sizes from 2.5 to 12.5 mm. We found that seepage mutation occurs with significant permeability enhancement by 2 orders of magnitude under a pore diameter of 12.5 mm and a specimen porosity of 26%. There is a strong linear relationship between specimen permeability and Reynolds number (Re) over seepage mutation. The mutation is caused by the sudden collapse of the specimen skeleton and subsequent quick outflow of the particles. Therefore, it is inferred that the KCP-related water inrush is more likely to happen when highly porous KCP fillings are present and mining-induced fractures are well developed.}, } @article {pmid37787128, year = {2023}, author = {Duraes, ADS and Gezelter, JD}, title = {A theory of pitch for the hydrodynamic properties of molecules, helices, and achiral swimmers at low Reynolds number.}, journal = {The Journal of chemical physics}, volume = {159}, number = {13}, pages = {}, doi = {10.1063/5.0152546}, pmid = {37787128}, issn = {1089-7690}, abstract = {We present a theory for pitch, a matrix property that is linked to the coupling of rotational and translational motion of rigid bodies at low Reynolds numbers. The pitch matrix is a geometric property of objects in contact with a surrounding fluid, and it can be decomposed into three principal axes of pitch and their associated moments of pitch. The moments of pitch predict the translational motion in a direction parallel to each pitch axis when the object is rotated around that axis and can be used to explain translational drift, particularly for rotating helices. We also provide a symmetrized boundary element model for blocks of the resistance tensor, allowing calculation of the pitch matrix for arbitrary rigid bodies. We analyze a range of chiral objects, including chiral molecules and helices. Chiral objects with a Cn symmetry axis with n > 2 show additional symmetries in their pitch matrices. We also show that some achiral objects have non-vanishing pitch matrices, and we use this result to explain recent observations of achiral microswimmers. We also discuss the small but non-zero pitch of Lord Kelvin's isotropic helicoid.}, } @article {pmid37774714, year = {2023}, author = {Zhu, Q}, title = {Locomotion performance of an axisymmetric 'flapping fin'.}, journal = {Bioinspiration & biomimetics}, volume = {}, number = {}, pages = {}, doi = {10.1088/1748-3190/acfeb9}, pmid = {37774714}, issn = {1748-3190}, abstract = {Inspired by the jet-propulsion mechanism of aquatic creatures such as sea salps, a novel locomotion system based on an axisymmetric body design is proposed. This system consists of an empty tube with two ends open. When the diameters of the front and back openings are changed periodically, the forward-backward symmetry is broken so that the system starts swimming. Viewed within a cross section, this system resembles a two-dimensional flapping fin with its leading edge located at the front opening and the trailing edge at the back opening. The feasibility of this system has been proven via numerical simulations using a fluid-structure interaction model based on the immersed-boundary framework. According to the results, at relatively low Reynolds number (O(100)), this simple locomotion method can easily achieve a mean swimming speed of 2 to 3 body lengthes per deformation period. Further simulations illustrate the following characteristics: 1) Within the chamber, the hydrodynamic interactions among different parts of the body leads to a performance-enhancing mechanism similar to the ground effect; 2) Reducing the diameter of the body can strengthen this effect so that both the swimming speed and the energy efficiency are improved; 3) For better performance the amplitude of diameter oscillation at the trailing edge should be larger or at least equal to the one at the leading edge. .}, } @article {pmid37763958, year = {2023}, author = {Juraeva, M and Kang, DJ}, title = {Design and Mixing Analysis of a Passive Micromixer Based on Curly Baffles.}, journal = {Micromachines}, volume = {14}, number = {9}, pages = {}, doi = {10.3390/mi14091795}, pmid = {37763958}, issn = {2072-666X}, support = {Daedong2023//Daedong Heavy Industry/ ; }, abstract = {A novel passive micromixer based on curly baffles is proposed and optimized through the signal-to-noise analysis of various design parameters. The mixing performance of the proposed design was evaluated across a wide Reynolds number range, from 0.1 to 80. Through the analysis, the most influential parameter was identified, and its value was found to be constant regardless of the mixing mechanism. The optimized design, refined using the signal-to-noise analysis, demonstrated a significant enhancement of mixing performance, particularly in the low Reynolds number range (Re< 10). The design set obtained at the diffusion dominance range shows the highest degree of mixing (DOM) in the low Reynolds number range of Re< 10, while the design set optimized for the convection dominance range exhibited the least pressure drop across the entire Reynolds number spectrum (Re< 80). The present design approach proved to be a practical tool for identifying the most influential design parameter and achieving excellent mixing and pressure drop characteristics. The enhancement is mainly due to the curvature of the most influential design parameter.}, } @article {pmid37757685, year = {2023}, author = {Jafari, E and Malayeri, MR and Brückner, H and Weimer, T and Krebs, P}, title = {Innovative spiral electrode configuration for enhancement of electrocoagulation-flotation.}, journal = {Journal of environmental management}, volume = {347}, number = {}, pages = {119085}, doi = {10.1016/j.jenvman.2023.119085}, pmid = {37757685}, issn = {1095-8630}, abstract = {The performance of electrocoagulation-flotation (ECF) process can profoundly be affected by the reactor design and electrode configuration. These may, in turn, influence the removal efficiency, flow hydrodynamic, floc formation, and flotation/settling characteristics. The present work aimed at developing a new spiral electrode configuration to enhance the ECF process. To do so, the impacts of parameters such as energy consumption, removal efficiency of the contaminants from industrial wastewater with a composition of turbidity, emulsified oil, and heavy metals (Si, Zn, Pb, Ni, Cu, Cr, and Cd), as well as stirring speed and foaming have been investigated. Comparison was also made between the experimental results of the new electrode configuration with the conventional rectangular cell with plate electrode configuration with the same volume and electrode surface area. The findings revealed that energy consumption of the spiral electrode configuration within the operating times of 10, 20, 30, 32, 48, and 70 min, was approximately 20% lower compared to that of the conventional ECF. Moreover, the maximum and minimum removal efficiency of 97% and 60% were obtained for turbidity and TOC for the stirring speed of 500 rpm and Reynolds number of 10,035, respectively. Finally, the formed gas bubbles tilted toward the center due to the enhanced flow hydrodynamic which resulted in substantial reduction of foam formation.}, } @article {pmid37756554, year = {2023}, author = {Rajendran, S and Jog, MA and Manglik, RM}, title = {Predicting the Splash of a Drop Impacting a Thin Liquid Film.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {}, number = {}, pages = {}, doi = {10.1021/acs.langmuir.3c02185}, pmid = {37756554}, issn = {1520-5827}, abstract = {An experimental study is carried out to investigate droplet-film interactions when a drop impinges on a thin stagnant film of the same liquid. The impacting drop causes either liquid deposition or splash, consisting of prompt generation of secondary drops or a delayed process. By varying the drop diameter and impact velocity, measurements are made to characterize the phenomena using five different liquids that are chosen to cover a wide range of liquid properties (viscosity and surface tension). The drop impact dynamics are captured with a high-speed digital camera with real-time, high-resolution image processing. The drop-splash threshold is found to scale with inertial and viscous forces, or Reynolds number (Re), as well as capillary forces, as described by the balance of gravitational and interfacial tension forces, or Bond number (Bo); fluid properties are described by their Morton number (Mo). A correlation, functionally expressed as Re = ϕ(Bo,Mo), is devised to determine the splash/no-splash (or deposition) boundary, and the predictions for the splash/no-splash outcomes agree well with the experimental outcomes as well as those readily available in the literature.}, } @article {pmid37756336, year = {2023}, author = {Hickey, DJ and Golestanian, R and Vilfan, A}, title = {Nonreciprocal interactions give rise to fast cilium synchronization in finite systems.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {120}, number = {40}, pages = {e2307279120}, doi = {10.1073/pnas.2307279120}, pmid = {37756336}, issn = {1091-6490}, support = {//Max Planck Society/ ; P1-0099//Javna Agencija za Raziskovalno Dejavnost RS (ARRS)/ ; }, abstract = {Motile cilia beat in an asymmetric fashion in order to propel the surrounding fluid. When many cilia are located on a surface, their beating can synchronize such that their phases form metachronal waves. Here, we computationally study a model where each cilium is represented as a spherical particle, moving along a tilted trajectory with a position-dependent active driving force and a position-dependent internal drag coefficient. The model thus takes into account all the essential broken symmetries of the ciliary beat. We show that taking into account the near-field hydrodynamic interactions, the effective coupling between cilia even over an entire beating cycle can become nonreciprocal: The phase of a cilium is more strongly affected by an adjacent cilium on one side than by a cilium at the same distance in the opposite direction. As a result, synchronization starts from a seed at the edge of a group of cilia and propagates rapidly across the system, leading to a synchronization time that scales proportionally to the linear dimension of the system. We show that a ciliary carpet is characterized by three different velocities: the velocity of fluid transport, the phase velocity of metachronal waves, and the group velocity of order propagation. Unlike in systems with reciprocal coupling, boundary effects are not detrimental for synchronization, but rather enable the formation of the initial seed.}, } @article {pmid37749273, year = {2023}, author = {Younis, O and Abderrahmane, A and Hatami, M and Mourad, A and Guedri, K}, title = {Nanoencapsulated phase change material in a trapezoidal prism wall under the magnetic field effect for energy storage purposes.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {16060}, pmid = {37749273}, issn = {2045-2322}, abstract = {Recently, Nano-encapsulated phase change materials (NEPCM) have attracted the attention of researchers due to their promising application in thermal management. This research investigates magnetohydrodynamic mixed convection of NEPCM contained within a lid-driven trapezoidal prism enclosure containing a hot-centered elliptical obstacle. The upper cavity wall is moving at a constant velocity; both inclined walls are cold, while the rest of the walls are insulated. The Galerkin Finite Element Method was used to solve the system's governing equations. The influence of Reynolds number (Re 1-500), Hartmann number (Ha = 0-100), NEPCM volumetric fraction φ (0-8%), and elliptical obstacle orientation α (0-3π/4) on thermal fields and flow patterns are introduced and analyzed. The results indicated that the maximum heat transfer rate is observed when the hot elliptic obstacle is oriented at 90°; an increment of 6% in the Nu number is obtained in this orientation compared to other orientations. Reducing Ha from 100 to 0 increased Nu by 14%. The Maximum value of the Bejan number was observed for the case of Ha = 0, α = 90° and φ = 0.08.}, } @article {pmid37749138, year = {2023}, author = {Abd-Alla, AM and Abo-Dahab, SM and Abdelhafez, MA and Elmhedy, Y}, title = {Effect of heat and mass transfer on the nanofluid of peristaltic flow in a ciliated tube.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {16008}, pmid = {37749138}, issn = {2045-2322}, abstract = {The current work focuses attention on discussing the peristaltic flow of Rabinowitsch nanofluid through ciliated tube. This technical study analyzes heat and mass transfer effects on the flow of a peristaltic flow, incompressible, nanofluid via a ciliated tube. The governing non-linear partial differential equations representing the flow model are transmuted into linear ones by employing the appropriate non-dimensional parameters under the assumption of long wavelength and low Reynolds number. The flow is examined in wave frame of reference moving with the velocity [Formula: see text]. The governing equations have been solved to determine velocity, temperature, concentration, the pressure gradient, pressure rise and the friction force. Using MATLAB R2023a software, a parametric analysis is performed, and the resulting data is represented graphically. The results indicate that the various emerging parameters of interest significantly affect the nanofluid properties within the tube. The present study enhances the comprehension of nanofluid dynamics in tube and offers valuable insights into the influence of heat and mass transfer in such setups. Convective heat transfer is found to be greater at the boundaries resulting in decreased temperature there.}, } @article {pmid37749119, year = {2023}, author = {Abbas, N and Shatanawi, W and Hasan, F and Mustafa, Z}, title = {Thermodynamic flow of radiative induced magneto modified Maxwell Sutterby fluid model at stretching sheet/cylinder.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {16002}, pmid = {37749119}, issn = {2045-2322}, abstract = {A steady flow of Maxwell Sutterby fluid is considered over a stretchable cylinder. The magnetic Reynolds number is considered very high and induced magnetic and electric fields are applied on the fluid flow. Joule heating and radiation impacts are studied under the temperature-dependent properties of the liquid. Having the above assumptions, the mathematical model has been evolving via differential equations. The differential equations are renovated in the dimensionless form of ordinary differential equations using the appropriate transformations. The numerical results have been developed employing numerical techniques on the ordinary differential equations. The impact of involving physical factors on velocity, induced magneto hydrodynamic, and temperature function is debated in graphical and tabular form. The velocity profile is boosted by thicker momentum boundary layers, which are caused by higher values of the magnetic field factor. So, the fluid flow becomes higher velocity due to enlarging values of the magnetic field factor. Heat transfer factor and friction at surface factor boosted up for increment of [Formula: see text] (Magnetic field factor). The [Formula: see text](Magnetic field factor) is larger which better-quality of heat transfer at surface and also offered the results of friction factor boosting up in both cases of stretching sheet/cylinder. The [Formula: see text](Magnetic Prandtl number) increased which provided better-quality of heat transfer at surface.}, } @article {pmid37741030, year = {2023}, author = {Wang, Z and Sedighi, M}, title = {Dispersion properties of nanoplastic spheres in granular media at low Reynolds numbers.}, journal = {Journal of contaminant hydrology}, volume = {259}, number = {}, pages = {104244}, doi = {10.1016/j.jconhyd.2023.104244}, pmid = {37741030}, issn = {1873-6009}, abstract = {Nanoplastic particles (<1 μm) are among the contaminants of emerging concern, and compared to microplastic (<5 mm), our understanding of the transport and fate of nanoplastic in water, sediments and soil is very limited. This paper focuses on developing fundamental insight into the dispersion behaviour (sum of hydrodynamic dispersion and diffusion) of nanoplastic spheres, which are likely the most mobile shape of nanoplastic. We measured the dispersion coefficient and dispersivity of nanoplastic spheres (100 nm, 300 nm and 1000 nm diameter) in granular media with a range of pore sizes. We investigated the mechanisms that control the behaviour at low Reynolds number (smaller than 2), relevant to the dispersion of nanoplastic across the riparian area at water velocities of the common river and shallow groundwater. The measured dispersion coefficients were compared with the predictions by two commonly used models. The results show that there are significant differences between measurements and predictions for the case of colloidal size nanoplastics (MAPE>100%). The retarded dispersion caused by the size-exclusion effect was observed to be important in the case of 1.7 mm and 0.4 mm granular media for 300 nm and 1000 nm nanoplastics, reducing the dispersivity and sensitivity to Reynolds number. The methodology in this paper can be adopted in studies on other sizes and shapes of nanoplastic, assisting with predicting the transport and fate of nanoplastic granular media.}, } @article {pmid37723692, year = {2023}, author = {Mamori, H and Nabae, Y and Fukuda, S and Gotoda, H}, title = {Dynamic state of low-Reynolds-number turbulent channel flow.}, journal = {Physical review. E}, volume = {108}, number = {2-2}, pages = {025105}, doi = {10.1103/PhysRevE.108.025105}, pmid = {37723692}, issn = {2470-0053}, abstract = {We numerically study the dynamic state of a low-Reynolds-number turbulent channel flow from the viewpoints of symbolic dynamics and nonlinear forecasting. A low-dimensionally (high-dimensionally) chaotic state of the streamwise velocity fluctuations emerges at a viscous sublayer (logarithmic layer). The possible presence of the chaotic states is clearly identified by orbital instability-based nonlinear forecasting and ordinal partition transition network entropy in combination with the surrogate data method.}, } @article {pmid37690262, year = {2023}, author = {Dong, B and Guo, Y and Yang, J and Yang, X and Wang, L and Huang, D}, title = {Turbulence induced shear controllable synthesis of nano FePO4 irregularly-shaped particles in a counter impinging jet flow T-junction reactor assisted by ultrasound irradiation.}, journal = {Ultrasonics sonochemistry}, volume = {99}, number = {}, pages = {106590}, doi = {10.1016/j.ultsonch.2023.106590}, pmid = {37690262}, issn = {1873-2828}, abstract = {FePO4 (FP) particles with a mesoporous structure amalgamated by nanoscale primary crystals were controllably prepared using an ultrasound-intensified turbulence T-junction microreactor (UTISR). The use of this type of reaction system can effectively enhance the micro-mixing and remarkably improve the mass transfer and chemical reaction rates. Consequently, the synergistic effects of the impinging streams and ultrasonic irradiation on the formation of mesoporous structure of FP nanoparticles have been systematically investigated through experimental validation and CFD simulation. The results revealed that the FP particles with a mesoporous structure can be well synthesised by precisely controlling the operation parameters by applying ultrasound irradiation with the input power in the range of 0-900 W and the impinging stream volumetric flow rate in the range of 17.15-257.22 mL·min[-1]. The findings obtained from the experimental observation and CFD modelling has clearly indicated that there exists a strong correlation between the particle size, morphology, and the local turbulence shear. The application of ultrasonic irradiation can effectively intensify the local turbulence shear in the reactor even at low Reynolds number based on the impinging stream diameter (Re < 2000), leading to an effective reduction in the particle size (from 273.48 to 56.1 nm) and an increase in the specific surface area (from 21.97 to 114.97 m[2]·g[-1]) of FP samples. The FPirregularly-shaped particles prepared by UTISR exhibited a mesoporous structure with a particle size of 56.10 nm, a specific surface area of 114.97 m[2]·g[-1]and a total pore adsorption volume of 0.570 cm[3]·g[-1] when the volumetric flow rate and ultrasound power are 85.74 mL·min[-1]and 600 W, respectively.}, } @article {pmid37689862, year = {2023}, author = {Fuciños, C and Rodríguez-Sanz, A and García-Caamaño, E and Gerbino, E and Torrado, A and Gómez-Zavaglia, A and Rúa, ML}, title = {Microfluidics potential for developing food-grade microstructures through emulsification processes and their application.}, journal = {Food research international (Ottawa, Ont.)}, volume = {172}, number = {}, pages = {113086}, doi = {10.1016/j.foodres.2023.113086}, pmid = {37689862}, issn = {1873-7145}, abstract = {The food sector continues to face challenges in developing techniques to increase the bioavailability of bioactive chemicals. Utilising microstructures capable of encapsulating diverse compounds has been proposed as a technological solution for their transport both in food and into the gastrointestinal tract. The present review discusses the primary elements that influence the emulsification process in microfluidic systems to form different microstructures for food applications. In microfluidic systems, reactions occur within small reaction channels (1-1000 μm), using small amounts of samples and reactants, ca. 102-103 times less than conventional assays. This geometry provides several advantages for emulsion and encapsulating structure production, like less waste generation, lower cost and gentle assays. Also, from a food application perspective, it allows the decrease in particle dispersion, resulting in a highly repeatable and efficient synthesis method that also improves the palatability of the food products into which the encapsulates are incorporated. However, it also entails some particular requirements. It is important to obtain a low Reynolds number (Re < approx. 250) for greater precision in droplet formation. Also, microfluidics requires fluid viscosity typically between 0.3 and 1400 mPa s at 20 °C. So, it is a challenge to find food-grade fluids that can operate at the micro-scale of these systems. Microfluidic systems can be used to synthesise different food-grade microstructures: microemulsions, solid lipid microparticles, microgels, or self-assembled structures like liposomes, niosomes, or polymersomes. Besides, microfluidics is particularly useful for accurately encapsulating bacterial cells to control their delivery and release on the action site. However, despite the significant advancement in these systems' development over the past several years, developing and implementing these systems on an industrial scale remains challenging for the food industry.}, } @article {pmid37676785, year = {2023}, author = {Giurgiu, V and Caridi, GCA and Alipour, M and De Paoli, M and Soldati, A}, title = {The TU Wien Turbulent Water Channel: Flow control loop and three-dimensional reconstruction of anisotropic particle dynamics.}, journal = {The Review of scientific instruments}, volume = {94}, number = {9}, pages = {}, doi = {10.1063/5.0157490}, pmid = {37676785}, issn = {1089-7623}, abstract = {A horizontal water channel facility was built to study particle dynamics in a turbulent flow. The channel is sufficiently long to produce fully developed turbulence at the test section, and the width-to-height ratio is sufficiently large to avoid the sidewall effect for a large proportion of the cross-section. The system was designed to study the dynamics of complex-shaped particles in wall-bounded turbulence, the characteristics of which can be finely controlled. A maximum bulk velocity of up to 0.8 m s-1 can be achieved, corresponding to a bulk Reynolds number of up to 7 × 104 (shear Reynolds number ≈1580), and flow parameters can be controlled within ±0.1%. The transparent channel design and aluminum structures allow easy optical access, which enables multiple laser and camera arrangements. With the current optical setup, a measurement volume of up to 54 × 14 × 54 mm3 can be imaged and reconstructed with six cameras from the top, bottom, and sides of the channel. Finally, the in-house developed reconstruction and tracking procedure allows us to measure the full motion of complex objects (i.e., shape reconstruction, translational, and rotational motions), and in this instance, it is applied to the case of microscopic, non-isotropic polyamide fibers.}, } @article {pmid37663493, year = {2023}, author = {Zheng, Y and Min, F and Zhu, H}, title = {Study on the Classification Performance of a Novel Wide-Neck Classifier.}, journal = {ACS omega}, volume = {8}, number = {34}, pages = {31237-31245}, pmid = {37663493}, issn = {2470-1343}, abstract = {A novelty-designed wide-neck classifier (WNC) was proposed to enhance the passing ability and classification efficiency of fine particles. Using computational fluid dynamics (CFD), we studied the flow field and velocity distribution in the newly designed WNC. The velocity of the fluid gradually decreased from the wall to the center and from the cylinder to the cone, which facilitates particle classification and thickening. The Reynolds number (Re) and turbulent intensity (I) inside the WNC were discussed. The turbulent intensity increased with increasing feed velocity and overflow outlet diameter and decreased with increasing feed concentration and spigot diameter. The classification of coal slurry was performed to analyze the performance of WNC. The classification efficiency increased with increasing feed velocity but decreased as the feed concentration, spigot diameter, and overflow outlet diameter increased. The predictive models for classification efficiency influenced by the operational and structural parameters were constructed at high correlation coefficients, and the average error of these models was analyzed at 0.28%. Our results can provide valuable insights into the development of mineral classification.}, } @article {pmid37663238, year = {2022}, author = {Beaver, LE and Wu, B and Das, S and Malikopoulos, AA}, title = {A First-Order Approach to Model Simultaneous Control of Multiple Microrobots.}, journal = {... International Conference on Manipulation Automation and Robotics at Small Scales (MARSS). International Conference on Manipulation Automation and Robotics at Small Scales}, volume = {2022}, number = {}, pages = {}, pmid = {37663238}, abstract = {The control of swarm systems is relatively well understood for simple robotic platforms at the macro scale. However, there are still several unanswered questions about how similar results can be achieved for microrobots. In this paper, we propose a modeling framework based on a dynamic model of magnetized self-propelling Janus microrobots under a global magnetic field. We verify our model experimentally and provide methods that can aim at accurately describing the behavior of microrobots while modeling their simultaneous control. The model can be generalized to other microrobotic platforms in low Reynolds number environments.}, } @article {pmid37660186, year = {2023}, author = {Mishra, NK and Sharma, BK and Sharma, P and Muhammad, T and Pérez, LM}, title = {Entropy generation optimization of cilia regulated MHD ternary hybrid Jeffery nanofluid with Arrhenius activation energy and induced magnetic field.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {14483}, pmid = {37660186}, issn = {2045-2322}, support = {SA77210040//Convocatoria Nacional Subvención a Instalación en la Academia Convocatoria Año 2021/ ; }, abstract = {This study deals with the entropy generation analysis of synthetic cilia using a ternary hybrid nanofluid (Al-Cu-Fe2O3/Blood) flow through an inclined channel. The objective of the current study is to investigate the effects of entropy generation optimization, heat, and mass transfer on ternary hybrid nanofluid passing through an inclined channel in the proximity of the induced magnetic field. The novelty of the current study is present in studying the combined effect of viscous dissipation, thermophoresis, Brownian motion, exponential heat sink/source, porous medium, endothermic-exothermic chemical reactions, and activation energy in the proximity of induced magnetic field is examined. The governing partial differential equations (PDEs) are transformed into the ordinary differential equations (ODEs) using appropriate transformations. Applying the low Reynolds number and the long-wavelength approximation, resultant ODEs are numerically solved using shooting technique via BVP5C in MATLAB. The velocity, temperature, concentration, and induced magnetism profiles are visually discussed and graphically analyzed for various fluid flow parameters. Graphical analysis of physical interest quantities like mass transfer rate, heat transfer rate, entropy generation optimization, and skin friction coefficient are also graphically discussed. The entropy generation improves for enhancing values of Reynolds number, solutal Grashof number, heat sink/source parameter, Brinkman number, magnetic Prandtl number, and endothermic-exothermic reaction parameter while the reverse effect is noticed for chemical reaction and induced magnetic field parameter. The findings of this study can be applied to enhance heat transfer efficiency in biomedical devices, optimizing cooling systems, designing efficient energy conversion processes, and spanning from renewable energy technologies to aerospace propulsion systems.}, } @article {pmid37659126, year = {2023}, author = {Adeyemi, I and Meribout, M and Khezzar, L and Kharoua, N and AlHammadi, K and Tiwari, V}, title = {Experimental and numerical analysis of the emulsification of oil droplets in water with high frequency focused ultrasound.}, journal = {Ultrasonics sonochemistry}, volume = {99}, number = {}, pages = {106566}, doi = {10.1016/j.ultsonch.2023.106566}, pmid = {37659126}, issn = {1873-2828}, abstract = {Focused high frequency ultrasound emulsification provides significant benefits such as enhanced stability, finer droplets, elevated focal pressure, lowered power usage, minimal surfactant usage and improved dispersion. Hence, in this study, the high frequency focused ultrasound emulsification of oil droplets in water was investigated through experiments and numerical modeling. The effect of transducer power (74-400 W), frequency (1.1 and 3.3 MHz), oil viscosity (10.6-512 mPas), interfacial tension (25-250 mN/m) and initial droplet radius (10-750 µm) on the emulsification process was assessed. In addition, the mechanism of droplet break-up was examined. The experiments showed that the acoustic pressure increased from 9.01 MPa to 26.24 MPa as the power was raised from 74 W to 400 W. At 74 W, the Weber number (We) at the surface and focal zone are 0.5 and 939.8, respectively. However, at 400 W, the We at the transducer surface and focal region reached 2.7 and 6451.8, respectively. Thus, bulb-like and weak catastrophic break up dominates the emulsification at 74 W. The catastrophic break up at 400 W is more vigorous because the ultrasound disruptive stress and We are higher. The time for the catastrophic dispersion of a single droplet at We = 939.8 and We = 6451.8 are 1.01 ms and 0.45 ms, respectively. The numerical model gives reasonable prediction of the trend and magnitude of the experimental acoustic pressure data. The surface and focal pressure amplitudes were estimated with errors of ∼ 6.5% and ∼ 10%, respectively. The predicted Reynolds number (Re) between 74 and 400 W were 8442 and 21364, respectively. The acoustic pressure at the focal region were ∼ 26 MPa and ∼ 69 MPa at frequencies of 1.1 MHz and 3.3 MHz, respectively. Moreover, the acoustic velocities were ∼ 16 m/s and ∼ 42 m/s at 1.1 MHz and 3.3 MHz, respectively. Hence, smaller droplets could be attained at higher frequency excitation under intense catastrophic modes. The Ohnesorge number (Oh) increased from 0.062 to 3.12 with the viscosity between 10.6 mPas and 530 mPas. However, the We remained constant at 856.14 for the studied range. Generally, higher critical We is required for the different breakup stages as the viscosity ratio is elevated. Moreover, the We increased from 25.68 to 1284.22 as the droplet radius was elevated from 15 to 750 µm. Larger droplets allow for higher possibility and intensity of breakup due to diminished viscous and interfacial resistance.}, } @article {pmid37655637, year = {2023}, author = {Gladman, NW and Askew, GN}, title = {The hydrodynamics of jet propulsion swimming in hatchling and juvenile European common cuttlefish Sepia officinalis, Linnaeus (1758).}, journal = {The Journal of experimental biology}, volume = {}, number = {}, pages = {}, doi = {10.1242/jeb.246225}, pmid = {37655637}, issn = {1477-9145}, abstract = {Cuttlefish swim using jet propulsion, taking a small volume of fluid into the mantle cavity before it is expelled through the siphon to generate thrust. Jet propulsion swimming has been shown to be more metabolically expensive than undulatory swimming, which has been suggested to be due to the lower efficiency of jet propulsion. The whole cycle propulsive efficiency of cephalopod molluscs ranges from 38-76%, indicating that in some instances jet propulsion can be relatively efficient. Here, we determined the hydrodynamics of hatchling and juvenile cuttlefish during jet propulsion swimming to understand the characteristics of their jets, and whether their whole cycle propulsive efficiency changes during development. Cuttlefish were found to utilise two jet types: isolated jet vortices (termed jet mode I) and elongated jets (leading edge vortex ring followed by a trailing jet; termed jet mode II). The use of these jet modes differed between the age classes, with newly hatched animals nearly exclusively utilising mode I jets, while juveniles showed no strong preferences. Whole cycle propulsive efficiency was found to be high, ranging from 72-80%, and did not differ between age-classes. During development, Strouhal number decreased as Reynolds number increased, which is consistent with animals adjusting their jetting behaviour in order to maximise whole cycle propulsive efficiency and locomotor performance. While jet propulsion swimming can have a relatively high energetic cost, in cuttlefish and nautilus, both neutrally buoyant species, the whole cycle propulsive efficiency is actually relatively high.}, } @article {pmid37651341, year = {2023}, author = {Sun, B and Zheng, W and Tong, A and Di, D and Li, Z}, title = {Prediction of the roughness coefficient for drainage pipelines with sediments using GA-BPNN.}, journal = {Water science and technology : a journal of the International Association on Water Pollution Research}, volume = {88}, number = {4}, pages = {1111-1130}, doi = {10.2166/wst.2023.249}, pmid = {37651341}, issn = {0273-1223}, abstract = {Accurate prediction of the roughness coefficient of sediment-containing drainage pipes can help engineers optimize urban drainage systems. In this paper, the variation of the roughness coefficient of circular drainage pipes containing different thicknesses of sediments under different flows and slopes was studied by experimental measurements. Back Propagation Neural Network (BPNN) and Genetic Algorithm-Back Propagation Neural Network (GA-BPNN) were used to predict the roughness coefficient. To explore the potential of artificial neural networks to predict the roughness coefficient, a formula based on drag segmentation was established to calculate the roughness coefficient. The results show that the variation trend of the roughness coefficient with flow, hydraulic radius, and Reynolds number is consistent. With the increase of the three parameters, the roughness coefficient decreases overall. Compared to the traditional empirical formula, the BPNN model and the GA-BPNN model increased the determination factors in the testing stage by 3.47 and 3.99%, respectively, and reduced the mean absolute errors by 41.18 and 47.06%, respectively. The study provides an intelligent method for accurate prediction of sediment-containing drainage pipes roughness coefficient.}, } @article {pmid37646074, year = {2023}, author = {Pandian, SK and Broom, M and Balzan, M and Willmott, GR}, title = {Influence of rheology and micropatterns on spreading, retraction and fingering of an impacting drop.}, journal = {Soft matter}, volume = {}, number = {}, pages = {}, doi = {10.1039/d3sm00944k}, pmid = {37646074}, issn = {1744-6848}, abstract = {Rheology and surface microstructure affect many drop impact processes, including in emerging printing and patterning applications. This study reports on experiments systematically addressing the influence of these parameters on drop impacts. The experiments involved drop impacts of water, glycerol, and shear-thinning carbopol solutions on ten different microstructured surfaces, captured using high-speed photography. The impact Weber number (We) was varied from 70 to 350, and the microstructures consisted of 20 μm wide pillars with circular and square cross sections arranged in square arrays. The data focus on maximum spreading, retraction rates, threshold conditions for asymmetric (non-circular) spreading, and fingers protruding from the spreading rim. The extent of spreading was reduced by the presence of micropillars, and was well-explained using a hybrid scaling model. The drop retraction rate ((?)) showed moderate agreement with the inertial regime scaling (?) ∝ We[-0.50], but did decrease with effective viscosity. Retraction was slower when the contact line was pinned on surfaces that were flat or had relatively tall or closely-spaced pillars, and was disrupted by drop break-up at We ≳ 250 for low-viscosity fluids. Impact velocities at the onset of asymmetric spreading had weak dependence on viscosity. Fingers were more numerous for greater We, lower effective viscosity, lower pillar height, and for pillars with square cross-sections. Fingers were favoured in directions parallel to the rows of the pillar array, especially near the onset of finger formation. Consistent comparisons between Newtonian and non-Newtonian fluids were enabled by calculating an effective Reynolds number.}, } @article {pmid37631640, year = {2023}, author = {Gao, S and Rui, X and Zeng, X and Zhou, J}, title = {EWOD Chip with Micro-Barrier Electrode for Simultaneous Enhanced Mixing during Transportation.}, journal = {Sensors (Basel, Switzerland)}, volume = {23}, number = {16}, pages = {}, doi = {10.3390/s23167102}, pmid = {37631640}, issn = {1424-8220}, support = {62274039//The National Natural Science Foundation of China/ ; }, abstract = {Digital microfluidic platforms have been extensively studied in biology. However, achieving efficient mixing of macromolecules in microscale, low Reynolds number fluids remains a major challenge. To address this challenge, this study presents a novel design solution based on dielectric electro-wetting (EWOD) by optimizing the geometry of the transport electrode. The new design integrates micro-barriers on the electrodes to generate vortex currents that promote mixing during droplet transport. This design solution requires only two activation signals, minimizing the number of pins required. The mixing performance of the new design was evaluated by analyzing the degree of mixing inside the droplet and quantifying the motion of the internal particles. In addition, the rapid mixing capability of the new platform was demonstrated by successfully mixing the sorbitol solution with the detection solution and detecting the resulting reaction products. The experimental results show that the transfer electrode with a micro-barrier enables rapid mixing of liquids with a six-fold increase in mixing efficiency, making it ideal for the development of EWOD devices.}, } @article {pmid37630135, year = {2023}, author = {Fu, Q and Liu, Z and Cao, S and Wang, Z and Liu, G}, title = {Topology-Optimized Micromixer Design with Enhanced Reverse Flow to Increase Mixing Efficiency.}, journal = {Micromachines}, volume = {14}, number = {8}, pages = {}, doi = {10.3390/mi14081599}, pmid = {37630135}, issn = {2072-666X}, abstract = {In this work, a serpentine mixing unit model based on topology optimization is proposed to enhance the reverse flow in both horizontal and vertical directions. The increase in reverse flow in both directions can enhance the chaotic advection phenomenon, leading to a rapid increase in the mixing index. The proposed mixing unit model is applied in a T-shaped micromixer to create a new micromixer design, named TOD. Numerical simulations of TOD are performed using Comsol Multiphysics software to analyze the characteristics of the liquid flow, mixing surface, and pressure drop. The simulation results confirm that TOD has an outstanding mixing performance. By widening the surface area of contact and enhancing the chaotic advection phenomenon, TOD shows an excellent mixing performance at both a high and low Reynolds number, making it a promising micromixer design. For Re > 5, the mixing indexes of TOD are all beyond 90%.}, } @article {pmid37630030, year = {2023}, author = {Knüppel, F and Sun, A and Wurm, FH and Hussong, J and Torner, B}, title = {Effect of Particle Migration on the Stress Field in Microfluidic Flows of Blood Analog Fluids at High Reynolds Numbers.}, journal = {Micromachines}, volume = {14}, number = {8}, pages = {}, doi = {10.3390/mi14081494}, pmid = {37630030}, issn = {2072-666X}, support = {469384587//Deutsche Forschungsgemeinschaft/ ; }, abstract = {In the present paper, we investigate how the reductions in shear stresses and pressure losses in microfluidic gaps are directly linked to the local characteristics of cell-free layers (CFLs) at channel Reynolds numbers relevant to ventricular assist device (VAD) applications. For this, detailed studies of local particle distributions of a particulate blood analog fluid are combined with wall shear stress and pressure loss measurements in two complementary set-ups with identical flow geometry, bulk Reynolds numbers and particle Reynolds numbers. For all investigated particle volume fractions of up to 5%, reductions in the stress and pressure loss were measured in comparison to a flow of an equivalent homogeneous fluid (without particles). We could explain this due to the formation of a CFL ranging from 10 to 20 μm. Variations in the channel Reynolds number between Re = 50 and 150 did not lead to measurable changes in CFL heights or stress reductions for all investigated particle volume fractions. These measurements were used to describe the complete chain of how CFL formation leads to a stress reduction, which reduces the apparent viscosity of the suspension and results in the Fåhræus-Lindqvist effect. This chain of causes was investigated for the first time for flows with high Reynolds numbers (Re∼100), representing a flow regime which can be found in the narrow gaps of a VAD.}, } @article {pmid37622989, year = {2023}, author = {Gojon, R and Parisot-Dupuis, H and Mellot, B and Jardin, T}, title = {Aeroacoustic radiation of low Reynolds number rotors in interaction with beams.}, journal = {The Journal of the Acoustical Society of America}, volume = {154}, number = {2}, pages = {1248-1260}, doi = {10.1121/10.0020672}, pmid = {37622989}, issn = {1520-8524}, abstract = {The radiation characteristics of rotor-beam interaction noise are studied experimentally for low Reynolds number small-scale rotors in interaction with beams of different shapes, sizes, and downstream positions. The number of blades ranges from two to four. For the two-bladed rotor, the presence of the beam has no effect on the mean aerodynamic performance. Moreover, the blade passing frequency (BPF) and the high frequency broadband noise (BBN) appear not to be affected by the presence of the beam. On the contrary, the magnitude of the 2×BPF-25×BPF harmonics increases up to 30 dB compared to the case without beam, with an envelope consisting of two humps: one centered around 5×BPF and another around 20×BPF-25×BPF. For the first hump, a dipole-like pattern with minimal amplitude aligned with the beam can be observed, whereas another dipole-like pattern is observed for the higher frequency hump, but with a minimal amplitude over all the rotor disk plane. Compared to the two-bladed rotor, the presence of the beam has an effect on the mean aerodynamic performance of the three- and four-bladed rotors, increasing both the torque and the thrust at iso-rotational speed. This change leads to a change in the directivity of the BPF tone that decreases at a latitude angle of θ=0° and increases at a latitude angle of θ=40°. Moreover, the same two competing humps are observed on the BPF harmonics envelope. Interestingly, the frequency range over which an amplification of the harmonic magnitude is observed seems not to be influenced by the number of blades. Finally, the magnitude of the low frequency hump increases with the beam diameter, the rotational speed, and the number of blades but decreases with the rotor-beam distance. That of the high frequency hump increases also with the rotational speed and the number of blades, but not anymore with the beam diameter, and reaches a maximum value when the rotor-beam distance is at an intermediate distance of L = 25 mm. This hump is also influenced, to a lesser extent, by the shape of the beam. The two different evolutions permit us to conclude that the noise generation mechanisms leading to the two humps must be different. Scaling laws of the acoustical energy are derived for all those parameters. As already done for previous experiments without beam, all of the results are made available as an open database, at https://dataverse.isae-supaero.fr/.}, } @article {pmid37611057, year = {2023}, author = {Cui, Z and Wang, Y and Zhang, S and Wang, T and den Toonder, JMJ}, title = {Miniaturized metachronal magnetic artificial cilia.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {120}, number = {35}, pages = {e2304519120}, doi = {10.1073/pnas.2304519120}, pmid = {37611057}, issn = {1091-6490}, support = {833214//EC | European Research Council (ERC)/ ; 833214//EC | European Research Council (ERC)/ ; 833214//EC | European Research Council (ERC)/ ; 833214//EC | European Research Council (ERC)/ ; }, abstract = {Biological cilia, hairlike organelles on cell surfaces, often exhibit collective wavelike motion known as metachrony, which helps generating fluid flow. Inspired by nature, researchers have developed artificial cilia as microfluidic actuators, exploring several methods to mimic the metachrony. However, reported methods are difficult to miniaturize because they require either control of individual cilia properties or the generation of a complex external magnetic field. We introduce a concept that generates metachronal motion of magnetic artificial cilia (MAC), even though the MAC are all identical, and the applied external magnetic field is uniform. This is achieved by integrating a paramagnetic substructure in the substrate underneath the MAC. Uniquely, we can create both symplectic and antiplectic metachrony by changing the relative positions of MAC and substructure. We demonstrate the flow generation of the two metachronal motions in both high and low Reynolds number conditions. Our research marks a significant milestone by breaking the size limitation barrier in metachronal artificial cilia. This achievement not only showcases the potential of nature-inspired engineering but also opens up a host of exciting opportunities for designing and optimizing microsystems with enhanced fluid manipulation capabilities.}, } @article {pmid37607926, year = {2023}, author = {Barbhuiya, NH and Yodh, AG and Mishra, CK}, title = {Direction-dependent dynamics of colloidal particle pairs and the Stokes-Einstein relation in quasi-two-dimensional fluids.}, journal = {Nature communications}, volume = {14}, number = {1}, pages = {5109}, pmid = {37607926}, issn = {2041-1723}, abstract = {Hydrodynamic interactions are important for diverse fluids, especially those with low Reynolds number such as microbial and particle-laden suspensions, and proteins diffusing in membranes. Unfortunately, while far-field (asymptotic) hydrodynamic interactions are fully understood in two- and three-dimensions, near-field interactions are not, and thus our understanding of motions in dense fluid suspensions is still lacking. In this contribution, we experimentally explore the hydrodynamic correlations between particles in quasi-two-dimensional colloidal fluids in the near-field. Surprisingly, the measured displacement and relaxation of particle pairs in the body frame exhibit direction-dependent dynamics that can be connected quantitatively to the measured near-field hydrodynamic interactions. These findings, in turn, suggest a mechanism for how and when hydrodynamics can lead to a breakdown of the ubiquitous Stokes-Einstein relation (SER). We observe this breakdown, and we show that the direction-dependent breakdown of the SER is ameliorated along directions where hydrodynamic correlations are smallest. In total, the work uncovers significant ramifications of near-field hydrodynamics on transport and dynamic restructuring of fluids in two-dimensions.}, } @article {pmid37595246, year = {2023}, author = {Bätge, T and Fouxon, I and Wilczek, M}, title = {Quantitative Prediction of Sling Events in Turbulence at High Reynolds Numbers.}, journal = {Physical review letters}, volume = {131}, number = {5}, pages = {054001}, doi = {10.1103/PhysRevLett.131.054001}, pmid = {37595246}, issn = {1079-7114}, abstract = {Collisional growth of droplets, such as occurring in warm clouds, is known to be significantly enhanced by turbulence. Whether particles collide depends on their flow history, in particular on their encounters with highly intermittent small-scale turbulent structures, which despite their rarity can dominate the overall collision rate. Here, we develop a quantitative criterion for sling events based on the velocity gradient history along particle paths. We show by a combination of theory and simulations that the problem reduces to a one-dimensional localization problem as encountered in condensed matter physics. The reduction demonstrates that the creation of slings is controlled by the minimal real eigenvalue of the velocity gradient tensor. We use fully resolved turbulence simulations to confirm our predictions and study their Stokes and Reynolds number dependence. We also discuss extrapolations to the parameter range relevant for typical cloud droplets, showing that sling events at high Reynolds numbers are enhanced by an order of magnitude for small Stokes numbers. Thus, intermittency could be a significant ingredient in the collisional growth of rain droplets.}, } @article {pmid37585463, year = {2023}, author = {Tian, Y and Woodward, M and Stepanov, M and Fryer, C and Hyett, C and Livescu, D and Chertkov, M}, title = {Lagrangian large eddy simulations via physics-informed machine learning.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {120}, number = {34}, pages = {e2213638120}, doi = {10.1073/pnas.2213638120}, pmid = {37585463}, issn = {1091-6490}, support = {20180059DR//DOE | NNSA | LDRD | Los Alamos National Laboratory (LANL)/ ; }, abstract = {High-Reynolds number homogeneous isotropic turbulence (HIT) is fully described within the Navier-Stokes (NS) equations, which are notoriously difficult to solve numerically. Engineers, interested primarily in describing turbulence at a reduced range of resolved scales, have designed heuristics, known as large eddy simulation (LES). LES is described in terms of the temporally evolving Eulerian velocity field defined over a spatial grid with the mean-spacing correspondent to the resolved scale. This classic Eulerian LES depends on assumptions about effects of subgrid scales on the resolved scales. Here, we take an alternative approach and design LES heuristics stated in terms of Lagrangian particles moving with the flow. Our Lagrangian LES, thus L-LES, is described by equations generalizing the weakly compressible smoothed particle hydrodynamics formulation with extended parametric and functional freedom, which is then resolved via Machine Learning training on Lagrangian data from direct numerical simulations of the NS equations. The L-LES model includes physics-informed parameterization and functional form, by combining physics-based parameters and physics-inspired Neural Networks to describe the evolution of turbulence within the resolved range of scales. The subgrid-scale contributions are modeled separately with physical constraints to account for the effects from unresolved scales. We build the resulting model under the differentiable programming framework to facilitate efficient training. We experiment with loss functions of different types, including physics-informed ones accounting for statistics of Lagrangian particles. We show that our L-LES model is capable of reproducing Eulerian and unique Lagrangian turbulence structures and statistics over a range of turbulent Mach numbers.}, } @article {pmid37583155, year = {2023}, author = {Keirsbulck, L and Cadot, O and Basley, J and Lippert, M}, title = {Base suction, entrainment flux, and wake modes in the vortex formation region at the rear of a three-dimensional blunt bluff body.}, journal = {Physical review. E}, volume = {108}, number = {1-2}, pages = {015101}, doi = {10.1103/PhysRevE.108.015101}, pmid = {37583155}, issn = {2470-0053}, abstract = {A slitted base cavity of constant depth with a varying filling ratio 0≤R_{f} ≤100% is experimentally investigated to reduce the form drag of a three-dimensional blunt body (the so-called squareback Ahmed body) at a Reynolds number Re=2.89×10^{5} . The drag reduction is achieved by a decrease of base suction (or, equivalently, the increase of pressure at the base). The plain cavity (R_{f} =100%) reduces the base suction by 22% compared to the case with no cavity (R_{f} =0). All intermediate filling ratio are obtained by the enlargement of the slits, initially having a zero width for the plain cavity case. It is shown that the gradual base suction change can be related to the level of the entrainment flux of the free shear layers developing from the rear separation and to the suppression of the transverse steady asymmetric instability of the wake. The model of the vortex formation region length of Gerrard [J. Fluid Mech. 25, 401 (1966)0022-112010.1017/S0022112066001721] is shown to provide an insightful interpretation of the drag reduction mechanism using ventilated base cavities.}, } @article {pmid37583143, year = {2023}, author = {Maji, M and Eswaran, KS and Ghosh, S and Seshasayanan, K and Shukla, V}, title = {Equivalence of nonequilibrium ensembles: Two-dimensional turbulence with a dual cascade.}, journal = {Physical review. E}, volume = {108}, number = {1-2}, pages = {015102}, doi = {10.1103/PhysRevE.108.015102}, pmid = {37583143}, issn = {2470-0053}, abstract = {We examine the conjecture of equivalence of nonequilibrium ensembles for turbulent flows in two dimensions in a dual-cascade setup. We construct a formally time-reversible Navier-Stokes equation in two dimensions by imposing global constraints of energy and enstrophy conservation. A comparative study of the statistical properties of its solutions with those obtained from the standard Navier-Stokes equations clearly shows that a formally time-reversible system is able to reproduce the features of a two-dimensional turbulent flow. Statistical quantities based on one- and two-point measurements show an excellent agreement between the two systems for the inverse- and direct-cascade regions. Moreover, we find that the conjecture holds very well for two-dimensional turbulent flows with both conserved energy and enstrophy at finite Reynolds number.}, } @article {pmid37576259, year = {2023}, author = {Uwadoka, O and Adelaja, AO and Olakoyejo, OT and Fadipe, OL and Efe, S}, title = {Numerical study of heat transfer, pressure drop and entropy production characteristics in inclined heat exchangers with uniform heat flux using mango bark/CO2 nanofluid.}, journal = {Heliyon}, volume = {9}, number = {8}, pages = {e18694}, pmid = {37576259}, issn = {2405-8440}, abstract = {For sustainable low-carbon cities, using sustainable urban energy system solutions is imperative. CO2-based bionanofluid is one proposed energy system solution that is sustainable and environmentally friendly. This paper examines the thermal-hydraulic and entropy production properties of mango bark/CO2 nanofluid for industrial-inclined gas cooling applications. The influence of gravitational force (in terms of tube inclination angle), volume fraction, and Reynolds number on the heat transfer, pressure drop, and entropy production of CO2-based mango bark nanofluids in laminar flow through a circular aluminum tube are numerically studied. The bionanofluid flows through a tube with an inner radius of 2.25 mm, a length of 970.0 mm, and an initial temperature of 320.0 K. A constant heat flux of -10.0 W/m[2] is applied to the flow at its walls. The laminar flow regime with Reynolds numbers of 100, 400, 700, and 1000 are subjected to flow inclinations of ±90°, ±60°, ±45°, ±30°, and 0° and bionanofluid volume fractions of 0.5%, 1.0%, and 2.0%. Results show that ±45° tube inclination angle offers the optimal heat transfer coefficient, maximum pressure drop, and minimum total entropy production rates for Re > 100; however, for Re = 100, these occur at the inclination angle of -30° and +60°. The pressure drop shows less sensitivity to the inclination angle; however, it offers peak values at the same inclination angles as the heat transfer coefficient for the respective Reynolds number values. The maximum thermal enhancements due to gravitational effect are 42%, 93.98%, 121.28%, and 150% for Reynolds numbers of 100, 400, 700, and 1000, respectively, while that due to nanofluid volume fraction are less than 16%.}, } @article {pmid37567889, year = {2023}, author = {Mohamed, RA and Abo-Dahab, SM and Abd-Alla, AM and Soliman, MS}, title = {Magnetohydrodynamic double-diffusive peristaltic flow of radiating fourth-grade nanofluid through a porous medium with viscous dissipation and heat generation/absorption.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {13096}, pmid = {37567889}, issn = {2045-2322}, abstract = {This article focuses on determining how to double diffusion affects the non-Newtonian fourth-grade nanofluids peristaltic motion within a symmetrical vertical elastic channel supported by a suitable porous medium as well as, concentrating on the impact of a few significant actual peculiarities on the development of the peristaltic liquid, such as rotation, initial pressure, non-linear thermal radiation, heat generation/absorption in the presence of viscous dissipation and joule heating with noting that the fluid inside the channel is subject to an externally induced magnetic field, giving it electromagnetic properties. Moreover, the constraints of the long-wavelength approximation and neglecting the wave number along with the low Reynolds number have been used to transform the nonlinear partial differential equations in two dimensions into a system of nonlinear ordinary differential equations in one dimension, which serve as the basic governing equations for fluid motion. The suitable numerical method for solving the new system of ordinary differential equations is the Runge-Kutta fourth-order numerical method with the shooting technique using the code MATLAB program. Using this code, a 2D and 3D graphical analysis was done to show how each physical parameter affected the distributions of axial velocity, temperature, nanoparticle volume fraction, solutal concentration, pressure gradients, induced magnetic field, magnetic forces, and finally the trapping phenomenon. Under the influence of rotation [Formula: see text], heat Grashof number [Formula: see text], solutal Grashof number [Formula: see text], and initial stress [Formula: see text], the axial velocity distribution [Formula: see text] changes from increasing to decreasing, according to some of the study's findings. On the other hand, increasing values of nonlinear thermal radiation [Formula: see text] and temperature ratio [Formula: see text] have a negative impact on the temperature distribution [Formula: see text] but a positive impact on the distributions of nanoparticle volume fraction [Formula: see text] and solutal concentration [Formula: see text]. Darcy number [Formula: see text] and mean fluid rate [Formula: see text] also had a positive effect on the distribution of pressure gradients, making it an increasing function.}, } @article {pmid37535112, year = {2023}, author = {Mounkaila Noma, D and Dagois-Bohy, S and Millet, S and Ben Hadid, H and Botton, V and Henry, D}, title = {Nonlinear evolution of viscoplastic film flows down an inclined plane.}, journal = {The European physical journal. E, Soft matter}, volume = {46}, number = {8}, pages = {68}, pmid = {37535112}, issn = {1292-895X}, abstract = {In this article, we experimentally investigate the nonlinear behaviour of a viscoplastic film flow down an inclined plane. We focus on the nonlinear instabilities that appear as roll waves. Roll waves are generated by perturbing a permanent flow of Herschel-Bulkley fluid (Carbopol 980) at low frequencies. To determine the local thickness of the film, we used a laser sensor and a camera to globally capture the transverse shape of the waves. For a regular forcing, the results show the existence of different regimes. First, we observe primary instabilities below the cut-off frequency at the entrance of the channel. After the exponential growth of the wave in the linear regime, we recognise the nonlinear dynamics with the existence of finite amplitude waves. This finite amplitude depends on the frequency, the Reynolds number and the inclination angle. The results show that this instability is supercritical. At moderate Reynolds numbers, the finite 2-D waves become sensitive to transverse perturbations, due to a secondary instability, and become 3-D waves. The experimental results illustrate a phenomenology of viscoplastic film flows similar to Newtonian fluids, except for the capillary waves.}, } @article {pmid37519826, year = {2023}, author = {Kechagidis, K and Owen, B and Guillou, L and Tse, H and Di Carlo, D and Krüger, T}, title = {Numerical investigation of the dynamics of a rigid spherical particle in a vortical cross-slot flow at moderate inertia.}, journal = {Microsystems & nanoengineering}, volume = {9}, number = {}, pages = {100}, pmid = {37519826}, issn = {2055-7434}, abstract = {The study of flow and particle dynamics in microfluidic cross-slot channels is of high relevance for lab-on-a-chip applications. In this work, we investigate the dynamics of a rigid spherical particle in a cross-slot junction for a channel height-to-width ratio of 0.6 and at a Reynolds number of 120 for which a steady vortex exists in the junction area. Using an in-house immersed-boundary-lattice-Boltzmann code, we analyse the effect of the entry position of the particle in the junction and the particle size on the dynamics and trajectory shape of the particle. We find that the dynamics of the particle depend strongly on its lateral entry position in the junction and weakly on its vertical entry position; particles that enter close to the centre show trajectory oscillations. Larger particles have longer residence times in the junction and tend to oscillate less due to their confinement. Our work contributes to the understanding of particle dynamics in intersecting flows and enables the design of optimised geometries for cytometry and particle manipulation.}, } @article {pmid37518499, year = {2023}, author = {Yokoo, H and Yamamoto, M and Matsumoto, T and Yamada, T and Kanda, T}, title = {Study of the reverse transition in pipe flow.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {12333}, pmid = {37518499}, issn = {2045-2322}, abstract = {In the reverse transition in pipe flow, turbulent flow changes to less disturbed laminar flow. The entropy of the flow appears to decrease. This study examined the reverse transition experimentally and theoretically using entropy change and momentum balance models, not in terms of disturbance in the flow. The reverse transition was accomplished by decreasing the Reynolds number. The transitions approximately correlated with local Reynolds numbers. The initial Reynolds number of the transition became larger, and the pressure at low Reynolds numbers was greater than in ordinary pipe flow. These behaviours were caused by turbulent flow in the pipe undergoing a reverse transition. We showed that the entropy did not decrease in the reverse transition by including the entropy due to friction in the development region.}, } @article {pmid37512778, year = {2023}, author = {Mihai, I and Suciu, C and Picus, CM}, title = {Assessment of Vapor Formation Rate and Phase Shift between Pressure Gradient and Liquid Velocity in Flat Mini Heat Pipes as a Function of Internal Structure.}, journal = {Micromachines}, volume = {14}, number = {7}, pages = {}, doi = {10.3390/mi14071468}, pmid = {37512778}, issn = {2072-666X}, abstract = {Flat mini heat pipes (FMHPs) are often used in cooling systems for various power electronic components, as they rapidly dissipate high heat flux densities. The main objective of the present work is to experimentally investigate whether differences in the rate of vapor formation occur on an internal structure containing trapezoidal microchannels and porous sintered copper powder material. Several parameters, such as hydraulic diameter and fluid velocity through the material, as a function of the internal structure porosity, were determined by calculation for a steady state regime. Reynolds number was determined as a function of porosity, according to Darcy's law, and the Nusselt number was calculated. Since the flow is Darcy-type through the porous medium inside the FMHP, the Darcy friction factor was calculated using five methods: Colebrook, Darcy-Weisbach, Swamee-Jain, Blasius, and Haaland. After experimental tests, it was found that when the porous and trapezoidal microchannel layers are wetted at the same time, the vaporization progresses at a faster rate in the porous material, and the duration of the process is shorter. This recommends the use of such an internal structure in FMHPs since the manufacturing technology is simpler, the materials are cheaper, and the heat flux transport capacity is higher.}, } @article {pmid37512729, year = {2023}, author = {Ray, DR and Das, DK}, title = {Simulations of Flows via CFD in Microchannels for Characterizing Entrance Region and Developing New Correlations for Hydrodynamic Entrance Length.}, journal = {Micromachines}, volume = {14}, number = {7}, pages = {}, doi = {10.3390/mi14071418}, pmid = {37512729}, issn = {2072-666X}, abstract = {Devices with microchannels are relatively new, and many correlations are not yet developed to design them efficiently. In microchannels, the flow regime is primarily laminar, where entrance length may occupy a significant section of the flow channel. Therefore, several computational fluid dynamic simulations were performed in this research to characterize the developing flow regime. The new correlations of entrance length were developed from a vast number of numerical results obtained from these simulations. A three-dimensional laminar flow for 37 Reynolds numbers (0.1, 0.2, …, 1, 2, …, 10, 20, …, 100, 200, …, 1000), primarily in low regime with water flow through six rectangular microchannels (aspect ratio: 1, 0.75, 0.5, 0.25, 0.2, 0.125), has been modeled, conducting 222 simulations to characterize flow developments and ascertain progressive velocity profile shapes. Examination of the fully developed flow condition was considered using traditional criteria such as velocity and incremental pressure drop number. Additionally, a new criterion was presented based on fRe. Numerical results from the present simulations were validated by comparing the fully developed velocity profile, friction factor, and hydrodynamic entrance length for Re > 100 in rectangular channels, for which accurate data are available in the literature. There is a need for hydrodynamic entrance length correlations in a low Reynolds number regime (Re < 100). So, the model was run numerous times to generate a vast amount of numerical data that yielded two new correlations based on the velocity and fRe criteria.}, } @article {pmid37507561, year = {2023}, author = {Singh, S and Suman, S and Mitra, S and Kumar, M}, title = {Optimization of a novel trapezoidal staggered ribs configuration for enhancement of a solar air heater performance using CFD.}, journal = {Environmental science and pollution research international}, volume = {}, number = {}, pages = {}, pmid = {37507561}, issn = {1614-7499}, abstract = {A novel transverse trapezoidal staggered ribs configuration as artificial roughness is investigated using CFD to understand the fluid flow and heat transfer behaviors for improving the performance of a solar air heater. In addition, experimental validation of Nusselt numbers for smooth duct against CFD results is established. The staggered ribs arrangement outperforms the continuous ribs and insights obtained from the thermal-fluid flow behaviors are further applied to optimize the staggered arrangements of the rib. Reynolds number Re is varied from 5000 to 24,000, and rib parameters are optimized with a special focus on understanding the effects of discontinuous rib width (w) and gap width (g). Two widely studied shapes of rib, namely, cylindrical and rectangular, are also investigated for the transverse staggered arrangement with the same optimized parameters for the comparison of thermo-hydraulic performances. Trapezoidal ribs having discontinuous rib width of 50 mm and gap width of 10 mm give the maximum thermo-hydraulic performance of 1.57 at Reynolds number of 5000. The optimized staggered trapezoidal ribs outperform the staggered cylindrical and rectangular ribs. However, staggered rectangular ribs give the highest increase in the Nusselt number and these may be preferred for application when pressure drop is not of concern.}, } @article {pmid37506216, year = {2023}, author = {Shinder, II and Johnson, AN and Filla, BJ and Khromchenko, VB and Moldover, MR and Boyd, J and Wright, JD and Stoup, J}, title = {Non-nulling protocols for fast, accurate, 3-D velocity measurements in stacks.}, journal = {Journal of the Air & Waste Management Association (1995)}, volume = {73}, number = {8}, pages = {600-617}, doi = {10.1080/10962247.2023.2218827}, pmid = {37506216}, issn = {2162-2906}, abstract = {The authors present protocols for making fast, accurate, 3D velocity measurements in the stacks of coal-fired power plants. The measurements are traceable to internationally-recognized standards; therefore, they provide a rigorous basis for measuring and/or regulating the emissions from stacks. The authors used novel, five-hole, hemispherical, differential-pressure probes optimized for non-nulling (no-probe rotation) measurements. The probes resist plugging from ash and water droplets. Integrating the differential pressures for only 5 seconds determined the axial velocity Va with an expanded relative uncertainty Ur(Va) ≤ 2% of the axial velocity at the probe's location, the flow's pitch (α) and yaw (β) angles with expanded uncertainties U(α) = U(β) = 1 °, and the static pressure ps with Ur(ps) = 0.1% of the static pressure. This accuracy was achieved 1) by calibrating each probe in a wind tunnel at 130, strategically-chosen values of (Va, α, β) spanning the conditions found in the majority of stacks (|α| ≤ 20 °; |β| ≤ 40 °; 4.5 m/s ≤ Va ≤27 m/s), and 2) by using a long-forgotten definition of the pseudo-dynamic pressure that scales with the dynamic pressure. The resulting calibration functions span the probe-diameter Reynolds number range from 7,600 to 45,000.Implications: The continuous emissions monitoring systems (CEMS) that measure the flue gas flow rate in coal-fired power plant smokestacks are calibrated (at least) annually by a velocity profiling method. The stack axial velocity profile is measured by traversing S-type pitot probes (or one of the other EPA-sanctioned pitot probes) across two orthogonal, diametric chords in the stack cross-section. The average area-weighted axial velocity calculated from the pitot traverse quantifies the accuracy of the CEMS flow monitor. Therefore, the flow measurement accuracy of coal-fired power plants greenhouse gas (GHG) emissions depends on the accuracy of pitot probe velocity measurements. Coal-fired power plants overwhelmingly calibrate CEMS flow monitors using S-type pitot probes. Almost always, stack testers measure the velocity without rotating or nulling the probe (i.e., the non-nulling method). These 1D non-nulling velocity measurements take significantly less time than the corresponding 2D nulling measurements (or 3D nulling measurements for other probe types). However, the accuracy of the 1D non-nulling velocity measurements made using S-type probes depends on the pitch and yaw angles of the flow. Measured axial velocities are accurate at pitch and yaw angles near zero, but the accuracy degrades at larger pitch and yaw angles.The authors developed a 5-hole hemispherical pitot probe that accurately measures the velocity vector in coal-fired smokestacks without needing to rotate or null the probe. This non-nulling, 3D probe is designed with large diameter pressure ports to prevent water droplets (or particulates) from obstructing its pressure ports when applied in stack flow measurement applications. This manuscript presents a wind tunnel calibration procedure to determine the non-nulling calibration curves for 1) dynamic pressure; 2) pitch angle; 3) yaw angle; and 4) static pressure. These calibration curves are used to determine axial velocities from 6 m/s to 27 m/s, yaw angles between ±40°, and pitch angles between ±20°. The uncertainties at the 95% confidence limit for axial velocity, yaw angle, and pitch angle are 2% (or less), 1°, and 1°, respectively. Therefore, in contrast to existing EPA-sanctioned probes, the non-nulling hemispherical probe provides fast, low uncertainty velocity measurements independent of the pitch and yaw angles of the stack flow.}, } @article {pmid37505953, year = {2023}, author = {Küchler, C and Bewley, GP and Bodenschatz, E}, title = {Universal Velocity Statistics in Decaying Turbulence.}, journal = {Physical review letters}, volume = {131}, number = {2}, pages = {024001}, doi = {10.1103/PhysRevLett.131.024001}, pmid = {37505953}, issn = {1079-7114}, abstract = {In turbulent flows, kinetic energy is transferred from large spatial scales to small ones, where it is converted to heat by viscosity. For strong turbulence, i.e., high Reynolds numbers, Kolmogorov conjectured in 1941 that this energy transfer is dominated by inertial forces at intermediate spatial scales. Since Kolmogorov's conjecture, the velocity difference statistics in this so-called inertial range have been expected to follow universal power laws for which theoretical predictions have been refined over the years. Here we present experimental results over an unprecedented range of Reynolds numbers in a well-controlled wind tunnel flow produced in the Max Planck Variable Density Turbulence Tunnel. We find that the measured second-order velocity difference statistics become independent of the Reynolds number, suggesting a universal behavior of decaying turbulence. However, we do not observe power laws even at the highest Reynolds number, i.e., at turbulence levels otherwise only attainable in atmospheric flows. Our results point to a Reynolds number-independent logarithmic correction to the classical power law for decaying turbulence that calls for theoretical understanding.}, } @article {pmid37501997, year = {2023}, author = {Aich, W and Javid, K and Tag-ElDin, ESM and Ghachem, K and Ullah, I and Iqbal, MA and Khan, SU and Kolsi, L}, title = {Thermal and physical impact of viscoplastic nanoparticles in a complex divergent channel due to peristalsis phenomenon: Heat generation and multiple slip effects.}, journal = {Heliyon}, volume = {9}, number = {7}, pages = {e17644}, pmid = {37501997}, issn = {2405-8440}, abstract = {In the advance studies, researchers have performed productive research contributions in the field of nanofluid mechanics under various biological assumptions. These contributions are fruitful to understand the applications of nanofluids in the various fields such as hybrid-powered engine, heart-diagnose, to prevent numerous diseases, heat exchanger, pharmaceutical processes, etc. The current analysis explores the combined effects of heat generation and chemical reaction on the peristaltic flow of viscoplastic nanofluid through a non-uniform (divergent) channel. The physical effects of second-order velocity slip, thermal slip and mass slip parameters on the rheological characteristics are also considered. To describe non-Newtonian effects, the Casson fluid is deployed. The greater wavelength assumption and low Reynolds number theory are used to attain the rheological equations. Numerical solutions of these governing equations associated with suitable boundary conditions are obtained via Mathematica symbolic software. The velocity magnitude of Casson fluid is higher than associated with Newtonian fluid. Radiation parameter has a vigorous impact in the reduction (enhancement) of temperature (mass concentration) profile. The porous parameter has a remarkable impact in reduction of temperature and velocity profile. Thermal enhancement is perceived by intensifying the chemical reaction parameter, and opposite inclination is noticed in mass concentration. Temperature has been demonstrated to be increased by increasing the Darcy number. The magnitudes of both axial velocity and temperature distribution are smaller in the presence of second-order velocity slip parameters effect as compared with no-slip condition. The magnitudes of axial velocity and mass (or, nanoparticle) concentration are augmented by accumulating the Prandtl number. A rise in Brownian parameter is noticed to depress the mass concentration. The present study has been used in bio-mechanical processes, nanomaterial devices, heat transfer enhancement, radiators, and electronics cooling systems.}, } @article {pmid37467268, year = {2023}, author = {Buaria, D and Sreenivasan, KR}, title = {Forecasting small-scale dynamics of fluid turbulence using deep neural networks.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {120}, number = {30}, pages = {e2305765120}, doi = {10.1073/pnas.2305765120}, pmid = {37467268}, issn = {1091-6490}, abstract = {Turbulence in fluid flows is characterized by a wide range of interacting scales. Since the scale range increases as some power of the flow Reynolds number, a faithful simulation of the entire scale range is prohibitively expensive at high Reynolds numbers. The most expensive aspect concerns the small-scale motions; thus, major emphasis is placed on understanding and modeling them, taking advantage of their putative universality. In this work, using physics-informed deep learning methods, we present a modeling framework to capture and predict the small-scale dynamics of turbulence, via the velocity gradient tensor. The model is based on obtaining functional closures for the pressure Hessian and viscous Laplacian contributions as functions of velocity gradient tensor. This task is accomplished using deep neural networks that are consistent with physical constraints and explicitly incorporate Reynolds number dependence to account for small-scale intermittency. We then utilize a massive direct numerical simulation database, spanning two orders of magnitude in the large-scale Reynolds number, for training and validation. The model learns from low to moderate Reynolds numbers and successfully predicts velocity gradient statistics at both seen and higher (unseen) Reynolds numbers. The success of our present approach demonstrates the viability of deep learning over traditional modeling approaches in capturing and predicting small-scale features of turbulence.}, } @article {pmid37464695, year = {2023}, author = {Zheng, JL and Liu, YL}, title = {Experimental study on the flow structures and dynamics of turbulent Rayleigh-Bénard convection in an annular cell.}, journal = {Physical review. E}, volume = {107}, number = {6-2}, pages = {065112}, doi = {10.1103/PhysRevE.107.065112}, pmid = {37464695}, issn = {2470-0053}, abstract = {We conduct an experimental study on the flow structures and dynamics of turbulent Rayleigh-Bénard convection in an annular cell with radius ratio η≃0.5 and aspect ratio Γ≃4. The working fluid is water with a Prandtl number of Pr≃5.4, and the Rayleigh number (Ra) ranges from 5.05×10^{7} to 5.05×10^{8} . The multithermal-probe method and the particle image velocimetry technique are employed to measure the temperature profiles and the velocity fields, respectively. Two distinct states with multiroll standing waves are observed, which are the quadrupole state (QS) characterized by a four-roll structure and the sextupole state (SS) by a six-roll structure. The scaling exponents of Reynolds number Re with Ra are different for the two states, which are 0.56 for QS and 0.41 for SS. In addition, the standing waves become unstable upon tilting the cell by 1^{∘} in relation to the horizontal plane, and they evolve into traveling waves. At relatively high Ra, for instance, Ra⩾2.55×10^{8}, it is observed that the traveling wave state SS undergoes a transition to the traveling wave state QS. However, the opposite transition from QS to SS is not observed in our experiments. Our findings provide insights into the flow structures and dynamics in the convection flow with rotation symmetry.}, } @article {pmid37455389, year = {2023}, author = {Zhang, T and Inglis, DW and Ngo, L and Wang, Y and Hosokawa, Y and Yalikun, Y and Li, M}, title = {Inertial Separation of Particles Assisted by Symmetrical Sheath Flows in a Straight Microchannel.}, journal = {Analytical chemistry}, volume = {}, number = {}, pages = {}, doi = {10.1021/acs.analchem.3c02089}, pmid = {37455389}, issn = {1520-6882}, abstract = {Over the past two decades, inertial microfluidics, which works at an intermediate range of Reynolds number (∼1 < Re < ∼100), has been widely used for particle separation due to its high-throughput and label-free features. This work proposes a novel method for continuous separation of particles by size using inertial microfluidics, with the assistance of symmetrical sheath flows in a straight microchannel. Here, larger particles (>3 μm) are arranged close to the channel sidewalls, while smaller particles (<2 μm) remain flowing along the channel centerline. This conclusion is supported by experimental data with particles of different sizes ranging from 0.79 to 10.5 μm. Symmetrical Newtonian sheath flows are injected on both sides of particle mixtures into a straight rectangular microchannel with an aspect ratio (AR = height/width) of 2.5. Results show that the separation performance of the developed microfluidic device is affected by three main factors: channel length, total flow rate, and flow rate ratio of sheath to sample. Besides, separation of platelets from whole blood is demonstrated. The developed microfluidic platform owns the advantages of low fabrication cost, simple experiment setup, versatile selections of particle candidates, and stable operations. This systematic study provides a new perspective for particle separation, which is expected to find applications across various fields spanning physics, biology, biomedicine, and industry.}, } @article {pmid37449188, year = {2023}, author = {Ahmad, S and Ali, K and Katbar, NM and Akhtar, Y and Cai, J and Jamshed, W and El Din, SM and Abd-Elmonem, A and Elmki Abdalla, NS}, title = {Vortex generation due to multiple localized magnetic fields in the hybrid nanofluid flow - A numerical investigation.}, journal = {Heliyon}, volume = {9}, number = {7}, pages = {e17756}, doi = {10.1016/j.heliyon.2023.e17756}, pmid = {37449188}, issn = {2405-8440}, abstract = {Vortices capture the attention of every scientist (as soon as they come into existence) while studying any flow problem because of their significance in comprehending fluid mixing and mass transport processes. A vortex is indeed a physical phenomenon that happens when a liquid or a gas flow in a circular motion. They are generated due to the velocity difference and may be seen in hurricanes, air moving across the plane wing, tornadoes, etc. The study of vortices is important for understanding various natural phenomena in different settings. This work explores the complex dynamics of the Lorentz force that drives the rotation of nanostructures and the emergence of intricate vortex patterns in a hybrid fluid with Fe3O4-Cu nanoparticles. The hybrid nanofluid is modeled as a single-phase fluid, and the partial differential equations (PDEs) that govern its behavior are solved numerically. This work also introduces a novel analysis that enables us to visualize the flow lines and isotherms around the magnetic strips in the flow domain. The Lorentz force confined to the strips causes the spinning of hybrid nanoparticles, resulting in complex vortex structures in the flow domain. The results indicate that the magnetic field lowers the Nusselt number by 34% while raising the skin friction by 9%. The Reynolds number amplifies the influence of the localized magnetic field on the flow dynamics. Lastly, the nano-scaled structures in the flow enhance the Nusselt number significantly while having a minor effect on the skin friction factor.}, } @article {pmid37449115, year = {2023}, author = {Li, S and Khan, MI and Alruqi, AB and Khan, SU and Abdullaev, SS and Fadhl, BM and Makhdoum, BM}, title = {Entropy optimized flow of Sutterby nanomaterial subject to porous medium: Buongiorno nanofluid model.}, journal = {Heliyon}, volume = {9}, number = {7}, pages = {e17784}, doi = {10.1016/j.heliyon.2023.e17784}, pmid = {37449115}, issn = {2405-8440}, abstract = {Owing to enhanced thermal impact of nanomaterials, different applications are suggested in engineering and industrial systems like heat transfer devices, energy generation, extrusion processes, engine cooling, thermal systems, heat exchanger, chemical processes, manufacturing systems, hybrid-powered plants etc. The current communication concerns the optimized flow of Sutterby nanofluid due to stretched surface in view of different thermal sources. The investigation is supported with the applications of external heat source, magnetic force and radiative phenomenon. The irreversibility investigation is deliberated with implementation of thermodynamics second law. The thermophoresis and random movement characteristics are also studied. Additionally, first order binary reaction is also examined. The nonlinear system of the governing problem is obtained which are numerically computed by s method. The physical aspects of prominent flow parameters are attributed graphically. Further, the analysis for entropy generation and Bejan number is focused. It is observed that the velocity profile increases due to Reynolds number and Deborah number. Larger Schmidt number reduces the concentration distribution. Further, the entropy generation is improved against Reynolds number and Brinkman parameter.}, } @article {pmid37437157, year = {2023}, author = {Saxena, A and Kroll-Rabotin, JS and Sanders, RS}, title = {Role of Flow Inertia in Aggregate Restructuring and Breakage at Finite Reynolds Numbers.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {}, number = {}, pages = {}, doi = {10.1021/acs.langmuir.3c01012}, pmid = {37437157}, issn = {1520-5827}, abstract = {Forces acting on aggregates depend on their properties, such as size and structure. Breakage rate, stable size, and structure of fractal aggregates in multiphase flows are strongly related to the imposed hydrodynamic forces. While these forces are prevalently viscous for finite Reynolds number conditions, flow inertia cannot be ignored, thereby requiring one to fully resolve the Navier-Stokes equations. To highlight the effect of flow inertia on aggregate evolution, numerical investigation of aggregate evolution in simple shear flow at the finite Reynolds number is conducted. The evolution of aggregates exposed to shear flow is tracked over time. Particle coupling with the flow is resolved with an immersed boundary method, and flow dynamics are solved using a lattice Boltzmann method. Particle dynamics are tracked by a discrete element method, accounting for interactions between primary particles composing the aggregates. Over the range of aggregate-scale Reynolds numbers tested, the breakage rate appears to be governed by the combined effect of momentum diffusion and the ratio of particle interaction forces to the hydrodynamic forces. For higher shear stresses, even when no stable size exists, breakage is not instantaneous because of momentum diffusion kinetics. Simulations with particle interaction forces scaled with the viscous drag, to isolate the effect of finite Reynolds hydrodynamics on aggregate evolution, show that flow inertia at such moderate aggregate Reynolds numbers has no impact on the morphology of nonbreaking aggregates but significantly favors breakage probability. This is a first-of-its-kind study that establishes the role of flow inertia in aggregate evolution. The findings present a novel perspective into breakage kinetics for systems in low but finite Reynolds number conditions.}, } @article {pmid37425484, year = {2023}, author = {Birtek, MT and Alseed, MM and Sarabi, MR and Ahmadpour, A and Yetisen, AK and Tasoglu, S}, title = {Machine learning-augmented fluid dynamics simulations for micromixer educational module.}, journal = {Biomicrofluidics}, volume = {17}, number = {4}, pages = {044101}, pmid = {37425484}, issn = {1932-1058}, abstract = {Micromixers play an imperative role in chemical and biomedical systems. Designing compact micromixers for laminar flows owning a low Reynolds number is more challenging than flows with higher turbulence. Machine learning models can enable the optimization of the designs and capabilities of microfluidic systems by receiving input from a training library and producing algorithms that can predict the outcomes prior to the fabrication process to minimize development cost and time. Here, an educational interactive microfluidic module is developed to enable the design of compact and efficient micromixers at low Reynolds regimes for Newtonian and non-Newtonian fluids. The optimization of Newtonian fluids designs was based on a machine learning model, which was trained by simulating and calculating the mixing index of 1890 different micromixer designs. This approach utilized a combination of six design parameters and the results as an input data set to a two-layer deep neural network with 100 nodes in each hidden layer. A trained model was achieved with R[2] = 0.9543 that can be used to predict the mixing index and find the optimal parameters needed to design micromixers. Non-Newtonian fluid cases were also optimized using 56700 simulated designs with eight varying input parameters, reduced to 1890 designs, and then trained using the same deep neural network used for Newtonian fluids to obtain R[2] = 0.9063. The framework was subsequently used as an interactive educational module, demonstrating a well-structured integration of technology-based modules such as using artificial intelligence in the engineering curriculum, which can highly contribute to engineering education.}, } @article {pmid37420830, year = {2023}, author = {Scheuer, KG and DeCorby, RG}, title = {All-Optical, Air-Coupled Ultrasonic Detection of Low-Pressure Gas Leaks and Observation of Jet Tones in the MHz Range.}, journal = {Sensors (Basel, Switzerland)}, volume = {23}, number = {12}, pages = {}, doi = {10.3390/s23125665}, pmid = {37420830}, issn = {1424-8220}, support = {Innovation Catalyst Grant//Government of Alberta/ ; AI//Alberta Innovates/ ; CREATE 495446-17//Natural Sciences and Engineering Research Council/ ; Quantum Technologies//Alberta EDT Major Innovation Fund/ ; }, abstract = {We used an ultrasensitive, broadband optomechanical ultrasound sensor to study the acoustic signals produced by pressurized nitrogen escaping from a variety of small syringes. Harmonically related jet tones extending into the MHz region were observed for a certain range of flow (i.e., Reynolds number), which is in qualitative agreement with historical studies on gas jets emitted from pipes and orifices of much larger dimensions. For higher turbulent flow rates, we observed broadband ultrasonic emission in the ~0-5 MHz range, which was likely limited on the upper end due to attenuation in air. These observations are made possible by the broadband, ultrasensitive response (for air-coupled ultrasound) of our optomechanical devices. Aside from being of theoretical interest, our results could have practical implications for the non-contact monitoring and detection of early-stage leaks in pressured fluid systems.}, } @article {pmid37420356, year = {2022}, author = {Li, X and Su, H}, title = {A Modular Grad-Div Stabilization Method for Time-Dependent Thermally Coupled MHD Equations.}, journal = {Entropy (Basel, Switzerland)}, volume = {24}, number = {10}, pages = {}, doi = {10.3390/e24101336}, pmid = {37420356}, issn = {1099-4300}, abstract = {In this paper, we consider a fully discrete modular grad-div stabilization algorithm for time-dependent thermally coupled magnetohydrodynamic (MHD) equations. The main idea of the proposed algorithm is to add an extra minimally intrusive module to penalize the divergence errors of velocity and improve the computational efficiency for increasing values of the Reynolds number and grad-div stabilization parameters. In addition, we provide the unconditional stability and optimal convergence analysis of this algorithm. Finally, several numerical experiments are performed and further indicated these advantages over the algorithm without grad-div stabilization.}, } @article {pmid37418738, year = {2023}, author = {Gotoh, T and Watanabe, T and Saito, I}, title = {Kinematic Effects on Probability Density Functions of Energy Dissipation Rate and Enstrophy in Turbulence.}, journal = {Physical review letters}, volume = {130}, number = {25}, pages = {254001}, doi = {10.1103/PhysRevLett.130.254001}, pmid = {37418738}, issn = {1079-7114}, abstract = {Direct numerical simulation and theoretical analyses showed that the probability density functions (PDFs) of the energy dissipation rate and enstrophy in turbulence are asymptotically stretched gamma distributions with the same stretching exponent, and both the left and right tails of the enstrophy PDF are longer than those of the energy dissipation rate regardless of the Reynolds number. The differences in PDF tails arise due to the kinematics, with differences in the number of terms contributing to the dissipation rate and enstrophy. Meanwhile, the stretching exponent is determined by the dynamics and likeliness of singularities.}, } @article {pmid37414852, year = {2023}, author = {Kim, M and Schanz, D and Novara, M and Godbersen, P and Yeom, E and Schröder, A}, title = {Experimental study on flow and turbulence characteristics of jet impinging on cylinder using three-dimensional Lagrangian particle tracking velocimetry.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {10929}, pmid = {37414852}, issn = {2045-2322}, support = {2021R1C1C2009287//National Research Foundation of Korea/ ; 2021R1I1A3047664//National Research Foundation of Korea/ ; DFG SPP 1881//Deutsche Forschungsgemeinschaft/ ; }, abstract = {When a round jet impinges on a convex cylindrical surface, complex three-dimensional (3D) flow structures occur, accompanied by the Coanda effect. To characterize the flow and turbulence properties of the general system, ensemble averages of 3D Lagrangian particle tracking velocimetry measurements were taken. The radial bin-averaging method was used in post-processing the tracked particles and corresponding instantaneous velocity vectors to generate appropriate ensemble-averaged statistics. Two impinging angles were selected, and at a fixed Reynolds number, the ensemble-averaged volumetric velocity field and turbulent stress tensor components were measured. The flow and turbulence characteristics of the impinging jet on the cylinder were notably different based on the impinging angle, especially in the downstream region. Surprisingly, the attached wall jet with a half-elliptic shape was abruptly thickened in the wall-normal direction, similar to the axis switching phenomenon observed in elliptic jets in the case of oblique impingement. In the jet-impinging region, the flow spread in all directions with high mean vorticity values. With the development of a 3D curved wall jet, both the Coanda effect and centrifugal force played a significant role in the flow behavior. A notable feature of the self-preserving region was the similarity of mean velocity profiles with scaling by the maximum velocity and the jet half-width for both impinging angle cases. Local isotropy of turbulent normal stresses was observed in this region, supporting the existence of self-preservation in the 3D curved wall jet. The volumetric ensemble-averaged Reynolds stress tensor revealed strong inhomogeneous turbulence in the boundary layer region and the curvature effect on the Reynolds shear stress in the free shear layer.}, } @article {pmid37407860, year = {2023}, author = {Dutt, N and Hedau, AJ and Kumar, A and Awasthi, MK and Singh, VP and Dwivedi, G}, title = {Thermo-hydraulic performance of solar air heater having discrete D-shaped ribs as artificial roughness.}, journal = {Environmental science and pollution research international}, volume = {}, number = {}, pages = {}, pmid = {37407860}, issn = {1614-7499}, abstract = {In this paper, the thermo-hydraulic performance of a solar air heater (SAH) duct roughened with discrete D-shaped ribs is numerically investigated using ANSYS Fluent 2020 R2. The numerical investigation is carried out at rib radius to transverse pitch ratio (r/Pt) from 0.1 to 0.35 and longitudinal pitch to rib radius ratio (Pl /r) from 4 to 10 under various operating conditions with Reynolds number (Re) varied from 10,200 to 20,200. The numerical results are validated with previous experimental results for the Nusselt number (Nu) values, and good agreement is found with mean absolute percentage error (MAPE) of 3.6%. Based on the results of the numerical investigation, it was found that the value of Nu and the friction factor (f) decreases with the increase of the value of Pl/r, while the ratio r/Pt is kept constant. From the overall analysis, it is concluded that the optimum results are obtained for r/Pt of 0.25 and Pl/r = 4, and the maximum thermo-hydraulic performance parameter is 1.12. Further correlations are developed for the value of Nu and f for the whole range of r/Pt as 0.10-0.35 and Pl/r as 4-10. According to the developed correlations, the values of Nu are within ± 2% of the results of CFD, while the values of f are within ± 2.7% of the results of CFD.}, } @article {pmid37391140, year = {2023}, author = {Firatoglu, ZA}, title = {The effect of natural ventilation on airborne transmission of the COVID-19 virus spread by sneezing in the classroom.}, journal = {The Science of the total environment}, volume = {}, number = {}, pages = {165113}, doi = {10.1016/j.scitotenv.2023.165113}, pmid = {37391140}, issn = {1879-1026}, abstract = {Since school classrooms are of vital importance due to their impact on public health in COVID-19 and similar epidemics, it is imperative to develop new ventilation strategies to reduce the risk of transmission of the virus in the classroom. To be able to develop new ventilation strategies, the effect of local flow behaviors in the classroom on the airborne transmission of the virus under the most dramatic conditions must first be determined. In this study, the effect of natural ventilation on the airborne transmission of COVID-19-like viruses in the classroom in the case of sneezing by two infected students in a reference secondary school classroom was investigated in five scenarios. Firstly, experimental measurements were carried out in the reference class to validate the computational fluid dynamics (CFD) simulation results and determine the boundary conditions. Next, the effects of local flow behaviors on the airborne transmission of the virus were evaluated for five scenarios using the Eulerian-Lagrange method, a discrete phase model, and a temporary three-dimensional CFD model. In all scenarios, immediately after sneezing, between 57 and 60.2 % of the droplets containing the virus, mostly large and medium-sized (150 μm < d < 1000 μm) settled on the infected student's desk, while small droplets continued to move in the flow field. In addition, it was determined that the effect of natural ventilation in the classroom on the travel of virus droplets in the case of Redh < 8.04 × 10[4] (Reynolds number, Redh=Udh/νu, dh and are fluid velocity, hydraulic diameters of the door and window sections of the class and kinematic viscosity, respectively) was negligible.}, } @article {pmid37388310, year = {2023}, author = {Théry, A and Maaß, CC and Lauga, E}, title = {Hydrodynamic interactions between squirmers near walls: far-field dynamics and near-field cluster stability.}, journal = {Royal Society open science}, volume = {10}, number = {6}, pages = {230223}, doi = {10.1098/rsos.230223}, pmid = {37388310}, issn = {2054-5703}, abstract = {Confinement increases contacts between microswimmers in dilute suspensions and affects their interactions. In particular, boundaries have been shown experimentally to lead to the formation of clusters that would not occur in bulk fluids. To what extent does hydrodynamics govern these boundary-driven encounters between microswimmers? We consider theoretically the symmetric boundary-mediated encounters of model microswimmers under gravity through far-field interaction of a pair of weak squirmers, as well as the lubrication interactions occurring after contact between two or more squirmers. In the far field, the orientation of microswimmers is controlled by the wall and the squirming parameter. The presence of a second swimmer influences the orientation of the original squirmer, but for weak squirmers, most of the interaction occurs after contact. We thus analyse next the near-field reorientation of circular groups of squirmers. We show that a large number of swimmers and the presence of gravity can stabilize clusters of pullers, while the opposite is true for pushers; to be stable, clusters of pushers thus need to be governed by other interactions (e.g. phoretic). This simplified approach to the phenomenon of active clustering enables us to highlight the hydrodynamic contribution, which can be hard to isolate in experimental realizations.}, } @article {pmid37366832, year = {2023}, author = {Saeed, A and Farooq, H and Akhtar, I and Tariq, MA and Khalid, MSU}, title = {Deep-Learning-Based Reduced-Order Model for Power Generation Capacity of Flapping Foils.}, journal = {Biomimetics (Basel, Switzerland)}, volume = {8}, number = {2}, pages = {}, doi = {10.3390/biomimetics8020237}, pmid = {37366832}, issn = {2313-7673}, support = {Digital Pakistan Lab, National Center for Big Data and Cloud Computing//Higher Education Commission/ ; }, abstract = {Inspired by nature, oscillating foils offer viable options as alternate energy resources to harness energy from wind and water. Here, we propose a proper orthogonal decomposition (POD)-based reduced-order model (ROM) of power generation by flapping airfoils in conjunction with deep neural networks. Numerical simulations are performed for incompressible flow past a flapping NACA-0012 airfoil at a Reynolds number of 1100 using the Arbitrary Lagrangian-Eulerian approach. The snapshots of the pressure field around the flapping foil are then utilized to construct the pressure POD modes of each case, which serve as the reduced basis to span the solution space. The novelty of the current research relates to the identification, development, and employment of long-short-term neural network (LSTM) models to predict temporal coefficients of the pressure modes. These coefficients, in turn, are used to reconstruct hydrodynamic forces and moment, leading to computations of power. The proposed model takes the known temporal coefficients as inputs and predicts the future temporal coefficients followed by previously estimated temporal coefficients, very similar to traditional ROM. Through the new trained model, we can predict the temporal coefficients for a long time duration that can be far beyond the training time intervals more accurately. It may not be attained by traditional ROMs that lead to erroneous results. Consequently, the flow physics including the forces and moment exerted by fluids can be reconstructed accurately using POD modes as the basis set.}, } @article {pmid37361718, year = {2023}, author = {Ben Mariem, I and Kaziz, S and Belkhiria, M and Echouchene, F and Belmabrouk, H}, title = {Numerical optimization of microfluidic biosensor detection time for the SARS-CoV-2 using the Taguchi method.}, journal = {Indian journal of physics and proceedings of the Indian Association for the Cultivation of Science (2004)}, volume = {}, number = {}, pages = {1-8}, doi = {10.1007/s12648-023-02632-z}, pmid = {37361718}, issn = {0973-1458}, abstract = {The performance of microfluidic biosensor of the SARS-Cov-2 was numerically analyzed through finite element method. The calculation results have been validated with comparison with experimental data reported in the literature. The novelty of this study is the use of the Taguchi method in the optimization analysis, and an L8(2[5]) orthogonal table of five critical parameters-Reynolds number (Re), Damköhler number (Da), relative adsorption capacity (σ), equilibrium dissociation constant (KD), and Schmidt number (Sc), with two levels was designed. ANOVA methods are used to obtain the significance of key parameters. The optimal combination of the key parameters is Re = 10[-2], Da = 1000, σ = 0.2, KD = 5, and Sc 10[4] to achieve the minimum response time (0.15). Among the selected key parameters, the relative adsorption capacity (σ) has the highest contribution (42.17%) to the reduction of the response time, while the Schmidt number (Sc) has the lowest contribution (5.19%). The presented simulation results are useful in designing microfluidic biosensors in order to reduce their response time.}, } @article {pmid37360015, year = {2023}, author = {Ahmed, A and Ul Islam, S and Khan, AQ and Wahid, A}, title = {Reduction of fluid forces for flow past side-by-side cylinders using downstream attached splitter plates.}, journal = {Computational particle mechanics}, volume = {}, number = {}, pages = {1-19}, doi = {10.1007/s40571-023-00565-2}, pmid = {37360015}, issn = {2196-4378}, abstract = {A two-dimensional numerical simulation is performed to investigate the drag reduction and vortex shedding suppression behind three square cylinders with attached splitter plates in the downstream region at a low Reynolds number (Re = 150). Numerical calculations are carried out using the lattice Boltzmann method. The study is carried out for various values of gap spacing between the cylinders and different splitter plate lengths. The vortices are completely chaotic at very small spacing, as observed. The splitter plates are critical in suppressing shedding and reducing drag on the objects. The splitter plates with lengths greater than two fully control the jet interaction at low spacing values. There is maximum percentage reduction in CDmean for small spacing and the selected largest splitter plate length. Furthermore, systematic investigation reveals that splitter plates significantly suppress the fluctuating lift in addition to drastically reducing the drag.}, } @article {pmid37344457, year = {2023}, author = {Baldygin, A and Ahmed, A and Baily, R and Ismail, MF and Khan, M and Rodrigues, N and Salehi, AR and Ramesh, M and Bhattacharya, S and Willers, T and Gowanlock, D and Waghmare, PR}, title = {Effect of gravity on the spreading of a droplet deposited by liquid needle deposition technique.}, journal = {NPJ microgravity}, volume = {9}, number = {1}, pages = {49}, pmid = {37344457}, issn = {2373-8065}, support = {19FAALBB36 - FAST 2019//Gouvernement du Canada | Canadian Space Agency (Agence Spatiale Canadienne)/ ; }, abstract = {This study represents an experimental investigation, complemented with a mathematical model, to decipher the effect of gravity on the spreading dynamics of a water droplet. For the theoretical discussion, an overall energy balance approach is adopted to explain the droplet spreading under both microgravity (μg) and terrestrial gravity condition. Besides explaining the mechanism of the droplet spreading under microgravity condition achieved during the parabolic flight, a technique with a detailed experimental set-up has also been developed for the successful deposition of droplet. A rational understanding is formulated through experimental investigation and theoretical analysis, which allows us to distinguish the transient variation of the spreading of a droplet, between microgravity and terrestrial gravity condition. The spreading of the droplet is predicted by the non-linear overall energy balance equation, which accounts for the operating parameters in the form of non-dimensional groups like Reynolds number ([Formula: see text]), Weber number (We) and Bond number (Bo). To distinctly identify the difference in the drop spreading at terrestrial and microgravity conditions, the Bo with transient gravitational field obtained through the on-board accelerometer is considered. The obtained theoretical results are further corroborated by experimental results which are obtained from the parabolic flight.}, } @article {pmid37338259, year = {2023}, author = {Qiao, S and Ouyang, H and Zheng, X and Qi, C and Ma, L}, title = {Magnetically actuated hydrogel-based capsule microrobots for intravascular targeted drug delivery.}, journal = {Journal of materials chemistry. B}, volume = {}, number = {}, pages = {}, doi = {10.1039/d3tb00852e}, pmid = {37338259}, issn = {2050-7518}, abstract = {Microrobots for targeted drug delivery in blood vessels have attracted increasing interest from researchers. In this work, hydrogel-based capsule microrobots are used to wrap drugs and deliver drugs in blood vessels. In order to prepare capsule microrobots of different sizes, a triaxial microfluidic chip is designed and built, and the formation mechanism of three flow phases including the plug flow phase, bullet flow phase and droplet phase during the preparation of capsule microrobots is studied. The analysis and simulation results show that the size of the capsule microrobots can be controlled by the flow rate ratio of two phases in the microfluidic chip, and when the flow rate of the outer phase is 20 times that of the inner phase in the microfluidic chip, irregular multicore capsule microrobots can be prepared. On this basis, a three degree of freedom magnetic drive system is developed to drive the capsule microrobots to reach the destination along the predetermined trajectory in the low Reynolds number environment, and the magnetic field performance of the magnetic drive system is simulated and analyzed. Finally, in order to verify the feasibility of targeted drug delivery of the capsule microrobots in the blood vessel, the motion process of the capsule microrobots in the vascular microchannel is simulated, and the relationship between the motion performance of the capsule microrobots and the magnetic field is studied. The experimental results show that the capsule microrobots can reach a speed of 800 μm s[-1] at a low frequency of 0.4 Hz. At the same time, the capsule microrobots can reach a peak speed of 3077 μm s[-1] and can continuously climb over a 1000 μm high obstacle under a rotating magnetic field of 2.4 Hz and 14.4 mT. Experiments show that the capsule microrobots have excellent drug delivery potential in similar vascular curved channels driven by this system.}, } @article {pmid37330555, year = {2023}, author = {Algehyne, EA and Ahammad, NA and Elnair, ME and Zidan, M and Alhusayni, YY and El-Bashir, BO and Saeed, A and Alshomrani, AS and Alzahrani, F}, title = {Entropy optimization and response surface methodology of blood hybrid nanofluid flow through composite stenosis artery with magnetized nanoparticles (Au-Ta) for drug delivery application.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {9856}, pmid = {37330555}, issn = {2045-2322}, abstract = {Entropy creation by a blood-hybrid nanofluid flow with gold-tantalum nanoparticles in a tilted cylindrical artery with composite stenosis under the influence of Joule heating, body acceleration, and thermal radiation is the focus of this research. Using the Sisko fluid model, the non-Newtonian behaviour of blood is investigated. The finite difference (FD) approach is used to solve the equations of motion and entropy for a system subject to certain constraints. The optimal heat transfer rate with respect to radiation, Hartmann number, and nanoparticle volume fraction is calculated using a response surface technique and sensitivity analysis. The impacts of significant parameters such as Hartmann number, angle parameter, nanoparticle volume fraction, body acceleration amplitude, radiation, and Reynolds number on the velocity, temperature, entropy generation, flow rate, shear stress of wall, and heat transfer rate are exhibited via the graphs and tables. Present results disclose that the flow rate profile increase by improving the Womersley number and the opposite nature is noticed in nanoparticle volume fraction. The total entropy generation reduces by improving radiation. The Hartmann number expose a positive sensitivity for all level of nanoparticle volume fraction. The sensitivity analysis revealed that the radiation and nanoparticle volume fraction showed a negative sensitivity for all magnetic field levels. It is seen that the presence of hybrid nanoparticles in the bloodstream leads to a more substantial reduction in the axial velocity of blood compared to Sisko blood. An increase in the volume fraction results in a noticeable decrease in the volumetric flow rate in the axial direction, while higher values of infinite shear rate viscosity lead to a significant reduction in the magnitude of the blood flow pattern. The blood temperature exhibits a linear increase with respect to the volume fraction of hybrid nanoparticles. Specifically, utilizing a hybrid nanofluid with a volume fraction of 3% leads to a 2.01316% higher temperature compared to the base fluid (blood). Similarly, a 5% volume fraction corresponds to a temperature increase of 3.45093%.}, } @article {pmid37329080, year = {2023}, author = {Kim, M and Borhan, A}, title = {Critical conditions for development of a second pair of Dean vortices in curved microfluidic channels.}, journal = {Physical review. E}, volume = {107}, number = {5-2}, pages = {055103}, doi = {10.1103/PhysRevE.107.055103}, pmid = {37329080}, issn = {2470-0053}, abstract = {The centrifugal force in flow through a curved channel initiates a hydrodynamic instability that results in the development of Dean vortices, a pair of counter-rotating roll cells across the channel that deflect the high velocity fluid in the center toward the outer (concave) wall. When this secondary flow toward the concave (outer) wall is too strong to be dissipated by viscous effects, an additional pair of vortices emerges near the outer wall. Combining numerical simulation and dimensional analysis, we find that the critical condition for the onset of the second vortex pair depends on γ^{1/2} Dn (γ: channel aspect ratio; Dn: Dean number). We also investigate the development length for the additional vortex pair in channels with different aspect ratios and curvatures. The larger centrifugal force at higher Dean numbers produces the additional vortices further upstream, with the required development length being inversely proportional to the Reynolds number and increasing linearly with the radius of curvature of the channel.}, } @article {pmid37329043, year = {2023}, author = {Mizerski, KA}, title = {Helical correction to turbulent magnetic diffusivity.}, journal = {Physical review. E}, volume = {107}, number = {5-2}, pages = {055205}, doi = {10.1103/PhysRevE.107.055205}, pmid = {37329043}, issn = {2470-0053}, abstract = {The effect of helicity in magnetohydrodynamic turbulence on the effective turbulent magnetic diffusion is considered here. The helical correction to turbulent diffusivity is analytically calculated with the use of the renormalization group approach. In agreement with previous numerical findings, this correction is shown to be negative and proportional to the second power of the magnetic Reynolds number, when the latter is small. In addition, the helical correction to turbulent diffusivity is found to obey a power-law-type dependence on the wave number of the most energetic turbulent eddies, k_{ℓ}, of the form k_{ℓ} ^{-10/3} .}, } @article {pmid37329025, year = {2023}, author = {Parfenyev, V and Mogilevskiy, E and Falkovich, G}, title = {Sum-of-squares bounds on correlation functions in a minimal model of turbulence.}, journal = {Physical review. E}, volume = {107}, number = {5-1}, pages = {054114}, doi = {10.1103/PhysRevE.107.054114}, pmid = {37329025}, issn = {2470-0053}, abstract = {We suggest a new computer-assisted approach to the development of turbulence theory. It allows one to impose lower and upper bounds on correlation functions using sum-of-squares polynomials. We demonstrate it on the minimal cascade model of two resonantly interacting modes when one is pumped and the other dissipates. We show how to present correlation functions of interest as part of a sum-of-squares polynomial using the stationarity of the statistics. That allows us to find how the moments of the mode amplitudes depend on the degree of nonequilibrium (analog of the Reynolds number), which reveals some properties of marginal statistical distributions. By combining scaling dependence with the results of direct numerical simulations, we obtain the probability densities of both modes in a highly intermittent inverse cascade. As the Reynolds number tends to infinity, we show that the relative phase between modes tends to π/2 and -π/2 in the direct and inverse cascades, respectively, and derive bounds on the phase variance. Our approach combines computer-aided analytical proofs with a numerical algorithm applied to high-degree polynomials.}, } @article {pmid37324036, year = {2023}, author = {Jiang, J and Wang, F and Huang, W and Sun, J and Ye, Y and Ou, J and Liu, M and Gao, J and Wang, S and Fu, D and Chen, B and Liu, L and Peng, F and Tu, Y}, title = {Mobile mechanical signal generator for macrophage polarization.}, journal = {Exploration (Beijing, China)}, volume = {3}, number = {2}, pages = {20220147}, pmid = {37324036}, issn = {2766-2098}, abstract = {The importance of mechanical signals in regulating the fate of macrophages is gaining increased attention recently. However, the recently used mechanical signals normally rely on the physical characteristics of matrix with non-specificity and instability or mechanical loading devices with uncontrollability and complexity. Herein, we demonstrate the successful fabrication of self-assembled microrobots (SMRs) based on magnetic nanoparticles as local mechanical signal generators for precise macrophage polarization. Under a rotating magnetic field (RMF), the propulsion of SMRs occurs due to the elastic deformation via magnetic force and hydrodynamics. SMRs perform wireless navigation toward the targeted macrophage in a controllable manner and subsequently rotate around the cell for mechanical signal generation. Macrophages are eventually polarized from M0 to anti-inflammatory related M2 phenotypes by blocking the Piezo1-activating protein-1 (AP-1)-CCL2 signaling pathway. The as-developed microrobot system provides a new platform of mechanical signal loading for macrophage polarization, which holds great potential for precise regulation of cell fate.}, } @article {pmid37323615, year = {2023}, author = {Madonia, M and Guzmán, AJA and Clercx, HJH and Kunnen, RPJ}, title = {Reynolds number scaling and energy spectra in geostrophic convection.}, journal = {Journal of fluid mechanics}, volume = {962}, number = {}, pages = {A36}, pmid = {37323615}, issn = {0022-1120}, abstract = {We report flow measurements in rotating Rayleigh-Bénard convection in the rotationally-constrained geostrophic regime. We apply stereoscopic particle image velocimetry to measure the three components of velocity in a horizontal cross-section of a water-filled cylindrical convection vessel. At a constant, small Ekman number Ek = 5 × 10[-8] we vary the Rayleigh number Ra between 10[11] and 4 × 10[12] to cover various subregimes observed in geostrophic convection. We also include one nonrotating experiment. The scaling of the velocity fluctuations (expressed as the Reynolds number Re) is compared to theoretical relations expressing balances of viscous-Archimedean-Coriolis (VAC) and Coriolis-inertial-Archimedean (CIA) forces. Based on our results we cannot decide which balance is most applicable here; both scaling relations match equally well. A comparison of the current data with several other literature datasets indicates a convergence towards diffusion-free scaling of velocity as Ek decreases. However, the use of confined domains leads at lower Ra to prominent convection in the wall mode near the sidewall. Kinetic energy spectra point at an overall flow organisation into a quadrupolar vortex filling the cross-section. This quadrupolar vortex is a quasi-two-dimensional feature; it only manifests in energy spectra based on the horizontal velocity components. At larger Ra the spectra reveal the development of a scaling range with exponent close to -5/3, the classical exponent for inertial-range scaling in three-dimensional turbulence. The steeper Re(Ra) scaling at low Ek and development of a scaling range in the energy spectra are distinct indicators that a fully developed, diffusion-free turbulent bulk flow state is approached, sketching clear perspectives for further investigation.}, } @article {pmid37308628, year = {2023}, author = {Sharma, M and Jilte, R}, title = {Heat transfer and hydraulics for a novel receiver pipe of solar parabolic trough: a computational approach.}, journal = {Environmental science and pollution research international}, volume = {}, number = {}, pages = {}, pmid = {37308628}, issn = {1614-7499}, abstract = {The effect of symmetrical convex-concave corrugations on receiver pipe of a parabolic trough solar collector is numerically investigated. Twelve distinct geometrically configured receiver pipes with corrugations have been examined for this purpose. The computational study is conducted for varying corrugation pitch (4 mm to 10 mm) and height (1.5 mm to 2.5 mm). Heat transfer enhancement, flow behavior, and overall thermal performance of fluid moving through a pipe under non-uniform heat flux condition are all determined in this work. The Reynolds number ranges from 5000 to 50,000. The findings reveal that presence of corrugations leads to axial whirling and vortices in the receiver pipe, thus enhancing the heat transfer. The receiver pipe having corrugations of 8 mm pitch and 2 mm height gave the best results. The maximum enhancement in average Nusselt number over smooth pipe has been observed as 28.51%. In addition, relationships of Nusselt number and friction factor against selected design parameters and operating conditions are also displayed as correlations.}, } @article {pmid37303552, year = {2023}, author = {Alizadeh, A and Shahabi Takami, SF and Iranmanesh, R and Pasha, P}, title = {Evaluation of AGM and FEM method for thermal radiation on nanofluid flow between two tubes in nearness of magnetism field.}, journal = {Heliyon}, volume = {9}, number = {6}, pages = {e16788}, doi = {10.1016/j.heliyon.2023.e16788}, pmid = {37303552}, issn = {2405-8440}, abstract = {The nanofluid flow through two orbicular cylinders is explored utilizing the overall Koo-Kleinstreuer-Li (KKL) model within the nearness of a magnetic field. The impact of thermal radiation is considered in the energy equation. The novelty of this study is examining convective heat transfer for nanofluid flow between two flat tubes with the Akbari-Ganji method and Finite Element Techniques to examine the heat flux field by implies of 2D forms of temperature and velocity at unprecedented Reynolds numbers. The approaches for solving ODEs are AGM and FEM. Semi-analytical methods are assessed for specific parameters of aspect ratio, Hartmann number, Eckert number, and Reynolds quantity with various values. Adding Ha, Ec, and G causes the temperature gradient to grow, while adding the Reynolds number causes it to decrease. As the Lorentz forces increase, the velocity decreases; nevertheless, as the Reynolds number rises, the velocity decreases. With the reduction of the fluid's dynamic viscosity, the temperature will decrease, which will decrease the thermal trend along the vertical length of the pipes.}, } @article {pmid37297077, year = {2023}, author = {Tang, TL and Salleh, H and Sadiq, MI and Mohd Sabri, MA and Ahmad, MIM and Ghopa, WAW}, title = {Experimental and Numerical Investigation of Flow Structure and Heat Transfer Behavior of Multiple Jet Impingement Using MgO-Water Nanofluids.}, journal = {Materials (Basel, Switzerland)}, volume = {16}, number = {11}, pages = {}, doi = {10.3390/ma16113942}, pmid = {37297077}, issn = {1996-1944}, abstract = {Nanofluids have attracted significant attention from researchers due to their ability to significantly enhance heat transfer, especially in jet impingement flows, which can improve their cooling performance. However, there is a lack of research on the use of nanofluids in multiple jet impingements, both in terms of experimental and numerical studies. Therefore, further investigation is necessary to fully understand the potential benefits and limitations of using nanofluids in this type of cooling system. Thus, an experimental and numerical investigation was performed to study the flow structure and heat transfer behavior of multiple jet impingement using MgO-water nanofluids with a 3 × 3 inline jet array at a nozzle-to-plate distance of 3 mm. The jet spacing was set to 3, 4.5, and 6 mm; the Reynolds number varies from 1000 to 10,000; and the particle volume fraction ranges from 0% to 0.15%. A 3D numerical analysis using ANSYS Fluent with SST k-ω turbulent model was presented. The single-phase model is adopted to predict the thermal physical nanofluid. The flow field and temperature distribution were investigated. Experimental results show that a nanofluid can provide a heat transfer enhancement at a small jet-to-jet spacing using a high particle volume fraction under a low Reynolds number; otherwise, an adverse effect on heat transfer may occur. The numerical results show that the single-phase model can predict the heat transfer trend of multiple jet impingement using nanofluids correctly but with significant deviation from experimental results because it cannot capture the effect of nanoparticles.}, } @article {pmid37296306, year = {2023}, author = {Liu, Y and Zou, Z and Pak, OS and Tsang, ACH}, title = {Learning to cooperate for low-Reynolds-number swimming: a model problem for gait coordination.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {9397}, pmid = {37296306}, issn = {2045-2322}, abstract = {Biological microswimmers can coordinate their motions to exploit their fluid environment-and each other-to achieve global advantages in their locomotory performance. These cooperative locomotion require delicate adjustments of both individual swimming gaits and spatial arrangements of the swimmers. Here we probe the emergence of such cooperative behaviors among artificial microswimmers endowed with artificial intelligence. We present the first use of a deep reinforcement learning approach to empower the cooperative locomotion of a pair of reconfigurable microswimmers. The AI-advised cooperative policy comprises two stages: an approach stage where the swimmers get in close proximity to fully exploit hydrodynamic interactions, followed a synchronization stage where the swimmers synchronize their locomotory gaits to maximize their overall net propulsion. The synchronized motions allow the swimmer pair to move together coherently with an enhanced locomotion performance unattainable by a single swimmer alone. Our work constitutes a first step toward uncovering intriguing cooperative behaviors of smart artificial microswimmers, demonstrating the vast potential of reinforcement learning towards intelligent autonomous manipulations of multiple microswimmers for their future biomedical and environmental applications.}, } @article {pmid37296249, year = {2023}, author = {Kumar, D and Layek, A and Kumar, A}, title = {Enhancement of thermal efficiency and development of Nusselt number correlation for the solar air heater collector roughened with artificial ribs for thermal applications.}, journal = {Environmental science and pollution research international}, volume = {}, number = {}, pages = {}, pmid = {37296249}, issn = {1614-7499}, abstract = {The thermal efficiency of conventional solar air heater is very low. This research article concentrates on incorporating V-shaped staggered twisted ribs over absorber surface of solar air heater. Various roughness parameters were tested to determine their effect on the Nusselt number, friction factor, thermo-hydraulic performance index, and thermal efficiency. During experiment, the Reynolds number is varied from 3000 to 21,000; while relative roughness length varied for 4.39 to 10.26 and relative staggered distance for 2 to 6. However, relative roughness pitch, twist length, and angle of attack were kept constant. The Nusselt number and friction factor of the roughened collector enhances to 3.41 and 2.56 times that of the smooth collector, respectively. The thermal efficiency of the roughened solar air heater increases to 73.64% of the roughened plate as it was noticed 42.63% for smooth surface due to breakage of the laminar sublayer. The correlations for Nusselt number and friction factor as function of Reynolds number and roughness parameters are also developed. The maximum thermohydraulic performance gained at the optimum parameters of d/e of 4 and S/e of 6.15 is 2.69. The percentage deviation between the developed correlations and the experimental findings shows very satisfactory outcomes. Therefore, it can be concluded that inclusion of twisted V staggered ribs enhances the thermal performance of solar air heater with the lowest frictional penalty.}, } @article {pmid37295437, year = {2023}, author = {Liu, F and Li, S and Dong, X and Wang, Z and Xiang, J and Li, D and Tu, Z}, title = {Design, modelling, and experimental validation of a self-rotating flapping wing rotorcraft with motor-spring resonance actuation system.}, journal = {Bioinspiration & biomimetics}, volume = {}, number = {}, pages = {}, doi = {10.1088/1748-3190/acdd3d}, pmid = {37295437}, issn = {1748-3190}, abstract = {Compared with traditional flapping motion, Flapping Wing Rotor (FWR) frees the rotating freedom by installing the two wings asymmetrically, which introduces rotor's motion characteristics and enables FWR to have higher lift and aerodynamic efficiency at low Reynolds number. However, most of the proposed FWRs contain linkage mechanical transmission structures, the fixed degrees of freedom (DoFs) of which prohibit the wings from achieving variable flapping trajectories, limiting the further optimization and controller design of FWRs. In order to fundamentally address the above challenges of FWRs, this paper presents a new type of FWR with two mechanically decoupled wings, which are directly driven by two independent motor- spring resonance actuation systems. The proposed FWR has 12.4 grams of system weight and 165-205mm wingspan. In addition, a theoretical electromechanical model based on the DC motor model and quasi-steady aerodynamic forces is established, and a series of experiments are conducted in order to figure out the ideal working point of the proposed FWR. It is notable that both our theoretical model and experiments exhibit uneven rotation of the FWR during flight, i.e., rotation speed dropping in the downstroke while boosting in the upstroke, which further tests the proposed theoretical model and uncover the relationship between flapping and passive rotation in the FWR. To further validate the performance of the design, free flight tests are conducted, and the proposed FWR demonstrates stable liftoff at the designed working point.}, } @article {pmid37295099, year = {2023}, author = {Zhu, HY and Xie, JH and Xia, KQ}, title = {Circulation in Quasi-2D Turbulence: Experimental Observation of the Area Rule and Bifractality.}, journal = {Physical review letters}, volume = {130}, number = {21}, pages = {214001}, doi = {10.1103/PhysRevLett.130.214001}, pmid = {37295099}, issn = {1079-7114}, abstract = {We present an experimental study of the velocity circulation in a quasi-two-dimensional turbulent flow. We show that the area rule of circulation around simple loops holds in both the forward cascade enstrophy inertial range (ΩIR) and the inverse cascade energy inertial range (EIR): When the side lengths of a loop are all within the same inertial range, the circulation statistics depend on the loop area alone. It is also found that, for circulation around figure-eight loops, the area rule still holds in EIR but is not applicable in ΩIR. In ΩIR, the circulation is nonintermittent; whereas in EIR, the circulation is bifractal: space filling for moments of the order of 3 and below and a monofractal with a dimension of 1.42 for higher orders. Our results demonstrate, as in a numerical study of 3D turbulence [K. P. Iyer et al., Circulation in High Reynolds Number Isotropic Turbulence is a Bifractal, Phys. Rev. X 9, 041006 (2019).PRXHAE2160-330810.1103/PhysRevX.9.041006], that, in terms of circulation, turbulent flows exhibit a simpler behavior than velocity increments, as the latter are multifractals.}, } @article {pmid37292291, year = {2023}, author = {Das, A and Mahmood, FT and Smriti, RB and Saha, S and Hasan, MN}, title = {CFD analysis of heat transfer enhancement by wall mounted flexible flow modulators in a channel with pulsatile flow.}, journal = {Heliyon}, volume = {9}, number = {6}, pages = {e16741}, pmid = {37292291}, issn = {2405-8440}, abstract = {The aim of the present study is to explore heat transfer and pressure drop characteristics in a pulsating channel flow due to wall-mounted flexible flow modulators (FFM). Cold air in pulsating fashion is forced to enter through the channel having isothermally heated top and bottom walls with one/multiple FFMs mounted on them. The dynamic conditions of pulsating inflow are characterized by Reynolds number, non-dimensional pulsation frequency and amplitude. Applying the Galerkin finite element method in an Arbitrary Lagrangian-Eulerian (ALE) framework, the present unsteady problem has been solved. Flexibility (10[-4] ≤ Ca ≤ 10[-7]), orientation angle (60° ≤ θ ≤ 120°), and location of FFM(s) have been considered in this study to find out the best-case scenario for heat transfer enhancement. The system characteristics have been analyzed by vorticity contours and isotherms. Heat transfer performance has been evaluated in terms of Nusselt number variations and pressure drop across the channel. Besides, power spectrum analysis of thermal field oscillation along with that of the FFM's motion induced by pulsating inflow has been performed. The present study reveals that single FFM having flexibility of Ca = 10[-5] and an orientation angle of θ = 90° offers the best-case scenario for heat transfer enhancement.}, } @article {pmid37285818, year = {2023}, author = {Derikvand, M and Salehi, AA and Solari, MS and Najafi, F}, title = {Investigation of the effects of hydrophobic surfaces on thermohydraulic characteristics and entropy generation of hybrid nanofluids with magnetic properties in a micro-heat sink under a magnetic field.}, journal = {Nanotechnology}, volume = {}, number = {}, pages = {}, doi = {10.1088/1361-6528/acdc2f}, pmid = {37285818}, issn = {1361-6528}, abstract = {The cooling process of the devices is a big challenge in the electronic industry, and most of the process units (graphical are central) experience defects under harsh temperature conditions, so dissipating generated heat under various working conditions should seriously be studied. This study investigates the magnetohydrodynamics of hybrid-ferro nanofluids in the presence of hydrophobic surfaces in a micro-heat sink. To scrutinize this study, a Finite Volume Method (FVM is applied. The ferro nanofluid includes water as base fluid and Multiwall Carbon Nanotubes (MWCNTs) and Fe3O4 as nano-additives, which are used in three concentrations (0, 1 and 3%). The other parameters such as Reynold number (5-120), Hartmann number (magnitude of the magnetic field from 0 to 6) and hydrophobicity of surfaces are considered to be scrutinized for their impacts on heat transfer and hydraulic variables as well as entropy generation ones. The outcomes indicate that increasing the level of hydrophobicity in surfaces leads to improve heat exchange and reduces the pressure drop simultaneously. Likewise, it decreases the frictional and thermal types of entropy generations. Intensifying the magnitude of the magnetic field enhances the heat exchange as much as the pressure drop. In the same result, it can decrease the thermal term in entropy generation equations for the fluid, but it increases the frictional one and adds a new term named magnetic entropy generation. Incrementing Reynolds number improves the convection heat transfer parameters although it intensifies the pressure drop in the length of the channel. Also, the thermal and frictional kinds of entropy generation decrease and increase with increasing the flow rate (Reynold number).}, } @article {pmid37280357, year = {2023}, author = {Ibrahim, MG and Abou-Zeid, MY}, title = {Computational simulation for MHD peristaltic transport of Jeffrey fluid with density-dependent parameters.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {9191}, pmid = {37280357}, issn = {2045-2322}, abstract = {This study aimed to give a new theoretical recommendation for non-dimensional parameters depending on the fluid temperature and concentration. This suggestion came from the fact of fluid density may change with the fluid temperature ([Formula: see text]) and concentration ([Formula: see text]). So, a newly released mathematical form of Jeffrey fluid with peristalsis through the inclined channel is constructed. The problem model defines a mathematical fluid model which converts using non-dimensional values. A sequentially used technique called the Adaptive shooting method for finding the problem solutions. Axial velocity behavior has become a novel concern to Reynolds number. In contradiction to different values of parameters, the temperature and concentration profiles are designated/sketched. The results show that the high value of the Reynolds number acts as a fluid temperature damper, while it boosts the concentration of the fluid particle. The non-constant fluid density recommendation makes the Darcy number controls with a fluid velocity which is virtually significant in drug carries applications or blood circulation systems. To verify the obtained results, a numerical comparison for obtained results has been made with a trustful algorithm with aid of AST using wolfram Mathematica version 13.1.1.}, } @article {pmid37278331, year = {2023}, author = {Shashank, HJ and Melikhov, Y and Ekiel-Jeżewska, ML}, title = {Dynamics of ball chains and highly elastic fibres settling under gravity in a viscous fluid.}, journal = {Soft matter}, volume = {}, number = {}, pages = {}, doi = {10.1039/d3sm00255a}, pmid = {37278331}, issn = {1744-6848}, abstract = {We study experimentally the dynamics of one and two ball chains settling under gravity in a highly viscous silicon oil at a Reynolds number much smaller than unity. We record the motion and shape deformation using two cameras. We demonstrate that single ball chains in most cases do not tend to be planar and often rotate, not keeping the ends at the same horizontal level. Shorter ball chains usually form shapes resembling distorted U. Longer ones in the early stage of the evolution form a shape resembling distorted W, and later deform non-symmetrically and significantly out of a plane. The typical evolution of shapes observed in our experiments with single ball chains is reproduced in our numerical simulations of a single elastic filament. In the computations, the filament is modelled as a chain of beads. Consecutive beads are connected by springs. Additional springs link consecutive pairs of beads. Elastic forces are assumed to be much smaller than gravity. As a result, the fibre is very flexible. We assume that the fluid sticks to the surfaces of the beads. We perform multipole expansion of the Stokes equations, with a lubrication correction. This method is implemented in the precise HYDROMULTIPOLE numerical codes. In our experiments, two ball chains, initially one above the other, later move away or approach each other, for a larger or smaller initial distance, respectively.}, } @article {pmid37276558, year = {2023}, author = {Lustro, JRT and Shimizu, Y and Kawahara, G}, title = {Homoclinic bifurcation and switching of edge state in plane Couette flow.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {33}, number = {6}, pages = {}, doi = {10.1063/5.0133492}, pmid = {37276558}, issn = {1089-7682}, abstract = {We identify the presence of three homoclinic bifurcations that are associated with edge states in a system that is governed by the full Navier-Stokes equation. In plane Couette flow with a streamwise period slightly longer than the minimal unit, we describe a rich bifurcation scenario that is related to new time-periodic solutions and the Nagata steady solution [M. Nagata, J. Fluid Mech. 217, 519-527 (1990)]. In this computational domain, the vigorous time-periodic solution (PO3) with comparable fluctuation amplitude to turbulence and the lower branch of the Nagata steady solution are considered as edge states at different ranges of Reynolds number. These edge states can help in understanding the mechanism of subcritical transition to turbulence in wall-bounded shear flows. At the Reynolds numbers at which the homoclinic bifurcations occur, we find the creation (or destruction) of the time-periodic solutions. At a higher Reynolds number, we observe the edge state switching from the lower-branch Nagata steady solution to PO3 at the creation of this vigorous cycle due to the homoclinic bifurcation. Consequently, the formation of the boundary separating the basins of attraction of the laminar attractor and the time-periodic/chaotic attractor also switches to the respective stable manifolds of the edge states, providing a change in the behavior of a typical amplitude of perturbation toward triggering the transition to turbulence.}, } @article {pmid37274523, year = {2023}, author = {Ijaz, S and Abdullah, M and Sadaf, H and Nadeem, S}, title = {Generalized complex cilia tip modeled flow through an electroosmotic region.}, journal = {Journal of Central South University}, volume = {30}, number = {4}, pages = {1217-1230}, pmid = {37274523}, issn = {2227-5223}, abstract = {In this analysis, we explore a nanofluid model that represents the role of ciliary carpets in the transport of magnetohydrodynamic fluid in an electroosmotic channel. Hybrid nanofluid features are also taken into interpretation. The equations leading the flow analysis are converted into non-dimensional form by supposing long wavelength and low Reynolds number approximations. Analytical solutions for velocity distribution, pressure gradient and stream function are acquired and solved by a mathematic solver. The effects of the relevant physical parameters are graphically noted. The consequence of the present model has remarkable applications, which can be used in various areas of biological transport processes, artificial cilia design and in the operation of other mechanical devices.}, } @article {pmid37263239, year = {2023}, author = {Ronco, C and Bellomo, R}, title = {The Process of Adsorption and Cartridge Design.}, journal = {Contributions to nephrology}, volume = {200}, number = {}, pages = {1-8}, doi = {10.1159/000529295}, pmid = {37263239}, issn = {1662-2782}, abstract = {The mechanism of adsorption is regulated by various factors including the nature of the sorbent and the molecules involved in the adsorption process. The design of a device for adsorption therapies must fulfil specific requirements. The device should allow the use of the minimum amount of sorbent material sufficient to achieve safe and effective blood purification therapy. Each component of the device must respond to criteria of safety and function in order to maximize the efficiency of the cartridge. The design should be optimized to enable utilization of all the sorbent surface available for adsorption. The structure and packing of the sorbent particles should allow the even distribution of flow inside the cartridge and the avoidance of channeling phenomena and excessive resistance to flow. All these factors depend on specific governing laws such as the Kozeny-Carman equation and Darcy's law. The system must also consider blood viscosity and possible turbulent flows (Reynolds number). The final manufacturing process of a sorbent unit must also consider the dimensions and the cost, and the final performance after sterilization and storage.}, } @article {pmid37259126, year = {2023}, author = {Bocanegra Evans, H and Segnini, JM and Doosttalab, A and Cordero, J and Castillo, L}, title = {Effect of cartilaginous rings in tracheal flow with stenosis.}, journal = {BMC biomedical engineering}, volume = {5}, number = {1}, pages = {5}, pmid = {37259126}, issn = {2524-4426}, abstract = {BACKGROUND: In respiratory fluid dynamics research, it is typically assumed that the wall of the trachea is smooth. However, the trachea is structurally supported by a series of cartilaginous rings that create undulations on the wall surface, which introduce perturbations into the flow. Even though many studies use realistic Computer Tomography (CT) scan data to capture the complex geometry of the respiratory system, its limited spatial resolution does not resolve small features, including those introduced by the cartilaginous rings.

RESULTS: Here we present an experimental comparison of two simplified trachea models with Grade II stenosis (70% blockage), one with smooth walls and second with cartilaginous rings. The use a unique refractive index-matching method provides unprecedented optical access and allowed us to perform non-intrusive velocity field measurements close to the wall (e.g., Particle Image Velocimetry (PIV)). Measurements were performed in a flow regime comparable to a resting breathing state (Reynolds number ReD = 3350). The cartilaginous rings induce velocity fluctuations in the downstream flow, enhancing the near-wall transport of momentum flux and thus reducing flow separation in the downstream flow. The maximum upstream velocity in the recirculation region is reduced by 38%, resulting in a much weaker recirculation zone- a direct consequence of the cartilaginous rings.

CONCLUSIONS: These results highlight the importance of the cartilaginous rings in respiratory flow studies and the mechanism to reduce flow separation in trachea stenosis.}, } @article {pmid37255166, year = {2023}, author = {Silva, MLFD and Gonçalves, SF and Haniel, J and Lucas, TC and Huebner, R}, title = {Comparative study between 1-way and 2-way coupled fluid-structure interaction in numerical simulation of aortic arch aneurysms.}, journal = {Anais da Academia Brasileira de Ciencias}, volume = {95}, number = {suppl 1}, pages = {e20210859}, doi = {10.1590/0001-3765202320210859}, pmid = {37255166}, issn = {1678-2690}, abstract = {Hemodynamic forces are related to pathological variations of the cardiovascular system, and numerical simulations for fluid-structure interaction have been systematically used to analyze the behavior of blood flow and the arterial wall in aortic aneurysms. This paper proposes a comparative analysis of 1-way and 2-way coupled fluid-structure interaction for aortic arch aneurysm. The coupling models of fluid-structure interaction were conducted using 3D geometry of the thoracic aorta from computed tomography. Hyperelastic anisotropic properties were estimated for the Holzapfel arterial wall model. The rheological behavior of the blood was modeled by the Carreau-Yasuda model. The results showed that the 1-way approach tends to underestimate von Mises stress, displacement, and strain over the entire cardiac cycle, compared to the 2-way approach. In contrast, the behavior of the variables of flow field, velocity, wall shear stress, and Reynolds number when coupled by the 1-way model was overestimated at the systolic moment and tends to be equal at the diastolic moment. The quantitative differences found, especially during the systole, suggest the use of 2-way coupling in numerical simulations of aortic arch aneurysms due to the hyperelastic nature of the arterial wall, which leads to a strong iteration between the fluid and the arterial wall.}, } @article {pmid37249683, year = {2023}, author = {Deng, X and Sheng, P}, title = {Evolution of channel flow and Darcy's law beyond the critical Reynolds number.}, journal = {The European physical journal. E, Soft matter}, volume = {46}, number = {6}, pages = {37}, pmid = {37249683}, issn = {1292-895X}, abstract = {For incompressible channel flow, there is a critical state, characterized by a critical Reynolds number Rec and a critical wavevector mc along the channel direction, beyond which the channel flow becomes unstable in the linear regime. In this work, we investigate the channel flow beyond the critical state and find the existence of a new fluctuating, quasi-stationary flow that comprises the laminar Poiseuille flow superposed with a counter-flow component, accompanied by vortices and anti-vortices. The net flow rate is reduced by ~ 15% from the linear, laminar regime. Our study is facilitated by the analytical solution of the linearized, incompressible, three-dimensional (3D) Navier-Stokes (NS) equation in the channel geometry, with the Navier boundary condition, alternatively denoted as the hydrodynamic modes (HMs). By using the HMs as the complete mathematical basis for expanding the velocity in the NS equation, the Rec is evaluated to 5-digit accuracy when compared to the well-known Orszag result, without invoking the standard Orr-Sommerfeld equation. Beyond Rec, the analytical solution is indispensable in offering physical insight to those features of the counter-flow component that differs from any of the pressure-driven channel flows. In particular, the counter flow is found to comprise multiple HMs, some with opposite flow direction, that can lead to a net boundary reaction force along the counter-flow direction. The latter is analyzed to be necessary for satisfying Newton's law. Experimental verification of the predictions is discussed.}, } @article {pmid37241559, year = {2023}, author = {Che, H and Xu, Q and Xu, G and Fu, X and Wang, X and He, N and Zhu, Z}, title = {Numerical Study on Characteristics of Convection and Temperature Evolution in Microchannel of Thermal Flowmeter.}, journal = {Micromachines}, volume = {14}, number = {5}, pages = {}, doi = {10.3390/mi14050935}, pmid = {37241559}, issn = {2072-666X}, abstract = {During practical usage, thermal flowmeters have a limited range of applications. The present work investigates the factors influencing thermal flowmeter measurements and observes the effects of buoyancy convection and forced convection on the flow rate measurement sensitivity. The results show that the gravity level, inclination angle, channel height, mass flow rate, and heating power affect the flow rate measurements by influencing the flow pattern and the temperature distribution. Gravity determines the generation of convective cells, while the inclination angle affects the location of the convective cells. Channel height affects the flow pattern and temperature distribution. Higher sensitivity can be achieved with smaller mass flow rates or higher heating power. According to the combined influence of the aforementioned parameters, the present work investigates the flow transition based on the Reynolds number and the Grashof number. When the Reynolds number is below the critical value corresponding to the Grashof number, convective cells emerge and affect the accuracy of flowmeter measurements. The research on influencing factors and flow transition presented in this paper has potential implications for the design and manufacture of thermal flowmeters under different working conditions.}, } @article {pmid37230014, year = {2023}, author = {Yeom, J and Park, J and Park, JY}, title = {Fluid dynamic simulation for cellular damage due to lymphatic flow within the anatomical arrangement of the outer hair cells in the cochlea.}, journal = {Computers in biology and medicine}, volume = {161}, number = {}, pages = {106986}, doi = {10.1016/j.compbiomed.2023.106986}, pmid = {37230014}, issn = {1879-0534}, abstract = {Damage to the sensory hair cells in the cochlea is a major cause of hearing loss since human sensory hair cells do not regenerate naturally after damage. As these sensory hair cells are exposed to a vibrating lymphatic environment, they may be affected by physical flow. It is known that the outer hair cells (OHCs) are physically more damaged by sound than the inner hair cells (IHCs). In this study, the lymphatic flow is compared using computational fluid dynamics (CFD) based on the arrangement of the OHCs, and the effects of such flow on the OHCs is analyzed. In addition, flow visualization is used to validate the Stokes flow. The Stokes flow behavior is attributed to the low Reynolds number, and the same behavior is observed even when the flow direction is reversed. When the distance between the rows of the OHCs is large, each row is independent, but when this distance is short, the flow change in each row influences the other rows. The stimulation caused by flow changes on the OHCs is confirmed through surface pressure and shear stress. The OHCs located at the base with a short distance between the rows receive excess hydrodynamic stimulation, and the tip of the V-shaped pattern receives an excess mechanical force. This study attempts to understand the contributions of lymphatic flow to OHC damage by quantitatively suggesting stimulation of the OHCs and is expected to contribute to the development of OHC regeneration technologies in the future.}, } @article {pmid37231052, year = {2023}, author = {Li, S and Mao, L and Alizadeh, A and Zhang, X and Mousavi, SV}, title = {The application of non-uniform magnetic field for thermal enhancement of the nanofluid flow inside the U-turn pipe at solar collectors.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {8471}, pmid = {37231052}, issn = {2045-2322}, abstract = {The improvement of heat transfer inside the solar heat exchangers is important for the development of solar energy in an urban area. In this study, the usage of a non-uniform magnetic field on the thermal efficiency of the nanofluid (Fe3O4) streaming inside the U-turn pipe of solar heat exchangers is examined. Computational fluid dynamic is applied to visualize the nanofluid flow inside the solar heat exchanger. The role of magnetic intensity and Reynolds number on thermal efficiency are fully investigated. The effect of single and triple sources of the magnetic field is also studied in our research. Obtained results indicate that the usage of the magnetic field results in the production of vortex in the base fluid and heat transfer improves inside the domain. Our finding indicates that the usage of the magnetic field with Mn = 25 K would improve the average heat transfer by about 21% along the U-turn pipe of solar heat exchangers.}, } @article {pmid37220708, year = {2023}, author = {Tisdell, CC}, title = {Improved perturbation solution for two-dimensional viscous flow between expanding or contracting permeable walls.}, journal = {Journal of biomechanics}, volume = {155}, number = {}, pages = {111642}, doi = {10.1016/j.jbiomech.2023.111642}, pmid = {37220708}, issn = {1873-2380}, abstract = {Despite the continuing interest in the transport of biological fluid within contracting or expanding vessels, our knowledge is yet to be fully developed, even in the two-dimensional case. For example, explicit solutions and close approximations to these models remain unknown, and the physical problem has been restricted to the "slow" expansion or contraction of the walls. Thus, the purpose of this short communication is to partially address such challenges and gaps by generating explicit solutions and improving approximations to the flow problem without the "slowness" restriction being imposed. We show that when the Reynolds number is zero (i.e., the inviscid case), the corresponding homogeneous differential equation under consideration may be completely solved. We then illustrate how this exact solution may be leveraged to form more precise approximations to the flow via perturbation techniques when the Reynolds number is small. Our perturbation approach is only in one parameter (the Reynolds number) instead of the usual two parameters (the Reynolds number and wall dilation rate), and thus we make no restriction regarding the "slowness" of wall expansion or contraction for our general perturbation scheme. Our act of "shining new light through old windows" improves and extends the results of Majdalani, Zhou and Dawson and, moreover, our method has significant potential to be applied by researchers to form more precise one-parameter perturbation approximations to flow problems in contrast to the limitations of the traditional two-parameter perturbation approaches that have dominated the literature.}, } @article {pmid37215871, year = {2023}, author = {Zhao, L and Wang, Y and Qi, Z}, title = {Investigation of periodic characteristics of perturbed flow over a slender body.}, journal = {Heliyon}, volume = {9}, number = {5}, pages = {e16194}, doi = {10.1016/j.heliyon.2023.e16194}, pmid = {37215871}, issn = {2405-8440}, abstract = {The asymmetric flow over a slender body was particularly sensitive to the nose at a high angle of attack (AoA). Two patterns of separation occurred on the noses of the pointed-nosed slender body and blunt-nosed slender body as open- and close-type separation, respectively. The effects of the bluntness were investigated at high AoA (α = 50°) to clarify the evolution of the separated pattern from open-to close-type separation by the nose and by the periodic characteristics of perturbed flow. Wind tunnel experimental tests were conducted to investigate the periodic characteristics of asymmetric flow at a Reynolds number ReD = 1.54 × 10[5], based on incoming free-stream velocity (U∞) and the diameter (D) of the model. A particle was attached to the tip of the nose to induce the perturbed flow and attain a definite and predictable asymmetric flow in experimental tests. The pressure scanning and surface oil-flow visualization techniques were used to capture the pressure distributions and flow separations. The major findings were that axial flow increases with the increase of bluntness, resulting in open-type separation turning into close-type separation, and the perturbation moved from downstream to upstream of starting points of the separation line. The critical bluntness of separation pattern switching from open-type to close-type located between 1.5 and 3. Thus, the management of perturbation on asymmetric flow pattern switched from directly participating in separation to influencing separation through micro-flow. Therefore, the locations of perturbation and starting points of the separation line were closely related to asymmetric flow management by perturbation, then affecting the periodic characteristics of perturbed flow.}, } @article {pmid37198775, year = {2023}, author = {Yoo, H and Wissocq, G and Jacob, J and Favier, J and Sagaut, P}, title = {Compressible lattice Boltzmann method with rotating overset grids.}, journal = {Physical review. E}, volume = {107}, number = {4-2}, pages = {045306}, doi = {10.1103/PhysRevE.107.045306}, pmid = {37198775}, issn = {2470-0053}, abstract = {The numerical instability of the lattice Boltzmann method (LBM) at high Mach or high Reynolds number flow is well identified, and it remains a major barrier to its application in more complex configurations such as moving geometries. This work combines the compressible lattice Boltzmann model with rotating overset grids (the so-called Chimera method, sliding mesh, or moving reference frame) for high Mach flows. This paper proposes to use the compressible hybrid recursive regularized collision model with fictitious forces (or inertial forces) in a noninertial rotating reference frame. Also, polynomial interpolations are investigated, which allow fixed inertial and rotating noninertial grids to communicate with each other. We suggest a way to effectively couple the LBM with the MUSCL-Hancock scheme in the rotating grid, which is needed to account for thermal effect of compressible flow. As a result, this approach is demonstrated to have an extended Mach stability limit for the rotating grid. It also demonstrates that this complex LBM scheme can maintain the second-order accuracy of the classic LBM by appropriately using numerical methods like polynomial interpolations and the MUSCL-Hancock scheme. Furthermore, the method shows a very good agreement on aerodynamic coefficients compared to experiments and the conventional finite-volume scheme. This work presents a thorough academic validation and error analysis of the LBM for simulating moving geometries in high Mach compressible flows.}, } @article {pmid37190405, year = {2023}, author = {Niven, RK}, title = {Dimensionless Groups by Entropic Similarity: I - Diffusion, Chemical Reaction and Dispersion Processes.}, journal = {Entropy (Basel, Switzerland)}, volume = {25}, number = {4}, pages = {}, pmid = {37190405}, issn = {1099-4300}, abstract = {Since the time of Buckingham in 1914, dimensional analysis and similarity arguments based on dimensionless groups have served as powerful tools for the analysis of systems in all branches of science and engineering. Dimensionless groups are generally classified into those arising from geometric similarity, based on ratios of length scales; kinematic similarity, based on ratios of velocities or accelerations; and dynamic similarity, based on ratios of forces. We propose an additional category of dimensionless groups based on entropic similarity, defined by ratios of (i) entropy production terms; (ii) entropy flow rates or fluxes; or (iii) information flow rates or fluxes. Since all processes involving work against friction, dissipation, diffusion, dispersion, mixing, separation, chemical reaction, gain of information or other irreversible changes are driven by (or must overcome) the second law of thermodynamics, it is appropriate to analyze them directly in terms of competing entropy-producing and transporting phenomena and the dominant entropic regime, rather than indirectly in terms of forces. In this study, entropic groups are derived for a wide variety of diffusion, chemical reaction and dispersion processes relevant to fluid mechanics, chemical engineering and environmental engineering. It is shown that many dimensionless groups traditionally derived by kinematic or dynamic similarity (including the Reynolds number) can also be recovered by entropic similarity-with a different entropic interpretation-while many new dimensionless groups can also be identified. The analyses significantly expand the scope of dimensional analysis and similarity arguments for the resolution of new and existing problems in science and engineering.}, } @article {pmid37186956, year = {2023}, author = {Guo, Q and Zhang, J and Li, D and Yu, H}, title = {Effect of Wettability on the Collision Behavior of Acoustically Excited Droplets.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {}, number = {}, pages = {}, doi = {10.1021/acs.langmuir.3c00571}, pmid = {37186956}, issn = {1520-5827}, abstract = {Acoustic droplet ejection (ADE) is a noncontact technique for micro-liquid handling (usually nanoliters or picoliters) that is not restricted by nozzles and enables high-throughput liquid dispensing without sacrificing precision. It is widely regarded as the most advanced solution for liquid handling in large-scale drug screening. Stable coalescence of the acoustically excited droplets on the target substrate is a fundamental requirement during the application of the ADE system. However, it is challenging to investigate the collision behavior of nanoliter droplets flying upward during the ADE. In particular, the dependence of the droplet's collision behavior on substrate wettability and droplet velocity has yet to be thoroughly analyzed. In this paper, the kinetic processes of binary droplet collisions were investigated experimentally for different wettability substrate surfaces. Four states occur as the droplet collision velocity increases: coalescence after minor deformation, complete rebound, coalescence during rebound, and direct coalescence. For the hydrophilic substrate, there are wider ranges of Weber number (We) and Reynolds number (Re) in the complete rebound state. And with the decrease of the substrate wettability, the critical Weber and Reynolds numbers for the coalescence during rebound and the direct coalescence decrease. It is further revealed that the hydrophilic substrate is susceptible to droplet rebound because the sessile droplet has a larger radius of curvature and the viscous energy dissipation is greater. Besides, the prediction model of the maximum spreading diameter was established by modifying the droplet morphology in the complete rebound state. It is found that, under the same Weber and Reynolds numbers, droplet collisions on the hydrophilic substrate achieve a smaller maximum spreading coefficient and greater viscous energy dissipation, so the hydrophilic substrate is prone to droplet bounce.}, } @article {pmid37123410, year = {2023}, author = {Ishimoto, K and Gaffney, EA and Smith, DJ}, title = {Squirmer hydrodynamics near a periodic surface topography.}, journal = {Frontiers in cell and developmental biology}, volume = {11}, number = {}, pages = {1123446}, pmid = {37123410}, issn = {2296-634X}, abstract = {The behaviour of microscopic swimmers has previously been explored near large-scale confining geometries and in the presence of very small-scale surface roughness. Here, we consider an intermediate case of how a simple microswimmer, the tangential spherical squirmer, behaves adjacent to singly and doubly periodic sinusoidal surface topographies that spatially oscillate with an amplitude that is an order of magnitude less than the swimmer size and wavelengths that are also within an order of magnitude of this scale. The nearest neighbour regularised Stokeslet method is used for numerical explorations after validating its accuracy for a spherical tangential squirmer that swims stably near a flat surface. The same squirmer is then introduced to different surface topographies. The key governing factor in the resulting swimming behaviour is the size of the squirmer relative to the surface topography wavelength. For instance, directional guidance is not observed when the squirmer is much larger, or much smaller, than the surface topography wavelength. In contrast, once the squirmer size is on the scale of the topography wavelength, limited guidance is possible, often with local capture in the topography troughs. However, complex dynamics can also emerge, especially when the initial configuration is not close to alignment along topography troughs or above topography crests. In contrast to sensitivity in alignment and topography wavelength, reductions in the amplitude of the surface topography or variations in the shape of the periodic surface topography do not have extensive impacts on the squirmer behaviour. Our findings more generally highlight that the numerical framework provides an essential basis to elucidate how swimmers may be guided by surface topography.}, } @article {pmid37115869, year = {2023}, author = {Ambruş, VE and Schlichting, S and Werthmann, C}, title = {Establishing the Range of Applicability of Hydrodynamics in High-Energy Collisions.}, journal = {Physical review letters}, volume = {130}, number = {15}, pages = {152301}, doi = {10.1103/PhysRevLett.130.152301}, pmid = {37115869}, issn = {1079-7114}, abstract = {We simulate the space-time dynamics of high-energy collisions based on a microscopic kinetic description in the conformal relaxation time approximation, in order to determine the range of applicability of an effective description in relativistic viscous hydrodynamics. We find that hydrodynamics provides a quantitatively accurate description of collective flow when the average inverse Reynolds number Re^{-1} is sufficiently small and the early preequilibrium stage is properly accounted for. We further discuss the implications of our findings for the (in)applicability of hydrodynamics in proton-proton, proton-nucleus, and light nucleus collisions.}, } @article {pmid37112102, year = {2023}, author = {Lin, W and Li, Z and Zhang, S and Lin, J}, title = {Numerical Study on the Distribution of Rodlike Particles in Laminar Flows of Power Law Fluids Past a Cylinder.}, journal = {Polymers}, volume = {15}, number = {8}, pages = {}, doi = {10.3390/polym15081956}, pmid = {37112102}, issn = {2073-4360}, abstract = {The contraction/expansion laminar flow containing rodlike particles in power-law fluid is studied numerically when the particles are in a dilute phase. The fluid velocity vector and streamline of flow are given at the finite Reynolds number (Re) region. The effects of Re, power index n and particle aspect ratio β on the spatial and orientation distributions of particles are analyzed. The results showed that for the shear-thickening fluid, particles are dispersed in the whole area in the contraction flow, while more particles are gathered near the two walls in the expansion flow. The spatial distribution of particles with small β is more regular. Β has a significant, n has a moderate, but Re has a small impact on the spatial distribution of particles in the contraction and expansion flow. In the case of large Re, most particles are oriented in the flow direction. The particles near the wall show obvious orientation along the flow direction. In shear-thickening fluid, when the flow changes from contraction to expansion, the orientation distribution of particles becomes more dispersed; while in shear-thinning fluid, the opposite is true. More particles orient to the flow direction in expansion flow than that in contraction flow. The particles with a large β tend to align with the flow direction more obviously. Re, n and β have great influence on the orientation distribution of particles in the contraction and expansion flow. Whether the particles initially located at the inlet can bypass the cylinder depends on the transverse position and initial orientation of the particles at the inlet. The number of particles with θ0 = 90° bypassing the cylinder is the largest, followed by θ0 = 45° and θ0 = 0°. The conclusions obtained in this paper have reference value for practical engineering applications.}, } @article {pmid37100809, year = {2023}, author = {Pilloton, C and Lugni, C and Graziani, G and Fedele, F}, title = {Wave dispersion in moderate channel turbulence.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {6801}, pmid = {37100809}, issn = {2045-2322}, abstract = {We study channel turbulence by interpreting its vorticity as a random sea of ocean wave packet analogues. In particular, we investigate the ocean-like properties of vortical packets applying stochastic methods developed for oceanic fields. Taylor's hypothesis of frozen eddies does not hold when turbulence is not weak, and vortical packets change shape as they are advected by the mean flow, altering their own speed. This is the physical manifestation of a hidden wave dispersion of turbulence. Our analysis at the bulk Reynolds number Reb = 5600 suggests that turbulent fluctuations behave dispersively as gravity-capillary waves, with capillarity being dominant near the wall region.}, } @article {pmid37097943, year = {2023}, author = {Prasad, V and Sharma, A and Kulkarni, SS}, title = {Chaotic advection in a recirculating flow: Effect of a fluid multiple-flexible-solid interaction.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {33}, number = {4}, pages = {}, doi = {10.1063/5.0132986}, pmid = {37097943}, issn = {1089-7682}, abstract = {This paper deals with chaotic advection due to a two-way interaction between flexible elliptical-solids and a laminar lid-driven cavity flow in two dimensions. The present Fluid multiple-flexible-Solid Interaction study involves various number N(= 1-120) of equal-sized neutrally buoyant elliptical-solids (aspect ratio β = 0.5) such that they result in the total volume fraction Φ = 10 % as in our recent study on single solid, done for non-dimensional shear modulus G ∗ = 0.2 and Reynolds number R e = 100. Results are presented first for flow-induced motion and deformation of the solids and later for chaotic advection of the fluid. After the initial transients, the fluid as well as solid motion (and deformation) attain periodicity for smaller N ≤ 10 while they attain aperiodic states for larger N > 10. Adaptive material tracking (AMT) and Finite-Time Lyapunov Exponent (FTLE)-based Lagrangian dynamical analysis revealed that the chaotic advection increases up to N = 6 and decreases at larger N(= 6-10) for the periodic state. Similar analysis for the transient state revealed an asymptotic increase in the chaotic advection with increasing N ≤ 120. These findings are demonstrated with the help of two types of chaos signatures: exponential growth of material blob's interface and Lagrangian coherent structures, revealed by the AMT and FTLE, respectively. Our work, which is relevant to several applications, presents a novel technique based on the motion of multiple deformable-solids for enhancement of chaotic advection.}, } @article {pmid37092929, year = {2023}, author = {Yang, C and Arcondoulis, EJG and Yang, Y and Guo, J and Maryami, R and Bi, C and Liu, Y}, title = {Active control of airfoil turbulent boundary layer noise with trailing-edge blowing.}, journal = {The Journal of the Acoustical Society of America}, volume = {153}, number = {4}, pages = {2115}, doi = {10.1121/10.0017787}, pmid = {37092929}, issn = {1520-8524}, abstract = {Large Eddy Simulation (LES) and Ffowcs Williams-Hawkings acoustic analogy are performed to study the effect of trailing-edge blowing on airfoil self-noise. Simulations were conducted using a National Advisory Committee for Aeronautics 0012 airfoil at zero angle of attack and a chord-based Reynolds number of 4 × 10 5. The aerodynamic and aeroacoustic characteristics of the baseline airfoil were thoroughly verified by comparison with previous numerical and experimental data. The noise reduction effects of continuous and local blowing with different blowing ratios and blowing momentum coefficients were compared. A maximum noise reduction of 20 dB was achieved via trailing-edge blowing and the noise reduction mechanisms of the two blowing methods were discussed. The LES results show a pair of recirculation bubbles in the airfoil wake which are suppressed by trailing-edge blowing. As the blowing vortices convect into the wake, they stretch and stabilize the shear flows from airfoil surfaces. Instantaneous vorticity and root mean square velocity fluctuations are also weakened. There is a decrease in the spanwise coherence and an increase in the phase difference, which contribute to noise reduction. It is concluded that the suppression of turbulence fluctuations in the near wake is the main mechanism of noise reduction for airfoil trailing-edge blowing.}, } @article {pmid37073470, year = {2023}, author = {Roggeveen, JV and Stone, HA and Kurzthaler, C}, title = {Transport of a passive scalar in wide channels with surface topography: An asymptotic theory.}, journal = {Journal of physics. Condensed matter : an Institute of Physics journal}, volume = {35}, number = {27}, pages = {}, doi = {10.1088/1361-648X/acc8ad}, pmid = {37073470}, issn = {1361-648X}, abstract = {We generalize classical dispersion theory for a passive scalar to derive an asymptotic long-time convection-diffusion equation for a solute suspended in a wide, structured channel and subject to a steady low-Reynolds-number shear flow. Our asymptotic theory relies on a domain perturbation approach for small roughness amplitudes of the channel and holds for general surface shapes expandable as a Fourier series. We determine an anisotropic dispersion tensor, which depends on the characteristic wavelengths and amplitude of the surface structure. For surfaces whose corrugations are tilted with respect to the applied flow direction, we find that dispersion along the principal direction (i.e. the principal eigenvector of the dispersion tensor) is at an angle to the main flow direction and becomes enhanced relative to classical Taylor dispersion. In contrast, dispersion perpendicular to it can decrease compared to the short-time diffusivity of the particles. Furthermore, for an arbitrary surface shape represented in terms of a Fourier decomposition, we find that each Fourier mode contributes at leading order a linearly-independent correction to the classical Taylor dispersion diffusion tensor.}, } @article {pmid37069324, year = {2023}, author = {Nyatchouba Nsangue, BT and Tang, H and Liu, W and Xu, L and Hu, F}, title = {Turbulent flow interacting with flexible trawl net structure including simulation catch in flume tank.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {6249}, pmid = {37069324}, issn = {2045-2322}, abstract = {The interaction between fluid and the midwater trawl with stocked catches is extremely complex, but essential to improve the understanding of the drag force acting on the trawl, the behavior of the fishing structure during a trawling process, and to predict its selectivity process. The present study assesses the turbulent characteristics inside and around the midwater trawls with catch and without catch linked to its fluttering motion. The analysis is based on three-dimensional electromagnetic current velocity meter measurements performed in the multiple points inside and outside different parts of a 1/35 scaled midwater trawl model with the aim of access the main turbulent flow structure inside and around the gear. Time-averaged normalized flow velocity fields and turbulent flow parameters were analyzed from the measured flow data. Furthermore, Fourier analysis was conducted by watching the time-frequency Power spectrum content of instantaneous flow velocities fields, the fluttering trawl motions, turbulent kinetic energy, and momentum flux. Based on successive analyzes of mean flow characteristics and turbulent flow parameters, it has been demonstrated that the presence of catch inside the trawl net impacts the evolution of unsteady turbulent flow by creating large trawl fluttering motions that strongly affect the flow passage. The results showed that the time-averaged normalized streamwise and transverse flow velocities inside and around the trawl net with catch were 12.41% lower compared with that obtained inside and around the trawl without catch. The turbulent length scale and turbulent Reynolds number obtained in the different part of the trawl net with catch were about 33.05% greater than those obtained on the trawl net without catch, confirming that the unsteady turbulent flow developing inside and around the midwater trawl is influence by the catch and liner. It is observed that the motions of both the trawl without catch and the trawl with catch are mainly of a low-frequency activity and another component related to unsteady turbulent flow street. A complex fluid-structure interaction is then demonstrated where the fluttering motions of the trawl net affect the fluid flow inside and around trawl net, the fluid force, turbulent pattern, and simultaneously, the periodic unsteady turbulent flow influence the trawl motions.}, } @article {pmid37064396, year = {2023}, author = {Ding, Y and Liu, Z and Wang, X and Xin, R and Shan, D and He, B and Jing, J and Gao, Q and Yang, J and Chen, Y}, title = {Validation of hemodynamic stress calculation in coronary computed tomography angiography versus intravascular ultrasound.}, journal = {Quantitative imaging in medicine and surgery}, volume = {13}, number = {4}, pages = {2339-2351}, pmid = {37064396}, issn = {2223-4292}, abstract = {BACKGROUND: Development in computational fluid dynamics and 3D construction could facilitate the calculation of hemodynamic stresses in coronary computed tomography angiography (CCTA). However, the agreement between CCTA derived stresses and intravascular ultrasound/intravascular coronary angiography (IVUS/ICA)-derived stresses remains undetermined. Thus, the purpose of this study is to investigate if CCTA can serve as alternative to IVUS/ICA for hemodynamic evaluation.

METHODS: In this retrospective study, 13 patients (14 arteries) with unstable angina who underwent both CCTA and IVUS/ICA at an interval of less than 7 days were consecutively included at the Chinese PLA General Hospital within the year of 2021. Slice-level minimal lumen area (MLA), percent area stenosis, velocity, pressure, Reynolds number, wall shear stress (WSS) and axial plaque stress (APS) were determined by both modalities. The agreement between CCTA and IVUS/ICA was assessed using the intraclass correlation coefficient (ICC), Pearson's correlation coefficient and Bland-Altman analysis.

RESULTS: CCTA overestimated the degree of area stenosis (50.22%±16.15% vs. 36.41%±19.37%, P=0.004) with the MLA showing no significant difference (5.81±2.24 vs. 6.72±2.04 mm[2], P=0.126). No statistical difference was observed in WSS (6.57±6.26 vs. 5.98±5.55 Pa, P=0.420) and APS (16.03±1,159.45 vs. -1.27±890.39 Pa, P=0.691) between CCTA and IVUS. Good correlation was found in velocity (ICC: 0.796, 95% CI: 0.752-0.833), Reynolds number (ICC: 0.810, 95% CI: 0.768-0.844) and WSS (ICC: 0.769, 95% CI: 0.718-0.810), while the ICC of APS was (ICC: 0.341, 95% CI: 0.197-0.458), indicating a relatively poor correlation.

CONCLUSIONS: CCTA can serve as a satisfactory alternative to the reference standard, IVUS/ICA in morphology simulation and hemodynamic stress calculation, especially in the calculation of WSS.}, } @article {pmid37064764, year = {2011}, author = {Fan, DL and Zhu, FQ and Cammarata, RC and Chien, CL}, title = {Electric Tweezers.}, journal = {Nano today}, volume = {6}, number = {4}, pages = {339-354}, pmid = {37064764}, issn = {1748-0132}, abstract = {Electric tweezers utilize DC and AC electric fields through voltages applied on patterned electrodes to manipulate nanoentities suspended in a liquid. Nanowires with a large aspect ratio are particularly suitable for use in electric tweezers for patterning, assembling, and manipulation. Despite operating in the regime of extremely small particle Reynolds number (of order 10[-5]), electric tweezers can manipulate nanowires with high precision to follow any prescribed trajectory, to rotate nanowires with controlled chirality, angular velocity and rotation angle, and to assemble nanowires to fabricate nanoelectromechanical system (NEMS) devices such as nanomotors and nano-oscillators. Electric tweezers have also been used to transport in a highly controlled manner drug-carrying functionalized nanowires for cell-specific drug delivery.}, } @article {pmid37039923, year = {2023}, author = {Guastoni, L and Rabault, J and Schlatter, P and Azizpour, H and Vinuesa, R}, title = {Deep reinforcement learning for turbulent drag reduction in channel flows.}, journal = {The European physical journal. E, Soft matter}, volume = {46}, number = {4}, pages = {27}, pmid = {37039923}, issn = {1292-895X}, support = {2021-CoG-101043998/ERC_/European Research Council/International ; }, abstract = {We introduce a reinforcement learning (RL) environment to design and benchmark control strategies aimed at reducing drag in turbulent fluid flows enclosed in a channel. The environment provides a framework for computationally efficient, parallelized, high-fidelity fluid simulations, ready to interface with established RL agent programming interfaces. This allows for both testing existing deep reinforcement learning (DRL) algorithms against a challenging task, and advancing our knowledge of a complex, turbulent physical system that has been a major topic of research for over two centuries, and remains, even today, the subject of many unanswered questions. The control is applied in the form of blowing and suction at the wall, while the observable state is configurable, allowing to choose different variables such as velocity and pressure, in different locations of the domain. Given the complex nonlinear nature of turbulent flows, the control strategies proposed so far in the literature are physically grounded, but too simple. DRL, by contrast, enables leveraging the high-dimensional data that can be sampled from flow simulations to design advanced control strategies. In an effort to establish a benchmark for testing data-driven control strategies, we compare opposition control, a state-of-the-art turbulence-control strategy from the literature, and a commonly used DRL algorithm, deep deterministic policy gradient. Our results show that DRL leads to 43% and 30% drag reduction in a minimal and a larger channel (at a friction Reynolds number of 180), respectively, outperforming the classical opposition control by around 20 and 10 percentage points, respectively.}, } @article {pmid37037634, year = {2023}, author = {Wang, YH and Lin, XY and Cheng, Y and Wang, H and Liu, W and Zhuge, XK and Huo, XL and Bao, N}, title = {Vibration for enhancement of electrochemical analysis of biomolecules in a droplet on the rough surface of a disposable working electrode.}, journal = {Analytica chimica acta}, volume = {1256}, number = {}, pages = {341158}, doi = {10.1016/j.aca.2023.341158}, pmid = {37037634}, issn = {1873-4324}, abstract = {Although electrochemical detection of microliters-level solutions is attractive for analysis of low-amount biological samples, its performance could be weakened by limited mass transfer due to low Reynolds number and laminar flow. Herein we designed a 3D-printed electroanalytical device to apply vibration for improvement of mass transfer during electrochemical detection. In our approach, the droplet-size sample solution containing Indole-3-acetic acid (IAA, as a model) was directly applied on the effective surface of a disposable working electrode. We demonstrated that vibration could enhance electrochemical responses of IAA more on the rough surface than on the smooth surface of the working electrodes. After optimization, the sensitivity for electrochemical detection of a 20-μL droplet under vibration with the voltage of 7 V increased more than 100% compared with the static condition. The enhanced electrochemical responses brought by vibration could be achieved reproducibly, which could be ascribed to improved mass transfer. Our strategy could be practically applied for differentiation of IAA in different tissues of Marchantia polymorpha with enhanced responses. This study suggested that vibration might become a simple and effective method to improve mass transfer in analysis of microliter-volume solutions, which might be extended for more biochemical assays.}, } @article {pmid37034318, year = {2023}, author = {Dyverfeldt, P and Trenti, C and Ziegler, M and Bjarnegård, N and Lindenberger, M}, title = {Helical flow in tortuous aortas and its relationship to turbulence: A whole-aorta 4D flow MRI study.}, journal = {Frontiers in cardiovascular medicine}, volume = {10}, number = {}, pages = {1124604}, pmid = {37034318}, issn = {2297-055X}, abstract = {BACKGROUND: Increased vascular tortuosity is a hallmark of ageing of the vascular system, including the aorta. However, the impact of tortuosity on aortic blood flow is unknown. We hypothesized that increased tortuosity would be associated with increased blood flow helicity and with decreased degree of blood flow turbulence as measured by the turbulent kinetic energy (TKE).

METHODS: 4D Flow MR images covering the entire aorta from the aortic valve to the iliac bifurcation were acquired in 23 normal volunteers aged 18-30 years ("Young") and 23 normal volunteers aged 66-76 years ("Old") without aortic disease. The aorta was segmented and divided into four regions: the ascending, descending, suprarenal abdominal and infrarenal abdominal aorta. Tortuosity, helicity, TKE, flow velocity, and Reynolds number were computed for the whole aorta and for each section.

RESULTS: Tortuosity and helicity were higher whereas TKE, velocity, and Reynolds number were lower in Old than in Young, for all aortic regions (p < 0.05) except for helicity in the descending aorta. Tortuosity correlated positively with helicity and negatively with TKE for all aortic regions (Spearman rho=±0.45-±0.72, p < =0.002) except for TKE in the ascending aorta. Further, helicity correlated with TKE in the descending, suprarenal abdominal and infrarenal abdominal aorta (Spearman rho=-0.56--0.77).

CONCLUSION: Tortuosity increases with age and blood flow in tortuous aortas is more helical. Increasing helicity, in turn, is associated with decreasing TKE.}, } @article {pmid37033871, year = {2023}, author = {Meng, M and Yang, Q}, title = {Investigation of the Microscopic Process of the Media Coalescence Treatment of Water-in-Oil Emulsion.}, journal = {ACS omega}, volume = {8}, number = {13}, pages = {11908-11915}, pmid = {37033871}, issn = {2470-1343}, abstract = {Medium coalescence technology is a research hotspot for the separation of oil-in-water emulsions. However, the coalescence mechanism is still unclear, making it challenging to effectively improve the separation performance. Herein, the microscopic mechanism of medium coalescence was revealed. We found that the effective collision positions under the action of the flow field include the exposed granule surface, adherent droplet surface, and three-phase contact line. Furthermore, a numerical model of the microscopic process of water-in-oil emulsion permeation through a granular bed was established. The effects of different parameters (including the number of medium layers, Reynolds number, and inlet concentration) on the microscopic process of capturing dispersed-phase droplets in the bed and the pressure drop in the coalescence area were studied. The numerical results show that the droplets form the bridging structure between the granules. On the one hand, the bridging structure promotes the capture of the droplets by the bed; on the other hand, it causes pressure-drop fluctuations in the coalescence area and asymmetric distribution of the velocity field.}, } @article {pmid37029144, year = {2023}, author = {Abdelhafez, MA and Abd-Alla, AM and Abo-Dahab, SM and Elmhedy, Y}, title = {Influence of an inclined magnetic field and heat and mass transfer on the peristaltic flow of blood in an asymmetric channel.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {5749}, pmid = {37029144}, issn = {2045-2322}, abstract = {This article presents a theoretical study on heat and mass transfer analysis of the peristaltic flow of blood conveying through an asymmetric channel in the presence of inclined to the magnetic field. The effects of ratio of relaxation to retardation times, non-uniform parameter, the non-dimensional amplitude, Hartman number and phase difference have been taken into account. The governing coupled non-linear partial differential equations representing the flow model are transmuted into linear ones by assuming that the wave is very long with a small Reynolds number. The converted mathematical formulations are solved analytically via the Mathematica software. Analytical expressions for the dimensionless velocity profiles of fluid, temperature, concentration, pressure gradient, increase in pressure, heat transfer coefficient and shear stress of the blood are derived. The velocity, temperature, concentration, pressure gradient, increase in pressure, heat transfer coefficient and shear stress were calculated numerically for different values of the parameters, which were represented graphically and find their physical meaning.}, } @article {pmid37025873, year = {2023}, author = {Nishu, IZ and Samad, MF}, title = {Modeling and simulation of a split and recombination-based passive micromixer with vortex-generating mixing units.}, journal = {Heliyon}, volume = {9}, number = {4}, pages = {e14745}, pmid = {37025873}, issn = {2405-8440}, abstract = {As a state-of-the-art technology, micromixers are being used in various chemical and biological processes, including polymerization, extraction, crystallization, organic synthesis, biological screening, drug development, drug delivery, etc. The ability of a micromixer to perform efficient mixing while consuming little power is one of its basic needs. In this paper, a passive micromixer having vortex-generating mixing units is proposed which shows effective mixing with a small pressure drop. The micromixer works on the split and recombination (SAR) flow principle. In this study, four micromixers are designed with different arrangements of mixing units, and the effect of the placement of connecting channels is evaluated in terms of mixing index, pressure drop, and mixing performance. The channel width of 200 μm, height of 300 μm, and size of mixing units are maintained constant for all the micromixers throughout the evaluation process. The numerical simulation is performed for the Reynolds number (Re) range of 0.1-100 using Comsol Multiphysics software. By categorizing the flow patterns into three regimes based on the range of Re, the fluid flow throughout the length of the micromixer is visualized. The micromixer with dislocated connecting channels provides a satisfactory result with the mixing index of 0.96 and 0.94, and the pressure drop of 2.5 Pa and 7.8 kPa at Re = 0.1 and Re = 100 respectively. It also outperformed the other models in terms of the mixing performance. The proposed micromixer might very well be used in microfluidic devices for a variety of analytical procedures due to its straightforward construction and outstanding performance.}, } @article {pmid37018723, year = {2023}, author = {Van Impe, M and Caboor, L and Deleeuw, V and Olbinado, M and De Backer, J and Sips, P and Segers, P}, title = {Fluid-Structure Interaction Modeling of the Aortic Hemodynamics in Adult Zebrafish: a Pilot Study based on Synchrotron X-Ray Tomography.}, journal = {IEEE transactions on bio-medical engineering}, volume = {PP}, number = {}, pages = {}, doi = {10.1109/TBME.2023.3236488}, pmid = {37018723}, issn = {1558-2531}, abstract = {OBJECTIVE: The zebrafish is increasingly used as a small animal model for cardiovascular disease, including vascular disorders. Nevertheless, a comprehensive biomechanical understanding of the zebrafish cardiovascular circulation is still lacking and possibilities for phenotyping the zebrafish heart and vasculature at adult - no longer optically transparent - stages are limited. To improve these aspects, we developed imaging-based 3D models of the cardiovascular system of wild-type adult zebrafish.

METHODS: In vivo high-frequency echocardiography and ex vivo synchrotron x-ray tomography were combined to build fluid-structure interaction finite element models of the fluid dynamics and biomechanics inside the ventral aorta.

RESULTS: We successfully generated a reference model of the circulation in adult zebrafish. The dorsal side of the most proximal branching region was found as the location of highest first principal wall stress and was also a location of low wall shear stress. Reynolds number and oscillatory shear were very low compared to mice and humans.

SIGNIFICANCE: The presented wild-type results provide a first extensive biomechanical reference for adult zebrafish. This framework can be used for advanced cardiovascular phenotyping of adult genetically engineered zebrafish models of cardiovascular disease, showing disruptions of the normal mechano-biology and homeostasis. By providing reference values for key biomechanical stimuli (including wall shear stress and first principal stress) in wild-type animals, and a pipeline for image-based animal-specific computational biomechanical models, this study contributes to a more comprehensive understanding of the role of altered biomechanics and hemodynamics in heritable cardiovascular pathologies.}, } @article {pmid37012373, year = {2023}, author = {Lee, S and Bui-Vinh, D and Baek, M and Kwak, DB and Lee, H}, title = {Modeling pressure drop values across ultra-thin nanofiber filters with various ranges of filtration parameters under an aerodynamic slip effect.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {5449}, pmid = {37012373}, issn = {2045-2322}, abstract = {Computational fluid dynamics simulations of fibrous filters with 56 combinations of different fiber sizes, packing densities, face velocities, and thicknesses were conducted for developing models that predict pressure drops across nanofiber filters. The accuracy of the simulation method was confirmed by comparing the numerical pressure drops to the experimental data obtained for polyacrylonitrile electrospun nanofiber filters. In the simulations, an aerodynamic slip effect around the surface of the small nanofibers was considered. The results showed that, unlike in the case of conventional filtration theory, pressure drops across the thin layers of electrospun nanofiber filters are not proportional to the thickness. This might be a critical factor for obtaining precise pressure drops across the electrospun nanofiber filters with extremely thin layers. Finally, we derived the product of drag coefficient and Reynolds number as a function of packing density, Knudsen number, and ratio of thickness to fiber diameter to get the correlation equation for pressure drop prediction. The obtained equation predicted the pressure drops across the nanofiber filters with the maximum relative difference of less than 15%.}, } @article {pmid37009788, year = {2023}, author = {Connor, AA and Webster, DR}, title = {Hydrodynamics of the fast-start caridoid escape response in Antarctic krill, Euphausia superba.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {5376}, pmid = {37009788}, issn = {2045-2322}, abstract = {Krill are shrimp-like crustaceans with a high degree of mobility and variety of documented swimming behaviors. The caridoid escape response, a fast-start mechanism unique to crustaceans, occurs when the animal performs a series of rapid abdominal flexions and tail flipping that results in powerful backward strokes. The current results quantify the animal kinematics and three-dimensional flow field around a free-swimming Euphausia superba as it performs the caridoid escape maneuver. The specimen performs a single abdominal flexion-tail flip combination that leads to an acceleration over a 42 ms interval allowing it to reach a maximum speed of 57.0 cm/s (17.3 body lengths/s). The krill's tail flipping during the abdominal closure is a significant contributor to the thrust generation during the maneuver. The krill sheds a complex chain of vortex rings in its wake due to the viscous flow effects while the organism accelerates. The vortex ring structure reveals a strong suction flow in the wake, which suggests that the pressure distribution and form drag play a role in the force balance for this maneuver. Antarctic krill typically swim in a low to intermediate Reynolds number (Re) regime where viscous forces are significant, but as shown by this analysis, its high maneuverability allows it to quickly change its body angle and swimming speed.}, } @article {pmid37004257, year = {2023}, author = {Ozawa, K and Nakamura, H and Shimamura, K and Dietze, GF and Yoshikawa, HN and Zoueshtiagh, F and Kurose, K and Mu, L and Ueno, I}, title = {Capillary-driven horseshoe vortex forming around a micro-pillar.}, journal = {Journal of colloid and interface science}, volume = {642}, number = {}, pages = {227-234}, doi = {10.1016/j.jcis.2023.03.039}, pmid = {37004257}, issn = {1095-7103}, abstract = {HYPOTHESIS: Horseshoe vortices are known to emerge around large-scale obstacles, such as bridge pillars, due to an inertia-driven adverse pressure gradient forming on the upstream-side of the obstacle. We contend that a similar flow structure can arise in thin-film Stokes flow around micro-obstacles, such as used in textured surfaces to improve wettability. This could be exploited to enhance mixing in microfluidic devices, typically limited to creeping-flow regimes.

EXPERIMENTS: Numerical simulations based on the Navier-Stokes equations are carried out to elucidate the flow structure associated with the wetting dynamics of a liquid film spreading around a 50 μm diameter micro-pillar. The employed multiphase solver, which is based on the volume of fluid method, accurately reproduces the wetting dynamics observed in current and previous (Mu et al., Langmuir, 2019) experiments.

FINDINGS: The flow structure within the liquid meniscus forming at the foot of the micro-pillar evinces a horseshoe vortex wrapping around the obstacle, notwithstanding that the Reynolds number in our system is extremely low. Here, the adverse pressure gradient driving flow reversal near the bounding wall is caused by capillarity instead of inertia. The horseshoe vortex is entangled with other vortical structures, leading to an intricate flow system with high-potential mixing capabilities.}, } @article {pmid36997565, year = {2023}, author = {Monti, A and Olivieri, S and Rosti, ME}, title = {Collective dynamics of dense hairy surfaces in turbulent flow.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {5184}, pmid = {36997565}, issn = {2045-2322}, abstract = {Flexible filamentous beds interacting with a turbulent flow represent a fundamental setting for many environmental phenomena, e.g., aquatic canopies in marine current. Exploiting direct numerical simulations at high Reynolds number where the canopy stems are modelled individually, we provide evidence on the essential features of the honami/monami collective motion experienced by hairy surfaces over a range of different flexibilities, i.e., Cauchy number. Our findings clearly confirm that the collective motion is essentially driven by fluid flow turbulence, with the canopy having in this respect a fully-passive behavior. Instead, some features pertaining to the structural response turn out to manifest in the motion of the individual canopy elements when focusing, in particular, on the spanwise oscillation and/or on sufficiently small Cauchy numbers.}, } @article {pmid36984947, year = {2023}, author = {Lei, Y and Wang, J and Li, Y and Gao, Q}, title = {In-Hover Aerodynamic Analysis of a Small Rotor with a Thin Circular-Arc Airfoil and a Convex Structure at Low Reynolds Number.}, journal = {Micromachines}, volume = {14}, number = {3}, pages = {}, doi = {10.3390/mi14030540}, pmid = {36984947}, issn = {2072-666X}, abstract = {This study focused on the in-hover aerodynamics of a small rotor with a thin circular-arc airfoil and a convex structure at a low Reynolds number. The method combined computational fluid dynamics (CFD) with the blade element momentum theory (BEMT). The former was used for studying the two-dimensional parametric aerodynamics of the airfoil at a low Reynolds number and the latter was used for the prediction of the rotor's hover performance. A novel thin circular-arc airfoil with a convex structure with a high aerodynamic performance, high structural strength, light weight and easy manufacturing process is presented in this paper. A convex curve on the upper surface was adopted to increase the thickness of the airfoil at partial chord, and a stiffener in the airfoil was installed to improve the structural strength of rotor span-wise. The aerodynamic performance of the airfoil was numerically simulated by the two-dimensional steady and incompressible Navier-Stokes equations. The in-hover performance of the rotor for small-scale vehicles was predicted by an improved version of the blade element momentum theory (BEMT). Finally, a carbon-fiber rotor with the presented airfoil was manufactured that had a diameter of 40 cm and a pitch of 6.2 inches. The analysis results were verified by experiments. It was shown that the maximum calculation errors were below 6%. The improved BEMT can be used in the analysis of in-hover micro-rotor aerodynamics at low Reynolds numbers.}, } @article {pmid36984677, year = {2023}, author = {Park, JE and Kang, TG and Moon, H}, title = {The Effect of the Rotating Disk Geometry on the Flow and Flux Enhancement in a Dynamic Filtration System.}, journal = {Membranes}, volume = {13}, number = {3}, pages = {}, doi = {10.3390/membranes13030291}, pmid = {36984677}, issn = {2077-0375}, abstract = {A numerical study was conducted to investigate the effect of rotating patterned disks on the flow and permeate flux in a dynamic filtration (DF) system. The DF system consists of a rotating patterned disk and a stationary housing with a circular flat membrane. The feed flow is driven by the rotating disk with the angular velocity ranging from 200 to 1000 rpm and the applied pressure difference between inlet and outlet ports. Wheel-shaped patterns are engraved on the disk surfaces to add perturbation to the flow field and improve the permeate flux in the filtration system. Five disks with varying numbers of patterns were used in numerical simulations to examine the effects of the number of patterns and the angular velocity of the disk on the flow and permeate flux in the DF system. The flow characteristics are studied using the velocity profiles, the cross-sectional velocity vectors, the vortex structures, and the shear stress distribution. The wheel-shaped patterns shift the central core layer in the circumferential velocity profile towards the membrane, leading to higher shear stresses at the membrane and higher flux compared to a plain disk. When the number of patterns on the disk exceeded eight at a fixed Reynolds number, there were significant increases in wall shear stress and permeate flux compared to a plain disk filtration system with no pattern.}, } @article {pmid36967929, year = {2023}, author = {Sakib, MN and Shuvo, MS and Rahman, R and Saha, S}, title = {Particle deposition and fluid flow characteristics in turbulent corrugated pipe flow using Eulerian-Lagrangian approach.}, journal = {Heliyon}, volume = {9}, number = {3}, pages = {e14603}, pmid = {36967929}, issn = {2405-8440}, abstract = {A numerical simulation of aerosol particle deposition in a horizontal circular pipe with a corrugated wall under turbulent flow has been carried out in this research. This paper uses the RNG k-ε turbulence model with Enhanced Wall Treatment to simulate fluid flow. Furthermore, the Lagrangian particle tracking model simulates particle deposition in the corrugated pipe. Air-particle interaction is influenced by Stokes number, surface roughness, flow velocity, particle diameter, and pipe diameter. For the parametric simulation, particle diameter varies from 1 to 30 μm, whereas the Reynolds number ranges from 5000 to 10,000. The effect of corrugation height and pipe diameter on deposition efficiency is also investigated. This study shows that corrugation height significantly increases particle deposition compared to the smooth wall pipe. As the pipe diameter decreases, keeping the corrugation ratio constant, deposition efficiency also increases. Moreover, high flow velocity enhances deposition efficiency for particle diameters lower than 5 μm.}, } @article {pmid36966222, year = {2023}, author = {Memon, AA and Memon, MA and Fenta, A}, title = {A laminar forced convection via transport of water-copper-aluminum hybrid nanofluid through heated deep and shallow cavity with Corcione model.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {4915}, pmid = {36966222}, issn = {2045-2322}, abstract = {The article explores how fluid flows and heat transfers in both deep and shallow cavities when using a nanofluid made of water, copper, and aluminum oxide. The study applies the Corcione model to hybrid nanofluids, which considers viscosity, conductivity, and the size of the nanoparticle, temperature, and Reynolds number. The cavity is connected to a rectangular channel, with the cavity's length being half the total length of the enclosure, and the aspect ratio (cavity height divided by height of the channel) is tested from 1 to 3. The study uses the Navier-Stokes equation and energy equation in two dimensions, along with finite element-based software, COMSOL 5.6, to simulate the combination of fluid flow and heat transmission. The results show a circular distribution of temperature in the cavity, and the average temperature drops as the volume fraction of copper upsurges. However, both the Reynolds number and volume fraction of copper improve the average Nusselt number, which shows how well the fluid transfers heat, along the cavity's middle line. The percentage change in the average Nusselt number decreases as the aspect ratio increases, indicating improved conduction.}, } @article {pmid36959904, year = {2023}, author = {Xiong, J and Zhang, J and Zhong, Y and Song, X and Wang, H and Cheang, UK}, title = {Magnetically-actuated hydrogel-based achiral planar microswimmers for SERS detection: In situ coprecipitation for continuous loading of iron oxide nanoparticles.}, journal = {Frontiers in bioengineering and biotechnology}, volume = {11}, number = {}, pages = {1086106}, pmid = {36959904}, issn = {2296-4185}, abstract = {Ultraviolet lithography is a very promising technology used for the batch fabrication of biomedical microswimmers. However, creating microswimmers that can swim at low Reynolds number using biocompatible materials while retaining strong magnetic properties and excellent biomedical functionality is a great challenge. Most of the previously reported biomedical microswimmers possess either strong magnetic properties by using non-biocompatible nickel coating or good biocompatibility by using iron oxide particle-embedded hydrogel with weak magnetism, but not both. Alternatively, iron oxide nanoparticles can be coated on the surface of microswimmers to improve magnetic properties; however, this method limited the usability of the microswimmers' surfaces. To address these shortcomings, this work utilized an in situ synthesis technique to generate high magnetic content inside hydrogel-based achiral planar microswimmers while leaving their surfaces free to be functionalized for SERS detection. The hydrogel matrices of the magnetically actuated hydrogel-based microswimmers were first prepared by ultraviolet lithography. Then, the high concentration of iron oxide was achieved through multiple continuous in situ coprecipitation cycles. Finally, the SERS detection capability of magnetically actuated hydrogel-based microswimmers was enabled by uniformly growing silver nanoparticles on the surface of the microswimmers. In the motion control tests, the microswimmers showed a high swimming efficiency, high step-out frequency, and consistent synchronized motion. Furthermore, the magnetically actuated hydrogel-based microswimmers were able to improve the detection efficiency of analytes under magnetic guidance.}, } @article {pmid36951265, year = {2023}, author = {Liu, D and Chen, S and Luo, X}, title = {Influence factors of channel geometry for separation of circulating tumor cells by four-ring inertial focusing microchannel.}, journal = {Cell biochemistry and function}, volume = {}, number = {}, pages = {}, doi = {10.1002/cbf.3791}, pmid = {36951265}, issn = {1099-0844}, abstract = {Inertial microfluidics is a high-throughput and high-efficiency cell separation approach to which attention has been progressively paid in recent years. However, research on the influencing factors that compromise the efficiency of cell separation is still lacking. Therefore, the aim of this study was to evaluate the cell separation efficiency by changing the influencing factors. A four-ring inertial focusing spiral microchannel was designed to separate two kinds of circulating tumor cells (CTCs) from blood. Human breast cancer (MCF-7) cells and human epithelial cervical cancer (HeLa) cells enter the four-ring inertial focusing spiral microchannel together with blood cells, and cancer cells and blood cells were separated from each other at the outlet of the channel by inertial force. The cell separation efficiency at the inlet flow rate in the Reynolds number range of 40-52 was studied by changing the influencing factors such as the cross-sectional shape of the microchannel, the average thickness of the cross-section, and the trapezoidal inclination angle. The results showed that the reduction of the channel thickness and the increase of a certain trapezoidal inclination enhanced the cell separation efficiency to a certain extent, the study showed that when the channel inclination was 6 ° and the average channel thickness was 160 μm. The two kinds of CTC cells could be completely separated from the blood and the efficiency could reached 100%.}, } @article {pmid36938115, year = {2023}, author = {Kitzinger, E and Leclercq, T and Marquet, O and Piot, E and Sipp, D}, title = {Attachment-line, crossflow and Tollmien-Schlichting instabilities on swept ONERA-D and Joukowski airfoils.}, journal = {Journal of fluid mechanics}, volume = {957}, number = {}, pages = {}, doi = {10.1017/jfm.2023.38}, pmid = {36938115}, issn = {0022-1120}, abstract = {Linear stability analyses are performed to investigate the boundary layer instabilities developing in an incompressible flow around the whole leading-edge of swept ONERA-D and Joukowski airfoils of infinite span. The stability analyses conducted in our study are global in the chordwise direction and local in the spanwise direction. A neutral curve is drawn at a given leading-edge Reynolds number ReR and several overlapping regions, called "lobes", are identified on a physical basis. A detailed study of the marginal modes reveals the presence of attachment-line and crossflow instabilities, as well as modes whose features do not fall within the standards of a specific type. Connected crossflow/Tollmien-Schlichting modes, that show a dominant spatial structure reminiscent of Tollmien-Schlichting waves but whose destabilization is linked to a crossflow mechanism, have been identified. The comparison of several neutral curves at different ReR values reveals the greater stabilizing effect of the increase of ReR on the crossflow instability compared to the attachment-line instability. The influence of the airfoil shape is also studied by comparing the neutral curves of the ONERA-D with the neutral curves of the Joukowski airfoil. These curves reveal similar characteristics with the presence of distinct lobes and their comparison at constant sweep angle shows that, under the conditions studied, the ONERA-D airfoil is more stable than the Joukowski airfoil, even for crossflow instabilities. The absolutely or convectively unstable nature of the flow in the spanwise direction is also tackled and our results suggest that the flow is only convectively unstable.}, } @article {pmid36936325, year = {2023}, author = {Rehman, S and Hashim, and Hassine, SBH and Tag Eldin, E and Shah, SO}, title = {Investigation of Entropy Production with Thermal Analysis under Soret and Dufour Effects in MHD Flow between Convergent and Divergent Channels.}, journal = {ACS omega}, volume = {8}, number = {10}, pages = {9121-9136}, pmid = {36936325}, issn = {2470-1343}, abstract = {Hydromagnetic flow and heat transport have sustainable importance in conventional system design along with high-performance thermal equipment and geothermal energy structures. The current computational study investigates the energy transport and entropy production due to the pressure-driven flow of non-Newtonian fluid filled inside the wedge-shaped channel. The nonlinear radiation flux and uniform magnetic field are incorporated into the flow analysis. To be more precise, non-Newtonian fluid initiates from an inlet with the bound of the parabolic profile and leaves at outlet of a convergent/divergent channel. We assume that the channel flow is adiabatic and influenced by the wall friction. The leading flow equations are modeled via the Carreau fluid model using fundamental conservation laws. The thermodynamical aspect of the system is visualized using a two-phase model and analyses of the entropy equation due to fluid friction, ohmic heating, and diffusion of heat and mass fluxes. The modeled system of equations is normalized using a dimensionless variable mechanism. The system was elevated for the significant variation of controlling parameters. The outcomes obtained from the computational investigation are validated with the theoretical results that are available in the literature. An increasing semivertex angle and Reynolds number increase the converging channel flow. In the core flow zone, an increase in the divergent semiangle causes the flow to decelerate, while near and at the channel wall it causes a slight acceleration. Outcomes designate that the main contribution to the irreversibility is due to ohmic loss, frictional loss, and heat loss. The thermal performance and entropy production is dominant for a diverging flow. The outcomes of this research will assist in comprehending the process of entropy minimization in conjunction with the flow of nanomaterials in a nonuniform channel, which is essential in engineering processes such as the creation of micro machines, supersonic Jets, nozzles, and clean energy.}, } @article {pmid36932601, year = {2023}, author = {Fan, Y and Cadot, O}, title = {Reynolds number effect on the bistable dynamic of a blunt-base bluff body.}, journal = {Physical review. E}, volume = {107}, number = {2-2}, pages = {025103}, doi = {10.1103/PhysRevE.107.025103}, pmid = {36932601}, issn = {2470-0053}, abstract = {A three-dimensional blunt-base bluff body in a uniform flow is subjected to long-time stochastic dynamics of switching between two opposite wake states. This dynamic is investigated experimentally within the Reynolds number range Re ≃10^{4} -10^{5} . Long-time statistics coupled to a sensitivity analysis to the body attitude (defined as the pitch angle of the body with respect to the incoming flow) show that the wake switching rate decreases as Re increases. Equipping the body with passive roughness elements (turbulators) modifies the boundary layers before separation, seen as the inlet condition for the wake dynamic. Depending on their location and Re, the viscous sublayer length scale and the turbulent layer thickness can be modified independently. This sensitivity analysis to the inlet condition shows that a decrease of the viscous sublayer length scale at a given turbulent layer thickness leads to a decrease in the switching rate, whereas the modification of the turbulent layer thickness has almost no effect on the switching rate.}, } @article {pmid36932550, year = {2023}, author = {Ginzburg, I and Silva, G and Marson, F and Chopard, B and Latt, J}, title = {Unified directional parabolic-accurate lattice Boltzmann boundary schemes for grid-rotated narrow gaps and curved walls in creeping and inertial fluid flows.}, journal = {Physical review. E}, volume = {107}, number = {2-2}, pages = {025303}, doi = {10.1103/PhysRevE.107.025303}, pmid = {36932550}, issn = {2470-0053}, abstract = {The goal of this work is to advance the characteristics of existing lattice Boltzmann Dirichlet velocity boundary schemes in terms of the accuracy, locality, stability, and mass conservation for arbitrarily grid-inclined straight walls, curved surfaces, and narrow fluid gaps, for both creeping and inertial flow regimes. We reach this objective with two infinite-member boundary classes: (1) the single-node "Linear Plus" (LI^{+} ) and (2) the two-node "Extended Multireflection" (EMR). The LI^{+} unifies all directional rules relying on the linear combinations of up to three pre- or postcollision populations, including their "ghost-node" interpolations and adjustable nonequilibrium approximations. On this basis, we propose three groups of LI^{+} nonequilibrium local corrections: (1) the LI_{1} ^{+} is parametrized, meaning that its steady-state solution is physically consistent: the momentum accuracy is viscosity-independent in Stokes flow, and it is fixed by the Reynolds number (Re) in inertial flow; (2) the LI_{3} ^{+} is parametrized, exact for arbitrary grid-rotated Poiseuille force-driven Stokes flow and thus most accurate in porous flow; and (3) the LI_{4} ^{+} is parametrized, exact for pressure and inertial term gradients, and hence advantageous in very narrow porous gaps and at higher Reynolds range. The directional, two-relaxation-time collision operator plays a crucial role for all these features, but also for efficiency and robustness of the boundary schemes due to a proposed nonequilibrium linear stability criterion which reliably delineates their suitable coefficients and relaxation space. Our methodology allows one to improve any directional rule for Stokes or Navier-Stokes accuracy, but their parametrization is not guaranteed. In this context, the parametrized two-node EMR class enlarges the single-node schemes to match exactness in a grid-rotated linear Couette flow modeled with an equilibrium distribution designed for the Navier-Stokes equation (NSE). However, exactness of a grid-rotated Poiseuille NSE flow requires us to perform (1) the modification of the standard NSE term for exact bulk solvability and (2) the EMR extension towards the third neighbor node. A unique relaxation and equilibrium exact configuration for grid-rotated Poiseuille NSE flow allows us to classify the Galilean invariance characteristics of the boundary schemes without any bulk interference; in turn, its truncated solution suggests how, when increasing the Reynolds number, to avoid a deterioration of the mass-leakage rate and momentum accuracy due to a specific Reynolds scaling of the kinetic relaxation collision rate. The optimal schemes and strategies for creeping and inertial regimes are then singled out through a series of numerical tests, such as grid-rotated channels and rotated Couette flow with wall-normal injection, cylindrical porous array, and Couette flow between concentric cylinders, also comparing them against circular-shape fitted FEM solutions.}, } @article {pmid36930713, year = {2023}, author = {Hu, T and Wang, H and Gomez, H}, title = {Direct van der Waals simulation (DVS) of phase-transforming fluids.}, journal = {Science advances}, volume = {9}, number = {11}, pages = {eadg3007}, doi = {10.1126/sciadv.adg3007}, pmid = {36930713}, issn = {2375-2548}, abstract = {We present the method of direct van der Waals simulation (DVS) to study computationally flows with liquid-vapor phase transformations. Our approach is based on a discretization of the Navier-Stokes-Korteweg equations, which couple flow dynamics with van der Waals' nonequilibrium thermodynamic theory of phase transformations, and opens an opportunity for first-principles simulation of a wide range of boiling and cavitating flows. The proposed algorithm enables unprecedented simulations of the Navier-Stokes-Korteweg equations involving cavitating flows at strongly under-critical conditions and 𝒪(10[5]) Reynolds number. The proposed technique provides a pathway for a fundamental understanding of phase-transforming flows with multiple applications in science, engineering, and medicine.}, } @article {pmid36929245, year = {2023}, author = {Sheikhshoaei, A and Rajabi, M}, title = {Utilizing passive elements to break time reversibility at low Reynolds number: a swimmer with one activated element.}, journal = {The European physical journal. E, Soft matter}, volume = {46}, number = {3}, pages = {15}, pmid = {36929245}, issn = {1292-895X}, abstract = {In the realm of low Reynolds number, the shape-changing biological and artificial matters need to break time reversibility in the course of their strokes to achieve motility. This necessity is well described in the so-called scallop theorem. In this work, considering low Reynolds number, a novel and versatile swimmer is proposed as an example of a new scheme to break time reversibility kinematically and, in turn, produce net motion. The swimmer consists of one sphere as a cargo or carried body, joined by one activated link with time-varying length, to another perpendicular rigid link, as the support of two passively flapping disks, at its end. The disks are free to rotate between their fixed minimum and maximum angles. The system's motion in two dimensions is simulated, and the maneuverability of the swimmer is discussed. The minimal operating parameters for steering of the swimmer are studied, and the limits of the swimmer are identified. The introduced swimming mechanism can be employed as a simple model system for biological living matters as well as artificial microswimmers.}, } @article {pmid36920868, year = {2023}, author = {Spatafora-Salazar, A and Kuei, S and Cunha, LHP and Biswal, SL}, title = {Coiling of semiflexible paramagnetic colloidal chains.}, journal = {Soft matter}, volume = {}, number = {}, pages = {}, doi = {10.1039/d3sm00066d}, pmid = {36920868}, issn = {1744-6848}, abstract = {Semiflexible filaments deform into a variety of configurations that dictate different phenomena manifesting at low Reynolds number. Harnessing the elasticity of these filaments to perform transport-related processes at the microfluidic scale requires structures that can be directly manipulated to attain controllable geometric features during their deformation. The configuration of semiflexible chains assembled from paramagnetic colloids can be readily controlled upon the application of external time-varying magnetic fields. In circularly rotating magnetic fields, these chains undergo coiling dynamics in which their ends close into loops that wrap inward, analogous to the curling of long nylon filaments under shear. The coiling is promising for the precise loading and targeted transport of small materials, however effective implementation requires an understanding of the role that field parameters and chain properties play on the coiling features. Here, we investigate the formation of coils in semiflexible paramagnetic chains using numerical simulations. We demonstrate that the size and shape of the initial coils are governed by the Mason and elastoviscous numbers, related to the field parameters and the chain bending stiffness. The size of the initial coil follows a nonmonotonic behavior with Mason number from which two regions are identified: (1) an elasticity-dependent nonlinear regime in which the coil size decreases with increasing field strength and for which loop shape tends to be circular, and (2) an elasticity-independent linear regime where the size increases with field strength and the shape become more elliptical. From the time scales associated to these regimes, we identify distinct coiling mechanisms for each case that relate the coiling dynamics to two other configurational dynamics of paramagnetic chains: wagging and folding behaviors.}, } @article {pmid36916641, year = {2023}, author = {Lim, S and Yadunandan, A and Khalid Jawed, M}, title = {Bacteria-inspired robotic propulsion from bundling of soft helical filaments at low Reynolds number.}, journal = {Soft matter}, volume = {}, number = {}, pages = {}, doi = {10.1039/d2sm01398c}, pmid = {36916641}, issn = {1744-6848}, abstract = {The bundling of flagella is known to create a "run" phase, where the bacteria moves in a nearly straight line rather than making changes in direction. Historically, mechanical explanations for the bundling phenomenon intrigued many researchers, and significant advances were made in physical models and experimental methods. Contributing to the field of research, we present a bacteria-inspired centimeter-scale soft robotic hardware platform and a computational framework for a physically plausible simulation model of the multi-flagellated robot under low Reynolds number (∼10[-1]). The fluid-structure interaction simulation couples the discrete elastic rods algorithm with the method of regularized Stokeslet segments. Contact between two flagella is handled by a penalty-based method. We present a comparison between our experimental and simulation results and verify that the simulation tool can capture the essential physics of this problem. Preliminary findings on robustness to buckling provided by the bundling phenomenon and the efficiency of a multi-flagellated soft robot are compared with the single-flagellated counterparts. Observations were made on the coupling between geometry and elasticity, which manifests itself in the propulsion of the robot by nonlinear dependency on the rotational speed of the flagella.}, } @article {pmid36907215, year = {2023}, author = {Kang, C and Mirbod, P}, title = {Transitions in Taylor-Couette flow of concentrated non-colloidal suspensions.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {381}, number = {2246}, pages = {20220126}, doi = {10.1098/rsta.2022.0126}, pmid = {36907215}, issn = {1471-2962}, abstract = {Taylor-Couette flow of concentrated non-colloidal suspensions with a rotating inner cylinder and a stationary outer one is numerically investigated. We consider suspensions of the bulk particle volume fraction ϕb = 0.2, 0.3 with the ratio of annular gap to the particle radius ε = 60 confined in a cylindrical annulus of the radius ratio (i.e. ratio of inner and outer radii) η = 0.877. Numerical simulations are performed by applying suspension-balance model and rheological constitutive laws. To observe flow patterns caused by suspended particles, the Reynolds number of the suspension, based on the bulk particle volume fraction and the rotating velocity of the inner cylinder, is varied up to 180. At high Reynolds number, modulated patterns undiscovered in the flow of a semi-dilute suspension emerge beyond a wavy vortex flow. Thus, a transition occurs from the circular Couette flow via ribbons, spiral vortex flow, wavy spiral vortex flow, wavy vortex flow and modulated wavy vortex flow for the concentrated suspensions. Moreover, friction and torque coefficients for suspensions are estimated. It turns out that suspended particles significantly enhance the torque on the inner cylinder while reducing friction coefficient and the pseudo-Nusselt number. In particular, the coefficients are reduced in the flow of more dense suspensions. This article is part of the theme issue 'Taylor-Couette and related flows on the centennial of Taylor's seminal Philosophical Transactions paper (Part 2)'.}, } @article {pmid36907213, year = {2023}, author = {Nagata, M}, title = {Taylor-Couette flow in the narrow-gap limit.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {381}, number = {2246}, pages = {20220134}, doi = {10.1098/rsta.2022.0134}, pmid = {36907213}, issn = {1471-2962}, abstract = {A Cartesian representation of the Taylor-Couette system in the vanishing limit of the gap between coaxial cylinders is presented, where the ratio, [Formula: see text], of the angular velocities, [Formula: see text] and [Formula: see text], of the inner and the outer cylinders, respectively, affects its axisymmetric flow structures. Our numerical stability study finds remarkable agreement with previous studies for the critical Taylor number, [Formula: see text], for the onset of axisymmetric instability. The Taylor number [Formula: see text] can be expressed as [Formula: see text], where [Formula: see text] (the rotation number) and [Formula: see text] (the Reynolds number) in the Cartesian system are related to the average and the difference of [Formula: see text] and [Formula: see text]. The instability sets in the region [Formula: see text], while the product of [Formula: see text] and [Formula: see text] is kept finite. Furthermore, we developed a numerical code to calculate nonlinear axisymmetric flows. It is found that the mean flow distortion of the axisymmetric flow is antisymmetric across the gap when [Formula: see text], while a symmetric part of the mean flow distortion appears additionally when [Formula: see text]. Our analysis also shows that for a finite [Formula: see text] all flows with [Formula: see text] approach the [Formula: see text] axis, so that the plane Couette flow system is recovered in the vanishing gap limit. This article is part of the theme issue 'Taylor-Couette and related flows on the centennial of Taylor's seminal Philosophical Transactions paper (Part 2)'.}, } @article {pmid36907211, year = {2023}, author = {Moazzen, M and Lacassagne, T and Thomy, V and Bahrani, SA}, title = {Friction dynamics of elasto-inertial turbulence in Taylor-Couette flow of viscoelastic fluids.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {381}, number = {2246}, pages = {20220300}, doi = {10.1098/rsta.2022.0300}, pmid = {36907211}, issn = {1471-2962}, abstract = {Dynamic properties of elasto-inertial turbulence (EIT) are studied in a Taylor-Couette geometry. EIT is a chaotic flow state that develops upon both non-negligible inertia and viscoelasticity. A combination of direct flow visualization and torque measurement allows to verify the earlier onset of EIT compared with purely inertial instabilities (and inertial turbulence). The scaling of the pseudo-Nusselt number with inertia and elasticity is discussed here for the first time. Variations in the friction coefficient, temporal frequency spectra and spatial power density spectra highlight that EIT undergoes an intermediate behaviour before transitioning to its fully developed chaotic state that requires both high inertia and elasticity. During this transition, the contribution of secondary flows to the overall friction dynamics is limited. This is expected to be of great interest in the aim of achieving efficiency mixing at low drag and low but finite Reynolds number. This article is part of the theme issue "Taylor-Couette and related flows on the centennial of Taylor's seminal Philosophical transactions paper (Part 2)".}, } @article {pmid36907210, year = {2023}, author = {Krivonosova, O and Gritsevich, M and Zhilenko, D and Read, P}, title = {Noise induced effects in the axisymmetric spherical Couette flow.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {381}, number = {2246}, pages = {20220124}, doi = {10.1098/rsta.2022.0124}, pmid = {36907210}, issn = {1471-2962}, abstract = {We study the axisymmetric, wide gap, spherical Couette flow in the presence of noise in numerical simulations and experiments. Such studies are important because most of the flows in nature are subjected to random fluctuations. Noise is introduced into the flow by adding fluctuations to the inner sphere rotation which are random in time with zero mean. Flows of a viscous incompressible fluid are induced either by rotation of the inner sphere only or by the co-rotation of the spheres. Mean flow generation was found to occur under the action of additive noise. A higher relative amplification of meridional kinetic energy compared to the azimuthal component was also observed under certain conditions. Calculated flow velocities were validated by laser Doppler anemometer measurements. A model is proposed to elucidate the rapid growth of meridional kinetic energy for flows induced by varying the co-rotation of the spheres. Our linear stability analysis for flows induced by the rotation of the inner sphere revealed a decrease in the critical Reynolds number, corresponding to the onset of the first instability. Also, in this case, a local minimum of the mean flow generation on approaching the critical Reynolds number was observed, which is consistent with the available theoretical predictions. This article is part of the theme issue 'Taylor-Couette and related flows on the centennial of Taylor's seminal Philosophical Transactions paper (Part 2)'.}, } @article {pmid36903819, year = {2023}, author = {Akram, S and Athar, M and Saeed, K and Razia, A and Muhammad, T and Alghamdi, HA}, title = {Mechanism of Double-Diffusive Convection on Peristaltic Transport of Thermally Radiative Williamson Nanomaterials with Slip Boundaries and Induced Magnetic Field: A Bio-Nanoengineering Model.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {13}, number = {5}, pages = {}, doi = {10.3390/nano13050941}, pmid = {36903819}, issn = {2079-4991}, abstract = {The present work has mathematically modeled the peristaltic flow in nanofluid by using thermal radiation, induced a magnetic field, double-diffusive convection, and slip boundary conditions in an asymmetric channel. Peristalsis propagates the flow in an asymmetric channel. Using the linear mathematical link, the rheological equations are translated from fixed to wave frames. Next, the rheological equations are converted to nondimensional forms with the help of dimensionless variables. Further, the flow evaluation is determined under two scientific assumptions: a finite Reynolds number and a long wavelength. Mathematica software is used to solve the numerical value of rheological equations. Lastly, the impact of prominent hydromechanical parameters on trapping, velocity, concentration, magnetic force function, nanoparticle volume fraction, temperature, pressure gradient, and pressure rise are evaluated graphically.}, } @article {pmid36902954, year = {2023}, author = {Liu, C and Wang, W and Hu, X and Liu, F}, title = {Drag Reduction Technology of Water Flow on Microstructured Surfaces: A Novel Perspective from Vortex Distributions and Densities.}, journal = {Materials (Basel, Switzerland)}, volume = {16}, number = {5}, pages = {}, doi = {10.3390/ma16051838}, pmid = {36902954}, issn = {1996-1944}, abstract = {Revealing the turbulent drag reduction mechanism of water flow on microstructured surfaces is beneficial to controlling and using this technology to reduce turbulence losses and save energy during water transportation. Two microstructured samples, including a superhydrophobic and a riblet surface, were fabricated near which the water flow velocity, and the Reynolds shear stress and vortex distribution were investigated using a particle image velocimetry. The dimensionless velocity was introduced to simplify the Ω vortex method. The definition of vortex density in water flow was proposed to quantify the distribution of different strength vortices. Results showed that the velocity of the superhydrophobic surface (SHS) was higher compared with the riblet surface (RS), while the Reynolds shear stress was small. The vortices on microstructured surfaces were weakened within 0.2 times that of water depth when identified by the improved ΩM method. Meanwhile, the vortex density of weak vortices on microstructured surfaces increased, while the vortex density of strong vortices decreased, proving that the reduction mechanism of turbulence resistance on microstructured surfaces was to suppress the development of vortices. When the Reynolds number ranged from 85,900 to 137,440, the drag reduction impact of the superhydrophobic surface was the best, and the drag reduction rate was 9.48%. The reduction mechanism of turbulence resistance on microstructured surfaces was revealed from a novel perspective of vortex distributions and densities. Research on the structure of water flow near the microstructured surface can promote the drag reduction application in the water field.}, } @article {pmid36899067, year = {2023}, author = {Suresh Kumar, Y and Hussain, S and Raghunath, K and Ali, F and Guedri, K and Eldin, SM and Khan, MI}, title = {Numerical analysis of magnetohydrodynamics Casson nanofluid flow with activation energy, Hall current and thermal radiation.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {4021}, pmid = {36899067}, issn = {2045-2322}, abstract = {In this study we analyzed the flow, heat and mass transfer behavior of Casson nanofluid past an exponentially stretching surface under the impact of activation energy, Hall current, thermal radiation, heat source/sink, Brownian motion and thermophoresis. Transverse magnetic field with the assumption of small Reynolds number is implemented vertically. The governing partial nonlinear differential equations of the flow, heat and mass transfer are transformed into ordinary differential equations by using similarity transformation and solved numerically by using Matlab bvp4c package. The impact of each of the Hall current parameter, thermal radiation parameter, heat source/sink parameter, Brownian motion parameter, Prandtl number, thermophoresis parameter and magnetic parameter on velocity, concentration and temperature, is discussed through graphs. The skin friction coefficient along the x-and z-directions, the local Nusselt number and the Sherwood number are calculated numerically to look into the inside behavior of the emerging parameters. It is witnessed that the flow velocity is a diminishing function of the thermal radiation parameter and the behavior has observed in the case of Hall parameter. Moreover, mounting values of Brownian motion parameter reduce the nanoparticle concentration profile.}, } @article {pmid36897856, year = {2023}, author = {Bae, AJ and Ahmad, R and Bodenschatz, E and Pumir, A and Gholami, A}, title = {Flagellum-driven cargoes: Influence of cargo size and the flagellum-cargo attachment geometry.}, journal = {PloS one}, volume = {18}, number = {3}, pages = {e0279940}, doi = {10.1371/journal.pone.0279940}, pmid = {36897856}, issn = {1932-6203}, abstract = {The beating of cilia and flagella, which relies on an efficient conversion of energy from ATP-hydrolysis into mechanical work, offers a promising way to propel synthetic cargoes. Recent experimental realizations of such micro-swimmers, in which micron-sized beads are propelled by isolated and demembranated flagella from the green algae Chlamydomonas reinhardtii (C. reinhardtii), revealed a variety of propulsion modes, depending in particular on the calcium concentration. Here, we investigate theoretically and numerically the propulsion of a bead as a function of the flagellar waveform and the attachment geometries between the bead and the flagellum. To this end, we take advantage of the low Reynolds number of the fluid flows generated by the micro-swimmer, which allows us to neglect fluid inertia. By describing the flagellar waveform as a superposition of a static component and a propagating wave, and using resistive-force theory, we show that the asymmetric sideways attachment of the flagellum to the bead makes a contribution to the rotational velocity of the micro-swimmer that is comparable to the contribution caused by the static component of the flagellar waveform. Remarkably, our analysis reveals the existence of a counter-intuitive propulsion regime in which an increase in the size of the cargo, and hence its drag, leads to an increase in some components of the velocity of the bead. Finally, we discuss the relevance of the uncovered mechanisms for the fabrication of synthetic, bio-actuated medical micro-robots for targeted drug delivery.}, } @article {pmid36895389, year = {2023}, author = {Lei, Y and Wang, X and Zhou, D and Qiu, T and Jin, W and Qin, C and Zhou, D}, title = {Experimental investigation on high-pressure methane jet characteristic single-hole injector.}, journal = {Heliyon}, volume = {9}, number = {3}, pages = {e13645}, doi = {10.1016/j.heliyon.2023.e13645}, pmid = {36895389}, issn = {2405-8440}, abstract = {High-pressure gas direct injection (DI) technology benefits engines with high efficiency and clean emissions, and the gas jet process causes crucial effects especially inside an mm-size space. This study presents an investigation on the high-pressure methane jet characteristics from a single-hole injector by analysing jet performance parameters including jet impact force, gas jet impulse, and jet mass flow rate. The results show that the methane jet exhibited a two-zone behaviour along the jet direction in the spatial dimension induced by high-speed jet flow from the nozzle: zone 1 near the nozzle-the jet impact force and jet impulse increased consistently except for a fluctuation due to shock wave effects induced by the sonic jet and no entrainment occurs, and zone II farther away from the nozzle-the jet impact force and jet impulse became stable when the shock wave effects became weak and the jet impulse was conserved with a linear conservation boundary. The Mach disk height was exactly the turning point of two zones. Moreover, the methane jet parameters, such as the methane jet mass flow rate, jet initial jet impact force, jet impulse, and Reynolds number had a monotonous and linearly increasing correlation with injection pressure.}, } @article {pmid36890189, year = {2023}, author = {Vieira, GS and Allshouse, MR and Mahadevan, A}, title = {Seagrass deformation affects fluid instability and tracer exchange in canopy flow.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {3910}, pmid = {36890189}, issn = {2045-2322}, abstract = {Monami is the synchronous waving of a submerged seagrass bed in response to unidirectional fluid flow. Here we develop a multiphase model for the dynamical instabilities and flow-driven collective motions of buoyant, deformable seagrass. We show that the impedance to flow due to the seagrass results in an unstable velocity shear layer at the canopy interface, leading to a periodic array of vortices that propagate downstream. Our simplified model, configured for unidirectional flow in a channel, provides a better understanding of the interaction between these vortices and the seagrass bed. Each passing vortex locally weakens the along-stream velocity at the canopy top, reducing the drag and allowing the deformed grass to straighten up just beneath it. This causes the grass to oscillate periodically even in the absence of water waves. Crucially, the maximal grass deflection is out of phase with the vortices. A phase diagram for the onset of instability shows its dependence on the fluid Reynolds number and an effective buoyancy parameter. Less buoyant grass is more easily deformed by the flow and forms a weaker shear layer, with smaller vortices and less material exchange across the canopy top. While higher Reynolds number leads to stronger vortices and larger waving amplitudes of the seagrass, waving amplitude is maximized at intermediate grass buoyancy. All together, our theory and computations develop an updated schematic of the instability mechanism consistent with experimental observations.}, } @article {pmid36889000, year = {2023}, author = {Zhu, Q}, title = {Wall effect on the start maneuver of a jet swimmer.}, journal = {Bioinspiration & biomimetics}, volume = {}, number = {}, pages = {}, doi = {10.1088/1748-3190/acc293}, pmid = {36889000}, issn = {1748-3190}, abstract = {Inspired by aquatic creatures such as squid, the novel propulsion method based on pulsed jetting is a promising way to achieve high speed and high maneuverability for soft-body robots. Since these robots are often designed to operate in confined space with complicated boundary conditions, it is critical to understand their dynamics in the vicinity of solid boundaries. In this study we numerically examine the start maneuver of an idealized jet swimmer near a wall. Our simulations illustrate three important mechanisms: 1) Due to the blocking effect of the wall the pressure inside the body is affected so that the forward acceleration is increased during deflation and decreased during inflation; 2) The wall affects the internal flow so that the momentum flux at the nozzle and subsequently the thrust generation during the jetting phase are slightly increased; 3) the wall affects the wake so that the refilling phase is influenced, leading to a scenario in which part of the energy expended during jetting is recovered during refilling to increase forward acceleration and reduce power expenditure. In general, the second mechanism is weaker than the other two. The exact effects of these mechanisms depend on physical parameters such as the initial phase of the body deformation, the distance between the swimming body and the wall, and the Reynolds number.}, } @article {pmid36888616, year = {2023}, author = {Gao, P and Wang, Q and Liu, T}, title = {Numerical method investigation on the aggregation characteristics of non-spherical particles.}, journal = {PloS one}, volume = {18}, number = {3}, pages = {e0282804}, doi = {10.1371/journal.pone.0282804}, pmid = {36888616}, issn = {1932-6203}, abstract = {Under the background of the mechanical mechanism research of microfluidic technology for separating and screening pipeline particulate matter, this paper proposes an improved relative motion model by combining the multiple reference frame method and the relative motion model. Worked with a quasi-fixed constant method, this model can numerically calculate the aggregation features of non-spherical particles in the low Reynolds number channels. The results demonstrate that when Re = 40~80, ellipsoids exhibit an aggregation trend similar to circular particles with the same diameter as its largest circumscribed sphere. The aggregation position is affected by the ratio of long and short axes of particles, and the distribution trend is determined by the relative size of these particles. When the channel's Reynolds number is less than the critical Reynolds number, the aggregation position of elliptical particles will be closer to the pipe center with the increase in the Reynolds number, which is contrary to the aggregation tendency of circular particles more proximate to the pipe wall with the increase in the Reynolds number. This finding provides a novel idea and method for further exploring the aggregation rules of non-spherical particles and offers substantial guidance for separating and monitoring pipeline particulate matter via microfluidic technology and other related industrial applications.}, } @article {pmid36871543, year = {2023}, author = {Ram, D and Bhandari, DS and Sharma, K and Tripathi, D}, title = {Progression of blood-borne viruses through bloodstream: A comparative mathematical study.}, journal = {Computer methods and programs in biomedicine}, volume = {232}, number = {}, pages = {107425}, doi = {10.1016/j.cmpb.2023.107425}, pmid = {36871543}, issn = {1872-7565}, abstract = {BACKGROUND AND OBJECTIVES: Blood-borne pathogens are contagious microorganisms that can cause life-threatening illnesses, and are found in human blood. It is crucial to examine how these viruses spread through blood flow in the blood vessel. Keeping that in view, this study aims to determine how blood viscosity, and diameter of the viruses can affect the virus transmission through the blood flow in the blood vessel. A comparative study of bloodborne viruses (BBVs) such as HIV, Hepatitis B, and C, has been addressed in the present model. A couple stress fluid model is used to represent blood as a carrying medium for virus transmission. The Basset-Boussinesq-Oseen equation is taken into account for the simulation of virus transmission.

METHODS: An analytical approach to derive the exact solutions under the assumption of long wavelength and low Reynolds number approximations is employed. For the computation of the results, a segment (wavelength) of blood vessels about 120 mm with wave velocities in the range of 49 - 190 mm/sec are considered, where the diameter of BBVs ranges from 40-120 nm. The viscosity of the blood varies from 3.5-5.5 × 10[-3]Ns/m[2] which affect the virion motion having a density range 1.03 - 1. 25 g/m[3].

RESULTS: It shows that the Hepatitis B virus is more harmful than other blood-borne viruses considered in the analysis. Patients with high blood pressure are highly susceptible for transmission of BBVs.

CONCLUSIONS: The present fluid dynamics approach for virus spread through blood flow can be helpful in understanding the dynamics of virus propagation inside the human circulatory system.}, } @article {pmid36869078, year = {2023}, author = {Ashin, K and Girishkumar, MS and D'Asaro, E and Jofia, J and Sherin, VR and Sureshkumar, N and Rao, EPR}, title = {Observational evidence of salt finger in the diurnal thermocline.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {3627}, pmid = {36869078}, issn = {2045-2322}, abstract = {Due to strong turbulent mixing, the ocean surface boundary layer region is generally not conducive to double diffusion. However, vertical microstructure profiles observations in the northeastern Arabian Sea during May 2019 imply the formation of salt fingers in the diurnal thermocline (DT) region during the daytime. In the DT layer, conditions are favorable for salt fingering: Turner angle values are between 50 and 55° with both temperature and salinity decreasing with depth; shear-driven mixing is weak with a turbulent Reynolds number of about 30. The presence of salt fingering in the DT is confirmed by the presence of staircase-like structures with step sizes larger than the Ozmidov length and by the dissipation ratio that is larger than the mixing coefficient. The unusual daytime salinity maximum in the mixed layer that supports salt fingering is primarily due to a daytime reduction in vertical entrainment of fresh water along with minor contributions from evaporation and horizontal advection and a significant contribution from detrainment processes.}, } @article {pmid36858981, year = {2023}, author = {Arif, I and Leung, RCK and Naseer, MR}, title = {A computational study of trailing edge noise suppression with embedded structural compliance.}, journal = {JASA express letters}, volume = {3}, number = {2}, pages = {023602}, doi = {10.1121/10.0017321}, pmid = {36858981}, issn = {2691-1191}, abstract = {A unique concept for suppression of trailing edge noise scattering from a splitter plate in a low Reynolds number flow is proposed. The key idea of the concept is the adoption of a structural compliance system embedded with a finite number of elastic panels. Specific compliance system designs are devised for promotion of panel structural resonance that effectively absorbs broadband flow/acoustic fluctuation energy responsible for noise scattering. The concept is examined using high-fidelity direct aeroacoustic simulation together with spatiotemporal aeroacoustic-structural interaction analysis. The concept is confirmed feasible and outperforms many similar trailing edge noise reduction approaches reported in the literature.}, } @article {pmid36853773, year = {2023}, author = {Stricker, M and Littfinski, T and Pecher, KH and Lübken, M and Wichern, M}, title = {Hydraulic modeling of a compact stormwater treatment device applying concepts of dynamic similitude.}, journal = {Water science and technology : a journal of the International Association on Water Pollution Research}, volume = {87}, number = {4}, pages = {954-968}, doi = {10.2166/wst.2023.025}, pmid = {36853773}, issn = {0273-1223}, abstract = {The development of compact treatment devices (CTDs) with high removal efficiencies and low space requirements is a key objective of urban stormwater treatment. Thus, many devices utilize a combination of sedimentation and upward-flow filtration in a single system. Here, sedimentation is used before filtration, which makes it difficult to evaluate the individual treatment stages separately. This study determines the removal efficiency by sedimentation and the expected filter load in a specific compact treatment device designed for a catchment area of up to 10,000 m[2]. In contrast to a full-scale investigation, small-scale physical hydraulic modeling is applied as a new cost-saving alternative. To validate upscaling laws, tracer signals and particle-size-specific removal efficiencies are determined for two geometrically similar models at different length scales. Thereby, Reynolds number similarity produces similar flow patterns, while the similarity of Hazen numbers allows to upscale removal efficiencies. Upscaling to the full-scale reveals that the filter in the device is only partly loaded by particulate matter that consists mostly of particles ≤63 μm. Thus, sedimentation upstream of a filter is of relevant importance in CTDs. The proposed dimensionless relationship may be used for particles from different catchments and helps to size the device accordingly.}, } @article {pmid36842977, year = {2023}, author = {Lyubimova, TP and Fomicheva, AA and Ivantsov, AO}, title = {Dynamics of a bubble in oscillating viscous liquid.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {381}, number = {2245}, pages = {20220085}, doi = {10.1098/rsta.2022.0085}, pmid = {36842977}, issn = {1471-2962}, abstract = {This article is devoted to the investigation of gaseous bubble dynamics in oscillating viscous liquids of different density values. The study is conducted numerically using the level-set method with a non-stationary approach. The bubble is initially located near the upper wall of the container. The effects of the inclusion and host liquid viscosities on interaction of the bubble with the wall are analysed. The calculations show that in the absence of gravity, for low-viscosity fluids the bubble is attracted to the nearest wall, which is consistent with previous analytical and experimental results. With increasing viscosity, the vibrational attraction to the wall becomes weaker and is then replaced by repulsion, which can be explained by the decelerative effect of viscosity in the boundary layer near the rigid surface, where the average flow becomes less intensive. The dependencies of the repulsion force on the parameter values are obtained by using the balance method (investigation of the gravity level needed to attain the quasi-equilibrium state at a certain distance between the bubble and the wall). The calculations show that the repulsion force grows with decreasing Reynolds number (increase of the viscosity). This article is part of the theme issue 'New trends in pattern formation and nonlinear dynamics of extended systems'.}, } @article {pmid36842115, year = {2023}, author = {Abe, K and Takabe, K and Nakamura, S}, title = {Force Measurement of Bacterial Swimming Using Optical Tweezers.}, journal = {Methods in molecular biology (Clifton, N.J.)}, volume = {2646}, number = {}, pages = {169-179}, pmid = {36842115}, issn = {1940-6029}, abstract = {Velocity is a physical parameter most commonly used to quantify bacterial swimming. In the steady-state motion at a low Reynolds number, the swimming force can be estimated from the swimming velocity and the drag coefficient based on the assumption that the swimming force balances with the drag force exerted on the bacterium. Though the velocity-force relation provides a significant clue to understand the swimming mechanism, the odd configuration of bacteria could develop problems with the accuracy of the force estimation. This chapter describes the force measurement using optical tweezers. The method uses parameters obtained from the shape and movement of a microsphere attached to the bacteria, improving the quantitativeness of force measurement.}, } @article {pmid36828913, year = {2023}, author = {Omrani, V and Targhi, MZ and Rahbarizadeh, F and Nosrati, R}, title = {High-throughput isolation of cancer cells in spiral microchannel by changing the direction, magnitude and location of the maximum velocity.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {3213}, pmid = {36828913}, issn = {2045-2322}, abstract = {Circulating tumor cells (CTCs) are scarce cancer cells that rarely spread from primary or metastatic tumors inside the patient's bloodstream. Determining the genetic characteristics of these paranormal cells provides significant data to guide cancer staging and treatment. Cell focusing using microfluidic chips has been implemented as an effective method for enriching CTCs. The distinct equilibrium positions of particles with different diameters across the microchannel width in the simulation showed that it was possible to isolate and concentrate breast cancer cells (BCCs) from WBCs at a moderate Reynolds number. Therefore we demonstrate high throughput isolation of BCCs using a passive, size-based, label-free microfluidic method based on hydrodynamic forces by an unconventional (combination of long loops and U-turn) spiral microfluidic device for isolating both CTCs and WBCs with high efficiency and purity (more than 90%) at a flow rate about 1.7 mL/min, which has a high throughput compared to similar ones. At this golden flow rate, up to 92% of CTCs were separated from the cell suspension. Its rapid processing time, simplicity, and potential ability to collect CTCs from large volumes of patient blood allow the practical use of this method in many applications.}, } @article {pmid36827557, year = {2023}, author = {Moore, CP and Husson, J and Boudaoud, A and Amselem, G and Baroud, CN}, title = {Clogging of a Rectangular Slit by a Spherical Soft Particle.}, journal = {Physical review letters}, volume = {130}, number = {6}, pages = {064001}, doi = {10.1103/PhysRevLett.130.064001}, pmid = {36827557}, issn = {1079-7114}, abstract = {The capture of a soft spherical particle in a rectangular slit leads to a nonmonotonic pressure-flow rate relation at low Reynolds number. Simulations reveal that the flow induced deformations of the trapped particle focus the streamlines and pressure drop to a small region. This increases the resistance to flow by several orders of magnitude as the driving pressure is increased. As a result, two regimes are observed in experiments and simulations: a flow-dominated regime for small particle deformations, where flow rate increases with pressure, and an elastic-dominated regime in which solid deformations block the flow.}, } @article {pmid36820228, year = {2023}, author = {Baba, YD and Chiacchia, M and Patwardhan, SV}, title = {A Novel Method for Understanding the Mixing Mechanisms to Enable Sustainable Manufacturing of Bioinspired Silica.}, journal = {ACS engineering Au}, volume = {3}, number = {1}, pages = {17-27}, pmid = {36820228}, issn = {2694-2488}, abstract = {Bioinspired silica (BIS) has received unmatched attention in recent times owing to its green synthesis, which offers a scalable, sustainable, and economical method to produce high-value silica for a wide range of applications, including catalysis, environmental remediation, biomedical, and energy storage. To scale-up BIS synthesis, it is critically important to understand how mixing affects the reaction at different scales. In particular, successful scale-up can be achieved if mixing time is measured, modeled, and kept constant across different production scales. To this end, a new image analysis technique was developed using pH, as one of the key parameters, to monitor the reaction and the mixing. Specifically, the technique involved image analysis of color (pH) change using a custom-written algorithm to produce a detailed pH map. The degree of mixing and mixing time were determined from this analysis for different impeller speeds and feed injection locations. Cross validation of the mean pH of selected frames with measurements using a pH calibration demonstrated the reliability of the image processing technique. The results suggest that the bioinspired silica formation is controlled by meso- and, to a lesser extent, micromixing. Based on the new data from this investigation, a mixing time correlation is developed as a function of Reynolds number-the first of a kind for green nanomaterials. Further, we correlated the effects of mixing conditions on the reaction and the product. These results provide valuable insights into the scale-up to enable sustainable manufacturing of BIS and other nanomaterials.}, } @article {pmid36813941, year = {2023}, author = {Han, F and Zhao, Y and Liu, M and Hu, F and Peng, Y and Ma, L}, title = {Wetting behavior during impacting bituminous coal surface for dust suppression droplets of fatty alcohol polyoxyethylene ether.}, journal = {Environmental science and pollution research international}, volume = {}, number = {}, pages = {}, pmid = {36813941}, issn = {1614-7499}, abstract = {The wetting behavior of droplets during impacting coal surface widely exists in the dust control process. Understanding the effect of surfactants on the diffusion of water droplets on coal surface is critical. To study the effect of fatty alcohol polyoxyethylene ether (AEO) on the dynamic wetting behavior of droplets on bituminous coal surface, a high-speed camera is used to record the impact process of ultrapure water droplets and three different molecular weight AEO solution droplets. A dynamic evaluation index, dimensionless spreading coefficient ([Formula: see text]), is used to evaluate the dynamic wetting process. The research results show that maximum dimensionless spreading coefficient ([Formula: see text]) of AEO-3, AEO-6, and AEO-9 droplets is greater than that of ultrapure water droplets. With the increase of impact velocity, the [Formula: see text] increases, but the required time decreases. Moderately increasing the impact velocity is conducive to promoting the spreading of droplets on the coal surface. Below the critical micelle concentration (CMC), the concentration of AEO droplets is positively correlated with the [Formula: see text] and the required time. When the polymerization degree increases, the Reynolds number ([Formula: see text]) and Weber number ([Formula: see text]) of droplets decrease, and the [Formula: see text] decreases. AEO can effectively enhance the spreading of droplets on the coal surface, but the increase in polymerization degree can inhibit this process. Viscous force hinders droplet spreading during droplet interaction with the coal surface, and surface tension promotes droplet retraction. Under the experimental conditions of this paper ([Formula: see text], [Formula: see text]), there is a power exponential relationship between [Formula: see text] and [Formula: see text].}, } @article {pmid36813725, year = {2023}, author = {Rahimi, A and Shahsavari, A and Pakzad, H and Moosavi, A and Nouri-Borujerdi, A}, title = {Laminar drag reduction ability of liquid-infused microchannels by considering different infused lubricants.}, journal = {The Journal of chemical physics}, volume = {158}, number = {7}, pages = {074702}, doi = {10.1063/5.0137100}, pmid = {36813725}, issn = {1089-7690}, abstract = {We numerically investigate the pressure drop reduction (PDR) performance of microchannels equipped with liquid-infused surfaces, along with determining the shape of the interface between the working fluid and lubricant within the microgrooves. The effects of different parameters, such as the Reynolds number of working fluid, density and viscosity ratios between the lubricant and working fluid, the ratio of the thickness of the lubricant layer over the ridges to the depth of the groove, and the Ohnesorge number as a representative of the interfacial tension, on the PDR and interfacial meniscus within the microgrooves are comprehensively studied. The results reveal that the density ratio and Ohnesorge number do not significantly affect the PDR. On the other hand, the viscosity ratio considerably affects the PDR, and a maximum PDR of 62% compared to a smooth non-lubricated microchannel is achieved for a viscosity ratio of 0.01. Interestingly, the higher the Reynolds number of the working fluid, the higher the PDR. The meniscus shape within the microgrooves is strongly affected by the Reynolds number of the working fluid. Despite the insignificant effect of interfacial tension on the PDR, the interface shape within the microgrooves is appreciably influenced by this parameter.}, } @article {pmid36810678, year = {2023}, author = {O'Callaghan, F and Lehmann, FO}, title = {Flow development and leading edge vorticity in bristled insect wings.}, journal = {Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology}, volume = {}, number = {}, pages = {}, pmid = {36810678}, issn = {1432-1351}, abstract = {Small flying insects such as the tiny thrip Gynaikothrips ficorum have wings with bristles attached to a solid shaft instead of solid membranes. Air passing through the bristle fringe, however, makes bristled insect wings less effective for aerodynamic force production. In this study, we quantified the ability of bristled wings to generate a leading edge vortex (LEV) for lift support during wing flapping, scored its circulation during wing translation, and investigated its behaviour at the stroke reversals. The data were measured in robotic model wings flapping with a generic kinematic pattern at Reynolds number of ~ 3.4, while applying two-dimensional particle image velocimetry. We found that aerodynamic performance due to LEV circulation linearly decreases with increasing bristle spacing. The wings of Gynaikothrips ficorum might thus produce approximately 9% less aerodynamic force for flight than a solid membranous wing. At the stroke reversals, leading and trailing edge vortices dissipate quickly within no more than ~ 2% of the stroke cycle duration. This elevated dissipation makes vortex shedding obsolete during the reversals and allows a quick build-up of counter-vorticity when the wing reverses flapping direction. In sum, our findings highlight the flow conditions associated with bristled wing design in insects and are thus significant for assessing biological fitness and dispersal of insects flying in a viscosity-dominated fluid regime.}, } @article {pmid36789875, year = {2023}, author = {Hamlet, CL and Strickland, WC and Battista, N and Miller, LA}, title = {Multiscale flow between the branches and polyps of gorgonians.}, journal = {The Journal of experimental biology}, volume = {}, number = {}, pages = {}, doi = {10.1242/jeb.244520}, pmid = {36789875}, issn = {1477-9145}, abstract = {Gorgonians, including sea fans, are soft corals well known for their elaborate branching structure and how they sway in the ocean. This branching structure can modify environmental flows to be beneficial for feeding in a particular range of velocities and, presumably, for a particular size of prey. As water moves through the elaborate branches, it is slowed, and recirculation zones can form downstream of the colony. At the smaller scale, individual polyps that emerge from the branches expand their tentacles, further slowing the flow. At the smallest scale, the tentacles are covered in tiny pinnules where exchange occurs. In this paper, we quantify the gap to diameter ratios for various gorgonians at the scale of the branches, the polyp tentacles, and the pinnules. We then use computational fluid dynamics to determine the flow patterns at all three levels of branching. We quantify the leakiness between the branches, tentacles, and pinnules over the biologically relevant range of Reynolds numbers and gap-to-diameter ratios. We find that the branches and tentacles can either act as leaky rakes or solid plates depending upon these dimensionless parameters. The pinnules, on the other hand, mostly impede the flow. Using an agent-based modeling framework, we quantify plankton capture as a function of the gap-to-diameter ratio of the branches and the Reynolds number. We find that the capture rate depends critically on both morphology and Reynolds number. The results of the study have implications for how gorgonians modify ambient flows for efficient feeding and exchange.}, } @article {pmid36785427, year = {2023}, author = {Liu, W and Yu, Z and Duan, F and Hu, H and Fu, X and Bao, R}, title = {Robust five-degree-of-freedom measurement system with self-compensation and air turbulence protection.}, journal = {Optics express}, volume = {31}, number = {3}, pages = {4652-4666}, doi = {10.1364/OE.480772}, pmid = {36785427}, issn = {1094-4087}, abstract = {A robust five-degree-of-freedom (5-DOF) measurement system is proposed in this paper. The compact optical configuration with high resolution is designed based on lens combination and multiple reflections. Beam drift and dual-beam parallelism are monitored and compensated by autocollimator units and a polarizer unit respectively. In addition, a protection method is proposed to reduce the intensity of air turbulence by reducing the Reynolds number of the beam path. The performance of the system is verified by experiments. The experimental results show that the self-compensation methods and air turbulence protection can effectively improve the accuracy and stability of the system under the long-term interference of external environments. The proposed system has high precision, desirable robustness, and convenient pre-calibration, which can be used for error measurement of precision machines.}, } @article {pmid36779398, year = {2023}, author = {Millett, PC}, title = {Rheology and structure of elastic capsule suspensions within rectangular channels.}, journal = {Soft matter}, volume = {}, number = {}, pages = {}, doi = {10.1039/d3sm00055a}, pmid = {36779398}, issn = {1744-6848}, abstract = {Three-dimensional simulations of the pressure-driven flow dynamics of elastic capsule suspensions within both slit and rectangular cross-section channels are presented. The simulations utilize the Immersed Boundary Method and the Lattice-Boltzmann Method models. The capsule volume fraction is fixed at 0.1 (i.e., a semi-dilute suspension), while the channel Reynolds number (Re), the capillary number (Ca), and the cross-sectional channel dimensions are systematically varied. Comparing results for slit and rectangular channels, it is found that multi-directional confinement hinders inertial focusing due to the capsule-free layers that develop in the two transverse directions. Furthermore, the thicknesses of the capsule-free layers in the two transverse directions differ when the height and width of the channel are not equal. Both the size and aspect ratio of the channel impact the apparent viscosity. It is found that square channels exhibit maximal viscosity and that holding one dimension fixed while increasing or decreasing the other results in a decrease in viscosity. The results therefore represent an expansion of the Fahraeus-Lindqvist effect from 1D cylindrical channels to 2D rectangular channels.}, } @article {pmid36736259, year = {2023}, author = {Yang, G and Yu, Z and Baki, ABM and Yao, W and Ross, M and Chi, W and Zhang, W}, title = {Settling behaviors of microplastic disks in water.}, journal = {Marine pollution bulletin}, volume = {188}, number = {}, pages = {114657}, doi = {10.1016/j.marpolbul.2023.114657}, pmid = {36736259}, issn = {1879-3363}, abstract = {Microplastic (MP) disks have not been studied for settling behaviors in aquatic environments, which affects the transport and fate of MPs. Therefore, settling experiments were conducted on MP disks of three shapes and four common-seen materials. Lighter MP disks (with density ρs = 1.038 g/cm[3] and length l ≤ 5 mm) followed rectilinear vertical trajectories, while heavier MP disks (ρs = 1.161-1.343 g/cm[3] and l = 5 mm) followed zigzag trajectories with oscillations and rotations. The mean terminal settling velocities of MP disks were 19.6-48.8 mm/s. Instantaneous settling velocities of heavier MP disks fluctuated. Existing formulas could not accurately predict the settling velocity of MP disks; thus, a new model was proposed with an error of 15.5 %. Finally, the Red - I* diagram (Red is the disk Reynolds number and I* is the dimensionless moment of inertia) was extended for MP disks to predict settling trajectories.}, } @article {pmid36733611, year = {2022}, author = {Fahim, T and Laouedj, S and Abderrahmane, A and Driss, Z and Tag-ElDin, ESM and Guedri, K and Younis, O}, title = {Numerical study of perforated obstacles effects on the performance of solar parabolic trough collector.}, journal = {Frontiers in chemistry}, volume = {10}, number = {}, pages = {1089080}, pmid = {36733611}, issn = {2296-2646}, abstract = {The current work presents and discusses a numerical analysis of improving heat transmission in the receiver of a parabolic trough solar collector by introducing perforated barriers. While the proposed approach to enhance the collector's performance is promising, the use of obstacles results in increased pressure loss. The Computational Fluid Dynamics (CFD) model analysis is conducted based on the renormalization-group (RNG) k-ɛ turbulent model associated with standard wall function using thermal oil D12 as working fluid The thermo-hydraulic analysis of the receiver tube with perforated obstacles is taken for various configurations and Reynolds number ranging from 18,860 to 81,728. The results are compared with that of the receiver without perforated obstacles. The receiver tube with three holes (PO3) showed better heat transfer characteristics. In addition, the Nusselt number (Nu) increases about 115% with the increase of friction factor 5-6.5 times and the performance evaluation criteria (PEC) changes from 1.22 to 1.24. The temperature of thermal oil fluid attains its maximum value at the exit, and higher temperatures (462.1 K) are found in the absorber tube with perforated obstacles with three holes (PO3). Accordingly, using perforated obstacles receiver for parabolic trough concentrator is highly recommended where significant enhancement of system's performance is achieved.}, } @article {pmid36725545, year = {2023}, author = {Chen, X and Sun, S and Tian, X and Liu, L and Yang, J}, title = {A quasi-two-dimensional fluid experimental apparatus based on tank-in-tank configuration.}, journal = {The Review of scientific instruments}, volume = {94}, number = {1}, pages = {015115}, doi = {10.1063/5.0125679}, pmid = {36725545}, issn = {1089-7623}, abstract = {The fluid tank is an essential facility for experimental research on fluid mechanics. However, owing to the hydrostatic fluid pressure, a fine uniformity of the narrow channel is difficult to be maintained in a tall narrow-channel tank. To address this issue, we proposed a quasi-two-dimensional fluid experimental apparatus based on a "tank-in-tank" configuration and built with an outer tank and an inner tank. The outer tank was cuboid-shaped and used to load the fluid medium, while the inner tank, consisting of two parallel glass plates, was embedded into the outer tank and served as the experimental channel. The hydrostatic pressure acting on the channel was balanced so that a high level of uniformity was maintained over the whole channel. The available height and width of the channel were 2800 and 1500 mm, respectively, while its gap distance could be adaptive from 0 to 120 mm. Experimental research on motion characteristics of circular disks falling in the quasi-2D channel was implemented to investigate the effects of the falling environment and disk geometry. Four distinct falling types were observed, and the wake flow fields of the falling disks were visualized. The Reynolds numbers of falling disks ranged from 400 to 63 000 presently. Chaotic motion and regular motion were demarcated at Re ≈ 30 000. An analytical model was established to predict the final average falling velocity and Reynolds number. Finally, potential directions for future research and improvements to the apparatus were suggested.}, } @article {pmid36718068, year = {2017}, author = {Niu, Z and Wang, R and Jiao, K and Du, Q and Yin, Y}, title = {Direct numerical simulation of low Reynolds number turbulent air-water transport in fuel cell flow channel.}, journal = {Science bulletin}, volume = {62}, number = {1}, pages = {31-39}, doi = {10.1016/j.scib.2016.11.010}, pmid = {36718068}, issn = {2095-9281}, abstract = {With performance improvement of low-temperature fuel cell (FC), high reactant supply and water generation rates may induce air-water turbulence in the FC flow channel. In this research, an air-water turbulent direct numerical simulation (DNS) model is developed to simulate different droplet sizes, locations and interactions in the air-water transport processes comprehensively. It is found that a larger droplet breaks up more easily in turbulence, and a smaller droplet tends to keep lumped. The droplet at corner does not break up because it is away from channel center. The droplet interaction simulations show that the small droplets merge to form slugs, but still keep lumped in turbulence. It is suggested that two conditions need to be satisfied for droplet break up in FC flow channel, one is turbulent flow, and another is that the droplet needs to be large enough and occupy the center region of flow channel to suffer sufficient turbulence fluctuations. The DNS results illustrate some unique phenomena in turbulent flow, and show that the turbulence has significant effect on the air-water flow behavior in FC flow channel.}, } @article {pmid36714791, year = {2023}, author = {Misiulia, D and Lidén, G and Antonyuk, S}, title = {Secondary Lip Flow in a Cyclone Separator.}, journal = {Flow, turbulence and combustion}, volume = {}, number = {}, pages = {1-20}, pmid = {36714791}, issn = {1573-1987}, abstract = {Three secondary flows, namely the inward radial flow along the cyclone lid, the downward axial flow along the external surface of the vortex finder, and the radial inward flow below the vortex finder (lip flow) have been studied at a wide range of flow rate 0.22-7.54 LPM using the LES simulations. To evaluate these flows the corresponding methods were originally proposed. The highly significant effect of the Reynolds number on these secondary flows has been described by equations. The main finding is that the magnitude of all secondary flows decrease with increasing Reynolds number. The secondary inward radial flow along the cyclone lid is not constant and reaches its maximum value at the central radial position between the vortex finder external wall and the cyclone wall. The secondary downward axial flow along the external surface of the vortex finder significantly increases at the lowest part of the vortex finder and it is much larger than the secondary flow along the cyclone lid. The lip flow is much larger than the secondary inward radial flow along the cyclone lid, which was assumed in cyclone models to be equal to the lip flow, and the ratio of these two secondary flows is practically independent of the Reynolds number.}, } @article {pmid36711805, year = {2023}, author = {Chang, R and Davydov, A and Jaroenlak, P and Budaitis, B and Ekiert, DC and Bhabha, G and Prakash, M}, title = {Energetics of the Microsporidian Polar Tube Invasion Machinery.}, journal = {bioRxiv : the preprint server for biology}, volume = {}, number = {}, pages = {}, doi = {10.1101/2023.01.17.524456}, pmid = {36711805}, abstract = {UNLABELLED: Microsporidia are eukaryotic, obligate intracellular parasites that infect a wide range of hosts, leading to health and economic burdens worldwide. Microsporidia use an un-usual invasion organelle called the polar tube (PT), which is ejected from a dormant spore at ultra-fast speeds, to infect host cells. The mechanics of PT ejection are impressive. Anncaliia algerae microsporidia spores (3-4 μ m in size) shoot out a 100-nm-wide PT at a speed of 300 μ m/sec, creating a shear rate of 3000 sec [- 1] . The infectious cargo, which contains two nuclei, is shot through this narrow tube for a distance of ~60-140 μ m [1] and into the host cell. Considering the large hydraulic resistance in an extremely thin tube and the low-Reynolds-number nature of the process, it is not known how microsporidia can achieve this ultrafast event. In this study, we use Serial Block-Face Scanning Electron Microscopy to capture 3-dimensional snapshots of A. algerae spores in different states of the PT ejection process. Grounded in these data, we propose a theoretical framework starting with a systematic exploration of possible topological connectivity amongst organelles, and assess the energy requirements of the resulting models. We perform PT firing experiments in media of varying viscosity, and use the results to rank our proposed hypotheses based on their predicted energy requirement, pressure and power. We also present a possible mechanism for cargo translocation, and quantitatively compare our predictions to experimental observations. Our study provides a comprehensive biophysical analysis of the energy dissipation of microsporidian infection process and demonstrates the extreme limits of cellular hydraulics.

STATEMENT OF SIGNIFICANCE: Microsporidia are a group of spore-forming, intracellular parasites that infect a wide range of hosts (including humans). Once triggered, microsporidian spores (3-4 μ m in size) shoot out a specialized organelle called the polar tube (PT) (60-140 μ m long, 100 nm wide) at ultrafast speed (300 μ m/sec), penetrating host cells and acting as a conduit for the transport of infectious cargo. Although this process has fascinated biologists for a century, the biophysical mechanisms underlying PT extrusion are not understood. We thus take a data-driven approach to generate models for the physical basis of PT firing and cargo transport through the PT. Our approach here demonstrates the extreme limits of cellular hydraulics and the potential applications of biophysical approaches to other cellular architectures.}, } @article {pmid36709783, year = {2023}, author = {Jeganathan, V and Alba, K and Ostilla-Mónico, R}, title = {Exploring the origin of turbulent Taylor rolls.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {381}, number = {2243}, pages = {20220130}, doi = {10.1098/rsta.2022.0130}, pmid = {36709783}, issn = {1471-2962}, abstract = {Since Taylor's seminal paper, the existence of large-scale quasi-axisymmetric structures has been a matter of interest when studying Taylor-Couette flow. In this article, we probe their formation in the highly turbulent regime by conducting a series of numerical simulations at a fixed Reynolds number [Formula: see text] while varying the Coriolis parameter to analyse the flow characteristics as the structures arise and dissipate. We show how the Coriolis force induces a one-way coupling between the radial and azimuthal velocity fields inside the boundary layer, but in the bulk, there is a two-way coupling that causes competing effects. We discuss how this complicates the analogy of narrow-gap Taylor-Couette to other convective flows. We then compare these statistics with a similar shear flow without no-slip boundary layers, showing how this double coupling causes very different effects. We finish by reflecting on the possible origins of turbulent Taylor rolls. This article is part of the theme issue 'Taylor-Couette and related flows on the centennial of Taylor's seminal Philosophical Transactions paper (part 1)'.}, } @article {pmid36709780, year = {2023}, author = {Baroudi, L and Majji, MV and Peluso, S and Morris, JF}, title = {Taylor-Couette flow of hard-sphere suspensions: overview of current understanding.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {381}, number = {2243}, pages = {20220125}, doi = {10.1098/rsta.2022.0125}, pmid = {36709780}, issn = {1471-2962}, abstract = {Although inertial particle-laden flows occur in a wide range of industrial and natural processes, there is both a lack of fundamental understanding of these flows and continuum-level governing equations needed to predict transport and particle distribution. Towards this effort, the Taylor-Couette flow (TCF) system has been used recently to study the flow behaviour of particle-laden fluids under inertia. This article provides an overview of experimental, theoretical and computational work related to the TCF of neutrally buoyant non-Brownian suspensions, with an emphasis on the effect of finite-sized particles on the series of flow transitions and flow structures. Particles, depending on their size and concentration, cause several significant deviations from Newtonian fluid behaviour, including shifting the Reynolds number corresponding to transitions in flow structure and changing the possible structures present in the flow. Furthermore, particles may also migrate depending on the flow structure, leading to hysteretic effects that further complicate the flow behaviour. The current state of theoretical and computational modelling efforts to describe the experimental observations is discussed, and suggestions for potential future directions to improve the fundamental understanding of inertial particle-laden flows are provided. This article is part of the theme issue 'Taylor-Couette and related flows on the centennial of Taylor's seminal Philosophical Transactions paper (part 1)'.}, } @article {pmid36688050, year = {2022}, author = {Hasan, HA and Sherza, JS and Abed, AM and Togun, H and Ben Khedher, N and Sopian, K and Mahdi, JM and Talebizadehsardari, P}, title = {Thermal and flow performance analysis of a concentrated linear Fresnel solar collector with transverse ribs.}, journal = {Frontiers in chemistry}, volume = {10}, number = {}, pages = {1074581}, pmid = {36688050}, issn = {2296-2646}, abstract = {This article deals with the impact of including transverse ribs within the absorber tube of the concentrated linear Fresnel collector (CLFRC) system with a secondary compound parabolic collector (CPC) on thermal and flow performance coefficients. The enhancement rates of heat transfer due to varying governing parameters were compared and analyzed parametrically at Reynolds numbers in the range 5,000-13,000, employing water as the heat transfer fluid. Simulations were performed to solve the governing equations using the finite volume method (FVM) under various boundary conditions. For all Reynolds numbers, the average Nusselt number in the circular tube in the CLFRC system with ribs was found to be larger than that of the plain absorber tube. Also, the inclusion of transverse ribs inside the absorber tube increases the average Nusselt number by approximately 115% at Re = 5,000 and 175% at Re = 13,000. For all Reynolds numbers, the skin friction coefficient of the circular tube with ribs in the CLFRC system is larger than that of the plain absorber tube. The coefficient of surface friction reduces as the Reynolds number increases. The performance assessment criterion was found to vary between 1.8 and 1.9 as the Reynolds number increases.}, } @article {pmid36673306, year = {2023}, author = {Fuchs, M and Lubos, N and Kabelac, S}, title = {Numerical Calculation of the Irreversible Entropy Production of Additively Manufacturable Off-Set Strip Fin Heat-Transferring Structures.}, journal = {Entropy (Basel, Switzerland)}, volume = {25}, number = {1}, pages = {}, doi = {10.3390/e25010162}, pmid = {36673306}, issn = {1099-4300}, abstract = {In this manuscript, off-set strip fin structures are presented which are adapted to the possibilities of additive manufacturing. For this purpose, the geometric parameters, including fin height, fin spacing, fin length, and fin longitudinal displacement, are varied, and the Colburn j-factor and the Fanning friction factor are numerically calculated in the Reynolds number range of 80-920. The structures are classified with respect to their entropy production number according to Bejan. This method is compared with the results from partial differential equations for the calculation of the irreversible entropy production rate due to shear stresses and heat conduction. This study reveals that the chosen temperature difference leads to deviation in terms of entropy production due to heat conduction, whereas the dissipation by shear stresses shows only small deviations of less than 2%. It is further shown that the variation in fin height and fin spacing has only a small influence on heat transfer and pressure drop, while a variation in fin length and fin longitudinal displacement shows a larger influence. With respect to the entropy production number, short and long fins, as well as large fin spacing and fin longitudinal displacement, are shown to be beneficial. A detailed examination of a single structure shows that the entropy production rate due to heat conduction is dominated by the entropy production rate in the wall, while the fluid has only a minor influence.}, } @article {pmid36673217, year = {2022}, author = {Rajupillai, K and Alessa, N and Eswaramoorthi, S and Loganathan, K}, title = {Thermal Behavior of the Time-Dependent Radiative Flow of Water-Based CNTs/Au Nanoparticles Past a Riga Plate with Entropy Optimization and Multiple Slip Conditions.}, journal = {Entropy (Basel, Switzerland)}, volume = {25}, number = {1}, pages = {}, doi = {10.3390/e25010076}, pmid = {36673217}, issn = {1099-4300}, abstract = {This communication deliberates the time-reliant and Darcy-Forchheimer flow of water-based CNTs/gold nanoparticles past a Riga plate. In addition, nonlinear radiation, heat consumption and multiple slip conditions are considered. Entropy generation is computed through various flow parameters. A suitable transformation with symmetry variables is invoked to remodel the governing mathematical flow models into the ODE equations. The homotopy analysis scheme and MATLAB bvp4c method are imposed to solve the reduced ODE equations analytically and numerically. The impact of sundry flow variables on nanofluid velocity, nanofluid temperature, skin friction coefficient, local Nusselt number, entropy profile and Bejan number are computed and analyzed through graphs and tables. It is found that the nanofluid velocity is reduced by greater porosity and slip factors. The thickness of the thermal boundary layer increases with increasing radiation, temperature ratio, and heat consumption/generation parameters. The surface drag force is reduced when there is a higher Forchheimer number, unsteadiness parameter and porosity parameter. The amount of entropy created is proportional to the radiation parameter, porosity parameter and Reynolds number. The Bejan number profile increases with radiation parameter, heat consumption/generation parameter and the Forchheimer number.}, } @article {pmid36658185, year = {2023}, author = {Méry, F and Sebbane, D}, title = {Aerodynamic characterisation of porous fairings: pressure drop and Laser Doppler Velocimetry measurements.}, journal = {Scientific data}, volume = {10}, number = {1}, pages = {39}, pmid = {36658185}, issn = {2052-4463}, abstract = {Wind tunnel measurements of pressure drop and steady and unsteady velocity field of a flow through fairing samples are described. 10 samples have been tested in pressure drop among which the velocity fields of 3 samples have been characterized by means of laser Doppler velocimetry. The samples are perforated plates, wiremesh plates or complex 3D geometries resulting from additive manufacturing methods. The Reynolds number of the experiments ranges from 55 000 to 117 000.}, } @article {pmid36649407, year = {2023}, author = {Li, Y and Pahlavan, AA and Chen, Y and Liu, S and Li, Y and Stone, HA and Granick, S}, title = {Oil-on-water droplets faceted and stabilized by vortex halos in the subphase.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {120}, number = {4}, pages = {e2214657120}, doi = {10.1073/pnas.2214657120}, pmid = {36649407}, issn = {1091-6490}, abstract = {For almost 200 y, the dominant approach to understand oil-on-water droplet shape and stability has been the thermodynamic expectation of minimized energy, yet parallel literature shows the prominence of Marangoni flow, an adaptive gradient of interfacial tension that produces convection rolls in the water. Our experiments, scaling arguments, and linear stability analysis show that the resulting Marangoni-driven high-Reynolds-number flow in shallow water overcomes radial symmetry of droplet shape otherwise enforced by the Laplace pressure. As a consequence, oil-on-water droplets are sheared to become polygons with distinct edges and corners. Moreover, subphase flows beneath individual droplets can inhibit the coalescence of adjacent droplets, leading to rich many-body dynamics that makes them look alive. The phenomenon of a "vortex halo" in the liquid subphase emerges as a hidden variable.}, } @article {pmid36648820, year = {2023}, author = {Jo, BW and Majid, T}, title = {Enhanced Range and Endurance Evaluation of a Camber Morphing Wing Aircraft.}, journal = {Biomimetics (Basel, Switzerland)}, volume = {8}, number = {1}, pages = {}, doi = {10.3390/biomimetics8010034}, pmid = {36648820}, issn = {2313-7673}, abstract = {Flight range, endurance, maneuverability, and agility are the key elements that determine an aircraft's performance. Both conventional and morphing wing aircraft have been well studied and estimated in all aspects of performance. When considering the performance of morphing aircraft, most works address aspects of the aerodynamical performance such as L and D as well as flight envelopes for flight dynamics and control perspectives. However, the actual benefits of adopting morphing technologies in practical aspects such as aircraft operation, mission planning, and sustainability have not been addressed so far. Thus, this paper addresses the practical aspect of the benefits when adopting a camber morphing wing aircraft. Identical geometrical and computational conditions were applied to an already-existing aircraft: the RQ-7a Shadow. The wing structure was switched between a fixed wing and a camber morphing wing to generate conventional and morphing wing geometries. The fixed-wing cases had varying flap deflection angles, and the camber morphing wing cases had varying camber rates from 4% to 8%. Once the CL values of the fixed and morphing wing cases were matched up to two significant figures, the CD and CL/CD were analyzed for these matching cases to calculate the flight endurance, range, and improvement. When NACA 6410 is adopted, a 17% improvement in flight range and endurance average was expected. In the case of NACA 8410, an average 60% improvement was expected.}, } @article {pmid36648720, year = {2023}, author = {Jain, PK and Lanjewar, A and Chaurasiya, PK and Tiwari, D and Sharma, VK}, title = {Experimental testing of solar-based air heater roughed with discrete V-down rib and staggered element.}, journal = {Environmental science and pollution research international}, volume = {}, number = {}, pages = {}, pmid = {36648720}, issn = {1614-7499}, abstract = {A rough rectangular channel of solar-based air heater (SBAH) is made and tested. The work consists of an effort to perceive the proportion of heat discharge and frictional behavior of air passing over a roughened rectangular channel. The absorber surface of SBAH is roughed with discrete V-down rib and staggered element roughness having different values of relative rib pitch (P/e) that ranged from 6 to 14. Fixed parameters such as relative gap size (g/e), relative staggered element pitch (P'/P), numeral of gaps (Ng), relative staggered element size (r/g), and relative rib height (e/D) are considered 4, 0.4, 3,1, and 0.0433, respectively, all throughout the study. The flow Reynolds number (Re) changes from 4000 to 14,000; consequently the Nusselt number (Nu) and friction factor (f) reach up to 2.16 and 2.73 times, respectively, with respect to plane surface. The optimum rise in terms of thermal-hydraulic performance (THP) is gained analogous to a P/e of 10. The correlation for heat transfer function, R(e[+]), and roughness function, G(e[+]), is given to anticipate the performance of roughness.}, } @article {pmid36643326, year = {2022}, author = {Voskoboinick, V and Onyshchenko, A and Voskoboinyk, O and Makarenkova, A and Voskobiinyk, A}, title = {Junction flow inside and around three-row cylindrical group on rigid flat surface.}, journal = {Heliyon}, volume = {8}, number = {12}, pages = {e12595}, doi = {10.1016/j.heliyon.2022.e12595}, pmid = {36643326}, issn = {2405-8440}, abstract = {Groups of bluff bodies are widespread in nature and technology. These are the supports of bridge crossings, high-rise buildings in cities, offshore drilling and wind platforms, algae and vegetation in the seas and rivers, forests and other objects. The flow of air or water around such structures has a complex vortex and jet character and requires significant efforts in the process of scientific research to improve the environmental situation and reduce material and technical costs in the process of operating such structures. The purpose of the research is study the features of the generation and evolution of vortex and jet flows near and inside the three-row group of cylinders, which are installed on the rigid flat surface. The results of experimental studies showed that the flow around the group of cylinders had a complex unsteady nature, which is due to the interaction of vortex and jet flows typical flow elements with the three-row cylindrical group, which was located installed on the rigid flat surface. The three-row cylindrical group (31 piles with a diameter of 0.027 m) is a model of a bridge support, which was streamlined at a velocity of 0.06 m/s to 0.5 m/s (Reynolds number Red=(1600-6700) and Froude number Fr=(0.04-0.18)). Visual investigations and measurements of the velocity field were carried out inside and around the three-row structure. The features of the formation and evolution of vortex and jet flows inside and near the cylindrical group were established. Integral, spectral and correlation characteristics of the velocity fluctuation field were obtained. Mean, root-mean-square values of velocity and probability density functions of velocity fluctuations integrally displayed the changes in the velocity field in the spatial and temporal domain in the junction area of grillage and plate. The power spectral densities of velocity fluctuations and mutual correlation functions made it possible to study the features of the generation of the velocity fluctuation field in the frequency domain and its interrelationships in space. It was revealed that the velocity field inside the horseshoe vortex structures was multimodal. The spectral levels of velocity fluctuations at the periphery of the quasistable horseshoe vortex structures were higher than in the cores of these structures. The highest levels of the velocity fluctuation spectra were observed in front of the second lateral cylinder where the interaction of the vortex and jet flows took place. Discrete peaks in the spectral levels of velocity fluctuations are found at the frequencies of formation of large-scale wake vortices and the frequencies of formation of small-scale vortex structures of the shear layer, which are due to the Kelvin-Helmholtz instability. It has been established that the frequency of formation of shear layer vortices is (10-40) times higher than the frequency of formation of wake vortices.}, } @article {pmid36622597, year = {2023}, author = {Munusamy, A and Barik, D and Sharma, P and Medhi, BJ and Bora, BJ}, title = {Performance analysis of parabolic type solar water heater by using copper-dimpled tube with aluminum coating.}, journal = {Environmental science and pollution research international}, volume = {}, number = {}, pages = {}, pmid = {36622597}, issn = {1614-7499}, abstract = {A solar water heater has been developed to convert solar radiation into heat for use in residential and commercial settings. The collector makes up the bulk of a solar water heating system. The solar energy is captured by the collector and transferred to the tube that delivers the working fluid, water. In addition to the collector's tube, which carries the working fluid, researchers have focused on the design of the collector's tube. This paper examines the performance of a parabolic plate solar water heater that uses a copper dimpled tube with aluminum-coated tube channels. During the test, the flow rate of base fluid was in the range of 1.0 to 3.0 kg/min in steps of 0.5. The performance of the solar water heater was also evaluated and verified using CFD. The test data such as friction factor, Reynolds number, uncertainty analysis, Nusselt number, solar collector efficiency, coefficient of convective heat transfer, linear dimpled tube velocity analysis, achieving maximum energy efficiency and thermal efficiency have been used to generate parametric values for parabolic plate solar water heaters. The results suggest that the best outcomes can be achieved with a mass flow rate of 2.5 kg/min and the overall thermal efficiency was raised to 31.85%, which is 11% greater than that of the plain tube with base fluid. At mass flow rates of 2.5 kg/min, the pressure drop was found to be 6.24% higher than that of 3.0 kg/min. The experimental results were analyzed and compared with the CFD results, and the overall deviation was ± 3.24% which is in the acceptable range.}, } @article {pmid36597964, year = {2023}, author = {Kanies, OS and Kremer, KR and Mason, BM and Dudley, MG and Hlavay, JM and Miller, CT and Spero, RC and Fisher, JK}, title = {A modular microfluidic device that uses magnetically actuatable microposts for enhanced magnetic bead-based workflows.}, journal = {Lab on a chip}, volume = {}, number = {}, pages = {}, doi = {10.1039/d2lc00859a}, pmid = {36597964}, issn = {1473-0189}, abstract = {Magnetic beads have been widely and successfully used for target enrichment in life science assays. There exists a large variety of commercially available magnetic beads functionalized for specific target capture, as well as options that enable simple surface modifications for custom applications. While magnetic beads are ideal for use in the macrofluidic context of typical laboratory workflows, their performance drops in microfluidic contexts, such as consumables for point-of-care diagnostics. A primary cause is the diffusion-limited analyte transport in these low Reynolds number environments. A new method, BeadPak, uses magnetically actuatable microposts to enhance analyte transport, improving yield of the desired targets. Critical parameters were defined for the operation of this technology and its performance characterized in canonical life-science assays. BeadPak achieved up to 1000× faster capture than a microfluidic chamber relying on diffusion alone, enabled a significant specimen concentration via volume reduction, and demonstrated compatibility with a range of biological specimens. The results shown in this work can be extended to other systems that utilize magnetic beads for target capture, concentration, and/or purification.}, } @article {pmid36597923, year = {2023}, author = {Tingting, Q and Jianzhong, L and Zhenyu, O and Jue, Z}, title = {Settling mode of a bottom-heavy squirmer in a narrow vessel.}, journal = {Soft matter}, volume = {}, number = {}, pages = {}, doi = {10.1039/d2sm01442d}, pmid = {36597923}, issn = {1744-6848}, abstract = {The lattice Boltzmann-immersed boundary (IB-LB) method is used to numerically simulate the sedimentation motion of a single two-dimensional, bottom-heavy squirmer in a narrow vessel. The effects of the swimming Reynolds number Res = 0.1-3, eccentricity distance l = 0.15d-0.75d, and density ratio of squirmer to fluid γ = 1.1-2.0 on the settlement motion characteristics are investigated and analyzed. The results showed that four settling modes exist: vertical motion, unilateral oscillation, oscillation, and tilt. The bottom-heavy neutral squirmer and puller settle in the vessel during vertical motion when Res is 0.1-1.5. By increasing Res and swimming strength |β|, the bottom-heavy squirmer becomes more self-driven, shifting its settling mode from vertical motion to unilateral oscillation or oscillation. Increasing l or |β| does not affect the bottom-heavy neutral squirmer and puller's vertical settling mode but shifts the bottom-heavy pusher's settling mode from unilateral oscillation to oscillation or oscillation to unilateral oscillation. Similarly, altering γ or |β| has no impact on the eccentric neutral squirmer and puller's settling mode; however, pushers will switch from oscillation mode to attraction mode or from oscillation mode to tilt mode. Additionally, it was found that after the squirmer collided with the bottom wall, the bottom-heavy squirmer settled at the bottom of the vessel in a different state of motion.}, } @article {pmid36583152, year = {2022}, author = {Abed, AM and Mouziraji, HR and Bakhshi, J and Dulaimi, A and Mohammed, HI and Ibrahem, RK and Ben Khedher, N and Yaïci, W and Mahdi, JM}, title = {Numerical analysis of the energy-storage performance of a PCM-based triplex-tube containment system equipped with arc-shaped fins.}, journal = {Frontiers in chemistry}, volume = {10}, number = {}, pages = {1057196}, pmid = {36583152}, issn = {2296-2646}, abstract = {This study numerically intends to evaluate the effects of arc-shaped fins on the melting capability of a triplex-tube confinement system filled with phase-change materials (PCMs). In contrast to situations with no fins, where PCM exhibits relatively poor heat response, in this study, the thermal performance is modified using novel arc-shaped fins with various circular angles and orientations compared with traditional rectangular fins. Several inline and staggered layouts are also assessed to maximize the fin's efficacy. The effect of the nearby natural convection is further investigated by adding a fin to the bottom of the heat-storage domain. Additionally, the Reynolds number and temperature of the heat-transfer fluid (HTF) are evaluated. The outcomes showed that the arc-shaped fins could greatly enhance the PCMs' melting rate and the associated heat-storage properties. The melting rate is 17% and 93.1% greater for the case fitted with an inline distribution of the fins with a circular angle of 90° and an upward direction, respectively, than the cases with uniform rectangular fins and no fins, which corresponded to the shorter melting time of 14.5% and 50.4%. For the case with arc-shaped fins with a 90° circular angle, the melting rate increases by 9% using a staggered distribution. Compared to the staggered fin distribution, adding an extra fin to the bottom of the domain indicates adverse effects. The charging time reduces by 5.8% and 9.2% when the Reynolds number (Re) rises from 500 to 1000 and 1500, respectively, while the heat-storage rate increases by 6.3% and 10.3%. When the fluid inlet temperature is 55°C or 50°C, compared with 45°C, the overall charging time increases by 98% and 47%, respectively.}, } @article {pmid36579881, year = {2022}, author = {Issa, M and Haupt, D and Muddemann, T and Kunz, U and Sievers, M}, title = {Investigation of an electrolysis system with boron-doped diamond anode and gas diffusion cathode to remove water micropollutants.}, journal = {Water science and technology : a journal of the International Association on Water Pollution Research}, volume = {86}, number = {12}, pages = {3236-3247}, doi = {10.2166/wst.2022.390}, pmid = {36579881}, issn = {0273-1223}, abstract = {Using electrolysis systems to degrade organics in wastewater encourages this technique to remove micropollutants (MPs) in different types of water. In this work, a cell consisting of an anode as a boron-doped diamond (BDD) electrode combined with a gas diffusion (GDE) cathode without a separator showed that MPs degradation can be effectively achieved. Investigating different operating parameters, it was stated that applying a low current density (2 mA/cm[2]) and setting the Reynolds number of the electrolyte flow through the cell at the laminar range raised the treatment time by 3-fold at the same energy demand. This arrangement increased the MPs removal. Some substances like diclofenac were removed up to 84% at a longer treatment time of 180 min coupled with an increase in energy demand. The results at the mentioned parameters indicated an adequate generation rate of radicals needed to remove MPs and the oxidation reactions were promoted. The results show high potential to the investigated electrolysis system in removing MPs in wastewater under considering the need for further reduction of the energy demand.}, } @article {pmid36574794, year = {2022}, author = {Abbas Al-Amshawee, SK and Bin Mohd Yunus, MY}, title = {Electrodialysis desalination: The impact of solution flowrate (or Reynolds number) on fluid dynamics throughout membrane spacers.}, journal = {Environmental research}, volume = {}, number = {}, pages = {115115}, doi = {10.1016/j.envres.2022.115115}, pmid = {36574794}, issn = {1096-0953}, abstract = {The incorporation of a spacer among membranes has a major influence on fluid dynamics and performance metrics. Spacers create feed channels and operate as turbulence promoters to increase mixing and reduce concentration/temperature polarization effects. However, spacer geometry remains unoptimized, and studies continue to investigate a wide range of commercial and custom-made spacer designs. The in-depth discussion of the present systematic review seeks to discover the influence of Reynolds number or solution flowrate on flow hydrodynamics throughout a spacer-filled channel. A fast-flowing solution sweeping one membrane's surface first, then the neighboring membrane's surface produces good mixing action, which does not happen commonly at laminar solution flowrates. A sufficient flowrate can suppress the polarization layer, which may normally require the utilization of a simple feed channel rather than complex spacer configurations. When a recirculation eddy occurs, it disrupts the continuous flow and effectively curves the linear fluid courses. The higher the flowrate, the better the membrane performance, the higher the critical flux (or recovery rate), and the lower the inherent limitations of spacer design, spacer shadow effect, poor channel hydrodynamics, and high concentration polarization. In fact, critical flow achieves an acceptable balance between improving flow dynamics and reducing the related trade-offs, such as pressure losses and the occurrence of concentration polarization throughout the cell. If the necessary technical flowrate is not used, the real concentration potential for transport is relatively limited at low velocities than would be predicted based on bulk concentrations. Electrodialysis stack therefore may suffer from the dissociation of water molecules. Next studies should consider that applying a higher flowrate results in greater process efficiency, increased mass transfer potential at the membrane interface, and reduced stack thermal and electrical resistance, where pressure drop should always be indicated as a consequence of the spacer and circumstances used, rather than a problem.}, } @article {pmid36562423, year = {2022}, author = {de Timary, G and Rousseau, CJ and Van Melderen, L and Scheid, B}, title = {Shear-enhanced sorting of ovoid and filamentous bacterial cells using pinch flow fractionation.}, journal = {Lab on a chip}, volume = {}, number = {}, pages = {}, doi = {10.1039/d2lc00969b}, pmid = {36562423}, issn = {1473-0189}, abstract = {In this paper, we experimentally investigate the influence of the flow rate on the trajectory of ovoid and filamentous bacterial cells of E. coli in a low aspect ratio pinch flow fractionation device. To that aim, we vary the Reynolds number over two orders of magnitude, while monitoring the dynamics of the cells across our device. At low flow rates, filamentous cells adopt several rotational motions in the pinched segment, which are induced both by the shear rate and by their close interactions with the nearest wall. As a result, the geometrical centre of the filamentous cells deviates towards the centre of the channel, which increases their effective sorting diameter depending on the length of their major axis as well as on the rotational mode they adopt in the pinch. As the flow rate increases, particles are forced to align vertically in the pinch, in the direction of the main shear gradient, which reduces the amplitude of the lateral deviation generated by their rotation. The trajectory of the particles in the expansion is directly determined by their position at the pinch outlet. As a consequence, the position of the filamentous cells at the outlet of the device strongly depends on the flow rate as well as on the length of their major axis. Based on these observations we optimized the flow conditions to successfully extract an ultra high purity sample of filamentous cells from a solution containing mainly ovoid cells.}, } @article {pmid36562333, year = {2022}, author = {Marnoto, S and Hashmi, SM}, title = {Application of droplet migration scaling behavior to microchannel flow measurements.}, journal = {Soft matter}, volume = {}, number = {}, pages = {}, doi = {10.1039/d2sm00980c}, pmid = {36562333}, issn = {1744-6848}, abstract = {In confined channels in low Reynolds number flow, droplets drift perpendicular to the flow, moving across streamlines. The phenomenon has proven useful for understanding microfluidic droplet separation, drug delivery vehicle optimization, and single-cell genomic amplification. Particles or droplets undergo several migration mechanisms including wall migration, hydrodynamic diffusion, and migration down gradients of shear. In simple shear flow only wall migration and hydrodynamic diffusion are present. In parabolic flow, droplets also move down gradients of shear. The resulting separation depends on parameters including particle size and stiffness, concentration, and flow rate. Computational methods can incorporate these effects in an exact manner to predict margination phenomena for specific systems, but do not generate a descriptive parametric dependence. In this paper, we present a scaling model that elucidates the parametric dependence of margination on emulsion droplet size, volume fraction, shear rate and suspending fluid viscosity. We experimentally measure the droplet depletion layer of silicone oil droplets and compare the results to theoretical scaling behavior that includes hydrodynamic diffusion and wall migration with and without an added shear-gradient migration. Results demonstrate the viability and limitations of applying a simple scaling behavior to experimental systems to describe parametric dependence. Our conclusions open the possibility for parametric descriptions of migration with broad applicability to particle and droplet systems.}, } @article {pmid36559702, year = {2022}, author = {Ayas, M and Skočilas, J and Štípek, J and Gutiérrez, CA and Žitný, R and Jirout, T}, title = {An Approximate Method for Predicting the Friction Factor of Viscoplastic Shear-Thinning Fluids in Non-Circular Channels of Regular Cross-Sections.}, journal = {Polymers}, volume = {14}, number = {24}, pages = {}, doi = {10.3390/polym14245337}, pmid = {36559702}, issn = {2073-4360}, abstract = {The objective of this study is to provide a straightforward generalized simple and quick method for the prediction of the friction factor for fully developed laminar flow of viscoplastic shear-thinning fluids in non-circular channels of regular cross-sections. The most frequently represented substances processed under these conditions are polymers in the processing and plastics industry. A generalized approximate method was proposed to express the relationship between the friction factor and the Reynolds number for the Herschel-Bulkley rheological model. This method uses the generalized Reynolds number for power-law fluids. Moreover, an additional simplified method for rapid engineering calculations was obtained as well. The suggested method was verified by comparing experimental data for concentric annulus found in the literature and results from simulations for concentric annulus, rectangular, square duct with a central cylindrical core and elliptical cross-sections. The results showed that the suggested methods enable us to estimate the friction factor with high accuracy for the investigated geometries.}, } @article {pmid36559442, year = {2022}, author = {Moriconi, L and Pereira, RM}, title = {Statistics of extreme turbulent circulation events from multifractality breaking.}, journal = {Physical review. E}, volume = {106}, number = {5-1}, pages = {054121}, doi = {10.1103/PhysRevE.106.054121}, pmid = {36559442}, issn = {2470-0053}, abstract = {Recent numerical explorations of extremely intense circulation fluctuations at high Reynolds number flows have brought to light novel aspects of turbulent intermittency. Vortex gas modeling ideas, which are related to a picture of turbulence as a dilute system of vortex tube structures, have been introduced alongside such developments, leading to accurate descriptions of the core and the intermediate tails of circulation probability distribution functions (cPDFs), as well as the scaling exponents associated to statistical moments of circulation. We extend the predictive reach of the vortex gas picture of turbulence by emphasizing that multifractality breaking, one of its salient phenomenological ingredients, is the key concept to disclose the asymptotic form of cPDF tails. A remarkable analytical agreement is found with previous results derived within the framework of the instanton approach to circulation intermittency, a functional formalism devised to single out the statistically dominant velocity configurations associated to extreme circulation events.}, } @article {pmid36559415, year = {2022}, author = {Maity, R and Burada, PS}, title = {Near- and far-field hydrodynamic interaction of two chiral squirmers.}, journal = {Physical review. E}, volume = {106}, number = {5-1}, pages = {054613}, doi = {10.1103/PhysRevE.106.054613}, pmid = {36559415}, issn = {2470-0053}, abstract = {Hydrodynamic interaction strongly influences the collective behavior of microswimmers. With this work, we study the behavior of two hydrodynamically interacting self-propelled chiral swimmers in the low Reynolds number regime, considering both the near- and far-field interactions. We use the chiral squirmer model [see Burada et al., Phys. Rev. E 105, 024603 (2022)2470-004510.1103/PhysRevE.105.024603], a spherically shaped body with nonaxisymmetric surface slip velocity, which generalizes the well-known squirmer model. The previous work was restricted only to the case, while the far-field hydrodynamic interaction was influential among the swimmers. It did not approach the scenario while both the swimmers are very close and lubrication effects become dominant. We calculate the lubrication force between the swimmers when they are very close. By varying the slip coefficients and the initial configuration of the swimmers, we investigate their hydrodynamic behavior. In the presence of lubrication force, the swimmers either repel each other or exhibit bounded motion where the distance between the swimmers alters periodically. We identify the possible behaviors exhibited by the chiral squirmers, such as monotonic divergence, divergence, and bounded, as was found in the previous study. However, in the current study, we observe that both the monotonic convergence and the convergence states are converted into divergence states due to the arising lubrication effects. The lubrication force favors the bounded motion in some parameter regimes. This study helps to understand the collective behavior of dense suspension of ciliated microorganisms and artificial swimmers.}, } @article {pmid36559353, year = {2022}, author = {Lutz, T and Richter, SK and Menzel, AM}, title = {Effect of boundaries on displacements and motion in two-dimensional fluid or elastic films and membranes.}, journal = {Physical review. E}, volume = {106}, number = {5-1}, pages = {054609}, doi = {10.1103/PhysRevE.106.054609}, pmid = {36559353}, issn = {2470-0053}, abstract = {Thin fluid or elastic films and membranes are found in nature and technology, for instance, as confinements of living cells or in loudspeakers. When applying a net force, the resulting flows in an unbounded two-dimensional incompressible low-Reynolds-number fluid or displacements in a two-dimensional linearly elastic solid seem to diverge logarithmically with the distance from the force center, which has led to some debate. Recently, we have demonstrated that such divergences cancel when the total (net) force vanishes. Here, we illustrate that if a net force is present, the boundaries play a prominent role. Already a single no-slip boundary regulates the flow and displacement fields and leads to their decay to leading order inversely in distance from a force center and the boundary. In other words, it is the boundary that stabilizes the system in this situation, unlike the three-dimensional case, where an unbounded medium by itself is able to absorb a net force. We quantify the mobility and displaceability of an inclusion as a function of the distance from the boundary, as well as interactions between different inclusions. In the case of free-slip boundary conditions, a kinked boundary is necessary to achieve stabilization.}, } @article {pmid36557435, year = {2022}, author = {Guan, X and Xie, Z and Nan, G and Xi, K and Lu, Z and Ge, Y}, title = {Thermal-Hydrodynamic Behavior and Design of a Microchannel Pin-Fin Hybrid Heat Sink.}, journal = {Micromachines}, volume = {13}, number = {12}, pages = {}, doi = {10.3390/mi13122136}, pmid = {36557435}, issn = {2072-666X}, abstract = {A three-dimensional convective heat transfer model of a microchannel pin-fin hybrid heat sink was established. Considering the non-uniform heat generation of 3D stacked chips, the splitting distance of pin-fins was optimized by minimizing the maximum heat sink temperature under different heat fluxes in the hotspot, the Reynolds numbers at the entrance of the microchannel, and the proportions of the pin-fin volume. The average pressure drop and the performance evaluation criteria were considered to be the performance indexes to analyze the influence of each parameter on the flow performance and comprehensive performance, respectively. The results showed that the maximum temperature of the hybrid heat sink attained a minimum value with an increase in the splitting distance. The average pressure drop in the center passage of the microchannel first increased and then decreased. Furthermore, the optimal value could not be simultaneously obtained with the maximum temperature. Therefore, it should be comprehensively considered in the optimization design. The heat flux in the hotspot was positively correlated with the maximum heat sink temperature. However, it had no effect on the flow pressure drop. When the Reynolds number and the pin-fin diameter increased, the maximum heat sink temperature decreased and the average pressure drop of the microchannel increased. The comprehensive performance of the hybrid heat sink was not good at small Reynolds numbers, but it significantly improved as the Reynolds number gradually increased. Choosing a bigger pin-fin diameter and the corresponding optimal value of the splitting distance in a given Reynolds number would further improve the comprehensive performance of a hybrid heat sink.}, } @article {pmid36547837, year = {2022}, author = {Salman, M and Chauhan, R and Singh, T and Prabakaran, R and Kim, SC}, title = {Experimental investigation and optimization of dimple-roughened impinging jet solar air collector using a novel AHP-MABAC approach.}, journal = {Environmental science and pollution research international}, volume = {}, number = {}, pages = {1-17}, pmid = {36547837}, issn = {1614-7499}, abstract = {The effect of the flow and geometric parameters of a dimple-roughened absorber plate on the enactment of solar air collectors (SACs) with air-impinged jets was investigated in this study. The performance-defining criteria (PDCs) of a jet-impinged dimple-roughened SAC (JIDRSAC)-forced convection airflow system are significantly affected by variations in the system's control factors (CFs), such as the arc angle (αaa) ranging from 30° to 75°, dimple pitch ratio (pd/Dh) ranging from 0.269 to 1.08, and dimple height ratio (ed/Dh) ranging from 0.016 to 0.0324. The constant parameters of the jet slot are a stream-wise pitch ratio (Xi/Dhd) is 1.079, a span-wise pitch ratio (Yi/Dhd) is 1.619, and a jet diameter(Di/Dhd) is 0.081. Based on the combined approach of the analytic hierarchy process and multi-attributive border approximation area comparison (AHP-MABAC), the Reynolds number (Re) = 15,000, αaa = 60°, pd/Dh = 0.27, and ed/Dh = 0.027 depicted the best alternative (A-9) set among 16 alternatives to deliver the optimal performance of the JIDRSAC. The jet impingement pass compared to the smooth pass, the Nusselt number increased by 2.16-2.81, and friction factor increased by 3.35-5.95, and JIDRSAC was compared to the jet impingement pass, exhibiting an enhancement in Nusselt number and friction factor in the range of 0.55-0.80 and 0.05-0.15, respectively. In addition, sensitivity analysis is used to examine the ranking's stability and reliability in relation to the PDC weights.}, } @article {pmid36547831, year = {2022}, author = {Raju, LB and Sastry, GR and Gugulothu, SK and Kumar, R and Balakrishnan, D}, title = {Computational analysis on solar air heater with combination of alternate dimple protrusions and intrusions on absorber plate with one rounded corner triangular duct.}, journal = {Environmental science and pollution research international}, volume = {}, number = {}, pages = {}, pmid = {36547831}, issn = {1614-7499}, abstract = {This study focuses on improving heat transfer by converting one of the corners of the duct to a rounded structure. To study the effect of dimpled shaped protrusions and intrusions on the rounded corner triangular duct with a constant radius of curvature by varying relative streamwise distance (z/e) with a constant transverse distance x'/e = 10,14 and 18. Steady-state, turbulent flow heat transfer under thermal boundary conditions is to be analyzed by varying different Reynolds numbers (5600 to 21000). The duct with dimple-shaped protrusions and intrusions is compared with a simple triangular duct. Optimization of relative horizontal distance (z'/e) by keeping constant protrusion to protrusion distance as z/e = 28 and relative transverse distance as x/e = 10, 14, and 18. It was noted that there was a significant loss in friction and a rise in heat transfer. The relationship between friction factor and Nusselt number was formulated using operating and roughness parameters, using the data collected from the numerical investigation. The friction factor increases significantly with roughness elements, and it is maximum for x'/e = 20 at a low Reynolds number. Nusselt number increases with roughness elements, and it is maximum for x'/e = 14 for all Reynolds numbers and all the models. Enhancement of Nusselt number is due to increase of local heat transfer because of local vortex neat heat transfer zone. The maximum outlet temperature is obtained at a low Reynolds number. The maximum temperature of the heated surface is obtained for Rc = 0.67 h and the minimum for Rc = 0.33 h.}, } @article {pmid36533860, year = {2022}, author = {Lim, S and Du, Y and Lee, Y and Panda, SK and Tong, D and Khalid Jawed, M}, title = {Fabrication, control, and modeling of robots inspired by flagella and cilia.}, journal = {Bioinspiration & biomimetics}, volume = {18}, number = {1}, pages = {}, doi = {10.1088/1748-3190/aca63d}, pmid = {36533860}, issn = {1748-3190}, abstract = {Flagella and cilia are slender structures that serve important functionalities in the microscopic world through their locomotion induced by fluid and structure interaction. With recent developments in microscopy, fabrication, biology, and modeling capability, robots inspired by the locomotion of these organelles in low Reynolds number flow have been manufactured and tested on the micro-and macro-scale, ranging from medicalin vivomicrobots, microfluidics to macro prototypes. We present a collection of modeling theories, control principles, and fabrication methods for flagellated and ciliary robots.}, } @article {pmid36517549, year = {2022}, author = {Hafez, NM and Alsemiry, RD and Alharbi, SA and Abd-Alla, AM}, title = {Peristaltic transport characteristics of a second-grade dusty fluid flown with heat transfer through a tube revisited.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {21605}, pmid = {36517549}, issn = {2045-2322}, abstract = {This paper provides a rudimentary insight into the influence of heat transfer on the transport characteristics of a second-grade dusty fluid flown in a flexible tube with walls subjected to the peristaltic motion. Both dust particles and fluid movements were modeled using the coupled differential equations. The effects of different types of parameters such as Reynolds number, Prandtl number, Grashof number, wave number, wave amplitude ratio, second grade parameter as well as nature of the heat source and sink are studies on the dust particles velocity, fluid velocity, temperature, pressure profiles of the fluid and streamline patterns of the fluid. The derived equations were solved analytically via the standard perturbation method to determine the fluid temperature, streamline pattern and velocity of the dust particles as well as fluid. The values in the increase of pressure and frictional forces were calculated numerically using DSolve of the Mathematica 11 software (https://www.wolfram.com/mathematica/new-in-11/). In addition, the trapping mechanisms were ascertained by computing the streamlines and various physical parameters. The obtained results were validated with the state-of-the-art literature reports. It was claimed that our systematic approach may constitute a basis for accurately examining the impact of heat transfer on the peristaltic transport of a complex fluid through narrow tubes, useful for diverse medical applications such as the gastric fluid flow through the small intestine during endoscopy. Numerical results are computed and discussed numerically and presented through graphs. The impacts of pertinent parameters on the aforementioned quantities are examined by plotting graphs on the basis of computational results. The results indicate that the effect of parameters is very pronounced. A suitable comparison has been made with the prior results in the literature as a limiting case of the considered problem.}, } @article {pmid36513785, year = {2022}, author = {Abd-Alla, AM and Abo-Dahab, SM and Thabet, EN and Abdelhafez, MA}, title = {Heat and mass transfer for MHD peristaltic flow in a micropolar nanofluid: mathematical model with thermophysical features.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {21540}, pmid = {36513785}, issn = {2045-2322}, abstract = {According to a survey of the literature, nanofluids are superior to traditional fluids at transferring heat. A detailed analysis of the models mentioned above is crucial since there are large gaps in the illumination of current solutions for improving heat transfer in nanomaterials. The ongoing investigation's purpose is to ascertain the tiny size gold particles drift in free with the heat and mass transfer, buoyancy forces, thermophoresis, and Brownian motion of a micropolar nanofluid being transported through a porous medium in an asymmetric channel with a uniform magnetic field using a long-wavelength and low Reynolds number approximation. The resulting dimensionless nonlinear governing equations have been numerically solved using a MATLAB software and the Runge-Kutta-Fehlberg integration scheme. Two comparisons with previously investigated problems are also made to confirm our findings, and an excellent concurrence is discovered. As a result, trustworthy results are being given. Numerical solutions are used to describe the effects of different thermal-fluidic parameters on velocity profiles, temperature, concentration, micropolar rotation, pressure gradient, shear stress, heat flux, and nanoparticle volume flux, etc. Tables, graphs, and bar charts are used to present and discuss numerical results that have been produced. A comparison of the resulting numerical solution to earlier literature also reveals a satisfactory level of agreement. Insight into real-world applications such nanofluidic, energy conservation, friction reduction, and power generation are provided by this work. Furthermore, the Brownian and thermophoresis parameters behave significantly differently in a concentration field. On the other hand, the study puts forward an important note that for peristaltic flow of a micropolar fluid with nanoparticles can be controlled by suitably adjusting the micropolar parameter, thermophoresis parameter, nanoparticle Grashof number, and Brownian motion parameter.}, } @article {pmid36506398, year = {2022}, author = {Shuvo, MS and Hasib, MH and Saha, S}, title = {Entropy generation and characteristics of mixed convection in lid-driven trapezoidal tilted enclosure filled with nanofluid.}, journal = {Heliyon}, volume = {8}, number = {12}, pages = {e12079}, pmid = {36506398}, issn = {2405-8440}, abstract = {The investigation of steady, incompressible, laminar mixed convective fluid flow within two different types of tilted lid-driven trapezoidal enclosures filled with nanofluid composed of water and Al2O3 nanoparticles has been carried out in this paper. The upper wall of the enclosure is an isothermal cold surface that travels at a constant speed, while the bottom surface of the cavity maintains a constant high temperature. Non-dimensional governing equations along with the appropriate boundary conditions are solved using Galerkin finite element technique. Parametric simulation has been conducted by varying tilt angle of the base wall from 0° to 45°, Reynolds number from 0.1 to 10[3], Grashof number from 10[-2] to 10[6], and Richardson number between 0.1 and 10 for three different cases. The streamlines and the isotherms are used to describe the fluid flow and heat transfer characteristics within the enclosure. Besides, the quantitative evaluations of thermal enhancement in terms of the average Nusselt number, average fluid temperature, and Bejan number of the enclosure are presented. Effects of base wall tilt angle and the presence of nanofluid on convection heat transmission characteristics as well as Bejan number are also explored.}, } @article {pmid36506374, year = {2022}, author = {Hamza, NFA and Aljabair, S}, title = {Evaluation of thermal performance factor by hybrid nanofluid and twisted tape inserts in heat exchanger.}, journal = {Heliyon}, volume = {8}, number = {12}, pages = {e11950}, pmid = {36506374}, issn = {2405-8440}, abstract = {The thermal performance parameters of an improved heat exchanger tube fitted with various vortex generator inserts were investigated using numerical and experimental methods. The governing equations have been solved numerically by a Finite Volume approach employing the turbulence model (κ - ε). Two twisted tape types, which being inserted across a circular pipe (plain twisted tape) and (Double V-cut twisted tape), have been achieved. The hybrid nanofluid is prepared by using metal oxide [Al2O3+CuO] with distilled water at volume fraction range (0.6%, 1.2% and 1.8%), Reynolds number range (3560-8320) at twisted ratio (9.25). The experimental data for a plain tube, plain twisted tapes and double v-cut twisted tape are validated using the standard correlations available in the literature. The effect of such variables upon the average Nusselt number, friction factor, and thermal performance factor have been investigated and compared with a plain tube at the same conditions. As compared to plain twisted tape, the tube equipped with a double V-cut twisted tape with hybrid nanofluid displayed increased thermal performance. The greater vortex flow induced by the V-cuts results in more active thermal boundary layer disturbance, resulting in a greater heat transfer rate. The results show that thermal performance factor for hybrid nanofluid in plain circular tube at (∅ = 1.8 %) and Reynolds number (8320) is about (1.068), when the plain twisted tape and double v-cut twisted tape inserted with hybrid nanofluid the thermal performance factor increased to (1.33) and (1.37), respectively. The results show a similar trend for both numerical and experimental cases. The comparison between the experimental and numerical results have maximum error was (9.7)%.}, } @article {pmid36500800, year = {2022}, author = {Arshad, M and Hassan, A and Haider, Q and Alharbi, FM and Alsubaie, N and Alhushaybari, A and Burduhos-Nergis, DP and Galal, AM}, title = {Rotating Hybrid Nanofluid Flow with Chemical Reaction and Thermal Radiation between Parallel Plates.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {12}, number = {23}, pages = {}, doi = {10.3390/nano12234177}, pmid = {36500800}, issn = {2079-4991}, abstract = {This research investigates the two different hybrid nanofluid flows between two parallel plates placed at two different heights, y0&nbsp;and yh, respectively. Water-based hybrid nanofluids are obtained by using Al2O3, TiO2 and Cu as nanoparticles, respectively. The upper-level plate is fixed, while the lower-level plate is stretchable. The fluid rotates along the y-axis. The governing equations of momentum, energy and concentration are transformed into partial differential equations by using similarity transformations. These transformed equations are grasped numerically at MATLAB by using the boundary value problem technique. The influence of different parameters are presented through graphs. The numerical outcomes for rotation, Nusselt, Prandtl, and Schmidt numbers are obtained in the form of tables. The heat transfer rate increases by augmentation in the thermophoresis parameter, while it decays by increasing the Reynolds number. Oxide nanoparticles hybrid nanofluid proved more efficient as compared to mixed nanoparticles hybrid nanofluid. This research suggests using oxide nanoparticles for good heat transfer.}, } @article {pmid36475799, year = {2022}, author = {Dong, C and Wang, L and Huang, YM and Comisso, L and Sandstrom, TA and Bhattacharjee, A}, title = {Reconnection-driven energy cascade in magnetohydrodynamic turbulence.}, journal = {Science advances}, volume = {8}, number = {49}, pages = {eabn7627}, doi = {10.1126/sciadv.abn7627}, pmid = {36475799}, issn = {2375-2548}, abstract = {Magnetohydrodynamic turbulence regulates the transfer of energy from large to small scales in many astrophysical systems, including the solar atmosphere. We perform three-dimensional magnetohydrodynamic simulations with unprecedentedly large magnetic Reynolds number to reveal how rapid reconnection of magnetic field lines changes the classical paradigm of the turbulent energy cascade. By breaking elongated current sheets into chains of small magnetic flux ropes (or plasmoids), magnetic reconnection leads to a previously undiscovered range of energy cascade, where the rate of energy transfer is controlled by the growth rate of the plasmoids. As a consequence, the turbulent energy spectra steepen and attain a spectral index of -2.2 that is accompanied by changes in the anisotropy of turbulence eddies. The omnipresence of plasmoids and their consequences on, for example, solar coronal heating, can be further explored with current and future spacecraft and telescopes.}, } @article {pmid36464577, year = {2022}, author = {Song, F and Yan, Y and Sun, J}, title = {Review of insect-inspired wing micro air vehicle.}, journal = {Arthropod structure & development}, volume = {}, number = {}, pages = {101225}, doi = {10.1016/j.asd.2022.101225}, pmid = {36464577}, issn = {1873-5495}, abstract = {Micro air vehicles (MAVs) have wide application prospects in environmental monitoring, disaster rescue and other civil fields because of their flexibility and maneuverability. Compared with fixed wing and rotary wing aircraft, flapping wing micro air vehicles (FWMAVs) have higher energy utilization efficiency and lower cost and have attracted extensive attention from scientists. Insects have become excellent bionic objects for the study of FWMAVs due to their characteristics of low Reynolds number, low noise, hoverability, small size and light weight. By mimicking flying insects, it may be possible to create highly efficient biomimetic FWMAVs. In this paper, insect flight aerodynamics are reviewed, and the mechanism designs of insect-inspired FWMAVs and their aerodynamics are summarized, including the wing type effect, vibration characteristics and aerodynamic characteristics of the flapping wing.}, } @article {pmid36462002, year = {2022}, author = {Jiang, H and Wang, D and Liu, S and Sun, C}, title = {Experimental Evidence for the Existence of the Ultimate Regime in Rapidly Rotating Turbulent Thermal Convection.}, journal = {Physical review letters}, volume = {129}, number = {20}, pages = {204502}, doi = {10.1103/PhysRevLett.129.204502}, pmid = {36462002}, issn = {1079-7114}, abstract = {What is the final state of turbulence when the driving parameter approaches infinity? For the traditional Rayleigh-Bénard convection, a possible ultimate scaling dependence of the heat transport (quantified by the Nusselt number Nu) on the Rayleigh number (Ra), which can be extrapolated to arbitrarily high Ra, is predicted by theories. The existence of the ultimate scaling has been intensively debated in the past decades. In this Letter, we adopt a novel supergravitational thermal convection experimental setup to study the possible transition to the ultimate regime. This system is characterized by the combined effects of radial-dependent centrifugal force, the Earth's gravity, and the Coriolis force. With an effective gravity up to 100 times the Earth's gravity, both Ra and shear Reynolds number can be boosted due to the increase of the buoyancy driving and the additional Coriolis forces. With over a decade of Ra range, we demonstrate the existence of ultimate regime with four direct evidences: the ultimate scaling dependence of Nu versus Ra; the appearance of the turbulent velocity boundary layer profile; the enhanced strength of the shear Reynolds number; and the new statistical properties of local temperature fluctuations. The present findings will greatly improve the understanding of the flow dynamics in geophysical and astrophysical flows.}, } @article {pmid36461968, year = {2022}, author = {Rorai, C and Toschi, F and Pagonabarraga, I}, title = {Coexistence of Active and Hydrodynamic Turbulence in Two-Dimensional Active Nematics.}, journal = {Physical review letters}, volume = {129}, number = {21}, pages = {218001}, doi = {10.1103/PhysRevLett.129.218001}, pmid = {36461968}, issn = {1079-7114}, abstract = {In active nematic liquid crystals, activity is able to drive chaotic spatiotemporal flows referred to as active turbulence. Active turbulence has been characterized through theoretical and experimental work as a low Reynolds number phenomenon. We show that, in two dimensions, the active forcing alone is able to trigger hydrodynamic turbulence leading to the coexistence of active and inertial turbulence. This type of flow develops for sufficiently active and extensile flow-aligning nematics. We observe that the combined effect of an extensile nematic and large values of the flow-aligning parameter leads to a broadening of the elastic energy spectrum that promotes a growth of kinetic energy able to trigger an inverse energy cascade.}, } @article {pmid36437305, year = {2022}, author = {Robles, V and Gonzalez-Parra, JC and Cuando-Espitia, N and Aguilar, G}, title = {The effect of scalable PDMS gas-entrapping microstructures on the dynamics of a single cavitation bubble.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {20379}, pmid = {36437305}, issn = {2045-2322}, abstract = {The effect of gas-entrapping polydimethylsiloxane (PDMS) microstructures on the dynamics of cavitation bubbles laser-induced next to the PDMS surface is investigated and compared against the cavitation dynamics next to a flat smooth boundary. Local pressure gradients produced by a cavitation bubble cause the air pockets entrapped in the PDMS microstructures to expand and oscillate, leading to a repulsion of the cavitation bubble. The microstructures were fabricated as boxed crevices via a simple and scalable laser ablation technique on cast acrylic, allowing for testing of variable structure sizes and reusable molds. The bubble dynamics were observed using high speed photography and the surrounding flows were visualized and quantified using particle tracking velocimetry. Smaller entrapped air pockets showed an enhanced ability to withstand deactivation at three stand-off distances and over 50 subsequent cavitation events. This investigation provides insight into the potential to direct the collapse of a cavitation bubble away from a surface to mitigate erosion or to enhance microfluidic mixing in low Reynolds number flows.}, } @article {pmid36429949, year = {2022}, author = {Luo, J and Ma, X and Wang, L and Zhang, B and Yang, X and Yue, T}, title = {The Influence of Short-Term Heavy Rainfall on Hydraulic Characteristics and Rill Formation in the Yuanmou Dry-Hot Valley.}, journal = {International journal of environmental research and public health}, volume = {19}, number = {22}, pages = {}, doi = {10.3390/ijerph192215232}, pmid = {36429949}, issn = {1660-4601}, mesh = {*Water Movements ; *Rain ; Geologic Sediments ; Soil ; Rivers ; }, abstract = {Rill erosion is one of the major environmental problems in the world; it is an important factor with regard to land degradation and has a serious impact on production and daily life in the region. The widely distributed Yuanmou group stratum promotes the development of rill erosion, whereby the strong time-concentrated rainfall and the alternating arid-humid climate prepare the ground for the development of rills in soils. Therefore, a study of the processes of slope rill erosion was carried out, and a gravel-soil slope in the Yuanmou dry-hot valley was chosen to simulate short-term heavy rainfall (25 mm/h) (No. 1 plot) and moderate rainfall (15 mm/h) (No. 2 plot), to study the erosion processes of soil and the dynamic characteristics of runoff involved in erosion. The study results showed that the width of runoff was significantly different between the two plots, while the depth of runoff was not significantly different. During the rill formation process, the width of the two plots first decreased and then increased with increasing washout duration, while its depth did not change significantly. Flow was the key factor in determining the hydraulic characteristics of runoff, and it had a significant or extremely significant positive correlation with hydraulic characteristics parameters, except in the case of Fr (Froude number) (r = 0.039). The total sediment content (CS) of plot No. 1 (0.158 g/cm[3]) was significantly different from that of plot No. 2 (0.153 g/cm[3]), and both CSs in the two plots decreased with increasing washout duration. The CS had an extremely significant negative correlation with τ (runoff shear force) (r = -0.863 **) and DW-f (Darcy-Weisbach drag coefficient) (r = -0.863 **) and a significant negative correlation with Re (Reynolds number) (r = -0.735 *) in the short-term heavy rainfall experiment, while the CS had a significant positive correlation with V (velocity) (r = 0.814 *), R (hydraulic radius) (r = 0.811 *) and P (unit stream power) (r = 0.811 *) in the moderate rainfall experiment. The results of this study will help guide further examination of the processes involved in the dynamic mechanisms of rill erosion on slopes under short-term heavy rainfall conditions.}, } @article {pmid36422415, year = {2022}, author = {Kumari, N and Alam, T and Ali, MA and Yadav, AS and Gupta, NK and Siddiqui, MIH and Dobrotă, D and Rotaru, IM and Sharma, A}, title = {A Numerical Investigation on Hydrothermal Performance of Micro Channel Heat Sink with Periodic Spatial Modification on Sidewalls.}, journal = {Micromachines}, volume = {13}, number = {11}, pages = {}, pmid = {36422415}, issn = {2072-666X}, abstract = {Electronic gadgets have been designed to incorporating very small components such as microcontrollers, electronic chips, transistors, microprocessors, etc. These components are exceptionally heat sensitive and can be wrecked if heat is not released. As a result, the thermal control of such components is critical to their optimum performance and extended life. The use of a microchannel heat sink (MCHS) has shown promising solutions to remove the excess heat. In this paper, we have proposed a novel design of MCHS and investigated it numerically. Four different surface modifications on the sidewall of the passage, namely, extended triangular surface (ETS), extended circular surface (ECS), triangular groove surface (TGS), and the circular groove surface (CGS) in the passage of the microchannel have been exploited in the Reynolds number of 100-900. In the presence of geometrical modification, the cooling capacities have been enhanced. The results show that the Nusselt numbers of ETS-MCHS, ECS-MCHS, TGS-MCHS, and CGS-MCHS are increased by 4.30, 3.61, 1.62, and 1.41 times in comparison to the Nusselt number of MCHS with smooth passage, while the friction factor values are increased by 7.33, 6.03, 2.74, and 1.68 times, respectively. In addition, the thermohydraulic performance parameter (THPP) has been evaluated and discussed. The fact that MCHS have THPP values greater than unity demonstrates that the passage's geometries are a practical means of achieving effective thermal management.}, } @article {pmid36411532, year = {2022}, author = {Toyama, K and Togi, F and Harada, S}, title = {Mass Transfer from Mobile to Immobile Regions in Irregularly Shaped Micro-Channels at Low Reynolds Number.}, journal = {Ground water}, volume = {}, number = {}, pages = {}, doi = {10.1111/gwat.13276}, pmid = {36411532}, issn = {1745-6584}, abstract = {Transient mass transfer in rough-walled micro-channels was investigated experimentally. We conducted experiments using rough-walled channels with various irregularities at small Reynolds number conditions. Mass transfer in the mainstream (mobile region) and dead water region (immobile region) were quantified using an image analysis technique based on absorption photometry. The experimental results showed that the solute dispersion in the mobile region was influenced by the irregular shape of the channel wall complicatedly. In contrast, mass transfer in the immobile region occurred by molecular diffusion independently on the wall roughness in our experimental conditions. The irregular shape of channel wall may enhance the mass transfer in mobile region by distorting the velocity distribution (Togi et al., 2020), while the solute redistribution to immobile region may suppress it in streamwise direction, just on a longer time scale. We developed a mass transfer model analogous to Mobile-Immobile model (MIM model) proposed by previous studies. The concept of the model is the same as the previous study (Zhou et al., 2019) and the coefficients of the model describing mass transfer in each region were quantified from the experimental results as functions of geometric characteristics of the rough-walled channel. In addition, mass transfer coefficient from mobile to immobile regions were derived mathematically based on the experimental results. The MIM model with the coefficients derived in this study well describes solute dispersion in variously shaped irregular channels quantitatively.}, } @article {pmid36405040, year = {2022}, author = {Kaziz, S and Ben Mariem, I and Echouchene, F and Belkhiria, M and Belmabrouk, H}, title = {Taguchi optimization of integrated flow microfluidic biosensor for COVID-19 detection.}, journal = {European physical journal plus}, volume = {137}, number = {11}, pages = {1235}, pmid = {36405040}, issn = {2190-5444}, abstract = {In this research, Taguchi's method was employed to optimize the performance of a microfluidic biosensor with an integrated flow confinement for rapid detection of the SARS-CoV-2. The finite element method was used to solve the physical model which has been first validated by comparison with experimental results. The novelty of this study is the use of the Taguchi approach in the optimization analysis. An L 8 2 7 orthogonal array of seven critical parameters-Reynolds number (Re), Damköhler number (Da), relative adsorption capacity (σ), equilibrium dissociation constant (KD), Schmidt number (Sc), confinement coefficient (α) and dimensionless confinement position (X), with two levels was designed. Analysis of variance (ANOVA) methods are also used to calculate the contribution of each parameter. The optimal combination of these key parameters was Re = 10[-2], Da = 1000, σ = 0.5, K D = 5, Sc = 10[5], α = 2 and X = 2 to achieve the lowest dimensionless response time (0.11). Among the all-optimization factors, the relative adsorption capacity (σ) has the highest contribution (37%) to the reduction of the response time, while the Schmidt number (Sc) has the lowest contribution (7%).}, } @article {pmid36399789, year = {2022}, author = {Jhun, CS and Xu, L and Siedlecki, C and Bartoli, CR and Yeager, E and Lukic, B and Scheib, CM and Newswanger, R and Cysyk, JP and Shen, C and Bohnenberger, K and Weiss, WJ and Rosenberg, G}, title = {Kinetic and Dynamic Effects on Degradation of von Willebrand Factor.}, journal = {ASAIO journal (American Society for Artificial Internal Organs : 1992)}, volume = {}, number = {}, pages = {}, doi = {10.1097/MAT.0000000000001848}, pmid = {36399789}, issn = {1538-943X}, abstract = {The loss of high molecular weight multimers (HMWM) of von Willebrand factor (vWF) in aortic stenosis (AS) and continuous-flow left ventricular assist devices (cf-LVADs) is believed to be associated with high turbulent blood shear. The objective of this study is to understand the degradation mechanism of HMWM in terms of exposure time (kinetic) and flow regime (dynamics) within clinically relevant pathophysiologic conditions. A custom high-shear rotary device capable of creating fully controlled exposure times and flows was used. The system was set so that human platelet-poor plasma flowed through at 1.75 ml/sec, 0.76 ml/sec, or 0.38 ml/sec resulting in the exposure time (texp) of 22, 50, or 100 ms, respectively. The flow was characterized by the Reynolds number (Re). The device was run under laminar (Re = 1,500), transitional (Re = 3,000; Re = 3,500), and turbulent (Re = 4,500) conditions at a given texp followed by multimer analysis. No degradation was observed at laminar flow at all given texp. Degradation of HMWM at a given texp increases with the Re. Re (p < 0.0001) and texp (p = 0.0034) are significant factors in the degradation of HMWM. Interaction between Re and texp, however, is not always significant (p = 0.73). http://links.lww.com/ASAIO/A920.}, } @article {pmid36399753, year = {2022}, author = {Bermudez, G and Alexakis, A}, title = {Saturation of Turbulent Helical Dynamos.}, journal = {Physical review letters}, volume = {129}, number = {19}, pages = {195101}, doi = {10.1103/PhysRevLett.129.195101}, pmid = {36399753}, issn = {1079-7114}, abstract = {The presence of large scale magnetic fields in nature is often attributed to the inverse cascade of magnetic helicity driven by turbulent helical dynamos. In this Letter, we show that in turbulent helical dynamos, the inverse flux of magnetic helicity toward the large scales Π_{H} is bounded by |Π_{H} |≤cεk_{η} ^{-1}, where ε is the energy injection rate, k_{η} is the Kolmogorov magnetic dissipation wave number, and c an order one constant. Assuming the classical isotropic turbulence scaling, the inverse flux of magnetic helicity Π_{H} decreases at least as a -3/4 power law with the magnetic Reynolds number Rm: |Π_{H} |≤cεℓ_{f} Rm^{-3/4} max[Pm,1]^{1/4}, where Pm is the magnetic Prandtl number and ℓ_{f} the forcing length scale. We demonstrate this scaling with Rm using direct numerical simulations of turbulent dynamos forced at intermediate scales. The results further indicate that nonlinear saturation is achieved by a balance between the inverse cascade and dissipation at domain size scales L for which the saturation value of the magnetic energy is bounded by E_{m} ≤cL(εℓ_{f} )^{2/3} Rm^{1/4} max[1,Pm]^{1/4} . Numerical simulations also demonstrate this bound. These results are independent of the dynamo mechanism considered. In our setup, they imply that inviscid mechanisms cannot explain large scale magnetic fields and have critical implications for the modeling of astrophysical dynamos.}, } @article {pmid36397500, year = {2022}, author = {Budanur, NB and Kantz, H}, title = {Scale-dependent error growth in Navier-Stokes simulations.}, journal = {Physical review. E}, volume = {106}, number = {4-2}, pages = {045102}, doi = {10.1103/PhysRevE.106.045102}, pmid = {36397500}, issn = {2470-0053}, abstract = {We estimate the maximal Lyapunov exponent at different resolutions and Reynolds numbers in large eddy simulations (LES) and direct numerical simulations of sinusoidally driven Navier-Stokes equations in three dimensions. Independent of the Reynolds number when nondimensionalized by Kolmogorov units, the LES Lyapunov exponent diverges as an inverse power of the effective grid spacing showing that the fine scale structures exhibit much faster error growth rates than the larger ones. Effectively, i.e., ignoring the cutoff of this phenomenon at the Kolmogorov scale, this behavior introduces an upper bound to the prediction horizon that can be achieved by improving the precision of initial conditions through refining of the measurement grid.}, } @article {pmid36388976, year = {2022}, author = {Yao, N and Wang, H and Wang, B and Wang, X and Huang, J}, title = {Convective thermal cloaks with homogeneous and isotropic parameters and drag-free characteristics for viscous potential flows.}, journal = {iScience}, volume = {25}, number = {11}, pages = {105461}, pmid = {36388976}, issn = {2589-0042}, abstract = {Although convective thermal cloaking has been advanced significantly, the majority of related researches have concentrated on creeping viscous potential flows. Here, we consider convective thermal cloaking works in non-creeping viscous potential flows, and propose a combination of the separation of variables method and the equivalent-medium integral method to analytically deduce the parameters of convective thermal cloaks with isotropic-homogeneous dynamic viscosity and thermal conductivity. Through numerical simulation, we demonstrate the cloaks can hide the object from thermo-hydrodynamic fields. Besides, by comparing the drag force cloaks bear in cloak case and the objects bear in object-existent case, we find convective thermal cloaks can considerably reduce the drag force, which appears drag-free characteristics. Finally, it is our hope that these developed methods can reduce the difficulties of metadevices fabrications, promote the development of drag reduction technology under higher Reynolds number, and shed light on the control of other multi-physics systems.}, } @article {pmid36384832, year = {2022}, author = {Cao, BZ and Wang, J and Zhao, YJ and Liu, C}, title = {[Hydrodynamic characteristics of grass swale runoff in Guanzhong area of Loess Plateau, Northwest China.].}, journal = {Ying yong sheng tai xue bao = The journal of applied ecology}, volume = {33}, number = {11}, pages = {2979-2986}, doi = {10.13287/j.1001-9332.202211.023}, pmid = {36384832}, issn = {1001-9332}, mesh = {*Poaceae ; *Water Movements ; Hydrodynamics ; Rain ; Soil ; China ; }, abstract = {Grass swale has been widely used in sponge city construction, which can effectively improve the urban ecological environment. To explore the regulation mechanism of runoff in grass swale, runoff scouring experiment was carried out to study the hydrodynamic characteristics of runoff and the distribution of cross-section velocity under the combined conditions of five slopes (1%, 2%, 3%, 4%, 5%) and five scour flows (20, 30, 40, 50, 60 L·min[-1]). With the increases of flow rate and slope, flow velocity, Reynolds number and Froude number all increased gradually, while the Manning roughness coefficient and Darcy-Weisbach friction coefficient decreased gradually. The velocity (V) could be expressed as a power function V=0.3387Q[0.555]S[0.6601] of flow rate (Q) and slope (S). The variation ranges of Reynolds number and Froude number were 1160.95-6596.82 and 0.17-1.21, respectively. The runoff flow patterns were all turbulent. The flow pattern was greatly affected by the slope. When flow rate and slope were small, they had great influence on friction coefficient. Under the experimental conditions, the Darcy-Weisbach friction coefficient was negatively correlated with Reynolds number. The velocity distribution of cross-section showed symmetrical distribution on both sides of the center. The maximum velocity point was located at the center of water surface. With the increases of flow rate and slope, the velocity contours of cross section gradually became dense and the gradient of the velocity change increased. Our results provide a theoretical basis for the design, application and hydraulic calculation of grass swale in the construction of sponge cities in loess areas, and reveal the runoff regulation mechanism by analyzing the hydraulic characteristics of grass swale runoff.}, } @article {pmid36383261, year = {2022}, author = {Karami, A and Ranjbar, B and Rahimi, M and Mohammadi, F}, title = {Novel hybrid neuro-fuzzy model to anticipate the heat transfer in a heat exchanger equipped with a new type of self-rotating tube insert.}, journal = {The European physical journal. E, Soft matter}, volume = {45}, number = {11}, pages = {92}, pmid = {36383261}, issn = {1292-895X}, mesh = {*Hot Temperature ; *Algorithms ; Friction ; }, abstract = {In this investigation, a combination of the wingsuit flying search (WFS) and teaching-learning-based optimization (TLBO) algorithms is developed as a new combinatorial optimization algorithm. The proposed combinatorial algorithm is tested over some well-known benchmark functions and then integrated with the artificial neural network (ANN) to construct a novel hybrid model. After that, the obtained hybrid model is employed to anticipate the experimentally obtained values of the average Nusselt number (Nu), average friction coefficient (f) as well as thermal-hydraulic performance ratio (η), in a heat exchanger equipped with a new type of self-rotating tube insert, against governing parameters. The insert is placed in the tube side of the water heater to heat natural gas. The proposed insert consists of various numbers of self-rotating modules. Indeed, the rotating insert is introduced to create effective secondary sweeping flow on the inner side of the tube. Since this type of tube insert simultaneously provides heat transfer enhancement and undesired pressure drop, a thermal-hydraulic performance ratio is defined to consider both of them. The governing parameters are the number of inserts (0 ≤ N ≤ 30), reservoir's temperature (40 °C ≤ TR ≤ 50 °C) as well as Reynolds number (6 × 10[3] ≤ Re ≤ 18 × 10[3]). It was found that the WFS-TLBO enhances the effectiveness of the main ANN in anticipating the Nusselt number (Nu), average friction coefficient (f) as well as performance ratio (η). Moreover, introducing the WFS-TLBO algorithm into the neural network provides an enhancement in the effectiveness of the hybrid models based on the single WFS and TLBO algorithms in anticipating the same parameters.}, } @article {pmid36378533, year = {2022}, author = {Wei, SX and Yang, H and Au, CT and Xie, TL and Yin, SF}, title = {Mixing Characteristic and High-Throughput Synthesis of Cadmium Sulfide Nanoparticles with Cubic Hexagonal Phase Junctions in a Chaotic Millireactor.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {38}, number = {47}, pages = {14439-14450}, doi = {10.1021/acs.langmuir.2c02087}, pmid = {36378533}, issn = {1520-5827}, abstract = {A four-stage oscillating feedback millireactor with splitters (S-OFM) was designed to improve the mixing performance based on chaotic advection. Three-dimensional CFD simulations were used to investigate its flow characteristics and mixing performance, and the generation mechanisms of secondary flows were examined. The results show that the mixing index (MIcup) increased with the increase in the Reynolds number (Re), and MIcup could reach 99.8% at Re = 663. Poincaré mapping and Kolmogorov entropy were adopted to characterize the chaotic advection intensity, which indicates that there is a intensity increase with the increase in Re. In addition, the results of Villermaux-Dushman experiments demonstrate that S-OFM performs excellently, and the mixing time could reach 1.04 ms at Re = 2764. Finally, S-OFM was successfully used to synthesize CdS nanoparticles with cubic hexagonal phase junctions. At a flow rate of 180 mL/min, the average particle size was 10.5 nm and the particle size distribution was narrow (with a coefficient of variation of 0.14).}, } @article {pmid36374705, year = {2022}, author = {Antunes, GC and Malgaretti, P and Harting, J and Dietrich, S}, title = {Pumping and Mixing in Active Pores.}, journal = {Physical review letters}, volume = {129}, number = {18}, pages = {188003}, doi = {10.1103/PhysRevLett.129.188003}, pmid = {36374705}, issn = {1079-7114}, abstract = {We show both numerically and analytically that a chemically patterned active pore can act as a micro- or nanopump for fluids, even if it is fore-aft symmetric. This is possible due to a spontaneous symmetry breaking which occurs when advection rather than diffusion is the dominant mechanism of solute transport. We further demonstrate that, for pumping and tuning the flow rate, a combination of geometrical and chemical inhomogeneities is required. For certain parameter values, the flow is unsteady, and persistent oscillations with a tunable frequency appear. Finally, we find that the flow exhibits convection rolls and hence promotes mixing in the low Reynolds number regime.}, } @article {pmid36374283, year = {2022}, author = {Hopkins, CC and Shen, AQ and Haward, SJ}, title = {Effect of blockage ratio on flow of a viscoelastic wormlike micellar solution past a cylinder in a microchannel.}, journal = {Soft matter}, volume = {18}, number = {46}, pages = {8856-8866}, doi = {10.1039/d2sm01162j}, pmid = {36374283}, issn = {1744-6848}, abstract = {We present experiments on the flow of a viscoelastic wormlike micellar solution around cylinders (radius R) confined in straight microchannels (width W). Thirteen flow geometries are tested where the blockage ratio is varied over a wide range 0.055 ≤ BR = 2R/W ≤ 0.63. Experiments are performed at negligible Reynolds number, and for Weissenberg numbers Wi = λU/R up to 1000, where U is the average flow speed and λ is the relaxation time of the fluid. Micro-particle image velocimetry is used to characterise the flow state at each BR and Wi. In all of the geometries, a first critical Weissenberg number marks a transition from symmetric flow to an asymmetric but time-steady flow state, while a second higher critical Weissenberg number marks the onset of time-dependent flows. However, we report a clear shift in behaviour over a narrow intermediate range of 0.33 ≲ BR ≲ 0.41. Channels with BR ≤ 0.33 fall in a 'low' BR regime, with instabilities that originate from the downstream stagnation point, while those with BR ≥ 0.44 fall in a 'high' BR regime, with instabilities developing at the upstream stagnation point. Behaviour within the newly-identified intermediate BR regime is complex due to the competing influence of the two stagnation points. We summarise all our results in a flow state diagram covering Wi-BR parameter space, clearly defining the different regimes of blockage ratio for the first time. Our results contribute to the understanding of the complexities of viscoelastic flow in this benchmark geometry.}, } @article {pmid36369608, year = {2022}, author = {Chen, Y and Feng, X and Shi, X and Cai, W and Li, B and Zhao, Y}, title = {Evaluation of computational fluid dynamics models for predicting pediatric upper airway airflow characteristics.}, journal = {Medical & biological engineering & computing}, volume = {}, number = {}, pages = {}, pmid = {36369608}, issn = {1741-0444}, abstract = {Computational fluid dynamics (CFD) has the potential for use as a clinical tool to predict the aerodynamics and respiratory function in the upper airway (UA) of children; however, careful selection of validated computational models is necessary. This study constructed a 3D model of the pediatric UA based on cone beam computed tomography (CBCT) imaging. The pediatric UA was 3D printed for pressure and velocity experiments, which were used as reference standards to validate the CFD simulation models. Static wall pressure and velocity distribution inside of the UA under inhale airflow rates from 0 to 266.67 mL/s were studied by CFD simulations based on the large eddy simulation (LES) model and four Reynolds-averaged Navier-Stokes (RANS) models. Our results showed that the LES performed best for pressure prediction; however, it was much more time-consuming than the four RANS models. Among the RANS models, the Low Reynolds number (LRN) SST k-ω model had the best overall performance at a series of airflow rates. Central flow velocity determined by particle image velocimetry was 3.617 m/s, while velocities predicted by the LES, LRN SST k-ω, and k-ω models were 3.681, 3.532, and 3.439 m/s, respectively. All models predicted jet flow in the oropharynx. These results suggest that the above CFD models have acceptable accuracy for predicting pediatric UA aerodynamics and that the LRN SST k-ω model has the most potential for clinical application in pediatric respiratory studies.}, } @article {pmid36365668, year = {2022}, author = {de Araujo, MT and Furlan, L and Brandi, A and Souza, L}, title = {A Semi-Analytical Method for Channel and Pipe Flows for the Linear Phan-Thien-Tanner Fluid Model with a Solvent Contribution.}, journal = {Polymers}, volume = {14}, number = {21}, pages = {}, pmid = {36365668}, issn = {2073-4360}, abstract = {This work presents a semi-analytical method for laminar steady-state channel and pipe flows of viscoelastic fluids using the Linear Phan-Thien-Tanner (LPTT) constitutive equation, with solvent viscosity contribution. For the semi-analytical method validation, it compares its results and two analytical solutions: the Oldroyd-B model and the simplified LPTT model (without solvent viscosity contribution). The results adopted different values of the dimensionless parameters, showing their influence on the viscoelastic fluid flow. The results include the distribution of the streamwise velocity component and the extra-stress tensor components in the wall-normal direction. In order to investigate the proposed semi-analytical method, different solutions were obtained, both for channel and pipe flows, considering different values of Reynolds number, solvent viscosity contribution in the homogeneous mixture, elongational parameter, shear parameter, and Weissenberg number. The results show that the proposed semi-analytical method can find a laminar solution using the non-Newtonian LPTT model with solvent viscosity contribution and verify the effect of the parameters in the resulting flow field.}, } @article {pmid36364597, year = {2022}, author = {Baig, MF and Chen, GM and Tso, CP}, title = {The Thermal Performance Analysis of an Al2O3-Water Nanofluid Flow in a Composite Microchannel.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {12}, number = {21}, pages = {}, pmid = {36364597}, issn = {2079-4991}, abstract = {Partial filling of porous medium insert in a channel alleviates the tremendous pressure drop associated with a porous medium saturated channel, and enhances heat transfer at an optimum fraction of porous medium filling. This study pioneered an investigation into the viscous dissipative forced convective heat transfer in a parallel-plate channel, partially occupied with a porous medium at the core, under local thermal non-equilibrium condition. Solving the thermal energy equation along the Darcy-Brinkman equation, new exact temperature fields and Nusselt number are presented under symmetrical isoflux thermal boundary condition. Noteworthy is the heat flux bifurcation at the interface between the clear fluid and porous medium driven by viscous dissipation, in cases where the combined hydrodynamic resistance to fluid flow and thermal resistance to fluid conduction is considerable in low Darcy number porous medium insert. However, viscous dissipation does not affect the qualitative variation of the Nusselt number with the fraction of porous medium filling. By using Al2O3-Water nanofluid as the working fluid in a uniformly heated microchannel, partially filled with an optimum volume fraction of porous medium, the heat transfer coefficient improves as compared to utilizing water. The accompanied viscous dissipation however has a more adverse impact on the heat transfer coefficient of nanofluids with an increasing Reynolds number.}, } @article {pmid36363954, year = {2022}, author = {Chen, Z and Wang, Y and Zhou, S}, title = {Numerical Analysis of Mixing Performance in an Electroosmotic Micromixer with Cosine Channel Walls.}, journal = {Micromachines}, volume = {13}, number = {11}, pages = {}, pmid = {36363954}, issn = {2072-666X}, abstract = {Micromixers have significant potential in the field of chemical synthesis and biological pharmaceuticals, etc. In this study, the design and numerical simulations of a passive micromixer and a novel active electroosmotic micromixer by assembling electrode pairs were both presented with a cosine channel wall. The finite element method (FEM) coupled with Multiphysics modeling was used. To propose an efficient micromixer structure, firstly, different geometrical parameters such as amplitude-to-wavelength ratio (a/c) and mixing units (N) in the steady state without an electric field were investigated. This paper aims to seek a high-quality mixing solution. Therefore, based on the optimization of the above parameters of the passive micromixer, a new type of electroosmotic micromixer with an AC electric field was proposed. The results show that the vortices generated by electroosmosis can effectively induce fluid mixing. The effects of key parameters such as the Reynolds number, the number of electrode pairs, phase shift, voltage, and electrode frequency on the mixing performance were specifically discussed through numerical analysis. The mixing efficiency of the electroosmotic micromixer is quantitatively analyzed, which can be achieved at 96%. The proposed micromixer has a simple structure that can obtain a fast response and high mixing index.}, } @article {pmid36363898, year = {2022}, author = {Dai, Y and Cha, H and Nguyen, NK and Ouyang, L and Galogahi, F and Yadav, AS and An, H and Zhang, J and Ooi, CH and Nguyen, NT}, title = {Dynamic Behaviours of Monodisperse Double Emulsion Formation in a Tri-Axial Capillary Device.}, journal = {Micromachines}, volume = {13}, number = {11}, pages = {}, pmid = {36363898}, issn = {2072-666X}, abstract = {We investigated experimentally, analytically, and numerically the formation process of double emulsion formations under a dripping regime in a tri-axial co-flow capillary device. The results show that mismatches of core and shell droplets under a given flow condition can be captured both experimentally and numerically. We propose a semi-analytical model using the match ratio between the pinch-off length of the shell droplet and the product of the core growth rate and its pinch-off time. The mismatch issue can be avoided if the match ratio is lower than unity. We considered a model with the wall effect to predict the size of the matched double emulsion. The model shows slight deviations with experimental data if the Reynolds number of the continuous phase is lower than 0.06 but asymptotically approaches good agreement if the Reynolds number increases from 0.06 to 0.14. The numerical simulation generally agrees with the experiments under various flow conditions.}, } @article {pmid36363842, year = {2022}, author = {Cao, M and Cao, S and Zhao, J and Zhu, J}, title = {Numerical Study of Thermal Enhancement in a Single- and Double-Layer Microchannel Heat Sink with Different Ribs.}, journal = {Micromachines}, volume = {13}, number = {11}, pages = {}, pmid = {36363842}, issn = {2072-666X}, abstract = {In this paper, a microchannel heat sink model was proposed to realize single- and double- layer flow through built-in ribs. The finite element volume method was used to analyze the influence of the length, thickness and angle of the inner rib on the flow and heat transfer characteristics of the microchannel heat sink. The pressure drop, temperature field, flow field, and thermal characteristics are given. The numerical simulation results show that the rectangular rib plate makes the fluid in the microchannel heat sink flow alternately in the upper and lower layers, which can effectively enhance heat transfer. However, with the increase in rib length, the comprehensive evaluation factor decreases. The change of the angle of the rectangular rib plate has little influence on the Nusselt number. The change rate of the comprehensive evaluation factor of the thickness of the rectangular rib plate is the largest. When the Reynolds number is 1724, the comprehensive evaluation factor of Case 9 is 4.7% higher than that of Case 2. According to the parameter study of the built-in rib plate, the optimal parameter combination is given, in which the angle is 0°, the length is 7.5 mm, and the thickness is 0.2-0.3 mm.}, } @article {pmid36363584, year = {2022}, author = {Cancilla, N and Tamburini, A and Tarantino, A and Visconti, S and Ciofalo, M}, title = {Friction and Heat Transfer in Membrane Distillation Channels: An Experimental Study on Conventional and Novel Spacers.}, journal = {Membranes}, volume = {12}, number = {11}, pages = {}, pmid = {36363584}, issn = {2077-0375}, abstract = {The results of an experimental investigation on pressure drop and heat transfer in spacer-filled plane channels, which are representative of Membrane Distillation units, are presented and discussed. Local and mean heat transfer coefficients were obtained by using Thermochromic Liquid Crystals and Digital Image Processing. The performances of a novel spacer geometry, consisting of spheres that are connected by cylindrical rods, and are hereafter named spheres spacers, were compared with those of more conventional woven and overlapped spacers at equal values of the Reynolds number Re (in the range ~150 to ~2500), the pitch-to-channel height ratio, the flow attack angle and the thermal boundary conditions (two-side heat transfer). For any flow rate, the novel spacer geometry provided the least friction coefficient and a mean Nusselt number intermediate between those of the overlapped and the woven spacers. For any pressure drop and for any pumping power, the novel spacer provided the highest mean Nusselt number over the whole Reynolds number range that was investigated. The influence of buoyancy was also assessed for the case of the horizontal channels. Under the experimental conditions (channel height H ≈ 1 cm, ΔT ≈ 10 °C), it was found to be large in empty (spacer-less) channels that were up to Re ≈ 1200 (corresponding to a Richardson number Ri of ~0.1), but it was much smaller and limited to the range Re < ~500 (Ri < ~0.5) in the spacer-filled channels.}, } @article {pmid36359756, year = {2022}, author = {Soulsbury, CD and Humphries, S}, title = {Biophysical Determinants and Constraints on Sperm Swimming Velocity.}, journal = {Cells}, volume = {11}, number = {21}, pages = {}, pmid = {36359756}, issn = {2073-4409}, mesh = {Animals ; Male ; *Sperm Motility ; *Semen ; Spermatozoa ; Biological Evolution ; Flagella ; }, abstract = {Over the last 50 years, sperm competition has become increasingly recognised as a potent evolutionary force shaping male ejaculate traits. One such trait is sperm swimming speed, with faster sperm associated with increased fertilisation success in some species. Consequently, sperm are often thought to have evolved to be longer in order to facilitate faster movement. However, despite the intrinsic appeal of this argument, sperm operate in a different biophysical environment than we are used to, and instead increasing length may not necessarily be associated with higher velocity. Here, we test four predictive models (ConstantPower Density, Constant Speed, Constant Power Transfer, Constant Force) of the relationship between sperm length and speed. We collated published data on sperm morphology and velocity from 141 animal species, tested for structural clustering of sperm morphology and then compared the model predictions across all morphologically similar sperm clusters. Within four of five morphological clusters of sperm, we did not find a significant positive relationship between total sperm length and velocity. Instead, in four morphological sperm clusters we found evidence for the Constant Speed model, which predicts that power output is determined by the flagellum and so is proportional to flagellum length. Our results show the relationship between sperm morphology (size, width) and swimming speed is complex and that traditional models do not capture the biophysical interactions involved. Future work therefore needs to incorporate not only a better understanding of how sperm operate in the microfluid environment, but also the importance of fertilising environment, i.e., internal and external fertilisers. The microenvironment in which sperm operate is of critical importance in shaping the relationship between sperm length and form and sperm swimming speed.}, } @article {pmid36351992, year = {2022}, author = {Abdizadeh, GR and Farokhinejad, M and Ghasemloo, S}, title = {Numerical investigation on the aerodynamic efficiency of bio-inspired corrugated and cambered airfoils in ground effect.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {19117}, pmid = {36351992}, issn = {2045-2322}, mesh = {Animals ; *Flight, Animal ; *Wings, Animal ; Models, Biological ; Computer Simulation ; }, abstract = {This research numerically investigates the flapping motion effect on the flow around two subsonic airfoils near a ground wall. Thus far, the aerodynamic efficiency of the dragonfly-inspired flapping airfoil has not been challenged by an asymmetric cambered airfoil considering the ground effect phenomenon, especially in the MAV flight range. The analysis is carried out on the basis of an unsteady Reynolds-averaged Navier-stokes (URANS) simulation, whereby the Transition SST turbulence model simulates the flow characteristics. Dragonfly-inspired and NACA4412 airfoils are selected in this research to assess the geometry effect on aerodynamic efficiency. Moreover, the impacts of Reynolds number (Re), Strouhal number (St), and average ground clearance of the flapping airfoil are investigated. The results indicate a direct relationship between the airfoil's aerodynamic performance ([Formula: see text]/[Formula: see text]) and the ground effect. The [Formula: see text]/[Formula: see text] increases by reducing the airfoil and ground distance, especially at [Formula: see text]. At [Formula: see text], by increasing the St from 0.2 to 0.6, the values of [Formula: see text]/[Formula: see text] decrease from 10.34 to 2.1 and 3.22 to 1.8 for NACA4412 and dragonfly airfoils, respectively. As a result, the [Formula: see text]/[Formula: see text] of the NACA4412 airfoil is better than that of the dragonfly airfoil, especially at low oscillation frequency. The efficiency difference between the two airfoils at St=0.6 is approximately 14%, indicating that the [Formula: see text]/[Formula: see text] difference decreases substantially with increasing frequency. For [Formula: see text], the results show the dragonfly airfoil to have better [Formula: see text]/[Formula: see text] in all frequencies than the NACA4412 airfoil.}, } @article {pmid36340085, year = {2022}, author = {Dang, J and Duan, X and Tian, S}, title = {Wall Effects for Spheroidal Particle in Confined Bingham Plastic Fluids.}, journal = {ACS omega}, volume = {7}, number = {43}, pages = {38717-38727}, pmid = {36340085}, issn = {2470-1343}, abstract = {The wall effects on the sedimentation motion of a single spheroidal particle in cylindrical tubes filled with Bingham plastic fluid are investigated with the fixed computational domain using the Computational Fluid Dynamic (CFD) model in steady-state mode. The CFD model is validated with literature in both bounded and unbounded mediums. The rheological model of the Bingham plastic fluid is regularized with a smoothly varying viscosity. The retardation effects of the tube wall are presented in functions of Reynolds number Re, radius ratio λ (the radius of the tube to the semiaxis of the particle normal to the flow λ = R/r), aspect ratio E (the ratio of the semiaxis of the particle along the flow to r, E = b/r), and Bingham number Bn. The simulation results demonstrate that the drag coefficient C D declines with the rise in Reynolds number. The relative contribution to drag coefficient from the pressure force increases with larger Bingham number comparing with that from the friction force. The formation and size of the recirculation wake is suppressed by the yield stress. While Bn is approaching infinity, the limiting behavior is observed in the location of yield surface and the value of yield-gravity parameter. The values of critical yield-gravity parameter are explicitly given at different values of E, showing independence with Re and λ. For the flow with Bn ≥ 100, the influence of wall can be even ignored while λ is larger than 5.}, } @article {pmid36337262, year = {2022}, author = {Rutledge, KM}, title = {Sniffing out Stingray Noses: The Functional Morphology of Batoid Olfaction.}, journal = {Integrative organismal biology (Oxford, England)}, volume = {4}, number = {1}, pages = {obac043}, pmid = {36337262}, issn = {2517-4843}, abstract = {Batoid fishes (rays, skates, sawfishes, and guitarfishes) are macrosmatic, meaning they rely on their sense of smell as one of the primary senses for survival and reproduction. Olfaction is important for long-distance tracking and navigation, predator and prey recognition, and conspecific signaling. However, the mechanisms by which batoids harness odorants is unknown. Without a direct pump-like system, it is hypothesized that batoids irrigate their nostrils via one or a combination of the following: the motion pump, buccopharyngeal pump, pressure (ex. pitot-like mechanism), or a shearing force (ex. viscous entrainment). These mechanisms rely on the size, shape, and position of the nostrils with respect to the head and to each other. Batoids are united as a group by their dorsoventrally compressed body plans, with nostrils on the ventral side of their body. This position presents several challenges for odor capture and likely limits the effectivity of the motion pump. Batoid fishes display an expansive nasal morphology, with inlet nostrils ranging from thin, vertical slits to wide, horizontal ovals to protruding, tube-like funnels, and more. In this paper, a morphometric model is developed to quantify the vast diversity in batoid nose shapes, sizes, and positions on the head in an ecological and functional framework. Specifically, swimming mode, lifestyle, habitat, and diet are examined for correlations with observed nasal morphotypes. Morphometric measurements were taken on all 4 orders present in Batoidea to broadly encompass batoid nasal diversity (Rhinopristiformes 4/5 families; Rajiformes 2/4 families; Torpediniformes 4/4 families; Myliobatiformes 8/11 families). All batoid external nasal diversity was found to be categorized into 5 major morphological groups and were termed: flush nare [circle, comma, intermediate], open nare, and protruding nare. Several morphometric traits remained significant when accounting for shared ancestry, including the position and angle of the nostril on the head, the width of the inlet hole, and the spacing of the nostrils from each other. These measurements were found to be closely correlated and statistically significant with the swimming mode of the animal. This study provides the first crucial step in understanding batoid olfaction, by understanding the diversity of the morphology of the system. Because odor capture is a strictly hydrodynamic process, it may be that factors relating more directly to the fluid dynamics (i.e., swimming mode, velocity, Reynolds number) may be more important in shaping the evolution of the diversity of batoid noses than other ecological factors like habitat and diet.}, } @article {pmid36332888, year = {2022}, author = {Saleem, T and Powell, T and Walker, W and Raju, S}, title = {Assessment of flow mechanics in the lower extremity venous system.}, journal = {Journal of vascular surgery. Venous and lymphatic disorders}, volume = {}, number = {}, pages = {}, doi = {10.1016/j.jvsv.2022.10.009}, pmid = {36332888}, issn = {2213-3348}, abstract = {BACKGROUND: The Reynolds number (Re) is a dimensionless parameter that describes fluid flow mechanics. Veins are compliant and collapsible vascular conduits that can accommodate large volume changes in response to small pressure changes. However, only sparse information is available about flow parameters such as the Re in the venous system.

METHODS: Bilateral duplex ultrasound examination of 15 healthy volunteers (30 limbs) was performed before and after exercise (four flights of stairs) of the veins of the lower extremity (left and right sides) and inferior vena cava. These volunteers had been confirmed to not have any signs or symptoms of lower extremity venous disease via focused history and physical examination findings.

RESULTS: Most of the volunteers were women (73%). Their mean age was 37 ± 12.8 years. The Re was highest in the inferior vena cava among all the veins examined (470 ± 144 before exercise and 589 ± 205 after exercise; P = .04). The association between the change in Re before and after exercise and the specific vein examined was also significant for the right and left external iliac veins, right and left common femoral veins, right and left profunda femoris veins, right and left femoral veins, and right common iliac vein. Resistance and velocity maps for the lower extremity venous system were also created. The velocity increased and the resistance decreased as one moved up the venous tree toward the right atrium.

CONCLUSIONS: The Re increased for most of the lower extremity veins after exercise in our healthy volunteers. However, the critical value for turbulent flow was not reached despite the exercise.}, } @article {pmid36329077, year = {2022}, author = {Roósz, A and Rónaföldi, A and Svéda, M and Veres, Z}, title = {Effect of crucible wall roughness on the laminar/turbulent flow transition of the Ga75In25 alloy stirred by a rotating magnetic field.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {18592}, pmid = {36329077}, issn = {2045-2322}, abstract = {The critical magnetic induction (Bcr) values of a melt flow produced by a rotating magnetic field (RMF), remaining laminar or turbulent, are essential in different solidification processes. In an earlier paper (Metall Res Technol 100: 1043-1061, 2003), we showed that Bcr depends on the crucible radius (R) and frequency of the magnetic field (f). The effect of wall roughness (WR) on Bcr was investigated in this study. Using ten different wall materials, we determined the angular frequency (ω) and Reynolds number (Re) as a function of the magnetic induction (B) and f using two different measuring methods (pressure compensation method, PCM; height measuring method, HMM). The experiments were performed at room temperature; therefore, the Ga75wt%In25wt% alloy was chosen for the experiments. Based on the measured and calculated results, a simple relationship was determined between Bcr and Re*, f, R, and WR, where the constants K1, K2, K3, and K4 depended on the physical properties of the melt and wall material:[Formula: see text].}, } @article {pmid36319372, year = {2022}, author = {Datta, R and Russell, DR and Tang, I and Clayson, T and Suttle, LG and Chittenden, JP and Lebedev, SV and Hare, JD}, title = {Time-resolved velocity and ion sound speed measurements from simultaneous bow shock imaging and inductive probe measurements.}, journal = {The Review of scientific instruments}, volume = {93}, number = {10}, pages = {103530}, doi = {10.1063/5.0098823}, pmid = {36319372}, issn = {1089-7623}, abstract = {We present a technique to measure the time-resolved velocity and ion sound speed in magnetized, supersonic high-energy-density plasmas. We place an inductive ("b-dot") probe in a supersonic pulsed-power-driven plasma flow and measure the magnetic field advected by the plasma. As the magnetic Reynolds number is large (RM > 10), the plasma flow advects a magnetic field proportional to the current at the load. This enables us to estimate the flow velocity as a function of time from the delay between the current at the load and the signal at the probe. The supersonic flow also generates a hydrodynamic bow shock around the probe, the structure of which depends on the upstream sonic Mach number. By imaging the shock around the probe with a Mach-Zehnder interferometer, we determine the upstream Mach number from the shock Mach angle, which we then use to determine the ion sound speed from the known upstream velocity. We use the sound speed to infer the value of Z̄Te, where Z̄ is the average ionization and Te is the electron temperature. We use this diagnostic to measure the time-resolved velocity and sound speed of a supersonic (MS ∼ 8), super-Alfvénic (MA ∼ 2) aluminum plasma generated during the ablation stage of an exploding wire array on the Magpie generator (1.4 MA, 250 ns). The velocity and Z̄Te measurements agree well with the optical Thompson scattering measurements reported in the literature and with 3D resistive magnetohydrodynamic simulations in GORGON.}, } @article {pmid36313190, year = {2022}, author = {Qiao, Y and Ma, Z and Onyango, C and Cheng, X and Dorfman, KD}, title = {DNA fragmentation in a steady shear flow.}, journal = {Biomicrofluidics}, volume = {16}, number = {5}, pages = {054109}, pmid = {36313190}, issn = {1932-1058}, abstract = {We have determined the susceptibility of T4 DNA (166 kilobase pairs, kbp) to fragmentation under steady shear in a cone-and-plate rheometer. After shearing for at least 30 min at a shear rate of 6000 s - 1 , corresponding to a Reynolds number of O (10 3) and a Weissenberg number of O (10 3) , 97.9 ± 1.3 % of the sample is broken into a polydisperse mixture with a number-averaged molecular weight of 62.6 ± 3.2 kbp and a polydispersity index of 1.29 ± 0.03 , as measured by pulsed-field gel electrophoresis (with a 95% confidence interval). The molecular weight distributions observed here from a shear flow are similar to those produced by a (dominantly extensional) sink flow of DNA and are qualitatively different than the midpoint scission observed in simple extensional flow. Given the inability of shear flow to produce a sharp coil-stretch transition, the data presented here support a model where polymers can be fragmented in flow without complete extension. These results further indicate that DNA fragmentation by shear is unlikely to be a significant issue in microfluidic devices, and anomalous molecular weight observations in experiments are due to DNA processing prior to observation in the device.}, } @article {pmid36301473, year = {2023}, author = {Bryan, MT}, title = {Assessing the Challenges of Nanotechnology-Driven Targeted Therapies: Development of Magnetically Directed Vectors for Targeted Cancer Therapies and Beyond.}, journal = {Methods in molecular biology (Clifton, N.J.)}, volume = {2575}, number = {}, pages = {105-123}, pmid = {36301473}, issn = {1940-6029}, mesh = {Humans ; *Neoplasms/genetics/therapy ; Nanotechnology ; Magnetics ; Drug Delivery Systems/methods ; Motion ; }, abstract = {Targeted delivery, in which therapeutic agents are preferentially concentrated at the diseased site, has the potential to improve therapeutic outcomes by minimizing off-target interactions in healthy tissue. Both passive and active methods of targeting delivery have been proposed, often with particular emphasis on cancer treatment. Passive methods rely on the overexpression of a biomarker in diseased tissue that can then be used to target the therapy. Active techniques involve physically guiding therapeutic agents toward the target region. Since the motion of magnetic particles can be remotely controlled by external magnetic fields, magnetic technologies have the potential to drive and hold drugs or other cargo at the required therapeutic site, increasing the localized dose while minimizing overall exposure. Directed motion may be generated either by simple magnetic attraction or by causing the particles to perform swimming strokes to produce propulsion. This chapter will compare the different strategies using magnetic nanotechnology to produce directed motion compatible with that required for targeted cargo delivery and magnetically assisted therapies and assess their potential to meet the challenges of operating within the human body.}, } @article {pmid36296816, year = {2022}, author = {Beck, J and Palmer, M and Inman, K and Wohld, J and Cummings, M and Fulmer, R and Scherer, B and Vafaei, S}, title = {Heat Transfer Enhancement in the Microscale: Optimization of Fluid Flow.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {12}, number = {20}, pages = {}, pmid = {36296816}, issn = {2079-4991}, abstract = {The focus of this paper is to investigate the effects of the addition of a connector between two serial microchannels. The idea of adding connector at the inlet of microchannels to enhance the random motion of molecules or nanoparticles in low Reynolds numbers was developed in our research group for the first time. It was experimentally determined that the shape of a connector between two microchannels has a significant impact on the enhancement of the random motion of molecules or nanoparticles. Consequently, the heat transfer coefficient is improved inside the second microchannel. The connector is large enough to refresh the memory of the fluid before entering the second channel, causing a higher maximum heat transfer coefficient in the second channel. It was also observed that the heat transfer coefficient can be increased at the end of the channel when the outlet temperature is relatively high. This may be explained by the fact that as temperature increases, the fluid viscosity tends to decrease, which generally drives an increase in the local random motion of base fluid molecules and nanoparticles. This causes an increase in the microchannel heat transfer coefficient. It was found that the addition of nanoparticles significantly modified the impact of the connector on the microchannel heat transfer coefficient. In addition, the effects of changing the Reynolds number and the shape of the connector were investigated through use of computational fluid dynamics (CFD) calculations. It was found that both factors have an important impact on the variation of velocity and enhancement of random motion of molecules and consequently significantly affect the heat transfer coefficient.}, } @article {pmid36296785, year = {2022}, author = {Chang, Q and Fu, Z and Zhang, S and Wang, M and Pan, X}, title = {Experimental Investigation of Reynolds Number and Spring Stiffness Effects on Vortex-Induced Vibration Driven Wind Energy Harvesting Triboelectric Nanogenerator.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {12}, number = {20}, pages = {}, pmid = {36296785}, issn = {2079-4991}, abstract = {Vortex-induced vibration (VIV) is a process that wind energy converts to the mechanical energy of the bluff body. Enhancing VIV to harvest wind energy is a promising method to power wireless sensor nodes in the Internet of Things. In this work, a VIV-driven square cylinder triboelectric nanogenerator (SC-TENG) is proposed to harvest broadband wind energy. The vibration characteristic and output performance are studied experimentally to investigate the effect of the natural frequency by using five different springs in a wide range of stiffnesses (27&nbsp;N/m 1) and (Jaffrin and Shapiro 1971Annu. Rev. Fluid Mech.33-37) for low Reynolds number (Re < 1) applications. We show that the apparatus is useful for biophysical peristaltic studies and has potential applications in other types of studies.}, } @article {pmid36266390, year = {2022}, author = {Benhanifia, K and Redouane, F and Lakhdar, R and Brahim, M and Al-Farhany, K and Jamshed, W and Eid, MR and El Din, SM and Raizah, Z}, title = {Investigation of mixing viscoplastic fluid with a modified anchor impeller inside a cylindrical stirred vessel using Casson-Papanastasiou model.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {17534}, pmid = {36266390}, issn = {2045-2322}, mesh = {*Bioreactors ; *Hydrodynamics ; }, abstract = {In process engineering as chemical and biotechnological industry, agitated vessels are commonly used for various applications; mechanical agitation and mixing are performed to enhance heat transfer and improve specific Physico-chemical characteristics inside a heated tank. The research subject of this work is a numerical investigation of the thermo-hydrodynamic behavior of viscoplastic fluid (Casson-Papanastasiou model) in a stirred tank, with introducing a new anchor impeller design by conducting some modifications to the standard anchor impeller shape. Four geometry cases have been presented for achieving the mixing process inside the stirred vessel, CAI; classical anchor impeller, AI1; anchor impeller with added horizontal arm blade, AI2 and AI3 anchor impeller with two and three added arm blades, respectively. The investigation is focused on the effect of inertia and plasticity on the thermo-hydrodynamic behavior (flow pattern, power consumption, and heat transfer) by varying the Reynolds number (Re = 1, 10, 100, 200), Bingham number (Bn = 1, 10, 50), in addition to the effect of geometry design in the overall stirred system parameters. The findings revealed an excellent enhancement of flow pattern and heat transfer in the stirred system relatively to the increase of inertia values. Also, an energy reduction has been remarked and the effect of anchor impeller shape. AI3 geometry design significantly improves the flow pattern and enhances heat transfer by an increased rate of 10.46% over the other cases.}, } @article {pmid36261993, year = {2022}, author = {Ji, Y and Cao, R and Wang, C and Xu, X and Zhu, L}, title = {Effect of flow regime on mass transfer diffusion and stability of aerobic granular sludge (AGS) in view of interfacial thermodynamic.}, journal = {Journal of environmental management}, volume = {323}, number = {}, pages = {116293}, doi = {10.1016/j.jenvman.2022.116293}, pmid = {36261993}, issn = {1095-8630}, mesh = {Humans ; *Sewage/chemistry ; *Waste Disposal, Fluid/methods ; Waste Water ; Bioreactors ; Aerobiosis ; Thermodynamics ; Proteins ; Oxygen ; Water ; }, abstract = {Aerobic granular sludge (AGS) technology has been widely studied as "The Next Generation Wastewater Treatment technology". The effect of hydraulic conditions on the structural stability of AGS has been widely studied. However, the function of flow regime on the AGS stability, especially dissolved oxygen (DO) mass transfer, is still unknown. In this study, we used the Reynolds number (Re) to quantify the flow regime and selected different stages of AGS as experimental subjects. Results showed that the relatively suitable Re (Re = 150) could create lower DO mass transfer limitation (Lc = 27.4 μm) and increase protein (PN) contents and the abundance of hydrophobic functional groups in AGS. At this condition (Re = 150), the interfacial Gibbs free energy of sludge-water (ΔGLS[a]) was at a lower state (-129.75 ± 2.15 mJ·m[-2]), which favored the stability of AGS. Principal component analysis (PCA) and correlation analysis indicated that the response of ΔGLS[a] was affected by Lc, PN, and hydrophobic groups. In addition, results obtained for unstable AGS further verified that suitable Re regulates the structural stability of AGS. This study deepens the understanding of Re as an important hydraulic parameter for structural stability of AGS, which is also of great significance for energy saving of sequential batch reactors (SBRs) with agitation in practical engineering.}, } @article {pmid36261048, year = {2022}, author = {Ben-Gida, H and Gurka, R}, title = {The leading-edge vortex over a swift-like high-aspect-ratio wing with nonlinear swept-back geometry.}, journal = {Bioinspiration & biomimetics}, volume = {17}, number = {6}, pages = {}, doi = {10.1088/1748-3190/ac9bb5}, pmid = {36261048}, issn = {1748-3190}, mesh = {Humans ; Animals ; *Flight, Animal ; *Wings, Animal ; Birds ; Rheology/methods ; Biomechanical Phenomena ; Models, Biological ; }, abstract = {The leading-edge vortex (LEV) is a common flow structure that forms over wings at high angles of attack. Over the years, LEVs were exploited for augmenting the lift of man-made slender delta wings aircraft. However, recent observations suggested that natural flyers with high-aspect-ratio (high-AR) wings, such as the common swift (Apus apus), can also generate LEVs while gliding. We hypothesize that the planform shape and nonlinear sweep (increasing towards the wingtip) enable the formation and control of such LEVs. In this paper, we investigate whether a stationary LEV can form over a nonlinear swept-back high-AR wing inspired by the swift's wing shape and evaluate its characteristics and potential aerodynamic benefit. Particle image velocimetry (PIV) measurements were performed in a water flume on a high-AR swept-back wing inspired by the swift wing. Experiments were performed at four spanwise sections and a range of angles of attack for a chord-based Reynolds number of20000. Stationary LEV structures were identified across the wingspan by utilizing the proper orthogonal decomposition (POD) method for angles of attack of 5[∘]-15[∘]. The size and circulation of the stationary LEV were found to grow towards the wingtip in a nonlinear manner due to shear layer feeding and spanwise transport of mass and vorticity within the LEV, thus confirming that nonlinear high-AR swept-back wings can generate stationary LEVs. Our results suggest that the common swift can generate stationary LEVs over its swept-back wings to glide slower and at a higher rate of descent, with the LEVs potentially supporting up to 60% of its weight.}, } @article {pmid36234399, year = {2022}, author = {Abderrahmane, A and Younis, O and Al-Khaleel, M and Laidoudi, H and Akkurt, N and Guedri, K and Marzouki, R}, title = {2D MHD Mixed Convection in a Zigzag Trapezoidal Thermal Energy Storage System Using NEPCM.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {12}, number = {19}, pages = {}, pmid = {36234399}, issn = {2079-4991}, abstract = {In a magnetic field, two-dimensional (2D) mixed convection is investigated within a zigzagged trapezoidal chamber. The lower side of the trapezoidal chamber is irregular, in particular, a zigzagged wall with different zigzag numbers N. The fluid particles move in the room due to the motion of the upper wall, while the porosity-enthalpy approach represents the melting process. The thermal parameters of the fluid are enhanced by what is called a nano-encapsulated phase change material (NEPCM) consisting of polyurethane as the shell and a nonadecane as the core, while water is used as the base fluid. In order to treat the governing equations, the well-known Galerkin finite element method (GFEM) is applied. In addition, the heat transfer (HT) irreversibility and the fluid friction (FF) irreversibility are compared in terms of the average Bejan number. The main results show that the melt band curve behaves parabolically at smaller values of Reynolds number (Re) and larger values of Hartmann number (Ha). Moreover, minimizing the wave number is better in order to obtain a higher heat transfer rate.}, } @article {pmid36229498, year = {2022}, author = {Khan, A and Khan, MS and Pasha, AA and Marzouki, R and Rahman, MM and Mahmoud, O and Galal, AM and Najati, SA}, title = {Hydrodynamic analysis of the magnetic field dependent viscous fluid flow and thermosolutal convection between rotating channels.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {17170}, pmid = {36229498}, issn = {2045-2322}, mesh = {Colloids ; *Convection ; Humans ; *Hydrodynamics ; Magnetic Fields ; Models, Theoretical ; Reproducibility of Results ; Viscosity ; }, abstract = {According to research, exposing a person to a magnetic field enhances blood flow and minimizes their risk of suffering a heart attack. Ferrohydrodynamics is the study of fluid motion mechanics that is affected by strong magnetic polarisation forces (FHD). Ferrofluids may transmit heat in a variety of ways by using magnetic fluids. This behaviour is demonstrated by liquid-cooled speakers, which utilise less ferrofluid to prevent heat from reaching the speaker coil. This modification boosts the coil's ability to expand, which enables the loudspeaker to create high-fidelity sound. It is investigated how the fluid dynamics of spinning, squeezing plates are affected by thermosolutal convection and a magnetic field dependent (MFD) viscosity. Standard differential equations are used to represent the equations of the modified form of Navier Stokes, Maxwell's, and thermosolutal convection. The magnetic field, modified velocity field equations, and thermosolutal convection equations all yield suitable answers. Additionally computed and thoroughly detailed are the MHD torque and fluid pressure that are imparted to the top plate. To create a technique with quick and certain convergence, the resulting equations for uniform plates are solved using the Homotopy Analysis Method (HAM) with appropriate starting estimates and auxiliary parameters. The validity and reliability of the HAM outcomes are shown by comparing the HAM solutions with the BVP4c numerical solver programme. It has been found that a magnetic Reynolds number lowers the temperature of the fluid as well as the tangential and axial components of the velocity field. Additionally, when the fluid's MFD viscosity rises, the axial and azimuthal components of the magnetic field behave in opposition to one another. This study has applications in the development of new aircraft take-off gear, magnetorheological airbags for automobiles, heating and cooling systems, bio-prosthetics, and biosensor systems.}, } @article {pmid36219300, year = {2022}, author = {Tang, P and Chen, L and Zhang, W and Zhou, Y}, title = {Bioclogging alleviation for constructed wetland based on the interaction among biofilm growth and hydrodynamics.}, journal = {Environmental science and pollution research international}, volume = {}, number = {}, pages = {}, pmid = {36219300}, issn = {1614-7499}, abstract = {Bioclogging is the most crucial operation problem of the constructed wetlands, which reduce its removal efficiency and life span. A strategy through properly increasing hydraulic loading is proposed in this study to alleviate the bioclogging for CWs. The two-dimensional porous media flow cell (2D PMFC) test indicated that a quadratic correlation was found between local biofilms growth rate and the near-wall Reynolds number (r > 0.765, p < 0.05). The biofilm growth rate declined with the flowrate when Re exceeded about 6.0. It was also found that the higher flowrate (6 mL/min) lead to the homogeneous biofilm and velocity distribution in the PMFC. The column test indicated that the highest hydraulic loading (9.2 cm/h) produced the smallest decrease in hydraulic conductivity, which was 80 times more than that of low hydraulic load (3.0 cm/h) at the end (40 days) of experiment. Moreover, the relatively homogenized distribution of biofilm was found along the column with the highest hydraulic loading, which confirmed that the proper increase in hydraulic loading can alleviate bioclogging.}, } @article {pmid36215970, year = {2022}, author = {Li, H and Nabawy, MRA}, title = {Capturing wake capture: a 2D numerical investigation into wing-wake interaction aerodynamics.}, journal = {Bioinspiration & biomimetics}, volume = {17}, number = {6}, pages = {}, doi = {10.1088/1748-3190/ac98e5}, pmid = {36215970}, issn = {1748-3190}, mesh = {Animals ; *Flight, Animal ; Models, Biological ; Wings, Animal ; Biomechanical Phenomena ; Insecta ; *Stroke ; }, abstract = {A wing generating lift leaves behind a region of disturbed air in the form of a wake. For a hovering insect, the wings must return through the wake produced by the previous half-stroke and this can have significant effects on the aerodynamic performance. This paper numerically investigates 2D wings interacting with their own wake at Reynolds numbers of 10[2]and 10[3], enabling an improved understanding of the underlying physics of the 'wake capture' aerodynamic mechanism of insect flight. We adopt a simple kinematic motion pattern comprised of a translational stroke motion followed by a complete stop to expose wake interaction effects. Representative stroke distance to chord ratios between 1.5 and 6.0 are considered, enabling different leading-edge vortex (LEV) attachment states. We also allow pitching rotation towards the end of stroke, leading to wake intercepting angles of 135°, 90°, and 45°, analogous to delayed, symmetric, and advanced pitching rotations of insect wings. It is shown that both vortex suction and jet flow impingement mechanisms can lead to either positive or negative effects depending on the LEV attachment state, and that stroke distances resulting in a detached/attached LEV lead to beneficial/detrimental wake interaction lift. Pitching rotation at the end of the stroke motion is found to induce a strong rotational trailing-edge vortex (RTEV). For advanced pitching, this RTEV serves to enable either a stronger flow impingement effect leading to positive wake interaction lift if the LEV is detached, or a less favourable vortex suction effect leading to negative wake interaction lift if the LEV is closely attached. The higher Reynolds number led to faster development of the wake vortices, but the primary wake interaction mechanisms remained the same for both Reynolds numbers.}, } @article {pmid36202970, year = {2022}, author = {Usman, and Memon, AA and Alghamdi, M and Muhammad, T}, title = {A forced convection of water aluminum oxide nanofluid flow and heat transfer study for a three dimensional annular with inner rotated cylinder.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {16735}, pmid = {36202970}, issn = {2045-2322}, abstract = {The article examines a water alumina nanofluid and heat transfer through the three-dimensional annular. The annular is constructed by the two concentric cylinders in which the inner cylinder can rotate along the tangential direction at a constant speed. A slip boundary condition will be imposed to vanish the viscous effect in the vicinity of the outer cylinder wall. Moreover, the rotating cylinder is kept at a hot temperature, and the outer one is at a cold temperature. A three-dimensional incompressible Navier Stokes and energy equations were carried in cylindrical coordinates. The simulation was observed using the emerging computational tool of COMSOL Multiphysics 5.6, which implements Least Square Galerkin's scheme of finite element method. The parametric study will be done by altering the speed of rotation of the inner cylinder from 1 to 4, volume fraction from 0.001 to 0.9, and the aspect ratio from 0.4 to 0.6 for a fixed Reynolds number of 35,000. The results will be displayed with graphs and tables for average values of the Nusselt number, the percentage change in the temperature, and the skin friction at the middle plan. It was found that the average Nusselt number at the middle of the annular increases before the volume fraction of 0.2 and then decreases for all values of the volume fraction for a fixed rotation of the inner cylinder. The average percentage change relative to the inner cylinder's hot temperature decreases with the volume fraction increase for the fixed rotation. Also, it was found that the quantity of nanoparticles in the domain is improving the average skin friction in the middle of the channel, and it can be reduced by improving the rotation of the inner cylinder by about 10-23% strictly depending upon the aspect ratio for a particular case.}, } @article {pmid36198707, year = {2022}, author = {Shoukat, G and Idrees, H and Sajid, M and Ali, S and Ayaz, Y and Nawaz, R and Ansari, AR}, title = {Numerical analysis of permeate flux in reverse osmosis by varying strand geometry.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {16636}, pmid = {36198707}, issn = {2045-2322}, mesh = {*Biofouling ; *Drinking Water ; Membranes, Artificial ; Osmosis ; *Water Purification/methods ; }, abstract = {In regions with limited potable water availability, membrane desalination is being employed to filter water using a pressure-driven approach. Because of the high energy consumption required to produce the pressure differential needed for this method, researchers have been trying different geometric designs of spacer filaments to enhance the amount of permeate flux in terms of energy utilization. The purpose of spacer filaments is to support membranes structurally and induce turbulent mixing in spiral wound membrane desalination. In this paper, the improvement of mass transfer in desalination driven by reverse osmosis has been studied using Computational Fluid Dynamics (CFD) with the introduction of spiral wound membranes that are lined with spacer filaments in a zig-zag formation having alternating diameters for strands. The fluid flow characteristics for a 2-dimensional geometric model were resolved using the open-source program OpenFOAM by changing the Reynolds number to just before the inception of instabilities. Ratios of alternate strand diameters were also varied between one and two. Based on a detailed analysis of velocity contours, pressure distribution, wall shear stresses, and steady-state vortex systems, the research findings offer guidance for employing alternating strand design in zig-zag formation for optimum mass transfer and minimal pressure drop when accounting for concentration polarization.}, } @article {pmid36193889, year = {2023}, author = {Pinto Costa, R and Nwotchouang, BST and Yao, J and Biswas, D and Casey, D and McKenzie, R and Sebastian, F and Amini, R and Steinman, DA and Loth, F}, title = {Impact of Blood Rheology on Transition to Turbulence and Wall Vibration Downstream of a Stenosis.}, journal = {Journal of biomechanical engineering}, volume = {145}, number = {4}, pages = {}, doi = {10.1115/1.4055856}, pmid = {36193889}, issn = {1528-8951}, mesh = {Humans ; Constriction, Pathologic ; Stress, Mechanical ; *Vibration ; Rheology ; Blood Flow Velocity ; *Models, Cardiovascular ; }, abstract = {Previous experimental flow studies have demonstrated a delay (∼20%) in transition to turbulence for whole blood compared to a Newtonian analog fluid in both a straight pipe and eccentric stenosis model with ridged walls. The impact of wall compliance on the transition to turbulence of blood compared to Newtonian analog and on wall vibration is unknown. The present study employed flexible walls downstream of an eccentric stenosis model and examined the wall vibration during the transition to turbulence with whole blood and a Newtonian analog. Measurements of tube wall vibration velocity (WVV) were used as an indicator of the turbulence level within the flexible tube. WVV was measured at 5, 10, and 15 diameters downstream of the stenosis using a laser Doppler vibrometer at Reynolds numbers 0, 200, 300, 350, 400, 450, 500, 550, 600, 650, 700, and 750. The root mean squares (RMS) of the measured WVV were utilized as an indirect measure of fluid velocity fluctuations present at that location, and hence, an indicator of transition to turbulence. WVV RMS was near-constant until approximately Reynolds number 400. It increased monotonically with Reynolds number for both whole blood and the Newtonian fluid. No differences in the transition to turbulence were observed between whole blood and the Newtonian fluid, as the WVV RMS curves were remarkably similar in shape. This result suggests that rheology had minimal impact on the WVV downstream of a stenosis for transition to turbulence since the fluids had a similar level of vibration.}, } @article {pmid36182967, year = {2022}, author = {Moon, J and Kang, G and Im, B and Kim, J and Cho, DH and Byun, D}, title = {Flapping and powering characteristics of a flexible piezoelectric nanogenerator at Reynolds number range simulating ocean current.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {16465}, pmid = {36182967}, issn = {2045-2322}, abstract = {For effective ocean energy harvesting, it is necessary to understand the coupled motion of the piezoelectric nanogenerator (PENG) and ocean currents. Herein, we experimentally investigate power performance of the PENG in the perspective of the fluid-structure interaction considering ocean conditions with the Reynolds number (Re) values ranging from 1 to 141,489. A piezoelectric polyvinylidene fluoride micromesh was constructed via electrohydrodynamic (EHD) jet printing technique to produce the β-phase dominantly that is desirable for powering performance. Water channel was set to generate water flow to vibrate the flexible PENG. By plotting the Re values as a function of nondimensional bending rigidity (KB) and the structure-to-fluid mass ratio (M*), we could find neutral curves dividing the stable and flapping regimes. Analyzing the flow velocities between the vortex and surroundings via a particle image velocimetry, the larger displacement of the PENG in the chaotic flapping regime than that in the flapping regime was attributed to the sharp pressure gradient. By correlating M*, Re, KB, and the PENG performance, we conclude that there is critical KB that generate chaotic flapping motion for effective powering. We believe this study contributes to the establishment of a design methodology for the flexible PENG harvesting of ocean currents.}, } @article {pmid36171438, year = {2022}, author = {Ismael, AM and Eldabe, NT and Abou Zeid, MY and El Shabouri, SM}, title = {Thermal micropolar and couple stresses effects on peristaltic flow of biviscosity nanofluid through a porous medium.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {16180}, pmid = {36171438}, issn = {2045-2322}, mesh = {*Gold ; *Metal Nanoparticles ; Peristalsis ; Porosity ; Viscosity ; }, abstract = {The main aim of the current study is to analyze couple stresses effects on MHD peristaltic transport of a micropolar non-Newtonian nanofluid. The fluid flows through a porous media between two horizontal co-axial tubes. The effects of radiation, chemical reaction, viscous and ohmic dissipation are considered. The inner tube is solid and uniform, while the outer tube has a sinusoidal wave traveling down its wall. The governing equations have been simplified using low-Reynolds number and long wave-length approximations, thus a semi-analytical solutions have been obtained using the homotopy perturbation method. Numerical results for the behaviors of the axial velocity, microrotation velocity, temperature and nanoparticles concentration with the physical parameters are depicted graphically through a set of graphs. Furthermore, the values of the skin friction coefficient, Nusselt and nano Sherwood numbers are computed and presented graphically through some draws. Moreover, the trapping phenomenon is discussed throughout a set of figures. The present study is very important in many medical applications, as the gastric juice motion in the small intestine when an endoscope is inserted through it. Further, gold nanoparticles are utilized in the remedy of cancer tumor.}, } @article {pmid36154406, year = {2022}, author = {Wang, Y and Gilson, EP and Ebrahimi, F and Goodman, J and Ji, H}, title = {Observation of Axisymmetric Standard Magnetorotational Instability in the Laboratory.}, journal = {Physical review letters}, volume = {129}, number = {11}, pages = {115001}, doi = {10.1103/PhysRevLett.129.115001}, pmid = {36154406}, issn = {1079-7114}, abstract = {We report the first direct evidence for the axisymmetric standard magnetorotational instability (SMRI) from a combined experimental and numerical study of a magnetized liquid-metal shear flow in a Taylor-Couette cell with independently rotating and electrically conducting end caps. When a uniform vertical magnetic field B_{i} is applied along the rotation axis, the measured radial magnetic field B_{r} on the inner cylinder increases linearly with a small magnetic Reynolds number Rm due to the magnetization of the residue Ekman circulation. Onset of the axisymmetric SMRI is identified from the nonlinear increase of B_{r} beyond a critical Rm in both experiments and nonlinear numerical simulations. The axisymmetric SMRI exists only at sufficiently large Rm and intermediate B_{i}, a feature consistent with theoretical predictions. Our simulations further show that the axisymmetric SMRI causes the velocity and magnetic fields to contribute an outward flux of axial angular momentum in the bulk region, just as it should in accretion disks.}, } @article {pmid36153578, year = {2022}, author = {}, title = {Correction to: Trends in Stroke Kinematics, Reynolds Number, and Swimming Mode in Shrimp-Like Organisms.}, journal = {Integrative and comparative biology}, volume = {}, number = {}, pages = {}, doi = {10.1093/icb/icac142}, pmid = {36153578}, issn = {1557-7023}, } @article {pmid36145671, year = {2022}, author = {Bernad, SI and Socoliuc, V and Susan-Resiga, D and Crăciunescu, I and Turcu, R and Tombácz, E and Vékás, L and Ioncica, MC and Bernad, ES}, title = {Magnetoresponsive Functionalized Nanocomposite Aggregation Kinetics and Chain Formation at the Targeted Site during Magnetic Targeting.}, journal = {Pharmaceutics}, volume = {14}, number = {9}, pages = {}, pmid = {36145671}, issn = {1999-4923}, abstract = {Drug therapy for vascular disease has been promoted to inhibit angiogenesis in atherosclerotic plaques and prevent restenosis following surgical intervention. This paper investigates the arterial depositions and distribution of PEG-functionalized magnetic nanocomposite clusters (PEG_MNCs) following local delivery in a stented artery model in a uniform magnetic field produced by a regionally positioned external permanent magnet; also, the PEG_MNCs aggregation or chain formation in and around the implanted stent. The central concept is to employ one external permanent magnet system, which produces enough magnetic field to magnetize and guide the magnetic nanoclusters in the stented artery region. At room temperature (25 °C), optical microscopy of the suspension model's aggregation process was carried out in the external magnetic field. According to the optical microscopy pictures, the PEG_MNC particles form long linear aggregates due to dipolar magnetic interactions when there is an external magnetic field. During magnetic particle targeting, 20 mL of the model suspensions are injected (at a constant flow rate of 39.6 mL/min for the period of 30 s) by the syringe pump in the mean flow (flow velocity is Um = 0.25 m/s, corresponding to the Reynolds number of Re = 232) into the stented artery model. The PEG_MNC clusters are attracted by the magnetic forces (generated by the permanent external magnet) and captured around the stent struts and the bottom artery wall before and inside the implanted stent. The colloidal interaction among the MNC clusters was investigated by calculating the electrostatic repulsion, van der Waals and magnetic dipole-dipole energies. The current work offers essential details about PEG_MNCs aggregation and chain structure development in the presence of an external magnetic field and the process underlying this structure formation.}, } @article {pmid36144168, year = {2022}, author = {Mostefa, T and Eddine, AD and Tayeb, NT and Hossain, S and Rahman, A and Mohamed, B and Kim, KY}, title = {Kinematic Properties of a Twisted Double Planetary Chaotic Mixer: A Three-Dimensional Numerical Investigation.}, journal = {Micromachines}, volume = {13}, number = {9}, pages = {}, pmid = {36144168}, issn = {2072-666X}, abstract = {In this study, a numerical investigation based on the CFD method is carried out to study the unsteady laminar flow of Newtonian fluid with a high viscosity in a three-dimensional simulation of a twisted double planetary mixer, which is composed of two agitating rods inside a moving tank. The considered stirring protocol is a "Continuous sine squared motion" by using the dynamic mesh model and user-defined functions (UDFs)to define the velocity profiles. The chaotic advection is obtained in our active mixers by the temporal modulation of rotational velocities of the moving walls in order to enhance the mixing of the fluid for a low Reynolds number and a high Peclet number. For this goal, we applied the Poincaré section and Lyapunov exponent as reliable mathematic tools for checking mixing quality by tracking a number of massless particles inside the fluid domain. Additionally, we investigated the development of fluid kinematics proprieties, such as vorticity, helicity, strain rate and elongation rate, at various time periods in order to view the impact of temporal modulation on the flow properties. The results of the mentioned simulation showed that it is possible to obtain a chaotic advection after a relatively short time, which can deeply enhance mixing fluid efficiency.}, } @article {pmid36144120, year = {2022}, author = {Ahmed, MF and Zaib, A and Ali, F and Bafakeeh, OT and Khan, NB and Mohamed Tag-ElDin, ES and Oreijah, M and Guedri, K and Galal, AM}, title = {Cattaneo-Christov Double Diffusion (CCDD) on Sutterby Nanofluid with Irreversibility Analysis and Motile Microbes Due to a RIGA Plate.}, journal = {Micromachines}, volume = {13}, number = {9}, pages = {}, pmid = {36144120}, issn = {2072-666X}, abstract = {In this article, a Riga plate is exhibited with an electric magnetization actuator consisting of permanent magnets and electrodes assembled alternatively. This Riga plate creates an electric and magnetic field, where a transverse Lorentz force is generated that contributes to the flow along the plate. A new study field has been created by Sutterby nanofluid flows down the Riga plate, which is crucial to the creation of several industrial advancements, including thermal nuclear reactors, flow metres, and nuclear reactor design. This article addresses the second law analysis of MHD Sutter by nanofluid over a stretching sheet with the Riga plate. The Cattaneo-Christov Double Diffusion heat and mass flux have been created to examine the behaviour of relaxation time. The bioconvection of motile microorganisms and chemical reactions are taken into consideration. Similarity transformations are used to make the governing equations non-dimensional ordinary differential equations (ODE's) that are subsequently solved through an efficient and powerful analytic technique, the homotopy analysis method (HAM). The effect of pertained variables on velocity, temperature, concentration, and motile microorganism distributions are elaborated through the plot in detail. Further, the velocity distribution enhances and reduces for greater value Deborah number and Reynold number for the two cases of pseudoplastic and dilatant flow. Microorganism distribution decreases with the augmented magnitude of Peclet number (Pe), Bioconvection Lewis number (Lb), and microorganism concentration difference number (ϖ). The entropy production distribution is increased for the greater estimations of the Reynolds number (ReL) and Brinkman parameter (Br). Two sets of graphical outputs are presented for the Sutterby fluid parameter. Finally, for the justification of these outcomes, tables of comparison are made with various variables.}, } @article {pmid36143998, year = {2022}, author = {Juraeva, M and Kang, DJ}, title = {Mixing Performance of the Modified Tesla Micromixer with Tip Clearance.}, journal = {Micromachines}, volume = {13}, number = {9}, pages = {}, pmid = {36143998}, issn = {2072-666X}, abstract = {A passive micromixer based on the modified Tesla mixing unit was designed by embedding tip clearance above the wedge-shape divider, and its mixing performance was simulated over a wider range of the Reynolds numbers from 0.1 to 80. The mixing performance was evaluated in terms of the degree of mixing (DOM) at the outlet and the required pressure load between inlet and outlet. The height of tip clearance was varied from 40 μm to 80 μm, corresponding to 25% to 33% of the micromixer depth. The numerical results show that the mixing enhancement by the tip clearance is noticeable over a wide range of the Reynolds numbers Re < 50. The height of tip clearance is optimized in terms of the DOM, and the optimum value is roughly h = 60 μm. It corresponds to 33% of the present micromixer depth. The mixing enhancement in the molecular diffusion regime of mixing, Re ≤ 1, is obtained by drag and connection of the interface in the two sub-streams of each Tesla mixing unit. It appears as a wider interface in the tip clearance zone. In the intermediate range of the Reynolds number, 1 < Re ≤ 50, the mixing enhancement is attributed to the interaction of the flow through the tip clearance and the secondary flow in the vortex zone of each Tesla mixing unit. When the Reynolds number is larger than about 50, vortices are formed at various locations and drive the mixing in the modified Tesla micromixer. For the Reynolds number of Re = 80, a pair of vortices is formed around the inlet and outlet of each Tesla mixing unit, and it plays a role as a governing mechanism in the convection-dominant regime of mixing. This vortex pattern is little affected as long as the tip clearance remains smaller than about h = 70 μm. The DOM at the outlet is little enhanced by the presence of tip clearance for the Reynolds numbers Re ≥ 50. The tip clearance contributes to reducing the required pressure load for the same value of the DOM.}, } @article {pmid36135913, year = {2022}, author = {Yokoyama, F and Nakajima, M and Ichikawa, S}, title = {Analysis of Calcium Sulfate Scaling Phenomena on Reverse Osmosis Membranes by Scaling-Based Flux Model.}, journal = {Membranes}, volume = {12}, number = {9}, pages = {}, pmid = {36135913}, issn = {2077-0375}, abstract = {In this study, the behavior of permeate flux decline due to scale precipitation of calcium sulfate on reverse osmosis membranes was investigated. The proposed scaling-based flux model is able to explain that permeate fluxes attributed to three mechanisms of scale precipitation-cake formation, surface blockage, and mixed crystallization-converge to the same newly defined scaling-based critical flux. In addition, a scaling index is defined, which determines whether scale precipitates on the membrane. The experimental results were analyzed based on this index. The mass-transfer coefficients of flat membrane cells used in the experiments were measured and, although the coefficients differed, they could be summarized in the same form as the Leveque equation. Considering the results of the scale precipitation experiments, where the operating conditions of pressure, solute concentration, temperature, and Reynolds number were varied, the convergent values of the permeate fluxes are explained by the scaling-based critical fluxes and the scale precipitation zones by the scaling indexes.}, } @article {pmid36120040, year = {2022}, author = {Shakeel, MR and Mokheimer, EMA}, title = {Numerical Study of Stratified Flames Using Reynolds Averaged Navier Stokes Modeling.}, journal = {ACS omega}, volume = {7}, number = {36}, pages = {31822-31833}, pmid = {36120040}, issn = {2470-1343}, abstract = {Reynolds averaged Navier Stokes technique was used to develop a validated numerical model for stratified flames. The validation was carried out with the experimental data of the non-swirl flames of the Cambridge dual annulus swirl burner. The RNG k-ε turbulence model along with the SG-35 skeletal chemical mechanism was found to give a good prediction of scalar and vector quantities while resulting in the reduction of computational time by 99.75% in comparison with that required for large eddy simulation techniques used in the literature. The effect of stratification at a constant input power, global equivalence ratio, and Reynolds number was examined. At stratification ratios (SRs = ϕin/ϕout) 1 and 2, intense burning, marked by the higher OH concentration, was observed close to the bluff body. Beyond SR = 2, the region of intense burning shifts downstream away from the bluff body. This is a result of the high equivalence ratio in the inner annulus, which is beyond the rich flammability limit of methane-air flames, and as a result, the primary flame region is shifted downstream after the mixtures from inner and outer annulus have mixed properly to produce a mixture with the equivalence ratio in the flammability limit. The maximum temperature was found to increase by 24.1% when the SR is increased from 1 to 2 and the combustion efficiency was found to significantly improve by 267%. The highest maximum temperature of 2249 K is observed for the mildly stratified flame at SR = 2. Beyond SR = 2, the maximum temperature decreases, while the combustion efficiency increases slightly.}, } @article {pmid36119891, year = {2022}, author = {Kotnurkar, AS and Talawar, VT}, title = {Influence of thermal jump and inclined magnetic field on peristaltic transport of Jeffrey fluid with silver nanoparticle in the eccentric annulus.}, journal = {Heliyon}, volume = {8}, number = {9}, pages = {e10543}, pmid = {36119891}, issn = {2405-8440}, abstract = {This study investigates the impacts of thermal jump and inclined magnetic field on the peristaltic transport of Jeffrey fluid containing silver nanoparticles in the eccentric annuls under the long wavelength and low Reynolds number assumption. In medical studies, the impact of thermal jumps and slanted magnetic fields on public health is of interest. Peristaltic motion's ability to transmit heat and create a magnetic field has several uses in biomedical and bioengineering. The non-Newtonian Jeffrey fluid with silver nanoparticles is considered in the space between two cylindrical tubes that are eccentrically aligned. The homotopic perturbation method is semi-analytical for modeling and nonlinear partial differential equations (HPM). Analytical solutions for velocity, pressure gradient, and pressure rise were found. To show how physical parameters affect temperature, velocity, concentration, frictional force, and pressure rise of inner and outer tubes were plotted. A comparison of the present method with the exact solution for temperature and nanoparticle concentration profile is shown graphically. The present analysis of analytical solution approaches to the exact solution. The most significant thing in the current investigation is that the Hartmann number and thermophoresis number make the velocity profile decline. Jeffrey fluid parameter and magnetic field angle make the velocity rise. The nanofluid's temperature rises as a result of the thermal jump. In addition, the Jeffrey nanofluid has a higher momentum and temperature than the Jeffrey fluid. This analysis can better evaluate the syringe's injection speed and fluid flow features during cancer treatment, artery blockage removal, and reduced bleeding throughout the surgery.}, } @article {pmid36115732, year = {2023}, author = {Akram, J and Akbar, NS and Tripathi, D}, title = {Blood-based graphene oxide nanofluid flow through capillary in the presence of electromagnetic fields: A Sutterby fluid model.}, journal = {Microvascular research}, volume = {145}, number = {}, pages = {104435}, doi = {10.1016/j.mvr.2022.104435}, pmid = {36115732}, issn = {1095-9319}, abstract = {Pumping devices with the electrokinetics phenomena are important in many microscale transport phenomena in physiology. This study presents a theoretical and numerical investigation on the peristaltic pumping of non-Newtonian Sutterby nanofluid through capillary in presence of electromagnetohydrodynamics. Here blood (Sutterby fluid) is taken as a base fluid and nanofluid is prepared by the suspension of graphene oxide nanoparticles in blood. Graphene oxide is extremely useful in the medical domain for drug delivery and cancer treatment. The modified Buongiorno model for nanofluids and Poisson-Boltzmann ionic distribution is adopted for the formulation of the present problem. Constitutive flow equations are linearized by the implementation of approximations of low Reynolds number, large wavelength, and the Debye-Hückel linearization. The numerical solution of reduced coupled and nonlinear set of equations is computed through Mathematica and graphical illustration is presented. Further, the impacts of buoyancy forces, thermal radiation, and mixed convection are also studied. It is revealed in this investigation that the inclusion of a large number of nanoparticles alters the flow characteristics significantly and boosts the heat transfer mechanism. Moreover, the pumping power of the peristaltic pump can be enhanced by the reduction in the width of the electric double layer which can be done by altering the electrolyte concentration.}, } @article {pmid36112448, year = {2022}, author = {Serafini, F and Battista, F and Gualtieri, P and Casciola, CM}, title = {Drag Reduction in Turbulent Wall-Bounded Flows of Realistic Polymer Solutions.}, journal = {Physical review letters}, volume = {129}, number = {10}, pages = {104502}, doi = {10.1103/PhysRevLett.129.104502}, pmid = {36112448}, issn = {1079-7114}, mesh = {*DNA ; Friction ; *Polymers ; Viscosity ; }, abstract = {Suspensions of DNA macromolecules (0.8 wppm, 60 kbp), modeled as finitely extensible nonlinear elastic dumbbells coupled to the Newtonian fluid, show drag reduction up to 27% at friction Reynolds number 180, saturating at the previously unachieved Weissenberg number ≃10^{4} . At a large Weissenberg number, the drag reduction is entirely induced by the fully stretched polymers, as confirmed by the extensional viscosity field. The polymer extension is strongly non-Gaussian, in contrast to the assumptions of classical viscoelastic models.}, } @article {pmid36109998, year = {2022}, author = {Parfenyev, V}, title = {Profile of a two-dimensional vortex condensate beyond the universal limit.}, journal = {Physical review. E}, volume = {106}, number = {2-2}, pages = {025102}, doi = {10.1103/PhysRevE.106.025102}, pmid = {36109998}, issn = {2470-0053}, abstract = {It is well known that an inverse turbulent cascade in a finite (2π×2π) two-dimensional periodic domain leads to the emergence of a system-sized coherent vortex dipole. We report a numerical hyperviscous study of the spatial vorticity profile inside one of the vortices. The exciting force was shortly correlated in time, random in space, and had a correlation length l_{f} =2π/k_{f} with k_{f} ranging from 100 to 12.5. Previously, it was found that in the asymptotic limit of small-scale forcing, the vorticity exhibits the power-law behavior Ω(r)=(3ε/α)^{1/2} r^{-1}, where r is the distance to the vortex center, α is the bottom friction coefficient, and ε is the inverse energy flux. Now we show that for a spatially homogeneous forcing with finite k_{f} the vorticity profile becomes steeper, with the difference increasing with the pumping scale but decreasing with the Reynolds number at the forcing scale. Qualitatively, this behavior is related to a decrease in the effective pumping of the coherent vortex with distance from its center. To support this statement, we perform an additional simulation with spatially localized forcing, in which the effective pumping of the coherent vortex, on the contrary, increases with r, and show that in this case the vorticity profile can be flatter than the asymptotic limit.}, } @article {pmid36109911, year = {2022}, author = {Koyano, Y and Kitahata, H}, title = {Anomalous diffusion and transport by a reciprocal convective flow.}, journal = {Physical review. E}, volume = {106}, number = {2-1}, pages = {024102}, doi = {10.1103/PhysRevE.106.024102}, pmid = {36109911}, issn = {2470-0053}, abstract = {Under low-Reynolds-number conditions, dynamics of convection and diffusion are usually considered separately because their dominant spatial and temporal scales are different, but cooperative effects of convection and diffusion can cause diffusion enhancement [Koyano et al., Phys. Rev. E 102, 033109 (2020)2470-004510.1103/PhysRevE.102.033109]. In this paper, such cooperative effects are investigated in detail. Numerical simulations based on the convection-diffusion equation revealed that anisotropic diffusion and net shift as well as diffusion enhancement occur under a reciprocal flow. Such anomalous diffusion and transport are theoretically derived by the analyses of the Langevin dynamics.}, } @article {pmid36109885, year = {2022}, author = {Agrawal, V and Mitra, D}, title = {Chaos and irreversibility of a flexible filament in periodically driven Stokes flow.}, journal = {Physical review. E}, volume = {106}, number = {2-2}, pages = {025103}, doi = {10.1103/PhysRevE.106.025103}, pmid = {36109885}, issn = {2470-0053}, abstract = {The flow of Newtonian fluid at low Reynolds number is, in general, regular and time-reversible due to absence of nonlinear effects. For example, if the fluid is sheared by its boundary motion that is subsequently reversed, then all the fluid elements return to their initial positions. Consequently, mixing in microchannels happens solely due to molecular diffusion and is very slow. Here, we show, numerically, that the introduction of a single, freely floating, flexible filament in a time-periodic linear shear flow can break reversibility and give rise to chaos due to elastic nonlinearities, if the bending rigidity of the filament is within a carefully chosen range. Within this range, not only the shape of the filament is spatiotemporally chaotic, but also the flow is an efficient mixer. Overall, we find five dynamical phases: the shape of a stiff filament is time-invariant-either straight or buckled; it undergoes a period-two bifurcation as the filament is made softer; becomes spatiotemporally chaotic for even softer filaments but, surprisingly, the chaos is suppressed if bending rigidity is decreased further.}, } @article {pmid36089943, year = {2022}, author = {Bohm, S and Phi, HB and Moriyama, A and Runge, E and Strehle, S and König, J and Cierpka, C and Dittrich, L}, title = {Highly efficient passive Tesla valves for microfluidic applications.}, journal = {Microsystems & nanoengineering}, volume = {8}, number = {}, pages = {97}, pmid = {36089943}, issn = {2055-7434}, abstract = {A multistage optimization method is developed yielding Tesla valves that are efficient even at low flow rates, characteristic, e.g., for almost all microfluidic systems, where passive valves have intrinsic advantages over active ones. We report on optimized structures that show a diodicity of up to 1.8 already at flow rates of 20 μl s[-] [1] corresponding to a Reynolds number of 36. Centerpiece of the design is a topological optimization based on the finite element method. It is set-up to yield easy-to-fabricate valve structures with a small footprint that can be directly used in microfluidic systems. Our numerical two-dimensional optimization takes into account the finite height of the channel approximately by means of a so-called shallow-channel approximation. Based on the three-dimensionally extruded optimized designs, various test structures were fabricated using standard, widely available microsystem manufacturing techniques. The manufacturing process is described in detail since it can be used for the production of similar cost-effective microfluidic systems. For the experimentally fabricated chips, the efficiency of the different valve designs, i.e., the diodicity defined as the ratio of the measured pressure drops in backward and forward flow directions, respectively, is measured and compared to theoretical predictions obtained from full 3D calculations of the Tesla valves. Good agreement is found. In addition to the direct measurement of the diodicities, the flow profiles in the fabricated test structures are determined using a two-dimensional microscopic particle image velocimetry (μPIV) method. Again, a reasonable good agreement of the measured flow profiles with simulated predictions is observed.}, } @article {pmid36080113, year = {2022}, author = {Xiao, X and Li, G and Liu, T and Gu, M}, title = {Experimental Study of the Jetting Behavior of High-Viscosity Nanosilver Inks in Inkjet-Based 3D Printing.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {12}, number = {17}, pages = {}, pmid = {36080113}, issn = {2079-4991}, abstract = {Inkjet printing of high-viscosity (up to 10[5] mPa·s) nanosilver inks is an interesting emerging technology to achieve the 3D fully printed fabrication of electronic products. The highly viscous force of the ink makes it impossible to achieve droplet ejection with the traditional piezoelectric-driven drop-on-demand inkjet method. In this study, a pneumatic needle jetting valve is adopted to provide sufficient driving force. A large number of high-viscosity inkjet printing tests are carried out, and the jetting behavior is recorded with a high-speed camera. Different jetting states are determined according to the recorded images, and the causes of their formation are revealed. Additionally, the effects of the operating pressure, preload angle, and fluid pressure on jetting states are elucidated. Furthermore, the jetting phase diagram is obtained with the characterization of the Reynolds number and the printable region is clarified. This provides a better understanding of high-viscosity inkjet printing and will promote the application of high-viscosity inkjet printing in 3D fully printed electronic products.}, } @article {pmid36067311, year = {2022}, author = {Zhao, D and Bittner, B and Clifton, G and Gravish, N and Revzen, S}, title = {Walking is like slithering: A unifying, data-driven view of locomotion.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {119}, number = {37}, pages = {e2113222119}, pmid = {36067311}, issn = {1091-6490}, mesh = {Animals ; Biomechanical Phenomena ; Foot ; Friction ; Gait ; *Locomotion ; *Models, Biological ; *Walking ; }, abstract = {Legged movement is ubiquitous in nature and of increasing interest for robotics. Most legged animals routinely encounter foot slipping, yet detailed modeling of multiple contacts with slipping exceeds current simulation capacity. Here we present a principle that unifies multilegged walking (including that involving slipping) with slithering and Stokesian (low Reynolds number) swimming. We generated data-driven principally kinematic models of locomotion for walking in low-slip animals (Argentine ant, 4.7% slip ratio of slipping to total motion) and for high-slip robotic systems (BigANT hexapod, slip ratio 12 to 22%; Multipod robots ranging from 6 to 12 legs, slip ratio 40 to 100%). We found that principally kinematic models could explain much of the variability in body velocity and turning rate using body shape and could predict walking behaviors outside the training data. Most remarkably, walking was principally kinematic irrespective of leg number, foot slipping, and turning rate. We find that grounded walking, with or without slipping, is governed by principally kinematic equations of motion, functionally similar to frictional swimming and slithering. Geometric mechanics thus leads to a unified model for swimming, slithering, and walking. Such commonality may shed light on the evolutionary origins of animal locomotion control and offer new approaches for robotic locomotion and motion planning.}, } @article {pmid36056085, year = {2022}, author = {Hasegawa, M and Chen, YC and Sakaue, H}, title = {Drag reduction study of a microfiber-coated cylinder.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {15022}, pmid = {36056085}, issn = {2045-2322}, abstract = {Drag reduction for a bluff body is imperative in a time of increasing awareness of the environmental impact and sustainability of air travel. Microfiber coating has demonstrated its ability to reduce drag on a bluff body. This was done by applying strips of the coating to a cylinder. To widen the application range of the microfiber coating, a fully microfiber-coated cylinder is studied as it has no directionality relative to incoming flow. It is hypothesized that a large coating coverage will cause a reduction in drag dependent on the Reynolds number Re. The fully microfiber-coated cylinder is studied in a wind tunnel and the drag coefficient is determined at a range of Re in the subcritical-flow regime. It is found that the drag coefficient of the microfiber-coated cylinder is a function of Re, and the critical Reynolds number, where the maximum drag reduction occurs, is lower for a microfiber-coated cylinder compared to that of a conventional smooth-surface cylinder.}, } @article {pmid36050069, year = {2022}, author = {Bearden, KP and Padilla, VE and Taubert, L and Craig, SA}, title = {Calibration and performance characterization of a Mach 5 Ludwieg tube.}, journal = {The Review of scientific instruments}, volume = {93}, number = {8}, pages = {085104}, doi = {10.1063/5.0093052}, pmid = {36050069}, issn = {1089-7623}, abstract = {Calibration, commissioning, and design features of a new Mach 5 Ludwieg Tube wind tunnel at the University of Arizona are discussed. Mach number uniformity and free-stream noise levels are measured using a Pitot rake at a range of unit Reynolds numbers and at multiple spanwise and streamwise positions. The wind tunnel is shown to have a free-stream Mach number of 4.82 with maximum variance less than 0.8% (and less than 0.5% at most streamwise positions). The average free-stream acoustic noise level in the core (based on Pitot pressure) is shown to be less than 1.2% at an intermediate Reynolds number with some regions dropping locally below 1.0%. The core flow region is measured to be 282.4 mm (11.1 in.) in diameter at the nozzle exit.}, } @article {pmid36044879, year = {2022}, author = {Luo, Y and Xiao, Q and Zhu, Q and Pan, G}, title = {Thrust and torque production of a squid-inspired swimmer with a bent nozzle for thrust vectoring.}, journal = {Bioinspiration & biomimetics}, volume = {17}, number = {6}, pages = {}, doi = {10.1088/1748-3190/ac8e3f}, pmid = {36044879}, issn = {1748-3190}, mesh = {Animals ; Biomechanical Phenomena ; *Decapodiformes ; *Swimming ; Torque ; Viscosity ; }, abstract = {A three-dimensional pulsed-jet propulsion model consisting of a flexible body and a steerable bent nozzle in tethered mode is presented and studied numerically. By prescribing the body deformation and nozzle angle, we examine the flow evolution and propulsive/turning performance via thrust vectoring. Our results show that the vortex ring is no longer axis-symmetric when the jet is ejected at an angle with the incoming flow. A torque peak is observed during jetting, which is mainly sourced from the suction force (negative pressure) at the lower part of the internal nozzle surface when the flow is directed downward through an acute angle. After this crest, the torque is dominated by the positive pressure at the upper part of the internal nozzle surface, especially at a relatively low jet-based Reynolds number (O(10[2])). The torque production increases with a larger nozzle bent angle as expected. Meanwhile, the thrust production remains almost unchanged, showing little trade-off between thrust and torque production which demonstrates the advantage of thrust vectoring via a bent nozzle. By decoupling the thrust at the internal and outer surfaces considering special characteristics of force generation by pulsed-jet propulsion, we find that variations in Reynolds number mostly affect the viscous friction at the outer surfaces. The influence of the maximum stroke ratio is also studied. Results show that both the time-averaged thrust and the torque decrease at a larger stroke ratio.}, } @article {pmid36043842, year = {2022}, author = {Werwinski, S and Wharton, JA and Nie, M and Stokes, KR}, title = {Monitoring Aerobic Marine Bacterial Biofilms on Gold Electrode Surfaces and the Influence of Nitric Oxide Attachment Control.}, journal = {Analytical chemistry}, volume = {94}, number = {36}, pages = {12323-12332}, pmid = {36043842}, issn = {1520-6882}, mesh = {Biofilms ; Electrodes ; *Gold/pharmacology ; *Nitric Oxide/metabolism ; Nitric Oxide Donors/pharmacology ; }, abstract = {Detection of aerobic marine bacterial biofilms using electrochemical impedance spectroscopy has been done to monitor the interfacial response of Pseudoalteromonas sp. NCIMB 2021 attachment and growth in order to identify characteristic events on a 0.2 mm diameter gold electrode surface. Uniquely, the applicability of surface charge density has been proven to be valuable in determining biofilm attachment and cell enumeration over a 72 h duration on a gold surface within a modified continuous culture flow cell (a controlled low laminar flow regime with Reynolds number ≈ 1). In addition, biofilm dispersal has been evaluated using 500 nM sodium nitroprusside, a nitric oxide donor (nitric oxide is important for the regulation of several diverse biological processes). Ex situ confocal microscopy studies have been performed to confirm biofilm coverage and morphology, plus the determination and quantification of the nitric oxide biofilm dispersal effects. Overall, the capability of the sensor to electrochemically detect the presence of initial bacterial biofilm formation and extent has been established and shown to have potential for real-time biofilm monitoring.}, } @article {pmid36036196, year = {2022}, author = {Khan, M and Sarfraz, M and Mehmood, S and Ullah, MZ}, title = {Irreversibility process analysis for SiO2-MoS2/water-based flow over a rotating and stretching cylinder.}, journal = {Journal of applied biomaterials & functional materials}, volume = {20}, number = {}, pages = {22808000221120329}, doi = {10.1177/22808000221120329}, pmid = {36036196}, issn = {2280-8000}, mesh = {Entropy ; *Hydrodynamics ; *Nanostructures ; Nanotechnology ; Water ; }, abstract = {Entropy is the measure of the amount of energy in any physical system that is not accessible for the useful work, which causes a decrease in a system's thermodynamic efficiency. The idea of entropy generation analysis plays a vital role in characterizing the evolution of thermal processes and minimizing the impending loss of available mechanical power in thermo-fluid systems from an analytical perspective. It has a wide range of applications in biological, information, and engineering systems, such as transportation, telecommunication, and rate processes. The analysis of the entropy generation of axisymmetric magnetohydrodynamic hybrid nanofluid (SiO2-MoS2)/water flow induced by rotating and stretching cylinder in the presence of heat radiation, ohmic heating, and the magnetic field is focus of this study. Thermal energy transport of hybrid nanofluids is performed by applying the Maxwell model. Heat transport is carried out by using convective boundary condition. The dimensionless ordinary differential equations are acquired by similarity transformations. The numerical solution for these differential equations is obtained by the bvp4c program in MATLAB. A comparison between nanofluid and hybrid nanofluid is made for flow field, temperature, and entropy generation. Comparison of nanofluid flow with hybrid nanofluid flow exhibits a higher rate of heat transmission, while entropy generation exhibits the opposite behavior. It is observed that the flow and heat distribution increase as the solid volume fraction's value grows. An increase in entropy is indicated by augmentation in the Brinkman number and temperature ratio parameter, but the Bejan number shows a declining trend. Furthermore, outcomes of the Nusselt number for hybrid nanofluid and nanofluid are calculated for various parameters. It is noticed that the Nusselt number is reduced for enlarging the magnetic field and Eckert number. The axial and azimuthal wall stress parameters are declined by augmenting the Reynolds number.}, } @article {pmid36031990, year = {2022}, author = {Saeed, A and Shah, RA and Khan, MS and Fernandez-Gamiz, U and Bani-Fwaz, MZ and Noeiaghdam, S and Galal, AM}, title = {Theoretical analysis of unsteady squeezing nanofluid flow with physical properties.}, journal = {Mathematical biosciences and engineering : MBE}, volume = {19}, number = {10}, pages = {10176-10191}, doi = {10.3934/mbe.2022477}, pmid = {36031990}, issn = {1551-0018}, abstract = {Theoretical analysis of physical characteristics of unsteady, squeezing nanofluid flow is studied. The flow of nanofluid between two plates that placed parallel in a rotating system by keeping the variable physical properties: viscosity and thermal conductivity. It is analyzed by using Navier Stokes Equation, Energy Equation and Concentration equation. The prominent equations are transformed by virtue of suitable similarity transformation. Nanofluid model includes the important effects of Thermophoresis and Brownian motion. For analysis graphical results are drawn for verity parameters of our interest i.e., Injection parameter, Squeezing number, Prandtle number and Schmidt number are investigated for the Velocity field, Temperature variation and Concentration profile numerically. The findings underline that the parameter of skin friction increases when the Squeezing Reynolds number, Injection parameter and Prandtle number increases. However, it shows inverse relationship with Schmidt number and Rotation parameter. Furthermore, direct relationship of Nusselt number with injection parameter and Reynolds number is observed while its relation with Schmidt number, Rotation parameter, Brownian parameter and Thermophoretic parameter shows an opposite trend. The results are thus obtained through Parametric Continuation Method (PCM) which is further validated through BVP4c. Moreover, the results are tabulated and set forth for comparison of findings through PCM and BVP4c which shows that the obtained results correspond to each other.}, } @article {pmid36030369, year = {2022}, author = {Marfoglio, S and Kovarovic, B and Fiorella, DJ and Sadasivan, C}, title = {A novel angiographic method to estimate arterial blood flow rates using contrast reflux: Effect of injection parameters.}, journal = {Medical physics}, volume = {}, number = {}, pages = {}, doi = {10.1002/mp.15948}, pmid = {36030369}, issn = {2473-4209}, abstract = {BACKGROUND: Contrast reflux, which is the retrograde movement of contrast against flow direction, is commonly observed during angiography. Despite a vast body of literature on angiography, the hemodynamic factors affecting contrast reflux have not been studied. Numerous methods have been developed to extract flow from angiography, but the reliability of these methods is not yet sufficient to be of routine clinical use.

PURPOSE: To evaluate the effect of baseline blood flow rates and injection conditions on the extent of contrast reflux. To estimate arterial flow rates based on measurement of contrast reflux length.

MATERIALS AND METHODS: Iodinated contrast was injected into an idealized tube as well as a physiologically accurate model of the cervico-cerebral vasculature. A total of 194 high-speed angiograms were acquired under varying "blood" flow rates and injection conditions (catheter size, injection rate, and injection time). The length of contrast reflux was compared to the input variables and to dimensionless fluid dynamics parameters at the catheter-tip. Arterial blood flow rates were estimated using contrast reflux length as well as a traditional transit-time method and compared to measured flow rates.

RESULTS: Contrast reflux lengths were significantly affected by contrast injection rate (p < 0.0001), baseline blood flow rate (p = 0.0004), and catheter size (p = 0.04), but not by contrast injection time (p = 0.4). Reflux lengths were found to be correlated to dimensionless fluid dynamics parameters by an exponential function (R[2]  = 0.6-0.99). When considering the entire dataset in unison, flow estimation errors with the reflux-length method (39% ± 33%) were significantly higher (p = 0.003) than the transit-time method (33% ± 36%). However, when subgrouped by catheter, the error with the reflux-length method was substantially reduced and was significantly lower (14% ± 14%, p < 0.0001) than the transit-time method.

CONCLUSION: Results show correlations between contrast reflux length and baseline hemodynamic parameters that have not been reported previously. Clinically relevant blood flow rate estimation is feasible by simple measurement of reflux length. In vivo and clinical studies are required to confirm these correlations and to refine the methodology of estimating blood flow by reflux.}, } @article {pmid36014668, year = {2022}, author = {Shi, R and Lin, J and Yang, H}, title = {Particle Distribution and Heat Transfer of SiO2/Water Nanofluid in the Turbulent Tube Flow.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {12}, number = {16}, pages = {}, pmid = {36014668}, issn = {2079-4991}, abstract = {In order to clarify the effect of particle coagulation on the heat transfer properties, the governing equations of nanofluid together with the equation for nanoparticles in the SiO2/water nanofluid flowing through a turbulent tube are solved numerically in the range of Reynolds number 3000 ≤ Re ≤ 16,000 and particle volume fraction 0.005 ≤ φ ≤ 0.04. Some results are validated by comparing with the experimental results. The effect of particle convection, diffusion, and coagulation on the pressure drop ∆P, particle distribution, and heat transfer of nanofluid are analyzed. The main innovation is that it gives the effect of particle coagulation on the pressure drop, particle distribution, and heat transfer. The results showed that ∆P increases with the increase in Re and φ. When inlet velocity is small, the increase in ∆P caused by adding particles is relatively large, and ∆P increases most obviously compared with the case of pure water when the inlet velocity is 0.589 m/s and φ is 0.004. Particle number concentration M0 decreases along the flow direction, and M0 near the wall is decreased to the original 2% and decreased by about 90% in the central area. M0 increases with increasing Re but with decreasing φ, and basically presents a uniform distribution in the core area of the tube. The geometric mean diameter of particle GMD increases with increasing φ, but with decreasing Re. GMD is the minimum in the inlet area, and gradually increases along the flow direction. The geometric standard deviation of particle diameter GSD increases sharply at the inlet and decreases in the inlet area, remains almost unchanged in the whole tube, and finally decreases rapidly again at the outlet. The effects of Re and φ on the variation in GSD along the flow direction are insignificant. The values of convective heat transfer coefficient h and Nusselt number Nu are larger for nanofluids than that for pure water. h and Nu increase with the increase in Re and φ. Interestingly, the variation in φ from 0.005 to 0.04 has little effect on h and Nu.}, } @article {pmid36014601, year = {2022}, author = {Akram, S and Athar, M and Saeed, K and Razia, A and Alghamdi, M and Muhammad, T}, title = {Impact of Partial Slip on Double Diffusion Convection of Sisko Nanofluids in Asymmetric Channel with Peristaltic Propulsion and Inclined Magnetic Field.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {12}, number = {16}, pages = {}, pmid = {36014601}, issn = {2079-4991}, abstract = {The current article discusses the outcomes of the double diffusion convection of peristaltic transport in Sisko nanofluids along an asymmetric channel having an inclined magnetic field. Consideration is given to the Sisko fluid model, which can forecast both Newtonian and non-Newtonian fluid properties. Lubricating greases are the best examples of Sisko fluids. Experimental research shows that most realistic fluids, including human blood, paint, dirt, and other substances, correspond to Sisko's proposed definition of viscosity. Mathematical modelling is considered to explain the flow behavior. The simpler non-linear PEDs are deduced by using an elongated wavelength and a minimal Reynolds number. The expression is also numerically calculated. The impacts of the physical variables on the quantities of flow are plotted graphically as well as numerically. The results reveal that there is a remarkable increase in the concentration, temperature, and nanoparticle fraction with the rise in the Dufour and thermophoresis variables.}, } @article {pmid36001259, year = {2022}, author = {Canli, E and Kucuksariyildiz, H and Carman, K}, title = {Impact assessment of new generation high-speed agricultural tractor aerodynamics on transportation fuel consumption and related phenomena.}, journal = {Environmental science and pollution research international}, volume = {}, number = {}, pages = {}, pmid = {36001259}, issn = {1614-7499}, abstract = {New generation agricultural tractors contribute to transportation by increased travel speeds. There is not any available aerodynamic data on the authentic agricultural tractor form. On-road transportation by tractors is between 8 and 30% of their operational time. In this work, two agricultural tractors are modelled via computational fluid dynamics for nine different speeds to determine aerodynamic resistances. Constant speed travel scenarios are analyzed. Corresponding speeds are 5 and 10 to 80 km/h with 10 km/h increments. Reynolds number changes between 1.6 × 10[5] and 2.98 × 10[6]. The characteristic lengths are taken as the square root of the streamwise projected area of the tractor geometries. Aerodynamic forces exerted on the tractors change between 3 and 746 N. The calculated drag coefficients are found as independent from Reynolds number and are 0.6 and 0.78 for the two different types of driver compartments. The approximated aerodynamic related fuel consumptions for 1-h changes between 0.002 and 8.28 lt/s which correspond to 0.001 to 5.76 kg/s carbon emission. A potential improvement in decreasing aerodynamic resistance about 20% is discussed by spatial data. Since the conducted work is being regarded as the first instance in the literature, it is estimated that several consecutive reports will be triggered.}, } @article {pmid35999194, year = {2022}, author = {Nan, K and Shi, Y and Zhao, T and Tang, X and Zhu, Y and Wang, K and Bai, J and Zhao, W}, title = {Mixing and Flow Transition in an Optimized Electrokinetic Turbulent Micromixer.}, journal = {Analytical chemistry}, volume = {94}, number = {35}, pages = {12231-12239}, doi = {10.1021/acs.analchem.2c02960}, pmid = {35999194}, issn = {1520-6882}, abstract = {Micromixer is a key element in a lab on a chip for broad applications in the analysis and measurement of chemistry and engineering. Previous investigations reported that electrokinetic (EK) turbulence could be realized in a "Y" type micromixer with a cross-sectional dimension of 100 μm order. Although the ultrafast turbulent mixing can be generated at a bulk flow Reynolds number on the order of unity, the micromixer has not been optimized. In this investigation, we systematically investigated the influence of electric field intensity, AC frequency, electric conductivity ratio, and channel width at the entrance on the mixing effect and transition electric Rayleigh number in the "Y" type electrokinetic turbulent micromixer. It is found that the optimal mixing is realized in a 350 μm wide micromixer, under 100 kHz and 1.14 × 10[5] V/m AC electric field, with an electric conductivity ratio of 1:3000. Under these conditions, a degree of mixedness of 0.93 can be achieved at 84 μm from the entrance and 100 ms. A further investigation of the critical electric field and the critical electric Rayleigh number indicates that the most unstable condition of EK flow instability is inconsistent with that of the optimal mixing in EK turbulence. To predict the evolution of EK flow under high Raσ and guide the design of EK turbulent micromixers, it is necessary to apply a computational turbulence model instead of linear instability analysis.}, } @article {pmid35990482, year = {2022}, author = {Mondal, T and Hnaien, N and Ajmi, M and Ghachem, K and Kolsi, L}, title = {CFD Investigation of Thermal Characteristics for a Dual Jet with a Parallel Co-flow.}, journal = {ACS omega}, volume = {7}, number = {32}, pages = {27864-27875}, pmid = {35990482}, issn = {2470-1343}, abstract = {A combined turbulent wall jet and offset jet (also known as the dual jet) with and without the presence of a parallel co-flow stream is studied. The standard k-ω turbulence model is used to predict the turbulent flow. The study focuses on the effects of the co-flow velocity (CFV) on the heat-transfer characteristics of the dual jet flow with the bottom wall maintained at a constant wall temperature. The CFV is varied up to 40% of the jet inlet velocity, and the height of the offset jet is varied from 5 to 11 times the jet width with the inlet Reynolds number taken as 15,000. The heat-transfer results reveal that the local Nusselt number (Nu x) along the bottom wall exhibits a peak at the immediate downstream of the nozzle exit, followed by a continuous decay in the rest of the converging region before showing a small rise for a short streamwise distance in the merging region. Further downstream, in the combined region, Nu x gradually decreases with the downstream distance. Except the merging region, no influence of co-flow is observed in the other two flow zones (converging and combined regions). In the merging region, for a given offset ratio (OR), Nu x remains nearly constant for a certain axial distance, and it decreases as the CFV increases. As a result of the increase in the CFV, the average Nusselt number decreases, indicating a reduction in overall convective heat transfer for higher values of the CFV. A regression analysis among the average Nusselt number (), CFV, and OR results in a correlation function in the form of within the range OR = 5-11 and CFV = 0-40%.}, } @article {pmid35965667, year = {2022}, author = {Wüthrich, D and Shi, R and Chanson, H}, title = {Hydraulic jumps with low inflow Froude numbers: air-water surface patterns and transverse distributions of two-phase flow properties.}, journal = {Environmental fluid mechanics (Dordrecht, Netherlands : 2001)}, volume = {22}, number = {4}, pages = {789-818}, pmid = {35965667}, issn = {1567-7419}, abstract = {ABSTRACT: Hydraulic jumps are commonly employed as energy dissipators to guarantee long-term operation of hydraulic structures. A comprehensive and in-depth understanding of their main features is therefore fundamental. In this context, the current study focused on hydraulic jumps with low Froude numbers, i.e. Fr1 = 2.1 and 2.4, at relatively high Reynolds number: Re ~2 × 10[5]. Experimental tests employed a combination of dual-tip phase-detection probes and ultra-high-speed video camera to provide a comprehensive characterisation of the main air-water flow properties of the hydraulic jump, including surface flow features, void fraction, bubble count rate and interfacial velocities. The current research also focused on the transverse distributions of air-water flow properties, i.e. across the channel width, with the results revealing lower values of void fraction and bubble count rate next to the sidewalls compared to the channel centreline data. Such a spatial variability in the transverse direction questions whether data near the side walls may be truly representative of the behaviour in the bulk of the flow, raising the issue of sidewall effects in image-based techniques. Overall, these findings provide new information to both researchers and practitioners for a better understanding of the physical processes inside the hydraulic jump with low Froude numbers, leading to an optimised design of hydraulic structures.

ARTICLE HIGHLIGHTS: Experimental investigation of air-water flow properties in hydraulic jumps with low Froude numbersDetailed description of the main air-water surface features on the breaking rollerTransversal distribution of the air-water flow properties across the channel width and comparison between centreline and sidewall.}, } @article {pmid35958096, year = {2022}, author = {Mohanty, RK and Setia, N and Khurana, G and Manchanda, G}, title = {High precision compact numerical approximation in exponential form for the system of 2D quasilinear elliptic BVPs on a discrete irrational region.}, journal = {MethodsX}, volume = {9}, number = {}, pages = {101790}, pmid = {35958096}, issn = {2215-0161}, abstract = {This article presents a new approximation of order four in exponential form for two-dimensional (2D) quasilinear partial differential equation (PDE) of elliptic form with solution domain being irrational. It is further extended for application to a system of quasilinear elliptic PDEs with Dirichlet boundary conditions (DBCs). The main highlights of the method framed in this article are as under:•It uses a 9-point stencil with unequal mesh to approach the solution. The error analysis is discussed to authenticate the order of convergence of the proposed numerical approximation.•Various validating problems, for instance the Burgers' equation, Poisson equation in cylindrical coordinates, Navier-Stokes (NS) equations in rectangular and cylindrical coordinates are solved using the proposed techniques to depict their stability. The proposed approximation produces solution free of oscillations for large values of Reynolds Number in the vicinity of a singularity.•The results of the proposed method are superior in comparison to the existing methods of [49] and [56].}, } @article {pmid35957150, year = {2022}, author = {Togun, H and Homod, RZ and Yaseen, ZM and Abed, AM and Dhabab, JM and Ibrahem, RK and Dhahbi, S and Rashidi, MM and Ahmadi, G and Yaïci, W and Mahdi, JM}, title = {Efficient Heat Transfer Augmentation in Channels with Semicircle Ribs and Hybrid Al2O3-Cu/Water Nanofluids.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {12}, number = {15}, pages = {}, pmid = {35957150}, issn = {2079-4991}, abstract = {Global technological advancements drive daily energy consumption, generating additional carbon-induced climate challenges. Modifying process parameters, optimizing design, and employing high-performance working fluids are among the techniques offered by researchers for improving the thermal efficiency of heating and cooling systems. This study investigates the heat transfer enhancement of hybrid "Al2O3-Cu/water" nanofluids flowing in a two-dimensional channel with semicircle ribs. The novelty of this research is in employing semicircle ribs combined with hybrid nanofluids in turbulent flow regimes. A computer modeling approach using a finite volume approach with k-ω shear stress transport turbulence model was used in these simulations. Six cases with varying rib step heights and pitch gaps, with Re numbers ranging from 10,000 to 25,000, were explored for various volume concentrations of hybrid nanofluids Al2O3-Cu/water (0.33%, 0.75%, 1%, and 2%). The simulation results showed that the presence of ribs enhanced the heat transfer in the passage. The Nusselt number increased when the solid volume fraction of "Al2O3-Cu/water" hybrid nanofluids and the Re number increased. The Nu number reached its maximum value at a 2 percent solid volume fraction for a Reynolds number of 25,000. The local pressure coefficient also improved as the Re number and volume concentration of "Al2O3-Cu/water" hybrid nanofluids increased. The creation of recirculation zones after and before each rib was observed in the velocity and temperature contours. A higher number of ribs was also shown to result in a larger number of recirculation zones, increasing the thermal performance.}, } @article {pmid35926485, year = {2022}, author = {Bhattacharjee, A and Jabbarzadeh, M and Kararsiz, G and Fu, HC and Kim, MJ}, title = {Bacteria-inspired magnetically actuated rod-like soft robot in viscous fluids.}, journal = {Bioinspiration & biomimetics}, volume = {17}, number = {6}, pages = {}, doi = {10.1088/1748-3190/ac870f}, pmid = {35926485}, issn = {1748-3190}, mesh = {Magnets ; Models, Biological ; *Robotics ; Swimming ; Viscosity ; }, abstract = {This paper seeks to design, develop, and explore the locomotive dynamics and morphological adaptability of a bacteria-inspired rod-like soft robot propelled in highly viscous Newtonian fluids. The soft robots were fabricated as tapered, hollow rod-like soft scaffolds by applying a robust and economic molding technique to a polyacrylamide-based hydrogel polymer. Cylindrical micro-magnets were embedded in both ends of the soft scaffolds, which allowed bending (deformation) and actuation under a uniform rotating magnetic field. We demonstrated that the tapered rod-like soft robot in viscous Newtonian fluids could perform two types of propulsion; boundary rolling was displayed when the soft robot was located near a boundary, and swimming was displayed far away from the boundary. In addition, we performed numerical simulations to understand the swimming propulsion along the rotating axis and the way in which this propulsion is affected by the soft robot's design, rotation frequency, and fluid viscosity. Our results suggest that a simple geometrical asymmetry enables the rod-like soft robot to perform propulsion in the low Reynolds number (Re≪ 1) regime; these promising results provide essential insights into the improvements that must be made to integrate the soft robots into minimally invasivein vivoapplications.}, } @article {pmid35918493, year = {2022}, author = {Xiao, L and Liu, Q and Huang, W}, title = {Experimental research and analysis on the resistance characteristics of simulated ore bin in water.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {13211}, pmid = {35918493}, issn = {2045-2322}, abstract = {In order to research the variation law of the longitudinal resistance coefficient of the ore bin in the marine mining system under different length-diameter ratio, external shape, additional weight and Reynolds number, a set of experimental system for testing the resistance coefficient was designed and built independently. By analyzing the experimental results, it can be seen that under the same conditions, the resistance coefficient decreases gradually with the increase of Reynolds number and finally fluctuates around a certain value. Increasing the excitation displacement will reduce the overall resistance coefficient of the ore bin. The smaller the length-diameter ratio is, the larger the corresponding force value when the vibration acceleration of the ore bin is 0, and the larger the overall resistance coefficient is. The resistance coefficient of the cylindrical section is greater than that of the rectangular shape. In order to reduce the longitudinal vibration and the transverse towing offset, the shape of the ore bin should be cylindrical in actual design and production. At low Reynolds number, the increase of added weight will increase the resistance coefficient, while at high Reynolds number, the change of added weight will not cause the change of resistance coefficient.}, } @article {pmid35912042, year = {2022}, author = {Ram, D and Bhandari, DS and Tripathi, D and Sharma, K}, title = {Propagation of H1N1 virus through saliva movement in oesophagus: a mathematical model.}, journal = {European physical journal plus}, volume = {137}, number = {7}, pages = {866}, pmid = {35912042}, issn = {2190-5444}, abstract = {H1N1 (Swine flu) is caused by the influenza A virus which belongs to the Orthomyxoviridae family. Influenza A is very harmful to the elderly, and people with chronic respiratory disease and cardiovascular disease. Therefore, it is essential to analyse the behaviour of virus transmission through the saliva movement in oesophagus. A mathematical paradigm is developed to study the saliva movement under the applications of transverse magnetic field. Jeffrey fluid model is considered for saliva to show the viscoelastic nature. The flow nature is considered creeping and assumptions of long wavelength and low Reynolds number are adopted for analytical solutions. The Basset-Boussinesq-Oseen equation is employed to understand the propagation of H1N1 virus through saliva under the effect of applicable forces such as gravity, virtual mass, basset force, and drag forces. The suitable data for saliva, oesophagus and H1N1 virus are taken from the existing literature for simulation of the results using MATLAB software. From the graphical results, it is observed that the susceptibility to viral infections is less because the magnetic field reduces the motion of the virus particle. Further, the chances of infections in males are more as compared to females and children due to variation in viscosity of saliva. Such findings provide an understanding of the mechanics of the virus floating through the saliva (viscoelastic fluids) in the oesophagus.}, } @article {pmid35912036, year = {2022}, author = {Strazzullo, M and Girfoglio, M and Ballarin, F and Iliescu, T and Rozza, G}, title = {Consistency of the full and reduced order models for evolve-filter-relax regularization of convection-dominated, marginally-resolved flows.}, journal = {International journal for numerical methods in engineering}, volume = {123}, number = {14}, pages = {3148-3178}, pmid = {35912036}, issn = {0029-5981}, abstract = {Numerical stabilization is often used to eliminate (alleviate) the spurious oscillations generally produced by full order models (FOMs) in under-resolved or marginally-resolved simulations of convection-dominated flows. In this article, we investigate the role of numerical stabilization in reduced order models (ROMs) of marginally-resolved, convection-dominated incompressible flows. Specifically, we investigate the FOM-ROM consistency, that is, whether the numerical stabilization is beneficial both at the FOM and the ROM level. As a numerical stabilization strategy, we focus on the evolve-filter-relax (EFR) regularization algorithm, which centers around spatial filtering. To investigate the FOM-ROM consistency, we consider two ROM strategies: (i) the EFR-noEFR, in which the EFR stabilization is used at the FOM level, but not at the ROM level; and (ii) the EFR-EFR, in which the EFR stabilization is used both at the FOM and at the ROM level. We compare the EFR-noEFR with the EFR-EFR in the numerical simulation of a 2D incompressible flow past a circular cylinder in the convection-dominated, marginally-resolved regime. We also perform model reduction with respect to both time and Reynolds number. Our numerical investigation shows that the EFR-EFR is more accurate than the EFR-noEFR, which suggests that FOM-ROM consistency is beneficial in convection-dominated, marginally-resolved flows.}, } @article {pmid35905362, year = {2022}, author = {Wang, X and Shih, HY and Goldenfeld, N}, title = {Stochastic Model for Quasi-One-Dimensional Transitional Turbulence with Streamwise Shear Interactions.}, journal = {Physical review letters}, volume = {129}, number = {3}, pages = {034501}, doi = {10.1103/PhysRevLett.129.034501}, pmid = {35905362}, issn = {1079-7114}, abstract = {The transition to turbulence in wall-bounded shear flows is typically subcritical, with a poorly understood interplay between spatial fluctuations, pattern formation, and stochasticity near the critical Reynolds number. Here, we present a spatially extended stochastic minimal model for the energy budget in transitional pipe flow, which successfully recapitulates the way localized patches of turbulence (puffs) decay, split, and grow, respectively, as the Reynolds number increases through the laminar-turbulent transition. Our approach takes into account the flow geometry, as we demonstrate by extending the model to quasi-one-dimensional Taylor-Couette flow, reproducing the observed directed percolation pattern of turbulent patches in space and time.}, } @article {pmid35899947, year = {2022}, author = {Godeau, AL and Leoni, M and Comelles, J and Guyomar, T and Lieb, M and Delanoë-Ayari, H and Ott, A and Harlepp, S and Sens, P and Riveline, D}, title = {3D single cell migration driven by temporal correlation between oscillating force dipoles.}, journal = {eLife}, volume = {11}, number = {}, pages = {}, pmid = {35899947}, issn = {2050-084X}, mesh = {*Actins/metabolism ; Cell Movement/physiology ; Cell Nucleus/metabolism ; *Cell Polarity/physiology ; Myosins/metabolism ; }, abstract = {Directional cell locomotion requires symmetry breaking between the front and rear of the cell. In some cells, symmetry breaking manifests itself in a directional flow of actin from the front to the rear of the cell. Many cells, especially in physiological 3D matrices, do not show such coherent actin dynamics and present seemingly competing protrusion/retraction dynamics at their front and back. How symmetry breaking manifests itself for such cells is therefore elusive. We take inspiration from the scallop theorem proposed by Purcell for micro-swimmers in Newtonian fluids: self-propelled objects undergoing persistent motion at low Reynolds number must follow a cycle of shape changes that breaks temporal symmetry. We report similar observations for cells crawling in 3D. We quantified cell motion using a combination of 3D live cell imaging, visualization of the matrix displacement, and a minimal model with multipolar expansion. We show that our cells embedded in a 3D matrix form myosin-driven force dipoles at both sides of the nucleus, that locally and periodically pinch the matrix. The existence of a phase shift between the two dipoles is required for directed cell motion which manifests itself as cycles with finite area in the dipole-quadrupole diagram, a formal equivalence to the Purcell cycle. We confirm this mechanism by triggering local dipolar contractions with a laser. This leads to directed motion. Our study reveals that these cells control their motility by synchronizing dipolar forces distributed at front and back. This result opens new strategies to externally control cell motion as well as for the design of micro-crawlers.}, } @article {pmid35896094, year = {2022}, author = {Zhang, JD and Sung, HJ and Huang, WX}, title = {Hydrodynamic interaction of dorsal fin and caudal fin in swimming tuna.}, journal = {Bioinspiration & biomimetics}, volume = {17}, number = {6}, pages = {}, doi = {10.1088/1748-3190/ac84b8}, pmid = {35896094}, issn = {1748-3190}, mesh = {*Animal Fins ; Animals ; Biomechanical Phenomena ; Hydrodynamics ; *Swimming ; Tuna ; }, abstract = {Tuna, which are known for high-performance swimming, possess a large crescent dorsal fin (DF) and a caudal fin (CF) that differ from those of other fishes. The hydrodynamic interaction between the DF and CF in tuna, which are represented by two tandem 3D flapping plates, is numerically explored in the present study. Hydrodynamic properties and wake structures of the models with and without a DF are compared to investigate the effects of the DF. The thrust on the CF is substantially enhanced by the DF, whereas the force on the DF is not affected by the CF. The constructive interaction between the leading-edge vortex (LEV) on the CF and the vortices shed from the dorsal fin (DFVs) is identified from 3D wake topology and 2D vorticity distributions. The circulation of spanwise vorticity quantitatively reveals that the LEV on the CF is strengthened by the same-signed DFV. The effect of the flapping phase of the CF is examined. The DF-CF interaction is sensitive to the flapping phase at a short spacing, whereas a long spacing between the two fins enables a robust constructive interaction in tuna swimming. A systematic study is carried out to explore the effects of the Strouhal number (St) and the Reynolds number (Re) on the interaction of the fins. The enhancement of thrust due to the DF is diminished at St = 0.63, whereas the Re does not substantially influence the constructive DF-CF interaction.}, } @article {pmid35892036, year = {2022}, author = {Mane, NS and Puri, DB and Mane, S and Hemadri, V and Banerjee, A and Tripathi, S}, title = {Separation of motile human sperms in a T-shaped sealed microchannel.}, journal = {Biomedical engineering letters}, volume = {12}, number = {3}, pages = {331-342}, pmid = {35892036}, issn = {2093-985X}, abstract = {UNLABELLED: Microfluidic methods act as an effective motile sperm separation technique used in infertility treatments. This work presents a standalone microfluidic device to separate motile sperm cells from non-motile sperm cells and debris. The separation mechanism is based on the centrifugal force acting on sperms and the ability of progressive motile sperms to swim upstream. The separation of motile sperm is carried out using a simple T-shaped microchannel which constitutes three reservoirs: one inlet and two outlets. Herein, one of the outlets is kept sealed. The sealed channel leads to a high-velocity gradient and a rheotaxis zone at the T junction resulting in the separation of motile sperms. Separated sperms are isolated in a sealed channel with a low Reynolds number flow so that sperms cannot have a net displacement, which ensures that the sperms do not re-enter the fluid flow. CFD simulation is conducted to study the flow fields inside the channel and experimental investigation is carried to observe the separation behaviour of sperms. The reported device provides 100% sperm separation efficiency and ensures the entrapment of sperm cells for a longer period. A modified colorimetric nitroblue tetrazolium test conducted on separated sperm cells shows that there is only a marginal increase in superoxide (O2 [-]) production, proving normal sperm integrity. This device offers an effective and safe alternative to conventional sperm sorting methods.

SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s13534-022-00229-9.}, } @article {pmid35889690, year = {2022}, author = {Ghachem, K and Selimefendigil, F and Alshammari, BM and Maatki, C and Kolsi, L}, title = {Coupled Effects of Using Magnetic Field, Rotation and Wavy Porous Layer on the Forced Convection of Hybrid Nanoliquid Flow over 3D-Backward Facing Step.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {12}, number = {14}, pages = {}, pmid = {35889690}, issn = {2079-4991}, abstract = {In the present study, the effects of using a corrugated porous layer on the forced convection of a hybrid nanofluid flow over a 3D backward facing step are analyzed under the coupled effects of magnetic field and surface rotation. The thermal analysis is conducted for different values of the Reynolds number (Re between 100 and 500), the rotational Reynolds number (Rew between 0 and 2000), the Hartmann number (Ha between 0 and 15), the permeability of the porous layer (the Darcy number, Da between 10-5 and 10-2) and the amplitude (ax between 0.01 ap and 0.7 ap) and wave number (N between 1 and 16) of the porous layer corrugation. When rotations are activated, the average Nusselt number (Nu) and pressure coefficient values rise, while the increment of the latter is less. The increment in the average Nu is higher for the case with a higher permeability of the layer. When the corrugation amplitude and wave number are increased, favorable impacts of the average Nu are observed, but at the same time pressure coefficients are increased. Successful thermal performance estimations are made by using a neural-based modeling approach with a four input-two output system.}, } @article {pmid35889569, year = {2022}, author = {Minea, AA and El-Maghlany, WM and Massoud, EZ}, title = {Heat Transfer Analysis of Nanocolloids Based on Zinc Oxide Nanoparticles Dispersed in PEG 400.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {12}, number = {14}, pages = {}, pmid = {35889569}, issn = {2079-4991}, abstract = {Cooling and heating are extremely important in many industrial applications, while the thermal performance of these processes generally depends on many factors, such as fluid flow rate, inlet temperature, and many more. Hence, tremendous efforts are dedicated to the investigation of several parameters to reach an efficient cooling or heating process. The interest in adding nanoparticles in regular heat transfer fluids delivered new fluids to the market, the nanofluids. In this paper, a new nanoparticle-enhanced fluid based on polyethylene glycol with ZnO nanoparticles is considered and its hydrothermal performance is investigated for HVAC applications. The thermophysical properties of PEG 400-ZnO and their variation with temperature at different nanoparticle loading are previously determined on experimental bases and here implemented in a numerical application. The numerical results are completed at Reynolds number from 200 to 2000, while the nanoparticle concentration varies from 0.5 to 5%. Results are discussed in terms of Nusselt number, friction factor, and dimensionless pressure drop ratio at different temperatures and ZnO loading in the PEG 400 base fluid. Additionally, the evaluation performance criteria (EC) are calculated and discussed. Concluding, the newly developed fluid enhances the heat transfer up to 16% with a 13% pressure drop penalty, while the performance evaluation criteria are enhanced. Plus, several correlations are developed for both Nusselt number and friction factor as a function of relevant operating conditions.}, } @article {pmid35888927, year = {2022}, author = {Wang, Y and Yin, Z and Bao, F and Shen, J}, title = {CFD-DEM Coupling Model for Deposition Process Analysis of Ultrafine Particles in a Micro Impinging Flow Field.}, journal = {Micromachines}, volume = {13}, number = {7}, pages = {}, pmid = {35888927}, issn = {2072-666X}, abstract = {Gas with ultrafine particle impaction on a solid surface is a unique case of curvilinear motion that can be widely used for the devices of surface coatings or instruments for particle size measurement. In this work, the Eulerian-Lagrangian method was applied to calculate the motion of microparticles in a micro impinging flow field with consideration of the interactions between particle to particle, particle to wall, and particle to fluid. The coupling computational fluid dynamics (CFD) with the discrete element method (DEM) was employed to investigate the different deposition patterns of microparticles. The vortex structure and two types of particle deposits ("halo" and "ring") have been discussed. The particle deposition characteristics are affected both by the flow Reynolds number (Re) and Stokes number (stk). Moreover, two particle deposition patterns have been categorized in terms of Re and stk. Finally, the characteristics and mechanism of particle deposits have been analyzed using the particle inertia, the process of impinging (particle rebound or no rebound), vortical structures, and the kinetic energy conversion in two-phase flow, etc.}, } @article {pmid35888885, year = {2022}, author = {Zhou, Y and Dai, L and Jiao, N}, title = {Review of Bubble Applications in Microrobotics: Propulsion, Manipulation, and Assembly.}, journal = {Micromachines}, volume = {13}, number = {7}, pages = {}, pmid = {35888885}, issn = {2072-666X}, abstract = {In recent years, microbubbles have been widely used in the field of microrobots due to their unique properties. Microbubbles can be easily produced and used as power sources or tools of microrobots, and the bubbles can even serve as microrobots themselves. As a power source, bubbles can propel microrobots to swim in liquid under low-Reynolds-number conditions. As a manipulation tool, microbubbles can act as the micromanipulators of microrobots, allowing them to operate upon particles, cells, and organisms. As a microrobot, microbubbles can operate and assemble complex microparts in two- or three-dimensional spaces. This review provides a comprehensive overview of bubble applications in microrobotics including propulsion, micromanipulation, and microassembly. First, we introduce the diverse bubble generation and control methods. Then, we review and discuss how bubbles can play a role in microrobotics via three functions: propulsion, manipulation, and assembly. Finally, by highlighting the advantages and current challenges of this progress, we discuss the prospects of microbubbles in microrobotics.}, } @article {pmid35888870, year = {2022}, author = {Juraeva, M and Kang, DJ}, title = {Mixing Enhancement of a Passive Micromixer with Submerged Structures.}, journal = {Micromachines}, volume = {13}, number = {7}, pages = {}, pmid = {35888870}, issn = {2072-666X}, abstract = {A passive micromixer combined with two different mixing units was designed by submerging planar structures, and its mixing performance was simulated over a wider range of the Reynolds numbers from 0.1 to 80. The two submerged structures are a Norman window and rectangular baffles. The mixing performance was evaluated in terms of the degree of mixing (DOM) at the outlet and the required pressure load between inlet and outlet. The amount of submergence was varied from 30 μm to 70 μm, corresponding to 25% to 58% of the micromixer depth. The enhancement of mixing performance is noticeable over a wide range of the Reynolds numbers. When the Reynolds number is 10, the DOM is improved by 182% from that of no submergence case, and the required pressure load is reduced by 44%. The amount of submergence is shown to be optimized in terms of the DOM, and the optimum value is about 40 μm. This corresponds to a third of the micromixer depth. The effects of the submerged structure are most significant in the mixing regime of convection dominance from Re = 5 to 80. In a circular passage along the Norman window, one of the two Dean vortices burst into the submerged space, promoting mixing in the cross-flow direction. The submerged baffles in the semi-circular mixing units generate a vortex behind the baffles that contributes to the mixing enhancement as well as reducing the required pressure load.}, } @article {pmid35888205, year = {2022}, author = {Vatsa, A and Alam, T and Siddiqui, MIH and Ali, MA and Dobrotă, D}, title = {Performance of Microchannel Heat Sink Made of Silicon Material with the Two-Sided Wedge.}, journal = {Materials (Basel, Switzerland)}, volume = {15}, number = {14}, pages = {}, pmid = {35888205}, issn = {1996-1944}, abstract = {New designs of the microchannel with a two-sided wedge shape at the base were studied numerically. Five different wedge angles ranging from 3° to 15° were incorporated into the microchannel design. Simulation of this novel microchannel was carried out using Computational Fluid Dynamics (CFD). Three-dimensional models of the microchannel heat sink were created, discretized, and based on Navier-Stokes and energy equations; laminar numerical solutions were obtained for heat transfer and pressure drop. Flow characteristics of water as coolant in a microchannel were studied. It was observed that numerical results are in good agreement with experimental results. It was found that the Nusselt number and friction factor are significantly varied with the increase in Reynolds number. The Nusselt number varies in the following ranges of 5.963-8.521, 5.986-8.550, 6.009-8.568, 6.040-8.609, and 6.078-8.644 at 3°, 6°, 9°, 12°, and 15°, respectively. The microchannel with a wedge angle of 15° was found to be better in terms of Nusselt number and thermo-hydraulic performance. The enhancement in the Nusselt number is found as 1.017-1.036 for a wedge angle of 15°; however, friction factors do not show the perceptible values at distinct values of wedge angle. Moreover, the thermo-hydraulic performance parameters (THPP) were evaluated and found to be maximum in the range of 1.027-1.045 for a wedge angle of 15°. However, minimum THPP was found in the range of 1.005-1.0185 for a wedge angle of 3°.}, } @article {pmid35885078, year = {2022}, author = {Qi, T and Lin, J and Ouyang, Z}, title = {Hydrodynamic Behavior of Self-Propelled Particles in a Simple Shear Flow.}, journal = {Entropy (Basel, Switzerland)}, volume = {24}, number = {7}, pages = {}, pmid = {35885078}, issn = {1099-4300}, abstract = {The hydrodynamic properties of a squirmer type of self-propelled particle in a simple shear flow are investigated using the immersed boundary-lattice Boltzmann method in the range of swimming Reynolds number 0.05 ≤ Res ≤ 2.0, flow Reynolds number 40 ≤ Rep ≤ 160, blocking rate 0.2 ≤ κ ≤ 0.5. Some results are validated by comparing with available other results. The effects of Res, Rep and κ on the hydrodynamic properties of squirmer are discussed. The results show that there exist four distinct motion modes for the squirmer, i.e., horizontal mode, attractive oscillation mode, oscillation mode, and chaotic mode. Increasing Res causes the motion mode of the squirmer to change from a constant tumbling near the centerline to a stable horizontal mode, even an oscillatory or appealing oscillatory mode near the wall. Increasing the swimming intensity of squirmer under the definite Res will induce the squirmer to make periodic and stable motion at a specific distance from the wall. Increasing Rep will cause the squirmer to change from a stable swimming state to a spiral motion or continuous rotation. Increasing κ will strengthen the wall's attraction to the squirmer. Increasing swimming intensity of squirmer will modify the strength and direction of the wall's attraction to the squirmer if κ remains constant.}, } @article {pmid35879876, year = {2022}, author = {Punyaratabandhu, N and Dechadilok, P and Triampo, W and Katavetin, P}, title = {Hydrodynamic model for renal microvascular filtration: Effects of physiological and hemodynamic changes on glomerular size-selectivity.}, journal = {Microcirculation (New York, N.Y. : 1994)}, volume = {29}, number = {8}, pages = {e12779}, doi = {10.1111/micc.12779}, pmid = {35879876}, issn = {1549-8719}, mesh = {Humans ; Hydrodynamics ; *Diabetic Nephropathies ; Models, Biological ; Hemodynamics/physiology ; *Hypertension ; Glomerular Filtration Rate/physiology ; }, abstract = {OBJECTIVE: The first step in renal urine formation is ultrafiltration across the glomerular barrier. The change in its nanostructure has been associated with nephrotic syndromes. Effects of physiological and hemodynamic factor alterations associated with diabetic nephropathy (DN) on glomerular permselectivity are examined through a mathematical model employing low-Reynolds-number hydrodynamics and hindered transport theory.

METHODS: Glomerular capillaries are represented as networks of cylindrical tubes with multilayered walls. Glomerular basement membrane (GBM) is a fibrous medium with bimodal fiber sizes. Epithelial slit fiber spacing follows a lognormal distribution based on reported electron micrographs with the highest resolution. Endothelial fenestrae are filled with fibers the size of glycosaminoglycans (GAGs). Effects of fiber-macromolecule steric and hydrodynamic interactions are included. Focusing on diabetic nephropathy, the physiological and hemodynamic factors employed in the computation are those reported for healthy humans and patients with early-but-overt diabetic nephropathy. The macromolecule concentration is obtained as a finite element solution of the convection-diffusion equation.

RESULTS: Computed sieving coefficients averaged along the capillary length agree well with ficoll sieving coefficients from studies in humans for most solute radii. GBM thickening and the loss of the slit diaphragm hardly affect glomerular permselectivity. GAG volume fraction reduction in the endothelial fenestrae, however, significantly increases macromolecule filtration. Increased renal plasma flow rate (RPF), glomerular hypertension, and reduction of lumen osmotic pressure cause a slight sieving coefficient decrease. These effects are amplified by an increased macromolecule size.

CONCLUSION: Our results indicate that glomerular hypertension and the reduction in the oncotic pressure decreases glomerular macromolecule filtration. Reduction of RPF and changes in the glomerular barrier structure associated with DN, however, increase the solute sieving. Damage to GAGs caused by hyperglycemia is likely to be the most prominent factor affecting glomerular size-selectivity.}, } @article {pmid35879342, year = {2022}, author = {Skotnicka-Siepsiak, A}, title = {Pressure distribution on a flat plate in the context of the phenomenon of the Coanda effect hysteresis.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {12687}, pmid = {35879342}, issn = {2045-2322}, abstract = {As a result of the Coanda effect, a symmetrical free jet will flow as an asymmetrical wall jet. At the same time, at the obstacle along which the flow is observed, the wall jet generates pressure distribution. In this study, the obstacle located at the diffuser outlet is a flat plate with a variable inclination angle. The article presents results of the study on pressure distributions on a flat plate with a variable angle of inclination. In the experiment, the Reynolds number ranged from 16,192 to 42,240. A fixed geometry diffuser (Witoszyński nozzle) with a height of 0.60 m, width of 0.02 m and outlet velocity of 11.33-29.57 m/s was used. A plate with a length of 1.00 m and a variable inclination angle was installed at the diffuser outlet. What is new, however, is that the presented results of the experimental research include the influence of the Coanda effect hysteresis on the pressure distribution on the plate. The article shows how pressure distributions change on the plate depending on whether the initial angle of inclination was 0° and was increased gradually in the course of the experiment until a detachment of the jet flowing from the plate was observed, or the initial angle of inclination was close to 90° in the primal state and as the angle of the plate inclination was decreased, the jet flowing towards the plate reached the state of attachment to the plate surface. The study demonstrated that for a turbulent jet, pressure distribution on a flat plate is determined not only by the plate's inclination angle, but also by the direction of its rotation.}, } @article {pmid35863190, year = {2022}, author = {Hatte, S and Pitchumani, R}, title = {Novel nonwetting solid-infused surfaces for superior fouling mitigation.}, journal = {Journal of colloid and interface science}, volume = {627}, number = {}, pages = {308-319}, doi = {10.1016/j.jcis.2022.06.155}, pmid = {35863190}, issn = {1095-7103}, mesh = {*Calcium Sulfate ; *Copper ; Lubricants ; }, abstract = {Fouling is a ubiquitous issue in several environmental and energy applications. Here we introduce novel nonwetting solid-infused surfaces (SIS) with superior anti-fouling characteristics that are durable than conventional nonwetting surfaces in a dynamic flow environment. A systematic study is presented to elucidate the fouling mitigation performance of SIS in comparison to lubricant-infused surface (LIS) and conventional smooth surface. Copper tubes with SIS, LIS or smooth inner walls are fabricated and subjected to accelerated calcium sulfate fouling in a flow fouling experimental setup. Fouling on the various surface types is quantified in terms of asymptotic fouling resistance, and the fundamental morphological differences in the interactions of the foulant and the various surface types are analyzed. Based on a systematic sweep of the parameter combinations using design of experiments and Taguchi analysis, an analytical dependence of asymptotic fouling resistance on the governing parameters namely, Reynolds number, foulant concentration and temperature is derived. The analytical model is shown to predict the asymptotic fouling resistance to within 20% accuracy with a 95% confidence. In addition, for the first time, the effects of shear durability on the fouling mitigation performance of LIS vis-à-vis SIS are studied. It is shown that the novel nonwetting SIS offers a robust option for superior fouling mitigation over LIS in the long run.}, } @article {pmid35859200, year = {2022}, author = {Pumm, AK and Engelen, W and Kopperger, E and Isensee, J and Vogt, M and Kozina, V and Kube, M and Honemann, MN and Bertosin, E and Langecker, M and Golestanian, R and Simmel, FC and Dietz, H}, title = {A DNA origami rotary ratchet motor.}, journal = {Nature}, volume = {607}, number = {7919}, pages = {492-498}, pmid = {35859200}, issn = {1476-4687}, support = {724261/ERC_/European Research Council/International ; }, mesh = {*DNA/chemistry ; *Facilitated Diffusion ; Hydrogen-Ion Concentration ; *Molecular Motor Proteins/chemistry/metabolism ; Motion ; Movement ; Osmolar Concentration ; Proton-Translocating ATPases/chemistry/metabolism ; Stochastic Processes ; Temperature ; Thermodynamics ; }, abstract = {To impart directionality to the motions of a molecular mechanism, one must overcome the random thermal forces that are ubiquitous on such small scales and in liquid solution at ambient temperature. In equilibrium without energy supply, directional motion cannot be sustained without violating the laws of thermodynamics. Under conditions away from thermodynamic equilibrium, directional motion may be achieved within the framework of Brownian ratchets, which are diffusive mechanisms that have broken inversion symmetry[1-5]. Ratcheting is thought to underpin the function of many natural biological motors, such as the F1F0-ATPase[6-8], and it has been demonstrated experimentally in synthetic microscale systems (for example, to our knowledge, first in ref. [3]) and also in artificial molecular motors created by organic chemical synthesis[9-12]. DNA nanotechnology[13] has yielded a variety of nanoscale mechanisms, including pivots, hinges, crank sliders and rotary systems[14-17], which can adopt different configurations, for example, triggered by strand-displacement reactions[18,19] or by changing environmental parameters such as pH, ionic strength, temperature, external fields and by coupling their motions to those of natural motor proteins[20-26]. This previous work and considering low-Reynolds-number dynamics and inherent stochasticity[27,28] led us to develop a nanoscale rotary motor built from DNA origami that is driven by ratcheting and whose mechanical capabilities approach those of biological motors such as F1F0-ATPase.}, } @article {pmid35854607, year = {2022}, author = {Bandak, D and Goldenfeld, N and Mailybaev, AA and Eyink, G}, title = {Dissipation-range fluid turbulence and thermal noise.}, journal = {Physical review. E}, volume = {105}, number = {6-2}, pages = {065113}, doi = {10.1103/PhysRevE.105.065113}, pmid = {35854607}, issn = {2470-0053}, abstract = {We revisit the issue of whether thermal fluctuations are relevant for incompressible fluid turbulence and estimate the scale at which they become important. As anticipated by Betchov in a prescient series of works more than six decades ago, this scale is about equal to the Kolmogorov length, even though that is several orders of magnitude above the mean free path. This result implies that the deterministic version of the incompressible Navier-Stokes equation is inadequate to describe the dissipation range of turbulence in molecular fluids. Within this range, the fluctuating hydrodynamics equation of Landau and Lifschitz is more appropriate. In particular, our analysis implies that both the exponentially decaying energy spectrum and the far-dissipation-range intermittency predicted by Kraichnan for deterministic Navier-Stokes will be generally replaced by Gaussian thermal equipartition at scales just below the Kolmogorov length. Stochastic shell model simulations at high Reynolds numbers verify our theoretical predictions and reveal furthermore that inertial-range intermittency can propagate deep into the dissipation range, leading to large fluctuations in the equipartition length scale. We explain the failure of previous scaling arguments for the validity of deterministic Navier-Stokes equations at any Reynolds number and we provide a mathematical interpretation and physical justification of the fluctuating Navier-Stokes equation as an "effective field theory" valid below some high-wave-number cutoff Λ, rather than as a continuum stochastic partial differential equation. At Reynolds number around a million, comparable to that in Earth's atmospheric boundary layer, the strongest turbulent excitations observed in our simulation penetrate down to a length scale of about eight microns, still two orders of magnitude greater than the mean free path of air. However, for longer observation times or for higher Reynolds numbers, more extreme turbulent events could lead to a local breakdown of fluctuating hydrodynamics.}, } @article {pmid35854520, year = {2022}, author = {Margazoglou, G and Biferale, L and Cencini, M and Gallavotti, G and Lucarini, V}, title = {Nonequilibrium ensembles for the three-dimensional Navier-Stokes equations.}, journal = {Physical review. E}, volume = {105}, number = {6-2}, pages = {065110}, doi = {10.1103/PhysRevE.105.065110}, pmid = {35854520}, issn = {2470-0053}, abstract = {At the molecular level fluid motions are, by first principles, described by time reversible laws. On the other hand, the coarse grained macroscopic evolution is suitably described by the Navier-Stokes equations, which are inherently irreversible, due to the dissipation term. Here, a reversible version of three-dimensional Navier-Stokes is studied, by introducing a fluctuating viscosity constructed in such a way that enstrophy is conserved, along the lines of the paradigm of microcanonical versus canonical treatment in equilibrium statistical mechanics. Through systematic simulations we attack two important questions: (a) What are the conditions that must be satisfied in order to have a statistical equivalence between the two nonequilibrium ensembles? (b) What is the empirical distribution of the fluctuating viscosity observed by changing the Reynolds number and the number of modes used in the discretization of the evolution equation? The latter point is important also to establish regularity conditions for the reversible equations. We find that the probability to observe negative values of the fluctuating viscosity becomes very quickly extremely small when increasing the effective Reynolds number of the flow in the fully resolved hydrodynamical regime, at difference from what was observed previously.}, } @article {pmid35854514, year = {2022}, author = {Choudhury, A and Samanta, A}, title = {Linear stability of a falling film over a heated slippery plane.}, journal = {Physical review. E}, volume = {105}, number = {6-2}, pages = {065112}, doi = {10.1103/PhysRevE.105.065112}, pmid = {35854514}, issn = {2470-0053}, abstract = {A detailed parametric study on the linear stability analysis of a three-dimensional thin liquid film flowing down a uniformly heated slippery inclined plane is carried out for disturbances of arbitrary wavenumbers, where the liquid film satisfies Newton's law of cooling at the film surface. A coupled system of boundary value problems is formulated in terms of the amplitudes of perturbation normal velocity and perturbation temperature, respectively. Analytical solution of the boundary value problems demonstrates the existence of three dominant modes, the so-called H mode, S mode, and P mode, where the S mode and P mode emerge due to the thermocapillary effect. It is found that the onset of instabilities for the H mode, S mode, and P mode reduces in the presence of wall slip and leads to a destabilizing influence. Numerical solution based on the Chebyshev spectral collocation method unveils that the finite wavenumber H-mode instability can be stabilized, but the S-mode instability and the finite wavenumber P-mode instability can be destabilized by increasing the value of the Marangoni number. On the other hand, the Biot number shows a dual role in the H-mode and S-mode instabilities. But the P-mode instability can be made stable with the increasing value of the Biot number and the decreasing values of the Marangoni number and the Prandtl number. Furthermore, the H-mode and S-mode instabilities become weaker, but the P-mode instability becomes stronger, with the increasing value of the spanwise wavenumber. In addition, the shear mode emerges in the numerical simulation when the Reynolds number is large, which can be destabilized slightly with the increasing value of the Marangoni number; however, it can be stabilized with the increasing value of the slip length and introducing the spanwise wavenumber to the infinitesimal perturbation.}, } @article {pmid35854482, year = {2022}, author = {Ishimoto, K and Moreau, C and Yasuda, K}, title = {Self-organized swimming with odd elasticity.}, journal = {Physical review. E}, volume = {105}, number = {6-1}, pages = {064603}, doi = {10.1103/PhysRevE.105.064603}, pmid = {35854482}, issn = {2470-0053}, abstract = {We theoretically investigate self-oscillating waves of an active material, which were recently introduced as a nonsymmetric part of the elastic moduli, termed odd elasticity. Using Purcell's three-link swimmer model, we reveal that an odd-elastic filament at low Reynolds number can swim in a self-organized manner and that the time-periodic dynamics are characterized by a stable limit cycle generated by elastohydrodynamic interactions. Also, we consider a noisy shape gait and derive a swimming formula for a general elastic material in the Stokes regime with its elasticity modulus being represented by a nonsymmetric matrix, demonstrating that the odd elasticity produces biased net locomotion from random noise.}, } @article {pmid35851297, year = {2022}, author = {Shahzad, H and Wang, X and Ghaffari, A and Iqbal, K and Hafeez, MB and Krawczuk, M and Wojnicz, W}, title = {Fluid structure interaction study of non-Newtonian Casson fluid in a bifurcated channel having stenosis with elastic walls.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {12219}, pmid = {35851297}, issn = {2045-2322}, mesh = {Arteries ; Blood Flow Velocity ; Computer Simulation ; Constriction, Pathologic ; *Hemodynamics ; Humans ; *Models, Cardiovascular ; Stress, Mechanical ; }, abstract = {Fluid-structure interaction (FSI) gained a huge attention of scientists and researchers due to its applications in biomedical and mechanical engineering. One of the most important applications of FSI is to study the elastic wall behavior of stenotic arteries. Blood is the suspension of various cells characterized by shear thinning, yield stress, and viscoelastic qualities that can be assessed by using non-Newtonian models. In this study we explored non-Newtonian, incompressible Casson fluid flow in a bifurcated artery with a stenosis. The two-dimensional Casson model is used to study the hemodynamics of the flow. The walls of the artery are supposed to be elastic and the stenosis region is constructed in both walls. Suitable scales are used to transform the nonlinear differential equations into a dimensionless form. The problem is formulated and discretized using Arbitrary Lagrangian-Eulerian (ALE) approach. The finite element method (FEM) technique is used to solve the system of equations, together with appropriate boundary conditions. The analysis is carried out for the Bingham number, Hartmann number, and Reynolds number. The graphical results of pressure field, velocity profile, and load on the walls are assessed and used to study the influence of hemodynamic effects on stenotic arteries, bifurcation region, and elastic walls. This study shows that there is an increase in wall shear stresses (WSS) with increasing values of Bingham number and Hartmann number. Also, for different values of the Bingham number, the load on the upper wall is computed against the Hartmann number. The result indicate that load at the walls increases as the values of Bingham number and Hartmann number increase.}, } @article {pmid35820476, year = {2022}, author = {Zhao, X and Zuo, H and Jia, G}, title = {Effects of the continuous pulsation regeneration on the soot combustion in diesel particulate filter for heavy-duty truck.}, journal = {Chemosphere}, volume = {306}, number = {}, pages = {135651}, doi = {10.1016/j.chemosphere.2022.135651}, pmid = {35820476}, issn = {1879-1298}, mesh = {Dust ; Motor Vehicles ; *Soot/analysis ; Temperature ; *Vehicle Emissions/analysis ; }, abstract = {Continuous pulsation regeneration combustion of soot is employed for sine and cosine simulation study. Data showed that pressure uniformity of sine condition is better than that of cosine condition with the maximum pressure difference of 4353.5 Pa under the same simulation boundary conditions. The maximum regeneration temperature under cosine pressure is 46.12 K which is higher than that in sine form. Regeneration combustion reaction zone tends to be more stable laminar flow and Reynolds number of sine condition is 435.23 less than that of under cosine condition. The maximum Stanton number of cosine pressure condition is 3.67 and that of sine pressure condition is 5.15, which investigates heat transfer capacity of the sine pressure condition is better than that of the pressure of cosine form. The regeneration efficiency of inlet gradually increased from the minimum regeneration efficiency 74.18%-88.45% of sine and cosine. The soot under both pressure forms has achieved complete regeneration and the regeneration efficiency has exceeded 88% of porous medium filter body section. The soot regeneration combustion efficiency of the porous media filter section and outlet section is more sufficient under sine condition and the heat carried by the fluid can maintain the soot regeneration.}, } @article {pmid35811899, year = {2022}, author = {Sun, R and Chen, P and Li, L and Liu, Y and Zhai, X}, title = {Experimental Investigation of the Combustion Behavior of Transformer Oil Jet Flame.}, journal = {ACS omega}, volume = {7}, number = {26}, pages = {22969-22976}, pmid = {35811899}, issn = {2470-1343}, abstract = {Transformer oil jet fire is one of the most dangerous types of fires in substations. The combustion behavior of transformer oil jet fire produces uncontrollable hazards to personnel and equipment and even triggers a domino effect. However, the jet fire combustion behavior of such materials as transformer oil has not been revealed before. Investigation of the combustion behavior of transformer oil jet fire has positive implications for the prevention and control of substation fires. In this paper, KI25X transformer oil was used as fuel. A series of transformer oil jet fire experiments were conducted with variable orifice diameters (5, 10, and 15 mm) with heat release rates ranging from 200 to 659.2 kW. The results showed that the entrainment coefficient of transformer oil jet fire was greater than that of pure gas phase jet fire. The entrainment coefficient of transformer oil jet fire was 0.029. Using dimensionless theory, it was proposed that the imaginary point source was proportional to the 0.317 power of Froude number. Based on the point source model, a dimensional analysis model with Reynolds number was developed. The radiation fraction of transformer oil jet fire was proportional to the -0.133 power of Reynolds number. This study played an important role in improving the jet combustion behavior of transformer oil.}, } @article {pmid35787191, year = {2022}, author = {Jamshed, W and Safdar, R and Rehman, Z and Lashin, MMA and Ehab, M and Moussa, M and Rehman, A}, title = {Computational technique of thermal comparative examination of Cu and Au nanoparticles suspended in sodium alginate as Sutterby nanofluid via extending PTSC surface.}, journal = {Journal of applied biomaterials & functional materials}, volume = {20}, number = {}, pages = {22808000221104004}, doi = {10.1177/22808000221104004}, pmid = {35787191}, issn = {2280-8000}, mesh = {*Alginates ; Copper ; Gold ; Hot Temperature ; *Metal Nanoparticles ; }, abstract = {Current research underscores entropy investigation in an infiltrating mode of Sutterby nanofluid (SNF) stream past a dramatically expanding flat plate that highlights Parabolic Trough Solar Collector (PTSC). Satisfactory likeness factors are utilized to change halfway differential conditions (PDEs) to nonlinear conventional differential conditions (ODEs) along with relating limit requirements. A productive Keller-box system is locked in to achieve approximated arrangement of decreased conventional differential conditions. In the review, two sorts of nanofluids including Copper-sodium alginate (Cu-SA) and Gold-sodium alginate (Au-SA) are dissected. Results are graphically plotted as well as talked about in actual viewpoints. As indicated by key discoveries, an improvement in Brinkmann, as well as Reynolds number, brings about expanding the general framework entropy. Sutterby nanofluid boundary improves heat rate in PTSC. Additionally, Copper-sodium alginate nanofluid is detected as a superior thermal conductor than Gold-sodium alginate nanofluid. Further to that, the reported breakthroughs are beneficial to updating extremely bright lighting bulbs, heating and cooling machinery, fiber required to generate light, power production, numerous boilers, and other similar technologies.}, } @article {pmid35771996, year = {2022}, author = {Saro-Cortes, V and Cui, Y and Dufficy, T and Boctor, A and Flammang, BE and Wissa, AW}, title = {An Adaptable Flying Fish Robotic Model for Aero- and Hydrodynamic Experimentation.}, journal = {Integrative and comparative biology}, volume = {}, number = {}, pages = {}, doi = {10.1093/icb/icac101}, pmid = {35771996}, issn = {1557-7023}, abstract = {Flying fishes (family Exocoetidae) are known for achieving multi-modal locomotion through air and water. Previous work on understanding this animal's aerodynamic and hydrodynamic nature has been based on observations, numerical simulations, or experiments on preserved dead fish, and has focused primarily on flying pectoral fins. The first half of this paper details the design and validation of a modular flying fish inspired robotic model organism (RMO). The second half delves into a parametric aerodynamic study of flying fish pelvic fins, which to date have not been studied in-depth. Using wind tunnel experiments at a Reynolds number of 30,000, we investigated the effect of the pelvic fin geometric parameters on aerodynamic efficiency and longitudinal stability. The pelvic fin parameters investigated in this study include the pelvic fin pitch angle and its location along the body. Results show that the aerodynamic efficiency is maximized for pelvic fins located directly behind the pectoral fins and is higher for more positive pitch angles. In contrast, pitching stability is neither achievable for positive pitching angles nor pelvic fins located directly below the pectoral fin. Thus, there is a clear a trade-off between stability and lift generation, and an optimal pelvic fin configuration depends on the flying fish locomotion stage, be it gliding, taxiing, or taking off. The results garnered from the RMO experiments are insightful for understanding the physics principles governing flying fish locomotion and designing flying fish inspired aerial-aquatic vehicles.}, } @article {pmid35764779, year = {2022}, author = {Wu, YK and Liu, YP and Sun, M}, title = {Aerodynamics of two parallel bristled wings in low Reynolds number flow.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {10928}, pmid = {35764779}, issn = {2045-2322}, mesh = {Animals ; Biomechanical Phenomena ; *Flight, Animal/physiology ; Insecta/physiology ; Models, Biological ; *Wings, Animal/physiology ; }, abstract = {Most of the smallest flying insects use bristled wings. It was observed that during the second half of their upstroke, the left and right wings become parallel and close to each other at the back, and move upward at zero angle of attack. In this period, the wings may produce drag (negative vertical force) and side forces which tend to push two wings apart. Here we study the aerodynamic forces and flows of two simplified bristled wings experiencing such a motion, compared with the case of membrane wings (flat-plate wings), to see if there is any advantage in using the bristled wings. The method of computational fluid dynamics is used in the study. The results are as follows. In the motion of two bristled wings, the drag acting on each wing is 40% smaller than the case of a single bristled wing conducting the same motion, and only a very small side force is produced. But in the case of the flat-plate wings, although there is similar drag reduction, the side force on each wing is larger than that of the bristled wing by an order of magnitude (the underlying physical reason is discussed in the paper). Thus, if the smallest insects use membrane wings, their flight muscles need to overcome large side forces in order to maintain the intended motion for less negative lift, whereas using bristled wings do not have this problem. Therefore, the adoption of bristled wings can be beneficial during upward movement of the wings near the end of the upstroke, which may be one reason why most of the smallest insects adopt them.}, } @article {pmid35755331, year = {2022}, author = {Huang, X and Wang, Y and Wang, L and Yu, G and Wang, F}, title = {Effect of Structural Optimization of Scrubbing Cooling Rings on Vertical Falling Film Flow Characteristics.}, journal = {ACS omega}, volume = {7}, number = {24}, pages = {21291-21305}, pmid = {35755331}, issn = {2470-1343}, abstract = {In order to study the influence of the structural optimization of the scrubbing cooling ring in the scrubbing cooling chamber on the flow characteristics of the vertical falling film, the flow characteristics of the turbulent falling film in the rising section of the development region at different internal platform heights of the scrubbing cooling ring and a high Reynolds number were studied by FLUENT software. First, the correctness of the model was verified by the maximum error of simulation and experimental results of no more than 9.836%. Then, the distribution of liquid film thickness (δ), velocity (V), and turbulence intensity (I z) at 0° of the tube in the axial direction x = 0-500 mm were calculated and obtained when the platform height (H) was 0-30 mm and the liquid film Reynolds number (Re l) = 1.1541 × 10[4]-3.4623 × 10[4]. The results showed that δ in the entrance region increased sharply due to the "jet" effect with solid wall constraints formed by the structure of the water inlet pipe and the scrubbing cooling ring. On the contrary, the liquid film in the fully developed region showed a stable fluctuation trend due to the weakening of the "jet" effect. When H = 30 mm, the change of δ was relatively stable and the change of I z was small, indicating that this platform height is conducive to the stable and uniform distribution of the liquid film. In addition, when Re l < 1.1541 × 10[4], the liquid film was unstable due to the low flow rate and insufficient cohesion of the liquid film, but V increased slightly. In addition, with the increase of Re l, δ did not change significantly along the axial direction, that is, the Plateau-Rayleigh hindered the growth of δ. Finally, the empirical formula for δ applicable to Re l = 1.1541 × 10[4]-3.4623 × 10[4] at the axial fixed position was fitted for the first time.}, } @article {pmid35751170, year = {2022}, author = {Ducos, S and Pugliese, S and Demolliens, M and Beraud, L and Boussard, A and Delmas, A and Agostini, S and Garcia, J and Aiello, A and Durieux, EDH}, title = {Ontogeny of swimming performance of hatchery-reared post-larvae and juvenile fish: a case of two threatened Mediterranean species.}, journal = {Journal of fish biology}, volume = {101}, number = {4}, pages = {846-856}, doi = {10.1111/jfb.15144}, pmid = {35751170}, issn = {1095-8649}, mesh = {Animals ; *Endangered Species ; Fishes/physiology ; Larva/physiology ; *Perciformes/physiology ; *Swimming/physiology ; }, abstract = {Swimming performance is a well-established key physiological parameter of fish that is highly linked to their fitness in the wild. In the context of fish restocking purposes, it therefore appears crucial to study this specific behaviour. Here, the authors investigated intra and interspecies differences in the swimming performance of hatchery-reared post-larvae and juveniles belonging to two Mediterranean candidate threatened species, the common dentex, Dentex dentex (Sparidae), and the brown meagre, Sciaena umbra (Sciaenidae), with body sizes ranging from 8 to 37 mm total length (TL, from 24 to 58 days post-hatch). The swimming abilities were estimated through the calculation of their critical swimming speed (Ucrit), their relative Ucrit and their Reynolds number (Re). Two different patterns were observed between D. dentex and S. umbra, showing a different effect of ontogeny on the performance of both species. The relative Ucrit of S. umbra decreased linearly through ontogeny, whereas the relative Ucrit and Ucrit of D. dentex increased linearly through the range of sizes tested. The ontogenetic change in Ucrit of S. umbra occurred in two stages: a first stage of sharp improvement and a second stage of a slow decrease in performance. Both stages were separated by a breakpoint that coincided with the appearance of a refusal to swim behaviour that occurred shortly after the end of metamorphosis and can potentially be associated with the establishment of this species sedentary behaviour. The swimming performance of both species showed ontogenetic differences. Sciaena umbra had the highest relative performance when its body sizes were the smallest, whereas D. dentex showed the highest relative performance when its body sizes were the largest. These results will be linked to future research on both of these species concerning their escape, exploratory and predatory behaviours, and for restocking purposes to draw a more realistic overview of hatchery-reared juvenile performance. Knowledge of both species' behavioural and swimming performance through ontogeny is important to consider when using hatchery-reared fish juveniles for restocking, as size-at-release can have a large impact on fish survival and thus on restocking success.}, } @article {pmid35750772, year = {2022}, author = {Zhang, S and Ahmad, F and Khan, A and Ali, N and Badran, M}, title = {Performance improvement and thermodynamic assessment of microchannel heat sink with different types of ribs and cones.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {10802}, pmid = {35750772}, issn = {2045-2322}, abstract = {The present study aims to investigate the performance of microchannel heat sink via numerical simulations, based on the first and second law of thermodynamics. The heat transfer and flow characteristics of rectangular microchannel heat sinks have been improved by adding six different types of surface enhancers. The cross-sections include rectangular, triangular, and hexagonal-shaped ribs and cones. The cones have been created from the same cross-sections of ribs by drafting them at an angle of 45° orthogonal to the base, which is expected to decrease the pressure drop, dramatically. The performance of ribs and cones has been evaluated using different parameters such as friction factor, wall shear stress, entropy generation rate, augmentation entropy generation number, thermal resistance, and transport efficiency of thermal energy. The results of the present study revealed that the novel effect of coning at an angle of 45° reduces frictional losses (Maximum pressure drop reduced is 85%), however; a compromise on thermal behavior has been shown (Maximum Nusselt number reduced is 25%). Similarly, the application of coning has caused a significant reduction in wall shear stress and friction factor which can lead to reducing the pumping power requirements. Moreover, triangular ribs have more ability to transfer thermal energy than rectangular and hexagonal ribs. Furthermore, it has been examined in the present study that the trend of total entropy generation rate for triangular ribs decreases up to Re = 400 and then increases onwards which means that thermal losses are more significant than frictional losses at lower Reynolds number. However, frictional losses dominate over thermal losses at higher Reynolds numbers, where vortex generation takes place, especially in triangular ribs.}, } @article {pmid35749192, year = {2022}, author = {Buaria, D and Sreenivasan, KR}, title = {Scaling of Acceleration Statistics in High Reynolds Number Turbulence.}, journal = {Physical review letters}, volume = {128}, number = {23}, pages = {234502}, doi = {10.1103/PhysRevLett.128.234502}, pmid = {35749192}, issn = {1079-7114}, abstract = {The scaling of acceleration statistics in turbulence is examined by combining data from the literature with new data from well-resolved direct numerical simulations of isotropic turbulence, significantly extending the Reynolds number range. The acceleration variance at higher Reynolds numbers departs from previous predictions based on multifractal models, which characterize Lagrangian intermittency as an extension of Eulerian intermittency. The disagreement is even more prominent for higher-order moments of the acceleration. Instead, starting from a known exact relation, we relate the scaling of acceleration variance to that of Eulerian fourth-order velocity gradient and velocity increment statistics. This prediction is in excellent agreement with the variance data. Our Letter highlights the need for models that consider Lagrangian intermittency independent of the Eulerian counterpart.}, } @article {pmid35745944, year = {2022}, author = {Chen, D and Lin, J}, title = {Steady State of Motion of Two Particles in Poiseuille Flow of Power-Law Fluid.}, journal = {Polymers}, volume = {14}, number = {12}, pages = {}, pmid = {35745944}, issn = {2073-4360}, abstract = {The steady state of motion of two particles in Poiseuille flow of power-law fluid is numerically studied using the lattice Boltzmann method in the range of Reynolds number 20 ≤ Re ≤ 60, diameter ratio of two particles 0.125 ≤ β ≤ 2.4, and power-law index of the fluid 0.4 ≤ n ≤ 1.2. Some results are validated by comparing with other available results. The effects of Re, β, and n on the steady state of motion of two particles are discussed. The results show that, for two particles of the same diameter, the particle spacing l in the steady state is independent of n. In shear-thinning fluid, l increases rapidly at first and then slowly, finally approaching a constant for different Re. In shear-thickening fluid, although l tends to be stable in the end, the values of l after stabilization are different. For two particles of different sizes, l does not always reach a stable state, and whether it reaches a stable state depends on n. When the small particle is downstream, l increases rapidly at first and then slowly in shear-thickening fluid, but increases rapidly at first and then decreases slowly, finally approaching a constant in a shear-thinning fluid. In shear-thinning fluid, the larger n is, the smaller l is. In shear-thickening fluid, β has no effect on l in steady-state. When the large particle is downstream, l increases rapidly at first and then slowly in shear-thinning fluid but increases rapidly at first and then decreases in a shear-thickening fluid. The effect of n on l in the steady state is obvious. In shear-thinning fluid, l increases rapidly at first and then slowly, the larger Re is, the smaller l is. In shear- thickening fluid, l will reach a stable state.}, } @article {pmid35745906, year = {2022}, author = {Bui, CM and Ho, AT and Nguyen, XB}, title = {Flow Behaviors of Polymer Solution in a Lid-Driven Cavity.}, journal = {Polymers}, volume = {14}, number = {12}, pages = {}, pmid = {35745906}, issn = {2073-4360}, abstract = {In this work, a numerical study of polymer flow behaviors in a lid-driven cavity, which is inspired by the coating process, at a broad range of Oldroyd numbers (0≤Od≤50), is carried out. The Reynolds number is height-based and kept at Re=0.001. The fluid investigated is of Carbopol gel possessing yield stress and shear-thinning properties. To express rheological characteristics, the Herschel-Bulkley model cooperated with Papanastasiou's regularization scheme is utilized. Results show that the polymer flow characteristics, i.e., velocity, viscosity, and vortex distributions, are considerably influenced by viscoplastic behaviors. Additionally, there exist solid-like regions which can be of either moving rigid or static dead types in the flow patterns; they become greater and tend to merge together to construct larger ones when Od increases. Furthermore, various polymer flow aspects in different cavity configurations are discussed and analyzed; the cavity width/aspect ratio and skewed angle are found to have significant impacts on the vortex structures and the formation of solid-like regions. Moreover, results for the critical aspect ratio at which the static dead zone is broken into two parts and the characteristic height of this zone are also reported in detail.}, } @article {pmid35744569, year = {2022}, author = {Saghir, MZ and Rahman, MM}, title = {Thermo-Hydraulic Performance of Pin-Fins in Wavy and Straight Configurations.}, journal = {Micromachines}, volume = {13}, number = {6}, pages = {}, pmid = {35744569}, issn = {2072-666X}, abstract = {Pin-fins configurations have been investigated recently for different engineering applications and, in particular, for a cooling turbine. In the present study, we investigated the performance of three different pin-fins configurations: pin-fins forming a wavy mini-channel, pin-fins forming a straight mini-channel, and a mini-channel without pin-fins considering water as the working fluid. The full Navier-Stokes equations and the energy equation are solved numerically using the finite element technique. Different flow rates are studied, represented by the Reynolds number in the laminar flow regime. The thermo-hydraulic performance of the three configurations is determined by examining the Nusselt number, the pressure drop, and the performance evaluation criterion. Results revealed that pin-fins forming a wavy mini-channel exhibited the highest Nusselt number, the lowest pressure drop, and the highest performance evaluation criterion. This finding is valid for any Reynolds number under investigation.}, } @article {pmid35744548, year = {2022}, author = {Tayeb, NT and Hossain, S and Khan, AH and Mostefa, T and Kim, KY}, title = {Evaluation of Hydrodynamic and Thermal Behaviour of Non-Newtonian-Nanofluid Mixing in a Chaotic Micromixer.}, journal = {Micromachines}, volume = {13}, number = {6}, pages = {}, pmid = {35744548}, issn = {2072-666X}, abstract = {Three-dimensional numerical investigations of a novel passive micromixer were carried out to analyze the hydrodynamic and thermal behaviors of Nano-Non-Newtonian fluids. Mass and heat transfer characteristics of two heated fluids have been investigated to understand the quantitative and qualitative fluid faction distributions with temperature homogenization. The effect of fluid behavior and different Al2O3 nanoparticles concentrations on the pressure drop and thermal mixing performances were studied for different Reynolds number (from 0.1 to 25). The performance improvement simulation was conducted in intervals of various Nanoparticles concentrations (φ = 0 to 5%) with Power-law index (n) using CFD. The proposed micromixer displayed a mixing energy cost of 50-60 comparable to that achieved for a recent micromixer (2021y) in terms of fluid homogenization. The analysis exhibited that for high nanofluid concentrations, having a strong chaotic flow enhances significantly the hydrodynamic and thermal performances for all Reynolds numbers. The visualization of vortex core region of mass fraction and path lines presents that the proposed design exhibits a rapid thermal mixing rate that tends to 0.99%, and a mass fraction mixing rate of more than 0.93% with very low pressure losses, thus the proposed micromixer can be utilized to enhance homogenization in different Nano-Non-Newtonian mechanism with minimum energy.}, } @article {pmid35739213, year = {2022}, author = {Abd-Alla, AM and Abo-Dahab, SM and Thabet, EN and Abdelhafez, MA}, title = {Peristaltic pump with heat and mass transfer of a fractional second grade fluid through porous medium inside a tube.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {10608}, pmid = {35739213}, issn = {2045-2322}, mesh = {Friction ; *Hot Temperature ; Magnetic Fields ; *Peristalsis ; Porosity ; }, abstract = {In magnetic resonance imaging (MRI), this MRI is used for the diagnosis of the brain. The dynamic of these particles occurs under the action of the peristaltic waves generated on the flexible walls of the brain. Studying such fluid flow of a Fractional Second-Grade under this action is therefore useful in treating tissues of cancer. This paper deals with a theoretical investigation of the interaction of heat and mass transfer in the peristaltic flow of a magnetic field fractional second-grade fluid through a tube, under the assumption of low Reynolds number and long-wavelength. The analytical solution to a problem is obtained by using Caputo's definition. The effect of different physical parameters, the material constant, magnetic field, and fractional parameter on the temperature, concentration, axial velocity, pressure gradient, pressure rise, friction forces, and coefficient of heat and mass transfer are discussed with particular emphasis. The computed results are presented in graphical form. It is because the nature of heat and mass transfer coefficient is oscillatory which is following the physical expectation due to the oscillatory nature of the tube wall. It is perceived that with an increase in Hartmann number, the velocity decreases. A suitable comparison has been made with the prior results in the literature as a limiting case of the considered problem.}, } @article {pmid35736684, year = {2022}, author = {Zubairova, US and Kravtsova, AY and Romashchenko, AV and Pushkareva, AA and Doroshkov, AV}, title = {Particle-Based Imaging Tools Revealing Water Flows in Maize Nodal Vascular Plexus.}, journal = {Plants (Basel, Switzerland)}, volume = {11}, number = {12}, pages = {}, pmid = {35736684}, issn = {2223-7747}, abstract = {In plants, water flows are the major driving force behind growth and play a crucial role in the life cycle. To study hydrodynamics, methods based on tracking small particles inside water flows attend a special place. Thanks to these tools, it is possible to obtain information about the dynamics of the spatial distribution of the flux characteristics. In this paper, using contrast-enhanced magnetic resonance imaging (MRI), we show that gadolinium chelate, used as an MRI contrast agent, marks the structural characteristics of the xylem bundles of maize stem nodes and internodes. Supplementing MRI data, the high-precision visualization of xylem vessels by laser scanning microscopy was used to reveal the structural and dimensional characteristics of the stem vascular system. In addition, we propose the concept of using prototype "Y-type xylem vascular connection" as a model of the elementary connection of vessels within the vascular system. A Reynolds number could match the microchannel model with the real xylem vessels.}, } @article {pmid35699409, year = {2022}, author = {Martin, AR and Finlay, WH}, title = {Empirical Deposition Correlations.}, journal = {Journal of aerosol medicine and pulmonary drug delivery}, volume = {35}, number = {3}, pages = {109-120}, doi = {10.1089/jamp.2022.29062.arm}, pmid = {35699409}, issn = {1941-2703}, mesh = {Administration, Inhalation ; Aerosols ; *Lung/diagnostic imaging ; Particle Size ; *Pharynx ; }, abstract = {Traditionally, empirical correlations for predicting respiratory tract deposition of inhaled aerosols have been developed using limited available in vivo data. More recently, advances in medical image segmentation and additive manufacturing processes have allowed researchers to conduct extensive in vitro deposition experiments in realistic replicas of the upper and central branching airways. This work has led to a collection of empirical equations for predicting regional aerosol deposition, especially in the upper, nasal and oral airways. The present section reviews empirical correlations based on both in vivo and in vitro data, which may be used to predict total and regional deposition. Equations are presented for predicting total respiratory deposition fraction, mouth-throat fraction, nasal, and nose-throat fractions for a large variety of aerosol sizes, subject age groups, and breathing maneuvers. Use of these correlations to estimate total lung deposition is also described.}, } @article {pmid35683052, year = {2022}, author = {George, GR and Bockelmann, M and Schmalhorst, L and Beton, D and Gerstle, A and Lindermeir, A and Wehinger, GD}, title = {Influence of Foam Morphology on Flow and Heat Transport in a Random Packed Bed with Metallic Foam Pellets-An Investigation Using CFD.}, journal = {Materials (Basel, Switzerland)}, volume = {15}, number = {11}, pages = {}, pmid = {35683052}, issn = {1996-1944}, abstract = {Open-cell metallic foams used as catalyst supports exhibit excellent transport properties. In this work, a unique application of metallic foam, as pelletized catalyst in a packed bed reactor, is examined. By using a wall-segment Computational Fluid Dynamics (CFD) setup, parametric analyses are carried out to investigate the influence of foam morphologies (cell size ϕ=0.45-3&nbsp;mm and porosity ε=0.55-0.95) and intrinsic conductivity on flow and heat transport characteristics in a slender packed bed (N=D/dp=6.78) made of cylindrical metallic foam pellets. The transport processes have been modeled using an extended version of conventional particle-resolved CFD, i.e., flow and energy in inter-particle spaces are fully resolved, whereas the porous-media model is used for the effective transport processes inside highly-porous foam pellets. Simulation inputs include the processing parameters relevant to Steam Methane Reforming (SMR), analyzed for low (Rep~100) and high (Rep~5000) flow regimes. The effect of foam morphologies on packed beds has shown that the desired requirements contradict each other, i.e., an increase in cell size and porosity favors the reduction in pressure drop, but, it reduces the heat transfer efficiency. A design study is also conducted to find the optimum foam morphology of a cylindrical foam pellet at a higher Rep~5000, which yields ϕ = 0.45, ε = 0.8. Suitable correlations to predict the friction factor and the overall heat transfer coefficient in a foam-packed bed have been presented, which consider the effect of different foam morphologies over a range of particle Reynolds number, 100≤Rep≤5000.}, } @article {pmid35676272, year = {2022}, author = {Castro, JM and Feisel, Y}, title = {Eruption of ultralow-viscosity basanite magma at Cumbre Vieja, La Palma, Canary Islands.}, journal = {Nature communications}, volume = {13}, number = {1}, pages = {3174}, pmid = {35676272}, issn = {2041-1723}, abstract = {The viscosity of magma exerts control on all aspects of its migration through the crust to eruption. This was particularly true for the 2021 eruption of Cumbre Vieja (La Palma), which produced exceptionally fast and fluid lava at high discharge rates. We have performed concentric cylinder experiments to determine the effective viscosities of the Cumbre Vieja magma, while accounting for its chemistry, crystallinity, and temperature. Here we show that this event produced a nepheline-normative basanite with the lowest viscosity of historical basaltic eruptions, exhibiting values of less than 10 to about 160 Pa s within eruption temperatures of ~1200 to ~1150 °C. The magma's low viscosity was responsible for many eruptive phenomena that lead to particularly impactful events, including high-Reynolds number turbulent flow and supercritical states. Increases in viscosity due to crystallization-induced melt differentiation were subdued in this eruption, due in part to subtle degrees of silica enrichment in alkaline magma.}, } @article {pmid35662323, year = {2022}, author = {Ruszczyk, M and Webster, DR and Yen, J}, title = {Trends in Stroke Kinematics, Reynolds Number, and Swimming Mode in Shrimp-Like Organisms.}, journal = {Integrative and comparative biology}, volume = {}, number = {}, pages = {}, doi = {10.1093/icb/icac067}, pmid = {35662323}, issn = {1557-7023}, abstract = {Metachronal propulsion is commonly seen in organisms with the caridoid facies body plan, i.e. shrimp-like organisms, as they beat their pleopods in an adlocomotory sequence. These organisms exist across length scales ranging several orders of Reynolds number magnitude, from 10 to 104, during locomotion. Further, by altering their stroke kinematics, these organisms achieve three distinct swimming modes. To better understand the relationship between Reynolds number, stroke kinematics, and resulting swimming mode, Euphausia pacifica stroke kinematics were quantified using high-speed digital recordings and compared to the results for the larger E. superba. Euphausia pacifica consistently operate with a greater beat frequency and smaller stroke amplitude than E. superba for each swimming mode, suggesting that length scale may affect the kinematics needed to achieve similar swimming modes. To expand on this observation, these euphausiid data are used in combination with previously-published stroke kinematics from mysids and stomatopods to identify broad trends across swimming mode and length scale in metachrony. Principal component analysis (PCA) reveals trends in stroke kinematics and Reynolds number as well as the variation among taxonomic order. Overall, larger beat frequencies, stroke amplitudes, between-cycle phase lags, and Reynolds numbers are more representative of the fast forward swimming mode compared to the slower hovering mode. Additionally, each species has a unique combination of kinematics that result in metachrony, indicating that there are other factors, perhaps morphological, which affect the overall metachronal characteristics of an organism. Finally, uniform phase lag, in which the timing between power strokes of all pleopods is equal, in 5-paddle systems is achieved at different Reynolds numbers for different swimming modes, highlighting the importance of taking into consideration stroke kinematics, length scale, and the resulting swimming mode.}, } @article {pmid35642428, year = {2022}, author = {Broadley, P and Nabawy, MRA and Quinn, MK and Crowther, WJ}, title = {Dynamic experimental rigs for investigation of insect wing aerodynamics.}, journal = {Journal of the Royal Society, Interface}, volume = {19}, number = {191}, pages = {20210909}, pmid = {35642428}, issn = {1742-5662}, mesh = {Animals ; Biomechanical Phenomena ; *Flight, Animal ; Insecta ; *Models, Biological ; Wings, Animal ; }, abstract = {This paper provides a systematic and critical review of dynamic experimental rigs used for insect wing aerodynamics research. The goal is to facilitate meaningful comparison of data from existing rigs and provide insights for designers of new rigs. The scope extends from simple one degree of freedom rotary rigs to multi degrees of freedom rigs allowing various rotation and translation motions. Experimental methods are characterized using a consistent set of parameters that allows objective comparison of different approaches. A comprehensive catalogue is presented for the tested flow conditions (assessed through Reynolds number, Rossby number and advance ratio), wing morphologies (assessed through aspect ratio, planform shape and thickness to mean chord ratio) and kinematics (assessed through motion degrees of freedom). Links are made between the type of aerodynamic characteristics being studied and the type of experimental set-up used. Rig mechanical design considerations are assessed, and the aerodynamic measurements obtained from these rigs are discussed.}, } @article {pmid35637889, year = {2022}, author = {Semenov, AP and Mendgaziev, RI and Stoporev, AS and Istomin, VA and Sergeeva, DV and Tulegenov, TB and Vinokurov, VA}, title = {Dataset for the dimethyl sulfoxide as a novel thermodynamic inhibitor of carbon dioxide hydrate formation.}, journal = {Data in brief}, volume = {42}, number = {}, pages = {108289}, pmid = {35637889}, issn = {2352-3409}, abstract = {The temperatures and pressures of the three-phase equilibrium V-Lw-H (gas - aqueous solution - gas hydrate) were measured in the CO2 - H2O - dimethyl sulfoxide (DMSO) system at concentrations of organic solute in the aqueous phase up to 50 mass%. Measurements of CO2 hydrate equilibrium conditions were carried out using a constant volume autoclave by continuous heating at a rate of 0.1 K/h with simultaneous stirring of fluids by a four-blade agitator at 600 rpm. The equilibrium temperature and pressure of CO2 hydrate were determined for the endpoint of the hydrate dissociation in each experiment. The CO2 gas fugacity was calculated by the equation of state for carbon dioxide for the measured points. The flow regime in the autoclave during the operation of the stirring system was characterized by calculating the Reynolds number using literature data on the viscosity and density of water and DMSO aqueous solutions. We employed regression analysis to approximate the dependences of equilibrium pressure (CO2 gas fugacity) on temperature by two- and three-parameter equations. For each measured point, the value of CO2 hydrate equilibrium temperature suppression ΔTh was computed. The dependences of this quantity on CO2 gas fugacity are considered for all DMSO concentrations. The coefficients of empirical correlation describing ΔTh as a function of the DMSO mass fraction in solution and the equilibrium gas pressure are determined. This article is a co-submission with a paper [1].}, } @article {pmid35635664, year = {2022}, author = {Eldesoukey, A and Hassan, H}, title = {Study of the performance of thermoelectric generator for waste heat recovery from chimney: impact of nanofluid-microchannel cooling system.}, journal = {Environmental science and pollution research international}, volume = {29}, number = {49}, pages = {74242-74263}, pmid = {35635664}, issn = {1614-7499}, abstract = {A huge number of chimneys all over the world utilized in many industrial applications and applications like restaurants, homes, etc. contribute badly on the global warming and climate change due to their waste heat. So, in this paper, the performance of thermoelectric generator (TEG) cooled by microchannel heat spreader having nanofluid and used for waste heat recovery from vertical chimney is investigated. Using heat spreader with microchannel cooling system increases the output TEG power compared to natural convection cooling system. In this paper, the impact of microchannel sizes, using nanofluid and heat spreader with different sizes on the TEG performance and cooling, is considered. Three-dimensional mathematical models including TEG, microchannel, nanofluid, and heat spreader are presented and solved by Ansys Fluent software utilizing user-defined memory, user-defined function, and user-defined scalar. All TEG effects (Joule, Seebeck, and Thomson) are considered in TEG model. Results indicate that TEG power rises with increasing the heat spreader and microchannel sizes together. Increasing microchannel and heat spreader sizes four times of TEG size raises the TEG output power by 10%. This also achieves the maximum cooling system efficiency of 88.9% and the maximum net output power. Microchannel heat spreader cooling system raises the system (TEG power-pumping power) net power by 125.2% compared to the normal channel and decreases the required cooling fluid flow rate. Utilizing copper-water and Al2O3-water nanofluids rises maximally the TEG output power by 14% and 4%, respectively; however, it increases the pumping power. Moreover, using nanofluids increases the net output power at low Reynolds number and decreases it at higher Reynolds number.}, } @article {pmid35630837, year = {2022}, author = {Souayeh, B and Ramesh, K and Hdhiri, N and Yasin, E and Alam, MW and Alfares, K and Yasin, A}, title = {Heat Transfer Attributes of Gold-Silver-Blood Hybrid Nanomaterial Flow in an EMHD Peristaltic Channel with Activation Energy.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {12}, number = {10}, pages = {}, pmid = {35630837}, issn = {2079-4991}, abstract = {The heat enhancement in hybrid nanofluid flow through the peristaltic mechanism has received great attention due to its occurrence in many engineering and biomedical systems, such as flow through canals, the cavity flow model and biomedicine. Therefore, the aim of the current study was to discuss the hybrid nanofluid flow in a symmetric peristaltic channel with diverse effects, such as electromagnetohydrodynamics (EMHD), activation energy, gyrotactic microorganisms and solar radiation. The equations governing this motion were simplified under the approximations of a low Reynolds number (LRN), a long wavelength (LWL) and Debye-Hückel linearization (DHL). The numerical solutions for the non-dimensional system of equations were tackled using the computational software Mathematica. The influences of diverse physical parameters on the flow and thermal characteristics were computed through pictorial interpretations. It was concluded from the results that the thermophoresis parameter and Grashof number increased the hybrid nanofluid velocity near the right wall. The nanoparticle temperature decreased with the radiation parameter and Schmidt number. The activation energy and radiation enhanced the nanoparticle volume fraction, and motile microorganisms decreased with an increase in the Peclet number and Schmidt number. The applications of the current investigation include chyme flow in the gastrointestinal tract, the control of blood flow during surgery by altering the magnetic field and novel drug delivery systems in pharmacological engineering.}, } @article {pmid35630375, year = {2022}, author = {Soares, A and Gomes, LC and Monteiro, GA and Mergulhão, FJ}, title = {Hydrodynamic Effects on Biofilm Development and Recombinant Protein Expression.}, journal = {Microorganisms}, volume = {10}, number = {5}, pages = {}, pmid = {35630375}, issn = {2076-2607}, abstract = {Hydrodynamics play an important role in the rate of cell attachment and nutrient and oxygen transfer, which can affect biofilm development and the level of recombinant protein production. In the present study, the effects of different flow conditions on the development of Escherichia coli biofilms and the expression of a model recombinant protein (enhanced green fluorescent protein, eGFP) were examined. Planktonic and biofilm cells were grown at two different flow rates in a recirculating flow cell system for 7 days: 255 and 128 L h[-1] (corresponding to a Reynolds number of 4600 and 2300, respectively). The fluorometric analysis showed that the specific eGFP production was higher in biofilms than in planktonic cells under both hydrodynamic conditions (3-fold higher for 255 L h[-1] and 2-fold higher for 128 L h[-1]). In the biofilm cells, the percentage of eGFP-expressing cells was on average 52% higher at a flow rate of 255 L h[-1]. Furthermore, a higher plasmid copy number (PCN) was obtained for the highest flow rate for both planktonic (244 PCN/cell versus 118 PCN/cell) and biofilm cells (43 PCN/cell versus 29 PCN/cell). The results suggested that higher flow velocities promoted eGFP expression in E. coli biofilms.}, } @article {pmid35626546, year = {2022}, author = {Alenezi, A and Almutairi, A and Alhajeri, H and Almekmesh, SF and Alzuwayer, BB}, title = {Impact of Surface Roughness on Flow Physics and Entropy Generation in Jet Impingement Applications.}, journal = {Entropy (Basel, Switzerland)}, volume = {24}, number = {5}, pages = {}, pmid = {35626546}, issn = {1099-4300}, abstract = {In this paper, a numerical investigation was performed of an air jet incident that normally occurs on a horizontal heated plane. Analysis of flow physics and entropy generation due to heat and friction is included using a simple easy-to-manufacture, surface roughening element: a circular rib concentric with the air jet. This study shows how varying the locations and dimensions of the rib can deliver a favorable trade-off between entropy generation and flow parameters, such as vortex generation and heat transfer. The performance of the roughness element was tested at three different radii; R/D = 1, 1.5 and 2, where D was the jet hydraulic diameter and R was the radial distance from the geometric center. At each location, the normalized rib height (e/D) was increased from 0.019 to 0.074 based on an increment of (e/D) = 0.019. The jet-to-target distance was H/D = 6 and the jet Reynolds number (Re) ranged from 10,000 to 50,000 Re, which was obtained from the jet hydraulic diameter (D), and the jet exit velocity (U). All results are presented in the form of entropy generation due to friction and heat exchange, as well as the total entropy generated. A detailed comparison of flow physics is presented for all ribs and compared with the baseline case of a smooth surface. The results show that at higher Reynolds numbers, adding a rib of a suitable height reduced the total entropy (St) by 31% compared to the no rib case. In addition, with ribs of heights 0.019, 0.037 and 0.054, respectively, the entropy generated by friction (Sf) was greater than that due to heat exchange (Sh) by about 42%, 26% and 4%, respectively. The rib of height e/D = 0.074 produced the minimum St at R/D = 1. As for varying R/D, varying rib location and Re values had a noticeable impact on Sh, Sf and (St). Placing the rib at R/D = 1 gave the highest total entropy generation (St) followed by R/D = 1.5 for all Re. Finally, the Bejan number increased as both rib height and rib location increased.}, } @article {pmid35626500, year = {2022}, author = {Dressler, L and Nicolai, H and Agrebi, S and Ries, F and Sadiki, A}, title = {Computation of Entropy Production in Stratified Flames Based on Chemistry Tabulation and an Eulerian Transported Probability Density Function Approach.}, journal = {Entropy (Basel, Switzerland)}, volume = {24}, number = {5}, pages = {}, pmid = {35626500}, issn = {1099-4300}, abstract = {This contribution presents a straightforward strategy to investigate the entropy production in stratified premixed flames. The modeling approach is grounded on a chemistry tabulation strategy, large eddy simulation, and the Eulerian stochastic field method. This enables a combination of a detailed representation of the chemistry with an advanced model for the turbulence chemistry interaction, which is crucial to compute the various sources of exergy losses in combustion systems. First, using detailed reaction kinetic reference simulations in a simplified laminar stratified premixed flame, it is demonstrated that the tabulated chemistry is a suitable approach to compute the various sources of irreversibilities. Thereafter, the effects of the operating conditions on the entropy production are investigated. For this purpose, two operating conditions of the Darmstadt stratified burner with varying levels of shear have been considered. The investigations reveal that the contribution to the entropy production through mixing emerging from the chemical reaction is much larger than the one caused by the stratification. Moreover, it is shown that a stronger shear, realized through a larger Reynolds number, yields higher entropy production through heat, mixing and viscous dissipation and reduces the share by chemical reaction to the total entropy generated.}, } @article {pmid35621794, year = {2022}, author = {Li, H and Nabawy, MRA}, title = {Wing Planform Effect on the Aerodynamics of Insect Wings.}, journal = {Insects}, volume = {13}, number = {5}, pages = {}, pmid = {35621794}, issn = {2075-4450}, abstract = {This study investigates the effect of wing planform shape on the aerodynamic performance of insect wings by numerically solving the incompressible Navier-Stokes equations. We define the wing planforms using a beta-function distribution and employ kinematics representative of normal hovering flight. In particular, we use three primary parameters to describe the planform geometry: aspect ratio, radial centroid location, and wing root offset. The force coefficients, flow structures, and aerodynamic efficiency for different wing planforms at a Reynolds number of 100 are evaluated. It is found that the wing with the lowest aspect ratio of 1.5 results in the highest peaks of lift and drag coefficients during stroke reversals, whereas the higher aspect ratio wings produce higher lift and drag coefficients during mid half-stroke translation. For the wings considered, the leading-edge vortex detachment is found to be approximately at a location that is 3.5-5 mean chord lengths from the wing center of rotation for all aspect ratios and root offsets investigated. Consequently, the detachment area increases with the increase of aspect ratio and root offset, resulting in reduced aerodynamic coefficients. The radial centroid location is found to influence the local flow evolution time, and this results in earlier formation/detachment of the leading-edge vortex for wings with a smaller radial centroid location. Overall, the best performance, when considering both average lift coefficient and efficiency, is found at the intermediate aspect ratios of 4.5-6; increasing the centroid location mainly increases efficiency; and increasing the root offset leads to a decreased average lift coefficient whilst leading to relatively small variations in aerodynamic efficiency for most aspect ratios.}, } @article {pmid35617810, year = {2022}, author = {Huang, F and Noël, R and Berg, P and Hosseini, SA}, title = {Simulation of the FDA nozzle benchmark: A lattice Boltzmann study.}, journal = {Computer methods and programs in biomedicine}, volume = {221}, number = {}, pages = {106863}, doi = {10.1016/j.cmpb.2022.106863}, pmid = {35617810}, issn = {1872-7565}, mesh = {*Benchmarking ; Computer Simulation ; *Hemodynamics ; Rheology ; }, abstract = {BACKGROUND AND OBJECTIVE: Contrary to flows in small intracranial vessels, many blood flow configurations such as those found in aortic vessels and aneurysms involve larger Reynolds numbers and, therefore, transitional or turbulent conditions. Dealing with such systems require both robust and efficient numerical methods.

METHODS: We assess here the performance of a lattice Boltzmann solver with full Hermite expansion of the equilibrium and central Hermite moments collision operator at higher Reynolds numbers, especially for under-resolved simulations. To that end the food and drug administration's benchmark nozzle is considered at three different Reynolds numbers covering all regimes: (1) laminar at a Reynolds number of 500, (2) transitional at a Reynolds number of 3500, and (3) low-level turbulence at a Reynolds number of 6500.

RESULTS: The lattice Boltzmann results are compared with previously published inter-laboratory experimental data obtained by particle image velocimetry. Our results show good agreement with the experimental measurements throughout the nozzle, demonstrating the good performance of the solver even in under-resolved simulations.

CONCLUSION: In this manner, fast but sufficiently accurate numerical predictions can be achieved for flow configurations of practical interest regarding medical applications.}, } @article {pmid35598483, year = {2022}, author = {Sharma, S and Jain, S and Saha, A and Basu, S}, title = {Evaporation dynamics of a surrogate respiratory droplet in a vortical environment.}, journal = {Journal of colloid and interface science}, volume = {623}, number = {}, pages = {541-551}, doi = {10.1016/j.jcis.2022.05.061}, pmid = {35598483}, issn = {1095-7103}, mesh = {Crystallization ; Gases ; *Respiratory Aerosols and Droplets ; *Sodium Chloride/chemistry ; Water/chemistry ; }, abstract = {HYPOTHESIS: Vortex droplet interaction is crucial for understanding the route of disease transmission through expiratory jet where several such embedded droplets continuously interact with vortical structures of different strengths and sizes.

EXPERIMENTS: A train of vortex rings with different vortex strength, quantified with vortex Reynolds number (Re[']=0,53,221,297) are made to interact with an isolated levitated droplet, and the evolution dynamics is captured using shadowgraphy, particle image velocimetry (PIV), and backlight imaging technique. NaCl-DI water solution of 0, 1, 10 and 20 wt% concentrations are used as test fluids for the droplet.

FINDINGS: The results show the dependence of evaporation characteristics on vortex strength, while the crystallization dynamics was found to be independent of it. A reduction of 12.23% and 14.6% in evaporation time was seen in case of de-ionized (DI) water and 1% wt NaCl solution respectively in presence of vortex ring train at Re[']=221. In contrast to this, a minimal reduction in evaporation time (0.6% and 0.9% for DI water and 1% wt NaCl solution, respectively) is observed when Re['] is increased from 221 to 297. The mechanisms for evaporation time reduction due to enhancement of convective heat and mass transfer from the droplet and shearing away of vapor layer by vortex ring interaction are discussed in this work.}, } @article {pmid35591423, year = {2022}, author = {Karmveer, and Kumar Gupta, N and Siddiqui, MIH and Dobrotă, D and Alam, T and Ali, MA and Orfi, J}, title = {The Effect of Roughness in Absorbing Materials on Solar Air Heater Performance.}, journal = {Materials (Basel, Switzerland)}, volume = {15}, number = {9}, pages = {}, pmid = {35591423}, issn = {1996-1944}, abstract = {Artificial roughness on the absorber of the solar air heater (SAH) is considered to be the best passive technology for performance improvement. The roughened SAHs perform better in comparison to conventional SAHs under the same operational conditions, with some penalty of higher pumping power requirements. Thermo-hydraulic performance, based on effective efficiency, is much more appropriate to design roughened SAH, as it considers both the requirement of pumping power and useful heat gain. The shape, size, and arrangement of artificial roughness are the most important factors for the performance optimization of SAHs. The parameters of artificial roughness and operating parameters, such as the Reynolds number (Re), temperature rise parameter (ΔT/I) and insolation (I) show a combined effect on the performance of SAH. In this case study, various performance parameters of SAH have been evaluated to show the effect of distinct artificial roughness, investigated previously. Therefore, thermal efficiency, thermal efficiency improvement factor (TEIF) and the effective efficiency of various roughened absorbers of SAH have been predicted. As a result, thermal and effective efficiencies strongly depend on the roughness parameter, Re and ΔT/I. Staggered, broken arc hybrid-rib roughness shows a higher value of TEIF, thermal and effective efficiencies consistently among all other distinct roughness geometries for the ascending values of ΔT/I. This roughness shows the maximum value of effective efficiency equals 74.63% at a ΔT/I = 0.01 K·m[2]/W. The unique combination of parameters p/e = 10, e/Dh = 0.043 and α = 60° are observed for best performance at a ΔT/I higher than 0.00789 K·m[2]/W.}, } @article {pmid35591154, year = {2022}, author = {Salem, S and Fraňa, K}, title = {A Wind Tunnel Study of the Flow-Induced Vibrations of a Cylindrical Piezoelectric Transducer.}, journal = {Sensors (Basel, Switzerland)}, volume = {22}, number = {9}, pages = {}, pmid = {35591154}, issn = {1424-8220}, abstract = {Piezoelectric transducers are used as a sensing device to study the fluids' motion. Moreover, they are used as a harvester of energy of Flow-Induced Vibration (FIV). The current FIV harvesters in the literature rely on piezoelectric cantilevers coupled with a bluff body that creates flow instabilities. This paper studies the use of piezoelectric cylinders as a novel transducer in the field of fluid mechanics, where the transducer makes use of its bluff geometry to create instability. The study was based on wind tunnel measurements performed on four piezoelectric cylinders of different sizes over a speed range of 1-7 m/s. The paper looks at the variation of the generated voltage across the Reynolds number. It also compares the spectra of the generated open-circuit voltage to the turbulence spectra features known from the literature.}, } @article {pmid35590864, year = {2022}, author = {Funatani, S and Tsukamoto, Y and Toriyama, K}, title = {Temperature Measurement of Hot Airflow Using Ultra-Fine Thermo-Sensitive Fluorescent Wires.}, journal = {Sensors (Basel, Switzerland)}, volume = {22}, number = {9}, pages = {}, pmid = {35590864}, issn = {1424-8220}, abstract = {In this paper, we propose a temperature measurement method that uses ultrafine fluorescent wires to reduce the wire diameter to a much lesser extent than a thermocouple. This is possible because its structure is simple and any material can be used for the wire. Hence, ultrafine wires with a Reynolds number of less than 1.0 can be selected. Ultra-fine wires less than 50 µm in diameter were set in the test volume. The wire surfaces were coated with fluorescent paint. The test volume was illuminated using an ultraviolet light-emitting diode. The paint emits very tiny, orange-colored fluorescent light with an intensity that changes with the temperature of the atmosphere. The experimental results showed that the heating/cooling layers were well visualized and the temperature field was well analyzed.}, } @article {pmid35590633, year = {2022}, author = {Wang, G and Fei, L and Luo, KH}, title = {Unified lattice Boltzmann method with improved schemes for multiphase flow simulation: Application to droplet dynamics under realistic conditions.}, journal = {Physical review. E}, volume = {105}, number = {4-2}, pages = {045314}, doi = {10.1103/PhysRevE.105.045314}, pmid = {35590633}, issn = {2470-0053}, abstract = {As a powerful mesoscale approach, the lattice Boltzmann method (LBM) has been widely used for the numerical study of complex multiphase flows. Recently, Luo et al. [Philos. Trans. R. Soc. A: Math. Phys. Eng. Sci. 379, 20200397 (2021)10.1098/rsta.2020.0397] proposed a unified lattice Boltzmann method (ULBM) to integrate the widely used lattice Boltzmann collision operators into a unified framework. In this study, we incorporate additional features into this ULBM in order to simulate multiphase flow under realistic conditions. A nonorthogonal moment set [Fei et al., Phys. Rev. E 97, 053309 (2018)10.1103/PhysRevE.97.053309] and the entropic-multi-relaxation-time (KBC) lattice Boltzmann model are used to construct the collision operator. An extended combined pseudopotential model is proposed to realize multiphase flow simulation at high-density ratio with tunable surface tension over a wide range. The numerical results indicate that the improved ULBM can significantly decrease the spurious velocities and adjust the surface tension without appreciably changing the density ratio. The ULBM is validated through reproducing various droplet dynamics experiments, such as binary droplet collision and droplet impingement on superhydrophobic surfaces. Finally, the extended ULBM is applied to complex droplet dynamics, including droplet pancake bouncing and droplet splashing. The maximum Weber number and Reynolds number in the simulation reach 800 and 7200, respectively, at a density ratio of 1000. The study demonstrates the generality and versatility of ULBM for incorporating schemes to tackle challenging multiphase problems.}, } @article {pmid35590627, year = {2022}, author = {Verma, S and Hemmati, A}, title = {Route to transition in propulsive performance of oscillating foil.}, journal = {Physical review. E}, volume = {105}, number = {4-2}, pages = {045102}, doi = {10.1103/PhysRevE.105.045102}, pmid = {35590627}, issn = {2470-0053}, abstract = {Transition in the propulsive performance and vortex synchronization of an oscillating foil in a combined heaving and pitching motion is numerically investigated at a range of reduced frequencies (0.16 ≤f^{*} ≤ 0.64), phase offsets (0^{∘} ≤ϕ≤ 315^{∘} ), and Reynolds number (1000≤Re≤16000). Focusing on the common case of Re=1000, the drag to thrust transition is identified on a ϕ-f^{*} phase map. Here, the range of 90^{∘} ≤ϕ≤ 225^{∘} depicted a drag-dominated regime for increasing reduced frequency. However, thrust-dominated regimes were observed for ϕ< 90^{∘} and ϕ> 225^{∘}, where increasing the reduced frequency led to an increased thrust production. The isoline-depicting drag-thrust boundary was further observed to coincide with transitions in the characteristic near-wake modes with increasing reduced frequency, which ranged from 2P+2S to 2P and reverse von Kármán modes. However, evaluation of the wake with changing phase offsets at individual reduced frequencies only depicted effects on the spatial configuration of the vortex structures, while the number of vortices shed in one oscillation period was unchanged. The existence of similar wake modes with significantly different propulsive performance clearly suggests that transitions of the wake topology may not always be a reliable tool for understanding propulsive mechanisms of fish swimming or development of underwater propulsion systems. We further assessed a possible route to drag production via investigation into the mean velocity fields at increasing phase offset and at intermediate reduced frequencies ranging from 0.24 to 0.40. This revealed bifurcation of a velocity jet behind the foil on account of the wake topology and dynamics of shed vortex structures. The changes posed by increasing ϕ on wake structure interactions further hints at potential mechanisms that limit the achievement of optimum efficiency in underwater locomotion.}, } @article {pmid35580542, year = {2022}, author = {Ge, M and Sun, C and Zhang, G and Coutier-Delgosha, O and Fan, D}, title = {Combined suppression effects on hydrodynamic cavitation performance in Venturi-type reactor for process intensification.}, journal = {Ultrasonics sonochemistry}, volume = {86}, number = {}, pages = {106035}, pmid = {35580542}, issn = {1873-2828}, abstract = {Hydrodynamic cavitation is an emerging intensification technology in water treatment or chemical processing, and Venturi-type cavitation reactors exhibit advantages for industrial-scale production. The effects of temperature on hydrodynamic cavitating flows are investigated to find the optimum reaction conditions enhancing cavitating treatment intensity. Results show that the cavitation performance, including the cavitation intensity and cavitation unsteady behavior, is influenced by (1) cavitation number σ (the pressure difference affecting the vaporization process), (2) Reynolds number Re (the inertial/viscous ratio affecting the bubble size and liquid-vapor interface area), and (3) thermodynamic parameter Σ (the thermal effect affecting the temperature drop). With increasing temperature, the cavitation length first increases and then decreases, with a cavitation intensity peak at the transition temperature of 58 °C. With the growth of cavitation extent, the cavity-shedding regimes tend to transition from the attached sheet cavity to the periodic cloud cavity, and the vapor volume fluctuating frequency decreases accordingly. A combined suppression parameter (CSP) is provided to predict that, with increasing CSP value, the cavitation intensity can be decreased. Recommendations are given that working under the low-CSP range (55-60 °C) could enhance the intensification of the cavitation process.}, } @article {pmid35567865, year = {2022}, author = {Cherkaoui, I and Bettaibi, S and Barkaoui, A and Kuznik, F}, title = {Magnetohydrodynamic blood flow study in stenotic coronary artery using lattice Boltzmann method.}, journal = {Computer methods and programs in biomedicine}, volume = {221}, number = {}, pages = {106850}, doi = {10.1016/j.cmpb.2022.106850}, pmid = {35567865}, issn = {1872-7565}, mesh = {*Atherosclerosis ; Blood Flow Velocity/physiology ; Computer Simulation ; Constriction, Pathologic ; *Coronary Vessels ; Hemodynamics/physiology ; Humans ; Hydrodynamics ; Models, Cardiovascular ; }, abstract = {BACKGROUND AND OBJECTIVE: Cardiovascular diseases such as atherosclerosis are the first engender of death in the world. The malfunctioning of cardiovascular system is attributed mainly to hemodynamics. However, blood magnetic properties are of major haemodynamic interest, with significant clinical applications. The aim of this work is to study numerically the effect of high magnetic field on blood flow in stenotic artery.

METHODS: In this paper, a double population D2Q9 lattice Boltzmann model is proposed. Velocity and magnetic field are both solved using Lattice Boltzmann method with single relaxation time. Blood is considered homogeneous and Newtonian bio-magnetic fluid. The results of the proposed model are compared and validated by recent numerical and experimental studies in the literature and show good agreement. In this study, simulations are carried out for both hydrodynamics and magneto-hydrodynamics. For the magneto-hydrodynamic case, five values of Hartmann number of 10, 30, 50, 75 and 100 at Reynolds number of 400, 600 and 800 are investigated Results: The results show that velocity and recirculation zone increase with the increase of the degree of stenosis and Reynolds number. In addition, a considerable decrease in velocity, recirculation zones and pressure drop across the stenotic artery is noticed with the increase of Hartmann number.

CONCLUSION: The suggested model is found to be effective and accurate in the treatment of magneto-hydrodynamic blood flow in stenotic artery. The found results can be used by clinicians in the treatment of certain cardiovascular disorders and in regulating blood flow movement, especially during surgical procedures.}, } @article {pmid35551230, year = {2022}, author = {Chew, SH and Hoi, SM and Tran, MV and Foo, JJ}, title = {Partially-covered fractal induced turbulence on fins thermal dissipation.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {7861}, pmid = {35551230}, issn = {2045-2322}, abstract = {The impacts of partially-covered fractal grids induced turbulence on the forced convective heat transfer across plate-fin heat sink at Reynolds number ReDh = 22.0 × 10[3] were numerically and experimentally investigated. Results showed that partially covered grids rendered a higher thermal dissipation performance, with partially-covered square fractal grid (PCSFG) registering an outstanding increase of 43% in Nusselt number relative to the no grid configuration. The analyzation via an in-house developed single particle tracking velocimetry (SPTV) system displayed the findings of unique "Turbulence Annulus" formation, which provided a small degree of predictivity in the periodic annulus oscillations. Further assessments on PCSFG revealed the preferred inter-fin flow dynamics of (i) high flow velocity, (ii) strong turbulence intensity, (iii) vigorous flow fluctuations, (iv) small turbulence length scale, and (v) heightened decelerated flow events. These features stemmed from the coupling effects of multilength-scale fractal bar thicknesses in generating a veracity of eddy sizes, and a vertical segmentation producing heightened mass flow rate while inducing favourable wake-flow structures to penetrate inter-fin regions. Teeming effects of such energetic eddies within plate-fin array unveiled a powerful vortex shedding effect, with PCSFG achieving fluctuation frequency f = 18.5 Hz close to an optimal magnitude. The coaction of such traits limits the growth of fin boundary layers, providing superior thermal transfer capabilities which benefits the community in developing for higher efficiency heat transfer systems.}, } @article {pmid35547578, year = {2022}, author = {Qiao, Y and Luo, K and Fan, J}, title = {Computational Prediction of Thrombosis in Food and Drug Administration's Benchmark Nozzle.}, journal = {Frontiers in physiology}, volume = {13}, number = {}, pages = {867613}, pmid = {35547578}, issn = {1664-042X}, abstract = {Thrombosis seriously threatens human cardiovascular health and the safe operation of medical devices. The Food and Drug Administration's (FDA) benchmark nozzle model was designed to include the typical structure of medical devices. However, the thrombosis in the FDA nozzle has yet not been investigated. The objective of this study is to predict the thrombus formation process in the idealized medical device by coupling computational fluid dynamics and a macroscopic hemodynamic-based thrombus model. We developed the hemodynamic-based thrombus model by considering the effect of platelet consumption. The thrombus model was quantitatively validated by referring to the latest thrombosis experiment, which was performed in a backward-facing step with human blood flow. The same setup was applied in the FDA nozzle to simulate the thrombus formation process. The thrombus shaped like a ring was firstly observed in the FDA benchmark nozzle. Subsequently, the accuracy of the shear-stress transport turbulence model was confirmed in different turbulent flow conditions. Five scenarios with different Reynolds numbers were carried out. We found that turbulence could change the shape of centrosymmetric thrombus to axisymmetric and high Reynolds number blood flow would delay or even prevent thrombosis. Overall, the present study reports the thrombosis process in the FDA benchmark nozzle using the numerical simulation method, and the primary findings may shed light on the effect of turbulence on thrombosis.}, } @article {pmid35546646, year = {2022}, author = {Gil, A and Navarro, R and Quintero, P and Mares, A and Pérez, M and Montero, JA}, title = {CFD analysis of the HVAD's hemodynamic performance and blood damage with insight into gap clearance.}, journal = {Biomechanics and modeling in mechanobiology}, volume = {21}, number = {4}, pages = {1201-1215}, pmid = {35546646}, issn = {1617-7940}, mesh = {Equipment Design ; *Heart Failure ; *Heart-Assist Devices ; Hemodynamics ; Hemolysis ; Humans ; }, abstract = {Mechanical circulatory support using ventricular assist devices has become commonplace in the treatment of patients suffering from advanced stages of heart failure. While blood damage generated by these devices has been evaluated in depth, their hemodynamic performance has been investigated much less. This work presents the analysis of the complete operating map of a left ventricular assist device, in terms of pressure head, power and efficiency. Further investigation into its hemocompatibility is included as well. To achieve these objectives, computational fluid dynamics simulations of a centrifugal blood pump with a wide-blade impeller were performed. Several conditions were considered by varying the rotational speed and volumetric flow rate. Regarding the device's hemocompatibility, blood damage was evaluated by means of the hemolysis index. By relating the hemocompatibility of the device to its hemodynamic performance, the results have demonstrated that the highest hemolysis occurs at low flow rates, corresponding to operating conditions of low efficiency. Both performance and hemocompatibility are affected by the gap clearance. An innovative investigation into the influence of this design parameter has yielded decreased efficiencies and increased hemolysis as the gap clearance is reduced. As a further novelty, pump operating maps were non-dimensionalized to highlight the influence of Reynolds number, which allows their application to any working condition. The pump's operating range places it in the transitional regime between laminar and turbulent, leading to enhanced efficiency for the highest Reynolds number.}, } @article {pmid35544978, year = {2022}, author = {Sander, A and Petračić, A and Zokić, I and Vrsaljko, D}, title = {Scaling up extractive deacidification of waste cooking oil.}, journal = {Journal of environmental management}, volume = {316}, number = {}, pages = {115222}, doi = {10.1016/j.jenvman.2022.115222}, pmid = {35544978}, issn = {1095-8630}, mesh = {*Biofuels/analysis ; Cooking ; *Fatty Acids, Nonesterified ; Plant Oils ; Solvents ; }, abstract = {Biodiesel produced from waste feedstocks can play a significant role in fighting climate change, improperly disposed waste and growing energy demand. Waste feedstocks such as used cooking oil have a great potential for energy production. However, they often have to be purified from free fatty acids prior to biodiesel production. Extractive deacidification with deep eutectic solvents is a promising alternative to conventional purification methods. To evaluate the process of extractive deacidification of waste cooking oil, a full set of physical, hydrodynamic and kinetic data were experimentally determined on a laboratory scale. Hydrodynamic and kinetic experiments were performed in three geometrically similar jacketed agitated vessels. Vessels were equipped with axial flow impeller (four pitched blade impeller). Physical properties (density, viscosity and surface tension) were experimentally determined. Preliminary hydrodynamic experiments involved several model systems without mass transfer. As a result, correlation between power number and Reynolds number as well as scale-up criterion was developed. Obtained dependencies were correlated with the physical properties. Mixing intensity for achieving complete dispersion was determined. Second stage of investigation involved two sets of experiments, hydrodynamic and kinetic, with interphase mass transfer (the extraction of free fatty acids from waste cooking oil with deep eutectic solvent, potassium carbonate:ethylene glycol, 1:10). Obtained results enabled understanding interphase mass transfer and prediction of mass transfer coefficient from the derived dimensionless correlations. The values of volumetric mass transfer coefficients were smaller for the dispersed phase, indicating that the prevailing mass transfer resistance was within the droplets. The working hypothesis was that the same process result should be achieved at the same dispersion rate, and that hypothesis was confirmed - at all scales extraction efficiency was 97.9 ± 0.1%.}, } @article {pmid35544559, year = {2022}, author = {Callaham, JL and Rigas, G and Loiseau, JC and Brunton, SL}, title = {An empirical mean-field model of symmetry-breaking in a turbulent wake.}, journal = {Science advances}, volume = {8}, number = {19}, pages = {eabm4786}, pmid = {35544559}, issn = {2375-2548}, abstract = {Improved turbulence modeling remains a major open problem in mathematical physics. Turbulence is notoriously challenging, in part due to its multiscale nature and the fact that large-scale coherent structures cannot be disentangled from small-scale fluctuations. This closure problem is emblematic of a greater challenge in complex systems, where coarse-graining and statistical mechanics descriptions break down. This work demonstrates an alternative data-driven modeling approach to learn nonlinear models of the coherent structures, approximating turbulent fluctuations as state-dependent stochastic forcing. We demonstrate this approach on a high-Reynolds number turbulent wake experiment, showing that our model reproduces empirical power spectra and probability distributions. The model is interpretable, providing insights into the physical mechanisms underlying the symmetry-breaking behavior in the wake. This work suggests a path toward low-dimensional models of globally unstable turbulent flows from experimental measurements, with broad implications for other multiscale systems.}, } @article {pmid35535750, year = {2022}, author = {Zhang, R and Toonder, JD and Onck, PR}, title = {Metachronal patterns by magnetically-programmable artificial cilia surfaces for low Reynolds number fluid transport and mixing.}, journal = {Soft matter}, volume = {18}, number = {20}, pages = {3902-3909}, doi = {10.1039/d1sm01680f}, pmid = {35535750}, issn = {1744-6848}, mesh = {Biological Transport ; *Cilia/metabolism ; *Magnetics ; Models, Biological ; Motion ; }, abstract = {Motile cilia can produce net fluid flows at low Reynolds number because of their asymmetric motion and metachrony of collective beating. Mimicking this with artificial cilia can find application in microfluidic devices for fluid transport and mixing. Here, we study the metachronal beating of nonidentical, magnetically-programmed artificial cilia whose individual non-reciprocal motion and collective metachronal beating pattern can be independently controlled. We use a finite element method that accounts for magnetic forces, cilia deformation and fluid flow in a fully coupled manner. Mimicking biological cilia, we study magnetic cilia subject to a full range of metachronal driving patterns, including antiplectic, symplectic, laeoplectic and diaplectic waves. We analyse the induced primary flow, secondary flow and mixing rate as a function of the phase lag between cilia and explore the underlying physical mechanism. Our results show that shielding effects between neighboring cilia lead to a primary flow that is larger for antiplectic than for symplectic metachronal waves. The secondary flow can be fully explained by the propagation direction of the metachronal wave. Finally, we show that the mixing rate can be strongly enhanced by laeoplectic and diaplectic metachrony resulting in large velocity gradients and vortex-like flow patterns.}, } @article {pmid35527637, year = {2022}, author = {Gomé, S and Tuckerman, LS and Barkley, D}, title = {Extreme events in transitional turbulence.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {380}, number = {2226}, pages = {20210036}, doi = {10.1098/rsta.2021.0036}, pmid = {35527637}, issn = {1471-2962}, abstract = {Transitional localized turbulence in shear flows is known to either decay to an absorbing laminar state or to proliferate via splitting. The average passage times from one state to the other depend super-exponentially on the Reynolds number and lead to a crossing Reynolds number above which proliferation is more likely than decay. In this paper, we apply a rare-event algorithm, Adaptative Multilevel Splitting, to the deterministic Navier-Stokes equations to study transition paths and estimate large passage times in channel flow more efficiently than direct simulations. We establish a connection with extreme value distributions and show that transition between states is mediated by a regime that is self-similar with the Reynolds number. The super-exponential variation of the passage times is linked to the Reynolds number dependence of the parameters of the extreme value distribution. Finally, motivated by instantons from Large Deviation theory, we show that decay or splitting events approach a most-probable pathway. This article is part of the theme issue 'Mathematical problems in physical fluid dynamics (part 2)'.}, } @article {pmid35527633, year = {2022}, author = {Drivas, TD}, title = {Self-regularization in turbulence from the Kolmogorov 4/5-law and alignment.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {380}, number = {2226}, pages = {20210033}, doi = {10.1098/rsta.2021.0033}, pmid = {35527633}, issn = {1471-2962}, abstract = {A defining feature of three-dimensional hydrodynamic turbulence is that the rate of energy dissipation is bounded away from zero as viscosity is decreased (Reynolds number increased). This phenomenon-anomalous dissipation-is sometimes called the 'zeroth law of turbulence' as it underpins many celebrated theoretical predictions. Another robust feature observed in turbulence is that velocity structure functions [Formula: see text] exhibit persistent power-law scaling in the inertial range, namely [Formula: see text] for exponents [Formula: see text] over an ever increasing (with Reynolds) range of scales. This behaviour indicates that the velocity field retains some fractional differentiability uniformly in the Reynolds number. The Kolmogorov 1941 theory of turbulence predicts that [Formula: see text] for all [Formula: see text] and Onsager's 1949 theory establishes the requirement that [Formula: see text] for [Formula: see text] for consistency with the zeroth law. Empirically, [Formula: see text] and [Formula: see text], suggesting that turbulent Navier-Stokes solutions approximate dissipative weak solutions of the Euler equations possessing (nearly) the minimal degree of singularity required to sustain anomalous dissipation. In this note, we adopt an experimentally supported hypothesis on the anti-alignment of velocity increments with their separation vectors and demonstrate that the inertial dissipation provides a regularization mechanism via the Kolmogorov 4/5-law. This article is part of the theme issue 'Mathematical problems in physical fluid dynamics (part 2)'.}, } @article {pmid35527631, year = {2022}, author = {Parente, E and Farano, M and Robinet, JC and De Palma, P and Cherubini, S}, title = {Continuing invariant solutions towards the turbulent flow.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {380}, number = {2226}, pages = {20210031}, doi = {10.1098/rsta.2021.0031}, pmid = {35527631}, issn = {1471-2962}, abstract = {A new mathematical framework is proposed for characterizing the coherent motion of fluctuations around a mean turbulent channel flow. We search for statistically invariant coherent solutions of the unsteady Reynolds-averaged Navier-Stokes equations written in a perturbative form with respect to the turbulent mean flow, using a suitable approximation of the Reynolds stress tensor. This is achieved by setting up a continuation procedure of known solutions of the perturbative Navier-Stokes equations, based on the continuous increase of the turbulent eddy viscosity towards its turbulent value. The recovered solutions, being sustained only in the presence of the Reynolds stress tensor, are representative of the statistically coherent motion of turbulent flows. For small friction Reynolds number and/or domain size, the statistically invariant motion is almost identical to the corresponding invariant solution of the Navier-Stokes equations. Whereas, for sufficiently large friction number and/or domain size, it considerably departs from the starting invariant solution of the Navier-Stokes equations, presenting spatial structures, main wavelengths and scaling very close to those characterizing both large- and small-scale motion of turbulent channel flows. This article is part of the theme issue 'Mathematical problems in physical fluid dynamics (part 2)'.}, } @article {pmid35523801, year = {2022}, author = {Tretola, G and Vogiatzaki, K}, title = {Unveiling the dynamics of ultra high velocity droplet impact on solid surfaces.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {7416}, pmid = {35523801}, issn = {2045-2322}, abstract = {The impact of a liquid droplet onto a solid surface is a phenomenon present in a wide range of natural processes and technological applications. In this study, we focus on impact conditions characterised by ultra high velocities (up to 500 m/s), to investigate-for the first time-how the impact dynamics change when the compressibility of the liquid in the droplet is no longer negligible. A water droplet impacting a dry substrate at four different velocities, from 50 to 500 m/s, is simulated. Such conditions are particularly relevant to aviation as well as industrial gas turbine engine risk management. Thus, numerical investigations as the one we present here provide a powerful tool to analyse the process. We find that increasing the impact velocity changes the flow field within and outside the droplet the moment that the compressibility can no longer be neglected, with the rise of pressure fronts in both regions. Increasing the impact velocity, the compressibility affects also the lamella formed and changes its ejection velocity observed over time (and thus the wetting behaviour) when the region shift from incompressible to compressible. Moreover, it is found that the maximum pressure observed at the wall during the impact is located at the corner of the impact, where the lamella is ejected, not in the centre, and it is influenced by the initial velocity. To predict the maximum pressure experienced by the surface during the high velocity impact, we propose a correlation based on the initial Weber and Reynolds number of the droplet. The complexity and the scales of the dynamics involved in the ultra-high velocity impact is limiting the experimental and analytical studies. To the best of our knowledge there are no experimental data currently available at such conditions. In this study, through numerical simulations, new insights about the impact dynamics at such conditions are provided.}, } @article {pmid35523157, year = {2022}, author = {D'Adamo, J and Collaud, M and Sosa, R and Godoy-Diana, R}, title = {Wake and aeroelasticity of a flexible pitching foil.}, journal = {Bioinspiration & biomimetics}, volume = {17}, number = {4}, pages = {}, doi = {10.1088/1748-3190/ac6d96}, pmid = {35523157}, issn = {1748-3190}, abstract = {A flexible foil undergoing pitching oscillations is studied experimentally in a wind tunnel with different imposed free stream velocities. The chord-based Reynolds number is in the range 1600-4000, such that the dynamics of the system is governed by inertial forces and the wake behind the foil exhibits the reverse Bénard-von Kármán vortex street characteristic of flapping-based propulsion. Particle image velocimetry (PIV) measurements are performed to examine the flow around the foil, whilst the deformation of the foil is also tracked. The first natural frequency of vibration of the foil is within the range of flapping frequencies explored, determining a strongly-coupled dynamics between the elastic foil deformation and the vortex shedding. Cluster-based reduced order modelling is applied on the PIV data in order to identify the coherent flow structures. Analysing the foil kinematics and using a control-volume calculation of the average drag forces from the corresponding velocity fields, we determine the optimal flapping configurations for thrust generation. We show that propulsive force peaks occur at dimensionless frequencies shifted with respect to the elastic resonances that are marked by maximum trailing edge oscillation amplitudes. The thrust peaks are better explained by a wake resonance, which we examine using the tools of classic hydrodynamic stability on the mean propulsive jet profiles.}, } @article {pmid35522515, year = {2022}, author = {Schindler, F and Eckert, S and Zürner, T and Schumacher, J and Vogt, T}, title = {Collapse of Coherent Large Scale Flow in Strongly Turbulent Liquid Metal Convection.}, journal = {Physical review letters}, volume = {128}, number = {16}, pages = {164501}, doi = {10.1103/PhysRevLett.128.164501}, pmid = {35522515}, issn = {1079-7114}, abstract = {The large-scale flow structure and the turbulent transfer of heat and momentum are directly measured in highly turbulent liquid metal convection experiments for Rayleigh numbers varied between 4×10^{5} and ≤5×10^{9} and Prandtl numbers of 0.025≤Pr≤0.033. Our measurements are performed in two cylindrical samples of aspect ratios Γ=diameter/height=0.5 and 1 filled with the eutectic alloy GaInSn. The reconstruction of the three-dimensional flow pattern by 17 ultrasound Doppler velocimetry sensors detecting the velocity profiles along their beam lines in different planes reveals a clear breakdown of coherence of the large-scale circulation for Γ=0.5. As a consequence, the scaling laws for heat and momentum transfer inherit a dependence on the aspect ratio. We show that this breakdown of coherence is accompanied with a reduction of the Reynolds number Re. The scaling exponent β of the power law Nu∝Ra^{β} crosses eventually over from β=0.221 to 0.124 when the liquid metal flow at Γ=0.5 reaches Ra≳2×10^{8} and the coherent large-scale flow is completely collapsed.}, } @article {pmid35512019, year = {2022}, author = {Fei, L and Qin, F and Zhao, J and Derome, D and Carmeliet, J}, title = {Pore-Scale Study on Convective Drying of Porous Media.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {38}, number = {19}, pages = {6023-6035}, doi = {10.1021/acs.langmuir.2c00267}, pmid = {35512019}, issn = {1520-5827}, abstract = {In this work, a numerical model for isothermal liquid-vapor phase change (evaporation) of the two-component air-water system is proposed based on the pseudopotential lattice Boltzmann method. Through the Chapman-Enskog multiscale analysis, we show that the model can correctly recover the macroscopic governing equations of the multicomponent multiphase system with a built-in binary diffusion mechanism. The model is verified based on the two-component Stefan problem where the measured binary diffusivity is consistent with theoretical analysis. The model is then applied to convective drying of a dual-porosity porous medium at the pore scale. The simulation captures a classical transition in the drying process of porous media, from the constant rate period (CRP, first phase) showing significant capillary pumping from large to small pores, to the falling rate period (FRP, second phase) with the liquid front receding in small pores. It is found that, in the CRP, the evaporation rate increases with the inflow Reynolds number (Re), while in the FRP, the evaporation curves almost collapse at different Res. The underlying mechanism is elucidated by introducing an effective Péclet number (Pe). It is shown that convection is dominant in the CRP and diffusion in the FRP, as evidenced by Pe > 1 and Pe < 1, respectively. We also find a log-law dependence of the average evaporation rate on the inflow Re in the CRP regime. The present work provides new insights into the drying physics of porous media and its direct modeling at the pore scale.}, } @article {pmid35493567, year = {2021}, author = {Salari, A and Appak-Baskoy, S and Coe, IR and Tsai, SSH and Kolios, MC}, title = {An ultrafast enzyme-free acoustic technique for detaching adhered cells in microchannels.}, journal = {RSC advances}, volume = {11}, number = {52}, pages = {32824-32829}, pmid = {35493567}, issn = {2046-2069}, abstract = {Adherent cultured cells are widely used biological tools for a variety of biochemical and biotechnology applications, including drug screening and gene expression analysis. One critical step in culturing adherent cells is the dissociation of cell monolayers into single-cell suspensions. Different enzymatic and non-enzymatic methods have been proposed for this purpose. Trypsinization, the most common enzymatic method for dislodging adhered cells, can be detrimental to cells, as it can damage cell membranes and ultimately cause cell death. Additionally, all available techniques require a prolonged treatment duration, typically on the order of minutes (5-10 min). Dissociation of cells becomes even more challenging in microfluidic devices, where, due to the nature of low Reynolds number flow and reduced mixing efficiency, multiple washing steps and prolonged trypsinization may be necessary to treat all cells. Here, we report a novel acoustofluidic method for the detachment of cells adhered onto a microchannel surface without exposing the cells to any enzymatic or non-enzymatic chemicals. This method enables a rapid (i.e., on the order of seconds), cost-effective, and easy-to-operate cell detachment strategy, yielding a detachment efficiency of ∼99% and cellular viability similar to that of the conventional trypsinization method. Also, as opposed to biochemical-based techniques (e.g., enzymatic), in our approach, cells are exposed to the dissociating agent (i.e., substrate-mediated acoustic excitation and microstreaming flow) only for as long as they remain attached to the substrate. After dissociation, the effect of acoustic excitation is reduced to microstreaming flow, therefore, minimizing unwanted effects of the dissociating agent on the cell phenotype. Additionally, our results suggest that cell excitation at acoustic powers lower than that required for complete cell detachment can potentially be employed for probing the adhesion strength of cell-substrate attachment. This novel approach can, therefore, be used for a wide range of lab-on-a-chip applications.}, } @article {pmid35489898, year = {2022}, author = {Das, A and Styslinger, M and Harris, DM and Zenit, R}, title = {Force and torque-free helical tail robot to study low Reynolds number micro-organism swimming.}, journal = {The Review of scientific instruments}, volume = {93}, number = {4}, pages = {044103}, doi = {10.1063/5.0079815}, pmid = {35489898}, issn = {1089-7623}, mesh = {Models, Biological ; *Robotics ; *Swimming/physiology ; Torque ; Viscosity ; }, abstract = {Helical propulsion is used by many micro-organisms to swim in viscous-dominated environments. Their swimming dynamics are relatively well understood, but a detailed study of the flow fields is still needed to understand wall effects and hydrodynamic interactions among swimmers. In this letter, we describe the development of an autonomous swimming robot with a helical tail that operates in the Stokes regime. The device uses a battery-based power system with a miniature motor that imposes a rotational speed on a helical tail. The speed, direction, and activation are controlled electronically using an infrared remote control. Since the robot is about 5 cm long, we use highly viscous fluids to match the Reynolds number, Re, to be less than 0.1. Measurements of swimming speeds are conducted for a range of helical wavelengths, λ, head geometries, and rotation rates, ω. We provide comparisons of the experimental measurements with analytical predictions derived from resistive force theory. This force and torque-free neutrally buoyant swimmer mimics the swimming strategy of bacteria more closely than previously used designs and offers a lot of potential for future applications.}, } @article {pmid35489862, year = {2022}, author = {Prasad, V and Kulkarni, SS and Sharma, A}, title = {Chaotic advection in a recirculating flow: Effect of a fluid-flexible-solid interaction.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {32}, number = {4}, pages = {043122}, doi = {10.1063/5.0079141}, pmid = {35489862}, issn = {1089-7682}, abstract = {The present work is on laminar recirculating flow-induced deformation as well as motion of a neutrally buoyant flexible elliptical solid, resulting in Lagrangian chaos in a two-dimensional lid-driven cavity flow. Using a fully Eulerian and monolithic approach-based single-solver for the fluid flow and flexible-solid deformation, a chaotic advection study is presented for various aspect ratios β (=0.5-1.0) and a constant volume fraction Φ=10% of an elliptical solid at a constant Ericksen number Er=0.05 and Reynolds number Re=100. Our initial analysis reveals maximum chaotic advection at β=0.5 for which a comprehensive nonlinear dynamical analysis is presented. The Poincaré map revealed elliptic islands and chaotic sea in the fluid flow. Three large elliptic islands, apart from certain smaller islands, were identified near the solid. Periodic point analysis revealed the lowest order hyperbolic/elliptic periodic points to be three. Adaptive material tracking gave a physical picture of a deforming material blob revealing its exponential stretch along with steep folds and demonstrated unstable/stable manifolds corresponding to lowest order hyperbolic points. Furthermore, adaptive material tracking demonstrates heteroclinic connections and tangles in the system that confirm the existence of chaos. For the transient as compared to the periodic flow, adaptive material tracking demonstrates a larger exponential increase of the blob's interfacial area. The finite-time Lyapunov exponent field revealed attracting/repelling Lagrangian coherent structures and entrapped fluid zones. Our work demonstrates an immersed deformable solid-based onset of chaotic advection, for the first time in the literature, which is relevant to a wide range of applications.}, } @article {pmid35487201, year = {2022}, author = {Akanyeti, O and Di Santo, V and Goerig, E and Wainwright, DK and Liao, JC and Castro-Santos, T and Lauder, GV}, title = {Fish-inspired segment models for undulatory steady swimming.}, journal = {Bioinspiration & biomimetics}, volume = {17}, number = {4}, pages = {}, doi = {10.1088/1748-3190/ac6bd6}, pmid = {35487201}, issn = {1748-3190}, support = {R01 DC010809/DC/NIDCD NIH HHS/United States ; }, mesh = {Animals ; Biological Evolution ; Biomechanical Phenomena/physiology ; *Fishes/physiology ; Hydrodynamics ; *Swimming/physiology ; }, abstract = {Many aquatic animals swim by undulatory body movements and understanding the diversity of these movements could unlock the potential for designing better underwater robots. Here, we analyzed the steady swimming kinematics of a diverse group of fish species to investigate whether their undulatory movements can be represented using a series of interconnected multi-segment models, and if so, to identify the key factors driving the segment configuration of the models. Our results show that the steady swimming kinematics of fishes can be described successfully using parsimonious models, 83% of which had fewer than five segments. In these models, the anterior segments were significantly longer than the posterior segments, and there was a direct link between segment configuration and swimming kinematics, body shape, and Reynolds number. The models representing eel-like fishes with elongated bodies and fishes swimming at high Reynolds numbers had more segments and less segment length variability along the body than the models representing other fishes. These fishes recruited their anterior bodies to a greater extent, initiating the undulatory wave more anteriorly. Two shape parameters, related to axial and overall body thickness, predicted segment configuration with moderate to high success rate. We found that head morphology was a good predictor of its segment length. While there was a large variation in head segments, the length of tail segments was similar across all models. Given that fishes exhibited variable caudal fin shapes, the consistency of tail segments could be a result of an evolutionary constraint tuned for high propulsive efficiency. The bio-inspired multi-segment models presented in this study highlight the key bending points along the body and can be used to decide on the placement of actuators in fish-inspired robots, to model hydrodynamic forces in theoretical and computational studies, or for predicting muscle activation patterns during swimming.}, } @article {pmid35481832, year = {2022}, author = {Hu, S and Zhang, J and Shelley, MJ}, title = {Enhanced clamshell swimming with asymmetric beating at low Reynolds number.}, journal = {Soft matter}, volume = {18}, number = {18}, pages = {3605-3612}, doi = {10.1039/d2sm00292b}, pmid = {35481832}, issn = {1744-6848}, abstract = {A single flexible filament can be actuated to escape from the scallop theorem and generate net propulsion at low Reynolds number. In this work, we study the dynamics of a simple boundary-driven multi-filament swimmer, a two-arm clamshell actuated at the hinged point, using a nonlocal slender body approximation with hydrodynamic interactions. We first consider an elastic clamshell consisted of flexible filaments with intrinsic curvature, and then build segmental models consisted of rigid segments connected by different mechanical joints with different forms of response torques. The simplicity of the system allows us to fully explore the effect of various parameters on the swimming performance. Optimal included angles and elastoviscous numbers are identified. The segmental models capture the characteristic dynamics of the elastic clamshell. We further demonstrate how the swimming performance can be significantly enhanced by the asymmetric beating patterns induced by biased torques.}, } @article {pmid35478056, year = {2022}, author = {Kotnurkar, A and Kallolikar, N}, title = {Effect of Joule heating and entropy generation on multi-slip condition of peristaltic flow of Casson nanofluid in an asymmetric channel.}, journal = {Journal of biological physics}, volume = {48}, number = {3}, pages = {273-293}, pmid = {35478056}, issn = {1573-0689}, mesh = {Entropy ; *Heating ; Hot Temperature ; *Nanoparticles ; Peristalsis/physiology ; }, abstract = {In the present investigation, the effect of multi-slip condition on peristaltic flow through asymmetric channel with Joule heating effect is considered. We also considered the incompressible non-Newtonian Casson nanofluid model for blood, which is electrically conducting. Second law of thermodynamics is used to examine the entropy generation. Multi-slip condition is used at the boundary of the wall and the analysis is also restricted under the low Reynolds number and long wavelength assumption. The governing equations were transformed into a non-dimensional form by using suitable terms. The reduced non-dimensional highly nonlinear partial differential equations are solved by using the Homotopy Perturbation Sumudu transformation method (HPSTM). The influence of different physical parameters on dimensionless velocity, pressure gradient, temperature, concentration and nanoparticle is graphically presented. From the results, one can understand that the Joule heating effect controls the heat transfer in the system and as the magnetic parameter is increased, there will be decay in the velocity of fluid. The outcomes of the present investigation can be applicable in examining the chyme motion in the gastrointestinal tract and controlling the blood flow during surgery. Present study shows an excellent agreement with the previously available studies in the limiting case.}, } @article {pmid35460986, year = {2022}, author = {Liu, J and Yang, Z and Li, M and Lu, K and Li, D}, title = {Evaluating the concrete grade-control structures built by modified fish-nest bricks in the river restoration: A lab-based case study.}, journal = {Journal of environmental management}, volume = {314}, number = {}, pages = {115056}, doi = {10.1016/j.jenvman.2022.115056}, pmid = {35460986}, issn = {1095-8630}, mesh = {Animals ; Ecosystem ; *Fishes ; *Rivers ; Water ; }, abstract = {Concrete grade-control structures (CGCSs) have broad application prospects in the restoration of large rivers. But there is a lack of indicators to evaluate CGCSs at laboratory study. In this study, we proposed two evaluation indicators from the perspective of the impact of CGCSs on geomorphology change and fish habitat, namely the spatial-averaged occurrence probability of sweep events near the bed and flow diversity. To verify the reasonableness of these indicators, flume experiments were conducted with CGCSs built by modified fish-nest bricks in different Reynolds number and layout condition. Data of the flow field around structures in streamwise, transverse and vertical direction was obtained and analyzed. Results of mean flow field show that large recirculation zones are found in the cavity and behind the element. The mechanism of suspended sediment deposition around CGCSs in the flow can be further clarified by combining sweep and ejection according to quadrant analysis. In the vertical direction, the ratio of sweep to total events near bed after spatial-averaged processing is found to be higher for the staggered array. According to the Shannon's entropy, water flow diversity was calculated to quantify the fish habitat. The water flow diversity index around the CGCSs is higher for the staggered. It can be concluded that the elements of CGCSs in staggered manners have a better protection for riverbed and can provide a more stable fish habitat suitability. The results anticipated by the spatial-averaged occurrence probability of sweep events near bed and flow diversity in the experiment are consistent with the result of previous research on landform change and fish habitat. The research could provide a theoretical basis for the application of CGCSs for river restoration.}, } @article {pmid35457904, year = {2022}, author = {Martin, E and Valeije, A and Sastre, F and Velazquez, A}, title = {Impact of Channels Aspect Ratio on the Heat Transfer in Finned Heat Sinks with Tip Clearance.}, journal = {Micromachines}, volume = {13}, number = {4}, pages = {}, pmid = {35457904}, issn = {2072-666X}, abstract = {A 3D numerical study is used to analyze the flow topology and performance, in terms of heat transfer efficiency and required pumping power, of heat sink devices with different channel aspect-ratio in the presence of tip-clearance. Seven different channel aspect ratios AR, from 0.25 to 1.75, were analyzed. The flow Reynolds numbers Re, based on the average velocity evaluated in the device channels region, were in the range of 200 to 1000. Two different behaviors of the global Nusselt were obtained depending on the flow Reynolds number: for Re<600, the heat transfer increased with the channels aspect ratio, e.g., for Re=400, the global Nusselt number increased by 14% for configuration AR=1.75 when compared to configuration AR=0.25. For Re>600, the maximum Nusselt is obtained for the squared-channel configuration, and, for some configurations, flow destabilization to a unsteady regime appeared. For Re=700, Nusselt number reduced when compared with the squared-channel device, 11% and 2% for configurations with AR=0.25 and 1.75, respectively. Dimensionless pressure drop decreased with the aspect ratio for all cases. In the context of micro-devices, where the Reynolds number is small, these results indicate that the use of channels with high aspect-ratios is more beneficial, both in terms of thermal and dynamic efficiency.}, } @article {pmid35454454, year = {2022}, author = {Ayub, R and Ahmad, S and Ahmad, S and Akhtar, Y and Alam, MM and Mahmoud, O}, title = {Numerical Assessment of Dipole Interaction with the Single-Phase Nanofluid Flow in an Enclosure: A Pseudo-Transient Approach.}, journal = {Materials (Basel, Switzerland)}, volume = {15}, number = {8}, pages = {}, pmid = {35454454}, issn = {1996-1944}, abstract = {Nanofluids substantially enhance the physical and thermal characteristics of the base or conducting fluids specifically when interacting with the magnetic field. Several engineering processes like geothermal energy extraction, metal casting, nuclear reactor coolers, nuclear fusion, magnetohydrodynamics flow meters, petrochemicals, and pumps incorporate magnetic field interaction with the nanofluids. On the other hand, an enhancement in heat transfer due to nanofluids is essentially required in various thermal systems. The goal of this study is to figure out that how much a magnetic field affects nanofluid flow in an enclosure because of a dipole. The nanofluid is characterized using a single-phase model, and the governing partial differential equations are computed numerically. A Pseudo time based numerical algorithm is developed to numerically solve the problem. It can be deduced that the Reynolds number and the magnetic parameter have a low effect on the Nusselt number and skin friction. The Nusselt number rises near the dipole location because of an increase in the magnetic parameter Mn and the Reynolds number Re. The imposed magnetic field alters the region of high temperature nearby the dipole, while newly generated vortices rotate in alternate directions. Furthermore, nanoparticle volume fraction causes a slight change in the skin friction while it marginally reduces the Nusselt number.}, } @article {pmid35448318, year = {2022}, author = {Chandrasekaran, AS and Fix, AJ and Warsinger, DM}, title = {Combined Membrane Dehumidification with Heat Exchangers Optimized Using CFD for High Efficiency HVAC Systems.}, journal = {Membranes}, volume = {12}, number = {4}, pages = {}, pmid = {35448318}, issn = {2077-0375}, abstract = {Traditional air conditioning systems use a significant amount of energy on dehumidification by condensing water vapor out from the air. Membrane-based air conditioning systems help overcome this problem by avoiding condensation and treating the sensible and latent loads separately, using membranes that allow water vapor transport, but not air (nitrogen and oxygen). In this work, a computational fluid dynamics (CFD) model has been developed to predict the heat and mass transfer and concentration polarization performance of a novel active membrane-based energy exchanger (AMX). The novel design is the first of its kind to integrate both vapor removal via membranes and air cooling into one device. The heat transfer results from the CFD simulations are compared with common empirical correlations for similar geometries. The performance of the AMX is studied over a broad range of operating conditions using the compared CFD model. The results show that strong tradeoffs result in optimal values for the channel length (0.6-0.8 m) and the ratio of coil diameter to channel height (~0.5). Water vapor transport is best if the flow is just past the turbulence transition around 3000-5000 Reynolds number. These trends hold over a range of conditions and dimensions.}, } @article {pmid35446443, year = {2022}, author = {Torres-Saucedo, OL and Morales-Cruzado, B and Pérez-Gutiérrez, FG}, title = {Experimental determination of shear stresses on an artificial transcoelomic metastasis model using optical tweezers: A comparison with numerical simulation.}, journal = {Lasers in surgery and medicine}, volume = {54}, number = {7}, pages = {1027-1037}, doi = {10.1002/lsm.23554}, pmid = {35446443}, issn = {1096-9101}, mesh = {Blood Flow Velocity ; Computer Simulation ; Humans ; *Neoplasms ; *Optical Tweezers ; Stress, Mechanical ; }, abstract = {BACKGROUND: One of the reported pathways of cancer spread is the transcoelomic pathway, which is understood as the spread of cancer cells in the abdominal and thoracic cavities through interstitial fluid. It has been proven that the shear stresses caused by microfluidic currents on cancer tumors in the abdominal and thoracic cavities cause the detachment of cancer cells triggering transcoelomic metastasis; however, the magnitude of shear stresses has not yet been measured experimentally.

OBJECTIVES: The objective of this study is to develop an experimental methodology using optical tweezers to approximate the shear stresses suffered by a nonporous, rigid artificial cancerous nodule model.

METHODS: Artificial cancerous nodule model was made by the agglomeration of 2 μm diameter polystyrene particles in a microfluidic platform. Optical tweezers were used as a velocimetry tool and shear stresses on the surface of the nodule model were approximated with the viscous shear stress equation. The results were verified with a numerical simulation performed in Ansys Fluent.

RESULTS: Shear stress originated by microflow over artificial cancerous nodule model were quantified both experimentally and numerically, showing good agreement between both methods. Such stress on the nodules' surface was much greater than that suffered by the wall on which the nodule model was located and dependent of the nodule model geometry. Although the experiment and simulation of this study were performed using a rigid and nonporous nodule model, the conclusion obtained about the increase of shear stresses applies to permeable, porous, and soft nodules as well, because the shear stresses are associated to the acceleration of the fluid originated by the reduction of the cross-sectional area.

CONCLUSIONS: Shear stress over artificial nodule model were successfully quantified using optical tweezer-based velocimetry technique and verified through numerical calculation. Advantages of experimental technique are: (1) it allows to control the position in a three-dimensional plane, allowing measurements in the vicinity of the analyzed surfaces, and (2) it is applicable for very low Reynolds number (Re  « 1). On the other hand, as disadvantages: (1) it tends to be complicated to perform velocity measurements over obstacles and (2) it is limited in trapping distance.}, } @article {pmid35436159, year = {2022}, author = {Ibrahim, MG}, title = {Numerical simulation to the activation energy study on blood flow of seminal nanofluid with mixed convection effects.}, journal = {Computer methods in biomechanics and biomedical engineering}, volume = {}, number = {}, pages = {1-11}, doi = {10.1080/10255842.2022.2063018}, pmid = {35436159}, issn = {1476-8259}, abstract = {This study sheds light on the influences of Arrhenius activation energy and variable velocity slip on MHD blood motion of Seminal nanofluid in a vertical symmetric channel. In addition, mixed convection, hall current and thermal jump are taken into consideration. The governing system of differential equations with highly nonlinear terms is simplified with facts of long wavelength and low Reynolds number. Pade' approximant and differential transform techniques are combined mathematically to obtain the semi-numerical solutions for the governing system of PDEs. The results are computed and verified graphically with aid of Mathematica 12.3. Physical parameters considered are studied in detail sketchily for the proposed model. Verification/signification of results is approved semi-numerically by comparing the prior results by the newest existing published results by Ahmad et al 2021. Results show that, Velocity of seminal fluid is diminishes with a rise in viscosity-dependent parameter that is a significant feature which can be utilized in controlling the transport of spermatozoa into the cervical canal.}, } @article {pmid35428793, year = {2022}, author = {Koo, D and So, H}, title = {Facile microfabrication of three dimensional-patterned micromixers using additive manufacturing technology.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {6346}, pmid = {35428793}, issn = {2045-2322}, mesh = {Computer Simulation ; Equipment Design ; *Lab-On-A-Chip Devices ; *Microtechnology ; Printing, Three-Dimensional ; }, abstract = {This study investigates the manufacturing method of oblique patterns in microchannels and the effect of these patterns on mixing performance in microchannels. To fabricate three-dimensional (3D) and oblique patterns in microchannels, 3D printing and replica methods were utilized to mold patterns and microchannels, respectively. The angle and size of the patterns were controlled by the printing angle and resolution, respectively. The mixing efficiency was experimentally characterized, and the mixing principle was analyzed using computational fluid dynamics simulation. The analysis showed that the mixing channel cast from the mold printed with a printing angle of 30° and resolution of 300 μm exhibited the best mixing efficiency with a segregation index of approximately 0.05 at a Reynolds number of 5.4. This was because, as the patterns inside the microchannel were more oblique, "split" and "recombine" behaviors between two fluids were enhanced owing to the geometrical effect. This study supports the use of the 3D printing method to create unique patterns inside microchannels and improve the mixing performance of two laminar flows for various applications such as point-of-care diagnostics, lab-on-a-chip, and chemical synthesis.}, } @article {pmid35428381, year = {2022}, author = {Ilg, P}, title = {Multiparticle collision dynamics for ferrofluids.}, journal = {The Journal of chemical physics}, volume = {156}, number = {14}, pages = {144905}, doi = {10.1063/5.0087981}, pmid = {35428381}, issn = {1089-7690}, abstract = {Detailed studies of the intriguing field-dependent dynamics and transport properties of confined flowing ferrofluids require efficient mesoscopic simulation methods that account for fluctuating ferrohydrodynamics. Here, we propose such a new mesoscopic model for the dynamics and flow of ferrofluids, where we couple the multi-particle collision dynamics method as a solver for the fluctuating hydrodynamics equations to the stochastic magnetization dynamics of suspended magnetic nanoparticles. This hybrid model is validated by reproducing the magnetoviscous effect in Poiseuille flow, obtaining the rotational viscosity in quantitative agreement with theoretical predictions. We also illustrate the new method for the benchmark problem of flow around a square cylinder. Interestingly, we observe that the length of the recirculation region is increased, whereas the drag coefficient is decreased in ferrofluids when an external magnetic field is applied compared with the field-free case at the same effective Reynolds number. The presence of thermal fluctuations and the flexibility of this particle-based mesoscopic method provide a promising tool to investigate a broad range of flow phenomena of magnetic fluids, and the method could also serve as an efficient way to simulate solvent effects when colloidal particles are immersed in ferrofluids.}, } @article {pmid35428147, year = {2022}, author = {Nagy, PT}, title = {Enstrophy change of the Reynolds-Orr solution in channel flow.}, journal = {Physical review. E}, volume = {105}, number = {3-2}, pages = {035108}, doi = {10.1103/PhysRevE.105.035108}, pmid = {35428147}, issn = {2470-0053}, abstract = {The plane Poiseuille flow is one of the elementary flow configurations. Although its laminar-turbulent transition mechanism has been investigated intensively in the last century, the significant difference in the critical Reynolds number between the experiments and the theory lacks a clear explanation. In this paper, an attempt is made to reduce this gap by analyzing the solution of the Reynolds-Orr equation. Recent published results have shown that the usage of enstrophy (the volume integral of the squared vorticity) instead of the kinetic energy as the norm of perturbations predicts higher Reynolds numbers in the two-dimensional case. In addition, other research show has shown an improvement of the original Reynolds-Orr energy equation using the weighted norm in a tilted coordinate system. In this paper the enstrophy is used in three dimensions combined with the tilted coordinate system approach. The zero-enstrophy-growth constraint is applied to the classical Reynolds-Orr equation, and then the solution is further refined in the tilted coordinate system. The results are compared to direct numerical simulations published previously.}, } @article {pmid35428113, year = {2022}, author = {Steiros, K}, title = {Balanced nonstationary turbulence.}, journal = {Physical review. E}, volume = {105}, number = {3-2}, pages = {035109}, doi = {10.1103/PhysRevE.105.035109}, pmid = {35428113}, issn = {2470-0053}, abstract = {Kolmogorov's 1941 (K41) framework remains central to the understanding of turbulent flows. However, in unsteady turbulence, K41's critical equilibrium assumption is expected to hold in an asymptotic manner, as the Reynolds number and wave numbers tend to infinity, rendering K41 not strictly valid at finite wave numbers. This work proposes a generalization of K41 for out-of-equilibrium effects and cascades far from initial conditions. The main result is a correction to the -5/3 law for out-of-equilibrium eddies, unrelated to intermittency effects. Experimental and numerical evidence is provided in support of the theoretical results.}, } @article {pmid35428103, year = {2022}, author = {Rana, N and Perlekar, P}, title = {Phase ordering, topological defects, and turbulence in the three-dimensional incompressible Toner-Tu equation.}, journal = {Physical review. E}, volume = {105}, number = {3}, pages = {L032603}, doi = {10.1103/PhysRevE.105.L032603}, pmid = {35428103}, issn = {2470-0053}, abstract = {We investigate the phase-ordering dynamics of the incompressible Toner-Tu equation in three dimensions. We show that the phase ordering proceeds via defect merger events and the dynamics is controlled by the Reynolds number Re. At low Re, the dynamics is similar to that of the Ginzburg-Landau equation. At high Re, turbulence controls phase ordering. In particular, we observe a forward energy cascade from the coarsening length scale to the dissipation scale, clustering of defects, and multiscaling in velocity correlations.}, } @article {pmid35420623, year = {2022}, author = {Thurgood, P and Chheang, C and Needham, S and Pirogova, E and Peter, K and Baratchi, S and Khoshmanesh, K}, title = {Generation of dynamic vortices in a microfluidic system incorporating stenosis barrier by tube oscillation.}, journal = {Lab on a chip}, volume = {22}, number = {10}, pages = {1917-1928}, doi = {10.1039/d2lc00135g}, pmid = {35420623}, issn = {1473-0189}, mesh = {Constriction, Pathologic ; Humans ; *Microfluidics/methods ; }, abstract = {Microfluidic systems incorporating sudden expansions are widely used for generation of vortex flow patterns. However, the formation of vortices requires high flow rates to induce inertial effects. Here, we introduce a new method for generating dynamic vortices in microfluidics at low static flow rates. Human blood is driven through a microfluidic channel incorporating a semi-circular stenosis barrier. The inlet tube of the channel is axially oscillated using a computer-controlled audio-speaker. The tube oscillation induces high transient flow rates in the channel, which generates dynamic vortices across the stenosis barrier. The size of the vortices can be modulated by varying the frequency and amplitude of tube oscillation. Various vortex flow patterns can be generated by varying the flow rate. The formation and size of the vortices can be predicted using the Reynolds number of the oscillating tube. We demonstrate the potential application of the system for investigating the adhesion and phagocytosis of circulating immune cells under pathologically high shear rates induced at the stenosis. This approach facilitates the development of versatile and controllable inertial microfluidic systems for performing various cellular assays while operating at low static flow rates and low sample volumes.}, } @article {pmid35407874, year = {2022}, author = {Behura, AK and Mohanty, CP and Singh, MR and Kumar, A and Linul, E and Rajak, DK}, title = {Performance Analysis of Three Side Roughened Solar Air Heater: A Preliminary Investigation.}, journal = {Materials (Basel, Switzerland)}, volume = {15}, number = {7}, pages = {}, pmid = {35407874}, issn = {1996-1944}, abstract = {In recent years, sunlight has been used in several fields such as photovoltaic cells, flat plate collectors, solar cookers, green buildings, and agricultural applications. Improved thermal performance has been seen which comes of three sides absorber plate with glass cover compared to the traditional one. This paper presents the Nusselt (Nu) number, collector efficiency factor (CEF), and collector heat removal factor (CHRF) for the optimal solution of three sides artificially roughened solar air heater. Five input variables such as Reynolds (Re) number, relative roughness pitch, relative roughness height, mass flow rate, and air temperature of the duct are taken into account for improved efficiency optimization of collector, collector heat removal factor, and Nu number. Technique for order of preference by similarity to ideal solution (TOPSIS) technique is used to identify the best alternative amongst a number of performance measures by converting them into an equivalent single variable. Moreover, the results revealed the high accuracy of the CEF, CHRF, and Nu number of 75-80%, 74-78%, and 63-71%, respectively. Meanwhile, it has been also observed that roughness Re number varies between 12,500 and 13,500, and height of relative roughness is 0.0245, including pitch of relative roughness 10 along with the rate of mass flow is 0.041 kg/s.}, } @article {pmid35407169, year = {2022}, author = {Bhatti, MM and Bég, OA and Abdelsalam, SI}, title = {Computational Framework of Magnetized MgO-Ni/Water-Based Stagnation Nanoflow Past an Elastic Stretching Surface: Application in Solar Energy Coatings.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {12}, number = {7}, pages = {}, pmid = {35407169}, issn = {2079-4991}, abstract = {In this article, motivated by novel nanofluid solar energy coating systems, a mathematical model of hybrid magnesium oxide (MgO) and nickel (Ni) nanofluid magnetohydrodynamic (MHD) stagnation point flow impinging on a porous elastic stretching surface in a porous medium is developed. The hybrid nanofluid is electrically conducted, and a magnetic Reynolds number is sufficiently large enough to invoke an induced magnetic field. A Darcy model is adopted for the isotropic, homogenous porous medium. The boundary conditions account for the impacts of the velocity slip and thermal slip. Heat generation (source)/absorption (sink) and also viscous dissipation effects are included. The mathematical formulation has been performed with the help of similarity variables, and the resulting coupled nonlinear dimensionless ordinary differential equations have been solved numerically with the help of the shooting method. In order to test the validity of the current results and the convergence of the solutions, a numerical comparison with previously published results is included. Numerical results are plotted for the effect of emerging parameters on velocity, temperature, magnetic induction, skin friction, and Nusselt number. With an increment in nanoparticle volume fraction of both MgO and Ni nanoparticles, the temperature and thermal boundary layer thickness of the nanofluid are elevated. An increase in the porous medium parameter (Darcy number), velocity slip, and thermal Grashof number all enhance the induced magnetic field. Initial increments in the nanoparticle volume fraction for both MgO and Ni suppress the magnetic induction near the wall, although, subsequently, when further from the wall, this effect is reversed. Temperature is enhanced with heat generation, whereas it is depleted with heat absorption and thermal slip effects. Overall, excellent thermal enhancement is achieved by the hybrid nanofluid.}, } @article {pmid35401713, year = {2022}, author = {Fang, L and Li, H and Li, B}, title = {Dynamic Analysis of Deep Water Highway Tunnel under Ocean Current.}, journal = {Computational intelligence and neuroscience}, volume = {2022}, number = {}, pages = {9551792}, pmid = {35401713}, issn = {1687-5273}, abstract = {Comprehensively comparing the merits and demerits of the existing means of transportation across the water, a new underwater transportation structure for crossing the wide water area, named as "deep water highway tunnel" (hereinafter called "DWHT"), is proposed. The characteristics of flow field around the typical section of DWHT at different flow velocities are investigated, which can provide reference for the values of hydrodynamic coefficient at high Reynolds number. The vibration modes and natural by the sound-solid coupling method. In addition, considering the factors of fluid-structure coupling, the dynamic response of displacement and internal force is analyzed based on CFD for the weak parts of the structure. The results show that the deepening of water and the increase of flow will significantly increase the flow field pressure and structure stress, and when the span (or width-span ratio) of the tunnel body extends beyond a certain range, the dynamic characteristics and dynamic response rules of the structure will change.}, } @article {pmid35393485, year = {2022}, author = {Ghorbani, N and Targhi, MZ and Heyhat, MM and Alihosseini, Y}, title = {Investigation of wavy microchannel ability on electronic devices cooling with the case study of choosing the most efficient microchannel pattern.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {5882}, pmid = {35393485}, issn = {2045-2322}, abstract = {A numerical study was conducted to investigate the ability of wavy microchannels to damp the temperature fluctuations generates in electronic devices. Five wavy patterns are considered with the amplitude and wavelength in the ranges of 62.5 to 250 μm and 1250 to 5000 μm, respectively to study the effect of governing phenomena of flow within wavy patterns on thermal-hydraulic performance. The flow regime is laminar and the Reynolds number is in the range of 300 to 900, and a relatively high heat flux of 80 W/cm[2] is applied to the microchannels substrate. Also, variable flux condition is studied for heat fluxes of 80, 120, 160, 200, and 240 W/cm[2] and for the most efficient wavy and straight microchannels. Results showed that the geometries with larger amplitude to wavelength ratio have a lower radius of curvature and larger Dean number, and as a result of transverse flow (secondary flow) amplification, they have enhanced heat transfer. Also, by comparing the ratio of the transverse velocity components to the axial component, it was found that by decreasing the radius of curvature and increasing the Dean number, transverse velocity increases, which intensifies the heat transfer between the wall and the fluid. The appraisement of the performance evaluation criterion (PEC) illustrates that the wavy case with an amplitude of 250 μm and wavelength of 2500 μm is the best geometry from the thermal-hydraulic point of view in the studied range. Finally, with variable flux condition, the wavy microchannel has responded well to the temperature increase and has created a much more uniform surface temperature compared to straight pattern. The proposed wavy pattern ensures that there are no hotspots which could damage the electronic chip. Presented wavy patterns can be used in heat sinks heat transfer enhancement to allow the chip to run in higher heat fluxes.}, } @article {pmid35390073, year = {2022}, author = {Almerol, JLO and Liponhay, MP}, title = {Clustering of fast gyrotactic particles in low-Reynolds-number flow.}, journal = {PloS one}, volume = {17}, number = {4}, pages = {e0266611}, pmid = {35390073}, issn = {1932-6203}, mesh = {Cluster Analysis ; Computer Simulation ; *Hydrodynamics ; Physical Phenomena ; *Swimming ; }, abstract = {Systems of particles in turbulent flows exhibit clustering where particles form patches in certain regions of space. Previous studies have shown that motile particles accumulate inside the vortices and in downwelling regions, while light and heavy non-motile particles accumulate inside and outside the vortices, respectively. While strong clustering is generated in regions of high vorticity, clustering of motile particles is still observed in fluid flows where vortices are short-lived. In this study, we investigate the clustering of fast swimming particles in a low-Reynolds-number turbulent flow and characterize the probability distributions of particle speed and acceleration and their influence on particle clustering. We simulate gyrotactic swimming particles in a cubic system with homogeneous and isotropic turbulent flow. Here, the swimming velocity explored is relatively faster than what has been explored in other reports. The fluid flow is produced by conducting a direct numerical simulation of the Navier-Stokes equation. In contrast with the previous results, our results show that swimming particles can accumulate outside the vortices, and clustering is dictated by the swimming number and is invariant with the stability number. We have also found that highly clustered particles are sufficiently characterized by their acceleration, where the increase in the acceleration frequency distribution of the most clustered particles suggests a direct influence of acceleration on clustering. Furthermore, the acceleration of the most clustered particles resides in acceleration values where a cross-over in the acceleration PDFs are observed, an indicator that particle acceleration generates clustering. Our findings on motile particles clustering can be applied to understanding the behavior of faster natural or artificial swimmers.}, } @article {pmid35389496, year = {2022}, author = {Letendre, F and Cameron, CB}, title = {The capture of crude oil droplets by filter feeders at high and low Reynolds numbers.}, journal = {The Journal of experimental biology}, volume = {225}, number = {8}, pages = {}, doi = {10.1242/jeb.243819}, pmid = {35389496}, issn = {1477-9145}, mesh = {Animals ; Daphnia ; Food Chain ; *Petroleum ; *Petroleum Pollution ; *Thoracica ; }, abstract = {Crustacean filter feeders capture oil droplets with the use of their ramified appendages. These appendages behave as paddles or sieves, based on the system's Reynolds number. Here, we used high-speed videography, scanning electron microscopy and fluid mechanics to study the capturing mechanisms of crude oil droplets and the filtering appendage's wettability by two species of barnacles (Balanus glandula and Balanus crenatus) and of the freshwater cladoceran Daphnia magna. Our results show that barnacle appendages behave as paddles and capture droplets in their boundary layers at low Reynolds number. At high Reynolds number, droplets are most likely to be captured via direct interception. There is an intermediate range of Reynolds number where droplets can be captured by both mechanisms at the same time. Daphnia magna captures droplets in the boundary layers of the third and fourth pair of thoracic legs with a metachronal motion of the appendages. All studied surfaces were revealed to be highly lipophobic, demonstrating captured oil droplets with high contact angles. We also discuss implications of such capture mechanisms and wettability on potential ingestion of crude oil by filter feeders. These results further our understanding of the capture of crude oil by filter feeders, shedding light on the main entry point of oil in marine food webs.}, } @article {pmid35385160, year = {2022}, author = {Wang, J and Dong, Y and Ma, P and Wang, Y and Zhang, F and Cai, B and Chen, P and Liu, BF}, title = {Intelligent Micro-/Nanorobots for Cancer Theragnostic.}, journal = {Advanced materials (Deerfield Beach, Fla.)}, volume = {}, number = {}, pages = {e2201051}, doi = {10.1002/adma.202201051}, pmid = {35385160}, issn = {1521-4095}, abstract = {Cancer is one of the most intractable diseases owing to its high mortality rate and lack of effective diagnostic and treatment tools. Advancements in micro-/nanorobot (MNR)-assisted sensing, imaging, and therapeutics offer unprecedented opportunities to develop MNR-based cancer theragnostic platforms. Unlike ordinary nanoparticles, which exhibit Brownian motion in biofluids, MNRs overcome viscous resistance in an ultralow Reynolds number (Re << 1) environment by effective self-propulsion. This unique locomotion property has motivated the advanced design and functionalization of MNRs as a basis for next-generation cancer-therapy platforms, which offer the potential for precise distribution and improved permeation of therapeutic agents. Enhanced barrier penetration, imaging-guided operation, and biosensing are additionally studied to enable the promising cancer-related applications of MNRs. Herein, the recent advances in MNR-based cancer therapy are comprehensively addresses, including actuation engines, diagnostics, medical imaging, and targeted drug delivery; promising research opportunities that can have a profound impact on cancer therapy over the next decade is highlighted.}, } @article {pmid35379035, year = {2022}, author = {Saeed Khan, MW and Ali, N and Bég, OA}, title = {Thermal entrance problem for blood flow inside an axisymmetric tube: The classical Graetz problem extended for Quemada's bio-rheological fluid with axial conduction.}, journal = {Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine}, volume = {236}, number = {6}, pages = {848-859}, doi = {10.1177/09544119221086479}, pmid = {35379035}, issn = {2041-3033}, mesh = {*Algorithms ; *Hemodynamics ; Hot Temperature ; Humans ; Rheology ; Viscosity ; }, abstract = {The heat-conducting nature of blood is critical in the human circulatory system and features also in important thermal regulation and blood processing systems in biomedicine. Motivated by these applications, in the present investigation, the classical Graetz problem in heat transfer is extended to the case of a bio-rheological fluid model. The Quemada bio-rheological fluid model is selected since it has been shown to be accurate in mimicking physiological flows (blood) at different shear rates and hematocrits. The steady two-dimensional energy equation without viscous dissipation in stationary regime is tackled via a separation of variables approach for the isothermal wall temperature case. Following the introduction of transformation variables, the ensuing dimensionless boundary value problem is solved numerically via MATLAB based algorithm known as bvp5c (a finite difference code that implements the four-stage Lobatto IIIa collocation formula). Numerical validation is also presented against two analytical approaches namely, series solutions and Kummer function techniques. Axial conduction in terms of Péclet number is also considered. Typical values of Reynolds number and Prandtl number are used to categorize the vascular regions. The graphical representation of mean temperature, temperature gradient, and Nusselt numbers along with detail discussions are presented for the effects of Quemada non-Newtonian parameters and Péclet number. The current analysis may also have potential applications for the development of microfluidic and biofluidic devices particularly which are used in the diagnosis of diseases in addition to blood oxygenation technologies.}, } @article {pmid35363001, year = {2022}, author = {Tan, S and Ni, R}, title = {Universality and Intermittency of Pair Dispersion in Turbulence.}, journal = {Physical review letters}, volume = {128}, number = {11}, pages = {114502}, doi = {10.1103/PhysRevLett.128.114502}, pmid = {35363001}, issn = {1079-7114}, abstract = {Turbulence can disperse a concentrated parcel of pollutants at a rate over nine orders of magnitude higher than its purely diffusive counterpart. One intriguing signature of turbulent dispersion is its superdiffusive scaling. However, the universality of this scaling law is still in question. By leveraging a new laboratory facility, particle pairs with small initial separations can be tracked over four decades of separation in time and five decades of separation in squared displacement, thereby observing the full range of dispersion scaling laws. The results show that the classical Richardson cubic scaling will be reached not for an initial separation asymptotically close to zero but at a critical value, and this value does not appear to depend on the Reynolds number, providing an effective way to study universal dispersion dynamics. Additionally, the results agree well with the prediction based on the multifractal model and may help reconcile different reported scaling laws from laboratory experiments and field studies.}, } @article {pmid35355005, year = {2022}, author = {Kamdar, S and Shin, S and Leishangthem, P and Francis, LF and Xu, X and Cheng, X}, title = {The colloidal nature of complex fluids enhances bacterial motility.}, journal = {Nature}, volume = {603}, number = {7903}, pages = {819-823}, pmid = {35355005}, issn = {1476-4687}, mesh = {Bacteria ; *Colloids ; *Ecosystem ; Humans ; Hydrodynamics ; Polymers ; }, abstract = {The natural habitats of microorganisms in the human microbiome, ocean and soil ecosystems are full of colloids and macromolecules. Such environments exhibit non-Newtonian flow properties, drastically affecting the locomotion of microorganisms[1-5]. Although the low-Reynolds-number hydrodynamics of swimming flagellated bacteria in simple Newtonian fluids has been well developed[6-9], our understanding of bacterial motility in complex non-Newtonian fluids is less mature[10,11]. Even after six decades of research, fundamental questions about the nature and origin of bacterial motility enhancement in polymer solutions are still under debate[12-23]. Here we show that flagellated bacteria in dilute colloidal suspensions display quantitatively similar motile behaviours to those in dilute polymer solutions, in particular a universal particle-size-dependent motility enhancement up to 80% accompanied by a strong suppression of bacterial wobbling[18,24]. By virtue of the hard-sphere nature of colloids, whose size and volume fraction we vary across experiments, our results shed light on the long-standing controversy over bacterial motility enhancement in complex fluids and suggest that polymer dynamics may not be essential for capturing the phenomenon[12-23]. A physical model that incorporates the colloidal nature of complex fluids quantitatively explains bacterial wobbling dynamics and mobility enhancement in both colloidal and polymeric fluids. Our findings contribute to the understanding of motile behaviours of bacteria in complex fluids, which are relevant for a wide range of microbiological processes[25] and for engineering bacterial swimming in complex environments[26,27].}, } @article {pmid35338884, year = {2022}, author = {Mezali, F and Benmamar, S and Naima, K and Ameur, H and Rafik, O}, title = {Evaluation of stent effect and thrombosis generation with different blood rheology on an intracranial aneurysm by the Lattice Boltzmann method.}, journal = {Computer methods and programs in biomedicine}, volume = {219}, number = {}, pages = {106757}, doi = {10.1016/j.cmpb.2022.106757}, pmid = {35338884}, issn = {1872-7565}, mesh = {Blood Flow Velocity ; Hemodynamics/physiology ; Humans ; *Intracranial Aneurysm/surgery ; Rheology ; Stents ; *Thrombosis/prevention & control ; }, abstract = {BACKGROUND AND OBJECTIVE: Treatment of intracranial aneurysms with flow-diverting stents prevents rupture by reducing blood flow and creating thrombosis within the aneurysm. This paper aims to assess the hemodynamic effect of placing stents with different struts (0, 3, 5, 7 struts) on intracranial aneurysms and to propose a simple prediction model of thrombosis zone without any further computational cost.

METHOD: Lattice Boltzmann method with different rheological models (Newtonian, Carreau-Yasuda, KL) of blood are used to study the hemodynamic effect of flow-diverting stents in the aneurysm. Pulsatile flow boundary conditions were applied in the inlet of the artery. The average Reynolds number was resulting Re = 111. The Lagrangian tracking of the particle was developed to assess the intra-aneurysmal blood stagnation. To predict the probable thrombose zone induced by flow-diverting stents, the shear rate threshold is utilized to determine the nodes of fluid to clot.

RESULTS: The results show that the flow patterns into the aneurysmal sac develop a vortex, decreasing after stent placement until disappearance for the stent with seven struts (porosity 71.4%). Velocity, shear rate, shear stress, trajectory, path length, and occlusion rate are compared before and after stent placement. These parameters decrease inversely with the porosity of the stent. The three models yield a closes result of the (velocity, shear rate, occlusion rate). Tracking the fluid-particle trajectory shows that the length of the particle paths decreases with the number of struts causing fluid to slow down and increase, consequently, the residence time into the sac.

CONCLUSION: The flow-diverting stents placement cause the reduction of dynamic flow within aneurysm. The reduction effect is almost the same below five struts (80% of porosity). The results show that, if our objective is restricted to estimating the hemodynamic effect, measured by (velocity, shear rate, occlusion rate), the differences between rheological behavior models are, practically, not significant, and the models can be used indifferently.}, } @article {pmid35334666, year = {2022}, author = {Nuwairan, MA and Souayeh, B}, title = {Simulation of Gold Nanoparticle Transport during MHD Electroosmotic Flow in a Peristaltic Micro-Channel for Biomedical Treatment.}, journal = {Micromachines}, volume = {13}, number = {3}, pages = {}, pmid = {35334666}, issn = {2072-666X}, abstract = {The study of gold nanoparticles (AuNPs) in the blood flow has emerged as an area of interest for numerous researchers, due to its many biomedical applications, such as cancer radiotherapy, DNA and antigens, drug and gene delivery, in vitro evaluation, optical bioimaging, radio sensitization and laser phototherapy of cancer cells and tumors. Gold nanoparticles can be amalgamated in various shapes and sizes. Due to this reason, gold nanoparticles can be diffused efficiently, target the diseased cells and destroy them. The current work studies the effect of gold nanoparticles of different shapes on the electro-magneto-hydrodynamic (EMHD) peristaltic propulsion of blood in a micro-channel under various effects, such as activation energy, bioconvection, radiation and gyrotactic microorganisms. Four kinds of nanoparticle shapes, namely bricks, cylinders and platelets, are considered. The governing equations are simplified under the approximations of low Reynolds number (LRN), long wavelength (LWL) and Debye-Hückel linearization (DHL). The numerical solutions for the non-dimensional equations are solved using the computational software MATLAB with the help of the bvp4c function. The influences of different physical parameters on the flow and thermal characteristics are computed through pictorial interpretations.}, } @article {pmid35329572, year = {2022}, author = {Sawka, A}, title = {Chemical Vapour Deposition of Scandia-Stabilised Zirconia Layers on Tubular Substrates at Low Temperatures.}, journal = {Materials (Basel, Switzerland)}, volume = {15}, number = {6}, pages = {}, pmid = {35329572}, issn = {1996-1944}, abstract = {The paper presents results of investigation on synthesis of non-porous ZrO2-Sc2O2 layers on tubular substrates by MOCVD (metalorganic chemical vapor deposition) method using Sc(tmhd)3 (Tris(2,2,6,6-tetramethyl-3,5-heptanedionato)scandium(III), 99%) and Zr(tmhd)4 (Tetrakis(2,2,6,6-tetramethyl-3,5-heptanedionato)zirconium)(IV), 99.9+%) as basic reactants. The molar content of Sc(tmhd)3 in the gas mixture was as follows: 14, 28%. The synthesis temperature was in the range of 600-700 °C. The value of extended Grx/Rex[2] expression (Gr-Grashof number, Re-Reynolds number and x-the distance from the gas inflow point) was less than 0.01. The layers were deposited under reduced pressure or close to atmospheric pressure. The layers obtained were tested using scanning electron microscope (SEM) with an energy dispersive X-ray spectroscope (EDS) microanalyzer, X-ray diffractometer and UV-Vis spectrophotometer. The layers deposited were non-porous, amorphous or nanocrystalline with controlled chemical composition. The layers synthesized at 700 °C were nanocrystalline. ZrO2-Sc2O3 layers with 14 mol.% Sc2O3 content had a rhombohedral structure.}, } @article {pmid35327926, year = {2022}, author = {Lin, W and Shi, R and Lin, J}, title = {Heat Transfer and Pressure Drop of Nanofluid with Rod-like Particles in Turbulent Flows through a Curved Pipe.}, journal = {Entropy (Basel, Switzerland)}, volume = {24}, number = {3}, pages = {}, pmid = {35327926}, issn = {1099-4300}, abstract = {Pressure drop, heat transfer, and energy performance of ZnO/water nanofluid with rodlike particles flowing through a curved pipe are studied in the range of Reynolds number 5000 ≤ Re ≤ 30,000, particle volume concentration 0.1% ≤ Φ ≤ 5%, Schmidt number 10[4] ≤ Sc ≤ 3 × 10[5], particle aspect ratio 2 ≤ λ ≤ 14, and Dean number 5 × 10[3] ≤ De ≤ 1.5 × 10[4]. The momentum and energy equations of nanofluid, together with the equation of particle number density for particles, are solved numerically. Some results are validated by comparing with the experimental results. The effect of Re, Φ, Sc, λ, and De on the friction factor f and Nusselt number Nu is analyzed. The results showed that the values of f are increased with increases in Φ, Sc, and De, and with decreases in Re and λ. The heat transfer performance is enhanced with increases in Re, Φ, λ, and De, and with decreases in Sc. The ratio of energy PEC for nanofluid to base fluid is increased with increases in Re, Φ, λ, and De, and with decreases in Sc. Finally, the formula of ratio of energy PEC for nanofluid to base fluid as a function of Re, Φ, Sc, λ, and De is derived based on the numerical data.}, } @article {pmid35327850, year = {2022}, author = {Dou, HS}, title = {No Existence and Smoothness of Solution of the Navier-Stokes Equation.}, journal = {Entropy (Basel, Switzerland)}, volume = {24}, number = {3}, pages = {}, pmid = {35327850}, issn = {1099-4300}, abstract = {The Navier-Stokes equation can be written in a form of Poisson equation. For laminar flow in a channel (plane Poiseuille flow), the Navier-Stokes equation has a non-zero source term (∇[2]u(x, y, z) = Fx (x, y, z, t) and a non-zero solution within the domain. For transitional flow, the velocity profile is distorted, and an inflection point or kink appears on the velocity profile, at a sufficiently high Reynolds number and large disturbance. In the vicinity of the inflection point or kink on the distorted velocity profile, we can always find a point where ∇[2]u(x, y, z) = 0. At this point, the Poisson equation is singular, due to the zero source term, and has no solution at this point due to singularity. It is concluded that there exists no smooth orphysically reasonable solutions of the Navier-Stokes equation for transitional flow and turbulence in the global domain due to singularity.}, } @article {pmid35299996, year = {2022}, author = {Marchello, R and Morandotti, M and Shum, H and Zoppello, M}, title = {The N -Link Swimmer in Three Dimensions: Controllability and Optimality Results.}, journal = {Acta applicandae mathematicae}, volume = {178}, number = {1}, pages = {6}, pmid = {35299996}, issn = {0167-8019}, abstract = {The controllability of a fully three-dimensional N -link swimmer is studied. After deriving the equations of motion in a low Reynolds number fluid by means of Resistive Force Theory, the controllability of the minimal 2-link swimmer is tackled using techniques from Geometric Control Theory. The shape of the 2-link swimmer is described by two angle parameters. It is shown that the associated vector fields that govern the dynamics generate, via taking their Lie brackets, all eight linearly independent directions in the combined configuration and shape space, leading to controllability; the swimmer can move from any starting configuration and shape to any target configuration and shape by operating on the two shape variables. The result is subsequently extended to the N -link swimmer. Finally, the minimal time optimal control problem and the minimization of the power expended are addressed and a qualitative description of the optimal strategies is provided.}, } @article {pmid35297830, year = {2022}, author = {Wang, Y and Zhao, W and Wang, B and Wang, Y}, title = {Prediction model of combustion characteristics of methane-air using hyperspectral imaging.}, journal = {Applied optics}, volume = {61}, number = {7}, pages = {D75-D84}, doi = {10.1364/AO.444118}, pmid = {35297830}, issn = {1539-4522}, abstract = {Hyperspectral imaging can obtain considerable flame information, which can improve the prediction accuracy of combustion characteristics. This paper studies the hyperspectral characteristics of methane flames and proposes several prediction models. The experimental results show that the radiation intensity and radiation types of free radicals are related to the equivalent ratio, and the radiation region of free radicals becomes larger with the increase of the Reynolds number. The polynomial regression prediction models include the linear model and quadratic model. It takes C2∗/CH[∗] as input parameters, and results can be available immediately. The three-dimensional convolutional neural network (3D-CNN) prediction model takes all spectral and spatial information in the flame hyperspectral image as input parameters. By improving the structural parameters of the convolution network, the final prediction errors of the equivalent ratio and Reynolds number are 2.84% and 3.11%, respectively. The method of combining the 3D-CNN model with hyperspectral imaging significantly improves the prediction accuracy, and it can be used to predict other combustion characteristics such as pollutant emissions and combustion efficiency.}, } @article {pmid35291149, year = {2022}, author = {Ma, X and Gong, X and Tang, Z and Jiang, N}, title = {Control of leading-edge separation on bioinspired airfoil with fluttering coverts.}, journal = {Physical review. E}, volume = {105}, number = {2-2}, pages = {025107}, doi = {10.1103/PhysRevE.105.025107}, pmid = {35291149}, issn = {2470-0053}, abstract = {In this work, the aerodynamic role of the artificial covert feathers (i.e., coverts) on an airfoil is experimentally studied in a wind tunnel to investigate the flow control effect on the leading-edge separation. We apply flexible featherlike devices on a high-angle-of-attack airfoil. We use a hot-wire anemometer to measure the velocity profiles and turbulent fluctuations in the downstream wake flow. As a baseline of flow separation, a two-dimensional NACA 0018 airfoil model is set at the angle of attack of 15 ° at the chord-based Reynolds number of 1.0×10^{5}, causing strong leading-edge and trailing-edge shear layers and a low-speed wake flow area in between as large as 0.35 chord length. When deployed on the upper wing surface, the flexible coverts adaptively flutter under the influence of the local unsteady airflow. Hot-wire measurement results show that the leading-edge coverts effectively suppress the flow separation and reduce the size of the wake flow area. The change of power spectral density shows that the predominant peaks as the fundamental and harmonic frequencies are both attenuated due to the suppression of unsteady motions of the shear layers. On the other hand, the fluttering coverts at the trailing edge modify the trailing-edge shear layer by redistributing the turbulent kinetic energy to the high-frequency components. By simultaneous double-point measurement, we find that the leading-edge and trailing-edge shear layers are drawn closer to each other, and the two shear layers show an increased peak in the coherence spectrum. Further multiscale wavelet analysis shows that the perturbations at the 60% chord length increase the large-scale amplitude modulation of small-scale turbulence and therefore they stabilize the leading-edge and trailing-edge shear layers. Meanwhile, the flow intermittency outside of the wake flow area is attenuated as well. The effective flow control effects in the present work are in good agreement with the previous direct observations of bird flight in literature that the coverts on the upper wing surface play an important role in flow separation control during high-angle-of-attack flight. These findings advance the understanding of aerodynamic contribution of the covers on bird wings and reveal the engineering potential of bioinspired coverts for flow separation control of aircrafts and unmanned air vehicles.}, } @article {pmid35270649, year = {2022}, author = {Ovando-Chacon, GE and Rodríguez-León, A and Ovando-Chacon, SL and Hernández-Ordoñez, M and Díaz-González, M and Pozos-Texon, FJ}, title = {Computational Study of Thermal Comfort and Reduction of CO2 Levels inside a Classroom.}, journal = {International journal of environmental research and public health}, volume = {19}, number = {5}, pages = {}, pmid = {35270649}, issn = {1660-4601}, mesh = {*Air Pollution, Indoor/analysis/prevention & control ; *COVID-19/epidemiology ; Carbon Dioxide/analysis ; Humans ; Pandemics ; SARS-CoV-2 ; }, abstract = {Due to the current COVID-19 pandemic, guaranteeing thermal comfort and low CO2 levels in classrooms through efficient ventilation has become vitally important. This study presents three-dimensional simulations based on computational fluid dynamics of airflow inside an air-conditioned classroom located in Veracruz, Mexico. The analysis included various positions of an air extractor, Reynolds numbers up to 3.5 × 10[4], four different concentrations of pollutant sources, and three different times of the day. The simulations produced velocity, air temperature, and CO2 concentrations fields, and we calculated average air temperatures, average CO2 concentrations, and overall ventilation effectiveness. Our results revealed an optimal extractor position and Reynolds number conducive to thermal comfort and low CO2 levels due to an adequate ventilation configuration. At high pollutant concentrations, it is necessary to reduce the number of students in the classroom to achieve safe CO2 levels.}, } @article {pmid35264611, year = {2022}, author = {Memon, AA and Memon, MA and Bhatti, K and Khan, I and Alshammari, N and Al-Johani, AS and Hamadneh, NN and Andualem, M}, title = {Thermal decomposition of propylene oxide with different activation energy and Reynolds number in a multicomponent tubular reactor containing a cooling jacket.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {4169}, pmid = {35264611}, issn = {2045-2322}, abstract = {In this article, we are focusing on heat and mass transfer through a Multicomponent tubular reactor containing a cooling jacket by thermal decomposition of propylene oxide in water. The chemical reaction is an irreversible, 1st order reaction and an exothermic reaction that yields propylene glycol with enthalpy = -84,666 J/mol. The constant rate of the reaction is followed by the Arrhenius equation in which the activation energy is taken on a trial basis in the range from 75,000 to 80,000 J/mol with a fixed frequency factor. For the fluid to flow, the Reynolds number is kept in the range from 100 to 1000. The three partial differential equations of mass, momentum, and energy are coupled to study heat and mass transfer in a tubular reactor by using the chemistry interface in COMSOL Multiphysics 5.4. The initial concentration of propylene oxide is tested in the range from 2 to 3% and the thermal conductivity of the mixture is tested in the range 0.599-0.799. It was found that the amount deactivated of the compound decreases with an increase in Reynolds number. Propylene oxide is decomposed at about 99.8% at Re = 100 at lower activation energy and gives the total maximum enthalpy change in the tubular reactor. Observing the relationship between Sherwood numbers to Nusselt numbers, it was deducted that the convective heat transfer is opposite to convective mass transfer for high Reynolds numbers.}, } @article {pmid35236870, year = {2022}, author = {Khan, Z and Ul Haq, S and Ali, F and Andualem, M}, title = {Free convection flow of second grade dusty fluid between two parallel plates using Fick's and Fourier's laws: a fractional model.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {3448}, pmid = {35236870}, issn = {2045-2322}, abstract = {The paper aims to investigate the channel flow of second grade visco-elastic fluid generated due to an oscillating wall. The effect of heat and mass transfer has been taken into account. The phenomenon has been modelled in terms of PDEs. The constitutive equations are fractionalized by using the definition of the Caputo fractional operator with Fick's and Fourier's Laws. The system of fractional PDEs is non-dimensionalized by using appropriate dimensionless variables. The closed-form solutions of thermal and concentration boundary layers are obtained by using the Laplace and finite Fourier-Sine transforms, while the momentum equation is solved by a numerical approach by Zakian using [Formula: see text]. Furthermore, the parametric influence of various embedded physical parameters on momentum, temperature, and concentration distributions is depicted through various graphs. It is observed that the fractional approach is more convenient and realistic as compared to the classical approach. It is worth noting that the increasing values of [Formula: see text], [Formula: see text] and [Formula: see text] retard the boundary layer profile. For instance, this behaviour of [Formula: see text] is significant where boundary control is necessary. That is, in the case of resonance, the physical solution may be obtained by adding the effect of MHD. The Reynolds number is useful in characterising the transport properties of a fluid or a particle travelling through a fluid. The Reynolds number is one of the main controlling parameters in all viscous flow. It determines whether the fluid flow is laminar or turbulent. The evolution of the rate of heat, mass transfer, and skin friction on the left plate with various physical parameters are presented in tables. These quantities are of high interest for engineers. Keeping in mind the effect of various parameters on these engineering quantities, they make their feasibility reports.}, } @article {pmid35233704, year = {2022}, author = {Cai, C and Wen, C and Guan, L and Huang, Y and Jiang, Q}, title = {Influence of sodium hypochlorite concentration on cavitation effect and fluid dynamics induced by photon-induced photoacoustic streaming (PIPS): A visualization study.}, journal = {Lasers in medical science}, volume = {37}, number = {5}, pages = {2537-2544}, pmid = {35233704}, issn = {1435-604X}, mesh = {Dental Pulp Cavity ; Hydrodynamics ; Photons/therapeutic use ; *Root Canal Irrigants/pharmacology ; Root Canal Preparation ; *Sodium Hypochlorite/pharmacology ; }, abstract = {PURPOSE: The aim of the present study was to visualize and compare the cavitation effect and fluid dynamics induced by photon-induced photoacoustic streaming (PIPS) using sodium hypochlorite (NaOCl) with different concentrations as irrigant.

METHODS: Forty artificial root canals were prepared using MTWO Niti file up to size #25/.06. The canals were randomly divided into four groups (n = 10/group). High-speed camera was used to visualize and compare the cavitation effect induced by PIPS in the artificial root canals containing saline or NaOCl. Fluid velocity and Reynolds number of saline, 1%-, 2.5%- and 5.25% NaOCl irrigants induced by PIPS in the apical region were calculated using TEMA 2D software while the fluid motions were recorded.

RESULTS: Visualization profile revealed that NaOCl presented a stronger cavitation effect and fluid dynamics than saline during PIPS activation. In the apical region, 1% NaOCl group presented the highest average velocity of 3.868 m/s, followed by 2.5% NaOCl group (3.685 m/s), 5.25% NaOCl group (2.353 m/s) and saline group (1.268 m/s), corresponding to Reynolds number of 1653.173, 1572.196, 995.503 and 477.692. Statistically higher fluid velocity was calculated in 1% and 2.5% NaOCl groups compared to saline group, respectively (p < 0.05).

CONCLUSIONS: The application of NaOCl and its concentration significantly influence the cavitation effect and fluid dynamics during PIPS activation. 1% and 2.5% NaOCl groups presented a more violent fluid motion in the apical region when activated by PIPS.}, } @article {pmid35232981, year = {2022}, author = {Abd-Alla, AM and Thabet, EN and Bayones, FS}, title = {Numerical solution for MHD peristaltic transport in an inclined nanofluid symmetric channel with porous medium.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {3348}, pmid = {35232981}, issn = {2045-2322}, abstract = {The significance of the study is to determine of transferred heat and mass impact on the magneto-hydrodynamic peristalsis of Jeffery nanofluid through porous media with inclined symmetric channels whose walls are induced by peristaltic motion within porous media. The aim of this investagtion is to study the influence of various types of parameters such as Brownian motion, thermophoresis, buoyancy forces, and magnetic fields are studies on concentration, temperature, and axial velocity. The numerical solution has been achieved according to the long-wavelength and low Reynolds number approximation utilizing the MATLAB bvp4c function. The resultant dimensions of nonlinear governing equations were approached numerically through the Runge-Kutta- Fehlberg integration scheme, a MATLAB program. The influence of different factors such as the ratio of relaxation to retardation times, nanoparticle Grashof number, and magnetic field was discussed on concentration, temperature, and velocity profiles. tables and graphs were used to demonstrate the numerically computed numerical results. Plotting graphs were utilized for evaluating the pertinent parameters impacts on the aforementioned quantities based on computational results. According to the findings, the effect of the parameters are significant.}, } @article {pmid35214965, year = {2022}, author = {Khan, NA and Sulaiman, M and Tavera Romero, CA and Alshammari, FS}, title = {Analysis of Nanofluid Particles in a Duct with Thermal Radiation by Using an Efficient Metaheuristic-Driven Approach.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {12}, number = {4}, pages = {}, pmid = {35214965}, issn = {2079-4991}, abstract = {This study investigated the steady two-phase flow of a nanofluid in a permeable duct with thermal radiation, a magnetic field, and external forces. The basic continuity and momentum equations were considered along with the Buongiorno model to formulate the governing mathematical model of the problem. Furthermore, the intelligent computational strength of artificial neural networks (ANNs) was utilized to construct the approximate solution for the problem. The unsupervised objective functions of the governing equations in terms of mean square error were optimized by hybridizing the global search ability of an arithmetic optimization algorithm (AOA) with the local search capability of an interior point algorithm (IPA). The proposed ANN-AOA-IPA technique was implemented to study the effect of variations in the thermophoretic parameter (Nt), Hartmann number (Ha), Brownian (Nb) and radiation (Rd) motion parameters, Eckert number (Ec), Reynolds number (Re) and Schmidt number (Sc) on the velocity profile, thermal profile, Nusselt number and skin friction coefficient of the nanofluid. The results obtained by the designed metaheuristic algorithm were compared with the numerical solutions obtained by the Runge-Kutta method of order 4 (RK-4) and machine learning algorithms based on a nonlinear autoregressive network with exogenous inputs (NARX) and backpropagated Levenberg-Marquardt algorithm. The mean percentage errors in approximate solutions obtained by ANN-AOA-IPA are around 10-6 to 10-7. The graphical analysis illustrates that the velocity, temperature, and concentration profiles of the nanofluid increase with an increase in the suction parameter, Eckert number and Schmidt number, respectively. Solutions and the results of performance indicators such as mean absolute deviation, Theil's inequality coefficient and error in Nash-Sutcliffe efficiency further validate the proposed algorithm's utility and efficiency.}, } @article {pmid35214944, year = {2022}, author = {Apmann, K and Fulmer, R and Scherer, B and Good, S and Wohld, J and Vafaei, S}, title = {Nanofluid Heat Transfer: Enhancement of the Heat Transfer Coefficient inside Microchannels.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {12}, number = {4}, pages = {}, pmid = {35214944}, issn = {2079-4991}, abstract = {The purpose of this paper is to investigate the effects of a connector between two microchannels, for the first time. A brief literature review is provided to offer a better understanding on the impacts of concentration and the characteristics of nanoparticles on thermal conductivity, viscosity, and, consequently, the heat transfer coefficient inside the microchannels. The given literature review aims to help engineer nanofluids to enhance the heat transfer coefficient inside the microchannels. In this research, Fe3O4 nanoparticles were introduced into the base liquid to enhance the heat transfer coefficient inside the microchannels and to provide a better understanding of the impact of the connector between two microchannels. It was observed that the connector has a significant impact on enhancing the heat transfer coefficient inside the second microchannel, by increasing the level of randomness of molecules and particles prior to entering the second channel. The connector would act to refresh the memory of the fluid before entering the second channel, and as a result, the heat transfer coefficient in the second channel would start at a maximum value. Therefore, the overall heat transfer coefficient in both microchannels would increase for given conditions. The impacts of the Reynolds number and introducing nanoparticles in the base liquid on effects induced by the connector were investigated, suggesting that both factors play a significant role on the connector's impact on the heat transfer coefficient.}, } @article {pmid35209192, year = {2022}, author = {Kim, GB and Park, KH and Kim, SJ}, title = {Hemodynamics and Wall Shear Stress of Blood Vessels in Aortic Coarctation with Computational Fluid Dynamics Simulation.}, journal = {Molecules (Basel, Switzerland)}, volume = {27}, number = {4}, pages = {}, pmid = {35209192}, issn = {1420-3049}, mesh = {Algorithms ; Aorta/abnormalities/diagnostic imaging/physiopathology ; Aortic Coarctation/*diagnosis/*physiopathology ; Blood Flow Velocity ; *Hemodynamics ; Humans ; *Models, Cardiovascular ; *Stress, Mechanical ; }, abstract = {The purpose of this study was to identify the characteristics of blood flow in aortic coarctation based on stenotic shape structure, stenosis rate, and the distribution of the wall load delivered into the blood vessels and to predict the impact on aneurysm formation and rupture of blood vessels by using a computational fluid dynamics modeling method. It was applied on the blood flow in abdominal aortic blood vessels in which stenosis occurred by using the commercial finite element software ADINA on fluid-solid interactions. The results of modeling, with an increasing stenosis rate and Reynolds number, showed the pressure drop was increased and the velocity was greatly changed. When the stenosis rate was the same, the pressure drop and the velocity change were larger in the stenosis with a symmetric structure than in the stenosis with an asymmetric one. Maximal changes in wall shear stress were observed in the area before stenosis and minimal changes were shown in stenosis areas. The minimal shear stress occurred at different locations depending on the stenosis shape models. With an increasing stenosis rate and Reynolds number, the maximal wall shear stress was increased and the minimal wall shear stress was decreased. Through such studies, it is thought that the characteristics of blood flow in the abdominal aorta where a stenosis is formed will be helpful in understanding the mechanism of growth of atherosclerosis and the occurrence and rupture of the abdominal aortic flow.}, } @article {pmid35208284, year = {2022}, author = {Antognoli, M and Tomasi Masoni, S and Mariotti, A and Mauri, R and Salvetti, MV and Brunazzi, E and Galletti, C}, title = {Mixing Improvement in a T-Shaped Micro-Junction through Small Rectangular Cavities.}, journal = {Micromachines}, volume = {13}, number = {2}, pages = {}, pmid = {35208284}, issn = {2072-666X}, abstract = {The T-shaped micro-junction is among the most used geometry in microfluidic applications, and many design modifications of the channel walls have been proposed to enhance mixing. In this work, we investigate through numerical simulations the introduction of one pair of small rectangular cavities in the lateral walls of the mixing channel just downstream of the confluence region. The aim is to preserve the simple geometry that has contributed to spread the practical use of the T-shaped micro-junction while suggesting a modification that should, in principle, work jointly with the vortical structures present in the mixing channel, further enhancing their efficiency in mixing without significant additional pressure drops. The performance is analyzed in the different flow regimes occurring by increasing the Reynolds number. The cavities are effective in the two highly-mixed flow regimes, viz., the steady engulfment and the periodic asymmetric regimes. This presence does not interfere with the formation of the vortical structures that promote mixing by convection in these two regimes, but it further enhances the mixing of the inlet streams in the near-wall region of the mixing channel without any additional cost, leading to better performance than the classical configuration.}, } @article {pmid35207114, year = {2022}, author = {Nichka, V and Mareev, S and Pismenskaya, N and Nikonenko, V and Bazinet, L}, title = {Mathematical Modeling of the Effect of Pulsed Electric Field Mode and Solution Flow Rate on Protein Fouling during Bipolar Membrane Electroacidificaiton of Caseinate Solution.}, journal = {Membranes}, volume = {12}, number = {2}, pages = {}, pmid = {35207114}, issn = {2077-0375}, abstract = {A one-dimensional non-stationary model was developed for a better understanding of the protein fouling formation mechanism during electroacidification of caseinate solution using electrodialysis with bipolar membranes (EDBM) in pulsed electric field (PEF) mode. Four different PEF modes were investigated with pulse-pause durations of 10-10 s, 10-20 s, 10-33 s, 10-50 s. For each current mode 3 different flow rates were considered, corresponding to Reynolds numbers, Re, equal to 187, 374 and 560. The processes are considered in the diffusion boundary layer between the surface of the cation-exchange layer of bipolar membrane and bulk solution of the desalination compartment. The Nernst-Planck and material balance equation systems describe the ion transport. The electroneutrality condition and equilibrium chemical reactions are taken into account. The calculation results using the developed model are in qualitative agreement with the experimental data obtained during the previous experimental part of the study. It is confirmed that both the electrical PEF mode and the flow rate have a significant effect on the thickness (and mass) of the protein fouling during EDBM. Moreover, the choice of the electric current mode has the main impact on the fouling formation rate; an increase in the PEF pause duration leads to a decrease in the amount of fouling. It was shown that an increase in the PEF pause duration from 10 s to 50 s, in combination with an increase in Reynolds number (the flow rate) from 187 to 560, makes it possible to reduce synergistically the mass of protein deposits from 6 to 1.3 mg/cm[2], which corresponds to a 78% decrease.}, } @article {pmid35205589, year = {2022}, author = {Yang, X and Yang, L}, title = {Numerical Study of Entropy Generation in Fully Developed Turbulent Circular Tube Flow Using an Elliptic Blending Turbulence Model.}, journal = {Entropy (Basel, Switzerland)}, volume = {24}, number = {2}, pages = {}, pmid = {35205589}, issn = {1099-4300}, abstract = {As computational fluid dynamics (CFD) advances, entropy generation minimization based on CFD becomes attractive for optimizing complex heat-transfer systems. This optimization depends on the accuracy of CFD results, such that accurate turbulence models, such as elliptic relaxation or elliptic blending turbulence models, become important. The performance of a previously developed elliptic blending turbulence model (the SST&nbsp;k-ω-φ-α model) to predict the rate of entropy generation in the fully developed turbulent circular tube flow with constant heat flux was studied to provide some guidelines for using this class of turbulence model to calculate entropy generation in complex systems. The flow and temperature fields were simulated by using a CFD package, and then the rate of entropy generation was calculated in post-processing. The analytical correlations and results of two popular turbulence models (the realizable k-ε and the shear stress transport (SST) k-ω models) were used as references to demonstrate the accuracy of the SST&nbsp;k-ω-φ-α model. The findings indicate that the turbulent Prandtl number (Prt) influences the entropy generation rate due to heat-transfer irreversibility. Prt = 0.85 produces the best results for the SST&nbsp;k-ω-φ-α model. For the realizable k-ε and SST k-ω models, Prt = 0.85 and Prt = 0.92 produce the best results, respectively. For the realizable k-ε and the SST k-ω models, the two methods used to predict the rate of entropy generation due to friction irreversibility produce the same results. However, for the SST&nbsp;k-ω-φ-α model, the rates of entropy generation due to friction irreversibility predicted by the two methods are different. The difference at a Reynolds number of 100,000 is about 14%. The method that incorporates the effective turbulent viscosity should be used to predict the rate of entropy generation due to friction irreversibility for the SST&nbsp;k-ω-φ-α model. Furthermore, when the temperature in the flow field changes dramatically, the temperature-dependent fluid properties must be considered.}, } @article {pmid35196405, year = {2022}, author = {Xia, N and Jin, B and Jin, D and Yang, Z and Pan, C and Wang, Q and Ji, F and Iacovacci, V and Majidi, C and Ding, Y and Zhang, L}, title = {Decoupling and Reprogramming the Wiggling Motion of Midge Larvae Using a Soft Robotic Platform.}, journal = {Advanced materials (Deerfield Beach, Fla.)}, volume = {34}, number = {17}, pages = {e2109126}, doi = {10.1002/adma.202109126}, pmid = {35196405}, issn = {1521-4095}, mesh = {Animals ; Biomimetics ; Larva ; Locomotion ; *Robotics ; Swimming ; }, abstract = {The efficient motility of invertebrates helps them survive under evolutionary pressures. Reconstructing the locomotion of invertebrates and decoupling the influence of individual basic motion are crucial for understanding their underlying mechanisms, which, however, generally remain a challenge due to the complexity of locomotion gaits. Herein, a magnetic soft robot to reproduce midge larva's key natural swimming gaits is developed, and the coupling effect between body curling and rotation on motility is investigated. Through the authors' systematically decoupling studies using programmed magnetic field inputs, the soft robot (named LarvaBot) experiences various coupled gaits, including biomimetic side-to-side flexures, and unveils that the optimal rotation amplitude and the synchronization of curling and rotation greatly enhance its motility. The LarvaBot achieves fast locomotion and upstream capability at the moderate Reynolds number regime. The soft robotics-based platform provides new insight to decouple complex biological locomotion, and design programmed swimming gaits for the fast locomotion of soft-bodied swimmers.}, } @article {pmid35193246, year = {2022}, author = {Czelusniak, LE and Mapelli, VP and Wagner, AJ and Cabezas-Gómez, L}, title = {Shaping the equation of state to improve numerical accuracy and stability of the pseudopotential lattice Boltzmann method.}, journal = {Physical review. E}, volume = {105}, number = {1-2}, pages = {015303}, doi = {10.1103/PhysRevE.105.015303}, pmid = {35193246}, issn = {2470-0053}, abstract = {It has recently been shown that altering the shape of the metastable and unstable branches of an equation of state (EOS) can substantially improve the numerical accuracy of liquid and vapor densities in the pseudopotential lattice Boltzmann method [Peng et al., Phys. Rev. E 101, 063309 (2020)2470-004510.1103/PhysRevE.101.063309]. We found that this approach reduces stability of the method in nonequilibrium conditions and is unstable for bubbles at low reduced temperatures. Here we present an improved method for altering the shape of the metastable and unstable branches of the EOS which remains stable for both equilibrium and nonequilibrium situations and has no issues with bubbles. We also performed a detailed study of the stability of the methods for a droplet impact on a liquid film for reduced temperatures down to 0.35 with Reynolds number of 300. Our approach remained stable for a density ratio of up to 3.38×10^{4} .}, } @article {pmid35193206, year = {2022}, author = {Richter, SK and Menzel, AM}, title = {Mediated interactions between rigid inclusions in two-dimensional elastic or fluid films.}, journal = {Physical review. E}, volume = {105}, number = {1-1}, pages = {014609}, doi = {10.1103/PhysRevE.105.014609}, pmid = {35193206}, issn = {2470-0053}, abstract = {Interactions between rigid inclusions in continuous three-dimensional linearly elastic solids and low-Reynolds-number viscous fluids have largely been quantified in the past. Prime example systems are given by functionalized elastic composite materials or fluid colloidal suspensions. Here, we address the significantly less frequently studied situation of rigid inclusions in two-dimensional elastic or low-Reynolds-number fluid films. We concentrate on the situation in which disklike inclusions remain well separated from each other and do not get into contact. Specifically, we demonstrate and explain that the logarithmic divergence of the associated Green's function is removed in the absence of net external forces on the inclusions, in line with physical intuition. For instance, this situation applies when only pairwise mutual interactions between the inclusions prevail. Our results will support, for example, investigations on membranes functionalized by appropriate inclusions, both of technical or biological origin, or the dynamics of active microswimmers in appropriately prepared thin films.}, } @article {pmid35190663, year = {2022}, author = {Hamzah, HK and Ali, FH and Hatami, M}, title = {MHD mixed convection and entropy generation of CNT-water nanofluid in a wavy lid-driven porous enclosure at different boundary conditions.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {2881}, pmid = {35190663}, issn = {2045-2322}, abstract = {In this study, Galerkin Finite Element Method or GFEM is used for the modeling of mixed convection with the entropy generation in wavy lid-driven porous enclosure filled by the CNT-water nanofluid under the magnetic field. Two different cases of boundary conditions for hot and cold walls are considered to study the fluid flow (streamlines) and heat transfer (local and average Nusselt numbers) as well as the entropy generation parameters. Richardson (Ri), Darcy (Da), Hartmann angle (γ), Amplitude (A), Number of peaks (N), Volume fraction (φ), Heat generation factor (λ), Hartmann number (Ha) and Reynolds number (Re) are studied parameters in this study which results indicated that at low Richardson numbers (< 1) increasing the inclined angle of magnetic field, decreases the Nu numbers, but at larger Richardson numbers (> 1) it improves the Nu numbers.}, } @article {pmid35184017, year = {2022}, author = {Bakos, V and Gyarmati, B and Csizmadia, P and Till, S and Vachoud, L and Nagy Göde, P and Tardy, GM and Szilágyi, A and Jobbágy, A and Wisniewski, C}, title = {Viscous and filamentous bulking in activated sludge: Rheological and hydrodynamic modelling based on experimental data.}, journal = {Water research}, volume = {214}, number = {}, pages = {118155}, doi = {10.1016/j.watres.2022.118155}, pmid = {35184017}, issn = {1879-2448}, abstract = {Although achieving good activated sludge settleability is a key requirement for meeting effluent quality criteria, wastewater treatment plants often face undesired floc structure changes. Filamentous bulking has widely been studied, however, viscous sludge formation much less investigated so far. Our main goal was to find relationship between sludge floc structure and related rheological properties, moreover, to estimate pressure loss in pipe networks through hydrodynamic modelling of the non-Newtonian flows in case of well settling (ideal-like), viscous and filamentous sludge. Severe viscous and filamentous kinds of bulking were generated separately in continuous-flow lab-scale systems initially seeded with the same reference (ideal-like) biomass and the entire evolution of viscous and filamentous bulking was monitored. The results suggested correlation between the rheological properties and the floc structure transformations, and showed the most appropriate fit for the Herschel-Bulkley model (vs. Power-law and Bingham). Validated computational fluid dynamics studies estimated the pipe pressure loss in a wide Reynolds number range for the initial well settling (reference) and the final viscous and filamentous sludge as well. A practical standard modelling protocol was developed for improving energy efficiency of sludge pumping in different floc structure scenarios.}, } @article {pmid35183949, year = {2022}, author = {Yu, Z and Yang, G and Zhang, W}, title = {A new model for the terminal settling velocity of microplastics.}, journal = {Marine pollution bulletin}, volume = {176}, number = {}, pages = {113449}, doi = {10.1016/j.marpolbul.2022.113449}, pmid = {35183949}, issn = {1879-3363}, mesh = {Environmental Monitoring ; *Microplastics ; Plastics ; *Water Pollutants, Chemical/analysis ; }, abstract = {Microplastic (MP) settling process is important for the transport of microplastic particles (MPs, <5 mm) in water bodies. However, for the control parameter of the drag coefficient (Cd), no generalized formula has been proposed for MPs of different shapes and materials. In this study, a total of 1343 MP settling data were collected from the literature. It was found that the drag law for perfect spheres cannot reasonably predict Cd for MPs with particle Reynolds number of 1-10[3]. A new formula for Cd was developed by introducing the dimensionless particle diameter (d⁎) and two shape descriptors. The absolute error of the new formula is 15.2%, smaller than those (42.5-72.8%) of other existing formulas. Moreover, an explicit model was developed for MP settling velocity by correlating Cd, d⁎, and shape descriptors, with lower absolute error (8.8%) than those (15.4-77.2%) of existing models.}, } @article {pmid35160419, year = {2022}, author = {Faroughi, SA and Roriz, AI and Fernandes, C}, title = {A Meta-Model to Predict the Drag Coefficient of a Particle Translating in Viscoelastic Fluids: A Machine Learning Approach.}, journal = {Polymers}, volume = {14}, number = {3}, pages = {}, pmid = {35160419}, issn = {2073-4360}, abstract = {This study presents a framework based on Machine Learning (ML) models to predict the drag coefficient of a spherical particle translating in viscoelastic fluids. For the purpose of training and testing the ML models, two datasets were generated using direct numerical simulations (DNSs) for the viscoelastic unbounded flow of Oldroyd-B (OB-set containing 12,120 data points) and Giesekus (GI-set containing 4950 data points) fluids past a spherical particle. The kinematic input features were selected to be Reynolds number, 0
METHODS: Computational Fluid Dynamics (CFD) approach is used to simulate the airflow in a neonate, an infant and an adult in sedentary breathing conditions. The healthy CT scans are segmented using MIMICS 21.0 (Materialise, Ann arbor, MI). The patient-specific 3D airway models are analyzed for low Reynolds number flow using ANSYS FLUENT 2020 R2. The applicability of the Grid Convergence Index (GCI) for polyhedral mesh adopted in this work is also verified.

RESULTS: This study shows that the inferior meatus of neonates accounted for only 15% of the total airflow. This was in contrast to the infants and adults who experienced 49 and 31% of airflow at the inferior meatus region. Superior meatus experienced 25% of total flow which is more than normal for the neonate. The highest velocity of 1.8, 2.6 and 3.7 m/s was observed at the nasal valve region for neonates, infants and adults, respectively. The anterior portion of the nasal cavity experienced maximum wall shear stress with average values of 0.48, 0.25 and 0.58 Pa for the neonates, infants and adults.

CONCLUSIONS: The neonates have an underdeveloped nasal cavity which significantly affects their airway distribution. The absence of inferior meatus in the neonates has limited the flow through the inferior regions and resulted in uneven flow distribution.}, } @article {pmid34846896, year = {2021}, author = {Kim, AR and Mitra, SK and Zhao, B}, title = {Reduced Pressure Drop in Viscoelastic Polydimethylsiloxane Wall Channels.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {37}, number = {49}, pages = {14292-14301}, doi = {10.1021/acs.langmuir.1c02087}, pmid = {34846896}, issn = {1520-5827}, mesh = {Biological Transport ; *Dimethylpolysiloxanes ; *Lab-On-A-Chip Devices ; Viscosity ; }, abstract = {Polydimethylsiloxane (PDMS) is an important viscoelastic material that finds applications in a large number of engineering systems, particularly lab-on-chip microfluidic devices built with a flexible substrate. Channels made of PDMS, used for transporting analytes, are integral to these applications. The PDMS viscoelastic nature can induce additional hydrodynamic contributions at the soft wall/fluid interface compared to rigid walls. In this research, we investigated the pressure drop within PDMS channels bounded by rigid tubes (cellulose tubes). The bulging effect of the PDMS was limited by the rigid tubes under flowing fluids. The PDMS viscoelasticity was modulated by changing the ratio of the base to the cross-linker from 10:1 to 35:1. We observed that the pressure drop of the flowing fluids within the channel decreased with the increased loss tangent of the PDMS in the examined laminar regime [Reynolds number (Re) ∼ 23-58.6 for water and Re ∼ 0.69-8.69 for glycerol solution]. The elastic PDMS 10:1 wall channels followed the classical Hagen Poiseuille's equation, but the PDMS walls with lower cross-linker concentrations and thicker walls decreased pressure drops. The friction factor (f) for the PDMS channels with the two working fluids could be approximated as f = 47/Re. We provide a correlation between the pressure drop and PDMS viscoelasticity based on experimental findings. In the correlation, the loss tangent predominates; the larger the loss tangent, the smaller is the pressure drop. The research findings appear to be unexpected if only considering the energy dissipation of viscoelastic PDMS walls. We attributed the reduction in the pressure drop to a lubricating effect of the viscoelastic PDMS walls in the presence of the working fluids. Our results reveal the importance of the subtle diffusion of the residual oligomers and water from the bulk to the soft wall/fluid interface for the observed pressure drop in soft wall channels.}, } @article {pmid34846030, year = {2021}, author = {Chen, X and Zhan, Y and Fu, YI and Lin, J and Ji, Y and Zhao, C and Fang, Y and Wu, J}, title = {The effect of stenosis rate and Reynolds number on local flow characteristics and plaque formation around the atherosclerotic stenosis.}, journal = {Acta of bioengineering and biomechanics}, volume = {23}, number = {1}, pages = {135-147}, pmid = {34846030}, issn = {1509-409X}, mesh = {*Atherosclerosis ; Constriction, Pathologic ; Hemodynamics ; Humans ; *Models, Cardiovascular ; Stress, Mechanical ; }, abstract = {PURPOSE: Atherosclerosis causes plaque to build-up in arteries. Effect of the specific local hemodynamic environment around an atherosclerotic plaque on the thrombosis formation does not remain quite clear but is believed to be crucial. The aim of this study is to uncover the flow effects on plaques formation.

METHODS: To study the mechanically regulated plaque formation, the flow fields in artery blood vessels with different stenosis rates at various Reynolds numbers were simulated numerically with the two-dimensional axisymmetric models, and the hemodynamic characteristics around the plaque were scaled with stenosis rate and Reynolds number.

RESULTS: The results showed that increases of both Reynolds number and stenosis rate facilitated the occurrence of flow separation phenomenon, extended recirculation zone, and upregulated the maximum normalized wall shear stress near the plaque throat section while downregulated the minimal normalized wall shear stress at the front shoulder of plaque, as it should be; in the atherosclerotic plaque leeside of the recirculation zone, an obvious catch bond region of wall shear stress might exist especially under low Reynolds number with stenosis rate smaller than 30%. This catch bond region in the plaque leeside might be responsible for the LBF (low blood flow)-enhanced formation of the atherosclerotic plaque.

CONCLUSIONS: This work may provide a novel insight into understanding the biomechanical effects behind the formation and damage of atherosclerotic plaques and propose a new strategy for preventing atherosclerotic diseases.}, } @article {pmid34845537, year = {2021}, author = {Patel, K and Stark, H}, title = {Instability of a liquid sheet with viscosity contrast in inertial microfluidics.}, journal = {The European physical journal. E, Soft matter}, volume = {44}, number = {11}, pages = {144}, pmid = {34845537}, issn = {1292-895X}, abstract = {Flows at moderate Reynolds numbers in inertial microfluidics enable high throughput and inertial focusing of particles and cells with relevance in biomedical applications. In the present work, we consider a viscosity-stratified three-layer flow in the inertial regime. We investigate the interfacial instability of a liquid sheet surrounded by a density-matched but more viscous fluid in a channel flow. We use linear stability analysis based on the Orr-Sommerfeld equation and direct numerical simulations with the lattice Boltzmann method (LBM) to perform an extensive parameter study. Our aim is to contribute to a controlled droplet production in inertial microfluidics. In the first part, on the linear stability analysis we show that the growth rate of the fastest growing mode [Formula: see text] increases with the Reynolds number [Formula: see text] and that its wavelength [Formula: see text] is always smaller than the channel width w for sufficiently small interfacial tension [Formula: see text]. For thin sheets we find the scaling relation [Formula: see text], where m is viscosity ratio and [Formula: see text] the sheet thickness. In contrast, for thicker sheets [Formula: see text] decreases with increasing [Formula: see text] or m due to the nearby channel walls. Examining the eigenvalue spectra, we identify Yih modes at the interface. In the second part on the LBM simulations, the thin liquid sheet develops two distinct dynamic states: waves traveling along the interface and breakup into droplets with bullet shape. For smaller flow rates and larger sheet thicknesses, we also observe ligament formation and the sheet eventually evolves irregularly. Our work gives some indication how droplet formation can be controlled with a suitable parameter set [Formula: see text].}, } @article {pmid34845318, year = {2021}, author = {Pang, M and Zhang, T and Meng, Y and Ling, Z}, title = {Experimental study on the permeability of crushed coal medium based on the Ergun equation.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {23030}, pmid = {34845318}, issn = {2045-2322}, abstract = {Accurate determination of the permeability of crushed coal medium is the basis for the study of their permeability characteristics. To investigate the permeability characteristics of this special porous medium composed of crushed coal particles, the permeability parameters of crushed coal specimens of different initial porosities were measured by designing a lateral-limit compression seepage test system. Parameters were determined separately for specimens of different initial porosities. (1) the Reynolds number distribution region characterising the seepage state was determined and obtained. Specimens with initial porosity distribution between 0.02 and 0.08, and seepage Reynolds number distribution in the low-permeability zone, under Darcy flow; (2) the intrinsic permeability of the crushed coal medium was obtained by using the Ergun equation. The complex inverse proportional relationship between the drag coefficient and Reynolds number was derived; (3) Through the determination of the permeability of the crushed coal medium, the mean value of βK value was obtained to be about 45.7, and the analysis of the permeability of porous medium can determine its critical permeability. The relationship between the Forchheimer number Fo and critical Reynolds number was measured. The results indicate that it conforms to a linear distribution. In-depth analysis of these two parameters can be used to explore the flow transition process between laminar, transition, and turbulent flow. This study provides insight into the permeability characteristics of the media in fractured coal bodies.}, } @article {pmid34840965, year = {2021}, author = {Krane, M}, title = {Vortex Formation Times in the Glottal Jet, Measured in a Scaled-Up Model.}, journal = {Fluids (Basel, Switzerland)}, volume = {6}, number = {11}, pages = {}, pmid = {34840965}, issn = {2311-5521}, support = {R01 DC005642/DC/NIDCD NIH HHS/United States ; }, abstract = {In this paper, the timing of vortex formation on the glottal jet is studied using previously published velocity measurements of flow through a scaled-up model of the human vocal folds. The relative timing of the pulsatile glottal jet and the instability vortices are acoustically important since they determine the harmonic and broadband content of the voice signal. Glottis exit jet velocity time series were extracted from time-resolved planar DPIV measurements. These measurements were acquired at four glottal flow speeds (u SS = 16.1-38 cm/s) and four glottis open times (T o = 5.67-23.7 s), providing a Reynolds number range Re = 4100-9700 and reduced vibration frequency f* = 0.01-0.06. Exit velocity waveforms showed temporal behavior on two time scales, one that correlates to the period of vibration and another characterized by short, sharp velocity peaks (which correlate to the passage of instability vortices through the glottis exit plane). The vortex formation time, estimated by computing the time difference between subsequent peaks, was shown to be not well-correlated from one vibration cycle to the next. The principal finding is that vortex formation time depends not only on cycle phase, but varies strongly with reduced frequency of vibration. In all cases, a strong high-frequency burst of vortex motion occurs near the end of the cycle, consistent with perceptual studies using synthesized speech.}, } @article {pmid34832781, year = {2021}, author = {Jbeili, M and Zhang, J}, title = {Effects of Microscopic Properties on Macroscopic Thermal Conductivity for Convective Heat Transfer in Porous Materials.}, journal = {Micromachines}, volume = {12}, number = {11}, pages = {}, pmid = {34832781}, issn = {2072-666X}, abstract = {Porous materials are widely used in many heat transfer applications. Modeling porous materials at the microscopic level can accurately incorporate the detailed structure and substance parameters and thus provides valuable information for the complex heat transfer processes in such media. In this study, we use the generalized periodic boundary condition for pore-scale simulations of thermal flows in porous materials. A two-dimensional porous model consisting of circular solid domains is considered, and comprehensive simulations are performed to study the influences on macroscopic thermal conductivity from several microscopic system parameters, including the porosity, Reynolds number, and periodic unit aspect ratio and the thermal conductance at the solid-fluid interface. Our results show that, even at the same porosity and Reynolds number, the aspect ratio of the periodic unit and the interfacial thermal conductance can significantly affect the macroscopic thermal behaviors of porous materials. Qualitative analysis is also provided to relate the apparent thermal conductivity to the complex flow and temperature distributions in the microscopic porous structure. The method, findings and discussions presented in this paper could be useful for fundamental studies, material development, and engineering applications of porous thermal flow systems.}, } @article {pmid34828226, year = {2021}, author = {Li, W and Xie, Z and Xi, K and Xia, S and Ge, Y}, title = {Constructal Optimization of Rectangular Microchannel Heat Sink with Porous Medium for Entropy Generation Minimization.}, journal = {Entropy (Basel, Switzerland)}, volume = {23}, number = {11}, pages = {}, pmid = {34828226}, issn = {1099-4300}, abstract = {A model of rectangular microchannel heat sink (MCHS) with porous medium (PM) is developed. Aspect ratio of heat sink (HS) cell and length-width ratio of HS are optimized by numerical simulation method for entropy generation minimization (EGM) according to constructal theory. The effects of inlet Reynolds number (Re) of coolant, heat flux on bottom, porosity and volume proportion of PM on dimensionless entropy generation rate (DEGR) are analyzed. From the results, there are optimal aspect ratios to minimize DEGR. Given the initial condition, DEGR is 33.10% lower than its initial value after the aspect ratio is optimized. With the increase of Re, the optimal aspect ratio declines, and the minimum DEGR drops as well. DEGR gets larger and the optimal aspect ratio remains constant with the increasing of heat flux on bottom. For the different volume proportion of PM, the optimal aspect ratios are diverse, but the minimum DEGR almost stays unchanged. The twice minimized DEGR, which results from aspect ratio and length-width ratio optimized simultaneously, is 10.70% lower than the once minimized DEGR. For a rectangular bottom, a lower DEGR can be reached by choosing the proper direction of fluid flow.}, } @article {pmid34828211, year = {2021}, author = {Khan, MF and Sulaiman, M and Tavera Romero, CA and Alkhathlan, A}, title = {A Hybrid Metaheuristic Based on Neurocomputing for Analysis of Unipolar Electrohydrodynamic Pump Flow.}, journal = {Entropy (Basel, Switzerland)}, volume = {23}, number = {11}, pages = {}, pmid = {34828211}, issn = {1099-4300}, abstract = {A unipolar electrohydrodynamic (UP-EHD) pump flow is studied with known electric potential at the emitter and zero electric potential at the collector. The model is designed for electric potential, charge density, and electric field. The dimensionless parameters, namely the electrical source number (Es), the electrical Reynolds number (ReE), and electrical slip number (Esl), are considered with wide ranges of variation to analyze the UP-EHD pump flow. To interpret the pump flow of the UP-EHD model, a hybrid metaheuristic solver is designed, consisting of the recently developed technique sine-cosine algorithm (SCA) and sequential quadratic programming (SQP) under the influence of an artificial neural network. The method is abbreviated as ANN-SCA-SQP. The superiority of the technique is shown by comparing the solution with reference solutions. For a large data set, the technique is executed for one hundred independent experiments. The performance is evaluated through performance operators and convergence plots.}, } @article {pmid34828180, year = {2021}, author = {Jia, Y and Huang, J and Wang, J and Li, H}, title = {Heat Transfer and Fluid Flow Characteristics of Microchannel with Oval-Shaped Micro Pin Fins.}, journal = {Entropy (Basel, Switzerland)}, volume = {23}, number = {11}, pages = {}, pmid = {34828180}, issn = {1099-4300}, abstract = {A novel microchannel heat sink with oval-shaped micro pin fins (MOPF) is proposed and the characteristics of fluid flow and heat transfer are studied numerically for Reynolds number (Re) ranging from 157 to 668. In order to study the influence of geometry on flow and heat transfer characteristics, three non-dimensional variables are defined, such as the fin axial length ratio (α), width ratio (β), and height ratio (γ). The thermal enhancement factor (η) is adopted as an evaluation criterion to evaluate the best comprehensive thermal-hydraulic performance of MOPF. Results indicate that the oval-shaped pin fins in the microchannel can effectively prevent the rise of heat surface temperature along the flow direction, which improves the temperature distribution uniformity. In addition, results show that for the studied Reynolds number range and microchannel geometries in this paper, the thermal enhancement factor η increases firstly and then decreases with the increase of α and β. In addition, except for Re = 157, η decreases first and then increases with the increase of the fin height ratio γ. The thermal enhancement factor for MOPF with α = 4, β = 0.3, and γ = 0.5 achieves 1.56 at Re = 668. The results can provide a theoretical basis for the design of a microchannel heat exchanger.}, } @article {pmid34818642, year = {2021}, author = {Hernández Meza, JM and Vélez-Cordero, JR and Ramírez Saito, A and Aranda-Espinoza, S and Arauz-Lara, JL and Yáñez Soto, B}, title = {Particle/wall electroviscous effects at the micron scale: comparison between experiments, analytical and numerical models.}, journal = {Journal of physics. Condensed matter : an Institute of Physics journal}, volume = {34}, number = {9}, pages = {}, doi = {10.1088/1361-648X/ac3cef}, pmid = {34818642}, issn = {1361-648X}, abstract = {We report a experimental study of the motion of 1 μm single particles interacting with functionalized walls at low and moderate ionic strengths conditions. The 3D particle's trajectories were obtained by analyzing the diffracted particle images (point spread function). The studied particle/wall systems include negatively charged particles interacting with bare glass, glass covered with polyelectrolytes and glass covered with a lipid monolayer. In the low salt regime (pure water) we observed a retardation effect of the short-time diffusion coefficients when the particle interacts with a negatively charged wall; this effect is more severe in the perpendicular than in the lateral component. The decrease of the diffusion as a function of the particle-wall distancehwas similar regardless the origin of the negative charge at the wall. When surface charge was screened or salt was added to the medium (10 mM), the diffusivity curves recover the classical hydrodynamic behavior. Electroviscous theory based on the thin electrical double layer (EDL) approximation reproduces the experimental data except for smallh. On the other hand, 2D numerical solutions of the electrokinetic equations showed good qualitative agreement with experiments. The numerical model also showed that the hydrodynamic and Maxwellian part of the electroviscous total drag tend to zero ash→ 0 and how this is linked with the merging of both EDL's at close proximity.}, } @article {pmid34816334, year = {2021}, author = {Díaz, MV}, title = {On the long-time persistence of hydrodynamic memory.}, journal = {The European physical journal. E, Soft matter}, volume = {44}, number = {11}, pages = {141}, pmid = {34816334}, issn = {1292-895X}, abstract = {The Basset-Boussinesq-Oseen (BBO) equation correctly describes the nonuniform motion of a spherical particle at a low Reynolds number. It contains an integral term with a singular kernel which accounts for the diffusion of vorticity around the particle throughout its entire history. However, if there are any departures in either rigidity or shape from a solid sphere, besides the integral force with a singular kernel, the Basset history force, we should add a second history force with a non-singular kernel, related to the shape or composition of the particle. In this work, we introduce a fractional generalized Basset-Boussinesq-Oseen equation which includes both history terms as fractional derivatives. Using the Laplace transform, an integral representation of the solution is obtained. For a driven single particle, the solution shows that memory effects persist indefinitely under rather general driving conditions.}, } @article {pmid34805706, year = {2021}, author = {Yin, B and Yue, W and Sohan, ASMMF and Zhou, T and Qian, C and Wan, X}, title = {Micromixer with Fine-Tuned Mathematical Spiral Structures.}, journal = {ACS omega}, volume = {6}, number = {45}, pages = {30779-30789}, pmid = {34805706}, issn = {2470-1343}, abstract = {Micromixers with the microchannel structure can enable rapid and efficient mixing of multiple types of fluids on a microfluidic chip. Herein, we report the mixing performance of three passive micromixers based on the different mathematical spiral structures. We study the fluid flow characteristics of Archimedes spiral, Fermat spiral, and hyperbolic spiral structures with various channel widths and Reynolds number (Re) ranging from 0 to 10 via numerical simulation and visualization experiments. In addition, we analyze the mechanism of streamlines and Dean vortices at different cross sections during fluid flows. As the fluid flows in the Fermat spiral channel, the centrifugal force induces the Dean vortex to form a chaotic advection, enhancing the fluid mixing performance. By integrating the Fermat spiral channel into a microfluidic chip, we successfully detect acute myocardial infarction (AMI) marker with the double-antibody sandwich method and reduce the detection time to 10 min. This method has a low reagent consumption and a high reaction efficiency and demonstrates great potential in point-of-care testing (POCT).}, } @article {pmid34797128, year = {2021}, author = {Jaccod, A and Chibbaro, S}, title = {Constrained Reversible System for Navier-Stokes Turbulence.}, journal = {Physical review letters}, volume = {127}, number = {19}, pages = {194501}, doi = {10.1103/PhysRevLett.127.194501}, pmid = {34797128}, issn = {1079-7114}, abstract = {Following a Gallavotti's conjecture, stationary states of Navier-Stokes fluids are proposed to be described equivalently by alternative equations besides the Navier-Stokes equation itself. We discuss a model system symmetric under time reversal based on the Navier-Stokes equations constrained to keep the enstrophy constant. It is demonstrated through highly resolved numerical experiments that the reversible model evolves to a stationary state which reproduces quite accurately all statistical observables relevant for the physics of turbulence extracted by direct numerical simulations (DNS) at different Reynolds numbers. The possibility of using reversible models to mimic turbulence dynamics is of practical importance for the coarse-grained version of Navier-Stokes equations, as used in large-eddy simulations. Furthermore, the reversible model appears mathematically simpler, since enstrophy is bounded to be constant for every Reynolds number. Finally, the theoretical interest in the context of statistical mechanics is briefly discussed.}, } @article {pmid34781498, year = {2021}, author = {An, X and Dong, B and Wang, Y and Zhang, Y and Zhou, X and Li, W}, title = {Coupled lattice Boltzmann-large eddy simulation model for three-dimensional multiphase flows at large density ratio and high Reynolds number.}, journal = {Physical review. E}, volume = {104}, number = {4-2}, pages = {045305}, doi = {10.1103/PhysRevE.104.045305}, pmid = {34781498}, issn = {2470-0053}, abstract = {A coupled lattice Boltzmann-large eddy simulation model is developed for modeling three-dimensional multiphase flows at large density ratios and high Reynolds numbers. In the framework of the lattice Boltzmann method, the model is proposed based on the standard Smagorinsky subgrid-scale approach, and a reconstructed multiple-relaxation-time collision operator is adopted. The conservative Allen-Cahn equation and Navier-Stokes equations are solved through the lattice Boltzmann discretization scheme for the interface tracking and velocity field evolution, respectively. Relevant benchmark cases are carried out to validate the performance of this model in simulating multiphase flows at a large density ratio and a high Reynolds number, including a stationary droplet, the process of spinodal decomposition, the Rayleigh-Taylor instability, the phenomenon of a droplet splashing on a thin liquid film, and the liquid jet breakup process. The maximum values of density ratio and Re number are 1000 and 10 240, respectively. The capability and reliability of the proposed model have been demonstrated by the good agreement between simulation results and the analytical solutions or the previously available results.}, } @article {pmid34776531, year = {2021}, author = {Braun, S and Scheichl, S and Kuzdas, D}, title = {The triple-deck stage of marginal separation.}, journal = {Journal of engineering mathematics}, volume = {128}, number = {1}, pages = {16}, pmid = {34776531}, issn = {0022-0833}, abstract = {UNLABELLED: The method of matched asymptotic expansions is applied to the investigation of transitional separation bubbles. The problem-specific Reynolds number is assumed to be large and acts as the primary perturbation parameter. Four subsequent stages can be identified as playing key roles in the characterization of the incipient laminar-turbulent transition process: due to the action of an adverse pressure gradient, a classical laminar boundary layer is forced to separate marginally (I). Taking into account viscous-inviscid interaction then enables the description of localized, predominantly steady, reverse flow regions (II). However, certain conditions (e.g. imposed perturbations) may lead to a finite-time breakdown of the underlying reduced set of equations. The ensuing consideration of even shorter spatio-temporal scales results in the flow being governed by another triple-deck interaction. This model is capable of both resolving the finite-time singularity and reproducing the spike formation (III) that, as known from experimental observations and direct numerical simulations, sets in prior to vortex shedding at the rear of the bubble. Usually, the triple-deck stage again terminates in the form of a finite-time blow-up. The study of this event gives rise to a noninteracting Euler-Prandtl stage (IV) associated with unsteady separation, where the vortex wind-up and shedding process takes place. The focus of the present paper lies on the triple-deck stage III and is twofold: firstly, a comprehensive numerical investigation based on a Chebyshev collocation method is presented. Secondly, a composite asymptotic model for the regularization of the ill-posed Cauchy problem is developed.

SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s10665-021-10125-3.}, } @article {pmid34766181, year = {2022}, author = {Yu, P and Durgesh, V}, title = {Application of Dynamic Mode Decomposition to Study Temporal Flow Behavior in a Saccular Aneurysm.}, journal = {Journal of biomechanical engineering}, volume = {144}, number = {5}, pages = {}, doi = {10.1115/1.4052999}, pmid = {34766181}, issn = {1528-8951}, mesh = {Blood Flow Velocity ; Hemodynamics ; Humans ; *Intracranial Aneurysm ; Models, Cardiovascular ; Rheology ; }, abstract = {Aneurysms are abnormal expansion of weakened blood vessels which can cause mortality or long-term disability upon rupture. Several studies have shown that inflow conditions spatially and temporally influence aneurysm flow behavior. The objective of this investigation is to identify impact of inflow conditions on spatio-temporal flow behavior in an aneurysm using dynamic mode decomposition (DMD). For this purpose, low-frame rate velocity field measurements are performed in an idealized aneurysm model using particle image velocimetry (PIV). The inflow conditions are precisely controlled using a ViVitro SuperPump system where nondimensional fluid parameters such as peak Reynolds number (Rep) and Womersely number (α) are varied from 50-270 and 2-5, respectively. The results show the ability of DMD to identify the spatial flow structures and their frequency content. Furthermore, DMD captured the impact of inflow conditions, and change in mode shapes, amplitudes, frequency, and growth rate information is observed. The DMD low-order flow reconstruction also showed the complex interplay of flow features for each inflow scenario. Furthermore, the low-order reconstruction results provided a mathematical description of the flow behavior in the aneurysm which captured the vortex formation, evolution, and convection in detail. These results indicated that the vortical structure behavior varied with the change in α while its strength and presence of secondary structures are influenced by the change in Rep.}, } @article {pmid34756978, year = {2022}, author = {Hu, F and Zhang, S and Wang, X and Wang, C and Wu, J and Poncin, S and Xu, L and Xu, G and Hu, Y and Li, HZ}, title = {Quantitative hydrodynamic characterization of high solid anaerobic digestion: Correlation of "mixing-fluidity-energy" and scale-up effect.}, journal = {Bioresource technology}, volume = {344}, number = {Pt B}, pages = {126237}, doi = {10.1016/j.biortech.2021.126237}, pmid = {34756978}, issn = {1873-2976}, mesh = {Anaerobiosis ; *Bioreactors ; *Hydrodynamics ; Rheology ; }, abstract = {High solid anaerobic digestion (HSAD)'s complex rheological behavior exhibits short-circuiting and dead zone. Mixing optimization is potential to enhance HSAD hydrodynamics. Besides, scale-up effect is quite essential for HSAD's applications, but remains rarely studied yet. Effect of impeller with different width on the correlation of "mixing-fluidity-energy" at different rotating speeds was first investigated at pilot-scale in present work. Then, scale-up effect based on rotating speed and a generalized Reynolds number was revealed from the aspects of fluidity and energy consumption. Results show that impeller width of 100 mm (10 rpm), 200 mm and 300 mm (5 and 10 rpm) are preferred for hydrodynamics and energy economics. Furthermore, Re similarity has better referential significance for the scale-up. In this study, new insight is gained into the correlation of "mixing-fluidity-energy" within a pilot-scale digester. Scale-up effect based Re similarity could potentially offer guidance for HSAD's application in the practical engineering.}, } @article {pmid34746583, year = {2021}, author = {Lian, SJ and Hu, ZX and Lan, Z and Wen, RF and Ma, XH}, title = {Optimal Operation of an Oscillatory Flow Crystallizer: Coupling Disturbance and Stability.}, journal = {ACS omega}, volume = {6}, number = {43}, pages = {28912-28922}, pmid = {34746583}, issn = {2470-1343}, abstract = {In the process of industrial crystallization, it is always difficult to balance the secondary nucleation rate and metastable zone width (MSZW). Herein, we report an experimental and numerical study for the cooling crystallization of paracetamol in an oscillatory flow crystallizer (OFC), finding the optimal operating conditions for balancing the secondary nucleation rate and MSZW. The results show that the MSZW decreases with the increase of oscillation Reynolds number (Re o). Compared to the traditional stirring system, the OFC has an MSZW three times larger than that of the stirring system under a similar power density of consumption. With the numerical simulation, the OFC can produce a stable space environment and instantaneous strong disturbance, which is conducive to the crystallization process. Above all, a high Re o is favorable to produce a sufficient nucleation rate, which may inevitably constrict the MSZW to a certain degree. Then, the optimization strategy of the operating parameter (Re o) in the OFC is proposed.}, } @article {pmid34739321, year = {2021}, author = {Browne, CA and Datta, SS}, title = {Elastic turbulence generates anomalous flow resistance in porous media.}, journal = {Science advances}, volume = {7}, number = {45}, pages = {eabj2619}, pmid = {34739321}, issn = {2375-2548}, abstract = {Many energy, environmental, industrial, and microfluidic processes rely on the flow of polymer solutions through porous media. Unexpectedly, the macroscopic flow resistance often increases above a threshold flow rate in a porous medium, but not in bulk solution. The reason why has been a puzzle for over half a century. Here, by directly visualizing flow in a transparent 3D porous medium, we demonstrate that this anomalous increase is due to the onset of an elastic instability in which the flow exhibits strong spatiotemporal fluctuations reminiscent of inertial turbulence, despite the small Reynolds number. Our measurements enable us to quantitatively establish that the energy dissipated by pore-scale fluctuations generates the anomalous increase in the overall flow resistance. Because the macroscopic resistance is one of the most fundamental descriptors of fluid flow, our results both help deepen understanding of complex fluid flows and provide guidelines to inform a broad range of applications.}, } @article {pmid34739267, year = {2021}, author = {Bott, AFA and Chen, L and Boutoux, G and Caillaud, T and Duval, A and Koenig, M and Khiar, B and Lantuéjoul, I and Le-Deroff, L and Reville, B and Rosch, R and Ryu, D and Spindloe, C and Vauzour, B and Villette, B and Schekochihin, AA and Lamb, DQ and Tzeferacos, P and Gregori, G and Casner, A}, title = {Inefficient Magnetic-Field Amplification in Supersonic Laser-Plasma Turbulence.}, journal = {Physical review letters}, volume = {127}, number = {17}, pages = {175002}, doi = {10.1103/PhysRevLett.127.175002}, pmid = {34739267}, issn = {1079-7114}, abstract = {We report a laser-plasma experiment that was carried out at the LMJ-PETAL facility and realized the first magnetized, turbulent, supersonic (Ma_{turb} ≈2.5) plasma with a large magnetic Reynolds number (Rm≈45) in the laboratory. Initial seed magnetic fields were amplified, but only moderately so, and did not become dynamically significant. A notable absence of magnetic energy at scales smaller than the outer scale of the turbulent cascade was also observed. Our results support the notion that moderately supersonic, low-magnetic-Prandtl-number plasma turbulence is inefficient at amplifying magnetic fields compared to its subsonic, incompressible counterpart.}, } @article {pmid34737529, year = {2021}, author = {Behera, S and Bhardwaj, R and Agrawal, A}, title = {Effect of co-flow on fluid dynamics of a cough jet with implications in spread of COVID-19.}, journal = {Physics of fluids (Woodbury, N.Y. : 1994)}, volume = {33}, number = {10}, pages = {101701}, pmid = {34737529}, issn = {1070-6631}, abstract = {We discuss the temporal evolution of a cough jet of an infected subject in the context of the spread of COVID-19. Computations were carried out using large eddy simulation, and, in particular, the effect of the co-flow (5% and 10% of maximum cough velocity) on the evolution of the jet was quantified. The Reynolds number (Re) of the cough jet, based on the mouth opening diameter (D) and the average cough velocity, is 13 002. The time-varying inlet velocity profile of the cough jet is represented as a combination of gamma-probability-distribution functions. Simulations reveal the detailed structure of cough jet with and without a co-flow for the first time, to the best of our knowledge. The cough jet temporal evolution is similar to that of a continuous free-jet and follows the same routes of instability, as documented for a free-jet. The convection velocity of the cough jet decays with time and distance, following a power-law variation. The cough jet is observed to travel a distance of approximately 1.1 m in half a second. However, in the presence of 10% co-flow, the cough jet travels faster and covers the similar distance in just 0.33 s. Therefore, in the presence of a co-flow, the probability of transmission of COVID-19 by airborne droplets and droplet nuclei increases, since they can travel a larger distance. The cough jet without the co-flow corresponds to a larger volume content compared to that with the co-flow and spreads more within the same range of distance. These simulations are significant as they help to reveal the intricate structure of the cough jet and show that the presence of a co-flow can significantly augment the risk of infection of COVID-19.}, } @article {pmid34732570, year = {2021}, author = {Choueiri, GH and Lopez, JM and Varshney, A and Sankar, S and Hof, B}, title = {Experimental observation of the origin and structure of elastoinertial turbulence.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {118}, number = {45}, pages = {}, pmid = {34732570}, issn = {1091-6490}, abstract = {Turbulence generally arises in shear flows if velocities and hence, inertial forces are sufficiently large. In striking contrast, viscoelastic fluids can exhibit disordered motion even at vanishing inertia. Intermediate between these cases, a state of chaotic motion, "elastoinertial turbulence" (EIT), has been observed in a narrow Reynolds number interval. We here determine the origin of EIT in experiments and show that characteristic EIT structures can be detected across an unexpectedly wide range of parameters. Close to onset, a pattern of chevron-shaped streaks emerges in qualitative agreement with linear and weakly nonlinear theory. However, in experiments, the dynamics remain weakly chaotic, and the instability can be traced to far lower Reynolds numbers than permitted by theory. For increasing inertia, the flow undergoes a transformation to a wall mode composed of inclined near-wall streaks and shear layers. This mode persists to what is known as the "maximum drag reduction limit," and overall EIT is found to dominate viscoelastic flows across more than three orders of magnitude in Reynolds number.}, } @article {pmid34732141, year = {2021}, author = {Zhou, Y and Wang, DM and Liu, L and Huang, P}, title = {The morphometric of lycopsid sporophylls and the evaluation of their dispersal potential: an example from the Upper Devonian of Zhejiang Province, China.}, journal = {BMC ecology and evolution}, volume = {21}, number = {1}, pages = {198}, pmid = {34732141}, issn = {2730-7182}, mesh = {China ; *Fossils ; }, abstract = {BACKGROUND: Previous studies have discussed the special structural adaptations of Late Palaeozoic lycopsids, for example, the dispersal potential of reproductive organs. Based on materials from the Upper Devonian Wutong Formation in Changxing County, Zhejiang Province, China, we now analyze the morphometric and perform some calculation to evaluate the dispersal of sporophyll units of lycopsids.

RESULTS: The fossil sporophyll units are divided into two types in view of obvious difference in shape and we name two new (form) species for them. We also analyze the falling process and give the calculation method of dispersal distance.

CONCLUSIONS: The fossil sporophyll units show relatively poor potential of wind dispersal compared with modern samaras, and show potential adaptation to the turbulent environment.}, } @article {pmid34731319, year = {2021}, author = {Miles, JG and Battista, NA}, title = {Exploring the sensitivity in jellyfish locomotion under variations in scale, frequency, and duty cycle.}, journal = {Journal of mathematical biology}, volume = {83}, number = {5}, pages = {56}, pmid = {34731319}, issn = {1432-1416}, mesh = {Animals ; Biomechanical Phenomena ; Locomotion ; *Models, Biological ; *Scyphozoa ; Swimming ; }, abstract = {Jellyfish have been called one of the most energy-efficient animals in the world due to the ease in which they move through their fluid environment, by product of their bell kinematics coupled with their morphological, muscular, material properties. We investigated jellyfish locomotion by conducting in silico comparative studies and explored swimming performance across different fluid scales (i.e., Reynolds Number), bell contraction frequencies, and contraction phase kinematics (duty cycle) for a jellyfish with a fineness ratio of 1 (ratio of bell height to bell diameter). To study these relationships, an open source implementation of the immersed boundary method was used (IB2d) to solve the fully coupled fluid-structure interaction problem of a flexible jellyfish bell in a viscous fluid. Thorough 2D parameter subspace explorations illustrated optimal parameter combinations in which give rise to enhanced swimming performance. All performance metrics indicated a higher sensitivity to bell actuation frequency than fluid scale or duty cycle, via Sobol sensitivity analysis, on a higher performance parameter subspace. Moreover, Pareto-like fronts were identified in the overall performance space involving the cost of transport and forward swimming speed. Patterns emerged within these performance spaces when highlighting different parameter regions, which complemented the global sensitivity results. Lastly, an open source computational model for jellyfish locomotion is offered to the science community that can be used as a starting place for future numerical experimentation.}, } @article {pmid34693101, year = {2021}, author = {Grande Gutiérrez, N and Shankar, KN and Sinno, T and Diamond, SL}, title = {Thrombosis and Hemodynamics: external and intrathrombus gradients.}, journal = {Current opinion in biomedical engineering}, volume = {19}, number = {}, pages = {}, pmid = {34693101}, issn = {2468-4511}, support = {R01 HL103419/HL/NHLBI NIH HHS/United States ; U01 HL131053/HL/NHLBI NIH HHS/United States ; }, abstract = {Distinct from dilute, isotropic, and homogeneous reaction systems typically used in laboratory kinetic assays, blood is concentrated, two-phase, flowing, and highly anisotropic when clotting on a surface. This review focuses on spatial gradients that are generated and can dictate thrombus structure and function. Novel experimental and computational tools have recently emerged to explore reaction-transport coupling during clotting. Multiscale simulations help bridge tissue length scales (the coronary arteries) to millimeter scales of a growing clot to the microscopic scale of single-cell signaling and adhesion. Microfluidic devices help create and control pathological velocity profiles, albeit at a low Reynolds number. Since rate processes and force loading are often coupled, this review highlights prevailing convective-diffusive transport physics that modulate cellular and molecular processes during thrombus formation.}, } @article {pmid34685088, year = {2021}, author = {Sun, X and Mohammed, HI and Tiji, ME and Mahdi, JM and Majdi, HS and Wang, Z and Talebizadehsardari, P and Yaïci, W}, title = {Investigation of Heat Transfer Enhancement in a Triple Tube Latent Heat Storage System Using Circular Fins with Inline and Staggered Arrangements.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {11}, number = {10}, pages = {}, pmid = {34685088}, issn = {2079-4991}, abstract = {Inherent fluctuations in the availability of energy from renewables, particularly solar, remain a substantial impediment to their widespread deployment worldwide. Employing phase-change materials (PCMs) as media, saving energy for later consumption, offers a promising solution for overcoming the problem. However, the heat conductivities of most PCMs are limited, which severely limits the energy storage potential of these materials. This study suggests employing circular fins with staggered distribution to achieve improved thermal response rates of PCM in a vertical triple-tube heat exchanger involving two opposite flow streams of the heat-transfer fluid (HTF). Since heat diffusion is not the same at various portions of the PCM unit, different fin configurations, fin dimensions and HTF flow boundary conditions were explored using computational studies of melting in the PCM triple-tube system. Staggered configuration of fin distribution resulted in significant increases in the rates of PCM melting. The results indicate that the melting rate and heat charging rate could be increased by 37.2 and 59.1%, respectively, in the case of staggered distribution. Furthermore, the use of lengthy fins with smaller thickness in the vertical direction of the storage unit resulted in a better positive role of natural convection; thus, faster melting rates were achieved. With fin dimensions of 0.666 mm × 15 mm, the melting rate was found to be increased by 23.6%, when compared to the base case of 2 mm × 5 mm. Finally, it was confirmed that the values of the Reynolds number and inlet temperatures of the HTF had a significant impact on melting time savings when circular fins of staggered distribution were included.}, } @article {pmid34683293, year = {2021}, author = {Yamashita, H and Akinaga, T and Sugihara-Seki, M}, title = {Pattern Transition on Inertial Focusing of Neutrally Buoyant Particles Suspended in Rectangular Duct Flows.}, journal = {Micromachines}, volume = {12}, number = {10}, pages = {}, pmid = {34683293}, issn = {2072-666X}, abstract = {The continuous separation and filtration of particles immersed in fluid flows are important interests in various applications. Although the inertial focusing of particles suspended in a duct flow is promising in microfluidics, predicting the focusing positions depending on the parameters, such as the shape of the duct cross-section and the Reynolds number (Re) has not been achieved owing to the diversity of the inertial-focusing phenomena. In this study, we aimed to elucidate the variation of the inertial focusing depending on Re in rectangular duct flows. We performed a numerical simulation of the lift force exerted on a spherical particle flowing in a rectangular duct and determined the lift-force map within the duct cross-section over a wide range of Re. We estimated the particle trajectories based on the lift map and Stokes drag, and identified the particle-focusing points appeared in the cross-section. For an aspect ratio of the duct cross-section of 2, we found that the blockage ratio changes transition structure of particle focusing. For blockage ratios smaller than 0.3, particles focus near the centres of the long sides of the cross-section at low Re and near the centres of both the long and short sides at relatively higher Re. This transition is expressed as a subcritical pitchfork bifurcation. For blockage ratio larger than 0.3, another focusing pattern appears between these two focusing regimes, where particles are focused on the centres of the long sides and at intermediate positions near the corners. Thus, there are three regimes; the transition between adjacent regimes at lower Re is found to be expressed as a saddle-node bifurcation and the other transition as a supercritical pitchfork bifurcation.}, } @article {pmid34678790, year = {2021}, author = {Christov, IC}, title = {Soft hydraulics: from Newtonian to complex fluid flows through compliant conduits.}, journal = {Journal of physics. Condensed matter : an Institute of Physics journal}, volume = {34}, number = {6}, pages = {}, doi = {10.1088/1361-648X/ac327d}, pmid = {34678790}, issn = {1361-648X}, mesh = {Cross-Sectional Studies ; *Hydrodynamics ; Lab-On-A-Chip Devices ; *Microfluidics/methods ; Viscosity ; }, abstract = {Microfluidic devices manufactured from soft polymeric materials have emerged as a paradigm for cheap, disposable and easy-to-prototype fluidic platforms for integrating chemical and biological assays and analyses. The interplay between the flow forces and the inherently compliant conduits of such microfluidic devices requires careful consideration. While mechanical compliance was initially a side-effect of the manufacturing process and materials used, compliance has now become a paradigm, enabling new approaches to microrheological measurements, new modalities of micromixing, and improved sieving of micro- and nano-particles, to name a few applications. This topical review provides an introduction to the physics of these systems. Specifically, the goal of this review is to summarize the recent progress towards a mechanistic understanding of the interaction between non-Newtonian (complex) fluid flows and their deformable confining boundaries. In this context, key experimental results and relevant applications are also explored, hand-in-hand with the fundamental principles for their physics-based modeling. The key topics covered include shear-dependent viscosity of non-Newtonian fluids, hydrodynamic pressure gradients during flow, the elastic response (deformation and bulging) of soft conduits due to flow within, the effect of cross-sectional conduit geometry on the resulting fluid-structure interaction, and key dimensionless groups describing the coupled physics. Open problems and future directions in this nascent field of soft hydraulics, at the intersection of non-Newtonian fluid mechanics, soft matter physics, and microfluidics, are noted.}, } @article {pmid34677517, year = {2021}, author = {Park, NS and Yoon, S and Jeong, W and Jeong, YW}, title = {A Study on the Evaluation of Flow Distribution Evenness in Parallel-Arrayed-Type Low-Pressure Membrane Module Piping.}, journal = {Membranes}, volume = {11}, number = {10}, pages = {}, pmid = {34677517}, issn = {2077-0375}, abstract = {The objectives of this study were to measure the flow rate distribution from a header pipe to each module installed in parallel for a water treatment membrane filtration process in operation and to investigate the reason for an uneven distribution of the flow rate via the CFD technique. In addition, this study attempted to propose the ratio of the branch pipe to the header pipe required to equalize the flow distribution for the same membrane filtration process. Finally, the relationship between the Reynolds number in the header pipe and the degree of the manifold flow distribution evenness was investigated. Mobile ultrasonic flow meter was used to measure the flow rate flowing from the membrane module pipe to each module, and the CFD technique was used to verify this. From the results of the actual measurement using ultrasonic flow meter and CFD simulation, it was confirmed that the outflow flow rate from the branch pipe located at the end of the header pipe was three times higher than that of the branch pipe near the inlet. The reason was that the differential pressure generated between each membrane module was higher toward the end of the header pipe. When the ratio of the sum of the cross-sectional area of the branch pipe and the cross-sectional area of the header pipe was reduced by about 30 times, it was confirmed that the flow rate flowing from each branch pipe to the membrane module was almost equal. Also, if the flow in the header pipe is transitional or laminar (Reynolds No. is approximately 4000 or less), the flow rate flowing from each branch pipe to the membrane module can be more even.}, } @article {pmid34677490, year = {2021}, author = {Kim, KT and Park, JE and Jung, SY and Kang, TG}, title = {Fouling Mitigation via Chaotic Advection in a Flat Membrane Module with a Patterned Surface.}, journal = {Membranes}, volume = {11}, number = {10}, pages = {}, pmid = {34677490}, issn = {2077-0375}, abstract = {Fouling mitigation using chaotic advection caused by herringbone-shaped grooves in a flat membrane module is numerically investigated. The feed flow is laminar with the Reynolds number (Re) ranging from 50 to 500. In addition, we assume a constant permeate flux on the membrane surface. Typical flow characteristics include two counter-rotating flows and downwelling flows, which are highly influenced by the groove depth at each Re. Poincaré sections are plotted to represent the dynamical systems of the flows and to analyze mixing. The flow systems become globally chaotic as the groove depth increases above a threshold value. Fouling mitigation via chaotic advection is demonstrated using the dimensionless average concentration (c¯w*) on the membrane and its growth rate. When the flow system is chaotic, the growth rate of c¯w* drops significantly compared to that predicted from the film theory, demonstrating that chaotic advection is an attractive hydrodynamic technique that mitigates membrane fouling. At each Re, there exists an optimal groove depth minimizing c¯w* and the growth rate of c¯w*. Under the optimum groove geometry, foulants near the membrane are transported back to the bulk flow via the downwelling flows, distributed uniformly in the entire channel via chaotic advection.}, } @article {pmid34663851, year = {2021}, author = {Khan, WU and Imran, A and Raja, MAZ and Shoaib, M and Awan, SE and Kausar, K and He, Y}, title = {A novel mathematical modeling with solution for movement of fluid through ciliary caused metachronal waves in a channel.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {20601}, pmid = {34663851}, issn = {2045-2322}, abstract = {In the present research, a novel mathematical model for the motion of cilia using non-linear rheological fluid in a symmetric channel is developed. The strength of analytical perturbation technique is employed for the solution of proposed physical process using mectachoronal rhythm based on Cilia induced flow for pseudo plastic nano fluid model by considering the low Reynolds number and long wave length approximation phenomena. The role of ciliary motion for the fluid transport in various animals is explained. Analytical expressions are gathered for stream function, concentration, temperature profiles, axial velocity, and pressure gradient. Whereas, transverse velocity, pressure rise per wave length, and frictional force on the wall of the tubule are investigated with aid of numerical computations and their outcomes are demonstrated graphically. A comprehensive analysis for comparison of Perturb and numerical solution is done. This analysis validates the analytical solution.}, } @article {pmid34659649, year = {2022}, author = {Cui, PY and Chen, WQ and Wang, JQ and Zhang, JH and Huang, YD and Tao, WQ}, title = {Numerical studies on issues of Re-independence for indoor airflow and pollutant dispersion within an isolated building.}, journal = {Building simulation}, volume = {15}, number = {7}, pages = {1259-1276}, pmid = {34659649}, issn = {1996-3599}, abstract = {This study conducted the numerical models validated by wind-tunnel experiments to investigate the issues of Re-independence of indoor airflow and pollutant dispersion within an isolated building. The window Reynolds number (Re w) was specified to characterize the indoor flow and dispersion. The indicators of RRC (ratio of relative change) or DR (K_DR) (difference ratio of dimensionless concentration) ≤ 5% were applied to quantitatively determine the critical Re w for indoor flow and turbulent diffusion. The results show that the critical Re (Re crit) value is position-dependent, and Re crit at the most unfavorable position should be suggested as the optimal value within the whole areas of interest. Thus Re H,crit = 27,000 is recommended for the outdoor flows; while Re w,crit = 15,000 is determined for the indoor flows due to the lower part below the window showing the most unfavorable. The suggested Re w,crit (=15,000) for indoor airflow and cross ventilation is independence of the window size. Moreover, taking K_DR ≤ 5% as the indicator, the suggested Re w,crit for ensuring indoor pollutant diffusion enter the Re-independence regime should also be 15,000, indicating that indoor passive diffusion is completely determined by the flow structures. The contours of dimensionless velocity (U/U 0) and concentration (K) against the increasing Re w further confirmed this critical value. This study further reveals the Re-independence issues for indoor flow and dispersion to ensure the reliability of the data obtained by reduced-scale numerical or wind-tunnel models.}, } @article {pmid34656560, year = {2022}, author = {Moitoi, AJ and Shaw, S}, title = {Magnetic drug targeting during Caputo-Fabrizio fractionalized blood flow through a permeable vessel.}, journal = {Microvascular research}, volume = {139}, number = {}, pages = {104262}, doi = {10.1016/j.mvr.2021.104262}, pmid = {34656560}, issn = {1095-9319}, mesh = {Antineoplastic Agents/*blood/chemistry/therapeutic use ; Blood Vessels/*metabolism ; Computer Simulation ; *Drug Carriers ; Drug Compounding ; *Magnetic Fields ; *Metal Nanoparticles ; *Models, Cardiovascular ; Nanotechnology ; Neoplasms/*blood supply/drug therapy/metabolism ; Numerical Analysis, Computer-Assisted ; Permeability ; Regional Blood Flow ; }, abstract = {Nanoparticle-based drug targeting is an important platform for the treatment of cardiovascular disorders. Magnetic drug targeting is more significant as it is a noninvasive procedure and biocompatible. The present problem aims to understand magnetic drug delivery to a specific location in a permeable blood vessel under the vibration and magnetic environment. Caputo-Fabrizio fractional-order time derivatives are used in the governing equations. The momentum equations are solved analytically and presented in the form of Lorenzo-Hartley and Robotonov-Hartley functions and convolution of the Laplace transform. Convolution integrations are solved by using the numerical integration technique. The Fourth order Runge-Kutta method (RK4) is used to solve the force balance equation. The influence of pertinent parameters such as Reynolds number, pulsatile frequency, magnetic field strength, Darcy number and fractional-order parameters are presented through graphs. It is observed that increasing Reynolds number results in decreasing the tendency of the drug to capture near the tumor site, whereas the pulsatile frequency presents an opposite phenomenon. Increasing the magnetic field strength and Darcy number boosts the capture efficiency of drug particles near the tumor site. The short memory effect efficiently captures the magnetic drug carriers to a specific location under the action of suitable magnetic field strength.}, } @article {pmid34654198, year = {2021}, author = {Calderer, MC and Golovaty, D and Yao, L and Zhao, L}, title = {Shear flow of active matter in thin channels.}, journal = {Physical review. E}, volume = {104}, number = {3-1}, pages = {034607}, doi = {10.1103/PhysRevE.104.034607}, pmid = {34654198}, issn = {2470-0053}, abstract = {We study the shear flow of active filaments confined in a thin channel for extensile and contractile fibers. We apply the Ericksen-Leslie equations of liquid crystal flow with an activity source term. The dimensionless form of this system includes the Ericksen, activity, and Reynolds numbers, together with the aspect ratio of the channel, as the main driving parameters. We perform a normal mode stability analysis of the base shear flow. For both types of fibers, we arrive at a comprehensive description of the stability properties and their dependence on the parameters of the system. The transition to unstable frequencies in extensile fibers occurs at a positive threshold value of the activity parameter, whereas for contractile ones a complex behavior is found at low absolute value of the activity number. The latter might be an indication of the biologically relevant plasticity and phase transition issues. In contrast with extensile fibers, flows of contractile ones are also found to be highly sensitive to the Reynolds number. The work on extensile fibers is guided by experiments on active filaments in confined channels and aims at quantifying their findings in the prechaotic regime.}, } @article {pmid34651149, year = {2021}, author = {Gallen, AF and Castro, M and Hernandez-Machado, A}, title = {Red blood cells in low Reynolds number flow: A vorticity-based characterization of shapes in two dimensions.}, journal = {Soft matter}, volume = {17}, number = {42}, pages = {9587-9594}, doi = {10.1039/d1sm00559f}, pmid = {34651149}, issn = {1744-6848}, mesh = {Cell Movement ; Cell Shape ; *Erythrocytes ; *Hydrodynamics ; Physical Phenomena ; }, abstract = {Studies on the mechanical properties of red blood cells improve the diagnosis of some blood-related diseases. Some existing numerical methods have successfully simulated the coupling between a fluid and red blood cells. This paper introduces an alternative phase-field model formulation of two-dimensional cells that solves the vorticity and stream function that simplifies the numerical implementation. We integrate red blood cell dynamics immersed in a Poiseuille flow and reproduce previously reported morphologies (slippers or parachutes). In the case of flow in a very wide channel, we discover a new metastable shape referred to as 'anti-parachute' that evolves into a horizontal slipper centered on the channel. This sort of metastable morphology may contribute to the dynamical response of the blood.}, } @article {pmid34644682, year = {2022}, author = {Truong, H and Engels, T and Wehmann, H and Kolomenskiy, D and Lehmann, FO and Schneider, K}, title = {An experimental data-driven mass-spring model of flexibleCalliphorawings.}, journal = {Bioinspiration & biomimetics}, volume = {17}, number = {2}, pages = {}, doi = {10.1088/1748-3190/ac2f56}, pmid = {34644682}, issn = {1748-3190}, mesh = {Animals ; Biomechanical Phenomena ; Elasticity ; *Flight, Animal ; Humans ; Insecta ; Models, Biological ; *Wings, Animal ; }, abstract = {Insect wings can undergo significant deformation during flapping motion owing to inertial, elastic and aerodynamic forces. Changes in shape then alter aerodynamic forces, resulting in a fully coupled fluid-structure interaction (FSI) problem. Here, we present detailed three-dimensional FSI simulations of deformable blowfly (Calliphora vomitoria) wings in flapping flight. A wing model is proposed using a multi-parameter mass-spring approach, chosen for its implementation simplicity and computational efficiency. We train the model to reproduce static elasticity measurements by optimizing its parameters using a genetic algorithm with covariance matrix adaptation (CMA-ES). Wing models trained with experimental data are then coupled to a high-performance flow solver run on massively parallel supercomputers. Different features of the modeling approach and the intra-species variability of elastic properties are discussed. We found that individuals with different wing stiffness exhibit similar aerodynamic properties characterized by dimensionless forces and power at the same Reynolds number. We further study the influence of wing flexibility by comparing between the flexible wings and their rigid counterparts. Under equal prescribed kinematic conditions for rigid and flexible wings, wing flexibility improves lift-to-drag ratio as well as lift-to-power ratio and reduces peak force observed during wing rotation.}, } @article {pmid34642447, year = {2021}, author = {Ali, A and Kanwal, T and Awais, M and Shah, Z and Kumam, P and Thounthong, P}, title = {Impact of thermal radiation and non-uniform heat flux on MHD hybrid nanofluid along a stretching cylinder.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {20262}, pmid = {34642447}, issn = {2045-2322}, abstract = {The current research investigates the thermal radiations and non-uniform heat flux impacts on magnetohydrodynamic hybrid nanofluid (CuO-Fe2O3/H2O) flow along a stretching cylinder, which is the main aim of this study. The velocity slip conditions have been invoked to investigate the slippage phenomenon on the flow. The impact of induced magnetic field with the assumption of low Reynolds number is imperceptible. Through the use of appropriate non-dimensional parameters and similarity transformations, the ruling PDE's (partial differential equations) are reduced to set of ODE's (ordinary differential equations), which are then numerically solved using Adams-Bashforth Predictor-Corrector method. Velocity and temperature fields with distinct physical parameters are investigated and explored graphically. The main observations about the hybrid nanofluid and non-uniform heat flux are analyzed graphically. A decrease in the velocity of the fluid is noted with addition of Hybrid nanofluid particles while temperature of the fluid increases by adding the CuO-Fe2O3 particles to the base fluid. Also, velocity of the fluid decreases when we incorporate the effects of magnetic field and slip. Raise in curvature parameter γ caused enhancement of velocity and temperature fields at a distance from the cylinder but displays opposite behavior nearby the surface of cylinder. The existence of heat generation and absorption for both mass dependent and time dependent parameters increases the temperature of the fluid.}, } @article {pmid34636830, year = {2021}, author = {Ho, TM and Yang, J and Tsai, PA}, title = {Microfluidic mass transfer of CO2 at elevated pressures: implications for carbon storage in deep saline aquifers.}, journal = {Lab on a chip}, volume = {21}, number = {20}, pages = {3942-3951}, doi = {10.1039/d1lc00106j}, pmid = {34636830}, issn = {1473-0189}, mesh = {*Carbon Dioxide ; *Groundwater ; Microfluidics ; Water ; }, abstract = {Carbon capture and sequestration (CCS) in a deep saline aquifer is one of the most promising technologies to mitigate anthropologically emitted carbon dioxide. Accurately quantifying the mass transport of CO2 at pore-scales is crucial but challenging for successful CCS deployment. Here, we conduct high-pressure microfluidic experiments, mimicking reservoir conditions up to 9.5 MPa and 35 °C, to elucidate the microfluidic mass transfer process of CO2 at three different states (i.e., gas, liquid, and supercritical phase) into water. We measure the size change of CO2 micro-bubbles/droplets generated using a microfluidic T-junction to estimate the volumetric mass transfer coefficient (kLa), quantifying the rate change of CO2 concentration under the driving force of concentration gradient. The results show that bubbles/droplets under high-pressure conditions reach a steady state faster than low pressure. The measured volumetric mass transfer coefficient increases with the Reynolds number (based on the liquid slug) and is nearly independent of the injection pressure for both the gas and liquid phases. In addition, kLa significantly enlarges with increasing high pressure at the supercritical state. Compared with various chemical engineering applications using millimeter-sized capillaries (with typical kLa measured ranging from ≈0.005 to 0.8 s[-1]), the microfluidic results show a significant increase in the volumetric mass transfer of CO2 into water by two to three orders of magnitude, O (10[2]-10[3]), with decreasing hydrodynamic diameter (of ≈50 μm).}, } @article {pmid34635693, year = {2021}, author = {Liao, Y and Mechulam, Y and Lassalle-Kaiser, B}, title = {A millisecond passive micromixer with low flow rate, low sample consumption and easy fabrication.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {20119}, pmid = {34635693}, issn = {2045-2322}, mesh = {Complex Mixtures/*analysis ; *Computer Simulation ; Equipment Design ; Humans ; Lab-On-A-Chip Devices/*standards ; Microfluidic Analytical Techniques/*instrumentation/*methods ; }, abstract = {Fast mixing of small volumes of solutions in microfluidic devices is essential for an accurate control and observation of the dynamics of a reaction in biological or chemical studies. It is often, however, a challenging task, as the Reynolds number (Re) in microscopic devices is typically < 100. In this report, we detail a novel mixer based on the "staggered herring bone" (SHB) pattern and "split-recombination" strategies with an optimized geometry, the periodic rotation of the flow structure can be controlled and recombined in a way that the vortices and phase shifts of the flow induce intertwined lamellar structures, thus increasing the contact surface and enhancing mixing. The optimization improves the mixing while using a low flow rate, hence a small volume for mixing and moderate pressure drops. The performances of the patterns were first simulated using COMSOL Multiphysics under different operating conditions. The simulation indicates that at very low flow rate (1-12 µL·min[-1]) and Re (3.3-40), as well as a very small working volume (~ 3 nL), a very good mixing (~ 98%) can be achieved in the ms time range (4.5-78 ms). The most promising design was then visualized experimentally, showing results that are consistent with the outcomes of the simulations. Importantly, the devices were fabricated using a classical soft-lithography method, as opposed to additive manufacturing often used to generate complex mixing structures. This new device minimizes the sample consumption and could therefore be applied for studies using precious samples.}, } @article {pmid34625588, year = {2021}, author = {Hussain, A and Hassan, A and Mdallal, QA and Ahmad, H and Sherif, EM and Rehman, A and Arshad, M}, title = {Comsolic solution of an elliptic cylindrical compressible fluid flow.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {20030}, pmid = {34625588}, issn = {2045-2322}, abstract = {In this article, the primary focus is to investigate the heat transfer effects with viscous compressible laminar flow in the permeable elliptic cylinder. The Reynolds number is kept 100 for flow to be laminar. The physics of heat transfer is selected to be coupled with the laminar flow. The results for particular step-size time for Velocity distribution, pressure profile, temperature profile, isothermal temperature contours, and drag coefficient have been analyzed. Mesh has been generated through COMSOL, mesh entities have been elaborated statistically. The maximum and minimum velocity profile is observed at the elliptical cylinder's walls and upper, lower boundary respectively. The maximum velocity observed is 2.22 m/s. Pressure profile around elliptic corners is found maximum, distinct patterns are observed even under the influence of applied heat. Temperature is observed maximum at walls but it gradually increases as moving from the upper boundary towards the lower boundary. The isothermal contour patterns are observed maximum near the walls, drag coefficient of gradual decrease is observed. COMSOL multi-physics is utilized for mathematical modeling of problems and the Backward-Differentiation-Formula has been exploited to handle problems numerically. The results will help greatly to understand the characterizations of viscous fluids and in industries like air furnaces and automobile cooling systems.}, } @article {pmid34623848, year = {2021}, author = {Khalid, M and Shankar, V and Subramanian, G}, title = {Continuous Pathway between the Elasto-Inertial and Elastic Turbulent States in Viscoelastic Channel Flow.}, journal = {Physical review letters}, volume = {127}, number = {13}, pages = {134502}, doi = {10.1103/PhysRevLett.127.134502}, pmid = {34623848}, issn = {1079-7114}, abstract = {Viscoelastic plane Poiseuille flow is shown to become linearly unstable in the absence of inertia, in the limit of high elasticities, for ultradilute polymer solutions. While inertialess elastic instabilities have been predicted for curvilinear shear flows, this is the first ever report of a purely elastic linear instability in a rectilinear shear flow. The novel instability continues up to a Reynolds number (Re) of O(1000), corresponding to the recently identified elasto-inertial turbulent state believed to underlie the maximum-drag-reduced regime. Thus, for highly elastic ultradilute polymer solutions, a single linearly unstable modal branch may underlie transition to elastic turbulence at zero Re and to elasto-inertial turbulence at moderate Re, implying the existence of continuous pathways connecting the turbulent states to each other and to the laminar base state.}, } @article {pmid34608161, year = {2021}, author = {Marusic, I and Chandran, D and Rouhi, A and Fu, MK and Wine, D and Holloway, B and Chung, D and Smits, AJ}, title = {An energy-efficient pathway to turbulent drag reduction.}, journal = {Nature communications}, volume = {12}, number = {1}, pages = {5805}, pmid = {34608161}, issn = {2041-1723}, abstract = {Simulations and experiments at low Reynolds numbers have suggested that skin-friction drag generated by turbulent fluid flow over a surface can be decreased by oscillatory motion in the surface, with the amount of drag reduction predicted to decline with increasing Reynolds number. Here, we report direct measurements of substantial drag reduction achieved by using spanwise surface oscillations at high friction Reynolds numbers ([Formula: see text]) up to 12,800. The drag reduction occurs via two distinct physical pathways. The first pathway, as studied previously, involves actuating the surface at frequencies comparable to those of the small-scale eddies that dominate turbulence near the surface. We show that this strategy leads to drag reduction levels up to 25% at [Formula: see text] = 6,000, but with a power cost that exceeds any drag-reduction savings. The second pathway is new, and it involves actuation at frequencies comparable to those of the large-scale eddies farther from the surface. This alternate pathway produces drag reduction of 13% at [Formula: see text] = 12,800. It requires significantly less power and the drag reduction grows with Reynolds number, thereby opening up potential new avenues for reducing fuel consumption by transport vehicles and increasing power generation by wind turbines.}, } @article {pmid34607142, year = {2022}, author = {Yogarathinam, LT and Velswamy, K and Gangasalam, A and Ismail, AF and Goh, PS and Narayanan, A and Abdullah, MS}, title = {Performance evaluation of whey flux in dead-end and cross-flow modes via convolutional neural networks.}, journal = {Journal of environmental management}, volume = {301}, number = {}, pages = {113872}, doi = {10.1016/j.jenvman.2021.113872}, pmid = {34607142}, issn = {1095-8630}, mesh = {*Cheese/analysis ; Filtration ; Membranes, Artificial ; Neural Networks, Computer ; *Whey ; Whey Proteins ; }, abstract = {Effluent originating from cheese production puts pressure onto environment due to its high organic load. Therefore, the main objective of this work was to compare the influence of different process variables (transmembrane pressure (TMP), Reynolds number and feed pH) on whey protein recovery from synthetic and industrial cheese whey using polyethersulfone (PES 30 kDa) membrane in dead-end and cross-flow modes. Analysis on the fouling mechanistic model indicates that cake layer formation is dominant as compared to other pore blocking phenomena evaluated. Among the input variables, pH of whey protein solution has the biggest influence towards membrane flux and protein rejection performances. At pH 4, electrostatic attraction experienced by whey protein molecules prompted a decline in flux. Cross-flow filtration system exhibited a whey rejection value of 0.97 with an average flux of 69.40 L/m[2]h and at an experimental condition of 250 kPa and 8 for TMP and pH, respectively. The dynamic behavior of whey effluent flux was modeled using machine learning (ML) tool convolutional neural networks (CNN) and recursive one-step prediction scheme was utilized. Linear and non-linear correlation indicated that CNN model (R[2] - 0.99) correlated well with the dynamic flux experimental data. PES 30 kDa membrane displayed a total protein rejection coefficient of 0.96 with 55% of water recovery for the industrial cheese whey effluent. Overall, these filtration studies revealed that this dynamic whey flux data studies using the CNN modeling also has a wider scope as it can be applied in sensor tuning to monitor flux online by means of enhancing whey recovery efficiency.}, } @article {pmid34599248, year = {2021}, author = {Almalki, MM and Alaidarous, ES and Maturi, DA and Raja, MAZ and Shoaib, M}, title = {Intelligent computing technique based supervised learning for squeezing flow model.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {19597}, pmid = {34599248}, issn = {2045-2322}, abstract = {In this study, the unsteady squeezing flow between circular parallel plates (USF-CPP) is investigated through the intelligent computing paradigm of Levenberg-Marquard backpropagation neural networks (LMBNN). Similarity transformation introduces the fluidic system of the governing partial differential equations into nonlinear ordinary differential equations. A dataset is generated based on squeezing fluid flow system USF-CPP for the LMBNN through the Runge-Kutta method by the suitable variations of Reynolds number and volume flow rate. To attain approximation solutions for USF-CPP to different scenarios and cases of LMBNN, the operations of training, testing, and validation are prepared and then the outcomes are compared with the reference data set to ensure the suggested model's accuracy. The output of LMBNN is discussed by the mean square error, dynamics of state transition, analysis of error histograms, and regression illustrations.}, } @article {pmid34588473, year = {2021}, author = {Ramzan, M and Khan, NS and Kumam, P}, title = {Mechanical analysis of non-Newtonian nanofluid past a thin needle with dipole effect and entropic characteristics.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {19378}, pmid = {34588473}, issn = {2045-2322}, abstract = {The study concerns with the mechanical characteristics of heat and mass transfer flow of a second grade nanofluid as well as gyrotatic microorganism motion past a thin needle with dipole effect, entropy generation, thermal radiation, Arrhenius activation energy and binar chemical reaction. The governing equations and boundary conditions are simplified by the use of suitable similarity transformations. Homotopy analysis method is implemented to obtain the series solution of non-linear ordinary differential equations. Physical behaviors of heat and mass transfer flow with gyrotatic microorganisms and entropy generation are investigated through the embedded parameters. The nanofluid velocity is enhanced for higher values of the ferromagnetic parameter, local Grashof number, bioconvection Rayleigh number and radiation parameter. The Reynolds number, radiation parameter and Eckert number decrease the nanofluid temperature. The entropy generation is increased with the enhancement of radiation parameter, Eckert number, Lewis number, temperature difference parameter, dimensionless constant parameter, Curie temperature, Prandtl number and concentration difference parameter.}, } @article {pmid34586089, year = {2021}, author = {Treiser, MD and Miles, MR and Albino, FP and Giladi, AM and Katz, RD and Higgins, JP}, title = {Long-Term Patency and Fluid Dynamics of Recipient Artery after End-to-Side Anastomosis for Free Tissue Transfer.}, journal = {Plastic and reconstructive surgery}, volume = {148}, number = {5}, pages = {800e-803e}, doi = {10.1097/PRS.0000000000008439}, pmid = {34586089}, issn = {1529-4242}, mesh = {Adolescent ; Adult ; Anastomosis, Surgical/methods ; Arteries/diagnostic imaging/physiology/*surgery ; Blood Flow Velocity ; Collateral Circulation ; Extremities/blood supply/*injuries/surgery ; Follow-Up Studies ; Free Tissue Flaps/blood supply/*transplantation ; Humans ; Middle Aged ; Reconstructive Surgical Procedures/*methods ; Treatment Outcome ; Ultrasonography, Doppler, Duplex ; *Vascular Patency ; Young Adult ; }, abstract = {BACKGROUND: End-to-end microvascular anastomoses sacrifice downstream inline perfusion of the recipient vessels. End-to-side anastomoses, in theory, maintain distal inline flow of the recipient vessel. The proposed benefit of the end-to-side technique depends on patency of the distal vessels and subsequent flow parameters, but maintenance of distal perfusion has not been conclusively demonstrated.

METHODS: Fifteen patients who underwent a successful extremity free flap procedure via end-to-side anastomoses to a noncritical vessel between 2003 and 2017 were enrolled. Recipient artery patency distal to the anastomosis was assessed using pulse volume recordings and duplex ultrasound imaging. Resistance indices, flow velocities, vessel diameters, volumetric flow, and turbulent flow dimensionless number (Reynolds number) were measured. Comparisons were made to the ipsilateral collateral vessel as well as to the vessels on the nonoperative contralateral limb using paired t tests.

RESULTS: Downstream flow was identified in 14 of 15 patients (93 percent patency). There was no statistical difference in resistive indices comparing the anastomotic vessel (0.859 ± 0.300) and the collateral vessel (0.853 ± 0.179) of the ipsilateral extremity. Ultrasound flows were similar; the anastomotic vessel demonstrated downstream volumetric flows of 139 ± 92.0 cm3/min versus 137 ± 41.6 cm3/min within the same vessel of the nonoperative contralateral limb. The anastomotic vessel had Reynolds numbers well below the turbulent threshold (448 ± 202 and 493 ± 127 for the anastomotic and nonoperative contralateral limb, respectively).

CONCLUSION: End-to-side anastomosis to noncritical vessels resulted in a 93 percent long-term recipient vessel patency rate, with no statistically significant changes in volumetric flows, resistive indices, or fluid dynamics in the vessels that remained patent.}, } @article {pmid34577719, year = {2021}, author = {Huang, L and Du, J and Zhu, Z}, title = {Neutrally Buoyant Particle Migration in Poiseuille Flow Driven by Pulsatile Velocity.}, journal = {Micromachines}, volume = {12}, number = {9}, pages = {}, pmid = {34577719}, issn = {2072-666X}, abstract = {A neutrally buoyant circular particle migration in two-dimensional (2D) Poiseuille channel flow driven by pulsatile velocity is numerical studied by using immersed boundary-lattice Boltzmann method (IB-LBM). The effects of Reynolds number (25≤Re≤200) and blockage ratio (0.15≤k≤0.40) on particle migration driven by pulsatile and non-pulsatile velocity are all numerically investigated for comparison. The results show that, different from non-pulsatile cases, the particle will migrate back to channel centerline with underdamped oscillation during the time period with zero-velocity in pulsatile cases. The maximum lateral travel distance of the particle in one cycle of periodic motion will increase with increasing Re, while k has little impact. The quasi frequency of such oscillation has almost no business with Re and k. Moreover, Re plays an essential role in the damping ratio. Pulsatile flow field is ubiquitous in aorta and other arteries. This article is conducive to understanding nanoparticle migration in those arteries.}, } @article {pmid34577699, year = {2021}, author = {Farahinia, A and Jamaati, J and Niazmand, H and Zhang, W}, title = {Numerical Analysis of the Heterogeneity Effect on Electroosmotic Micromixers Based on the Standard Deviation of Concentration and Mixing Entropy Index.}, journal = {Micromachines}, volume = {12}, number = {9}, pages = {}, pmid = {34577699}, issn = {2072-666X}, abstract = {One approach to achieve a homogeneous mixture in microfluidic systems in the quickest time and shortest possible length is to employ electroosmotic flow characteristics with heterogeneous surface properties. Mixing using electroosmotic flow inside microchannels with homogeneous walls is done primarily under the influence of molecular diffusion, which is not strong enough to mix the fluids thoroughly. However, surface chemistry technology can help create desired patterns on microchannel walls to generate significant rotational currents and improve mixing efficiency remarkably. This study analyzes the function of a heterogeneous zeta-potential patch located on a microchannel wall in creating mixing inside a microchannel affected by electroosmotic flow and determines the optimal length to achieve the desired mixing rate. The approximate Helmholtz-Smoluchowski model is suggested to reduce computational costs and simplify the solving process. The results show that the heterogeneity length and location of the zeta-potential patch affect the final mixing proficiency. It was also observed that the slip coefficient on the wall has a more significant effect than the Reynolds number change on improving the mixing efficiency of electroosmotic micromixers, benefiting the heterogeneous distribution of zeta-potential. In addition, using a channel with a heterogeneous zeta-potential patch covered by a slip surface did not lead to an adequate mixing in low Reynolds numbers. Therefore, a homogeneous channel without any heterogeneity would be a priority in such a range of Reynolds numbers. However, increasing the Reynolds number and the presence of a slip coefficient on the heterogeneous channel wall enhances the mixing efficiency relative to the homogeneous one. It should be noted, though, that increasing the slip coefficient will make the mixing efficiency decrease sharply in any situation, especially in high Reynolds numbers.}, } @article {pmid34575038, year = {2021}, author = {Gimsa, J and Gimsa, U}, title = {Contributions to a Discussion of Spinosaurus aegyptiacus as a Capable Swimmer and Deep-Water Predator.}, journal = {Life (Basel, Switzerland)}, volume = {11}, number = {9}, pages = {}, pmid = {34575038}, issn = {2075-1729}, abstract = {The new findings on Spinosaurus' swim tail strongly suggest that Spinosaurus was a specialized deep-water predator. However, the tail must be seen in the context of the propelled body. The comparison of the flow characteristics of Spinosaurus with geometrically similar animals and their swimming abilities under water must take their Reynolds numbers into account and provide a common context for the properties of Spinosaurus' tail and dorsal sail. Head shape adaptations such as the head crest reduced hydrodynamic disturbance and facilitated stealthy advance, especially when hunting without visual contact, when Spinosaurus could have used its rostral integumentary mechanoreceptors for prey detection. The muscular neck permitted 'pivot' feeding, where the prey's escape abilities were overcome by rapid dorsoventral head movement, facilitated by crest-mediated lower friction.}, } @article {pmid34549120, year = {2021}, author = {Wu, R and Xie, F and Wei, J and Song, X and Yang, H and Lv, P and Yu, G}, title = {Study on Soot Emission Characteristics of Methane/Oxygen Inverse Diffusion Flame.}, journal = {ACS omega}, volume = {6}, number = {36}, pages = {23191-23202}, pmid = {34549120}, issn = {2470-1343}, abstract = {Inverse diffusion flame (IDF) is an effective and widely used reaction form in the process of noncatalytic partial oxidation (NC-POX) of gaseous hydrocarbons (such as natural gas and coke oven gas). However, soot is generated in the combustion chamber in the case of unreasonable feeding conditions, and thus causes serious damage to the wall and nozzle. In this study, the effects of the equivalence ratio ([O/C]e), the oxygen flow rate, and the Reynolds number on the soot and CH* emission characteristics of CH4/O2 inverse diffusion flame were comprehensively analyzed based on a hyperspectral imaging system. In addition, the relationship between CH* and soot is explored using Ansys Fluent simulation. The experimental results show that the soot radiation core generation area is located in the outer ring of the flame, and the radial distribution of the radiation intensity is bimodal. With the increase in [O/C]e, the initial position for soot radiation and the overall radiation intensity of soot decrease. In addition, the CH* radiation intensity decreases as [O/C]e increases, and CH* exists in the whole flame. The simulation results clearly show that the existence of CH* is conducive to soot production. The emission intensity and the core area of soot formation increase with the increase in the oxygen velocity. Additionally, the soot emission region increases and the flame tip changes from a round blunt to symmetrical tip with the increase in the Reynolds number.}, } @article {pmid34547732, year = {2021}, author = {Haider, N and Shahzad, A and Qadri, MNM and Shams, TA}, title = {Aerodynamic analysis of hummingbird-like hovering flight.}, journal = {Bioinspiration & biomimetics}, volume = {16}, number = {6}, pages = {}, doi = {10.1088/1748-3190/ac28eb}, pmid = {34547732}, issn = {1748-3190}, mesh = {Animals ; Biomechanical Phenomena ; Birds ; Computer Simulation ; *Flight, Animal ; Insecta ; Models, Biological ; *Wings, Animal ; }, abstract = {Flapping wing micro aerial vehicles are studied as the substitute for fixed and rotary wing micro aerial vehicles because of the advantages such as agility, maneuverability, and employability in confined environments. Hummingbird's sustainable hovering capability inspires many researchers to develop micro aerial vehicles with similar dynamics. In this research, a wing of a ruby-throated hummingbird is modeled as an insect wing using membrane and stiffeners. The effect of flexibility on the aerodynamic performance of a wing in hovering flight has been studied numerically by using a fluid-structure interaction scheme at a Reynolds number of 3000. Different wings have been developed by using different positions and thicknesses of the stiffeners. The chordwise and spanwise flexural stiffnesses of all the wings modeled in this work are comparable to insects of similar span and chord length. When the position of the stiffener is varied, the best-performing wing has an average lift coefficient of 0.51. Subsequently, the average lift coefficient is increased to 0.56 when the appropriate thickness of the stiffeners is chosen. The best flexible wing outperforms its rigid counterpart and produces lift and power economy comparable to a real hummingbird's wing. That is, the average lift coefficient and power economy of 0.56 and 0.88 for the best flexible wing as compared to 0.61 and 1.07 for the hummingbird's wing. It can be concluded that a simple manufacturable flexible wing design based on appropriate positioning and thickness of stiffeners can serve as a potential candidate for bio-inspired flapping-wing micro aerial vehicles.}, } @article {pmid34528156, year = {2021}, author = {Javid, K and Hassan, M and Tripathi, D and Khan, S and Bobescu, E and Bhatti, MM}, title = {Double-diffusion convective biomimetic flow of nanofluid in a complex divergent porous wavy medium under magnetic effects.}, journal = {Journal of biological physics}, volume = {47}, number = {4}, pages = {477-498}, pmid = {34528156}, issn = {1573-0689}, mesh = {*Biomimetics ; Diffusion ; *Magnetic Fields ; *Nanotechnology ; Porosity ; }, abstract = {We explore the physical influence of magnetic field on double-diffusive convection in complex biomimetic (peristaltic) propulsion of nanofluid through a two-dimensional divergent channel. Additionally, porosity effects along with rheological properties of the fluid are also retained in the analysis. The mathematical model is developed by equations of continuity, momentum, energy, and mass concentration. First, scaling analysis is introduced to simplify the rheological equations in the wave frame of reference and then get the final form of equations after applying the low Reynolds number and lubrication approach. The obtained equations are solved analytically by using integration method. Physical interpretation of velocity, pressure gradient, pumping phenomena, trapping phenomena, heat, and mass transfer mechanisms are discussed in detail under magnetic and porous environment. The magnitude of velocity profile is reduced by increasing Grashof parameter. The bolus circulations disappeared from trapping phenomena for larger strength of magnetic and porosity medium. The magnitude of temperature profile and mass concentration are increasing by enhancing the Brownian motion parameter. This study can be productive in manufacturing non-uniform and divergent shapes of micro-lab-chip devices for thermal engineering, industrial, and medical technologies.}, } @article {pmid34505131, year = {2022}, author = {Costa, RP and Simplice Talla Nwotchouang, B and Yao, J and Biswas, D and Casey, D and McKenzie, R and Steinman, DA and Loth, F}, title = {Transition to Turbulence Downstream of a Stenosis for Whole Blood and a Newtonian Analog Under Steady Flow Conditions.}, journal = {Journal of biomechanical engineering}, volume = {144}, number = {3}, pages = {}, doi = {10.1115/1.4052370}, pmid = {34505131}, issn = {1528-8951}, mesh = {Animals ; Blood Flow Velocity ; Constriction, Pathologic ; *Glycerol ; *Models, Cardiovascular ; Rheology ; Stress, Mechanical ; Swine ; Water ; }, abstract = {Blood, a multiphase fluid comprised of plasma, blood cells, and platelets, is known to exhibit a shear-thinning behavior at low shear rates and near-Newtonian behavior at higher shear rates. However, less is known about the impact of its multiphase nature on the transition to turbulence. In this study, we experimentally determined the critical Reynolds number at which the flow began to transition to turbulence downstream of eccentric stenosis for whole porcine blood and a Newtonian blood analog (water-glycerin mixture). Velocity profiles for both fluids were measured under steady-state flow conditions using an ultrasound Doppler probe placed 12 diameters downstream of eccentric stenosis. Velocity was recorded at 21 locations along the diameter at 11 different flow rates. Normalized turbulent kinetic energy was used to determine the critical Reynolds number for each fluid. Blood rheology was measured before and after each experiment. Tests were conducted on five samples of each fluid inside a temperature-controlled in vitro flow system. The viscosity at a shear rate of 1000 s-1 was used to define the Reynolds number for each fluid. The mean critical Reynolds numbers for blood and water-glycerin were 470 ± 27.5 and 395 ± 10, respectively, indicating a ∼19% delay in transition to turbulence for whole blood compared to the Newtonian fluid. This finding is consistent with a previous report for steady flow in a straight pipe, suggesting some aspect of blood rheology may serve to suppress, or at least delay, the onset of turbulence in vivo.}, } @article {pmid34497885, year = {2021}, author = {Bu, X and Zhou, S and Sun, M and Alheshibri, M and Khan, MS and Xie, G and Chelgani, SC}, title = {Exploring the Relationships between Gas Dispersion Parameters and Differential Pressure Fluctuations in a Column Flotation.}, journal = {ACS omega}, volume = {6}, number = {34}, pages = {21900-21908}, pmid = {34497885}, issn = {2470-1343}, abstract = {Flotation separation, which is the most important mineral beneficiation technique, is dependent on gas dispersion (hydrodynamic conditions). Thus, many investigations have focused on the precise determination of hydrodynamic conditions such as Reynolds number of the bubbles, bubble velocity, and bubble diameter. However, few studies have examined their relationships with pressure fluctuations in a column flotation. This study introduced the differential pressure fluctuations as an actual variable that could be considered to determine the collection zone's hydrodynamic conditions in a cyclonic microbubble flotation column. In general, the outcomes indicated that superficial gas velocity had the most substantial relationship with the differential pressure fluctuations among other flotation factors (such as pump speed, superficial gas velocity, superficial water velocity, and frother dosage). Furthermore, a high coefficient of determination (R [2] > 0.77) for the equation generated to assess the relationships demonstrated that differential pressure fluctuations could be used as a promising tool to determine the hydrodynamic parameters' characteristics in the flotation columns.}, } @article {pmid34497293, year = {2021}, author = {Aghamiri, H and Niknejadi, M and Toghraie, D}, title = {Analysis of the forced convection of two-phase Ferro-nanofluid flow in a completely porous microchannel containing rotating cylinders.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {17811}, pmid = {34497293}, issn = {2045-2322}, abstract = {In the present work, the forced convection of nanofluid flow in a microchannel containing rotating cylinders is investigated in different geometries. The heat flux applied to the microchannel wall is 10,000 W m[-2]. The effects of Reynolds number, the volume fraction of nanoparticles, and the porosity percentage of the porous medium are investigated on the flow fields, temperature, and heat transfer rate. Reynolds number values vary from Re = 250-1000, non-dimensional rotational velocities 1 and 2, respectively, and volume fraction of nanoparticles 0-2%. The results show that increasing the velocity of rotating cylinders increases the heat transfer; also, increasing the Reynolds number and volume fraction of nanoparticles increases the heat transfer, pressure drop, and Cf,ave. By comparing the porosity percentages with each other, it is concluded that due to the greater contact of the nanofluid with the porous medium and the creation of higher velocity gradients, the porosity percentage is 45% and the values of are 90% higher than the porosity percentage. Comparing porosity percentages with each other, at porosity percentage 90% is greater than at porosity percentage 45%. On the other hand, increasing the Reynolds number reduces the entropy generation due to heat transfer and increases the entropy generation due to friction. Increasing the volume fraction of nanoparticles increases the entropy generations due to heat transfer and friction.}, } @article {pmid34482836, year = {2021}, author = {Mandell, JG and Loke, YH and Mass, PN and Cleveland, V and Delaney, M and Opfermann, J and Aslan, S and Krieger, A and Hibino, N and Olivieri, LJ}, title = {Altered hemodynamics by 4D flow cardiovascular magnetic resonance predict exercise intolerance in repaired coarctation of the aorta: an in vitro study.}, journal = {Journal of cardiovascular magnetic resonance : official journal of the Society for Cardiovascular Magnetic Resonance}, volume = {23}, number = {1}, pages = {99}, pmid = {34482836}, issn = {1532-429X}, support = {R01 HL143468/HL/NHLBI NIH HHS/United States ; R38 AI140298/AI/NIAID NIH HHS/United States ; R38AI140298/AI/NIAID NIH HHS/United States ; R01HL143468-0/HL/NHLBI NIH HHS/United States ; }, mesh = {Aorta ; Aorta, Thoracic/diagnostic imaging/surgery ; *Aortic Coarctation/diagnostic imaging/surgery ; Blood Flow Velocity ; Hemodynamics ; Humans ; Magnetic Resonance Spectroscopy ; Predictive Value of Tests ; Retrospective Studies ; }, abstract = {BACKGROUND: Coarctation of the aorta (CoA) is associated with decreased exercise capacity despite successful repair. Altered flow patterns have been identified due to abnormal aortic arch geometry. Our previous work demonstrated aorta size mismatch to be associated with exercise intolerance in this population. In this study, we studied aortic flow patterns during simulations of exercise in repaired CoA using 4D flow cardiovascular magnetic resonance (CMR) using aortic replicas connected to an in vitro flow pump and correlated findings with exercise stress test results to identify biomarkers of exercise intolerance.

METHODS: Patients with CoA repair were retrospectively analyzed after CMR and exercise stress test. Each aorta was manually segmented and 3D printed. Pressure gradient measurements from ascending aorta (AAo) to descending aorta (DAo) and 4D flow CMR were performed during simulations of rest and exercise using a mock circulatory flow loop. Changes in wall shear stress (WSS) and secondary flow formation (vorticity and helicity) from rest to exercise were quantified, as well as estimated DAo Reynolds number. Parameters were correlated with percent predicted peak oxygen consumption (VO2max) and aorta size mismatch (DAAo/DDAo).

RESULTS: Fifteen patients were identified (VO2max 47 to 126% predicted). Pressure gradient did not correlate with VO2max at rest or exercise. VO2max correlated positively with the change in peak vorticity (R = 0.55, p = 0.03), peak helicity (R = 0.54, p = 0.04), peak WSS in the AAo (R = 0.68, p = 0.005) and negatively with peak WSS in the DAo (R = - 0.57, p = 0.03) from rest to exercise. DAAo/DDAo correlated strongly with change in vorticity (R = - 0.38, p = 0.01), helicity (R = - 0.66, p = 0.007), and WSS in the AAo (R = - 0.73, p = 0.002) and DAo (R = 0.58, p = 0.02). Estimated DAo Reynolds number negatively correlated with VO2max for exercise (R = - 0.59, p = 0.02), but not rest (R = - 0.28, p = 0.31). Visualization of streamline patterns demonstrated more secondary flow formation in aortic arches with better exercise capacity, larger DAo, and lower Reynolds number.

CONCLUSIONS: There are important associations between secondary flow characteristics and exercise capacity in repaired CoA that are not captured by traditional pressure gradient, likely due to increased turbulence and inefficient flow. These 4D flow CMR parameters are a target of investigation to identify optimal aortic arch geometry and improve long term clinical outcomes after CoA repair.}, } @article {pmid34455847, year = {2021}, author = {Simonis, S and Haussmann, M and Kronberg, L and Dörfler, W and Krause, MJ}, title = {Linear and brute force stability of orthogonal moment multiple-relaxation-time lattice Boltzmann methods applied to homogeneous isotropic turbulence.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {379}, number = {2208}, pages = {20200405}, doi = {10.1098/rsta.2020.0405}, pmid = {34455847}, issn = {1471-2962}, abstract = {Multiple-relaxation-time (MRT) lattice Boltzmann methods (LBM) based on orthogonal moments exhibit lattice Mach number dependent instabilities in diffusive scaling. The present work renders an explicit formulation of stability sets for orthogonal moment MRT LBM. The stability sets are defined via the spectral radius of linearized amplification matrices of the MRT collision operator with variable relaxation frequencies. Numerical investigations are carried out for the three-dimensional Taylor-Green vortex benchmark at Reynolds number 1600. Extensive brute force computations of specific relaxation frequency ranges for the full test case are opposed to the von Neumann stability set prediction. Based on that, we prove numerically that a scan over the full wave space, including scaled mean flow variations, is required to draw conclusions on the overall stability of LBM in turbulent flow simulations. Furthermore, the von Neumann results show that a grid dependence is hardly possible to include in the notion of linear stability for LBM. Lastly, via brute force stability investigations based on empirical data from a total number of 22 696 simulations, the existence of a deterministic influence of the grid resolution is deduced. This article is part of the theme issue 'Progress in mesoscale methods for fluid dynamics simulation'.}, } @article {pmid34455509, year = {2021}, author = {Ali, A and Jana, RN and Das, S}, title = {Significance of entropy generation and heat source: the case of peristaltic blood flow through a ciliated tube conveying Cu-Ag nanoparticles using Phan-Thien-Tanner model.}, journal = {Biomechanics and modeling in mechanobiology}, volume = {20}, number = {6}, pages = {2393-2412}, pmid = {34455509}, issn = {1617-7940}, mesh = {Copper/*chemistry ; *Entropy ; *Hot Temperature ; Metal Nanoparticles/*chemistry ; *Models, Biological ; Peristalsis/*physiology ; Pressure ; Reproducibility of Results ; Silver/*chemistry ; }, abstract = {The present speculative investigation is concentrated to analyze the entropy generation and heat transfer phenomena in ciliary induced peristalsis of blood with the suspension of hybrid nanoparticles in a tube with heat source impact. The blood is assumed to contain copper (Cu) and silver (Ag) nanoparticles (NPs). The ciliary inner wall of the tube has been considered with small hair-like structures. The Phan-Thien-Tanner (PTT) fluid model is employed to describe the non-Newtonian rheological characteristics of blood. The conservative equations are normalized and simplified by utilizing scaling analysis with the assumption of low Reynolds number and large wavelength approximations. The analytical inspection exposes that the total entropy generation gets a decrement for mounting values of cilia length, while reversed impact is detected for an increment in heat source parameter. Hybrid nano-blood exhibits a greater total entropy number than mono nano-blood. This research study may be beneficial to medical experts and researchers in the field of embryology. Cysts in the ciliated fallopian tube, where embryos develop, are removed by using nanoparticles (nano-drug delivery).}, } @article {pmid34442509, year = {2021}, author = {Parveen, N and Awais, M and Awan, SE and Khan, WU and He, Y and Malik, MY}, title = {Entropy Generation Analysis and Radiated Heat Transfer in MHD (Al2O3-Cu/Water) Hybrid Nanofluid Flow.}, journal = {Micromachines}, volume = {12}, number = {8}, pages = {}, pmid = {34442509}, issn = {2072-666X}, abstract = {This research concerns the heat transfer and entropy generation analysis in the MHD axisymmetric flow of Al2O3-Cu/H2O hybrid nanofluid. The magnetic induction effect is considered for large magnetic Reynolds number. The influences of thermal radiations, viscous dissipation and convective temperature conditions over flow are studied. The problem is modeled using boundary layer theory, Maxwell's equations and Fourier's conduction law along with defined physical factors. Similarity transformations are utilized for model simplification which is analytically solved with the homotopy analysis method. The h-curves up to 20th order for solutions establishes the stability and convergence of the adopted computational method. Rheological impacts of involved parameters on flow variables and entropy generation number are demonstrated via graphs and tables. The study reveals that entropy in system of hybrid nanofluid affected by magnetic induction declines for β while it enhances for Bi, R and λ. Moreover, heat transfer rate elevates for large Bi with convective conditions at surface.}, } @article {pmid34441209, year = {2021}, author = {Ahammad, NA and Badruddin, IA and Kamangar, S and Khaleed, HMT and Saleel, CA and Mahlia, TMI}, title = {Heat Transfer and Entropy in a Vertical Porous Plate Subjected to Suction Velocity and MHD.}, journal = {Entropy (Basel, Switzerland)}, volume = {23}, number = {8}, pages = {}, pmid = {34441209}, issn = {1099-4300}, abstract = {This article presents an investigation of heat transfer in a porous medium adjacent to a vertical plate. The porous medium is subjected to a magnetohydrodynamic effect and suction velocity. The governing equations are nondepersonalized and converted into ordinary differential equations. The resulting equations are solved with the help of the finite difference method. The impact of various parameters, such as the Prandtl number, Grashof number, permeability parameter, radiation parameter, Eckert number, viscous dissipation parameter, and magnetic parameter, on fluid flow characteristics inside the porous medium is discussed. Entropy generation in the medium is analyzed with respect to various parameters, including the Brinkman number and Reynolds number. It is noted that the velocity profile decreases in magnitude with respect to the Prandtl number, but increases with the radiation parameter. The Eckert number has a marginal effect on the velocity profile. An increased radiation effect leads to a reduced thermal gradient at the hot surface.}, } @article {pmid34432464, year = {2021}, author = {Gu, R and Lehn, JM}, title = {Constitutional Dynamic Selection at Low Reynolds Number in a Triple Dynamic System: Covalent Dynamic Adaptation Driven by Double Supramolecular Self-Assembly.}, journal = {Journal of the American Chemical Society}, volume = {143}, number = {35}, pages = {14136-14146}, doi = {10.1021/jacs.1c04446}, pmid = {34432464}, issn = {1520-5126}, abstract = {A triple dynamic complex system has been designed, implementing a dynamic covalent process coupled to two supramolecular self-assembly steps. To this end, two dynamic covalent libraries (DCLs), DCL-1 and DCL-2, have been established on the basis of dynamic covalent C═C/C═N organo-metathesis between two Knoevenagel derivatives and two imines. Each DCL contains a barbituric acid-based Knoevenagel constituent that may undergo a sequential double self-organization process involving first the formation of hydrogen-bonded hexameric supramolecular macrocycles that subsequently undergo stacking to generate a supramolecular polymer SP yielding a viscous gel state. Both DCLs display selective self-organization-driven amplification of the constituent that leads to the SP. Dissociation of the SP on heating causes reversible randomization of the constituent distributions of the DCLs as a function of temperature. Furthermore, diverse distribution patterns of DCL-2 were induced by modulation of temperature and solvent composition. The present dynamic systems display remarkable self-organization-driven constitutional adaption and tunable composition by coupling between dynamic covalent component selection and two-stage supramolecular organization. In more general terms, they reveal dynamic adaptation by component selection in low Reynolds number conditions of living systems where frictional effects dominate inertial behavior.}, } @article {pmid34410363, year = {2021}, author = {Herrera-Amaya, A and Seber, EK and Murphy, DW and Patry, WL and Knowles, TS and Bubel, MM and Maas, AE and Byron, ML}, title = {Spatiotemporal Asymmetry in Metachronal Rowing at Intermediate Reynolds Numbers.}, journal = {Integrative and comparative biology}, volume = {61}, number = {5}, pages = {1579-1593}, doi = {10.1093/icb/icab179}, pmid = {34410363}, issn = {1557-7023}, mesh = {Animals ; Biomechanical Phenomena ; Body Size ; *Extremities ; Models, Theoretical ; *Swimming ; }, abstract = {In drag-based swimming, individual propulsors operating at low Reynolds numbers (where viscous forces dominate over inertial forces) must execute a spatially asymmetric stroke to produce net fluid displacement. Temporal asymmetry (that is, differing duration between the power vs. recovery stroke) does not affect the overall generated thrust in this time-reversible regime. Metachronal rowing, in which multiple appendages beat sequentially, is used by a wide variety of organisms from low to intermediate Reynolds numbers. At the upper end of this range, inertia becomes important, and increasing temporal asymmetry can be an effective way to increase thrust. However, the combined effects of spatial and temporal asymmetry are not fully understood in the context of metachronal rowing. To explore the role of spatiotemporal asymmetry in metachronal rowing, we combine laboratory experiments and reduced-order analytical modeling. We measure beat kinematics and generated flows in two species of lobate ctenophores across a range of body sizes, from 7 to 40 mm in length. We observe characteristically different flows in ctenophores of differing body size and Reynolds number, and a general decrease in spatial asymmetry and increase in temporal asymmetry with increasing Reynolds number. We also construct a one-dimensional mathematical model consisting of a row of oscillating flat plates whose flow-normal areas change with time, and use it to explore the propulsive forces generated across a range of Reynolds numbers and kinematic parameters. The model results show that while both types of asymmetry increase force production, they have different effects in different regions of the parameter space. These results may have strong biological implications, as temporal asymmetry can be actively controlled while spatial asymmetry is likely to be partially or entirely driven by passive fluid-structure interaction.}, } @article {pmid34391375, year = {2022}, author = {Pattnaik, PK and Abbas, MA and Mishra, S and Khan, SU and Bhatti, MM}, title = {Free Convective Flow of Hamilton-Crosser Model Gold-water Nanofluid Through a Channel with Permeable Moving Walls.}, journal = {Combinatorial chemistry & high throughput screening}, volume = {25}, number = {7}, pages = {1103-1114}, doi = {10.2174/1386207324666210813112323}, pmid = {34391375}, issn = {1875-5402}, mesh = {Computer Simulation ; Gold ; Hot Temperature ; *Metal Nanoparticles ; *Water ; }, abstract = {BACKGROUND: The present manuscript analyzes the influence of buoyant forces of a conducting time-dependent nanofluid flow through porous moving walls. The medium is also filled with porous materials. In addition to that, uniform heat source and absorption parameters are considered that affect the nanofluid model.

INTRODUCTION: The model is based on the thermophysical properties of Hamilton-Crosser's nanofluid model, in which a gold nanoparticle is submerged into the base fluid water. Before simulation is obtained by a numerical method, suitable transformation is used to convert nonlinear coupled PDEs to ODEs.

METHOD: Runge-Kutta's fourth-order scheme is applied successfully for the first-order ODEs in conjunction with the shooting technique.

RESULT: Computations for the coefficients of rate constants are presented through graphs, along with the behavior of several physical parameters augmented by the flow phenomena.

CONCLUSION: The present investigation may be compatible with the applications of biotechnology. It is seen that the inclusion of volume concentration and the fluid velocity enhances near the middle layer of the channel and retards near the permeable walls. Also, augmented values of the Reynolds number and both cooling and heating of the wall increase the rate of shear stress.}, } @article {pmid34384065, year = {2021}, author = {Luo, Y and Wright, M and Xiao, Q and Yue, H and Pan, G}, title = {Fluid-structure interaction analysis on motion control of a self-propelled flexible plate near a rigid body utilizing PD control.}, journal = {Bioinspiration & biomimetics}, volume = {16}, number = {6}, pages = {}, doi = {10.1088/1748-3190/ac1cee}, pmid = {34384065}, issn = {1748-3190}, mesh = {Animals ; Biomechanical Phenomena ; Fishes ; *Models, Biological ; Motion ; *Swimming ; }, abstract = {Inspired by a previous experimental study of fish swimming near a cylinder, we numerically investigate the swimming and station-holding behavior of a flexible plate ahead of a circular cylinder whose motion is controlled by a proportional-derivative (PD) controller. Specifically, the deformation of this two-dimensional plate is actuated by a periodically varying external force applied on the body surface, which mimics the fish muscle force to produce propulsive thrust. The actuation force amplitude is dynamically adjusted by a feedback controller to instruct the plate to swim the desired distance from an initial position to a target location and then hold the station there. Instead of directly using the instantaneous position signal, an average speed measured over one force actuation period is proposed with the inclusion of instantaneous position information to form the tracking error for the PD control. Our results show that the motion control of swimming and station holding has been achieved by this simple but effective feedback control without large overshoot when approaching the target at different flow conditions and actuation force formulas. Although the swimming distance remains the same, a plate whose initial position is closer to the cylinder requires less energy expenditure to swim to the target location and hold the station there. This is because the low-pressure zone near the trailing edge of the plate is reduced in size, which provides drag reduction, contributing to reduced swimming energy. A higher Reynolds number also leads to energy savings. Under the same control strategy, the swimming performance is more affected by the force-frequency while the phase shift of the actuation force has a less significant impact.}, } @article {pmid34381068, year = {2021}, author = {Lin, P and Liu, X and Xiong, N and Wang, X and Shang, M and Liu, G and Tao, Y}, title = {Numerical study on the influence of wall temperature gradient on aerodynamic characteristics of low aspect ratio flying wing configuration.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {16295}, pmid = {34381068}, issn = {2045-2322}, abstract = {With the aim for a low-aspect-ratio flying wing configuration, this study explores the influence of wall temperature gradient on the laminar and turbulent boundary layers of aircraft surface and determines the effect on the transition Reynolds number and wall friction drag. A four-equation turbulence model with transition mode is used to numerically simulate the flow around the model. The variation of wall friction coefficient, transition Reynolds number, and turbulent boundary layer flow with wall temperature are emphatically investigated. Results show that when the wall temperature increases from 288 to 500 K, the boundary layer transition Reynolds number for the wing section increased by approximately 28% and the surface friction drags decreases by approximately 10.7%. The hot wall enhances the viscous effects of the laminar temperature boundary layer, reduces the Reynolds shear stress and turbulent kinetic energy, and increases the flow stability. However, the velocity gradient and shear stress in the bottom of the turbulent boundary layer decreases, which leads to reduced friction shear stress on the wall surface. Therefore, for the low-aspect-ratio flying wing model, the hot wall can delay the boundary layer transition and reduce the friction drag coefficient in the turbulent region.}, } @article {pmid34373556, year = {2021}, author = {Xia, WF and Hafeez, MU and Khan, MI and Shah, NA and Chung, JD}, title = {Entropy optimized dissipative flow of hybrid nanofluid in the presence of non-linear thermal radiation and Joule heating.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {16067}, pmid = {34373556}, issn = {2045-2322}, abstract = {Present article reads three dimensional flow analysis of incompressible viscous hybrid nanofluid in a rotating frame. Ethylene glycol is used as a base liquid while nanoparticles are of copper and silver. Fluid is bounded between two parallel surfaces in which the lower surface stretches linearly. Fluid is conducting hence uniform magnetic field is applied. Effects of non-linear thermal radiation, Joule heating and viscous dissipation are entertained. Interesting quantities namely surface drag force and Nusselt number are discussed. Rate of entropy generation is examined. Bvp4c numerical scheme is used for the solution of transformed O.D.Es. Results regarding various flow parameters are obtained via bvp4c technique in MATLAB Software version 2019, and displayed through different plots. Our obtained results presents that velocity field decreases with respect to higher values of magnetic parameter, Reynolds number and rotation parameter. It is also observed that the temperature field boots subject to radiation parameter. Results are compared with Ishak et al. (Nonlinear Anal R World Appl 10:2909-2913, 2009) and found very good agreement with them. This agreement shows that the results are 99.99% match with each other.}, } @article {pmid34373493, year = {2021}, author = {Alihosseini, Y and Azaddel, MR and Moslemi, S and Mohammadi, M and Pormohammad, A and Targhi, MZ and Heyhat, MM}, title = {Effect of liquid cooling on PCR performance with the parametric study of cross-section shapes of microchannels.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {16072}, pmid = {34373493}, issn = {2045-2322}, abstract = {In recent years, PCR-based methods as a rapid and high accurate technique in the industry and medical fields have been expanded rapidly. Where we are faced with the COVID-19 pandemic, the necessity of a rapid diagnosis has felt more than ever. In the current interdisciplinary study, we have proposed, developed, and characterized a state-of-the-art liquid cooling design to accelerate the PCR procedure. A numerical simulation approach is utilized to evaluate 15 different cross-sections of the microchannel heat sink and select the best shape to achieve this goal. Also, crucial heat sink parameters are characterized, e.g., heat transfer coefficient, pressure drop, performance evaluation criteria, and fluid flow. The achieved result showed that the circular cross-section is the most efficient shape for the microchannel heat sink, which has a maximum heat transfer enhancement of 25% compared to the square shape at the Reynolds number of 1150. In the next phase of the study, the circular cross-section microchannel is located below the PCR device to evaluate the cooling rate of the PCR. Also, the results demonstrate that it takes 16.5 s to cool saliva samples in the PCR well, which saves up to 157.5 s for the whole amplification procedure compared to the conventional air fans. Another advantage of using the microchannel heat sink is that it takes up a little space compared to other common cooling methods.}, } @article {pmid34372345, year = {2021}, author = {Costantini, M and Henne, U and Klein, C and Miozzi, M}, title = {Skin-Friction-Based Identification of the Critical Lines in a Transonic, High Reynolds Number Flow via Temperature-Sensitive Paint.}, journal = {Sensors (Basel, Switzerland)}, volume = {21}, number = {15}, pages = {}, pmid = {34372345}, issn = {1424-8220}, abstract = {In this contribution, three methodologies based on temperature-sensitive paint (TSP) data were further developed and applied for the optical determination of the critical locations of flow separation and reattachment in compressible, high Reynolds number flows. The methodologies rely on skin-friction extraction approaches developed for low-speed flows, which were adapted in this work to study flow separation and reattachment in the presence of shock-wave/boundary-layer interaction. In a first approach, skin-friction topological maps were obtained from time-averaged surface temperature distributions, thus enabling the identification of the critical lines as converging and diverging skin-friction lines. In the other two approaches, the critical lines were identified from the maps of the propagation celerity of temperature perturbations, which were determined from time-resolved TSP data. The experiments were conducted at a freestream Mach number of 0.72 and a chord Reynolds number of 9.7 million in the Transonic Wind Tunnel Göttingen on a VA-2 supercritical airfoil model, which was equipped with two exchangeable TSP modules specifically designed for transonic, high Reynolds number tests. The separation and reattachment lines identified via the three different TSP-based approaches were shown to be in mutual agreement, and were also found to be in agreement with reference experimental and numerical data.}, } @article {pmid34359055, year = {2021}, author = {Diaz, K and Robinson, TL and Aydin, YO and Aydin, E and Goldman, DI and Wan, KY}, title = {A minimal robophysical model of quadriflagellate self-propulsion.}, journal = {Bioinspiration & biomimetics}, volume = {16}, number = {6}, pages = {}, doi = {10.1088/1748-3190/ac1b6e}, pmid = {34359055}, issn = {1748-3190}, mesh = {Flagella ; Gait ; Locomotion ; *Robotics ; *Swimming ; }, abstract = {Locomotion at the microscale is remarkably sophisticated. Microorganisms have evolved diverse strategies to move within highly viscous environments, using deformable, propulsion-generating appendages such as cilia and flagella to drive helical or undulatory motion. In single-celled algae, these appendages can be arranged in different ways around an approximately 10 μm long cell body, and coordinated in distinct temporal patterns. Inspired by the observation that some quadriflagellates (bearing four flagella) have an outwardly similar morphology and flagellar beat pattern, yet swim at different speeds, this study seeks to determine whether variations in swimming performance could arise solely from differences in swimming gait. Robotics approaches are particularly suited to such investigations, where the phase relationships between appendages can be readily manipulated. Here, we developed autonomous, algae-inspired robophysical models that can self-propel in a viscous fluid. These macroscopic robots (length and width = 8.5 cm, height = 2 cm) have four independently actuated 'flagella' (length = 13 cm) that oscillate under low-Reynolds number conditions (Re∼O(10-1)). We tested the swimming performance of these robot models with appendages arranged two distinct configurations, and coordinated in three distinct gaits. The gaits, namely the pronk, the trot, and the gallop, correspond to gaits adopted by distinct microalgal species. When the appendages are inserted perpendicularly around a central 'body', the robot achieved a net performance of 0.15-0.63 body lengths per cycle, with the trot gait being the fastest. Robotic swimming performance was found to be comparable to that of the algal microswimmers across all gaits. By creating a minimal robot that can successfully reproduce cilia-inspired drag-based swimming, our work paves the way for the design of next-generation devices that have the capacity to autonomously navigate aqueous environments.}, } @article {pmid34357216, year = {2021}, author = {Li, L and Chen, Q and Sui, G and Qian, J and Tsai, CT and Cheng, X and Jing, W}, title = {A Three-Dimensional Micromixer Using Oblique Embedded Ridges.}, journal = {Micromachines}, volume = {12}, number = {7}, pages = {}, pmid = {34357216}, issn = {2072-666X}, abstract = {A micromixer is one of the most significant components in a microfluidic system. A three-dimensional micromixer was developed with advantages of high efficiency, simple fabrication, easy integration, and ease of mass production. The designed principle is based on the concepts of splitting-recombination and chaotic advection. A numerical model of this micromixer was established to characterize the mixing performance for different parameters. A critical Reynolds number (Re) was obtained from the simulation results. When the Re number is smaller than the critical value, the fluid mixing is mainly dependent on the mechanism of splitting-recombination, therefore, the length of the channel capable of complete mixing (complete mixing length) increases as the Re number increases. When the Re number is larger than the critical value, the fluid mixing is dominated by chaotic advection, and the complete mixing length decreases as the Re number increases. For normal fluids, a complete mixing length of 500 µm can be achieved at a very small Re number of 0.007 and increases to 2400 µm as the Re number increases to the critical value of 4.7. As the Re number keep increasing and passes the critical Re number, the complete mixing length continues to descend to 650 µm at the Re number of 66.7. For hard-to-mix fluids (generally referring to fluids with high viscosity and low diffusion coefficient, which are difficult to mix), even though no evidence of strong chaotic advection is presented in the simulation, the micromixer can still achieve a complete mixing length of 2550 µm. The mixing performance of the micromixer was also verified by experiments. The experimental results showed a consistent trend with the numerical simulation results, which both climb upward when the Re number is around 0.007 (flow rate of 0.03 μm/min) to around 10 (flow rate of 50 μm/min), then descend when the Re number is around 13.3 (flow rate of 60 µm/min).}, } @article {pmid34357184, year = {2021}, author = {Nichka, VS and Nikonenko, VV and Bazinet, L}, title = {Fouling Mitigation by Optimizing Flow Rate and Pulsed Electric Field during Bipolar Membrane Electroacidification of Caseinate Solution.}, journal = {Membranes}, volume = {11}, number = {7}, pages = {}, pmid = {34357184}, issn = {2077-0375}, abstract = {The efficiency of separation processes using ion exchange membranes (IEMs), especially in the food industry, is significantly limited by the fouling phenomenon, which is the process of the attachment and growth of certain species on the surface and inside the membrane. Pulsed electric field (PEF) mode, which consists in the application of constant current density pulses during a fixed time (Ton) alternated with pause lapses (Toff), has a positive antifouling impact. The aim of this study was to investigate the combined effect of three different relatively high flow rates of feed solution (corresponding to Reynolds numbers of 187, 374 and 560) and various pulse-pause ratios of PEF current regime on protein fouling kinetics during electrodialysis with bipolar membranes (EDBM) of a model caseinate solution. Four different pulse/pause regimes (with Ton/Toff ratios equal to 10 s/10 s, 10 s/20 s, 10 s/33 s and 10 s/50 s) during electrodialysis (ED) treatment were evaluated at a current density of 5 mA/cm[2]. It was found that increasing the pause duration and caseinate solution flow rate had a positive impact on the minimization of protein fouling occurring on the cationic surface of the bipolar membrane (BPM) during the EDBM. Both a long pause and high flow rate contribute to a more effective decrease in the concentration of protons and caseinate anions at the BPM surface: a very good membrane performance was achieved with 50 s of pause duration of PEF and a flow rate corresponding to Re = 374. A further increase in PEF pause duration (above 50 s) or flow rate (above Re = 374) did not lead to a significant decrease in the amount of fouling.}, } @article {pmid34349343, year = {2021}, author = {Ferroni, C and Bracconi, M and Ambrosetti, M and Maestri, M and Groppi, G and Tronconi, E}, title = {A Fundamental Investigation of Gas/Solid Heat and Mass Transfer in Structured Catalysts Based on Periodic Open Cellular Structures (POCS).}, journal = {Industrial & engineering chemistry research}, volume = {60}, number = {29}, pages = {10522-10538}, pmid = {34349343}, issn = {0888-5885}, abstract = {In this work, we investigate the gas-solid heat and mass transfer in catalytically activated periodic open cellular structures, which are considered a promising solution for intensification of catalytic processes limited by external transport, aiming at the derivation of suitable correlations. Computational fluid dynamics is employed to investigate the Tetrakaidekahedral and Diamond lattice structures. The influence of the morphological features and flow conditions on the external transport properties is assessed. The strut diameter is an adequate characteristic length for the formulation of heat and mass transfer correlations; accordingly, a power-law dependence of the Sherwood number to the Reynolds number between 0.33 and 0.67 was found according to the flow regimes in the range 1-128 of the Reynolds number. An additional -1.5-order dependence on the porosity is found. The formulated correlations are in good agreement with the simulation results and allow for the accurate evaluation of the external transfer coefficients for POCS.}, } @article {pmid34335006, year = {2021}, author = {Liu, K and Allahyari, M and Salinas, J and Zgheib, N and Balachandar, S}, title = {Investigation of theoretical scaling laws using large eddy simulations for airborne spreading of viral contagion from sneezing and coughing.}, journal = {Physics of fluids (Woodbury, N.Y. : 1994)}, volume = {33}, number = {6}, pages = {063318}, pmid = {34335006}, issn = {1070-6631}, abstract = {Using a set of large eddy point-particle simulations, we explore the fluid dynamics of an ejected puff resulting from a cough/sneeze. The ejection contains over 61 000 potentially virus-laden droplets at an injection Reynolds number of about 46 000, comparable to an actual cough/sneeze. We observe that global puff properties, such as centroid, puff volume, momentum, and buoyancy vary little across realizations. Other properties, such as maximum extent, shape, and edge velocity of the puff, may exhibit substantial variation. In many realizations, a portion of the puff splits off and advances along a random direction, while keeping airborne droplet nuclei afloat. This peeled-off portion provides a mechanism for virus-laden droplets to travel over large distances in a short amount of time. We also observe that the vast majority of droplets remain suspended within the puff after all liquid has evaporated. The main objectives of the study are to (i) evaluate assumptions of Balachandar's et al. theory [Int. J. Multiphase Flow 132, 103439 (2020)], which include buoyancy effects, shape of the puff, and droplet evaporation rate, (ii) obtain values of closure parameters, which include location and time of the virtual origin, and puff entrainment and drag coefficients, and (iii) evaluate the accuracy of the theory in predicting the shape, size, and location of the puff, as well as droplet number density long after ejection. The theory adequately predicts global puff properties including size, velocity, and distance traveled, the largest size of droplets that exit the puff due to settling, and the droplet size distribution within the puff long after ejection.}, } @article {pmid34319753, year = {2021}, author = {Singh, RK and Mahato, LK and Mandal, DK}, title = {Airflow-Assisted Impact of Drops of Various Viscosities: The Role of Viscous Dissipation, Normal Imposed Pressure, and Shear Flow of Air.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {37}, number = {31}, pages = {9504-9517}, doi = {10.1021/acs.langmuir.1c01367}, pmid = {34319753}, issn = {1520-5827}, abstract = {The role of liquid viscosity on the spreading for an airflow-assisted impact of drops on a surface is investigated. The spreading diameter is found to increase with the Reynolds number of the airflow (Reair) for a given viscosity and impact Weber number (We) compared to the still air. The increment is higher at a low We for viscous drops, whereas the effect of Reair dominates at the intermediate We as the viscosity decreases. Two extra forces, the normal imposed pressure and shear force of air, act on the drop and influence the spreading along with the viscous dissipation. The drop's curvature decreases depending on the viscosity and impact velocity while spreading. Large-scale eddies near the drop-surface region are observed due to the separation of the incident airflow. The formation of eddies signifies low-pressure zones, which extract the trapped air, causing the spreading diameter of the viscous drop to increase at a low We. With the increase in the We, the lamella thickness of low-viscosity drops decreases and is pushed out by the air shear causing the spreading factor to increase. The boundary layer thickness is estimated using the energy balance method to predict the maximum spreading factor. The prediction compares well with the experimental one for higher viscosities. The accuracy improves when the effect of low pressure is incorporated. To confirm, the experimental spreading is compared with that obtained from three existing models, and one, which considers the influence, is observed to provide a better prediction.}, } @article {pmid34297252, year = {2021}, author = {Sharifi, A and Gendernalik, A and Garrity, D and Bark, D}, title = {Valveless pumping behavior of the simulated embryonic heart tube as a function of contractile patterns and myocardial stiffness.}, journal = {Biomechanics and modeling in mechanobiology}, volume = {20}, number = {5}, pages = {2001-2012}, pmid = {34297252}, issn = {1617-7940}, mesh = {Animals ; Biomechanical Phenomena ; Cardiac Output ; Computer Simulation ; Electric Impedance ; Heart/*embryology/*physiology ; Heart Rate ; *Hemodynamics ; Models, Cardiovascular ; Models, Theoretical ; *Myocardial Contraction ; Myocardium/*pathology ; Peristalsis ; Pressure ; Stress, Mechanical ; Zebrafish/*embryology ; }, abstract = {During development, the heart begins pumping as a valveless multilayered tube capable of driving blood flow throughout the embryonic vasculature. The mechanical properties and how they interface with pumping function are not well-defined at this stage. Here, we evaluate pumping patterns using a fluid-structure interaction computational model, combined with experimental data and an energetic analysis to investigate myocardial mechanical properties. Through this work, we propose that a myocardium modeled as a Neo-Hookean material with a material constant on the order of 10 kPa is necessary for the heart tube to function with an optimal pressure and cardiac output.}, } @article {pmid34293964, year = {2021}, author = {Akram, S and Athar, M and Saeed, K and Razia, A}, title = {Crossbreed impact of double-diffusivity convection on peristaltic pumping of magneto Sisko nanofluids in non-uniform inclined channel: A bio-nanoengineering model.}, journal = {Science progress}, volume = {104}, number = {3}, pages = {368504211033677}, doi = {10.1177/00368504211033677}, pmid = {34293964}, issn = {2047-7163}, abstract = {The consequences of double-diffusivity convection on the peristaltic transport of Sisko nanofluids in the non-uniform inclined channel and induced magnetic field are discussed in this article. The mathematical modeling of Sisko nanofluids with induced magnetic field and double-diffusivity convection is given. To simplify PDEs that are highly nonlinear in nature, the low but finite Reynolds number, and long wavelength estimation are used. The Numerical solution is calculated for the non-linear PDEs. The exact solution of concentration, temperature and nanoparticle are obtained. The effect of various physical parameters of flow quantities is shown in numerical and graphical data. The outcomes show that as the thermophoresis and Dufour parameters are raised, the profiles of temperature, concentration, and nanoparticle fraction all significantly increase.}, } @article {pmid34286832, year = {2021}, author = {Kasoju, VT and Moen, DS and Ford, MP and Ngo, TT and Santhanakrishnan, A}, title = {Interspecific variation in bristle number on forewings of tiny insects does not influence clap-and-fling aerodynamics.}, journal = {The Journal of experimental biology}, volume = {224}, number = {18}, pages = {}, doi = {10.1242/jeb.239798}, pmid = {34286832}, issn = {1477-9145}, mesh = {Animals ; Biomechanical Phenomena ; *Flight, Animal ; Insecta ; Models, Biological ; Phylogeny ; *Wings, Animal ; }, abstract = {Miniature insects must overcome significant viscous resistance in order to fly. They typically possess wings with long bristles on the fringes and use a clap-and-fling mechanism to augment lift. These unique solutions to the extreme conditions of flight at tiny sizes (<2 mm body length) suggest that natural selection has optimized wing design for better aerodynamic performance. However, species vary in wingspan, number of bristles (n) and bristle gap (G) to diameter (D) ratio (G/D). How this variation relates to body length (BL) and its effects on aerodynamics remain unknown. We measured forewing images of 38 species of thrips and 21 species of fairyflies. Our phylogenetic comparative analyses showed that n and wingspan scaled positively and similarly with BL across both groups, whereas G/D decreased with BL, with a sharper decline in thrips. We next measured aerodynamic forces and visualized flow on physical models of bristled wings performing clap-and-fling kinematics at a chord-based Reynolds number of 10 using a dynamically scaled robotic platform. We examined the effects of dimensional (G, D, wingspan) and non-dimensional (n, G/D) geometric variables on dimensionless lift and drag. We found that: (1) increasing G reduced drag more than decreasing D; (2) changing n had minimal impact on lift generation; and (3) varying G/D minimally affected aerodynamic forces. These aerodynamic results suggest little pressure to functionally optimize n and G/D. Combined with the scaling relationships between wing variables and BL, much wing variation in tiny flying insects might be best explained by underlying shared growth factors.}, } @article {pmid34283850, year = {2021}, author = {Dvoriashyna, M and Lauga, E}, title = {Hydrodynamics and direction change of tumbling bacteria.}, journal = {PloS one}, volume = {16}, number = {7}, pages = {e0254551}, pmid = {34283850}, issn = {1932-6203}, mesh = {Biomechanical Phenomena ; Escherichia coli/chemistry/*physiology ; Flagella/*physiology ; *Hydrodynamics ; Models, Biological ; Movement/*physiology ; Rotation ; Swimming/physiology ; }, abstract = {The bacterium Escherichia coli (E. coli) swims in viscous fluids by rotating several helical flagellar filaments, which are gathered in a bundle behind the cell during 'runs' wherein the cell moves steadily forward. In between runs, the cell undergoes quick 'tumble' events, during which at least one flagellum reverses its rotation direction and separates from the bundle, resulting in erratic motion in place and a random reorientation of the cell. Alternating between runs and tumbles allows cells to sample space by stochastically changing their propulsion direction after each tumble. The change of direction during a tumble is not uniformly distributed but is skewed towards smaller angles with an average of about 62°-68°, as first measured by Berg and Brown (1972). Here we develop a theoretical approach to model the angular distribution of swimming E. coli cells during tumbles. We first use past experimental imaging results to construct a kinematic description of the dynamics of the flagellar filaments during a tumble. We then employ low-Reynolds number hydrodynamics to compute the consequences of the kinematic model on the force and torque balance of the cell and to deduce the overall change in orientation. The results of our model are in good agreement with experimental observations. We find that the main change of direction occurs during the 'bundling' part of the process wherein, at the end of a tumble, the dispersed flagellar filaments are brought back together in the helical bundle, which we confirm using a simplified forced-sphere model.}, } @article {pmid34282226, year = {2021}, author = {Ishak, MS and Alsabery, AI and Hashim, I and Chamkha, AJ}, title = {Entropy production and mixed convection within trapezoidal cavity having nanofluids and localised solid cylinder.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {14700}, pmid = {34282226}, issn = {2045-2322}, abstract = {The entropy production and mixed convection within a trapezoidal nanofluid-filled cavity having a localised solid cylinder is numerically examined using the finite element technique. The top horizontal surface moving at a uniform velocity is kept at a cold temperature, while the bottom horizontal surface is thermally activated. The remaining surfaces are maintained adiabatic. Water-based nanofluids ([Formula: see text] nanoparticles) are used in this study, and the Boussinesq approximation applies. The influence of the Reynolds number, Richardson number, nanoparticles volume fraction, dimensionless radius and location of the solid cylinder on the streamlines, isotherms and isentropic are examined. The results show that the solid cylinder's size and location are significant control parameters for optimising the heat transfer and the Bejan number inside the trapezoidal cavity. Furthermore, the maximum average Nusselt numbers are obtained for high R values, where the average Nusselt number is increased by 30% when R is raised from 0 to 0.25.}, } @article {pmid34275183, year = {2021}, author = {Gurovich, AN and Rodriguez, L and Morales-Acuna, F}, title = {There are no differences in brachial artery endothelial shear stress and blood flow patterns between males and females during exercise.}, journal = {Clinical physiology and functional imaging}, volume = {41}, number = {6}, pages = {471-479}, doi = {10.1111/cpf.12722}, pmid = {34275183}, issn = {1475-097X}, mesh = {*Brachial Artery/diagnostic imaging ; Cross-Sectional Studies ; *Endothelium, Vascular ; Exercise ; Female ; Hemodynamics ; Humans ; Male ; Regional Blood Flow ; Vasodilation ; }, abstract = {Premenopausal females have a lower cardiovascular risk than males. Sex differences on exercise-induced endothelial shear stress (ESS) and blood flow patterns may explain part of this risk reduction. The purpose of this cross-sectional study was to determine the differences in brachial artery exercise-induced ESS and blood flow patterns between males and females. Thirty subjects (13 females) were recruited to perform a three-workload steady-state exercise test based on blood lactate levels (i.e. <2.0, 2.0-4.0, >4.0 mmol/l). ESS and blood flow patterns were estimated at rest and during each workload using Womersley's approximation and Reynolds number, respectively. Both males and females showed an exercise intensity-dependent increase in antegrade and retrograde ESS. There was no significant sex effect or interaction for antegrade ESS (F(1, 30) = 0.715, p = 0.405 and F(1·672, 60) = 1.511, p = 0.232, respectively) or retrograde ESS (F(1, 30) = 0.794, p = 0.380 and F(1·810, 60) = 1.022, p = 0.361, respectively). Additionally, antegrade blood flow was turbulent during all bouts of exercise while retrograde blood flow became disturbed at moderate and high exercise intensities in both groups. There are no differences in exercise-induced ESS and blood flow patterns between males and females when the exercise load is equivalent. This suggests that the vascular benefits of exercise training are similar in both sexes from a haemodynamic standpoint.}, } @article {pmid34272432, year = {2021}, author = {Gul, H and Ramzan, M and Chung, JD and Chu, YM and Kadry, S}, title = {Multiple slips impact in the MHD hybrid nanofluid flow with Cattaneo-Christov heat flux and autocatalytic chemical reaction.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {14625}, pmid = {34272432}, issn = {2045-2322}, abstract = {The present study deliberates the nanofluid flow containing multi and single-walled carbon nanotubes submerged into Ethylene glycol in a Darcy-Forchheimer permeable media over a stretching cylinder with multiple slips. The innovation of the envisaged mathematical model is enriched by considering the impacts of non-uniform source/sink and modified Fourier law in the energy equation and autocatalytic chemical reaction in the concentration equation. Entropy optimization analysis of the mathematical model is also performed in the present problem. Pertinent transformations procedure is implemented for the conversion of the non-linear system to the ordinary differential equations. The succor of the Shooting technique combined with the bvp4c MATLAB software is utilized for the solution of a highly nonlinear system of equations. The impacts of the leading parameters versus engaged fields are inspected through graphical sketches. The outcomes show that a strong magnetic field strengthens the temperature profile and decays the velocity profile. Also, the fluid velocity is lessened for growing estimates of the parameter of slip. Additionally, it is detected that entropy number augmented for higher thermal relaxation parameter and Reynolds number. To substantiate the existing mathematical model, a comparison table is also added. An excellent correlation is achieved here.}, } @article {pmid34272408, year = {2021}, author = {Wang, H and Enders, A and Preuss, JA and Bahnemann, J and Heisterkamp, A and Torres-Mapa, ML}, title = {3D printed microfluidic lab-on-a-chip device for fiber-based dual beam optical manipulation.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {14584}, pmid = {34272408}, issn = {2045-2322}, abstract = {3D printing of microfluidic lab-on-a-chip devices enables rapid prototyping of robust and complex structures. In this work, we designed and fabricated a 3D printed lab-on-a-chip device for fiber-based dual beam optical manipulation. The final 3D printed chip offers three key features, such as (1) an optimized fiber channel design for precise alignment of optical fibers, (2) an optically clear window to visualize the trapping region, and (3) a sample channel which facilitates hydrodynamic focusing of samples. A square zig-zag structure incorporated in the sample channel increases the number of particles at the trapping site and focuses the cells and particles during experiments when operating the chip at low Reynolds number. To evaluate the performance of the device for optical manipulation, we implemented on-chip, fiber-based optical trapping of different-sized microscopic particles and performed trap stiffness measurements. In addition, optical stretching of MCF-7 cells was successfully accomplished for the purpose of studying the effects of a cytochalasin metabolite, pyrichalasin H, on cell elasticity. We observed distinct changes in the deformability of single cells treated with pyrichalasin H compared to untreated cells. These results demonstrate that 3D printed microfluidic lab-on-a-chip devices offer a cost-effective and customizable platform for applications in optical manipulation.}, } @article {pmid34271062, year = {2021}, author = {Dubey, A and B, V and Bég, OA and Gorla, RSR}, title = {Finite element computation of magneto-hemodynamic flow and heat transfer in a bifurcated artery with saccular aneurysm using the Carreau-Yasuda biorheological model.}, journal = {Microvascular research}, volume = {138}, number = {}, pages = {104221}, doi = {10.1016/j.mvr.2021.104221}, pmid = {34271062}, issn = {1095-9319}, mesh = {Aorta/*physiopathology ; Aortic Aneurysm/*physiopathology ; Blood Flow Velocity ; Computer Simulation ; Electric Conductivity ; Energy Transfer ; Finite Element Analysis ; *Hemorheology ; Hot Temperature ; Humans ; *Magnetic Fields ; *Models, Cardiovascular ; Pulsatile Flow ; Regional Blood Flow ; Stress, Mechanical ; Time Factors ; }, abstract = {"Existing computational fluid dynamics studies of blood flows have demonstrated that the lower wall stress and higher oscillatory shear index might be the cause of acceleration in atherogenesis of vascular walls in hemodynamics. To prevent the chances of aneurysm wall rupture in the saccular aneurysm at distal aortic bifurcation, clinical biomagnetic studies have shown that extra-corporeal magnetic fields can be deployed to regulate the blood flow. Motivated by these developments, in the current study a finite element computational fluid dynamics simulation has been conducted of unsteady two-dimensional non-Newtonian magneto-hemodynamic heat transfer in electrically conducting blood flow in a bifurcated artery featuring a saccular aneurysm. The fluid flow is assumed to be pulsatile, non-Newtonian and incompressible. The Carreau-Yasuda model is adopted for blood to mimic non-Newtonian characteristics. The transformed equations with appropriate boundary conditions are solved numerically by employing the finite element method with the variational approach in the FreeFEM++ code. Hydrodynamic and thermal characteristics are elucidated in detail for the effects of key non-dimensional parameters i.e. Reynolds number (Re = 14, 21, 100, 200), Prandtl number (Pr = 14, 21) and magnetic body force parameter (Hartmann number) (M = 0.6, 1.2, 1.5) at the aneurysm and throughout the arterial domain. The influence of vessel geometry on blood flow characteristics i.e. velocity, pressure and temperature fields are also visualized through instantaneous contour patterns. It is found that an increase in the magnetic parameter reduces the pressure but increases the skin-friction coefficient in the domain. The temperature decreases at the parent artery (inlet) and both the distant and prior artery with the increment in the Prandtl number. A higher Reynolds number also causes a reduction in velocity as well as in pressure. The blood flow shows different characteristic contours with time variation at the aneurysm as well as in the arterial segment. The novelty of the current research is therefore to present a combined approach amalgamating the Carreau-Yasuda model, heat transfer and magnetohydrodynamics with complex geometric features in realistic arterial hemodynamics with extensive visualization and interpretation, in order to generalize and extend previous studies. In previous studies these features have been considered separately and not simultaneously as in the current study. The present simulations reveal some novel features of biomagnetic hemodynamics in bifurcated arterial transport featuring a saccular aneurysm which are envisaged to be of relevance in furnishing improved characterization of the rheological biomagnetic hemodynamics of realistic aneurysmic bifurcations in clinical assessment, diagnosis and magnetic-assisted treatment of cardiovascular disease."}, } @article {pmid34266946, year = {2021}, author = {Han, E and Zhu, L and Shaevitz, JW and Stone, HA}, title = {Low-Reynolds-number, biflagellated Quincke swimmers with multiple forms of motion.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {118}, number = {29}, pages = {}, pmid = {34266946}, issn = {1091-6490}, mesh = {Hydrodynamics ; Locomotion/*physiology ; *Models, Biological ; Motion ; Rheology ; Rotation ; }, abstract = {In the limit of zero Reynolds number (Re), swimmers propel themselves exploiting a series of nonreciprocal body motions. For an artificial swimmer, a proper selection of the power source is required to drive its motion, in cooperation with its geometric and mechanical properties. Although various external fields (magnetic, acoustic, optical, etc.) have been introduced, electric fields are rarely utilized to actuate such swimmers experimentally in unbounded space. Here we use uniform and static electric fields to demonstrate locomotion of a biflagellated sphere at low Re via Quincke rotation. These Quincke swimmers exhibit three different forms of motion, including a self-oscillatory state due to elastohydrodynamic-electrohydrodynamic interactions. Each form of motion follows a distinct trajectory in space. Our experiments and numerical results demonstrate a method to generate, and potentially control, the locomotion of artificial flagellated swimmers.}, } @article {pmid34260387, year = {2021}, author = {Zhang, B and Leishangthem, P and Ding, Y and Xu, X}, title = {An effective and efficient model of the near-field hydrodynamic interactions for active suspensions of bacteria.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {118}, number = {28}, pages = {}, pmid = {34260387}, issn = {1091-6490}, mesh = {Computer Simulation ; Escherichia coli/*physiology ; *Hydrodynamics ; *Models, Biological ; Suspensions ; }, abstract = {Near-field hydrodynamic interactions in active fluids are essential to determine many important emergent behaviors observed, but have not been successfully modeled so far. In this work, we propose an effective model capturing the essence of the near-field hydrodynamic interactions through a tensorial coefficient of resistance, validated numerically by a pedagogic model system consisting of an Escherichia coli bacterium and a passive sphere. In a critical test case that studies the scattering angle of the bacterium-sphere pair dynamics, we prove that the near-field hydrodynamics can make a qualitative difference even for this simple two-body system: Calculations based on the proposed model reveal a region in parameter space where the bacterium is trapped by the passive sphere, a phenomenon that is regularly observed in experiments but cannot be explained by any existing model. In the end, we demonstrate that our model also leads to efficient simulation of active fluids with tens of thousands of bacteria, sufficiently large for investigations of many emergent behaviors.}, } @article {pmid34251258, year = {2021}, author = {Charakopoulos, A and Karakasidis, T and Sarris, I}, title = {Analysis of magnetohydrodynamic channel flow through complex network analysis.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {31}, number = {4}, pages = {043123}, doi = {10.1063/5.0043817}, pmid = {34251258}, issn = {1089-7682}, abstract = {Velocity time series of hydrodynamic and magnetohydrodynamic (MHD) turbulent flow are analyzed by means of complex network analysis in order to understand the mechanism of fluid patterns modification due to the external magnetic field. Direct numerical simulations of two cases are used, one for the plane hydrodynamic turbulent channel flow at the low Reynolds number of 180, based on the friction velocity, and the corresponding MHD flow with an external streamwise magnetic field with a magnetic interaction number of 0.1. By applying the visibility graph algorithm, we first transformed the time series into networks and then we evaluated the network topological properties. Results show that the proposed network analysis is not only able to identify and detect dynamical transitions in the system's behavior that identifies three distinct fluid areas in accordance with turbulent flow theory but also can quantify the effect of the magnetic field on the time series transitions. Moreover, we find that the topological measures of networks without a magnetic field and as compared to the one with a magnetic field are statistically different within a 95% confidence interval. These results provide a way to discriminate and characterize the influence of the magnetic field on the turbulent flows.}, } @article {pmid34247118, year = {2021}, author = {Tang, TQ and Hsu, SY and Dahiya, A and Soh, CH and Lin, KC}, title = {Numerical modeling of pulsatile blood flow through a mini-oxygenator in artificial lungs.}, journal = {Computer methods and programs in biomedicine}, volume = {208}, number = {}, pages = {106241}, doi = {10.1016/j.cmpb.2021.106241}, pmid = {34247118}, issn = {1872-7565}, mesh = {Equipment Design ; Humans ; Hydrodynamics ; Lung ; *Oxygen ; *Oxygenators, Membrane ; Pulsatile Flow ; }, abstract = {While previous in vitro studies showed divergent results concerning the influence of pulsatile blood flow on oxygen advection in oxygenators, no study was done to investigate the uncertainty affected by blood flow dynamics. The aim of this study is to utilize a computational fluid dynamics model to clarify the debate concerning the influence of pulsatile blood flow on the oxygen transport. The computer model is based on a validated 2D finite volume approach that predicts oxygen transfer in pulsatile blood flow passing through a 300-micron hollow-fiber membrane bundle with a length of 254 mm, a building block for an artificial lung device. In this study, the flow parameters include the steady Reynolds number (Re = 2, 5, 10 and 20), Womersley parameter (Wo = 0.29, 0.38 and 0.53) and sinusoidal amplitude (A = 0.25, 0.5 and 0.75). Specifically, the computer model is extended to verify, for the first time, the previously measured O2 transport that was observed to be hindered by pulsating flow in the Biolung, developed by Michigan Critical Care Consultants. A comprehensive analysis is carried out on computed profiles and fields of oxygen partial pressure (PO2) and oxygen saturation (SO2) as a function of Re, Wo and A. Based on the present results, we observe the positive and negative effects of pulsatile flow on PO2 at different blood flow rates. Besides, the SO2 variation is not much influenced by the pulsatile flow conditions investigated. While being consistent with a recent experimental study, the computed O2 volume flow rate is found to be increased at high blood flow rates operated with low frequency and high amplitude. Furthermore, the present study qualitatively explains that divergent outcomes reported in previous in vitro experimental studies could be owing to the different blood flow rates adopted. Finally, the contour analysis reveals how the spatial distributions of PO2 and SO2 vary over time.}, } @article {pmid34243174, year = {2021}, author = {Meng, X and Ghaffar, A and Zhang, Y and Deng, C}, title = {Very low Reynolds number causes a monotonic force enhancement trend for a three-dimensional hovering wing in ground effect.}, journal = {Bioinspiration & biomimetics}, volume = {16}, number = {5}, pages = {}, doi = {10.1088/1748-3190/ac1308}, pmid = {34243174}, issn = {1748-3190}, mesh = {Animals ; Biomechanical Phenomena ; *Flight, Animal ; Insecta ; Models, Biological ; *Wings, Animal ; }, abstract = {This research reports the numerical results of the ground effect trend for a three-dimensional flapping insect wing at a very low Reynolds number (Re = 10). It demonstrates that the ground effect trend at this Re has a 'single force regime,' i.e. the forces only enhance as the ground distance decreases. This phenomenon is unlike the widely expected non-monotonic trend publicized in previous studies for higher Reynolds numbers, that shows 'three force regimes,' i.e. the forces reduce, recover, and also enhance as the ground distance decreases. The force trend in the ground effect correlates to a similar trend in wing-wake interaction or the downwash strength on the wing's head. At very low Re (10), the very large viscosity causes diffused vortices and less advected vortex wake, while at relatively high Re, the vortices are easily separated from the wing and then advected downwards. This different development of the vortex wake caused different force trends for the flapping wing in the ground effect. Furthermore, by examining only the first stroke when there is no vortex wake, we found that the 'ramming effect' enhances the forces on the wing. This effect increases the pressure of the lower wing surface due to the squeezed air between the wing and the ground. The 'ramming effect', combined with the reduced downwash (or wing-wake interaction) effect, causes the force enhancement of the wing near the ground's vicinity. It is further comprehended that the trend is dependent on Re. As the Re is increased, the trend becomes non-monotonic. The effect of varying angles of attack, flapping amplitude and wing planform at very low Re does not change this trend. This ground effect might help insects by enhancing their lift while they hover above the surface. This finding might prove beneficial for developing micro air vehicles.}, } @article {pmid34241532, year = {2021}, author = {Iyer, KP and Bewley, GP and Biferale, L and Sreenivasan, KR and Yeung, PK}, title = {Oscillations Modulating Power Law Exponents in Isotropic Turbulence: Comparison of Experiments with Simulations.}, journal = {Physical review letters}, volume = {126}, number = {25}, pages = {254501}, doi = {10.1103/PhysRevLett.126.254501}, pmid = {34241532}, issn = {1079-7114}, abstract = {Inertial-range features of turbulence are investigated using data from experimental measurements of grid turbulence and direct numerical simulations of isotropic turbulence simulated in a periodic box, both at the Taylor-scale Reynolds number R_{λ} ∼1000. In particular, oscillations modulating the power-law scaling in the inertial range are examined for structure functions up to sixth-order moments. The oscillations in exponent ratios decrease with increasing sample size in simulations, although in experiments they survive at a low value of 4 parts in 1000 even after massive averaging. The two datasets are consistent in their intermittent character but differ in small but observable respects. Neither the scaling exponents themselves nor all the viscous effects are consistently reproduced by existing models of intermittency.}, } @article {pmid34241478, year = {2021}, author = {Gojon, R and Jardin, T and Parisot-Dupuis, H}, title = {Experimental investigation of low Reynolds number rotor noise.}, journal = {The Journal of the Acoustical Society of America}, volume = {149}, number = {6}, pages = {3813}, doi = {10.1121/10.0005068}, pmid = {34241478}, issn = {1520-8524}, abstract = {In this paper, an experimental characterisation of low Reynolds number rotors is performed in an anechoic room. Two commercially available two-bladed rotors as well as four three-dimensional (3D)-printed rotors with different numbers of blades (from two to five) are tested. The latter have canonical geometry, with an NACA0012 blade section profile, extruded in the radial direction with constant chord and constant 10° pitch. The experimental setup and the 3D printing strategy are first validated using results from the literature for the commercially available rotors. For all the tested rotors, four noise characteristics are analysed: the overall sound pressure level (OASPL), the amplitude of the blade passing frequency (BPF), and the amplitude of its first harmonic and the high-frequency broadband noise. For all the rotors, an increase in all noise characteristics is observed with the rotational speed (rpm) for all directivity angles. Moreover, an interesting change of pattern is observed for the amplitudes of the BPF and of its first harmonic, with, in the vicinity of the rotor plane, a minimum value for low rpm and/or high number of blades, and a maximum value for high rpm and/or low number of blades. This change in directivity leads to a similar change of directivity of the OASPL. For the broadband noise, a dipole-like pattern is obtained with a minimum value at θ=-10°, i.e., aligned with the trailing edge and thus indicating the generation of trailing edge noise. Finally, scaling laws that characterise the amplitude of the different noise components with respect to the rpm are proposed.}, } @article {pmid34234957, year = {2021}, author = {Mazharmanesh, S and Stallard, J and Medina, A and Fisher, A and Ando, N and Tian, FB and Young, J and Ravi, S}, title = {Effects of uniform vertical inflow perturbations on the performance of flapping wings.}, journal = {Royal Society open science}, volume = {8}, number = {6}, pages = {210471}, pmid = {34234957}, issn = {2054-5703}, abstract = {Flapping wings have attracted significant interest for use in miniature unmanned flying vehicles. Although numerous studies have investigated the performance of flapping wings under quiescent conditions, effects of freestream disturbances on their performance remain under-explored. In this study, we experimentally investigated the effects of uniform vertical inflows on flapping wings using a Reynolds-scaled apparatus operating in water at Reynolds number ≈ 3600. The overall lift and drag produced by a flapping wing were measured by varying the magnitude of inflow perturbation from J Vert = -1 (downward inflow) to J Vert = 1 (upward inflow), where J Vert is the ratio of the inflow velocity to the wing's velocity. The interaction between flapping wing and downward-oriented inflows resulted in a steady linear reduction in mean lift and drag coefficients, C ¯ L and C ¯ D , with increasing inflow magnitude. While a steady linear increase in C ¯ L and C ¯ D was noted for upward-oriented inflows between 0 < J Vert < 0.3 and J Vert > 0.7, a significant unsteady wing-wake interaction occurred when 0.3 ≤ J Vert < 0.7, which caused large variations in instantaneous forces over the wing and led to a reduction in mean performance. These findings highlight asymmetrical effects of vertically oriented perturbations on the performance of flapping wings and pave the way for development of suitable control strategies.}, } @article {pmid34234155, year = {2021}, author = {Connolly, S and Newport, D and McGourty, K}, title = {Cell specific variation in viability in suspension in in vitro Poiseuille flow conditions.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {13997}, pmid = {34234155}, issn = {2045-2322}, mesh = {Algorithms ; Cell Line, Tumor ; *Cell Survival ; Fibroblasts ; Humans ; *Lab-On-A-Chip Devices ; *Microfluidic Analytical Techniques ; *Models, Theoretical ; Neoplastic Cells, Circulating ; Suspensions ; T-Lymphocytes ; }, abstract = {The influence of Poiseuille flow on cell viability has applications in the areas of cancer metastasis, lab-on-a-chip devices and flow cytometry. Indeed, retaining cell viability is important in the emerging field of adoptive cell therapy, as cells need to be returned to patients' bodies, while the viability of other cells, which are perhaps less accustomed to suspension in a fluidic environment, is important to retain in flow cytometers and other such devices. Despite this, it is unclear how Poiseuille flow affects cell viability. Following on from previous studies which investigated the viability and inertial positions of circulating breast cancer cells in identical flow conditions, this study investigated the influence that varying flow rate, and the corresponding Reynolds number has on the viability of a range of different circulating cells in laminar pipe flow including primary T-cells, primary fibroblasts and neuroblastoma cells. It was found that Reynolds numbers as high as 9.13 had no effect on T-cells while the viabilities of neuroblastoma cells and intestinal fibroblasts were significantly reduced in comparison. This indicates that in vitro flow devices need to be tailored to cell-specific flow regimes.}, } @article {pmid34208685, year = {2021}, author = {Shanbrom, C and Balisacan, J and Wilkens, G and Chyba, M}, title = {Geometric Methods for Efficient Planar Swimming of Copepod Nauplii.}, journal = {Micromachines}, volume = {12}, number = {6}, pages = {}, pmid = {34208685}, issn = {2072-666X}, abstract = {Copepod nauplii are larval crustaceans with important ecological functions. Due to their small size, they experience an environment of low Reynolds number within their aquatic habitat. Here we provide a mathematical model of a swimming copepod nauplius with two legs moving in a plane. This model allows for both rotation and two-dimensional displacement by the periodic deformation of the swimmer's body. The system is studied from the framework of optimal control theory, with a simple cost function designed to approximate the mechanical energy expended by the copepod. We find that this model is sufficiently realistic to recreate behavior similar to those of observed copepod nauplii, yet much of the mathematical analysis is tractable. In particular, we show that the system is controllable, but there exist singular configurations where the degree of non-holonomy is non-generic. We also partially characterize the abnormal extremals and provide explicit examples of families of abnormal curves. Finally, we numerically simulate normal extremals and observe some interesting and surprising phenomena.}, } @article {pmid34204328, year = {2021}, author = {Ali, A and Bukhari, Z and Umar, M and Ismail, MA and Abbas, Z}, title = {Cu and Cu-SWCNT Nanoparticles' Suspension in Pulsatile Casson Fluid Flow via Darcy-Forchheimer Porous Channel with Compliant Walls: A Prospective Model for Blood Flow in Stenosed Arteries.}, journal = {International journal of molecular sciences}, volume = {22}, number = {12}, pages = {}, pmid = {34204328}, issn = {1422-0067}, mesh = {Algorithms ; Arteries/pathology/physiopathology ; Blood Circulation ; Constriction, Pathologic ; *Copper/chemistry ; *Hemodynamics ; Humans ; *Hydrodynamics ; *Metal Nanoparticles/chemistry ; *Models, Cardiovascular ; Porosity ; *Pulsatile Flow ; Suspensions ; }, abstract = {The use of experimental relations to approximate the efficient thermophysical properties of a nanofluid (NF) with Cu nanoparticles (NPs) and hybrid nanofluid (HNF) with Cu-SWCNT NPs and subsequently model the two-dimensional pulsatile Casson fluid flow under the impact of the magnetic field and thermal radiation is a novelty of the current study. Heat and mass transfer analysis of the pulsatile flow of non-Newtonian Casson HNF via a Darcy-Forchheimer porous channel with compliant walls is presented. Such a problem offers a prospective model to study the blood flow via stenosed arteries. A finite-difference flow solver is used to numerically solve the system obtained using the vorticity stream function formulation on the time-dependent governing equations. The behavior of Cu-based NF and Cu-SWCNT-based HNF on the wall shear stress (WSS), velocity, temperature, and concentration profiles are analyzed graphically. The influence of the Casson parameter, radiation parameter, Hartmann number, Darcy number, Soret number, Reynolds number, Strouhal number, and Peclet number on the flow profiles are analyzed. Furthermore, the influence of the flow parameters on the non-dimensional numbers such as the skin friction coefficient, Nusselt number, and Sherwood number is also discussed. These quantities escalate as the Reynolds number is enhanced and reduce by escalating the porosity parameter. The Peclet number shows a high impact on the microorganism's density in a blood NF. The HNF has been shown to have superior thermal properties to the traditional one. These results could help in devising hydraulic treatments for blood flow in highly stenosed arteries, biomechanical system design, and industrial plants in which flow pulsation is essential.}, } @article {pmid34203635, year = {2021}, author = {Ju, Y and Zhu, T and Mashayekhi, R and Mohammed, HI and Khan, A and Talebizadehsardari, P and Yaïci, W}, title = {Evaluation of Multiple Semi-Twisted Tape Inserts in a Heat Exchanger Pipe Using Al2O3 Nanofluid.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {11}, number = {6}, pages = {}, pmid = {34203635}, issn = {2079-4991}, abstract = {The hydrothermal performance of multiple semi-twisted tape inserts inside a heat exchanger pipe is numerically examined in three-dimensions. This study aims to find the optimum case for having the highest heat transfer enhancement with the lowest friction factor using nanofluid (Al2O3/water). A performance evaluation criterion (PEC) is defined to characterize the performance based on both friction factor and heat transfer. It was found that increasing the number of semi-twisted tapes increases the number of swirl flow streams and leads to an enhancement in the local Nusselt number as well as the friction factor. The average Nusselt number increases from 15.13 to 28.42 and the average friction factor enhances from 0.022 to 0.052 by increasing the number of the semi-twisted tapes from 0 to 4 for the Reynolds number of 1000 for the base fluid. By using four semi-twisted tapes, the average Nusselt number increases from 12.5 to 28.5, while the friction factor reduces from 0.155 to 0.052 when the Reynolds number increases from 250 to 1000 for the base fluid. For the Reynolds number of 1000, the increase in nanofluid concentration from 0 to 3% improves the average Nusselt number and friction factor by 6.41% and 2.29%, respectively. The highest PEC is equal to 1.66 and belongs to the Reynolds number of 750 using four semi-twisted tape inserts with 3% nanoparticles. This work offers instructions to model an advanced design of twisted tape integrated with tubes using multiple semi-twisted tapes, which helps to provide a higher amount of energy demand for solar applications.}, } @article {pmid34199619, year = {2021}, author = {Elsafy, KM and Saghir, MZ}, title = {Forced Convection in Wavy Microchannels Porous Media Using TiO2 and Al2O3-Cu Nanoparticles in Water Base Fluids: Numerical Results.}, journal = {Micromachines}, volume = {12}, number = {6}, pages = {}, pmid = {34199619}, issn = {2072-666X}, abstract = {In the present work, an attempt is made to investigate the performance of three fluids with forced convection in a wavy channel. The fluids are water, a nanofluid of 1% TiO2 in a water solution and a hybrid fluid which consists of 1% Al2O3-Cu nanoparticles in a water solution. The wavy channel has a porous insert with a permeability of 10 PPI, 20 PPI and 40 PPI, respectively. Since Reynolds number is less than 1000, the flow is assumed laminar, Newtonian and steady state. Results revealed that wavy channel provides a better heat enhancement than a straight channel of the same dimension. Porous material increases heat extraction at the expenses of the pressure drop. The nanofluid of 1% TiO2 in water provided the highest performance evaluation criteria.}, } @article {pmid34185996, year = {2021}, author = {Ahmed, S and Perez-Mercader, J}, title = {Autonomous Low-Reynolds-Number Soft Robots with Structurally Encoded Motion and Their Thermodynamic Efficiency.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {37}, number = {27}, pages = {8148-8156}, doi = {10.1021/acs.langmuir.1c00765}, pmid = {34185996}, issn = {1520-5827}, mesh = {Biocompatible Materials ; Motion ; *Robotics ; Thermodynamics ; }, abstract = {Soft low-Reynolds-number robotics hold the potential to significantly impact numerous fields including drug delivery, sensing, and diagnostics. Realizing this potential is predicated upon the ability to design soft robots tailored to their intended function. In this work, we identify the effect of different geometric and symmetry parameters on the motion of soft, autonomous robots that operate in the low-Reynolds-number regime and use organic fuel. The ability to power low-Reynolds-number soft robots using an organic fuel would provide a new avenue for their potential use in biomedical applications, as is the use of a polymeric biocompatible material as is done here. We introduce a simple and cost-effective 3D-printer-assisted method to fabricate robots of different shapes that is scalable and widely applicable for a variety of materials. The efficiency of chemical energy to mechanical energy conversion is measured in soft low-Reynolds-number robots for the first time, and their mechanism of motion is assessed. Motion is a result of a periodic and oscillatory change in the charge state of the gel. This work lays the groundwork for the structure-function design of soft, chemically operated, and autonomous low-Reynolds-number robots.}, } @article {pmid34184223, year = {2021}, author = {Yang, F and Zeng, YH and Huai, WX}, title = {A new model for settling velocity of non-spherical particles.}, journal = {Environmental science and pollution research international}, volume = {28}, number = {43}, pages = {61636-61646}, pmid = {34184223}, issn = {1614-7499}, mesh = {*Ecosystem ; Particle Size ; }, abstract = {The settlement of non-spherical particles, such as propagules of plants and natural sediments, is commonly observed in riverine ecosystems. The settling process is influenced by both particle properties (size, density, and shape) and fluid properties (density and viscosity). Therefore, the drag law of non-spherical particles is a function of both particle Reynolds number and particle shape. Herein, a total of 828 settling data are collected from the literatures, which cover a wide range of particle Reynolds number (0.008-10000). To characterize the influence of particle shapes, sphericity is adopted as the general shape factor, which varies from 0.421 to 1.0. By comparing the measured drag with the standard drag curve of spheres, we modify the spherical drag law with three shape-dependent functions to develop a new drag law for non-spherical particles. Combined with an iterative procedure, a new model is thus obtained to predict the settling velocity of non-spherical particles of various shapes and materials. Further applications in hydrochorous propagule dispersal and sediment transport are projected based on deeper understanding of the settling process.}, } @article {pmid34143104, year = {2021}, author = {Hill, JL and Hsu, PS and Jiang, N and Grib, SW and Roy, S and Borg, M and Thomas, L and Reeder, M and Schumaker, SA}, title = {Hypersonic N2 boundary layer flow velocity profile measurements using FLEET.}, journal = {Applied optics}, volume = {60}, number = {15}, pages = {C38-C46}, doi = {10.1364/AO.417470}, pmid = {34143104}, issn = {1539-4522}, abstract = {Femtosecond laser electronic excitation tagging (FLEET) velocimetry was used in the boundary layer of an ogive-cylinder model in a Mach-6 Ludwieg tube. One-dimensional velocity profiles were extracted from the FLEET signal in laminar boundary layers from pure N2 flows at unit Reynolds numbers ranging from 3.4×10[6]/m to3.9×10[6]/m. The effects of model tip bluntness and the unit Reynolds number on the velocity profiles were investigated. The challenges and strategies of applying FLEET for direct boundary layer velocity measurement are discussed. The potential of utilizing FLEET velocimetry for understanding the dynamics of laminar and turbulent boundary layers in hypersonic flows is demonstrated.}, } @article {pmid34139680, year = {2021}, author = {Mazharmanesh, S and Stallard, J and Medina, A and Fisher, A and Ando, N and Tian, FB and Young, J and Ravi, S}, title = {Performance of passively pitching flapping wings in the presence of vertical inflows.}, journal = {Bioinspiration & biomimetics}, volume = {16}, number = {5}, pages = {}, doi = {10.1088/1748-3190/ac0c60}, pmid = {34139680}, issn = {1748-3190}, mesh = {Animals ; Biomechanical Phenomena ; *Flight, Animal ; *Models, Biological ; Wings, Animal ; }, abstract = {The successful implementation of passively pitching flapping wings strongly depends on their ability to operate efficiently in wind disturbances. In this study, we experimentally investigated the interaction between a uniform vertical inflow perturbation and a passive-pitching flapping wing using a Reynolds-scaled apparatus operating in water at Reynolds number ≈3600. A parametric study was performed by systematically varying the Cauchy number (Ch) of the wings from 0.09 to 11.52. The overall lift and drag, and pitch angle of the wing were measured by varying the magnitude of perturbation fromJVert= -0.6 (downward inflow) toJVert= 0.6 (upward inflow) at eachCh, whereJVertis the ratio of the inflow velocity to the wing's velocity. We found that the lift and drag had remarkably different characteristics in response to bothChandJVert. Across allCh, while mean lift tended to increase as the inflow perturbation varied from -0.6 to 0.6, drag was significantly less sensitive to the perturbation. However effect of the vertical inflow on drag was dependent onCh, where it tended to vary from an increasing to a decreasing trend asChwas changed from 0.09 to 11.52. The differences in the lift and drag with perturbation magnitude could be attributed to the reorientation of the net force over the wing as a result of the interaction with the perturbation. These results highlight the complex interactions between passively pitching flapping wings and freestream perturbations and will guide the design of miniature flying crafts with such architectures.}, } @article {pmid34134196, year = {2021}, author = {Li, H and Tian, B and He, Z and Zhang, Y}, title = {Growth mechanism of interfacial fluid-mixing width induced by successive nonlinear wave interactions.}, journal = {Physical review. E}, volume = {103}, number = {5-1}, pages = {053109}, doi = {10.1103/PhysRevE.103.053109}, pmid = {34134196}, issn = {2470-0053}, abstract = {Interfacial fluid mixing induced by successive waves, such as shock, rarefaction, and compression waves, plays a fundamental role in engineering applications, e.g., inertial confinement fusion, and in natural phenomena, e.g., supernova explosion. These waves bring nonuniform, unsteady external forces into the mixing zone, which leads to a complex mixing process. The growth rate of the mixing width is analyzed by decomposing the turbulent flow field into the averaged field and the fluctuating counterpart. The growth rate is thus divided into three parts: (i) the stretching or compression (S(C)) effect induced by the averaged-velocity difference between two ends of the mixing zone, (ii) the penetration effect induced by the fluctuations which represent the penetration of the two species into each other, and (iii) the diffusive effect, which is induced by the molecular diffusion and is negligible in high-Reynolds-number flows at Schmidt number of order unity. The penetration effect is further divided into the Richtmyer-Meshkov (RM) effect, which is induced by fluctuations that were deposited by earlier wave interactions, and the Rayleigh-Taylor (RT) effect, which is caused by the fluctuations that arise in an overall acceleration of the mixing zone. During the passage of the rarefaction waves, the mixing zone is stretched, while during the passage of the compression waves or shock waves, the mixing zone is compressed. To illustrate these effects, a physical model of RM mixing with reshock is used. By combining the S(C), RM, and RT effects, the entire evolution of mixing width is restructured, which agrees well with numerical simulations for problems with a wide range of density ratios.}, } @article {pmid34129919, year = {2021}, author = {Ahookhosh, K and Saidi, M and Mohammadpourfard, M and Aminfar, H and Hamishehkar, H and Farnoud, A and Schmid, O}, title = {Flow Structure and Particle Deposition Analyses for Optimization of a Pressurized Metered Dose Inhaler (pMDI) in a Model of Tracheobronchial Airway.}, journal = {European journal of pharmaceutical sciences : official journal of the European Federation for Pharmaceutical Sciences}, volume = {164}, number = {}, pages = {105911}, doi = {10.1016/j.ejps.2021.105911}, pmid = {34129919}, issn = {1879-0720}, mesh = {Administration, Inhalation ; Adult ; Aerosols ; Equipment Design ; Female ; Humans ; Lung ; *Metered Dose Inhalers ; *Nebulizers and Vaporizers ; Particle Size ; }, abstract = {Inhalation therapy plays an important role in management or treatment of respiratory diseases such asthma and chronic obstructive pulmonary diseases (COPDs). For decades, pressurized metered dose inhalers (pMDIs) have been the most popular and prescribed drug delivery devices for inhalation therapy. The main objectives of the present computational work are to study flow structure inside a pMDI, as well as transport and deposition of micron-sized particles in a model of human tracheobronchial airways and their dependence on inhalation air flow rate and characteristic pMDI parameters. The upper airway geometry, which includes the extrathoracic region, trachea, and bronchial airways up to the fourth generation in some branches, was constructed based on computed tomography (CT) images of an adult healthy female. Computational fluid dynamics (CFD) simulation was employed using the k-ω model with low-Reynolds number (LRN) corrections to accomplish the objectives. The deposition results of the present study were verified with the in vitro deposition data of our previous investigation on pulmonary drug delivery using a hollow replica of the same airway geometry as used for CFD modeling. It was found that the flow structure inside the pMDI and extrathoracic region strongly depends on inhalation flow rate and geometry of the inhaler. In addition, regional aerosol deposition patterns were investigated at four inhalation flow rates between 30 and 120 L/min and for 60 L/min yielding highest deposition fractions of 24.4% and 3.1% for the extrathoracic region (EX) and the trachea, respectively. It was also revealed that particle deposition was larger in the right branches of the bronchial airways (right lung) than the left branches (left lung) for all of the considered cases. Also, optimization of spray characteristics showed that the optimum values for initial spray velocity, spray cone angle and spray duration were 100 m/s, 10° and 0.1 sec, respectively. Moreover, spray cone angle, more than any other of the investigated pMDI parameters can change the deposition pattern of inhaled particles in the airway model. In conclusion, the present investigation provides a validated CFD model for particle deposition and new insights into the relevance of flow structure for deposition of pMDI-emitted pharmaceutical aerosols in the upper respiratory tract.}, } @article {pmid34127716, year = {2021}, author = {Shah, Z and Jafaryar, M and Sheikholeslami, M and Ikramullah, and Kumam, P}, title = {Heat transfer intensification of nanomaterial with involve of swirl flow device concerning entropy generation.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {12504}, pmid = {34127716}, issn = {2045-2322}, abstract = {The thermal features of hybrid nano-powder turbulent motion through a pipe employing helical turbulator is numerically simulated via Finite Volume Method (FVM). The hybrid nanofluid (MWCNTs + Fe3O4 + H2O) is obtained by uniformly dispersing MWCNTs + Fe3O4 nanomaterials in H2O. The characteristics features of thermal energy transfer of hybrid nanofluid are investigated by varying the pitch ratio (P) of the helical turbulator and Reynolds number (Re) of the fluid. The outputs of the study are depicted in terms of contour plots of temperature, velocity, frictional irreversibility Sgen,f, and thermal irreversibility Sgen,th. The variation of Sgen,f, and Sgen,th with changing P and Re are also displayed by 3D plots. It is found that making the fluid more turbulent by increasing Re, the temperature of the fluid drops whereas the fluid velocity augments. The frictional irreversibility enhances, whereas the thermal irreversibility drops with the increasing turbulent motion. The decreasing P causes to drop the temperature of the higher turbulent fluid flow, while opposite effect is observed for smaller Re. The decreasing P causes to enhance the fluid mixing and thus augments the fluid velocity. Sgen,f and Sgen,th both augment with decreasing P. The comparison of current outputs with the older article shows an acceptable accuracy. The results of the present investigation will be useful in modelling of efficient thermal energy transfer systems.}, } @article {pmid34124445, year = {2021}, author = {Tian, G and Zhu, Y and Feng, X and Zhou, H and Zhang, Y}, title = {Investigation of the Turbulent Boundary Layer Structure over a Sparsely Spaced Biomimetic Spine-Covered Protrusion Surface.}, journal = {ACS omega}, volume = {6}, number = {22}, pages = {14220-14229}, pmid = {34124445}, issn = {2470-1343}, abstract = {Multiperspective particle image velocimetry was used to investigate the turbulent boundary layer structure over biomimetic spine-covered protrusion (BSCP) samples inspired by dorsal skin of pufferfish. The comparison of BSCP samples of two sparse "k-type" arrangements (aligned and staggered) with roughness height k [+] = 5-7 (nearly hydraulically smooth) and smooth case were manufactured in bulk Reynolds number Re b = 37,091, 44,510. The negative value of the roughness function ΔU [+] shows a downward shift of the mean velocity profile of BSCP samples, which shows a drag reduction effect. The results of turbulent statistics present strong fluctuation over the aligned case in the streamwise direction, while little influence is observed in the wall-normal and spanwise direction, which promotes turbulence stability. The same phenomenon was found based on the probability density function of fluctuation velocity that the suppression of turbulent flow is better over the staggered case. It is obvious that the shear stress induced is governed by the streamwise fluctuations. Furthermore, the Q-criterion and the λci-criterion improved with vorticity ω were introduced for vortex identification, which indicates less prograde vortex population and weaker swirling strength over BSCP samples than over the smooth one. Finally, the spatial coherent structure appeared similar and more orderly over the staggered case in the streamwise and wall-normal direction based on the analysis of two-point correlations R uu. These results provide further guidance to reveal the mechanism of drag reduction on the BSCP surface.}, } @article {pmid34111118, year = {2021}, author = {Velho Rodrigues, MF and Lisicki, M and Lauga, E}, title = {The bank of swimming organisms at the micron scale (BOSO-Micro).}, journal = {PloS one}, volume = {16}, number = {6}, pages = {e0252291}, pmid = {34111118}, issn = {1932-6203}, mesh = {Biodiversity ; Biomechanical Phenomena ; Flagella ; Locomotion ; *Microbiology ; Swimming ; }, abstract = {Unicellular microscopic organisms living in aqueous environments outnumber all other creatures on Earth. A large proportion of them are able to self-propel in fluids with a vast diversity of swimming gaits and motility patterns. In this paper we present a biophysical survey of the available experimental data produced to date on the characteristics of motile behaviour in unicellular microswimmers. We assemble from the available literature empirical data on the motility of four broad categories of organisms: bacteria (and archaea), flagellated eukaryotes, spermatozoa and ciliates. Whenever possible, we gather the following biological, morphological, kinematic and dynamical parameters: species, geometry and size of the organisms, swimming speeds, actuation frequencies, actuation amplitudes, number of flagella and properties of the surrounding fluid. We then organise the data using the established fluid mechanics principles for propulsion at low Reynolds number. Specifically, we use theoretical biophysical models for the locomotion of cells within the same taxonomic groups of organisms as a means of rationalising the raw material we have assembled, while demonstrating the variability for organisms of different species within the same group. The material gathered in our work is an attempt to summarise the available experimental data in the field, providing a convenient and practical reference point for future studies.}, } @article {pmid34091219, year = {2021}, author = {Amani, M and Amani, P and Bahiraei, M and Ghalambaz, M and Ahmadi, G and Wang, LP and Wongwises, S and Mahian, O}, title = {Latest developments in nanofluid flow and heat transfer between parallel surfaces: A critical review.}, journal = {Advances in colloid and interface science}, volume = {294}, number = {}, pages = {102450}, doi = {10.1016/j.cis.2021.102450}, pmid = {34091219}, issn = {1873-3727}, abstract = {The enhancement of heat transfer between parallel surfaces, including parallel plates, parallel disks, and two concentric pipes, is vital because of their wide applications ranging from lubrication systems to water purification processes. Various techniques can be utilized to enhance heat transfer in such systems. Adding nanoparticles to the conventional working fluids is an effective solution that could remarkably enhance the heat transfer rate. No published review article focuses on the recent advances in nanofluid flow between parallel surfaces; therefore, the present paper aims to review the latest experimental and numerical studies on the flow and heat transfer of nanofluids (mixtures of nanoparticles and conventional working fluids) in such configurations. For the performance analysis of thermal systems composed of parallel surfaces and operating with nanofluids, it is necessary to know the physical phenomena and parameters that influence the flow and heat transfer characteristics in these systems. Significant results obtained from this review indicate that, in most cases, the heat transfer rate between parallel surfaces is enhanced with an increase in the Rayleigh number, the Reynolds number, the magnetic number, and Brownian motion. On the other hand, an increase in thermophoresis parameter, as well as flow parameters, including the Eckert number, buoyancy ratio, Hartmann number, and Lewis number, leads to heat transfer rate reduction.}, } @article {pmid34081994, year = {2021}, author = {Das, S and Pal, TK and Jana, RN and Giri, B}, title = {Significance of Hall currents on hybrid nano-blood flow through an inclined artery having mild stenosis: Homotopy perturbation approach.}, journal = {Microvascular research}, volume = {137}, number = {}, pages = {104192}, doi = {10.1016/j.mvr.2021.104192}, pmid = {34081994}, issn = {1095-9319}, mesh = {Animals ; Arterial Occlusive Diseases/*physiopathology ; Arteries/*physiopathology ; Constriction, Pathologic ; Copper/*chemistry ; *Hemodynamics ; Humans ; *Metal Nanoparticles ; *Models, Cardiovascular ; *Nanotechnology ; Porosity ; Regional Blood Flow ; Stress, Mechanical ; }, abstract = {The rheological perspective of blood flow with the suspension of metallic or non-metallic nanoparticles through arteries having cardiovascular diseases is getting more attention due to momentous applications in obstructed hemodynamics, nano-hemodynamics, nano-pharmacology, blood purification system, treatment of hemodynamic ailments, etc. Motivated by the novel significance and research in this direction, a mathematical hemodynamics model is developed to mimic the hemodynamic features of blood flow under the concentration of hybrid nanoparticles through an inclined artery with mild stenosis in the existence of dominating electromagnetic field force, Hall currents, heat source, and porous substance. Copper (Cu) and copper oxide (CuO) nanoparticles are submerged into the blood to form hybrid nano-blood suspension (Cu-CuO/blood). The attribute of the medium porosity on the blood flow is featured by Darcy's law. The mathematical equations describing the flow are formulated and simplified under mild stenosis and small Reynolds number assumptions. To determine the analytical solution of the resulting nonlinear momentum equation, the homotopy perturbation method (HPM) is employed. Several figures are graphed to assess the hemodynamical contributions of various intricate physical parameters on blood flow phenomena through the inclined stenosed artery. Significant outcomes from graphical elucidation envisage that the hemodynamic resistance to the blood flow is reduced due to the dispersion of more hybrid nanoparticles in the blood. The hemodynamic resistance (impedance) increases approximately two times by dispersing 0.11% hybrid nanoparticles in the blood flow. The temperature of Cu-CuO/blood is found to be lower in comparison to Cu-blood and pure blood. Intensification of Hall parameter attenuates the wall shear stress at the arterial wall. The trapping phenomena are also outlined via streamline plots which exemplify the blood flow pattern in the stenosed artery under the variation of the emerging parameters. As anticipated, the addition of a large number of hybrid nanoparticles significantly modulates the blood flow pattern in the stenotic region. The novel feature of this model is the impressive impact of Hall currents on hybrid nanoparticle doped blood flow through the stenosed artery. There is another piece of significance is that HPM is the most suitable method to handle the nonlinear momentum equation under the aforementioned flow constraints. Outcomes of this simulation may be valuable for advanced study and research in biomedical engineering, bio-nanofluid mechanics, nano-pharmacodynamics.}, } @article {pmid34078976, year = {2021}, author = {Usman, AH and Khan, NS and Humphries, UW and Ullah, Z and Shah, Q and Kumam, P and Thounthong, P and Khan, W and Kaewkhao, A and Bhaumik, A}, title = {Computational optimization for the deposition of bioconvection thin Oldroyd-B nanofluid with entropy generation.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {11641}, pmid = {34078976}, issn = {2045-2322}, abstract = {The behavior of an Oldroyd-B nanoliquid film sprayed on a stretching cylinder is investigated. The system also contains gyrotactic microorganisms with heat and mass transfer flow. Similarity transformations are used to make the governing equations non-dimensional ordinary differential equations and subsequently are solved through an efficient and powerful analytic technique namely homotopy analysis method (HAM). The roles of all dimensionless profiles and spray rate have been investigated. Velocity decreases with the magnetic field strength and Oldroyd-B nanofluid parameter. Temperature is increased with increasing the Brownian motion parameter while it is decreased with the increasing values of Prandtl and Reynolds numbers. Nanoparticle's concentration is enhanced with the higher values of Reynolds number and activation energy parameter. Gyrotactic microorganism density increases with bioconvection Rayleigh number while it decreases with Peclet number. The film size naturally increases with the spray rate in a nonlinear way. A close agreement is achieved by comparing the present results with the published results.}, } @article {pmid34076781, year = {2021}, author = {Kadiri, VM and Günther, JP and Kottapalli, SN and Goyal, R and Peter, F and Alarcón-Correa, M and Son, K and Barad, HN and Börsch, M and Fischer, P}, title = {Light- and magnetically actuated FePt microswimmers.}, journal = {The European physical journal. E, Soft matter}, volume = {44}, number = {6}, pages = {74}, pmid = {34076781}, issn = {1292-895X}, abstract = {Externally controlled microswimmers offer prospects for transport in biological research and medical applications. This requires biocompatibility of the swimmers and the possibility to tailor their propulsion mechanisms to the respective low Reynolds number environment. Here, we incorporate low amounts of the biocompatible alloy of iron and platinum (FePt) in its [Formula: see text] phase in microstructures by a versatile one-step physical vapor deposition process. We show that the hard magnetic properties of [Formula: see text] FePt are beneficial for the propulsion of helical micropropellers with rotating magnetic fields. Finally, we find that the FePt coatings are catalytically active and also make for Janus microswimmers that can be light-actuated and magnetically guided.}, } @article {pmid34069236, year = {2021}, author = {Choe, YW and Sim, SB and Choo, YM}, title = {New Equation for Predicting Pipe Friction Coefficients Using the Statistical Based Entropy Concepts.}, journal = {Entropy (Basel, Switzerland)}, volume = {23}, number = {5}, pages = {}, pmid = {34069236}, issn = {1099-4300}, abstract = {In general, this new equation is significant for designing and operating a pipeline to predict flow discharge. In order to predict the flow discharge, accurate determination of the flow loss due to pipe friction is very important. However, existing pipe friction coefficient equations have difficulties in obtaining key variables or those only applicable to pipes with specific conditions. Thus, this study develops a new equation for predicting pipe friction coefficients using statistically based entropy concepts, which are currently being used in various fields. The parameters in the proposed equation can be easily obtained and are easy to estimate. Existing formulas for calculating pipe friction coefficient requires the friction head loss and Reynolds number. Unlike existing formulas, the proposed equation only requires pipe specifications, entropy value and average velocity. The developed equation can predict the friction coefficient by using the well-known entropy, the mean velocity and the pipe specifications. The comparison results with the Nikuradse's experimental data show that the R2 and RMSE values were 0.998 and 0.000366 in smooth pipe, and 0.979 to 0.994 or 0.000399 to 0.000436 in rough pipe, and the discrepancy ratio analysis results show that the accuracy of both results in smooth and rough pipes is very close to zero. The proposed equation will enable the easier estimation of flow rates.}, } @article {pmid34064079, year = {2021}, author = {Zhou, T and Chen, B and Liu, H}, title = {Study of the Performance of a Novel Radiator with Three Inlets and One Outlet Based on Topology Optimization.}, journal = {Micromachines}, volume = {12}, number = {6}, pages = {}, pmid = {34064079}, issn = {2072-666X}, abstract = {In recent years, in order to obtain a radiator with strong heat exchange capacity, researchers have proposed a lot of heat exchangers to improve heat exchange capacity significantly. However, the cooling abilities of heat exchangers designed by traditional design methods is limited even if the geometric parameters are optimized at the same time. However, using topology optimization to design heat exchangers can overcome this design limitation. Furthermore, researchers have used topology optimization theory to designed one-to-one and many-to-many inlet and outlet heat exchangers because it can effectively increase the heat dissipation rate. In particular, it can further decrease the hot-spot temperature for many-to-many inlet and outlet heat exchangers. Therefore, this article proposes novel heat exchangers with three inlets and one outlet designed by topology optimization to decrease the fluid temperature at the outlet. Subsequently, the effect of the channel depth on the heat exchanger design is also studied. The results show that the type of exchanger varies with the channel depth, and there exists a critical depth value for obtaining the minimum substrate temperature difference. Then, the flow and heat transfer performance of the heat exchangers are numerically investigated. The numerical results show that the heat exchanger derived by topology optimization with the minimum temperature difference as the goal (Model-2) is the best design for flow and heat transfer performance compared to other heat sink designs, including the heat exchanger derived by topology optimization having the average temperature as the goal (Model-1) and conventional straight channels (Model-3). The temperature difference of Model-1 can be reduced by 37.5%, and that of Model-2 can be decreased by 62.5% compared to Model-3. Compared with Model-3, the thermal resistance of Model-1 can be reduced by 21.86%, while that of Model-2 can be decreased by 47.99%. At room temperature, we carried out the forced convention experimental test for Model-2 to measure its physical parameters (temperature, pressure drop) to verify the numerical results. The error of the average wall temperature between experimental results and simulation results is within 2.6 K, while that of the fluid temperature between the experimental and simulation results is within 1.4 K, and the maximum deviation of the measured Nu and simulated Nu was less than 5%. This indicated that the numerical results agreed well with the experimental results.}, } @article {pmid34062924, year = {2021}, author = {Gu, B and Adjiman, CS and Xu, XY}, title = {Correlations for Concentration Polarization and Pressure Drop in Spacer-Filled RO Membrane Modules Based on CFD Simulations.}, journal = {Membranes}, volume = {11}, number = {5}, pages = {}, pmid = {34062924}, issn = {2077-0375}, abstract = {Empirical correlations for mass transfer coefficient and friction factor are often used in process models for reverse osmosis (RO) membrane systems. These usually involve four dimensionless groups, namely Reynolds number (Re), Sherwood number (Sh), friction factor (f), and Schmidt number (Sc), with the associated coefficients and exponents being obtained by fitting to experimental data. However, the range of geometric and operating conditions covered by the experiments is often limited. In this study, new dimensionless correlations for concentration polarization (CP) modulus and friction factor are presented, which are obtained by dimensional analysis and using simulation data from computational fluid dynamics (CFD). Two-dimensional CFD simulations are performed on three configurations of spacer-filled channels with 76 combinations of operating and geometric conditions for each configuration, covering a broad range of conditions encountered in RO membrane systems. Results obtained with the new correlations are compared with those from existing correlations in the literature. There is good consistency in the predicted CP with mean discrepancies less than 6%, but larger discrepancies for pressure gradient are found among the various friction factor correlations. Furthermore, the new correlations are implemented in a process model with six spiral wound modules in series and the predicted recovery, pressure drop, and specific energy consumption are compared with a reference case obtained by ROSA (Reverse Osmosis System Analysis, The Dow Chemical Company). Differences in predicted recovery and pressure drop are up to 5% and 83%, respectively, highlighting the need for careful selection of correlations when using predictive models in process design. Compared to existing mass transfer correlations, a distinct advantage of our correlations for CP modulus is that they can be directly used to estimate the impact of permeate flux on CP at a membrane surface without having to resort to the film theory.}, } @article {pmid34059714, year = {2021}, author = {Pang, M and Zhang, T and Guo, Y and Zhang, L}, title = {Re-crushing process and non-Darcian seepage characteristics of broken coal medium in coal mine water inrush.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {11380}, pmid = {34059714}, issn = {2045-2322}, abstract = {The initiation process of the mine water inrush accident, the essence of this process is the sudden change of the seepage state of the broken coal medium under pressure and the instability of the skeleton. In order to study the re-crushing mechanism and seepage characteristics of the broken coal medium under load, a set of three-axis seepage system was designed independently. Using the steady-state infiltration method, multiple flow factors under different particle size combinations and different stress conditions of the broken coal medium were obtained. The results of the study indicate: in one hand, the reduction of the porosity of the broken coal medium will cause the flow channel to be rebuilt, and the sudden change of flow rate will directly lead to the non-Darcian flow behavior. The early stage of compaction mainly affects the permeability k value, and the later stage of compaction mainly affects the non-Darcian β value; On the other hand, the seepage throat in the broken coal medium may have a sharp increase in its flow rate, leading to a sudden change in the flow pattern. The critical Reynolds number is also used to determine whether non-Darcian flow is formed, and its value in the water inrush system is about 40-133; at the same time, the non-Darcian flow in the broken coal medium conforms to the Forchheimer-type flow law. By analyzing the dependence relationship between factors, a seepage factor representation algebraic relationship suitable for Forchheimer type non-Darcian flow of broken coal medium is given, which can be used as a calculation basis in the prevention and treatment of mine water inrush accidents.}, } @article {pmid34056212, year = {2021}, author = {Agarwal, JR and Torres, CF and Shah, S}, title = {Development of Dimensionless Parameters and Groups of Heat and Mass Transfer to Predict Wax Deposition in Crude Oil Pipelines.}, journal = {ACS omega}, volume = {6}, number = {16}, pages = {10578-10591}, pmid = {34056212}, issn = {2470-1343}, abstract = {A new methodology has been developed for analyzing heat and mass transfer to predict wax deposition in crude oil pipelines using the law of the wall dimensionless parameters. A set of physically meaningful dimensionless groups and parameters has laid a strong foundation behind the proposed methodology. The paper presents a discussion regarding the development of scale-up correlations from laboratory scale to field scale, considering the combination of both analytical groups and empirical correlations. Data from previous literature studies were employed for determining realistic values for the developed parameters and scale-up correlations. The utilization of new dimensionless scale-up parameters indicated that the wax deposition in crude oil pipelines is independent of the Reynolds number and the inner diameter of the pipeline. It further indicates that wax deposition in crude oil pipelines is mainly dependent on the heat transfer process and not on the shear reduction process. The dimensionless technique developed here can be utilized for determining the optimum pipe size and pigging frequencies to reduce and mitigate the effect of the wax deposition process.}, } @article {pmid34050744, year = {2021}, author = {Ford, MP and Santhanakrishnan, A}, title = {Closer Appendage Spacing Augments Metachronal Swimming Speed by Promoting Tip Vortex Interactions.}, journal = {Integrative and comparative biology}, volume = {61}, number = {5}, pages = {1608-1618}, doi = {10.1093/icb/icab112}, pmid = {34050744}, issn = {1557-7023}, mesh = {Animals ; Biomechanical Phenomena ; *Extremities ; Hydrodynamics ; Invertebrates ; *Swimming ; }, abstract = {Numerous species of aquatic invertebrates, including crustaceans, swim by oscillating multiple closely spaced appendages. The coordinated, out-of-phase motion of these appendages, known as "metachronal paddling," has been well-established to improve swimming performance relative to synchronous paddling. Invertebrates employing this propulsion strategy cover a wide range of body sizes and shapes, but the ratio of appendage spacing (G) to the appendage length (L) has been reported to lie in a comparatively narrow range of 0.2 < G/L ≤ 0.65. The functional role of G/L on metachronal swimming performance is unknown. We hypothesized that for a given Reynolds number and stroke amplitude, hydrodynamic interactions promoted by metachronal stroke kinematics with small G/L can increase forward swimming speed. We used a dynamically scaled self-propelling robot to comparatively examine swimming performance and wake development of metachronal and synchronous paddling under varying G/L, phase lag, and stroke amplitude. G/L was varied from 0.4 to 1.5, with the expectation that when G/L is large, there should be no performance difference between metachronal and synchronous paddling due to a lack of interaction between vortices that form on the appendages. Metachronal stroking at nonzero phase lag with G/L in the biological range produced faster swimming speeds than synchronous stroking. As G/L increased and as stroke amplitude decreased, the influence of phase lag on the swimming speed of the robot was reduced. For smaller G/L, vortex interactions between adjacent appendages generated a horizontally oriented wake and increased momentum fluxes relative to larger G/L, which contributed to increasing swimming speed. We find that while metachronal motion augments swimming performance for closely spaced appendages (G/L <1), moderately spaced appendages (1.0 ≤ G/L ≤ 1.5) can benefit from the metachronal motion only when the stroke amplitude is large.}, } @article {pmid34035439, year = {2021}, author = {Shankar, BM and Shivakumara, IS}, title = {Benchmark solution for the stability of plane Couette flow with net throughflow.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {10901}, pmid = {34035439}, issn = {2045-2322}, abstract = {This paper investigates the stability of an incompressible viscous fluid flow between relatively moving horizontal parallel plates in the presence of a uniform vertical throughflow. A linear stability analysis has been performed by employing the method of normal modes and the resulting stability equation is solved numerically using the Chebyshev collocation method. Contrary to the stability of plane Couette flow (PCF) to small disturbances for all values of the Reynolds number in the absence of vertical throughflow, it is found that PCF becomes unstable owing to the change in the sign of growth rate depending on the magnitude of throughflow. The critical Reynolds number triggering the instability is computed for different values of throughflow dependent Reynolds number and it is shown that throughflow instills both stabilizing and destabilizing effect on the base flow. It is seen that the direction of throughflow has no influence on the stability of fluid flow. A comparative study between plane Poiseuille flow and PCF has also been carried out and the similarities and differences are highlighted.}, } @article {pmid34034247, year = {2021}, author = {Kasoju, VT and Santhanakrishnan, A}, title = {Pausing after clap reduces power required to fling wings apart at low Reynolds number.}, journal = {Bioinspiration & biomimetics}, volume = {16}, number = {5}, pages = {}, doi = {10.1088/1748-3190/ac050a}, pmid = {34034247}, issn = {1748-3190}, mesh = {Animals ; Biomechanical Phenomena ; *Flight, Animal ; Insecta ; Models, Biological ; *Thysanoptera ; Wings, Animal ; }, abstract = {The smallest flying insects, such as thrips (body length < 2 mm), are challenged with needing to move in air at a chord-based Reynolds number (Rec) of the order of 10. Pronounced viscous dissipation at such a low Recrequires considerable energetic expenditure for tiny insects to stay aloft. Thrips flap their densely bristled wings at large stroke amplitudes, bringing both wings in close proximity to each other at the end of upstroke ('clap') and moving their wings apart at the start of downstroke ('fling'). From high-speed videos of free take-off flights of thrips, we observed that their forewings remain clapped for approximately 10% of the wingbeat cycle before the start of downstroke (fling stroke). We sought to examine if there are aerodynamic advantages associated with pausing wing motion after upstroke (clap stroke) and before downstroke (fling stroke) at Rec= 10. A dynamically scaled robotic clap and fling platform was used to measure lift and drag forces generated by physical models of solid (non-bristled) and bristled wings in single wing and wing pair configurations, for pause times ranging between 0% to 41% of the cycle. For solid and bristled wing pairs, pausing before the start of downstroke (fling stroke) dissipated vorticity generated at the end of upstroke (clap stroke). This resulted in a decrease in the drag coefficient averaged across downstroke (fling stroke) and in turn reduced power requirements. Also, increasing the pause time resulted in a larger decrease in the dimensionless power coefficient for the wing-pair configurations compared to the single-wing configurations. Our findings show that wing-wing interaction observed in the clap and fling motion of tiny insect wings is necessary to realize the aerodynamic benefits of pausing before fling, by reducing the power required to clap and fling for a small compromise in lift.}, } @article {pmid34030500, year = {2021}, author = {Wanzheng, A and Pengfei, Z}, title = {Correction and laboratory investigation for energy loss coefficient of square-edged orifice plate.}, journal = {Science progress}, volume = {104}, number = {2}, pages = {368504211018571}, doi = {10.1177/00368504211018571}, pmid = {34030500}, issn = {2047-7163}, abstract = {A lot of studies have shown that the hydraulic characteristics of orifice plate are mainly controlled by its contraction ratio, but the thickness of square-edged orifice plate also has many impacts on energy loss characteristics. The primary objective of this study was to investigated the effects of square-edged orifice plate thickness on energy loss characteristics. In this paper, the effects of square-edged orifice plate thickness on energy loss characteristics are investigated by numerical simulation using CFD. Orifice plate discharge tunnel is axial symmetric, two dimensional numerical simulations of orifice plate discharge tunnel flow was used. The equation (9) for calculating energy loss coefficient of square-edged orifice plate energy dissipater considering the influence of thickness is proposed. The results of the present research demonstrate that energy loss coefficient decreases with increase of the orifice plate thickness. The results of model experiment are consistence with the results calculated by using rectified equation in present paper. The CFD simulations and Model experiment for the flow through an orifice plate are carried out. For square-edged orifice plate energy dissipater, the relative orifice plate thickness T/D has remarkable impacts on its energy loss coefficient ξ. The Traditional equation (8) is corrected by numerical results. The equation (9) for calculating energy loss coefficient of square-edged orifice plate energy dissipater considering the influence of thickness is proposed and this equation is available in the condition of d/D = 0.4-0.8, T/D = 0.05-0.25, and Re > 105(Re is Reynolds number). Comparing with the physical model experimental data, the relative errors of equation (9) is smaller than 15%.}, } @article {pmid34026737, year = {2021}, author = {Murayama, Y and Nakata, T and Liu, H}, title = {Flexible Flaps Inspired by Avian Feathers Can Enhance Aerodynamic Robustness in low Reynolds Number Airfoils.}, journal = {Frontiers in bioengineering and biotechnology}, volume = {9}, number = {}, pages = {612182}, pmid = {34026737}, issn = {2296-4185}, abstract = {Unlike rigid rotors of drones, bird wings are composed of flexible feathers that can passively deform while achieving remarkable aerodynamic robustness in response to wind gusts. In this study, we conduct an experimental study on the effects of the flexible flaps inspired by the covert of bird wings on aerodynamic characteristics of fixed-wings in disturbances. Through force measurements and flow visualization in a low-speed wind tunnel, it is found that the flexible flaps can suppress the large-scale vortex shedding and hence reduce the fluctuations of aerodynamic forces in a disturbed flow behind an oscillating plate. Our results demonstrate that the stiffness of the flaps strongly affects the aerodynamic performance, and the force fluctuations are observed to be reduced when the deformation synchronizes with the strong vortex generation. The results point out that the simple attachment of the flexible flaps on the upper surface of the wing is an effective method, providing a novel biomimetic design to improve the aerodynamic robustness of small-scale drones with fixed-wings operating in unpredictable aerial environments.}, } @article {pmid34024939, year = {2021}, author = {Chassagne, F and Barbour, MC and Chivukula, VK and Machicoane, N and Kim, LJ and Levitt, MR and Aliseda, A}, title = {The effect of Dean, Reynolds, and Womersley number on the flow in a spherical cavity on a curved round pipe. Part 1. Fluid mechanics in the cavity as a canonical flow representing intracranial aneurysms.}, journal = {Journal of fluid mechanics}, volume = {915}, number = {}, pages = {}, pmid = {34024939}, issn = {0022-1120}, support = {18CDA34110295/AHA/American Heart Association-American Stroke Association/United States ; R01 NS088072/NS/NINDS NIH HHS/United States ; R01 NS105692/NS/NINDS NIH HHS/United States ; R03 NS078539/NS/NINDS NIH HHS/United States ; }, abstract = {Flow in side-wall cerebral aneurysms can be ideally modelled as the combination of flow over a spherical cavity and flow in a curved circular pipe, two canonical flows. Flow in a curved pipe is known to depend on the Dean number De, combining the effects of Reynolds number, Re, and of the curvature along the pipe centreline, κ. Pulsatility in the flow introduces a dependency on the Womersley number Wo. Using stereo PIV measurements, this study investigated the effect of these three key non-dimensional parameters, by modifying pipe curvature (De), flow-rate (Re), and pulsatility frequency (Wo), on the flow patterns in a spherical cavity. A single counter-rotating vortex was observed in the cavity for all values of pipe curvature κ and Re, for both steady and pulsatile inflow conditions. Increasing the pipe curvature impacted both the flow patterns in the pipe and the cavity, by shifting the velocity profile towards the cavity opening and increasing the flow rate into the cavity. The circulation in the cavity was found to collapse well with only the Dean number, for both steady and pulsatile inflows. For pulsatile inflow, the counter-rotating vortex was unstable and the location of its centre over time was impacted by the curvature of the pipe, as well as the Re and the Wo in the freestream. The circulation in the cavity was higher for steady inflow than for the equivalent average Reynolds and Dean number pulsatile inflow, with very limited impact of the Womersley in the range studied.}, } @article {pmid34007926, year = {2021}, author = {Aljabair, S and Ekaid, AL and Ibrahim, SH and Alesbe, I}, title = {Mixed convection in sinusoidal lid driven cavity with non-uniform temperature distribution on the wall utilizing nanofluid.}, journal = {Heliyon}, volume = {7}, number = {5}, pages = {e06907}, pmid = {34007926}, issn = {2405-8440}, abstract = {Mixed convection heat transfer of Cu-water nanofluid in an arc cavity with non-uniform heating has been numerically studied. The top flat moving wall is isothermally cooled at Tc and moved with a constant velocity. While the heated arc stationary wall of the cavity is maintained at a hot temperature Th. FORTRAN code is used to solve the mass, momentum, and energy equations in dimensionless form with suitable boundary conditions. In this study, the Reynolds number changed from 1 to 2000, and the Rayleigh number changed from 0 to 10[7]. Also, the range of nanoparticles volume fraction extends from ϕ = 0 to 0.07. Stream vorticity method selected for the discretization of flow and energy equations. The present results are compared with the previous results for the validation part, where the results found a good agreement with the others works. The isotherms are regulated near the arc-shape wall causing a steep temperature gradient at these regions and the local and average heat transfer rate increases with increased volume fraction or Reynolds number or Rayleigh number. Finally, Correlation equations of the average Nusselt number from numerical results are presented.}, } @article {pmid34006011, year = {2021}, author = {Fouxon, I and Feinberg, J and Mond, M}, title = {Linear and nonlinear hydromagnetic stability in laminar and turbulent flows.}, journal = {Physical review. E}, volume = {103}, number = {4-1}, pages = {043104}, doi = {10.1103/PhysRevE.103.043104}, pmid = {34006011}, issn = {2470-0053}, abstract = {We consider the evolution of arbitrarily large perturbations of a prescribed pure hydrodynamical flow of an electrically conducting fluid. We study whether the flow perturbations as well as the generated magnetic fields decay or grow with time and constitute a dynamo process. For that purpose we derive a generalized Reynolds-Orr equation for the sum of the kinetic energy of the hydrodynamic perturbation and the magnetic energy. The flow is confined in a finite volume so the normal component of the velocity at the boundary is zero. The tangential component is left arbitrary in contrast with previous works. For the magnetic field we mostly employ the classical boundary conditions where the field extends in the whole space. We establish critical values of hydrodynamic and magnetic Reynolds numbers below which arbitrarily large initial perturbations of the hydrodynamic flow decay. This involves generalization of the Rayleigh-Faber-Krahn inequality for the smallest eigenvalue of an elliptic operator. For high Reynolds number turbulence we provide an estimate of critical magnetic Reynolds number below which arbitrarily large fluctuations of the magnetic field decay.}, } @article {pmid34005982, year = {2021}, author = {Gissinger, JR and Zinchenko, AZ and Davis, RH}, title = {Internal circulation and mixing within tight-squeezing deformable droplets.}, journal = {Physical review. E}, volume = {103}, number = {4-1}, pages = {043106}, doi = {10.1103/PhysRevE.103.043106}, pmid = {34005982}, issn = {2470-0053}, abstract = {The internal flow and mixing properties inside deformable droplets, after reaching the steady state within two types of passive droplet traps, are visualized and analyzed as dynamical systems. The first droplet trap (constriction) is formed by three spheres arranged in an equilateral triangle, while the second consists of two parallel spherocylinders (capsules). The systems are assumed to be embedded in a uniform far-field flow at low Reynolds number, and the steady shapes and interfacial velocities on the drops are generated using the boundary-integral method. The internal velocity field is recovered by solving the internal Dirichlet problem, also via a desingularized boundary-integral method. Calculation of 2D streamlines within planes of symmetry reveals the internal equilibria of the flow. The type of each equilibrium is classified in 3D and their interactions probed using passive tracers and their Poincaré maps. For the two-capsule droplet, saddle points located on orthogonal symmetry planes influence the regular flow within the drop. For the three-sphere droplet, large regions of chaos are observed, embedded with simple periodic orbits. Flow is visualized via passive dyes, using material lines and surfaces. In 2D, solely the interface between two passive interior fluids is advected using an adaptive number of linked tracer particles. The reduction in dimension decreases the number of required tracer points, and also resolves arbitrarily thin filaments, in contrast to backward cell-mapping methods. In 3D, the advection of a material surface, bounded by the droplet interface, is enabled using an adaptive mesh scheme. Off-lattice 3D contour advection allows for highly resolved visualizations of the internal flow and quantification of the associated degree of mixing. Analysis of the time-dependent growth of material surfaces and 3D mixing numbers suggests the three-sphere droplet exhibits superior mixing properties compared to the two-capsule droplet.}, } @article {pmid34005876, year = {2021}, author = {Brahmachary, S and Natarajan, G and Kulkarni, V and Sahoo, N and Ashok, V and Kumar, V}, title = {Role of solution reconstruction in hypersonic viscous computations using a sharp interface immersed boundary method.}, journal = {Physical review. E}, volume = {103}, number = {4-1}, pages = {043302}, doi = {10.1103/PhysRevE.103.043302}, pmid = {34005876}, issn = {2470-0053}, abstract = {This work discusses the development of a sharp interface immersed boundary (IB) method for viscous compressible flows and its assessment for accurate computations of wall shear and heat fluxes in hypersonic flows. The IB method is implemented in an unstructured Cartesian finite-volume (FV) framework and resolves the geometric interface sharply on the nonconformal mesh through direct imposition of boundary conditions employing a local reconstruction approach. The efficacy of the IB-FV solver is investigated for canonical high-speed viscous flows over a range of Mach numbers. The numerical results indicate that the surface pressure and shear stress distributions are computed with reasonable accuracy, whereas surface heat fluxes for aerodynamically blunt configurations are underpredicted. Employing a set of carefully designed experiments and simple diagnostic tools, we probe the possible causes for the underprediction in heat flux. We show that there exist two sources of error-one due to grid resolution and the other due to solution reconstruction, with the latter being more prominent and responsible for the observed underprediction in heat fluxes. Studies reveal that the heat flux estimates are sensitive to the choice of temperature reconstruction and linear interpolations could lead to poor estimates of heat flux. Our investigations conclusively point out the fact that existing polynomial-based reconstruction approaches for sharp interface IB techniques are not necessarily adequate for heat transfer predictions in high Reynolds number hypersonic flows.}, } @article {pmid34001882, year = {2021}, author = {Nguyen, QM and Abouezzi, J and Ristroph, L}, title = {Early turbulence and pulsatile flows enhance diodicity of Tesla's macrofluidic valve.}, journal = {Nature communications}, volume = {12}, number = {1}, pages = {2884}, pmid = {34001882}, issn = {2041-1723}, abstract = {Microfluidics has enabled a revolution in the manipulation of small volumes of fluids. Controlling flows at larger scales and faster rates, or macrofluidics, has broad applications but involves the unique complexities of inertial flow physics. We show how such effects are exploited in a device proposed by Nikola Tesla that acts as a diode or valve whose asymmetric internal geometry leads to direction-dependent fluidic resistance. Systematic tests for steady forcing conditions reveal that diodicity turns on abruptly at Reynolds number [Formula: see text] and is accompanied by nonlinear pressure-flux scaling and flow instabilities, suggesting a laminar-to-turbulent transition that is triggered at unusually low [Formula: see text]. To assess performance for unsteady forcing, we devise a circuit that functions as an AC-to-DC converter, rectifier, or pump in which diodes transform imposed oscillations into directed flow. Our results confirm Tesla's conjecture that diodic performance is boosted for pulsatile flows. The connections between diodicity, early turbulence and pulsatility uncovered here can inform applications in fluidic mixing and pumping.}, } @article {pmid33998932, year = {2021}, author = {Chen, X and Zhang, Y and Wang, J}, title = {Simulation analysis of mixing in passive microchannel with fractal obstacles based on Murray's law.}, journal = {Computer methods in biomechanics and biomedical engineering}, volume = {24}, number = {15}, pages = {1670-1678}, doi = {10.1080/10255842.2021.1906867}, pmid = {33998932}, issn = {1476-8259}, mesh = {Computer Simulation ; Diffusion ; *Fractals ; }, abstract = {In this paper, we designed fractal obstacles according to Murray's law and set them in a microchannel. We study the influence of the numbers of fractal obstacles, channel widths, branch widths, and the distance between fractal obstacles on mixing efficiency. The optimized micromixer has a high mixing efficiency of more than 90% at all velocities. This paper focuses on the analysis of the variation of mixing efficiency and pressure drop in the range of Reynolds number (Re) 0.1-150. The simulation results show that when the fluid velocity is low, the mixing efficiency of the fluids is mainly improved by molecular diffusion, when the fluid velocity is high, the microchannel with fractal obstacles can promote chaotic convection of the fluids and improve the mixing efficiency. The fractal structure based on Murray's law can be widely used in the design of passive micromixer.}, } @article {pmid33998624, year = {2021}, author = {Su, J and Chen, X and Zhu, Y and Hu, G}, title = {Machine learning assisted fast prediction of inertial lift in microchannels.}, journal = {Lab on a chip}, volume = {21}, number = {13}, pages = {2544-2556}, doi = {10.1039/d1lc00225b}, pmid = {33998624}, issn = {1473-0189}, mesh = {Cross-Sectional Studies ; Lab-On-A-Chip Devices ; Machine Learning ; *Microfluidic Analytical Techniques ; Microfluidics ; }, abstract = {Inertial effect has been extensively used in manipulating both engineered particles and biocolloids in microfluidic platforms. The design of inertial microfluidic devices largely relies on precise prediction of particle migration that is determined by the inertial lift acting on the particle. In spite of being the only means to accurately obtain the lift forces, direct numerical simulation (DNS) often consumes high computational cost and even becomes impractical when applied to microchannels with complex geometries. Herein, we proposed a fast numerical algorithm in conjunction with machine learning techniques for the analysis and design of inertial microfluidic devices. A database of inertial lift forces was first generated by conducting DNS over a wide range of operating parameters in straight microchannels with three types of cross-sectional shapes, including rectangular, triangular and semicircular shapes. A machine learning assisted model was then developed to gain the inertial lift distribution, by simply specifying the cross-sectional shape, Reynolds number and particle blockage ratio. The resultant inertial lift was integrated into the Lagrangian tracking method to quickly predict the particle trajectories in two types of microchannels in practical devices and yield good agreement with experimental observations. Our database and the associated codes allow researchers to expedite the development of the inertial microfluidic devices for particle manipulation.}, } @article {pmid33997904, year = {2021}, author = {Garayev, K and Murphy, DW}, title = {Metachronal Swimming of Mantis Shrimp: Kinematics and Interpleopod Vortex Interactions.}, journal = {Integrative and comparative biology}, volume = {61}, number = {5}, pages = {1631-1643}, doi = {10.1093/icb/icab052}, pmid = {33997904}, issn = {1557-7023}, mesh = {Animals ; Biomechanical Phenomena ; *Copepoda ; *Decapoda ; Extremities ; Models, Biological ; Swimming ; }, abstract = {Mantis shrimp swim via metachronal rowing, a pattern in which the pleopods (swimming limbs) stroke sequentially, starting with the last pair and followed by anterior neighbors. A similar swimming pattern is used at various sizes, Reynolds numbers, and advance ratios by diverse organisms including ciliates, ctenophores, copepods, krill, and lobsters. Understanding this type of locomotion is important because it is widespread and may inspire the design of underwater vehicles where efficiency, robustness, and maneuverability are desired. However, detailed measurements of the flow around free-swimming, metachronally rowing organisms are scarce, especially for organisms swimming in a high Reynolds number regime (Re ≥ 104). In this study, we present time-resolved, planar PIV measurements of a swimming peacock mantis shrimp (Odontodactylus scyllarus). Simultaneous kinematics measurements of the animal, which had body and pleopod lengths of 114 and 20 mm, respectively, reveal mean swimming speeds of 0.2-1.9 m s-1 and pleopod beat frequencies of 3.6-13 Hz, corresponding to advance ratios of 0.75-1.84 and body-based Reynolds numbers of 23,000-217,000. Further, the animal's stroke is not purely metachronal, with a long phase lag between initiation of the first and fifth pleopod power strokes. Flow measurements in the sagittal plane show that each stroking pleopod pair creates a posteriorly moving tip vortex which evades destruction by the recovery strokes of other pleopod pairs. The vortex created by the anteriormost pleopod pair is the strongest and, owing to the animal's high advance ratio, is intercepted by the power stroke of the posteriormost pleopod pair. The vortex strength increases as a result of this interaction, which may increase swimming speed or efficiency. A relationship for vortex interception by the posterior pleopod is proposed that relates the phase lag between the interacting pleopods to the beat frequency, distance between those pleopods, and speed of the vortex relative to the animal. We describe this interaction with a novel parameter called the interpleopod vortex phase matching Strouhal number StIVPM which is equal to the phase lag between interacting pleopods. This new nondimensional parameter may be useful in predicting the conditions where a constructive interaction may occur in other species or in physical models. Finally, we relate the advance ratio to the Reynolds number ratio, the ratio between the body-based Reynolds number and the pleopod-based Reynolds number. The importance of these parameters in promoting the interpleopod vortex interactions identified here, in dynamically scaled experiments, and in wake signatures behind schooling metachronal swimmers is discussed.}, } @article {pmid33986400, year = {2021}, author = {Mehboudi, A and Yeom, J}, title = {A passive Stokes flow rectifier for Newtonian fluids.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {10182}, pmid = {33986400}, issn = {2045-2322}, abstract = {Non-linear effects of the Navier-Stokes equations disappear under the Stokes regime of Newtonian fluid flows disallowing a flow rectification behavior. Here we show that passive flow rectification of Newtonian fluids is obtainable under the Stokes regime of both compressible and incompressible flows by introducing nonlinearity into the otherwise linear Stokes equations. Asymmetric flow resistances arise in shallow nozzle/diffuser microchannels with deformable ceiling, in which the fluid flow is governed by a non-linear coupled fluid-solid mechanics equation. The proposed model captures the unequal deflection profile of the deformable ceiling depending on the flow direction under the identical applied pressure, permitting a larger flow rate in the nozzle configuration. Ultra-low aspect ratio microchannels sealed by a flexible membrane have been fabricated to demonstrate passive flow rectification for low-Reynolds-number flows (0.001 < Re < 10) of common Newtonian fluids such as water, methanol, and isopropyl alcohol. The proposed rectification mechanism is also extended to compressible flows, leading to the first demonstration of rectifying equilibrium gas flows under the Stokes flow regime. While the maximum rectification ratio experimentally obtained in this work is limited to 1.41, a higher value up to 1.76 can be achieved by optimizing the width profile of the asymmetric microchannels.}, } @article {pmid33976300, year = {2021}, author = {Kazemi, A and Castillo, L and Curet, OM}, title = {Mangrove roots model suggest an optimal porosity to prevent erosion.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {9969}, pmid = {33976300}, issn = {2045-2322}, abstract = {Mangrove swamps are extremely productive ecosystems providing many ecological services in coastal regions. The hydrodynamic interactions of mangrove roots and water flow have been proposed as a key element to mitigate erosion. Several studies reveal that precise prediction of the morphological evolution of coastal areas, in the face of global warming and the consequent sea-level rise, requires an understanding of interactions between root porosity (the fraction of the volume of void space over the total volume), water flows, and sediment transport. Water flows around the mangrove prop roots create a complex energetic process that mixes up sediments and generates a depositional region posterior to the roots. In this work, we investigated the boundary layer behind permeable arrays of cylinders (patch) that represent the mangrove roots to explore the impact of patch porosity on the onset of sediment transport. The flow measurements were performed in a vertical plane along the water depth downstream of the mangrove root models. A high-resolution Particle Image Velocimetry (PIV) was used in a flume to observe the impact of porosity on the mean flow, velocity derivatives, skin friction coefficient, and production of turbulent kinetic energy for Reynolds number of 2500 (based on patch diameter length-scale). Here, we proposed a predictive model for critical velocity for incipient motion that takes into account the mangrove roots porosity and the near-bed turbulence effect. It is found that the patch with the [Formula: see text] porosity, has the maximum critical velocity over which the sediment transport initiates. We found the optimum porosity has the minimum sediment erosion and creates negative vorticity sources near the bed that increases the critical velocity. This signifies an optimum porosity for the onset of sediment transport consistent with the porosity of mangroves in nature. The phenomenological model is elucidated based on an analysis of the vorticity evolution equation for viscous incompressible flows. For the optimum porous patch, a sink of vorticity was formed which yielded to lower the near-bed turbulence and vorticity. The minimum velocity fluctuations were sufficient to initiate the boundary layer transition, however, the viscous dissipation dominated the turbulence production to obstruct the sediment transport. This work identified the pivotal role of mangrove root porosity in sediment transport in terms of velocity and its derivatives in wall-bounded flows. Our work also provides insight into the sediment transport and erosion processes that govern the evolution of the shapes of shorelines.}, } @article {pmid33956314, year = {2021}, author = {Vasilopoulos, K and Lekakis, I and Sarris, IE and Tsoutsanis, P}, title = {Large eddy simulation of dispersion of hazardous materials released from a fire accident around a cubical building.}, journal = {Environmental science and pollution research international}, volume = {28}, number = {36}, pages = {50363-50377}, pmid = {33956314}, issn = {1614-7499}, mesh = {Accidents ; *Air Pollutants/analysis ; *Hazardous Substances ; Models, Theoretical ; Wind ; }, abstract = {The turbulent smoke dispersion from a pool fire around a cubical building is studied using large eddy simulation at a high Reynolds number, corresponding to existing experimental measurements both in laboratory and field test scales. Emphasis of this work is on the smoke dispersion due to two different fuel pool fire accident scenarios, initiated behind the building. For the setup of fire in the first case, crude oil was used with a heat release rate of 7.8 MW, and in the second, diesel oil with a heat release rate of 13.5 MW. It is found that in both fire scenarios, the downstream extent of the toxic zone is approximately the same. This is explained in terms of the fact that the smoke concentration and dispersion are influenced mainly by the convective buoyant forces and the strong turbulence mixing processes within the wake zone of the building. It is suggested that wind is the dominating factor in these accident scenarios, which represent the conditions resulting in the highest toxicity levels.}, } @article {pmid33953255, year = {2021}, author = {Asai, T and Hong, S}, title = {Aerodynamics of the newly approved football for the English Premier League 2020-21 season.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {9578}, pmid = {33953255}, issn = {2045-2322}, abstract = {Footballs are typically constructed with 32 panels. Recently, the number of panels has been successively reduced to 14, 8, and 6 panels, and official balls have been adopted with complex panel shapes and aerodynamics that differ from those of 32-panel balls. The official ball for the 2020-21 season of the English Premier League comprises just four panels with a complex panel shape and surface groove design; however, its aerodynamics have not yet been clarified. This study aims to clarify the aerodynamic characteristics (drag, side force, lift force, their deviations, and critical Reynolds number) of the new 4-panel ball (Flight 2020, Nike) in comparison to a 6-panel ball (Tsubasa 2020, Adidas) and conventional 32-panel ball (Pelada 2020, Molten) using a wind tunnel test, surface design measurement, and a simple 2D flight simulation. The results showed that Flight 2020 has greater surface roughness and smaller critical Reynolds number than Pelada 2020 and Tsubasa 2020, resulting to its marginally greater drag force in the supercritical region, and slightly smaller fluctuations of the side and lift forces. Furthermore, Flight with a symmetrical orientation exhibits a significantly higher drag coefficient in the supercritical region, suggesting its greater air resistance during flight under this condition.}, } @article {pmid33949106, year = {2021}, author = {Sharan, P and Nsamela, A and Lesher-Pérez, SC and Simmchen, J}, title = {Microfluidics for Microswimmers: Engineering Novel Swimmers and Constructing Swimming Lanes on the Microscale, a Tutorial Review.}, journal = {Small (Weinheim an der Bergstrasse, Germany)}, volume = {17}, number = {26}, pages = {e2007403}, doi = {10.1002/smll.202007403}, pmid = {33949106}, issn = {1613-6829}, mesh = {Engineering ; *Microfluidics ; *Swimming ; }, abstract = {This paper provides an updated review of recent advances in microfluidics applied to artificial and biohybrid microswimmers. Sharing the common regime of low Reynolds number, the two fields have been brought together to take advantage of the fluid characteristics at the microscale, benefitting microswimmer research multifold. First, microfluidics offer simple and relatively low-cost devices for high-fidelity production of microswimmers made of organic and inorganic materials in a variety of shapes and sizes. Microscale confinement and the corresponding fluid properties have demonstrated differential microswimmer behaviors in microchannels or in the presence of various types of physical or chemical stimuli. Custom environments to study these behaviors have been designed in large part with the help of microfluidics. Evaluating microswimmers in increasingly complex lab environments such as microfluidic systems can ensure more effective implementation for in-field applications. The benefits of microfluidics for the fabrication and evaluation of microswimmers are balanced by the potential use of microswimmers for sample manipulation and processing in microfluidic systems, a large obstacle in diagnostic and other testing platforms. In this review various ways in which these two complementary technology fields will enhance microswimmer development and implementation in various fields are introduced.}, } @article {pmid33947812, year = {2021}, author = {Hartl, B and Hübl, M and Kahl, G and Zöttl, A}, title = {Microswimmers learning chemotaxis with genetic algorithms.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {118}, number = {19}, pages = {}, pmid = {33947812}, issn = {1091-6490}, mesh = {Algorithms ; Animals ; Caenorhabditis elegans/physiology ; Chemotaxis/*genetics/*physiology ; Computer Simulation ; Flagella/physiology ; Learning/*physiology ; Machine Learning ; Models, Biological ; Motion ; Neural Networks, Computer ; Swimming/*physiology ; }, abstract = {Various microorganisms and some mammalian cells are able to swim in viscous fluids by performing nonreciprocal body deformations, such as rotating attached flagella or by distorting their entire body. In order to perform chemotaxis (i.e., to move toward and to stay at high concentrations of nutrients), they adapt their swimming gaits in a nontrivial manner. Here, we propose a computational model, which features autonomous shape adaptation of microswimmers moving in one dimension toward high field concentrations. As an internal decision-making machinery, we use artificial neural networks, which control the motion of the microswimmer. We present two methods to measure chemical gradients, spatial and temporal sensing, as known for swimming mammalian cells and bacteria, respectively. Using the genetic algorithm NeuroEvolution of Augmenting Topologies, surprisingly simple neural networks evolve. These networks control the shape deformations of the microswimmers and allow them to navigate in static and complex time-dependent chemical environments. By introducing noisy signal transmission in the neural network, the well-known biased run-and-tumble motion emerges. Our work demonstrates that the evolution of a simple and interpretable internal decision-making machinery coupled to the environment allows navigation in diverse chemical landscapes. These findings are of relevance for intracellular biochemical sensing mechanisms of single cells or for the simple nervous system of small multicellular organisms such as Caenorhabditis elegans.}, } @article {pmid33938005, year = {2021}, author = {Wang, S and Liu, Z and Wu, S and Sun, H and Zeng, W and Wei, J and Fan, Z and Sui, Z and Liu, L and Pan, X}, title = {Microalgae separation by inertia-enhanced pinched flow fractionation.}, journal = {Electrophoresis}, volume = {42}, number = {21-22}, pages = {2223-2229}, doi = {10.1002/elps.202000325}, pmid = {33938005}, issn = {1522-2683}, mesh = {Chemical Fractionation ; Chlorella ; *Microalgae ; Ships ; Water ; }, abstract = {To improve the accuracy and efficiency of ships' ballast water detection, the separation of microalgae according to size is significant. In this article, a method to separate microalgae based on inertia-enhanced pinched flow fractionation (iPFF) was reported. The method utilized the inertial lift force induced by flow to separate microalgae according to size continuously. The experimental results show that, as the Reynolds number increases, the separation effect becomes better at first, but then stays unchanged. The best separation effect can be obtained when the Reynolds number is 12.3. In addition, with the increase of the flow rate ratio between sheath fluid and microalgae mixture, the separation effect becomes better and the best separation effect can be obtained when the flow rate ratio reaches 10. In this case, the recovery rate of Tetraselmis sp. is about 90%, and the purity is about 86%; the recovery rate of Chlorella sp. is as high as 99%, and the purity is about 99%. After that, the separation effect keeps getting better but very slowly. In general, this study provides a simple method for the separation of microalgae with different sizes, and lays a foundation for the accurate detection of microalgae in the ballast water.}, } @article {pmid33924044, year = {2021}, author = {Rao, Y and Li, L and Wang, S and Zhao, S and Zhou, S}, title = {Numerical Simulation Study on Flow Laws and Heat Transfer of Gas Hydrate in the Spiral Flow Pipeline with Long Twisted Band.}, journal = {Entropy (Basel, Switzerland)}, volume = {23}, number = {4}, pages = {}, pmid = {33924044}, issn = {1099-4300}, abstract = {The natural gas hydrate plugging problems in the mixed pipeline are becoming more and more serious. The hydrate plugging has gradually become an important problem to ensure the safety of pipeline operation. The deposition and heat transfer characteristics of natural gas hydrate particles in the spiral flow pipeline have been studied. The DPM model (discrete phase model) was used to simulate the motion of solid particles, which was used to simulate the complex spiral flow characteristics of hydrate in the pipeline with a long twisted band. The deposition and heat transfer characteristics of gas hydrate particles in the spiral flow pipeline were studied. The velocity distribution, pressure drop distribution, heat transfer characteristics, and particle settling characteristics in the pipeline were investigated. The numerical results showed that compared with the straight flow without a long twisted band, two obvious eddies are formed in the flow field with a long twisted band, and the velocities are maximum at the center of the vortices. Along the direction of the pipeline, the two vortices move toward the pipe wall from near the twisted band, which can effectively carry the hydrate particles deposited on the wall. With the same Reynolds number, the twisted rate was greater, the spiral strength was weaker, the tangential velocity was smaller, and the pressure drop was smaller. Therefore, the pressure loss can be reduced as much as possible with effect of the spiral flow. In a straight light flow, the Nusselt number is in a parabolic shape with the opening downwards. At the center of the pipe, the Nusselt number gradually decreased toward the pipe wall at the maximum, and at the near wall, the attenuation gradient of the Nu number was large. For spiral flow, the curve presented by the Nusselt number was a trough at the center of the pipe and a peak at 1/2 of the pipe diameter. With the reduction of twist rate, the Nusselt number becomes larger. Therefore, the spiral flow can make the temperature distribution more even and prevent the large temperature difference, resulting in the mass formation of hydrate particles in the pipeline wall. Spiral flow has a good carrying effect. Under the same condition, the spiral flow carried hydrate particles at a distance about 3-4 times farther than that of the straight flow.}, } @article {pmid33923993, year = {2021}, author = {Yuan, S and Jiang, B and Peng, T and Li, Q and Zhou, M}, title = {An Investigation of Flow Patterns and Mixing Characteristics in a Cross-Shaped Micromixer within the Laminar Regime.}, journal = {Micromachines}, volume = {12}, number = {4}, pages = {}, pmid = {33923993}, issn = {2072-666X}, abstract = {A fast mixing is critical for subsequent practical development of microfluidic devices, which are often used for assays in the detection of reagents and samples. The present work sets up computational fluid dynamics simulations to explore the flow characteristic and mixing mechanism of fluids in cross-shaped mixers within the laminar regime. First, the effects of increasing an operating parameter on local mixing quality along the microchannels are investigated. It is found that sufficient diffusion cannot occur even though the concentration gradient is large at a high Reynolds number. Meanwhile, a method for calculating local mixing efficiency is also characterized. The mixing efficiency varies exponentially with the flow distance. Second, in order to optimize the cross-shaped mixer, the effects of design parameters, namely aspect ratio, mixing angle and blockage, on mixing quality are captured and the visualization of velocity and concentration distribution are demonstrated. The results show that the aspect ratio and the blockage play an important role in accelerating the mixing process. They can improve the mixing efficiency by increasing the mass transfer area and enhancing the chaotic advection, respectively. In contrast, the inflow angle that affects dispersion length is not an effective parameter. Besides, the surface roughness, which makes the disturbance of fluid flow by roughness more obvious, is considered. Three types of rough elements bring benefits for enhancing mixing quality due to the convection induced by the lateral velocity.}, } @article {pmid33922337, year = {2021}, author = {Ansari, A and Kavousi, S and Helfer, F and Millar, G and Thiel, DV}, title = {An Improved Modelling Approach for the Comprehensive Study of Direct Contact Membrane Distillation.}, journal = {Membranes}, volume = {11}, number = {5}, pages = {}, pmid = {33922337}, issn = {2077-0375}, abstract = {Direct Contact Membrane Distillation (DCMD) is a promising and feasible technology for water desalination. Most of the models used to simulate DCMD are one-dimensional and/or use a linear function of vapour pressure which relies on experimentally determined parameters. In this study, the model of DCMD using Nusselt correlations was improved by coupling the continuity, momentum, and energy equations to better capture the downstream alteration of flow field properties. A logarithmic function of vapour pressure, which is independent from experiments, was used. This allowed us to analyse DCMD with different membrane properties. The results of our developed model were in good agreement with the DCMD experimental results, with less than 7% deviation. System performance metrics, including water flux, temperature, and concentration polarisation coefficient and thermal efficiency, were analysed by varying inlet feed and permeate temperature, inlet velocity, inlet feed concentration, channel length. In addition, twenty-two commercial membranes were analysed to obtain a real vision on the influence of membrane characteristics on system performance metrics. The results showed that the feed temperature had the most significant effect on water flux and thermal efficiency. The increased feed temperature enhanced the water flux and thermal efficiency; however, it caused more concentration and temperature polarisation. On the other hand, the increased inlet velocity was found to provide increased water flux and reduced temperature and concertation polarisation as well. It was also found that the membrane properties, especially thickness and porosity, can affect the DCMD performance significantly. A two-fold increase of feed temperature increased the water flux and thermal efficiency, 10-fold and 27%, respectively; however, it caused an increase in temperature and concertation polarisation, at 48% and 34%, respectively. By increasing Reynolds number from 80 to 1600, the water flux, CPC, and TPC enhanced by 2.3-fold, 2%, and 21%, respectively. The increased feed concentration from 0 to 250 [g/L] caused a 26% reduction in water flux. To capture the downstream alteration of flow properties, it was shown that the ratio of inlet value to outlet value of system performance metrics decreased significantly throughout the module. Therefore, improvement over the conventional model is undeniable, as the new model can assist in achieving optimal operation conditions.}, } @article {pmid33922099, year = {2021}, author = {Yuan, C and Zhang, H and Li, X and Oishi, M and Oshima, M and Yao, Q and Li, F}, title = {Numerical Investigation of T-Shaped Microfluidic Oscillator with Viscoelastic Fluid.}, journal = {Micromachines}, volume = {12}, number = {5}, pages = {}, pmid = {33922099}, issn = {2072-666X}, abstract = {Oscillatory flow has many applications in micro-scaled devices. The methods of realizing microfluidic oscillators reported so far are typically based on the impinging-jet and Coanda effect, which usually require the flow Reynolds number to be at least at the order of unity. Another approach is to introduce elastomeric membrane into the microfluidic units; however, the manufacturing process is relatively complex, and the membrane will become soft after long-time operation, which leads to deviation from the design condition. From the perspective of the core requirement of a microfluidic circuit, i.e., nonlinearity, the oscillatory microfluidic flow can be realized via the nonlinear characteristics of viscoelastic fluid flow. In this paper, the flow characteristics of viscoelastic fluid (Boger-type) in a T-shaped channel and its modified structures are studied by two-dimensional direct numerical simulation (DNS). The main results obtained from the DNS study are as follows: (1) Both Weissenberg (Wi) number and viscosity ratio need to be within a certain range to achieve a periodic oscillating performance; (2) With the presence of the dynamic evolution of the pair of vortices in the upstream near the intersection, the oscillation intensity increases as the elasticity-dominated area in the junction enlarges; (3) Considering the simplicity of the T-type channel as a potential oscillator, the improved structure should have a groove carved toward the entrance near the upper wall. The maximum oscillation intensity measured by the standard deviation of flow rate at outlet is increased by 129% compared with that of the original standard T-shaped channel under the same condition. To sum up, with Wi number and viscosity ratio within a certain range, the regular periodic oscillation characteristics of Oldroyd-B type viscoelastic fluid flow in standard T-shaped and its modified channels can be obtained. This structure can serve as a passive microfluidic oscillator with great potential value at an extremely low Reynolds number, which has the advantages of simplicity, no moving parts and fan-out of two.}, } @article {pmid33920267, year = {2021}, author = {Abbasnezhad, N and Kebdani, M and Shirinbayan, M and Champmartin, S and Tcharkhtchi, A and Kouidri, S and Bakir, F}, title = {Development of a Model Based on Physical Mechanisms for the Explanation of Drug Release: Application to Diclofenac Release from Polyurethane Films.}, journal = {Polymers}, volume = {13}, number = {8}, pages = {}, pmid = {33920267}, issn = {2073-4360}, abstract = {In this study, we present a method for prediction of the drug-release profile based on the physical mechanisms that can intervene in drug release from a drug-carrier. The application presented here incorporates the effects of drug concentration and Reynolds number defining the circulating flow in the testing vein. The experimental data used relate to the release of diclofenac from samples of non-degradable polyurethane subjected to static and continuous flow. This case includes simultaneously three mechanisms: burst-release, diffusion and osmotic pressure, identified beforehand here as being able to contribute to the drug liberation. For this purpose, authors coded the Sequential Quadratic Programming Algorithm to solve the problem of non-linear optimization. The experimental data used to develop the mathematical model obtained from release studies carried out in water solution at 37 °C, for three concentrations of diclofenac and two water flow rates. We discuss the contribution of mechanisms and kinetics by considering two aforementioned parameters and, following that, we obtain the specific-model and compare the calculated results with the experimental results for the reserved cases. The results showed that drug percentage mostly affect the burst release, however flow rate has affected the osmotic release. In addition, release kinetics of all the mechanisms have increased by increasing the values of two considered parameters.}, } @article {pmid33917762, year = {2021}, author = {Wang, R and Duan, R and Jia, H}, title = {Experimental Validation of Falling Liquid Film Models: Velocity Assumption and Velocity Field Comparison.}, journal = {Polymers}, volume = {13}, number = {8}, pages = {}, pmid = {33917762}, issn = {2073-4360}, abstract = {This publication focuses on the experimental validation of film models by comparing constructed and experimental velocity fields based on model and elementary experimental data. The film experiment covers Kapitza numbers Ka = 278.8 and Ka = 4538.6, a Reynolds number range of 1.6-52, and disturbance frequencies of 0, 2, 5, and 7 Hz. Compared to previous publications, the applied methodology has boundary identification procedures that are more refined and provide additional adaptive particle image velocimetry (PIV) method access to synthetic particle images. The experimental method was validated with a comparison with experimental particle image velocimetry and planar laser induced fluorescence (PIV/PLIF) results, Nusselt's theoretical prediction, and experimental particle tracking velocimetry (PTV) results of flat steady cases, and a good continuity equation reproduction of transient cases proves the method's fidelity. The velocity fields are reconstructed based on different film flow model velocity profile assumptions such as experimental film thickness, flow rates, and their derivatives, providing a validation method of film model by comparison between reconstructed velocity experimental data and experimental velocity data. The comparison results show that the first-order weighted residual model (WRM) and regularized model (RM) are very similar, although they may fail to predict the velocity field in rapidly changing zones such as the front of the main hump and the first capillary wave troughs.}, } @article {pmid33915686, year = {2021}, author = {Rasool, G and Shafiq, A and Alqarni, MS and Wakif, A and Khan, I and Bhutta, MS}, title = {Numerical Scrutinization of Darcy-Forchheimer Relation in Convective Magnetohydrodynamic Nanofluid Flow Bounded by Nonlinear Stretching Surface in the Perspective of Heat and Mass Transfer.}, journal = {Micromachines}, volume = {12}, number = {4}, pages = {}, pmid = {33915686}, issn = {2072-666X}, abstract = {The aim of this research is mainly concerned with the numerical examination of Darcy-Forchheimer relation in convective magnetohydrodynamic nanofluid flow bounded by non-linear stretching sheet. A visco-elastic and strictly incompressible liquid saturates the designated porous medium under the direct influence of the Darcy-Forchheimer model and convective boundary. The magnetic effect is taken uniformly normal to the flow direction. However, the model is bounded to a tiny magnetic Reynolds number for practical applications. Boundary layer formulations are taken into consideration. The so-formulated leading problems are converted into highly nonlinear ordinary problems using effectively modified transformations. The numerical scheme is applied to solve the governing problems. The outcomes stipulate that thermal layer receives significant modification in the incremental direction for augmented values of thermal radiation parameter Rd. Elevation in thermal Biot number γ1 apparently results a significant rise in thermal layer and associated boundary layer thickness. The solute Biot number is found to be an enhancing factor the concentration profile. Besides the three main profiles, the contour and density graphs are sketched for both the linear and non-linear cases. Furthermore, skin friction jumps for larger porosity and larger Forchheimer number. Both the heat and mass flux numbers receive a reduction for augmented values of the Forchheimer number. Heat flux enhances, while mass flux reduces, the strong effect of thermal Biot number. The considered problem could be helpful in any several industrial and engineering procedures, such as rolling, polymeric extrusion, continuously stretching done in plastic thin films, crystal growth, fiber production, and metallic extrusion, etc.}, } @article {pmid33905256, year = {2021}, author = {Sasaki, K and Okue, T and Nakai, T and Uchida, Y and Nishiyama, N}, title = {Lateral Growth of Uniformly Thin Gold Nanosheets Facilitated by Two-Dimensional Precursor Supply.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {37}, number = {19}, pages = {5872-5877}, doi = {10.1021/acs.langmuir.1c00344}, pmid = {33905256}, issn = {1520-5827}, abstract = {The nanosheets of highly symmetric materials with a face-centered cubic lattice such as gold have been synthesized by adsorbing the precursors on a flat surface, whose chemical specificity induces the anisotropy of growth rates. We have succeeded in the fabrication of gold nanosheets in a hydrophilic space inside highly separated bilayers, which work as two-dimensional hydrophilic reactors, in a hyperswollen lamellar liquid crystalline phase of an amphiphile solution. One of the physical properties, amphiphilicity, confines the ingredients therein. The nanosheets can only grow in the in-plane direction due to the inhibition of the out-of-plane growth rather than the anisotropy of growth rates probably. Thus, the synthesis can be accelerated; the particles can be completed within 15 min. As not relying on chemical specificity, silver nanosheets could also be synthesized in the same way. The suspension of gold and silver nanosheets without any amphiphiles could be obtained, and the solvent is replaceable. We found that the width of the obtained gold nanosheets is proportional to the Reynolds number of the solution because the area of the bilayer in the hyperswollen lamellar phase depends on shear stress. This implies that the areas of gold nanosheets depend on the areas of the bilayers, and it can be controlled by changing the Reynolds number. This method could be widely used to continuously obtain large-area nanosheets of various materials in a roll-to-roll manufacturing process.}, } @article {pmid33902681, year = {2021}, author = {Heyland, A and Roszell, J and Chau, J and Chai, K and Eaton, A and Nolan, K and Madden, K and Ahmed, WH}, title = {Mass transfer and flow characterization of novel algae-based nutrient removal system.}, journal = {Biotechnology for biofuels}, volume = {14}, number = {1}, pages = {104}, pmid = {33902681}, issn = {1754-6834}, abstract = {BACKGROUND: Recirculating aquaculture systems (RAS) are an essential component of sustainable inland seafood production. Still, nutrient removal from these systems can result in substantial environmental problems, or present a major cost factor with few added value options. In this study, an innovative and energy-efficient algae based nutrient removal system (NRS) was developed that has the potential to generate revenue through algal commercialization. We optimized mass transfer in our NRS design using novel aeration and mixing technology, using air lift pumps and developed an original membrane cartridge for the continuous operation of nutrient removal and algae production. Specifically, we designed, manufactured and tested a 60-L NRS prototype. Based on specific airlift mixing conditions as well as concentration gradients, we assessed NRS nutrient removal capacity. We then examined the effects of different internal bioreactor geometries and radial orientations on the mixing efficiency.

RESULTS: Using the start-up dynamic method, the overall mass transfer coefficient was found to be in the range of 0.00164-0.0074 [Formula: see text], depending on flow parameters and we confirmed a scaling relationship of mass transfer across concentration gradients. We found the optimal Reynolds number to be 500 for optimal mass transfer, as higher Reynolds numbers resulted in a relatively reduced increase of mass transfer. This relationship between mass transfer and Reynolds number is critical to assess scalability of our system. Our results demonstrate an even distribution of dissolved oxygen levels across the reactor core, demonstrating adequate mixing by the airlift pump, a critical consideration for optimal algal growth. Distribution of dissolved gases in the reactor was further assessed using flow visualization in order to relate the bubble distribution to the mass transfer capabilities of the reactor. We run a successful proof of principle trial using the green alga Dunaliella tertiolecta to assess mass transfer of nutrients across the membrane and biomass production.

CONCLUSIONS: Manipulation of the concentration gradient across the membrane demonstrates a more prominent role of airlift mixing at higher concentration gradients. Specifically, the mass transfer rate increased threefold when the concentration gradient was increased 2.5-fold. We found that we can grow algae in the reactor chamber at rates comparable to those of other production systems and that the membrane scaffolds effectively remove nutrients form the wastewater. Our findings provide support for scalability of the design and support the use of this novel NRS for nutrient removal in aquaculture and potentially other applications.}, } @article {pmid33895456, year = {2021}, author = {Song, Z and Tong, J and Pfleging, W and Sun, J}, title = {A review: Learning from the flight of beetles.}, journal = {Computers in biology and medicine}, volume = {133}, number = {}, pages = {104397}, doi = {10.1016/j.compbiomed.2021.104397}, pmid = {33895456}, issn = {1879-0534}, mesh = {Animals ; Biomechanical Phenomena ; *Coleoptera ; Mechanical Phenomena ; Miniaturization ; Wings, Animal ; }, abstract = {Some Coleoptera (popularly referred to as beetles) can fly at a low Reynolds number with their deployable hind wings, which directly enables a low body weight-a good bioinspiration strategy for miniaturization of micro-air vehicles (MAVs). The hind wing is a significant part of the body and has a folding/unfolding mechanism whose unique function benefits from different structures and materials. This review summarizes the actions, factors, and mechanisms of beetle flight and bioinspired MAVs with deployable wings. The elytron controlled by muscles is the protected part for the folded hind wing and influences flight performance. The resilin, the storage material for elasticity, is located in the folding parts. The hind wings' folding/unfolding mechanism and flight performance can be influenced by vein structures of hollow, solid and wrinkled veins, the hemolymph that flows in hollow veins and its hydraulic mechanism, and various mechanical properties of veins. The action of beetle flight includes flapping flight, hovering, gliding, and landing. The hind wing is passively deformed through force and hemolymph, and the attack angle of the hind wing and the nanomechanics of the veins, muscles and mass body determine the flight performance. Based these factors, bioinspired MAVs with a new deployable wing structure and new materials will be designed to be much more effective and miniaturized. The new fuels and energy supply are significant aspects of MAVs.}, } @article {pmid33889684, year = {2021}, author = {Sadeq, AM and Ahmed, SF and Sleiti, AK}, title = {Dataset for transient 3D simulations of turbulent premixed flames of Gas-to-Liquid (GTL) fuel.}, journal = {Data in brief}, volume = {36}, number = {}, pages = {106956}, pmid = {33889684}, issn = {2352-3409}, abstract = {A fan-stirred combustion vessel is used to study the premixed turbulent combustion of diesel, Gas to Liquids (GTL) and 50/50 diesel-GTL and to generate these datasets. A numerical simulation approach is implemented for modelling the premixed combustion of the three fuels under different thermodynamics and turbulence initial conditions, using Zimont Turbulent Flame Speed Closure (Zimont TFC) model. Different parameters are obtained from these simulation runs such as turbulent eddy viscosity (µ), turbulent kinetic energy (k), Damkohler number (Da), Reynolds number (ReT) and turbulent flame speed (St). The raw, filtered and pre-processed data are imported from ANSYS Fluent and then listed on filtered tables for the ease of accessibility. These datasets can be then used to perform research in different related areas such as chemical kinetic mechanisms, ignition delay time, flame ignition mechanisms and flame extinction and diffusion. Also, they can be employed to further understand trends, patterns, and anomalies in data. In addition, they can be compared with other numerical models to establish a robust knowledge about the modelling of premixed turbulent combustion. For more information and discussion of the dataset creation, the reader is directed to the full-length article, "Abdellatif M. Sadeq, Samer F. Ahmed, Ahmad K. Sleiti, Transient 3D simulations of turbulent premixed flames of gas-to-liquid (GTL) fuel in a fan-stirred combustion vessel, Fuel, Volume 291, 2021, 120,184, ISSN 0016 2361, https://doi.org/10.1016/j.fuel.2021.120184" [1].}, } @article {pmid33871634, year = {2021}, author = {Lamont, EI and Emlet, RB}, title = {Swimming Kinematics of Cyprids of the Barnacle Balanus glandula.}, journal = {Integrative and comparative biology}, volume = {61}, number = {5}, pages = {1567-1578}, doi = {10.1093/icb/icab028}, pmid = {33871634}, issn = {1557-7023}, mesh = {Animals ; Biomechanical Phenomena ; *Copepoda ; Larva ; Swimming ; *Thoracica ; }, abstract = {Larvae of barnacles typically pass through naupliar and cyprid planktonic stages before settlement and metamorphosis. As the final larval stage, cyprids swim much faster than nauplii and in turbulent fluid environments with high shears as they seek habitat. Cyprids swim with six pairs of reciprocating thoracic appendages and use two anterior antennules during settlement. Our understanding of how thoracic appendages generate movement is limited due to short stroke intervals (∼5 ms) that impede observations of the shape and trajectory of appendages. Here, we used high-speed videography to observe both free-swimming and tethered cyprids of the intertidal acorn barnacle Balanus glandula to produce a comprehensive description of thoracic appendage swimming kinematics. Cyprids used a drag-based method of swimming: their six pairs of thoracic appendages moved through metachronal power strokes and synchronous recovery strokes similar to the thoracopod motions in calanoid copepods during escape swimming. During the power stroke, plumose setae on each appendage pair spread laterally into a high surface area and high drag paddle composed of a meshwork of fused setules. This interconnected setal array collapsed into a low surface area and low drag shape during the recovery stroke. These effective swimming appendages allowed cyprids to move upward at an average speed of 1.4 cm/s (∼25 body lengths/s) with an average beat frequency of 16 beats/s, and reach an instantaneous velocity of up to 6 cm/s. Beat frequency of the thoracic appendages was significantly associated with speed, with higher beat frequencies indicating faster swimming speed. At their average speed, cyprids moved at the intermediate Reynolds number of ∼10, in which both viscous and inertial forces affected movement. Cyprids could alter swimming direction by sweeping the posterior-most appendage pair to one side and beating the remaining thoracic appendages synchronously through the power stroke with greater motion on the outside of their turn. These results greatly enhance our understanding both of cyprid motility and how small planktonic organisms can use swimming appendages with fused setule arrays to reach high swimming speeds and affect directional changes.}, } @article {pmid33870835, year = {2021}, author = {Si, XA and Talaat, M and Su, WC and Xi, J}, title = {Inhalation dosimetry of nasally inhaled respiratory aerosols in the human respiratory tract with locally remodeled conducting lungs.}, journal = {Inhalation toxicology}, volume = {33}, number = {4}, pages = {143-159}, doi = {10.1080/08958378.2021.1912860}, pmid = {33870835}, issn = {1091-7691}, mesh = {*Administration, Inhalation ; Aerosols/*administration & dosage ; *Airway Remodeling ; Dose-Response Relationship, Drug ; Humans ; Lung/anatomy & histology/pathology ; Models, Biological ; Nanoparticles/*administration & dosage ; Nose/anatomy & histology ; }, abstract = {Objective: Respiratory diseases are often accompanied by alterations to airway morphology. However, inhalation dosimetry data in remodeled airways are scarce due to the challenges in reconstructing diseased respiratory morphologies. This study aims to study the airway remodeling effects on the inhalation dosimetry of nasally inhaled nanoparticles in a nose-lung geometry that extends to G9 (ninth generation).Materials and methods: Statistical shape modeling was used to develop four diseased lung models with varying levels of bronchiolar dilation/constriction in the left-lower (LL) lobe (i.e. M1-M4). Respiratory airflow and particle deposition were simulated using a low Reynolds number k-ω turbulence model and a Lagrangian tracking approach.Results: Significant discrepancies were observed in the flow partitions between the left and right lungs, as well as between the lower and upper lobes of the left lung, which changed by 10-fold between the most dilated and constricted models.Much lower doses were predicted on the surface of the constricted LL bronchioles G4-G9, as well as into the peripheral airways beyond G9 of the LL lung. However, the LL lobar remodeling had little effect on the dosimetry in the nasopharynx, as well as on the total dosimetry in the nose-lung geometry (up to G9).Conclusion: It is suggested that airway remodeling may pose a higher viral infection risk to the host by redistributing the inhaled viruses to healthy lung lobes. Airway remodeling effects should also be considered in the treatment planning of inhalation therapies, not only because of the dosimetry variation from altered lung morphology but also its evolution as the disease progresses.}, } @article {pmid33863724, year = {2021}, author = {Trkulja, CL and Jungholm, O and Davidson, M and Jardemark, K and Marcus, MM and Hägglund, J and Karlsson, A and Karlsson, R and Bruton, J and Ivarsson, N and Srinivasa, SP and Cavallin, A and Svensson, P and Jeffries, GDM and Christakopoulou, MN and Reymer, A and Ashok, A and Willman, G and Papadia, D and Johnsson, E and Orwar, O}, title = {Rational antibody design for undruggable targets using kinetically controlled biomolecular probes.}, journal = {Science advances}, volume = {7}, number = {16}, pages = {}, pmid = {33863724}, issn = {2375-2548}, mesh = {*Antibodies, Monoclonal/chemistry ; *Antigens ; Binding Sites, Antibody ; Epitopes ; Humans ; }, abstract = {Several important drug targets, e.g., ion channels and G protein-coupled receptors, are extremely difficult to approach with current antibody technologies. To address these targets classes, we explored kinetically controlled proteases as structural dynamics-sensitive druggability probes in native-state and disease-relevant proteins. By using low-Reynolds number flows, such that a single or a few protease incisions are made, we could identify antibody binding sites (epitopes) that were translated into short-sequence antigens for antibody production. We obtained molecular-level information of the epitope-paratope region and could produce high-affinity antibodies with programmed pharmacological function against difficult-to-drug targets. We demonstrate the first stimulus-selective monoclonal antibodies targeting the transient receptor potential vanilloid 1 (TRPV1) channel, a clinically validated pain target widely considered undruggable with antibodies, and apoptosis-inducing antibodies selectively mediating cytotoxicity in KRAS-mutated cells. It is our hope that this platform will widen the scope of antibody therapeutics for the benefit of patients.}, } @article {pmid33862704, year = {2021}, author = {Fouxon, I and Feinberg, J and Käpylä, P and Mond, M}, title = {Reynolds number dependence of Lyapunov exponents of turbulence and fluid particles.}, journal = {Physical review. E}, volume = {103}, number = {3-1}, pages = {033110}, doi = {10.1103/PhysRevE.103.033110}, pmid = {33862704}, issn = {2470-0053}, abstract = {The Navier-Stokes equations generate an infinite set of generalized Lyapunov exponents defined by different ways of measuring the distance between exponentially diverging perturbed and unperturbed solutions. This set is demonstrated to be similar, yet different, from the generalized Lyapunov exponent that provides moments of distance between two fluid particles below the Kolmogorov scale. We derive rigorous upper bounds on dimensionless Lyapunov exponent of the fluid particles that demonstrate the exponent's decay with Reynolds number Re in accord with previous studies. In contrast, terms of cumulant series for exponents of the moments have power-law growth with Re. We demonstrate as an application that the growth of small fluctuations of magnetic field in ideal conducting turbulence is hyperintermittent, being exponential in both time and Reynolds number. We resolve the existing contradiction between the theory, that predicts slow decrease of dimensionless Lyapunov exponent of turbulence with Re, and observations exhibiting quite fast growth. We demonstrate that it is highly plausible that a pointwise limit for the growth of small perturbations of the Navier-Stokes equations exists.}, } @article {pmid33854256, year = {2021}, author = {Waringer, J and Vitecek, S and Martini, J and Zittra, C and Handschuh, S and Vieira, A and Kuhlmann, HC}, title = {Hydraulic niche utilization by larvae of the three Drusinae clades (Insecta: Trichoptera).}, journal = {Biologia}, volume = {76}, number = {5}, pages = {1465-1473}, pmid = {33854256}, issn = {0006-3088}, support = {P 31258/FWF_/Austrian Science Fund FWF/Austria ; }, abstract = {Hydraulic niche descriptors of final instar larvae of nine Drusus species (Trichoptera) were studied in small, spring-fed, first-order headwaters located in the Mühlviertel (Upper Austria), Koralpe (Carinthia, Austria), and in the Austrian and Italian Alps. The species investigated covered all three clades of Drusinae: the shredder clade (Drusus franzi, D. alpinus), the grazer clade (D. biguttatus, D. chauvinianus, D. dudor, D. monticola), and the filtering carnivore clade (D. chrysotus, D. katagelastos, D. muelleri). Flow velocity was measured at front center of 68 larvae, head upstream, on the top of mineral substrate particles at water depths of 10-30 mm, using a tripod-stabilized Micro propeller meter (propeller diameter = 10 mm). Each data series consisted of a sampled measurement lasting 30 s (measuring interval = 1 s). In total, 2040 single velocity measurements were taken. Instantaneous flow velocities and drag at the sites of the 68 larvae varied from 0 to 0.93 m s[-1] and 0 to 8346 *10[-6] N, respectively. Flow velocities and drag between the three clades were highly significantly different (p < 0.001); mean velocity (± 95% confidence limits) for the three clades were 0.09 ± 0.00 m s[-1] for the shredder, 0.25 ± 0.00 m s[-1] for the grazer, and 0.31 ± 0.01ms[-1] for the filtering carnivore clade; the corresponding data for drag were (85 ± 18)*10[-6] N, (422 ± 61)*10[-6] N and (1125 ± 83)*10[-6] N, respectively. Adhesive friction ranged from (41.07 ± 53.03)*10[-6] N in D. franzi to (255.24 ± 216.87)*10[-6] N in D. chrysotus. Except in D. franzi and D. dudor adhesive friction was always well below drag force, indicating that submerged weight alone was not sufficient to stabilize the larvae in their hydraulic environment. Reynolds numbers varied between 0 in D. franzi and D. alpinus, and 12,634 in D. katagelastos, with 7% of the total in the laminar (R < 500), 30%in the transitional (R = 500-2000), and 61%in the fully turbulent stage (R > 2000). Froude numbers (Fr) varied from 0 to 2.97. The two Drusus species of the shredder clade and three out of four species of the grazer clade were exposed to subcritical Fr < 1, one species of the grazer clade and two out of three species of the filtering clade to supercritical Froude numbers >1.}, } @article {pmid33853049, year = {2021}, author = {Wang, Q and Wu, H}, title = {Mathematical modeling of chemotaxis guided amoeboid cell swimming.}, journal = {Physical biology}, volume = {18}, number = {4}, pages = {}, doi = {10.1088/1478-3975/abf7d8}, pmid = {33853049}, issn = {1478-3975}, support = {S10 OD016290/OD/NIH HHS/United States ; }, mesh = {*Chemotaxis ; Computational Biology ; Dictyostelium/*physiology ; Models, Biological ; Swimming/physiology ; }, abstract = {Cells and microorganisms adopt various strategies to migrate in response to different environmental stimuli. To date, many modeling research has focused on the crawling-basedDictyostelium discoideum(Dd) cells migration induced by chemotaxis, yet recent experimental results reveal that even without adhesion or contact to a substrate, Dd cells can still swim to follow chemoattractant signals. In this paper, we develop a modeling framework to investigate the chemotaxis induced amoeboid cell swimming dynamics. A minimal swimming system consists of one deformable Dd amoeboid cell and a dilute suspension of bacteria, and the bacteria produce chemoattractant signals that attract the Dd cell. We use themathematical amoeba modelto generate Dd cell deformation and solve the resulting low Reynolds number flows, and use a moving mesh based finite volume method to solve the reaction-diffusion-convection equation. Using the computational model, we show that chemotaxis guides a swimming Dd cell to follow and catch bacteria, while on the other hand, bacterial rheotaxis may help the bacteria to escape from the predator Dd cell.}, } @article {pmid33834308, year = {2021}, author = {Solovev, A and Friedrich, BM}, title = {Lagrangian mechanics of active systems.}, journal = {The European physical journal. E, Soft matter}, volume = {44}, number = {4}, pages = {49}, pmid = {33834308}, issn = {1292-895X}, abstract = {We present a multi-scale modeling and simulation framework for low-Reynolds number hydrodynamics of shape-changing immersed objects, e.g., biological microswimmers and active surfaces. The key idea is to consider principal shape changes as generalized coordinates and define conjugate generalized hydrodynamic friction forces. Conveniently, the corresponding generalized friction coefficients can be pre-computed and subsequently reused to solve dynamic equations of motion fast. This framework extends Lagrangian mechanics of dissipative systems to active surfaces and active microswimmers, whose shape dynamics is driven by internal forces. As an application case, we predict in-phase and anti-phase synchronization in pairs of cilia for an experimentally measured cilia beat pattern.}, } @article {pmid33833251, year = {2021}, author = {Abdal, S and Hussain, S and Siddique, I and Ahmadian, A and Ferrara, M}, title = {On solution existence of MHD Casson nanofluid transportation across an extending cylinder through porous media and evaluation of priori bounds.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {7799}, pmid = {33833251}, issn = {2045-2322}, abstract = {It is a theoretical exportation for mass transpiration and thermal transportation of Casson nanofluid over an extending cylindrical surface. The Stagnation point flow through porous matrix is influenced by magnetic field of uniform strength. Appropriate similarity functions are availed to yield the transmuted system of leading differential equations. Existence for the solution of momentum equation is proved for various values of Casson parameter [Formula: see text], magnetic parameter M, porosity parameter [Formula: see text] and Reynolds number Re in two situations of mass transpiration (suction/injuction). The core interest for this study aroused to address some analytical aspects. Therefore, existence of solution is proved and uniqueness of this results is discussed with evaluation of bounds for existence of solution. Results for skin friction factor are established to attain accuracy for large injection values. Thermal and concentration profiles are delineated numerically by applying Runge-Kutta method and shooting technique. The flow speed retards against M, [Formula: see text] and [Formula: see text] for both situations of mass injection and suction. The thermal boundary layer improves with Brownian and thermopherotic diffusions.}, } @article {pmid33809995, year = {2021}, author = {Abramowicz-Gerigk, T and Burciu, Z and Jachowski, J and Kreft, O and Majewski, D and Stachurska, B and Sulisz, W and Szmytkiewicz, P}, title = {Experimental Method for the Measurements and Numerical Investigations of Force Generated on the Rotating Cylinder under Water Flow.}, journal = {Sensors (Basel, Switzerland)}, volume = {21}, number = {6}, pages = {}, pmid = {33809995}, issn = {1424-8220}, abstract = {The paper presents the experimental test setup and measurement method of hydrodynamic force generated on the rotating cylinder (rotor) under uniform flow including the free surface effect. The experimental test setup was a unique construction installed in the flume tank equipped with advanced flow generating and measuring systems. The test setup consisted of a bearing mounted platform with rotor drive and sensors measuring the hydrodynamic force. The low length to diameter ratio cylinders were selected as models of bow rotor rudders of a shallow draft river barge. The rotor dynamics was tested for the rotational speeds up to 550 rpm and water current velocity up to 0.85 m/s. The low aspect ratio of the cylinder and free surface effect had significant impacts on the phenomena influencing the generated hydrodynamic force. The effects of the rotor length to diameter ratio, rotational velocity to flow velocity ratio, and the Reynolds number on the lift force were analyzed. The validation of the computational model against experimental results is presented. The results show a similar trend of results for the simulation and experiment.}, } @article {pmid33808487, year = {2021}, author = {Okuducu, MB and Aral, MM}, title = {Toward the Next Generation of Passive Micromixers: A Novel 3-D Design Approach.}, journal = {Micromachines}, volume = {12}, number = {4}, pages = {}, pmid = {33808487}, issn = {2072-666X}, abstract = {Passive micromixers are miniaturized instruments that are used to mix fluids in microfluidic systems. In microchannels, combination of laminar flows and small diffusion constants of mixing liquids produce a difficult mixing environment. In particular, in very low Reynolds number flows, e.g., Re < 10, diffusive mixing cannot be promoted unless a large interfacial area is formed between the fluids to be mixed. Therefore, the mixing distance increases substantially due to a slow diffusion process that governs fluid mixing. In this article, a novel 3-D passive micromixer design is developed to improve fluid mixing over a short distance. Computational Fluid Dynamics (CFD) simulations are used to investigate the performance of the micromixer numerically. The circular-shaped fluid overlapping (CSFO) micromixer design proposed is examined in several fluid flow, diffusivity, and injection conditions. The outcomes show that the CSFO geometry develops a large interfacial area between the fluid bodies. Thus, fluid mixing is accelerated in vertical and/or horizontal directions depending on the injection type applied. For the smallest molecular diffusion constant tested, the CSFO micromixer design provides more than 90% mixing efficiency in a distance between 260 and 470 µm. The maximum pressure drop in the micromixer is found to be less than 1.4 kPa in the highest flow conditioned examined.}, } @article {pmid33807063, year = {2021}, author = {Rudl, J and Hanzelmann, C and Feja, S and Meyer, A and Potthoff, A and Buschmann, MH}, title = {Laminar Pipe Flow with Mixed Convection under the Influence of Magnetic Field.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {11}, number = {3}, pages = {}, pmid = {33807063}, issn = {2079-4991}, abstract = {Magnetic influence on ferronanofluid flow is gaining increasing interest from not only the scientific community but also industry. The aim of this study is the examination of the potentials of magnetic forces to control heat transfer. Experiments are conducted to investigate the interaction between four different configurations of permanent magnets and laminar pipe flow with mixed convection. For that purpose a pipe flow test rig is operated with a water-magnetite ferronanofluid. The Reynolds number is varied over one order of magnitude (120-1200). To characterise this suspension, density, solid content, viscosity, thermal conductivity, and specific heat capacity are measured. It is found that, depending on the positioning of the magnet(s) and the Reynolds number, heat transfer is either increased or decreased. The experiments indicate that this is a local effect. After relaxation lengths ranging between 2 and 3.5 lengths of a magnet, all changes disappeared. The conclusion from these findings is that magnetic forces are rather a tool to control heat transfer locally than to enhance the overall heat transfer of heat exchangers or the like. Magnetically caused disturbances decay due to viscous dissipation and the flow approaches the basic state again.}, } @article {pmid33800534, year = {2021}, author = {Naas, TT and Hossain, S and Aslam, M and Rahman, A and Hoque, ASM and Kim, KY and Islam, SMR}, title = {Kinematic Measurements of Novel Chaotic Micromixers to Enhance Mixing Performances at Low Reynolds Numbers: Comparative Study.}, journal = {Micromachines}, volume = {12}, number = {4}, pages = {}, pmid = {33800534}, issn = {2072-666X}, abstract = {In this work, a comparative investigation of chaotic flow behavior inside multi-layer crossing channels was numerically carried out to select suitable micromixers. New micromixers were proposed and compared with an efficient passive mixer called a Two-Layer Crossing Channel Micromixer (TLCCM), which was investigated recently. The computational evaluation was a concern to the mixing enhancement and kinematic measurements, such as vorticity, deformation, stretching, and folding rates for various low Reynolds number regimes. The 3D continuity, momentum, and species transport equations were solved by a Fluent ANSYS CFD code. For various cases of fluid regimes (0.1 to 25 values of Reynolds number), the new configuration displayed a mixing enhancement of 40%-60% relative to that obtained in the older TLCCM in terms of kinematic measurement, which was studied recently. The results revealed that all proposed micromixers have a strong secondary flow, which significantly enhances the fluid kinematic performances at low Reynolds numbers. The visualization of mass fraction and path-lines presents that the TLCCM configuration is inefficient at low Reynolds numbers, while the new designs exhibit rapid mixing with lower pressure losses. Thus, it can be used to enhance the homogenization in several microfluidic systems.}, } @article {pmid33800140, year = {2021}, author = {De Bartolo, S and Vittorio, M and Francone, A and Guido, F and Leone, E and Mastronardi, VM and Notaro, A and Tomasicchio, GR}, title = {Direct Scaling of Measure on Vortex Shedding through a Flapping Flag Device in the Open Channel around a Cylinder at Re∼10[3]: Taylor's Law Approach.}, journal = {Sensors (Basel, Switzerland)}, volume = {21}, number = {5}, pages = {}, pmid = {33800140}, issn = {1424-8220}, abstract = {The problem of vortex shedding, which occurs when an obstacle is placed in a regular flow, is governed by Reynolds and Strouhal numbers, known by dimensional analysis. The present work aims to propose a thin films-based device, consisting of an elastic piezoelectric flapping flag clamped at one end, in order to determine the frequency of vortex shedding downstream an obstacle for a flow field at Reynolds number Re∼103 in the open channel. For these values, Strouhal number obtained in such way is in accordance with the results known in literature. Moreover, the development of the voltage over time, generated by the flapping flag under the load due to flow field, shows a highly fluctuating behavior and satisfies Taylor's law, observed in several complex systems. This provided useful information about the flow field through the constitutive law of the device.}, } @article {pmid33794172, year = {2021}, author = {Chen, WH and Mutuku, JK and Yang, ZW and Hwang, CJ and Lee, WJ and Ashokkumar, V}, title = {An investigation for airflow and deposition of PM2.5 contaminated with SAR-CoV-2 virus in healthy and diseased human airway.}, journal = {Environmental research}, volume = {197}, number = {}, pages = {111096}, doi = {10.1016/j.envres.2021.111096}, pmid = {33794172}, issn = {1096-0953}, mesh = {*Asthma ; Computer Simulation ; Humans ; Italy ; *Lung ; Mexico ; Models, Biological ; Particulate Matter/toxicity ; }, abstract = {This study is motivated by the amplified transmission rates of the SAR-CoV-2 virus in areas with high concentrations of fine particulates (PM2.5) as reported in northern Italy and Mexico. To develop a deeper understanding of the contribution of PM2.5 in the propagation of the SAR-CoV-2 virus in the population, the deposition patterns and efficiencies (DEs) of PM2.5 laced with the virus in healthy and asthmatic airways are studied. Physiologically correct 3-D models for generations 10-12 of the human airways are applied to carry out a numerical analysis of two-phase flow for full breathing cycles. Two concentrations of PM2.5 are applied for the simulation, i.e., 30 μg⋅m[-3] and 80 μg⋅m[-3] for three breathing statuses, i.e., rest, light exercise, and moderate activity. All the PM2.5 injected into the control volume is assumed to be 100% contaminated with the SAR-CoV-2 virus. Skewed air-flow phenomena at the bifurcations are proportional to the Reynolds number at the inlet, and their intensity in the asthmatic airway exceeded that of the healthy one. Upon exhalation, two peak air-flow vectors from daughter branches combine to form one big vector in the parent generation. Asthmatic airway models has higher deposition efficiencies (DEs) for contaminated PM2.5 as compared to the healthy one. Higher DEs arise in the asthmatic airway model due to complex secondary flows which increase the impaction of contaminated PM2.5 on airways' walls.}, } @article {pmid33768184, year = {2021}, author = {Edomwonyi-Otu, LC and Dosumu, AI and Yusuf, N}, title = {Effect of oil on the performance of biopolymers as drag reducers in fresh water flow.}, journal = {Heliyon}, volume = {7}, number = {3}, pages = {e06535}, doi = {10.1016/j.heliyon.2021.e06535}, pmid = {33768184}, issn = {2405-8440}, abstract = {This study looks at the effectiveness of natural polymers (biopolymers) as drag reducers in flows of oil-water mixtures. The technique of using drag reducers to minimize the frictional drag in pipeline transportation of fluids is getting more challenging and there is need to be more environmentally friendly by using natural polymers. In this report, two natural polymers: xanthan gum (XG) and guar gum (GG), were used as drag reducers in a 12-mm ID straight conduit with water. The concentration of the gums was varied from 50 to 250 pm while 25, 0.50 and 0.75 fractions of oil were mixed with freshwater. The molecular weight of the gums was also determined to gain insight into their influence on the rheology of the fluids. The result showed that the gums (natural polymers) performed better as drag reducer in freshwater than in mixture with oil. Specifically, the drag reduction (DR) of 200 pm GG and XG solutions at Reynolds number of 59000 in freshwater was 39% and 44% respectively, while with the addition of 50% oil fraction, it was reduced to 19% and 32% respectively. DR reduced with oil fraction. It was concluded that XG performs better in the presence of oil than GG.}, } @article {pmid33767256, year = {2021}, author = {Wang, L and Ni, P and Xi, G}, title = {The effect of off-center placement of twisted tape on flow and heat transfer characteristics in a circular tube.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {6844}, pmid = {33767256}, issn = {2045-2322}, abstract = {This study is conducted to investigate the effect of off-center placement of twisted tape on flow distribution and heat transfer in a circular tube. The effect of tape width of 20, 18, 16, 14 and 12 mm on the heat transfer performance is discussed under the same twist ratio of 2.0. The numerical analysis of the flow field, average Nusselt number, friction factor and thermo-hydraulic performance parameter of the tube are discussed with Reynolds number ranged from 2600 to 8760. The results indicate that the Nusselt number of the tube fitted with center-placed twisted tapes at various width is 7-51% higher than the plain tube, and performance in low Reynolds region was found more effective than that in high Reynolds region. The heat transfer for circular tube with twisted tape attached to the wall shows better performance than that for the tube with center-placed twisted tape. With a smaller tape width, a higher increasing ratio of Nu-wall/Nu-center is obtained. The increasing ratio for Nusselt number ranged from 3 to 18%. However, the use of twisted tape inserts is not beneficial for energy saving. The thermo-hydraulic performance parameters for convective heat transfer of helium gas flowing in a circular tube are below unity for the calculated Reynolds region.}, } @article {pmid33766315, year = {2021}, author = {Wang, X and Liu, Z and Cai, Y and Wang, B and Luo, X}, title = {A cost-effective serpentine micromixer utilizing ellipse curve.}, journal = {Analytica chimica acta}, volume = {1155}, number = {}, pages = {338355}, doi = {10.1016/j.aca.2021.338355}, pmid = {33766315}, issn = {1873-4324}, abstract = {Due to high mixing performance and simple geometry structure, serpentine micromixer is one typical passive micromixer that has been widely investigated. Traditional zigzag and square-wave serpentine micromixers can achieve sufficient mixing, but tend to induce significant pressure drop. The excessive pressure drop means more energy consumption, which leads to low cost-performance of mixing. To mitigate excessive pressure drop, a novel serpentine micromixer utilizing ellipse curve is proposed. While fluids flowing through ellipse curve microchannels, the flow directions keep continuous changing. Therefore, the Dean vortices are induced throughout the whole flow path. Numerical simulation and visualization experiments are conducted at Reynolds number (Re) ranging from 0.1 to 100. Dean vortices varies with the changing curvature in different ellipse curves, and local Dean numbers are calculated for quantitative evaluation. The results suggest that the ellipse with a larger eccentricity induces stronger Dean vortices, thus better mixing performance can be obtained. A parameter, named mixing performance cost (Mec), is proposed to evaluate the cost-performance of micromixers. Compared with the zigzag, square-wave and other improved serpentine micromixers, the ellipse curve micromixer produces lower pressure drop while have the capability to maintain excellent mixing performance. The ellipse curve micromixer is proved to be more cost-effective for rapid mixing in complex microfluidic systems.}, } @article {pmid33765646, year = {2021}, author = {Ghosh, UU and Ali, H and Ghosh, R and Kumar, A}, title = {Bacterial streamers as colloidal systems: Five grand challenges.}, journal = {Journal of colloid and interface science}, volume = {594}, number = {}, pages = {265-278}, doi = {10.1016/j.jcis.2021.02.102}, pmid = {33765646}, issn = {1095-7103}, mesh = {*Bacteria ; *Biofilms ; Hydrodynamics ; Rivers ; }, abstract = {Bacteria can thrive in biofilms, which are intricately organized communities with cells encased in a self-secreted matrix of extracellular polymeric substances (EPS). Imposed hydrodynamic stresses can transform this active colloidal dispersion of bacteria and EPS into slender thread-like entities called streamers. In this perspective article, the reader is introduced to the world of such deformable 'bacteria-EPS' composites that are a subclass of the generic flow-induced colloidal structures. While bacterial streamers have been shown to form in a variety of hydrodynamic conditions (turbulent and creeping flows), its abiotic analogues have only been demonstrated in low Reynolds number (Re < 1) particle-laden polymeric flows. Streamers are relevant to a variety of situations ranging from natural formations in caves and river beds to clogging of biomedical devices and filtration membranes. A critical review of the relevant biophysical aspects of streamer formation phenomena and unique attributes of its material behavior are distilled to unveil five grand scientific challenges. The coupling between colloidal hydrodynamics, device geometry and streamer formation are highlighted.}, } @article {pmid33759003, year = {2021}, author = {Mohammadinejad, S and Faivre, D and Klumpp, S}, title = {Stokesian dynamics simulations of a magnetotactic bacterium.}, journal = {The European physical journal. E, Soft matter}, volume = {44}, number = {3}, pages = {40}, pmid = {33759003}, issn = {1292-895X}, mesh = {*Bacteria ; Chemotaxis ; *Magnetic Fields ; *Models, Biological ; }, abstract = {The swimming of bacteria provides insight into propulsion and steering under the conditions of low-Reynolds number hydrodynamics. Here we address the magnetically steered swimming of magnetotactic bacteria. We use Stokesian dynamics simulations to study the swimming of single-flagellated magnetotactic bacteria (MTB) in an external magnetic field. Our model MTB consists of a spherical cell body equipped with a magnetic dipole moment and a helical flagellum rotated by a rotary motor. The elasticity of the flagellum as well as magnetic and hydrodynamic interactions is taken into account in this model. We characterized how the swimming velocity is dependent on parameters of the model. We then studied the U-turn motion after a field reversal and found two regimes for weak and strong fields and, correspondingly, two characteristic time scales. In the two regimes, the U-turn time is dominated by the turning of the cell body and its magnetic moment or the turning of the flagellum, respectively. In the regime for weak fields, where turning is dominated by the magnetic relaxation, the U-turn time is approximately in agreement with a theoretical model based on torque balance. In the strong-field regime, strong deformations of the flagellum are observed. We further simulated the swimming of a bacterium with a magnetic moment that is inclined relative to the flagellar axis. This scenario leads to intriguing double helical trajectories that we characterize as functions of the magnetic moment inclination and the magnetic field. For small inclination angles ([Formula: see text]) and typical field strengths, the inclination of the magnetic moment has only a minor effect on the swimming of MTB in an external magnetic field. Large inclination angles result in a strong reduction in the velocity in direction of the magnetic field, consistent with recent observations that bacteria with large inclination angles use a different propulsion mechanism.}, } @article {pmid33756187, year = {2021}, author = {Jamil, DF and Saleem, S and Roslan, R and Al-Mubaddel, FS and Rahimi-Gorji, M and Issakhov, A and Din, SU}, title = {Analysis of non-Newtonian magnetic Casson blood flow in an inclined stenosed artery using Caputo-Fabrizio fractional derivatives.}, journal = {Computer methods and programs in biomedicine}, volume = {203}, number = {}, pages = {106044}, doi = {10.1016/j.cmpb.2021.106044}, pmid = {33756187}, issn = {1872-7565}, mesh = {Arteries ; *Atherosclerosis ; Blood Flow Velocity ; Constriction, Pathologic ; Hemodynamics ; Humans ; *Models, Cardiovascular ; }, abstract = {BACKGROUND AND OBJECTIVE: Arterial diseases would lead to several serious disorders in the cardiovascular system such as atherosclerosis. These disorders are mainly caused by the presence of fatty deposits, cholesterol and lipoproteins inside blood vessel. This paper deals with the analysis of non-Newtonian magnetic blood flow in an inclined stenosed artery.

METHODS: The Casson fluid was used to model the blood that flows under the influences of uniformly distributed magnetic field and oscillating pressure gradient. The governing fractional differential equations were expressed using the Caputo Fabrizio fractional derivative without singular kernel.

RESULTS: The analytical solutions of velocities for non-Newtonian model were then calculated by means of Laplace and finite Hankel transforms. These velocities were then presented graphically. The result shows that the velocity increases with respect to Reynolds number and Casson parameter, while decreases when Hartmann number increases.

CONCLUSIONS: Casson blood was treated as the non-Newtonian fluid. The MHD blood flow was accelerated by pressure gradient. These findings are beneficial for studying atherosclerosis therapy, the diagnosis and therapeutic treatment of some medical problems.}, } @article {pmid33754747, year = {2021}, author = {Mouzourides, P and Kyprianou, A and Neophytou, MK}, title = {Exploring the multi-fractal nature of the air flow and pollutant dispersion in a turbulent urban atmosphere and its implications for long range pollutant transport.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {31}, number = {1}, pages = {013110}, doi = {10.1063/1.5123918}, pmid = {33754747}, issn = {1089-7682}, abstract = {This work investigates the multi-fractal nature of a turbulent urban atmosphere using high-resolution atmospheric data. Meteorological and concentration measurements of passive and reactive pollutants collected over a 3-year period in a sub-urban high-Reynolds number atmospheric field were analyzed. Scaling laws characterizing the self-similarity and thereby depicting the multi-fractal nature are determined by calculating the singularity spectra, where a range of Hölder exponents, h, are estimated. In doing so, the complexity of the urban atmosphere entailing different stability regimes was addressed. Using the Monin-Obukhov length (LMO) as a marker of atmospheric stability and thereby an indication of the magnitude of anisotropy, we find where and how self-similarity is manifested relative to the different regimes and we estimate corresponding appropriate scaling laws. We find that the wind speed obeys the -5/3 law suggested by Kolmogorov only when the atmosphere lies within the stable regime as defined by Monin-Obukhov theory. Specifically, when the ratio of the atmospheric boundary layer height (Hb.l) over LMO is greater than 15, and at the same time, the ratio of the height above ground of the wind measurements (z0) over LMO is higher than 3 (i.e., in stable regime), then the singularity spectra of wind speed time series indicate that the dominant Hölder exponent, hmax, coincides with Kolmogorov's second hypothesis. On the contrary under unstable regimes in the atmosphere where the anisotropy is approached, different scaling laws are estimated. In detail, when z0/LMO<0, the dominant Hölder exponent, hmax, of the singularity spectra of the wind speed time series is either negative or close to zero, which is an indication of an impulse-like singularity, that is associated with rapid changes. For the ambient temperature and air quality measurements such as of carbon monoxide and particulate matter concentrations, it was found that they obey different laws, which are related with the long-term correlation of their data fluctuation.}, } @article {pmid33754568, year = {2021}, author = {Ji, JY and Zhao, YG and Yang, K and Zhang, WT and Gao, LQ and Ming, J and Wang, SS}, title = {Effects of the distribution of biological soil crust on the hydrodynamic characteristics of surface runoff.}, journal = {Ying yong sheng tai xue bao = The journal of applied ecology}, volume = {32}, number = {3}, pages = {1015-1022}, doi = {10.13287/j.1001-9332.202103.017}, pmid = {33754568}, issn = {1001-9332}, mesh = {Geologic Sediments ; Hydrodynamics ; *Rain ; *Soil ; }, abstract = {The distribution pattern of biological soil crusts (biocrusts) is one of the main factors affecting runoff and sediment yield. The relationship between runoff and sediment yield and biocrusts' distribution pattern is not clear, which hinders understanding the mechanism underlying the effects of biocrusts on runoff and sediment from slopes. To fill the knowledge gap, we investigated the relationship between the landscape indices of three biocrusts' distribution patterns, i.e. zonation, chessboard and random, and the hydraulic parameters, using of simulated rainfall experiments and landscape ecology methods. The results showed that biocrust significantly affected the erosion force of slopes and that its distribution pattern could affect slope erosion dynamics. Compared to bare soil, the presence of biocrusts significantly reduced the runoff velocity (54.6%) and Froude number (67.0%), increased the runoff depth (86.2%) and Darcy-Weisbach resistance coefficient (10.68 times), but did not affect the Reynolds number and runoff power. Expect for the runoff depth, there were significant differences in the hydraulic parameters of the three biocrusts' distribution patterns, with the random pattern having the strongest impacts on the dynamics of slope erosion. Based on factor analysis and cluster analysis, five indices of percentage of patch to landscape area, patch density, landscape shape index, patch cohesion and splitting could be used as the indicators for the distribution characteristics of biocrust patches. The patch cohesion and splitting of biocrust patches were the main distribution pattern indices of the hydrodynamics of surface runoff. As the patches patch cohesion decreased, the splitting increased, which caused the surface runoff velocity increase, the resistance decrease, and the slope erosion became more severe.}, } @article {pmid33752093, year = {2021}, author = {Pejcic, S and Najjari, MR and Bisleri, G and Rival, DE}, title = {Characterization of the dynamic viscoelastic response of the ascending aorta imposed via pulsatile flow.}, journal = {Journal of the mechanical behavior of biomedical materials}, volume = {118}, number = {}, pages = {104395}, doi = {10.1016/j.jmbbm.2021.104395}, pmid = {33752093}, issn = {1878-0180}, mesh = {Animals ; *Aorta ; Elastic Modulus ; Elasticity ; Pulsatile Flow ; Stress, Mechanical ; Swine ; }, abstract = {This study characterizes the material properties of a viscoelastic, ex vivo porcine ascending aorta under dynamic-loading conditions via pulsatile flow. The deformation of the opaque vessel wall and the pulsatile flow field inside the vessel were recorded using ultrasound imaging. The internal pressure was extracted from the pulsatile flow results and, when coupled with the vessel-wall expansion, was used to calculate the instantaneous elastic modulus from a novel, time-resolved two-dimensional (i.e. axial and circumferential) stress model. The circumferential instantaneous elasticity obtained from the two-dimensional stress model was found to match the uniaxial tensile test for strains below 50%. The agreement in elasticity between the two stress states reveals that the two-dimensional stress model accurately resolves the circumferential stress of the viscoelastic aorta at physiological strains (8%-30%). At higher strains, results from pulsatile flow generated a more compliant response than the uniaxial measurements. Viscoelastic properties (storage modulus and loss factor) were also calculated using the two-dimensional stress model and compared to those obtained from uniaxial tests. While instantaneous elasticity matched between the cylindrical and uniaxial loading, the viscoelastic behaviour significantly diverged between stress states. The storage modulus obtained from the pulsatile flow data was dependent on mean Reynolds number, while the uniaxial storage modulus results exhibited a strong inverse dependency on the frequency. The loss factor for the pulsatile flow data increased alongside the frequency, while the uniaxial data indicated a constant loss factor over the entire frequency range. The results of the current study show that the two-dimensional stress model can accurately extract the material properties of the ex vivo porcine aorta.}, } @article {pmid33748634, year = {2021}, author = {Lu, H and Chen, L and Wang, J and Zhang, X and Li, G and Wang, J and Chen, W and Yan, B}, title = {Using a Modified Turian-Yuan Model to Enhance Heterogeneous Resistance in Municipal Sludge Transportation Pipeline.}, journal = {ACS omega}, volume = {6}, number = {10}, pages = {7199-7211}, pmid = {33748634}, issn = {2470-1343}, abstract = {Based on the Turian-Yuan heterogeneous resistance model, the simulation results of three urban sludge pipelines with a volumetric concentration of 2.38, 3.94, and 5.39% were analyzed. The reasons for the large deviation of the simulation results under high Reynolds number conditions were also analyzed. The results showed that the deviation of the simulation was mainly caused by the difference between the sludge volumetric concentration (C V), the settlement resistance coefficient (C D), and the values of the two parameters in the Turian-Yuan heterogeneous resistance model. Consequently, it was necessary to optimize the index m 1 of C V and the index m 2 of C D. Taking mean square deviation as the objective function, using Matlab programming, the abovementioned two indexes were optimized by the simulated annealing algorithm. The optimized index m 1 of C V was 0.887, and the index m 2 of C D was -0.162. Hence, a modified Turian-Yuan heterogeneous resistance model was obtained. The model verified that the minimum value of the regression coefficient, R [2], of the simulated value reached 0.9701, proving that, the model can be used to simulate the heterogeneous resistance of urban sludge pipeline transportation.}, } @article {pmid33736076, year = {2021}, author = {Tajfirooz, S and Meijer, JG and Kuerten, JGM and Hausmann, M and Fröhlich, J and Zeegers, JCH}, title = {Statistical-learning method for predicting hydrodynamic drag, lift, and pitching torque on spheroidal particles.}, journal = {Physical review. E}, volume = {103}, number = {2-1}, pages = {023304}, doi = {10.1103/PhysRevE.103.023304}, pmid = {33736076}, issn = {2470-0053}, abstract = {A statistical learning approach is presented to predict the dependency of steady hydrodynamic interactions of thin oblate spheroidal particles on particle orientation and Reynolds number. The conventional empirical correlations that approximate such dependencies are replaced by a neural-network-based correlation which can provide accurate predictions for high-dimensional input spaces occurring in flows with nonspherical particles. By performing resolved simulations of steady uniform flow at 1≤Re≤120 around a 1:10 spheroidal body, a database consisting of Reynolds number- and orientation-dependent drag, lift, and pitching torque acting on the particle is collected. A multilayer perceptron is trained and validated with the generated database. The performance of the neural network is tested in a point-particle simulation of the buoyancy-driven motion of a 1:10 disk. Our statistical approach outperforms existing empirical correlations in terms of accuracy. The agreement between the numerical results and the experimental observations prove the potential of the method.}, } @article {pmid33731341, year = {2021}, author = {Corbetta, A and Menkovski, V and Benzi, R and Toschi, F}, title = {Deep learning velocity signals allow quantifying turbulence intensity.}, journal = {Science advances}, volume = {7}, number = {12}, pages = {}, pmid = {33731341}, issn = {2375-2548}, abstract = {Turbulence, the ubiquitous and chaotic state of fluid motions, is characterized by strong and statistically nontrivial fluctuations of the velocity field, and it can be quantitatively described only in terms of statistical averages. Strong nonstationarities impede statistical convergence, precluding quantifying turbulence, for example, in terms of turbulence intensity or Reynolds number. Here, we show that by using deep neural networks, we can accurately estimate the Reynolds number within 15% accuracy, from a statistical sample as small as two large-scale eddy turnover times. In contrast, physics-based statistical estimators are limited by the convergence rate of the central limit theorem and provide, for the same statistical sample, at least a hundredfold larger error. Our findings open up previously unexplored perspectives and the possibility to quantitatively define and, therefore, study highly nonstationary turbulent flows as ordinarily found in nature and in industrial processes.}, } @article {pmid33730564, year = {2021}, author = {Wiputra, H and Lim, M and Yap, CH}, title = {A transition point for the blood flow wall shear stress environment in the human fetal left ventricle during early gestation.}, journal = {Journal of biomechanics}, volume = {120}, number = {}, pages = {110353}, doi = {10.1016/j.jbiomech.2021.110353}, pmid = {33730564}, issn = {1873-2380}, mesh = {Computer Simulation ; Female ; *Heart Ventricles/diagnostic imaging ; *Hemodynamics ; Humans ; Hydrodynamics ; Models, Cardiovascular ; Pregnancy ; Stress, Mechanical ; }, abstract = {Development of the fetal heart is a fascinating process that involves a tremendous amount of growth. Here, we performed image-based flow simulations of 3 human fetal left ventricles (LV), and investigated the hypothetical scenario where the sizes of the hearts are scaled down, leading to reduced Reynolds number, to emulate earlier fetal stages. The shape and motion of the LV were retained over the scaling to isolate and understand the effects of length scaling on its fluid dynamics. We observed an interesting cut-off point in Reynolds number (Re), across which the dependency of LV wall shear stress (WSS) on Re changed. This was in line with classical fluid mechanic theory where skin friction coefficient exhibited first a decreasing trend and then a plateauing trend with increasing Re. Below this cut-off point, viscous effects dominated, stifling the formation of LV diastolic vorticity structures, and WSS was roughly independent of Reynolds number. However, above this cut-off, inertial effects dominated to cause diastolic vortex ring formation and detachment, and to cause WSS to scale linearly with Reynolds number. Results suggested that this transition point is found at approximately 11 weeks of gestation. Since WSS is thought to be a biomechanical stimuli for growth, this may have implications on normal fetal heart growth and malformation diseases like Hypoplastic Left Heart Syndrome.}, } @article {pmid33728053, year = {2021}, author = {Kumar, VRS and Choudhary, SK and Radhakrishnan, PK and Bharath, RS and Chandrasekaran, N and Sankar, V and Sukumaran, A and Oommen, C}, title = {Lopsided Blood-Thinning Drug Increases the Risk of Internal Flow Choking Leading to Shock Wave Generation Causing Asymptomatic Cardiovascular Disease.}, journal = {Global challenges (Hoboken, NJ)}, volume = {5}, number = {3}, pages = {2000076}, pmid = {33728053}, issn = {2056-6646}, abstract = {The discovery of Sanal flow choking in the cardiovascular-system calls for multidisciplinary and global action to develop innovative treatments and to develop new drugs to negate the risk of asymptomatic-cardiovascular-diseases. Herein, it is shown that when blood-pressure-ratio (BPR) reaches the lower-critical-hemorrhage-index (LCHI) internal-flow-choking and shock wave generation can occur in the cardiovascular-system, with sudden expansion/divergence/vasospasm or bifurcation regions, without prejudice to the percutaneous-coronary-intervention (PCI). Analytical findings reveal that the relatively high and the low blood-viscosity are cardiovascular-risk factors. In vitro studies have shown that nitrogen, oxygen, and carbon dioxide gases are dominant in fresh blood samples of humans/guinea pigs at a temperature range of 98.6-104 F. An in silico study demonstrated the Sanal flow choking phenomenon leading to shock-wave generation and pressure-overshoot in the cardiovascular-system. It has been established that disproportionate blood-thinning treatment increases the risk of the internal-flow-choking due to the enhanced boundary-layer-blockage-factor, resulting from an increase in flow-turbulence level in the cardiovascular-system, caused by an increase in Reynolds number as a consequence of low blood-viscosity. The cardiovascular-risk can be diminished by concurrently lessening the viscosity of biofluid/blood and flow-turbulence by raising the thermal-tolerance-level in terms of blood-heat-capacity-ratio (BHCR) and/or by decreasing the systolic-to-diastolic blood-pressure-ratio.}, } @article {pmid33723624, year = {2021}, author = {Challita, EJ and Alexander, SLM and Han, SI and Blackledge, TA and Coddington, JA and Jung, S and Bhamla, MS}, title = {Slingshot spiders build tensed, underdamped webs for ultrafast launches and speedy halts.}, journal = {Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology}, volume = {207}, number = {2}, pages = {205-217}, pmid = {33723624}, issn = {1432-1351}, mesh = {Animals ; Biomechanical Phenomena/*physiology ; *Models, Theoretical ; Predatory Behavior/physiology ; Silk/*physiology ; Spiders/*physiology ; Time Factors ; Video Recording/methods ; Walking Speed/*physiology ; }, abstract = {We develop a mathematical model to capture the web dynamics of slingshot spiders (Araneae: Theridiosomatidae), which utilize a tension line to deform their orb webs into conical springs to hunt flying insects. Slingshot spiders are characterized by their ultrafast launch speeds and accelerations (exceeding 1300 [Formula: see text]), however a theoretical approach to characterize the underlying spatiotemporal web dynamics remains missing. To address this knowledge gap, we develop a 2D-coupled damped oscillator model of the web. Our model reveals three key insights into the dynamics of slingshot motion. First, the tension line plays a dual role: enabling the spider to load elastic energy into the web for a quick launch (in milliseconds) to displacements of 10-15 body lengths, but also enabling the spider to halt quickly, attenuating inertial oscillations. Second, the dominant energy dissipation mechanism is viscous drag by the silk lines - acting as a low Reynolds number parachute. Third, the web exhibits underdamped oscillatory dynamics through a finely-tuned balance between the radial line forces, the tension line force and viscous drag dissipation. Together, our work suggests that the conical geometry and tension-line enables the slingshot web to act as both an elastic spring and a shock absorber, for the multi-functional roles of risky predation and self-preservation.}, } @article {pmid33721123, year = {2021}, author = {Basha, HT and Sivaraj, R}, title = {Exploring the heat transfer and entropy generation of Ag/Fe[Formula: see text]O[Formula: see text]-blood nanofluid flow in a porous tube: a collocation solution.}, journal = {The European physical journal. E, Soft matter}, volume = {44}, number = {3}, pages = {31}, pmid = {33721123}, issn = {1292-895X}, mesh = {*Entropy ; *Hot Temperature ; Hydrodynamics ; Iron/*chemistry ; Nanotechnology/*instrumentation ; Porosity ; Silver/*chemistry ; }, abstract = {Evaluating the entropy generation is essential in thermal systems to avoid the unnecessarily wasted thermal energy during the thermal processes. Nowadays, researchers are greatly fascinated to scrutinize the entropy generation in a human system because it is utilized as a thermodynamic approach to understand the heat transfer characteristics of cancer systems or wounded tissue and their accessibility status. Further, numerous nanoparticles have been employed as an agent to control the heat transfer of blood and wounded tissue. As a result, the present model manifests the entropy generation, flow characteristics and heat transport of Ag/Fe[Formula: see text]O[Formula: see text]-blood flow of a nanofluid in a permeable circular tube with the influence of variable electrical conductivity and linear radiation. Nonlinear transport equations are converted into ordinary differential equations by suitable similarity variables which are solved with weighted residual method. Significant parameters like Reynolds number, dimensionless permeability parameter, extending/contracting parameter, Eckert number and Hartmann number on the radial pressure, axial velocity, radial velocity and temperature are explored through graphs. The obtained results show that temperature distribution of Fe[Formula: see text]O[Formula: see text] nanoparticles is higher than Ag nanoparticle, in case of suction. The dimensionless permeability parameter has an opposite nature on the radial pressure for the suction and injection cases. Growing values of Hartmann number enhance the total entropy generation for the cases of suction and injection.}, } @article {pmid33719755, year = {2021}, author = {Liu, Z and Zhang, H and Lai, H}, title = {Fluid flow effects on the degradation kinetics of bioresorbable polymers.}, journal = {Computer methods in biomechanics and biomedical engineering}, volume = {24}, number = {10}, pages = {1073-1084}, doi = {10.1080/10255842.2020.1867115}, pmid = {33719755}, issn = {1476-8259}, mesh = {*Absorbable Implants ; Biocompatible Materials ; Kinetics ; *Polymers ; Tissue Scaffolds ; }, abstract = {Implants, tissue engineering scaffolds made of biodegradable polymers are widely used in biomedical engineering. The degradation of polymers plays a critical role in the effectiveness of these applications. In this paper, the mechanism of the hydrolytic degradation affected by the flow medium is studied. The results indicate that both high porosity and dynamic conditions may significantly slow down degradation speed. A critical value of the Reynolds number is found to exist. When the Reynolds number is higher than the critical value, the autocatalysis was suppressed. The models reported in this article might serve as a guide to design 3D biodegradable implants.}, } @article {pmid33713991, year = {2021}, author = {Al-Mubarak, HFI and Vallatos, A and Holmes, WM}, title = {Impact of turbulence-induced asymmetric propagators on the accuracy of phase-contrast velocimetry.}, journal = {Journal of magnetic resonance (San Diego, Calif. : 1997)}, volume = {325}, number = {}, pages = {106929}, doi = {10.1016/j.jmr.2021.106929}, pmid = {33713991}, issn = {1096-0856}, abstract = {Phase-contrast magnetic resonance velocimetry (PC-MRI) has been widely used to investigate flow properties in numerous systems. In a horizontal cylindrical pipe (3 mm diameter), we investigated the accuracy of PC-MRI as the flow transitioned from laminar to turbulent flow (Reynolds number 352-2708). We focus primarily on velocimetry errors introduced by skewed intra-voxel displacement distributions, a consequence of PC-MRI theory assuming symmetric distributions. We demonstrated how rapid fluctuations in the velocity field, can produce broad asymmetric intravoxel displacement distributions near the wall. Depending on the shape of the distribution, this resulted in PC-MRI measurements under-estimating (positive skewness) or over-estimating (negative skewness) the true mean intravoxel velocity, which could have particular importance to clinical wall shear stress measurements. The magnitude of these velocity errors was shown to increase with the variance and decrease with the kurtosis of the intravoxel displacement distribution. These experimental results confirm our previous theoretical analysis, which gives a relationship for PC-MRI velocimetry errors, as a function of the higher moments of the intravoxel displacement distribution (skewness, variance, and kurtosis) and the experimental parameters q and Δ. This suggests that PC-MRI errors in such unsteady/turbulent flow conditions can potentially be reduced by employing lower q values or shorter observation times Δ.}, } @article {pmid33712884, year = {2021}, author = {Cho, M}, title = {Aerodynamics and the role of the earth's electric field in the spiders' ballooning flight.}, journal = {Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology}, volume = {207}, number = {2}, pages = {219-236}, pmid = {33712884}, issn = {1432-1351}, mesh = {Animals ; *Earth, Planet ; Electrophysiological Phenomena/*physiology ; Flight, Animal/*physiology ; Silk/*physiology ; Spiders/*physiology ; Static Electricity ; }, abstract = {Some spiders aerially disperse relying on their fine fibres. This behaviour has been known as 'ballooning'. Observations on the ballooning behaviour of spiders have a long history and have more recently received special attention, yet its underlying physics is still poorly understood. It was traditionally believed that spiders rely on the airflows by atmospheric thermal convection to do ballooning. However, a recent experiment showed that exposure to an electric field alone can induce spiders' pre-ballooning behaviours (tiptoe and dropping/dangling) and even pulls them upwards in the air. The controversy between explanations of ballooning by aerodynamic flow or the earth's electric field has long existed. The major obstacle in studying the physics of ballooning is the fact that airflow and electric field are both invisible and our naked eyes can hardly recognise the ballooning silk fibres of spiders. This review explores the theory and evidence for the physical mechanisms of spiders' ballooning connects them to the behavioural physiology of spiders for ballooning. Knowledge gaps that need to be addressed in future studies are identified.}, } @article {pmid33683671, year = {2021}, author = {Riley, JM and Price, NS and Saaid, HM and Good, BC and Aycock, KI and Craven, BA and Manning, KB}, title = {In Vitro Clot Trapping Efficiency of the FDA Generic Inferior Vena Cava Filter in an Anatomical Model: An Experimental Fluid-Structure Interaction Benchmark.}, journal = {Cardiovascular engineering and technology}, volume = {12}, number = {3}, pages = {339-352}, doi = {10.1007/s13239-021-00524-z}, pmid = {33683671}, issn = {1869-4098}, mesh = {Animals ; Benchmarking ; Cattle ; Models, Cardiovascular ; Rheology ; *Thrombosis ; *Vena Cava Filters ; }, abstract = {PURPOSE: Robust experimental data for performing validation of fluid-structure interaction (FSI) simulations of the transport of deformable solid bodies in internal flow are currently lacking. This in vitro experimental study characterizes the clot trapping efficiency of a new generic conical-type inferior vena cava (IVC) filter in a rigid anatomical model of the IVC with carefully characterized test conditions, fluid rheological properties, and clot mechanical properties.

METHODS: Various sizes of spherical and cylindrical clots made of synthetic materials (nylon and polyacrylamide gel) and bovine blood are serially injected into the anatomical IVC model under worst-case exercise flow conditions. Clot trapping efficiencies and their uncertainties are then quantified for each combination of clot shape, size, and material.

RESULTS: Experiments reveal the clot trapping efficiency increases with increasing clot diameter and length, with trapping efficiencies ranging from as low as approximately 42% for small 3.2 mm diameter spherical clots up to 100% for larger clot sizes. Because of the asymmetry of the anatomical IVC model, the data also reveal the iliac vein of clot origin influences the clot trapping efficiency, with the trapping efficiency for clots injected into the left iliac vein up to a factor of 7.5 times greater than that for clots injected into the right iliac (trapping efficiencies of approximately 10% versus 75%, respectively).

CONCLUSION: Overall, this data set provides a benchmark for validating simulations predicting IVC filter clot trapping efficiency and, more generally, low-Reynolds number FSI modeling.}, } @article {pmid33673667, year = {2021}, author = {Mariotti, A and Antognoli, M and Galletti, C and Mauri, R and Salvetti, MV and Brunazzi, E}, title = {A Study on the Effect of Flow Unsteadiness on the Yield of a Chemical Reaction in a T Micro-Reactor.}, journal = {Micromachines}, volume = {12}, number = {3}, pages = {}, pmid = {33673667}, issn = {2072-666X}, abstract = {Despite the very simple geometry and the laminar flow, T-shaped microreactors have been found to be characterized by different and complex steady and unsteady flow regimes, depending on the Reynolds number. In particular, flow unsteadiness modifies strongly the mixing process; however, little is known on how this change may affect the yield of a chemical reaction. In the present work, experiments and 3-dimensional numerical simulations are carried out jointly to analyze mixing and reaction in a T-shaped microreactor with the ultimate goal to investigate how flow unsteadiness affects the reaction yield. The onset of the unsteady asymmetric regime enhances the reaction yield by more than 30%; however, a strong decrease of the yield back to values typical of the vortex regime is observed when the flow undergoes a transition to the unsteady symmetric regime.}, } @article {pmid33672972, year = {2021}, author = {Gao, Y and Magaud, P and Baldas, L and Wang, Y}, title = {Inertial Migration of Neutrally Buoyant Spherical Particles in Square Channels at Moderate and High Reynolds Numbers.}, journal = {Micromachines}, volume = {12}, number = {2}, pages = {}, pmid = {33672972}, issn = {2072-666X}, abstract = {The inertial migration of particles in microchannel flows has been deeply investigated in the last two decades. In spite of numerous reports on the inertial focusing patterns in a square channel, the particle inertial focusing and longitudinal ordering processes remain unclear at high Reynolds numbers (>200) in square microchannels smaller than 100 µm in width. Thus, in this work, in situ visualization of particles flowing in square micro-channels at Reynolds numbers Re ranging from 5 to 280 has been conducted and their migration behaviors have been analyzed. The obtained results confirm that new equilibrium positions appear above a critical Re depending on the particle to channel size ratio and the particle volume fraction. It is also shown that, for a given channel length, an optimal Reynolds number can be identified, for which the ratio of particles located on equilibrium positions is maximal. Moreover, the longitudinal ordering process, i.e., the formation of trains of particles on equilibrium positions and the characterization of their length, has also been analyzed for the different flow conditions investigated in this study.}, } @article {pmid33670962, year = {2021}, author = {Xie, GF and Zhao, L and Dong, YY and Li, YG and Zhang, SL and Yang, C}, title = {Hydraulic and Thermal Performance of Microchannel Heat Sink Inserted with Pin Fins.}, journal = {Micromachines}, volume = {12}, number = {3}, pages = {}, pmid = {33670962}, issn = {2072-666X}, abstract = {With the development of micromachining technologies, a wider use of microchannel heat sink (MCHS) is achieved in many fields, especially for cooling electronic chips. A microchannel with a width of 500 μm and a height of 500 μm is investigated through the numerical simulation method. Pin fins are arranged at an inclined angle of 0°, 30°, 45°, and 60°, when arrangement method includes in-lined pattern and staggered pattern. The effects of inclined angle and arrangement method on flow field and temperature field of MCHSs are studied when Reynolds number ranges from 10 to 300. In addition to this, quantitative analyses of hydraulic and thermal performance are also discussed in this work. With the increase of inclined angle, the variation of friction factor and Nusselt number do not follow certain rules. The best thermal performance is achieved in MCHS with in-lined fines at an inclined angle of 30° accompanied with the largest friction factor. Arrangement method of pin fins plays a less significant role compared with inclined angle from a general view, particularly in the Reynolds number range of 100~300.}, } @article {pmid33670569, year = {2021}, author = {Malviya, R and Jha, S and Fuloria, NK and Subramaniyan, V and Chakravarthi, S and Sathasivam, K and Kumari, U and Meenakshi, DU and Porwal, O and Sharma, A and Kumar, DH and Fuloria, S}, title = {Determination of Temperature-Dependent Coefficients of Viscosity and Surface Tension of Tamarind Seeds (Tamarindus indica L.) Polymer.}, journal = {Polymers}, volume = {13}, number = {4}, pages = {}, pmid = {33670569}, issn = {2073-4360}, abstract = {The rheological properties of tamarind seed polymer are characterized for its possible commercialization in the food and pharmaceutical industry. Seed polymer was extracted using water as a solvent and ethyl alcohol as a precipitating agent. The temperature's effect on the rheological behavior of the polymeric solution was studied. In addition to this, the temperature coefficient, viscosity, surface tension, activation energy, Gibbs free energy, Reynolds number, and entropy of fusion were calculated by using the Arrhenius, Gibbs-Helmholtz, Frenkel-Eyring, and Eotvos equations, respectively. The activation energy of the gum was found to be 20.46 ± 1.06 kJ/mol. Changes in entropy and enthalpy were found to be 23.66 ± 0.97 and -0.10 ± 0.01 kJ/mol, respectively. The calculated amount of entropy of fusion was found to be 0.88 kJ/mol. A considerable decrease in apparent viscosity and surface tension was produced when the temperature was raised. The present study concludes that the tamarind seed polymer solution is less sensitive to temperature change in comparison to Albzia lebbac gum, Ficus glumosa gum and A. marcocarpa gum. This study also concludes that the attainment of the transition state of viscous flow for tamarind seed gum is accompanied by bond breaking. The excellent physicochemical properties of tamarind seed polymers make them promising excipients for future drug formulation and make their application in the food and cosmetics industry possible.}, } @article {pmid33669613, year = {2021}, author = {Hossain, S and Tayeb, NT and Islam, F and Kaseem, M and Bui, PDH and Bhuiya, MMK and Aslam, M and Kim, KY}, title = {Enhancement of Mixing Performance of Two-Layer Crossing Micromixer through Surrogate-Based Optimization.}, journal = {Micromachines}, volume = {12}, number = {2}, pages = {}, pmid = {33669613}, issn = {2072-666X}, abstract = {Optimum configuration of a micromixer with two-layer crossing microstructure was performed using mixing analysis, surrogate modeling, along with an optimization algorithm. Mixing performance was used to determine the optimum designs at Reynolds number 40. A surrogate modeling method based on a radial basis neural network (RBNN) was used to approximate the value of the objective function. The optimization study was carried out with three design variables; viz., the ratio of the main channel thickness to the pitch length (H/PI), the ratio of the thickness of the diagonal channel to the pitch length (W/PI), and the ratio of the depth of the channel to the pitch length (d/PI). Through a primary parametric study, the design space was constrained. The design points surrounded by the design constraints were chosen using a well-known technique called Latin hypercube sampling (LHS). The optimal design confirmed a 32.0% enhancement of the mixing index as compared to the reference design.}, } @article {pmid33667105, year = {2021}, author = {Brik, M and Harmand, S and Zaaroura, I and Saboni, A}, title = {Experimental and Numerical Study for the Coalescence Dynamics of Vertically Aligned Water Drops in Oil.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {37}, number = {10}, pages = {3139-3147}, doi = {10.1021/acs.langmuir.0c03624}, pmid = {33667105}, issn = {1520-5827}, abstract = {In this paper, we propose an experimental and numerical investigation for the impact of the surface tension and the continuous phase viscosity on the dynamics of the liquid bridge during the coalescence process in liquid-liquid systems. A specific configuration of a sessile drop in direct contact with another drop placed over it has been studied. Calculating the redefined Reynolds number Re, it is found that for all studied cases, the coalescence process is dominated by the inertial force. The first step of the work was the validation of the numerical model that has been performed in an axisymmetric coordinate system. This has been done by the comparison between numerical and experimental results obtained in the framework of experimental series realized in parallel for two different liquid-liquid (LL) systems: water drops in silicone oil (SilOil M40.165) and water drops in sunflower oil. A good agreement was found between different results for numerous parameters used for comparisons. It is found that for the first stages of the coalescence (at the start of the drops merging), for a given drop's viscosity, the dynamics of the dimensionless liquid bridge is conducted by the viscosity of the continuous phase where it is illustrated that the more the surrounded viscosity is large, the lower the rate of the liquid bridge growth, the lower the earlier radial velocity of the bridge, and the higher the external capillary pressure generated around the bridge. Moreover, it is depicted that the impact of the surface tension starts appearing after the complete development of the liquid bridge where it is observed that for the same surrounding phase viscosity, the propagation of the capillary wave is faster for a LL system with higher surface tensions than those of lower surface tensions.}, } @article {pmid33666462, year = {2021}, author = {Buaria, D and Clay, MP and Sreenivasan, KR and Yeung, PK}, title = {Turbulence is an Ineffective Mixer when Schmidt Numbers Are Large.}, journal = {Physical review letters}, volume = {126}, number = {7}, pages = {074501}, doi = {10.1103/PhysRevLett.126.074501}, pmid = {33666462}, issn = {1079-7114}, abstract = {We solve the advection-diffusion equation for a stochastically stationary passive scalar θ, in conjunction with forced 3D Navier-Stokes equations, using direct numerical simulations in periodic domains of various sizes, the largest being 8192^{3} . The Taylor-scale Reynolds number varies in the range 140-650 and the Schmidt number Sc≡ν/D in the range 1-512, where ν is the kinematic viscosity of the fluid and D is the molecular diffusivity of θ. Our results show that turbulence becomes an ineffective mixer when Sc is large. First, the mean scalar dissipation rate ⟨χ⟩=2D⟨|∇θ|^{2} ⟩, when suitably nondimensionalized, decreases as 1/logSc. Second, 1D cuts through the scalar field indicate increasing density of sharp fronts on larger scales, oscillating with large excursions leading to reduced mixing, and additionally suggesting weakening of scalar variance flux across the scales. The scaling exponents of the scalar structure functions in the inertial-convective range appear to saturate with respect to the moment order and the saturation exponent approaches unity as Sc increases, qualitatively consistent with 1D cuts of the scalar.}, } @article {pmid33665269, year = {2021}, author = {Sleiti, AK}, title = {Dataset for measured viscosity of Polyalpha-Olefin- boron nitride nanofluids.}, journal = {Data in brief}, volume = {35}, number = {}, pages = {106881}, pmid = {33665269}, issn = {2352-3409}, abstract = {Datasets of measured viscosity of Polyalpha-Olefin- boron nitride (PAO/hBN) nanofluids are reported. An AR-G2 rheometer (from TA Instruments) experimental setup is used for measuring the rheological property of PAO/hBN nanofluids, which is a combined motor and transducer (CMT) instrument. The test fluid sample size is approximately 1.5 ml and the tests were conducted over a temperature range of the tested fluids from - 20 °C to 70 °C by a water circulator chamber. The dataset includes measured viscosities as a function of the BN volumetric concentration (ϕ) of 0, 0.6 and 1%. Two sets of viscosity measurements are conducted insuring the thermal equilibrium conditions are reached for all experiments. In set (1), the viscosity is measured at intervals of 10 °C by fixing the temperature at each interval (at -20, -10, 0, 10, 20, 30, 40, 50, 60 and 70 °C), while the shear stress and shear rate are varied. In set (2), the temperature is varied from -20 °C to 70 °C at intervals of 0.5 °C, while the shear stress is fixed and the shear rate is varied accordingly. Set (1) is designed to verify whether the fluids are Newtonian or not and set (2) is designed to derive correlations for the viscosity as a function of temperature. Several characteristics data are recorded including rotational speed of the spindle (RPM), torque, viscosity (Pa- s), shear stress (Pa), shear strain rate (1/s) and temperature (°C). The reuse potential of the dataset includes calculating Reynolds number for further flow studies; heat transfer performance studies of nanofluids; lubrication and lubricants' development studies and characteristics of Newtonian and non-Newtonian fluids. The dataset reported here were used (but not published) in the article published by the author in [1] (https://doi.org/10.1016/j.csite.2020.100776).}, } @article {pmid33652896, year = {2021}, author = {Charlton, AJ and Blandin, G and Leslie, G and Le-Clech, P}, title = {Impact of Forward Osmosis Operating Pressure on Deformation, Efficiency and Concentration Polarisation with Novel Links to CFD.}, journal = {Membranes}, volume = {11}, number = {3}, pages = {}, pmid = {33652896}, issn = {2077-0375}, abstract = {Forward osmosis (FO) modules currently suffer from performance efficiency limitations due to concentration polarisation (CP), as well as pressure drops during operation. There are incentives to further reduce CP effects, as well as optimise spacer design for pressure drop improvements and mechanical support. In this study, the effects of applying transmembrane pressure (TMP) on FO membrane deformation and the subsequent impact on module performance was investigated by comparing experimental data to 3D computational fluid dynamics (CFD) simulations for three commercial FO modules. At a TMP of 1.5 bar the occlusion of the draw-channel induced by longitudinal pressure hydraulic drop was comparable for the Toray (16%) and HTI modules (12%); however, the hydraulic perimeter of the Profiera module was reduced by 46%. CFD simulation of the occluded channels indicated that a change in hydraulic perimeter due to a 62% increase in shear strain resulted in a 31% increase in the Reynolds number. This reduction in channel dimensions enhanced osmotic efficiency by reducing CP via improved draw-channel hydrodynamics, which significantly disrupted the external concentration polarization (ECP) layer. Furthermore, simulations indicated that the Reynolds number experienced only modest increases with applied TMP and that shear strain at the membrane surface was found to be the most important factor when predicting flux performance enhancement, which varied between the different modules. This work suggests that a numerical approach to assess the effects of draw-spacers on pressure drop and CP can optimize and reduce investment in the design and validation of FO module designs.}, } @article {pmid33639789, year = {2021}, author = {Ramadan, IA and Bailliet, H and Valière, JC}, title = {Experimental investigation of oscillating flow characteristics at the exit of a stacked mesh grid regenerator.}, journal = {The Journal of the Acoustical Society of America}, volume = {149}, number = {2}, pages = {807}, doi = {10.1121/10.0003375}, pmid = {33639789}, issn = {1520-8524}, abstract = {The aim of this study is to investigate the oscillating flow velocity field at the exit of different stacked mesh grid regenerators using Particle Image Velocimetry measurements. Twelve different experimental cases are discussed, yielding oscillating flow fields at the exit of four kinds of regenerators for different acoustic levels. The regenerators are classified according to the mesh wire size to viscous penetration depth ratio and according to the method of stacking the mesh grids. Based on the analysis of the vorticity fields at the exit of the regenerator, three groups of flow patterns are identified. This classification is correctly verified by using the Reynolds number (based on the acoustic amplitude and wire diameter) and the Strouhal number (based on the acoustic displacement amplitude and wire diameter). The characteristics of the fluctuating velocity components are investigated for these various flow patterns. The critical Reynolds number, past which the flow is highly dissipative, is determined. The dissipation timescale is investigated and the quasi-steady approximation is found to be valid for the analysis of the oscillating flow at the exit of the regenerator mesh.}, } @article {pmid33635696, year = {2021}, author = {Bakhuis, D and Ezeta, R and Bullee, PA and Marin, A and Lohse, D and Sun, C and Huisman, SG}, title = {Catastrophic Phase Inversion in High-Reynolds-Number Turbulent Taylor-Couette Flow.}, journal = {Physical review letters}, volume = {126}, number = {6}, pages = {064501}, doi = {10.1103/PhysRevLett.126.064501}, pmid = {33635696}, issn = {1079-7114}, abstract = {Emulsions are omnipresent in the food industry, health care, and chemical synthesis. In this Letter the dynamics of metastable oil-water emulsions in highly turbulent (10^{11} ≤Ta≤3×10^{13} ) Taylor-Couette flow, far from equilibrium, is investigated. By varying the oil-in-water void fraction, catastrophic phase inversion between oil-in-water and water-in-oil emulsions can be triggered, changing the morphology, including droplet sizes, and rheological properties of the mixture, dramatically. The manifestation of these different states is exemplified by combining global torque measurements and local in situ laser induced fluorescence microscopy imaging. Despite the turbulent state of the flow and the dynamic equilibrium of the oil-water mixture, the global torque response of the system is found to be as if the fluid were Newtonian, and the effective viscosity of the mixture was found to be several times bigger or smaller than either of its constituents.}, } @article {pmid33635462, year = {2021}, author = {Jain, PK and Lanjewar, A and Jain, R and Rana, KB}, title = {Performance analysis of multi-gap V-roughness with staggered elements of solar air heater based on artificial neural network and experimental investigations.}, journal = {Environmental science and pollution research international}, volume = {}, number = {}, pages = {}, pmid = {33635462}, issn = {1614-7499}, abstract = {Among all renewable energy sources, solar power is one of the major sources which contributes for pollution control and protection of environment. For a number of decades, technologies for utilizing the solar power have been the area of research and development. In the current research, thermal performance parameters of multi-gap V-roughness with staggered elements of a solar air heater (SAH) are experimentally investigated. The artificial neural network (ANN) is also utilized for predicting the thermal performance parameters of SAH. Experiments were executed in a rectangular channel with one roughened side at the top exposed to a uniform heat flux. A significant rise in thermal efficiency performance was reported under a predefined range of Reynolds number (Re) from 3000 to 14000 with an optimized value of relative roughness pitch ratio (P/e) and relative staggered rib length (w/g) as 12 and 1, respectively. The maximum thermal efficiency was attained in the range from 42.15 to 87.02% under considered Reynolds numbers for optimum value of P/e as 12 and w/g as 1. A multilayered perceptron (MLP) feed-forward ANN trained by the Broyden-Fletcher-Goldfarb-Shanno (BFGS) algorithm was utilized to predict the thermal efficiency (ηth), friction (f), and Nusselt number (Nu). The thermal performance parameters such as P/e, w/g, Re, and temperature at the inlet, outlet, and plate were the critical input parameters/signals used in the ANN method. The optimum ANN arrangement/structure to predict the Nu, f, and ηth demonstrate higher accurateness in assessing the performance characteristics of SAH by attaining the root mean squared error (RMSE) in prediction and the Pearson coefficient of association (R[2]) of 1.591 and 0.994; 0.0012 and 0.851; and 0.025 and 0.981, respectively. The prediction profile plots of the ANN demonstrate the influence of various input parameters on the thermal performance parameters.}, } @article {pmid33633249, year = {2021}, author = {Altmeyer, S}, title = {On the ridge of instability in ferrofluidic Couette flow via alternating magnetic field.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {4705}, pmid = {33633249}, issn = {2045-2322}, abstract = {There is a huge number of natural and industrial flows, which are subjected to time-dependent boundary conditions. The flow of a magnetic fluid under the influence of temporal modulations is such an example. Here, we perform numerical simulations of ferrofluidic Couette flow subject to time-periodic modulation (with frequency [Formula: see text]) in a spatially homogeneous magnetic field and report how such a modulation can lead to a significant Reynolds number Re enhancement. Consider a modified Niklas approximation we explain the relation between modulation amplitude, driving frequency and stabilization effect. From this, we describe the system response around the primary instability to be sensitive/critical by an alternating field. We detected that such an alternating field provides an easy and in particular accurate controllable key parameter to trigger the system to change from subcritical to supercritical and vice versa. Our findings provide a framework to study other types of magnetic flows driven by time-dependent forcing.}, } @article {pmid33625506, year = {2021}, author = {Sera, T and Kamiya, N and Fukushima, T and Tanaka, G}, title = {Visualizing the Flow Patterns in an Expanding and Contracting Pulmonary Alveolated Duct Based on Microcomputed Tomography Images.}, journal = {Journal of biomechanical engineering}, volume = {143}, number = {7}, pages = {}, doi = {10.1115/1.4050285}, pmid = {33625506}, issn = {1528-8951}, mesh = {*Lung ; }, abstract = {We visualized the flow patterns in an alveolated duct model with breathing-like expanding and contracting wall motions using particle image velocimetry, and then, we investigated the effect of acinar deformation on the flow patterns. We reconstructed a compliant, scaled-up model of an alveolated duct from synchrotron microcomputed tomography images of a mammalian lung. The alveolated duct did not include any bifurcation, and its entire surface was covered with alveoli. We embedded the alveolated duct in a sealed container that was filled with fluid. We oscillated the fluid in the duct and container simultaneously and independently to control the flow and duct volume. We examined the flow patterns in alveoli, with the Reynolds number (Re) at 0.03 or 0.22 and the acinar volume change at 0%, 20%, or 80%. At the same Re, the heterogeneous deformation induced different inspiration and expiration flow patterns, and the recirculating regions in alveoli changed during respiratory cycle. During a larger acinar deformation at Re = 0.03, the flow patterns tended to change from recirculating flow to radial flow during inspiration and vice versa during expiration. Additionally, the alveolar geometric characteristics, particularly the angle between the alveolar duct and mouth, affected these differences in flow patterns. At Re = 0.22, recirculating flow patterns tended to form during inspiration and expiration, regardless of the magnitude of the acinar deformation. Our in vitro experiments suggest that the alveolated flows with nonself-similar and heterogeneous wall motions may promote particle mixing and deposition.}, } @article {pmid33622143, year = {2021}, author = {Pepper, RE and Riley, EE and Baron, M and Hurot, T and Nielsen, LT and Koehl, MAR and Kiørboe, T and Andersen, A}, title = {The effect of external flow on the feeding currents of sessile microorganisms.}, journal = {Journal of the Royal Society, Interface}, volume = {18}, number = {175}, pages = {20200953}, pmid = {33622143}, issn = {1742-5662}, mesh = {*Ecosystem ; *Feeding Behavior ; Suspensions ; }, abstract = {Microscopic sessile suspension feeders live attached to surfaces and, by consuming bacteria-sized prey and by being consumed, they form an important part of aquatic ecosystems. Their environmental impact is mediated by their feeding rate, which depends on a self-generated feeding current. The feeding rate has been hypothesized to be limited by recirculating eddies that cause the organisms to feed from water that is depleted of food particles. However, those results considered organisms in still water, while ambient flow is often present in their natural habitats. We show, using a point-force model, that even very slow ambient flow, with speed several orders of magnitude less than that of the self-generated feeding current, is sufficient to disrupt the eddies around perpendicular suspension feeders, providing a constant supply of food-rich water. However, the feeding rate decreases in external flow at a range of non-perpendicular orientations due to the formation of recirculation structures not seen in still water. We quantify the feeding flow and observe such recirculation experimentally for the suspension feeder Vorticella convallaria in external flows typical of streams and rivers.}, } @article {pmid33622097, year = {2021}, author = {Ge-JiLe, H and Javid, K and Khan, SU and Raza, M and Khan, MI and Qayyum, S}, title = {Double diffusive convection and Hall effect in creeping flow of viscous nanofluid through a convergent microchannel: a biotechnological applications.}, journal = {Computer methods in biomechanics and biomedical engineering}, volume = {24}, number = {12}, pages = {1326-1343}, doi = {10.1080/10255842.2021.1888373}, pmid = {33622097}, issn = {1476-8259}, mesh = {*Convection ; Diffusion ; *Peristalsis ; Rheology ; Viscosity ; }, abstract = {Current analysis presents the mathematical modeling for peristaltic transport of nanofluid with applications of double-diffusive convection and Hall features. The flow has been induced by a convergent channel due to peristaltic propulsion. These rheological equations are transformed from fixed to wave frames by using a linear mathematical relation between these two frames. The dimensionless variables are used to transform these rheological equations into nondimensional forms. The flow analysis is carried out under two distinct scientific biological assumptions, one is known as long wavelength and the second one is low Reynolds number. The analytical solutions of these rheological equations are obtained with the help of a rigorous analytical method known as integration in the term of stream function. The physical effects of magnetic and Hall devices, respectively, on the flow features are also considered in the present analysis. The physical influences of dominant hydro-mechanical parameters on the axial velocity, pressure gradient, trapping, volumetric fraction of nanofluid, heat and mass transfer phenomena are studied. The complex scenario of biomimetic propulsions are considered in boundary walls to boost the proficiency of peristaltic micropumps.}, } @article {pmid33601572, year = {2021}, author = {Bao, G and Jian, Y}, title = {Odd-viscosity-induced instability of a falling thin film with an external electric field.}, journal = {Physical review. E}, volume = {103}, number = {1-1}, pages = {013104}, doi = {10.1103/PhysRevE.103.013104}, pmid = {33601572}, issn = {2470-0053}, abstract = {The influence of odd viscosity of Newtonian fluid on the instability of thin film flowing along an inclined plane under a normal electric field is studied. By odd viscosity, we mean apart from the well-known coefficient of shear viscosity, a classical liquid with broken time-reversal symmetry is endowed with a second viscosity coefficient in biological, colloidal, and granular systems. Under the long wave approximation, a nonlinear evolution equation of the free surface is derived by the method of systematic asymptotic expansion. The effects of the odd viscosity and external electric field are considered in this evolution equation and an analytical expression of critical Reynolds number is obtained. It is interesting to find that, by linear stability analysis, the critical Reynolds number increases with odd viscosity and decreases with external strength of electric field. In other words, odd viscosity has a stable effect and electric field has a destabilized effect on flowing of thin film. In addition, through nonlinear analysis, we obtain a Ginsburg-Landau equation and find that the film has not only the supercritical stability zone and the subcritical instability zone but also the unconditional stability zone and the explosive zone. The variations of each zone with related parameters, such as the strength of electric field, odd viscosity, and Reynolds number, etc., are investigated. The results are conducive to the further development of related experiments.}, } @article {pmid33601565, year = {2021}, author = {Pereira, FS and Grinstein, FF and Israel, DM and Rauenzahn, R}, title = {Molecular viscosity and diffusivity effects in transitional and shock-driven mixing flows.}, journal = {Physical review. E}, volume = {103}, number = {1-1}, pages = {013106}, doi = {10.1103/PhysRevE.103.013106}, pmid = {33601565}, issn = {2470-0053}, abstract = {This paper investigates the importance of molecular viscosity and diffusivity for the prediction of transitional and shock-driven mixing flows featuring high and low Reynolds and Mach number regions. Two representative problems are computed with implicit large-eddy simulations using the inviscid Euler equations (EE) and viscous Navier-Stokes equations (NSE): the Taylor-Green vortex at Reynolds number Re=3000 and initial Mach number Ma=0.28, and an air-SF_{6} -air gas curtain subjected to two shock waves at Ma=1.2. The primary focus is on differences between NSE and EE predictions due to viscous effects. The outcome of the paper illustrates the advantages of utilizing NSE. In contrast to the EE, where the effective viscosity decreases upon grid refinement, NSE predictions can be assessed for simulations of flows with transition to turbulence at prescribed constant Re. The NSE can achieve better agreement between solutions and reference data, and the results converge upon grid refinement. On the other hand, the EE predictions do not converge with grid refinement, and can only exhibit similarities with the NSE results at coarse grid resolutions. We also investigate the effect of viscous effects on the dynamics of the coherent and turbulent fields, as well as on the mechanisms contributing to the production and diffusion of vorticity. The results show that nominally inviscid calculations can exhibit significantly varying flow dynamics driven by changing effective resolution-dependent Reynolds number, and highlight the role of viscous processes affecting the vorticity field. These tendencies become more pronounced upon grid refinement. The discussion of the results concludes with the assessment of the computational cost of inviscid and viscous computations.}, } @article {pmid33601495, year = {2021}, author = {Livi, C and Di Staso, G and Clercx, HJH and Toschi, F}, title = {Influence of numerical resolution on the dynamics of finite-size particles with the lattice Boltzmann method.}, journal = {Physical review. E}, volume = {103}, number = {1-1}, pages = {013303}, doi = {10.1103/PhysRevE.103.013303}, pmid = {33601495}, issn = {2470-0053}, abstract = {We investigate and compare the accuracy and efficiency of different numerical approaches to model the dynamics of finite-size particles using the lattice Boltzmann method (LBM). This includes the standard bounce-back (BB) and the equilibrium interpolation (EI) schemes. To accurately compare the different implementations, we first introduce a boundary condition to approximate the flow properties of an unbounded fluid in a finite simulation domain, taking into account the perturbation induced by a moving particle. We show that this boundary treatment is efficient in suppressing detrimental effects on the dynamics of spherical and ellipsoidal particles arising from the finite size of the simulation domain. We then investigate the performances of the BB and EI schemes in modeling the dynamics of a spherical particle settling under Stokes conditions, which can now be reproduced with great accuracy thanks to the treatment of the exterior boundary. We find that the EI scheme outperforms the BB scheme in providing a better accuracy scaling with respect to the resolution of the settling particle, while suppressing finite-size effects due to the particle discretization on the lattice grid. Additionally, in order to further increase the capability of the algorithm in modeling particles of sizes comparable to the lattice spacing, we propose an improvement to the EI scheme, the complete equilibrium interpolation (CEI). This approach allows us to accurately capture the boundaries of the particle also when located between two fluid nodes. We evaluate the CEI performance in solving the dynamics of an under-resolved particle under analogous Stokes conditions and also for the case of a rotating ellipsoid in a shear flow. Finally, we show that EI and CEI are able to recover the correct flow solutions also at small, but finite, Reynolds number. Adopting the CEI scheme it is not only possible to detect particles with zero lattice occupation, but also to increase up to one order of magnitude the accuracy of the dynamics of particles with a size comparable to the lattice spacing with respect to the BB and the EI schemes.}, } @article {pmid33590890, year = {2021}, author = {Pskowski, A and Bagchi, P and Zahn, JD}, title = {Investigation of red blood cell partitioning in an in vitro microvascular bifurcation.}, journal = {Artificial organs}, volume = {45}, number = {9}, pages = {1083-1096}, doi = {10.1111/aor.13941}, pmid = {33590890}, issn = {1525-1594}, mesh = {Blood Flow Velocity ; Equipment Design ; Erythrocytes/*physiology ; *Hematocrit ; Hemorheology/*physiology ; Humans ; In Vitro Techniques ; Microcirculation ; Models, Cardiovascular ; }, abstract = {There is a long history of research examining red blood cell (RBC) partitioning in microvasculature bifurcations. These studies commonly report results describing partitioning that exists as either regular partitioning, which occurs when the RBC flux ratio is greater than the bulk fluid flowrate ratio, or reverse partitioning when the RBC flux ratio is less than or equal to that of the bulk fluid flowrate. This paper presents a study of RBC partitioning in a single bifurcating microchannel with dimensions of 6 to 16 μm, investigating the effects of hematocrit, channel width, daughter channel flowrate ratio, and bifurcation angle. The erythrocyte flux ratio, N*, manifests itself as either regular or reverse partitioning, and time-dependent partitioning is much more dynamic, occurring as both regular and reverse partitioning. We report a significant reduction in the well-known sigmoidal variation of the erythrocyte flux ratio (N*) versus the volumetric flowrate ratio (Q*), partitioning behavior with increasing hematocrit in microchannels when the channel dimensions are comparable with cell size. RBCs "lingering" or jamming at the bifurcation were also observed and quantified in vitro. Results from trajectory analyses suggest that the RBC position in the feeder channel strongly affects both partitioning and lingering frequency of RBCs, with both being significantly reduced when RBCs flow on streamlines near the edge of the channel as opposed to the center of the channel. Furthermore, our experiments suggest that even at low Reynolds number, partitioning is affected by the bifurcation angle by increasing cell-cell interactions. The presented results provide further insight into RBC partitioning as well as perfusion throughout the microvasculature.}, } @article {pmid33580288, year = {2021}, author = {Ender, H and Kierfeld, J}, title = {From diffusive mass transfer in Stokes flow to low Reynolds number Marangoni boats.}, journal = {The European physical journal. E, Soft matter}, volume = {44}, number = {1}, pages = {4}, pmid = {33580288}, issn = {1292-895X}, abstract = {We present a theory for the self-propulsion of symmetric, half-spherical Marangoni boats (soap or camphor boats) at low Reynolds numbers. Propulsion is generated by release (diffusive emission or dissolution) of water-soluble surfactant molecules, which modulate the air-water interfacial tension. Propulsion either requires asymmetric release or spontaneous symmetry breaking by coupling to advection for a perfectly symmetrical swimmer. We study the diffusion-advection problem for a sphere in Stokes flow analytically and numerically both for constant concentration and constant flux boundary conditions. We derive novel results for concentration profiles under constant flux boundary conditions and for the Nusselt number (the dimensionless ratio of total emitted flux and diffusive flux). Based on these results, we analyze the Marangoni boat for small Marangoni propulsion (low Peclet number) and show that two swimming regimes exist, a diffusive regime at low velocities and an advection-dominated regime at high swimmer velocities. We describe both the limit of large Marangoni propulsion (high Peclet number) and the effects from evaporation by approximative analytical theories. The swimming velocity is determined by force balance, and we obtain a general expression for the Marangoni forces, which comprises both direct Marangoni forces from the surface tension gradient along the air-water-swimmer contact line and Marangoni flow forces. We unravel whether the Marangoni flow contribution is exerting a forward or backward force during propulsion. Our main result is the relation between Peclet number and swimming velocity. Spontaneous symmetry breaking and, thus, swimming occur for a perfectly symmetrical swimmer above a critical Peclet number, which becomes small for large system sizes. We find a supercritical swimming bifurcation for a symmetric swimmer and an avoided bifurcation in the presence of an asymmetry.}, } @article {pmid33573067, year = {2021}, author = {Hosseini, SA and Safari, H and Thevenin, D}, title = {Lattice Boltzmann Solver for Multiphase Flows: Application to High Weber and Reynolds Numbers.}, journal = {Entropy (Basel, Switzerland)}, volume = {23}, number = {2}, pages = {}, pmid = {33573067}, issn = {1099-4300}, abstract = {The lattice Boltzmann method, now widely used for a variety of applications, has also been extended to model multiphase flows through different formulations. While already applied to many different configurations in low Weber and Reynolds number regimes, applications to higher Weber/Reynolds numbers or larger density/viscosity ratios are still the topic of active research. In this study, through a combination of a decoupled phase-field formulation-the conservative Allen-Cahn equation-and a cumulant-based collision operator for a low-Mach pressure-based flow solver, we present an algorithm that can be used for higher Reynolds/Weber numbers. The algorithm was validated through a variety of test cases, starting with the Rayleigh-Taylor instability in both 2D and 3D, followed by the impact of a droplet on a liquid sheet. In all simulations, the solver correctly captured the flow dynamics andmatched reference results very well. As the final test case, the solver was used to model droplet splashing on a thin liquid sheet in 3D with a density ratio of 1000 and kinematic viscosity ratio of 15, matching the water/air system at We = 8000 and Re = 1000. Results showed that the solver correctly captured the fingering instabilities at the crown rim and their subsequent breakup, in agreement with experimental and numerical observations reported in the literature.}, } @article {pmid33571986, year = {2021}, author = {Gungor, A and Hemmati, A}, title = {Implications of changing synchronization in propulsive performance of side-by-side pitching foils.}, journal = {Bioinspiration & biomimetics}, volume = {16}, number = {3}, pages = {}, doi = {10.1088/1748-3190/abe54b}, pmid = {33571986}, issn = {1748-3190}, mesh = {Animals ; Biomechanical Phenomena ; Fishes ; Hydrodynamics ; *Models, Biological ; *Swimming ; }, abstract = {The unsteady hydrodynamics of side-by-side pitching foils are studied numerically at Reynolds number of 4000 with altering phase differences in the middle of an oscillation cycle. This represents a change in synchronization of oscillating foils, inspired by experimental observations on group swimming of red nose tetra fish. The hybrid oscillation cases are based on an initially out-of-phase pitching that switch to in-phase at the 20th cycle of oscillation. Various sequential combinations of out-of-phase and in-phase pitching are also examined in terms of foil propulsive performance. It is observed that out-of-phase pitching foils initially produce zero total side-force. However, they start producing negative total side-force after 13 oscillation cycles. Contrarily for the in-phase oscillation cases, the initially positive total side-force reverted to zero over time. In hybrid oscillation cases, the negative total side-force produced during the initial out-of-phase oscillations abruptly adjusted to zero following a change of synchronization that led to in-phase oscillations, which is inspired from a particular swimming behavior in fish. Based on three hybrid modes, defined on the onset of mid-cycle switch to in-phase oscillations, it was apparent that the benefit of synchronization, or there lack of, greatly depended on the timing of the change in synchronization. Thus, mid-swimming change of synchronization in side-by-side systems inspired by fish schools compensates for their non-zero total side-force production to maintain their lateral position. Such changes do not translate to significant gains in neither thrust generation nor efficiency.}, } @article {pmid33561405, year = {2021}, author = {Longo, SJ and Ray, W and Farley, GM and Harrison, J and Jorge, J and Kaji, T and Palmer, AR and Patek, SN}, title = {Snaps of a tiny amphipod push the boundary of ultrafast, repeatable movement.}, journal = {Current biology : CB}, volume = {31}, number = {3}, pages = {R116-R117}, doi = {10.1016/j.cub.2020.12.025}, pmid = {33561405}, issn = {1879-0445}, mesh = {*Amphipoda ; Animals ; Biomechanical Phenomena ; Humans ; Male ; *Movement ; Water ; }, abstract = {Surprisingly, the fastest motions are not produced by large animals or robots. Rather, small organisms or structures, including cnidarian stinging cells, fungal shooting spores, and mandible strikes of ants, termites, and spiders, hold the world acceleration records.[1-5] These diverse systems share common features: they rapidly convert potential energy - stored in deformed material or fluid - into kinetic energy when a latch is released.[4-6] However, the fastest of these are not repeatable, because mechanical components are broken or ejected.[5,6] Furthermore, some of these systems must overcome the added challenge of moving in water, where high density and viscosity constrain acceleration at small sizes. Here we report the kinematics of repeatable, ultrafast snaps by tiny marine amphipods (Dulichiella cf. appendiculata). Males use their enlarged major claw, which can exceed 30% of body mass, to snap a 1 mm-long dactyl with a diameter equivalent to a human hair (184 μm). The claw snaps closed extremely rapidly, averaging 93 μs, 17 m s[-1], and 2.4 x 10[5] m s[-2]. These snaps are among the smallest and fastest of any documented repeatable movement, and are sufficiently fast to operate in the inertial hydrodynamic regime (Reynolds number (Re) >10,000). They generate audible pops and rapid water jets, which occasionally yield cavitation, and may be used for defense. These amphipod snaps push the boundaries of acceleration and size for repeatable movements, particularly in water, and exemplify how new biomechanical insights can arise from unassuming animals. VIDEO ABSTRACT.}, } @article {pmid33544100, year = {2021}, author = {Yang, F}, title = {Homogeneous nucleation in a Poiseuille flow.}, journal = {Physical chemistry chemical physics : PCCP}, volume = {23}, number = {6}, pages = {3974-3982}, doi = {10.1039/d0cp06132h}, pmid = {33544100}, issn = {1463-9084}, abstract = {Nucleation in a dynamical environment plays an important role in the synthesis and manufacturing of quantum dots and nanocrystals. In this work, we investigate the effects of fluid flow (low Reynolds number flow) on the homogeneous nucleation in a circular microchannel in the framework of the classical nucleation theory. The contributions of the configuration entropy from the momentum-phase space and the kinetic energy and strain energy of a microcluster are incorporated in the calculation of the change of the Gibbs free energy from a flow state without a microcluster to a flow state with a microcluster. An analytical equation is derived for the determination of the critical nucleus size. Using this analytical equation, an analytical solution of the critical nucleus size for the formation of a critical liquid nucleus is found. For the formation of a critical solid nucleus, the contributions from both the kinetic energy and the strain energy are generally negligible. We perform numerical analysis of the homogeneous nucleation of a sucrose microcluster in a representative volume element of an aqueous solution, which flows through a circular microchannel. The numerical results reveal the decrease of the critical nucleus size and the corresponding work of formation of a critical nucleus with the increase of the distance to axisymmetric axis for the same numbers of solvent atoms and solute atoms/particles.}, } @article {pmid33543985, year = {2021}, author = {Buaria, D and Clay, MP and Sreenivasan, KR and Yeung, PK}, title = {Small-Scale Isotropy and Ramp-Cliff Structures in Scalar Turbulence.}, journal = {Physical review letters}, volume = {126}, number = {3}, pages = {034504}, doi = {10.1103/PhysRevLett.126.034504}, pmid = {33543985}, issn = {1079-7114}, abstract = {Passive scalars advected by three-dimensional Navier-Stokes turbulence exhibit a fundamental anomaly in odd-order moments because of the characteristic ramp-cliff structures, violating small-scale isotropy. We use data from direct numerical simulations with grid resolution of up to 8192^{3} at high Péclet numbers to understand this anomaly as the scalar diffusivity, D, diminishes, or as the Schmidt number, Sc=ν/D, increases; here ν is the kinematic viscosity of the fluid. The microscale Reynolds number varies from 140 to 650 and Sc varies from 1 to 512. A simple model for the ramp-cliff structures is developed and shown to characterize the scalar derivative statistics very well. It accurately captures how the small-scale isotropy is restored in the large-Sc limit, and additionally suggests a possible correction to the Batchelor length scale as the relevant smallest scale in the scalar field.}, } @article {pmid33543965, year = {2021}, author = {Nasouri, B and Vilfan, A and Golestanian, R}, title = {Minimum Dissipation Theorem for Microswimmers.}, journal = {Physical review letters}, volume = {126}, number = {3}, pages = {034503}, doi = {10.1103/PhysRevLett.126.034503}, pmid = {33543965}, issn = {1079-7114}, abstract = {We derive a theorem for the lower bound on the energy dissipation rate by a rigid surface-driven active microswimmer of arbitrary shape in a fluid at a low Reynolds number. We show that, for any swimmer, the minimum dissipation at a given velocity can be expressed in terms of the resistance tensors of two passive bodies of the same shape with a no-slip and perfect-slip boundary. To achieve the absolute minimum dissipation, the optimal swimmer needs a surface velocity profile that corresponds to the flow around the perfect-slip body, and a propulsive force density that corresponds to the no-slip body. Using this theorem, we propose an alternative definition of the energetic efficiency of microswimmers that, unlike the commonly used Lighthill efficiency, can never exceed unity. We validate the theory by calculating the efficiency limits of spheroidal swimmers.}, } @article {pmid33537715, year = {2021}, author = {Yu, P and Durgesh, V and Xing, T and Budwig, R}, title = {Application of Proper Orthogonal Decomposition to Study Coherent Flow Structures in a Saccular Aneurysm.}, journal = {Journal of biomechanical engineering}, volume = {143}, number = {6}, pages = {}, doi = {10.1115/1.4050032}, pmid = {33537715}, issn = {1528-8951}, mesh = {*Intracranial Aneurysm ; }, abstract = {Aneurysms are localized expansions of weakened blood vessels that can be debilitating or fatal upon rupture. Previous studies have shown that flow in an aneurysm exhibits complex flow structures that are correlated with its inflow conditions. Therefore, the objective of this study was to demonstrate the application of proper orthogonal decomposition (POD) to study the impact of different inflow conditions on energetic flow structures and their temporal behavior in an aneurysm. To achieve this objective, experiments were performed on an idealized rigid sidewall aneurysm model. A piston pump system was used for precise inflow control, i.e., peak Reynolds number (Rep) and Womersley number (α) were varied from 50 to 270 and 2 to 5, respectively. The velocity flow field measurements at the midplane location of the idealized aneurysm model were performed using particle image velocimetry (PIV). The results demonstrate the efficacy of POD in decomposing complex data, and POD was able to capture the energetic flow structures unique to each studied inflow condition. Furthermore, the time-varying coefficient results highlighted the interplay between the coefficients and their corresponding POD modes, which in turn helped explain how POD modes impact certain flow features. The low-order reconstruction results were able to capture the flow evolution and provide information on complex flow in an aneurysm. The POD and low-order reconstruction results also indicated that vortex formation, evolution, and convection varied with an increase in α, while vortex strength and formation of secondary structures were correlated with an increase in Rep.}, } @article {pmid33530578, year = {2021}, author = {Selimefendigil, F and Öztop, HF}, title = {Thermal Management and Modeling of Forced Convection and Entropy Generation in a Vented Cavity by Simultaneous Use of a Curved Porous Layer and Magnetic Field.}, journal = {Entropy (Basel, Switzerland)}, volume = {23}, number = {2}, pages = {}, pmid = {33530578}, issn = {1099-4300}, abstract = {The effects of using a partly curved porous layer on the thermal management and entropy generation features are studied in a ventilated cavity filled with hybrid nanofluid under the effects of inclined magnetic field by using finite volume method. This study is performed for the range of pertinent parameters of Reynolds number (100≤Re≤1000), magnetic field strength (0≤Ha≤80), permeability of porous region (10-4≤Da≤5×10-2), porous layer height (0.15H≤tp≤0.45H), porous layer position (0.25H≤yp≤0.45H), and curvature size (0≤b≤0.3H). The magnetic field reduces the vortex size, while the average Nusselt number of hot walls increases for Ha number above 20 and highest enhancement is 47% for left vertical wall. The variation in the average Nu with permeability of the layer is about 12.5% and 21% for left and right vertical walls, respectively, while these amounts are 12.5% and 32.5% when the location of the porous layer changes. The entropy generation increases with Hartmann number above 20, while there is 22% increase in the entropy generation for the case at the highest magnetic field. The porous layer height reduced the entropy generation for domain above it and it give the highest contribution to the overall entropy generation. When location of the curved porous layer is varied, the highest variation of entropy generation is attained for the domain below it while the lowest value is obtained at yp=0.3H. When the size of elliptic curvature is varied, the overall entropy generation decreases from b=0 to b=0.2H by about 10% and then increases by 5% from b=0.2H to b=0.3H.}, } @article {pmid33510410, year = {2021}, author = {Sato, N and Kawashima, D and Takei, M}, title = {Concentration profiles of ions and particles under hydrodynamic focusing in Y-shaped square microchannel.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {2585}, pmid = {33510410}, issn = {2045-2322}, abstract = {Three-dimensional ion and particle concentrations under hydrodynamic focusing in a Y-shaped square microchannel are numerically simulated to clarify the decrease of the ion concentration along the flow direction within the focused particle stream. The simulation model is theoretically governed by the laminar flow and advection-diffusion equations. The governing equations are solved by the finite volume method. The ion and particle concentration distributions at five cross sections after the confluence of the branch channels are analyzed in 30 cases in which the sheath to sample flow rate ratio Qsh/Qsam and the Reynolds number Re are varied as parameters. The results show that the decrease of the cross-sectional average ion concentration along the flow direction within the particle stream [Formula: see text] is described by the diffusion length during the residence time with a characteristic velocity scale. In addition, the deformation of the particle stream due to inertial effects is described by a scaled Reynolds number that is a function of the flow rate ratio. The simulated particle stream thicknesses are validated by theory and a simple experiment. This paper reveals the relationship between the ion and particle concentrations and the dimensionless parameters for hydrodynamic focusing in the Y-shaped square microchannel under typical conditions.}, } @article {pmid33509927, year = {2021}, author = {Andreotti, B and Claudin, P and Iversen, JJ and Merrison, JP and Rasmussen, KR}, title = {A lower-than-expected saltation threshold at Martian pressure and below.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {118}, number = {5}, pages = {}, pmid = {33509927}, issn = {1091-6490}, abstract = {Aeolian sediment transport is observed to occur on Mars as well as other extraterrestrial environments, generating ripples and dunes as on Earth. The search for terrestrial analogs of planetary bedforms, as well as environmental simulation experiments able to reproduce their formation in planetary conditions, are powerful ways to question our understanding of geomorphological processes toward unusual environmental conditions. Here, we perform sediment transport laboratory experiments in a closed-circuit wind tunnel placed in a vacuum chamber and operated at extremely low pressures to show that Martian conditions belong to a previously unexplored saltation regime. The threshold wind speed required to initiate saltation is only quantitatively predicted by state-of-the art models up to a density ratio between grain and air of [Formula: see text] but unexpectedly falls to much lower values for higher density ratios. In contrast, impact ripples, whose emergence is continuously observed on the granular bed over the whole pressure range investigated, display a characteristic wavelength and propagation velocity essentially independent of pressure. A comparison of these findings with existing models suggests that sediment transport at low Reynolds number but high grain-to-fluid density ratio may be dominated by collective effects associated with grain inertia in the granular collisional layer.}, } @article {pmid33503087, year = {2021}, author = {Hoeger, K and Ursell, T}, title = {Steric scattering of rod-like swimmers in low Reynolds number environments.}, journal = {Soft matter}, volume = {17}, number = {9}, pages = {2479-2489}, doi = {10.1039/d0sm01551b}, pmid = {33503087}, issn = {1744-6848}, mesh = {*Ecosystem ; Hydrodynamics ; *Models, Biological ; Movement ; Swimming ; }, abstract = {Microbes form integral components of all natural ecosystems. In most cases, the surrounding micro-environment has physical variations that affect the movements of micro-swimmers, including solid objects of varying size, shape and density. As swimmers move through viscous environments, a combination of hydrodynamic and steric forces are known to significantly alter their trajectories in a way that depends on surface curvature. In this work, our goal was to clarify the role of steric forces when rod-like swimmers interact with solid objects comparable to cell size. We imaged hundreds-of-thousands of scattering interactions between swimming bacteria and micro-fabricated pillars with radii from ∼1 to ∼10 cell lengths. Scattering interactions were parameterized by the angle of the cell upon contact with the pillar, and primarily produced forward-scattering events that fell into distinct chiral distributions for scattering angle - no hydrodynamic trapping was observed. The chirality of a scattering event was a stochastic variable whose probability smoothly and symmetrically depended on the contact angle. Neglecting hydrodynamics, we developed a model that only considers contact forces and torques for a rear-pushed thin-rod scattering from a cylinder - the model predictions were in good agreement with measured data. Our results suggest that alteration of bacterial trajectories is subject to distinct mechanisms when interacting with objects of different size; primarily steric for objects below ∼10 cell lengths and requiring incorporation of hydrodynamics at larger scales. These results contribute to a mechanistic framework in which to examine (and potentially engineer) microbial movements through natural and synthetic environments that present complex steric structure.}, } @article {pmid33494348, year = {2021}, author = {Ambreen, T and Saleem, A and Park, CW}, title = {Homogeneous and Multiphase Analysis of Nanofluids Containing Nonspherical MWCNT and GNP Nanoparticles Considering the Influence of Interfacial Layering.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {11}, number = {2}, pages = {}, pmid = {33494348}, issn = {2079-4991}, abstract = {The practical implication of nanofluids is essentially dependent on their accurate modelling, particularly in comparison with the high cost of experimental investigations, yet the accuracy of different computational approaches to simulate nanofluids remains controversial to this day. Therefore, the present study is aimed at analysing the homogenous, multiphase Eulerian-Eulerian (volume of fluid, mixture, Eulerian) and Lagrangian-Eulerian approximation of nanofluids containing nonspherical nanoparticles. The heat transfer and pressure drop characteristics of the multiwalled carbon nanotubes (MWCNT)-based and multiwalled carbon nanotubes/graphene nanoplatelets (MWCNT/GNP)-based nanofluids are computed by incorporating the influence of several physical mechanisms, including interfacial nanolayering. The accuracy of tested computational approaches is evaluated by considering particle concentration and Reynolds number ranges of 0.075-0.25 wt% and 200-470, respectively. The results demonstrate that for all nanofluid combinations and operational conditions, the Lagrangian-Eulerian approximation provides the most accurate convective heat transfer coefficient values with a maximum deviation of 5.34% for 0.25 wt% of MWCNT-water nanofluid at the largest Reynolds number, while single-phase and Eulerian-Eulerian multiphase models accurately estimate the thermal fields of the diluted nanofluids at low Reynolds numbers, but overestimate the results for denser nanofluids at high Reynolds numbers.}, } @article {pmid33493237, year = {2021}, author = {Mahrous, SA and Sidik, NAC and Saqr, KM}, title = {Numerical study on the energy cascade of pulsatile Newtonian and power-law flow models in an ICA bifurcation.}, journal = {PloS one}, volume = {16}, number = {1}, pages = {e0245775}, pmid = {33493237}, issn = {1932-6203}, mesh = {Humans ; Intracranial Aneurysm/pathology/*physiopathology ; Kinetics ; *Models, Biological ; *Pulsatile Flow ; }, abstract = {The complex physics and biology underlying intracranial hemodynamics are yet to be fully revealed. A fully resolved direct numerical simulation (DNS) study has been performed to identify the intrinsic flow dynamics in an idealized carotid bifurcation model. To shed the light on the significance of considering blood shear-thinning properties, the power-law model is compared to the commonly used Newtonian viscosity hypothesis. We scrutinize the kinetic energy cascade (KEC) rates in the Fourier domain and the vortex structure of both fluid models and examine the impact of the power-law viscosity model. The flow intrinsically contains coherent structures which has frequencies corresponding to the boundary frequency, which could be associated with the regulation of endothelial cells. From the proposed comparative study, it is found that KEC rates and the vortex-identification are significantly influenced by the shear-thinning blood properties. Conclusively, from the obtained results, it is found that neglecting the non-Newtonian behavior could lead to underestimation of the hemodynamic parameters at low Reynolds number and overestimation of the hemodynamic parameters by increasing the Reynolds number. In addition, we provide physical insight and discussion onto the hemodynamics associated with endothelial dysfunction which plays significant role in the pathogenesis of intracranial aneurysms.}, } @article {pmid33490686, year = {2021}, author = {Ibrahim, W and Hirpho, M}, title = {Finite element analysis of mixed convection flow in a trapezoidal cavity with non-uniform temperature.}, journal = {Heliyon}, volume = {7}, number = {1}, pages = {e05933}, doi = {10.1016/j.heliyon.2021.e05933}, pmid = {33490686}, issn = {2405-8440}, abstract = {A two dimensional flow analysis in a cavity shaped isosceles trapezium is carried out. Non-parallel sides of a trapezium are adiabatic. A varying sinusoidal temperature is applied to the lower wall while the upper wall is at constant temperature. Upper wall of the cavity moves with a velocity η 0 in the positive x-direction. Also, B 0 is constant magnetic field of strength aligned in the same x-direction and Newtonian fluid is considered. The values of magnetic field parameter used are H a = 0 , 50 , the Richardson number is R i = 0.1 , 1 , 10 , R e = 100 is Reynolds number used for the analysis, the amplitude of sinusoidal temperature is m = 0.25 , 0.5 , 1 . The impacts of different leading parameters are analyzed by plotting streamlines for flow fields and isotherm contours for temperature of the flow dynamics. The graphs that signify the variation of average Nusselt number and local Nusselt number are sketched for both lower and upper walls of the cavity. Result indicated that with constant temperature the top wall of the boundary layer thickness decreases as Richardson number Ri increases and for bottom wall with variable temperature. The Nusselt number gets higher with an increment in the amplitude of the oscillation of temperature function. Furthermore, the study revealed that the average Nusselt number gets reduced as the intensity of magnetic field is enhanced. The variation in transit of heat at the bottom wall is similar but the maximum value of heat transfer at the bottom wall shows a variation from 3.8 to 20 when H a = 0 and from 3 to 18 when H a = 50 . The accuracy of the present numerical algorithms is also established.}, } @article {pmid33477950, year = {2021}, author = {Kim, GY and Son, J and Han, JI and Park, JK}, title = {Inertial Microfluidics-Based Separation of Microalgae Using a Contraction-Expansion Array Microchannel.}, journal = {Micromachines}, volume = {12}, number = {1}, pages = {}, pmid = {33477950}, issn = {2072-666X}, abstract = {Microalgae separation technology is essential for both executing laboratory-based fundamental studies and ensuring the quality of the final algal products. However, the conventional microalgae separation technology of micropipetting requires highly skilled operators and several months of repeated separation to obtain a microalgal single strain. This study therefore aimed at utilizing microfluidic cell sorting technology for the simple and effective separation of microalgae. Microalgae are characterized by their various morphologies with a wide range of sizes. In this study, a contraction-expansion array microchannel, which utilizes these unique properties of microalgae, was specifically employed for the size-based separation of microalgae. At Reynolds number of 9, two model algal cells, Chlorella vulgaris (C. vulgaris) and Haematococcus pluvialis (H. pluvialis), were successfully separated without showing any sign of cell damage, yielding a purity of 97.9% for C. vulgaris and 94.9% for H. pluvialis. The result supported that the inertia-based separation technology could be a powerful alternative to the labor-intensive and time-consuming conventional microalgae separation technologies.}, } @article {pmid33465973, year = {2020}, author = {Liu, C and Gayme, DF}, title = {Input-output inspired method for permissible perturbation amplitude of transitional wall-bounded shear flows.}, journal = {Physical review. E}, volume = {102}, number = {6-1}, pages = {063108}, doi = {10.1103/PhysRevE.102.063108}, pmid = {33465973}, issn = {2470-0053}, abstract = {The precise set of parameters governing transition to turbulence in wall-bounded shear flows remains an open question; many theoretical bounds have been obtained, but there is not yet a consensus between these bounds and experimental or simulation results. In this work, we focus on a method to provide a provable Reynolds-number-dependent bound on the amplitude of perturbations a flow can sustain while maintaining the laminar state. Our analysis relies on an input-output approach that partitions the dynamics into a feedback interconnection of the linear and nonlinear dynamics (i.e., a Luré system that represents the nonlinearity as static feedback). We then construct quadratic constraints of the nonlinear term that is restricted by system physics to be energy-conserving (lossless) and to have bounded input-output energy. Computing the region of attraction of the laminar state (set of safe perturbations) and permissible perturbation amplitude are then reformulated as linear matrix inequalities, which allows more computationally efficient solutions than prevailing nonlinear approaches based on the sum of squares programming. The proposed framework can also be used for energy method computations and linear stability analysis. We apply our approach to low-dimensional nonlinear shear flow models for a range of Reynolds numbers. The results from our analytically derived bounds are consistent with the bounds identified through exhaustive simulations. However, they have the added benefit of being achieved at a much lower computational cost and providing a provable guarantee that a certain level of perturbation is permissible.}, } @article {pmid33462593, year = {2021}, author = {Shaheen, S and Anwar Bég, O and Gul, F and Maqbool, K}, title = {Electro-Osmotic Propulsion of Jeffrey Fluid in a Ciliated Channel Under the Effect of Nonlinear Radiation and Heat Source/Sink.}, journal = {Journal of biomechanical engineering}, volume = {143}, number = {5}, pages = {}, doi = {10.1115/1.4049810}, pmid = {33462593}, issn = {1528-8951}, mesh = {*Hot Temperature ; Rheology ; }, abstract = {Mathematical modeling of mechanical system in microfluidics is an emerging area of interest in microscale engineering. Since microfluidic devices use the hair-like structure of artificial cilia for pumping, mixing, and sensing in different fields, electro-osmotic cilia-driven flow helps to generate the fluid velocity for the Newtonian and viscoelastic fluid. Due to the deployment of artificial ciliated walls, the present research reports the combined effect of an electro-osmotic flow and convective heat transfer on Jeffrey viscoelastic electrolytic fluid flow in a two-dimensional ciliated vertical channel. Heat generation/absorption and nonlinear radiation effects are included in the present mathematical model. After applying Debye-Huckel approximation and small Reynolds number approximation to momentum and energy equation, the system of nonlinear partial differential equation is reduced into nonhomogenous boundary value problem. The problem determines the velocity, pressure, and temperature profiles by the application of semi-analytical technique known as homotopy perturbation method (HPM) with the help of software Mathematica. The graphical results of the study suggest that HPM is a reliable methodology for thermo physical electro-osmotic rheological transport in microchannels.}, } @article {pmid33450503, year = {2021}, author = {Javid, K and Riaz, M and Chu, YM and Ijaz Khan, M and Ullah Khan, S and Kadry, S}, title = {Peristaltic activity for electro-kinetic complex driven cilia transportation through a non-uniform channel.}, journal = {Computer methods and programs in biomedicine}, volume = {200}, number = {}, pages = {105926}, doi = {10.1016/j.cmpb.2020.105926}, pmid = {33450503}, issn = {1872-7565}, mesh = {*Body Fluids ; *Cilia ; Kinetics ; Peristalsis ; Viscosity ; }, abstract = {MOTIVATIONS: Now-a-days in medical science, the transport study of biological fluids through non-uniform vessels are going to increase due to their close relation to the reality. Motivated through such type of complex transportation, the current study is presented of cilia hydro-dynamics of an aqueous electrolytic viscous fluid through a non-uniform channel under an applied axial electric field. Mathematical Formulations: Because of the complexity shape and nature of flow channel, we have used curvilinear coordinates in the derivation of continuity and momentum equationsin a fixed frame of reference. A linear transformation is used to renovate the flow system of equations from fixed (laboratory) to moving (wave) frame. For further simplification, the dimensionless variables are introduced to make the flow system of equations into the dimensionless form and at last convert these equations in term of stream function by using the mathematical terminologies of streamlines. The whole analysis is performed under (low Reynolds number) creeping phenomena and long wavelength approximation, respectively. Additionally, small ionic Peclet number and Debye-Huckel linearization are used to simplify the Nernst-Planck and Poisson-Boltzmann equations. The BVP4C technique is used to obtain the numerical solution for velocity distribution, pressure gradient, pressure rise and stream function through MATLAB.

MAIN OUTCOMES: The amplitude of velocity distribution is increased (decreased) at larger values of non-uniform parameter (cilia length). The non-uniform parameter played a vital role not only in the enhancement of circulation at the upper half of the channel but also the length of bolus increased. Results of straight channel are gained for larger value of the dimensionless radius of curvature parameter as well as cilia length.}, } @article {pmid33449773, year = {2020}, author = {Pan, Z and Nunes, JK and Stone, HA}, title = {Regime Map and Triple Point in Selective Withdrawal.}, journal = {Physical review letters}, volume = {125}, number = {26}, pages = {264502}, doi = {10.1103/PhysRevLett.125.264502}, pmid = {33449773}, issn = {1079-7114}, abstract = {Entrainment in selective withdrawal occurs when both the top and bottom phases are withdrawn through a capillary tube oriented perpendicular to a flat gravitationally separated liquid-liquid interface. The tube introduces two distinct features to the conditions for fluid entrainment. First, the ratio of the two phases being withdrawn is affected by the region of influence of the flow upstream of the tube's orifice. Second, a minimum withdrawal flow rate must be reached for entrainment regardless of the distance between the interface and the tube. We show that these phenomena can be understood based on the Reynolds number that governs the external flow field around the capillary tube and the capillary number that regulates the effect of the viscosity and capillarity.}, } @article {pmid33438620, year = {2020}, author = {Shit, GC and Bera, A}, title = {Mathematical model to verify the role of magnetic field on blood flow and its impact on thermal behavior of biological tissue for tumor treatment.}, journal = {Biomedical physics & engineering express}, volume = {6}, number = {1}, pages = {015032}, doi = {10.1088/2057-1976/ab6e22}, pmid = {33438620}, issn = {2057-1976}, mesh = {Blood Flow Velocity ; Computer Simulation ; Hemodynamics ; Humans ; Hyperthermia, Induced/*methods ; *Magnetic Fields ; Microvessels/*pathology ; Models, Biological ; *Models, Theoretical ; Neoplasms/blood supply/*pathology/therapy ; }, abstract = {The numerical computation has been performed to study the effects of static magnetic field on thermal behavior of tumor surrounded by living biological tissues and blood vessels. A small rectangular shaped tumor enclosing the blood vessel surrounded by healthy tissue is considered. The model consists of two-layer composite system in which the microvessel for blood flow is considered as a fluid layer and the living biological tissue including tumor as a solid layer. The wave bioheat transfer equation in the tissue layer together with energy transport equation for blood flow layer has been used in the cylindrical polar coordinates. The analytical expression for blood velocity in the presence of magnetic field has been used from Gold's solution. The computational work has been performed by employing the Crank-Nicolson finite difference method. A comparison has been made to validate our numerical results with the previous solution by setting some parameters. The temperature profiles have been plotted at different locations of the axial tissue length for various values of the Hartmann number, Prandtl number, Womersley number and Reynolds number. It is observed that the application of magnetic field increases heat transfer rate within tumor tissues which in turn attribute to an enhancement of temperature about 316 K or above for hyperthermic treatment in cancer therapy.}, } @article {pmid33430317, year = {2021}, author = {Gnapowski, E and Pytka, J and Józwik, J and Laskowski, J and Michałowska, J}, title = {Wind Tunnel Testing of Plasma Actuator with Two Mesh Electrodes to Boundary Layer Control at High Angle of Attack.}, journal = {Sensors (Basel, Switzerland)}, volume = {21}, number = {2}, pages = {}, pmid = {33430317}, issn = {1424-8220}, abstract = {The manuscript presents experimental research carried out on the wing model with the SD 7003 profile. A plasma actuator with DBD (Dielectric Barrier Discharge) discharges was placed on the wing surface to control boundary layer. The experimental tests were carried out in the AeroLab wind tunnel where the forces acting on the wing during the tests were measured. The conducted experimental research concerns the analysis of the phenomena that take place on the surface of the wing with the DBD plasma actuator turned off and on. The plasma actuator used during the experimental tests has a different structure compared to the classic plasma actuator. The commonly tested plasma actuator uses solid/impermeable electrodes, while in the research, the plasma actuator uses a new type of electrodes, two mesh electrodes separated by an impermeable Kapton dielectric. The experimental research was carried out for the angle of attack α = 15° and several air velocities V = 5-15 m/s with a step of 5 m/s for the Reynolds number Re = 87,500-262,500. The critical angle of attack at which the SD 7003 profile has the maximum lift coefficient is about 11°; during the experimental research, the angle was 15°. Despite the high angle of attack, it was possible to increase the lift coefficient. The use of a plasma actuator with two mesh electrodes allowed to increase the lift by 5%, even at a high angle of attack. During experimental research used high voltage power supply for powering the DBD plasma actuator in the voltage range from 7.5 to 15 kV.}, } @article {pmid33416336, year = {2020}, author = {Monsalve, E and Brunet, M and Gallet, B and Cortet, PP}, title = {Quantitative Experimental Observation of Weak Inertial-Wave Turbulence.}, journal = {Physical review letters}, volume = {125}, number = {25}, pages = {254502}, doi = {10.1103/PhysRevLett.125.254502}, pmid = {33416336}, issn = {1079-7114}, abstract = {We report the quantitative experimental observation of the weak inertial-wave turbulence regime of rotating turbulence. We produce a statistically steady homogeneous turbulent flow that consists of nonlinearly interacting inertial waves, using rough top and bottom boundaries to prevent the emergence of a geostrophic flow. As the forcing amplitude increases, the temporal spectrum evolves from a discrete set of peaks to a continuous spectrum. Maps of the bicoherence of the velocity field confirm such a gradual transition between discrete wave interactions at weak forcing amplitude and the regime described by weak turbulence theory (WTT) for stronger forcing. In the former regime, the bicoherence maps display a near-zero background level, together with sharp localized peaks associated with discrete resonances. By contrast, in the latter regime, the bicoherence is a smooth function that takes values of the order of the Rossby number in line with the infinite-domain and random-phase assumptions of WTT. The spatial spectra then display a power-law behavior, both the spectral exponent and the spectral level being accurately predicted by WTT at high Reynolds number and low Rossby number.}, } @article {pmid33404675, year = {2022}, author = {Klein, AK and Dietzel, A}, title = {A Primer on Microfluidics: From Basic Principles to Microfabrication.}, journal = {Advances in biochemical engineering/biotechnology}, volume = {179}, number = {}, pages = {17-35}, pmid = {33404675}, issn = {0724-6145}, mesh = {*Microfluidics/methods ; *Microtechnology/methods ; }, abstract = {Microfluidic systems enable manipulating fluids in different functional units which are integrated on a microchip. This chapter describes the basics of microfluidics, where physical effects have a different impact compared to macroscopic systems. Furthermore, an overwiew is given on the microfabrication of these systems. The focus lies on clean-room fabrication methods based on photolithography and soft lithography. Finally, an outlook on advanced maskless micro- and nanofabrication methods is given. Special attention is paid to laser structuring processes.}, } @article {pmid33398321, year = {2021}, author = {Chen, W and Wen, Y and Fan, X and Sun, M and Tian, C and Yang, M and Xie, H}, title = {Magnetically actuated intelligent hydrogel-based child-parent microrobots for targeted drug delivery.}, journal = {Journal of materials chemistry. B}, volume = {9}, number = {4}, pages = {1030-1039}, doi = {10.1039/d0tb02384a}, pmid = {33398321}, issn = {2050-7518}, mesh = {Cells, Cultured ; Child ; Doxorubicin/*chemistry ; *Drug Delivery Systems ; Humans ; Hydrogels/*chemistry ; Lab-On-A-Chip Devices ; Magnetic Phenomena ; Magnetite Nanoparticles/*chemistry ; Particle Size ; *Robotics/instrumentation ; Surface Properties ; }, abstract = {Small intestine-targeted drug delivery by oral administration has aroused the growing interest of researchers. In this work, the child-parent microrobot (CPM) as a vehicle protects the child microrobots (CMs) under a gastric acid environment and releases them in the small intestinal environment. The intelligent hydrogel-based CPMs with sphere, mushroom, red blood cell, and teardrop shapes are fabricated by an extrusion-dripping method. The CPMs package uniform CMs, which are fabricated by designed microfluidic (MF) devices. The fabrication mechanism and tunability of CMs and CPMs with different sizes and shapes are analyzed, modeled, and simulated. The shape of CPM can affect its drug release efficiency and kinetic characteristics. A vision-feedback magnetic driving system (VMDS) actuates and navigates CPM along the predefined path to the destination and continuously releases drug in the simulated intestinal fluid (SIF, a low Reynolds number (Re) regime) using a new motion control method with the tracking-learning-detection (TLD) algorithm. The newly designed CPM combines the advantages of powerful propulsion, good biocompatibility, and remarkable drug loading and release capacity at the intestinal level, which is expected to be competent for oral administration of small intestine-targeted therapy in the future.}, } @article {pmid33396499, year = {2020}, author = {Avila, K and Hof, B}, title = {Second-Order Phase Transition in Counter-Rotating Taylor-Couette Flow Experiment.}, journal = {Entropy (Basel, Switzerland)}, volume = {23}, number = {1}, pages = {}, pmid = {33396499}, issn = {1099-4300}, abstract = {In many basic shear flows, such as pipe, Couette, and channel flow, turbulence does not arise from an instability of the laminar state, and both dynamical states co-exist. With decreasing flow speed (i.e., decreasing Reynolds number) the fraction of fluid in laminar motion increases while turbulence recedes and eventually the entire flow relaminarizes. The first step towards understanding the nature of this transition is to determine if the phase change is of either first or second order. In the former case, the turbulent fraction would drop discontinuously to zero as the Reynolds number decreases while in the latter the process would be continuous. For Couette flow, the flow between two parallel plates, earlier studies suggest a discontinuous scenario. In the present study we realize a Couette flow between two concentric cylinders which allows studies to be carried out in large aspect ratios and for extensive observation times. The presented measurements show that the transition in this circular Couette geometry is continuous suggesting that former studies were limited by finite size effects. A further characterization of this transition, in particular its relation to the directed percolation universality class, requires even larger system sizes than presently available.}, } @article {pmid33362423, year = {2020}, author = {Elsinga, GE and Ishihara, T and Hunt, JCR}, title = {Extreme dissipation and intermittency in turbulence at very high Reynolds numbers.}, journal = {Proceedings. Mathematical, physical, and engineering sciences}, volume = {476}, number = {2243}, pages = {20200591}, pmid = {33362423}, issn = {1364-5021}, abstract = {Extreme dissipation events in turbulent flows are rare, but they can be orders of magnitude stronger than the mean dissipation rate. Despite its importance in many small-scale physical processes, there is presently no accurate theory or model for predicting the extrema as a function of the Reynolds number. Here, we introduce a new model for the dissipation probability density function (PDF) based on the concept of significant shear layers, which are thin regions of elevated local mean dissipation. At very high Reynolds numbers, these significant shear layers develop layered substructures. The flow domain is divided into the different layer regions and a background region, each with their own PDF of dissipation. The volume-weighted regional PDFs are combined to obtain the overall PDF, which is subsequently used to determine the dissipation variance and maximum. The model yields Reynolds number scalings for the dissipation maximum and variance, which are in agreement with the available data. Moreover, the power law scaling exponent is found to increase gradually with the Reynolds numbers, which is also consistent with the data. The increasing exponent is shown to have profound implications for turbulence at atmospheric and astrophysical Reynolds numbers. The present results strongly suggest that intermittent significant shear layer structures are key to understanding and quantifying the dissipation extremes, and, more generally, extreme velocity gradients.}, } @article {pmid33362112, year = {2021}, author = {Foo, CT and Unterberger, A and Menser, J and Mohri, K}, title = {Tomographic imaging using multi-simultaneous measurements (TIMes) for flame emission reconstructions.}, journal = {Optics express}, volume = {29}, number = {1}, pages = {244-255}, doi = {10.1364/OE.412048}, pmid = {33362112}, issn = {1094-4087}, abstract = {The method of tomographic imaging using multi-simultaneous measurements (TIMes) for flame emission reconstructions is presented. Measurements of the peak natural CH* chemiluminescence in the flame and luminescence from different vaporised alkali metal salts that were seeded in a multi-annulus burner were used. An array of 29 CCD cameras around the Cambridge-Sandia burner was deployed, with 3 sets of cameras each measuring a different colour channel using bandpass optical filters. The three-dimensional instantaneous and time-averaged fields of the individual measured channels were reconstructed and superimposed for two new operating conditions, with differing cold flow Reynolds numbers. The contour of the reconstructed flame front followed the interface between the burnt side of the flame, where the alkali salt luminescence appears, and the cold gas region. The increased mixing between different reconstructed channels in the downstream direction that is promoted by the higher levels of turbulence in the larger Reynolds number case was clearly demonstrated. The TIMes method enabled combustion zones originating from different streams and the flame front to be distinguished and their overlap regions to be identified, in the entire volume.}, } @article {pmid33361564, year = {2021}, author = {Brum, J and Bernal, M and Barrere, N and Negreira, C and Cabeza, C}, title = {Vortex dynamics and transport phenomena in stenotic aortic models using Echo-PIV.}, journal = {Physics in medicine and biology}, volume = {66}, number = {5}, pages = {}, doi = {10.1088/1361-6560/abd670}, pmid = {33361564}, issn = {1361-6560}, mesh = {Aortic Valve Stenosis/*diagnostic imaging/physiopathology ; Hemodynamics ; Humans ; *Models, Cardiovascular ; Pulsatile Flow ; *Rheology ; Ultrasonography ; }, abstract = {Atherosclerosis is the most fatal cardiovascular disease. As disease progresses, stenoses grow inside the arteries blocking their lumen and altering blood flow. Analysing flow dynamics can provide a deeper insight on the stenosis evolution. In this work we combined Eulerian and Lagrangian descriptors to analyze blood flow dynamics and fluid transport in stenotic aortic models with morphology, mechanical and optical properties close to those of real arteries. To this end, vorticity, particle residence time (PRT), particle's final position (FP) and finite time Lyapunov's exponents (FTLE) were computed from the experimental fluid velocity fields acquired using ultrasonic particle imaging velocimetry (Echo-PIV). For the experiments, CT-images were used to create morphological realistic models of the descending aorta with 0%, 35% and 50% occlusion degree with same mechanical properties as real arteries. Each model was connected to a circuit with a pulsatile programmable pump which mimics physiological flow and pressure conditions. The pulsatile frequency was set to ≈0.9 Hz (55 bpm) and the upstream peak Reynolds number (Re) was changed from 1100 to 2000. Flow in the post-stenotic region was composed of two main structures: a high velocity jet over the stenosis throat and a recirculation region behind the stenosis where vortex form and shed. We characterized vortex kinematics showing that vortex propagation velocity increases withRe. Moreover, from the FTLE field we identified Lagrangian coherent structures (i.e. material barriers) that dictate transport behind the stenosis. The size and strength of those barriers increased withReand the occlusion degree. Finally, from the PRT and FP maps, we showed that independently ofRe, the same amount of fluid remains on the stenosis over more than a pulsatile period.}, } @article {pmid33352968, year = {2020}, author = {Wu, CY and Lai, BH}, title = {Numerical Study of T-Shaped Micromixers with Vortex-Inducing Obstacles in the Inlet Channels.}, journal = {Micromachines}, volume = {11}, number = {12}, pages = {}, pmid = {33352968}, issn = {2072-666X}, abstract = {To enhance fluid mixing, a new approach for inlet flow modification by adding vortex-inducing obstacles (VIOs) in the inlet channels of a T-shaped micromixer is proposed and investigated in this work. We use a commercial computational fluid dynamics code to calculate the pressure and the velocity vectors and, to reduce the numerical diffusion in high-Peclet-number flows, we employ the particle-tracking simulation with an approximation diffusion model to calculate the concentration distribution in the micromixers. The effects of geometric parameters, including the distance between the obstacles and the angle of attack of the obstacles, on the mixing performance of micromixers are studied. From the results, we can observe the following trends: (i) the stretched contact surface between different fluids caused by antisymmetric VIOs happens for the cases with the Reynolds number (Re) greater than or equal to 27 and the enhancement of mixing increases with the increase of Reynolds number gradually, and (ii) the onset of the engulfment flow happens at Re≈125 in the T-shaped mixer with symmetric VIOs or at Re≈140 in the standard planar T-shaped mixer and results in a sudden increase of the degree of mixing. The results indicate that the early initiation of transversal convection by either symmetric or antisymmetric VIOs can enhance fluid mixing at a relatively lower Re.}, } @article {pmid33333847, year = {2020}, author = {Li, YH and Chen, SC}, title = {Propulsion Mechanism of Flexible Microbead Swimmers in the Low Reynolds Number Regime.}, journal = {Micromachines}, volume = {11}, number = {12}, pages = {}, pmid = {33333847}, issn = {2072-666X}, abstract = {A propulsion mechanism for a flexible microswimmer constructed from superparamagnetic microbeads with different diameters and subjected to an oscillating field was studied experimentally and theoretically herein. Various types of artificial swimmers with different bending patterns were fabricated to determine the flexibility and an effective waveform for a planar beating flagellum. Waveform evolutions for various swimmer configurations were studied to determine the flexible mechanism of the swimmers. A one-armed microswimmer can propel itself only if the friction of its wavelike body is anisotropic. A swimmer with a larger head and a stronger magnetic dipole moment with a flexible tail allows the bending wave to propagate from the head toward the tail to generate forward thrust. The oscillating head and tail do not simultaneously generate positive thrust all the time within a period of oscillation. To increase the propulsion for a bending swimmer, this study proposes a novel configuration for a microbead swimmer that ensures better swimming efficiency. The ratio of the oscillation amplitude of the head to the length of the swimmer (from 0.26 to 0.28) produces a faster swimmer. On the other hand, the swimmer is propelled more effectively if the ratio of the oscillation amplitude of the tail to the length of the swimmer is from 0.29 to 0.33. This study determined the optimal configuration for a flexible microbead swimmer that generates the greatest propulsion in a low Reynolds number environment.}, } @article {pmid33331388, year = {2021}, author = {Dou, Y and Tzelios, PM and Livitz, D and Bishop, KJM}, title = {Programmable topotaxis of magnetic rollers in time-varying fields.}, journal = {Soft matter}, volume = {17}, number = {6}, pages = {1538-1547}, doi = {10.1039/d0sm01443e}, pmid = {33331388}, issn = {1744-6848}, abstract = {We describe how spatially uniform, time-periodic magnetic fields can be designed to power and direct the migration of ferromagnetic spheres up (or down) local gradients in the topography of a solid substrate. Our results are based on a dynamical model that considers the time-varying magnetic torques on the particle and its motion through the fluid at low Reynolds number. We use both analytical theory and numerical simulation to design magnetic fields that maximize the migration velocity up (or down) an inclined plane. We show how "topotaxis" of spherical particles relies on differences in the hydrodynamic resistance to rotation about axes parallel and perpendicular to the plane. Importantly, the designed fields can drive multiple independent particles to move simultaneously in different directions as determined by gradients in their respective environments. Experiments on ferromagnetic spheres provide evidence for topotactic motions up inclined substrates. The ability to program the autonomous navigation of driven particles within anisotropic environments is relevant to the design of colloidal robots.}, } @article {pmid33327115, year = {2020}, author = {Slanina, F}, title = {Colloid particles in microfluidic inertial hydrodynamic ratchet at moderate Reynolds number.}, journal = {Physical review. E}, volume = {102}, number = {5-1}, pages = {052601}, doi = {10.1103/PhysRevE.102.052601}, pmid = {33327115}, issn = {2470-0053}, abstract = {The movement of spherical Brownian particle carried by an alternating fluid flow in a tube of periodically variable diameter is investigated. On the basis of our previous results [Phys. Rev. E 99, 012604 (2019)10.1103/PhysRevE.99.012604] on the hydrodynamics of the problem, we look at the competition of hydrodynamics and diffusion. We use the method of Fick-Jacobs mapping on an effective one-dimensional problem. We calculate the ratchet current and show that is is strictly related to finite size of the particles. The ratchet current grows quadratically with particle radius. We also show that the dominant contribution to the ratchet current is due to inertial hydrodynamic effects. This means that Reynolds number must be at least of order one. We discuss the possible use for separation of particles by size and perspectives of optimization of the tube shape.}, } @article {pmid33325030, year = {2021}, author = {Turon, V and Ollivier, S and Cwicklinski, G and Willison, JC and Anxionnaz-Minvielle, Z}, title = {H2 production by photofermentation in an innovative plate-type photobioreactor with meandering channels.}, journal = {Biotechnology and bioengineering}, volume = {118}, number = {3}, pages = {1342-1354}, doi = {10.1002/bit.27656}, pmid = {33325030}, issn = {1097-0290}, mesh = {Hydrogen/*metabolism ; *Photobioreactors ; Rhodobacter capsulatus/*growth & development ; }, abstract = {Hydrogen production by Rhodobacter capsulatus is an anaerobic, photobiological process requiring specific mixing conditions. In this study, an innovative design of a photobioreactor is proposed. The design is based on a plate-type photobioreactor with an interconnected meandering channel to allow culture mixing and H2 degassing. The culture flow was characterized as a quasi-plug-flow with radial mixing caused by a turbulent-like regime achieved at a low Reynolds number. The dissipated volumetric power was decreased 10-fold while maintaining PBR performances (production and yields) when compared with a magnetically stirred tank reactor. To increase hydrogen production flow rate, several bacterial concentrations were tested by increasing the glutamate concentration using fed-batch cultures. The maximum hydrogen production flow rate (157.7 ± 9.3 ml H2 /L/h) achieved is one of the highest values so far reported for H2 production by R. capsulatus. These first results are encouraging for future scale-up of the plate-type reactor.}, } @article {pmid33322374, year = {2020}, author = {Liu, J and Xiao, Y and Li, M and Tao, J and Xu, S}, title = {Intermittency, Moments, and Friction Coefficient during the Subcritical Transition of Channel Flow.}, journal = {Entropy (Basel, Switzerland)}, volume = {22}, number = {12}, pages = {}, pmid = {33322374}, issn = {1099-4300}, abstract = {The intermittent distribution of localized turbulent structures is a key feature of the subcritical transitions in channel flows, which are studied in this paper with a wind channel and theoretical modeling. Entrance disturbances are introduced by small beads, and localized turbulent patches can be triggered at low Reynolds numbers (Re). High turbulence intensity represents strong ability of perturbation spread, and a maximum turbulence intensity is found for every test case as Re ≥ 950, where the turbulence fraction increases abruptly with Re. Skewness can reflect the velocity defects of localized turbulent patches and is revealed to become negative when Re is as low as about 660. It is shown that the third-order moments of the midplane streamwise velocities have minima, while the corresponding forth-order moments have maxima during the transition. These kinematic extremes and different variation scenarios of the friction coefficient during the transition are explained with an intermittent structure model, where the robust localized turbulent structure is simplified as a turbulence unit, a structure whose statistical properties are only weak functions of the Reynolds number.}, } @article {pmid33289747, year = {2021}, author = {Yang, PJ and Lee, AB and Chan, M and Kowalski, M and Qiu, K and Waid, C and Cervantes, G and Magondu, B and Biagioni, M and Vogelnest, L and Martin, A and Edwards, A and Carver, S and Hu, DL}, title = {Intestines of non-uniform stiffness mold the corners of wombat feces.}, journal = {Soft matter}, volume = {17}, number = {3}, pages = {475-488}, doi = {10.1039/d0sm01230k}, pmid = {33289747}, issn = {1744-6848}, mesh = {Animals ; Australia ; Feces ; Fungi ; Intestines ; *Marsupialia ; }, abstract = {The bare-nosed wombat (Vombatus ursinus) is a fossorial, herbivorous, Australian marsupial, renowned for its cubic feces. However, the ability of the wombat's soft intestine to sculpt flat faces and sharp corners in feces is poorly understood. In this combined experimental and numerical study, we show one mechanism for the formation of corners in a highly damped environment. Wombat dissections show that cubes are formed within the last 17 percent of the intestine. Using histology and tensile testing, we discover that the cross-section of the intestine exhibits regions with a two-fold increase in thickness and a four-fold increase in stiffness, which we hypothesize facilitates the formation of corners by contractions of the intestine. Using a mathematical model, we simulate a series of azimuthal contractions of a damped elastic ring composed of alternating stiff and soft regions. Increased stiffness ratio and higher Reynolds number yield shapes that are more square. The corners arise from faster contraction in the stiff regions and relatively slower movement in the center of the soft regions. These results may have applications in manufacturing, clinical pathology, and digestive health.}, } @article {pmid33286895, year = {2020}, author = {Agrawal, R and Ng, HC and Davis, EA and Park, JS and Graham, MD and Dennis, DJC and Poole, RJ}, title = {Low- and High-Drag Intermittencies in Turbulent Channel Flows.}, journal = {Entropy (Basel, Switzerland)}, volume = {22}, number = {10}, pages = {}, pmid = {33286895}, issn = {1099-4300}, abstract = {Recent direct numerical simulations (DNS) and experiments in turbulent channel flow have found intermittent low- and high-drag events in Newtonian fluid flows, at Reτ=uτh/ν between 70 and 100, where uτ, h and ν are the friction velocity, channel half-height and kinematic viscosity, respectively. These intervals of low-drag and high-drag have been termed "hibernating" and "hyperactive", respectively, and in this paper, a further investigation of these intermittent events is conducted using experimental and numerical techniques. For experiments, simultaneous measurements of wall shear stress and velocity are carried out in a channel flow facility using hot-film anemometry (HFA) and laser Doppler velocimetry (LDV), respectively, for Reτ between 70 and 250. For numerical simulations, DNS of a channel flow is performed in an extended domain at Reτ = 70 and 85. These intermittent events are selected by carrying out conditional sampling of the wall shear stress data based on a combined threshold magnitude and time-duration criteria. The use of three different scalings (so-called outer, inner and mixed) for the time-duration criterion for the conditional events is explored. It is found that if the time-duration criterion is kept constant in inner units, the frequency of occurrence of these conditional events remain insensitive to Reynolds number. There exists an exponential distribution of frequency of occurrence of the conditional events with respect to their duration, implying a potentially memoryless process. An explanation for the presence of a spike (or dip) in the ensemble-averaged wall shear stress data before and after the low-drag (or high-drag) events is investigated. During the low-drag events, the conditionally-averaged streamwise velocities get closer to Virk's maximum drag reduction (MDR) asymptote, near the wall, for all Reynolds numbers studied. Reynolds shear stress (RSS) characteristics during these conditional events are investigated for Reτ = 70 and 85. Except very close to the wall, the conditionally-averaged RSS is higher than the time-averaged value during the low-drag events.}, } @article {pmid33286770, year = {2020}, author = {Kashyap, PV and Duguet, Y and Dauchot, O}, title = {Flow Statistics in the Transitional Regime of Plane Channel Flow.}, journal = {Entropy (Basel, Switzerland)}, volume = {22}, number = {9}, pages = {}, pmid = {33286770}, issn = {1099-4300}, abstract = {The transitional regime of plane channel flow is investigated above the transitional point below which turbulence is not sustained, using direct numerical simulation in large domains. Statistics of laminar-turbulent spatio-temporal intermittency are reported. The geometry of the pattern is first characterized, including statistics for the angles of the laminar-turbulent stripes observed in this regime, with a comparison to experiments. High-order statistics of the local and instantaneous bulk velocity, wall shear stress and turbulent kinetic energy are then provided. The distributions of the two former quantities have non-trivial shapes, characterized by a large kurtosis and/or skewness. Interestingly, we observe a strong linear correlation between their kurtosis and their skewness squared, which is usually reported at much higher Reynolds number in the fully turbulent regime.}, } @article {pmid33286441, year = {2020}, author = {Lee, T}, title = {Lognormality in Turbulence Energy Spectra.}, journal = {Entropy (Basel, Switzerland)}, volume = {22}, number = {6}, pages = {}, pmid = {33286441}, issn = {1099-4300}, abstract = {The maximum entropy principle states that the energy distribution will tend toward a state of maximum entropy under the physical constraints, such as the zero energy at the boundaries and a fixed total energy content. For the turbulence energy spectra, a distribution function that maximizes entropy with these physical constraints is a lognormal function due to its asymmetrical descent to zero energy at the boundary lengths scales. This distribution function agrees quite well with the experimental data over a wide range of energy and length scales. For turbulent flows, this approach is effective since the energy and length scales are determined primarily by the Reynolds number. The total turbulence kinetic energy will set the height of the distribution, while the ratio of length scales will determine the width. This makes it possible to reconstruct the power spectra using the Reynolds number as a parameter.}, } @article {pmid33286423, year = {2020}, author = {Wang, R and Xie, Z and Yin, Y and Chen, L}, title = {Constructal Design of Elliptical Cylinders with Heat Generating for Entropy Generation Minimization.}, journal = {Entropy (Basel, Switzerland)}, volume = {22}, number = {6}, pages = {}, pmid = {33286423}, issn = {1099-4300}, abstract = {A heat dissipation model of discrete elliptical cylinders with heat generation on a thermal conduction pedestal cooled by forced convection is established. Constructal design is conducted numerically by taking the distributions of thermal conductivity and heat generating intensity as design variables, the dimensionless entropy generation rate (DEGR) as performance indicator. The optimal designs for discrete elliptical cylinders with heat generating are obtained respectively, i.e., there are optimal distributions of heat generating intensity with its fixed total amount of heat sources, and there are optimal distributions of thermal conductivity with its fixed total amount of heat sources. These optimums for minimum DEGRs are different at different Reynolds numbers of airflow. The heat generating intensity can be decreased one by one appropriately in the fluid flow direction to achieve the best effect. When the Reynolds number of airflow is smaller, the thermal conductivity of heat source can be increased one by one appropriately in the fluid flow direction to achieve the best effect; when the Reynolds number of airflow is larger, the thermal conductivity of each heat source should be equalized to achieve the best effect. The results can give thermal design guidelines for the practical heat generating devices with different materials and heat generating intensities.}, } @article {pmid33285959, year = {2020}, author = {Yu, S and Tang, T and Li, J and Yu, P}, title = {Effect of Prandtl Number on Mixed Convective Heat Transfer from a Porous Cylinder in the Steady Flow Regime.}, journal = {Entropy (Basel, Switzerland)}, volume = {22}, number = {2}, pages = {}, pmid = {33285959}, issn = {1099-4300}, abstract = {The effect of the Prandtl number (Pr) on the flow and heat transfer from a porous circular cylinder with internal heat generation in the mixed convection regime is numerically investigated. The steady flow regime is considered over the ranges of the Reynolds number (Re), Darcy number (Da), and Richardson number (Ri), varying from 5 to 40, 10[-6] to 10[-2], and 0 to 2, respectively. The wake structure, the temperature distribution, and the heat transfer rate are discussed. Besides precipitating the growth of the recirculating wake, the Prandtl number is found to have a significant impact on the thermal characteristics. The concave isotherms, resembling a saddle-shaped structure, occur behind the cylinder at larger Pr, resulting in swells of the isotherms pairing off at the lateral sides. These swells are found to have a negative effect on heat transfer owing to a relatively smaller temperature gradient there. Then, the heat transfer rate in terms of the local Nusselt number (Nu) and enhancement ratio (Er) is calculated, which is closely related to Pr, Re, Da, and Ri. The local minimum heat transfer rate along the cylinder surface is found at the position where the swells of the isotherms form.}, } @article {pmid33285875, year = {2020}, author = {Deriszadeh, A and de Monte, F}, title = {On Heat Transfer Performance of Cooling Systems Using Nanofluid for Electric Motor Applications.}, journal = {Entropy (Basel, Switzerland)}, volume = {22}, number = {1}, pages = {}, pmid = {33285875}, issn = {1099-4300}, abstract = {This paper studies the fluid flow and heat transfer characteristics of nanofluids as advance coolants for the cooling system of electric motors. Investigations are carried out using numerical analysis for a cooling system with spiral channels. To solve the governing equations, computational fluid dynamics and 3D fluid motion analysis are used. The base fluid is water with a laminar flow. The fluid Reynolds number and turn-number of spiral channels are evaluation parameters. The effect of nanoparticles volume fraction in the base fluid on the heat transfer performance of the cooling system is studied. Increasing the volume fraction of nanoparticles leads to improving the heat transfer performance of the cooling system. On the other hand, a high-volume fraction of the nanofluid increases the pressure drop of the coolant fluid and increases the required pumping power. This paper aims at finding a trade-off between effective parameters by studying both fluid flow and heat transfer characteristics of the nanofluid.}, } @article {pmid33285793, year = {2019}, author = {Rasool, G and Zhang, T and Chamkha, AJ and Shafiq, A and Tlili, I and Shahzadi, G}, title = {Entropy Generation and Consequences of Binary Chemical Reaction on MHD Darcy-Forchheimer Williamson Nanofluid Flow Over Non-Linearly Stretching Surface.}, journal = {Entropy (Basel, Switzerland)}, volume = {22}, number = {1}, pages = {}, pmid = {33285793}, issn = {1099-4300}, abstract = {The current article aims to present a numerical analysis of MHD Williamson nanofluid flow maintained to flow through porous medium bounded by a non-linearly stretching flat surface. The second law of thermodynamics was applied to analyze the fluid flow, heat and mass transport as well as the aspects of entropy generation using Buongiorno model. Thermophoresis and Brownian diffusion is considered which appears due to the concentration and random motion of nanoparticles in base fluid, respectively. Uniform magnetic effect is induced but the assumption of tiny magnetic Reynolds number results in zero magnetic induction. The governing equations (PDEs) are transformed into ordinary differential equations (ODEs) using appropriately adjusted transformations. The numerical method is used for solving the so-formulated highly nonlinear problem. The graphical presentation of results highlights that the heat flux receives enhancement for augmented Brownian diffusion. The Bejan number is found to be increasing with a larger Weissenberg number. The tabulated results for skin-friction, Nusselt number and Sherwood number are given. A decent agreement is noted in the results when compared with previously published literature on Williamson nanofluids.}, } @article {pmid33285790, year = {2019}, author = {Xu, L and Xiong, Y and Xi, L and Gao, J and Li, Y and Zhao, Z}, title = {Numerical Simulation of Swirling Impinging Jet Issuing from a Threaded Hole under Inclined Condition.}, journal = {Entropy (Basel, Switzerland)}, volume = {22}, number = {1}, pages = {}, pmid = {33285790}, issn = {1099-4300}, abstract = {There are some inclined jet holes in the cooling structure of the leading edge region of gas turbine blades. In order to improve the cooling effect of traditional round holes, this paper proposes to replace the round holes with threaded holes, and studies the complex flow and heat transfer performance of the swirling impinging jet (SIJ) issuing from the 45° threaded holes in the inclined condition by numerical simulation. The influencing factors include jet inclination angle α (45°-90°), jet-to-plate distance (H/d = 2, 4, 6), and Reynolds number (6000-24,000). The results show that the inclination angle and jet-to-plate distance have a great influence on the size, shape, and position of vortices in the jet space, while the Reynolds number has little effect on the vortices. In the inclined state, the impinging cooling effect of the swirling impinging jet is better than that of the circular impinging jet (CIJ), both heat transfer coefficients will degrade significantly when the inclination angle is 45°. When the inclination angle is greater than 45°, compared with the round hole, the enhanced heat transfer region for the swirling jet is in the region of r/d < 3, while both of the Nusselt numbers in the wall jet region are weak, with a value of just 20. At the same time, with the increasing of the inclination angle (α > 45°), the average Nusselt number on target surface holds a constant value. Under the inclined conditions, the heat transfer coefficient on the target surface for the swirling jet is increased totally with the increasing of the Re, but when the Re is larger than 18,000, the rate of enhanced heat transfer gradually weakens.}, } @article {pmid33285453, year = {2021}, author = {Maurer, L and Villette, C and Reiminger, N and Jurado, X and Laurent, J and Nuel, M and Mosé, R and Wanko, A and Heintz, D}, title = {Distribution and degradation trend of micropollutants in a surface flow treatment wetland revealed by 3D numerical modelling combined with LC-MS/MS.}, journal = {Water research}, volume = {190}, number = {}, pages = {116672}, doi = {10.1016/j.watres.2020.116672}, pmid = {33285453}, issn = {1879-2448}, mesh = {Chromatography, Liquid ; Tandem Mass Spectrometry ; Waste Disposal, Fluid ; Waste Water/analysis ; *Water Pollutants, Chemical/analysis ; *Wetlands ; }, abstract = {Conventional wastewater treatment plants are not designed to treat micropollutants; thus, for 20 years, several complementary treatment systems, such as surface flow wetlands have been used to address this issue. Previous studies demonstrate that higher residence time and low global velocities promote nutrient removal rates or micropollutant photodegradation. Nevertheless, these studies were restricted to the system limits (inlet/outlet). Therefore, detailed knowledge of water flow is crucial for identifying areas that promote degradation and optimise surface flow wetlands. The present study combines 3D water flow numerical modelling and liquid chromatography coupled with high-resolution mass spectrometry (LC-HRMS/MS). Using this numerical model, validated by tracer experimental data, several velocity areas were distinguished in the wetland. Four areas were selected to investigate the waterflow influence and led to the following results: on the one hand, the number and concentration of micropollutants are independent of the waterflow, which could be due to several assumptions, such as the chronic exposure associated with a low Reynolds number; on the other hand, the potential degradation products (metabolites) were also assessed in the sludge to investigate the micropollutant biodegradation processes occurring in the wetland; micropollutant metabolites or degradation products were detected in higher proportions (both number and concentration) in lower flow rate areas. The relation to higher levels of plant and microorganism metabolites suggests higher biological activity that promotes degradation.}, } @article {pmid33268359, year = {2020}, author = {Milana, E and Zhang, R and Vetrano, MR and Peerlinck, S and De Volder, M and Onck, PR and Reynaerts, D and Gorissen, B}, title = {Metachronal patterns in artificial cilia for low Reynolds number fluid propulsion.}, journal = {Science advances}, volume = {6}, number = {49}, pages = {}, pmid = {33268359}, issn = {2375-2548}, abstract = {Cilia are hair-like organelles, present in arrays that collectively beat to generate flow. Given their small size and consequent low Reynolds numbers, asymmetric motions are necessary to create a net flow. Here, we developed an array of six soft robotic cilia, which are individually addressable, to both mimic nature's symmetry-breaking mechanisms and control asymmetries to study their influence on fluid propulsion. Our experimental tests are corroborated with fluid dynamics simulations, where we find a good agreement between both and show how the kymographs of the flow are related to the phase shift of the metachronal waves. Compared to synchronous beating, we report a 50% increase of net flow speed when cilia move in an antiplectic wave with phase shift of -π/3 and a decrease for symplectic waves. Furthermore, we observe the formation of traveling vortices in the direction of the wave when metachrony is applied.}, } @article {pmid33266252, year = {2020}, author = {Morimatsu, H and Tsukahara, T}, title = {Laminar-Turbulent Intermittency in Annular Couette-Poiseuille Flow: Whether a Puff Splits or Not.}, journal = {Entropy (Basel, Switzerland)}, volume = {22}, number = {12}, pages = {}, pmid = {33266252}, issn = {1099-4300}, abstract = {Direct numerical simulations were carried out with an emphasis on the intermittency and localized turbulence structure occurring within the subcritical transitional regime of a concentric annular Couette-Poiseuille flow. In the annular system, the ratio of the inner to outer cylinder radius is an important geometrical parameter affecting the large-scale nature of the intermittency. We chose a low radius ratio of 0.1 and imposed a constant pressure gradient providing practically zero shear on the inner cylinder such that the base flow was approximated to that of a circular pipe flow. Localized turbulent puffs, that is, axial uni-directional intermittencies similar to those observed in the transitional circular pipe flow, were observed in the annular Couette-Poiseuille flow. Puff splitting events were clearly observed rather far from the global critical Reynolds number, near which given puffs survived without a splitting event throughout the observation period, which was as long as 104 outer time units. The characterization as a directed-percolation universal class was also discussed.}, } @article {pmid33252039, year = {2020}, author = {Asadzadeh, SS and Kiørboe, T and Larsen, PS and Leys, SP and Yahel, G and Walther, JH}, title = {Hydrodynamics of sponge pumps and evolution of the sponge body plan.}, journal = {eLife}, volume = {9}, number = {}, pages = {}, pmid = {33252039}, issn = {2050-084X}, support = {7014-00033B//Danish council for Independent Research/International ; 9278//Villum Fonden/International ; 2016-05446//NSERC/International ; }, mesh = {Animals ; *Biological Evolution ; Hydrodynamics ; Porifera/*anatomy & histology/*physiology ; }, abstract = {Sponges are suspension feeders that filter vast amounts of water. Pumping is carried out by flagellated chambers that are connected to an inhalant and exhalant canal system. In 'leucon' sponges with relatively high-pressure resistance due to a complex and narrow canal system, pumping and filtering are only possible owing to the presence of a gasket-like structure (forming a canopy above the collar filters). Here, we combine numerical and experimental work and demonstrate how sponges that lack such sealing elements are able to efficiently pump and force the flagella-driven flow through their collar filter, thanks to the formation of a 'hydrodynamic gasket' above the collar. Our findings link the architecture of flagellated chambers to that of the canal system, and lend support to the current view that the sponge aquiferous system evolved from an open-type filtration system, and that the first metazoans were filter feeders.}, } @article {pmid33244217, year = {2020}, author = {Arumuru, V and Pasa, J and Samantaray, SS}, title = {Experimental visualization of sneezing and efficacy of face masks and shields.}, journal = {Physics of fluids (Woodbury, N.Y. : 1994)}, volume = {32}, number = {11}, pages = {115129}, pmid = {33244217}, issn = {1070-6631}, abstract = {In the present work, we propose and demonstrate a simple experimental visualization to simulate sneezing by maintaining dynamic similarity to actual sneezing. A pulsed jet with Reynolds number Re = 30 000 is created using compressed air and a solenoid valve. Tracer particles are introduced in the flow to capture the emulated turbulent jet formed due to a sneeze. The visualization is accomplished using a camera and laser illumination. It is observed that a typical sneeze can travel up to 25 ft in ∼22 s in a quiescent environment. This highlights that the present widely accepted safe distance of 6 ft is highly underestimated, especially under the act of a sneeze. Our study demonstrates that a three-layer homemade mask is just adequate to impede the penetration of fine-sized particles, which may cause the spreading of the infectious pathogen responsible for COVID-19. However, a surgical mask cannot block the sneeze, and the sneeze particle can travel up to 2.5 ft. We strongly recommend using at least a three-layer homemade mask with a social distancing of 6 ft to combat the transmission of COVID-19 virus. In offices, we recommend the use of face masks and shields to prevent the spreading of droplets carrying the infectious pathogen. Interestingly, an N-95 mask blocks the sneeze in the forward direction; however, the leakage from the sides and top spreads the sneeze in the backward direction up to 2 ft. We strongly recommend using the elbow or hands to prevent droplet leakage even after wearing a mask during sneezing and coughing.}, } @article {pmid33244213, year = {2020}, author = {Mallik, AK and Mukherjee, S and Panchagnula, MV}, title = {An experimental study of respiratory aerosol transport in phantom lung bronchioles.}, journal = {Physics of fluids (Woodbury, N.Y. : 1994)}, volume = {32}, number = {11}, pages = {111903}, pmid = {33244213}, issn = {1070-6631}, abstract = {The transport and deposition of micrometer-sized particles in the lung is the primary mechanism for the spread of aerosol borne diseases such as corona virus disease-19 (COVID-19). Considering the current situation, modeling the transport and deposition of drops in human lung bronchioles is of utmost importance to determine their consequences on human health. The current study reports experimental observations on deposition in micro-capillaries, representing distal lung bronchioles, over a wide range of Re that imitates the particle dynamics in the entire lung. The experiment investigated deposition in tubes of diameter ranging from 0.3 mm to 2 mm and over a wide range of Reynolds number (10[-2] ⩽ Re ⩽ 10[3]). The range of the tube diameter and Re used in this study is motivated by the dimensions of lung airways and typical breathing flow rates. The aerosol fluid was loaded with boron doped carbon quantum dots as fluorophores. An aerosol plume was generated from this mixture fluid using an ultrasonic nebulizer, producing droplets with 6.5 µm as a mean diameter and over a narrow distribution of sizes. The amount of aerosol deposited on the tube walls was measured using a spectrofluorometer. The experimental results show that dimensionless deposition (δ) varies inversely with the bronchiole aspect ratio (L ¯), with the effect of the Reynolds number (Re) being significant only at low L ¯ . δ also increased with increasing dimensionless bronchiole diameter (D ¯), but it is invariant with the particle size based Reynolds number. We show that δ L ¯ ∼ R e - 2 for 10[-2] ⩽ Re ⩽ 1, which is typical of a diffusion dominated regime. For Re ⩾ 1, in the impaction dominated regime, δ L ¯ is shown to be independent of Re. We also show a crossover regime where sedimentation becomes important. The experimental results conclude that lower breathing frequency and higher breath hold time could significantly increase the chances of getting infected with COVID-19 in crowded places.}, } @article {pmid33220061, year = {2020}, author = {Battista, NA}, title = {Diving into a Simple Anguilliform Swimmer's Sensitivity.}, journal = {Integrative and comparative biology}, volume = {60}, number = {5}, pages = {1236-1250}, doi = {10.1093/icb/icaa131}, pmid = {33220061}, issn = {1557-7023}, mesh = {Animals ; Biomechanical Phenomena ; Caenorhabditis elegans ; *Locomotion ; *Models, Biological ; Motion ; *Swimming ; }, abstract = {Computational models of aquatic locomotion range from modest individual simple swimmers in 2D to sophisticated 3D multi-swimmer models that attempt to parse collective behavioral dynamics. Each of these models contain a multitude of model input parameters to which its outputs are inherently dependent, that is, various performance metrics. In this work, the swimming performance's sensitivity to parameters is investigated for an idealized, simple anguilliform swimming model in 2D. The swimmer considered here propagates forward by dynamically varying its body curvature, similar to motion of a Caenorhabditis elegans. The parameter sensitivities were explored with respect to the fluid scale (Reynolds number), stroke (undulation) frequency, as well as a kinematic parameter controlling the velocity and acceleration of each upstroke and downstroke. The input Reynolds number and stroke frequencies sampled were from [450, 2200] and [1, 3] Hz, respectively. In total, 5000 fluid-structure interaction simulations were performed, each with a unique parameter combination selected via a Sobol sequence, in order to conduct global sensitivity analysis. Results indicate that the swimmer's performance is most sensitive to variations in its stroke frequency. Trends in swimming performance were discovered by projecting the performance data onto particular 2D subspaces. Pareto-like optimal fronts were identified. This work is a natural extension of the parameter explorations of the same model from Battista in 2020.}, } @article {pmid33212661, year = {2020}, author = {Gungor, A and Hemmati, A}, title = {Wake symmetry impacts the performance of tandem hydrofoils during in-phase and out-of-phase oscillations differently.}, journal = {Physical review. E}, volume = {102}, number = {4-1}, pages = {043104}, doi = {10.1103/PhysRevE.102.043104}, pmid = {33212661}, issn = {2470-0053}, abstract = {The hydrodynamics of two oscillating foils in side-by-side configuration is numerically investigated for in-phase and out-of-phase pitching at Reynolds number of 4000 and Strouhal numbers of St=0.25-0.5. The effects of phase difference (in-phase and out-of-phase) and Strouhal number on symmetric attributes of the wake and unsteady propulsive performance of the foils are studied in detail. At lower Strouhal numbers, there is a quasisteady performance in both thrust generation and power consumption, which coincides with persistence of the wake symmetry. As Strouhal number increases, however, in-phase and out-of-phase pitching display unsteady cycle-averaged behavior with very different wake characteristics. The asymmetric wake of in-phase pitching foils at high Strouhal numbers transitions to a quasisymmetric wake, when an extensive interaction between the two vortex streets is observed in the wake. This coincides with an improvement on the propulsive performance of the foils. In contrast, the symmetric wake of the out-of-phase pitching foils at a high Strouhal number transitions to an asymmetric wake. The adverse effect of this transition is only observed on the propulsive performance of one foil while the other exploits the wake towards a better performance. The collective performance of the the out-of-phase pitching system, however, remains unchanged. There is also a strong correlation between the wake symmetric characteristics and total nonzero side-force production.}, } @article {pmid33212599, year = {2020}, author = {Inubushi, M and Goto, S}, title = {Transfer learning for nonlinear dynamics and its application to fluid turbulence.}, journal = {Physical review. E}, volume = {102}, number = {4-1}, pages = {043301}, doi = {10.1103/PhysRevE.102.043301}, pmid = {33212599}, issn = {2470-0053}, abstract = {We introduce transfer learning for nonlinear dynamics, which enables efficient predictions of chaotic dynamics by utilizing a small amount of data. For the Lorenz chaos, by optimizing the transfer rate, we accomplish more accurate inference than the conventional method by an order of magnitude. Moreover, a surprisingly small amount of learning is enough to infer the energy dissipation rate of the Navier-Stokes turbulence because we can, thanks to the small-scale universality of turbulence, transfer a large amount of the knowledge learned from turbulence data at lower Reynolds number.}, } @article {pmid33211148, year = {2021}, author = {Ikoma, T and Suwa, K and Sano, M and Ushio, T and Saotome, M and Ogawa, N and Satoh, H and Maekawa, Y}, title = {Early changes of pulmonary arterial hemodynamics in patients with systemic sclerosis: flow pattern, WSS, and OSI analysis with 4D flow MRI.}, journal = {European radiology}, volume = {31}, number = {6}, pages = {4253-4263}, pmid = {33211148}, issn = {1432-1084}, mesh = {Blood Flow Velocity ; Hemodynamics ; Humans ; *Hypertension, Pulmonary/diagnostic imaging ; Magnetic Resonance Imaging ; Pulmonary Artery/diagnostic imaging ; *Scleroderma, Systemic/complications/diagnostic imaging ; Stress, Mechanical ; }, abstract = {OBJECTIVES: To study the pulmonary artery (PA) hemodynamics in patients with systemic sclerosis (SSc) using 4D flow MRI (4D-flow).

METHODS: Twenty-three patients with SSc (M/F: 2/21, 57 ± 15 years, 3 manifest PA hypertension (PAH) by right heart catheterization) and 10 control subjects (M/F: 1/9, 55 ± 17 years) underwent 4D-flow for the in vivo measurement of 3D blood flow velocities in the PA. Data analysis included area-averaged flow quantification at the main PA, 3D wall shear stress (WSS), oscillatory shear index (OSI) calculation along the PA surface, and Reynolds number. The composite outcome of all-cause death and major adverse cardiac events was also investigated.

RESULTS: The maximum PA flow at the systole did not differ, but the minimum flow at the diastole was significantly greater in patients with SSc compared with that in control subjects (7.7 ± 16.0 ml/s vs. ‑ 13.0 ± 17.3 ml/s, p < 0.01). The maximum WSS at the peak systole was significantly lower and OSI was significantly greater in patients with SSc compared with those in control subjects (maximum WSS: 1.04 ± 0.20 Pa vs. 1.33 ± 0.34 Pa, p < 0.01, OSI: 0.139 ± 0.031 vs. 0.101 ± 0.037, p < 0.01). The cumulative event-free rate for the composite event was significantly lower in patients with minimum flow in main PA ≤ 9.22 ml/s (p = 0.012) and in patients with Reynolds number ≤ 2560 (p < 0.001).

CONCLUSIONS: 4D-flow has the potential to detect changes of PA hemodynamics noninvasively and predict the outcome in patients with SSc at the stage before manifest PAH.

KEY POINTS: • The WSS at the peak systolic phase was significantly lower (p < 0.05), whereas OSI was greater (p < 0.01) in patients with SSc without manifest PAH than in controls. • The hemodynamic change detected by 4D-flow may help patient management even at the stage before manifest PAH in SSc. • The minimum PA flow and Reynolds number by 4D-flow will serve as a predictive marker for SSc.}, } @article {pmid33201951, year = {2021}, author = {Lochab, V and Prakash, S}, title = {Combined electrokinetic and shear flows control colloidal particle distribution across microchannel cross-sections.}, journal = {Soft matter}, volume = {17}, number = {3}, pages = {611-620}, pmid = {33201951}, issn = {1744-6848}, support = {P30 CA016058/CA/NCI NIH HHS/United States ; R01 HL141941/HL/NHLBI NIH HHS/United States ; }, abstract = {Recent experimental observations on combined electrokinetic and shear flows of colloidal suspensions in rectangular cross-section microfluidic channels have shown unusual cross-stream colloidal particle migration and dynamic assembly. Although a new electrophoresis-induced lift force has been postulated to cause the lateral migration of colloidal particles, little is known about how fluid properties and flow conditions impact this force and therefore subsequent colloidal particle migration. Furthermore, no experimental quantification of this electrophoresis-induced lift force is available. We report several key advances by demonstrating that the kinematic viscosity of the fluid can be used to modulate the spatial distribution of particles over the entire microchannel cross-section, with suppression of the colloidal particle migration observed with increase in fluid kinematic viscosity. Colloidal particle migration of ∼10 μm from not only the top and bottom microchannel walls but also from the side walls is shown with the corresponding electrophoresis-induced lift force of up to ∼30 fN. The breadth of flow conditions tested capture the channel Reynolds number in the 0.1-1.1 range, with inertial migration of colloidal particles shown in flow regimes where the migration was previously thought to be ineffective, if not for the electrophoresis-induced lift force. The ability of the electrophoresis-induced lift force to migrate colloidal particles across the entire microchannel cross-section establishes a new paradigm for three-dimensional control of colloidal particles within confined microchannels.}, } @article {pmid33199601, year = {2020}, author = {Omori, T and Ito, H and Ishikawa, T}, title = {Swimming microorganisms acquire optimal efficiency with multiple cilia.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {117}, number = {48}, pages = {30201-30207}, pmid = {33199601}, issn = {1091-6490}, mesh = {Bacteria/*metabolism ; Cilia/*physiology ; Hydrodynamics ; Movement ; Rheology ; }, abstract = {Planktonic microorganisms are ubiquitous in water, and their population dynamics are essential for forecasting the behavior of global aquatic ecosystems. Their population dynamics are strongly affected by these organisms' motility, which is generated by their hair-like organelles, called cilia or flagella. However, because of the complexity of ciliary dynamics, the precise role of ciliary flow in microbial life remains unclear. Here, we have used ciliary hydrodynamics to show that ciliates acquire the optimal propulsion efficiency. We found that ciliary flow highly resists an organism's propulsion and that the swimming velocity rapidly decreases with body size, proportional to the power of minus two. Accordingly, the propulsion efficiency decreases as the cube of body length. By increasing the number of cilia, however, efficiency can be significantly improved, up to 100-fold. We found that there exists an optimal number density of cilia, which provides the maximum propulsion efficiency for all ciliates. The propulsion efficiency in this case decreases inversely proportionally to body length. Our estimated optimal density of cilia corresponds to those of actual microorganisms, including species of ciliates and microalgae, which suggests that now-existing motile ciliates and microalgae have survived by acquiring the optimal propulsion efficiency. These conclusions are helpful for better understanding the ecology of microorganisms, such as the energetic costs and benefits of multicellularity in Volvocaceae, as well as for the optimal design of artificial microswimmers.}, } @article {pmid33199599, year = {2020}, author = {Andersen, A and Kiørboe, T}, title = {The effect of tethering on the clearance rate of suspension-feeding plankton.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {117}, number = {48}, pages = {30101-30103}, pmid = {33199599}, issn = {1091-6490}, mesh = {Feeding Behavior/*physiology ; Models, Biological ; Plankton/*physiology ; Rheology ; Suspensions ; Swimming ; }, abstract = {Many planktonic suspension feeders are attached to particles or tethered by gravity when feeding. It is commonly accepted that the feeding flows of tethered suspension feeders are stronger than those of their freely swimming counterparts. However, recent flow simulations indicate the opposite, and the cause of the opposing conclusions is not clear. To explore the effect of tethering on suspension feeding, we use a low-Reynolds-number flow model. We find that it is favorable to be freely swimming instead of tethered since the resulting feeding flow past the cell body is stronger, leading to a higher clearance rate. Our result underscores the significance of the near-field flow in shaping planktonic feeding modes, and it suggests that organisms tether for reasons that are not directly fluid dynamical (e.g., to stay near surfaces where the concentration of bacterial prey is high).}, } @article {pmid33197195, year = {2020}, author = {Hatte, S and Pitchumani, R}, title = {Fractal Model for Drag Reduction on Multiscale Nonwetting Rough Surfaces.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {36}, number = {47}, pages = {14386-14402}, doi = {10.1021/acs.langmuir.0c02790}, pmid = {33197195}, issn = {1520-5827}, abstract = {Rough surfaces in contact with a flow of fluid exhibit alternating no-slip and free shear boundary conditions at the solid-liquid and air-liquid interfaces, respectively, thereby potentially offering drag reduction benefits. The balance between the dynamic pressure in the flow and the restoring capillary pressure in the interasperity spaces determines the stability of the Cassie state of wettability and is a function of the relative extent of no-slip and free shear regions per unit surface area. In the present study, using a fractal representation of rough surface topography, an analytical model is developed to quantify the stability of the Cassie state of wettability as well as drag reduction and the friction factor for laminar flow in a rectangular channel between nonwetting multiscale rough surfaces. A systematic study is conducted to quantify the effects of fractal parameters of the surfaces and the flow Reynolds number on drag reduction and the friction factor. The studies are used to develop friction factor curves extending the classical Moody diagram to hydrophobic and superhydrophobic surfaces. On the basis of the studies, regime maps are derived for estimating the extent of drag reduction offered by hydrophobic and superhydrophobic surfaces, revealing that superhydrophobic surfaces do not always offer the best drag reduction performance. The application of the fractal model to practical topographies of nonwetting surfaces of copper, aluminum, and zinc oxide fabricated via electrodeposition and etching is also discussed.}, } @article {pmid33184652, year = {2020}, author = {Rader, JA and Hedrick, TL and He, Y and Waldrop, LD}, title = {Functional Morphology of Gliding Flight II. Morphology Follows Predictions of Gliding Performance.}, journal = {Integrative and comparative biology}, volume = {60}, number = {5}, pages = {1297-1308}, doi = {10.1093/icb/icaa126}, pmid = {33184652}, issn = {1557-7023}, mesh = {Animals ; Biomechanical Phenomena ; *Birds ; *Flight, Animal ; Models, Biological ; *Wings, Animal ; }, abstract = {The evolution of wing morphology among birds, and its functional consequences, remains an open question, despite much attention. This is in part because the connection between form and function is difficult to test directly. To address this deficit, in prior work, we used computational modeling and sensitivity analysis to interrogate the impact of altering wing aspect ratio (AR), camber, and Reynolds number on aerodynamic performance, revealing the performance landscapes that avian evolution has explored. In the present work, we used a dataset of three-dimensionally scanned bird wings coupled with the performance landscapes to test two hypotheses regarding the evolutionary diversification of wing morphology associated with gliding flight behavior: (1) gliding birds would exhibit higher wing AR and greater chordwise camber than their non-gliding counterparts; and (2) that two strategies for gliding flight exist, with divergent morphological conformations. In support of our first hypothesis, we found evidence of morphological divergence in both wing AR and camber between gliders and non-gliders, suggesting that wing morphology of birds that utilize gliding flight is under different selective pressures than the wings of non-gliding taxa. Furthermore, we found that these morphological differences also yielded differences in coefficient of lift measured both at the maximum lift to drag ratio and at minimum sinking speed, with gliding taxa exhibiting higher coefficient of lift in both cases. Minimum sinking speed was also lower in gliders than non-gliders. However, contrary to our hypothesis, we found that the maximum ratio of the coefficient of lift to the coefficient of drag differed between gliders and non-gliders. This may point to the need for gliders to maintain high lift capability for takeoff and landing independent of gliding performance or could be due to the divergence in flight styles among gliders, as not all gliders are predicted to optimize either quantity. However, direct evidence for the existence of two morphologically defined gliding flight strategies was equivocal, with only slightly stronger support for an evolutionary model positing separate morphological optima for these strategies than an alternative model positing a single peak. The absence of a clear result may be an artifact of low statistical power owing to a relatively small sample size of gliding flyers expected to follow the "aerial search" strategy.}, } @article {pmid33184554, year = {2020}, author = {Lee, JY and Kottke, PA and Fedorov, AG}, title = {Hydrodynamics of Vortical Gas Jets Coupled to Point-Like Suction.}, journal = {Physics of fluids (Woodbury, N.Y. : 1994)}, volume = {32}, number = {10}, pages = {}, pmid = {33184554}, issn = {1070-6631}, support = {R01 GM112662/GM/NIGMS NIH HHS/United States ; }, abstract = {Vortical jet flows in the Reynolds number (Re) range from 1000 to 3425 and swirl number (S) below 0.5, alone and in combination with suction through a small aperture, are experimentally investigated using optical visualization. Schlieren photography is employed to assess the vortical flow structure and establish the fundamental understanding of the source-to-sink gas-dynamic coupling, including the role played by flow rate, jet diameter, and the separation distance between the gas jet source and the suction sink. Compared to vortex-free jets, vortical jets for Re>2700 with swirl number S>0.27 experience earlier laminar-to-turbulent transition, with resulting rapid growth of the jet boundary. The ability to control growth of the jet expansion and mass and momentum dissipation into the surrounding is demonstrated via use of a coaxially aligned flow suction placed in the path of a jet. When a swirling jet is completely coupled with a flow suction, jet expansion is significantly suppressed. The suction/sink flow rate imposes a limit on the maximum input/source flow rate of gas jet to achieve complete coupling. Furthermore, there is a maximum distance over which effective coupling can occur, and for all Reynolds numbers considered this distance is shorter than the distance at which the jet structure breaks up into turbulent eddies in the absence of a sink.}, } @article {pmid33172214, year = {2020}, author = {Astudillo-Castro, C and Cordova, A and Oyanedel-Craver, V and Soto-Maldonado, C and Valencia, P and Henriquez, P and Jimenez-Flores, R}, title = {Prediction of the Limiting Flux and Its Correlation with the Reynolds Number during the Microfiltration of Skim Milk Using an Improved Model.}, journal = {Foods (Basel, Switzerland)}, volume = {9}, number = {11}, pages = {}, pmid = {33172214}, issn = {2304-8158}, abstract = {Limiting flux (JL) determination is a critical issue for membrane processing. This work presents a modified exponential model for JL calculation, based on a previously published version. Our research focused on skim milk microfiltrations. The processing variables studied were the crossflow velocity (CFV), membrane hydraulic diameter (dh), temperature, and concentration factor, totaling 62 experimental runs. Results showed that, by adding a new parameter called minimum transmembrane pressure, the modified model not only improved the fit of the experimental data compared to the former version (R[2] > 97.00%), but also revealed the existence of a minimum transmembrane pressure required to obtain flux (J). This result is observed as a small shift to the right on J versus transmembrane pressure curves, and this shift increases with the flow velocity. This fact was reported in other investigations, but so far has gone uninvestigated. The JL predicted values were correlated with the Reynolds number (Re) for each dh tested. Results showed that for a same Re; JL increased as dh decreased; in a wide range of Re within the turbulent regime. Finally, from dimensionless correlations; a unique expression JL = f (Re, dh) was obtained; predicting satisfactorily JL (R[2] = 84.11%) for the whole set of experiments.}, } @article {pmid33171451, year = {2021}, author = {Ford, MP and Santhanakrishnan, A}, title = {On the role of phase lag in multi-appendage metachronal swimming of euphausiids.}, journal = {Bioinspiration & biomimetics}, volume = {16}, number = {6}, pages = {}, doi = {10.1088/1748-3190/abc930}, pmid = {33171451}, issn = {1748-3190}, mesh = {Biomechanical Phenomena ; *Extremities ; Gait ; *Swimming ; }, abstract = {Metachronal paddling is a common method of drag-based aquatic propulsion, in which a series of swimming appendages are oscillated, with the motion of each appendage phase-shifted relative to the neighboring appendages. Ecologically and economically important euphausiid species such as Antarctic krill (Euphausia superba) swim constantly by stroking their paddling appendages (pleopods), with locomotion accounting for the bulk of their metabolic expenditure. They tailor their swimming gaits for behavioral and energetic needs by changing pleopod kinematics. The functional importance of inter-pleopod phase lag (ϕ) to metachronal swimming performance and wake structure is unknown. To examine this relation, we developed a geometrically and dynamically scaled robot ('krillbot') capable of self-propulsion. Krillbot pleopods were prescribed to mimic published kinematics of fast-forward swimming (FFW) and hovering (HOV) gaits ofE. superba, and the Reynolds number and Strouhal number of the krillbot matched well with those calculated for freely-swimmingE. superba. In addition to examining published kinematics with unevenϕbetween pleopod pairs, we modifiedE. superbakinematics to uniformly varyϕfrom 0% to 50% of the cycle. Swimming speed and thrust were largest for FFW withϕbetween 15%-25%, coincident withϕrange observed in FFW gait ofE. superba. In contrast to synchronous rowing (ϕ= 0%) where distances between hinged joints of adjacent pleopods were nearly constant throughout the cycle, metachronal rowing (ϕ> 0%) brought adjacent pleopods closer together and moved them farther apart. This factor minimized body position fluctuation and augmented metachronal swimming speed. Though swimming speed was lowest for HOV, a ventrally angled downward jet was generated that can assist with weight support during feeding. In summary, our findings show that inter-appendage phase lag can drastically alter both metachronal swimming speed and the large-scale wake structure.}, } @article {pmid33159347, year = {2020}, author = {Ichikawa, C and Ishikawa, D and Yang, JM and Fujii, T}, title = {Phenomenological analysis on whipping behavior of rice flour batter.}, journal = {Journal of food science}, volume = {85}, number = {12}, pages = {4327-4334}, pmid = {33159347}, issn = {1750-3841}, mesh = {Edible Grain/*chemistry ; *Food ; Food Handling ; Oryza/*chemistry ; Particle Size ; Powders ; Surface Tension ; Viscosity ; Wettability ; }, abstract = {In this study, the bubbles in rice flour batter were investigated under a constant temperature, because the bubble size distribution is important for the control of food texture. We obtained experimental data using a hand mixer and compared the properties of doughs prepared using six rice flours; each flour was prepared through a different milling process. We also added the size effect of the rice flour particles as the Bond number. Furthermore, we performed a dynamic wettability test to estimate the wettability of the rice flour surface. The results of this test were described well by the Washburn equation, and dc cosθ/dp was calculated as a wettability parameter (where, dc = effective diameter of a capillary in a powder bed, cosθ = the contact angle, dp = mean particle diameter of rice flour). If bubble sizes depend mainly on the inertial force, viscous force, surface tension, and gravity, then the normalized mean bubble diameter should be a function of the Reynolds number, Weber number, and Froude number. The mean bubble diameter (dbm) generated by whipping was expected to be affected by the thickness (d) of the rod of the mixer, its movement speed, and physical properties of the material. Therefore, dimensionless mean diameter (dbm /d) was expressed based on a dimensionless equation. In the three-phase dispersion, different empirical equations were obtained depending on the amount of rice flour added, and the bubble diameter could be predicted using dimensionless parameters. In addition, the equations were generally applicable to the various materials selected for this study. PRACTICAL APPLICATION: The powder properties of rice flour were investigated, and dimensionless parameters were analyzed to construct an appropriate process control system for rice flour-based food products. Although the process method optimized for flour products is also used for rice flour products in practical situations, the comprehensive evaluation based on dimensionless parameters leads to optimization of the process for rice-flour based products. Moreover, this optimization might strongly support the creation of a new texture, and thus, the potential for market expansion of rice-flour based products is considerable.}, } @article {pmid33158219, year = {2020}, author = {Sana, S and Zivkovic, V and Boodhoo, K}, title = {Empirical Modelling of Hydrodynamic Effects on Starch Nanoparticles Precipitation in a Spinning Disc Reactor.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {10}, number = {11}, pages = {}, pmid = {33158219}, issn = {2079-4991}, abstract = {Empirical correlations have been developed to relate experimentally determined starch nanoparticle size obtained in a solvent-antisolvent precipitation process with key hydrodynamic parameters of a spinning disc reactor (SDR). Three different combinations of dimensionless groups including a conventional Reynolds number (Re), rotational Reynolds number (Reω) and Rossby number (Ro) have been applied in individual models for two disc surfaces (smooth and grooved) to represent operating variables affecting film flow such as liquid flowrate and disc rotational speed, whilst initial supersaturation (S) has been included to represent varying antisolvent concentrations. Model 1 featuring a combination of Re, Reω and S shows good agreement with the experimental data for both the grooved and smooth discs. For the grooved disc, Re has a greater impact on particle size, whereas Reω is more influential on the smooth disc surface, the difference likely being due to the passive mixing induced by the grooves irrespective of the magnitude of the disc speed. Supersaturation has little impact on particle size within the limited initial supersaturation range studied. Model 2 which characterises both flow rate and disc rotational speed through Ro alone and combined with Re was less accurate in predicting particle size due to several inherent limitations.}, } @article {pmid33157545, year = {2021}, author = {Harvey, C and Inman, DJ}, title = {Aerodynamic efficiency of gliding birds vs comparable UAVs: a review.}, journal = {Bioinspiration & biomimetics}, volume = {16}, number = {3}, pages = {}, doi = {10.1088/1748-3190/abc86a}, pmid = {33157545}, issn = {1748-3190}, mesh = {Animals ; Biomechanical Phenomena ; Birds ; *Flight, Animal ; *Wings, Animal ; }, abstract = {Here, we reviewed published aerodynamic efficiencies of gliding birds and similar sized unmanned aerial vehicles (UAVs) motivated by a fundamental question: are gliding birds more efficient than comparable UAVs? Despite a multitude of studies that have quantified the aerodynamic efficiency of gliding birds, there is no comprehensive summary of these results. This lack of consolidated information inhibits a true comparison between birds and UAVs. Such a comparison is complicated by variable uncertainty levels between the different techniques used to predict avian efficiency. To support our comparative approach, we began by surveying theoretical and experimental estimates of avian aerodynamic efficiency and investigating the uncertainty associated with each estimation method. We found that the methodology used by a study affects the estimated efficiency and can lead to incongruent conclusions on gliding bird aerodynamic efficiency. Our survey showed that studies on live birds gliding in wind tunnels provide a reliable minimum estimate of a birds' aerodynamic efficiency while simultaneously quantifying the wing configurations used in flight. Next, we surveyed the aeronautical literature to collect the published aerodynamic efficiencies of similar-sized, non-copter UAVs. The compiled information allowed a direct comparison of UAVs and gliding birds. Contrary to our expectation, we found that there is no definitive evidence that any gliding bird species is either more or less efficient than a comparable UAV. This non-result highlights a critical need for new technology and analytical advances that can reduce the uncertainty associated with estimating a gliding bird's aerodynamic efficiency. Nevertheless, our survey indicated that species flying within subcritical Reynolds number regimes may inspire UAV designs that can extend their operational range to efficiently operate in subcritical regimes. The survey results provided here point the way forward for research into avian gliding flight and enable informed UAV designs.}, } @article {pmid33156686, year = {2020}, author = {Friedrich, J and Gallon, S and Pumir, A and Grauer, R}, title = {Stochastic Interpolation of Sparsely Sampled Time Series via Multipoint Fractional Brownian Bridges.}, journal = {Physical review letters}, volume = {125}, number = {17}, pages = {170602}, doi = {10.1103/PhysRevLett.125.170602}, pmid = {33156686}, issn = {1079-7114}, abstract = {We propose and test a method to interpolate sparsely sampled signals by a stochastic process with a broad range of spatial and/or temporal scales. To this end, we extend the notion of a fractional Brownian bridge, defined as fractional Brownian motion with a given scaling (Hurst) exponent H and with prescribed start and end points, to a bridge process with an arbitrary number of intermediate and nonequidistant points. Determining the optimal value of the Hurst exponent H_{opt}, appropriate to interpolate the sparse signal, is a very important step of our method. We demonstrate the validity of our method on a signal from fluid turbulence in a high Reynolds number flow and discuss the implications of the non-self-similar character of the signal. The method introduced here could be instrumental in several physical problems, including astrophysics, particle tracking, and specific tailoring of surrogate data, as well as in domains of natural and social sciences.}, } @article {pmid33153075, year = {2020}, author = {Coclite, A and Coclite, GM and De Tommasi, D}, title = {Capsules Rheology in Carreau-Yasuda Fluids.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {10}, number = {11}, pages = {}, pmid = {33153075}, issn = {2079-4991}, abstract = {In this paper, a Multi Relaxation Time Lattice Boltzmann scheme is used to describe the evolution of a non-Newtonian fluid. Such method is coupled with an Immersed-Boundary technique for the transport of arbitrarily shaped objects navigating the flow. The no-slip boundary conditions on immersed bodies are imposed through a convenient forcing term accounting for the hydrodynamic force generated by the presence of immersed geometries added to momentum equation. Moreover, such forcing term accounts also for the force induced by the shear-dependent viscosity model characterizing the non-Newtonian behavior of the considered fluid. Firstly, the present model is validated against well-known benchmarks, namely the parabolic velocity profile obtained for the flow within two infinite laminae for five values of the viscosity model exponent, n = 0.25, 0.50, 0.75, 1.0, and 1.5. Then, the flow within a squared lid-driven cavity for Re = 1000 and 5000 (being Re the Reynolds number) is computed as a function of n for a shear-thinning (n < 1) fluid. Indeed, the local decrements in the viscosity field achieved in high-shear zones implies the increment in the local Reynolds number, thus moving the position of near-walls minima towards lateral walls. Moreover, the revolution under shear of neutrally buoyant plain elliptical capsules with different Aspect Ratio (AR = 2 and 3) is analyzed for shear-thinning (n < 1), Newtonian (n = 1), and shear-thickening (n > 1) surrounding fluids. Interestingly, the power law by Huang et al. describing the revolution period of such capsules as a function of the Reynolds number and the existence of a critical value, Rec, after which the tumbling is inhibited in confirmed also for non-Newtonian fluids. Analogously, the equilibrium lateral position yeq of such neutrally buoyant capsules when transported in a plane-Couette flow is studied detailing the variation of yeq as a function of the Reynolds number as well as of the exponent n.}, } @article {pmid33152635, year = {2020}, author = {Kim, J and Jin, D and Choi, H and Kweon, J and Yang, DH and Kim, YH}, title = {A zero-dimensional predictive model for the pressure drop in the stenotic coronary artery based on its geometric characteristics.}, journal = {Journal of biomechanics}, volume = {113}, number = {}, pages = {110076}, doi = {10.1016/j.jbiomech.2020.110076}, pmid = {33152635}, issn = {1873-2380}, mesh = {Blood Flow Velocity ; Constriction, Pathologic ; Coronary Angiography ; *Coronary Stenosis/diagnostic imaging ; *Coronary Vessels/diagnostic imaging ; Humans ; Models, Cardiovascular ; Models, Statistical ; }, abstract = {The diameter- or area-reduction ratio measured from coronary angiography, commonly used in clinical practice, is not accurate enough to represent the functional significance of the stenosis, i.e., the pressure drop across the stenosis. We propose a new zero-dimensional model for the pressure drop across the stenosis considering its geometric characteristics and flow rate. To identify the geometric parameters affecting the pressure drop, we perform three-dimensional numerical simulations for thirty-three patient-specific coronary stenoses. From these numerical simulations, we show that the pressure drop is mostly determined by the curvature as well as the area-reduction ratio of the stenosis before the minimal luminal area (MLA), but heavily depends on the area-expansion ratio after the MLA due to flow separation. Based on this result, we divide the stenosis into the converging and diverging parts in the present zero-dimensional model. The converging part is segmented into a series of straight and curved pipes with curvatures, and the loss of each pipe is estimated by an empirical relation between the total pressure drop, flow rate, and pipe geometric parameters (length, diameter, and curvature). The loss in the diverging part is predicted by a relation among the total pressure drop, Reynolds number, and area expansion ratio with the coefficients determined by a machine learning method. The pressure drops across the stenoses predicted by the present zero-dimensional model agree very well with those obtained from three-dimensional numerical simulations.}, } @article {pmid33147949, year = {2020}, author = {Wang, Y and Zhou, G and Yan, Y and Shao, B and Hou, J}, title = {Construction of Natural Loofah/Poly(vinylidene fluoride) Core-Shell Electrospun Nanofibers via a Controllable Janus Nozzle for Switchable Oil-Water Separation.}, journal = {ACS applied materials & interfaces}, volume = {12}, number = {46}, pages = {51917-51926}, doi = {10.1021/acsami.0c12912}, pmid = {33147949}, issn = {1944-8252}, abstract = {Developing microstructure and multifunctional membranes toward switchable oil-water separation has been highly desired in oily wastewater treatment. Herein, a controllable Janus nozzle was employed to innovatively electrospin natural loofah/poly(vinylidene fluoride) (PVDF) nanofibers with a core-shell structure for gravity-driven water purification. By adjusting flow rates of the PVDF component, a core-shell structure of the composite fibers was obtained caused by the lower viscosity and surface tension of PVDF. In addition, a steady laminar motion of fluids was constructed based on the Reynolds number of flow fields being less than 2300. In order to investigate the formation mechanism of the microstructure, a series of Janus nozzles with different lengths were controlled to study the blending of the two immiscible components. The gravity difference between the two components might cause disturbance of the jet motion, and the PVDF component unidirectionally encapsulated the loofah to form the shell layer. Most importantly, the dry loofah/PVDF membranes could separate oil from an oil-water mixture, while the water-wetted membrane exhibited switchable separation that could separate water from the mixtures because of the hydroxyl groups of the hydrophilic loofah hydrogen-bonding with water molecules and forming a hydration layer. The composite fibers can be applied in water remediation in practice, and the method to produce core-shell structures seems attractive for technological applications involving macroscopic core-shell nano- or microfibers.}, } @article {pmid33136360, year = {2020}, author = {Jeon, W and Ahn, J and Kim, T and Kim, SM and Baik, S}, title = {Intertube Aggregation-Dependent Convective Heat Transfer in Vertically Aligned Carbon Nanotube Channels.}, journal = {ACS applied materials & interfaces}, volume = {12}, number = {45}, pages = {50355-50364}, doi = {10.1021/acsami.0c13361}, pmid = {33136360}, issn = {1944-8252}, abstract = {The heat transfer of carbon nanotube fin geometry has received considerable attention. However, the flow typically occurred over or around the pillars of nanotubes due to the greater flow resistance between the tubes. Here, we investigated the forced convective heat transfer of water through the interstitial space of vertically aligned multiwalled carbon nanotubes (VAMWNTs, intertube distance = 69 nm). The water flow provided significantly a greater Reynolds number (Re) and Nusselt number (Nu) than air flow due to the greater density, heat capacity, and thermal conductivity. However, it resulted in surface tension-induced nanotube aggregation after the flow and drying process, generating random voids in the nanotube channel. This increased permeability (1.27 × 10[-11] m[2]) and Re (2.83 × 10[-1]) but decreased the heat transfer coefficient (h, 9900 W m[-2] K[-1]) and Nu (53.77), demonstrating a trade-off relationship. The h (25,927 W m[-2] K[-1]) and Nu (153.49) could be further increased, at an equivalent permeability or Re, by increasing nanotube areal density from 2.08 × 10[10] to 1.04 × 10[11] cm[-2]. The area-normalized thermal resistance of the densified and aggregated VAMWNTs was smaller than those of the Ni foam, Si microchannel, and carbon nanotube fin array, demonstrating excellent heat transfer characteristics.}, } @article {pmid33119653, year = {2020}, author = {Lyons, K and Murphy, CT and Franck, JA}, title = {Flow over seal whiskers: Importance of geometric features for force and frequency response.}, journal = {PloS one}, volume = {15}, number = {10}, pages = {e0241142}, pmid = {33119653}, issn = {1932-6203}, mesh = {Animals ; Computer Simulation ; *Hydrodynamics ; Phoca/*anatomy & histology ; *Vibration ; Vibrissae/*anatomy & histology ; }, abstract = {The complex undulated geometry of seal whiskers has been shown to substantially modify the turbulent structures directly downstream, resulting in a reduction of hydrodynamic forces as well as modified vortex-induced-vibration response when compared with smooth whiskers. Although the unique hydrodynamic response has been well documented, an understanding of the fluid flow effects from each geometric feature remains incomplete. In this computational investigation, nondimensional geometric parameters of the seal whisker morphology are defined in terms of their hydrodynamic relevance, such that wavelength, aspect ratio, undulation amplitudes, symmetry and undulation off-set can be varied independently of one another. A two-factor fractional factorial design of experiments procedure is used to create 16 unique geometries, each of which dramatically amplifies or attenuates the geometric parameters compared with the baseline model. The flow over each unique topography is computed with a large-eddy simulation at a Reynolds number of 500 with respect to the mean whisker thickness and the effects on force and frequency are recorded. The results determine the specific fluid flow impact of each geometric feature which will inform both biologists and engineers who seek to understand the impact of whisker morphology or lay out a framework for biomimetic design of undulated structures.}, } @article {pmid33095615, year = {2020}, author = {Neuhaus, L and Hölling, M and Bos, WJT and Peinke, J}, title = {Generation of Atmospheric Turbulence with Unprecedentedly Large Reynolds Number in a Wind Tunnel.}, journal = {Physical review letters}, volume = {125}, number = {15}, pages = {154503}, doi = {10.1103/PhysRevLett.125.154503}, pmid = {33095615}, issn = {1079-7114}, abstract = {Generating laboratory flows resembling atmospheric turbulence is of prime importance to study the effect of wind fluctuations on objects such as buildings, vehicles, or wind turbines. A novel driving of an active grid following a stochastic process is used to generate velocity fluctuations with correlation lengths, and, thus, integral scales, much larger than the transverse dimension of the wind tunnel. The combined action of the active grid and a modulation of the fan speed allows one to generate a flow characterized by a four-decade inertial range and an integral scale Reynolds number of 2×10^{7} .}, } @article {pmid33092016, year = {2020}, author = {Domínguez-Pumar, M and Kowalski, L and Jiménez, V and Rodríguez, I and Soria, M and Bermejo, S and Pons-Nin, J}, title = {Analyzing the Performance of a Miniature 3D Wind Sensor for Mars.}, journal = {Sensors (Basel, Switzerland)}, volume = {20}, number = {20}, pages = {}, pmid = {33092016}, issn = {1424-8220}, abstract = {This paper analyzes the behavior of a miniature 3D wind sensor designed for Mars atmosphere. The sensor is a spherical structure of 10 mm diameter divided in four sectors. By setting all the sectors to constant temperature, above that of the air, the 3D wind velocity vector can be measured. Two sets of experiments have been performed. First, an experimental campaign made under typical Mars conditions at the Aarhus Wind Tunnel Simulator is presented. The results demonstrate that both wind speed and angle can be efficiently measured, using a simple inverse algorithm. The effect of sudden wind changes is also analyzed and fast response times in the range of 0.7 s are obtained. The second set of experiments is focused on analyzing the performance of the sensor under extreme Martian wind conditions, reaching and going beyond the Dust Devil scale. To this purpose, both high-fidelity numerical simulations of fluid dynamics and heat transfer and experiments with the sensor have been performed. The results of the experiments, made for winds in the Reynolds number 1000-2000 range, which represent 65-130 m/s of wind speed under typical Mars conditions, further confirm the simulation predictions and show that it will be possible to successfully measure wind speed and direction even under these extreme regimes.}, } @article {pmid33076024, year = {2020}, author = {Czelusniak, LE and Mapelli, VP and Guzella, MS and Cabezas-Gómez, L and Wagner, AJ}, title = {Force approach for the pseudopotential lattice Boltzmann method.}, journal = {Physical review. E}, volume = {102}, number = {3-1}, pages = {033307}, doi = {10.1103/PhysRevE.102.033307}, pmid = {33076024}, issn = {2470-0053}, abstract = {One attractive feature of the original pseudopotential method consists on its simplicity of adding a force dependent on a nearest-neighbor potential function. In order to improve the method, regarding thermodynamic consistency and control of surface tension, different approaches were developed in the literature, such as multirange interactions potential and modified forcing schemes. In this work, a strategy to combine these enhancements with an appropriate interaction force field using only nearest-neighbor interactions is devised, starting from the desired pressure tensor. The final step of our procedure is implementing this external force by using the classical Guo forcing scheme. Numerical tests regarding static and dynamic flow conditions were performed. Static tests showed that current procedure is suitable to control the surface tension and phase densities. Based on thermodynamic principles, it is devised a solution for phase densities in a droplet, which states explicitly dependence on the surface tension and interface curvature. A comparison with numerical results suggest a physical inconsistency in the pseudopotential method. This fact is not commonly discussed in the literature, since most of studies are limited to the Maxwell equal area rule. However, this inconsistency is shown to be dependent on the equation of state (EOS), and its effects can be mitigated by an appropriate choice of Carnahan-Starling EOS parameters. Also, a droplet oscillation test was performed, and the most divergent solution under certain flow conditions deviated 7.5% from the expected analytical result. At the end, a droplet impact test against a solid wall was performed to verify the method stability, and it was possible to reach stable simulation results with density ratio of almost 2400 and Reynolds number of Re=373. The observed results corroborate that the proposed method is able to replicate the desired macroscopic multiphase behavior.}, } @article {pmid33076003, year = {2020}, author = {Rana, N and Perlekar, P}, title = {Coarsening in the two-dimensional incompressible Toner-Tu equation: Signatures of turbulence.}, journal = {Physical review. E}, volume = {102}, number = {3-1}, pages = {032617}, doi = {10.1103/PhysRevE.102.032617}, pmid = {33076003}, issn = {2470-0053}, abstract = {We investigate coarsening dynamics in the two-dimensional, incompressible Toner-Tu equation. We show that coarsening proceeds via vortex merger events, and the dynamics crucially depend on the Reynolds number Re. For low Re, the coarsening process has similarities to Ginzburg-Landau dynamics. On the other hand, for high Re, coarsening shows signatures of turbulence. In particular, we show the presence of an enstrophy cascade from the intervortex separation scale to the dissipation scale.}, } @article {pmid33075904, year = {2020}, author = {Bos, WJT and Laadhari, F and Agoua, W}, title = {Linearly forced isotropic turbulence at low Reynolds numbers.}, journal = {Physical review. E}, volume = {102}, number = {3-1}, pages = {033105}, doi = {10.1103/PhysRevE.102.033105}, pmid = {33075904}, issn = {2470-0053}, abstract = {We investigate the forcing strength needed to sustain a flow using linear forcing. A critical Reynolds number R_{c} is determined, based on the longest wavelength allowed by the system, the forcing strength and the viscosity. A simple model is proposed for the dissipation rate, leading to a closed expression for the kinetic energy of the flow as a function of the Reynolds number. The dissipation model and the prediction for the kinetic energy are assessed using direct numerical simulations and two-point closure integrations. An analysis of the dissipation-rate equation and the triadic structure of the nonlinear transfer allows to refine the model in order to reproduce the low-Reynolds-number asymptotic behavior, where the kinetic energy is proportional to R-R_{c} .}, } @article {pmid33075884, year = {2020}, author = {Rinoshika, H and Rinoshika, A and Wang, JJ}, title = {Three-dimensional multiscale flow structures behind a wall-mounted short cylinder based on tomographic particle image velocimetry and three-dimensional orthogonal wavelet transform.}, journal = {Physical review. E}, volume = {102}, number = {3-1}, pages = {033101}, doi = {10.1103/PhysRevE.102.033101}, pmid = {33075884}, issn = {2470-0053}, abstract = {Three-dimensional (3D) flow structures around a wall-mounted short cylinder of height-to-diameter ratio 1 were instantaneously measured by a high-resolution tomographic particle image velocimetry (Tomo-PIV) at Reynolds number of 10 720 in a water tunnel. 3D velocity fields, 3D vorticity, the Q criterion, the rear separation region, and the characteristic of arch type vortex and tip vortices were first discussed. We found a strong 3D W-type arch vortex behind the short cylinder, which was originated by the interaction between upwash and downwash flows. This W-type arch vortex was reshaped to the M-shaped arch vortex downstream. It indicated that the head shape of the arch vortex structure depended on the aspect ratio of the cylinder. The large-scale streamwise vortices were originated by the downwash and upwash flows near the center location of W-type arch vortex. Then the 3D orthogonal wavelet multiresolution technique was developed to analyze instantaneous 3D velocity fields of Tomo-PIV in order to clarify 3D multiscale wake flow structures. The W-type shape arch vortex was extracted in the time-averaged intermediate-scale structure, while an M-shaped arch vortex was identified in the time-averaged large-scale structure. The tip vortices distributed in the time-averaged large- and intermediate-scale structures. The instantaneous intermediate-scale upwash vortices played an essential role in producing W-type head of arch structure. It was also observed that strong small-scale vortices appeared in the shear layer or near the bottom plate and most of them were contained in the intermediate-scale structures.}, } @article {pmid33057044, year = {2020}, author = {Riasat, S and Ramzan, M and Kadry, S and Chu, YM}, title = {Significance of magnetic Reynolds number in a three-dimensional squeezing Darcy-Forchheimer hydromagnetic nanofluid thin-film flow between two rotating disks.}, journal = {Scientific reports}, volume = {10}, number = {1}, pages = {17208}, pmid = {33057044}, issn = {2045-2322}, abstract = {The remarkable aspects of carbon nanotubes like featherweight, durability, exceptional electrical and thermal conduction capabilities, and physicochemical stability make them desirous materials for electrochemical devices. Having such astonishing characteristics of nanotubes in mind our aspiration is to examine the squeezing three dimensional Darcy-Forchheimer hydromagnetic nanofluid thin-film flow amid two rotating disks with suspended multiwalled carbon nanotubes (MWCNTs) submerged into the base fluid water. The analysis is done by invoking partial slip effect at the boundary in attendance of autocatalytic reactions. The mathematical model consists of axial and azimuthal momentum and magnetic fields respectively. The tangential and axial velocity profiles and components of the magnetic field are examined numerically by employing the bvp4c method for varying magnetic, rotational, and squeezing Reynolds number. The torque effect near the upper and lower disks are studied critically using their graphical depiction. The values of the torque at the upper and lower disks are obtained for rotational and squeezed Reynolds numbers and are found in an excellent concurrence when compared with the existing literature. Numerically it is computed that the torque at the lower disk is higher in comparison to the upper disk for mounting estimates of the squeezed Reynolds number and the dimensionless parameter for magnetic force in an axial direction. From the graphical illustrations, it is learned that thermal profile declines for increasing values of the squeezed Reynolds number.}, } @article {pmid33049170, year = {2020}, author = {Wong, JY and Chan, BKK and Chan, KYK}, title = {Swimming kinematics and hydrodynamics of barnacle larvae throughout development.}, journal = {Proceedings. Biological sciences}, volume = {287}, number = {1936}, pages = {20201360}, pmid = {33049170}, issn = {1471-2954}, mesh = {Animals ; Biomechanical Phenomena ; Extremities ; Hydrodynamics ; Larva/physiology ; Rheology ; Swimming/*physiology ; Thoracica/*physiology ; Zooplankton ; }, abstract = {Changes in size strongly influence organisms' ecological performances. For aquatic organisms, they can transition from viscosity- to inertia-dominated fluid regimes as they grow. Such transitions are often associated with changes in morphology, swimming speed and kinematics. Barnacles do not fit into this norm as they have two morphologically distinct planktonic larval phases that swim differently but are of comparable sizes and operate in the same fluid regime (Reynolds number 10[0]-10[1]). We quantified the hydrodynamics of the rocky intertidal stalked barnacle Capitulum mitella from the nauplius II to cyprid stage and examined how kinematics and size increases affect its swimming performance. Cyprids beat their appendages in a metachronal wave to swim faster, more smoothly, and with less backwards slip per beat cycle than did all naupliar stages. Micro-particle image velocimetry showed that cyprids generated trailing viscous vortex rings that pushed water backwards for propulsion, contrary to the nauplii's forward suction current for particle capture. Our observations highlight that zooplankton swimming performance can shift via morphological and kinematic modifications without a significant size increase. The divergence in ecological functions through ontogeny in barnacles and the removal of feeding requirement likely contributed to the evolution of the specialized, taxonomically unique cyprid phase.}, } @article {pmid33026993, year = {2021}, author = {Jakob, J and Gross, M and Gunther, T}, title = {A Fluid Flow Data Set for Machine Learning and its Application to Neural Flow Map Interpolation.}, journal = {IEEE transactions on visualization and computer graphics}, volume = {27}, number = {2}, pages = {1279-1289}, doi = {10.1109/TVCG.2020.3028947}, pmid = {33026993}, issn = {1941-0506}, mesh = {Computer Graphics ; *Deep Learning ; Machine Learning ; Neural Networks, Computer ; }, abstract = {In recent years, deep learning has opened countless research opportunities across many different disciplines. At present, visualization is mainly applied to explore and explain neural networks. Its counterpart-the application of deep learning to visualization problems-requires us to share data more openly in order to enable more scientists to engage in data-driven research. In this paper, we construct a large fluid flow data set and apply it to a deep learning problem in scientific visualization. Parameterized by the Reynolds number, the data set contains a wide spectrum of laminar and turbulent fluid flow regimes. The full data set was simulated on a high-performance compute cluster and contains 8000 time-dependent 2D vector fields, accumulating to more than 16 TB in size. Using our public fluid data set, we trained deep convolutional neural networks in order to set a benchmark for an improved post-hoc Lagrangian fluid flow analysis. In in-situ settings, flow maps are exported and interpolated in order to assess the transport characteristics of time-dependent fluids. Using deep learning, we improve the accuracy of flow map interpolations, allowing a more precise flow analysis at a reduced memory IO footprint.}, } @article {pmid33022594, year = {2020}, author = {Di Luca, M and Mintchev, S and Su, Y and Shaw, E and Breuer, K}, title = {A bioinspired Separated Flow wing provides turbulence resilience and aerodynamic efficiency for miniature drones.}, journal = {Science robotics}, volume = {5}, number = {38}, pages = {}, doi = {10.1126/scirobotics.aay8533}, pmid = {33022594}, issn = {2470-9476}, abstract = {Small-scale drones have enough sensing and computing power to find use across a growing number of applications. However, flying in the low-Reynolds number regime remains challenging. High sensitivity to atmospheric turbulence compromises vehicle stability and control, and low aerodynamic efficiency limits flight duration. Conventional wing designs have thus far failed to address these two deficiencies simultaneously. Here, we draw inspiration from nature's small flyers to design a wing with lift generation robust to gusts and freestream turbulence without sacrificing aerodynamic efficiency. This performance is achieved by forcing flow separation at the airfoil leading edge. Water and wind tunnel measurements are used to demonstrate the working principle and aerodynamic performance of the wing, showing a substantial reduction in the sensitivity of lift force production to freestream turbulence, as compared with the performance of an Eppler E423 low-Reynolds number wing. The minimum cruise power of a custom-built 104-gram fixed-wing drone equipped with the Separated Flow wing was measured in the wind tunnel indicating an upper limit for the flight time of 170 minutes, which is about four times higher than comparable existing fixed-wing drones. In addition, we present scaling guidelines and outline future design and manufacturing challenges.}, } @article {pmid33020499, year = {2020}, author = {Phelps, PR and Lee, CA and Morton, DM}, title = {Episodes of fast crystal growth in pegmatites.}, journal = {Nature communications}, volume = {11}, number = {1}, pages = {4986}, pmid = {33020499}, issn = {2041-1723}, abstract = {Pegmatites are shallow, coarse-grained magmatic intrusions with crystals occasionally approaching meters in length. Compared to their plutonic hosts, pegmatites are thought to have cooled rapidly, suggesting that these large crystals must have grown fast. Growth rates and conditions, however, remain poorly constrained. Here we investigate quartz crystals and their trace element compositions from miarolitic cavities in the Stewart pegmatite in southern California, USA, to quantify crystal growth rates. Trace element concentrations deviate considerably from equilibrium and are best explained by kinetic effects associated with rapid crystal growth. Kinetic crystal growth theory is used to show that crystals accelerated from an initial growth rate of 10[-6]-10[-7] m s[-1] to 10[-5]-10[-4] m s[-1] (10-100 mm day[-1] to 1-10 m day[-1]), indicating meter sized crystals could have formed within days, if these rates are sustained throughout pegmatite formation. The rapid growth rates require that quartz crystals grew from thin (micron scale) chemical boundary layers at the fluid-crystal interfaces. A strong advective component is required to sustain such thin boundary layers. Turbulent conditions (high Reynolds number) in these miarolitic cavities are shown to exist during crystallization, suggesting that volatile exsolution, crystallization, and cavity generation occur together.}, } @article {pmid32992553, year = {2020}, author = {Qiu, Y and Hu, W and Wu, C and Chen, W}, title = {An Experimental Study of Microchannel and Micro-Pin-Fin Based On-Chip Cooling Systems with Silicon-to-Silicon Direct Bonding.}, journal = {Sensors (Basel, Switzerland)}, volume = {20}, number = {19}, pages = {}, pmid = {32992553}, issn = {1424-8220}, abstract = {This paper describes an experimental study of the cooling capabilities of microchannel and micro-pin-fin based on-chip cooling systems. The on-chip cooling systems integrated with a micro heat sink, simulated power IC (integrated circuit) and temperature sensors are fabricated by micromachining and silicon-to-silicon direct bonding. Three micro heat sink structures: a microchannel heat sink (MCHS), an inline micro-pin-fin heat sink (I-MPFHS) and a staggered micro-pin-fin heat sink (S-MPFHS) are tested in the Reynolds number range of 79.2 to 882.3. The results show that S-MPFHS is preferred if the water pump can provide enough pressure drop. However, S-MPFHS has the worst performance when the rated pressure drop of the pump is lower than 1.5 kPa because the endwall effect under a low Reynolds number suppresses the disturbance generated by the staggered micro pin fins but S-MPFHS is still preferred when the rated pressure drop of the pump is in the range of 1.5 to 20 kPa. When the rated pressure drop of the pump is higher than 20 kPa, I-MPFHS will be the best choice because of high heat transfer enhancement and low pressure drop price brought by the unsteady vortex street.}, } @article {pmid32992113, year = {2021}, author = {Chen, Y and Chen, Y and Hu, S and Ni, Z}, title = {Continuous ultrasonic flow measurement for aerospace small pipelines.}, journal = {Ultrasonics}, volume = {109}, number = {}, pages = {106260}, doi = {10.1016/j.ultras.2020.106260}, pmid = {32992113}, issn = {1874-9968}, abstract = {Aerospace explorations stimulate extensive research on innovative propellant flow measurement technologies in microgravity conditions. Ultrasonic-based measurements have advantages of non-invasive and non-moving-component constructions as well as fast responses to bi-directional flow detection, its applications in aerospace explorations have already been reported. To avoid the shortages of pulse ultrasonic measurement configurations, flow measurement of continuous ultrasonic wave propagation is presented to match the requirements of large measurement range and high precision. Fabrication process and laboratory validations using water flow are presented. Ground experiments show that the linearity of the proposed ultrasonic flow meter is obtained in the measurement range [0, 80 ml/s] which is typical requirement in aerospace applications. Meanwhile, the fitted linear feature from the experimental data matches well the theoretical prediction except the flow prediction of stationary fluid. Under specific configurations, the absolute measurement error is significantly affected by the corresponding Reynolds number. Furthermore, the absolute measurement error is smaller when excitation signals with higher frequency are used if the phase tracking performance for different frequencies is identical.}, } @article {pmid32984706, year = {2020}, author = {Ye, Y and Luo, X and Dong, C and Xu, Y and Zhang, Z}, title = {Numerical and Experimental Investigation of Soot Suppression by Acoustic Oscillated Combustion.}, journal = {ACS omega}, volume = {5}, number = {37}, pages = {23866-23875}, pmid = {32984706}, issn = {2470-1343}, abstract = {The soot suppression by acoustic oscillations for acetylene diffusion flames was investigated combining numerical and experimental studies. The combustion and soot formation were predicted by the finite-rate detailed chemistry model and modified Moss-Brookes model, respectively, while the turbulence was predicted by the detached eddy simulation (DES) with a low Reynolds number correction. Experimental results showed that the soot rate almost decreased linearly with the amplitude of acoustic oscillation, and the pinch-off of the flame occurred at a large acoustic oscillation. Numerical results showed that the flame structure was well predicted, while the soot rate was over-predicted at large acoustic oscillations; the consumption of O2 increased obviously with the acoustic oscillation. The soot suppression was mainly caused by the decrease of the surface growth rate when the air was pushed toward the flame.}, } @article {pmid32982135, year = {2020}, author = {Dbouk, T and Drikakis, D}, title = {Weather impact on airborne coronavirus survival.}, journal = {Physics of fluids (Woodbury, N.Y. : 1994)}, volume = {32}, number = {9}, pages = {093312}, pmid = {32982135}, issn = {1070-6631}, abstract = {The contribution of this paper toward understanding of airborne coronavirus survival is twofold: We develop new theoretical correlations for the unsteady evaporation of coronavirus (CoV) contaminated saliva droplets. Furthermore, we implement the new correlations in a three-dimensional multiphase Eulerian-Lagrangian computational fluid dynamics solver to study the effects of weather conditions on airborne virus transmission. The new theory introduces a thermal history kernel and provides transient Nusselt (Nu) and Sherwood (Sh) numbers as a function of the Reynolds (Re), Prandtl (Pr), and Schmidt numbers (Sc). For the first time, these new correlations take into account the mixture properties due to the concentration of CoV particles in a saliva droplet. We show that the steady-state relationships induce significant errors and must not be applied in unsteady saliva droplet evaporation. The classical theory introduces substantial deviations in Nu and Sh values when increasing the Reynolds number defined at the droplet scale. The effects of relative humidity, temperature, and wind speed on the transport and viability of CoV in a cloud of airborne saliva droplets are also examined. The results reveal that a significant reduction of virus viability occurs when both high temperature and low relative humidity occur. The droplet cloud's traveled distance and concentration remain significant at any temperature if the relative humidity is high, which is in contradiction with what was previously believed by many epidemiologists. The above could explain the increase in CoV cases in many crowded cities around the middle of July (e.g., Delhi), where both high temperature and high relative humidity values were recorded one month earlier (during June). Moreover, it creates a crucial alert for the possibility of a second wave of the pandemic in the coming autumn and winter seasons when low temperatures and high wind speeds will increase airborne virus survival and transmission.}, } @article {pmid32973078, year = {2020}, author = {York, CA and Bartol, IK and Krueger, PS and Thompson, JT}, title = {Squids use multiple escape jet patterns throughout ontogeny.}, journal = {Biology open}, volume = {9}, number = {11}, pages = {}, pmid = {32973078}, issn = {2046-6390}, mesh = {Age Factors ; Animals ; Biomechanical Phenomena ; Decapodiformes/*anatomy & histology/*physiology ; Escape Reaction ; Models, Theoretical ; *Predatory Behavior ; Rheology ; Swimming ; }, abstract = {Throughout their lives, squids are both predators and prey for a multitude of animals, many of which are at the top of ocean food webs, making them an integral component of the trophic structure of marine ecosystems. The escape jet, which is produced by the rapid expulsion of water from the mantle cavity through a funnel, is central to a cephalopod's ability to avoid predation throughout its life. Although squid undergo morphological and behavioral changes and experience remarkably different Reynolds number regimes throughout their development, little is known about the dynamics and propulsive efficiency of escape jets throughout ontogeny. We examine the hydrodynamics and kinematics of escape jets in squid throughout ontogeny using 2D/3D velocimetry and high-speed videography. All life stages of squid produced two escape jet patterns: (1) 'escape jet I' characterized by short rapid pulses resulting in vortex ring formation and (2) 'escape jet II' characterized by long high-volume jets, often with a leading-edge vortex ring. Paralarvae exhibited higher propulsive efficiency than adult squid during escape jet ejection, and propulsive efficiency was higher for escape jet I than escape jet II in juveniles and adults. These results indicate that although squid undergo major ecological transitions and morphology changes from paralarvae to adults, all life stages demonstrate flexibility in escape jet responses and produce escape jets of surprisingly high propulsive efficiency.This article has an associated First Person interview with the first author of the paper.}, } @article {pmid32968087, year = {2020}, author = {Saqr, KM and Tupin, S and Rashad, S and Endo, T and Niizuma, K and Tominaga, T and Ohta, M}, title = {Physiologic blood flow is turbulent.}, journal = {Scientific reports}, volume = {10}, number = {1}, pages = {15492}, pmid = {32968087}, issn = {2045-2322}, mesh = {Blood Circulation/*physiology ; Blood Vessels/physiology ; Hemodynamics ; Humans ; Hydrodynamics ; Models, Biological ; Nonlinear Dynamics ; Pulsatile Flow/physiology ; }, abstract = {Contemporary paradigm of peripheral and intracranial vascular hemodynamics considers physiologic blood flow to be laminar. Transition to turbulence is considered as a driving factor for numerous diseases such as atherosclerosis, stenosis and aneurysm. Recently, turbulent flow patterns were detected in intracranial aneurysm at Reynolds number below 400 both in vitro and in silico. Blood flow is multiharmonic with considerable frequency spectra and its transition to turbulence cannot be characterized by the current transition theory of monoharmonic pulsatile flow. Thus, we decided to explore the origins of such long-standing assumption of physiologic blood flow laminarity. Here, we hypothesize that the inherited dynamics of blood flow in main arteries dictate the existence of turbulence in physiologic conditions. To illustrate our hypothesis, we have used methods and tools from chaos theory, hydrodynamic stability theory and fluid dynamics to explore the existence of turbulence in physiologic blood flow. Our investigation shows that blood flow, both as described by the Navier-Stokes equation and in vivo, exhibits three major characteristics of turbulence. Womersley's exact solution of the Navier-Stokes equation has been used with the flow waveforms from HaeMod database, to offer reproducible evidence for our findings, as well as evidence from Doppler ultrasound measurements from healthy volunteers who are some of the authors. We evidently show that physiologic blood flow is: (1) sensitive to initial conditions, (2) in global hydrodynamic instability and (3) undergoes kinetic energy cascade of non-Kolmogorov type. We propose a novel modification of the theory of vascular hemodynamics that calls for rethinking the hemodynamic-biologic links that govern physiologic and pathologic processes.}, } @article {pmid32959981, year = {2021}, author = {Gibson, BM and Furbish, DJ and Rahman, IA and Schmeeckle, MW and Laflamme, M and Darroch, SAF}, title = {Ancient life and moving fluids.}, journal = {Biological reviews of the Cambridge Philosophical Society}, volume = {96}, number = {1}, pages = {129-152}, pmid = {32959981}, issn = {1469-185X}, mesh = {Animals ; *Biological Evolution ; Biota ; Computer Simulation ; *Ecosystem ; Fossils ; }, abstract = {Over 3.7 billion years of Earth history, life has evolved complex adaptations to help navigate and interact with the fluid environment. Consequently, fluid dynamics has become a powerful tool for studying ancient fossils, providing insights into the palaeobiology and palaeoecology of extinct organisms from across the tree of life. In recent years, this approach has been extended to the Ediacara biota, an enigmatic assemblage of Neoproterozoic soft-bodied organisms that represent the first major radiation of macroscopic eukaryotes. Reconstructing the ways in which Ediacaran organisms interacted with the fluids provides new insights into how these organisms fed, moved, and interacted within communities. Here, we provide an in-depth review of fluid physics aimed at palaeobiologists, in which we dispel misconceptions related to the Reynolds number and associated flow conditions, and specify the governing equations of fluid dynamics. We then review recent advances in Ediacaran palaeobiology resulting from the application of computational fluid dynamics (CFD). We provide a worked example and account of best practice in CFD analyses of fossils, including the first large eddy simulation (LES) experiment performed on extinct organisms. Lastly, we identify key questions, barriers, and emerging techniques in fluid dynamics, which will not only allow us to understand the earliest animal ecosystems better, but will also help to develop new palaeobiological tools for studying ancient life.}, } @article {pmid32959135, year = {2021}, author = {Sonnenberg, AH and Taylor, E and Mondoñedo, JR and Jawde, SB and Amin, SD and Song, J and Grinstaff, MW and Suki, B}, title = {Breath Hold Facilitates Targeted Deposition of Aerosolized Droplets in a 3D Printed Bifurcating Airway Tree.}, journal = {Annals of biomedical engineering}, volume = {49}, number = {2}, pages = {812-821}, pmid = {32959135}, issn = {1573-9686}, support = {U01 HL-139466/HL/NHLBI NIH HHS/United States ; U01 HL-139466/HL/NHLBI NIH HHS/United States ; }, mesh = {Aerosols ; *Breath Holding ; Computer Simulation ; Humans ; Lung/*metabolism ; *Models, Anatomic ; *Models, Biological ; Particle Size ; Printing, Three-Dimensional ; }, abstract = {The lungs have long been considered a desired route for drug delivery but, there is still a lack of strategies to rationally target delivery sites especially in the presence of heterogeneous airway disease. Furthermore, no standardized system has been proposed to rapidly test different ventilation strategies and how they alter the overall and regional deposition pattern in the airways. In this study, a 3D printed symmetric bifurcating tree model mimicking part of the human airway tree was developed that can be used to quantify the regional deposition patterns of different delivery methodologies. The model is constructed in a novel way that allows for repeated measurements of regional deposition using reusable parts. During ventilation, nebulized ~3-micron-sized fluid droplets were delivered into the model. Regional delivery, quantified by precision weighing individual airways, was highly reproducible. A successful strategy to control regional deposition was achieved by combining an inspiratory wave form with a "breath hold" pause after each inspiration. Specifically, the second generation of the tree was successfully targeted, and deposition was increased by up to four times in generation 2 when compared to a ventilation without the breath hold (p < 0.0001). Breath hold was also demonstrated to facilitate deposition into blocked regions of the model, which mimic airway closure during an asthma that receive no flow during inhalation. Additionally, visualization experiments demonstrated that in the absence of fluid flow, the deposition of 3-micron water droplets is dominated by gravity, which, to our knowledge, has not been confirmed under standard laboratory conditions.}, } @article {pmid32952737, year = {2020}, author = {Bortot, M and Sharifi, A and Ashworth, K and Walker, F and Cox, A and Ruegg, K and Clendenen, N and Neeves, KB and Bark, D and Di Paola, J}, title = {Pathologic Shear and Elongation Rates Do Not Cause Cleavage of Von Willebrand Factor by ADAMTS13 in a Purified System.}, journal = {Cellular and molecular bioengineering}, volume = {13}, number = {4}, pages = {379-390}, pmid = {32952737}, issn = {1865-5025}, support = {R01 HL120728/HL/NHLBI NIH HHS/United States ; R33 HL141794/HL/NHLBI NIH HHS/United States ; R61 HL141794/HL/NHLBI NIH HHS/United States ; }, abstract = {INTRODUCTION: Pathological flows in patients with severe aortic stenosis are associated with acquired von Willebrand syndrome. This syndrome is characterized by excessive cleavage of von Willebrand factor by its main protease, A Disintegrin and Metalloproteinase with a Thrombospondin Type 1 Motif, Member 13 (ADAMTS13) leading to decreased VWF function and mucocutaneous bleeding. Aortic valve replacement and correction of the flow behavior to physiological levels reverses the syndrome, supporting the association between pathological flow and acquired von Willebrand syndrome. We investigated the effects of shear and elongational rates on von Willebrand factor cleavage in the presence of ADAMTS13.

METHODS: We identified acquired von Willebrand syndrome in five patients with severe aortic stenosis. Doppler echography values from these patients were used to develop three computational fluid dynamic (CFD) aortic valve models (normal, mild and severe stenosis). Shear, elongational rates and exposure times identified in the CFD simulations were used as parameters for the design of microfluidic devices to test the effects of pathologic shear and elongational rates on the structure and function of von Willebrand factor.

RESULTS: The shear rates (0-10,000s[-1]), elongational rates (0-1000 s[-1]) and exposure times (1-180 ms) tested in our microfluidic designs mimicked the flow features identified in patients with aortic stenosis. The shear and elongational rates tested in vitro did not lead to excessive cleavage or decreased function of von Willebrand factor in the presence of the protease.

CONCLUSIONS: High shear and elongational rates in the presence of ADAMTS13 are not sufficient for excessive cleavage of von Willebrand Factor.}, } @article {pmid32946425, year = {2020}, author = {Gao, D and Bai, M and Hu, C and Lv, J and Wang, C and Zhang, X}, title = {Investigating control of convective heat transfer and flow resistance of Fe3O4/deionized water nanofluid in magnetic field in laminar flow.}, journal = {Nanotechnology}, volume = {31}, number = {49}, pages = {495402}, doi = {10.1088/1361-6528/abb15c}, pmid = {32946425}, issn = {1361-6528}, abstract = {This paper studies the convective heat transfer and flow resistance of Fe3O4/deionized water nanofluids in laminar flow under the control of an external magnetic field. The basic thermophysical parameters including viscosity, specific heat capacity and thermal conductivity are investigated to describe the fundamental performance of heat transfer and flow resistance. In the absence of the magnetic field, the heat transfer coefficients and flow friction could not change significantly at nanoparticle volume concentration of 0.05%. In the presence of the magnetic field, it can enhance heat transfer and flow resistance by 6% and 3.5% when the magnets interlace on both sides of the tube. The dynamic magnetic experiments discussed the heat transfer increase process in detail. The heat transfer and the flow resistance increase by 11.7% and 5.4% when magnetic field strength is 600 Gs, nanoparticle volume concentration is 2% and Reynolds number is 2000. The radial shuttle movement of magnetic nanoparticles in the cross-section, micro convection in base fluid and the slip velocity between the nanoparticles and the base fluid are considered the main reasons for heat transfer enhancement.}, } @article {pmid32942486, year = {2020}, author = {Mukhopadhyay, S and Mukhopadhyay, A}, title = {Waves and instabilities of viscoelastic fluid film flowing down an inclined wavy bottom.}, journal = {Physical review. E}, volume = {102}, number = {2-1}, pages = {023117}, doi = {10.1103/PhysRevE.102.023117}, pmid = {32942486}, issn = {2470-0053}, abstract = {Evolution of waves and hydrodynamic instabilities of a thin viscoelastic fluid film flowing down an inclined wavy bottom of moderate steepness have been analyzed analytically and numerically. The classical long-wave expansion method has been used to formulate a nonlinear evolution equation for the development of the free surface. A normal-mode approach has been adopted to discuss the linear stability analysis from the viewpoint of the spatial and temporal study. The method of multiple scales is used to derive a Ginzburg-Landau-type nonlinear equation for studying the weakly nonlinear stability solutions. Two significant wave families, viz., γ_{1} and γ_{2}, are found and discussed in detail along with the traveling wave solution of the evolution system. A time-dependent numerical study is performed with Scikit-FDif. The entire investigation is conducted primarily for a general periodic bottom, and the detailed results of a particular case study of sinusoidal topography are then discussed. The case study reveals that the bottom steepness ζ plays a dual role in the linear regime. Increasing ζ has a stabilizing effect in the uphill region, and the opposite occurs in the downhill region. While the viscoelastic parameter Γ has a destabilizing effect throughout the domain in both the linear and the nonlinear regime. Both supercritical and subcritical solutions are possible through a weakly nonlinear analysis. It is interesting to note that the unconditional zone decreases and the explosive zone increases in the downhill region rather than the uphill region for a fixed Γ and ζ. The same phenomena occur in a particular region if we increase Γ and keep ζ fixed. The traveling wave solution reveals the fact that to get the γ_{1} family of waves we need to increase the Reynolds number a bit more than the value at which the γ_{2} family of waves is found. The spatiotemporal evolution of the nonlinear surface equation indicates that different kinds of finite-amplitude permanent waves exist.}, } @article {pmid32942407, year = {2020}, author = {Hassan, MR and Wang, C}, title = {Lateral migration of a ferrofluid droplet in a plane Poiseuille flow under uniform magnetic fields.}, journal = {Physical review. E}, volume = {102}, number = {2-1}, pages = {022611}, doi = {10.1103/PhysRevE.102.022611}, pmid = {32942407}, issn = {2470-0053}, abstract = {The lateral migration of a two-dimensional (2D) viscous ferrofluid droplet in a plane Poiseuille flow under a uniform magnetic field is studied numerically by using the level set method. Focusing on low droplet Reynolds number flows (Re_{d} ≤0.05), several numerical simulations are carried out to analyze the effects of magnetic field direction and strength, droplet size, and viscosity ratio on the lateral migration behavior of the droplet. The results indicate that the magnetic field direction plays a pivotal role in the trajectory of lateral migration of the droplet and the final equilibrium position in the channel. When the magnetic field is parallel to the channel, i.e., α=0^{∘} (the direction of magnetic field), the droplet is found to settle closer to the wall with an increase in magnetic Bond number Bo_{m}, while at α=45^{∘}, the droplet settles closer to the channel center. Varying the initial droplet sizes at a fixed magnetic Bond number Bo_{m} and viscosity ratio λ results in different final equilibrium positions within the channel. Additionally, the effect of different viscosity ratios on the migration behavior of the droplet is examined at variable magnetic Bond numbers Bo_{m} . At α=45^{∘}, a critical steady state of deformation is found for λ=0.5 and 1 where the droplet changes its migration direction and shifts toward the center of the channel, while at λ=0.05, the droplet crosses the center. At α=90^{∘}, the droplet is found to settle exactly at the center of the flow domain irrespective of different magnetic Bond numbers, droplet sizes, and viscosity ratios.}, } @article {pmid32926106, year = {2020}, author = {Beratlis, N and Capuano, F and Krishnan, K and Gurka, R and Squires, K and Balaras, E}, title = {Direct Numerical Simulations of a Great Horn Owl in Flapping Flight.}, journal = {Integrative and comparative biology}, volume = {60}, number = {5}, pages = {1091-1108}, doi = {10.1093/icb/icaa127}, pmid = {32926106}, issn = {1557-7023}, mesh = {Animals ; Biomimetics ; *Flight, Animal ; *Models, Biological ; *Strigiformes ; Wings, Animal ; }, abstract = {The fluid dynamics of owls in flapping flight is studied by coordinated experiments and computations. The great horned owl was selected, which is nocturnal, stealthy, and relatively large sized raptor. On the experimental side, perch-to-perch flight was considered in an open wind tunnel. The owl kinematics was captured with multiple cameras from different view angles. The kinematic extraction was central in driving the computations, which were designed to resolve all significant spatio-temporal scales in the flow with an unprecedented level of resolution. The wing geometry was extracted from the planform image of the owl wing and a three-dimensional model, the reference configuration, was reconstructed. This configuration was then deformed in time to best match the kinematics recorded during flights utilizing an image-registration technique based on the large deformation diffeomorphic metric mapping framework. All simulations were conducted using an eddy-resolving, high-fidelity, solver, where the large displacements/deformations of the flapping owl model were introduced with an immersed boundary formulation. We report detailed information on the spatio-temporal flow dynamics in the near wake including variables that are challenging to measure with sufficient accuracy, such as aerodynamic forces. At the same time, our results indicate that high-fidelity computations over smooth wings may have limitations in capturing the full range of flow phenomena in owl flight. The growth and subsequent separation of the laminar boundary layers developing over the wings in this Reynolds number regime is sensitive to the surface micro-features that are unique to each species.}, } @article {pmid32920676, year = {2020}, author = {Sprenger, AR and Shaik, VA and Ardekani, AM and Lisicki, M and Mathijssen, AJTM and Guzmán-Lastra, F and Löwen, H and Menzel, AM and Daddi-Moussa-Ider, A}, title = {Towards an analytical description of active microswimmers in clean and in surfactant-covered drops.}, journal = {The European physical journal. E, Soft matter}, volume = {43}, number = {9}, pages = {58}, doi = {10.1140/epje/i2020-11980-9}, pmid = {32920676}, issn = {1292-895X}, mesh = {Computer Simulation ; *Hydrodynamics ; *Models, Theoretical ; Rheology ; Stress, Mechanical ; *Surface-Active Agents ; Suspensions ; Swimming ; Viscosity ; }, abstract = {Geometric confinements are frequently encountered in the biological world and strongly affect the stability, topology, and transport properties of active suspensions in viscous flow. Based on a far-field analytical model, the low-Reynolds-number locomotion of a self-propelled microswimmer moving inside a clean viscous drop or a drop covered with a homogeneously distributed surfactant, is theoretically examined. The interfacial viscous stresses induced by the surfactant are described by the well-established Boussinesq-Scriven constitutive rheological model. Moreover, the active agent is represented by a force dipole and the resulting fluid-mediated hydrodynamic couplings between the swimmer and the confining drop are investigated. We find that the presence of the surfactant significantly alters the dynamics of the encapsulated swimmer by enhancing its reorientation. Exact solutions for the velocity images for the Stokeslet and dipolar flow singularities inside the drop are introduced and expressed in terms of infinite series of harmonic components. Our results offer useful insights into guiding principles for the control of confined active matter systems and support the objective of utilizing synthetic microswimmers to drive drops for targeted drug delivery applications.}, } @article {pmid32916991, year = {2020}, author = {Khan, MZU and Uddin, E and Akbar, B and Akram, N and Naqvi, AA and Sajid, M and Ali, Z and Younis, MY and García Márquez, FP}, title = {Investigation of Heat Transfer and Pressure Drop in Microchannel Heat Sink Using Al2O3 and ZrO2 Nanofluids.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {10}, number = {9}, pages = {}, pmid = {32916991}, issn = {2079-4991}, abstract = {A new micro heat exchanger was analyzed using numerical formulation of conjugate heat transfer for single-phase fluid flow across copper microchannels. The flow across bent channels harnesses asymmetric laminar flow and dean vortices phenomena for heat transfer enhancement. The single-channel analysis was performed to select the bent channel aspect ratio by varying width and height between 35-300 μm for Reynolds number and base temperature magnitude range of 100-1000 and 320-370 K, respectively. The bent channel results demonstrate dean vortices phenomenon at the bend for Reynolds number of 500 and above. Thermal performance factor analysis shows an increase of 18% in comparison to straight channels of 200 μm width and height. Alumina nanoparticles at 1% and 3% concentration enhance the Nusselt number by an average of 10.4% and 23.7%, respectively, whereas zirconia enhances Nusselt number by 16% and 33.9% for same concentrations. On the other hand, thermal performance factor analysis shows a significant increase in pressure drop at high Reynolds number with 3% particle concentration. Using zirconia for nanofluid, Nusselt number of the bent multi-channel model is improved by an average of 18% for a 3% particle concentration as compared to bent channel with deionized water.}, } @article {pmid32910129, year = {2020}, author = {Tang, W and Zhu, S and Jiang, D and Zhu, L and Yang, J and Xiang, N}, title = {Channel innovations for inertial microfluidics.}, journal = {Lab on a chip}, volume = {20}, number = {19}, pages = {3485-3502}, doi = {10.1039/d0lc00714e}, pmid = {32910129}, issn = {1473-0189}, abstract = {Inertial microfluidics has gained significant attention since first being proposed in 2007 owing to the advantages of simplicity, high throughput, precise manipulation, and freedom from an external field. Superior performance in particle focusing, filtering, concentrating, and separating has been demonstrated. As a passive technology, inertial microfluidics technology relies on the unconventional use of fluid inertia in an intermediate Reynolds number range to induce inertial migration and secondary flow, which depend directly on the channel structure, leading to particle migration to the lateral equilibrium position or trapping in a specific cavity. With the advances in micromachining technology, many channel structures have been designed and fabricated in the past decade to explore the fundamentals and applications of inertial microfluidics. However, the channel innovations for inertial microfluidics have not been discussed comprehensively. In this review, the inertial particle manipulations and underlying physics in conventional channels, including straight, spiral, sinusoidal, and expansion-contraction channels, are briefly described. Then, recent innovations in channel structure for inertial microfluidics, especially channel pattern modification and unconventional cross-sectional shape, are reviewed. Finally, the prospects for future channel innovations in inertial microfluidic chips are also discussed. The purpose of this review is to provide guidance for the continued study of innovative channel designs to improve further the accuracy and throughput of inertial microfluidics.}, } @article {pmid32901617, year = {2021}, author = {Oâ Neill, G and Tolley, NS}, title = {Modelling nasal airflow coefficients: an insight into the nature of airflow.}, journal = {Rhinology}, volume = {59}, number = {1}, pages = {66-74}, doi = {10.4193/Rhin19.440}, pmid = {32901617}, issn = {0300-0729}, mesh = {Computer Simulation ; Humans ; Hydrodynamics ; *Nose ; *Pulmonary Ventilation ; }, abstract = {BACKGROUND: There has been considerable discussion and conflicting views regarding the presence of laminar or turbulent flow within the nose. The aim of this study was to investigate how the modelling of variable flow coefficients can assist in the evalua- tion of the characteristics of flow in the resistive segments of the nose.

METHODOLOGY: A comparison was made between the flow coefficient for the nasal valve, obtained from a mathematical model, and resistive flow components such as a Venturi meter and orifice tube. Also, a variable loss coefficient was formulated for the whole (unilateral) nose which, by utilising the intersection of the laminar and turbulent asymptotes, provided an estimation for the critical Reynolds number (Rcrit).

RESULTS: The results show that the flow resistance of the nasal valve is considerably greater than that for both a Venturi meter and an orifice tube implying turbulent or turbulent-like flow for much of nasal inspiration. Regarding the loss coefficient for the whole (unilateral) nose, normal respiration flowrates are displaced well away from the laminar asymptote. The critical Reynolds number was estimated to be 450.

CONCLUSIONS: A novel method of determining the flow characteristics of the nose, particularly the critical Reynolds number, is presented. The analysis indicates a higher degree of turbulence than is assumed from a simple traditional calculation using a hy- draulic diameter and flow through straight tubes. There are implications for computational fluid dynamics (CFD) modelling where either the entire nasal airflow is assumed to be laminar or a low turbulence model implemented.}, } @article {pmid32895674, year = {2020}, author = {Tegze, G and Podmaniczky, F and Somfai, E and Börzsönyi, T and Gránásy, L}, title = {Orientational order in dense suspensions of elliptical particles in the non-Stokesian regime.}, journal = {Soft matter}, volume = {16}, number = {38}, pages = {8925-8932}, doi = {10.1039/d0sm00370k}, pmid = {32895674}, issn = {1744-6848}, abstract = {Suspensions of neutrally buoyant elliptic particles are modeled in 2D using fully resolved simulations that provide two-way interaction between the particle and the fluid medium. Forces due to particle collisions are represented by a diffuse interface approach that allows the investigation of dense suspensions (up to 47% packing fraction). We focus on the role inertial forces play at low and high particle Reynolds numbers termed low Reynolds number and inertial regimes, respectively. The suspensions are characterized by the orientation distribution function (ODF) that reflects shear induced rotation of the particles at low Reynolds numbers, and nearly stationary (swaying) particles at high Reynolds numbers. In both cases, orientational ordering differs qualitatively from the behavior observed in the Stokesian-regime. The ODF becomes flatter with increasing packing fraction, as opposed to the sharpening previous work predicted in the Stokesian regime. The ODF at low particle concentrations differs significantly for the low Reynolds number and inertial regimes, whereas with increasing packing fraction convergence is observed. For dense suspensions, the particle-particle interactions dominate the particle motion.}, } @article {pmid32881533, year = {2020}, author = {Cui, G and Jacobi, I}, title = {Magnetic Control of Ferrofluid Droplet Adhesion in Shear Flow and on Inclined Surfaces.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {36}, number = {36}, pages = {10885-10891}, doi = {10.1021/acs.langmuir.0c02369}, pmid = {32881533}, issn = {1520-5827}, abstract = {The manipulation of ferrofluidic droplets by magnetic fields is a popular technique for controlling fluid transport in open microfluidic systems. We examine the effect of gravity and shear flow external forces on the adhesion properties of sessile ferrofluidic droplets in the presence of a uniform magnetic field. The magnetic field was found to enhance the critical Bond number at which sliding begins on a tilting substrate but suppress the critical Weber number at which sliding begins in a moderate Reynolds number channel flow. The divergent adhesion trends are explained in terms of the shape deformation induced in the ferrofluidic droplet, the substrate wettability, and the apparent contact angle variation induced by the droplet deformation.}, } @article {pmid32879533, year = {2019}, author = {Battista, F and Mollicone, JP and Gualtieri, P and Messina, R and Casciola, CM}, title = {Exact regularized point particle (ERPP) method for particle-laden wall-bounded flows in the two-way coupling regime.}, journal = {Journal of fluid mechanics}, volume = {878}, number = {}, pages = {420-444}, pmid = {32879533}, issn = {0022-1120}, support = {339446/ERC_/European Research Council/International ; }, abstract = {The Exact Regularized Point Particle (ERPP) method is extended to treat the interphase momentum coupling between particles and fluid in the presence of walls by accounting for the vorticity generation due to the particles close to solid boundaries. The ERPP method overcomes the limitations of other methods by allowing the simulation of an extensive parameter space (Stokes number, mass loading, particle-to-fluid density ratio and Reynolds number) and of particle spatial distributions that are uneven (few particles per computational cell). The enhanced ERPP method is explained in detail and validated by considering the global impulse balance. In conditions when particles are located close to the wall, a common scenario in wall-bounded turbulent flows, the main contribution to the total impulse arises from the particle-induced vorticity at the solid boundary. The method is applied to direct numerical simulations of particle-laden turbulent pipe flow in the two-way coupling regime to address the turbulence modulation. The effects of the mass loading, the Stokes number and the particle-to-fluid density ratio are investigated. The drag is either unaltered or increased by the particles with respect to the uncoupled case. No drag reduction is found in the parameter space considered. The momentum stress budget, which includes an extra stress contribution by the particles, provides the rationale behind the drag behaviour. The extra stress produces a momentum flux towards the wall that strongly modifies the viscous stress, the culprit of drag at solid boundaries.}, } @article {pmid32876861, year = {2020}, author = {Mottaghi, S and Nazari, M and Fattahi, SM and Nazari, M and Babamohammadi, S}, title = {Droplet size prediction in a microfluidic flow focusing device using an adaptive network based fuzzy inference system.}, journal = {Biomedical microdevices}, volume = {22}, number = {3}, pages = {61}, doi = {10.1007/s10544-020-00513-4}, pmid = {32876861}, issn = {1572-8781}, mesh = {*Fuzzy Logic ; *Hydrodynamics ; *Lab-On-A-Chip Devices ; *Neural Networks, Computer ; }, abstract = {Microfluidics has wide applications in different technologies such as biomedical engineering, chemistry engineering, and medicine. Generating droplets with desired size for special applications needs costly and time-consuming iterations due to the nonlinear behavior of multiphase flow in a microfluidic device and the effect of several parameters on it. Hence, designing a flexible way to predict the droplet size is necessary. In this paper, we use the Adaptive Neural Fuzzy Inference System (ANFIS), by mixing the artificial neural network (ANN) and fuzzy inference system (FIS), to study the parameters which have effects on droplet size. The four main dimensionless parameters, i.e. the Capillary number, the Reynolds number, the flow ratio and the viscosity ratio are regarded as the inputs and the droplet diameter as the output of the ANFIS. Using dimensionless groups cause to extract more comprehensive results and avoiding more experimental tests. With the ANFIS, droplet sizes could be predicted with the coefficient of determination of 0.92.}, } @article {pmid32873833, year = {2020}, author = {McGurk, KA and Owen, B and Watson, WD and Nethononda, RM and Cordell, HJ and Farrall, M and Rider, OJ and Watkins, H and Revell, A and Keavney, BD}, title = {Heritability of haemodynamics in the ascending aorta.}, journal = {Scientific reports}, volume = {10}, number = {1}, pages = {14356}, pmid = {32873833}, issn = {2045-2322}, support = {RG/12/16/29939/BHF_/British Heart Foundation/United Kingdom ; RG/07/012/24110/BHF_/British Heart Foundation/United Kingdom ; MR/K501311/1/MRC_/Medical Research Council/United Kingdom ; RG/15/12/31616/BHF_/British Heart Foundation/United Kingdom ; CH/13/2/30154/BHF_/British Heart Foundation/United Kingdom ; }, mesh = {Adult ; Aged ; Aorta/*diagnostic imaging/*physiopathology ; Blood Flow Velocity ; Cardiovascular Abnormalities/*genetics ; Cohort Studies ; Female ; Genetic Predisposition to Disease/*genetics ; Genotyping Techniques ; Hemodynamics/*genetics ; Humans ; Magnetic Resonance Imaging/methods ; Male ; Middle Aged ; *Pedigree ; Phenotype ; *Polymorphism, Single Nucleotide ; Young Adult ; }, abstract = {Blood flow in the vasculature can be characterised by dimensionless numbers commonly used to define the level of instabilities in the flow, for example the Reynolds number, Re. Haemodynamics play a key role in cardiovascular disease (CVD) progression. Genetic studies have identified mechanosensitive genes with causal roles in CVD. Given that CVD is highly heritable and abnormal blood flow may increase risk, we investigated the heritability of fluid metrics in the ascending aorta calculated using patient-specific data from cardiac magnetic resonance (CMR) imaging. 341 participants from 108 British Caucasian families were phenotyped by CMR and genotyped for 557,124 SNPs. Flow metrics were derived from the CMR images to provide some local information about blood flow in the ascending aorta, based on maximum values at systole at a single location, denoted max, and a 'peak mean' value averaged over the area of the cross section, denoted pm. Heritability was estimated using pedigree-based (QTDT) and SNP-based (GCTA-GREML) methods. Estimates of Reynolds number based on spatially averaged local flow during systole showed substantial heritability ([Formula: see text], [Formula: see text]), while the estimated heritability for Reynolds number calculated using the absolute local maximum velocity was not statistically significant (12-13%; [Formula: see text]). Heritability estimates of the geometric quantities alone; e.g. aortic diameter ([Formula: see text], [Formula: see text]), were also substantially heritable, as described previously. These findings indicate the potential for the discovery of genetic factors influencing haemodynamic traits in large-scale genotyped and phenotyped cohorts where local spatial averaging is used, rather than instantaneous values. Future Mendelian randomisation studies of aortic haemodynamic estimates, which are swift to derive in a clinical setting, will allow for the investigation of causality of abnormal blood flow in CVD.}, } @article {pmid32859015, year = {2020}, author = {Nichka, VS and Geoffroy, TR and Nikonenko, V and Bazinet, L}, title = {Impacts of Flow Rate and Pulsed Electric Field Current Mode on Protein Fouling Formation during Bipolar Membrane Electroacidification of Skim Milk.}, journal = {Membranes}, volume = {10}, number = {9}, pages = {}, pmid = {32859015}, issn = {2077-0375}, abstract = {Fouling is one of the major problems in electrodialysis. The aim of the present work was to investigate the effect of five different solution flow rates (corresponding to Reynolds numbers of 162, 242, 323, 404 and 485) combined with the use of pulsed electric field (PEF) current mode on protein fouling of bipolar membrane (BPM) during electrodialysis with bipolar membranes (EDBM) of skim milk. The application of PEF prevented the fouling formation by proteins on the cationic interface of the BPM almost completely, regardless of the flow rate or Reynolds number. Indeed, under PEF mode of current the weight of protein fouling was negligible in comparison with CC current mode (0.07 ± 0.08 mg/cm[2] versus 5.56 ± 2.40 mg/cm[2]). When a continuous current (CC) mode was applied, Reynolds number equals or higher than 323 corresponded to a minimal value of protein fouling of BPM. This positive effect of both increasing the flow rate and using PEF is due to the facts that during pauses, the solution flow flushes the accumulated protein from the membrane while in the same time there is a decrease in concentration polarization (CP) and consequently decrease in H[+] generation at the cationic interface of the BPM, minimizing fouling formation and accumulation.}, } @article {pmid32858042, year = {2020}, author = {Tripathi, D and Prakash, J and Tiwari, AK and Ellahi, R}, title = {Thermal, microrotation, electromagnetic field and nanoparticle shape effects on Cu-CuO/blood flow in microvascular vessels.}, journal = {Microvascular research}, volume = {132}, number = {}, pages = {104065}, doi = {10.1016/j.mvr.2020.104065}, pmid = {32858042}, issn = {1095-9319}, mesh = {Animals ; Blood Flow Velocity ; Copper/*chemistry ; *Electromagnetic Fields ; Humans ; Hydrodynamics ; *Microcirculation ; *Microfluidic Analytical Techniques ; Microvessels/*physiology ; *Models, Cardiovascular ; *Nanoparticles ; Pulsatile Flow ; Regional Blood Flow ; Rotation ; *Temperature ; Time Factors ; }, abstract = {A thermal analysis of Cu-CuO/ blood nanofluids flow in asymmetric microchannel propagating with wave velocity is presented in this study. For the blood, a micropolar fluid model is considered to investigate the microrotation effects of blood flow. Thermal radiation effects and the influence of nanoparticle shape, electric double layer thickness, and electromagnetic fields on the flow are studied. Three types of nanoparticles shapes namely cylinder, bricks and platelets are taken into account. Governing equations are solved under the approximations of long wavelength, low Reynolds number, and Debye-Hückel linearization. Numerical computations are performed for the axial pressure gradient, axial velocity, spin velocity and temperature distribution. The effects of various physical parameters on flow and thermal characteristics are computed and their physical interpretation is also discussed. The outcomes indicate that the axial velocity of Cu-CuO/blood nanoparticles strongly depends on applied electromagnetic field and microrotation. The model's finding will be applicable in designing the smart electromagnetic micro pumps for the hemodialysis and lungs-on-chip devices for the pumping of the blood.}, } @article {pmid32850285, year = {2020}, author = {Zhu, L and Xu, B and Wu, X and Lei, J and Hacker, DL and Liang, X and Wurm, FM}, title = {Analysis of volumetric mass transfer coefficient (k L a) in small- (250 mL) to large-scale (2500 L) orbitally shaken bioreactors.}, journal = {3 Biotech}, volume = {10}, number = {9}, pages = {397}, pmid = {32850285}, issn = {2190-572X}, abstract = {In this study, the combination of dimensional analysis (DA) and analysis of variance (ANOVA) was used to predict the volumetric mass transfer coefficient (k L a) values under different operating conditions for orbitally shaken bioreactors (OSRs) with different filling volumes. It was found that Reynolds number and the interaction between Froude number and geometric number have the largest impact on k L a with impact indexes of 7.41 and 7.50, respectively. Moreover, the volume number has the largest negative impact on k L a, with an impact index of - 5.34. Thus, an effective way to increase the oxygen supply is by increasing the shaking speed and shaking diameter or decreasing the vessel diameter. However, cell cultivation with a higher filling volume will have an increased risk of oxygen scarcity. Therefore, with the help of the k L a prediction model, a suitable operating condition can be determined effectively and easily.}, } @article {pmid32846914, year = {2020}, author = {Ghalambaz, M and Arasteh, H and Mashayekhi, R and Keshmiri, A and Talebizadehsardari, P and Yaïci, W}, title = {Investigation of Overlapped Twisted Tapes Inserted in a Double-Pipe Heat Exchanger Using Two-Phase Nanofluid.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {10}, number = {9}, pages = {}, pmid = {32846914}, issn = {2079-4991}, abstract = {This study investigated the laminar convective heat transfer and fluid flow of Al2O3 nanofluid in a counter flow double-pipe heat exchanger equipped with overlapped twisted tape inserts in both inner and outer tubes. Two models of the same (co-swirling twisted tapes) and opposite (counter-swirling twisted tapes) angular directions for the stationary twisted tapes were considered. The computational fluid dynamic simulations were conducted through varying the design parameters, including the angular direction of twisted tape inserts, nanofluid volume concentration, and Reynolds number. It was found that inserting the overlapped twisted tapes in the heat exchanger significantly increases the thermal performance as well as the friction factor compared with the plain heat exchanger. The results indicate that models of co-swirling twisted tapes and counter-swirling twisted tapes increase the average Nusselt number by almost 35.2-66.2% and 42.1-68.7% over the Reynolds number ranging 250-1000, respectively. To assess the interplay between heat transfer enhancement and pressure loss penalty, the dimensionless number of performance evaluation criterion was calculated for all the captured configurations. Ultimately, the highest value of performance evaluation criterion is equal to 1.40 and 1.26 at inner and outer tubes at the Reynolds number of 1000 and the volume fraction of 3% in the case of counter-swirling twisted tapes model.}, } @article {pmid32845950, year = {2020}, author = {Zhang, S and Cui, Z and Wang, Y and den Toonder, JMJ}, title = {Metachronal actuation of microscopic magnetic artificial cilia generates strong microfluidic pumping.}, journal = {Lab on a chip}, volume = {20}, number = {19}, pages = {3569-3581}, doi = {10.1039/d0lc00610f}, pmid = {32845950}, issn = {1473-0189}, mesh = {*Cilia ; Magnetic Fields ; Magnetics ; *Microfluidics ; Motion ; }, abstract = {Biological cilia that generate fluid flow or propulsion are often found to exhibit a collective wavelike metachronal motion, i.e. neighboring cilia beat slightly out-of-phase rather than synchronously. Inspired by this observation, this article experimentally demonstrates that microscopic magnetic artificial cilia (μMAC) performing a metachronal motion can generate strong microfluidic flows, though, interestingly, the mechanism is different from that in biological cilia, as is found through a systematic experimental study. The μMAC are actuated by a facile magnetic setup, consisting of an array of rod-shaped magnets. This arrangement imposes a time-dependent non-uniform magnetic field on the μMAC array, resulting in a phase difference between the beatings of adjacent μMAC, while each cilium exhibits a two-dimensional whip-like motion. By performing the metachronal 2D motion, the μMAC are able to generate a strong flow in a microfluidic chip, with velocities of up to 3000 μm s[-1] in water, which, different from biological cilia, is found to be a result of combined metachronal and inertial effects, in addition to the effect of asymmetric beating. The pumping performance of the metachronal μMAC outperforms all previously reported microscopic artificial cilia, and is competitive with that of most of the existing microfluidic pumping methods, while the proposed platform requires no physical connection to peripheral equipment, reduces the usage of reagents by minimizing "dead volumes", avoids undesirable electrical effects, and accommodates a wide range of different fluids. The 2D metachronal motion can also generate a flow with velocities up to 60 μm s[-1] in pure glycerol, where Reynolds number is less than 0.05 and the flow is primarily caused by the metachronal motion of the μMAC. These findings offer a novel solution to not only create on-chip integrated micropumps, but also design swimming and walking microrobots, as well as self-cleaning and antifouling surfaces.}, } @article {pmid32833583, year = {2020}, author = {Latt, J and Coreixas, C and Beny, J and Parmigiani, A}, title = {Efficient supersonic flow simulations using lattice Boltzmann methods based on numerical equilibria.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {378}, number = {2175}, pages = {20190559}, pmid = {32833583}, issn = {1471-2962}, abstract = {A double-distribution-function based lattice Boltzmann method (DDF-LBM) is proposed for the simulation of polyatomic gases in the supersonic regime. The model relies on a numerical equilibrium that has been extensively used by discrete velocity methods since the late 1990s. Here, it is extended to reproduce an arbitrary number of moments of the Maxwell-Boltzmann distribution. These extensions to the standard 5-constraint (mass, momentum and energy) approach lead to the correct simulation of thermal, compressible flows with only 39 discrete velocities in 3D. The stability of this BGK-LBM is reinforced by relying on Knudsen-number-dependent relaxation times that are computed analytically. Hence, high Reynolds-number, supersonic flows can be simulated in an efficient and elegant manner. While the 1D Riemann problem shows the ability of the proposed approach to handle discontinuities in the zero-viscosity limit, the simulation of the supersonic flow past a NACA0012 aerofoil confirms the excellent behaviour of this model in a low-viscosity and supersonic regime. The flow past a sphere is further simulated to investigate the 3D behaviour of our model in the low-viscosity supersonic regime. The proposed model is shown to be substantially more efficient than the previous 5-moment D3Q343 DDF-LBM for both CPU and GPU architectures. It then opens up a whole new world of compressible flow applications that can be realistically tackled with a purely LB approach. This article is part of the theme issue 'Fluid dynamics, soft matter and complex systems: recent results and new methods'.}, } @article {pmid32828761, year = {2020}, author = {Akram, J and Akbar, NS and Tripathi, D}, title = {Blood-based graphene oxide nanofluid flow through capillary in the presence of electromagnetic fields: A Sutterby fluid model.}, journal = {Microvascular research}, volume = {132}, number = {}, pages = {104062}, doi = {10.1016/j.mvr.2020.104062}, pmid = {32828761}, issn = {1095-9319}, mesh = {Animals ; Blood Flow Velocity ; Capillaries/*physiology ; Computer Simulation ; *Electromagnetic Fields ; Graphite/*chemistry ; Humans ; *Microcirculation ; *Models, Cardiovascular ; *Nanoparticles ; Numerical Analysis, Computer-Assisted ; *Pulsatile Flow ; Time Factors ; }, abstract = {Pumping devices with the electrokinetics phenomena are important in many microscale transport phenomena in physiology. This study presents a theoretical and numerical investigation on the peristaltic pumping of non-Newtonian Sutterby nanofluid through capillary in presence of electromagnetohydrodynamics. Here blood (Sutterby fluid) is taken as a base fluid and nanofluid is prepared by the suspension of graphene oxide nanoparticle in blood. Graphene oxide is extremely useful in the medical domain for drug delivery and cancer treatment. The modified Buongiorno model for nanofluids and Poisson-Boltzmann ionic distribution is adopted for the formulation of the present problem. Constitutive flow equations are linearized by the implementation of approximations low Reynolds number, large wavelength, and the Debye-Hückel linearization. The numerical solution of reduced coupled and nonlinear set of equations is computed through Mathematica and graphical illustration is presented. Further, the impacts of buoyancy forces, thermal radiation, and mixed convection are also studied. It is revealed in this investigation that the inclusion of a large number of nanoparticles alters the flow characteristics significantly and boosts the heat transfer mechanism. Moreover, the pumping power of the peristaltic pump can be enhanced by the reduction in the width of the electric double layer which can be done by altering the electrolyte concentration.}, } @article {pmid32810744, year = {2020}, author = {Moruzzi, RB and Campos, LC and Sharifi, S and da Silva, PG and Gregory, J}, title = {Nonintrusive investigation of large Al-kaolin fractal aggregates with slow settling velocities.}, journal = {Water research}, volume = {185}, number = {}, pages = {116287}, doi = {10.1016/j.watres.2020.116287}, pmid = {32810744}, issn = {1879-2448}, mesh = {Flocculation ; *Fractals ; *Kaolin ; Particle Size ; Rheology ; }, abstract = {Although a combination of aggregate characteristics dictate particle settling, it is commonly assumed that large particles have higher terminal velocities. This simplifying assumption often leads to overprediction of large aggregate settling velocities which in turn negatively impacts on estimates of sedimentation clarification efficiency. Despite its importance, little attention has been given to large aggregates with slow-settling velocities. This paper addresses this gap by investigating slow-settling velocities of large, heterodisperse and multi-shape Al-kaolin aggregates using non-intrusive methods. A particle image velocimetry technique (PIV) was applied to track aggregate velocity and a non-intrusive image technique was used to determine aggregate characteristics, including size (df), three-dimensional fractal dimension (Df), density (ρf), aggregate velocity (Vexp) and Reynolds number (Re). Results showed no strict dependence of settling velocity on large aggregate size, shape and density, as Al-kaolin aggregates with the same size exhibited different settling velocities. A comparison of the results with the well-known Stokes' law for velocity modified by a shape factor showed that the settling velocities measured here can vary from 2 to 14 fold lower than the predicted values for perfect sphere-shape aggregates with the same density and size. Furthermore, results have also shown large Al-kaolin aggregate's drag coefficient (Cd) to be around 56/Re, for average fractal aggregate sphericity of around 0.58.}, } @article {pmid32809129, year = {2021}, author = {Cui, J and Liu, Y and Xiao, L and Chen, S and Fu, BM}, title = {Numerical study on the adhesion of a circulating tumor cell in a curved microvessel.}, journal = {Biomechanics and modeling in mechanobiology}, volume = {20}, number = {1}, pages = {243-254}, pmid = {32809129}, issn = {1617-7940}, mesh = {Cell Adhesion ; Computer Simulation ; Humans ; Membranes ; Microvessels/*pathology ; Neoplastic Cells, Circulating/*pathology ; *Numerical Analysis, Computer-Assisted ; Probability ; Time Factors ; }, abstract = {The adhesion of a circulating tumor cell (CTC) in a three-dimensional curved microvessel was numerically investigated. Simulations were first performed to characterize the differences in the dynamics and adhesion of a CTC in the straight and curved vessels. After that, a parametric study was performed to investigate the effects of the applied driven force density f (or the flow Reynolds number Re) and the CTC membrane bending modulus Kb on the CTC adhesion. Our simulation results show that the CTC prefers to adhere to the curved vessel as more bonds are formed around the transition region of the curved part due to the increased cell-wall contact by the centrifugal force. The parametric study also indicates that when the flow driven force f (or Re) increases or when the CTC becomes softer (Kb decreases), the bond formation probability increases and the bonds will be formed at more sites of a curved vessel. The increased f (or Re) brings a larger centrifugal force, while the decreased Kb generates more contact areas at the cell-wall interface, both of which are beneficial to the bond formation. In the curved vessel, it is found that the site where bonds are formed the most (hotspot) varies with the applied f and the Kb. For our vessel geometry, when f is small, the hotspot tends to be within the first bend of the vessel, while as f increases or Kb decreases, the hotspot may shift to the second bend of the vessel.}, } @article {pmid32805051, year = {2020}, author = {Rao, C and Liu, H}, title = {Effects of Reynolds Number and Distribution on Passive Flow Control in Owl-Inspired Leading-Edge Serrations.}, journal = {Integrative and comparative biology}, volume = {60}, number = {5}, pages = {1135-1146}, doi = {10.1093/icb/icaa119}, pmid = {32805051}, issn = {1557-7023}, mesh = {Animals ; Biomechanical Phenomena ; Computer Simulation ; Feathers ; *Flight, Animal ; *Models, Biological ; Wings, Animal ; }, abstract = {As a sophisticated micro device for noise reduction, the owl-inspired leading-edge (LE) serrations have been confirmed capable of achieving passive control of laminar-turbulent transition while normally paying a cost of lowering the aerodynamic performance in low Reynolds number (Re∼O[103]) regime. In order to explore potential applications of the owl-inspired serrated airfoils or blades in developing low noise wind turbines or multi-copters normally operating at higher Res, we conducted a large-eddy simulation (LES)-based study of Re effects on the aerodynamic performance of 2D clean and serrated models. Our results show that the LE serrations keep working effectively in mitigating turbulent fluctuations over a broad range of Re (O[103] ∼ O[105]), capable of achieving marked improvement in lift-to-drag ratio with increasing Res. As the aeroacoustic fields are in close association with the propagation of the turbulence sources, it is observed that the tradeoff between passive mitigation of turbulent fluctuations (hence aeroacoustic noise suppression) and aerodynamic performance can be noticeably mitigated at large angles of attack (AoAs) and at high Res. This indicates that the LE serrations present an alternative passive flow control mechanism at high Res through a straightforward local excitation of the flow transition while capable of mitigating the turbulent intensity passively. We further developed a 3D LES model of clean and partially serrated rectangular wings to investigate the effects of the LE serrations' distribution on aerodynamic features, on the basis of the observation that longer serrations are often distributed intensively in the mid-span of real owl's feathers. We find that the mid-span distributed LE serrations can facilitate the break-up of LE vortices and the turbulent transition passively and effectively while achieving a low level of turbulence kinetic energy over the upper suction surface of the wing.}, } @article {pmid32801384, year = {2020}, author = {Ardeshiri, H and Cassiani, M and Park, SY and Stohl, A and Pisso, I and Dinger, AS}, title = {On the Convergence and Capability of the Large-Eddy Simulation of Concentration Fluctuations in Passive Plumes for a Neutral Boundary Layer at Infinite Reynolds Number.}, journal = {Boundary-layer meteorology}, volume = {176}, number = {3}, pages = {291-327}, pmid = {32801384}, issn = {0006-8314}, abstract = {Large-eddy simulation (LES) experiments have been performed using the Parallelized LES Model (PALM). A methodology for validating and understanding LES results for plume dispersion and concentration fluctuations in an atmospheric-like flow is presented. A wide range of grid resolutions is shown to be necessary for investigating the convergence of statistical characteristics of velocity and scalar fields. For the scalar, the statistical moments up to the fourth order and the shape of the concentration probability density function (p.d.f.) are examined. The mean concentration is influenced by grid resolution, with the highest resolution simulation showing a lower mean concentration, linked to larger turbulent structures. However, a clear tendency to convergence of the concentration variance is observed at the two higher resolutions. This behaviour is explained by showing that the mechanisms driving the mean and the variance are differently influenced by the grid resolution. The analysis of skewness and kurtosis allows also the obtaining of general results on plume concentration fluctuations. Irrespective of grid resolution, a family of Gamma p.d.f.s well represents the shape of the concentration p.d.f. but only beyond the peak of the concentration fluctuation intensity. In the early plume dispersion phases, the moments of the p.d.f. are in good agreement with those generated by a fluctuating plume model. To the best of our knowledge, our study demonstrates for the first time that, if resolution and averaging time are adequate, atmospheric LES provides a trustworthy representation of the high order moments of the concentration field, up to the fourth order, for a dispersing plume.}, } @article {pmid32796948, year = {2020}, author = {Ryan, DP and Chen, Y and Nguyen, P and Goodwin, PM and Carey, JW and Kang, Q and Werner, JH and Viswanathan, HS}, title = {3D particle transport in multichannel microfluidic networks with rough surfaces.}, journal = {Scientific reports}, volume = {10}, number = {1}, pages = {13848}, pmid = {32796948}, issn = {2045-2322}, abstract = {The transport of particles and fluids through multichannel microfluidic networks is influenced by details of the channels. Because channels have micro-scale textures and macro-scale geometries, this transport can differ from the case of ideally smooth channels. Surfaces of real channels have irregular boundary conditions to which streamlines adapt and with which particle interact. In low-Reynolds number flows, particles may experience inertial forces that result in trans-streamline movement and the reorganization of particle distributions. Such transport is intrinsically 3D and an accurate measurement must capture movement in all directions. To measure the effects of non-ideal surface textures on particle transport through complex networks, we developed an extended field-of-view 3D macroscope for high-resolution tracking across large volumes ([Formula: see text]) and investigated a model multichannel microfluidic network. A topographical profile of the microfluidic surfaces provided lattice Boltzmann simulations with a detailed feature map to precisely reconstruct the experimental environment. Particle distributions from simulations closely reproduced those observed experimentally and both measurements were sensitive to the effects of surface roughness. Under the conditions studied, inertial focusing organized large particles into an annular distribution that limited their transport throughout the network while small particles were transported uniformly to all regions.}, } @article {pmid32783851, year = {2020}, author = {Deng, D and Pan, Y and Liu, G and Liu, W and Ma, L}, title = {Seeking the hotspots of nitrogen removal: A comparison of sediment denitrification rate and denitrifier abundance among wetland types with different hydrological conditions.}, journal = {The Science of the total environment}, volume = {737}, number = {}, pages = {140253}, doi = {10.1016/j.scitotenv.2020.140253}, pmid = {32783851}, issn = {1879-1026}, mesh = {China ; Denitrification ; Hydrology ; *Nitrogen ; *Wetlands ; }, abstract = {Wetlands play a vital role in removing nitrogen (N) from aquatic environments via the denitrification process, which is regulated by multiple environmental and biological factors. Until now, the mechanisms by which environmental factors and microbial abundance regulate denitrification rates in wetlands under different hydrological conditions remain poorly understood. Here, we investigated sediment potential denitrification rate (PDR) and unamended denitrification rate (UDR), and quantified denitrifier abundance (nirS, nirK, and nosZ genes) in 36 stream, river, pond, and ditch wetland sites along the Dan River, a nitrogen-rich river in central China. The result indicated that ditches had the highest denitrification rates and denitrifier abundance. Both PDR and UDR showed strong seasonality, and were observed to be negatively correlated with water velocity in streams and rivers. Moreover, denitrification rates were significantly related to denitrifier abundance and many water quality parameters and sediment properties. Interestingly, PDR and UDR were generally positively associated with N and carbon (C) availability in streams and rivers, but such correlations were not found in ponds and ditches. Using a scaling analysis, we found that environmental parameters, including Reynolds number, sediment total C ratio, and interstitial space, coupled with relative nirS gene abundance could predict the hotspots of denitrification rates in wetlands with varying hydrologic regimes. Our findings highlight that hydrological conditions, especially water velocity and hydrologic pulsing, play a nonnegligible role in determining N biogeochemical processes in wetlands.}, } @article {pmid32770358, year = {2020}, author = {Patterson, LHC and Walker, JL and Naivar, MA and Rodriguez-Mesa, E and Hoonejani, MR and Shields, K and Foster, JS and Doyle, AM and Valentine, MT and Foster, KL}, title = {Inertial flow focusing: a case study in optimizing cellular trajectory through a microfluidic MEMS device for timing-critical applications.}, journal = {Biomedical microdevices}, volume = {22}, number = {3}, pages = {52}, doi = {10.1007/s10544-020-00508-1}, pmid = {32770358}, issn = {1572-8781}, support = {1631656//Division of Chemical, Bioengineering, Environmental, and Transport Systems/International ; 1254893//Division of Civil, Mechanical and Manufacturing Innovation/International ; }, mesh = {Buffers ; Equipment Design ; *Lab-On-A-Chip Devices ; Micro-Electrical-Mechanical Systems/*instrumentation ; Microspheres ; Particle Size ; Polystyrenes/chemistry ; Temperature ; Viscosity ; }, abstract = {Although microfluidic micro-electromechanical systems (MEMS) are well suited to investigate the effects of mechanical force on large populations of cells, their high-throughput capabilities cannot be fully leveraged without optimizing the experimental conditions of the fluid and particles flowing through them. Parameters such as flow velocity and particle size are known to affect the trajectories of particles in microfluidic systems and have been studied extensively, but the effects of temperature and buffer viscosity are not as well understood. In this paper, we explored the effects of these parameters on the timing of our own cell-impact device, the μHammer, by first tracking the velocity of polystyrene beads through the device and then visualizing the impact of these beads. Through these assays, we find that the timing of our device is sensitive to changes in the ratio of inertial forces to viscous forces that particles experience while traveling through the device. This sensitivity provides a set of parameters that can serve as a robust framework for optimizing device performance under various experimental conditions, without requiring extensive geometric redesigns. Using these tools, we were able to achieve an effective throughput over 360 beads/s with our device, demonstrating the potential of this framework to improve the consistency of microfluidic systems that rely on precise particle trajectories and timing.}, } @article {pmid32766844, year = {2020}, author = {Waldrop, LD and He, Y and Hedrick, TL and Rader, JA}, title = {Functional Morphology of Gliding Flight I: Modeling Reveals Distinct Performance Landscapes Based on Soaring Strategies.}, journal = {Integrative and comparative biology}, volume = {60}, number = {5}, pages = {1283-1296}, doi = {10.1093/icb/icaa114}, pmid = {32766844}, issn = {1557-7023}, mesh = {Animals ; Biomechanical Phenomena ; *Birds ; *Flight, Animal ; *Wings, Animal ; }, abstract = {The physics of flight influences the morphology of bird wings through natural selection on flight performance. The connection between wing morphology and performance is unclear due to the complex relationships between various parameters of flight. In order to better understand this connection, we present a holistic analysis of gliding flight that preserves complex relationships between parameters. We use a computational model of gliding flight, along with analysis by uncertainty quantification, to (1) create performance landscapes of gliding based on output metrics (maximum lift-to-drag ratio, minimum gliding angle, minimum sinking speed, and lift coefficient at minimum sinking speed) and (2) predict what parameters of flight (chordwise camber, wing aspect ratio [AR], and Reynolds number) would differ between gliding and nongliding species of birds. We also examine performance based on the soaring strategy for possible differences in morphology within gliding birds. Gliding birds likely have greater ARs than non-gliding birds, due to the high sensitivity of AR on most metrics of gliding performance. Furthermore, gliding birds can use two distinct soaring strategies based on performance landscapes. First, maximizing distance traveled (maximizing lift-to-drag ratio and minimizing gliding angle) should result in wings with high ARs and middling-to-low wing chordwise camber. Second, maximizing lift extracted from updrafts should result in wings with middling ARs and high wing chordwise camber. Following studies can test these hypotheses using morphological measurements.}, } @article {pmid32762434, year = {2020}, author = {Arrieta, J and Cartwright, JHE and Gouillart, E and Piro, N and Piro, O and Tuval, I}, title = {Geometric mixing.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {378}, number = {2179}, pages = {20200168}, pmid = {32762434}, issn = {1471-2962}, abstract = {Mixing fluids often involves a periodic action, like stirring one's tea. But reciprocating motions in fluids at low Reynolds number, in Stokes flows where inertia is negligible, lead to periodic cycles of mixing and unmixing, because the physics, molecular diffusion excepted, is time reversible. So how can fluid be mixed in such circumstances? The answer involves a geometric phase. Geometric phases are found everywhere in physics as anholonomies, where after a closed circuit in the parameters, some system variables do not return to their original values. We discuss the geometric phase in fluid mixing: geometric mixing. This article is part of the theme issue 'Stokes at 200 (part 2)'.}, } @article {pmid32752686, year = {2020}, author = {Seyler, SL and Pressé, S}, title = {Surmounting potential barriers: Hydrodynamic memory hedges against thermal fluctuations in particle transport.}, journal = {The Journal of chemical physics}, volume = {153}, number = {4}, pages = {041102}, doi = {10.1063/5.0013722}, pmid = {32752686}, issn = {1089-7690}, abstract = {Recently, trapped-particle experiments have probed the instantaneous velocity of Brownian motion revealing that, at early times, hydrodynamic history forces dominate Stokes damping. In these experiments, nonuniform particle motion is well described by the Basset-Boussinesq-Oseen (BBO) equation, which captures the unsteady Basset history force at a low Reynolds number. Building off of these results, earlier we showed that, at low temperature, BBO particles could exploit fluid inertia in order to overcome potential barriers (generically modeled as a tilted washboard), while its Langevin counter-part could not. Here, we explore the behavior of neutrally buoyant BBO particles at finite temperature for moderate Stokes damping. Remarkably, we find that the transport of particles injected into a bumpy potential with sufficiently high barriers can be completely quenched at intermediate temperatures, whereas itinerancy may be possible above and below that temperature window. This effect is present for both Langevin and BBO dynamics, though these occur over drastically different temperature ranges. Furthermore, hydrodynamic memory mitigates these effects by sustaining initial particle momentum, even in the difficult intermediate temperature regime.}, } @article {pmid32752632, year = {2020}, author = {Romanò, F and Türkbay, T and Kuhlmann, HC}, title = {Lagrangian chaos in steady three-dimensional lid-driven cavity flow.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {30}, number = {7}, pages = {073121}, doi = {10.1063/5.0005792}, pmid = {32752632}, issn = {1089-7682}, abstract = {Steady three-dimensional flows in lid-driven cavities are investigated numerically using a high-order spectral-element solver for the incompressible Navier-Stokes equations. The focus is placed on critical points in the flow field, critical limit cycles, their heteroclinic connections, and on the existence, shape, and dependence on the Reynolds number of Kolmogorov-Arnold-Moser (KAM) tori. In finite-length cuboidal cavities at small Reynolds numbers, a thin layer of chaotic streamlines covers all walls. As the Reynolds number is increased, the chaotic layer widens and the complementary KAM tori shrink, eventually undergoing resonances, until they vanish. Accurate data for the location of closed streamlines and of KAM tori are provided, both of which reach very close to the moving lid. For steady periodic Taylor-Görtler vortices in spanwise infinitely extended cavities with a square cross section, chaotic streamlines occupy a large part of the flow domain immediately after the onset of Taylor-Görtler vortices. As the Reynolds number increases, the remaining KAM tori vanish from the Taylor-Görtler vortices, while KAM tori grow in the central region further away from the solid walls.}, } @article {pmid32752610, year = {2020}, author = {Chatterjee, S and Verma, MK}, title = {Kolmogorov flow: Linear stability and energy transfers in a minimal low-dimensional model.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {30}, number = {7}, pages = {073110}, doi = {10.1063/5.0002751}, pmid = {32752610}, issn = {1089-7682}, abstract = {In this paper, we derive a four-mode model for the Kolmogorov flow by employing Galerkin truncation and the Craya-Herring basis for the decomposition of velocity field. After this, we perform a bifurcation analysis of the model. Though our low-dimensional model has fewer modes than past models, it captures the essential features of the primary bifurcation of the Kolmogorov flow. For example, it reproduces the critical Reynolds number for the supercritical pitchfork bifurcation and the flow structures of past works. We also demonstrate energy transfers from intermediate scales to large scales. We perform direct numerical simulations of the Kolmogorov flow and show that our model predictions match the numerical simulations very well.}, } @article {pmid32752609, year = {2020}, author = {Josserand, C and Le Berre, M and Pomeau, Y}, title = {Scaling laws in turbulence.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {30}, number = {7}, pages = {073137}, doi = {10.1063/1.5144147}, pmid = {32752609}, issn = {1089-7682}, abstract = {Following the idea that dissipation in turbulence at high Reynolds number is dominated by singular events in space-time and described by solutions of the inviscid Euler equations, we draw the conclusion that in such flows, scaling laws should depend only on quantities appearing in the Euler equations. This excludes viscosity or a turbulent length as scaling parameters and constrains drastically possible analytical pictures of this limit. We focus on the drag law deduced by Newton for a projectile moving quickly in a fluid at rest. Inspired by this Newton's drag force law (proportional to the square of the speed of the moving object in the limit of large Reynolds numbers), which is well verified in experiments when the location of the detachment of the boundary layer is defined, we propose an explicit relationship between the Reynolds stress in the turbulent wake and quantities depending on the velocity field (averaged in time but depending on space). This model takes the form of an integrodifferential equation for the velocity which is eventually solved for a Poiseuille flow in a circular pipe.}, } @article {pmid32751881, year = {2020}, author = {Voglhuber-Brunnmaier, T and Jakoby, B}, title = {Higher-Order Models for Resonant Viscosity and Mass-Density Sensors.}, journal = {Sensors (Basel, Switzerland)}, volume = {20}, number = {15}, pages = {}, pmid = {32751881}, issn = {1424-8220}, abstract = {Advanced fluid models relating viscosity and density to resonance frequency and quality factor of vibrating structures immersed in fluids are presented. The numerous established models which are ultimately all based on the same approximation are refined, such that the measurement range for viscosity can be extended. Based on the simple case of a vibrating cylinder and dimensional analysis, general models for arbitrary order of approximation are derived. Furthermore, methods for model parameter calibration and the inversion of the models to determine viscosity and/or density from measured resonance parameters are shown. One of the two presented fluid models is a viscosity-only model, where the parameters of it can be calibrated without knowledge of the fluid density. The models are demonstrated for a tuning fork-based commercial instrument, where maximum deviations between measured and reference viscosities of approximately ±0.5% in the viscosity range from 1.3 to 243 mPas could be achieved. It is demonstrated that these results show a clear improvement over the existing models.}, } @article {pmid32738822, year = {2020}, author = {Manchester, EL and Xu, XY}, title = {The effect of turbulence on transitional flow in the FDA's benchmark nozzle model using large-eddy simulation.}, journal = {International journal for numerical methods in biomedical engineering}, volume = {36}, number = {10}, pages = {e3389}, doi = {10.1002/cnm.3389}, pmid = {32738822}, issn = {2040-7947}, mesh = {*Benchmarking ; *Computer Simulation ; *Models, Cardiovascular ; Stress, Mechanical ; United States ; *United States Food and Drug Administration ; }, abstract = {The Food and Drug Administration's (FDA) benchmark nozzle model has been studied extensively both experimentally and computationally. Although considerable efforts have been made on validations of a variety of numerical models against available experimental data, the transitional flow cases are still not fully resolved, especially with regards to detailed comparison of predicted turbulence quantities with experimental measurements. This study aims to fill this gap by conducting large-eddy simulations (LES) of flow through the FDA's benchmark model, at a transitional Reynolds number of 2000. Numerical results are compared to previous interlaboratory experimental results, with an emphasis on turbulence characteristics. Our results show that the LES methodology can accurately capture laminar quantities throughout the model. In the pre-jet breakdown region, predicted turbulence quantities are generally larger than high resolution experimental data acquired with laser Doppler velocimetry. In the jet breakdown regions, where maximum Reynolds stresses occur, Reynolds shear stresses show excellent agreement. Differences of up to 4% and 20% are observed near the jet core in the axial and radial normal Reynolds stresses, respectively. Comparisons between viscous and Reynolds shear stresses show that peak viscous shear stresses occur in the nozzle throat reaching a value of 18 Pa in the boundary layer, whilst peak Reynolds shear stresses occur in the jet breakdown region reaching a maximum value of 87 Pa. Our results highlight the importance in considering both laminar and turbulent contributions towards shear stresses and that neglecting the turbulence effect can significantly underestimate the total shear force exerted on the fluid.}, } @article {pmid32731122, year = {2020}, author = {Ahmed, R and Ali, N and Al-Khaled, K and Khan, SU and Tlili, I}, title = {Finite difference simulations for non-isothermal hydromagnetic peristaltic flow of a bio-fluid in a curved channel: Applications to physiological systems.}, journal = {Computer methods and programs in biomedicine}, volume = {195}, number = {}, pages = {105672}, doi = {10.1016/j.cmpb.2020.105672}, pmid = {32731122}, issn = {1872-7565}, mesh = {*Body Fluids ; Equipment Design ; *Peristalsis ; Rheology ; Temperature ; }, abstract = {Owing to the fundamental significances of peristalsis phenomenon in various biological systems like circulation of blood in vessels, lungs devices, pumping of blood in heart and movement of chyme in the gastrointestinal tract, variety of research by scientist on this topic has been presented in recently years. The peristaltic pumping plays a novel role in various industrial processes like transfer of sanitary materials, the pumping equipment design of roller pumps and many more. The present article investigates numerically the theoretical aspects of heat and mass transportation in peristaltic pattern of Carreau fluid through a curved channel. The computations for axial velocity, pressure rise, temperature field, mass concentration, and stream function are carried out under low Reynolds number and long wavelength approximation in the wave frame of reference by utilizing appropriate numerical implicit finite difference technique (FDM). The implementation of numerical procedure and graphical representation of the computations are accomplished using MATLAB language. The impacts of rheological parameters of Carreau fluid, Brinkmann number, curvature parameter and Hartmann number are shown and discussed briefly. The study shows that for shear thinning of bio-materials, the velocity exhibits the boundary layer character near the boundary walls for greater Hartmann number. The interesting observations based on numerical simulations are graphically elaborated. The results show that the curvature of channel with larger value allows more heat transportation within the flow domain. On the contrary, inside the channel wall, the solutal mass concentration follows an increasing trend with decreasing the channel curvature. The temperature profile enhanced with increment of power-law index and curvature parameter. Moreover, the concentration profile increases with Brinkmann number and Hartmann number.}, } @article {pmid32728231, year = {2020}, author = {Boukharfane, R and Parsani, M and Bodart, J}, title = {Characterization of pressure fluctuations within a controlled-diffusion blade boundary layer using the equilibrium wall-modelled LES.}, journal = {Scientific reports}, volume = {10}, number = {1}, pages = {12735}, pmid = {32728231}, issn = {2045-2322}, abstract = {In this study, the generation of airfoil trailing edge broadband noise that arises from the interaction of turbulent boundary layer with the airfoil trailing edge is investigated. The primary objectives of this work are: (i) to apply a wall-modelled large-eddy simulation (WMLES) approach to predict the flow of air passing a controlled-diffusion blade, and (ii) to study the blade broadband noise that is generated from the interaction of a turbulent boundary layer with a lifting surface trailing edge. This study is carried out for two values of the Mach number, [Formula: see text] and 0.5, two values of the chord Reynolds number, [Formula: see text] and [Formula: see text], and two angles of attack, AoA [Formula: see text] and [Formula: see text]. To examine the influence of the grid resolution on aerodynamic and aeroacoustic quantities, we compare our results with experimental data available in the literature. We also compare our results with two in-house numerical solutions generated from two wall-resolved LES (WRLES) calculations, one of which has a DNS-like resolution. We show that WMLES accurately predicts the mean pressure coefficient distribution, velocity statistics (including the mean velocity), and the traces of Reynolds tensor components. Furthermore, we observe that the instantaneous flow structures computed by the WMLES resemble those found in the reference WMLES database, except near the leading edge region. Some of the differences observed in these structures are associated with tripping and the transition to a turbulence mechanism near the leading edge, which are significantly affected by the grid resolution. The aeroacoustic noise calculations indicate that the power spectral density profiles obtained using the WMLES compare well with the experimental data.}, } @article {pmid32709009, year = {2020}, author = {Wang, Y and Zhang, Y and Qiao, Z and Wang, W}, title = {A 3D Printed Jet Mixer for Centrifugal Microfluidic Platforms.}, journal = {Micromachines}, volume = {11}, number = {7}, pages = {}, pmid = {32709009}, issn = {2072-666X}, abstract = {Homogeneous mixing of microscopic volume fluids at low Reynolds number is of great significance for a wide range of chemical, biological, and medical applications. An efficient jet mixer with arrays of micronozzles was designed and fabricated using additive manufacturing (three-dimensional (3D) printing) technology for applications in centrifugal microfluidic platforms. The contact surface of miscible liquids was enhanced significantly by impinging plumes from two opposite arrays of micronozzles to improve mixing performance. The mixing efficiency was evaluated and compared with the commonly used Y-shaped micromixer. Effective mixing in the jet mixer was achieved within a very short timescale (3s). This 3D printed jet mixer has great potential to be implemented in applications by being incorporated into multifarious 3D printing devices in microfluidic platforms.}, } @article {pmid32702453, year = {2020}, author = {Emami, MS and Haghshenasfard, M and Zarghami, R and Sadeghi, R and Esfahany, MN}, title = {Experimental study on the reduction of loratadine particle size through confined liquid impinging jets.}, journal = {International journal of pharmaceutics}, volume = {587}, number = {}, pages = {119668}, doi = {10.1016/j.ijpharm.2020.119668}, pmid = {32702453}, issn = {1873-3476}, mesh = {*Loratadine ; *Nanoparticles ; Particle Size ; Solubility ; Solvents ; }, abstract = {The confined liquid impinging jets (CLIJ) technique was applied as a simple and effective approach to reducing the particle size of loratadine to enhance its solubility. The effect of anti-solvent (AS) to solution (S) flow rate ratio, organic phase concentration, Reynolds number (Re), and stabilizer concentration was investigated in this reduction process. After the synthesis, the chemical and physical properties of loratadine nanoparticles were determined through different characterization and analytical techniques. The results indicated that the particle size of loratadine decreases from 320 nm to 80 nm by increasing the AS/S ratio from 1 to 25. It was found that the particle size of loratadine was unchanged at the higher AS/S ratios. The loratadine nanoparticle size was optimized by changing the solution concentration, Re, and Tween 80 as a stabilizer. The finest loratadine nanoparticle size of about 53 nm was obtained with a narrow size distribution, which corresponds to solution concentration of 35 mg/mL, Re of 5687, and 0.1% (w/v) stabilizer concentration. It was revealed that the optimized loratadine nanoparticles completely dissolved after 11 min, indicating the loratadine nanoparticle dissolution rate 50 times faster than raw loratadine.}, } @article {pmid32688541, year = {2020}, author = {Fouxon, I and Lee, C}, title = {Large deviations, singularity, and lognormality of energy dissipation in turbulence.}, journal = {Physical review. E}, volume = {101}, number = {6-1}, pages = {061101}, doi = {10.1103/PhysRevE.101.061101}, pmid = {32688541}, issn = {2470-0053}, abstract = {We study implications of the assumption of power-law dependence of moments of energy dissipation in turbulence on the Reynolds number Re, holding due to intermittency. We demonstrate that at Re→∞ the dissipation's logarithm divided by lnRe converges with probability one to a negative constant. This implies that the dissipation is singular in the limit, as is known phenomenologically. The proof uses a large deviations function, whose existence is implied by the power-law assumption, and which provides the general asymptotic form of the dissipation's distribution. A similar function exists for vorticity and for velocity differences where it proves the moments representation of the multifractal model (MF). Then we observe that derivative of the scaling exponents of the dissipation, considered as a function of the order of the moment, is small at the origin. Thus the variation with the order is slow and can be described by a quadratic function. Indeed, the quadratic function, which corresponds to log-normal statistics, fits the data. Moreover, combining the lognormal scaling with the MF we derive a formula for the anomalous scaling exponents of turbulence which also fits the data. Thus lognormality, not to be confused with the Kolmogorov (1962) assumption of lognormal dissipation in the inertial range, when used in conjunction with the MF provides a concise way to get all scaling exponents of turbulence available at present.}, } @article {pmid32688510, year = {2020}, author = {Morita, T and Omori, T and Nakayama, Y and Toyabe, S and Ishikawa, T}, title = {Harnessing random low Reynolds number flow for net migration.}, journal = {Physical review. E}, volume = {101}, number = {6-1}, pages = {063101}, doi = {10.1103/PhysRevE.101.063101}, pmid = {32688510}, issn = {2470-0053}, abstract = {Random noise in low Reynolds number flow has rarely been used to obtain net migration of microscale objects. In this study, we numerically show that net migration of a microscale object can be extracted from random directional fluid forces in Stokes flow, by introducing deformability and inhomogeneous density into the object. We also developed a mathematical framework to describe the deformation-induced migration caused by noise. These results provide a basis for understanding the noise-induced migration of a microswimmer and are useful for harnessing energy from low Reynolds number flow.}, } @article {pmid32685735, year = {2020}, author = {Askar, AH and Kadham, SA and Mshehid, SH}, title = {The surfactants effect on the heat transfer enhancement and stability of nanofluid at constant wall temperature.}, journal = {Heliyon}, volume = {6}, number = {7}, pages = {e04419}, doi = {10.1016/j.heliyon.2020.e04419}, pmid = {32685735}, issn = {2405-8440}, abstract = {Surfactants role in the enhancement of the heat transfer and stability of alumina oxide - distilled water nanofluid was introduced in this research, where there are limited studies that conjugate between the stability improvement and its effect on the heat transfer coefficients. Four weight concentrations for the experiment were used (0.1, 0.3, 0.6, and 0.9%) with 20 nm particle size under a constant wall temperature. The selection of appropriate surfactants weight was tested too by implementing three weight concentrations (0.5, 1, 1.5, and 2 %) related to each nanofluid concentration via measuring their effect on the zeta potential value. The heat transfer augmentation was tested through a double horizontal pipe under a constant wall temperature at entrance region with Reynolds number range (4000-11800). The results manifested the use of nanofluid worked on enhancement the heat transfer performance better than water, and the stable nanofluid elucidated better results.}, } @article {pmid32680965, year = {2020}, author = {Yang, T and Sprinkle, B and Guo, Y and Qian, J and Hua, D and Donev, A and Marr, DWM and Wu, N}, title = {Reconfigurable microbots folded from simple colloidal chains.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {117}, number = {31}, pages = {18186-18193}, pmid = {32680965}, issn = {1091-6490}, support = {R01 NS102465/NS/NINDS NIH HHS/United States ; R21 AI138214/AI/NIAID NIH HHS/United States ; }, mesh = {*Chemical Engineering ; Colloids/*chemistry ; Magnetics ; *Robotics ; }, abstract = {To overcome the reversible nature of low-Reynolds-number flow, a variety of biomimetic microrobotic propulsion schemes and devices capable of rapid transport have been developed. However, these approaches have been typically optimized for a specific function or environment and do not have the flexibility that many real organisms exhibit to thrive in complex microenvironments. Here, inspired by adaptable microbes and using a combination of experiment and simulation, we demonstrate that one-dimensional colloidal chains can fold into geometrically complex morphologies, including helices, plectonemes, lassos, and coils, and translate via multiple mechanisms that can be varied with applied magnetic field. With chains of multiblock asymmetry, the propulsion mode can be switched from bulk to surface-enabled, mimicking the swimming of microorganisms such as flagella-rotating bacteria and tail-whipping sperm and the surface-enabled motion of arching and stretching inchworms and sidewinding snakes. We also demonstrate that reconfigurability enables navigation through three-dimensional and narrow channels simulating capillary blood vessels. Our results show that flexible microdevices based on simple chains can transform both shape and motility under varying magnetic fields, a capability we expect will be particularly beneficial in complex in vivo microenvironments.}, } @article {pmid32680443, year = {2020}, author = {Ma, Y and Zhang, M and Luo, H}, title = {Numerical and experimental studies of gas-liquid flow and pressure drop in multiphase pump valves.}, journal = {Science progress}, volume = {103}, number = {3}, pages = {36850420940885}, doi = {10.1177/0036850420940885}, pmid = {32680443}, issn = {2047-7163}, abstract = {A numerical and experimental study was carried out to investigate the two-phase flow fields of the typical three valves used in the multiphase pumps. Under the gas volume fraction conditions in the range of 0%-100%, the three-dimensional steady and dynamic two-phase flow characteristics, pressure drops, and their multipliers of the ball valve, cone valve, and disk valve were studied, respectively, using Eulerian-Eulerian approach and dynamic grid technique in ANSYS FLUENT. In addition, a valve test system was built to verify the simulated results by the particle image velocimetry and pressure test. The flow coefficient CQ (about 0.989) of the disk valve is greater than those of the other valves (about 0.864) under the steady flow with a high Reynolds number. The two-phase pressure drops of the three valves fluctuate in different forms with the vibration of the cores during the dynamic opening. The two-phase multipliers of the fully opened ball valve are consistent with the predicted values of the Morris model, while those of the cone valve and disk valve had the smallest differences with the predicted values of the Chisholm model. Through the comprehensive analysis of the flow performance, pressure drop, and dynamic stability of the three pump valves, the disk valve is found to be more suitable for the multiphase pumps due to its smaller axial space, resistance loss, and better flow capacity.}, } @article {pmid32679732, year = {2020}, author = {Juraeva, M and Kang, DJ}, title = {Mixing Performance of a Cross-Channel Split-and-Recombine Micro-Mixer Combined with Mixing Cell.}, journal = {Micromachines}, volume = {11}, number = {7}, pages = {}, pmid = {32679732}, issn = {2072-666X}, abstract = {A new cross-channel split-and-recombine (CC-SAR) micro-mixer was proposed, and its performance was demonstrated numerically. A numerical study was carried out over a wide range of volume flow rates from 3.1 μL/min to 826.8 μL/min. The corresponding Reynolds number ranges from 0.3 to 80. The present micro-mixer consists of four mixing units. Each mixing unit is constructed by combining one split-and-recombine (SAR) unit with a mixing cell. The mixing performance was analyzed in terms of the degree of mixing and relative mixing cost. All numerical results show that the present micro-mixer performs better than other micro-mixers based on SARs over a wide range of volume flow rate. The mixing enhancement is realized by a particular motion of vortex flow: the Dean vortex in the circular sub-channel and another vortex inside the mixing cell. The two vortex flows are generated on the different planes perpendicular to each other. They cause the two fluids to change their relative position as the fluids flow into the circular sub-channel of the SAR, eventually promoting violent mixing. High vorticity in the mixing cell elongates the flow interface between two fluids, and promotes mixing in the flow regime of molecular diffusion dominance.}, } @article {pmid32675836, year = {2020}, author = {Liu, J and Yang, W and Dong, M and Marsden, AL}, title = {The nested block preconditioning technique for the incompressible Navier-Stokes equations with emphasis on hemodynamic simulations.}, journal = {Computer methods in applied mechanics and engineering}, volume = {367}, number = {}, pages = {}, pmid = {32675836}, issn = {0045-7825}, support = {R01 EB018302/EB/NIBIB NIH HHS/United States ; R01 HL121754/HL/NHLBI NIH HHS/United States ; R01 HL123689/HL/NHLBI NIH HHS/United States ; R01 HL139796/HL/NHLBI NIH HHS/United States ; }, abstract = {We develop a novel iterative solution method for the incompressible Navier-Stokes equations with boundary conditions coupled with reduced models. The iterative algorithm is designed based on the variational multiscale formulation and the generalized-α scheme. The spatiotemporal discretization leads to a block structure of the resulting consistent tangent matrix in the Newton-Raphson procedure. As a generalization of the conventional block preconditioners, a three-level nested block preconditioner is introduced to attain a better representation of the Schur complement, which plays a key role in the overall algorithm robustness and efficiency. This approach provides a flexible, algorithmic way to handle the Schur complement for problems involving multiscale and multiphysics coupling. The solution method is implemented and benchmarked against experimental data from the nozzle challenge problem issued by the US Food and Drug Administration. The robustness, efficiency, and parallel scalability of the proposed technique are then examined in several settings, including moderately high Reynolds number flows and physiological flows with strong resistance effect due to coupled downstream vasculature models. Two patient-specific hemodynamic simulations, covering systemic and pulmonary flows, are performed to further corroborate the efficacy of the proposed methodology.}, } @article {pmid32666327, year = {2020}, author = {Xue, Y and Hellmuth, R and Shin, DH}, title = {Formation of Vortices in Idealised Branching Vessels: A CFD Benchmark Study.}, journal = {Cardiovascular engineering and technology}, volume = {11}, number = {5}, pages = {544-559}, doi = {10.1007/s13239-020-00477-9}, pmid = {32666327}, issn = {1869-4098}, mesh = {Arteries/pathology/*physiopathology ; Atherosclerosis/pathology/*physiopathology ; Blood Flow Velocity ; Computer Simulation ; *Hemodynamics ; Humans ; Hydrodynamics ; *Models, Cardiovascular ; Numerical Analysis, Computer-Assisted ; Plaque, Atherosclerotic ; Stress, Mechanical ; }, abstract = {PURPOSE: Atherosclerosis preferentially occurs near the junction of branching vessels, where blood recirculation tends to occur (Malek et al. in J Am Med Assoc 282(21):2035-2042, 1999, https://doi.org/10.1001/jama.282.21.2035). For decades, CFD has been used to predict flow patterns such as separation and recirculation zones in hemodynamic models, but those predictions have rarely been validated with experimental data. In the context of verification and validation (V&V), we first conduct a CFD benchmark calculation that reproduces the vortex detection experiments of Karino and Goldsmith (1980) with idealised branching blood vessels (Karino and Goldsmith in Trans. Am. Soc. Artif. Internal Organs 26:500-506, 1980). The critical conditions for the formation of recirculation vortices, the so-called critical Reynolds numbers, are the main parameters for comparison with the experimental data to demonstrate the credibility of the CFD workflow. We then characterise the wall shear stresses and develop a surrogate model for the size of formed vortices.

METHODS: An automated parametric study generating more than 12,000 CFD simulations was performed, sweeping the geometries and flow conditions found in the experiments by Karino and Goldsmith. The flow conditions were restricted to steady-state laminar flow, with a range of inflow Reynolds numbers up to 350, with various flow ratios between the main branch outlet and side branch outlet. The side branch diameter was scaled relative to the main branch diameter, ranging from 1.05/3 to 3/3; and the branching angles ranged in size from [Formula: see text] to [Formula: see text]. Recirculation vortices were detected by the inversion of the velocity vector at certain locations, as well as by the inversion of the wall shear stress (WSS) vector.

RESULTS: The CFD simulations demonstrated good agreement with the experimental data on the critical Reynolds numbers. The spatial distributions of WSS on each branch were analysed to identify potential regions of disease. Once a vortex is formed, the size of the vortex increases by the square root of the Reynolds number. The CFD data was fitted to a surrogate model that accurately predicts the vortex size without the need to run computationally more expensive CFD simulations.

CONCLUSIONS: This benchmark study validates the CFD simulation of vortex detection in idealised branching vessels under comprehensive flow conditions. This work also proposes a surrogate model for the size of the vortex, which could reduce the computational requirements in the studies related to branching vessels and complex vascular systems.}, } @article {pmid32664605, year = {2020}, author = {Forte, P and Morais, JE and P Neiva, H and Barbosa, TM and Marinho, DA}, title = {The Drag Crisis Phenomenon on an Elite Road Cyclist-A Preliminary Numerical Simulations Analysis in the Aero Position at Different Speeds.}, journal = {International journal of environmental research and public health}, volume = {17}, number = {14}, pages = {}, pmid = {32664605}, issn = {1660-4601}, mesh = {Arm ; *Bicycling ; Head Protective Devices ; Humans ; *Hydrodynamics ; Male ; *Sports ; }, abstract = {The drag crisis phenomenon is the drop of drag coefficient (Cd) with increasing Reynolds number (Re) or speed. The aim of this study was to assess the hypothetical drag crisis phenomenon in a sports setting, assessing it in a bicycle-cyclist system. A male elite-level cyclist was recruited for this research and his competition bicycle, helmet, suit, and shoes were used. A three-dimensional (3D) geometry was obtained with a 3D scan with the subject in a static aero position. A domain with 7 m of length, 2.5 m of width and 2.5 m of height was created around the cyclist. The domain was meshed with 42 million elements. Numerical simulations by computer fluid dynamics (CFD) fluent numerical code were conducted at speeds between 1 m/s and 22 m/s, with increments of 1 m/s. The drag coefficient ranged between 0.60 and 0.95 across different speeds and Re. The highest value was observed at 2 m/s (Cd = 0.95) and Re of 3.21 × 10[5], whereas the lower Cd was noted at 9 m/s (Cd = 0.60) and 9.63 × 10[5]. A drag crisis was noted between 3 m/s and 9 m/s. Pressure Cd ranged from 0.35 to 0.52 and the lowest value was observed at 3 m/s and the highest at 2 m/s. The viscous drag coefficient ranged between 0.15 and 0.43 and presented a trend decreasing from 4 m/s to 22 m/s. Coaches, cyclists, researchers, and support staff must consider that Cd varies with speed and Re, and the bicycle-cyclist dimensions, shape, or form may affect drag and performance estimations. As a conclusion, this preliminary work noted a drag crisis between 3 m/s and 9 m/s in a cyclist in the aero position.}, } @article {pmid32660001, year = {2020}, author = {Granados-Ortiz, FJ and Ortega-Casanova, J}, title = {Mechanical Characterisation and Analysis of a Passive Micro Heat Exchanger.}, journal = {Micromachines}, volume = {11}, number = {7}, pages = {}, pmid = {32660001}, issn = {2072-666X}, abstract = {Heat exchangers are widely used in many mechanical, electronic, and bioengineering applications at macro and microscale. Among these, the use of heat exchangers consisting of a single fluid passing through a set of geometries at different temperatures and two flows in T-shape channels have been extensively studied. However, the application of heat exchangers for thermal mixing over a geometry leading to vortex shedding has not been investigated. This numerical work aims to analyse and characterise a heat exchanger for microscale application, which consists of two laminar fluids at different temperature that impinge orthogonally onto a rectangular structure and generate vortex shedding mechanics that enhance thermal mixing. This work is novel in various aspects. This is the first work of its kind on heat transfer between two fluids (same fluid, different temperature) enhanced by vortex shedding mechanics. Additionally, this research fully characterise the underlying vortex mechanics by accounting all geometry and flow regime parameters (longitudinal aspect ratio, blockage ratio and Reynolds number), opposite to the existing works in the literature, which usually vary and analyse blockage ratio or longitudinal aspect ratio only. A relevant advantage of this heat exchanger is that represents a low-Reynolds passive device, not requiring additional energy nor moving elements to enhance thermal mixing. This allows its use especially at microscale, for instance in biomedical/biomechanical and microelectronic applications.}, } @article {pmid32656413, year = {2020}, author = {Dai, X and Liu, C and Zhao, J and Li, L and Yin, S and Liu, H}, title = {Optimization of Application Conditions of Drag Reduction Agent in Product Oil Pipelines.}, journal = {ACS omega}, volume = {5}, number = {26}, pages = {15931-15935}, pmid = {32656413}, issn = {2470-1343}, abstract = {Drag reduction performance was studied with a rotating disk instrument in the laboratory, and experiments show that there is an initial rapid growth stage and stability stage for drag reduction ratio change. The higher the rotational speed, the larger the initial drag reduction ratio is; the larger the concentration, the shorter the drag reduction stabilization time is. Under high concentration and high speed, the drag reduction onset time is short. Because of the shear degradation, the Reynolds number should be taken into account during use. Through a comparison of diesel properties after adding agents with national standard, it is confirmed that drag reduction agents could be used in this pipeline.}, } @article {pmid32639756, year = {2020}, author = {Pusztai, I and Juno, J and Brandenburg, A and TenBarge, JM and Hakim, A and Francisquez, M and Sundström, A}, title = {Dynamo in Weakly Collisional Nonmagnetized Plasmas Impeded by Landau Damping of Magnetic Fields.}, journal = {Physical review letters}, volume = {124}, number = {25}, pages = {255102}, doi = {10.1103/PhysRevLett.124.255102}, pmid = {32639756}, issn = {1079-7114}, abstract = {We perform fully kinetic simulations of flows known to produce dynamo in magnetohydrodynamics (MHD), considering scenarios with low Reynolds number and high magnetic Prandtl number, relevant for galaxy cluster scale fluctuation dynamos. We find that Landau damping on the electrons leads to a rapid decay of magnetic perturbations, impeding the dynamo. This collisionless damping process operates on spatial scales where electrons are nonmagnetized, reducing the range of scales where the magnetic field grows in high magnetic Prandtl number fluctuation dynamos. When electrons are not magnetized down to the resistive scale, the magnetic energy spectrum is expected to be limited by the scale corresponding to magnetic Landau damping or, if smaller, the electron gyroradius scale, instead of the resistive scale. In simulations we thus observe decaying magnetic fields where resistive MHD would predict a dynamo.}, } @article {pmid32620000, year = {2020}, author = {Silverberg, O and Demir, E and Mishler, G and Hosoume, B and Trivedi, N and Tisch, C and Plascencia, D and Pak, OS and Araci, IE}, title = {Realization of a push-me-pull-you swimmer at low Reynolds numbers.}, journal = {Bioinspiration & biomimetics}, volume = {15}, number = {6}, pages = {}, doi = {10.1088/1748-3190/aba2b9}, pmid = {32620000}, issn = {1748-3190}, mesh = {Locomotion ; Models, Biological ; *Robotics ; *Swimming ; Viscosity ; }, abstract = {Locomotion at low Reynolds numbers encounters stringent physical constraints due to the dominance of viscous over inertial forces. A variety of swimming microorganisms have demonstrated diverse strategies to generate self-propulsion in the absence of inertia. In particular, ameboid and euglenoid movements exploit shape deformations of the cell body for locomotion. Inspired by these biological organisms, the 'push-me-pull-you' (PMPY) swimmer (Avron J Eet al2005New J. Phys.7234) represents an elegant artificial swimmer that can escape from the constraints of the scallop theorem and generate self-propulsion in highly viscous fluid environments. In this work, we present the first experimental realization of the PMPY swimmer, which consists of a pair of expandable spheres connected by an extensible link. We designed and constructed robotic PMPY swimmers and characterized their propulsion performance in highly viscous silicone oil in dynamically similar, macroscopic experiments. The proof-of-concept demonstrates the feasibility and robustness of the PMPY mechanism as a viable locomotion strategy at low Reynolds numbers.}, } @article {pmid32618067, year = {2021}, author = {Kashima, Y and Ninomiya, S}, title = {Hemodialysis efficiency management from the viewpoint of blood removal pressure.}, journal = {Therapeutic apheresis and dialysis : official peer-reviewed journal of the International Society for Apheresis, the Japanese Society for Apheresis, the Japanese Society for Dialysis Therapy}, volume = {25}, number = {2}, pages = {152-159}, doi = {10.1111/1744-9987.13557}, pmid = {32618067}, issn = {1744-9987}, mesh = {Blood Flow Velocity/*physiology ; Blood Pressure ; Blood Viscosity/*physiology ; Equipment Design ; Hematocrit ; Humans ; *Needles ; Regression Analysis ; Renal Dialysis/instrumentation/*methods ; Reproducibility of Results ; }, abstract = {Degradation of dialysis efficiency during hemodialysis, caused by incompatible indwelling needle size or increase in hematocrit, is a serious problem that can threaten a patient's life. This study aims to derive a quantitative index for determining the indwelling needle diameter that can maintain an appropriate blood flow rate, and presents an effective method to prevent a decrease in the actual blood flow rate. The relationships between the set flow rate and various parameters such as indwelling needle diameter, blood viscosity, and arterial line pressure are analyzed. A simple and reliable method for estimating the actual blood flow rate is derived from these relationships. A correlation between viscosity and actual blood flow rate is estimated adequately by regression analysis using a least-squares method. The relationship between Reynolds number and the flow rate reduction ratio is also evaluated. A new parameter (simple estimation method for actual blood flow) is derived by measuring the blood removal pressure. A pump control approach that uses blood removal pressure is suggested, which can be a future research direction in the field of hemodialysis.}, } @article {pmid32611152, year = {2020}, author = {Zhou, T and Zhang, X and Zhong, S}, title = {An experimental study of trailing edge noise from a heaving airfoil.}, journal = {The Journal of the Acoustical Society of America}, volume = {147}, number = {6}, pages = {4020}, doi = {10.1121/10.0001419}, pmid = {32611152}, issn = {1520-8524}, abstract = {In this study, the far-field noise and near-field flow properties from a heaving NACA 0012 airfoil at the Reynolds number of 6.6×10[4] were investigated experimentally in a 0.4 m[2] anechoic wind tunnel. The airfoil had an incident angle of 0° and followed a sinusoidal heaving motion. The Strouhal number, controlled by changing the heaving frequency and amplitude, varied from 0.0024 to 0.008. The acoustic properties were measured by a free-field microphone placed at a distance of 1.2 m away from the tunnel central line, and the flow structures near the trailing edge were acquired using the particle image velocimetry. It was found that the heaving motion could reduce the sound pressure level (SPL) of the primary peak in the time-averaged spectra. The spectrograms obtained by the short-time Fourier transform revealed that the discrete tones were produced when the airfoil passed through the maximum heaving position. During the corresponding period, a sequence of large-scaled vortices convected on the airfoil surface was observed, and then was shed from the trailing edge to the wake region at the same frequency as the primary tone of the induced sound. With the increase of Strouhal number, the sound signals tended to be broadband, and the overall SPL was increased in the far field.}, } @article {pmid32609698, year = {2020}, author = {Xu, W and Luo, W and Wang, Y and You, Y}, title = {Data-driven three-dimensional super-resolution imaging of a turbulent jet flame using a generative adversarial network.}, journal = {Applied optics}, volume = {59}, number = {19}, pages = {5729-5736}, doi = {10.1364/AO.392803}, pmid = {32609698}, issn = {1539-4522}, abstract = {Three-dimensional (3D) computed tomography (CT) is becoming a well-established tool for turbulent combustion diagnostics. However, the 3D CT technique suffers from contradictory demands of spatial resolution and domain size. This work therefore reports a data-driven 3D super-resolution approach to enhance the spatial resolution by two times along each spatial direction. The approach, named 3D super-resolution generative adversarial network (3D-SR-GAN), builds a generator and a discriminator network to learn the topographic information and infer high-resolution 3D turbulent flame structure with a given low-resolution counterpart. This work uses numerically simulated 3D turbulent jet flame structures as training data to update model parameters of the GAN network. Extensive performance evaluations are then conducted to show the superiority of the proposed 3D-SR-GAN network, compared with other direct interpolation methods. The results show that a convincing super-resolution (SR) operation with the overall error of ∼4% and the peak signal-to-noise ratio of 37 dB can be reached with an upscaling factor of 2, representing an eight times enhancement of the total voxel number. Moreover, the trained network can predict the SR structure of the jet flame with a different Reynolds number without retraining the network parameters.}, } @article {pmid32600217, year = {2021}, author = {Moum, JN}, title = {Variations in Ocean Mixing from Seconds to Years.}, journal = {Annual review of marine science}, volume = {13}, number = {}, pages = {201-226}, doi = {10.1146/annurev-marine-031920-122846}, pmid = {32600217}, issn = {1941-0611}, mesh = {El Nino-Southern Oscillation ; *Hydrodynamics ; *Models, Theoretical ; Oceans and Seas ; Rheology ; Seasons ; Seawater/*chemistry ; Temperature ; Tidal Waves ; Time Factors ; }, abstract = {Over the past several decades, there has developed a community-wide appreciation for the importance of mixing at the smallest scales to geophysical fluid dynamics on all scales. This appreciation has spawned greater participation in the investigation of ocean mixing and new ways to measure it. These are welcome developments given the tremendous separation in scales between the basins, [Formula: see text]) m, and the turbulence, [Formula: see text]) m, and the fact that turbulence that leads to thermodynamically irreversible mixing in high-Reynolds-number geophysical flows varies by at least eight orders of magnitude in both space and time. In many cases, it is difficult to separate the dependencies because measurements are sparse, also in both space and time. Comprehensive shipboard turbulence profiling experiments supplemented by Doppler sonar current measurements provide detailed observations of the evolution of the vertical structure of upper-ocean turbulence on timescales of minutes to weeks. Recent technical developments now permit measurements of turbulence in the ocean, at least at a few locations, for extended periods. This review summarizes recent and classic results in the context of our expanding knowledge of the temporal variability of ocean mixing, beginning with a discussion of the timescales of the turbulence itself (seconds to minutes) and how turbulence-enhanced mixing varies over hours, days, tidal cycles, monsoons, seasons, and El Niño-Southern Oscillation timescales (years).}, } @article {pmid32581842, year = {2020}, author = {Campinho, P and Vilfan, A and Vermot, J}, title = {Blood Flow Forces in Shaping the Vascular System: A Focus on Endothelial Cell Behavior.}, journal = {Frontiers in physiology}, volume = {11}, number = {}, pages = {552}, pmid = {32581842}, issn = {1664-042X}, abstract = {The endothelium is the cell monolayer that lines the interior of the blood vessels separating the vessel lumen where blood circulates, from the surrounding tissues. During embryonic development, endothelial cells (ECs) must ensure that a tight barrier function is maintained whilst dynamically adapting to the growing vascular tree that is being formed and remodeled. Blood circulation generates mechanical forces, such as shear stress and circumferential stretch that are directly acting on the endothelium. ECs actively respond to flow-derived mechanical cues by becoming polarized, migrating and changing neighbors, undergoing shape changes, proliferating or even leaving the tissue and changing identity. It is now accepted that coordinated changes at the single cell level drive fundamental processes governing vascular network morphogenesis such as angiogenic sprouting, network pruning, lumen formation, regulation of vessel caliber and stability or cell fate transitions. Here we summarize the cell biology and mechanics of ECs in response to flow-derived forces, discuss the latest advances made at the single cell level with particular emphasis on in vivo studies and highlight potential implications for vascular pathologies.}, } @article {pmid32575895, year = {2020}, author = {Nichols, A and Rubinato, M and Cho, YH and Wu, J}, title = {Optimal Use of Titanium Dioxide Colourant to Enable Water Surfaces to Be Measured by Kinect Sensors.}, journal = {Sensors (Basel, Switzerland)}, volume = {20}, number = {12}, pages = {}, pmid = {32575895}, issn = {1424-8220}, abstract = {Recent studies have sought to use Microsoft Kinect sensors to measure water surface shape in steady flows or transient flow processes. They have typically employed a white colourant, usually titanium dioxide (TiO2), in order to make the surface opaque and visible to the infrared-based sensors. However, the ability of Kinect Version 1 (KV1) and Kinect Version 2 (KV2) sensors to measure the deformation of ostensibly smooth reflective surfaces has never been compared, with most previous studies using a V1 sensor with no justification. Furthermore, the TiO2 has so far been used liberally and indeterminately, with no consideration as to the type of TiO2 to use, the optimal proportion to use or the effect it may have on the very fluid properties being measured. This paper examines the use of anatase TiO2 with two generations of the Microsoft Kinect sensor. Assessing their performance for an ideal flat surface, it is shown that surface data obtained using the V2 sensor is substantially more reliable. Further, the minimum quantity of colourant to enable reliable surface recognition is discovered (0.01% by mass). A stability test shows that the colourant has a strong tendency to settle over time, meaning the fluid must remain well mixed, having serious implications for studies with low Reynolds number or transient processes such as dam breaks. Furthermore, the effect of TiO2 concentration on fluid properties is examined. It is shown that previous studies using concentrations in excess of 1% may have significantly affected the viscosity and surface tension, and thus the surface behaviour being measured. It is therefore recommended that future studies employ the V2 sensor with an anatase TiO2 concentration of 0.01%, and that the effects of TiO2 on the fluid properties are properly quantified before any TiO2-Kinect-derived dataset can be of practical use, for example, in validation of numerical models or in physical models of hydrodynamic processes.}, } @article {pmid32574537, year = {2020}, author = {Rhodeland, B and Hoeger, K and Ursell, T}, title = {Bacterial surface motility is modulated by colony-scale flow and granular jamming.}, journal = {Journal of the Royal Society, Interface}, volume = {17}, number = {167}, pages = {20200147}, pmid = {32574537}, issn = {1742-5662}, mesh = {*Bacillus subtilis ; Biophysical Phenomena ; Cell Movement ; *Surface-Active Agents ; Water ; }, abstract = {Microbes routinely face the challenge of acquiring territory and resources on wet surfaces. Cells move in large groups inside thin, surface-bound water layers, often achieving speeds of 30 µm s[-1] within this environment, where viscous forces dominate over inertial forces (low Reynolds number). The canonical Gram-positive bacterium Bacillus subtilis is a model organism for the study of collective migration over surfaces with groups exhibiting motility on length-scales three orders of magnitude larger than themselves within a few doubling times. Genetic and chemical studies clearly show that the secretion of endogenous surfactants and availability of free surface water are required for this fast group motility. Here, we show that: (i) water availability is a sensitive control parameter modulating an abiotic jamming-like transition that determines whether the group remains fluidized and therefore collectively motile, (ii) groups self-organize into discrete layers as they travel, (iii) group motility does not require proliferation, rather groups are pulled from the front, and (iv) flow within expanding groups is capable of moving material from the parent colony into the expanding tip of a cellular dendrite with implications for expansion into regions of varying nutrient content. Together, these findings illuminate the physical structure of surface-motile groups and demonstrate that physical properties, like cellular packing fraction and flow, regulate motion from the scale of individual cells up to length scales of centimetres.}, } @article {pmid32564722, year = {2020}, author = {Coreixas, C and Wissocq, G and Chopard, B and Latt, J}, title = {Impact of collision models on the physical properties and the stability of lattice Boltzmann methods.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {378}, number = {2175}, pages = {20190397}, doi = {10.1098/rsta.2019.0397}, pmid = {32564722}, issn = {1471-2962}, abstract = {The lattice Boltzmann method (LBM) is known to suffer from stability issues when the collision model relies on the BGK approximation, especially in the zero viscosity limit and for non-vanishing Mach numbers. To tackle this problem, two kinds of solutions were proposed in the literature. They consist in changing either the numerical discretization (finite-volume, finite-difference, spectral-element, etc.) of the discrete velocity Boltzmann equation (DVBE), or the collision model. In this work, the latter solution is investigated in detail. More precisely, we propose a comprehensive comparison of (static relaxation time based) collision models, in terms of stability, and with preliminary results on their accuracy, for the simulation of isothermal high-Reynolds number flows in the (weakly) compressible regime. It starts by investigating the possible impact of collision models on the macroscopic behaviour of stream-and-collide based D2Q9-LBMs, which clarifies the exact physical properties of collision models on LBMs. It is followed by extensive linear and numerical stability analyses, supplemented with an accuracy study based on the transport of vortical structures over long distances. In order to draw conclusions as generally as possible, the most common moment spaces (raw, central, Hermite, central Hermite and cumulant), as well as regularized approaches, are considered for the comparative studies. LBMs based on dynamic collision mechanisms (entropic collision, subgrid-scale models, explicit filtering, etc.) are also briefly discussed. This article is part of the theme issue 'Fluid dynamics, soft matter and complex systems: recent results and new methods'.}, } @article {pmid32563162, year = {2020}, author = {Sonwani, RK and Giri, BS and Jaiswal, RP and Singh, RS and Rai, BN}, title = {Performance evaluation of a continuous packed bed bioreactor: Bio-kinetics and external mass transfer study.}, journal = {Ecotoxicology and environmental safety}, volume = {201}, number = {}, pages = {110860}, doi = {10.1016/j.ecoenv.2020.110860}, pmid = {32563162}, issn = {1090-2414}, mesh = {Bacillales/growth & development/metabolism ; Biodegradation, Environmental ; Bioreactors/*microbiology ; Cells, Immobilized/microbiology ; Kinetics ; Naphthalenes/*analysis ; Polyethylene/chemistry ; Water Pollutants, Chemical/*analysis ; Water Purification/*methods ; }, abstract = {The biodegradation of naphthalene using low-density polyethylene (LDPE) immobilized Exiguobacterium sp. RKS3 (MG696729) in a packed bed bioreactor (PBBR) was studied. The performance of a continuous PBBR was evaluated at different inlet flow rates (IFRs) (20-100 mL/h) under 64 days of operation. The maximum naphthalene removal efficiency (RE) was found at low IFR, and it further decreased with increasing IFRs. In a continuous PBBR, the external mass transfer (EMT) aspect was analysed at various IFRs, and experimental data were interrelated between Colburn factor (JD) and Reynolds number (NRe) as [Formula: see text] . A new correlation [Formula: see text] was obtained to predict the EMT aspect of naphthalene biodegradation. Andrew-Haldane model was used to evaluate the bio-kinetic parameters of naphthalene degradation, and kinetic constant νmax, Js, and Ji were found as 0.386 per day, 13.6 mg/L, and 20.54 mg/L, respectively.}, } @article {pmid32557795, year = {2020}, author = {Dial, TR and Lauder, GV}, title = {Longer development provides first-feeding fish time to escape hydrodynamic constraints.}, journal = {Journal of morphology}, volume = {281}, number = {8}, pages = {956-969}, doi = {10.1002/jmor.21224}, pmid = {32557795}, issn = {1097-4687}, mesh = {Animals ; Biomechanical Phenomena ; Bone and Bones/anatomy & histology ; Feeding Behavior/*physiology ; Female ; *Hydrodynamics ; Larva/growth & development ; Male ; Models, Biological ; Predatory Behavior ; Time Factors ; Viscosity ; Zebrafish/*growth & development ; }, abstract = {What is the functional effect of prolonged development? By controlling for size, we quantify first-feeding performance and hydrodynamics of zebrafish and guppy offspring (5 ± 0.5 mm in length), which differ fivefold in developmental time and twofold in ontogenetic state. By manipulating water viscosity, we control the hydrodynamic regime, measured as Reynolds number. We predicted that if feeding performance were strictly the result of hydrodynamics, and not development, feeding performance would scale with Reynolds number. We find that guppy offspring successfully feed at much greater distances to prey (1.0 vs. 0.2 mm) and with higher capture success (90 vs. 20%) compared with zebrafish larvae, and that feeding performance was not a result of Reynolds number alone. Flow visualization shows that zebrafish larvae produce a bow wave ~0.2 mm in length, and that the flow field produced during suction does not extend beyond this bow wave. Due to well-developed oral jaw protrusion, the similar-sized suction field generated by guppy offspring extends beyond the horizon of their bow wave, leading to successful prey capture from greater distances. These findings suggest that prolonged development and increased ontogenetic state provides first-feeding fish time to escape the pervasive hydrodynamic constraints (bow wave) of being small.}, } @article {pmid32555272, year = {2020}, author = {Gangfu, L and Haiwang, L and Ruquan, Y and Huijie, W and Zhi, T and Shuangzhi, X}, title = {Experimental Investigation on Velocity and Temperature Field in a Rotating Non-isothermal Turbulent Boundary Layer using Hot-wire.}, journal = {Scientific reports}, volume = {10}, number = {1}, pages = {9892}, pmid = {32555272}, issn = {2045-2322}, abstract = {This experiment measured the instantaneous temperature and velocity field synchronously in non-isothermal turbulent boundary layer in a rotating straight channel with a parallel-array hot-wire probe. The Reynolds number based on the bulk mean velocity (U) and hydraulic diameter (D) is 19000, and the rotation numbers are 0, 0.07, 0.14, 0.21 and 0.28. The mean velocity u and mean temperature T as well as their fluctuating quantity u' and T' were measured at three streamwise locations (x/D = 4.06, 5.31, 6.56). A method for temperature-changing calibration with constant temperature hot-wire anemometers was proposed. It achieved the calibration in operational temperature range (15.5 °C-50 °C) of the hot-wire via a home-made heating section. The measurement system can obtain the velocity and temperature in a non-isothermal turbulent boundary layer at rotating conditions. The result analysis mainly contains the dimensionless mean temperature, temperature fluctuation as well as its skewness and flatness and streamwise turbulent heat flux. For the trailing side, the rotation effect is more obvious, and makes the dimensionless temperature profiles lower than that under static conditions. The dimensionless streamwise heat flux shows a linear decrease trend in the boundary layer. It is hoped that this research can improve our understanding of the flow and heat transfer mechanism in the internal cooling passages of turbine rotor blades.}, } @article {pmid32555239, year = {2020}, author = {Gepner, SW and Floryan, JM}, title = {Use of Surface Corrugations for Energy-Efficient Chaotic Stirring in Low Reynolds Number Flows.}, journal = {Scientific reports}, volume = {10}, number = {1}, pages = {9865}, pmid = {32555239}, issn = {2045-2322}, abstract = {We demonstrate that an intensive stirring can be achieved in laminar channel flows in a passive manner by utilizing the recently discovered instability waves which lead to chaotic particle movements. The stirring is suitable for mixtures made of delicate constituents prone to mechanical damage, such as bacteria and DNA samples, as collisions between the stream and both the bounding walls as well as mechanical mixing devices are avoided. Debris accumulation is prevented as no stagnant fluid zones are formed. Groove symmetries can be used to limit stirring to selected parts of the flow domain. The energy cost of flows with such stirring is either smaller or marginally larger than the energy cost of flows through smooth channels.}, } @article {pmid32543084, year = {2020}, author = {Xu, K and Wang, M and Tang, W and Ding, Y and Hu, A}, title = {Flash nanoprecipitation with Gd(III)-based metallosurfactants to fabricate polylactic acid nanoparticles as highly efficient contrast agents for magnetic resonance imaging.}, journal = {Chemistry, an Asian journal}, volume = {15}, number = {16}, pages = {2475-2479}, doi = {10.1002/asia.202000624}, pmid = {32543084}, issn = {1861-471X}, mesh = {Biocompatible Materials/chemistry ; Contrast Media/*chemistry ; Gadolinium/*chemistry ; Hydrophobic and Hydrophilic Interactions ; Magnetic Resonance Imaging/*methods ; Nanoparticles/*chemistry ; Particle Size ; Polyesters/*chemistry ; Polyethylene Glycols/chemistry ; Surface-Active Agents/chemistry ; }, abstract = {Polylactic acid (PLA) nanoparticles coated with Gd(III)-based metallosurfactants (MS) are prepared using a simple and rapid one-step method, flash nanoprecipitation (FNP), for magnetic resonance imaging (MRI) applications. By co-assembling the Gd(III)-based MS and an amphiphilic polymer, methoxy poly(ethylene glycol)-b-poly(ϵ-caprolactone) (mPEG-b-PCL), PLA cores were rapidly encapsulated to form biocompatible T1 contrast agents with tunable particle size and narrow size distribution. The hydrophobic property of Gd(III)-based MS were finely tuned to achieve their high loading efficiency. The size of the nanoparticles was easily controlled by tuning the stream velocity, Reynolds number and the amount of the amphiphilic block copolymer during the FNP process. Under the optimized condition, the relaxivity of the nanoparticles was achieved up to 35.39 mM[-1] s[-1] (at 1.5 T), which is over 8 times of clinically used MRI contrast agents, demonstrating the potential application for MR imaging.}, } @article {pmid32537967, year = {2020}, author = {Zhao, M and Yang, XN and Chen, PY and Sun, WY and Mu, XM and Gao, P and Zhao, GJ}, title = {[Effects of shrub patch pattern on runoff and sediment yield].}, journal = {Ying yong sheng tai xue bao = The journal of applied ecology}, volume = {31}, number = {3}, pages = {735-743}, doi = {10.13287/j.1001-9332.202003.017}, pmid = {32537967}, issn = {1001-9332}, mesh = {*Environmental Monitoring ; *Geologic Sediments ; Rivers ; Soil ; }, abstract = {Understanding the changes of runoff, sediment transport, and hydrodynamic parameters of slopes under the influence of landscape patch coverage and connectivity is of great significance for revealing the hydrodynamic mechanism and hydrological connectivity of slope soil erosion process. In this study, the changes of runoff, sediment transport and hydrodynamic parameters of downhill surface in different coverage levels (0%, 20%, 40%, 60%, 90%) and different connectivity modes (vertical path, horizonal path, S-shaped path, random patches) of shrublands were analyzed by field artificial simulated rainfall test. The results showed that, with the increases of shrub cove-rage, runoff yield and sediment yield decreased exponentially. When the coverage increased to more than 60%, the capacity of shrubs to reduce runoff and sediment became stable. With the increases of shrub coverage, flow velocity, flow depth, Reynolds number, Froude number, stream power, and flow shear resistance significantly decreased, while Manning's roughness coefficient and Darcy-Weisbach resistance coefficient increased significantly. When shrub coverage increased to more than 60%, there was no significant difference in the eigenvalues of hydraulic parameters. The runoff rate under the four connectivity modes followed the order of vertical path > S-shaped path > horizonal path > random patches. The sediment rate was the largest in the vertical path, followed by the S-shaped path, and the horizonal path was not significantly different from the random patches. The path with poor connectivity (horizonal path, random patches) exhibited stronger resistance of hydraulic transmission and poor hydraulic sedimentation capacity than the well-connected path (vertical path, S-shaped path). Our results could provide important theoretical basis for soil erosion control on the Loess Plateau and high-quality development of the Yellow River basin.}, } @article {pmid32531594, year = {2020}, author = {Lequette, K and Ait-Mouheb, N and Wéry, N}, title = {Hydrodynamic effect on biofouling of milli-labyrinth channel and bacterial communities in drip irrigation systems fed with reclaimed wastewater.}, journal = {The Science of the total environment}, volume = {738}, number = {}, pages = {139778}, doi = {10.1016/j.scitotenv.2020.139778}, pmid = {32531594}, issn = {1879-1026}, mesh = {Bacteria ; Biofilms ; *Biofouling ; Hydrodynamics ; Membranes, Artificial ; Waste Water ; *Water Purification ; }, abstract = {The clogging of drippers due to the development of biofilms reduces the benefits and is an obstacle to the implementation of drip irrigation technology in a reclaimed water context. The narrow section and labyrinth geometry of the dripper channel results the development of a heterogeneous flow behaviours with the vortex zones which it enhance the fouling mechanisms. The objective of this study was to analyse the influence of the three dripper types, defined by their geometric and hydraulic parameters, fed with reclaimed wastewater, on the biofouling kinetics and the bacterial communities. Using optical coherence tomography, we demonstrated that the inlet of the drippers (mainly the first baffle) and vortex zones are the most sensitive area for biofouling. Drippers with the lowest Reynolds number and average cross-section velocity v (1 l·h[-1]) were the most sensible to biofouling, even if detachment events seemed more frequent in this dripper type. Therefore, dripper flow path with larger v should be consider to improve the anti-clogging performance. In addition, the dripper type and the geometry of the flow path influenced the structure of the bacterial communities from dripper biofilms. Relative abundancy of filamentous bacteria belonging to Chloroflexi phylum was higher in 1 l·h[-1] drippers, which presented a higher level of biofouling. However, further research on the role of this phylum in dripper biofouling is required.}, } @article {pmid32521517, year = {2020}, author = {Gamble, LL and Harvey, C and Inman, DJ}, title = {Load alleviation of feather-inspired compliant airfoils for instantaneous flow control.}, journal = {Bioinspiration & biomimetics}, volume = {15}, number = {5}, pages = {}, doi = {10.1088/1748-3190/ab9b6f}, pmid = {32521517}, issn = {1748-3190}, mesh = {Animals ; Biomechanical Phenomena ; Birds/physiology ; *Feathers/physiology ; *Flight, Animal/physiology ; Models, Biological ; Wings, Animal/physiology ; }, abstract = {Birds morph their wing shape to adjust to changing environments through muscle-activated morphing of the skeletal structure and passive morphing of the flexible skin and feathers. The role of feather morphing has not been well studied and its impact on aerodynamics is largely unknown. Here we investigate the aero-structural response of a flexible airfoil, designed with biologically accurate structural and material data from feathers, and compared the results to an equivalent rigid airfoil. Two coupled aero-structural models are developed and validated to simulate the response of a bioinspired flexible airfoil across a range of aerodynamic flight conditions. We found that the bioinspired flexible airfoil maintained lift at Reynolds numbers below 1.5 × 10[5], within the avian flight regime, performing similarly to its rigid counterpart. At greater Reynolds numbers, the flexible airfoil alleviated the lift force and experienced trailing edge tip displacement. Principal component analysis identified that the Reynolds number dominated this passive shape change which induced a decambering effect, although the angle of attack was found to effect the location of maximum camber. These results imply that birds or aircraft that have tailored chordwise flexible wings will respond like rigid wings while operating at low speeds, but will passively unload large lift forces while operating at high speeds.}, } @article {pmid32519077, year = {2020}, author = {Wierzchowski, K and Grabowska, I and Pilarek, M}, title = {Efficient propagation of suspended HL-60 cells in a disposable bioreactor supporting wave-induced agitation at various Reynolds number.}, journal = {Bioprocess and biosystems engineering}, volume = {43}, number = {11}, pages = {1973-1985}, pmid = {32519077}, issn = {1615-7605}, mesh = {Biomass ; *Bioreactors ; *Cell Culture Techniques ; Culture Media ; Equipment Design ; Glucose/chemistry ; HL-60 Cells/*cytology ; Humans ; Hydrodynamics ; Models, Theoretical ; Oscillometry ; Oxygen ; }, abstract = {Growth of human nonadherent HL-60 cell cultures performed in disposable bioreactor under various hydrodynamic conditions of 2-D wave-assisted agitation has been compared and discussed. Influence of Reynolds number for liquid (ReL) and the kLa coefficient, as key parameters characterized the bioprocessing of HL-60 cells in ReadyToProcess WAVE[TM] 25 system, on reached values of the apparent maximal specific growth rate (μmax) and the specific yield of biomass (Y[*]X/S) has been identified. The values of ReL (i.e., 510-10,208), as well as kLa coefficient (i.e., 2.83-13.55 h[-1]), have been estimated for the cultures subjected to wave-induced mixing, based on simplified dimensionless correlation for various presents of WAVE 25 system. The highest values of apparent μmax = 0.038 h[-1] and Y[*]X/S = 25.64 × 10[8] cells gglc[-1] have been noted for cultures independently performed at wave-induced agitation characterized by ReL equaled to 5104 and 510, respectively. The presented results have high applicability potential in scale-up of bioprocesses focused on nonadherent animal cells, or in the case of any application of disposable bioreactors presenting similitude.}, } @article {pmid32518305, year = {2020}, author = {Waini, I and Ishak, A and Pop, I}, title = {Hybrid nanofluid flow towards a stagnation point on a stretching/shrinking cylinder.}, journal = {Scientific reports}, volume = {10}, number = {1}, pages = {9296}, pmid = {32518305}, issn = {2045-2322}, abstract = {This paper examines the stagnation point flow towards a stretching/shrinking cylinder in a hybrid nanofluid. Here, copper (Cu) and alumina (Al2O3) are considered as the hybrid nanoparticles while water as the base fluid. The governing equations are reduced to the similarity equations using a similarity transformation. The resulting equations are solved numerically using the boundary value problem solver, bvp4c, available in the Matlab software. It is found that the heat transfer rate is greater for the hybrid nanofluid compared to the regular nanofluid as well as the regular fluid. Besides, the non-uniqueness of the solutions is observed for certain physical parameters. It is also noticed that the bifurcation of the solutions occurs in the shrinking regions. In addition, the heat transfer rate and the skin friction coefficients increase in the presence of nanoparticles and for larger Reynolds number. It is found that between the two solutions, only one of them is stable as time evolves.}, } @article {pmid32516363, year = {2020}, author = {Cho, M and Koref, IS}, title = {The Importance of a Filament-like Structure in Aerial Dispersal and the Rarefaction Effect of Air Molecules on a Nanoscale Fiber: Detailed Physics in Spiders' Ballooning.}, journal = {Integrative and comparative biology}, volume = {60}, number = {4}, pages = {864-875}, doi = {10.1093/icb/icaa063}, pmid = {32516363}, issn = {1557-7023}, mesh = {Animals ; Physics ; *Silk ; *Spiders ; }, abstract = {Many flying insects utilize a membranous structure for flight, which is known as a "wing." However, some spiders use silk fibers for their aerial dispersal. It is well known that spiders can disperse over hundreds of kilometers and rise several kilometers above the ground in this way. However, little is known about the ballooning mechanisms of spiders, owing to the lack of quantitative data. Recently, Cho et al. discovered previously unknown information on the types and physical properties of spiders' ballooning silks. According to the data, a crab spider weighing 20 mg spins 50-60 ballooning silks simultaneously, which are about 200 nm thick and 3.22 m long for their flight. Based on these physical dimensions of ballooning silks, the significance of these filament-like structures is explained by a theoretical analysis reviewing the fluid-dynamics of an anisotropic particle (like a filament or a high-slender body). (1) The filament-like structure is materially efficient geometry to produce (or harvest, in the case of passive flight) fluid-dynamic force in a low Reynolds number flow regime. (2) Multiple nanoscale fibers are the result of the physical characteristics of a thin fiber, the drag of which is proportional to its length but not to its diameter. Because of this nonlinear characteristic of a fiber, spinning multiple thin ballooning fibers is, for spiders, a better way to produce drag forces than spinning a single thick spider silk, because spiders can maximize their drag on the ballooning fibers using the same amount of silk dope. (3) The mean thickness of fibers, 200 nm, is constrained by the mechanical strength of the ballooning fibers and the rarefaction effect of air molecules on a nanoscale fiber, because the slip condition on a fiber could predominate if the thickness of the fiber becomes thinner than 100 nm.}, } @article {pmid32508348, year = {2020}, author = {van Hooft, JA}, title = {A Note on Scalar-Gradient Sharpening in the Stable Atmospheric Boundary Layer.}, journal = {Boundary-layer meteorology}, volume = {176}, number = {1}, pages = {149-156}, pmid = {32508348}, issn = {0006-8314}, abstract = {The scalar front generated by the horizontal self advection of a dipolar vortex through a modest scalar gradient is investigated. This physical scenario is an idealization of the emergence of strong temperature ramps in the stable atmospheric boundary layer. The proposed mechanism is discussed and a two-dimensional analogy is studied in depth using direct numerical simulation. More specifically, the scalar-gradient sharpening is investigated as a function of the Reynolds number. It appears that the process of gradient sharpening at large-eddy scales may be challenging for turbulence-resolving methods applied to the stable-boundary-layer regime.}, } @article {pmid32507933, year = {2020}, author = {Jain, K}, title = {Efficacy of the FDA nozzle benchmark and the lattice Boltzmann method for the analysis of biomedical flows in transitional regime.}, journal = {Medical & biological engineering & computing}, volume = {58}, number = {8}, pages = {1817-1830}, pmid = {32507933}, issn = {1741-0444}, mesh = {Benchmarking/*methods ; Computer Simulation ; Equipment and Supplies ; United States ; United States Food and Drug Administration ; }, abstract = {Flows through medical devices as well as in anatomical vessels despite being at moderate Reynolds number may exhibit transitional or even turbulent character. In order to validate numerical methods and codes used for biomedical flow computations, the US Food and Drug Administration (FDA) established an experimental benchmark, which was a pipe with gradual contraction and sudden expansion representing a nozzle. The experimental results for various Reynolds numbers ranging from 500 to 6500 were publicly released. Previous and recent computational investigations of flow in the FDA nozzle found limitations in various CFD approaches and some even questioned the adequacy of the benchmark itself. This communication reports the results of a lattice Boltzmann method (LBM) - based direct numerical simulation (DNS) approach applied to the FDA nozzle benchmark for transitional cases of Reynolds numbers 2000 and 3500. The goal is to evaluate if a simple off the shelf LBM would predict the experimental results without the use of complex models or synthetic turbulence at the inflow. LBM computations with various spatial and temporal resolutions are performed-in the extremities of 45 million to 2.88 billion lattice cells-executed respectively on 32 CPU cores of a desktop to more than 300,000 cores of a modern supercomputer to explore and characterize miniscule flow details and quantify Kolmogorov scales. The LBM simulations transition to turbulence at a Reynolds number 2000 like the FDA's experiments and acceptable agreement in jet breakdown locations, average velocity, shear stress, and pressure is found for both the Reynolds numbers. Graphical Abstract A bisecting plane showing the FDA nozzle and vorticity magnitude at t = 10 s for throat Reynolds numbers of 2000 and 3500.}, } @article {pmid32505518, year = {2020}, author = {Cui, X and Wu, W and Ge, H}, title = {Investigation of airflow field in the upper airway under unsteady respiration pattern using large eddy simulation method.}, journal = {Respiratory physiology & neurobiology}, volume = {279}, number = {}, pages = {103468}, doi = {10.1016/j.resp.2020.103468}, pmid = {32505518}, issn = {1878-1519}, mesh = {*Computer Simulation ; Humans ; Larynx ; Models, Biological ; Mouth ; Nose ; Pharynx ; *Respiratory Mechanics ; *Respiratory Physiological Phenomena ; Trachea ; }, abstract = {In this paper, the airflow field in the upper airway under unsteady respiration process is predicted using large eddy simulation. The geometrical model is created by combining a popular cast-based mouth-throat model with tracheo-bronchial airways modeled with a trumpet-shaped conduit. The respiration process is simulated by sinusoidal displacing the bottom surface of the geometrical model. Large eddy simulation with dynamic sub-grid scale model is adopted for modeling the turbulent flow via a commercial CFD software, Converge. This study has found that (1) the secondary vortices in the mouth cavity are much more complex considering the lung expansion than setting the quasi-steady inspiration flow at the mouth-inlet; (2) the properties of secondary vortices in the trachea are not evidently different at the same Reynolds number at the accelerating and decelerating inspiration phases; (3) the reversed pharynx jet as well as recirculation zone is much unsteadier at the accelerating expiration phase than decelerating expiration phase for the same Reynolds number. We conclude that the properties of airflow structures are highly impacted by the respiration pattern and more investigations should be conducted, particularly, on the airflow structures during expiration phase for further understanding the properties of flow field.}, } @article {pmid32505137, year = {2020}, author = {Howard, MP and Statt, A and Stone, HA and Truskett, TM}, title = {Stability of force-driven shear flows in nonequilibrium molecular simulations with periodic boundaries.}, journal = {The Journal of chemical physics}, volume = {152}, number = {21}, pages = {214113}, doi = {10.1063/5.0010697}, pmid = {32505137}, issn = {1089-7690}, abstract = {We analyze the hydrodynamic stability of force-driven parallel shear flows in nonequilibrium molecular simulations with three-dimensional periodic boundary conditions. We show that flows simulated in this way can be linearly unstable, and we derive an expression for the critical Reynolds number as a function of the geometric aspect ratio of the simulation domain. Approximate periodic extensions of Couette and Poiseuille flows are unstable at Reynolds numbers two orders of magnitude smaller than their aperiodic equivalents because the periodic boundaries impose fundamentally different constraints on the flow. This instability has important implications for simulating shear rheology and for designing nonequilibrium simulation methods that are compatible with periodic boundary conditions.}, } @article {pmid32499595, year = {2020}, author = {Meloni, S and Di Marco, A and Mancinelli, M and Camussi, R}, title = {Experimental investigation of jet-induced wall pressure fluctuations over a tangential flat plate at two Reynolds numbers.}, journal = {Scientific reports}, volume = {10}, number = {1}, pages = {9140}, pmid = {32499595}, issn = {2045-2322}, abstract = {The wall pressure fluctuations induced by a subsonic circular jet on a rigid flat plate have been investigated considering two jets with different exit section diameters at the same Mach number. The analysis is aimed at completing the series of papers presented by the authors on the interaction between a subsonic jet and infinite tangential flat plate where the exit Mach number was the only parameter of the jet flow that was varied. In order to analyse other effects out of the Mach number, two configurations with different nozzle exhaust diameters were explored with the objective of isolating the Reynolds number effect keeping fixed the exit Mach number. The nozzle exhaust diameters are 12 mm and 25.4 mm and the instrumented flat plate, installed parallel to the jet flow, is moved at different radial distances from the jet axis. The pressure footprint on the plate has been measured in the stream-wise direction by means of a pair of flush-mounted pressure transducers, providing point-wise pressure signals. Wall pressure fluctuations have been characterised in terms of spectral and statistical quantities. The effect of Reynolds is evidenced and possible scaling relationships that account for the Reynolds dependence are proposed. Implications for modeling the spectral coherence have been considered by the application of the Corcos' model and the effect of the jet Reynolds number on the model coefficients is analyzed.}, } @article {pmid32498258, year = {2020}, author = {Benedict, F and Kumar, A and Kadirgama, K and Mohammed, HA and Ramasamy, D and Samykano, M and Saidur, R}, title = {Thermal Performance of Hybrid-Inspired Coolant for Radiator Application.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {10}, number = {6}, pages = {}, pmid = {32498258}, issn = {2079-4991}, abstract = {Due to the increasing demand in industrial application, nanofluids have attracted the considerable attention of researchers in recent decades. The addition of nanocellulose (CNC) with water (W) and ethylene glycol (EG) to a coolant for a radiator application exhibits beneficial properties to improve the efficiency of the radiator. The focus of the present work was to investigate the performance of mono or hybrid metal oxide such as Al2O3 and TiO2 with or without plant base-extracted CNC with varying concentrations as a better heat transfer nanofluid in comparison to distilled water as a radiator coolant. The CNC is dispersed in the base fluid of EG and W with a 60:40 ratio. The highest absorption peak was noticed at 0.9% volume concentration of TiO2, Al2O3, CNC, Al2O3/TiO2, and Al2O3/CNC nanofluids which indicates a better stability of the nanofluids' suspension. Better thermal conductivity improvement was observed for the Al2O3 nanofluids in all mono nanofluids followed by the CNC and TiO2 nanofluids, respectively. The thermal conductivity of the Al2O3/CNC hybrid nanofluids with 0.9% volume concentration was found to be superior than that of the Al2O3/TiO2 hybrid nanofluids. Al2O3/CNC hybrid nanofluid dominates over other mono and hybrid nanofluids in terms of viscosity at all volume concentrations. CNC nanofluids (all volume concentrations) exhibited the highest specific heat capacity than other mono nanofluids. Additionally, in both hybrid nanofluids, Al2O3/CNC showed the lowest specific heat capacity. The optimized volume concentration from the statistical analytical tool was found to be 0.5%. The experimental results show that the heat transfer coefficient, convective heat transfer, Reynolds number and the Nusselt number have a proportional relationship with the volumetric flow rate. Hybrid nanofluids exhibit better thermal conductivity than mono nanofluids. For instance, a better thermal conductivity improvement was shown by the mono Al2O3 nanofluids than the CNC and TiO2 nanofluids. On the other hand, superior thermal conductivity was observed for the Al2O3/CNC hybrid nanofluids compared to the other mono and hybrid ones (Al2O3/TiO2).}, } @article {pmid32495156, year = {2020}, author = {Ahasan, K and Landry, CM and Chen, X and Kim, JH}, title = {Effect of angle-of-attacks on deterministic lateral displacement (DLD) with symmetric airfoil pillars.}, journal = {Biomedical microdevices}, volume = {22}, number = {2}, pages = {42}, doi = {10.1007/s10544-020-00496-2}, pmid = {32495156}, issn = {1572-8781}, support = {1707056//Division of Chemical, Bioengineering, Environmental, and Transport Systems/International ; 1917299//Division of Electrical, Communications and Cyber Systems/International ; }, mesh = {Microfluidic Analytical Techniques/*methods ; Particle Size ; Pressure ; }, abstract = {Deterministic lateral displacement (DLD) is a microfluidic technique for size fractionation of particles/cells in continuous flow with a great potential for biological and clinical applications. Growing interest of DLD devices in enabling high-throughput operation for practical applications, such as circulating tumor cell (CTC) separation, necessitates employing higher flow rates, leading to operation at moderate to high Reynolds number (Re) regimes. Recently, it has been shown that symmetric airfoil shaped pillars with neutral angle-of-attack (AoA) can be used for high-throughput design of DLD devices due to their mitigation of vortex effects and preservation of flow symmetry under high Re conditions. While high-Re operation with symmetric airfoil shaped pillars has been established, the effect of AoAs on the DLD performance has not been investigated. In this paper, we have characterized the airfoil DLD device with various AoAs. The transport behavior of microparticles has been observed and analyzed with various AoAs in realistic high-Re. Furthermore, we have modeled the flow fields and anisotropy in a representative airfoil pillar array, for both positive and negative AoA configurations. Unlike the conventional DLD device, lateral displacement has been suppressed with +5° and + 15° AoA configurations regardless of particle sizes. On the other hand, stronger lateral displacement has been seen with -5° and - 15° AoAs. This can be attributed to growing flow anisotropy as Re climbs, and significant expansion or compression of streamlines between airfoils with AoAs. The findings in this study can be utilized for the design and optimization of airfoil DLD microfluidic devices with various AoAs.}, } @article {pmid32488023, year = {2020}, author = {Li, X and Gao, J and Guo, Z and Yin, Y and Zhang, X and Sun, P and Gao, Z}, title = {A Study of Rainfall-Runoff Movement Process on High and Steep Slopes Affected by Double Turbulence Sources.}, journal = {Scientific reports}, volume = {10}, number = {1}, pages = {9001}, pmid = {32488023}, issn = {2045-2322}, abstract = {To increase the available land area, a large-scale land remediation campaign was carried out in the loess hilly and gully area. A large number of high and steep slopes have been produced in the construction of road engineering and water conservancy engineering, and these slopes will cause serious soil erosion under rainfall conditions. Because rainfall runoff is simultaneously affected by slope, bed surface and rainfall, the runoff movement characteristics are complex. It is difficult to consider all influencing factors in the existing models, especially for steep slopes. In this study, artificial rainfall experiments were conducted to study the rainfall-runoff hydraulic processes under different rainfall intensities and slope gradients, and a modified method was proposed to model the key hydraulic parameters (i.e., equilibrium time, water surface line, and runoff processes) on steep slopes. The results showed that (1) For steep slopes (a 70° slope compared to a 5° slope), the runoff generation time, confluence time and equilibrium time of the slope decreased significantly. At the same time, the single width runoff of the steep slope had a power function relationship with the rainfall intensity and gradient. (2) The runoff patterns of steep slopes were different from those on gentle slopes and runoff patterns were more likely to change. The Reynolds number and Froude number for slope flow changed slowly when the slope was less than the critical gradient and increased significantly when the slope exceeded the critical gradient. (3) Based on the analysis of the "double turbulent model theory of thin-layer flow on a high-steep slope", combined with the dispersed motion wave model, a modified method for calculating the hydrodynamic factors of rainfall runoff was proposed. Then, this method was verified with indoor and outdoor experiments. The research results not only have theoretical significance, but also provide a more accurate calculation method for the design of high and steep slopes involved in land treatment engineering, road engineering and water conservancy engineering.}, } @article {pmid32481597, year = {2020}, author = {Robles-Romero, JM and Romero-Martín, M and Conde-Guillén, G and Cruces-Romero, D and Gómez-Salgado, J and Ponce-Blandón, JA}, title = {The Physics of Fluid Dynamics Applied to Vascular Ulcers and Its Impact on Nursing Care.}, journal = {Healthcare (Basel, Switzerland)}, volume = {8}, number = {2}, pages = {}, pmid = {32481597}, issn = {2227-9032}, abstract = {The high incidence of vascular ulcers and the difficulties encountered in their healing process require the understanding of their multiple etiologies to develop effective strategies focused on providing different treatment options. This work provides a description of the principles of the physics of fluid dynamics related to vascular ulcers. The morphological characteristics of the cardiovascular system promote blood flow. The contraction force of the left ventricle is enhanced by its ability to reduce its radius of curvature and by increasing the thickness of the ventricular wall (Laplace's Law). Arterial flow must overcome vascular resistance (Ohm's equation). The elastic nature of the artery and the ability to reduce its diameter as flow rate progresses facilitate blood conduction at high speed up to arteriolar level, and this can be determined by the second equation of continuity. As it is a viscous fluid, we must discuss laminar flow, calculated by the Reynolds number, which favors proper conduction while aiming at the correct net filtration pressure. Any endothelial harmful process that affects the muscle wall of the vessel increases the flow speed, causing a decrease in capillary hydrostatic pressure, thus reducing the exchange of nutrients at the interstitial level. With regard to the return system, the flow direction is anti-gravity and requires endogenous aid to establish the Starling's equilibrium. Knowledge on the physics of vascular fluid dynamics makes it easier to understand the processes of formation of these ulcers so as to choosing the optimal healing and prevention techniques for these chronic wounds.}, } @article {pmid32466224, year = {2020}, author = {Charlton, AJ and Lian, B and Blandin, G and Leslie, G and Le-Clech, P}, title = {Impact of FO Operating Pressure and Membrane Tensile Strength on Draw-Channel Geometry and Resulting Hydrodynamics.}, journal = {Membranes}, volume = {10}, number = {5}, pages = {}, pmid = {32466224}, issn = {2077-0375}, abstract = {In an effort to improve performances of forward osmosis (FO) systems, several innovative draw spacers have been proposed. However, the small pressure generally applied on the feed side of the process is expected to result in the membrane bending towards the draw side, and in the gradual occlusion of the channel. This phenomenon potentially presents detrimental effects on process performance, including pressure drop and external concentration polarization (ECP) in the draw channel. A flat sheet FO system with a dot-spacer draw channel geometry was characterized to determine the degree of draw channel occlusion resulting from feed pressurization, and the resulting implications on flow performance. First, tensile testing was performed on the FO membrane to derive a Young's modulus, used to assess the membrane stretching, and the resulting draw channel characteristics under a range of moderate feed pressures. Membrane apex reached up to 67% of the membrane channel height when transmembrane pressure (TMP) of 1.4 bar was applied. The new FO channels considerations were then processed by computational fluid dynamics model (computational fluid dynamics (CFD) by ANSYS Fluent v19.1) and validated against previously obtained experimental data. Further simulations were conducted to better assess velocity profiles, Reynolds number and shear rate. Reynolds number on the membrane surface (draw side) increased by 20% and shear rate increased by 90% when occlusion changed from 0 to 70%, impacting concentration polarisation (CP) on the membrane surface and therefore FO performance. This paper shows that FO draw channel occlusion is expected to have a significant impact on fluid hydrodynamics when the membrane is not appropriately supported in the draw side.}, } @article {pmid32462438, year = {2020}, author = {Asghar, Z and Ali, N and Waqas, M and Nazeer, M and Khan, WA}, title = {Locomotion of an efficient biomechanical sperm through viscoelastic medium.}, journal = {Biomechanics and modeling in mechanobiology}, volume = {19}, number = {6}, pages = {2271-2284}, pmid = {32462438}, issn = {1617-7940}, mesh = {Algorithms ; Animals ; Biomechanical Phenomena ; *Computer Simulation ; Elasticity ; Fourier Analysis ; Humans ; Locomotion ; *Magnetic Fields ; *Magnetics ; Male ; Models, Theoretical ; *Movement ; *Rheology ; Spermatozoa/*physiology ; Viscosity ; }, abstract = {Every group of microorganism utilizes a diverse mechanical strategy to propel through complex environments. These swimming problems deal with the fluid-organism interaction at micro-scales in which Reynolds number is of the order of 10[-3]. By adopting the same propulsion mechanism of so-called Taylor's sheet, here we address the biomechanical principle of swimming via different wavy surfaces. The passage (containing micro-swimmers) is considered to be passive two-dimensional channel filled with viscoelastic liquid, i.e., Oldroyd-4 constant fluid. For some initial value of unknowns, i.e., cell speed and flow rate of surrounding liquid, the resulting boundary value problem is solved by robust finite difference scheme. This convergent solution is further employed in the equilibrium conditions which will obviously not be satisfied for such crude values of unknowns. These unknowns are further refined (to satisfy the equilibrium conditions) by modified Newton-Raphson algorithm. These computed pairs are also utilized to compute the energy losses. The speed of swimming sheet its power delivered and flow rate of Oldroyd-4 constant fluid are compared for different kinds of wavy sheets. These results are also useful in the manufacturing of artificial (soft) microbots and the optimization of locomotion strategies.}, } @article {pmid32438546, year = {2020}, author = {Cassineri, S and Cioncolini, A and Smith, L and Curioni, M and Scenini, F}, title = {Experiments on Liquid Flow through Non-Circular Micro-Orifices.}, journal = {Micromachines}, volume = {11}, number = {5}, pages = {}, pmid = {32438546}, issn = {2072-666X}, abstract = {Microfluidics is an active research area in modern fluid mechanics, with several applications in science and engineering. Despite their importance in microfluidic systems, micro-orifices with non-circular cross-sections have not been extensively investigated. In this study, micro-orifice discharge with single-phase liquid flow was experimentally investigated for seven square and rectangular cross-section micro-orifices with a hydraulic diameter in the range of 326-510 µm. The discharge measurements were carried out in pressurized water (12 MPa) at ambient temperature (298 K) and high temperature (503 K). During the tests, the Reynolds number varied between 5883 and 212,030, significantly extending the range in which data are currently available in the literature on non-circular micro-orifices. The results indicate that the cross-sectional shape of the micro-orifice has little, if any, effect on the hydrodynamic behavior. Thus, existing methods for the prediction of turbulent flow behavior in circular micro-orifices can be used to predict the flow behavior in non-circular micro-orifices, provided that the flow geometry of the non-circular micro-orifice is described using a hydraulic diameter.}, } @article {pmid32422718, year = {2020}, author = {Moriconi, L}, title = {Magnetic dissipation of near-wall turbulent coherent structures in magnetohydrodynamic pipe flows.}, journal = {Physical review. E}, volume = {101}, number = {4-1}, pages = {043111}, doi = {10.1103/PhysRevE.101.043111}, pmid = {32422718}, issn = {2470-0053}, abstract = {Relaminarization of wall-bounded turbulent flows by means of external static magnetic fields is a long-known phenomenon in the physics of electrically conducting fluids at low magnetic Reynolds numbers. Despite the large literature on the subject, it is not yet completely clear what combination of the Hartmann (M) and the Reynolds number has to be used to predict the laminar-turbulent transition in channel or pipe flows fed by upstream turbulent flows free of magnetic perturbations. Relying upon standard phenomenological approaches related to mixing length and structural concepts, we put forward that M/R_{τ}, where R_{τ} is the friction Reynolds number, is the appropriate controlling parameter for relaminarization, a proposal which finds good support from available experimental data.}, } @article {pmid32422715, year = {2020}, author = {Ekanem, EM and Berg, S and De, S and Fadili, A and Bultreys, T and Rücker, M and Southwick, J and Crawshaw, J and Luckham, PF}, title = {Signature of elastic turbulence of viscoelastic fluid flow in a single pore throat.}, journal = {Physical review. E}, volume = {101}, number = {4-1}, pages = {042605}, doi = {10.1103/PhysRevE.101.042605}, pmid = {32422715}, issn = {2470-0053}, abstract = {When a viscoelastic fluid, such as an aqueous polymer solution, flows through a porous medium, the fluid undergoes a repetitive expansion and contraction as it passes from one pore to the next. Above a critical flow rate, the interaction between the viscoelastic nature of the polymer and the pore configuration results in spatial and temporal flow instabilities reminiscent of turbulentlike behavior, even though the Reynolds number Re≪1. To investigate whether this is caused by many repeated pore body-pore throat sequences, or simply a consequence of the converging (diverging) nature present in a single pore throat, we performed experiments using anionic hydrolyzed polyacrylamide (HPAM) in a microfluidic flow geometry representing a single pore throat. This allows the viscoelastic fluid to be characterized at increasing flow rates using microparticle image velocimetry in combination with pressure drop measurements. The key finding is that the effect, popularly known as "elastic turbulence," occurs already in a single pore throat geometry. The critical Deborah number at which the transition in rheological flow behavior from pseudoplastic (shear thinning) to dilatant (shear thickening) strongly depends on the ionic strength, the type of cation in the anionic HPAM solution, and the nature of pore configuration. The transition towards the elastic turbulence regime was found to directly correlate with an increase in normal stresses. The topology parameter, Q_{f}, computed from the velocity distribution, suggests that the "shear thickening" regime, where much of the elastic turbulence occurs in a single pore throat, is a consequence of viscoelastic normal stresses that cause a complex flow field. This flow field consists of extensional, shear, and rotational features around the constriction, as well as upstream and downstream of the constriction. Furthermore, this elastic turbulence regime, has high-pressure fluctuations, with a power-law decay exponent of up to |-2.1| which is higher than the Kolmogorov value for turbulence of |-5/3|.}, } @article {pmid32388985, year = {2020}, author = {Jain, SK and Banerjee, U and Sen, AK}, title = {Trapping and Coalescence of Diamagnetic Aqueous Droplets Using Negative Magnetophoresis.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {36}, number = {21}, pages = {5960-5966}, doi = {10.1021/acs.langmuir.0c00846}, pmid = {32388985}, issn = {1520-5827}, abstract = {The manipulation of aqueous droplets has a profound significance in biochemical assays. Magnetic field-driven droplet manipulation, offering unique advantages, is consequently gaining attention. However, the phenomenon relating to diamagnetic droplets is not well understood. Here, we report the understanding of trapping and coalescence of flowing diamagnetic aqueous droplets in a paramagnetic (oil-based ferrofluid) medium using negative magnetophoresis. Our study revealed that the trapping phenomenon is underpinned by the interplay of magnetic energy (Em) and frictional (viscous) energy (Ef), in terms of magnetophoretic stability number, Sm = (Em/Ef). The trapping and nontrapping regimes are characterized based on the peak value of magnetophoretic stability number, Smp, and droplet size, D*. The study of coalescence of a trapped droplet with a follower droplet (and a train of droplets) revealed that the film-drainage Reynolds number (Refd) representing the coalescence time depends on the magnetic Bond number, Bom. The coalesced droplet continues to remain trapped or gets self-released obeying the Smp and D* criterion. Our study offers an understanding of the magnetic manipulation of diamagnetic aqueous droplets that can potentially be used for biochemical assays in microfluidics.}, } @article {pmid32357661, year = {2020}, author = {Garcia, F and Seilmayer, M and Giesecke, A and Stefani, F}, title = {Chaotic wave dynamics in weakly magnetized spherical Couette flows.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {30}, number = {4}, pages = {043116}, doi = {10.1063/1.5140577}, pmid = {32357661}, issn = {1089-7682}, abstract = {Direct numerical simulations of a liquid metal filling the gap between two concentric spheres are presented. The flow is governed by the interplay between the rotation of the inner sphere (measured by the Reynolds number Re) and a weak externally applied axial magnetic field (measured by the Hartmann number Ha). By varying the latter, a rich variety of flow features, both in terms of spatial symmetry and temporal dependence, is obtained. Flows with two or three independent frequencies describing their time evolution are found as a result of Hopf bifurcations. They are stable on a sufficiently large interval of Hartmann numbers where regions of multistability of two, three, and even four types of these different flows are detected. The temporal character of the solutions is analyzed by means of an accurate frequency analysis and Poincaré sections. An unstable branch of flows undergoing a period doubling cascade and frequency locking of three-frequency solutions is described as well.}, } @article {pmid32357025, year = {2020}, author = {Kang, S and Kwak, R}, title = {Pattern Formation of Three-Dimensional Electroconvection on a Charge Selective Surface.}, journal = {Physical review letters}, volume = {124}, number = {15}, pages = {154502}, doi = {10.1103/PhysRevLett.124.154502}, pmid = {32357025}, issn = {1079-7114}, abstract = {When a charge selective surface consumes or transports only cations or anions in the electrolyte, biased ion rejection initiates hydrodynamic instability, resulting in vortical fluid motions called electroconvection. In this Letter, we describe the first laboratory observation of three-dimensional electroconvection on a charge selective surface. Combining experiment and scaling analysis, we successfully categorized three distinct patterns of 3D electroconvection according to [(Ra_{E} )/(Re^{2} Sc)] [electric Rayleigh number (Ra_{E} ), Reynolds number (Re), Schmidt number (Sc)] as (i) polygonal, (ii) transverse, or (iii) longitudinal rolls. If Re increases or Ra_{E} decreases, pure longitudinal rolls are presented. On the other hand, transverse rolls are formed between longitudinal rolls, and two rolls are transformed as polygonal one at higher Ra_{E} or lower Re. In this pattern selection scenario, Sc determines the critical electric Rayleigh number (Ra_{E} ^{*} ) for the onset of each roll, resulting in Ra_{E} ^{*} ∼Re^{2} Sc. We also verify that convective ion flux by electroconvection (represented by an electric Nusselt number Nu_{E} ) is fitted to a power law, Nu_{E} ∼[(Ra_{E} -Ra_{E} ^{*} )/(Re^{2} Sc)]^{α_{1} } Re^{α_{2} } Pe^{α_{3} } [Péclet number (Pe)], where each term represents the characteristics of electroconvection, shear flow, and ion transport.}, } @article {pmid32349452, year = {2020}, author = {Raza, W and Hossain, S and Kim, KY}, title = {A Review of Passive Micromixers with a Comparative Analysis.}, journal = {Micromachines}, volume = {11}, number = {5}, pages = {}, pmid = {32349452}, issn = {2072-666X}, abstract = {A wide range of existing passive micromixers are reviewed, and quantitative analyses of ten typical passive micromixers were performed to compare their mixing indices, pressure drops, and mixing costs under the same axial length and flow conditions across a wide Reynolds number range of 0.01-120. The tested micromixers were selected from five types of micromixer designs. The analyses of flow and mixing were performed using continuity, Navier-Stokes and convection-diffusion equations. The results of the comparative analysis were presented for three different Reynolds number ranges: low-Re (Re ≤ 1), intermediate-Re (1 < Re ≤ 40), and high-Re (Re > 40) ranges, where the mixing mechanisms are different. The results show a two-dimensional micromixer of Tesla structure is recommended in the intermediate- and high-Re ranges, while two three-dimensional micromixers with two layers are recommended in the low-Re range due to their excellent mixing performance.}, } @article {pmid32342660, year = {2020}, author = {Storm, TJ and Nolan, KE and Roberts, EM and Sanderson, SL}, title = {Oropharyngeal morphology related to filtration mechanisms in suspension-feeding American shad (Clupeidae).}, journal = {Journal of experimental zoology. Part A, Ecological and integrative physiology}, volume = {333}, number = {7}, pages = {493-510}, doi = {10.1002/jez.2363}, pmid = {32342660}, issn = {2471-5646}, support = {/HHMI/Howard Hughes Medical Institute/United States ; }, mesh = {Animals ; *Feeding Behavior ; Fishes/*anatomy & histology/physiology ; Gills ; Oropharynx/*anatomy & histology ; }, abstract = {To assess potential filtration mechanisms, scanning electron microscopy was used in a comprehensive quantification and analysis of the morphology and surface ultrastructure for all five branchial arches in the ram suspension-feeding fish, American shad (Alosa sapidissima, Clupeidae). The orientation of the branchial arches and the location of mucus cells on the gill rakers were more consistent with mechanisms of crossflow filtration and cross-step filtration rather than conventional dead-end sieving. The long, thin gill rakers could lead to a large area for the exit of water from the oropharyngeal cavity during suspension feeding (high fluid exit ratio). The substantial elongation of gill rakers along the dorsal-ventral axis formed d-type ribs with a groove aspect ratio of 0.5 and a Reynolds number of approximately 500, consistent with the potential operation of cross-step filtration. Mucus cell abundance differed significantly along the length of the raker and the height of the raker. The mucus cell abundance data and the observed sloughing of denticles along the gill raker margins closest to the interior of the oropharyngeal cavity suggest that gill raker growth may occur primarily at the raker tips, the denticle bases, and the internal raker margins along the length of the raker. These findings will be applied in ongoing experiments with 3D-printed physical models of fish oral cavities in flow tanks, and in future ecological studies on the diet and nutrition of suspension-feeding fishes.}, } @article {pmid32340402, year = {2020}, author = {Singh, AV and Ansari, MHD and Mahajan, M and Srivastava, S and Kashyap, S and Dwivedi, P and Pandit, V and Katha, U}, title = {Sperm Cell Driven Microrobots-Emerging Opportunities and Challenges for Biologically Inspired Robotic Design.}, journal = {Micromachines}, volume = {11}, number = {4}, pages = {}, pmid = {32340402}, issn = {2072-666X}, abstract = {With the advent of small-scale robotics, several exciting new applications like Targeted Drug Delivery, single cell manipulation and so forth, are being discussed. However, some challenges remain to be overcome before any such technology becomes medically usable; among which propulsion and biocompatibility are the main challenges. Propulsion at micro-scale where the Reynolds number is very low is difficult. To overcome this, nature has developed flagella which have evolved over millions of years to work as a micromotor. Among the microscopic cells that exhibit this mode of propulsion, sperm cells are considered to be fast paced. Here, we give a brief review of the state-of-the-art of Spermbots - a new class of microrobots created by coupling sperm cells to mechanical loads. Spermbots utilize the flagellar movement of the sperm cells for propulsion and as such do not require any toxic fuel in their environment. They are also naturally biocompatible and show considerable speed of motion thereby giving us an option to overcome the two challenges of propulsion and biocompatibility. The coupling mechanisms of physical load to the sperm cells are discussed along with the advantages and challenges associated with the spermbot. A few most promising applications of spermbots are also discussed in detail. A brief discussion of the future outlook of this extremely promising category of microrobots is given at the end.}, } @article {pmid32325022, year = {2020}, author = {Zhou, Q and Fidalgo, J and Calvi, L and Bernabeu, MO and Hoskins, PR and Oliveira, MSN and Krüger, T}, title = {Spatiotemporal Dynamics of Dilute Red Blood Cell Suspensions in Low-Inertia Microchannel Flow.}, journal = {Biophysical journal}, volume = {118}, number = {10}, pages = {2561-2573}, pmid = {32325022}, issn = {1542-0086}, mesh = {Computer Simulation ; *Erythrocytes ; *Hydrodynamics ; Reproducibility of Results ; Suspensions ; }, abstract = {Microfluidic technologies are commonly used for the manipulation of red blood cell (RBC) suspensions and analyses of flow-mediated biomechanics. To enhance the performance of microfluidic devices, understanding the dynamics of the suspensions processed within is crucial. We report novel, to our knowledge, aspects of the spatiotemporal dynamics of RBC suspensions flowing through a typical microchannel at low Reynolds number. Through experiments with dilute RBC suspensions, we find an off-center two-peak (OCTP) profile of cells contrary to the centralized distribution commonly reported for low-inertia flows. This is reminiscent of the well-known "tubular pinch effect," which arises from inertial effects. However, given the conditions of negligible inertia in our experiments, an alternative explanation is needed for this OCTP profile. Our massively parallel simulations of RBC flow in real-size microfluidic dimensions using the immersed-boundary-lattice-Boltzmann method confirm the experimental findings and elucidate the underlying mechanism for the counterintuitive RBC pattern. By analyzing the RBC migration and cell-free layer development within a high-aspect-ratio channel, we show that such a distribution is co-determined by the spatial decay of hydrodynamic lift and the global deficiency of cell dispersion in dilute suspensions. We find a cell-free layer development length greater than 46 and 28 hydraulic diameters in the experiment and simulation, respectively, exceeding typical lengths of microfluidic designs. Our work highlights the key role of transient cell distribution in dilute suspensions, which may negatively affect the reliability of experimental results if not taken into account.}, } @article {pmid32317809, year = {2020}, author = {Navah, F and de la Llave Plata, M and Couaillier, V}, title = {A High-Order Multiscale Approach to Turbulence for Compact Nodal Schemes.}, journal = {Computer methods in applied mechanics and engineering}, volume = {363}, number = {}, pages = {}, pmid = {32317809}, issn = {0045-7825}, support = {R01 DC005788/DC/NIDCD NIH HHS/United States ; }, abstract = {This article presents a formulation that extends the multiscale modelling for compressible large-eddy simulation to a vast family of compact nodal numerical methods represented by the high-order flux reconstruction scheme. The theoretical aspects of the proposed formulation are laid down via mathematical derivations which clearly expose the underlying assumptions and approximations and provide sufficient details for accurate reproduction of the methodology. The final form is assessed on a Taylor-Green vortex benchmark with Reynolds number of 5000 and compared to filtered direct numerical simulation data. These numerical experiments exhibit the important role of sufficient de-aliasing, appropriate amount of upwinding from Roe's numerical flux and large/small scale partition, in achieving better agreement with reference data, especially on coarse grids, when compared to the baseline implicit large-eddy simulation.}, } @article {pmid32315915, year = {2020}, author = {Banerjee, A and Sharma, T and Nautiyal, AK and Dasgupta, D and Hazra, S and Bhaskar, T and Ghosh, D}, title = {Scale-up strategy for yeast single cell oil production for Rhodotorula mucilagenosa IIPL32 from corn cob derived pentosan.}, journal = {Bioresource technology}, volume = {309}, number = {}, pages = {123329}, doi = {10.1016/j.biortech.2020.123329}, pmid = {32315915}, issn = {1873-2976}, mesh = {Fermentation ; *Rhodotorula ; Xylose ; Yeasts ; *Zea mays ; }, abstract = {This work was aimed to strategically scale-up the yeast lipid production process using Reynolds number as a standard rheological parameter from 50 mL to 50 L scale. Oleaginous yeast Rhodotorula mucilaginosa IIPL32 was cultivated in xylose rich corncob hydrolysate. The fermentation process for growth and maturation was operated in fed-batch with two different C/N ratios of 40 and 60. The hydrodynamic parameters were used to standardize and represent the effect of rheology on the fermentation process. The growth pattern of the yeast was found similar in both shake flask and fermenter with the maximum growth observed at 48 h. The lipid yield increased from 0.4 g/L and 0.5 g/L to 1.3 g/L and 1.83 g/L for 50 mL to 50 L for C/N ratio 40 and 60 respectively. The increase in productivity during the growth phase and lipid accumulation during the maturation phase showed that the scale-up strategy was successful.}, } @article {pmid32295138, year = {2020}, author = {Erdem, K and Ahmadi, VE and Kosar, A and Kuddusi, L}, title = {Differential Sorting of Microparticles Using Spiral Microchannels with Elliptic Configurations.}, journal = {Micromachines}, volume = {11}, number = {4}, pages = {}, pmid = {32295138}, issn = {2072-666X}, abstract = {Label-free, size-dependent cell-sorting applications based on inertial focusing phenomena have attracted much interest during the last decade. The separation capability heavily depends on the precision of microparticle focusing. In this study, five-loop spiral microchannels with a height of 90 µm and a width of 500 µm are introduced. Unlike their original spiral counterparts, these channels have elliptic configurations of varying initial aspect ratios, namely major axis to minor axis ratios of 3:2, 11:9, 9:11, and 2:3. Accordingly, the curvature of these configurations increases in a curvilinear manner through the channel. The effects of the alternating curvature and channel Reynolds number on the focusing of fluorescent microparticles with sizes of 10 and 20 µm in the prepared suspensions were investigated. At volumetric flow rates between 0.5 and 3.5 mL/min (allowing separation), each channel was tested to collect samples at the designated outlets. Then, these samples were analyzed by counting the particles. These curved channels were capable of separating 20 and 10 µm particles with total yields up to approximately 95% and 90%, respectively. The results exhibited that the level of enrichment and the focusing behavior of the proposed configurations are promising compared to the existing microfluidic channel configurations.}, } @article {pmid32294955, year = {2020}, author = {Sun, HCM and Liao, P and Wei, T and Zhang, L and Sun, D}, title = {Magnetically Powered Biodegradable Microswimmers.}, journal = {Micromachines}, volume = {11}, number = {4}, pages = {}, pmid = {32294955}, issn = {2072-666X}, abstract = {The propulsive efficiency and biodegradability of wireless microrobots play a significant role in facilitating promising biomedical applications. Mimicking biological matters is a promising way to improve the performance of microrobots. Among diverse locomotion strategies, undulatory propulsion shows remarkable efficiency and agility. This work proposes a novel magnetically powered and hydrogel-based biodegradable microswimmer. The microswimmer is fabricated integrally by 3D laser lithography based on two-photon polymerization from a biodegradable material and has a total length of 200 μm and a diameter of 8 μm. The designed microswimmer incorporates a novel design utilizing four rigid segments, each of which is connected to the succeeding segment by spring to achieve undulation, improving structural integrity as well as simplifying the fabrication process. Under an external oscillating magnetic field, the microswimmer with multiple rigid segments connected by flexible spring can achieve undulatory locomotion and move forward along with the directions guided by the external magnetic field in the low Reynolds number (Re) regime. In addition, experiments demonstrated that the microswimmer can be degraded successfully, which allows it to be safely applied in real-time in vivo environments. This design has great potential in future in vivo applications such as precision medicine, drug delivery, and diagnosis.}, } @article {pmid32290599, year = {2020}, author = {Huang, B and Li, H and Xu, T}, title = {Experimental Investigation of the Flow and Heat Transfer Characteristics in Microchannel Heat Exchangers with Reentrant Cavities.}, journal = {Micromachines}, volume = {11}, number = {4}, pages = {}, pmid = {32290599}, issn = {2072-666X}, abstract = {The application of microchannel heat exchangers is of great significance in industrial fields due to their advantages of miniaturized scale, large surface-area-to-volume ratio, and high heat transfer rate. In this study, microchannel heat exchangers with and without fan-shaped reentrant cavities were designed and manufactured, and experiments were conducted to investigate the flow and heat-transfer characteristics. The impact rising from the radius of reentrant cavities, as well as the Reynolds number on the heat transfer and the pressure drop, is also analyzed. The results indicate that, compared with straight microchannels, microchannels with reentrant cavities could enhance the heat transfer and, more importantly, reduce the pressure drop at the same time. For the ranges of parameters studied, increasing the radius of reentrant cavities could augment the effect of pressure-drop reduction, while the corresponding variation of heat transfer is complicated. It is considered that adding reentrant cavities in microchannel heat exchangers is an ideal approach to improve performance.}, } @article {pmid32290016, year = {2020}, author = {Alboussière, T and Drif, K and Plunian, F}, title = {Dynamo action in sliding plates of anisotropic electrical conductivity.}, journal = {Physical review. E}, volume = {101}, number = {3-1}, pages = {033107}, doi = {10.1103/PhysRevE.101.033107}, pmid = {32290016}, issn = {2470-0053}, abstract = {With materials of anisotropic electrical conductivity, it is possible to generate a dynamo with a simple velocity field, of the type precluded by Cowling's theorems with isotropic materials. Following a previous study by Ruderman and Ruzmaikin [M. S. Ruderman and A. A. Ruzmaikin, Magnetic field generation in an anisotropically conducting fluid, Geophys. Astrophys. Fluid Dyn. 28, 77 (1984)GAFDD30309-192910.1080/03091928408210135], who considered the dynamo effect induced by a uniform shear flow, we determine the conditions for the dynamo threshold when a solid plate is sliding over another one, both with anisotropic electrical conductivity. We obtain numerical solutions for a general class of anisotropy and obtain the conditions for the lowest magnetic Reynolds number, using a collocation Chebyshev method. In a particular geometry of anisotropy and wave number, we also derive an analytical solution, where the eigenvectors are just combinations of four exponential functions. An explicit analytical expression is obtained for the critical magnetic Reynolds number. Above the critical magnetic Reynolds number, we have also derived an analytical expression for the growth rate showing that this is a "very fast" dynamo, extrapolating on the "slow" and "fast" terminology introduced by Vainshtein and Zeldovich [S. I. Vainshtein and Y. B. Zeldovich, Reviews of topical problems: Origin of magnetic fields in astrophysics (turbulent "dynamo" mechanisms), Sov. Phys. Usp. 15, 159 (1972)SOPUAP0038-567010.1070/PU1972v015n02ABEH004960].}, } @article {pmid32289979, year = {2020}, author = {Reyes, F and Torrejón, V and Falcón, C}, title = {Wave damping of a sloshing wave by an interacting turbulent vortex flow.}, journal = {Physical review. E}, volume = {101}, number = {3-1}, pages = {033106}, doi = {10.1103/PhysRevE.101.033106}, pmid = {32289979}, issn = {2470-0053}, abstract = {We report on the enhancement of the hydrodynamic damping of gravity waves at the surface of a fluid layer as they interact with a turbulent vortex flow in a sloshing experiment. Gravity surface waves are excited by oscillating horizontally a square container holding our working fluid (water). At the bottom of the container, four impellers in a quadrupole configuration generate a vortex array at moderate to high Reynolds number, which interact with the wave. We measure the surface fluctuations using different optical nonintrusive methods and the local velocity of the flow. In our experimental range, we show that as we increase the angular velocity of the impellers, the gravity wave amplitude decreases without changing the oscillation frequency or generating transverse modes. This wave dissipation enhancement is contrasted with the increase of the turbulent velocity fluctuations from particle image velocimetry measurements via a turbulent viscosity. To rationalize the damping enhancement a periodically forced shallow water model including viscous terms is presented, which is used to calculate the sloshing wave resonance curve. The enhanced viscous dissipation coefficient is found to scale linearly with the measured turbulent viscosity. Hence, the proposed scheme is a good candidate as an active surface gravity wave dampener via vortex flow reconfiguration.}, } @article {pmid32284987, year = {2020}, author = {Spandan, V and Putt, D and Ostilla-Mónico, R and Lee, AA}, title = {Fluctuation-induced force in homogeneous isotropic turbulence.}, journal = {Science advances}, volume = {6}, number = {14}, pages = {eaba0461}, pmid = {32284987}, issn = {2375-2548}, abstract = {Understanding force generation in nonequilibrium systems is a notable challenge in statistical physics. We uncover a fluctuation-induced force between two plates immersed in homogeneous isotropic turbulence using direct numerical simulations. The force is a nonmonotonic function of plate separation. The mechanism of force generation reveals an intriguing analogy with fluctuation-induced forces: In a fluid, energy and vorticity are localized in regions of defined length scales. When varying the distance between the plates, we exclude energy structures modifying the overall pressure on the plates. At intermediate plate distances, the intense vorticity structures (worms) are forced to interact in close vicinity between the plates. This interaction affects the pressure in the slit and the force between the plates. The combination of these two effects causes a nonmonotonic attractive force with a complex Reynolds number dependence. Our study sheds light on how length scale-dependent distributions of energy and high-intensity vortex structures determine Casimir forces.}, } @article {pmid32260002, year = {2020}, author = {Asakawa, J and Nishii, K and Nakagawa, Y and Koizumi, H and Komurasaki, K}, title = {Direct measurement of 1-mN-class thrust and 100-s-class specific impulse for a CubeSat propulsion system.}, journal = {The Review of scientific instruments}, volume = {91}, number = {3}, pages = {035116}, doi = {10.1063/1.5121411}, pmid = {32260002}, issn = {1089-7623}, abstract = {This paper presents the development of a thrust stand to enable direct measurement of thrust and specific impulse for a CubeSat propulsion system during firing. The thrust stand is an inverted pendulum and incorporates a mass balance for direct in situ mass measurement. The proposed calibration procedure allows precise performance characterization and achieves a resolution of 80 μN thrust and 0.01 g mass loss, by taking into account the drift of the thrust-stand zero caused by propellant consumption. The performance of a water micro-resistojet propulsion system for CubeSats was directly characterized as a proof of concept of the thrust stand. Continuous profiles of thrust, specific impulse, and mass consumption were acquired under various conditions in a single firing test. A thrust from 1 mN to 10 mN and a specific impulse from 45 s to 100 s with a maximum measurement uncertainty of ±15.3% were measured for the throat Reynolds number in the range 100-400.}, } @article {pmid32244961, year = {2020}, author = {Joseph, J and Rehman, D and Delanaye, M and Morini, GL and Nacereddine, R and Korvink, JG and Brandner, JJ}, title = {Numerical and Experimental Study of Microchannel Performance on Flow Maldistribution.}, journal = {Micromachines}, volume = {11}, number = {3}, pages = {}, pmid = {32244961}, issn = {2072-666X}, abstract = {Miniaturized heat exchangers are well known for their superior heat transfer capabilities in comparison to macro-scale devices. While in standard microchannel systems the improved performance is provided by miniaturized distances and very small hydraulic diameters, another approach can also be followed, namely, the generation of local turbulences. Localized turbulence enhances the heat exchanger performance in any channel or tube, but also includes an increased pressure loss. Shifting the critical Reynolds number to a lower value by introducing perturbators controls pressure losses and improves thermal efficiency to a considerable extent. The objective of this paper is to investigate in detail collector performance based on reduced-order modelling and validate the numerical model based on experimental observations of flow maldistribution and pressure losses. Two different types of perturbators, Wire-net and S-shape, were analyzed. For the former, a metallic wire mesh was inserted in the flow passages (hot and cold gas flow) to ensure stiffness and enhance microchannel efficiency. The wire-net perturbators were replaced using an S-shaped perturbator model for a comparative study in the second case mentioned above. An optimum mass flow rate could be found when the thermal efficiency reaches a maximum. Investigation of collectors with different microchannel configurations (s-shaped, wire-net and plane channels) showed that mass flow rate deviation decreases with an increase in microchannel resistance. The recirculation zones in the cylindrical collectors also changed the maldistribution pattern. From experiments, it could be observed that microchannels with S-shaped perturbators shifted the onset of turbulent transition to lower Reynolds number values. Experimental studies on pressure losses showed that the pressure losses obtained from numerical studies were in good agreement with the experiments (<4%).}, } @article {pmid32168670, year = {2020}, author = {Thirani, S and Gupta, P and Scalo, C}, title = {Knudsen number effects on the nonlinear acoustic spectral energy cascade.}, journal = {Physical review. E}, volume = {101}, number = {2-1}, pages = {023101}, doi = {10.1103/PhysRevE.101.023101}, pmid = {32168670}, issn = {2470-0053}, abstract = {We present a numerical investigation of the effects of gas rarefaction on the energy dynamics of resonating planar nonlinear acoustic waves. The problem setup is a gas-filled, adiabatic tube, excited from one end by a piston oscillating at the fundamental resonant frequency of the tube and closed at the other end; nonlinear wave steepening occurs until a limit cycle is reached, resulting in shock formation for sufficiently high densities. The Knudsen number, defined here as the ratio of the characteristic molecular collision timescale to the resonance period, is varied in the range Kn=10^{-1} -10^{-5}, from rarefied to dense regime, by changing the base density of the gas. The working fluid is Argon. A numerical solution of the Boltzmann equation, closed with the Bhatnagar-Gross-Krook model, is used to simulate cases for Kn≥0.01. The fully compressible one-dimensional Navier-Stokes equations are used for Kn<0.01 with adaptive mesh refinement to resolve the resonating weak shocks, reaching wave Mach numbers up to 1.01. Nonlinear wave steepening and shock formation are associated with spectral broadening of the acoustic energy in the wavenumber-frequency domain; the latter is defined based on the exact energy corollary for second-order nonlinear acoustics derived by Gupta and Scalo [Phys. Rev. E 98, 033117 (2018)2470-004510.1103/PhysRevE.98.033117], representing the Lyapunov function of the system. At the limit cycle, the acoustic energy spectra exhibit an equilibrium energy cascade with a -2 slope in the inertial range, also observed in freely decaying nonlinear acoustic waves by the same authors. In the present system, energy is introduced externally via a piston at low wavenumbers or frequencies and balanced by thermoviscous dissipation at high wavenumbers or frequencies, responsible for the base temperature increase in the system. The thermoviscous dissipation rate is shown to scale as Kn^{2} for fixed Reynolds number based on the maximum velocity amplitude, i.e., increasing with the degree of flow rarefaction; consistently, the smallest length scale of the steepened waves at the limit cycle, corresponding to the thickness of the shock (when present) also increases with Kn. For a given fixed piston velocity amplitude, the bandwidth of the inertial range of the spectral energy cascade decreases with increasing Knudsen numbers, resulting in a reduced resonant response of the system. By exploiting dimensionless scaling laws borrowed by Kolmogorov's theory of hydrodynamic turbulence, it is shown that an inertial range for spectral energy transfer can be expected for acoustic Reynolds numbers Re_{U_{max} } >100, based on the maximum acoustic velocity amplitude in the domain.}, } @article {pmid32151621, year = {2020}, author = {Krieg, M and Mohseni, K}, title = {Transient pressure modeling in jetting animals.}, journal = {Journal of theoretical biology}, volume = {494}, number = {}, pages = {110237}, doi = {10.1016/j.jtbi.2020.110237}, pmid = {32151621}, issn = {1095-8541}, mesh = {Animals ; *Aquatic Organisms ; Biomechanical Phenomena ; *Decapodiformes/physiology ; Larva/anatomy & histology/physiology ; *Models, Biological ; Odonata/physiology ; Pressure ; *Scyphozoa/physiology ; *Swimming ; }, abstract = {There are many marine animals that employ a form of jet propulsion to move through the water, often creating the jets by expanding and collapsing internal fluid cavities. Due to the unsteady nature of this form of locomotion and complex body/nozzle geometries, standard modeling techniques prove insufficient at capturing internal pressure dynamics, and hence swimming forces. This issue has been resolved with a novel technique for predicting the pressure inside deformable jet producing cavities (M. Krieg and K. Mohseni, J. Fluid Mech., 769, 2015), which is derived from evolution of the surrounding fluid circulation. However, this model was only validated for an engineered jet thruster with simple geometry and relatively high Reynolds number (Re) jets. The purpose of this manuscript is twofold: (i) to demonstrate how the circulation based pressure model can be used to analyze different animal body motions as they relate to propulsive output, for multiple species of jetting animals, (ii) and to quantitatively validate the pressure modeling for biological jetting organisms (typically characterized by complicated cavity geometry and low/intermediate Re flows). Using jellyfish (Sarsia tubulosa) as an example, we show that the pressure model is insensitive to complex cavity geometry, and can be applied to lower Re swimming. By breaking down the swimming behavior of the jellyfish, as well as that of squid and dragonfly larvae, according to circulation generating mechanisms, we demonstrate that the body motions of Sarsia tubulosa are optimized for acceleration at the beginning of pulsation as a survival response. Whereas towards the end of jetting, the velar morphology is adjusted to decrease the energetic cost. Similarly, we show that mantle collapse rates in squid maximize propulsive efficiency. Finally, we observe that the hindgut geometry of dragonfly larvae minimizes the work required to refill the cavity. Date Received: 10-18-2019, Date Accepted: 99-99-9999 *kriegmw@hawaii.edu, UHM Ocean and Res Eng, 2540 Dole St, Honolulu, HI 96822.}, } @article {pmid32125866, year = {2020}, author = {Fang, WZ and Ham, S and Qiao, R and Tao, WQ}, title = {Magnetic Actuation of Surface Walkers: The Effects of Confinement and Inertia.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {36}, number = {25}, pages = {7046-7055}, doi = {10.1021/acs.langmuir.9b03487}, pmid = {32125866}, issn = {1520-5827}, abstract = {Driven by a magnetic field, the rotation of a particle near a wall can be rectified into a net translation. The particles thus actuated, or surface walkers, are a kind of active colloid that finds application in biology and microfluidics. Here, we investigate the motion of spherical surface walkers confined between two walls using simulations based on the immersed-boundary lattice Boltzmann method. The degree of confinement and the nature of the confining walls (slip vs no-slip) significantly affect a particle's translational speed and can even reverse its translational direction. When the rotational Reynolds number Reω is larger than 1, inertia effects reduce the critical frequency of the magnetic field, beyond which the sphere can no longer follow the external rotating field. The reduction of the critical frequency is especially pronounced when the sphere is confined near a no-slip wall. As Reω increases beyond 1, even when the sphere can still rotate in the synchronous regime, its translational Reynolds number ReT no longer increases linearly with Reω and even decreases when Reω exceeds ∼10.}, } @article {pmid32098945, year = {2020}, author = {Stixrude, L and Scipioni, R and Desjarlais, MP}, title = {A silicate dynamo in the early Earth.}, journal = {Nature communications}, volume = {11}, number = {1}, pages = {935}, pmid = {32098945}, issn = {2041-1723}, abstract = {The Earth's magnetic field has operated for at least 3.4 billion years, yet how the ancient field was produced is still unknown. The core in the early Earth was surrounded by a molten silicate layer, a basal magma ocean that may have survived for more than one billion years. Here we use density functional theory-based molecular dynamics simulations to predict the electrical conductivity of silicate liquid at the conditions of the basal magma ocean: 100-140 GPa, and 4000-6000 K. We find that the electrical conductivity exceeds 10,000 S/m, more than 100 times that measured in silicate liquids at low pressure and temperature. The magnetic Reynolds number computed from our results exceeds the threshold for dynamo activity and the magnetic field strength is similar to that observed in the Archean paleomagnetic record. We therefore conclude that the Archean field was produced by the basal magma ocean.}, } @article {pmid32093331, year = {2020}, author = {Rehman, D and Joseph, J and Morini, GL and Delanaye, M and Brandner, J}, title = {A Hybrid Numerical Methodology Based on CFD and Porous Medium for Thermal Performance Evaluation of Gas to Gas Micro Heat Exchanger.}, journal = {Micromachines}, volume = {11}, number = {2}, pages = {}, pmid = {32093331}, issn = {2072-666X}, abstract = {In micro heat exchangers, due to the presence of distributing and collecting manifolds as well as hundreds of parallel microchannels, a complete conjugate heat transfer analysis requires a large amount of computational power. Therefore in this study, a novel methodology is developed to model the microchannels as a porous medium where a compressible gas is used as a working fluid. With the help of such a reduced model, a detailed flow analysis through individual microchannels can be avoided by studying the device as a whole at a considerably less computational cost. A micro heat exchanger with 133 parallel microchannels (average hydraulic diameter of 200 μ m) in both cocurrent and counterflow configurations is investigated in the current study. Hot and cold streams are separated by a stainless-steel partition foil having a thickness of 100 μ m. Microchannels have a rectangular cross section of 200 μ m × 200 μ m with a wall thickness of 100 μ m in between. As a first step, a numerical study for conjugate heat transfer analysis of microchannels only, without distributing and collecting manifolds is performed. Mass flow inside hot and cold fluid domains is increased such that inlet Reynolds number for both domains remains within the laminar regime. Inertial and viscous coefficients extracted from this study are then utilized to model pressure and temperature trends within the porous medium model. To cater for the density dependence of inertial and viscous coefficients due to the compressible nature of gas flow in microchannels, a modified formulation of Darcy-Forschheimer law is adopted. A complete model of a double layer micro heat exchanger with collecting and distributing manifolds where microchannels are modeled as the porous medium is finally developed and used to estimate the overall heat exchanger effectiveness of the investigated micro heat exchanger. A comparison of computational results using proposed hybrid methodology with previously published experimental results of the same micro heat exchanger showed that adopted methodology can predict the heat exchanger effectiveness within the experimental uncertainty for both cocurrent and counterflow configurations.}, } @article {pmid32082068, year = {2020}, author = {Luo, J and Chen, L and Li, K and Jackson, A}, title = {Optimal kinematic dynamos in a sphere.}, journal = {Proceedings. Mathematical, physical, and engineering sciences}, volume = {476}, number = {2233}, pages = {20190675}, pmid = {32082068}, issn = {1364-5021}, abstract = {A variational optimization approach is used to optimize kinematic dynamos in a unit sphere and locate the enstrophy-based critical magnetic Reynolds number for dynamo action. The magnetic boundary condition is chosen to be either pseudo-vacuum or perfectly conducting. Spectra of the optimal flows corresponding to these two magnetic boundary conditions are identical since theory shows that they are relatable by reversing the flow field (Favier & Proctor 2013 Phys. Rev. E 88, 031001 (doi:10.1103/physreve.88.031001)). A no-slip boundary for the flow field gives a critical magnetic Reynolds number of 62.06, while a free-slip boundary reduces this number to 57.07. Optimal solutions are found to possess certain rotation symmetries (or anti-symmetries) and optimal flows share certain common features. The flows localize in a small region near the sphere's centre and spiral upwards with very large velocity and vorticity, so that they are locally nearly Beltrami. We also derive a new lower bound on the magnetic Reynolds number for dynamo action, which, for the case of enstrophy normalization, is five times larger than the previous best bound.}, } @article {pmid32082060, year = {2020}, author = {Jose, S and Govindarajan, R}, title = {Non-normal origin of modal instabilities in rotating plane shear flows.}, journal = {Proceedings. Mathematical, physical, and engineering sciences}, volume = {476}, number = {2233}, pages = {20190550}, pmid = {32082060}, issn = {1364-5021}, abstract = {Small variations introduced in shear flows are known to affect stability dramatically. Rotation of the flow system is one example, where the critical Reynolds number for exponential instabilities falls steeply with a small increase in rotation rate. We ask whether there is a fundamental reason for this sensitivity to rotation. We answer in the affirmative, showing that it is the non-normality of the stability operator in the absence of rotation which triggers this sensitivity. We treat the flow in the presence of rotation as a perturbation on the non-rotating case, and show that the rotating case is a special element of the pseudospectrum of the non-rotating case. Thus, while the non-rotating flow is always modally stable to streamwise-independent perturbations, rotating flows with the smallest rotation are unstable at zero streamwise wavenumber, with the spanwise wavenumbers close to that of disturbances with the highest transient growth in the non-rotating case. The instability critical rotation number scales inversely as the square of the Reynolds number, which we demonstrate is the same as the scaling obeyed by the minimum perturbation amplitude in non-rotating shear flow needed for the pseudospectrum to cross the neutral line. Plane Poiseuille flow and plane Couette flow are shown to behave similarly in this context.}, } @article {pmid32067001, year = {2020}, author = {Razavi Bazaz, S and Mashhadian, A and Ehsani, A and Saha, SC and Krüger, T and Ebrahimi Warkiani, M}, title = {Computational inertial microfluidics: a review.}, journal = {Lab on a chip}, volume = {20}, number = {6}, pages = {1023-1048}, doi = {10.1039/c9lc01022j}, pmid = {32067001}, issn = {1473-0189}, abstract = {Since the discovery of inertial focusing in 1961, numerous theories have been put forward to explain the migration of particles in inertial flows, but a complete understanding is still lacking. Recently, computational approaches have been utilized to obtain better insights into the underlying physics. In particular, fundamental aspects of particle focusing inside straight and curved microchannels have been explored in detail to determine the dependence of focusing behavior on particle size, channel shape, and flow Reynolds number. In this review, we differentiate between the models developed for inertial particle motion on the basis of whether they are semi-analytical, Navier-Stokes-based, or built on the lattice Boltzmann method. This review provides a blueprint for the consideration of numerical solutions for modeling of inertial particle motion, whether deformable or rigid, spherical or non-spherical, and whether suspended in Newtonian or non-Newtonian fluids. In each section, we provide the general equations used to solve particle motion, followed by a tutorial appendix and specified sections to engage the reader with details of the numerical studies. Finally, we address the challenges ahead in the modeling of inertial particle microfluidics for future investigators.}, } @article {pmid32066045, year = {2020}, author = {Tanveer, A and Salahuddin, T and Khan, M and Malik, MY and Alqarni, MS}, title = {Theoretical analysis of non-Newtonian blood flow in a microchannel.}, journal = {Computer methods and programs in biomedicine}, volume = {191}, number = {}, pages = {105280}, doi = {10.1016/j.cmpb.2019.105280}, pmid = {32066045}, issn = {1872-7565}, mesh = {*Electroosmosis ; Hemodynamics ; Hydrodynamics ; *Models, Biological ; Models, Statistical ; Nanotechnology ; Rheology ; Viscosity ; }, abstract = {BACKGROUND: In this work the theoretical analysis is presented for a electroosmotic flow of Bingham nanofluid induced by applied electrostatic potential. The linearized Poisson-Boltzmann equation is considered in the presence of Electric double layer (EDL). A Bingham fluid model is employed to describe the rheological behavior of the non-Newtonian fluid. Mathematical formulation is presented under the assumption of long wavelength and small Reynolds number. Flow characteristics are investigated by employing Debye-Huckel linearization principle. Such preferences have not been reported previously for non-Newtonian Bingham nanofluid to the best of author's knowledge.

METHOD: The transformed equations for electroosmotic flow are solved to seek values for the nanofluid velocity, concentration and temperature along the channel length.

RESULTS: The effects of key parameters like Brinkmann number, Prandtl number, Debey Huckel parameter, thermophoresis parameter, Brownian motion parameter are plotted on velocity, temperature and concentration profiles. Graphical results for the flow phenomenon are discussed briefly.

CONCLUSIONS: Non-uniformity in channel as well as yield stress τ0 cause velocity declaration for both positive and negative values of U. Nanofluid temperature is found an increasing function of electro osmotic parameter κ if U is positive while it is a decreasing function if U is negative. A completely reverse response is seen in case of concentration profile. The thermophoresis parameter Nt, the Brow nian motion parameter Nb and Brinkman number Br cause an enhancement in temperature. The results are new in case of U.}, } @article {pmid32062487, year = {2020}, author = {Yan, SR and Sedeh, S and Toghraie, D and Afrand, M and Foong, LK}, title = {Analysis and manegement of laminar blood flow inside a cerebral blood vessel using a finite volume software program for biomedical engineering.}, journal = {Computer methods and programs in biomedicine}, volume = {190}, number = {}, pages = {105384}, doi = {10.1016/j.cmpb.2020.105384}, pmid = {32062487}, issn = {1872-7565}, mesh = {Adult ; Algorithms ; *Biomedical Engineering ; *Blood Flow Velocity ; *Cerebral Veins/physiology ; Female ; *Hemodynamics ; Humans ; Image Processing, Computer-Assisted ; Shear Strength ; *Software ; }, abstract = {BACKGROUND AND OBJECTIVE: Hemodynamic blood flow analysis in the cerebrovascular is has become one of the important research topics in the bio-mechanic in recent decades. The primary duty of the cerebral blood vessel is supplying Glucose and oxygen for the brain.

METHODS: In this investigation, the non-Newtonian blood flow in the cerebral blood vessels studied. For modeling the geometry of this problem, we used Magnetic Resonance Image (MRI) approach to take Digital Imaging and Communications in Medicine (DICOM) images and using an open-source software package to construct the geometry, which is a complicated one. The power-law indexes, heat flux, and Reynolds number range in the investigation are 0.6 ≤ n ≤ 0.8, 5 ≤ q ≤ 15Wm[-2] and 160≤Re≤310. Effects of Reynolds number, power-law indexes and heat fluxes are investigated.

RESULTS: We found that the pressure drop increase with increasing the Reynolds number and power-law index. The maximum Nusselt number in the cerebral blood vessels accrued in the running position of the body in n = 0.8. Also, the highest average wall shear stress occurs in maximum power-law indexes and Reynolds number.

CONCLUSION: By increasing the power-law index and Reynolds number, the wall shear stress increases.}, } @article {pmid32052248, year = {2020}, author = {Waheed, S and Noreen, S and Tripathi, D and Lu, DC}, title = {Electrothermal transport of third-order fluids regulated by peristaltic pumping.}, journal = {Journal of biological physics}, volume = {46}, number = {1}, pages = {45-65}, pmid = {32052248}, issn = {1573-0689}, mesh = {Electroosmosis/*instrumentation ; *Hot Temperature ; Hydrodynamics ; Models, Theoretical ; }, abstract = {The study of heat and electroosmotic characteristics in the flow of a third-order fluid regulated by peristaltic pumping is examined by using governing equations, i.e., the continuity equation, momentum equation, energy equation, and concentration equation. The wavelength is considered long compared to its height and a low Reynolds number is assumed. The velocity slip condition is employed. Analytical solutions are performed through the perturbation technique. The expressions for the dimensionless velocity components, temperature, concentration, and heat transfer rate are obtained. Pumping features were computed numerically for discussion of results. Trapping and heat transfer coefficient distributions were also studied graphically. The findings of the present study can be applied to design biomicrofluidic devices like tumor-on-a-chip and organ-on-a-chip.}, } @article {pmid32042893, year = {2020}, author = {Cerbus, RT and Liu, CC and Gioia, G and Chakraborty, P}, title = {Small-scale universality in the spectral structure of transitional pipe flows.}, journal = {Science advances}, volume = {6}, number = {4}, pages = {eaaw6256}, pmid = {32042893}, issn = {2375-2548}, abstract = {Turbulent flows are not only everywhere, but every turbulent flow is the same at small scales. The extraordinary simplification engendered by this "small-scale universality" is a hallmark of turbulence theory. However, on the basis of the restrictive assumptions invoked by A. N. Kolmogorov to demonstrate this universality, it is widely thought that only idealized turbulent flows conform to this framework. Using experiments and simulations that span a wide range of Reynolds number, we show that small-scale universality governs the spectral structure of a class of flows with no apparent ties to the idealized flows: transitional pipe flows. Our results not only extend the universality of Kolmogorov's framework beyond expectation but also establish an unexpected link between transitional pipe flows and Kolmogorovian turbulence.}, } @article {pmid32041775, year = {2020}, author = {Usherwood, JR and Cheney, JA and Song, J and Windsor, SP and Stevenson, JPJ and Dierksheide, U and Nila, A and Bomphrey, RJ}, title = {High aerodynamic lift from the tail reduces drag in gliding raptors.}, journal = {The Journal of experimental biology}, volume = {223}, number = {Pt 3}, pages = {}, pmid = {32041775}, issn = {1477-9145}, support = {/WT_/Wellcome Trust/United Kingdom ; 202854/Z/16/Z/WT_/Wellcome Trust/United Kingdom ; }, mesh = {Animals ; Biomechanical Phenomena ; Flight, Animal/*physiology ; Hawks/*physiology ; Species Specificity ; Strigiformes/*physiology ; Tail/*physiology ; }, abstract = {Many functions have been postulated for the aerodynamic role of the avian tail during steady-state flight. By analogy with conventional aircraft, the tail might provide passive pitch stability if it produced very low or negative lift. Alternatively, aeronautical principles might suggest strategies that allow the tail to reduce inviscid, induced drag: if the wings and tail act in different horizontal planes, they might benefit from biplane-like aerodynamics; if they act in the same plane, lift from the tail might compensate for lift lost over the fuselage (body), reducing induced drag with a more even downwash profile. However, textbook aeronautical principles should be applied with caution because birds have highly capable sensing and active control, presumably reducing the demand for passive aerodynamic stability, and, because of their small size and low flight speeds, operate at Reynolds numbers two orders of magnitude below those of light aircraft. Here, by tracking up to 20,000, 0.3 mm neutrally buoyant soap bubbles behind a gliding barn owl, tawny owl and goshawk, we found that downwash velocity due to the body/tail consistently exceeds that due to the wings. The downwash measured behind the centreline is quantitatively consistent with an alternative hypothesis: that of constant lift production per planform area, a requirement for minimizing viscous, profile drag. Gliding raptors use lift distributions that compromise both inviscid induced drag minimization and static pitch stability, instead adopting a strategy that reduces the viscous drag, which is of proportionately greater importance to lower Reynolds number fliers.}, } @article {pmid32024757, year = {2020}, author = {Wu, Z and Zaki, TA and Meneveau, C}, title = {High-Reynolds-number fractal signature of nascent turbulence during transition.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {117}, number = {7}, pages = {3461-3468}, pmid = {32024757}, issn = {1091-6490}, abstract = {Transition from laminar to turbulent flow occurring over a smooth surface is a particularly important route to chaos in fluid dynamics. It often occurs via sporadic inception of spatially localized patches (spots) of turbulence that grow and merge downstream to become the fully turbulent boundary layer. A long-standing question has been whether these incipient spots already contain properties of high-Reynolds-number, developed turbulence. In this study, the question is posed for geometric scaling properties of the interface separating turbulence within the spots from the outer flow. For high-Reynolds-number turbulence, such interfaces are known to display fractal scaling laws with a dimension [Formula: see text], where the 1/3 excess exponent above 2 (smooth surfaces) follows from Kolmogorov scaling of velocity fluctuations. The data used in this study are from a direct numerical simulation, and the spot boundaries (interfaces) are determined by using an unsupervised machine-learning method that can identify such interfaces without setting arbitrary thresholds. Wide separation between small and large scales during transition is provided by the large range of spot volumes, enabling accurate measurements of the volume-area fractal scaling exponent. Measurements show a dimension of [Formula: see text] over almost 5 decades of spot volume, i.e., trends fully consistent with high-Reynolds-number turbulence. Additional observations pertaining to the dependence on height above the surface are also presented. Results provide evidence that turbulent spots exhibit high-Reynolds-number fractal-scaling properties already during early transitional and nonisotropic stages of the flow evolution.}, } @article {pmid32024433, year = {2020}, author = {Xu, Z and Qin, H and Li, P and Liu, R}, title = {Computational fluid dynamics approaches to drag and wake of a long-line mussel dropper under tidal current.}, journal = {Science progress}, volume = {103}, number = {1}, pages = {36850419901235}, doi = {10.1177/0036850419901235}, pmid = {32024433}, issn = {2047-7163}, mesh = {Animals ; *Bivalvia ; *Hydrodynamics ; Porosity ; Tidal Waves ; }, abstract = {Hydrodynamic effects of mussel farms have attracted increased research attentions in recent years. The understanding of the hydrodynamic impacts is essential for predicting the sustainability of mussel farms. A large mussel farm includes thousands of mussel droppers, and the combined drag on the mussel droppers is sufficient to possibly affect the longevity of the entire long-lines. This article intends to study the drag and wake of an individual long-line mussel dropper using computational fluid dynamics approaches. Two equivalent rough cylinders, namely, Curved-Model and Sharp-Model, have been utilized to simulate the mussel dropper, and each rough cylinder is assigned with surface roughness. The porosity is not considered in this article due to its complexity from inhalant and exhalant of mussels. Two-dimensional laminar simulations are conducted at Reynolds number from 10 to 200, and three-dimensional large eddy simulations are conducted at subcritical Reynolds number ranging from 3900 to 105. The results show that larger drag coefficients and Strouhal numbers are attributed to surface roughness and sharp crowns on the rough cylinder. The obtained drag coefficient ranges from 1.1 to 1.2 with respect to the diameter of the mussel dropper and the peak value of the tidal velocities. Wakes behind rough cylinders fluctuate more actively compared to those of smooth cylinders. This research work provides new insight for further investigations on hydrodynamic interactions between fluid and mussel droppers.}, } @article {pmid32007018, year = {2020}, author = {Ganta, N and Mahato, B and Bhumkar, YG}, title = {Prediction of the aerodynamic sound generated due to flow over a cylinder performing combined steady rotation and rotary oscillations.}, journal = {The Journal of the Acoustical Society of America}, volume = {147}, number = {1}, pages = {325}, doi = {10.1121/10.0000585}, pmid = {32007018}, issn = {1520-8524}, abstract = {Analysis of sound generated due to a laminar flow past a circular cylinder subjected to the mean rotation along with the rotary oscillating motion has been performed for the Reynolds number Re = 150 and the Mach number M = 0.2. The direct numerical simulation approach has been used to study modifications in the generated sound field over a range of forcing parameters using disturbance pressure field information. Flow and sound fields are accurately resolved over a nondimensional radial distance r≤100 from the center of the cylinder. Frequencies, as well as wavelengths of generated sound waves, have been effectively altered by varying the forcing frequency-ratio, whereas the directivity nature of the radiated sound field has been modified by varying the forcing amplitude-ratio. Doak's decomposition technique has been used to understand the reasons behind changes in the radiated sound fields as the forcing parameters are varied.}, } @article {pmid32006194, year = {2020}, author = {Alouges, F and Di Fratta, G}, title = {Parking 3-sphere swimmer: II. The long-arm asymptotic regime.}, journal = {The European physical journal. E, Soft matter}, volume = {43}, number = {2}, pages = {6}, pmid = {32006194}, issn = {1292-895X}, abstract = {The paper carries on our previous investigations on the complementary version of Purcell's rotator (sPr3): a low-Reynolds-number swimmer composed of three balls of equal radii. In the asymptotic regime of very long arms, the Stokes-induced governing dynamics is derived, and then experimented in the context of energy-minimizing self-propulsion characterized in the first part of the paper.}, } @article {pmid34095645, year = {2020}, author = {Zhang, X and Graham, MD}, title = {Multiplicity of stable orbits for deformable prolate capsules in shear flow.}, journal = {Physical review fluids}, volume = {5}, number = {2}, pages = {}, pmid = {34095645}, issn = {2469-990X}, support = {R21 MD011590/MD/NIMHD NIH HHS/United States ; R35 HL145000/HL/NHLBI NIH HHS/United States ; }, abstract = {This work investigates the orbital dynamics of a fluid-filled deformable prolate capsule in unbounded simple shear flow at zero Reynolds number using direct simulations. The motion of the capsule is simulated using a model that incorporates shear elasticity, area dilatation, and bending resistance. Here the deformability of the capsule is characterized by the nondimensional capillary number Ca, which represents the ratio of viscous stresses to elastic restoring stresses on the capsule. For a capsule with small bending stiffness, at a given Ca, the orientation converges over time towards a unique stable orbit independent of the initial orientation. With increasing Ca, four dynamical modes are found for the stable orbit, namely, rolling, wobbling, oscillating-swinging, and swinging. On the other hand, for a capsule with large bending stiffness, multiplicity in the orbit dynamics is observed. When the viscosity ratio λ ≲ 1, the long-axis of the capsule always tends towards a stable orbit in the flow-gradient plane, either tumbling or swinging, depending on Ca. When λ ≳ 1, the stable orbit of the capsule is a tumbling motion at low Ca, irrespective of the initial orientation. Upon increasing Ca, there is a symmetry-breaking bifurcation away from the tumbling orbit, and the capsule is observed to adopt multiple stable orbital modes including nonsymmetric precessing and rolling, depending on the initial orientation. As Ca further increases, the nonsymmetric stable orbit loses existence at a saddle-node bifurcation, and rolling becomes the only attractor at high Ca, whereas the rolling state coexists with the nonsymmetric state at intermediate values of Ca. A symmetry-breaking bifurcation away from the rolling orbit is also found upon decreasing Ca. The regime with multiple attractors becomes broader as the aspect ratio of the capsule increases, while narrowing as viscosity ratio increases. We also report the particle contribution to the stress, which also displays multiplicity.}, } @article {pmid34045778, year = {2020}, author = {Sherman, E and Lambert, L and White, B and Krane, MH and Wei, T}, title = {Cycle-to-cycle flow variations in a square duct with a symmetrically oscillating constriction.}, journal = {Fluid dynamics research}, volume = {52}, number = {1}, pages = {}, pmid = {34045778}, issn = {0169-5983}, support = {R01 DC005642/DC/NIDCD NIH HHS/United States ; }, abstract = {Spatially and temporally resolved Digital Particle Image Velocimetry (DPIV) measurements are presented of flow complexities in a nominally two-dimensional, symmetric, duct with an oscillating constriction. The motivation for this research lies in advancing the state-of-the-art in applying integral control volume analysis to modeling unsteady internal flows. The specific target is acoustic modeling of human phonation. The integral mass and momentum equations are directly coupled to the acoustic equations and provide quantitative insight into acoustic source strengths in addition to the dynamics of the fluid-structure interactions in the glottis. In this study, a square cross-section duct was constructed with symmetric, computer controlled, oscillating constrictions that incorporate both rocking as well as oscillatory open/close motions. Experiments were run in a free-surface water tunnel over a Strouhal number range, based on maximum jet speed and model length, of 0.012 - 0.048, for a fixed Reynolds number, based on maximum gap opening and maximum jet speed, of 8000. In this study, the constriction motions were continuous with one open-close cycle immediately following another. While the model and its motions were nominally two-dimensional and symmetric, flow asymmetries and oscillation frequency dependent cycle-to-cycle variations were observed. These are examined in the context of terms in the integral conservation equations.}, } @article {pmid31999751, year = {2020}, author = {Liu, P and Liu, H and Yang, Y and Wang, M and Sun, Y}, title = {Comparison of design methods for negative pressure gradient rotary bodies: A CFD study.}, journal = {PloS one}, volume = {15}, number = {1}, pages = {e0228186}, pmid = {31999751}, issn = {1932-6203}, mesh = {Animals ; Computer Simulation ; *Hydrodynamics ; Models, Theoretical ; *Pressure ; Ships ; Stress, Mechanical ; Surface Properties ; }, abstract = {Computational fluid dynamics (CFD) simulation is used to test two body design methods which use negative pressure gradient to suppress laminar flow separation and drag reduction. The steady-state model of the Transition SST model is used to calculate the pressure distribution, wall shear stress, and drag coefficient under zero angle of attack at different velocities. Four bodies designed by two different methods are considered. Our results show the first method is superior to the body of Hansen in drag reduction and the body designed by the first method is more likely to obtain the characteristics of suppressing or eliminating separation, which can effectively improve laminar flow coverage to achieve drag reduction under higher Reynolds number conditions. The results show that the negative pressure gradient method can suppress separation and drag reduction better than the second method. This successful design method is expected to open a promising prospect for its application in the design of small drag, small noise subsonic hydrodynamic hull and underwater weapons.}, } @article {pmid31991147, year = {2020}, author = {Nguyen, KH and Gemmell, BJ and Rohr, JR}, title = {Effects of temperature and viscosity on miracidial and cercarial movement of Schistosoma mansoni: ramifications for disease transmission.}, journal = {International journal for parasitology}, volume = {50}, number = {2}, pages = {153-159}, pmid = {31991147}, issn = {1879-0135}, support = {HHSN272201000005C/AI/NIAID NIH HHS/United States ; HHSN272201000005I/AI/NIAID NIH HHS/United States ; R01 TW010286/TW/FIC NIH HHS/United States ; }, mesh = {Animals ; Biomphalaria/parasitology ; Cercaria/*physiology ; Climate Change ; Host-Parasite Interactions ; Humans ; Larva/physiology ; Life Cycle Stages ; Movement/*physiology ; Schistosoma mansoni/*physiology ; Schistosomiasis mansoni/*transmission ; Temperature ; Viscosity ; }, abstract = {Parasites with complex life cycles can be susceptible to temperature shifts associated with seasonal changes, especially as free-living larvae that depend on a fixed energy reserve to survive outside the host. The life cycle of Schistosoma, a trematode genus containing some species that cause human schistosomiasis, has free-living, aquatic miracidial and cercarial larval stages that swim using cilia or a forked tail, respectively. The small size of these swimmers (150-350 µm) dictates that their propulsion is dominated by viscous forces. Given that viscosity inhibits the swimming ability of small organisms and is inversely correlated with temperature, changes in temperature should affect the ability of free-living larval stages to swim and locate a host. By recording miracidial and cercarial movement of Schistosoma mansoni using a high-speed camera and manipulating temperature and viscosity independently, we assessed the role each factor plays in the swimming mechanics of the parasite. We found a positive effect of temperature and a negative effect of viscosity on miracidial and cercarial speed. Reynolds numbers, which describe the ratio of inertial to viscous forces exerted on an aquatic organism, were <1 across treatments. Q10 values were <2 when comparing viscosity treatments at 20 °C and 30 °C, further supporting the influence of viscosity on miracidial and cercarial speed. Given that both larval stages have limited energy reserves and infection takes considerable energy, successful transmission depends on both speed and lifespan. We coupled our speed data with mortality measurements across temperatures and discovered that the theoretical maximum distance travelled increased with temperature and decreased with viscosity for both larval stages. Thus, our results suggest that S. mansoni transmission is high during warm times of the year, partly due to improved swimming performance of the free-living larval stages, and that increases in temperature variation associated with climate change might further increase transmission.}, } @article {pmid31989130, year = {2020}, author = {Fauzi, FB and Ismail, E and Syed Abu Bakar, SN and Ismail, AF and Mohamed, MA and Md Din, MF and Illias, S and Ani, MH}, title = {The role of gas-phase dynamics in interfacial phenomena during few-layer graphene growth through atmospheric pressure chemical vapour deposition.}, journal = {Physical chemistry chemical physics : PCCP}, volume = {22}, number = {6}, pages = {3481-3489}, doi = {10.1039/c9cp05346h}, pmid = {31989130}, issn = {1463-9084}, abstract = {The complicated chemical vapour deposition (CVD) is currently the most viable method of producing graphene. Most studies have extensively focused on chemical aspects either through experiments or computational studies. However, gas-phase dynamics in CVD reportedly plays an important role in improving graphene quality. Given that mass transport is the rate-limiting step for graphene deposition in atmospheric-pressure CVD (APCVD), the interfacial phenomena at the gas-solid interface (i.e., the boundary layer) are a crucial controlling factor. Accordingly, only by understanding and controlling the boundary-layer thickness can uniform full-coverage graphene deposition be achieved. In this study, a simplified computational fluid dynamics analysis of APCVD was performed to investigate gas-phase dynamics during deposition. Boundary-layer thickness was also estimated through the development of a customised homogeneous gas model. Interfacial phenomena, particularly the boundary layer and mass transport within it, were studied. The effects of Reynolds number on these factors were explored and compared with experimentally obtained results of the characterised graphene deposit. We then discussed and elucidated the important relation of fluid dynamics to graphene growth through APCVD.}, } @article {pmid31982669, year = {2020}, author = {Asghar, Z and Ali, N and Javid, K and Waqas, M and Dogonchi, AS and Khan, WA}, title = {Bio-inspired propulsion of micro-swimmers within a passive cervix filled with couple stress mucus.}, journal = {Computer methods and programs in biomedicine}, volume = {189}, number = {}, pages = {105313}, doi = {10.1016/j.cmpb.2020.105313}, pmid = {31982669}, issn = {1872-7565}, mesh = {Algorithms ; Cervix Uteri/*physiology ; Female ; Humans ; Male ; Models, Biological ; Mucus/*physiology ; Rheology ; Spermatozoa ; Stress, Psychological/metabolism ; }, abstract = {BACKGROUND AND OBJECTIVE: The swimming mechanism of self-propelling organisms has been imitated by biomedical engineers to design the mechanical micro bots. The interaction of these swimmers with surrounding environment is another important aspect. The present swimming problem integrates Taylor sheet model with couple stress fluid model. The thin passage containing micro-swimmers and mucus is approximated as a rigid (passive) two-dimensional channel. The spermatozoa forms a pack quite similar as a complex wavy sheet.

METHODS: Swimming problem with couple stress cervical liquid (at low Reynolds number) leads to a linear sixth order differential equation. The boundary value problem (BVP) is solved analytically with two unknowns i.e. speed of complex wavy sheet and flow rate of couple stress mucus. After utilizing this solution into equilibrium conditions these unknowns can be computed via Newton-Raphson algorithm. Furthermore, the pairs of numerically calculated organism speed and flow rate are utilized in the expression of power dissipation.

RESULTS: This work describes that the speed of micro-swimmers can be enhanced by suitable rheology of the surrounding liquid. The usage of couple stress fluid as compared to Newtonian fluid enhances the energy dissipation and reduces the flow rate. On the other hand complex wavy surface also aids the organisms to swim faster.}, } @article {pmid31978919, year = {2020}, author = {Zhu, Y and Yang, G and Zhuang, C and Li, C and Hu, D}, title = {Oral cavity flow distribution and pressure drop in balaenid whales feeding: a theoretical analysis.}, journal = {Bioinspiration & biomimetics}, volume = {15}, number = {3}, pages = {036004}, doi = {10.1088/1748-3190/ab6fb8}, pmid = {31978919}, issn = {1748-3190}, mesh = {Animals ; Biomechanical Phenomena ; Bionics ; Feeding Behavior/*physiology ; Models, Theoretical ; Mouth/*physiology ; Whales/*physiology ; }, abstract = {Balaenid whales, as continuous ram filter feeders, can efficiently separate prey from water by baleen. The feeding process of balaenid whales is extremely complex, in which the flow distribution and pressure drop in the oral cavity play a significant role. In this paper, a theoretical model coupled with oral cavity velocity and pressure in balaenid whales is established based on mass conservation, momentum conservation and pressure drop equations, considering both the inertial and the friction terms. A discrete method with section-by-section calculation is adopted to solve the theoretical model. The effects of four crucial parameters, i.e. the ratio of filtration area to inlet area (S), the Reynolds number of entrance (Re in), the ratio of thickness to permeability of the porous media formed by the fringe layer (ϕ) and the width ratio of the anteroposterior canal within the mouth along the tongue (APT channel) to that along the lip (APL channel) (H) are discussed. The results show that, for a given case, the flow distribution and the pressure drop both show increasing trends with the flow direction. For different cases, when S is small, Re in is small and ϕ is large, a good flow pattern emerges with a smoother flow speed near the oropharynx, better drainage, better shunting and filtration, and higher energy efficiency. However, for smaller values of H, some energy efficiency is sacrificed to achieve additional average transverse flow in order to produce better shunting and filtration. The research in this paper provides a reference for the design of high-efficiency bionic filters.}, } @article {pmid31978870, year = {2020}, author = {Afrouzi, HH and Ahmadian, M and Hosseini, M and Arasteh, H and Toghraie, D and Rostami, S}, title = {Simulation of blood flow in arteries with aneurysm: Lattice Boltzmann Approach (LBM).}, journal = {Computer methods and programs in biomedicine}, volume = {187}, number = {}, pages = {105312}, doi = {10.1016/j.cmpb.2019.105312}, pmid = {31978870}, issn = {1872-7565}, mesh = {Algorithms ; Aneurysm/*diagnostic imaging ; Arteries/diagnostic imaging ; *Blood Flow Velocity ; Cardiovascular Diseases/*diagnostic imaging ; Computer Simulation ; Hemodynamics ; Humans ; Hydrodynamics ; Models, Cardiovascular ; Rheology ; Shear Strength ; Stress, Mechanical ; Stroke/*diagnostic imaging ; Viscosity ; }, abstract = {BACKGROUND AND OBJECTIVE: In most countries, the higher death rates are due to cardiovascular disease and stroke. These problems often derive from irregular blood flow and the circulatory system disorder.

METHODS: In this paper, the blood flow is simulated in a created aneurysm in the artery upon using Lattice Boltzmann Method (LBM). Blood is selected as a non-Newtonian fluid which was simulated with power-law model. The lattice Boltzmann results for non-Newtonian fluid flow with power-law model and the curved boundary are compared and validated with previous studies which show a good agreement. In this study, simulations are carried out for two types of aneurysms. For the first aneurysm, three power-law exponents of 0.6, 0.8 and 1.0 at Reynolds number of 100 for three different cases are investigated.

RESULTS: The results show that the wall shear stress increases with increasing the power-law exponent. In addition, in the main duct of artery where the velocity is larger, shear stress is lower due to the smaller velocity gradient. For the second Aneurysm, the simulations are done for three Reynolds numbers of 100, 150 and 200, and three Womersley numbers of 4, 12 and 20. The blood flow is pulsating at the inlet such as the real pulsating wave in the blood. Results show that with increasing the Womersley number, the velocity profiles in the middle of the aneurysm are closer at a constant Reynolds number.

CONCLUSIONS: With increasing the Reynolds number, the range of vortices and values of velocity and tension grow in the aneurysm.}, } @article {pmid31975701, year = {2020}, author = {Porté-Agel, F and Bastankhah, M and Shamsoddin, S}, title = {Wind-Turbine and Wind-Farm Flows: A Review.}, journal = {Boundary-layer meteorology}, volume = {174}, number = {1}, pages = {1-59}, pmid = {31975701}, issn = {0006-8314}, abstract = {Wind energy, together with other renewable energy sources, are expected to grow substantially in the coming decades and play a key role in mitigating climate change and achieving energy sustainability. One of the main challenges in optimizing the design, operation, control, and grid integration of wind farms is the prediction of their performance, owing to the complex multiscale two-way interactions between wind farms and the turbulent atmospheric boundary layer (ABL). From a fluid mechanical perspective, these interactions are complicated by the high Reynolds number of the ABL flow, its inherent unsteadiness due to the diurnal cycle and synoptic-forcing variability, the ubiquitous nature of thermal effects, and the heterogeneity of the terrain. Particularly important is the effect of ABL turbulence on wind-turbine wake flows and their superposition, as they are responsible for considerable turbine power losses and fatigue loads in wind farms. These flow interactions affect, in turn, the structure of the ABL and the turbulent fluxes of momentum and scalars. This review summarizes recent experimental, computational, and theoretical research efforts that have contributed to improving our understanding and ability to predict the interactions of ABL flow with wind turbines and wind farms.}, } @article {pmid31962497, year = {2019}, author = {Kaminsky, J and Klewicki, J and Birnir, B}, title = {Application of the stochastic closure theory to the Townsend-Perry constants.}, journal = {Physical review. E}, volume = {100}, number = {6-1}, pages = {061101}, doi = {10.1103/PhysRevE.100.061101}, pmid = {31962497}, issn = {2470-0053}, abstract = {We compare the stochastic closure theory (SCT) to the Townsend-Perry constants as estimated from measurements in the Flow Physic Facility (FPF) at the University of New Hampshire. First, we explain the derivation of the Townsend-Perry constants, which were originally formulated by Meneveau and Marusic, in analogy with a Gaussian distribution. However, this was not supported by the data. Instead, the data show a sub-Gaussian relation that was explained by Birnir and Chen. We show herein how the SCT can be used to compute the constants, which explains their sub-Gaussian relations. We then compare the SCT theory predictions, including Reynolds-number-dependent corrections, with the data, showing good agreement.}, } @article {pmid31962492, year = {2019}, author = {Jin, Y and Cheng, S and Chamorro, LP}, title = {Active pitching of short splitters past a cylinder: Drag increase and wake.}, journal = {Physical review. E}, volume = {100}, number = {6-1}, pages = {063106}, doi = {10.1103/PhysRevE.100.063106}, pmid = {31962492}, issn = {2470-0053}, abstract = {The flow and drag induced by active pitching of plates in the wake of a cylinder of diameter d were experimentally studied for various plate lengths L as well as pitching frequencies f_{p} and amplitudes A_{0} at Reynolds number Re=1.6×10^{4} . Planar particle image velocimetry and a load cell were used to characterize the flow statistics and mean drag of a variety of cylinder-splitter assemblies. Results show the distinctive effect of active pitching on these quantities. In particular, flow recovery was significantly modulated by L, f_{p}, or A_{0} . Specific pitching settings resulted in a wake with dominant meandering patterns and faster flow recovery. We defined a modified version of the amplitude-based Strouhal number of the system St_{A} to account for the effect of the cylinder in active pitching. It characterizes the drag coefficient C_{d} across all the cases studied, and reveals two regions intersecting at a critical value of St_{A} ≈0.035. Below this value, the C_{d} remained nearly constant; however, it exhibited a linear increase with increasing St_{A} past this critical point. Inspection of the integral momentum equation showed the dominant role of velocity fluctuations in modulating C_{d} past the critical St_{A} .}, } @article {pmid31955110, year = {2020}, author = {Rajwa-Kuligiewicz, A and Radecki-Pawlik, A and Skalski, T and Plesiński, K and Rowiński, PM and Manson, JR}, title = {Hydromorphologically-driven variability of thermal and oxygen conditions at the block ramp hydraulic structure: The Porębianka River, Polish Carpathians.}, journal = {The Science of the total environment}, volume = {713}, number = {}, pages = {136661}, doi = {10.1016/j.scitotenv.2020.136661}, pmid = {31955110}, issn = {1879-1026}, abstract = {Growing anthropopressure in mountain streams aimed at limiting erosion and flood protection often caused adverse effects on the natural environment. In recent years, great attention has been paid to the restoration and conservation of natural habitats in mountain streams using environmentally friendly solutions such as the Block Ramp (BR) Hydraulic Structures. In this study we investigated the factors responsible for spatial variability in thermal and oxygen conditions at the single BR structure in the growing season, and the relation between water temperature and dissolved oxygen (DO) concentration. This has been done by measurements of hydraulic characteristics along with physicochemical properties of water, such as water temperature and DO concentration, at two different discharges. The redundancy analysis has been applied in order to describe the relationships among hydraulic parameters and physicochemical variables, and extract potential sources of water temperature and DO variability within the BR hydraulic structure. Results have shown that DO and water temperature distributions within the BR hydraulic structure depend on discharge conditions and are associated with the submergence of the block ramp. The highest heterogeneity in hydraulic, DO and water temperature conditions occurs at low flow and is associated with the presence of crevices between protruding cobbles at the block ramp. The lowest variability, in turn, occurs at high discharge, when the block ramp is completely submerged. The results indicated that thermal and oxygen conditions within the BR hydraulic structure are independent of hydraulic parameters at low flow. Moreover, the relation between DO concentration and water temperature is positive at low flow indicating potential impact of biological processes. On the contrary, at high discharge both, the DO concentrations and water temperature within the BR structure, depend on bed shear velocity and maximum Reynolds number.}, } @article {pmid31948589, year = {2020}, author = {Haghighinia, A and Movahedirad, S}, title = {Mass transfer in a novel passive micro-mixer: Flow tortuosity effects.}, journal = {Analytica chimica acta}, volume = {1098}, number = {}, pages = {75-85}, doi = {10.1016/j.aca.2019.11.028}, pmid = {31948589}, issn = {1873-4324}, abstract = {Hydroynamic fluid tortuosity is a parameter to describe the fluid streamlines average elongation. The motivation of the present study is introducing a new concept for theoretical predictions of dynamic tortuosity effects on mass transfer in a novel three-dimensional passive T-shape micro-mixer both experimentally and by numerical simulation. In the numerical analysis, continuity, motion, and diffusion-convection equations were solved, and the amount of mass transfer and the fluid tortuosity was calculated for different rectangular winglet angles. The Reynolds number is considered in the range of 0.1-93. The results show that when the angle of winglet tends to 22.5°, the fluid tortuosity, lateral velocity, and fluid mass transfer tend to maximum values. Furthermore, the effect of fluid tortuosity on the fluid stretching as a theory of chaotic mixing is investigated.}, } @article {pmid31947897, year = {2020}, author = {Rhoades, T and Kothapalli, CR and Fodor, PS}, title = {Mixing Optimization in Grooved Serpentine Microchannels.}, journal = {Micromachines}, volume = {11}, number = {1}, pages = {}, pmid = {31947897}, issn = {2072-666X}, abstract = {Computational fluid dynamics modeling at Reynolds numbers ranging from 10 to 100 was used to characterize the performance of a new type of micromixer employing a serpentine channel with a grooved surface. The new topology exploits the overlap between the typical Dean flows present in curved channels due to the centrifugal forces experienced by the fluids, and the helical flows induced by slanted groove-ridge patterns with respect to the direction of the flow. The resulting flows are complex, with multiple vortices and saddle points, leading to enhanced mixing across the section of the channel. The optimization of the mixers with respect to the inner radius of curvature (Rin) of the serpentine channel identifies the designs in which the mixing index quality is both high (M > 0.95) and independent of the Reynolds number across all the values investigated.}, } @article {pmid31947174, year = {2019}, author = {Oktamuliani, S and Hasegawa, K and Saijo, Y}, title = {Left Ventricular Vortices in Myocardial Infarction Observed with Echodynamography.}, journal = {Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual International Conference}, volume = {2019}, number = {}, pages = {5816-5819}, doi = {10.1109/EMBC.2019.8856394}, pmid = {31947174}, issn = {2694-0604}, mesh = {Blood Flow Velocity ; Case-Control Studies ; Echocardiography, Doppler, Color ; Heart Ventricles ; Hemodynamics ; Humans ; Myocardial Infarction/*diagnostic imaging ; *Ventricular Function, Left ; }, abstract = {Echodynamography (EDG) is a computational method to deduce two-dimensional (2D) blood flow vector from conventional color Doppler ultrasound image by considering that the blood flow is divided into vortex and base flow components. Left ventricular (LV) vortices indicate cardiac flow status influenced by LV wall motion. Thus, quantitative assessment of LV vortices may become new and sensitive parameters for cardiac function. In the present study, quantitative parameters of LV vortices such as vortex index, vortex size, and Reynolds number were calculated and relation between each parameter was assessed. Six healthy volunteers and three patients with myocardial infarction (MI) who underwent color Doppler echocardiography (CDE) were involved in the study. Serial CDE images in apical three-chamber view were recorded and 2D blood flow vector was superimposed on the CDE image. Vortex index, vortex size, and Reynolds number were compared between the normal volunteers and the MI patients. The results showed that vortex index (3.09±2.06 vs. 3.34±2.33, p<; 0.05), vortex size (1.76 0.69 vs. 2.01 ±0.68, p<; 0.05), Reynolds number (1020±603 vs.±1312 1046, p<; ±0.05) were significantly greater in the MI patients than in the healthy volunteers. Vortex equivalent diameter in LV showed significant positive correlation with Reynolds number (R[2] = 0.799, y = 0.001x + 0.7098, p <; 0.05) in healthy volunteers and (R[2] = 0.6404, y = 0.0005x+1.3185, p<; 0.05) in MI patients. Vortex index showed positive correlation with Reynolds number (R[2] = 0.9351, y = 0.002x+0.1397, p<; 0.05) in healthy volunteers and (R[2] = 0.758, y = 0.0019x+0.7957, p<; 0.05) in MI patients. In conclusion, EDG provides information on LV hemodynamics by quantitative LV vortices parameters both in healthy volunteers and MI patients.}, } @article {pmid31946085, year = {2019}, author = {Hamad, EM and Sawalmeh, B and Mhawsh, AA and Mansour, M and Awad, M and Al-Halhouli, AT and Al-Gharabli, SI}, title = {Investigation of Bifurcation Effect on Various Microfluidic Designs for Blood Separation.}, journal = {Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual International Conference}, volume = {2019}, number = {}, pages = {1097-1100}, doi = {10.1109/EMBC.2019.8856380}, pmid = {31946085}, issn = {2694-0604}, mesh = {Equipment Design ; *Lab-On-A-Chip Devices ; *Microfluidic Analytical Techniques ; *Microfluidics ; Plasma ; Software ; }, abstract = {In this project, a microfluidic device for blood separation will be designed and tested in order to separate plasma from whole blood for diagnostic purposes. The design will be based on previously implemented designs that will be further discussed in the next sections. When designing microfluidic devices, it is essential to consider the different physical phenomena that arise from switching from the macro scale to the micro scale. Parameters such as the Reynolds number and the forces affecting the fluid must be studied in order to produce a suitable and effective design. Finite element methods have been implemented prior to the production of the microfluidic devices. Various geometries/designs have been tested using Fluent ANSYS software. Later on, the successful design was fabricated using micromachining on an acrylic substrate and was tested using simulated blood through of a syringe pump.}, } @article {pmid31942792, year = {2020}, author = {Martínez-Merino, P and Midgley, SD and Martín, EI and Estellé, P and Alcántara, R and Sánchez-Coronilla, A and Grau-Crespo, R and Navas, J}, title = {Novel WS2-Based Nanofluids for Concentrating Solar Power: Performance Characterization and Molecular-Level Insights.}, journal = {ACS applied materials & interfaces}, volume = {12}, number = {5}, pages = {5793-5804}, doi = {10.1021/acsami.9b18868}, pmid = {31942792}, issn = {1944-8252}, abstract = {Nano-colloidal suspensions of nanomaterials in a fluid, nanofluids, are appealing because of their interesting properties related to heat transfer processes. While nanomaterials based on transition metal chalcogenides (TMCs) have been widely studied in catalysis, sensing, and energy storage applications, there are few studies of nanofluids based on TMCs for heat transfer applications. In this study, the preparation and analysis of nanofluids based on 2D-WS2 in a typical heat transfer fluid (HTF) used in concentrating solar power (CSP) plants are reported. Nanofluids prepared using an exfoliation process exhibited well-defined nanosheets and were highly stable. The nanofluids were characterized in terms of properties related to their application in CSP. The presence of WS2 nanosheets did not modify significantly the surface tension, the viscosity, or the isobaric specific heat, but the thermal conductivity was improved by up to 30%. The Ur factor, which characterizes the thermal efficiency of the fluid in the solar collector, shows an enhancement of up to 22% in the nanofluid, demonstrating great promise for CSP applications. The Reynolds number and friction factor of the fluid were not significantly modified by the addition of the nanomaterial to the HTF, which is also positive for practical applications in CSP plants. Ab initio molecular dynamics simulations of the nanoparticle/fluid interface showed an irreversible dissociative adsorption of diphenyl oxide molecules on the WS2 edge, with very low kinetic barrier. The resulting "decoration" of the WS2 edge dramatically affects the nature of the interface interactions and is therefore expected to affect significantly the rheological and transport properties of the nanofluids.}, } @article {pmid31938721, year = {2020}, author = {Zhang, T and Moreau, D and Geyer, T and Fischer, J and Doolan, C}, title = {Dataset on tip vortex formation noise produced by wall-mounted finite airfoils with flat and rounded tip geometries.}, journal = {Data in brief}, volume = {28}, number = {}, pages = {105058}, pmid = {31938721}, issn = {2352-3409}, abstract = {The vortex generated at the tip of an airfoil such as an aircraft wing, wind turbine blade, submarine fin or propeller blade can dominate its wake and be a significant source of unwanted noise. The data collection presented in this paper consists of measurements of tip vortex formation noise produced by finite length airfoils with flat and rounded tips. These data were obtained using the specialist aeroacoustic test facilities at the Brandenburg University of Technology (BTU) in Cottbus, Germany and a 47-channel planar microphone array. Over 1200 unique test cases with variations in airfoil profile shape, tip geometry, angle of attack and Reynolds number were measured during the experimental campaign. The dataset contains one-third-octave band tip noise spectra that have been processed using Acoular, a Python module for acoustic beamforming.}, } @article {pmid31935152, year = {2020}, author = {Salazar-Magallón, JA and Huerta de la Peña, A}, title = {Production of antifungal saponins in an airlift bioreactor with a cell line transformed from Solanum chrysotrichum and its activity against strawberry phytopathogens.}, journal = {Preparative biochemistry & biotechnology}, volume = {50}, number = {2}, pages = {204-214}, doi = {10.1080/10826068.2019.1676781}, pmid = {31935152}, issn = {1532-2297}, mesh = {Antifungal Agents/*chemical synthesis/pharmacology ; *Bioreactors ; Cell Line, Transformed ; Fragaria/*microbiology ; Saponins/*chemical synthesis/*pharmacology ; Solanum/*chemistry ; }, abstract = {Biotechnology through plant cell cultures in bioreactors is a tool that allows increasing the production of secondary metabolites of commercial interest. The hydrodynamic characterization, in addition to the transfer (OTR) and uptake (OUR) of oxygen through the dynamic method with different aeration rate, were used to see their influence on the production of biomass and saponins. The culture poisoning technique was used to determine the antifungal activity of the SC-2 and SC-3 saponins in vitro. Likewise, the shear or hydrodynamic stress of 273.6 mN/m[2] were calculated based on the Reynolds Number. The oxygen supply (OTR) was always greater than the demand (OUR) for all the aeration rate evaluated. Dry weight values of 8.6 gDW/L and a concentration of 2.7 mg/L and 187.3 mg/L of the saponins SC-2 and SC-3 respectively were obtained with an air flow of 0.1 vvm. In addition, it was possible to inhibit the growth of phytopathogenic fungi in vitro by up to 93%, while in vivo it was possible to reduce the infections of strawberry seeds inoculated with phytopathogens, obtaining up to 94% of germinated seeds. This information will facilitate the rational operation of the bioreactor culture system that produces secondary metabolites.}, } @article {pmid31933715, year = {2020}, author = {Hu, X and Lin, J and Chen, D and Ku, X}, title = {Influence of non-Newtonian power law rheology on inertial migration of particles in channel flow.}, journal = {Biomicrofluidics}, volume = {14}, number = {1}, pages = {014105}, pmid = {31933715}, issn = {1932-1058}, abstract = {In this paper, the inertial migration of particles in the channel flow of power-law fluid is numerically investigated. The effects of the power-law index (n), Reynolds number (Re), blockage ratio (k), and channel aspect ratio (AR) on the inertial migration of particles and equilibrium position are explored. The results show that there exist two stages of particle migration and four stable equilibrium positions for particles in the cross section of a square channel. The particle equilibrium positions in a rectangular channel are much different from those in a square channel. In shear-thinning fluids, the long channel face equilibrium position and two kinds of particle trajectories are found at low Re. With increasing Re, the short channel face equilibrium position turns to be stable, multiequilibrium positions, and three kinds of particle trajectories along the long wall start to form. Only two stable equilibrium positions exist in shear-thickening fluids. The equilibrium positions are getting closer to the channel centerline with increasing n and k and with decreasing Re. The inertial focusing length L 2 in the second stage of particle migration is much longer than inertial focusing length L 1 in the first stage. In the square channel, L 2 is decreased with increasing Re and k and with decreasing n. In the rectangular channel, L 2 is the shortest in the shear-thinning fluid.}, } @article {pmid31931378, year = {2020}, author = {Feng, Y and Wang, Q and Duan, JL and Li, XY and Ma, JY and Wu, L and Han, Y and Liu, XY and Zhang, YB and Yuan, XZ}, title = {Attachment and adhesion force between biogas bubbles and anaerobic granular sludge in the up-flow anaerobic sludge blanket.}, journal = {Water research}, volume = {171}, number = {}, pages = {115458}, doi = {10.1016/j.watres.2019.115458}, pmid = {31931378}, issn = {1879-2448}, mesh = {Anaerobiosis ; *Biofuels ; Bioreactors ; *Sewage ; Waste Disposal, Fluid ; }, abstract = {The performance of the up-flow anaerobic sludge blanket (UASB) is significantly governed by the hydrodynamics of the reactor. Though the influence of hydrodynamics on mass transfer, granular size distribution, and biogas production was well studied, the interaction between biogas bubbles and anaerobic granular sludge (AGS) is poorly understood. This study used the impinging-jet technique and bubble probe atomic force microscope (AFM) to investigate the attachment and adhesion force between biogas bubbles (CH4 and CO2) and AGS. The fluxes of normalized CH4 or CO2 bubble-attachment on two kinds of AGS were directly affected by gas velocity and decreased with an increase in the Reynolds number ranged from 40 to 140. The bubble-attachment had a positive linear relationship with the contact angles, ratio of exopolymeric protein and polysaccharide, and hydrophilic functional groups of AGS. A bubble probe AFM was used to explore the adhesion force between a single bubble and AGS. The results indicated that the adhesion force between the bubbles and the two kinds of AGS also decreased with increasing approach velocity. Overall, these results contribute to a new insight into the understanding of interaction between biogas bubbles and AGS in UASB reactors.}, } @article {pmid31923819, year = {2020}, author = {Muhammad, R and Khan, MI and Jameel, M and Khan, NB}, title = {Fully developed Darcy-Forchheimer mixed convective flow over a curved surface with activation energy and entropy generation.}, journal = {Computer methods and programs in biomedicine}, volume = {188}, number = {}, pages = {105298}, doi = {10.1016/j.cmpb.2019.105298}, pmid = {31923819}, issn = {1872-7565}, mesh = {Algorithms ; Computer Simulation ; Convection ; Diffusion ; Elasticity ; Entropy ; *Hot Temperature ; Hydrodynamics ; *Models, Theoretical ; Nanotechnology/methods ; *Rheology ; Software ; Viscosity ; }, abstract = {BACKGROUND: Mixed convection (forced+natural convection) is frequently observed in exceptionally high output devices where the forced convection isn't sufficient to dissipate all of the heat essential. At this point, consolidating natural convection with forced convection will frequently convey the ideal outcomes. Nuclear reactor technology and a few features of electronic cooling are the examples of these processes. Mixed convection problems are categorized by Richardson number (Ri), which is the ratio of Grashof number (for natural convection) and Reynolds number (for forced convection). For buoyancy or mixed convection the relative effect can be addressed by Richardson number. Typically, the natural convection is negligible when Richardson number is less than 0.1 (Ri < 0.1), forced convection is negligible when Richardson number is greater than 10 (Ri > 10) and neither is negligible when (0.1 < Ri < 10). It might be noticed that generally the forced convection is large comparative with natural convection except in case of remarkably low forced flow velocities. The current work gives significant insights regarding dissipative mixed convective Darcy-Forchheimer flow with entropy generation over a stretched curved surface. The energy equation is developed with respect to nonlinear radiation, dissipation and Ohmic heating (Joule heating). Binary reaction via activation energy is accounted.

METHOD: Curvilinear transformations are utilized to change the nonlinear PDE's into ordinary ones. Computational outcomes are obtained via NDSolve MATHEMATICA. The results are computed and discussed graphically.

RESULTS: Velocity decays for Forchheimer number. Entropy generation enhances for diffusion parameter and chemical reaction parameter. Concentration profile reduces chemical reaction parameter and enhances for activation parameter.}, } @article {pmid31923536, year = {2020}, author = {Rane, YS and Marston, JO}, title = {Computational study of fluid flow in tapered orifices for needle-free injectors.}, journal = {Journal of controlled release : official journal of the Controlled Release Society}, volume = {319}, number = {}, pages = {382-396}, doi = {10.1016/j.jconrel.2020.01.013}, pmid = {31923536}, issn = {1873-4995}, mesh = {Injections, Jet ; *Rheology ; Viscosity ; }, abstract = {Transdermal drug delivery using spring-powered jet injection has been studied for several decades and continues to be highly sought after due to the advent of targeted needle-free techniques, especially for viscous and complex fluids. As such, this paper reports results from numerical simulations to study the role of fluid rheology and cartridge geometry on characteristics such as jet exit velocity, total pressure drop and boundary layer thickness, since these all factor in to jet stability and collimation. The numerical approach involves incompressible steady flow with turbulence modelling based on the system Reynolds number at the orifice (Re = ρdovj/μ). The results are experimentally validated for a given geometry over a wide range of Reynolds numbers (10[1] < Re < 10[4]), and our results indicate a sharp decrease in dimensionless pressure drop (Eu = 2∆P/ρvj[2]) for Re < 10[2)] and gradually approaching the inviscid limit at Re ≥ 10[4]. By extending the study to non-Newtonian fluids, whose rheological profile is approximated by the Carreau model, we also elucidated the effect of different rheological parameters. Lastly by studying a range of nozzle geometries such as conical, sigmoid taper and multi-tier tapers, we observe that fluid acceleration suppresses the boundary layer growth, which indicates there may be optimal geometries for creating jets to target specific tissue depths.}, } @article {pmid35072172, year = {2020}, author = {McCain, JL and Pohly, JA and Sridhar, MK and Kang, CK and Landrum, DB and Aono, H}, title = {Experimental Force and Deformation Measurements of Bioinspired Flapping Wings in Ultra-Low Martian Density Environment.}, journal = {Applied aerodynamics : papers presented at the AIAA SciTech Forum and Exposition 2020 : Orlando, Florida, USA, 6-10 January 2020. AIAA SciTech Forum and Exposition (2020 : Orlando, Fla.)}, volume = {2020}, number = {}, pages = {}, pmid = {35072172}, support = {80NSSC18K0870/ImNASA/Intramural NASA/United States ; }, abstract = {A Mars flight vehicle could provide a third-dimension for ground-based rovers and supplement orbital observation stations, providing a much more detailed aerial view of the landscape as well as unprecedented survey of the atmosphere of Mars. However, flight on Mars is a difficult proposition due to the very low atmospheric density, which is approximately 1.3% of sea level density on Earth. While traditional aircraft efficiency suffers in the low Reynolds number environment, insect inspired flapping wing flyers on Mars might be able to take advantage of the same lift enhancing effects as insects on Earth. The present work investigates the feasibility of using a bioinspired, flapping wing flight vehicle to produce lift in an ultra-low-density Martian atmosphere. A four-wing prototype, inspired by a prior computational study, was placed in an atmospheric chamber to simulate Martian density. Lift and wing deformation were simultaneously recorded. In Earth density conditions, the passive pitch wing deflection increased monotonically with flapping frequency. On the other hand, in the Martian density environment, the passive pitch deflection angles were very erratic. The measured lift peaked at around 8 grams at 16 Hz. These measurements suggest that sufficient aerodynamic forces for hover on Mars can be generated for a 6-gram flapping wing vehicle. Also, the performance can potentially be improved by better understanding the fluid-structure interaction in ultra-low Mars density condition.}, } @article {pmid31907556, year = {2020}, author = {Pan, X and Tang, L and Feng, J and Liang, R and Pu, X and Li, R and Li, K}, title = {Experimental Research on the Degradation Coefficient of Ammonia Nitrogen Under Different Hydrodynamic Conditions.}, journal = {Bulletin of environmental contamination and toxicology}, volume = {104}, number = {2}, pages = {288-292}, doi = {10.1007/s00128-019-02781-0}, pmid = {31907556}, issn = {1432-0800}, mesh = {Ammonia/*analysis/chemistry ; Environmental Monitoring ; Hydrodynamics ; Kinetics ; Nitrogen/*analysis/chemistry ; Rivers/chemistry ; Water Pollutants, Chemical/*analysis/chemistry ; }, abstract = {Degradation coefficients for pollutants in water are important parameters that are significantly influenced by environmental conditions. In controlled experiments, the processes and trends of ammonia nitrogen (NH3-N) degradation in raw waters were studied under different flow conditions using a laboratory annular flume. Analysis of the observed change in NH3-N concentration with time under various flow conditions allowed calculation of a degradation efficiency (concentration change amount/initial concentration) which for NH3-N increased as the flow velocity increased. According to a first-order kinetic equation to fit the experimental data, the range of variation of the degradation coefficient of NH3-N at different flowrates was between 0.047 per day (0.01 m/s) and 0.203 per day (0.30 m/s). Dimensional analysis was used to analyze the relationship between the degradation coefficient and flow velocity (v), water depth (H), Froude number (Fr), and Reynolds number (Re), which was verified through field data collected in the Chishui River.}, } @article {pmid31905597, year = {2019}, author = {Sobecki, C and Zhang, J and Wang, C}, title = {Numerical Study of Paramagnetic Elliptical Microparticles in Curved Channels and Uniform Magnetic Fields.}, journal = {Micromachines}, volume = {11}, number = {1}, pages = {}, pmid = {31905597}, issn = {2072-666X}, abstract = {We numerically investigated the dynamics of a paramagnetic elliptical particle immersed in a low Reynolds number Poiseuille flow in a curved channel and under a uniform magnetic field by direct numerical simulation. A finite element method, based on an arbitrary Lagrangian-Eulerian approach, analyzed how the channel geometry, the strength and direction of the magnetic field, and the particle shape affected the rotation and radial migration of the particle. The net radial migration of the particle was analyzed after executing a π rotation and at the exit of the curved channel with and without a magnetic field. In the absence of a magnetic field, the rotation is symmetric, but the particle-wall distance remains the same. When a magnetic field is applied, the rotation of symmetry is broken, and the particle-wall distance increases as the magnetic field strength increases. The causation of the radial migration is due to the magnetic angular velocity caused by the magnetic torque that constantly changes directions during particle transportation. This research provides a method of magnetically manipulating non-spherical particles on lab-on-a-chip devices for industrial and biological applications.}, } @article {pmid31893769, year = {2019}, author = {Bahrami, A and Hoseinzadeh, S and Heyns, PS and Mirhosseini, SM}, title = {Experimental investigation of co-flow jet's airfoil flow control by hot wire anemometer.}, journal = {The Review of scientific instruments}, volume = {90}, number = {12}, pages = {125107}, doi = {10.1063/1.5113592}, pmid = {31893769}, issn = {1089-7623}, abstract = {An experimental flow control technique is given in this paper to study the jet effect on the coflow jet's airfoil with injection and suction and compared with the jet-off condition. The airfoil is CFJ0025-065-196, and the Reynolds number based on the airfoil's chord length is 10[5]. To measure the turbulence components of flow, a hot wire anemometry apparatus in a wind tunnel has been used. In this paper, the effect of the average velocity and boundary layer thickness on the coflow jet's airfoil is analyzed. The test is done for two different coflow velocities and for different angles of attack. It is also shown that, by increasing the velocity difference between the jet and the main flow, separation is delayed, and this delay can be preserved by raising coflow velocity at higher angles of attack. So, this flow control method has a good efficiency, and it is possible to reach higher numbers of lift and lower numbers of drag coefficients.}, } @article {pmid31890822, year = {2020}, author = {Pendse, V and Mazumdar, B and Kumar, H}, title = {Formulation of experimental data based model for solid-liquid mass transfer enhancement in three phase fluidized bed using nanofluid.}, journal = {Data in brief}, volume = {28}, number = {}, pages = {104990}, pmid = {31890822}, issn = {2352-3409}, abstract = {This experimental data based model in three phase fluidized bed was designed to enhance the solid-liquid mass transfer. This data focuses on mass transfer enhancement using nanomaterial. In present investigation benzoic acid-water-air system was used as three phases ie solid, liquid and gas respectively with Arachitol nano as nanomaterial in different volume percent in three phase fluidized bed. Data from experiment were collected by varying gas velocity, bed height, nanomaterial percentage and time. After a convenient selection various correlation have been derived. The data presented here is the full set of experimental value and coefficients and exponents in correlation were estimated from nonlinear optimization technique in MATLAB.}, } @article {pmid31882681, year = {2019}, author = {Krishnan, SR and Bal, J and Putnam, SA}, title = {A simple analytic model for predicting the wicking velocity in micropillar arrays.}, journal = {Scientific reports}, volume = {9}, number = {1}, pages = {20074}, pmid = {31882681}, issn = {2045-2322}, abstract = {Hemiwicking is the phenomena where a liquid wets a textured surface beyond its intrinsic wetting length due to capillary action and imbibition. In this work, we derive a simple analytical model for hemiwicking in micropillar arrays. The model is based on the combined effects of capillary action dictated by interfacial and intermolecular pressures gradients within the curved liquid meniscus and fluid drag from the pillars at ultra-low Reynolds numbers [Formula: see text]. Fluid drag is conceptualized via a critical Reynolds number: [Formula: see text], where v0 corresponds to the maximum wetting speed on a flat, dry surface and x0 is the extension length of the liquid meniscus that drives the bulk fluid toward the adsorbed thin-film region. The model is validated with wicking experiments on different hemiwicking surfaces in conjunction with v0 and x0 measurements using Water [Formula: see text], viscous FC-70 [Formula: see text] and lower viscosity Ethanol [Formula: see text].}, } @article {pmid31881751, year = {2019}, author = {Li, H and Li, Y and Huang, B and Xu, T}, title = {Flow Characteristics of the Entrance Region with Roughness Effect within Rectangular Microchannels.}, journal = {Micromachines}, volume = {11}, number = {1}, pages = {}, pmid = {31881751}, issn = {2072-666X}, abstract = {We conducted systematic numerical investigations of the flow characteristics within the entrance region of rectangular microchannels. The effects of the geometrical aspect ratio and roughness on entrance lengths were analyzed. The incompressible laminar Navier-Stokes equations were solved using finite volume method (FVM). In the simulation, hydraulic diameters (Dh) ranging from 50 to 200 µm were studied, and aspect ratios of 1, 1.25, 1.5, 1.75, and 2 were considered as well. The working fluid was set as water, and the Reynolds number ranged from 0.5 to 100. The results showed a good agreement with the conducted experiment. Correlations are proposed to predict the entrance lengths of microchannels with respect to different aspect ratios. Compared with other correlations, these new correlations are more reliable because a more practical inlet condition was considered in our investigations. Instead of considering the influence of the width and height of the microchannels, in our investigation we proved that the critical role is played by the aspect ratio, representing the combination of the aforementioned parameters. Furthermore, the existence of rough elements obviously shortens the entrance region, and this effect became more pronounced with increasing relative roughness and Reynolds number. A similar effect could be seen by shortening the roughness spacing. An asymmetric distribution of rough elements decreased the entrance length compared with a symmetric distribution, which can be extrapolated to other irregularly distributed forms.}, } @article {pmid31878263, year = {2019}, author = {Kang, DJ}, title = {Effects of Channel Wall Twisting on the Mixing in a T-Shaped Micro-Channel.}, journal = {Micromachines}, volume = {11}, number = {1}, pages = {}, pmid = {31878263}, issn = {2072-666X}, abstract = {A new design scheme is proposed for twisting the walls of a microchannel, and its performance is demonstrated numerically. The numerical study was carried out for a T-shaped microchannel with twist angles in the range of 0 to 34π. The Reynolds number range was 0.15 to 6. The T-shaped microchannel consists of two inlet branches and an outlet branch. The mixing performance was analyzed in terms of the degree of mixing and relative mixing cost. All numerical results show that the twisting scheme is an effective way to enhance the mixing in a T-shaped microchannel. The mixing enhancement is realized by the swirling of two fluids in the cross section and is more prominent as the Reynolds number decreases. The twist angle was optimized to maximize the degree of mixing (DOM), which increases with the length of the outlet branch. The twist angle was also optimized in terms of the relative mixing cost (MC). The two optimum twisting angles are generally not coincident. The optimum twist angle shows a dependence on the length of the outlet branch but it is not affected much by the Reynolds number.}, } @article {pmid31875772, year = {2020}, author = {Zhang, L and Zhou, J and Zhang, B and Gong, W}, title = {Numerical investigation on the solid particle erosion in elbow with water-hydrate-solid flow.}, journal = {Science progress}, volume = {103}, number = {1}, pages = {36850419897245}, doi = {10.1177/0036850419897245}, pmid = {31875772}, issn = {2047-7163}, abstract = {Erosion in pipeline caused by solid particles, which may lead to premature failure of the pipe system, is regarded as one of the most important concerns in the field of oil and gas. Therefore, the Euler-Lagrange, erosion model, and discrete phase model are applied for the purpose of simulating the erosion of water-hydrate-solid flow in submarine hydrate transportation pipeline. In this article, the flow and erosion characteristics are well verified on the basis of experiments. Moreover, analysis is conducted to have a good understanding of the effects of hydrate volume, mean curvature radius/pipe diameter (R/D) rate, flow velocity, and particle diameter on elbow erosion. It is finally obtained that the hydrate volume directly affects the Reynolds number through viscosity and the trend of the Reynolds number is consistent with the trend of erosion rate. Taking into account different R/D rates, the same Stokes number reflects different dynamic transforms of the maximum erosion zone. However, the outmost wall (zone D) will be the final erosion zone when the value of the Stokes number increases to a certain degree. In addition, the erosion rate increases sharply along with the increase of flow velocity and particle diameter. The effect of flow velocity on the erosion zone can be ignored in comparison with the particle diameter. Moreover, it is observed that flow velocity is deemed as the most sensitive factor on erosion rate among these factors employed in the orthogonal experiment.}, } @article {pmid31874992, year = {2019}, author = {Liu, X and Fan, D and Yu, X and Liu, Z and Sun, J}, title = {Effects of Simulated Gravel on Hydraulic Characteristics of Overland Flow Under Varying Flow Discharges, Slope Gradients and Gravel Coverage Degrees.}, journal = {Scientific reports}, volume = {9}, number = {1}, pages = {19781}, pmid = {31874992}, issn = {2045-2322}, abstract = {To quantify the hydraulic characteristics of overland flow on gravel-covered slopes, eight flow discharges (Q) (8.44-122 L/min), five slope gradients (J) (2°-10°) and four gravel coverage degrees (Cr) (0-30%) were examined via a laboratory flume. The results showed that (1) gravel changed flow regime. Gravel increased the Reynolds number (Re) by 2.94-33.03%. Re were less affected by J and positively correlated with Cr and Q. Gravel decreased the Froude number (Fr) by 6.83-77.31%. Fr was positively correlated with Q and J and negatively correlated with Cr. (2) Gravel delayed the flow velocity (u) and increased the flow depth (h) and flow resistance (f). Gravel reduced u by 1.20-58.95%. u was positively correlated with Q and J and negatively correlated with Cr. Gravel increased h by 0.12-2.41 times. h was positively correlated with Q and Cr and negatively correlated with J. Gravel increased f by 0.15-18.42 times. f were less affected by J, positively correlated with Cr and negatively correlated with Q. (3) The relationships between hydraulic parameters and Q, J and Cr identified good power functions. Hydraulic parameters were mainly affected by Cr. These results can guide the ecological construction of soil and water conservation.}, } @article {pmid31868425, year = {2019}, author = {Panickacheril John, J and Donzis, DA and Sreenivasan, KR}, title = {Solenoidal Scaling Laws for Compressible Mixing.}, journal = {Physical review letters}, volume = {123}, number = {22}, pages = {224501}, doi = {10.1103/PhysRevLett.123.224501}, pmid = {31868425}, issn = {1079-7114}, abstract = {Mixing of passive scalars in compressible turbulence does not obey the same classical Reynolds number scaling as its incompressible counterpart. We first show from a large database of direct numerical simulations that even the solenoidal part of the velocity field fails to follow the classical incompressible scaling when the forcing includes a substantial dilatational component. Though the dilatational effects on the flow remain significant, our main results are that both the solenoidal energy spectrum and the passive scalar spectrum assume incompressible forms, and that the scalar gradient essentially aligns with the most compressive eigenvalue of the solenoidal part, provided that only the solenoidal components are consistently used for scaling. A slight refinement of this statement is also pointed out.}, } @article {pmid31862924, year = {2019}, author = {Nath, R and Krishnan, M}, title = {Optimization of double diffusive mixed convection in a BFS channel filled with Alumina nanoparticle using Taguchi method and utility concept.}, journal = {Scientific reports}, volume = {9}, number = {1}, pages = {19536}, pmid = {31862924}, issn = {2045-2322}, abstract = {This research work focuses on the implementation of Taguchi method and utility concept for optimization of flow, geometrical and thermo-physical parameters for mixed convective heat and mass transfer in a backward facing step (BFS) channel filled with Alumina nanoparticle doped in water-ethylene glycol mixture. Mass, momentum, energy and solutal conservation equations for the flow field are cast in velocity-vorticity form of Navier-Stokes equations, which are solved using Galerkin's weighted residual finite element method through isoparametric formulation. The following six parameters, expansion ratio of the BFS channel (H/h), Reynolds number (Re), buoyancy ratio (N), nanoparticle volume fraction (χ), shape of nanoparticles and thermal Grashof number (GrT) at three levels are considered as controlling parameters for optimization using Taguchi method. An L27 orthogonal array has been chosen to get the levels of the six parameters for the 27 trial runs. Simulation results were obtained for 27 trial runs from which three different sets of optimum levels of the control parameters were obtained for maximum Nu and Sh and minimum wall shear stress during double diffusive mixed convection in the channel. Then, in order to obtain a single set of optimum levels of the control parameters to achieve maximum heat and mass transfer and minimum wall shear stress concurrently, utility concept has been implemented. Taguchi results indicate that expansion ratio and volume fraction of nanoparticles are the significant contributing parameters to achieve maximum heat and mass transfer and minimum wall shear stress. Utility concept predicts the average Nusselt number less by 2% and Sherwood number less by 3% compared to the Taguchi method with equal weightage of 40% assumed for Nusselt and Sherwood numbers and 20% for wall shear stress.}, } @article {pmid31861736, year = {2019}, author = {Maklad, O and Eliasy, A and Chen, KJ and Theofilis, V and Elsheikh, A}, title = {Simulation of Air Puff Tonometry Test Using Arbitrary Lagrangian-Eulerian (ALE) Deforming Mesh for Corneal Material Characterisation.}, journal = {International journal of environmental research and public health}, volume = {17}, number = {1}, pages = {}, pmid = {31861736}, issn = {1660-4601}, mesh = {Cornea/*diagnostic imaging ; Corneal Injuries/*diagnosis ; Humans ; Intraocular Pressure/*physiology ; Manometry/*methods ; *Surgical Mesh ; Tonometry, Ocular/*methods ; }, abstract = {UNLABELLED: : Purpose: To improve numerical simulation of the non-contact tonometry test by using arbitrary Lagrangian-Eulerian deforming mesh in the coupling between computational fluid dynamics model of an air jet and finite element model of the human eye.

METHODS: Computational fluid dynamics model simulated impingement of the air puff and employed Spallart-Allmaras model to capture turbulence of the air jet. The time span of the jet was 30 ms and maximum Reynolds number was Re=2.3×104, with jet orifice diameter 2.4 mm and impinging distance 11 mm. The model of the human eye was analysed using finite element method with regional hyperelastic material variation and corneal patient-specific topography starting from stress-free configuration. The cornea was free to deform as a response to the air puff using an adaptive deforming mesh at every time step of the solution. Aqueous and vitreous humours were simulated as a fluid cavity filled with incompressible fluid with a density of 1000 kg/m[3].

RESULTS: Using the adaptive deforming mesh in numerical simulation of the air puff test improved the traditional understanding of how pressure distribution on cornea changes with time of the test. There was a mean decrease in maximum pressure (at corneal apex) of 6.29 ± 2.2% and a development of negative pressure on a peripheral corneal region 2-4 mm away from cornea centre.

CONCLUSIONS: The study presented an improvement of numerical simulation of the air puff test, which will lead to more accurate intraocular pressure (IOP) and corneal material behaviour estimation. The parametric study showed that pressure of the air puff is different from one model to another, value-wise and distribution-wise, based on cornea biomechanical parameters.}, } @article {pmid31847758, year = {2019}, author = {Sum Wu, K and Nowak, J and Breuer, KS}, title = {Scaling of the performance of insect-inspired passive-pitching flapping wings.}, journal = {Journal of the Royal Society, Interface}, volume = {16}, number = {161}, pages = {20190609}, pmid = {31847758}, issn = {1742-5662}, mesh = {Animals ; Biomechanical Phenomena ; Biomimetics/*methods ; *Computer Simulation ; Flight, Animal/*physiology ; Insecta/*physiology ; Models, Biological ; *Robotics ; Wings, Animal/*physiology ; }, abstract = {Flapping flight using passive pitch regulation is a commonly used mode of thrust and lift generation in insects and has been widely emulated in flying vehicles because it allows for simple implementation of the complex kinematics associated with flapping wing systems. Although robotic flight employing passive pitching to regulate angle of attack has been previously demonstrated, there does not exist a comprehensive understanding of the effectiveness of this mode of aerodynamic force generation, nor a method to accurately predict its performance over a range of relevant scales. Here, we present such scaling laws, incorporating aerodynamic, inertial and structural elements of the flapping-wing system, validating the theoretical considerations using a mechanical model which is tested for a linear elastic hinge and near-sinusoidal stroke kinematics over a range of scales, hinge stiffnesses and flapping frequencies. We find that suitably defined dimensionless parameters, including the Reynolds number, Re, the Cauchy number, Ch, and a newly defined 'inertial-elastic' number, IE, can reliably predict the kinematic and aerodynamic performance of the system. Our results also reveal a consistent dependency of pitching kinematics on these dimensionless parameters, providing a connection between lift coefficient and kinematic features such as angle of attack and wing rotation.}, } @article {pmid31835453, year = {2019}, author = {Tan, L and Ali, J and Cheang, UK and Shi, X and Kim, D and Kim, MJ}, title = {µ-PIV Measurements of Flows Generated by Photolithography-Fabricated Achiral Microswimmers.}, journal = {Micromachines}, volume = {10}, number = {12}, pages = {}, pmid = {31835453}, issn = {2072-666X}, abstract = {Robotic micro/nanoswimmers can potentially be used as tools for medical applications, such as drug delivery and noninvasive surgery. Recently, achiral microswimmers have gained significant attention because of their simple structures, which enables high-throughput fabrication and size scalability. Here, microparticle image velocimetry (µ-PIV) was used to study the hydrodynamics of achiral microswimmers near a boundary. The structures of these microswimmers resemble the letter L and were fabricated using photolithography and thin-film deposition. Through µ-PIV measurements, the velocity flow fields of the microswimmers rotating at different frequencies were observed. The results herein yield an understanding of the hydrodynamics of the L-shaped microswimmers, which will be useful in applications such as fluidic manipulation.}, } @article {pmid31824735, year = {2019}, author = {Ford, MP and Lai, HK and Samaee, M and Santhanakrishnan, A}, title = {Hydrodynamics of metachronal paddling: effects of varying Reynolds number and phase lag.}, journal = {Royal Society open science}, volume = {6}, number = {10}, pages = {191387}, pmid = {31824735}, issn = {2054-5703}, abstract = {Negatively buoyant freely swimming crustaceans such as krill must generate downward momentum in order to maintain their position in the water column. These animals use a drag-based propulsion strategy, where pairs of closely spaced swimming limbs are oscillated rhythmically from the tail to head. Each pair is oscillated with a phase delay relative to the neighbouring pair, resulting in a metachronal wave travelling in the direction of animal motion. It remains unclear how oscillations of limbs in the horizontal plane can generate vertical momentum. Using particle image velocimetry measurements on a robotic model, we observed that metachronal paddling with non-zero phase lag created geometries of adjacent paddles that promote the formation of counter-rotating vortices. The interaction of these vortices resulted in generating large-scale angled downward jets. Increasing phase lag resulted in more vertical orientation of the jet, and phase lags in the range used by Antarctic krill produced the most total momentum. Synchronous paddling produced lower total momentum when compared with metachronal paddling. Lowering Reynolds number by an order of magnitude below the range of adult krill (250-1000) showed diminished downward propagation of the jet and lower vertical momentum. Our findings show that metachronal paddling is capable of producing flows that can generate both lift (vertical) and thrust (horizontal) forces needed for fast forward swimming and hovering.}, } @article {pmid31824223, year = {2019}, author = {Wang, X and Christov, IC}, title = {Theory of the flow-induced deformation of shallow compliant microchannels with thick walls.}, journal = {Proceedings. Mathematical, physical, and engineering sciences}, volume = {475}, number = {2231}, pages = {20190513}, pmid = {31824223}, issn = {1364-5021}, abstract = {Long, shallow microchannels embedded in thick, soft materials are widely used in microfluidic devices for lab-on-a-chip applications. However, the bulging effect caused by fluid-structure interactions between the internal viscous flow and the soft walls has not been completely understood. Previous models either contain a fitting parameter or are specialized to channels with plate-like walls. This work is a theoretical study of the steady-state response of a compliant microchannel with a thick wall. Using lubrication theory for low-Reynolds-number flows and the theory for linearly elastic isotropic solids, we obtain perturbative solutions for the flow and deformation. Specifically, only the channel's top wall deformation is considered, and the ratio between its thickness t and width w is assumed to be (t/w)[2]≫1. We show that the deformation at each stream-wise cross section can be considered independently, and that the top wall can be regarded as a simply supported rectangle subject to uniform pressure at its bottom. The stress and displacement fields are found using Fourier series, based on which the channel shape and the hydrodynamic resistance are calculated, yielding a new flow rate-pressure drop relation without fitting parameters. Our results agree favourably with, and thus rationalize, previous experiments.}, } @article {pmid31816973, year = {2019}, author = {Raza, W and Kim, KY}, title = {Asymmetrical Split-and-Recombine Micromixer with Baffles.}, journal = {Micromachines}, volume = {10}, number = {12}, pages = {}, pmid = {31816973}, issn = {2072-666X}, abstract = {The present work proposes a planar micromixer design comprising hybrid mixing modules of split-and-recombine units and curved channels with radial baffles. The mixing performance was evaluated numerically by solving the continuity and momentum equations along with the advection-diffusion equation in a Reynolds number range of 0.1-80. The variance of the concentration of the mixed species was considered to quantify the mixing index. The micromixer showed far better mixing performance over whole Reynolds number range than an earlier split-and-recombine micromixer. The mixer achieved mixing indices greater than 90% at Re ≥ 20 and a mixing index of 99.8% at Re = 80. The response of the mixing quality to the change of three geometrical parameters was also studied. A mixing index over 80% was achieved within 63% of the full length at Re = 20.}, } @article {pmid31808773, year = {2020}, author = {Abay, A and Recktenwald, SM and John, T and Kaestner, L and Wagner, C}, title = {Cross-sectional focusing of red blood cells in a constricted microfluidic channel.}, journal = {Soft matter}, volume = {16}, number = {2}, pages = {534-543}, doi = {10.1039/c9sm01740b}, pmid = {31808773}, issn = {1744-6848}, mesh = {Erythrocytes/*chemistry ; Humans ; Microfluidics/instrumentation ; Rheology ; }, abstract = {Constrictions in blood vessels and microfluidic devices can dramatically change the spatial distribution of passing cells or particles and are commonly used in biomedical cell sorting applications. However, the three-dimensional nature of cell focusing in the channel cross-section remains poorly investigated. Here, we explore the cross-sectional distribution of living and rigid red blood cells passing a constricted microfluidic channel by tracking individual cells in multiple layers across the channel depth and across the channel width. While cells are homogeneously distributed in the channel cross-section pre-contraction, we observe a strong geometry-induced focusing towards the four channel faces post-contraction. The magnitude of this cross-sectional focusing effect increases with increasing Reynolds number for both living and rigid red blood cells. We discuss how this non-uniform cell distribution downstream of the contraction results in an apparent double-peaked velocity profile in particle image velocimetry analysis and show that trapping of red blood cells in the recirculation zones of the abrupt construction depends on cell deformability.}, } @article {pmid31805484, year = {2020}, author = {Shah, Z and Khan, A and Khan, W and Kamran Alam, M and Islam, S and Kumam, P and Thounthong, P}, title = {Micropolar gold blood nanofluid flow and radiative heat transfer between permeable channels.}, journal = {Computer methods and programs in biomedicine}, volume = {186}, number = {}, pages = {105197}, doi = {10.1016/j.cmpb.2019.105197}, pmid = {31805484}, issn = {1872-7565}, mesh = {Gold/*chemistry ; *Hot Temperature ; *Hydrodynamics ; Nanotechnology/*methods ; Permeability ; }, abstract = {This article characterizes flow and heat transmission of blood that carries the micropolar nanofluid of gold in a permeable channel. The thermal radiations are also present in the channel while its walls are either moving or stationary. The base-fluid is considered as blood while micro polar nanofluid is taken as gold. By using similarity transformations along with dimensionless quantities the modeled equations of the problem are transmuted into a system of non-linear ODEs with a set of appropriate boundary conditions. The semi-analytical method, HAM is then applied to determine the solution of a set of resultant equations. The results obtained by HAM have also compared with numerical solutions. The influence of non-dimensional parameters like fractional parameter suction/injection β, Reynolds Number Re, Darcys Number Da, micropolar parameter K, Prandtl number Pr and Radiation parameter Rd etc., which provides physical interpretations of temperature, microrotation n and velocity fields are discussed in detail with the help of graphical representations. Nusselt number is calculated and presented through table. This study determined that the temperature of micropolar nanofluid augmented along with augmentation in the volume fraction. Radiation Rd augmented the heat transfer rate at the upper wall and reduce it at the lower wall. The suction/injection parameter 'β' reduces the heat transfer rate in case of β < 0 at the upper wall, where it is augmented at lower wall.}, } @article {pmid31805457, year = {2020}, author = {Pandey, R and Kumar, M and Majdoubi, J and Rahimi-Gorji, M and Srivastav, VK}, title = {A review study on blood in human coronary artery: Numerical approach.}, journal = {Computer methods and programs in biomedicine}, volume = {187}, number = {}, pages = {105243}, doi = {10.1016/j.cmpb.2019.105243}, pmid = {31805457}, issn = {1872-7565}, mesh = {Aneurysm/diagnostic imaging/physiopathology ; Biomedical Engineering ; Coronary Artery Bypass ; Coronary Artery Disease/diagnostic imaging/physiopathology ; Coronary Vessels/*anatomy & histology/diagnostic imaging/*physiology ; Hemodynamics ; Humans ; Hydrodynamics ; Image Processing, Computer-Assisted ; Imaging, Three-Dimensional ; Models, Cardiovascular ; Tomography, Optical Coherence ; Viscosity ; }, abstract = {Computational fluid dynamics (CFD) study of blood flow in human coronary artery is one of the emerging fields of Biomed- ical engineering. In present review paper, Finite Volume Method with governing equations and boundary conditions are briefly discussed for different coronary models. Many researchers have come up with astonishing results related to the various factors (blood viscosity, rate of blood flow, shear stress on the arterial wall, Reynolds number, etc.) affecting the hemodynamic of blood in the right/left coronary artery. The aim of this paper is to present an overview of all those work done by the researchers to justify their work related to factors which hampers proper functioning of heart and lead to Coronary Artery Disease (CAD). Governing equations like Navier-stokes equations, continuity equations etc. are widely used and are solved using CFD solver to get a clearer view of coronary artery blockage. Different boundary conditions and blood properties published in the last ten years are summarized in the tabulated form. This table will help new researchers to work on this area.}, } @article {pmid31801127, year = {2020}, author = {Pöhnl, R and Popescu, MN and Uspal, WE}, title = {Axisymmetric spheroidal squirmers and self-diffusiophoretic particles.}, journal = {Journal of physics. Condensed matter : an Institute of Physics journal}, volume = {32}, number = {16}, pages = {164001}, doi = {10.1088/1361-648X/ab5edd}, pmid = {31801127}, issn = {1361-648X}, abstract = {We study, by means of an exact analytical solution, the motion of a spheroidal, axisymmetric squirmer in an unbounded fluid, as well as the low Reynolds number hydrodynamic flow associated to it. In contrast to the case of a spherical squirmer-for which, e.g. the velocity of the squirmer and the magnitude of the stresslet associated with the flow induced by the squirmer are respectively determined by the amplitudes of the first two slip ('squirming') modes-for the spheroidal squirmer each squirming mode either contributes to the velocity, or contributes to the stresslet. The results are straightforwardly extended to the self-phoresis of axisymmetric, spheroidal, chemically active particles in the case when the phoretic slip approximation holds.}, } @article {pmid31797965, year = {2019}, author = {Rajappan, A and McKinley, GH}, title = {Epidermal biopolysaccharides from plant seeds enable biodegradable turbulent drag reduction.}, journal = {Scientific reports}, volume = {9}, number = {1}, pages = {18263}, pmid = {31797965}, issn = {2045-2322}, mesh = {Engineering ; Flax/*chemistry ; Friction ; Lubrication ; Plant Mucilage/*chemistry ; Polyethylene Glycols/*chemistry ; *Rheology ; Seeds/*chemistry ; Viscosity ; Water ; }, abstract = {The high cost of synthetic polymers has been a key impediment limiting the widespread adoption of polymer drag reduction techniques in large-scale engineering applications, such as marine drag reduction. To address consumable cost constraints, we investigate the use of high molar mass biopolysaccharides, present in the mucilaginous epidermis of plant seeds, as inexpensive drag reducers in large Reynolds number turbulent flows. Specifically, we study the aqueous mucilage extracted from flax seeds (Linum usitatissimum) and compare its drag reduction efficacy to that of poly(ethylene oxide) or PEO, a common synthetic polymer widely used as a drag reducing agent in aqueous flows. Macromolecular and rheological characterisation confirm the presence of high molar mass (≥2 MDa) polysaccharides in the extracted mucilage, with an acidic fraction comprising negatively charged chains. Frictional drag measurements, performed inside a bespoke Taylor-Couette apparatus, show that the as-extracted mucilage has comparable drag reduction performance under turbulent flow conditions as aqueous PEO solutions, while concurrently offering advantages in terms of raw material cost, availability, and bio-compatibility. Our results indicate that plant-sourced mucilage can potentially serve as a cost-effective and eco-friendly substitute for synthetic drag reducing polymers in large scale turbulent flow applications.}, } @article {pmid31786449, year = {2020}, author = {Ibrahim, M and Ijaz Khan, M}, title = {Mathematical modeling and analysis of SWCNT-Water and MWCNT-Water flow over a stretchable sheet.}, journal = {Computer methods and programs in biomedicine}, volume = {187}, number = {}, pages = {105222}, doi = {10.1016/j.cmpb.2019.105222}, pmid = {31786449}, issn = {1872-7565}, mesh = {Algorithms ; Biomechanical Phenomena ; Carbon/*chemistry ; Computer Simulation ; Convection ; Hot Temperature ; Hydrodynamics ; Models, Theoretical ; Nanotechnology/*methods ; Nanotubes, Carbon/*chemistry ; Porosity ; Temperature ; Viscosity ; Water/*chemistry ; }, abstract = {In this article we focused on the mixed convection flow of SWCNT-Water and MWCNT-Water over a stretchable permeable sheet. The nanofluid occupied porous medium. Darcy's law is used to characterize porous medium. The impact of viscous dissipation is considered. Transformation procedure is adopted to transform the governing PDE's system into dimensionless form. In order to solve the dimensionless PDE's system we used numerical method known as Finite difference method. Effects of flow variables i.e porosity parameter, suction parameter, Grashof number and Reynolds number on velocity, skin friction, temperature and Nusselt number are described graphically. The obtained results shows that velocity is dominant in SWCNT-Water over MWCNT-Water. Temperature is dominant in MWCNT-Water over SWCNT-Water.}, } @article {pmid31785535, year = {2020}, author = {Turkyilmazoglu, M}, title = {Single phase nanofluids in fluid mechanics and their hydrodynamic linear stability analysis.}, journal = {Computer methods and programs in biomedicine}, volume = {187}, number = {}, pages = {105171}, doi = {10.1016/j.cmpb.2019.105171}, pmid = {31785535}, issn = {1872-7565}, mesh = {Algorithms ; Colloids/chemistry ; Hot Temperature ; *Hydrodynamics ; Linear Models ; *Nanoparticles ; Nanotechnology/*methods ; *Rheology ; Software ; Viscosity ; }, abstract = {BACKGROUND AND OBJECTIVE: The hydrodynamic stability of nanofluids of one phase is investigated in this paper based on linear stability theory. The overall thrust here is that the linear stability features of nanofluids can be estimated from their corresponding working fluid, at least in special circumstances.

METHODS: The approach uses the adjusting parameter to make assertions about stability. This is possible by certain correlations between the resulting eigenvalues.

RESULTS: It is shown that as the nanoparticles are added, the mean flow of nanofluids is slightly modified and the resulting eigen space of nano disturbances is built on the corresponding pure flow eigen space of perturbations. Several fluid dynamics problems are revisited to verify the usefulness of the obtained correlations.

CONCLUSION: The presented approach in this work serves us to understand the stabilizing/destabilizing effects of nanofluids as compared to the standard base fluids in terms of stability of viscous/inviscid and temporal/spatial senses. To illustrate, the critical Reynolds number in a traditional boundary layer flow is shown to be pushed to higher values with the dispersed nanoparticles in a working fluid, clearly implying the delay in transition from laminar to turbulent state.}, } @article {pmid31784839, year = {2019}, author = {Chen, J and He, Y and Wang, J and Huang, M and Guo, C}, title = {Dynamics of nitrogen transformation and bacterial community with different aeration depths in malodorous river.}, journal = {World journal of microbiology & biotechnology}, volume = {35}, number = {12}, pages = {196}, pmid = {31784839}, issn = {1573-0972}, mesh = {Bacteria/classification/genetics/*metabolism ; China ; Geologic Sediments/microbiology ; Microbiota/*physiology ; Nitrogen/*metabolism ; Oxygen/metabolism ; Phylogeny ; RNA, Ribosomal, 16S ; Rivers/*chemistry/*microbiology ; Sulfur/metabolism ; }, abstract = {In this research, the dynamics of nitrogen transformation and bacterial community in malodorous river were investigated with different aeration depths. Computational flow dynamics (CFD) and Reynolds number (Re) were specially used to characterize the hydrodynamics condition under different aeration depths. The results indicated that aeration depth had vital impact on nitrogen transformation and bacterial community structure. It was found that a range of aeration depth (0.20-0.45 m above sediment-water interface) facilitated the removal of NH4[+]-N and TN with Re ranging between 6211 and 8930. Proteobacteria took over Firmicutes to become the predominant phylum (36-78%) under aeration, and the main subdivisions of γ-, β- and δ-Proteobacteria also varied greatly with different aeration depths. Interestingly, there was a marked shift of the inferentially identified dominant functional role within Proteobacteria from organic-matter degradation to nitrogen metabolism and then to sulfur metabolism as well as the coupling of nitrogen and sulfur with the increase of disturbance. The redundancy analysis (RDA) further confirmed the importance of aeration disturbance in shaping bacterial community. These findings help to gain improved understanding of endogenous N-behavior and aquatic microbial ecology, and underline the need for integrating the hydrodynamics factors with microbial community.}, } @article {pmid31779425, year = {2019}, author = {Singh, H and Bonnesoeur, A and Besnard, H and Houssin, C and Prigent, A and Crumeyrolle, O and Mutabazi, I}, title = {A large thermal turbulent Taylor-Couette (THETACO) facility for investigation of turbulence induced by simultaneous action of rotation and radial temperature gradient.}, journal = {The Review of scientific instruments}, volume = {90}, number = {11}, pages = {115112}, doi = {10.1063/1.5119811}, pmid = {31779425}, issn = {1089-7623}, abstract = {A thermal turbulent Taylor-Couette facility has been designed to investigate turbulent flows generated by differential rotation and radial temperature gradient. It consists of a cylindrical annulus with a rotating inner cylinder and a fixed outer cylinder. The electric heating system is installed inside the inner cylinder, and the annulus is immersed in a large cylindrical container filled with cooling fluid. Temperature regulators independently control the temperature of the inner surface of the inner cylinder and that of the cooling fluid. The facility allows us to reach values of the Reynolds number (Re ∼ 5 × 10[5]) and of the Rayleigh number (Ra ∼ 3 × 10[6]) for water as the working fluid. The facility provides torque measurements, a full optical access at the side and from the bottom for velocity measurements using particle image velocimetry (2D, stereoscopic, and tomographic). Temperature measurements in the flow can be performed by thermochromic liquid crystals or laser induced fluorescence.}, } @article {pmid31777765, year = {2019}, author = {Zhang, X and Lam, WA and Graham, MD}, title = {Dynamics of deformable straight and curved prolate capsules in simple shear flow.}, journal = {Physical review fluids}, volume = {4}, number = {4}, pages = {}, pmid = {31777765}, issn = {2469-990X}, support = {R21 MD011590/MD/NIMHD NIH HHS/United States ; }, abstract = {This work investigates the motion of neutrally-buoyant, slightly deformable straight and curved prolate fluid-filled capsules in unbounded simple shear flow at zero Reynolds number using direct simulations. The curved capsules serve as a model for the typical crescent-shaped sickle red blood cells in sickle cell disease (SCD). The effects of deformability and curvature on the dynamics are revealed. We show that with low deformability, straight prolate spheroidal capsules exhibit tumbling in the shear plane as their unique asymptotically stable orbit. This result contrasts with that for rigid spheroids, where infinitely many neutrally stable Jeffery orbits exist. The dynamics of curved prolate capsules are more complicated due to a combined effect of deformability and curvature. At short times, depending on the initial orientation, slightly deformable curved prolate capsules exhibit either a Jeffery-like motion such as tumbling or kayaking, or a non-Jeffery-like behavior in which the director (end-to-end vector) of the capsule crosses the shear-gradient plane back and forth. At long times, however, a Jeffery-like quasiperiodic orbit is taken regardless of the initial orientation. We further show that the average of the long-time trajectory can be well approximated using the analytical solution for Jeffery orbits with an effective orbit constant C eff and aspect ratio ℓ eff. These parameters are useful for characterizing the dynamics of curved capsules as a function of given deformability and curvature. As the capsule becomes more deformable or curved, C eff decreases, indicating a shift of the orbit towards log-rolling motion, while ℓ eff increases weakly as the degree of curvature increases but shows negligible dependency on deformability. These features are not changed substantially as the viscosity ratio between the inner and outer fluids is changed from 1 to 5. As cell deformability, cell shape, and cell-cell interactions are all pathologically altered in blood disorders such as SCD, these results will have clear implications on improving our understanding of the pathophysiology of hematologic disease.}, } @article {pmid31771023, year = {2019}, author = {Shan, X}, title = {Central-moment-based Galilean-invariant multiple-relaxation-time collision model.}, journal = {Physical review. E}, volume = {100}, number = {4-1}, pages = {043308}, doi = {10.1103/PhysRevE.100.043308}, pmid = {31771023}, issn = {2470-0053}, abstract = {Aiming at systematically correcting the non-Galilean-invariant thermal diffusivity in the previous multiple-relaxation-time Boltzmann equation collision model [Shan and Chen, Int. J. Mod. Phys. C 18, 635 (2007)IJMPEO0129-183110.1142/S0129183107010887], we show that by separately relaxing the central moments of the distribution function, Chapman-Enskog calculation leads to the correct hydrodynamic equations with mutually independent and Galilean invariant viscosity and thermal diffusivity, provided the velocity-space discretization preserves moments up to the fourth order. By transforming the central moments back to the absolute reference frame and evaluating using fixed discrete velocities, the efficient and accurate streaming-collision time-stepping algorithm is preserved. The lattice Boltzmann model is found to have excellent numerical stability in high-Reynolds-number simulations.}, } @article {pmid31771016, year = {2019}, author = {Berera, A and Clark, D}, title = {Information production in homogeneous isotropic turbulence.}, journal = {Physical review. E}, volume = {100}, number = {4-1}, pages = {041101}, doi = {10.1103/PhysRevE.100.041101}, pmid = {31771016}, issn = {2470-0053}, abstract = {We study the Reynolds number scaling of the Kolmogorov-Sinai entropy and attractor dimension for three-dimensional homogeneous isotropic turbulence through the use of direct numerical simulation. To do so, we obtain Lyapunov spectra for a range of different Reynolds numbers by following the divergence of a large number of orthogonal fluid trajectories. We find that the attractor dimension grows with the Reynolds number as Re^{2.35} with this exponent being larger than predicted by either dimensional arguments or intermittency models. The distribution of Lyapunov exponents is found to be finite around λ≈0 contrary to a possible divergence suggested by Ruelle. The relevance of the Kolmogorov-Sinai entropy and Lyapunov spectra in comparing complex physical systems is discussed.}, } @article {pmid31770976, year = {2019}, author = {Chitsaz, M and Fathali, M}, title = {Impact of an initial random magnetic field on the evolution of two-dimensional shearless mixing layers.}, journal = {Physical review. E}, volume = {100}, number = {4-1}, pages = {043106}, doi = {10.1103/PhysRevE.100.043106}, pmid = {31770976}, issn = {2470-0053}, abstract = {The impact of an initial random magnetic field on the temporal evolution of a two-dimensional incompressible turbulent shearless mixing layer is investigated using direct numerical simulation. Different intensities of the initial random magnetic field are imposed with uniform probability distribution on an identical flow field. The initial flow field condition is the turbulent shearless mixing layer with different kinetic energy ratio (E_{H} /E_{L} =6.7) and identical integral length scale. Simulations are carried out in a moderate magnetic Reynolds number, which causes a two-way interaction between the velocity and magnetic fields. In order to analyze the effect of the initial random magnetic field on the mixing characteristics, the intermittency inside the mixing layer and the mixing evolution parameters are investigated. It is found that with small initial magnetic field intensity, the intermittency in both large and small scales are larger than those values in hydrodynamic flow. However, increasing the intensity of the initial magnetic field reduces the intermittency in the mixing region to lower values compared to the hydrodynamic flow. The mixing layer growth rate and the mixing efficiency both show reduction by increasing the initial magnetic field intensity, which is attributed to the reduction of the averaged Reynolds number of both homogenous isotropic turbulent regions due to the suppressing effect of the Lorentz force on the velocity fields of these regions.}, } @article {pmid31759716, year = {2020}, author = {Ćmiel, AM and Strużyński, A and Wyrębek, M and Lipińska, AM and Zając, K and Zając, T}, title = {Response of freshwater mussel recruitment to hydrological changes in a eutrophic floodplain lake.}, journal = {The Science of the total environment}, volume = {703}, number = {}, pages = {135467}, doi = {10.1016/j.scitotenv.2019.135467}, pmid = {31759716}, issn = {1879-1026}, mesh = {Animals ; Ecosystem ; Endangered Species ; Eutrophication ; Hydrology ; *Lakes ; *Unionidae ; }, abstract = {Although eutrophication of freshwaters is a natural process, the human impact often leads to inland waters becoming overloaded with nutrients, impoverishing many valuable and vanishing habitats, such as floodplain lakes. These changes need to be reversed if the occurrence of endangered aquatic species is to be restored. In this paper we analyse the impact of a change in the water regime of a naturally eutrophic floodplain lake, which harbours a large diversity of Unionidae (large freshwater mussels), a globally threatened taxonomic group that provides important ecosystem functions and services. We found that a slight increase in the discharge from this waterbody, following the construction of an additional outflow pipe, positively influenced recruitment in three of the five mussel species inhabiting the lake. We also found that, after the construction of this additional outflow, the niches of juveniles of Anodonta cygnea and Unio spp. changed, revealing differences in their hydrological requirements. Our results suggest that, as in lotic habitats, complex hydraulic parameters are highly significant to unionid mussels in lentic conditions.}, } @article {pmid31744080, year = {2019}, author = {Taheri, RA and Goodarzi, V and Allahverdi, A}, title = {Mixing Performance of a Cost-effective Split-and-Recombine 3D Micromixer Fabricated by Xurographic Method.}, journal = {Micromachines}, volume = {10}, number = {11}, pages = {}, pmid = {31744080}, issn = {2072-666X}, abstract = {This paper presents experimental and numerical investigations of a novel passive micromixer based on the lamination of fluid layers. Lamination-based mixers benefit from increasing the contact surface between two fluid phases by enhancing molecular diffusion to achieve a faster mixing. Novel three-dimensional split and recombine (SAR) structures are proposed to generate fluid laminations. Numerical simulations were conducted to model the mixer performance. Furthermore, experiments were conducted using dyes to observe fluid laminations and evaluate the proposed mixer's characteristics. Mixing quality was experimentally obtained by means of image-based mixing index (MI) measurement. The multi-layer device was fabricated utilizing the Xurography method, which is a simple and low-cost method to fabricate 3D microfluidic devices. Mixing indexes of 96% and 90% were obtained at Reynolds numbers of 0.1 and 1, respectively. Moreover, the device had an MI value of 67% at a Reynolds number of 10 (flow rate of 116 µL/min for each inlet). The proposed micromixer, with its novel design and fabrication method, is expected to benefit a wide range of lab-on-a-chip applications, due to its high efficiency, low cost, high throughput and ease of fabrication.}, } @article {pmid31737769, year = {2019}, author = {Shaikh, MM and Massan, SU and Wagan, AI}, title = {A sixteen decimal places' accurate Darcy friction factor database using non-linear Colebrook's equation with a million nodes: A way forward to the soft computing techniques.}, journal = {Data in brief}, volume = {27}, number = {}, pages = {104733}, doi = {10.1016/j.dib.2019.104733}, pmid = {31737769}, issn = {2352-3409}, abstract = {The Colebrook's equation is considered as an empirical model to accurately compute the Darcy friction factor in pipes under fully-developed turbulent flow. Due to non-linearity and implicitness of the Colebrook's equation, one needs to use numerical methods to acquire reasonably good approximation to the true friction factor values. However, such idea is not preferred by practitioners as it demands use of computers - also more computational time and effort. To overcome this, explicit equations that can describe Darcy friction factor directly in terms of the Reynolds number and relative roughness are essential. Using Fixed point iteration method in the MATLAB software, we have developed a 16 decimal places' accurate friction factor database for the Darcy friction factor for a 1000 by 1000 mesh of Reynolds number and relative roughness values. The accurate dataset described in this work will serve to be basis for the construction of new and more reliable explicit equations using regression modeling, artificial intelligence techniques and other soft computing methods.}, } @article {pmid31736648, year = {2019}, author = {Papageorgiou, DT and Tanveer, S}, title = {Analysis and computations of a non-local thin-film model for two-fluid shear driven flows.}, journal = {Proceedings. Mathematical, physical, and engineering sciences}, volume = {475}, number = {2230}, pages = {20190367}, pmid = {31736648}, issn = {1364-5021}, abstract = {This paper is concerned with analysis and computations of a non-local thin-film model developed in Kalogirou & Papageorgiou (J. Fluid Mech. 802, 5-36, 2016) for a perturbed two-layer Couette flow when the thickness of the more viscous fluid layer next to the stationary wall is small compared to the thickness of the less viscous fluid. Travelling wave solutions and their stability are determined numerically, and secondary bifurcation points are identified in the process. We also determine regions in parameter space where bistability is observed with two branches being linearly stable at the same time. The travelling wave solutions are mathematically justified through a quasi-solution analysis in a neighbourhood of an empirically constructed approximate solution. This relies in part on precise asymptotics of integrals of Airy functions for large wave numbers. The primary bifurcation about the trivial state is shown rigorously to be supercritical, and the dependence of bifurcation points, as a function of Reynolds number R and the primary wavelength 2πν [-1/2] of the disturbance, is determined analytically.}, } @article {pmid31734470, year = {2020}, author = {Farooq, S and Hayat, T and Khan, MI and Alsaedi, A}, title = {Entropy generation minimization (EGM) in magneto peristalsis with variable properties.}, journal = {Computer methods and programs in biomedicine}, volume = {186}, number = {}, pages = {105045}, doi = {10.1016/j.cmpb.2019.105045}, pmid = {31734470}, issn = {1872-7565}, mesh = {*Entropy ; *Magnetics ; Thermal Conductivity ; *Viscosity ; }, abstract = {OBJECTIVE AND BACKGROUND: This article featuring the peristaltic transport of viscous material with variable properties (i.e. temperature dependent viscosity and thermal conductivity) through curved configuration. Fluid saturating through porous channel walls of uniform space. Entropy generation consideration here is to analyze irreversibility aspects. Channel boundaries retain the velocity and thermal slip conditions.

METHOD: Wave frame of reference is attained with the utilization of long wavelength and small Reynolds number approach. Solution of the simplified coupled system of dimensionless constraints is obtained numerically. Detailed analysis of important quantities of interest has been presented in discussion portion.

RESULTS: Entropy generation variation near center is very small whereas in the vicinity of the channel wall is larger. Bejan number has reverse variation as observed for entropy generation.

CONCLUSION: Variable characteristics of viscosity has opposite impact on velocity and temperature is observed. It is also noticed small irreversibility effects are obtained for higher varying viscosity and thermal conductivity near the vicinity of the channel walls.}, } @article {pmid31719582, year = {2019}, author = {Ying, Y and Lin, Y}, title = {Inertial Focusing and Separation of Particles in Similar Curved Channels.}, journal = {Scientific reports}, volume = {9}, number = {1}, pages = {16575}, pmid = {31719582}, issn = {2045-2322}, abstract = {Inertial particle focusing in curved channels has enormous potential for lab-on-a-chip applications. This paper compares a zigzag channel, which has not been used previously for inertial focusing studies, with a serpentine channel and a square wave channel to explore their differences in terms of focusing performance and separation possibilities. The particle trajectories and fluid fields in the curved channels are studied by a numerical simulation. The effects of different conditions (structure, Reynolds number, and particle size) on the competition between forces and the focusing performance are studied. The results indicate that the zigzag channel has the best focusing effect at a high Reynolds number and that the serpentine channel is second in terms of performance. Regarding the particle separation potential, the zigzag channel has a good performance in separating 5 μm and 10 μm particles at ReC = 62.5. In addition, the pressure drop of the channel is also considered to evaluate the channel performance, which has not been taken into account in the literature on inertial microfluidics. This result is expected to be instructive for the selection and optimization of inertial microchannel structures.}, } @article {pmid31718189, year = {2019}, author = {Zhang, Z and Zhang, P}, title = {Numerical Interpretation to the Roles of Liquid Viscosity in Droplet Spreading at Small Weber Numbers.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {35}, number = {49}, pages = {16164-16171}, doi = {10.1021/acs.langmuir.9b02736}, pmid = {31718189}, issn = {1520-5827}, abstract = {Droplet impacting a free-slip plane at small Weber numbers (We < 30) was numerically investigated by a front tracking method, with particular emphasis on clarifying the roles of the liquid viscosity and the "left-over" internal kinetic energy in droplet spreading. The most interesting discovery is that there exists a certain range of We in which the maximum diameter rate, D̃m, shows a nonmonotonic variation with the Reynolds number, Re. This non-monotonic variation is owing to the dual role of liquid viscosity in influencing droplet spreading. Specifically, when the initial surface energy is comparable to the initial kinetic energy (the corresponding We is around 10-30), the high strain rates of the droplet internal flow dominate its viscous dissipation at a relatively large Re, while the liquid viscosity dominates the viscous dissipation at a relatively small Re. Furthermore, to unravel the influence of droplet attachment and detachment on droplet spreading, we considered two limiting situations such as full attachment (with no gas film throughout droplet spreading) and full detachment (with a gas film throughout droplet spreading). The results show that the droplet with a gas film tends to generate a stronger vortical motion in its rim, results in a larger left-over kinetic energy, and hence causes a smaller spreading.}, } @article {pmid31718021, year = {2019}, author = {Kottmeier, J and Wullenweber, M and Blahout, S and Hussong, J and Kampen, I and Kwade, A and Dietzel, A}, title = {Accelerated Particle Separation in a DLD Device at Re > 1 Investigated by Means of µPIV.}, journal = {Micromachines}, volume = {10}, number = {11}, pages = {}, pmid = {31718021}, issn = {2072-666X}, abstract = {A pressure resistant and optically accessible deterministic lateral displacement (DLD) device was designed and microfabricated from silicon and glass for high-throughput fractionation of particles between 3.0 and 7.0 µm comprising array segments of varying tilt angles with a post size of 5 µm. The design was supported by computational fluid dynamic (CFD) simulations using OpenFOAM software. Simulations indicated a change in the critical particle diameter for fractionation at higher Reynolds numbers. This was experimentally confirmed by microparticle image velocimetry (µPIV) in the DLD device with tracer particles of 0.86 µm. At Reynolds numbers above 8 an asymmetric flow field pattern between posts could be observed. Furthermore, the new DLD device allowed successful fractionation of 2 µm and 5 µm fluorescent polystyrene particles at Re = 0.5-25.}, } @article {pmid31715344, year = {2019}, author = {Di, D and Qu, X and Liu, C and Fang, L and Quan, P}, title = {Continuous production of celecoxib nanoparticles using a three-dimensional-coaxial-flow microfluidic platform.}, journal = {International journal of pharmaceutics}, volume = {572}, number = {}, pages = {118831}, doi = {10.1016/j.ijpharm.2019.118831}, pmid = {31715344}, issn = {1873-3476}, mesh = {Animals ; Biological Availability ; Celecoxib/*administration & dosage/chemistry/pharmacokinetics ; Glass ; High-Throughput Screening Assays ; Male ; *Microfluidic Analytical Techniques ; *Nanoparticles ; Particle Size ; Rats ; Rats, Wistar ; Solubility ; Water/chemistry ; }, abstract = {Increasing the dissolution rate of water insoluble drugs by decreasing the particle size of the drugs into nano-size is a well-known strategy. However, continuous production of drug nanoparticles with uniform particle size is critical for clinical application of the strategy. Here we report a simple microfluidic mixing method that can achieve continuous production of celecoxib nanoparticles with uniform particle size and high dissolution rate. A three-dimensional (3D) coaxial-flow microfluidic device was fabricated by assembling two coaxial aligned borosilicate glass capillaries on a glass slide, and a tapered glass capillary was inserted into another bigger cylindrical one with coaxial alignment. Celecoxib nanoparticles were prepared by the microfluidic device under the turbulent jet regime. The 3D-coaxial-flow pattern and high Reynolds number ensured the extremely short mixing time, consequently, resulted in the high throughput production of drug nanoparticles with uniform particle size. The obtained nanoparticles were spherical in shape, and showed superior dissolution rate compared with the coarse powder both in sink and non-sink conditions. The bioavailability of the water insoluble drug was also significantly improved by the reduction of particle size into nano-size.}, } @article {pmid31700559, year = {2019}, author = {Herrmann, N and Neubauer, P and Birkholz, M}, title = {Spiral microfluidic devices for cell separation and sorting in bioprocesses.}, journal = {Biomicrofluidics}, volume = {13}, number = {6}, pages = {061501}, pmid = {31700559}, issn = {1932-1058}, abstract = {Inertial microfluidic systems have been arousing interest in medical applications due to their simple and cost-efficient use. However, comparably small sample volumes in the microliter and milliliter ranges have so far prevented efficient applications in continuous bioprocesses. Nevertheless, recent studies suggest that these systems are well suited for cell separation in bioprocesses because of their facile adaptability to various reactor sizes and cell types. This review will discuss potential applications of inertial microfluidic cell separation systems in downstream bioprocesses and depict recent advances in inertial microfluidics for bioprocess intensification. This review thereby focusses on spiral microchannels that separate particles at a moderate Reynolds number in a laminar flow (Re < 2300) according to their size by applying lateral hydrodynamic forces. Spiral microchannels have already been shown to be capable of replacing microfilters, extracting dead cells and debris in perfusion processes, and removing contaminant microalgae species. Recent advances in parallelization made it possible to process media on a liter-scale, which might pave the way toward industrial applications.}, } @article {pmid31674812, year = {2019}, author = {Sharzehee, M and Chang, Y and Song, JP and Han, HC}, title = {Hemodynamic effects of myocardial bridging in patients with hypertrophic cardiomyopathy.}, journal = {American journal of physiology. Heart and circulatory physiology}, volume = {317}, number = {6}, pages = {H1282-H1291}, doi = {10.1152/ajpheart.00466.2019}, pmid = {31674812}, issn = {1522-1539}, mesh = {Adolescent ; Adult ; Aged ; Cardiomyopathy, Hypertrophic/complications/pathology/*physiopathology ; Coronary Circulation ; Female ; *Hemodynamics ; Humans ; Male ; Middle Aged ; *Models, Cardiovascular ; Myocardial Bridging/complications/pathology/*physiopathology ; *Patient-Specific Modeling ; }, abstract = {Myocardial bridging (MB) is linked to angina and myocardial ischemia and may lead to sudden cardiac death in patients with hypertrophic cardiomyopathy (HCM). However, it remains unclear how MB affect the coronary blood flow in HCM patients. The aim of this study was to assess the effects of MB on coronary hemodynamics in HCM patients. Fifteen patients with MB (7 HCM and 8 non-HCM controls) in their left anterior descending (LAD) coronary artery were chosen. Transient computational fluid dynamics (CFD) simulations were conducted in anatomically realistic models of diseased (with MB) and virtually healthy (without MB) LAD from these patients, reconstructed from biplane angiograms. Our CFD simulation results demonstrated that dynamic compression of MB led to diastolic flow disturbances and could significantly reduce the coronary flow in HCM patients as compared with non-HCM group (P < 0.01). The pressure drop coefficient was remarkably higher (P < 0.05) in HCM patients. The flow rate change is strongly correlated with both upstream Reynolds number and MB compression ratio, while the MB length has less impact on coronary flow. The hemodynamic results and clinical outcomes revealed that HCM patients with an MB compression ratio higher than 65% required a surgical intervention. In conclusion, the transient MB compression can significantly alter the diastolic flow pattern and wall shear stress distribution in HCM patients. HCM patients with severe MB may need a surgical intervention.NEW & NOTEWORTHY In this study, the hemodynamic significance of myocardial bridging (MB) in patients with hypertrophic cardiomyopathy (HCM) was investigated to provide valuable information for surgical decision-making. Our results illustrated that the transient MB compression led to complex flow patterns, which can significantly alter the diastolic flow and wall shear stress distribution. The hemodynamic results and clinical outcomes demonstrated that patients with HCM and an MB compression ratio higher than 65% required a surgical intervention.}, } @article {pmid31671753, year = {2019}, author = {Shanko, ES and van de Burgt, Y and Anderson, PD and den Toonder, JMJ}, title = {Microfluidic Magnetic Mixing at Low Reynolds Numbers and in Stagnant Fluids.}, journal = {Micromachines}, volume = {10}, number = {11}, pages = {}, pmid = {31671753}, issn = {2072-666X}, abstract = {Microfluidic mixing becomes a necessity when thorough sample homogenization is required in small volumes of fluid, such as in lab-on-a-chip devices. For example, efficient mixing is extraordinarily challenging in capillary-filling microfluidic devices and in microchambers with stagnant fluids. To address this issue, specifically designed geometrical features can enhance the effect of diffusion and provide efficient mixing by inducing chaotic fluid flow. This scheme is known as "passive" mixing. In addition, when rapid and global mixing is essential, "active" mixing can be applied by exploiting an external source. In particular, magnetic mixing (where a magnetic field acts to stimulate mixing) shows great potential for high mixing efficiency. This method generally involves magnetic beads and external (or integrated) magnets for the creation of chaotic motion in the device. However, there is still plenty of room for exploiting the potential of magnetic beads for mixing applications. Therefore, this review article focuses on the advantages of magnetic bead mixing along with recommendations on improving mixing in low Reynolds number flows (Re ≤ 1) and in stagnant fluids.}, } @article {pmid31671339, year = {2020}, author = {Ijaz Khan, M and Ali, A and Hayat, T and Alsaedi, A}, title = {Entropy optimized dissipative CNTs based flow with probable error and statistical declaration.}, journal = {Computer methods and programs in biomedicine}, volume = {185}, number = {}, pages = {105137}, doi = {10.1016/j.cmpb.2019.105137}, pmid = {31671339}, issn = {1872-7565}, mesh = {*Entropy ; Nanotubes, Carbon/*chemistry ; Probability ; Thermodynamics ; }, abstract = {BACKGROUND: CNTs are categorized subject to their structures i.e., SWCNTs (single wall nanotubes), DWCNTs (double wall nanotubes) and MWCNTs (multi-wall nanotubes). The various structures have distinct characteristics that make the nanotubes suitable for various physical applications. It is due their unique electrical, mechanical and thermal attributes CNTs present thrilling opportunities for mechanical engineering, industrial, scientific research and commercial applications. There is fruitful potential for carbon nanotubes in the composites business and industry. Today, CNTs find utilization in frequent various products, and analyst continue to explore new applications. Currently applications comprise wind turbines, bicycle components, scanning probe microscopes, flat panel displays, marine paints, sensing devices, electronics, batteries with longer lifetime and electrical circuitry etc. Such applications in mind, entropy optimized dissipative CNTs based flow of nanomaterial by a stretched surface. Flow is caused due to stretching phenomenon and studied in 3D coordinates. Both types of CNTs are studied i.e., SWCNTs and MWCNTs. CNTs are considered for nanoparticles and water for continuous phase fluid. Special consideration is given to the analysis of statistical declaration and probable error for skin friction and Nusselt number. Furthermore, entropy rate is calculated. Entropy rate is discussed in the presence of four main irreversibilities i.e., heat transfer, Joule heating, porosity and dissipation.

METHOD: Homotopy technique is utilized to develop the convergence series solutions.

RESULTS: Impacts of sundry variables subject to both SWCNTs (single) and MWCNTs (multi) are graphically discussed. Statistical analysis and probable error for surface drag force and Nusselt number are numerically calculated subject to various flow variables. Numerical results for such engineering quantities are displayed through tables. In addition, comparative analysis for SWCNTs and MWCNTs are presented for the velocity, concentration and thermal fields.

CONCLUSIONS: Results for entropy rate is calculated in the presence of various sundry variable through implementation of second law of thermodynamics. It is examined from the results that velocity decreases for both CNTs via higher magnetic, inertia coefficient and porosity parameters. Secondary velocity i.e., velocity in g-direction boosts up versus rotation parameter while it declines for larger slip parameter for both CNTs. thermal field intensifies for both CNTs via larger heat generation/absorption parameter. Concentration which shows the mass transfer of species increases subject to higher homogeneous parameter and Schmidt number in case of both CNTs. Entropy rate in more for larger magnetic, Reynolds number and slip parameter. Bejan number boosts up for higher Reynold number and slip parameter while it declines for magnetic parameter.}, } @article {pmid31657131, year = {2020}, author = {Dincau, B and Dressaire, E and Sauret, A}, title = {Pulsatile Flow in Microfluidic Systems.}, journal = {Small (Weinheim an der Bergstrasse, Germany)}, volume = {16}, number = {9}, pages = {e1904032}, doi = {10.1002/smll.201904032}, pmid = {31657131}, issn = {1613-6829}, mesh = {Cell Culture Techniques ; Hydrodynamics ; *Microfluidics/trends ; *Pulsatile Flow ; }, abstract = {This review describes the current knowledge and applications of pulsatile flow in microfluidic systems. Elements of fluid dynamics at low Reynolds number are first described in the context of pulsatile flow. Then the practical applications in microfluidic processes are presented: the methods to generate a pulsatile flow, the generation of emulsion droplets through harmonic flow rate perturbation, the applications in mixing and particle separation, and the benefits of pulsatile flow for clog mitigation. The second part of the review is devoted to pulsatile flow in biological applications. Pulsatile flows can be used for mimicking physiological systems, to alter or enhance cell cultures, and for bioassay automation. Pulsatile flows offer unique advantages over a steady flow, especially in microfluidic systems, but also require some new physical insights and more rigorous investigation to fully benefit future applications.}, } @article {pmid31656395, year = {2019}, author = {Folkersma, M and Schmehl, R and Viré, A}, title = {Boundary layer transition modeling on leading edge inflatable kite airfoils.}, journal = {Wind energy (Chichester, England)}, volume = {22}, number = {7}, pages = {908-921}, pmid = {31656395}, issn = {1099-1824}, abstract = {We present a computational fluid dynamic analysis of boundary layer transition on leading edge inflatable kite airfoils used for airborne wind energy generation. Because of the operation in pumping cycles, the airfoil is generally subject to a wide range of Reynolds numbers. The analysis is based on the combination of the shear stress transport turbulence model with the γ - R ˜ e θ t transition model, which can handle the laminar boundary layer and its transition to turbulence. The implementation of both models in OpenFOAM is described. We show a validation of the method for a sailwing (ie, a wing with a membrane) airfoil and an application to a leading edge inflatable kite airfoil. For the sailwing airfoil, the results computed with transition model agree well with the existing low Reynolds number experiment over the whole range of angles of attack. For the leading edge inflatable kite airfoil, the transition modeling has both favorable and unfavorable effects on the aerodynamics. On the one hand, the aerodynamics suffer from the laminar separation. But, on the other hand, the laminar boundary layer thickens slower than the turbulent counterpart, which, in combination with transition, delays the separation. The results also indicate that the aerodynamics of the kite airfoil could be improved by delaying the boundary layer transition during the traction phase and tripping the transition in the retraction phase.}, } @article {pmid31648622, year = {2020}, author = {Ozden, K and Sert, C and Yazicioglu, Y}, title = {Numerical investigation of wall pressure fluctuations downstream of concentric and eccentric blunt stenosis models.}, journal = {Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine}, volume = {234}, number = {1}, pages = {48-60}, doi = {10.1177/0954411919884167}, pmid = {31648622}, issn = {2041-3033}, mesh = {Acoustics ; Blood Vessels/*physiopathology ; *Constriction, Pathologic ; *Models, Biological ; *Pressure ; }, abstract = {Pressure fluctuations that cause acoustic radiation from vessel models with concentric and eccentric blunt stenoses are investigated. Large eddy simulations of non-pulsatile flow condition are performed using OpenFOAM. Calculated amplitude and spatial-spectral distribution of acoustic pressures at the post-stenotic region are compared with previous experimental and theoretical results. It is found that increasing the Reynolds number does not change the location of the maximum root mean square wall pressure, but causes a general increase in the spectrum level, although the change in the shape of the spectrum is not significant. On the contrary, compared to the concentric model at the same Reynolds number, eccentricity leads to an increase both at the distance of the location of the maximum root mean square wall pressure from the stenosis exit and the spectrum level. This effect becomes more distinct when radial eccentricity of the stenosis increases. Both the flow rate and the eccentricity of the stenosis shape are evaluated to be clinically important parameters in diagnosing stenosis.}, } @article {pmid31640254, year = {2019}, author = {Su, L and Duan, Z and He, B and Ma, H and Xu, Z}, title = {Thermally Developing Flow and Heat Transfer in Elliptical Minichannels with Constant Wall Temperature.}, journal = {Micromachines}, volume = {10}, number = {10}, pages = {}, pmid = {31640254}, issn = {2072-666X}, abstract = {Laminar convective heat transfer of elliptical minichannels is investigated for hydrodynamically fully developed but thermal developing flow with no-slip condition. A three-dimensional numerical model is developed in different elliptical geometries with the aspect ratio varying from 0.2 to 1. The effect of Reynolds number (25 ≤ Re ≤ 2000) on the local Nusselt number is examined in detail. The results indicate that the local Nusselt number is a decreasing function of Reynolds number and it is sensitive to Reynolds number especially for Re less than 250. The effect of aspect ratio on local Nusselt number is small when compared with the effect of Reynolds number on local Nusselt number. The local Nusselt number is independent of cross-section geometry at the inlet. The maximum effect of aspect ratio on local Nusselt number arises at the transition section rather than the fully developed region. However, the non-dimensional thermal entrance length is a monotonic decreasing concave function of aspect ratio but a weak function of Reynolds number. Correlations for the local Nusselt number and the thermal developing length for elliptical channels are developed with good accuracy, which may provide guidance for design and optimization of elliptical minichannel heat sinks.}, } @article {pmid31640175, year = {2019}, author = {Raza, W and Ma, SB and Kim, KY}, title = {Single and Multi-Objective Optimization of a Three-Dimensional Unbalanced Split-and-Recombine Micromixer.}, journal = {Micromachines}, volume = {10}, number = {10}, pages = {}, pmid = {31640175}, issn = {2072-666X}, abstract = {The three-dimensional geometry of a micromixer with an asymmetrical split-and-recombine mechanism was optimized to enhance the fluid-mixing capability at a Reynolds number of 20. Single and multi-objective optimizations were carried out by using particle swarm optimization and a genetic algorithm on a modeled surrogate surface. Surrogate modeling was performed using the computational results for the mixing. Mixing and flow analyses were carried out by solving the convection-diffusion equation in combination with the three-dimensional continuity and momentum equations. The optimization was carried out with two design variables related to dimensionless geometric parameters. The mixing effectiveness was chosen as the objective function for the single-objective optimization, and the pressure drop and mixing index at the outlet were chosen for the multi-objective optimization. The sampling points in the design space were determined using a design of experiment technique called Latin hypercube sampling. The surrogates for the objective functions were developed using a Kriging model. The single-objective optimization resulted in 58.9% enhancement of the mixing effectiveness compared to the reference design. The multi-objective optimization provided Pareto-optimal solutions that showed a maximum increase of 48.5% in the mixing index and a maximum decrease of 55.0% in the pressure drop in comparison to the reference design.}, } @article {pmid31639948, year = {2019}, author = {Basu, A and Bhattacharjee, JK}, title = {Kolmogorov or Bolgiano-Obukhov scaling: Universal energy spectra in stably stratified turbulent fluids.}, journal = {Physical review. E}, volume = {100}, number = {3-1}, pages = {033117}, doi = {10.1103/PhysRevE.100.033117}, pmid = {31639948}, issn = {2470-0053}, abstract = {We set up the scaling theory for stably stratified turbulent fluids. For a system having infinite extent in the horizontal directions, but with a finite width in the vertical direction, this theory predicts that the inertial range can display three possible scaling behavior, which are essentially parametrized by the buoyancy frequency N, or dimensionless horizontal Froude number F_{h}, and the vertical length scale l_{v} that sets the scale of variation of the velocity field in the vertical direction for a fixed Reynolds number. For very low N or very high Re_{b} or F_{h}, and with l_{v} ≫l_{h}, the typical horizontal length scale, buoyancy forces are irrelevant and hence, unsurprisingly, the kinetic energy spectra show the well-known K41 scaling in the inertial range. In this regime, the local temperature behaves as a passively advected scalar, without any effect on the flow fields. For intermediate ranges of values of N,F_{h} ∼O(1), corresponding to moderate stratification, buoyancy forces are important enough to affect the scaling. This leads to the Bolgiano-Obukhov scaling which is isotropic, when l_{v} ∼l_{h} . Finally, for very large N, corresponding to strong stratification, together with a very small l_{v}, the inertial-range flow fields effectively two-dimensionalize. The kinetic energy spectra are predicted to be anisotropic with only the horizontal part of the kinetic energy spectra following the K41 scaling. This suggests an intriguing re-entrant K41 scaling, as a function of stratification, for the horizontal components of the velocity field in this regime. The scaling theory further predicts the scaling of the thermal energy in each of these three scaling regimes. Our theory can be tested in large-scale simulations and appropriate laboratory-based experiments.}, } @article {pmid31631905, year = {2019}, author = {Bae, HJ and Lozano-Durán, A and Bose, ST and Moin, P}, title = {Dynamic slip wall model for large-eddy simulation.}, journal = {Journal of fluid mechanics}, volume = {859}, number = {}, pages = {400-432}, pmid = {31631905}, issn = {0022-1120}, support = {NNX15AU93A//NASA/United States ; }, abstract = {Wall modelling in large-eddy simulation (LES) is necessary to overcome the prohibitive near-wall resolution requirements in high-Reynolds-number turbulent flows. Most existing wall models rely on assumptions about the state of the boundary layer and require a priori prescription of tunable coefficients. They also impose the predicted wall stress by replacing the no-slip boundary condition at the wall with a Neumann boundary condition in the wall-parallel directions while maintaining the no-transpiration condition in the wall-normal direction. In the present study, we first motivate and analyse the Robin (slip) boundary condition with transpiration (non-zero wall-normal velocity) in the context of wall-modelled LES. The effect of the slip boundary condition on the one-point statistics of the flow is investigated in LES of turbulent channel flow and a flat-plate turbulent boundary layer. It is shown that the slip condition provides a framework to compensate for the deficit or excess of mean momentum at the wall. Moreover, the resulting non-zero stress at the wall alleviates the well-known problem of the wall-stress under-estimation by current subgrid-scale (SGS) models (Jiménez & Moser, AIAA J., vol. 38 (4), 2000, pp. 605-612). Second, we discuss the requirements for the slip condition to be used in conjunction with wall models and derive the equation that connects the slip boundary condition with the stress at the wall. Finally, a dynamic procedure for the slip coefficients is formulated, providing a dynamic slip wall model free of a priori specified coefficients. The performance of the proposed dynamic wall model is tested in a series of LES of turbulent channel flow at varying Reynolds numbers, non-equilibrium three-dimensional transient channel flow and a zero-pressure-gradient flat-plate turbulent boundary layer. The results show that the dynamic wall model is able to accurately predict one-point turbulence statistics for various flow configurations, Reynolds numbers and grid resolutions.}, } @article {pmid31631902, year = {2019}, author = {Lozano-Durán, A and Bae, HJ}, title = {Error scaling of large-eddy simulation in the outer region of wall-bounded turbulence.}, journal = {Journal of computational physics}, volume = {392}, number = {}, pages = {532-555}, pmid = {31631902}, issn = {0021-9991}, support = {NNX15AU93A//NASA/United States ; }, abstract = {We study the error scaling properties of large-eddy simulation (LES) in the outer region of wall-bounded turbulence at moderately high Reynolds numbers. In order to avoid the additional complexity of wall-modeling, we perform LES of turbulent channel flows in which the no-slip condition at the wall is replaced by a Neumann condition supplying the exact mean wall-stress. The statistics investigated are the mean velocity profile, turbulence intensities, and kinetic energy spectra. The errors follow (Δ / L) α R e τ γ , where Δ is the characteristic grid resolution, Re τ is the friction Reynolds number, and L is the meaningful length-scale to normalize Δ in order to collapse the errors across the wall-normal distance. We show that Δ can be expressed as the L 2-norm of the grid vector and that L is well represented by the ratio of the friction velocity and mean shear. The exponent α is estimated from theoretical arguments for each statistical quantity of interest and shown to roughly match the values computed by numerical simulations. For the mean profile and kinetic energy spectra, α ≈ 1, whereas the turbulence intensities converge at a slower rate α < 1. The exponent γ is approximately 0, i.e. the LES solution is independent of the Reynolds number. The expected behavior of the turbulence intensities at high Reynolds numbers is also derived and shown to agree with the classic log-layer profiles for grid resolutions lying within the inertial range. Further examination of the LES turbulence intensities and spectra reveals that both quantities resemble their filtered counterparts from direct numerical simulation (DNS) data, but that the mechanism responsible for this similarity is related to the balance between the input power and dissipation rather than to filtering.}, } @article {pmid31627151, year = {2020}, author = {Hayat, T and Waqar Ahmad, M and Ijaz Khan, M and Alsaedi, A}, title = {Entropy optimization in CNTs based nanomaterial flow induced by rotating disks: A study on the accuracy of statistical declaration and probable error.}, journal = {Computer methods and programs in biomedicine}, volume = {184}, number = {}, pages = {105105}, doi = {10.1016/j.cmpb.2019.105105}, pmid = {31627151}, issn = {1872-7565}, mesh = {*Entropy ; Models, Theoretical ; Nanostructures/*chemistry ; Nanotubes, Carbon/*chemistry ; Probability ; Reproducibility of Results ; }, abstract = {BACKGROUND: CNTs (Carbon nanotubes) being allotropes of carbon, made of graphene and diameters of single and multi-walls carbon nanotubes are typically 0.8 to 2 nm and 5 to 20 mn, although diameter of MWCNTs can exceed 100 nm. Carbon nanotubes lengths range from less than 100 nm to 0.5 m. Their impressive structural, electronic and mechanical attributes subject to their small size and mass, their high electrical and thermal conductivities, and their strong mechanical potency. CNTs based materials are successfully applied in medicine and pharmacy subject to their huge surface area that is proficient of conjugating or adsorbing with a wide variety of genes, drugs, antibodies, vaccines and biosensors etc. Therefore, we have presented a theoretical study about mathematical modeling of CNTs based viscous material flow between two rotating disks. Both types of nanotubes i.e., SWCNTs and MWCNTs are considered. Xue model is used for the mathematical modeling. Fluid flow is due to rotating disks. Main focus here is given to probable error and statistical declaration. Entropy is calculated for both single and multi-walls nanotubes.

METHOD: Nonlinear PDEs are first converted into ODEs and then computed for homotopy convergent solutions.

RESULTS AND CONCLUSION: Statistical declaration and probable error for skin friction and Nusselt number are numerically computed and discussed through Tables. From obtained outcomes it is concluded that magnitude of skin friction increases at both disks surface for higher values of Reynolds number, lower stretching parameter and porosity parameter while it decays for both of disks versus larger rotation parameter. Nusselt number or heat transfer rate also enhances at both disks in the presence of radiation and Reynolds number while it decays against Eckert number.}, } @article {pmid31620754, year = {2019}, author = {Bukowicki, M and Ekiel-Jeżewska, ML}, title = {Sedimenting pairs of elastic microfilaments.}, journal = {Soft matter}, volume = {15}, number = {46}, pages = {9405-9417}, doi = {10.1039/c9sm01373c}, pmid = {31620754}, issn = {1744-6848}, abstract = {The dynamics of two identical elastic filaments settling under gravity in a viscous fluid in the low Reynolds number regime is investigated numerically. A large family of initial configurations symmetric with respect to a vertical plane is considered, as well as their non-symmetric perturbations. The behaviour of the filaments is primarily governed by the elasto-gravitational number, which depends on the filament's length and flexibility, and the strength of the external force. Flexible filaments usually converge toward horizontal and parallel orientation. We explain this phenomenon and show that it occurs also for curved rigid particles of similar shapes. Once aligned, the two fibres either converge toward a stationary, flexibility-dependent distance, or tend to collide or continuously repel each other. Rigid and straight rods perform periodic motions while settling down. Apart from very stiff particles, the dynamics is robust to non-symmetric perturbations.}, } @article {pmid31611726, year = {2019}, author = {Holdenried-Chernoff, D and Chen, L and Jackson, A}, title = {A trio of simple optimized axisymmetric kinematic dynamos in a sphere.}, journal = {Proceedings. Mathematical, physical, and engineering sciences}, volume = {475}, number = {2229}, pages = {20190308}, pmid = {31611726}, issn = {1364-5021}, abstract = {Planetary magnetic fields are generated by the motion of conductive fluid in the planet's interior. Complex flows are not required for dynamo action; simple flows have been shown to act as efficient kinematic dynamos, whose physical characteristics are more straightforward to study. Recently, Chen et al. (2018, J. Fluid Mech. 839, 1-32. (doi:10.1017/jfm.2017.924)) found the optimal, unconstrained kinematic dynamo in a sphere, which, despite being of theoretical importance, is of limited practical use. We extend their work by restricting the optimization to three simple two-mode axisymmetric flows based on the kinematic dynamos of Dudley & James (1989, Proc. R. Soc. Lond. A 425, 407-429. (doi:10.1098/rspa.1989.0112)). Using a Lagrangian optimization, we find the smallest critical magnetic Reynolds number for each flow type, measured using an enstrophy-based norm. A Galerkin method is used, in which the spectral coefficients of the fluid flow and magnetic field are updated in order to maximize the final magnetic energy. We consider the t [0] 1 s [0] 1, t [0] 1 s [0] 2 and t [0] 2 s [0] 2 flows and find enstrophy-based critical magnetic Reynolds numbers of 107.7, 142.4 and 125.5 (13.7, 19.6 and 16.4, respectively, with the energy-based definition). These are up to four times smaller than the original flows. These simple and efficient flows may be used as benchmarks in future studies.}, } @article {pmid31602809, year = {2020}, author = {Browne, CA and Shih, A and Datta, SS}, title = {Pore-Scale Flow Characterization of Polymer Solutions in Microfluidic Porous Media.}, journal = {Small (Weinheim an der Bergstrasse, Germany)}, volume = {16}, number = {9}, pages = {e1903944}, doi = {10.1002/smll.201903944}, pmid = {31602809}, issn = {1613-6829}, abstract = {Polymer solutions are frequently used in enhanced oil recovery and groundwater remediation to improve the recovery of trapped nonaqueous fluids. However, applications are limited by an incomplete understanding of the flow in porous media. The tortuous pore structure imposes both shear and extension, which elongates polymers; moreover, the flow is often at large Weissenberg numbers, Wi, at which polymer elasticity in turn strongly alters the flow. This dynamic elongation can even produce flow instabilities with strong spatial and temporal fluctuations despite the low Reynolds number, Re. Unfortunately, macroscopic approaches are limited in their ability to characterize the pore-scale flow. Thus, understanding how polymer conformations, flow dynamics, and pore geometry together determine these nontrivial flow patterns and impact macroscopic transport remains an outstanding challenge. This review describes how microfluidic tools can shed light on the physics underlying the flow of polymer solutions in porous media at high Wi and low Re. Specifically, microfluidic studies elucidate how steady and unsteady flow behavior depends on pore geometry and solution properties, and how polymer-induced effects impact nonaqueous fluid recovery. This work thus provides new insights for polymer dynamics, non-Newtonian fluid mechanics, and applications such as enhanced oil recovery and groundwater remediation.}, } @article {pmid31594959, year = {2019}, author = {Houba, T and Dasgupta, A and Gopalakrishnan, S and Gosse, R and Roy, S}, title = {Supersonic turbulent flow simulation using a scalable parallel modal discontinuous Galerkin numerical method.}, journal = {Scientific reports}, volume = {9}, number = {1}, pages = {14442}, doi = {10.1038/s41598-019-50546-w}, pmid = {31594959}, issn = {2045-2322}, abstract = {The scalability and efficiency of numerical methods on parallel computer architectures is of prime importance as we march towards exascale computing. Classical methods like finite difference schemes and finite volume methods have inherent roadblocks in their mathematical construction to achieve good scalability. These methods are popularly used to solve the Navier-Stokes equations for fluid flow simulations. The discontinuous Galerkin family of methods for solving continuum partial differential equations has shown promise in realizing parallel efficiency and scalability when approaching petascale computations. In this paper an explicit modal discontinuous Galerkin (DG) method utilizing Implicit Large Eddy Simulation (ILES) is proposed for unsteady turbulent flow simulations involving the three-dimensional Navier-Stokes equations. A study of the method was performed for the Taylor-Green vortex case at a Reynolds number ranging from 100 to 1600. The polynomial order P = 2 (third order accurate) was found to closely match the Direct Navier-Stokes (DNS) results for all Reynolds numbers tested outside of Re = 1600, which had a normalized RMS error of 3.43 × 10[-4] in the dissipation rate for a 60[3] element mesh. The scalability and performance study of the method was then conducted for a Reynolds number of 1600 for polynomials orders from P = 2 to P = 6. The highest order polynomial that was tested (P = 6) was found to have the most efficient scalability using both the MPI and OpenMP implementations.}, } @article {pmid31590559, year = {2019}, author = {Porteous, R and Moreau, DJ and Doolan, CJ}, title = {The effect of the incoming boundary layer thickness on the aeroacoustics of finite wall-mounted square cylinders.}, journal = {The Journal of the Acoustical Society of America}, volume = {146}, number = {3}, pages = {1808}, doi = {10.1121/1.5126693}, pmid = {31590559}, issn = {1520-8524}, abstract = {This paper is concerned with the influence of the incoming wall boundary layer thickness on the noise produced by a square finite wall-mounted cylinder in cross-flow. Acoustic and near wake velocity measurements have been taken in an anechoic wind tunnel for a cylinder in two different near-zero-pressure gradient turbulent boundary layers with thicknesses of 130% and 370% of the cylinder width, W. The cylinders have an aspect ratio of 0.29≤L/W≤22.9 (where L is the cylinder span) and were examined at a Reynolds number, based on width, of ReW = 1.4 × 10[4]. The results presented in this paper demonstrate that increasing the height of the boundary layer delays the production of acoustic tones to higher aspect ratios. The height of the boundary layer changes the balance between upwash and downwash across the cylinder span, resulting in a delayed onset of the shedding regimes and correspondingly, the production of acoustic tones.}, } @article {pmid31590317, year = {2019}, author = {Kawaguchi, M and Fukui, T and Funamoto, K and Tanaka, M and Tanaka, M and Murata, S and Miyauchi, S and Hayase, T}, title = {Viscosity Estimation of a Suspension with Rigid Spheres in Circular Microchannels Using Particle Tracking Velocimetry.}, journal = {Micromachines}, volume = {10}, number = {10}, pages = {}, pmid = {31590317}, issn = {2072-666X}, abstract = {Suspension flows are ubiquitous in industry and nature. Therefore, it is important to understand the rheological properties of a suspension. The key to understanding the mechanism of suspension rheology is considering changes in its microstructure. It is difficult to evaluate the influence of change in the microstructure on the rheological properties affected by the macroscopic flow field for non-colloidal particles. In this study, we propose a new method to evaluate the changes in both the microstructure and rheological properties of a suspension using particle tracking velocimetry (PTV) and a power-law fluid model. Dilute suspension (0.38%) flows with fluorescent particles in a microchannel with a circular cross section were measured under low Reynolds number conditions (Re ≈ 10[-4]). Furthermore, the distribution of suspended particles in the radial direction was obtained from the measured images. Based on the power-law index and dependence of relative viscosity on the shear rate, we observed that the non-Newtonian properties of the suspension showed shear-thinning. This method will be useful in revealing the relationship between microstructural changes in a suspension and its rheology.}, } @article {pmid35527935, year = {2019}, author = {Krainer, S and Smit, C and Hirn, U}, title = {The effect of viscosity and surface tension on inkjet printed picoliter dots.}, journal = {RSC advances}, volume = {9}, number = {54}, pages = {31708-31719}, pmid = {35527935}, issn = {2046-2069}, abstract = {In this study, we investigated the effect of liquid viscosity and surface tension for inkjet printing on porous cellulose sheets. We used five model liquids, representing the operational field of an industrial high speed inkjet printer, as specified by Ohnesorge- and Reynolds number. Drops with 30 pl and 120 pl drop size were jetted with a commercial HSI printhead. We printed on four uncoated papers representing the most relevant grades on the market in terms of hydrophobisation and surface treatment. We are presenting a quantitative analysis of viscosity and surface tension on the print outcome, evaluating dot size, liquid penetration (print through) and surface coverage of the printed dots. The most important finding is that for liquids within the jetting window the variation of the liquid viscosity typically has a 2-3 times higher impact on the print outcome than variation of the liquid surface tension. Increased viscosity in all cases reduces dot area, liquid penetration and liquid surface coverage. Surface tension plays a smaller role for liquid spreading and penetration, except for hydrophobised substrates, where both are reduced for higher surface tension. Interestingly, higher surface tension consistently increases liquid surface coverage for all papers and drop sizes. A detailed analysis on the competing effect of dot spreading and liquid penetration is presented, in terms of viscosity, surface tension and surface coverage of the liquid.}, } @article {pmid31574775, year = {2019}, author = {Singh, G and Lakkaraju, R}, title = {Wall-mounted flexible plates in a two-dimensional channel trigger early flow instabilities.}, journal = {Physical review. E}, volume = {100}, number = {2-1}, pages = {023109}, doi = {10.1103/PhysRevE.100.023109}, pmid = {31574775}, issn = {2470-0053}, abstract = {A high level of mixing by passive means is a desirable feature in microchannels for various applications, and use of flexible obstacles (or plates) is one of the prime choices in that regard. To gain further insight, we carry out two-dimensional numerical simulations for flow past one or two flexible plates anchored to a channel's opposite walls using a fluid-structure interaction framework. For the inlet flow Reynolds number vs the Strouhal number plane, we observe a sudden flow change from a laminar to a time-periodic vortex shedding state when flexible plates are present in the channel. We found the critical Reynolds number to be Re_{cr} ≈370 when a single plate is anchored on the channel wall and Re_{cr} ≈290 or even lower when two plates are anchored. With an increase in the inlet flow Reynolds number (up to 3200), we found that vortices detach regularly at the plates' tips, which causes the flow to meander in the channel. In a two-plate anchored configuration, primary vortices generated at the first plate are constrained by the second plate and result in an energetic secondary vortex generation in the downstream side. The overall flow features and the energy dissipation in the channel are mainly controlled by the separation gap between the plates. At high-inlet-flow Reynolds numbers (≥1600), the probability density function (F) of the kinetic energy dissipation in a flexible plate configuration shows a stretched exponential shape in the form F(Z)∼1/sqrt[Z]e^{-pZ^{q} }, where Z is the normalized kinetic energy dissipation and the constants p=0.89 and q=0.86. The observed increase in energy dissipation comes at the cost of an increase in pressure loss in the channel, and we found that the loss is inversely related to the plates' separation gap. From our simulations, we found that if high mixing levels are desired, then two flexible plates anchored to the channel walls is a better choice than a channel flow without obstacles or flow past a single plate. The two-plate configuration with zero separation gap between the plates is best suited to achieve a high mixing level.}, } @article {pmid31574747, year = {2019}, author = {Feng, Y and Boivin, P and Jacob, J and Sagaut, P}, title = {Hybrid recursive regularized lattice Boltzmann simulation of humid air with application to meteorological flows.}, journal = {Physical review. E}, volume = {100}, number = {2-1}, pages = {023304}, doi = {10.1103/PhysRevE.100.023304}, pmid = {31574747}, issn = {2470-0053}, abstract = {An extended version of the hybrid recursive regularized lattice-Boltzmann model which incorporates external force is developed to simulate humid air flows with phase change mechanisms under the Boussinesq approximation. Mass and momentum conservation equations are solved by a regularized lattice Boltzmann approach well suited for high Reynolds number flows, whereas the energy and humidity related equations are solved by a finite volume approach. Two options are investigated to account for cloud formation in atmospheric flow simulations. The first option considers a single conservation equation for total water and an appropriate invariant variable of temperature. In the other approach, liquid and vapor are considered via two separated equations, and phase transition is accounted for via a relaxation procedure. The obtained models are then systematically validated on four well-established benchmark problems including a double diffusive Rayleigh Bénard convection of humid air, two- and three-dimensional thermal moist rising bubble under convective atmospheric environment, as well as a shallow cumulus convection in the framework of large-eddy simulation.}, } @article {pmid31574698, year = {2019}, author = {Topayev, S and Nouar, C and Bernardin, D and Neveu, A and Bahrani, SA}, title = {Taylor-vortex flow in shear-thinning fluids.}, journal = {Physical review. E}, volume = {100}, number = {2-1}, pages = {023117}, doi = {10.1103/PhysRevE.100.023117}, pmid = {31574698}, issn = {2470-0053}, abstract = {This paper deals with the Taylor-Couette flow of shear-thinning fluids. It focuses on the first principles understanding of the influence of the viscosity stratification and the nonlinear variation of the effective viscosity μ with the shear rate γ[over ̇] on the flow structure in the Taylor-vortex flow regime. A wide gap configuration (η=0.4) is mainly considered. A weakly nonlinear analysis, using the amplitude expansion method at high order, is adopted as a first approach to study nonlinear effects. For the numerical computation, the shear-thinning behavior is described by the Carreau model. The rheological parameters are varied in a wide range. The results indicate that the flow field undergoes a significant change as shear-thinning effects increase. First, vortices are squeezed against the inner wall and the center of the patterns is shifted axially toward the radial outflow boundaries (z=0,z/λ_{z} =1). This axial shift leads to increasing concentration of vorticity at these positions. The outflow becomes stronger than the inflow and the extent of the inflow zone where the vorticity is low increases acoordingly. Nevertheless, the strength of the vortices relative to the velocity of the inner cylinder is weaker. Second, the pseudo-Nusselt number, ratio of the torque to that obtained in the laminar flow, decreases. Third, higher harmonics become more relevant and grow faster with Reynolds number. Finally, the modification of the viscosity field is described.}, } @article {pmid31574640, year = {2019}, author = {Krämer, A and Wilde, D and Küllmer, K and Reith, D and Foysi, H}, title = {Pseudoentropic derivation of the regularized lattice Boltzmann method.}, journal = {Physical review. E}, volume = {100}, number = {2-1}, pages = {023302}, doi = {10.1103/PhysRevE.100.023302}, pmid = {31574640}, issn = {2470-0053}, abstract = {The lattice Boltzmann method (LBM) facilitates efficient simulations of fluid turbulence based on advection and collision of local particle distribution functions. To ensure stable simulations on underresolved grids, the collision operator must prevent drastic deviations from local equilibrium. This can be achieved by various methods, such as the multirelaxation time, entropic, quasiequilibrium, regularized, and cumulant schemes. Complementing a part of a unified theoretical framework of these schemes, the present work presents a derivation of the regularized lattice Boltzmann method (RLBM), which follows a recently introduced entropic multirelaxation time LBM by Karlin, Bösch, and Chikatamarla (KBC). It is shown that both methods can be derived by locally maximizing a quadratic Taylor expansion of the entropy function. While KBC expands around the local equilibrium distribution, the RLBM is recovered by expanding entropy around a global equilibrium. Numerical tests were performed to elucidate the role of pseudoentropy maximization in these models. Simulations of a two-dimensional shear layer show that the RLBM successfully reproduces the largest eddies even on a 16×16 grid, while the conventional LBM becomes unstable for grid resolutions of 128×128 and lower. The RLBM suppresses spurious vortices more effectively than KBC. In contrast, simulations of the three-dimensional Taylor-Green and Kida vortices show that KBC performs better in resolving small scale vortices, outperforming the RLBM by a factor of 1.8 in terms of the effective Reynolds number.}, } @article {pmid31574614, year = {2019}, author = {Morris, RG and Rao, M}, title = {Active morphogenesis of epithelial monolayers.}, journal = {Physical review. E}, volume = {100}, number = {2-1}, pages = {022413}, doi = {10.1103/PhysRevE.100.022413}, pmid = {31574614}, issn = {2470-0053}, mesh = {Epithelium/*growth & development/metabolism ; Hydrodynamics ; *Models, Biological ; *Morphogenesis ; Thermodynamics ; }, abstract = {During typical early-stage embryo development, single-cell-thick tissues of tightly bound epithelial cells autonomously generate profound changes in their shape, forming the basis of organism anatomy. We report on a (covariant) active-hydrodynamic theory of such monolayer morphogenesis that is closed under its shape-changing dynamics-i.e., the degrees of freedom that encode monolayer geometry appear properly as broken-symmetry variables. In our theory, the salient physics of tissue-scale deformations emerges from a balance between the displacement and/or shear of a low-Reynolds-number embedding fluid (the "yolk") and cell-autonomous stresses, themselves a result of combining apical contractile stresses with an elastic-like mechanical response under the constraint of constant cell volume. The leading-order hydrodynamic instabilities include both passive constrained-buckling and active deformation, which can be further categorized by cell shape changes that are either "squamous to columnar" or "regular-prism to truncated-pyramid." The deformations resulting from the latter qualitatively reproduce in vivo observations of the onset of both mesoderm and posterior midgut invaginations, which take place during gastrulation in the model organism Drosophila melanogaster.}, } @article {pmid31546025, year = {2020}, author = {Phuong, NL and Quang, TV and Khoa, ND and Kim, JW and Ito, K}, title = {CFD analysis of the flow structure in a monkey upper airway validated by PIV experiments.}, journal = {Respiratory physiology & neurobiology}, volume = {271}, number = {}, pages = {103304}, doi = {10.1016/j.resp.2019.103304}, pmid = {31546025}, issn = {1878-1519}, mesh = {Animals ; *Computer Simulation ; Haplorhini ; *Hydrodynamics ; Inhalation Exposure ; Macaca fascicularis ; Male ; Mouth/diagnostic imaging/physiology ; Nasal Cavity/diagnostic imaging/*physiology ; *Particle Size ; Respiratory Mechanics/*physiology ; Rheology/*methods ; }, abstract = {Inhalation exposure to airborne contaminants has adverse effects on humans; however, related research is typically conducted using in vivo/in vitro tests on animals. Extrapolating the test results is complicated by anatomical and physiological differences between animals and humans and a lack of understanding of the transport mechanism inside their respective respiratory tracts. This study determined the detailed air-flow structure in the upper airway of a monkey. A steady computational fluid dynamics simulation, which was validated by previous particle image velocimetry measurements, was adopted for flow rates of 4 L/min and 10 L/min to analyze the flow structure from the nasal/oral cavities to the trachea region in a monkey airway model. The low Reynolds number type k-ε model provided a reasonably accurate prediction of the airflow in a monkey upper airway. Furthermore, it was confirmed that large velocity gradients were generated in the nasal vestibule and larynx regions, as well as increased turbulent air kinetic energy and wall sheer stress.}, } @article {pmid31542476, year = {2020}, author = {Shi, L and Wu, J and Krenn, HW and Yang, Y and Yan, S}, title = {Temporal model of fluid-feeding mechanisms in a long proboscid orchid bee compared to the short proboscid honey bee.}, journal = {Journal of theoretical biology}, volume = {484}, number = {}, pages = {110017}, doi = {10.1016/j.jtbi.2019.110017}, pmid = {31542476}, issn = {1095-8541}, mesh = {Animals ; *Bees/anatomy & histology/physiology ; *Feeding Behavior/physiology ; Flowers ; *Models, Biological ; Plant Nectar ; Time ; Tongue/anatomy & histology ; }, abstract = {Bees (Apidae) are flower-visiting insects that possess highly efficient mouthparts for the ingestion of nectar and other sucrose fluids. Their mouthparts are composed of mandibles and a tube-like proboscis. The proboscis forms a food canal, which encompasses a protrusible and hairy tongue to load and imbibe nectar, representing a fluid-feeding technique with a low Reynolds number. The western honey bee, Apis mellifera ligustica, can rhythmically erect the tongue microtrichia to regulate the glossal shape, achieving a tradeoff between nectar intake rate and viscous drag. Neotropical orchid bees (Euglossa imperialis) possess a proboscis longer than the body and combines this lapping-sucking mode of fluid-feeding with suction feeding. This additional technique of nectar uptake may have different biophysics. In order to reveal the effect of special structures of mouthparts in terms of feeding efficiency, we build a temporal model for orchid bees considering fluid transport in multi-states including active suction, tongue protraction and viscous dipping. Our model indicates that the dipping technique employed by honey bees can contribute to more than seven times the volumetric and energetic intake rate at a certain nectar concentration compared with the combined mode used by orchid bees. The high capability of the honey bee's proboscis to ingest nectar may inspire micropumps for transporting viscous liquid with higher efficiency.}, } @article {pmid31538112, year = {2019}, author = {Onyiriuka, EJ and Ighodaro, OO and Adelaja, AO and Ewim, DRE and Bhattacharyya, S}, title = {A numerical investigation of the heat transfer characteristics of water-based mango bark nanofluid flowing in a double-pipe heat exchanger.}, journal = {Heliyon}, volume = {5}, number = {9}, pages = {e02416}, pmid = {31538112}, issn = {2405-8440}, abstract = {In this study, the heat transfer characteristics of a new class of nanofluids made from mango bark was numerically simulated and studied during turbulent flow through a double pipe heat exchanger. A range of volume fractions was considered for a particle size of 100 nm. A two-phase flow was considered using the mixture model. The mixture model governing equations of continuity, momentum, energy and volume fraction were solved using the finite-volume method. The results showed an increase of the Nusselt number by 68% for a Reynolds number of 5,000 and 45% for a Reynolds number of 13 000, and the heat transfer coefficient of the nanofluid was about twice that of the base fluid. In addition, the Nusselt number decreased by an average value of 0.76 with an increase of volume fraction by 1%. It was also found that there was a range of Reynolds numbers in which the trend of the average heat transfer coefficient of the nanofluid was completely reversed, and several plots showing zones of higher heat transfer which if taken advantage of in design will lead to higher heat transfer while avoiding other zones that have low heat transfer. It is hoped that these results will influence the thermal design of new heat exchangers.}, } @article {pmid31534269, year = {2019}, author = {Blumenthal, BT and Elmiligui, AA and Geiselhart, KA and Campbell, RL and Maughmer, MD and Schmitz, S}, title = {Computational Investigation of a Boundary-Layer Ingesting Propulsion System for the Common Research Model.}, journal = {Journal of aircraft}, volume = {55}, number = {3}, pages = {1141-1153}, doi = {10.2514/1.C034454}, pmid = {31534269}, issn = {0021-8669}, support = {//Langley Research Center NASA/United States ; N-999999//Intramural NASA/United States ; }, abstract = {The present paper examines potential propulsive and aerodynamic benefits of integrating a Boundary-Layer Ingestion (BLI) propulsion system into the Common Research Model (CRM) geometry and the NASA Tetrahedral Unstructured Software System (TetrUSS). The Numerical Propulsion System Simulation (NPSS) environment is used to generate engine conditions for Computational Fluid Dynamics (CFD) analyses. Improvements to the BLI geometry are made using the Constrained Direct Iterative Surface Curvature (CDISC) design method. Potential benefits of the BLI system relating to cruise propulsive power are quantified using a power balance method, and a comparison to the baseline case is made. Iterations of the BLI geometric design are shown, and improvements between subsequent BLI designs are presented. Simulations are conducted for a cruise flight condition of Mach 0.85 at an altitude of 38,500 feet, with Reynolds number of 40 million based on mean aerodynamic chord and an angle of attack of 2° for all geometries. Results indicate an 8% reduction in engine power requirements at cruise for the BLI configuration compared to the baseline geometry. Small geometric alterations of the aft portion of the fuselage using CDISC has been shown to marginally increase the benefit from boundary-layer ingestion further, resulting in an 8.7% reduction in power requirements for cruise, as well as a drag reduction of approximately twelve counts over the baseline geometry.}, } @article {pmid31533305, year = {2019}, author = {Wang, R and Wang, J and Yuan, W}, title = {Analysis and Optimization of a Microchannel Heat Sink with V-Ribs Using Nanofluids for Micro Solar Cells.}, journal = {Micromachines}, volume = {10}, number = {9}, pages = {}, pmid = {31533305}, issn = {2072-666X}, abstract = {It is crucial to control the temperature of solar cells for enhancing efficiency with the increasing power intensity of multiple photovoltaic systems. In order to improve the heat transfer efficiency, a microchannel heat sink (MCHS) with V-ribs using a water-based nanofluid as a coolant for micro solar cells was designed. Numerical simulations were carried out to investigate the flows and heat transfers in the MCHS when the Reynolds number ranges from 200 to 1000. The numerical results showed that the periodically arranged V-ribs can interrupt the thermal boundary, induce chaotic convection, increase heat transfer area, and subsequently improve the heat transfer performance of a MCHS. In addition, the preferential values of the geometric parameters of V-ribs and the physical parameters of the nanofluid were obtained on the basis of the Nusselt numbers at identical pump power. For MCHS with V-ribs on both the top and bottom wall, preferential values of V-rib are rib width d / W = 1 , flare angle α = 75 ° , rib height h r / H = 0.3 , and ratio of two slant sides b / a = 0.75 , respectively. This can provide sound foundations for the design of a MCHS in micro solar cells.}, } @article {pmid31533232, year = {2019}, author = {Tang, L and Pan, X and Feng, J and Pu, X and Liang, R and Li, R and Li, K}, title = {Experimental Investigation on the Relationship Between COD Degradation and Hydrodynamic Conditions in Urban Rivers.}, journal = {International journal of environmental research and public health}, volume = {16}, number = {18}, pages = {}, pmid = {31533232}, issn = {1660-4601}, mesh = {*Biological Oxygen Demand Analysis ; China ; Cities ; Hydrodynamics ; Rivers/*chemistry ; Water Pollution, Chemical/*analysis ; *Water Quality ; }, abstract = {Due to extensive pollution and the relatively weak flow replacement in urban rivers, determining how to fully utilize the self-purification abilities of water bodies for water quality protection has been a complex and popular topic of research and social concern. Organic pollution is an important type of urban river pollution, and COD (chemical oxygen demand) is one of the key pollution factors. Currently, there is a lack of research on the relationship between COD degradation and the flow characteristics of urban rivers. In this paper, COD degradation experiments were conducted in an annular flume with Jinjiang River water at controlled flow velocities and the COD degradation coefficients under different hydraulic conditions were analyzed. A good correlation was observed between the degradation coefficient and hydraulic conditions. According to dimensional analysis, the relationship between the COD degradation coefficient and hydraulic conditions such as the flow velocity, water depth, Reynolds number (Re), and Froude number (Fr) was established as K COD = 86400 u h F r 0.8415 R e - 1.2719 + 0.258 . The COD degradation coefficients of the Chishui River in Guizhou Province ranged from 0.175-0.373 1/d based on this formula, and the field-measured values varied from 0.234-0.463 1/d. The error in the formula ranged from 5.4-25.3%. This study provides a scientific basis for the prediction of the COD degradation coefficients of urban rivers.}, } @article {pmid31533091, year = {2019}, author = {Wang, C and Ren, F and Tang, H}, title = {Enhancing propulsion performance of a flexible heaving foil through dynamically adjusting its flexibility.}, journal = {Bioinspiration & biomimetics}, volume = {14}, number = {6}, pages = {064002}, doi = {10.1088/1748-3190/ab45d9}, pmid = {31533091}, issn = {1748-3190}, mesh = {Algorithms ; Animals ; Biomechanical Phenomena ; Biomimetics/instrumentation/*methods ; Fishes/*physiology ; Hydrodynamics ; Models, Biological ; Robotics/instrumentation/methods ; }, abstract = {This study investigates how dynamically adjusting the bending stiffness of a heaving foil affects its propulsion performance in a flow of Reynolds number 200. The foil is forced to oscillate sinusoidally at the leading edge, and its bending stiffness is tuned in a square-wave manner. Such a fluid-structure interaction (FSI) problem is explored using an immersed boundary lattice Boltzmann method (IBLBM) based numerical framework. The results reveal that when the lower and upper bounds of the foil's time-dependent bending stiffness are moderate, the net thrust can be evidently enhanced compared to those in the corresponding constant-bending-stiffness cases, while the propulsion efficiency is not apparently ameliorated. The most significant enhancement is observed when the bending stiffness has lower and upper bounds of the same duration (i.e. a duty cycle of 1/2) and also it remains at the lower bound during stroke reversals (corresponding to an actuation phase angle of [Formula: see text]). When the two bounds simultaneously increase or decrease, however, dynamically adjusting the bending stiffness fails to improve the net thrust. Through this study, competitions among various forces/moments, including the inertial force, tension force, bending moment and fluid loading, acting on the foil and their influences on the foil's dynamics are also unveiled.}, } @article {pmid31511924, year = {2019}, author = {Acosta-Avalos, D and Rodrigues, E}, title = {On the motion of magnetotactic bacteria: theoretical predictions and experimental observations.}, journal = {European biophysics journal : EBJ}, volume = {48}, number = {8}, pages = {691-700}, pmid = {31511924}, issn = {1432-1017}, mesh = {*Bacteria ; *Bacterial Physiological Phenomena ; Biomechanical Phenomena ; *Magnetic Fields ; *Models, Biological ; *Movement ; }, abstract = {The movement of magnetotactic bacteria is done in a viscous media in the low Reynolds number regime. In the present research, the simple model for magnetotactic bacteria motion, proposed by Nogueira and Lins de Barros (Eur Biophys J 24:13-21, 1995), was used to numerically simulate their trajectory. The model was done considering a spherical bacterium with a single flagellum and a magnetic moment positioned in the sphere center and parallel to the flagella. The numerical solution shows that the trajectory is a cylindrical helix and that the body Euler angles have linear dependencies on time. Using that information, analytical expressions were obtained for the first time for the center-of-mass coordinates, showing that the trajectories are helixes oriented to the magnetic field direction. They also show that the magnetic moment does not align to the magnetic field, but it precesses around it, being fully oriented only for very high magnetic fields. The analytical solution obtained permits to relate for the first time the flagellar force to the axial velocity and helical radius. Trajectories of uncultivated magnetotactic bacteria were registered in video and the coordinates were obtained for several bacteria in different magnetic fields. The trajectories showed to be a complex mixture of two oscillating functions: one with frequency lower than 5 Hz and the other one with frequency higher than 10 Hz. The simple model of Nogueira and Lins de Barros shows to be incomplete, because is unable to explain the trajectories composed of two oscillating functions observed in uncultivated magnetotactic bacteria.}, } @article {pmid31499817, year = {2019}, author = {Falsaperla, P and Giacobbe, A and Mulone, G}, title = {Nonlinear stability results for plane Couette and Poiseuille flows.}, journal = {Physical review. E}, volume = {100}, number = {1-1}, pages = {013113}, doi = {10.1103/PhysRevE.100.013113}, pmid = {31499817}, issn = {2470-0053}, abstract = {We prove that the plane Couette and Poiseuille flows are nonlinearly stable if the Reynolds number is less than Re_{Orr} (2π/(λsinθ))/sinθ when a perturbation is a tilted perturbation in the direction x^{'} which forms an angle θ∈(0,π/2] with the direction i of the basic motion and does not depend on x^{'} . Re_{Orr} is the critical Orr-Reynolds number for spanwise perturbations which is computed for wave number 2π/(λsinθ), with λ being any positive wavelength. By taking the minimum with respect to λ, we obtain the critical energy Reynolds number for a fixed inclination angle and any wavelength: for plane Couette flow, it is Re_{Orr} =44.3/sinθ, and for plane Poiseuille flow, it is Re_{Orr} =87.6/sinθ (in particular, for θ=π/2 we have the classical values Re_{Orr} =44.3 for plane Couette flow and Re_{Orr} =87.6 for plane Poiseuille flow). Here the nondimensional interval between the planes bounding the channel is [-1,1]. In particular, these results improve those obtained by Joseph, who found for streamwise perturbations a critical nonlinear value of 20.65 in the plane Couette case, and those obtained by Joseph and Carmi who found the value 49.55 for plane Poiseuille flow for streamwise perturbations. If we fix some wavelengths from the experimental data and the numerical simulations, the critical Reynolds numbers that we obtain are in a very good agreement both with the the experiments and the numerical simulation. These results partially solve the Couette-Sommerfeld paradox.}, } @article {pmid31499421, year = {2019}, author = {Shah, F and Khan, MI and Hayat, T and Khan, MI and Alsaedi, A and Khan, WA}, title = {Theoretical and mathematical analysis of entropy generation in fluid flow subject to aluminum and ethylene glycol nanoparticles.}, journal = {Computer methods and programs in biomedicine}, volume = {182}, number = {}, pages = {105057}, doi = {10.1016/j.cmpb.2019.105057}, pmid = {31499421}, issn = {1872-7565}, mesh = {Aluminum/*chemistry ; *Entropy ; Ethylene Glycol/*chemistry ; *Hydrodynamics ; *Models, Theoretical ; Nanoparticles/*chemistry ; }, abstract = {BACKGROUND: Here we have conducted a magnetohydrodynamic (MHD) flow of viscous material with alumina water and ethylene glycol over a stretched surface. The flow is discussed with and without effective Prandtl number. MHD liquid is considered. Electric field is absent. Effect of uniform magnetic field is taken in the vertical direction to the surface. Influence of thermal radiation as well as Joule heating are taken into account for both aluminum oxide-water and aluminum oxide-Ethylene glycol nanofluids. Velocity slip and melting heat effects are considered.

METHODS: The nonlinear flow expressions are numerically solved via ND-solve technique (built-in-Shooting).

RESULTS: The physical impacts of flow variables like mixed convection parameter, magnetic parameter, Reynold number, Eckert number, melting parameter and heat source/sink parameter are graphically discussed. Moreover, entropy generation (irreversibility) and Bejan number are discussed graphically through various flow variables. Physical quantities like skin friction coefficient and Sherwood and Nusselt numbers are numerically calculated and discussed through Tables.

CONCLUSIONS: Impact of magnetic and slip parameters on the velocity field show decreasing behavior for both effective and without effective Prandtl number. Temperature field increases for both effective and without effective Prandtl number for higher values of magnetic and radiative parameters. Entropy number is an increasing function of Reynolds number while Bejan number shows opposite impact against Reynolds number. Moreover, heat transfer rate upsurges versus larger melting and radiative parameter.}, } @article {pmid31481279, year = {2021}, author = {DeJonckere, P and Lebacq, J}, title = {Intraglottal Aerodynamics at Vocal Fold Vibration Onset.}, journal = {Journal of voice : official journal of the Voice Foundation}, volume = {35}, number = {1}, pages = {156.e23-156.e32}, doi = {10.1016/j.jvoice.2019.08.002}, pmid = {31481279}, issn = {1873-4588}, mesh = {Glottis ; Humans ; Models, Biological ; Phonation ; Pressure ; *Vibration ; *Vocal Cords ; }, abstract = {The most frequently observed type of voice onset in spontaneous speech in normal subjects is the soft onset, and it may be considered as the "physiological" onset. It starts from an immobile narrow glottal slit crossed by a continuous airflow, and then a few oscillations (even a single one in some cases) precede the first glottal closure. It is a transient event, during which the acting forces, lung pressure, intraglottal pressure, myoelastic tension of the vocal fold (VF) oscillator and inertance of the supraglottal vocal tract, interact to progressively reach the steady state of a sustained oscillation. Combined measurements of flow, area, and pressure provide a detailed qualitative and quantitative analysis of the intraglottal mechanical events at the precise moment of starting oscillation in a physiological (soft or soft/breathy) onset. Our in vivo measurements of airflow and glottal area show that the very first oscillation occurs exactly at the time when turbulence appears at the level of the glottal narrowing, ie, when the Reynolds number reaches its critical value. The turbulence may be assumed to trigger an oscillator consisting in the ensemble of the VFs and the air of the vocal tract, which is known to be weakly damped. Turbulence can act here as an aspecific flick, triggering the oscillator, the frequency of oscillation being determined by its mechanical properties. Furthermore, the first noticeable glottal oscillations are sinusoidal: the VFs are neither steeply sucked together by a negative Bernoulli pressure, nor burst apart by the lung pressure. Our measurements show that, at the critical time, the rising positive lung pressure is balanced by the rising negative Bernoulli pressure generated by the transglottal flow.}, } @article {pmid31480452, year = {2019}, author = {Tsai, CD and Lin, XY}, title = {Experimental Study on Microfluidic Mixing with Different Zigzag Angles.}, journal = {Micromachines}, volume = {10}, number = {9}, pages = {}, pmid = {31480452}, issn = {2072-666X}, abstract = {This paper presents experimental investigations of passive mixing in a microfluidic channel with different zigzag angles. Zigzag channel is commonly used for microfluidic mixing because it does not need an additional control unit and can be easily implemented in a lab-on-a-chip system. In this work, microfluidic channels with six different zigzag angles, from θ = 0° to θ = 75°, are tested under ten different flow rates corresponding to Reynolds number from 0.309 to 309. Two colored liquids are mixed with the zigzag channels and mixing performance is evaluated based on the color of the pixels on the region of interest from captured images. According to the results, we found that the mixing performance is almost independent of the zigzag angle in the low-speed regime where its Reynolds number is less than 4. The mixing became very much depending on the zigzag angle in the high-speed regime where its Reynolds number is greater than 100. Microfluidic mixing is needed for Lab-on-a-chip applications in both low flow speed, such as medium perfusion for cell culture, and high flow speed, such as high-speed sensing on a point-of-care device. This work is aimed to provide practical information on zigzag mixing for chip design and applications.}, } @article {pmid31473843, year = {2020}, author = {Waheed, W and Alazzam, A and Al-Khateeb, AN and Abu-Nada, E}, title = {Dissipative particle dynamics for modeling micro-objects in microfluidics: application to dielectrophoresis.}, journal = {Biomechanics and modeling in mechanobiology}, volume = {19}, number = {1}, pages = {389-400}, doi = {10.1007/s10237-019-01216-3}, pmid = {31473843}, issn = {1617-7940}, mesh = {*Algorithms ; Animals ; *Electrophoresis ; Erythrocytes/physiology ; Humans ; *Microfluidics ; *Models, Theoretical ; }, abstract = {The dissipative particle dynamics (DPD) technique is employed to model the trajectories of micro-objects in a practical microfluidic device. The simulation approach is first developed using an in-house Fortran code to model Stokes flow at Reynolds number of 0.01. The extremely low Reynolds number is achieved by adjusting the DPD parameters, such as force coefficients, thermal energies of the particles, and time steps. After matching the numerical flow profile with the analytical results, the technique is developed further to simulate the deflection of micro-objects under the effect of a deflecting external force in a rectangular microchannel. A mapping algorithm is introduced to establish the scaling relationship for the deflecting force between the physical device and the DPD domain. Dielectrophoresis is studied as a case study for the deflecting force, and the trajectory of a single red blood cell under the influence of the dielectrophoretic force is simulated. The device is fabricated using standard microfabrication techniques, and the experiments involving a dilute sample of red blood cells are performed at two different cases of the actuation voltage. Good agreement between the numerical and experimental results is achieved.}, } @article {pmid31473190, year = {2019}, author = {Chaput, R and Majoris, JE and Buston, PM and Paris, CB}, title = {Hydrodynamic and biological constraints on group cohesion in plankton.}, journal = {Journal of theoretical biology}, volume = {482}, number = {}, pages = {109987}, doi = {10.1016/j.jtbi.2019.08.018}, pmid = {31473190}, issn = {1095-8541}, mesh = {Animals ; Behavior, Animal/*physiology ; Coral Reefs ; *Ecosystem ; Environment ; Fishes/growth & development/*physiology ; *Hydrodynamics ; Larva ; *Mass Behavior ; Plankton/*physiology ; Social Behavior ; Swimming/physiology ; Viscosity ; }, abstract = {The dynamics of plankton in the ocean are determined by biophysical interactions. Although physics and biotic behaviors are known to influence the observed patchiness of planktonic populations, it is still unclear how much, and if, group behavior contributes to this biophysical interaction. Here, we demonstrate how simple rules of behavior can enhance or inhibit active group cohesion in plankton in a turbulent environment. In this study, we used coral-reef fish larvae as a model to investigate the interaction between microscale turbulence and planktonic organisms. We synthesized available information on the swimming speeds and sizes of reef fish larvae, and developed a set of equations to investigate the effects of viscosity and turbulence on larvae dispersion. We then calculated the critical dispersion rates for three different swimming strategies - cruise, random-walk, and pause-travel - to determine which strategies could facilitate group cohesion during dispersal. Our results indicate that swimming strategies and migration to low-turbulence regions are the key to maintaining group cohesion, suggesting that many reef fish species have the potential to remain together, from hatching to settlement. In addition, larvae might change their swimming strategies to maintain group cohesion, depending on environmental conditions and/or their ontogenic stage. This study provides a better understanding of the hydrodynamic and biological constraints on group formation and cohesion in planktonic organisms, and reveals a wide range of conditions under which group formation may occur.}, } @article {pmid31472558, year = {2019}, author = {Zhang, C and Sanjose, M and Moreau, S}, title = {Aeolian noise of a cylinder in the critical regime.}, journal = {The Journal of the Acoustical Society of America}, volume = {146}, number = {2}, pages = {1404}, doi = {10.1121/1.5122185}, pmid = {31472558}, issn = {1520-8524}, abstract = {The noise from the flow around a circular cylinder in the critical regime is investigated by combining a compressible wall-resolved large eddy simulation and a Ffowcs Williams and Hawkings analogy on solid and porous surfaces. This simulation is validated by comparing several flow parameters with previous experimental and numerical data in the same flow regime. Significantly reduced drag and increased vortex shedding Strouhal number (0.33) are observed. Two slightly asymmetric laminar separation bubbles (LSBs) on the cylinder surface at about 100° are shown to trigger turbulence through Kelvin-Helmholtz (KH) shear-layer instability. The latter contributes to a narrowband hump in the wall-pressure fluctuations with a tone at a Strouhal number of 27, which can be as intense as the dominant vortex shedding tone. The ratio of the corresponding Strouhal numbers is consistent with the proposed variation with the Reynolds number by Prasad and Williamson [(1997). J. Fluid Mech. 333, 375-402]. The dominant far-field noise source is still the vortex shedding dipolar tone radiating mostly at 90°. Yet, two additional broadband noise sources are evidenced in the wake, one at low frequencies caused by the wake oscillation and another one at high frequencies caused by the KH instability mostly directly toward the LSB locations.}, } @article {pmid31462974, year = {2019}, author = {Gholampour, S and Bahmani, M and Shariati, A}, title = {Comparing the Efficiency of Two Treatment Methods of Hydrocephalus: Shunt Implantation and Endoscopic Third Ventriculostomy.}, journal = {Basic and clinical neuroscience}, volume = {10}, number = {3}, pages = {185-198}, pmid = {31462974}, issn = {2008-126X}, abstract = {INTRODUCTION: Hydrocephalus is one of the most common diseases in children, and its treatment requires brain operation. However, the pathophysiology of the disease is very complicated and still unknown.

METHODS: Endoscopic Third Ventriculostomy (ETV) and Ventriculoperitoneal Shunt (VPS) implantation are among the common treatments of hydrocephalus. In this study, Cerebrospinal Fluid (CSF) hydrodynamic parameters and efficiency of the treatment methods were compared with numerical simulation and clinical follow-up of the treated patients.

RESULTS: Studies have shown that in patients under 19 years of age suffering from hydrocephalus related to a Posterior Fossa Brain Tumor (PFBT), the cumulative failure rate was 21% and 29% in ETV and VPS operation, respectively. At first, the ETV survival curve shows a sharp decrease and after two months it gets fixed while VPS curve makes a gradual decrease and reaches to a level lower than ETV curve after 5.7 months. Post-operative complications in ETV and VPS methods are 17% and 31%, respectively. In infants younger than 12 months with hydrocephalus due to congenital Aqueduct Stenosis (AS), and also in the elderly patients suffering from Normal Pressure Hydrocephalus (NPH), ETV is a better treatment option. Computer simulations show that the maximum CSF pressure is the most reliable hydrodynamic index for the evaluation of the treatment efficacy in these patients. After treatment by ETV and shunt methods, CSF pressure decreases about 9 and 5.3 times, respectively and 2.5 years after shunt implantation, this number returns to normal range.

CONCLUSION: In infants with hydrocephalus, initial treatment by ETV was more reasonable than implanting the shunt. In adult with hydrocephalus, the initial failure in ETV occurred sooner compared to shunt therapy; however, ETV was more efficient.}, } @article {pmid31446522, year = {2020}, author = {Foo, YY and Pant, S and Tay, HS and Imangali, N and Chen, N and Winkler, C and Yap, CH}, title = {4D modelling of fluid mechanics in the zebrafish embryonic heart.}, journal = {Biomechanics and modeling in mechanobiology}, volume = {19}, number = {1}, pages = {221-232}, doi = {10.1007/s10237-019-01205-6}, pmid = {31446522}, issn = {1617-7940}, mesh = {Algorithms ; Animals ; Blood Flow Velocity ; Computer Simulation ; Embryo, Nonmammalian/*physiology ; Heart/diagnostic imaging/*embryology/*physiology ; *Hydrodynamics ; *Models, Cardiovascular ; Myocardial Contraction ; Ventricular Function ; Zebrafish/*embryology ; }, abstract = {Abnormal blood flow mechanics can result in pathological heart malformation, underlining the importance of understanding embryonic cardiac fluid mechanics. In the current study, we performed image-based computational fluid dynamics simulation of the zebrafish embryonic heart ventricles and characterized flow mechanics, organ dynamics, and energy dynamics in detail. 4D scans of 5 days post-fertilization embryonic hearts with GFP-labelled myocardium were acquired using line-scan focal modulation microscopy. This revealed that the zebrafish hearts exhibited a wave-like contractile/relaxation motion from the inlet to the outlet during both systole and diastole, which we showed to be an energy efficient configuration. No impedance pumping effects of pressure and velocity waves were observed. Due to its tube-like configuration, inflow velocities were higher near the inlet and smaller at the outlet and vice versa for outflow velocities. This resulted in an interesting spatial wall shear stress (WSS) pattern where WSS waveforms near the inlet and those near the outlet were out of phase. There was large spatial variability in WSS magnitudes. Peak WSS was in the range of 47.5-130 dyne/cm[2] at the inflow and outflow tracts, but were much smaller, in the range of 4-11 dyne/cm[2], in the mid-ventricular segment. Due to very low Reynolds number and the highly viscous environment, intraventricular pressure gradients were high, suggesting substantial energy losses of flow through the heart.}, } @article {pmid31431815, year = {2019}, author = {Rackus, DG and Riedel-Kruse, IH and Pamme, N}, title = {"Learning on a chip:" Microfluidics for formal and informal science education.}, journal = {Biomicrofluidics}, volume = {13}, number = {4}, pages = {041501}, pmid = {31431815}, issn = {1932-1058}, abstract = {Microfluidics is a technique for the handling of small volumes of liquids on the order of picoliters to nanoliters and has impact for miniaturized biomedical science and fundamental research. Because of its multi- and interdisciplinary nature (i.e., combining the fields of biology, chemistry, physics, and engineering), microfluidics offers much potential for educational applications, both at the university level as well as primary and secondary education. Microfluidics is also an ideal "tool" to enthuse and educate members of the general public about the interdisciplinary aspects of modern sciences, including concepts of science, technology, engineering, and mathematics subjects such as (bio)engineering, chemistry, and biomedical sciences. Here, we provide an overview of approaches that have been taken to make microfluidics accessible for formal and informal learning. We also point out future avenues and desired developments. At the extreme ends, we can distinguish between projects that teach how to build microfluidic devices vs projects that make various microscopic phenomena (e.g., low Reynolds number hydrodynamics, microbiology) accessible to learners and the general public. Microfluidics also enables educators to make experiments low-cost and scalable, and thereby widely accessible. Our goal for this review is to assist academic researchers working in the field of microfluidics and lab-on-a-chip technologies as well as educators with translating research from the laboratory into the lecture hall, teaching laboratory, or public sphere.}, } @article {pmid31421603, year = {2019}, author = {Hayat, T and Aslam, N and Ijaz Khan, M and Imran Khan, M and Alsaedi, A}, title = {MHD peristaltic motion of Johnson-Segalman fluid in an inclined channel subject to radiative flux and convective boundary conditions.}, journal = {Computer methods and programs in biomedicine}, volume = {180}, number = {}, pages = {104999}, doi = {10.1016/j.cmpb.2019.104999}, pmid = {31421603}, issn = {1872-7565}, mesh = {Algorithms ; Body Fluids/physiology ; Elasticity ; Humans ; *Hydrodynamics ; *Models, Biological ; Peristalsis/*physiology ; Rheology ; }, abstract = {BACKGROUND: In abundant of a digestive tract like smooth muscle tissue, human gastrointestinal tract contracts in sequence to generate a peristaltic wave, which pushes a food along the tract. The peristaltic motion contains circular relaxation smooth muscles, then their shrinkage (contraction) behind the chewed material to keep it from moving backward, then longitudinal contraction to shove it ahead. Therefore, we have conducted a theoretical investigation on peristaltic transport in flow of Johnson-Segalman liquid subject to inclined magnetic field. The energy equation is developed with extra heat transport assumptions like thermal radiative flux and dissipation. The channel walls are heated convectively.

METHODS: Dimensionless problems subject to small Reynolds number and long wavelength are tackled. Perturbation technique is implemented for small Weissenberg number.

RESULTS: The physical importance of involved parameters that directly affect the heat transfer rate temperature and velocity. The pertinent variables are amplitude ratio, wave number, Reynolds number, Hartman number, Prandtl number, Weissenberg number, thermal radiative heat flux, Biot number, elasticity variables and Froude number are graphically discussed. The obtained outcome shows that the velocity field increases against higher values of elasticity variables but velocity the material decays through higher fluid parameter. Temperature field declines through higher Hartman number. Furthermore, it is also examined that the heat transfer rate decays against rising Hartman number.

CONCLUSIONS: The impact of complaint walls on radiative peristaltic transport of Johnson-Segalman liquid in symmetric channel subject to inclined angle. The influence of Johnson-Segalman variable on the velocity field shows decreasing behavior. Velocity also declines against larger Hartman number. Temperature and heat transfer rate boosts through rising values of E1 E2 while decays versus larger E3. Furthermore, reduction in heat transfer coefficient is observed when the values of α and Br are increased.}, } @article {pmid31421600, year = {2019}, author = {Tanveer, A and Khan, M and Salahuddin, T and Malik, MY}, title = {Numerical simulation of electroosmosis regulated peristaltic transport of Bingham nanofluid.}, journal = {Computer methods and programs in biomedicine}, volume = {180}, number = {}, pages = {105005}, doi = {10.1016/j.cmpb.2019.105005}, pmid = {31421600}, issn = {1872-7565}, mesh = {*Electroosmosis ; Hydrodynamics ; Models, Statistical ; *Nanoparticles ; Peristalsis/*physiology ; Rheology ; Solutions/chemistry ; Thermal Conductivity ; }, abstract = {The effects of slip condition and Joule heating on the peristaltic flow of Bingham nanofluid are investigated. The flow is taken in a porous channel with elastic walls. Mathematical formulation is presented under the assumption of long wavelength and small Reynolds number. The transformed equations for the flow are solved to seek values for the nanoparticles velocity, concentration and temperature along the channel length. Graphs are plotted to evaluate the behavior of various physical parameters on flow quantities in both slip and no-slip cases. The main features of the physical parameters are highlighted on the inclined non uniform channel. The results show an increment in velocity with rise in inclination and porosity while it reduces with magnetic field. Moreover, nanofluid favors the heat transfer and decline the concentration.}, } @article {pmid31417749, year = {2019}, author = {Lambert, WB and Stanek, MJ and Gurka, R and Hackett, EE}, title = {Leading-edge vortices over swept-back wings with varying sweep geometries.}, journal = {Royal Society open science}, volume = {6}, number = {7}, pages = {190514}, pmid = {31417749}, issn = {2054-5703}, abstract = {Micro air vehicles are used in a myriad of applications, such as transportation and surveying. Their performance can be improved through the study of wing designs and lift generation techniques including leading-edge vortices (LEVs). Observation of natural fliers, e.g. birds and bats, has shown that LEVs are a major contributor to lift during flapping flight, and the common swift (Apus apus) has been observed to generate LEVs during gliding flight. We hypothesize that nonlinear swept-back wings generate a vortex in the leading-edge region, which can augment the lift in a similar manner to linear swept-back wings (i.e. delta wing) during gliding flight. Particle image velocimetry experiments were performed in a water flume to compare flow over two wing geometries: one with a nonlinear sweep (swift-like wing) and one with a linear sweep (delta wing). Experiments were performed at three spanwise planes and three angles of attack at a chord-based Reynolds number of 26 000. Streamlines, vorticity, swirling strength, and Q-criterion were used to identify LEVs. The results show similar LEV characteristics for delta and swift-like wing geometries. These similarities suggest that sweep geometries other than a linear sweep (i.e. delta wing) are capable of creating LEVs during gliding flight.}, } @article {pmid31411455, year = {2020}, author = {Brown, AI and Sivak, DA}, title = {Theory of Nonequilibrium Free Energy Transduction by Molecular Machines.}, journal = {Chemical reviews}, volume = {120}, number = {1}, pages = {434-459}, doi = {10.1021/acs.chemrev.9b00254}, pmid = {31411455}, issn = {1520-6890}, abstract = {Biomolecular machines are protein complexes that convert between different forms of free energy. They are utilized in nature to accomplish many cellular tasks. As isothermal nonequilibrium stochastic objects at low Reynolds number, they face a distinct set of challenges compared with more familiar human-engineered macroscopic machines. Here we review central questions in their performance as free energy transducers, outline theoretical and modeling approaches to understand these questions, identify both physical limits on their operational characteristics and design principles for improving performance, and discuss emerging areas of research.}, } @article {pmid31406979, year = {2019}, author = {Berg, O and Singh, K and Hall, MR and Schwaner, MJ and Müller, UK}, title = {Thermodynamics of the Bladderwort Feeding Strike-Suction Power from Elastic Energy Storage.}, journal = {Integrative and comparative biology}, volume = {59}, number = {6}, pages = {1597-1608}, doi = {10.1093/icb/icz144}, pmid = {31406979}, issn = {1557-7023}, mesh = {Biomechanical Phenomena ; Energy Transfer/*physiology ; *Food Chain ; Lamiales/*physiology ; Thermodynamics ; }, abstract = {The carnivorous plant bladderwort exemplifies the use of accumulated elastic energy to power motion: respiration-driven pumps slowly load the walls of its suction traps with elastic energy (∼1 h). During a feeding strike, this energy is released suddenly to accelerate water (∼1 ms). However, due to the traps' small size and concomitant low Reynolds number, a significant fraction of the stored energy may be dissipated as viscous friction. Such losses and the mechanical reversibility of Stokes flow are thought to degrade the feeding success of other suction feeders in this size range, such as larval fish. In contrast, triggered bladderwort traps are generally successful. By mapping the energy budget of a bladderwort feeding strike, we illustrate how this smallest of suction feeders can perform like an adult fish.}, } @article {pmid31394810, year = {2019}, author = {Alazzam, A and Al-Khaleel, M and Riahi, MK and Mathew, B and Gawanmeh, A and Nerguizian, V}, title = {Dielectrophoresis Multipath Focusing of Microparticles through Perforated Electrodes in Microfluidic Channels.}, journal = {Biosensors}, volume = {9}, number = {3}, pages = {}, pmid = {31394810}, issn = {2079-6374}, mesh = {Biosensing Techniques ; Electrodes ; Electrophoresis/methods ; Microfluidics/instrumentation/*methods ; *Models, Theoretical ; Particle Size ; Polystyrenes/analysis ; Silicon Dioxide/analysis ; }, abstract = {This paper presents focusing of microparticles in multiple paths within the direction of the flow using dielectrophoresis. The focusing of microparticles is realized through partially perforated electrodes within the microchannel. A continuous electrode on the top surface of the microchannel is considered, while the bottom side is made of a circular meshed perforated electrode. For the mathematical model of this microfluidic channel, inertia, buoyancy, drag and dielectrophoretic forces are brought up in the motion equation of the microparticles. The dielectrophoretic force is accounted for through a finite element discretization taking into account the perforated 3D geometry within the microchannel. An ordinary differential equation is solved to track the trajectories of the microparticles. For the case of continuous electrodes using the same mathematical model, the numerical simulation shows a very good agreement with the experiments, and this confirms the validation of focusing of microparticles within the proposed perforated electrode microchannel. Microparticles of silicon dioxide and polystyrene are used for this analysis. Their initial positions and radius, the Reynolds number, and the radius of the pore in perforated electrodes mainly conduct microparticles trajectories. Moreover, the radius of the pore of perforated electrode is the dominant factor in the steady state levitation height.}, } @article {pmid31386484, year = {2019}, author = {Samanta, T and Tian, H and Nakariakov, VM}, title = {Evidence for Vortex Shedding in the Sun's Hot Corona.}, journal = {Physical review letters}, volume = {123}, number = {3}, pages = {035102}, doi = {10.1103/PhysRevLett.123.035102}, pmid = {31386484}, issn = {1079-7114}, abstract = {Vortex shedding is an oscillating flow that is commonly observed in fluids due to the presence of a blunt body in a flowing medium. Numerical simulations have shown that the phenomenon of vortex shedding could also develop in the magnetohydrodynamic (MHD) domain. The dimensionless Strouhal number, the ratio of the blunt body diameter to the product of the period of vortex shedding and the speed of a flowing medium, is a robust indicator for vortex shedding, and, generally of the order of 0.2 for a wide range of Reynolds number. Using an observation from the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory, we report a wavelike or oscillating plasma flow propagating upward against the Sun's gravitational force. A newly formed shrinking loop in the postflare region possibly generates the oscillation of the upflow in the wake of the hot and dense loop through vortex shedding. The computed Strouhal number is consistent with the prediction from previous MHD simulations. Our observation suggests the possibility of vortex shedding in the solar corona.}, } @article {pmid31382385, year = {2019}, author = {Yu, X and Li, Y and Liu, Y and Yang, Y and Wu, Y}, title = {Flow Patterns of Viscoelastic Fracture Fluids in Porous Media: Influence of Pore-Throat Structures.}, journal = {Polymers}, volume = {11}, number = {8}, pages = {}, pmid = {31382385}, issn = {2073-4360}, abstract = {Viscoelastic surfactant (VES) fluid and hydrolyzed polyacryamide (HPAM) solution are two of the most common fracturing fluids used in the hydraulic fracturing development of unconventional reservoirs. The filtration of fracturing fluids in porous media is mainly determined by the flow patterns in pore-throat structures. In this paper, three different microdevices analogue of porous media allow access to a large range of Deborah number (De) and concomitantly low Reynolds number (Re). Continuous pore-throat structures were applied to study the feedback effect of downstream structure on upstream flow of VES fluid and HPAM solution with Deborah (De) number from 1.11 to 146.4. In the infinite straight channel, flow patterns between VES fluids and HPAM solution were similar. However, as pore length shortened to 800 μm, flow field of VES fluid exhibited the triangle shape with double-peaks velocity patterns. The flow field of HPAM solution presented stable and centralized streamlines when Re was larger than 4.29 × 10[-2]. Additionally, when the pore length was further shortened to 400 μm, double-peaks velocity patterns were vanished for VES fluid and the stable convergent flow characteristic of HPAM solution was observed with all flow rates.}, } @article {pmid31380864, year = {2019}, author = {Feng, X and Ren, Y and Hou, L and Tao, Y and Jiang, T and Li, W and Jiang, H}, title = {Tri-fluid mixing in a microchannel for nanoparticle synthesis.}, journal = {Lab on a chip}, volume = {19}, number = {17}, pages = {2936-2946}, doi = {10.1039/c9lc00425d}, pmid = {31380864}, issn = {1473-0189}, abstract = {It is becoming more difficult to use bulk mixing and bi-fluid micromixing in multi-step continuous-flow reactions, multicomponent reactions, and nanoparticle synthesis because they typically involve multiple reactants. To date, most micromixing studies, both passive and active, have focused on how to efficiently mix two fluids, while micromixing of three or more fluids together (multi-fluid mixing) has been rarely explored. This study is the first on tri-fluid mixing in microchannels. We investigated tri-fluid mixing in three microchannel models: a straight channel, a classical staggered herringbone mixing (SHM) channel, and a three-dimensional (3D) X-crossing microchannel. Numerical simulations and experiments were jointly conducted. A two-step experimental process was performed to determine the tri-fluid mixing efficiencies of these microchannels. We found that the SHM cannot significantly enhance mixing of three streams especially for a Reynolds number (Re) higher than 10. However, the 3D X-crossing channel based on splitting-and-recombination (SAR) showed effective tri-mixing performance over a wide Re range up to 275 (with a corresponding flow rate of 1972.5 μL min[-1]), thereby enabling high microchannel throughput. Furthermore, this tri-fluid micromixing process was used to synthesize a kind of Si-based nanoparticle. This achieved a narrower particle size distribution than traditional bulk mixing. Therefore, SAR-based tri-fluid mixing is an alternative for chemical and biochemical reactions where three reactants need to be mixed.}, } @article {pmid31374925, year = {2019}, author = {Henein, C and Awwad, S and Ibeanu, N and Vlatakis, S and Brocchini, S and Tee Khaw, P and Bouremel, Y}, title = {Hydrodynamics of Intravitreal Injections into Liquid Vitreous Substitutes.}, journal = {Pharmaceutics}, volume = {11}, number = {8}, pages = {}, pmid = {31374925}, issn = {1999-4923}, abstract = {Intravitreal injections have become the cornerstone of retinal care and one of the most commonly performed procedures across all medical specialties. The impact of hydrodynamic forces of intravitreal solutions when injected into vitreous or vitreous substitutes has not been well described. While computational models do exist, they tend to underestimate the starting surface area of an injected bolus of a drug. Here, we report the dispersion profile of a dye bolus (50 µL) injected into different vitreous substitutes of varying viscosities, surface tensions, and volumetric densities. A novel 3D printed in vitro model of the vitreous cavity of the eye was designed to visualize the dispersion profile of solutions when injected into the following vitreous substitutes-balanced salt solution (BSS), sodium hyaluronate (HA), and silicone oils (SO)-using a 30G needle with a Reynolds number (Re) for injection ranging from approximately 189 to 677. Larger bolus surface areas were associated with faster injection speeds, lower viscosity of vitreous substitutes, and smaller difference in interfacial surface tensions. Boluses exhibited buoyancy when injected into standard S1000. The hydrodynamic properties of liquid vitreous substitutes influence the initial injected bolus dispersion profile and should be taken into account when simulating drug dispersion following intravitreal injection at a preclinical stage of development, to better inform formulations and performance.}, } @article {pmid31370481, year = {2019}, author = {Gvozdić, B and Dung, OY and van Gils, DPM and Bruggert, GH and Alméras, E and Sun, C and Lohse, D and Huisman, SG}, title = {Twente mass and heat transfer water tunnel: Temperature controlled turbulent multiphase channel flow with heat and mass transfer.}, journal = {The Review of scientific instruments}, volume = {90}, number = {7}, pages = {075117}, doi = {10.1063/1.5092967}, pmid = {31370481}, issn = {1089-7623}, abstract = {A new vertical water tunnel with global temperature control and the possibility for bubble and local heat and mass injection has been designed and constructed. The new facility offers the possibility to accurately study heat and mass transfer in turbulent multiphase flow (gas volume fraction up to 8%) with a Reynolds-number range from 1.5 × 10[4] to 3 × 10[5] in the case of water at room temperature. The tunnel is made of high-grade stainless steel permitting the use of salt solutions in excess of 15% mass fraction. The tunnel has a volume of 300 l. The tunnel has three interchangeable measurement sections of 1 m height but with different cross sections (0.3 × 0.04 m[2], 0.3 × 0.06 m[2], and 0.3 × 0.08 m[2]). The glass vertical measurement sections allow for optical access to the flow, enabling techniques such as laser Doppler anemometry, particle image velocimetry, particle tracking velocimetry, and laser-induced fluorescent imaging. Local sensors can be introduced from the top and can be traversed using a built-in traverse system, allowing, for example, local temperature, hot-wire, or local phase measurements. Combined with simultaneous velocity measurements, the local heat flux in single phase and two phase turbulent flows can thus be studied quantitatively and precisely.}, } @article {pmid31369336, year = {2019}, author = {O'Neill, G and Tolley, NS}, title = {The complexities of nasal airflow: theory and practice.}, journal = {Journal of applied physiology (Bethesda, Md. : 1985)}, volume = {127}, number = {5}, pages = {1215-1223}, doi = {10.1152/japplphysiol.01118.2018}, pmid = {31369336}, issn = {1522-1601}, mesh = {Humans ; *Inhalation ; *Models, Biological ; Turbinates/*physiology ; }, abstract = {The objective of this study was to investigate the effects of nasal valve area, valve stiffness, and turbinate region cross-sectional area on airflow rate, nasal resistance, flow limitation, and inspiratory "hysteresis" by the use of a mathematical model of nasal airflow. The model of O'Neill and Tolley (Clin Otolaryngol Allied Sci 13: 273-277, 1988) describing the effects of valve area and stiffness on the nasal pressure-flow relationship was improved by the incorporation of additional terms involving 1) airflow through the turbinate region, 2) the dependence of the flow coefficients for the valve and turbinate region on the Reynolds number, and 3) effects of unsteady flow. The model was found to provide a good fit for normal values for nasal resistance and for pressure-flow curves reported in the literature for both congested and decongested states. Also, by showing the relative contribution of the nasal valve and turbinate region to nasal resistance, the model sheds light in explaining the generally poor correlation between nasal resistance measurements and the results from acoustic rhinometry. Furthermore, by proposing different flow conditions for the acceleration and deceleration phases of inspiration, the model produces an inspiratory loop (commonly referred to as hysteresis) consistent with those reported in the literature. With simulation of nasal flaring, the magnitude of the loop, the nasal resistance, and flow limitation all show change similar to that observed in the experimental results.NEW & NOTEWORTHY The present model provides considerable insight into some difficult conundrums in both clinical and technical aspects of nasal airflow. Also, the description of nasal airflow mechanics based on the Hagen-Poiseuille equation and Reynolds laminar-turbulent transition in long straight tubes, which has figured prominently in medical textbooks and journal articles for many years, is shown to be seriously in error at a fundamental level.}, } @article {pmid31363000, year = {2019}, author = {R Ferreira, R and Fukui, H and Chow, R and Vilfan, A and Vermot, J}, title = {The cilium as a force sensor-myth versus reality.}, journal = {Journal of cell science}, volume = {132}, number = {14}, pages = {}, doi = {10.1242/jcs.213496}, pmid = {31363000}, issn = {1477-9137}, mesh = {Animals ; Biomechanical Phenomena ; Cilia/*physiology ; Humans ; Mechanotransduction, Cellular ; Organ Specificity ; Rheology ; }, abstract = {Cells need to sense their mechanical environment during the growth of developing tissues and maintenance of adult tissues. The concept of force-sensing mechanisms that act through cell-cell and cell-matrix adhesions is now well established and accepted. Additionally, it is widely believed that force sensing can be mediated through cilia. Yet, this hypothesis is still debated. By using primary cilia sensing as a paradigm, we describe the physical requirements for cilium-mediated mechanical sensing and discuss the different hypotheses of how this could work. We review the different mechanosensitive channels within the cilium, their potential mode of action and their biological implications. In addition, we describe the biological contexts in which cilia are acting - in particular, the left-right organizer - and discuss the challenges to discriminate between cilium-mediated chemosensitivity and mechanosensitivity. Throughout, we provide perspectives on how quantitative analysis and physics-based arguments might help to better understand the biological mechanisms by which cells use cilia to probe their mechanical environment.}, } @article {pmid31359287, year = {2020}, author = {Jain, K}, title = {Transition to turbulence in an oscillatory flow through stenosis.}, journal = {Biomechanics and modeling in mechanobiology}, volume = {19}, number = {1}, pages = {113-131}, doi = {10.1007/s10237-019-01199-1}, pmid = {31359287}, issn = {1617-7940}, mesh = {Blood Flow Velocity ; Computer Simulation ; Constriction, Pathologic ; Numerical Analysis, Computer-Assisted ; Pressure ; *Rheology ; }, abstract = {Onset of flow transition in a sinusoidally oscillating flow through a rigid, constant area circular pipe with a smooth sinusoidal obstruction in the center of the pipe is studied by performing direct numerical simulations, with resolutions close to the Kolmogorov microscales. The studied pipe is stenosed in the center with a 75% reduction in area in two distinct configurations-one that is symmetric to the axis of the parent pipe and the other that is offset by 0.05 diameters to introduce an eccentricity, which disturbs the flow thereby triggering the onset of flow transition. The critical Reynolds number at which the flow transitions to turbulence for a zero-mean oscillatory flow through a stenosis is shown to be nearly tripled in comparison with studies of pulsating unidirectional flow through the same stenosis. The onset of transition is further explored with three different flow pulsation frequencies resulting in a total of 90 simulations conducted on a supercomputer. It is found that the critical Reynolds number at which the oscillatory flow transitions is not affected by the pulsation frequencies. The locations of flow breakdown and re-stabilization post-stenosis are, however, respectively shifted closer to the stenosis throat with increasing pulsation frequencies. The results show that oscillatory physiological flows, while more stable, exhibit fluctuations due to geometric complexity and have implications in studies of dispersion and solute transport in the cerebrospinal fluid flow and understanding of pathological conditions.}, } @article {pmid33267453, year = {2019}, author = {Ma, H and Duan, Z and Su, L and Ning, X and Bai, J and Lv, X}, title = {Fluid Flow and Entropy Generation Analysis of Al2O3-Water Nanofluid in Microchannel Plate Fin Heat Sinks.}, journal = {Entropy (Basel, Switzerland)}, volume = {21}, number = {8}, pages = {}, pmid = {33267453}, issn = {1099-4300}, abstract = {The flow in channels of microdevices is usually in the developing regime. Three-dimensional laminar flow characteristics of a nanofluid in microchannel plate fin heat sinks are investigated numerically in this paper. Deionized water and Al2O3-water nanofluid are employed as the cooling fluid in our work. The effects of the Reynolds number (100 < Re < 1000), channel aspect ratio (0 < ε < 1), and nanoparticle volume fraction (0.5% < Φ < 5%) on pressure drop and entropy generation in microchannel plate fin heat sinks are examined in detail. Herein, the general expression of the entropy generation rate considering entrance effects is developed. The results revealed that the frictional entropy generation and pressure drop increase as nanoparticle volume fraction and Reynolds number increase, while decrease as the channel aspect ratio increases. When the nanoparticle volume fraction increases from 0 to 3% at Re = 500, the pressure drop of microchannel plate fin heat sinks with ε = 0.5 increases by 9%. It is demonstrated that the effect of the entrance region is crucial for evaluating the performance of microchannel plate fin heat sinks. The study may shed some light on the design and optimization of microchannel heat sinks.}, } @article {pmid31345119, year = {2020}, author = {Krishnam, U and Sharma, V and Jha, PK}, title = {The Reynolds number modulated low frequency dynamical modes of aqueous medium embedded spherical virus and implications to detecting and killing viruses.}, journal = {Journal of biomolecular structure & dynamics}, volume = {38}, number = {10}, pages = {3123-3129}, doi = {10.1080/07391102.2019.1648320}, pmid = {31345119}, issn = {1538-0254}, mesh = {*Viruses ; Water ; }, } @article {pmid31342935, year = {2019}, author = {Liu, G and Xue, Q and Zheng, X}, title = {Phase-difference on seal whisker surface induces hairpin vortices in the wake to suppress force oscillation.}, journal = {Bioinspiration & biomimetics}, volume = {14}, number = {6}, pages = {066001}, doi = {10.1088/1748-3190/ab34fe}, pmid = {31342935}, issn = {1748-3190}, mesh = {Animals ; Biomechanical Phenomena ; Biomimetics/*instrumentation ; Hydrodynamics ; Models, Biological ; Phoca/*physiology ; Vibrissae/*physiology ; }, abstract = {Seals are able to use their uniquely shaped whiskers to track hydrodynamic trails generated 30 s ago and detect hydrodynamic velocities as low as 245 [Formula: see text]m s[-1]. The high sensibility has long thought to be related to the wavy shape of the whiskers. This work revisited the hydrodynamics of a seal whisker model in a uniform flow, and discovered a new mechanism of seal whiskers in reducing self-induced noises, which is different from the long thought-of effect of the wavy shape. It was reported that the major and minor axes of the elliptical cross-sections of seal whisker are out of phase by approximately 180 degrees. Three-dimensional numerical simulations of laminar flow (Reynolds number range: 150-500) around seal-whisker-like cylinders were performed to examine the effect of the phase-difference on hydrodynamic forces and wake structures. It was found that the phase-difference induced hairpin vortices in the wake over a wide range of geometric and flow parameters (wavelength, wavy amplitude and Reynolds number), therefore substantially reducing lift-oscillations and self-induced noises. The formation mechanism of the hairpin vortices was analyzed and is discussed in details. The results provide valuable insights into an innovative vibration reduction and hydrodynamic sensing mechanism.}, } @article {pmid31330717, year = {2019}, author = {Jian, X and Zhang, W and Deng, Q and Huang, Y}, title = {Turbulent lithosphere deformation in the Tibetan Plateau.}, journal = {Physical review. E}, volume = {99}, number = {6-1}, pages = {062122}, doi = {10.1103/PhysRevE.99.062122}, pmid = {31330717}, issn = {2470-0053}, abstract = {In this work, we show that the Tibetan Plateau deformation demonstrates turbulence-like statistics, e.g., spatial invariance across continuous scales. A dual-power-law behavior is evident to show the existence of two possible conservation laws for the enstrophy-like cascade in the range 500≲r≲2000km and kinetic-energy-like cascade in the range 50≲r≲500km. The measured second-order structure-function scaling exponents ζ(2) are similar to their counterparts in the Fourier scaling exponents observed in the atmosphere, where in the latter case the earth's rotation is relevant. The turbulent statistics observed here for nearly zero-Reynolds-number flow can be interpreted by the geostrophic turbulence theory. Moreover, the intermittency correction is recognized with an intensity close to that of the hydrodynamic turbulence of high-Reynolds-number turbulent flows, implying a universal scaling feature of very different turbulent flows. Our results not only shed new light on the debate regarding the mechanism of the Tibetan Plateau deformation but also lead to new challenges for the geodynamic modeling using Newton or non-Newtonian models because the observed turbulence-like features have to be taken into account.}, } @article {pmid31318280, year = {2019}, author = {Dölger, J and Kiørboe, T and Andersen, A}, title = {Dense Dwarfs versus Gelatinous Giants: The Trade-Offs and Physiological Limits Determining the Body Plan of Planktonic Filter Feeders.}, journal = {The American naturalist}, volume = {194}, number = {2}, pages = {E30-E40}, doi = {10.1086/703656}, pmid = {31318280}, issn = {1537-5323}, mesh = {Animals ; Body Composition/*physiology ; Body Size ; Energy Metabolism ; Feeding Behavior/*physiology ; Models, Theoretical ; Predatory Behavior ; Zooplankton/*physiology ; }, abstract = {Most marine plankton have a high energy (carbon) density, but some are gelatinous with approximately 100 times more watery bodies. How do those distinctly different body plans emerge, and what are the trade-offs? We address this question by modeling the energy budget of planktonic filter feeders across life-forms, from micron-sized unicellular microbes such as choanoflagellates to centimeter-sized gelatinous tunicates such as salps. We find two equally successful strategies, one being small with high energy density (dense dwarf) and the other being large with low energy density (gelatinous giant). The constraint that forces large-but not small-filter feeders to be gelatinous is identified as a lower limit to the size-specific filter area, below which the energy costs lead to starvation. A further limit is found from the maximum size-specific motor force that restricts the access to optimum strategies. The quantified constraints are discussed in the context of other resource-acquisition strategies. We argue that interception feeding strategies can be accessed by large organisms only if they are gelatinous. On the other hand, organisms that use remote prey sensing do not need to be gelatinous, even if they are large.}, } @article {pmid31315935, year = {2019}, author = {Samson, JE and Miller, LA and Ray, D and Holzman, R and Shavit, U and Khatri, S}, title = {A novel mechanism of mixing by pulsing corals.}, journal = {The Journal of experimental biology}, volume = {222}, number = {Pt 15}, pages = {}, doi = {10.1242/jeb.192518}, pmid = {31315935}, issn = {1477-9145}, mesh = {Animals ; Anthozoa/*physiology ; *Hydrodynamics ; Models, Theoretical ; Rheology ; Video Recording ; Water Movements ; }, abstract = {The dynamic pulsation of xeniid corals is one of the most fascinating phenomena observed in coral reefs. We quantify for the first time the flow near the tentacles of these soft corals, the active pulsations of which are thought to enhance their symbionts' photosynthetic rates by up to an order of magnitude. These polyps are approximately 1 cm in diameter and pulse at frequencies between approximately 0.5 and 1 Hz. As a result, the frequency-based Reynolds number calculated using the tentacle length and pulse frequency is on the order of 10 and rapidly decays as with distance from the polyp. This introduces the question of how these corals minimize the reversibility of the flow and bring in new volumes of fluid during each pulse. We estimate the Péclet number of the bulk flow generated by the coral as being on the order of 100-1000 whereas the flow between the bristles of the tentacles is on the order of 10. This illustrates the importance of advective transport in removing oxygen waste. Flow measurements using particle image velocimetry reveal that the individual polyps generate a jet of water with positive vertical velocities that do not go below 0.1 cm s[-1] and with average volumetric flow rates of approximately 0.71 cm[3] s[-1] Our results show that there is nearly continual flow in the radial direction towards the polyp with only approximately 3.3% back flow. 3D numerical simulations uncover a region of slow mixing between the tentacles during expansion. We estimate that the average flow that moves through the bristles of the tentacles is approximately 0.03 cm s[-1] The combination of nearly continual flow towards the polyp, slow mixing between the bristles, and the subsequent ejection of this fluid volume into an upward jet ensures the polyp continually samples new water with sufficient time for exchange to occur.}, } @article {pmid31314164, year = {2019}, author = {Liao, P and Xing, L and Zhang, S and Sun, D}, title = {Magnetically Driven Undulatory Microswimmers Integrating Multiple Rigid Segments.}, journal = {Small (Weinheim an der Bergstrasse, Germany)}, volume = {15}, number = {36}, pages = {e1901197}, doi = {10.1002/smll.201901197}, pmid = {31314164}, issn = {1613-6829}, mesh = {Biosensing Techniques/methods ; Holography/methods ; Lasers ; Locomotion ; Microtechnology/*methods ; *Robotics ; }, abstract = {Mimicking biological locomotion strategies offers important possibilities and motivations for robot design and control methods. Among bioinspired microrobots, flexible microrobots exhibit remarkable efficiency and agility. These microrobots traditionally rely on soft material components to achieve undulatory propulsion, which may encounter challenges in design and manufacture including the complex fabrication processes and the interfacing of rigid and soft components. Herein, a bioinspired magnetically driven microswimmer that mimics the undulatory propulsive mechanism is proposed. The designed microswimmer consists of four rigid segments, and each segment is connected to the succeeding segment by joints. The microswimmer is fabricated integrally by 3D laser lithography without further assembly, thereby simplifying microrobot fabrication while enhancing structural integrity. Experimental results show that the microswimmer can successfully swim forward along guided directions via undulatory locomotion in the low Reynolds number (Re) regime. This work demonstrates for the first time that the flexible characteristic of microswimmers can be emulated by 3D structures with multiple rigid segments, which broadens possibilities in microrobot design. The proposed magnetically driven microswimmer can potentially be used in biomedical applications, such as medical diagnosis and treatment in precision medicine.}, } @article {pmid35519474, year = {2019}, author = {Peng, Y and Alsagri, AS and Afrand, M and Moradi, R}, title = {A numerical simulation for magnetohydrodynamic nanofluid flow and heat transfer in rotating horizontal annulus with thermal radiation.}, journal = {RSC advances}, volume = {9}, number = {39}, pages = {22185-22197}, pmid = {35519474}, issn = {2046-2069}, abstract = {The impact of an axial magnetic field on the heat transfer and nanofluid flow among two horizontal coaxial tubes in the presence of thermal radiation was considered in this study. The impact of viscous dissipation was also considered. The well-known KKL (Koo-Kleinsteuer-Li) model was applied to approximate the viscosity of the nanofluid and the effective thermal conductivity. Furthermore, proper transformations for the velocity and temperature were applied in this study to obtain a set of ODEs (ordinary differential equations) for basic equations governing the flow, heat and mass transfer. In addition, the 4th order Runge-Kutta (RK) numerical scheme was applied to solve the differential equations along with the associated boundary conditions. The impacts of different parameters, including Hartmann number, Reynolds number, radiation parameter and aspect ratio, on the heat transfer and flow features were studied. According to the results, the value of the Nusselt number increases with an increase in the radiation parameter, Hartmann number and aspect ratio and a decrease in the Reynolds number and Eckert number.}, } @article {pmid31300927, year = {2019}, author = {Hoell, C and Löwen, H and Menzel, AM and Daddi-Moussa-Ider, A}, title = {Creeping motion of a solid particle inside a spherical elastic cavity: II. Asymmetric motion.}, journal = {The European physical journal. E, Soft matter}, volume = {42}, number = {7}, pages = {89}, pmid = {31300927}, issn = {1292-895X}, abstract = {An analytical method is proposed for computing the low-Reynolds-number hydrodynamic mobility function of a small colloidal particle asymmetrically moving inside a large spherical elastic cavity, the membrane of which is endowed with resistance toward shear and bending. In conjunction with the results obtained in the first part (A. Daddi-Moussa-Ider, H. Löwen, S. Gekle, Eur. Phys. J. E 41, 104 (2018)), in which the axisymmetric motion normal to the surface of an elastic cavity is investigated, the general motion for an arbitrary force direction can now be addressed. The elastohydrodynamic problem is formulated and solved using the classic method of images through expressing the hydrodynamic flow fields as a multipole expansion involving higher-order derivatives of the free-space Green's function. In the quasi-steady limit, we demonstrate that the particle self-mobility function of a particle moving tangent to the surface of the cavity is larger than that predicted inside a rigid stationary cavity of equal size. This difference is justified by the fact that a stationary rigid cavity introduces additional hindrance to the translational motion of the encapsulated particle, resulting in a reduction of its hydrodynamic mobility. Furthermore, the motion of the cavity is investigated, revealing that the translational pair (composite) mobility, which linearly couples the velocity of the elastic cavity to the force exerted on the solid particle, is solely determined by membrane shear properties. Our analytical predictions are favorably compared with fully-resolved computer simulations based on a completed-double-layer boundary integral method.}, } @article {pmid31299253, year = {2019}, author = {Novelli, GL and Ferrari, LA and Vargas, GG and Loureiro, BV}, title = {A synergistic analysis of drag reduction on binary polymer mixtures containing guar gum.}, journal = {International journal of biological macromolecules}, volume = {137}, number = {}, pages = {1121-1129}, doi = {10.1016/j.ijbiomac.2019.07.042}, pmid = {31299253}, issn = {1879-0003}, mesh = {Acrylic Resins/*chemistry ; Feasibility Studies ; Galactans/*chemistry ; Mannans/*chemistry ; Molecular Weight ; *Motion ; Plant Gums/*chemistry ; Polyethylene Glycols/*chemistry ; Polysaccharides, Bacterial/chemistry ; Rheology ; Rotation ; Shear Strength ; }, abstract = {Drag reduction by the addition of polymer additives has been widely studied. However, there are only a few studies on binary polymer mixtures, here named blends. In this work, xanthan gum, polyacrylamide and poly(ethylene oxide) were associated with guar gum and drag reduction was used as a parameter to determine the synergistic interaction between polymers. The aim was to verify the relation of the synergy with the rigidity of the polymeric chains, the molecular weights and the magnitude of the molecular interactions between the studied polymers. To that end, several ratios of mixtures were tested at different Reynolds numbers in a rotational rheometer with double-gap concentric cylinders geometry. Finally, experiments were done to verify the behaviour of the blends over time at a fixed Reynolds number. From all these tests, it was documented that blends containing rigid chain polymers show positive synergism in the interaction in at least one of the ratios and that this interaction is more pronounced when the molecular weights are closer and intermolecular forces are stronger. It was also noted that, in general, blends are great substitutes for solutions containing only one type of polymer.}, } @article {pmid31294955, year = {2019}, author = {Mazinani, S and Al-Shimmery, A and Chew, YMJ and Mattia, D}, title = {3D Printed Fouling-Resistant Composite Membranes.}, journal = {ACS applied materials & interfaces}, volume = {11}, number = {29}, pages = {26373-26383}, doi = {10.1021/acsami.9b07764}, pmid = {31294955}, issn = {1944-8252}, abstract = {Fouling remains a long-standing unsolved problem that hinders the widespread use of membrane applications in industry. This article reports the use of numerical simulations coupled with extensive material synthesis and characterization to fabricate fouling-resistant 3D printed composite membranes. The membranes consist of a thin polyethersulfone selective layer deposited onto a 3D printed flat and double sinusoidal (wavy) support. Fouling and cleaning of the composite membranes were tested by using bovine serum albumin solution in a cross-flow ultrafiltration setup. The transmembrane pressure was regulated at 1 bar and the cross-flow Reynolds number (Re) varied between 400 and 1000. In comparison to the flat membrane, the wavy membrane showed superior performance in terms of pure water permeance (PWP) (10% higher) and permeance recovery ratio (87% vs 53%) after the first filtration cycle at Re = 1000. Prolong testing showed that the wavy membrane could retain approximately 87% of its initial PWP after 10 complete filtration cycles. This impressive fouling-resistant behavior is attributed to the localized fluid turbulence induced by the 3D printed wavy structure. These results show that not only the lifetime of membrane operations could be favorably extended but also the operational costs and environmental damage of membrane-based processes could also be significantly reduced.}, } @article {pmid33267389, year = {2019}, author = {Lee, TW}, title = {Maximum Entropy Method for Solving the Turbulent Channel Flow Problem.}, journal = {Entropy (Basel, Switzerland)}, volume = {21}, number = {7}, pages = {}, pmid = {33267389}, issn = {1099-4300}, abstract = {There are two components in this work that allow for solutions of the turbulent channel flow problem: One is the Galilean-transformed Navier-Stokes equation which gives a theoretical expression for the Reynolds stress (u'v'); and the second the maximum entropy principle which provides the spatial distribution of turbulent kinetic energy. The first concept transforms the momentum balance for a control volume moving at the local mean velocity, breaking the momentum exchange down to its basic components, u'v', u'[2], pressure and viscous forces. The Reynolds stress gradient budget confirms this alternative interpretation of the turbulence momentum balance, as validated with DNS data. The second concept of maximum entropy principle states that turbulent kinetic energy in fully-developed flows will distribute itself until the maximum entropy is attained while conforming to the physical constraints. By equating the maximum entropy state with maximum allowable (viscous) dissipation at a given Reynolds number, along with other constraints, we arrive at function forms (inner and outer) for the turbulent kinetic energy. This allows us to compute the Reynolds stress, then integrate it to obtain the velocity profiles in channel flows. The results agree well with direct numerical simulation (DNS) data at Reτ = 400 and 1000.}, } @article {pmid31283274, year = {2019}, author = {Chajwa, R and Menon, N and Ramaswamy, S}, title = {Kepler Orbits in Pairs of Disks Settling in a Viscous Fluid.}, journal = {Physical review letters}, volume = {122}, number = {22}, pages = {224501}, doi = {10.1103/PhysRevLett.122.224501}, pmid = {31283274}, issn = {1079-7114}, abstract = {We show experimentally that a pair of disks settling at negligible Reynolds number (∼10^{-4} ) displays two classes of bound periodic orbits, each with transitions to scattering states. We account for these dynamics, at leading far-field order, through an effective Hamiltonian in which gravitational driving endows orientation with the properties of momentum. This treatment is successfully compared against the measured properties of orbits and critical parameters of transitions between types of orbits. We demonstrate a precise correspondence with the Kepler problem of planetary motion for a wide range of initial conditions, find and account for a family of orbits with no Keplerian analog, and highlight the role of orientation as momentum in the many-disk problem.}, } @article {pmid31266939, year = {2019}, author = {Ren, Z and Hu, W and Dong, X and Sitti, M}, title = {Multi-functional soft-bodied jellyfish-like swimming.}, journal = {Nature communications}, volume = {10}, number = {1}, pages = {2703}, pmid = {31266939}, issn = {2041-1723}, mesh = {Animals ; Biomechanical Phenomena ; Elastomers/chemistry ; *Equipment Design ; Locomotion ; Magnetics/instrumentation ; Robotics/*instrumentation ; Scyphozoa/*physiology ; Swimming ; }, abstract = {The functionalities of the untethered miniature swimming robots significantly decrease as the robot size becomes smaller, due to limitations of feasible miniaturized on-board components. Here we propose an untethered jellyfish-inspired soft millirobot that could realize multiple functionalities in moderate Reynolds number by producing diverse controlled fluidic flows around its body using its magnetic composite elastomer lappets, which are actuated by an external oscillating magnetic field. We particularly investigate the interaction between the robot's soft body and incurred fluidic flows due to the robot's body motion, and utilize such physical interaction to achieve different predation-inspired object manipulation tasks. The proposed lappet kinematics can inspire other existing jellyfish-like robots to achieve similar functionalities at the same length and time scale. Moreover, the robotic platform could be used to study the impacts of the morphology and kinematics changing in ephyra jellyfish.}, } @article {pmid35136273, year = {2019}, author = {Kempski, P and Quataert, E and Squire, J and Kunz, MW}, title = {Shearing-box simulations of MRI-driven turbulence in weakly collisional accretion discs.}, journal = {Monthly notices of the Royal Astronomical Society}, volume = {486}, number = {3}, pages = {4013-4029}, pmid = {35136273}, issn = {0035-8711}, support = {NNX17AK63G/NASA/NASA/United States ; }, abstract = {We present a systematic shearing-box investigation of MRI-driven turbulence in a weakly collisional plasma by including the effects of an anisotropic pressure stress, i.e. anisotropic (Braginskii) viscosity. We constrain the pressure anisotropy (Δp) to lie within the stability bounds that would be otherwise imposed by kinetic microinstabilities. We explore a broad region of parameter space by considering different Reynolds numbers and magnetic-field configurations, including net vertical flux, net toroidal-vertical flux and zero net flux. Remarkably, we find that the level of turbulence and angular-momentum transport are not greatly affected by large anisotropic viscosities: the Maxwell and Reynolds stresses do not differ much from the MHD result. Angular-momentum transport in Braginskii MHD still depends strongly on isotropic dissipation, e.g., the isotropic magnetic Prandtl number, even when the anisotropic viscosity is orders of magnitude larger than the isotropic diffusivities. Braginskii viscosity nevertheless changes the flow structure, rearranging the turbulence to largely counter the parallel rate of strain from the background shear. We also show that the volume-averaged pressure anisotropy and anisotropic viscous transport decrease with increasing isotropic Reynolds number (Re); e.g., in simulations with net vertical field, the ratio of anisotropic to Maxwell stress (α A/α M) decreases from ~ 0.5 to ~ 0.1 as we move from Re ~ 10[3] to Re ~ 10[4], while 〈4πΔp/B [2]〉 → 0. Anisotropic transport may thus become negligible at high Re. Anisotropic viscosity nevertheless becomes the dominant source of heating at large Re, accounting for ≳50% of the plasma heating. We conclude by briefly discussing the implications of our results for RIAFs onto black holes.}, } @article {pmid31236828, year = {2019}, author = {Klusak, E and Quinlan, NJ}, title = {High-Resolution Measurements of Leakage Flow Inside the Hinge of a Large-scale Bileaflet Mechanical Heart Valve Hinge Model.}, journal = {Cardiovascular engineering and technology}, volume = {10}, number = {3}, pages = {469-481}, doi = {10.1007/s13239-019-00423-4}, pmid = {31236828}, issn = {1869-4098}, mesh = {Blood Flow Velocity ; *Heart Valve Prosthesis ; Heart Valve Prosthesis Implantation/adverse effects/*instrumentation ; *Hemodynamics ; Humans ; Materials Testing ; Prosthesis Design ; Stress, Mechanical ; Thrombosis/etiology/physiopathology ; }, abstract = {PURPOSE: It is believed that non-physiological leakage flow through hinge gaps during diastole contributes to thrombus formation in Bileaflet Mechanical Heart Valves (BMHVs). Because of the small scale and difficulty of experimental access, fluid dynamics inside the hinge cavity has not yet been characterised in detail. The objective is to investigate small-scale structure inside the hinge experimentally, and gain insight into its role in stimulating cellular responses.

METHODS: An optically accessible scaled-up model of a BMHV hinge was designed and built, preserving dynamic similarity to a clinical BMHV. Particle Image Velocimetry (PIV) was used to visualize and quantify the flow fields inside the hinge at physiological Reynolds number and dimensionless pressure drop. The flow was measured at in-plane and out-of-plane spatial resolution of 32 and 86 μm, respectively, and temporal resolution of [Formula: see text] RESULTS: Likely flow separation on the ventricular surface of the cavity has been observed for the first time, and is a source of unsteadiness and perhaps turbulence. The shear stress found in all planes exceeds the threshold of platelet activation, ranging up to 168 Pa.

CONCLUSIONS: The scale-up approach provided new insight into the nature of the hinge flow and enhanced understanding of its complexity. This study revealed flow features that may induce blood element damage.}, } @article {pmid31236057, year = {2019}, author = {Cafiero, G and Vassilicos, JC}, title = {Non-equilibrium turbulence scalings and self-similarity in turbulent planar jets.}, journal = {Proceedings. Mathematical, physical, and engineering sciences}, volume = {475}, number = {2225}, pages = {20190038}, pmid = {31236057}, issn = {1364-5021}, abstract = {We study the self-similarity and dissipation scalings of a turbulent planar jet and the theoretically implied mean flow scalings. Unlike turbulent wakes where such studies have already been carried out (Dairay et al. 2015 J. Fluid Mech. 781, 166-198. (doi:10.1017/jfm.2015.493); Obligado et al. 2016 Phys. Rev. Fluids 1, 044409. (doi:10.1103/PhysRevFluids.1.044409)), this is a boundary-free turbulent shear flow where the local Reynolds number increases with distance from inlet. The Townsend-George theory revised by (Dairay et al. 2015 J. Fluid Mech. 781, 166-198. (doi:10.1017/jfm.2015.493)) is applied to turbulent planar jets. Only a few profiles need to be self-similar in this theory. The self-similarity of mean flow, turbulence dissipation, turbulent kinetic energy and Reynolds stress profiles is supported by our experimental results from 18 to at least 54 nozzle sizes, the furthermost location investigated in this work. Furthermore, the non-equilibrium dissipation scaling found in turbulent wakes, decaying grid-generated turbulence, various instances of periodic turbulence and turbulent boundary layers (Dairay et al. 2015 J. Fluid Mech. 781, 166-198. (doi:10.1017/jfm.2015.493); Vassilicos 2015 Annu. Rev. Fluid Mech. 95, 114. (doi:10.1146/annurev-fluid-010814-014637); Goto & Vassilicos 2015 Phys. Lett. A 3790, 1144-1148. (doi:10.1016/j.physleta.2015.02.025); Nedic et al. 2017 Phys. Rev. Fluids 2, 032601. (doi:10.1103/PhysRevFluids.2.032601)) is also observed in the present turbulent planar jet and in the turbulent planar jet of (Antonia et al. 1980 Phys. Fluids 23, 863055. (doi:10.1063/1.863055)). Given these observations, the theory implies new mean flow and jet width scalings which are found to be consistent with our data and the data of (Antonia et al. 1980 Phys. Fluids 23, 863055. (doi:10.1063/1.863055)). In particular, it implies a hitherto unknown entrainment behaviour: the ratio of characteristic cross-stream to centreline streamwise mean flow velocities decays as the -1/3 power of streamwise distance in the region, where the non-equilibrium dissipation scaling holds.}, } @article {pmid31229600, year = {2019}, author = {Garwood, RJ and Behnsen, J and Haysom, HK and Hunt, JN and Dalby, LJ and Quilter, SK and Maclaine, JS and Cox, JPL}, title = {Olfactory flow in the sturgeon is externally driven.}, journal = {Comparative biochemistry and physiology. Part A, Molecular & integrative physiology}, volume = {235}, number = {}, pages = {211-225}, doi = {10.1016/j.cbpa.2019.06.013}, pmid = {31229600}, issn = {1531-4332}, mesh = {Animals ; Computer Simulation ; Fishes/*physiology ; Models, Anatomic ; Nasal Cavity/physiology ; Nose/*physiology ; *Odorants ; Smell/*physiology ; Swimming/physiology ; }, abstract = {Fluid dynamics plays an important part in olfaction. Using the complementary techniques of dye visualisation and computational fluid dynamics (CFD), we investigated the hydrodynamics of the nasal region of the sturgeon Huso dauricus. H. dauricus offers several experimental advantages, including a well-developed, well-supported, radial array (rosette) of visible-by-eye olfactory sensory channels. We represented these features in an anatomically accurate rigid model derived from an X-ray scan of the head of a preserved museum specimen. We validated the results from the CFD simulation by comparing them with data from the dye visualisation experiments. We found that flow through both the nasal chamber and, crucially, the sensory channels could be induced by an external flow (caused by swimming in vivo) at a physiologically relevant Reynolds number. Flow through the nasal chamber arises from the anatomical arrangement of the incurrent and excurrent nostrils, and is assisted by the broad, cartilage-supported, inner wall of the incurrent nostril. Flow through the sensory channels arises when relatively high speed flow passing through the incurrent nostril encounters the circular central support of the olfactory rosette, decelerates, and is dispersed amongst the sensory channels. Vortices within the olfactory flow may assist odorant transport to the sensory surfaces. We conclude that swimming alone is sufficient to drive olfactory flow in H. dauricus, and consider the implications of our results for the three other extant genera of sturgeons (Acipenser, Pseudoscaphirhynchus and Scaphirhynchus), and for other fishes with olfactory rosettes.}, } @article {pmid31215548, year = {2019}, author = {Man, Y and Kanso, E}, title = {Morphological transitions of axially-driven microfilaments.}, journal = {Soft matter}, volume = {15}, number = {25}, pages = {5163-5173}, doi = {10.1039/c8sm02397b}, pmid = {31215548}, issn = {1744-6848}, mesh = {Actin Cytoskeleton/*metabolism ; Biomechanical Phenomena ; Elasticity ; *Models, Molecular ; }, abstract = {The interactions of microtubules with motor proteins are ubiquitous in cellular and sub-cellular processes that involve motility and cargo transport. In vitro motility assays have demonstrated that motor-driven microtubules exhibit rich dynamical behaviors from straight to curved configurations. Here, we theoretically investigate the dynamic instabilities of elastic filaments, with free-ends, driven by single follower forces that emulate the action of molecular motors. Using the resistive force theory at low Reynolds number, and a combination of numerical techniques with linear stability analysis, we show the existence of four distinct regimes of filament behavior, including a novel buckled state with locked curvature. These successive instabilities recapitulate the full range of experimentally-observed microtubule behavior, implying that neither structural nor actuation asymmetry are needed to elicit this rich repertoire of motion.}, } @article {pmid31212518, year = {2019}, author = {He, G and Wang, J and Rinoshika, A}, title = {Orthogonal wavelet multiresolution analysis of the turbulent boundary layer measured with two-dimensional time-resolved particle image velocimetry.}, journal = {Physical review. E}, volume = {99}, number = {5-1}, pages = {053105}, doi = {10.1103/PhysRevE.99.053105}, pmid = {31212518}, issn = {2470-0053}, abstract = {The turbulent boundary layer flow measured by two-dimensional time-resolved particle image velocimetry is analyzed using the discrete orthogonal wavelet method. The Reynolds number of the turbulent boundary layer based on the friction velocity is Re_{τ} =235. The flow field is decomposed into a number of wavelet levels which have different characteristic scales. The velocity statistics and coherent structures at different wavelet levels are investigated. It is found that the fluctuation intensities and their peak locations differ for varying scales. The proper orthogonal decomposition (POD) of different wavelet components reveals a cascade of scales of coherent structures, especially the small-scale ones that are usually difficult to be identified in POD modes of the undecomposed flow field. The interactions among the scales are investigated in terms of large-scale amplitude modulations of the small-scale structures. In previous studies the velocity fluctuations are separated into two parts, the large scale and the small scale, divided usually by the boundary layer thickness. In the present study, however, the scales smaller than the boundary layer thickness are further separated. Therefore, the modulation analysis is a refined investigation that differentiates the modulation effects on separated small scales. The results reveal that the modulation effects vary among the small scales.}, } @article {pmid31212497, year = {2019}, author = {Puljiz, M and Menzel, AM}, title = {Displacement field around a rigid sphere in a compressible elastic environment, corresponding higher-order Faxén relations, as well as higher-order displaceability and rotateability matrices.}, journal = {Physical review. E}, volume = {99}, number = {5-1}, pages = {053002}, doi = {10.1103/PhysRevE.99.053002}, pmid = {31212497}, issn = {2470-0053}, abstract = {An efficient route to the displacement field around a rigid spherical inclusion in an infinitely extended homogeneous elastic medium is presented in a slightly alternative way when compared to some common textbook methods. Moreover, two Faxén relations of next-higher order beyond the stresslet are calculated explicitly for compressible media. They quantify higher-order moments involving the force distribution on a rigid spherical particle in a deformed elastic medium. As a consequence, additional contributions to the distortions of the deformed elastic medium are identified that are absent to lower order. Furthermore, the displaceability and rotateability matrices for an ensemble of rigid spheres are calculated up to (including) sixth order in inverse particle separation distance. These matrices describe the interactions mediated between the rigid embedded particles by the elastic environment. In this way, additional coupling effects are identified that are absent to lower order, particularly when rotations and torques are involved. All methods and results can formally be transferred to the corresponding case of incompressible hydrodynamic low-Reynolds-number Stokes flow by considering the limit of an incompressible environment. The roles of compressibility of the embedding medium and of the here additionally derived higher-order contributions are highlighted by some selected example configurations.}, } @article {pmid31212461, year = {2019}, author = {Nie, D and Lin, J}, title = {Discontinuity in the sedimentation system with two particles having different densities in a vertical channel.}, journal = {Physical review. E}, volume = {99}, number = {5-1}, pages = {053112}, doi = {10.1103/PhysRevE.99.053112}, pmid = {31212461}, issn = {2470-0053}, abstract = {The two-dimensional lattice Boltzmann method was used to numerically study a sedimentation system with two particles having different densities in a vertical channel for Galileo numbers in the range of 5≤Ga≤15 (resulting in a Reynolds number, based on the settling velocity, approximately ranging between 0.6 and 7). Two types of periodic motion, differing from each other in terms of the size of the limit cycle, the magnitude of the time period, and their changes upon increasing the density difference between particles, are identified depending on whether there is a wake effect. The most prominent features of this system are discontinuous changes in the settling velocity (6.7≤Ga<9.7) and time period of oscillation (10.5≤Ga≤15) at a critical value of the density difference between particles. The first discontinuity results in an abrupt increase in the Reynolds number, associated with a Hopf bifurcation without the presence of vortex shedding. The second discontinuity is accompanied by the disappearance of "abnormal rotation" (referring to the situation in which a particle appears to roll up a wall when settling) of the heavy particle, which directly results from a sharp increase in the amplitude of oscillation induced by the enhanced wake effect at another critical density difference between particles. The wall effects on these discontinuous changes were also examined.}, } @article {pmid31212451, year = {2019}, author = {Wang, L and Tian, FB}, title = {Numerical simulation of flow over a parallel cantilevered flag in the vicinity of a rigid wall.}, journal = {Physical review. E}, volume = {99}, number = {5-1}, pages = {053111}, doi = {10.1103/PhysRevE.99.053111}, pmid = {31212451}, issn = {2470-0053}, abstract = {Flow over a parallel cantilevered flag in the vicinity of a rigid wall is numerically studied using an immersed boundary-lattice Boltzmann method (IB-LBM) in two-dimensional domain, where the dynamics of the fluid and structure are, respectively, solved by the LBM and a finite-element method (FEM), with a penalty IB to handle the fluid-structure interaction (FSI). Specifically, a benchmark case considering a plate attached to the downstream of a stationary cylinder is first conducted to validate the current solver. Then, the wall effects on the flag are systemically studied, considering the effects of off-wall distance, structure-to-fluid mass ratio, bending rigidity, and Reynolds number. Three flapping modes, including symmetrical flapping, asymmetrical flapping, and chaotic flapping, along with a steady state are observed in the simulations. It is found that the flag is vibrating or stable with a mean angle inclined in the fluid when it is mounted in the vicinity of a rigid wall. The mean inclined angle first increases in the steady state and then decreases in the unsteady state with the off-wall distance. In the unsteady regime, the dependency of the inclined angle on the off-wall distance is similar to that of the gradient of the fluid velocity. In addition, the rigid wall near the flag decreases the lift and drag generation and further stabilizes the flag-fluid system. Contrarily, the flag inertia destabilizes the flag, and large flag inertia induces chaotic vibrating modes.}, } @article {pmid31207995, year = {2019}, author = {Zhang, H and Li, X and Chuai, R and Zhang, Y}, title = {Chaotic Micromixer Based on 3D Horseshoe Transformation.}, journal = {Micromachines}, volume = {10}, number = {6}, pages = {}, pmid = {31207995}, issn = {2072-666X}, abstract = {To improve the efficiency of mixing under laminar flow with a low Reynolds number (Re), a novel three-dimensional Horseshoe Transformation (3D HT) was proposed as the basis for the design of a micromixer. Compared with the classical HT, the Lyapunov exponent of the 3D HT, which was calculated based on a symbolic dynamic system, proved the chaotic enhancement. Based on the 3D HT, a micromixer with a mixing length of 12 mm containing six mixing units was obtained by sequentially applying "squeeze", "stretch", "twice fold", "inverse transformation", and "intersection" operations. Numerical simulation and Peclet Number (Pe) calculations indicated that when the squeeze amplitude 0 < α < 1/2, 0 < β < 1/2, the stretch amplitude γ > 4, and Re ≥ 1, the mass transfer in the mixer was dominated by convective diffusion induced by chaotic flow. When Re = 10, at the outlet of the mixing chamber, the simulated mixing index was 96.4%, which was far less than the value at Re = 0.1 (σ = 0.041). Microscope images of the mixing chamber and the curve trend of pH buffer solutions obtained from a mixing experiment were both consistent with the results of the simulation. When Re = 10, the average mixing index of the pH buffer solutions was 91.75%, which proved the excellent mixing efficiency of the mixer based on the 3D HT.}, } @article {pmid31206776, year = {2019}, author = {Belut, E and Sánchez Jiménez, A and Meyer-Plath, A and Koivisto, AJ and Koponen, IK and Jensen, ACØ and MacCalman, L and Tuinman, I and Fransman, W and Domat, M and Bivolarova, M and van Tongeren, M}, title = {Indoor dispersion of airborne nano and fine particles: Main factors affecting spatial and temporal distribution in the frame of exposure modeling.}, journal = {Indoor air}, volume = {29}, number = {5}, pages = {803-816}, doi = {10.1111/ina.12579}, pmid = {31206776}, issn = {1600-0668}, mesh = {Aerosols/*analysis ; Air Pollutants/*analysis ; Air Pollution, Indoor/*analysis ; Environmental Monitoring ; Humans ; Models, Theoretical ; Nanoparticles ; Particle Size ; Spatio-Temporal Analysis ; Ventilation ; }, abstract = {A particle exposure experiment inside a large climate-controlled chamber was conducted. Data on spatial and temporal distribution of nanoscale and fine aerosols in the range of mobility diameters 8-600 nm were collected with high resolution, for sodium chloride, fluorescein sodium, and silica particles. Exposure scenarios studied included constant and intermittent source emissions, different aggregation conditions, high (10 h[-1]) and low (3.5 h[-1]) air exchange rates (AERs) corresponding to chamber Reynolds number, respectively, equal to 1 × 10[5] and 3 × 10[4] . Results are presented and analyzed to highlight the main determinants of exposure and to determine whether the assumptions underlying two-box models hold under various scenarios. The main determinants of exposure found were the source generation rate and the ventilation rate. The effect of particles nature was indiscernible, and the decrease of airborne total number concentrations attributable to surface deposition was estimated lower than 2% when the source was active. A near-field/far-field structure of aerosol concentration was always observed for the AER = 10 h[-1] but for AER = 3.5 h[-1] , a single-field structure was found. The particle size distribution was always homogeneous in space but a general shift of particle diameter (-8% to +16%) was observed between scenarios in correlation with the AER and with the source position, presumably largely attributable to aggregation.}, } @article {pmid33267306, year = {2019}, author = {Abd El-Aziz, M and Afify, AA}, title = {MHD Casson Fluid Flow over a Stretching Sheet with Entropy Generation Analysis and Hall Influence.}, journal = {Entropy (Basel, Switzerland)}, volume = {21}, number = {6}, pages = {}, pmid = {33267306}, issn = {1099-4300}, abstract = {The impacts of entropy generation and Hall current on MHD Casson fluid over a stretching surface with velocity slip factor have been numerically analyzed. Numerical work for the governing equations is established by using a shooting method with a fourth-order Runge-Kutta integration scheme. The outcomes show that the entropy generation is enhanced with a magnetic parameter, Reynolds number and group parameter. Further, the reverse behavior is observed with the Hall parameter, Eckert number, Casson parameter and slip factor. Also, it is viewed that Bejan number reduces with a group parameter.}, } @article {pmid31186821, year = {2019}, author = {Aghilinejad, A and Aghaamoo, M and Chen, X}, title = {On the transport of particles/cells in high-throughput deterministic lateral displacement devices: Implications for circulating tumor cell separation.}, journal = {Biomicrofluidics}, volume = {13}, number = {3}, pages = {034112}, pmid = {31186821}, issn = {1932-1058}, abstract = {Deterministic lateral displacement (DLD), which takes advantage of the asymmetric bifurcation of laminar flow around the embedded microposts, has shown promising capabilities in separating cells and particles of different sizes. Growing interest in utilizing high-throughput DLD devices for practical applications, such as circulating tumor cell separation, necessitates employing higher flow rates in these devices, leading to operating in moderate to high Reynolds number (Re) regimes. Despite extensive research on DLD devices in the creeping regime, limited research has focused on the physics of flow, critical size of the device, and deformable cell behavior in DLD devices at moderate to high Re. In this study, the transport behavior of particles/cells is investigated in realistic high-throughput DLD devices with hundreds of microposts by utilizing multiphysics modeling. A practical formula is proposed for the prediction of the device critical size, which could serve as a design guideline for high-throughput DLD devices. Then, the complex hydrodynamic interactions between a deformable cell and DLD post arrays are investigated. A dimensionless index is utilized for comparing different post designs to quantify the cell-post interaction. It is shown that the separation performances in high-throughput devices are highly affected by Re as well as the micropost shapes. These findings can be utilized for the design and optimization of high-throughput DLD microfluidic devices.}, } @article {pmid31185351, year = {2019}, author = {Tshumah-Mutingwende, RRMS and Takahashi, F}, title = {Physio-chemical effects of freshwaters on the dissolution of elementary mercury.}, journal = {Environmental pollution (Barking, Essex : 1987)}, volume = {252}, number = {Pt A}, pages = {627-636}, doi = {10.1016/j.envpol.2019.05.130}, pmid = {31185351}, issn = {1873-6424}, mesh = {Ecosystem ; Environmental Monitoring/methods ; Fresh Water/*chemistry ; Gold/analysis ; Humans ; Mercury/*analysis/chemistry ; Methylmercury Compounds/analysis ; Solubility ; Water Pollutants, Chemical/*analysis/chemistry ; }, abstract = {Elemental mercury (Hg[0]) is widely used by Artisanal and small-scale gold miners (ASGMs) to extract gold from ore. Due to the unavailability of appropriate waste disposal facilities, Hg[0]-rich amalgamation tailings are often discharged into nearby aquatic systems where the Hg[0] droplets settle in bottom sediment and sediment-water interfaces. Hg[0] dissolution and following biogeochemical transformations to methylmercury (MeHg) have been concerned owing to its potential risk to human health and the ecosystem. For reliable estimates of Hg exposure to human bodies using pollutant environmental fate and transport models, knowledge of the Hg[0] dissolution rate is important. However, only limited literature is available. Therefore, it was investigated in this study. Dissolution tests in a 'dark chamber' revealed that an increase in medium pH resulted in a decrease in the dissolution rate, whereas, a large Hg[0] droplet surface area (SA) and high Reynolds number (Re) resulted in a faster dissolution. A multivariate first order dissolution model of the form:kˆ=-7.9×10[-5][pH]+7.0×10[-4][logRe]+7.9×10[-4][SA]-2.5×10[-3] was proposed (adjusted R[2] = 0.99). The Breusch-Pagan and White heteroscedasticity tests revealed that the model residuals are homoscedastic (p-value = 0.05) at the 5% significance level. Parameter sensitivity analysis suggests that slow mercury dissolution from the Hg[0] droplets to aquatic systems might mask emerging environmental risk of mercury. Even after mercury usage in ASGM is banned, mercury dissolution and following contamination will continue for about 40 years or longer owing to previously discharged Hg[0] droplets.}, } @article {pmid31176976, year = {2019}, author = {Almohammadi, H and Amirfazli, A}, title = {Droplet impact: Viscosity and wettability effects on splashing.}, journal = {Journal of colloid and interface science}, volume = {553}, number = {}, pages = {22-30}, doi = {10.1016/j.jcis.2019.05.101}, pmid = {31176976}, issn = {1095-7103}, abstract = {HYPOTHESES: The wettability of a surface affects the splashing behavior of a droplet upon impact onto a surface only when surface exhibits either a very high or a very low contact angle. Viscosity affects the splashing threshold in a non-monotony way.

EXPERIMENTS: To examine the roles of drop viscosity and surface wettability on splashing, a wide range of liquid viscosities (1-100 cSt), surface wettabilities (from hydrophilic to hydrophobic), drop velocities (0.5-3.3 m/s), and liquid surface tensions (∼20 and 70 mN/m) were examined. High speed imaging was used.

FINDINGS: Wettability affects the splashing threshold at very extreme limits of the wettability i.e. at very high or very low contact angle values; however, the wettability effect is less prominent on spreading-splashing regime map. For drops of any surface tension impacting surfaces with any wettability, an increase in viscosity (up to ∼5 cSt or Reynolds number of 2000) promotes splashing; whereas using liquids with viscosities larger than 5 cSt, suppress splashing. We explained such behaviors using evolution of the lamella rim, dynamic contact angle, and velocity of the expanding lamella. Finally, to predict the splashing, we developed a general empirical relationship which explains all of ours, and previously reported data.}, } @article {pmid31167483, year = {2019}, author = {Siddiqui, AA and Turkyilmazoglu, M}, title = {A New Theoretical Approach of Wall Transpiration in the Cavity Flow of the Ferrofluids.}, journal = {Micromachines}, volume = {10}, number = {6}, pages = {}, pmid = {31167483}, issn = {2072-666X}, abstract = {An idea of permeable (suction/injection) chamber is proposed in the current work to control the secondary vortices appearing in the well-known lid-driven cavity flow by means of the water based ferrofluids. The Rosensweig model is conveniently adopted for the mathematical analysis of the physical problem. The governing equation of model is first transformed into the vorticity transport equation. A special finite difference method in association with the successive over-relaxation method (SOR) is then employed to numerically simulate the flow behavior. The effects of intensity of magnetic source (controlled by the Stuart number), aspect ratio of the cavity, rate of permeability (i.e., α p = V 0 U), ratio of speed of suction/injection V 0 to the sliding-speed U of the upper wall of a cavity, and Reynolds number on the ferrofluid in the cavity are fully examined. It is found that the secondary vortices residing on the lower wall of the cavity are dissolved by the implementation of the suction/injection chamber. Their character is dependent on the rate of permeability. The intensity of magnetic source affects the system in such a way to alter the flow and to transport the fluid away from the magnetic source location. It also reduces the loading effects on the walls of the cavity. If the depth of cavity (or the aspect ratio) is increased, the secondary vortices join together to form a single secondary vortex. The number of secondary vortices is shown to increase if the Reynolds number is increased for both the clear fluid as well as the ferrofluids. The suction and injection create resistance in settlement of solid ferroparticles on the bottom. The results obtained are validated with the existing data in the literature and satisfactory agreement is observed. The presented problem may find applications in biomedical, pharmaceutical, and engineering industries.}, } @article {pmid31165744, year = {2019}, author = {Arumuru, V and Dash, JN and Dora, D and Jha, R}, title = {Vortex Shedding Optical Flowmeter based on Photonic Crystal Fiber.}, journal = {Scientific reports}, volume = {9}, number = {1}, pages = {8313}, pmid = {31165744}, issn = {2045-2322}, abstract = {In the present work we propose a PCF (photonic crystal fiber) based Modal interferometer detector for sensing low flow velocity by detecting the frequency of vortices shed from a bluff body. The proposed novel design encapsulates the interferometric arm inside a metal casing to protect the sensor from harsh process fluids. The characterization of the developed probe is conducted under no flow conditions using a piezo actuator to evaluate the sensor response over wide frequency range (0-500 Hz). The developed sensors shows a reasonably flat response in the tested frequency range. Experiments are conducted by employing the developed sensor behind a bluff body of a vortex flowmeter to measure the frequency of the shed vortices and hence, the fluid flow rate. The low flow rate sensitivity of the vortex flowmeter is improved many folds by using the present sensor and the minimum Reynolds number detected is Re = 5000. A linear trend is observed between the frequency of the vortices and the flow velocity which is desirable for fluid flow measurement. The PCF based interferometric sensor with metal encapsulation makes the vortex flowmeter, sensitive at low flow rates, robust and economical to be used in industrial application.}, } @article {pmid31153354, year = {2019}, author = {Farouk, B and Antao, DS and Hasan, N}, title = {Acoustically driven oscillatory flow fields in a cylindrical resonator at resonance.}, journal = {The Journal of the Acoustical Society of America}, volume = {145}, number = {5}, pages = {2932}, doi = {10.1121/1.5097594}, pmid = {31153354}, issn = {1520-8524}, abstract = {Generation and development of acoustic waves in an air-filled cylindrical resonator driven by a conical electro-mechanical speaker are studied experimentally and simulated numerically. The driving frequencies of the speaker are chosen such that a standing wave field is produced at each chosen frequency in the resonator. The amplitude of the generated acoustic (pressure) waves is measured along the axis of the resonator by a fast response piezo-resistive pressure transducer, while the radial distribution of the oscillatory axial velocities is measured at the corresponding velocity anti-node locations by a constant temperature hot-film anemometer. For the cases studied, the acoustic Reynolds number ranged between 20.0 and 60.0 and the flow fields were always found to be in the laminar regime. The flow field in the resonator is also simulated by a high-fidelity numerical scheme with low numerical diffusion. Formation of the standing wave and quasi-steady acoustic streaming are numerically simulated by solving the fully compressible form of the Navier-Stokes equations. The effects of the sound field intensity (i.e., input power to the speaker) and driving frequency on the standing wave field and the resultant formation process of the streaming structures are also investigated.}, } @article {pmid31144946, year = {2019}, author = {Kaneda, Y and Yamamoto, Y and Tsuji, Y}, title = {Linear Response Theory for One-Point Statistics in the Inertial Sublayer of Wall-Bounded Turbulence.}, journal = {Physical review letters}, volume = {122}, number = {19}, pages = {194502}, doi = {10.1103/PhysRevLett.122.194502}, pmid = {31144946}, issn = {1079-7114}, abstract = {The idea of linear response theory well known in the statistical mechanics for thermal equilibrium systems is applied to one-point statistics in the inertial sublayer of wall-bounded turbulence (WBT). A close analogy between the energy transfer from large to small scales in isotropic turbulence and the momentum transfer in the wall normal direction in WBT plays a key role in the application. The application gives estimates of the influence of the finite Reynolds number on the statistics. The estimates are consistent with data by high-resolution direct numerical simulations of turbulent channel flow.}, } @article {pmid31140495, year = {2019}, author = {Fadel, M and Daurelle, JV and Fourmond, V and Vicente, J}, title = {A new electrochemical cell with a uniformly accessible electrode to study fast catalytic reactions.}, journal = {Physical chemistry chemical physics : PCCP}, volume = {21}, number = {23}, pages = {12360-12371}, doi = {10.1039/c9cp01487j}, pmid = {31140495}, issn = {1463-9084}, abstract = {The electrochemical study of fast catalytic reactions is limited by mass transport when using the conventional electrochemical cell with a rotating disk electrode (RDE). To overcome this issue, it is important to find a new device with improved transport properties that respects electrochemical constraints. We used numerical simulations of computational fluid dynamics to design a new electrochemical cell based on the so-called "jet flow" design for the kinetic studies of catalytic chemical reactions at the surface of an electrode. The new cell is characterized by a high, reliable and uniform mass transport over the electroactive part of its surface. We investigated the effects of the nozzle and the electrode diameters, the nozzle-electrode distance and the Reynolds number on the performance of the jet-electrode in the flow system. Through the optimization of the geometry of this jet electrode cell, we achieved a factor of 3 enhancement in transport compared to the rotating disk electrode. We succeeded in constructing the designed electrode, characterized it with electrochemical techniques, and found an excellent agreement between the transport properties deduced from the numerical simulations and those from the measurements.}, } @article {pmid31137243, year = {2019}, author = {Maqbool, K and Shaheen, S and Siddiqui, AM}, title = {Effect of nano-particles on MHD flow of tangent hyperbolic fluid in a ciliated tube: an application to fallopian tube.}, journal = {Mathematical biosciences and engineering : MBE}, volume = {16}, number = {4}, pages = {2927-2941}, doi = {10.3934/mbe.2019144}, pmid = {31137243}, issn = {1551-0018}, mesh = {Cilia/*physiology ; Copper ; Electromagnetic Phenomena ; Fallopian Tube Diseases/therapy ; Fallopian Tubes/blood supply/*physiology ; Female ; Hemodynamics ; Hot Temperature/therapeutic use ; Humans ; *Hydrodynamics ; Magnetic Field Therapy/methods ; Mathematical Concepts ; Metal Nanoparticles ; Models, Biological ; Thrombosis/therapy ; }, abstract = {This study shows the effects of magnetic field and copper nanoparticles on the flow of tangent hyperbolic fluid (blood) through a ciliated tube (fallopian tube). The present study will be very helpful for those patients who are facing blood clotting in fallopian tube that may cause for infertility or cancer. The nanoparticles and magnetic field are very helpful to break the clots in blood flowing in fallopian tube. Since blood flows in fallopian tube due to ciliary movement, therefore medicines containing copper nanoparticles and magnetic field with radiation therapy help to improve the patient. Ciliary movement has a particular pattern of motion i.e., metachronal wavy motion which helps to fluid flow. For the forced convective MHD flow of tangent hyperbolic nano-fluid, momentum and energy equations are solved by the small Reynolds' number approximation and Adomian decomposition method by constructing the recursive relation of ADM and solved by software "MATHEMATICA". The effects of parameters such as nanoparticle volume fraction, Hartmann number, entropy generation and Bejan's number have been discussed through graphs plotted in software "MATHEMATICA". It is found that blood flow is accelerated and heat transfer enhancement is maximum in the presence of nano particles, also magnetic effects accelerates the blood flow and help to enhance the heat transfer whereas the presence of porous medium increases the fluid's velocity and reduce the transfer of heat through fluid flow.}, } @article {pmid31123743, year = {2019}, author = {Wang, P and Zhang, Q and Wang, M and Yin, B and Hou, D and Zhang, Y}, title = {Atomistic insights into cesium chloride solution transport through the ultra-confined calcium-silicate-hydrate channel.}, journal = {Physical chemistry chemical physics : PCCP}, volume = {21}, number = {22}, pages = {11892-11902}, doi = {10.1039/c8cp07676f}, pmid = {31123743}, issn = {1463-9084}, abstract = {The transport of water and ions in the gel pores of calcium silicate hydrate (C-S-H) determines the durability of cement material. In this study, molecular dynamics was employed to investigate the capillary imbibition process of CsCl solution in the C-S-H channel. The advanced frontier of CsCl solution flow inside the C-S-H capillary shows a concave meniscus shape, which reflects the hydrophilic properties of the C-S-H substrate. Reynolds number calculations show that the transport process is laminar flow and dominated by viscous forces. The invading depth of the CsCl solution deviates from the theoretical prediction of the classic Lucas-Washburn (L-W) equation, but the modified theoretical equation, by incorporating the effect of slip length, dynamic contact angle, and effective viscosity into the L-W equation, can describe the penetration curve of the solution very well. The validity of our developed theoretical equation was confirmed by additional systems with different ion concentrations. In addition, the local structure of ions was analyzed to elucidate the effect of ion concentration on the transport process. The adsorption and accumulation of ions retard the transport process of water. With an increase in the ionic concentration, the effects of immobilization and cluster accumulation became more pronounced, further reducing the transport rate of water. This study provides fundamental insight into the transport behavior of liquid in the gel pores of cement-based material.}, } @article {pmid31120757, year = {2019}, author = {Zhang, J and Liu, H and Ba, Y}, title = {Numerical Study of Droplet Dynamics on a Solid Surface with Insoluble Surfactants.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {35}, number = {24}, pages = {7858-7870}, doi = {10.1021/acs.langmuir.9b00495}, pmid = {31120757}, issn = {1520-5827}, abstract = {Surfactants are widely used in many industrial processes, where the presence of surfactants not only reduces the interfacial tension between fluids but also alters the wetting properties of solid surfaces. To understand how the surfactants influence the droplet motion on a solid surface, a hybrid method for interfacial flows with insoluble surfactants and contact-line dynamics is developed. This method solves immiscible two-phase flows through a lattice Boltzmann color-gradient model and simultaneously solves the convection-diffusion equation for surfactant concentration through a finite difference method. In addition, a dynamic contact angle formulation that describes the dependence of the local contact angle on the surfactant concentration is derived, and the resulting contact angle is enforced by a geometrical wetting condition. Our method is first used to simulate static contact angles for a droplet resting on a solid surface, and the results show that the presence of surfactants can significantly modify surface wettability, especially when the surface is more hydrophilic or more hydrophobic. This is then applied to simulate a surfactant-laden droplet moving on a substrate subject to a linear shear flow for varying effective capillary number (Cae), Reynolds number (Re), and surface wettability, where the results are often compared with those of a clean droplet. For varying Cae, the simulations are conducted by considering a neutral surface. At low values of Cae, the droplet eventually reaches a steady deformation and moves at a constant velocity. In either a clean or surfactant-laden case, the moving velocity of the droplet linearly increases with the moving wall velocity, but the slope is always higher (i.e., the droplet moves faster) in the surfactant-laden case where the droplet exhibits a bigger deformation. When Cae is increased beyond a critical value (Cae,c), the droplet breakup would happen. The presence of surfactants is found to decrease the value of Cae,c, but it shows a non-monotonic effect on the droplet breakup. An increase in Re is able to increase not only droplet deformation but also surfactant dilution. The role of surfactants in the droplet behavior is found to greatly depend upon the surface wettability. For a hydrophilic surface, the presence of surfactants can decrease the wetting length and enables the droplet to reach a steady state faster; while for a hydrophobic surface, it increases the wetting length and delays the departure of the droplet from the solid surface.}, } @article {pmid33267233, year = {2019}, author = {de Divitiis, N}, title = {Statistical Lyapunov Theory Based on Bifurcation Analysis of Energy Cascade in Isotropic Homogeneous Turbulence: A Physical-Mathematical Review.}, journal = {Entropy (Basel, Switzerland)}, volume = {21}, number = {5}, pages = {}, pmid = {33267233}, issn = {1099-4300}, abstract = {This work presents a review of previous articles dealing with an original turbulence theory proposed by the author and provides new theoretical insights into some related issues. The new theoretical procedures and methodological approaches confirm and corroborate the previous results. These articles study the regime of homogeneous isotropic turbulence for incompressible fluids and propose theoretical approaches based on a specific Lyapunov theory for determining the closures of the von Kármán-Howarth and Corrsin equations and the statistics of velocity and temperature difference. While numerous works are present in the literature which concern the closures of the autocorrelation equations in the Fourier domain (i.e., Lin equation closure), few articles deal with the closures of the autocorrelation equations in the physical space. These latter, being based on the eddy-viscosity concept, describe diffusive closure models. On the other hand, the proposed Lyapunov theory leads to nondiffusive closures based on the property that, in turbulence, contiguous fluid particles trajectories continuously diverge. Therefore, the main motivation of this review is to present a theoretical formulation which does not adopt the eddy-viscosity paradigm and summarizes the results of the previous works. Next, this analysis assumes that the current fluid placements, together with velocity and temperature fields, are fluid state variables. This leads to the closures of the autocorrelation equations and helps to interpret the mechanism of energy cascade as due to the continuous divergence of the contiguous trajectories. Furthermore, novel theoretical issues are here presented among which we can mention the following ones. The bifurcation rate of the velocity gradient, calculated along fluid particles trajectories, is shown to be much larger than the corresponding maximal Lyapunov exponent. On that basis, an interpretation of the energy cascade phenomenon is given and the statistics of finite time Lyapunov exponent of the velocity gradient is shown to be represented by normal distribution functions. Next, the self-similarity produced by the proposed closures is analyzed and a proper bifurcation analysis of the closed von Kármán-Howarth equation is performed. This latter investigates the route from developed turbulence toward the non-chaotic regimes, leading to an estimate of the critical Taylor scale Reynolds number. A proper statistical decomposition based on extended distribution functions and on the Navier-Stokes equations is presented, which leads to the statistics of velocity and temperature difference.}, } @article {pmid31083953, year = {2019}, author = {Tian, C and Wang, X and Liu, Y and Yang, W and Hu, H and Pei, X and Zhou, F}, title = {In Situ Grafting Hydrophilic Polymeric Layer for Stable Drag Reduction.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {35}, number = {22}, pages = {7205-7211}, doi = {10.1021/acs.langmuir.9b00321}, pmid = {31083953}, issn = {1520-5827}, abstract = {Developing drag reduction techniques has attracted great attention because of their need in practical applications. However, many of the proposed strategies exhibit some inevitable limitations, especially for long period of adhibition. In this work, the dynamic but stable drag reduction effect of superhydrophilic hydrogel-coated iron sphere falling freely in a cylindrical water tank was investigated. The absolute instantaneous velocities and displacements of either the hydrogel-encapsulated or unmodified iron sphere falling freely in water were monitored via a high-speed video. It was revealed that, in the range of Reynolds number from 10[4] to 10[6], the optimized hydrogel-coated iron sphere with uniform stability could reduce the resistance by up to 40%, which was mainly due to the boundary slip of water and the delayed boundary separation that resulted from the coated hydrogel. Besides, the deliberate experiments and analysis further indicated that the superhydrophilic hydrogel layer accompanied by the emergence of the drag crisis has largely effected the distribution of flow field at the boundary around the sphere. More importantly, the drag reduction behavior based on the proposed method was thermodynamically stable and resistant to external stimulus, including fluidic oscillator and hydrodynamic pressure. The effective long-term drag reduction performance of the hydrophilic substrate can be expected, correspondingly, and also provides a novel preliminary protocol and avenues for the development of durable drag reduction technologies.}, } @article {pmid31083496, year = {2019}, author = {Li, H and Huang, B and Wu, M}, title = {Experimental and Numerical Investigations on the Flow Characteristics within Hydrodynamic Entrance Regions in Microchannels.}, journal = {Micromachines}, volume = {10}, number = {5}, pages = {}, pmid = {31083496}, issn = {2072-666X}, abstract = {Flow characteristics within entrance regions in microchannels are important due to their effect on heat and mass transfer. However, relevant research is limited and some conclusions are controversial. In order to reveal flow characteristics within entrance regions and to provide empiric correlation estimating hydrodynamic entrance length, experimental and numerical investigations were conducted in microchannels with square cross-sections. The inlet configuration was elaborately designed in a more common pattern for microdevices to diminish errors caused by separation flow near the inlet and fabrication faults so that conclusions which were more applicable to microchannels could be drawn. Three different microchannels with hydraulic diameters of 100 μm, 150 μm, and 200 μm were investigated with Reynolds (Re) number ranging from 0.5 to 50. For the experiment, deionized water was chosen as the working fluid and microscopic particle image velocimetry (micro-PIV) was adopted to record and analyze velocity profiles. For numerical simulation, the test-sections were modeled and incompressible laminar Navier-Stokes equations were solved with commercial software. Strong agreement was achieved between the experimental data and the simulated data. According to the results of both the experiments and the simulations, new correlations were proposed to estimate entrance length. Re numbers ranging from 12.5 to 15 was considered as the transition region where the relationship between entrance length and Re number converted. For the microchannels and the Reynolds number range investigated compared with correlations for conventional channels, noticeable deviation was observed for lower Re numbers (Re < 12.5) and strong agreement was found for higher Re numbers (Re > 15).}, } @article {pmid31074118, year = {2019}, author = {Xin, C and Yang, L and Li, J and Hu, Y and Qian, D and Fan, S and Hu, K and Cai, Z and Wu, H and Wang, D and Wu, D and Chu, J}, title = {Conical Hollow Microhelices with Superior Swimming Capabilities for Targeted Cargo Delivery.}, journal = {Advanced materials (Deerfield Beach, Fla.)}, volume = {31}, number = {25}, pages = {e1808226}, doi = {10.1002/adma.201808226}, pmid = {31074118}, issn = {1521-4095}, abstract = {Inspired by flagellate microorganisms in nature, the microhelix is considered as an ideal model for transportation in fluid environment with low Reynolds number. However, how to promote the swimming and loading capabilities of microhelices with controllable geometries remains challenging. In this study, a novel kind of conical hollow microhelices is proposed and a method is developed to rapidly fabricate these microhelices with controllable parameters by femtosecond vortex beams generated from spatial light modulation along helical scanning. Conical hollow microhelices with designable heights (H = 45-75 µm), diameters (D = 6-18 µm), pitch numbers (Pi = 2-4), taper angles (T = 0.1-0.6 rad), and pitch periods (ΔP = 10-30 µm) are efficiently fabricated. In addition, compared with straight microhelices, the forward swimming capability of conical microhelices increases by 50% and the lateral drift of the conical hollow microhelices is reduced by 70%. Finally, the capabilities of these conical hollow microhelices for nanocargo loading and release by the inner hollow core, as well as transportation of neural stem cells by the outer surface are demonstrated. This work provides new insights into faster and simultaneous transportation of multicargoes for hybrid drug delivery, targeted therapy, and noninvasive surgery in vivo.}, } @article {pmid33793688, year = {2019}, author = {Kenaley, CP and Stote, A and Ludt, WB and Chakrabarty, P}, title = {Comparative Functional and Phylogenomic Analyses of Host Association in the Remoras (Echeneidae), a Family of Hitchhiking Fishes.}, journal = {Integrative organismal biology (Oxford, England)}, volume = {1}, number = {1}, pages = {obz007}, pmid = {33793688}, issn = {2517-4843}, abstract = {The family Echeneidae consists of eight species of marine fishes that hitchhike by adhering to a wide variety of vertebrate hosts via a sucking disc. While several studies have focused on the interrelationships of the echeneids and the adhesion performance of a single species, no clear phylogenetic hypothesis has emerged and the morphological basis of adhesion remains largely unknown. We first set out to resolve the interrelationships of the Echeneidae by taking a phylogenomic approach using ultraconserved elements. Then, within this framework, we characterized disc morphology through µ-CT analysis, evaluated host specificity through an analysis of host phylogenetic distance, and determined which axes of disc morphological variation are associated with host diversity, skin surface properties, mean pairwise phylogenetic distance (MPD obs.), and swimming regime. We recovered an extremely well-supported topology, found that the specificity of host choice is more variable in a pelagic group and less variable in a reef-generalist group than previously proposed, and that axes of disc morphospace are best explained by models that include host skin surface roughness, host MPD obs., and maximum host Reynolds number. This suggests that ecomorphological diversification was driven by the selection pressures of host skin surface roughness, host specialization, and hydrodynamic regime.}, } @article {pmid33267198, year = {2019}, author = {Abd El-Aziz, M and Saleem, S}, title = {Numerical Simulation of Entropy Generation for Power-Law Liquid Flow over a Permeable Exponential Stretched Surface with Variable Heat Source and Heat Flux.}, journal = {Entropy (Basel, Switzerland)}, volume = {21}, number = {5}, pages = {}, pmid = {33267198}, issn = {1099-4300}, abstract = {This novel work explored the second law analysis and heat transfer in a magneto non-Newtonian power-law fluid model with the presence of an internal non-uniform heat source/sink. In this investigation, the motion of the studied fluid was induced by an exponentially stretching surface. The rheological behavior of the fluid model, including the shear thinning and shear thickening properties, are also considered as special case studies. The physical problem developed meaningfully with the imposed heat flux and the porosity of the stretched surface. Extensive numerical simulations were carried out for the present boundary layer flow, in order to study the influence of each control parameter on the boundary layer flow and heat transfer characteristics via various tabular and graphical illustrations. By employing the Shooting Runge-Kutta-Fehlberg Method (SRKFM), the resulting nonlinear ordinary differential equations were solved accurately. Based on this numerical procedure, the velocity and temperature fields are displayed graphically. By applying the second law of thermodynamics, and characterizing the entropy generation and Bejan number, the present physical problem was examined and discussed thoroughly in different situations. The attained results showed that the entropy generation can be improved significantly by raising the magnetic field strength and the group parameter. From an energetic point of view, it was found that the Reynolds number boosts the entropy generation of the fluidic medium and reduces the Bejan number. Also, it was observed that an amplification of the power-law index diminished the entropy generation near the stretched surface. As main results, it was proven that the heat transfer rate can be reduced with both the internal heat source intensity and the magnetic field strength.}, } @article {pmid31067939, year = {2019}, author = {Feng, Y and Gao, Y and Tang, K and Jin, T}, title = {Numerical investigation on turbulent oscillatory flow through a jet pump.}, journal = {The Journal of the Acoustical Society of America}, volume = {145}, number = {3}, pages = {1417}, doi = {10.1121/1.5094346}, pmid = {31067939}, issn = {1520-8524}, abstract = {A jet pump with an asymmetrical channel can induce a time-averaged pressure drop in oscillatory flow, which can effectively suppress Gedeon streaming in looped thermoacoustic engines. In this work, the flow characteristics and time-averaged pressure drop caused by a jet pump in turbulent oscillatory flow are investigated through numerical simulation. Through the analysis of the dimensionless governing equations, the emphasis is put on the effects of Womersley number and maximum acoustic Reynolds number on the performance of the jet pump. Meanwhile, the steady flow resistance coefficients are also measured numerically. The results indicate that the oscillatory flow resistance coefficients are relatively insensitive to Womersley number when it is less than 46. Moreover, the oscillatory flow resistance coefficients agree well with the steady state flow results, which validate the quasi-static assumption in turbulent oscillatory flow. However, further increasing Womersley number will lead to a reduction in the time-averaged pressure drop. The simulation method and results, as well as the hydrodynamic mechanism beneath the results, are presented and discussed in detail.}, } @article {pmid31067919, year = {2019}, author = {Ramadan, AB and Abd El-Rahman, AI and Sabry, AS}, title = {Assessment of the transition k-k-ω model application to transitional oscillatory pipe flows.}, journal = {The Journal of the Acoustical Society of America}, volume = {145}, number = {3}, pages = {1195}, doi = {10.1121/1.5092605}, pmid = {31067919}, issn = {1520-8524}, abstract = {The flow transition from laminar to turbulent inside of typical thermoacoustic devices influences the heat-exchange capacities of these devices and dramatically impacts overall performances as well. A few measurements [Eckmann and Grotberg (1991), J. Fluid Mech. 222, 329-350; Hino, Sawamoto, and Takasu (1976). J. Fluid Mech. 75, 193-207] and direct simulations [Feldmann and Wagner (2012). J. Turbul. 13(32), 1-28; Feldmann and Wagner (2016a). New Results in Numerical and Experimental Fluid Mechanics X, pp. 113-122] were reported that describe the transitional oscillatory flows; however, almost no turbulence model has been developed that enables accurate detection and characterization of the reported intermittent turbulent fluctuations. The present work aims to assess the applicability of the k-kL-ω transition model to transitional oscillatory pipe flows. A sinusoidal pressure gradient is introduced into ANSYS finite-volume solver for flow field simulation at different acoustic frequencies, while a friction Reynolds number of 1440 is retained. The stationary turbulent and the laminar oscillatory pipe flows are first considered for validation and model calibration against published LDA measurements [Durst, Kikura, Lekakis, Jovanovic, and Ye (1996). Exp. Fluids 20, 417-428] and DNS results [Feldmann and Wagner (2012). J. Turbul. 13(32), 1-28] in addition to the Sexl's laminar-flow theory [Sexl (1930). Zeitschrift Phys. 61(5), 349-362]. Investigation of the total fluctuation kinetic energy of transitional oscillations reveals the appearance of intermittent fluctuations within the near-wall region at Wo = 13 during deceleration, while fully turbulent oscillations are predicted in the entire pipe domain at Wo = 5. Although the present results are qualitatively in good agreement with reported experimental [Eckmann and Grotberg (1991). J. Fluid Mech. 222, 329-350] and DNS findings [Feldmann and Wagner (2012). J. Turbul. 13(32), 1-28], the velocity profiles show poor agreement with corresponding DNS data during flow acceleration at Wo = 5.}, } @article {pmid33267194, year = {2019}, author = {Hussien, AA and Abdullah, MZ and Yusop, NM and Al-Kouz, W and Mahmoudi, E and Mehrali, M}, title = {Heat Transfer and Entropy Generation Abilities of MWCNTs/GNPs Hybrid Nanofluids in Microtubes.}, journal = {Entropy (Basel, Switzerland)}, volume = {21}, number = {5}, pages = {}, pmid = {33267194}, issn = {1099-4300}, abstract = {Massive improvements in the thermophysical properties of nanofluids over conventional fluids have led to the rapid evolution of using multiwalled carbon nanotubes (MWCNTs) and graphene nanoplatelets (GNPs) in the field of heat transfer. In this study, the heat transfer and entropy generation abilities of MWCNTs/GNPs hybrid nanofluids were explored. Experiments on forced convective flow through a brass microtube with 300 µm inner diameter and 0.27 m in length were performed under uniform heat flux. MWCNTs/GNPs hybrid nanofluids were developed by adding 0.035 wt.% GNPs to MWCNTs water-based nanofluids with mass fractions of 0.075-0.125 wt.%. The range of the Reynolds number in this experiment was maintained at Re = 200-500. Results showed that the conventional approach for predicting the heat transfer coefficient was applicable for microtubes. The heat transfer coefficient increased markedly with the use of MWCNTs and MWCNTs/GNPs nanofluids, with increased pressure dropping by 12.4%. Results further showed a reduction by 37.5% in the total entropy generation rate in microtubes for hybrid nanofluids. Overall, MWCNTs/GNPs hybrid nanofluids can be used as alternative fluids in cooling systems for thermal applications.}, } @article {pmid31046340, year = {2019}, author = {Zhou, T and Sun, Y and Fattah, R and Zhang, X and Huang, X}, title = {An experimental study of trailing edge noise from a pitching airfoil.}, journal = {The Journal of the Acoustical Society of America}, volume = {145}, number = {4}, pages = {2009}, doi = {10.1121/1.5094898}, pmid = {31046340}, issn = {1520-8524}, abstract = {In this study, the far-field noise from a pitching NACA 0012 airfoil was measured at a Reynolds number of 6.6 × 10[4]. The pitching motion was in sinusoidal functions with a mean incident angle of 0°. Cases with the pitching amplitude varying from 7.5° to 15° and frequency from 3 to 8 Hz were tested, corresponding to the reduced frequency from 0.094 to 0.25. A microphone was placed in the far-field and the particle image velocimetry technique was utilized to study the flow structures near the trailing edge. The short-time Fourier transformation results of the noise signals revealed that a high-level narrow-band noise hump occurred at a specific angle of attack in a pitching cycle. At the corresponding moment, a coherent vortex street convecting on the airfoil surface was observed, and the vortex shedding frequency was in good agreement with the central frequency of the noise hump. The occurrence of the noise humps was attributed to the laminar boundary layer separation. In one pitching period, the moment when the narrow-band noise hump occurs is independent from the pitching amplitude and it is delayed as the pitching frequency increases. Larger pitching frequency or amplitude results in lower peak level of the noise humps.}, } @article {pmid31045081, year = {2019}, author = {Gao, Y and Yang, X and Fu, C and Yang, Y and Li, Z and Zhang, H and Qi, F}, title = {10 kHz simultaneous PIV/PLIF study of the diffusion flame response to periodic acoustic forcing.}, journal = {Applied optics}, volume = {58}, number = {10}, pages = {C112-C120}, doi = {10.1364/AO.58.00C112}, pmid = {31045081}, issn = {1539-4522}, abstract = {Response of a laminar diffusion dimethyl-ether flame forced by an acoustic field is provided. A forcing frequency of 100 Hz, which is chosen based on the typical thermo-acoustic instability frequency in a practical combustor, is applied to the flame at a Reynolds number of 250. The development of the forced vortical structures present in this flame has been investigated utilizing a burst mode laser with a repetition rate of 10 kHz. Flame/vortex interaction is visualized by planar laser-induced fluorescence (PLIF) of formaldehyde, which is used to identify the early-stage fuel decomposition in the flame. The flame structure is also correlated with the velocity field, which is obtained utilizing particle imaging velocimetry (PIV). The resulting phase-resolved and time-averaged velocity and vortex images indicate that the amplitude of excitation has pronounced effects on the flame via modifying the local heat release.}, } @article {pmid31045033, year = {2019}, author = {Wang, S and Liu, X and Wang, G and Xu, L and Li, L and Liu, Y and Huang, Z and Qi, F}, title = {High-repetition-rate burst-mode-laser diagnostics of an unconfined lean premixed swirling flame under external acoustic excitation.}, journal = {Applied optics}, volume = {58}, number = {10}, pages = {C68-C78}, doi = {10.1364/AO.58.000C68}, pmid = {31045033}, issn = {1539-4522}, abstract = {Lean premixed swirling flames are important in practical combustors, but a commonly encountered problem of practical swirl combustors is thermo-acoustic instability, which may cause internal structure damage to combustors. In this research, a high-repetition-rate burst-mode laser is used for simultaneous particle image velocimetry and planar laser-induced fluorescence measurement in an unconfined acoustically excited swirl burner. The time-resolved flow field and transient flame response to the acoustic perturbation are visualized at 20 kHz, offering insight into the heat release rate oscillation. The premixed mixture flow rate and acoustic modulation are varied to study the effects of Reynolds number, Strouhal number, and acoustic modulation amplitude on the swirling flame. The results suggest that the Strouhal number has a notable effect on the periodic movements of the inner recirculation zone and swirling flame configuration.}, } @article {pmid31039316, year = {2019}, author = {Mozhi Devan Padmanathan, A and Sneha Ravi, A and Choudhary, H and Varanakkottu, SN and Dalvi, SV}, title = {Predictive Framework for the Spreading of Liquid Drops and the Formation of Liquid Marbles on Hydrophobic Particle Bed.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {35}, number = {20}, pages = {6657-6668}, doi = {10.1021/acs.langmuir.9b00698}, pmid = {31039316}, issn = {1520-5827}, abstract = {In this work, we have developed a model to describe the behavior of liquid drops upon impaction on hydrophobic particle bed and verified it experimentally. Poly(tetrafluoroethylene) (PTFE) particles were used to coat drops of water, aqueous solutions of glycerol (20, 40, and 60% v/v), and ethanol (5 and 12% v/v). The experiments were conducted for Weber number (We) ranging from 8 to 130 and Reynolds number (Re) ranging from 370 to 4460. The bed porosity was varied from 0.8 to 0.6. The experimental values of βmax (ratio of the diameter at the maximum spreading condition to the initial drop diameter) were estimated from the time-lapsed images captured using a high-speed camera. The theoretical βmax was estimated by making energy balances on the liquid drop. The proposed model accounts for the energy losses due to viscous dissipation and crater formation along with a change in kinetic energy and surface energy. A good agreement was obtained between the experimental βmax and the estimated theoretical βmax. The proposed model yielded a least % absolute average relative deviation (% AARD) of 5.5 ± 4.3 compared to other models available in the literature. Further, it was found that the liquid drops impacting on particle bed are completely coated with PTFE particles with βmax values greater than 2.}, } @article {pmid31037445, year = {2019}, author = {Hatoum, H and Mo, XM and Crestanello, JA and Dasi, LP}, title = {Modeling of the Instantaneous Transvalvular Pressure Gradient in Aortic Stenosis.}, journal = {Annals of biomedical engineering}, volume = {47}, number = {8}, pages = {1748-1763}, pmid = {31037445}, issn = {1573-9686}, support = {R01 HL119824/HL/NHLBI NIH HHS/United States ; R01 HL135505/HL/NHLBI NIH HHS/United States ; R03 EB014255/EB/NIBIB NIH HHS/United States ; }, mesh = {Aortic Valve/*physiopathology ; Aortic Valve Stenosis/*physiopathology ; Cardiac Output ; Hemodynamics ; Humans ; *Models, Cardiovascular ; Pressure ; }, abstract = {The simplified and modified Bernoulli equations break down in estimating the true pressure gradient across the stenotic aortic valve due to their over simplifying assumptions of steady and inviscid conditions as well as the fundamental nature in which aortic valves are different than idealized orifices. Nevertheless, despite having newer models based on time-dependent momentum balance across an orifice, the simplified and modified Bernoulli continue to be the clinical standard because to date, they remain the only models clinically implementable. The objective of this study is to (1) illustrate the fundamental considerations necessary to accurately model the time-dependent instantaneous pressure gradient across a fixed orifice and (2) propose empirical corrections when applying orifice based models to severely stenotic aortic valves. We introduce a general model to predict the time-dependent instantaneous pressure gradient across an orifice that explicitly model the Reynolds number dependence of both the steady and unsteady terms. The accuracy of this general model is assessed with respect to previous models through pulse duplicator experiments on a round orifice model as well as an explanted stenotic surgical aortic valve both with geometric areas of 0.6 cm[2] (less than 1 cm[2] which is the threshold for stenosis determination) over cardiac outputs of 3 and 5 L/min and heart rates of 60, 90 and 120 bpm. The model and the raw experimental data corresponding to the orifice showed good agreement over a wide range of cardiac outputs and heart rates (R[2] exceeding 0.91). The derived average and peak transvalvular pressure gradients also demonstrated good agreement with no significant differences between the respective peaks (p > 0.09). The new model proposed holds promise with its physical and closed form representation of pressure drop, however accurate modeling of the time-variability of the valve area is necessary for the model to be applied on stenotic valves.}, } @article {pmid31028849, year = {2019}, author = {Heidarinejad, G and Roozbahani, MH and Heidarinejad, M}, title = {Studying airflow structures in periodic cylindrical hills of human tracheal cartilaginous rings.}, journal = {Respiratory physiology & neurobiology}, volume = {266}, number = {}, pages = {103-114}, doi = {10.1016/j.resp.2019.04.012}, pmid = {31028849}, issn = {1878-1519}, mesh = {Cartilage/*anatomy & histology ; Computer Simulation ; Humans ; *Models, Anatomic ; *Models, Biological ; *Respiratory Physiological Phenomena ; Trachea/*anatomy & histology ; }, abstract = {The objective of this study is to assess tracheobronchial flow features with the cartilaginous rings during a light exercising. Tracheobronchial is part of human's body airway system that carries oxygen-rich air to human's lungs as well as takes carbon dioxide out of the human's lungs. Consequently, evaluation of the flow structures in tracheobronchial is important to support diagnosis of tracheal disorders. Computational Fluid Dynamics (CFD) allows evaluating effectiveness of tracheal cartilage rings in human body under different configurations. This study utilizes Large Eddy Simulation (LES) to model an anatomically-based human large conducting airway model with and without cartilaginous rings at the breathing conditions at Reynolds number of 5,176 in trachea region. It is observed that small recirculating areas shaped between rings cavities. While these recirculating areas are decaying, similar to periodic 2D-hills, the cartilaginous rings contribute to the construction of a vortical flow structure in the main flow. The separated vortically-shaped zone creates a wake in the flow and passes inside of the next ring cavity and disturb its boundary layer. At last, the small recirculation flow impinges onto tracheal wall. The outcome of this impinge flow is a latitudinal rotating flow perpendicular to the main flow in a cavity between the two cartilaginous rings crest which appear and disappear within a hundredth of a second. Kelvin-Helmholtz instability is observed in trachea caused by shear flow created behind of interaction between these flow structures near to tracheal wavy wall and main flow. A comparison of the results between a smooth wall model named simplified model and a rough wall model named modified model shows that these structures do not exist in simplified model, which is common in modeling tracheobronchial flow. This study proposes to consider macro surface roughness to account for the separating and rotating instantaneous flow structures. Finally, solving trachea airflow with its cartilages can become one of major issues in measuring the validity and capability of solving flow in developing types of sub-grid scale models as a turbulence studies benchmark.}, } @article {pmid31008408, year = {2019}, author = {Vasilopoulos, K and Sarris, IE and Tsoutsanis, P}, title = {Assessment of air flow distribution and hazardous release dispersion around a single obstacle using Reynolds-averaged Navier-Stokes equations.}, journal = {Heliyon}, volume = {5}, number = {4}, pages = {e01482}, pmid = {31008408}, issn = {2405-8440}, abstract = {The flow around a cubical building, with a pollution source at the central point of the top of the cube, is studied. The Reynolds-averaged Navier-Stokes and species concentration equations are solved for Reynolds number, Re = 40,000, is based on the height of the cube. The predictions obtained with the standard, the Kato-Launder, and the low-Reynolds number k-epsilon models are examined with various wall functions for the near wall treatment of the flow. Results are compared against Martinuzzi and Tropea measurements (J. of Fluids Eng., 115, 85-92, 1993) for the flow field and against Li and Meroney (J. of Wind Eng. and Industrial Aerodynamics, 81, 333-345, 1983) experiments and Gaussian models for the concentration distribution. It is found that the present unstructured mesh model performs similarly to the structured mesh models. Results from the Kato-Launder model are closer to the experimental data for the flow patterns and contaminant distribution on the cube's roof. However, the Kato-Launder model has an over-prediction for the recirculation zone and the contaminant distribution windward of the cube. The standard k-epsilon and the low-Reynolds number k-epsilon models predict similar flow patterns and are closer to the experimental data of the cube's windward and side face.}, } @article {pmid31007546, year = {2019}, author = {Martins Afonso, M and Mitra, D and Vincenzi, D}, title = {Kazantsev dynamo in turbulent compressible flows.}, journal = {Proceedings. Mathematical, physical, and engineering sciences}, volume = {475}, number = {2223}, pages = {20180591}, pmid = {31007546}, issn = {1364-5021}, abstract = {We consider the kinematic fluctuation dynamo problem in a flow that is random, white-in-time, with both solenoidal and potential components. This model is a generalization of the well-studied Kazantsev model. If both the solenoidal and potential parts have the same scaling exponent, then, as the compressibility of the flow increases, the growth rate decreases but remains positive. If the scaling exponents for the solenoidal and potential parts differ, in particular if they correspond to typical Kolmogorov and Burgers values, we again find that an increase in compressibility slows down the growth rate but does not turn it off. The slow down is, however, weaker and the critical magnetic Reynolds number is lower than when both the solenoidal and potential components display the Kolmogorov scaling. Intriguingly, we find that there exist cases, when the potential part is smoother than the solenoidal part, for which an increase in compressibility increases the growth rate. We also find that the critical value of the scaling exponent above which a dynamo is seen is unity irrespective of the compressibility. Finally, we realize that the dimension d = 3 is special, as for all other values of d the critical exponent is higher and depends on the compressibility.}, } @article {pmid31003548, year = {2019}, author = {Zhang, M and Zhang, W and Wu, Z and Shen, Y and Chen, Y and Lan, C and Li, F and Cai, W}, title = {Comparison of Micro-Mixing in Time Pulsed Newtonian Fluid and Viscoelastic Fluid.}, journal = {Micromachines}, volume = {10}, number = {4}, pages = {}, pmid = {31003548}, issn = {2072-666X}, abstract = {Fluid mixing plays an essential role in many microfluidic applications. Here, we compare the mixing in time pulsing flows for both a Newtonian fluid and a viscoelastic fluid at different pulsing frequencies. In general, the mixing degree in the viscoelastic fluid is higher than that in the Newtonian fluid. Particularly, the mixing in Newtonian fluid with time pulsing is decreased when the Reynolds number Re is between 0.002 and 0.01, while it is enhanced when Re is between 0.1 and 0.2 compared with that at a constant flow rate. In the viscoelastic fluid, on the other hand, the time pulsing does not change the mixing degree when the Weissenberg number Wi ≤ 20, while a larger mixing degree is realized at a higher pulsing frequency when Wi = 50.}, } @article {pmid30999540, year = {2019}, author = {Duran-Matute, M and van Gorp, MD and van Heijst, GJF}, title = {Wavelength selection of vortex ripples in an oscillating cylinder: The effect of curvature and background rotation.}, journal = {Physical review. E}, volume = {99}, number = {3-1}, pages = {033105}, doi = {10.1103/PhysRevE.99.033105}, pmid = {30999540}, issn = {2470-0053}, abstract = {We present results of laboratory experiments on the formation, evolution, and wavelength selection of vortex ripples. These ripples formed on a sediment bed at the bottom of a water-filled oscillating cylindrical tank mounted on top of a rotating table. The table is made to oscillate sinusoidally in time, while a constant background rotation was added for some experiments. The changes in bed thickness are measured using a light attenuation technique. It was found that the wavelength normalized with the excursion length depends on both a Reynolds number and the Strouhal number. This differs from straight or annular geometries where the wavelength is proportional to the excursion length. The flow in an oscillating cylinder has the peculiarity that it develops a secondary flow in the radial direction that depends on the excursion length. The effect of this secondary circulation is evident in the radial transport for small values of the Strouhal number or in the orientation of the ripples for strong enough background rotation. Additionally, ripples in an oscillating cylinder present a rich dynamic behavior where the number of ripples can oscillate even with constant forcing parameters.}, } @article {pmid30999463, year = {2019}, author = {Dutta, AK and Ramachandran, G and Chaudhuri, S}, title = {Investigating thermoacoustic instability mitigation dynamics with a Kuramoto model for flamelet oscillators.}, journal = {Physical review. E}, volume = {99}, number = {3-1}, pages = {032215}, doi = {10.1103/PhysRevE.99.032215}, pmid = {30999463}, issn = {2470-0053}, abstract = {In this paper, we present experimental observations and phenomenological modeling of the intermittent dynamics that emerge while mitigating thermoacoustic instability by rotating the otherwise static swirler in a lean premixed, laboratory-scale combustor. Starting with a self-excited thermoacoustically unstable combustor, here we find that a progressive increase in swirler rotation rate does not uniformly decrease amplitudes of coherent, sinusoidal pressure or heat-release-rate oscillations. Instead, these oscillations emerge as high-amplitude bursts separated by low-amplitude noise in the signal. At increased rotational speeds, the high-amplitude coherent oscillations become scarce and their duration in the signal reduces. The velocity field from high-speed particle image velocimetry and simultaneous pressure and chemiluminescence data support these observations. Such an intermittent route to instability mitigation is reminiscent of the opposite transition implemented by changing the Reynolds number from a fully chaotic state to a fully unstable state. To model such dynamics phenomenologically, we discretize the swirling turbulent premixed flame into an ensemble of flamelet oscillators arranged circumferentially around the center body of the swirler. The Kuramoto model is proposed for these flamelet oscillators which is subsequently used to analyze their synchronization dynamics. The order parameter r, which is a measure of the synchronization between the oscillator phases, provides critical insights on the transition from the thermoacoustically unstable to stable states via intermittency. Finally, it is shown that the Kuramoto model for flamelet oscillator can qualitatively reproduce the time-averaged and intermittent dynamics while transitioning from the state of thermoacoustic instability to a state of incoherent noisy oscillations.}, } @article {pmid30999454, year = {2019}, author = {Shaik, VA and Ardekani, AM}, title = {Swimming sheet near a plane surfactant-laden interface.}, journal = {Physical review. E}, volume = {99}, number = {3-1}, pages = {033101}, doi = {10.1103/PhysRevE.99.033101}, pmid = {30999454}, issn = {2470-0053}, abstract = {In this work we analyze the velocity of a swimming sheet near a plane surfactant-laden interface by assuming the Reynolds number and the sheet's deformation to be small. We observe a nonmonotonic dependence of the sheet's velocity on the Marangoni number (Ma) and the surface Péclet number (Pe_{s} ). For a sheet passing only transverse waves, the swimming velocity increases with an increase in Ma for any fixed Pe_{s} . When Pe_{s} is increasing, on the other hand, the swimming velocity of the same sheet either increases (at large Ma) or it initially increases and then decreases (at small Ma). This dependence of the swimming velocity on Ma and Pe_{s} is altered if the sheet is passing longitudinal waves in addition to the transverse waves along its surface.}, } @article {pmid30993773, year = {2019}, author = {Cheng, JL and Au, JS and MacDonald, MJ}, title = {Peripheral artery endothelial function responses to altered shear stress patterns in humans.}, journal = {Experimental physiology}, volume = {104}, number = {7}, pages = {1126-1135}, doi = {10.1113/EP087597}, pmid = {30993773}, issn = {1469-445X}, support = {DG #238819-13//Natural Sciences and Engineering Research Council/International ; }, mesh = {Adult ; Blood Flow Velocity/*physiology ; Brachial Artery/*physiology ; Electrocardiography/methods ; Endothelium, Vascular/*physiology ; Hand Strength/physiology ; Hot Temperature ; Humans ; Male ; Regional Blood Flow/*physiology ; Shear Strength/*physiology ; *Stress, Mechanical ; Vasodilation/physiology ; Young Adult ; }, abstract = {NEW FINDINGS: What is the central question of this study? What is the effect of altered shear stress pattern, with or without concurrent neurohumoral and metabolic activation, on the acute endothelial function response assessed via brachial artery flow-mediated dilatation? What is the main finding and its importance? Despite generating distinctive shear stress patterns (i.e. increases in anterograde only, anterograde only with neurohumoral and metabolic activation, and both anterograde and retrograde), similar acute improvements were observed in the brachial artery flow-mediated dilatation response in all conditions, indicating that anterograde and/or turbulent shear stress might be the essential element to induce acute increases in endothelial function.

ABSTRACT: Endothelial function is influenced by both the direction and the magnitude of shear stress. Acute improvements in endothelial function have mostly been attributed to increased anterograde shear, whereas results from many interventional models in humans suggest that enhancing shear stress in an oscillatory manner (anterograde and retrograde) might be optimal. Here, we determined the acute brachial artery shear stress (SS) and flow-mediated dilatation (FMD) responses to three shear-altering interventions [passive heat stress (HEAT), mechanical forearm compression (CUFF) and handgrip exercise (HGEX)] and examined the relationship between changes in oscillatory shear index (OSI) and changes in FMD. During separate visits, 10 young healthy men (22 ± 3 years old) underwent 10 min of HEAT, CUFF or HGEX in their left forearm. Anterograde and retrograde SS, Reynolds number, OSI and FMD were assessed at rest and during/after each intervention. Anterograde SS increased during all interventions in a stepwise manner (P < 0.05 between interventions), with the change in HGEX (∆37.7 ± 12.2 dyn cm[-2] , P < 0.05) > CUFF (∆25.1 ± 11.9 dyn cm[-2] , P < 0.05) > HEAT (∆14.5 ± 7.9 dyn cm[-2] , P < 0.05). Retrograde SS increased during CUFF (∆-19.6 ± 4.3 dyn cm[-2] , P < 0.05). Anterograde blood flow was turbulent (i.e. Reynolds number ≥ |2000|) during all interventions (P < 0.05). The relative FMD improved after all interventions (P = 0.01), and there was no relationship between ∆OSI and ∆FMD. We elicited changes in SS profiles including increased anterograde SS (HEAT and HGEX) and both increased anterograde and retrograde SS (CUFF); regardless of the SS pattern, FMD improved to the same extent. These findings suggest that the presence of anterograde and/or turbulent SS might be the key to optimizing endothelial function in acute assessment protocols.}, } @article {pmid30978086, year = {2019}, author = {Wei, D and Dehnavi, PG and Aubin-Tam, ME and Tam, D}, title = {Is the Zero Reynolds Number Approximation Valid for Ciliary Flows?.}, journal = {Physical review letters}, volume = {122}, number = {12}, pages = {124502}, doi = {10.1103/PhysRevLett.122.124502}, pmid = {30978086}, issn = {1079-7114}, abstract = {Stokes equations are commonly used to model the hydrodynamic flow around cilia on the micron scale. The validity of the zero Reynolds number approximation is investigated experimentally with a flow velocimetry approach based on optical tweezers, which allows the measurement of periodic flows with high spatial and temporal resolution. We find that beating cilia generate a flow, which fundamentally differs from the stokeslet field predicted by Stokes equations. In particular, the flow velocity spatially decays at a faster rate and is gradually phase delayed at increasing distances from the cilia. This indicates that the quasisteady approximation and use of Stokes equations for unsteady ciliary flow are not always justified and the finite timescale for vorticity diffusion cannot be neglected. Our results have significant implications in studies of synchronization and collective dynamics of microswimmers.}, } @article {pmid30978052, year = {2019}, author = {Shekar, A and McMullen, RM and Wang, SN and McKeon, BJ and Graham, MD}, title = {Critical-Layer Structures and Mechanisms in Elastoinertial Turbulence.}, journal = {Physical review letters}, volume = {122}, number = {12}, pages = {124503}, doi = {10.1103/PhysRevLett.122.124503}, pmid = {30978052}, issn = {1079-7114}, abstract = {Simulations of elastoinertial turbulence (EIT) of a polymer solution at low Reynolds number are shown to display localized polymer stretch fluctuations. These are very similar to structures arising from linear stability (Tollmien-Schlichting modes) and resolvent analyses, i.e., critical-layer structures localized where the mean fluid velocity equals the wave speed. Computations of self-sustained nonlinear Tollmien-Schlichting waves reveal that the critical layer exhibits stagnation points that generate sheets of large polymer stretch. These kinematics may be the genesis of similar structures in EIT.}, } @article {pmid30976530, year = {2019}, author = {M, AA and V, M}, title = {Demand factor definition-A dimensionless parameter for Vertical Axis Wind Turbines.}, journal = {MethodsX}, volume = {6}, number = {}, pages = {567-581}, pmid = {30976530}, issn = {2215-0161}, abstract = {The use of dimensionless numbers like Reynolds Number, Froude Number and Webber Number has historically simplified the process of comparison of phenomena irrespective of their scales and in their classification into different categories. This paper deals with the derivational aspects of a dimensionless parameter named "Demand Factor" for optimization of Vertical Axis Wind Turbine (VAWT). •The input parameters considered in this derivation are power, wind velocity, the aspect ratio of the turbine, density of air and viscosity of air and the output parameters are length of the blade, number of blades, chord length, aerofoil shape, radius of the turbine and angular velocity at rated speed.•Four rounds of variable definition trials are carried out through the arrangement of the input parameters on the numerator and denominator positions. With the filtering out of unsuitable combinations at different stages of elimination, out of 32 combinations the expression that holds the potential to represent demand factor was identified. The process of carrying out single point optimization based on Demand factor expression is discussed along with the steps involved in numerically calculating output parameters.•The expression of Demand factor developed provides a different perspective on the process of design and optimization of VAWTs.}, } @article {pmid30960580, year = {2019}, author = {Wang, Y and Wang, Y and Cheng, Z}, title = {Direct Numerical Simulation of Gas-Liquid Drag-Reducing Cavity Flow by the VOSET Method.}, journal = {Polymers}, volume = {11}, number = {4}, pages = {}, pmid = {30960580}, issn = {2073-4360}, abstract = {Drag reduction by polymer is an important energy-saving technology, which can reduce pumping pressure or promote the flow rate of the pipelines transporting fluid. It has been widely applied to single-phase pipelines, such as oil pipelining, district heating systems, and firefighting. However, the engineering application of the drag reduction technology in two-phase flow systems has not been reported. The reason is an unrevealed complex mechanism of two-phase drag reduction and lack of numerical tools for mechanism study. Therefore, we aim to propose governing equations and numerical methods of direct numerical simulation (DNS) for two-phase gas-liquid drag-reducing flow and try to explain the reason for the two-phase drag reduction. Efficient interface tracking method-coupled volume-of-fluid and level set (VOSET) and typical polymer constitutive model Giesekus are combined in the momentum equation of the two-phase turbulent flow. Interface smoothing for conformation tensor induced by polymer is used to ensure numerical stability of the DNS. Special features and corresponding explanations of the two-phase gas-liquid drag-reducing flow are found based on DNS results. High shear in a high Reynolds number flow depresses the efficiency of the gas-liquid drag reduction, while a high concentration of polymer promotes the efficiency. To guarantee efficient drag reduction, it is better to use a high concentration of polymer drag-reducing agents (DRAs) for high shear flow.}, } @article {pmid30958231, year = {2018}, author = {Stocking, JB and Laforsch, C and Sigl, R and Reidenbach, MA}, title = {The role of turbulent hydrodynamics and surface morphology on heat and mass transfer in corals.}, journal = {Journal of the Royal Society, Interface}, volume = {15}, number = {149}, pages = {20180448}, pmid = {30958231}, issn = {1742-5662}, mesh = {Animals ; Anthozoa/*physiology ; *Coral Reefs ; *Hot Temperature ; *Hydrodynamics ; *Models, Biological ; }, abstract = {Corals require efficient heat and mass transfer with the overlying water column to support key biological processes, such as nutrient uptake and mitigation of thermal stress. Transfer rates are primarily determined by flow conditions, coral morphology and the physics of the resulting fluid-structure interaction, yet the relationship among these parameters is poorly understood especially for wave-dominated coral habitats. To investigate the interactive effects of these factors on fluxes of heat and mass, we measure hydrodynamic characteristics in situ over three distinct surface morphologies of massive stony corals in a Panamanian reef. Additionally, we implement a numerical model of flow and thermal transport for both current and wave conditions past a natural coral surface, as well as past three simplified coral morphologies with varying ratios of surface roughness spacing-to-height. We find oscillatory flow enhances rates of heat and mass transfer by 1.2-2.0× compared with unidirectional flow. Additionally, increases in Reynolds number and in surface roughness ratio produce up to a 3.3× and a 2.0× enhancement, respectively. However, as waves begin to dominate the flow regime relative to unidirectional currents, the underlying physical mechanisms mediating transfer rates shift from predominantly turbulence-driven to greater control by inertial accelerations, resulting in larger heat and mass transfer for small surface roughness ratios. We show that for rough corals in wave-dominated flows, novel trade-off dynamics for heat and mass transfer exist between broadly spaced roughness that enhances turbulence production versus narrowly spaced roughness that produces greater surface area. These findings have important implications for differential survivorship during heat-induced coral bleaching, particularly as thermal stress events become increasingly common with global climate change.}, } @article {pmid30958200, year = {2019}, author = {Tuttle, LJ and Robinson, HE and Takagi, D and Strickler, JR and Lenz, PH and Hartline, DK}, title = {Going with the flow: hydrodynamic cues trigger directed escapes from a stalking predator.}, journal = {Journal of the Royal Society, Interface}, volume = {16}, number = {151}, pages = {20180776}, pmid = {30958200}, issn = {1742-5662}, mesh = {Animals ; *Biobehavioral Sciences ; Copepoda/*physiology ; Escape Reaction/*physiology ; Fishes/*physiology ; Food Chain ; Predatory Behavior/*physiology ; Zooplankton/*physiology ; }, abstract = {In the coevolution of predator and prey, different and less well-understood rules for threat assessment apply to freely suspended organisms than to substrate-dwelling ones. Particularly vulnerable are small prey carried with the bulk movement of a surrounding fluid and thus deprived of sensory information within the bow waves of approaching predators. Some planktonic prey have solved this apparent problem, however. We quantified cues generated by the slow approach of larval clownfish (Amphiprion ocellaris) that triggered a calanoid copepod (Bestiolina similis) to escape before the fish could strike. To estimate water deformation around the copepod immediately preceding its jump, we represented the body of the fish as a rigid sphere in a hydrodynamic model that we parametrized with measurements of fish size, approach speed and distance to the copepod. Copepods of various developmental stages (CII-CVI) were sensitive to the water flow caused by the live predator, at deformation rates as low as 0.04 s[-1]. This rate is far lower than that predicted from experiments that used artificial predator-mimics. Additionally, copepods localized the source, with 87% of escapes directed away (greater than or equal to 90°) from the predator. Thus, copepods' survival in life-threatening situations relied on their detection of small nonlinear signals within an environment of locally linear deformation.}, } @article {pmid30958167, year = {2019}, author = {Nguyen, H and Koehl, MAR and Oakes, C and Bustamante, G and Fauci, L}, title = {Effects of cell morphology and attachment to a surface on the hydrodynamic performance of unicellular choanoflagellates.}, journal = {Journal of the Royal Society, Interface}, volume = {16}, number = {150}, pages = {20180736}, pmid = {30958167}, issn = {1742-5662}, mesh = {Cell Adhesion/*physiology ; Choanoflagellata/cytology/*physiology ; *Hydrodynamics ; *Models, Biological ; Surface Properties ; Swimming/*physiology ; }, abstract = {Choanoflagellates, eukaryotes that are important predators on bacteria in aquatic ecosystems, are closely related to animals and are used as a model system to study the evolution of animals from protozoan ancestors. The choanoflagellate Salpingoeca rosetta has a complex life cycle with different morphotypes, some unicellular and some multicellular. Here we use computational fluid dynamics to study the hydrodynamics of swimming and feeding by different unicellular stages of S. rosetta: a swimming cell with a collar of prey-capturing microvilli surrounding a single flagellum, a thecate cell attached to a surface and a dispersal-stage cell with a slender body, long flagellum and short collar. We show that a longer flagellum increases swimming speed, longer microvilli reduce speed and cell shape only affects speed when the collar is very short. The flux of prey-carrying water into the collar capture zone is greater for swimming than sessile cells, but this advantage decreases with collar size. Stalk length has little effect on flux for sessile cells. We show that ignoring the collar, as earlier models have done, overestimates flux and greatly overestimates the benefit to feeding performance of swimming versus being attached, and of a longer stalk for attached cells.}, } @article {pmid30958164, year = {2019}, author = {Asadzadeh, SS and Nielsen, LT and Andersen, A and Dölger, J and Kiørboe, T and Larsen, PS and Walther, JH}, title = {Hydrodynamic functionality of the lorica in choanoflagellates.}, journal = {Journal of the Royal Society, Interface}, volume = {16}, number = {150}, pages = {20180478}, pmid = {30958164}, issn = {1742-5662}, mesh = {*Choanoflagellata/physiology/ultrastructure ; *Hydrodynamics ; *Models, Biological ; Movement/*physiology ; }, abstract = {Choanoflagellates are unicellular eukaryotes that are ubiquitous in aquatic habitats. They have a single flagellum that creates a flow toward a collar filter composed of filter strands that extend from the cell. In one common group, the loricate choanoflagellates, the cell is suspended in an elaborate basket-like structure, the lorica, the function of which remains unknown. Here, we use Computational Fluid Dynamics to explore the possible hydrodynamic function of the lorica. We use the choanoflagellate Diaphaoneca grandis as a model organism. It has been hypothesized that the function of the lorica is to prevent refiltration (flow recirculation) and to increase the drag and, hence, increase the feeding rate and reduce the swimming speed. We find no support for these hypotheses. On the contrary, motile prey are encountered at a much lower rate by the loricate organism. The presence of the lorica does not affect the average swimming speed, but it suppresses the lateral motion and rotation of the cell. Without the lorica, the cell jiggles from side to side while swimming. The unsteady flow generated by the beating flagellum causes reversed flow through the collar filter that may wash away captured prey while it is being transported to the cell body for engulfment. The lorica substantially decreases such flow, hence it potentially increases the capture efficiency. This may be the main adaptive value of the lorica.}, } @article {pmid30958143, year = {2019}, author = {Asadzadeh, SS and Larsen, PS and Riisgård, HU and Walther, JH}, title = {Hydrodynamics of the leucon sponge pump.}, journal = {Journal of the Royal Society, Interface}, volume = {16}, number = {150}, pages = {20180630}, pmid = {30958143}, issn = {1742-5662}, mesh = {Animals ; Flagella/*physiology ; *Hydrodynamics ; *Models, Biological ; Porifera/*anatomy & histology/*physiology ; }, abstract = {Leuconoid sponges are filter-feeders with a complex system of branching inhalant and exhalant canals leading to and from the close-packed choanocyte chambers. Each of these choanocyte chambers holds many choanocytes that act as pumping units delivering the relatively high pressure rise needed to overcome the system pressure losses in canals and constrictions. Here, we test the hypothesis that, in order to deliver the high pressures observed, each choanocyte operates as a leaky, positive displacement-type pump owing to the interaction between its beating flagellar vane and the collar, open at the base for inflow but sealed above. The leaking backflow is caused by small gaps between the vaned flagellum and the collar. The choanocyte pumps act in parallel, each delivering the same high pressure, because low-pressure and high-pressure zones in the choanocyte chamber are separated by a seal (secondary reticulum). A simple analytical model is derived for the pump characteristic, and by imposing an estimated system characteristic we obtain the back-pressure characteristic that shows good agreement with available experimental data. Computational fluid dynamics is used to verify a simple model for the dependence of leak flow through gaps in a conceptual collar-vane-flagellum system and then applied to models of a choanocyte tailored to the parameters of the freshwater demosponge Spongilla lacustris to study its flows in detail. It is found that both the impermeable glycocalyx mesh covering the upper part of the collar and the secondary reticulum are indispensable features for the choanocyte pump to deliver the observed high pressures. Finally, the mechanical pump power expended by the beating flagellum is compared with the useful (reversible) pumping power received by the water flow to arrive at a typical mechanical pump efficiency of about 70%.}, } @article {pmid30940542, year = {2019}, author = {Janke, T and Koullapis, P and Kassinos, SC and Bauer, K}, title = {PIV measurements of the SimInhale benchmark case.}, journal = {European journal of pharmaceutical sciences : official journal of the European Federation for Pharmaceutical Sciences}, volume = {133}, number = {}, pages = {183-189}, doi = {10.1016/j.ejps.2019.03.025}, pmid = {30940542}, issn = {1879-0720}, mesh = {Acrylic Resins ; Benchmarking ; Butadienes ; Computer Simulation ; Humans ; Lung/*metabolism ; *Models, Biological ; Polystyrenes ; Printing, Three-Dimensional ; *Rheology ; }, abstract = {Particle Image Velocimetry (PIV) measurements with the aim of providing experimental data for the SimInhale benchmark case are presented within this work. We, therefore, present a refractive index matched, transparent model of the benchmark geometry, in which the velocity and turbulent kinetic energy fields are examined at flow rates comparable to 15, 30 and 60 L/min (Re ≈ 1000-4500) in air. Furthermore, these results are compared with Large Eddy Simulations (LES). The results reveal a Reynolds number independence of the qualitative velocity field in the range covered within this work. Good agreement is found between the PIV and LES data, with a slight over-prediction of turbulent kinetic energies by the simulations. The obtained experimental data will be part of a common, publicly accessible ERCOFTAC database along with additional results published recently.}, } @article {pmid30937853, year = {2019}, author = {Mancini, V and Bergersen, AW and Vierendeels, J and Segers, P and Valen-Sendstad, K}, title = {High-Frequency Fluctuations in Post-stenotic Patient Specific Carotid Stenosis Fluid Dynamics: A Computational Fluid Dynamics Strategy Study.}, journal = {Cardiovascular engineering and technology}, volume = {10}, number = {2}, pages = {277-298}, pmid = {30937853}, issn = {1869-4098}, mesh = {Aged ; Asymptomatic Diseases ; Blood Flow Velocity ; Carotid Artery, Common/*physiopathology ; Carotid Stenosis/*diagnosis/physiopathology ; Computed Tomography Angiography ; Finite Element Analysis ; *Hemodynamics ; Humans ; Hydrodynamics ; Male ; *Models, Cardiovascular ; Numerical Analysis, Computer-Assisted ; *Patient-Specific Modeling ; Predictive Value of Tests ; Proof of Concept Study ; Pulsatile Flow ; Regional Blood Flow ; Time Factors ; Vibration ; }, abstract = {PURPOSE: Screening of asymptomatic carotid stenoses is performed by auscultation of the carotid bruit, but the sensitivity is poor. Instead, it has been suggested to detect carotid bruit as neck's skin vibrations. We here take a first step towards a computational fluid dynamics proof-of-concept study, and investigate the robustness of our numerical approach for capturing high-frequent fluctuations in the post-stenotic flow. The aim was to find an ideal solution strategy from a pragmatic point of view, balancing accuracy with computational cost comparing an under-resolved direct numerical simulation (DNS) approach vs. three common large eddy simulation (LES) models (static/dynamic Smagorinsky and Sigma).

METHOD: We found a reference solution by performing a spatial and temporal refinement study of a stenosed carotid bifurcation with constant flow rate. The reference solution [Formula: see text] was compared against LES for both a constant and pulsatile flow.

RESULTS: Only the Sigma and Dynamic Smagorinsky models were able to replicate the flow field of the reference solution for a pulsatile simulation, however the computational cost of the Sigma model was lower. However, none of the sub-grid scale models were able to replicate the high-frequent flow in the peak-systolic constant flow rate simulations, which had a higher mean Reynolds number.

CONCLUSIONS: The Sigma model was the best combination between accuracy and cost for simulating the pulsatile post-stenotic flow field, whereas for the constant flow rate, the under-resolved DNS approach was better. These results can be used as a reference for future studies investigating high-frequent flow features.}, } @article {pmid30934360, year = {2019}, author = {Ma, J and Xu, L and Tian, FB and Young, J and Lai, JCS}, title = {Dynamic characteristics of a deformable capsule in a simple shear flow.}, journal = {Physical review. E}, volume = {99}, number = {2-1}, pages = {023101}, doi = {10.1103/PhysRevE.99.023101}, pmid = {30934360}, issn = {2470-0053}, abstract = {The dynamic characteristics of a two-dimensional deformable capsule in a simple shear flow are studied with an immersed boundary-lattice Boltzmann method. Simulations are conducted by varying the Reynolds number (Re) from 0.0125 to 2000 and the dimensionless shear rate (G) from 0.001 to 0.5. The G-Re plane can be divided into four regions according to the deformation dependence on the parameters considered: viscous dominant, inertia dominant, transitional, and anomalous regions. There are four typical dynamic behaviors over the G-Re plane: steady deformation, prerupture state, quasisteady deformation, and continuous elongation. Analysis indicates that the pressure distribution and its variations due to the interplay of the fluid inertia force, the viscous shear stress, and the membrane elastic force determines the complex behaviors of the capsule. The effects of the bending rigidity and the internal-to-external viscosity ratio on the dynamics of the capsule are further studied. It is found that the capsule experiences smaller deformation when the higher bending rigidity is included, and the low bending rigidity does not have a remarkable influence on the capsule deformation. The capsule normally experiences smaller deformation due to the increase of the internal-to-external viscosity ratio.}, } @article {pmid30934349, year = {2019}, author = {Pereira, M and Gissinger, C and Fauve, S}, title = {1/f noise and long-term memory of coherent structures in a turbulent shear flow.}, journal = {Physical review. E}, volume = {99}, number = {2-1}, pages = {023106}, doi = {10.1103/PhysRevE.99.023106}, pmid = {30934349}, issn = {2470-0053}, abstract = {A shear flow of liquid metal (Galinstan) is driven in an annular channel by counter-rotating traveling magnetic fields imposed at the end caps. When the traveling velocities are large, the flow is turbulent and its azimuthal component displays random reversals. Power spectra of the velocity field exhibit a 1/f^{α} power law on several decades and are related to power-law probability distributions P(τ)∼τ^{-β} of the waiting times between successive reversals. This 1/f type spectrum is observed only when the Reynolds number is large enough. In addition, the exponents α and β are controlled by the symmetry of the system; a continuous transition between two different types of Flicker noise is observed as the equatorial symmetry of the flow is broken, in agreement with theoretical predictions.}, } @article {pmid33267040, year = {2019}, author = {Geneste, D and Faller, H and Nguyen, F and Shukla, V and Laval, JP and Daviaud, F and Saw, EW and Dubrulle, B}, title = {About Universality and Thermodynamics of Turbulence.}, journal = {Entropy (Basel, Switzerland)}, volume = {21}, number = {3}, pages = {}, pmid = {33267040}, issn = {1099-4300}, abstract = {This paper investigates the universality of the Eulerian velocity structure functions using velocity fields obtained from the stereoscopic particle image velocimetry (SPIV) technique in experiments and direct numerical simulations (DNS) of the Navier-Stokes equations. It shows that the numerical and experimental velocity structure functions up to order 9 follow a log-universality (Castaing et al. Phys. D Nonlinear Phenom. 1993); this leads to a collapse on a universal curve, when units including a logarithmic dependence on the Reynolds number are used. This paper then investigates the meaning and consequences of such log-universality, and shows that it is connected with the properties of a "multifractal free energy", based on an analogy between multifractal and thermodynamics. It shows that in such a framework, the existence of a fluctuating dissipation scale is associated with a phase transition describing the relaminarisation of rough velocity fields with different Hölder exponents. Such a phase transition has been already observed using the Lagrangian velocity structure functions, but was so far believed to be out of reach for the Eulerian data.}, } @article {pmid30899783, year = {2019}, author = {Tang, X and Staack, D}, title = {Bioinspired mechanical device generates plasma in water via cavitation.}, journal = {Science advances}, volume = {5}, number = {3}, pages = {eaau7765}, pmid = {30899783}, issn = {2375-2548}, abstract = {Nature can generate plasma in liquids more efficiently than human-designed devices using electricity, acoustics, or light. In the animal world, snapping shrimp can induce cavitation that collapses to produce high pressures and temperatures, leading to efficient plasma formation with photon and shock wave emission via energy focusing. Here, we report a bioinspired mechanical device that mimics the plasma generation technique of the snapping shrimp. This device was manufactured using additive manufacturing based on micro-x-ray computed tomography of a snapping shrimp claw molt. A spring fixture was designed to reliably actuate the claw with appropriate force and velocity to produce a high-speed water jet that matches the cavitation number and Reynolds number of the shrimp. Light emission and shocks were imaged, which indicate that our device reproduces the shrimp's plasma generation technique and is more efficient than other plasma generation methods.}, } @article {pmid30891517, year = {2019}, author = {Nagaraju, G and Garvandha, M}, title = {Magnetohydrodynamic viscous fluid flow and heat transfer in a circular pipe under an externally applied constant suction.}, journal = {Heliyon}, volume = {5}, number = {2}, pages = {e01281}, pmid = {30891517}, issn = {2405-8440}, abstract = {An analytical investigation of two-dimensional heat transfer behavior of an axisymmetric incompressible dissipative viscous fluid flow in a circular pipe is considered. The flow is subjected to an externally applied uniform suction over the pipe wall in the transverse direction and a constant magnetic field opposite to the wall. The reduced Navier-Stokes equations in the cylindrical system are applied for the velocity and temperature fields. Constant wall temperature is considered as the thermal boundary condition. The velocity components are expressed into stream function and its solution is acquired by the Homotopy analysis method (HAM). The effects of magnetic body force parameter(M), suction Reynolds number (Re), Prandtl number (Pr)and Eckert number (Ec) on velocity and temperature are examined and are presented in a graphical frame. Streamlines, isotherms and pressure contours are likewise pictured. It is observed that with increasing suction Reynold number decelerates axial flow, whereas it enhances the radial flow. The temperature distribution increases with an increase in Prandtl number, whereas it decreases with an increase in Eckert number (viscous dissipation effect).}, } @article {pmid30879156, year = {2019}, author = {El-Sapa, S}, title = {Settling slip velocity of a spherical particle in an unbounded micropolar fluid.}, journal = {The European physical journal. E, Soft matter}, volume = {42}, number = {3}, pages = {32}, pmid = {30879156}, issn = {1292-895X}, abstract = {The gravitational settling of small spherical particles in an unbounded micropolar fluid with slip surfaces is considered. The motion is studied under the assumption of low Reynolds number. The slip boundary conditions on velocity and microrotation at the surface of the spherical particle is used. The solution for the stream function of the fluid flow is obtained analytically. The settling velocity is obtained and is plotted against the Knudsen number for various values of the micropolarity parameter and constants depending on the material of the solid surface. The problem of rotational motion of a particle with slip surface is also solved and the torque coefficient acting on the spherical particle is obtained and is plotted against Knudsen number for different values of micropolarity parameter, spin parameter, and the material constants. The correction to the Basset equation for settling velocity under gravity for slip particle in micropolar fluids is discussed with the range of Knudsen number which has been proven with known results available in the literature.}, } @article {pmid30875616, year = {2019}, author = {Sun, J and Liu, C and Bhushan, B}, title = {A review of beetle hindwings: Structure, mechanical properties, mechanism and bioinspiration.}, journal = {Journal of the mechanical behavior of biomedical materials}, volume = {94}, number = {}, pages = {63-73}, doi = {10.1016/j.jmbbm.2019.02.031}, pmid = {30875616}, issn = {1878-0180}, mesh = {Animals ; Biomechanical Phenomena ; *Biomimetics ; Coleoptera/*anatomy & histology/physiology ; *Mechanical Phenomena ; Movement ; Wings, Animal/*anatomy & histology/physiology ; }, abstract = {Insects have a small mass and size and a low flying Reynolds number. Consequently, they serve as an excellent bionic representation of a micro air vehicle (MAV). Coleoptera (popularly referred to as beetles) have different characteristics from other flying insects. Not only can they fly at a low Reynolds number, but they also have deployable hindwings, which directly leads to a reduction in the size of their bodies. In narrow working spaces or unfavorable environments, a beetle's hindwings can fold automatically under the hard elytron. When the environment becomes conducive to flight, the hindwings can extend and help the beetle take off. This characteristic provides inspiration for the design of a bionic deployable wing system. In this paper, the structures and mechanical properties of hindwings and the mechanism of hindwing movement are reviewed, in addition to research on bioinspired deployable wings.}, } @article {pmid30873209, year = {2019}, author = {Sepehr, H and Nikrityuk, P and Breakey, D and Sanders, RS}, title = {Numerical study of crude oil batch mixing in a long channel.}, journal = {Petroleum science}, volume = {16}, number = {1}, pages = {187-198}, pmid = {30873209}, issn = {1672-5107}, abstract = {The main objective of this work is to predict the mixing of two different miscible oils in a very long channel. The background to this problem relates to the mixing of heavy and light oil in a pipeline. As a first step, a 2D channel with an aspect ratio of 250 is considered. The batch-mixing of two miscible crude oils with different viscosities and densities is modeled using an unsteady laminar model and unsteady RANS model available in the commercial CFD solver ANSYS-Fluent. For a comparison, a LES model was used for a 3D version of the 2D channel. The distinguishing feature of this work is the Lagrangian coordinate system utilized to set no-slip wall boundary conditions. The global CFD model has been validated against classical analytical solutions. Excellent agreement has been achieved. Simulations were carried out for a Reynolds number of 6300 (calculated using light oil properties) and a Schmidt number of 10 4 . The results show that, in contrast to the unsteady RANS model, the LES and unsteady laminar models produce comparable mixing dynamics for two oils in the channel. Analysis of simulations also shows that, for a channel length of 100 m and a height of 0.4 m, the complete mixing of two oils across the channel has not been achieved. We showed that the mixing zone consists of the three different mixing sub-zones, which have been identified using the averaged mass fraction of the heavy oil along the flow direction. The first sub-zone corresponds to the main front propagation area with a length of several heights of the channel. The second and third sub-zones are characterized by so-called shear-flow-driven mixing due to the Kelvin-Helmholtz vortices occurring between oils in the axial direction. It was observed that the third sub-zone has a steeper mass fraction gradient of the heavy oil in the axial direction in comparison with the second sub-zone, which corresponds to the flow-averaged mass fraction of 0.5 for the heavy oil.}, } @article {pmid30867881, year = {2019}, author = {Kawale, D and Jayaraman, J and Boukany, PE}, title = {Microfluidic rectifier for polymer solutions flowing through porous media.}, journal = {Biomicrofluidics}, volume = {13}, number = {1}, pages = {014111}, pmid = {30867881}, issn = {1932-1058}, abstract = {Fluidic rectification refers to anisotropic flow resistance upon changing the flow direction. Polymeric solutions, in contrast to Newtonian fluids, can exhibit an anisotropic flow resistance in microfluidic devices by tuning the channel shape at low Reynolds number. Such a concept has not been investigated in an anisotropic porous medium. We have developed a fluidic rectifier based on an anisotropic porous medium consisting of a periodic array of triangular pillars that can operate at a low Reynolds number. Rectification is achieved, when the type of high Weissenberg number elastic instabilities changes with the flow direction. The flow resistance differs across the two directions of the anisotropic porous medium geometry. We have identified the type of elastic instabilities that appear in both forward and backward directions. Particularly, we found a qualitative relation between the dead-zone instability and the onset of fluidic rectification.}, } @article {pmid30866409, year = {2019}, author = {Faris Abdullah, M and Zulkifli, R and Harun, Z and Abdullah, S and Wan Ghopa, WA and Soheil Najm, A and Humam Sulaiman, N}, title = {Impact of the TiO2 Nanosolution Concentration on Heat Transfer Enhancement of the Twin Impingement Jet of a Heated Aluminum Plate.}, journal = {Micromachines}, volume = {10}, number = {3}, pages = {}, pmid = {30866409}, issn = {2072-666X}, abstract = {Here, the researchers carried out an experimental analysis of the effect of the TiO2 nanosolution concentration on the heat transfer of the twin jet impingement on an aluminum plate surface. We used three different heat transfer enhancement processes. We considered the TiO2 nanosolution coat, aluminum plate heat sink, and a twin jet impingement system. We also analyzed several other parameters like the nozzle spacing, nanosolution concentration, and the nozzle-to-plate distance and noted if these parameters could increase the heat transfer rate of the twin jet impingement system on a hot aluminum surface. The researchers prepared different nanosolutions, which consisted of varying concentrations, and coated them on the metal surface. Thereafter, we carried out an X-ray diffraction (XRD) and a Field Emission Scanning Electron Microscopy (FESEM) analysis for determining the structure and the homogeneous surface coating of the nanosolutions. This article also studied the different positions of the twin jets for determining the maximal Nusselt number (Nu). The researchers analyzed all the results and noted that the flow structure of the twin impingement jets at the interference zone was the major issue affecting the increase in the heat transfer rate. The combined influence of the spacing and nanoparticle concentration affected the flow structure, and therefore the heat transfer properties, wherein the Reynolds number (1% by volume concentration) maximally affected the Nusselt number. This improved the performance of various industrial and engineering applications. Hypothesis: Nusselt number was affected by the ratio of the nanoparticle size to the surface roughness. Heat transfer characteristics could be improved if the researchers selected an appropriate impingement system and selected the optimal levels of other factors. The surface coating with the TiO2 nanosolution also positively affected the heat transfer rate.}, } @article {pmid30863983, year = {2019}, author = {Hamid, AH and Javed, T and Ali, N}, title = {Numerical study of hydromagnetic axisymmetric peristaltic flow at high Reynolds number and wave number.}, journal = {Biophysical reviews}, volume = {11}, number = {2}, pages = {139-147}, pmid = {30863983}, issn = {1867-2450}, abstract = {The computational study of MHD peristaltic motion is investigated for axisymmetric flow problem. The developed model is present in the form of partial differential equations. Then obtained partial differential equations are transferred into stream-vorticity (ψ - ω) form. Then Galerkin Finite element method is used to find the computational results of governing problem. The current study is compared with the existing well-known results at low Reynolds number and wave number. It is revealed that the present results are in well agreement with existing results in the literature. So, it is effective for higher values of Reynolds number and wave number. The variations of streamline are present graphically against high Reynolds number. It concludes that high Reynolds number and Hartmann number increase pressure rise per unit wavelength in positive pumping region sharply.}, } @article {pmid30861480, year = {2019}, author = {Luo, X and Yin, H and Ren, J and Yan, H and Huang, X and Yang, D and He, L}, title = {Enhanced mixing of binary droplets induced by capillary pressure.}, journal = {Journal of colloid and interface science}, volume = {545}, number = {}, pages = {35-42}, doi = {10.1016/j.jcis.2019.03.016}, pmid = {30861480}, issn = {1095-7103}, abstract = {The mixing of binary droplets is of paramount importance in microfluidic systems. In order to reveal the mixing mechanism of two free droplets suspended in the immiscible phase, we have developed a novel experimental setup to study the internal mixing in coalescing droplets with varying interfacial tension differences and droplet sizes. It is confirmed that the interfacial energy of droplets supports the jet flow and liquid bridge expansion during the coalescence of droplets. The increase of interfacial tension difference can increase the intensity of jet flow accompanied with slower liquid bridge expansion, which enhances the mixing of droplets. The decrease of droplet size can increase the initial velocity of jet flow. However, the intensity of jet flow decreases due to the rapid expansion of the liquid bridge, which results in weaker internal mixing. On this basis, a Reynolds number incorporating the jet velocity and droplet size is proposed to characterize the vortex size, which represents the degree of droplet mixing. This study presents an effective approach for enhancing the mixing of droplets.}, } @article {pmid30845732, year = {2019}, author = {Ye, C and Liu, J and Wu, X and Wang, B and Zhang, L and Zheng, Y and Xu, T}, title = {Hydrophobicity Influence on Swimming Performance of Magnetically Driven Miniature Helical Swimmers.}, journal = {Micromachines}, volume = {10}, number = {3}, pages = {}, pmid = {30845732}, issn = {2072-666X}, abstract = {Helical microswimmers have been involved in a wide variety of applications, ranging from in vivo tasks such as targeted drug delivery to in vitro tasks such as transporting micro objects. Over the past decades, a number of studies have been established on the swimming performance of helical microswimmers and geometrical factors influencing their swimming performance. However, limited studies have focused on the influence of the hydrophobicity of swimmers' surface on their swimming performance. In this paper, we first demonstrated through theoretical analysis that the hydrophobicity of swimmer's surface material of the swimmer does affect its swimming performance: the swimmer with more hydrophobic surface is exerted less friction drag torque, and should therefore exhibit a higher step-out frequency, indicating that the swimmer with more hydrophobic surface should have better swimming performance. Then a series of experiments were conducted to verify the theoretical analysis. As a result, the main contribution of this paper is to demonstrate that one potential approach to improve the helical microswimmers' swimming performance could be making its surface more hydrophobic.}, } @article {pmid30845671, year = {2019}, author = {Xia, Z and Xiao, Y and Yang, Z and Li, L and Wang, S and Liu, X and Tian, Y}, title = {Droplet Impact on the Super-Hydrophobic Surface with Micro-Pillar Arrays Fabricated by Hybrid Laser Ablation and Silanization Process.}, journal = {Materials (Basel, Switzerland)}, volume = {12}, number = {5}, pages = {}, pmid = {30845671}, issn = {1996-1944}, abstract = {A super-hydrophobic aluminum alloy surface with decorated pillar arrays was obtained by hybrid laser ablation and further silanization process. The as-prepared surface showed a high apparent contact angle of 158.2 ± 2.0° and low sliding angle of 3 ± 1°. Surface morphologies and surface chemistry were explored to obtain insights into the generation process of super-hydrophobicity. The main objective of this current work is to investigate the maximum spreading factor of water droplets impacting on the pillar-patterned super-hydrophobic surface based on the energy conservation concept. Although many previous studies have investigated the droplet impacting behavior on flat solid surfaces, the empirical models were proposed based on a few parameters including the Reynolds number (Re), Weber number (We), as well as the Ohnesorge number (Oh). This resulted in limitations for the super-hydrophobic surfaces due to the ignorance of the geometrical parameters of the pillars and viscous energy dissipation for liquid flow within the pillar arrays. In this paper, the maximum spreading factor was deduced from the perspective of energy balance, and the predicted results were in good agreement with our experimental results with a mean error of 4.99% and standard deviation of 0.10.}, } @article {pmid30842437, year = {2019}, author = {Yang, G and Hou, C and Zhao, M and Mao, W}, title = {Comparison of convective heat transfer for Kagome and tetrahedral truss-cored lattice sandwich panels.}, journal = {Scientific reports}, volume = {9}, number = {1}, pages = {3731}, pmid = {30842437}, issn = {2045-2322}, abstract = {The aim of this paper is to make a thorough comparison between Kagome and tetrahedral truss-cored lattices both experimentally and numerically. Two titanium sandwich panels -one cored with the Kagome lattice and the other with the tetrahedral lattice -are manufactured by 3D printing technology. Comparisons of the thermal insulation, the inner flow pattern and the heat transfer between the two sandwich panels are completed subsequently according to the results from forced convective experiments and numerical simulation. Within the Reynolds number range of interest for this study, the Kagome lattice exhibits excellent heat dissipation compared with the tetrahedral lattice. In particular, when the cooling air flows in the direction OB of the two sandwich panels, the Kagome lattice provides an 8~37% higher overall Nusselt number for the sandwich panel compared to the tetrahedral lattice. The superiority of the Kagome lattice comes from a unique configuration in which the centre vertex acting as the vortex generator not only disturbs the primary flow but also induces more serious flow stagnation and separation. The complex fluid flow behaviours enhance heat transfer on both the endwalls and the trusses while causing a pressure drop that is almost two times higher than that of the tetrahedral lattice in the flow direction OB.}, } @article {pmid30830969, year = {2019}, author = {Khair, AS and Balu, B}, title = {The lift force on a charged sphere that translates and rotates in an electrolyte.}, journal = {Electrophoresis}, volume = {40}, number = {18-19}, pages = {2407-2414}, doi = {10.1002/elps.201900029}, pmid = {30830969}, issn = {1522-2683}, support = {CBET-135064//National Science Foundation/International ; }, mesh = {Colloids/*chemistry ; Diffusion ; Electrolytes/*chemistry ; Electrophoresis/*methods ; Ions/*chemistry ; Kinetics ; Rotation ; }, abstract = {The distortion of the charge cloud around a uniformly charged, dielectric, rigid sphere that translates and rotates in an unbounded binary, symmetric electrolyte at zero Reynolds number is examined. The zeta potential of the particle ζ is assumed small relative to the thermal voltage scale. It is assumed that the equilibrium structure of the cloud is slightly distorted, which requires that the Péclet numbers characterizing distortion due to particle translation, Pet=Ua/D , and rotation, Per=Ωa2/D , are small compared to unity. Here, a is radius of the particle; D is the ionic diffusion coefficient; U=|U| and Ω=|Ω| , where U and Ω are the rectilinear and angular velocities of the particle, respectively. Perturbation expansions for small Pet and Per are employed to calculate the nonequilibrium structure of the cloud, whence the force and torque on the particle are determined. In particular, we predict that the sphere experiences a force orthogonal to its directions of translation and rotation. This "lift" force arises from the nonlinear distortion of the cloud under the combined actions of particle translation and rotation. The lift force is given by Flift=L(κa)(εa3ζ2/D2)U×Ω[1+O(Pet,Per)] . Here, ε is the permittivity of the electrolyte; κ-1 is the Debye length; and L(κa) is a negative function that decreases in magnitude with increasing κa . The lift force implies that an unconstrained particle would follow a curved path; an electrokinetic analog of the inertial Magnus effect. Finally, the implication of the lift force on cross-streamline migration of an electrophoretic particle in shear flow is discussed.}, } @article {pmid30823482, year = {2019}, author = {Rehman, D and Morini, GL and Hong, C}, title = {A Comparison of Data Reduction Methods for Average Friction Factor Calculation of Adiabatic Gas Flows in Microchannels.}, journal = {Micromachines}, volume = {10}, number = {2}, pages = {}, pmid = {30823482}, issn = {2072-666X}, abstract = {In this paper, a combined numerical and experimental approach for the estimation of the average friction factor along adiabatic microchannels with compressible gas flows is presented. Pressure-drop experiments are performed for a rectangular microchannel with a hydraulic diameter of 295 μ m by varying Reynolds number up to 17,000. In parallel, the calculation of friction factor has been repeated numerically and results are compared with the experimental work. The validated numerical model was also used to gain an insight of flow physics by varying the aspect ratio and hydraulic diameter of rectangular microchannels with respect to the channel tested experimentally. This was done with an aim of verifying the role of minor loss coefficients for the estimation of the average friction factor. To have laminar, transitional, and turbulent regimes captured, numerical analysis has been performed by varying Reynolds number from 200 to 20,000. Comparison of numerically and experimentally calculated gas flow characteristics has shown that adiabatic wall treatment (Fanno flow) results in better agreement of average friction factor values with conventional theory than the isothermal treatment of gas along the microchannel. The use of a constant value for minor loss coefficients available in the literature is not recommended for microflows as they change from one assembly to the other and their accurate estimation for compressible flows requires a coupling of numerical analysis with experimental data reduction. Results presented in this work demonstrate how an adiabatic wall treatment along the length of the channel coupled with the assumption of an isentropic flow from manifold to microchannel inlet results in a self-sustained experimental data reduction method for the accurate estimation of friction factor values even in presence of significant compressibility effects. Results also demonstrate that both the assumption of perfect expansion and consequently wrong estimation of average temperature between inlet and outlet of a microchannel can be responsible for an apparent increase in experimental average friction factor in choked flow regime.}, } @article {pmid33479548, year = {2019}, author = {Hein, S and Theiss, A and Di Giovanni, A and Stemmer, C and Schilden, T and Schröder, W and Paredes, P and Choudhari, MM and Li, F and Reshotko, E}, title = {Numerical Investigation of Roughness Effects on Transition on Spherical Capsules.}, journal = {Journal of spacecraft and rockets}, volume = {56}, number = {2}, pages = {388-404}, pmid = {33479548}, issn = {0022-4650}, support = {/ARMD/Aeronautics NASA/United States ; }, abstract = {To address the hitherto unknown mechanism of boundary-layer transition on blunt reentry capsules, the role of roughness-induced disturbance growth on a spherical-section forebody is assessed via optimal transient growth theory and direct numerical simulations (DNS). Optimal transient-growth studies have been performed for the blunt capsule experiments at Mach 5.9 in the Hypersonic Ludwieg tube Braunschweig (HLB) of the Technische Universität Braunschweig, which included measurements behind a patch of controlled, distributed micron-sized surface roughness. Transient-growth results for the HLB capsule indicate similar trends as the corresponding numerical data for a Mach 6 experiment in the Actively Controlled Expansion (ACE) facility of the Texas A&M University (TAMU) at a lower Reynolds number. Both configurations indicate a similar dependence on surface temperature ratio, and more important, rather low values of maximum energy gain. DNS are performed for the conditions of the HLB experiment to understand the generation of stationary disturbances by the roughness patch and the accompanying evolution of unsteady perturbations. However, no evidence of either modal or nonmodal disturbance growth in the wake of the roughness patch is found in the DNS data; thus, the physical mechanism underlying the observed onset of transition still remains unknown.}, } @article {pmid30818010, year = {2019}, author = {Xia, Y and Yuan, M and Chen, M and Li, J and Ci, T and Ke, X}, title = {Liquid jet breakup: A new method for the preparation of poly lactic-co-glycolic acid microspheres.}, journal = {European journal of pharmaceutics and biopharmaceutics : official journal of Arbeitsgemeinschaft fur Pharmazeutische Verfahrenstechnik e.V}, volume = {137}, number = {}, pages = {140-147}, doi = {10.1016/j.ejpb.2019.02.021}, pmid = {30818010}, issn = {1873-3441}, mesh = {Chemistry, Pharmaceutical/methods ; Delayed-Action Preparations ; Drug Carriers/*chemistry ; Drug Compounding/methods ; Drug Liberation ; Microspheres ; Particle Size ; Polylactic Acid-Polyglycolic Acid Copolymer/*chemistry ; Risperidone/*administration & dosage/chemistry ; Surface Tension ; Technology, Pharmaceutical/*methods ; Viscosity ; }, abstract = {The purpose of this study was to apply the phenomenon of liquid jet breakup to the preparation of sustained-release microspheres. The mechanisms of liquid jet breakup in different jet states were investigated and the single factor method was used to study the effect of each process parameter on the particle size and size distribution of microspheres. Meantime, the prepared microspheres were characterized by morphology, drug loading, encapsulation efficiency and in vitro release. The results indicated that the process of liquid jet breakup could have 5 different states. The laminar flow state dominated when the Reynolds number (Re) was low, and the prepared microspheres had larger particle sizes. When the Re was high, the turbulent state was dominant and the microspheres had smaller particle sizes. And during the transition state from the laminar flow to the turbulence, the microspheres had a wide particle size distribution. Different process parameters could affect the particle size and distribution of microspheres by changing the Re, surface tension coefficient and viscosity. The microspheres prepared by liquid jet breakup were smooth and round with the drug loading of 35% and the encapsulation efficiency of 88%. In addition, when the polymeric carrier materials were different, the microspheres could have various drug release models such as sustained release with a lag phase, sustained release with no lag phase, pulsed release and so on, which could be applied widespread in the future.}, } @article {pmid30813604, year = {2019}, author = {Kim, J and Davidson, S and Mani, A}, title = {Characterization of Chaotic Electroconvection near Flat Inert Electrodes under Oscillatory Voltages.}, journal = {Micromachines}, volume = {10}, number = {3}, pages = {}, pmid = {30813604}, issn = {2072-666X}, abstract = {The onset of electroconvective instability in an aqueous binary electrolyte under external oscillatory electric fields at a single constant frequency is investigated in a 2D parallel flat electrode setup. Direct numerical simulations (DNS) of the Poisson[-]Nernst[-]Planck equations coupled with the Navier[-]Stokes equations at a low Reynolds number are carried out. Previous studies show that direct current (DC) electric field can create electroconvection near ion-selecting membranes in microfluidic devices. In this study, we show that electroconvection can be generated near flat inert electrodes when the applied electric field is oscillatory in time. A range of applied voltage, the oscillation frequency and the ratio of ionic diffusivities is examined to characterize the regime in which electroconvection takes place. Similar to electroconvection under DC voltages, AC electroconvection occurs at sufficiently high applied voltages in units of thermal volts and is characterized by transverse instabilities, physically manifested by an array of counter-rotating vortices near the electrode surfaces. The oscillating external electric field periodically generate and destroy such unsteady vortical structures. As the oscillation frequency is reduced to O (10 - 1) of the intrinsic resistor[-]capacitor (RC) frequency of electrolyte, electroconvective instability is considerably amplified. This is accompanied by severe depletion of ionic species outside the thin electric double layer and by vigorous convective transport involving a wide range of scales including those comparable to the distance L between the parallel electrodes. The underlying mechanisms are distinctly nonlinear and multi-dimensional. However, at higher frequencies of order of the RC frequency, the electrolyte response becomes linear, and the present DNS prediction closely resembles those explained by 1D asymptotic studies. Electroconvective instability supports increased electric current across the system. Increasing anion diffusivity results in stronger amplification of electroconvection over all oscillation frequencies examined in this study. Such asymmetry in ionic diffusivity, however, does not yield consistent changes in statistics and energy spectrum at all wall-normal locations and frequencies, implying more complex dynamics and different scaling for electrolytes with unequal diffusivities. Electric current is substantially amplified beyond the ohmic current at high oscillation frequencies. Also, it is found that anion diffusivity higher than cation has stronger impact on smaller-scale motions (≲ 0.1 L).}, } @article {pmid30811449, year = {2019}, author = {Khani, M and Lawrence, BJ and Sass, LR and Gibbs, CP and Pluid, JJ and Oshinski, JN and Stewart, GR and Zeller, JR and Martin, BA}, title = {Characterization of intrathecal cerebrospinal fluid geometry and dynamics in cynomolgus monkeys (macaca fascicularis) by magnetic resonance imaging.}, journal = {PloS one}, volume = {14}, number = {2}, pages = {e0212239}, pmid = {30811449}, issn = {1932-6203}, support = {P20 GM103408/GM/NIGMS NIH HHS/United States ; U54 GM104944/GM/NIGMS NIH HHS/United States ; }, mesh = {Animals ; Central Nervous System Diseases/*diagnostic imaging ; Cerebrospinal Fluid/*diagnostic imaging ; Female ; Hydrodynamics ; Macaca fascicularis ; *Magnetic Resonance Imaging ; Male ; Spine/*diagnostic imaging ; }, abstract = {Recent advancements have been made toward understanding the diagnostic and therapeutic potential of cerebrospinal fluid (CSF) and related hydrodynamics. Increased understanding of CSF dynamics may lead to improved detection of central nervous system (CNS) diseases and optimized delivery of CSF based CNS therapeutics, with many proposed therapeutics hoping to successfully treat or cure debilitating neurological conditions. Before significant strides can be made toward the research and development of interventions designed for human use, additional research must be carried out with representative subjects such as non-human primates (NHP). This study presents a geometric and hydrodynamic characterization of CSF in eight cynomolgus monkeys (Macaca fascicularis) at baseline and two-week follow-up. Results showed that CSF flow along the entire spine was laminar with a Reynolds number ranging up to 80 and average Womersley number ranging from 4.1-7.7. Maximum CSF flow rate occurred ~25 mm caudal to the foramen magnum. Peak CSF flow rate ranged from 0.3-0.6 ml/s at the C3-C4 level. Geometric analysis indicated that average intrathecal CSF volume below the foramen magnum was 7.4 ml. The average surface area of the spinal cord and dura was 44.7 and 66.7 cm2 respectively. Subarachnoid space cross-sectional area and hydraulic diameter ranged from 7-75 mm2 and 2-3.7 mm, respectively. Stroke volume had the greatest value of 0.14 ml at an axial location corresponding to C3-C4.}, } @article {pmid30808870, year = {2019}, author = {Mayzel, J and Steinberg, V and Varshney, A}, title = {Stokes flow analogous to viscous electron current in graphene.}, journal = {Nature communications}, volume = {10}, number = {1}, pages = {937}, pmid = {30808870}, issn = {2041-1723}, abstract = {Electron transport in two-dimensional conducting materials such as graphene, with dominant electron-electron interaction, exhibits unusual vortex flow that leads to a nonlocal current-field relation (negative resistance), distinct from the classical Ohm's law. The transport behavior of these materials is best described by low Reynolds number hydrodynamics, where the constitutive pressure-speed relation is Stoke's law. Here we report evidence of such vortices observed in a viscous flow of Newtonian fluid in a microfluidic device consisting of a rectangular cavity-analogous to the electronic system. We extend our experimental observations to elliptic cavities of different eccentricities, and validate them by numerically solving bi-harmonic equation obtained for the viscous flow with no-slip boundary conditions. We verify the existence of a predicted threshold at which vortices appear. Strikingly, we find that a two-dimensional theoretical model captures the essential features of three-dimensional Stokes flow in experiments.}, } @article {pmid30802483, year = {2019}, author = {Tassew, FA and Bergland, WH and Dinamarca, C and Bakke, R}, title = {Settling velocity and size distribution measurement of anaerobic granular sludge using microscopic image analysis.}, journal = {Journal of microbiological methods}, volume = {159}, number = {}, pages = {81-90}, doi = {10.1016/j.mimet.2019.02.013}, pmid = {30802483}, issn = {1872-8359}, mesh = {Anaerobiosis ; Bioreactors/microbiology ; Microscopy/*methods ; Particle Size ; Sewage/*chemistry/microbiology ; }, abstract = {Settling velocity and size distribution of anaerobic granular sludge samples were studied using microscopic image analysis and settling column experiments. Five granule samples were considered in this study. Three samples were collected at the Top, Middle and Bottom sections of a lab scale upflow anaerobic sludge bed reactor (UASB). Two other granule samples were obtained from industries. This paper aims to establish a method that uses microscopic image analysis and shape factor as a tool to determine the size distribution and settling velocity of anaerobic granules. Image analysis technique was used to calculate the shape factor and equivalent diameter of granules. The equivalent diameter was then used to calculate the theoretical settling velocities based on Allen's formula and estimate size distributions. The results showed that there was a good agreement between the theoretical and experimental mean settling velocity values. Both measured and calculated settling velocities increased with increasing Reynolds number (Re). However, the agreement between measured and calculated values was found to be weaker at higher Re values. Size distribution analyses of the granules have revealed that there was significant difference in the size distribution of granule samples collected at different heights of the lab scale reactor. Overall, granules from the bottom section of the reactor had larger diameter, settling velocity and shape factor than those at the middle and top section granules. Whereas granules collected from the top section exhibited the smallest granular diameter, settling velocity and shape factor.}, } @article {pmid30800393, year = {2019}, author = {Marner, F and Scholle, M and Herrmann, D and Gaskell, PH}, title = {Competing Lagrangians for incompressible and compressible viscous flow.}, journal = {Royal Society open science}, volume = {6}, number = {1}, pages = {181595}, pmid = {30800393}, issn = {2054-5703}, abstract = {A recently proposed variational principle with a discontinuous Lagrangian for viscous flow is reinterpreted against the background of stochastic variational descriptions of dissipative systems, underpinning its physical basis from a different viewpoint. It is shown that additional non-classical contributions to the friction force occurring in the momentum balance vanish by time averaging. Accordingly, the discontinuous Lagrangian can alternatively be understood from the standpoint of an analogous deterministic model for irreversible processes of stochastic character. A comparison is made with established stochastic variational descriptions and an alternative deterministic approach based on a first integral of Navier-Stokes equations is undertaken. The applicability of the discontinuous Lagrangian approach for different Reynolds number regimes is discussed considering the Kolmogorov time scale. A generalization for compressible flow is elaborated and its use demonstrated for damped sound waves.}, } @article {pmid30795856, year = {2019}, author = {Medici, G and West, LJ and Banwart, SA}, title = {Groundwater flow velocities in a fractured carbonate aquifer-type: Implications for contaminant transport.}, journal = {Journal of contaminant hydrology}, volume = {222}, number = {}, pages = {1-16}, doi = {10.1016/j.jconhyd.2019.02.001}, pmid = {30795856}, issn = {1873-6009}, mesh = {Carbonates ; England ; *Groundwater ; *Water Movements ; Water Wells ; }, abstract = {Contaminants that are highly soluble in groundwater are rapidly transported via fractures in mechanically resistant sedimentary rock aquifers. Hence, a rigorous methodology is needed to estimate groundwater flow velocities in such fractured aquifers. Here, we propose an approach using borehole hydraulic testing to compute flow velocities in an un-faulted area of a fractured carbonate aquifer by applying the cubic law to a parallel plate model. The Cadeby Formation (Yorkshire, NE England) - a Permian dolostone aquifer present beneath the University of Leeds Farm - is the fractured aquifer selected for this hydraulic experiment. The bedding plane fractures of this dolostone aquifer, which are sub-horizontal, sub-parallel and laterally persistent, largely dominate the flow at shallow (<~40 mBGL) depths. These flowing bedding plane discontinuities are separated by a rock matrix which is relatively impermeable (Kwell-test/Kcore-plug~10[4]) as is common in fractured carbonate aquifers. In the workflow reported here, the number of flowing fractures - mainly bedding plane fractures - intersecting three open monitoring wells are found from temperature/fluid conductivity and acoustic/optical televiewer logging. Following well installation, average fracture hydraulic apertures for screened intervals are found from analysis of slug tests. For the case study aquifer, this workflow predicts hydraulic apertures ranging from 0.10 up to 0.54 mm. However, groundwater flow velocities range within two order of magnitude from 13 up to 242 m/day. Notably, fracture apertures and flow velocities rapidly reduce with increasing depth below the water table; the upper ~10 m shows relatively high values of hydraulic conductivity (0.30-2.85 m/day) and corresponding flow velocity (33-242 m/day). Permeability development around the water table in carbonate aquifer-types is common, and arises where high pCO2 recharge water from the soil zone causes calcite/dolomite dissolution. Hence, agricultural contaminants entering the aquifer with recharge water are laterally transported rapidly within this upper part. Computation of groundwater flow velocities allows determination of the Reynolds number. Values of up ~1, indicating the lower limit of the transition from laminar to turbulent flow, are found at the studied site, which is situated away from major fault traces. Hence, turbulent flow is likely to arise in proximity to tectonic structures, such as normal faults, which localize flow and enhance karstification. The occurrence of turbulent flow in correspondence of such tectonic structures should be represented in regional groundwater flow simulations.}, } @article {pmid30790045, year = {2019}, author = {Hyeon, J and So, H}, title = {Microfabricaton of microfluidic check valves using comb-shaped moving plug for suppression of backflow in microchannel.}, journal = {Biomedical microdevices}, volume = {21}, number = {1}, pages = {19}, doi = {10.1007/s10544-019-0365-1}, pmid = {30790045}, issn = {1572-8781}, mesh = {Equipment Design ; Humans ; *Lab-On-A-Chip Devices ; *Microfluidic Analytical Techniques/instrumentation/methods ; *Microfluidics/instrumentation/methods ; }, abstract = {This study reports on an efficient microscale one-way valve system that combines the physical properties of photopolymerized microstructures and viscoelastic microchannels to rectify flows with low Reynolds numbers. The comb-shaped moving plug in the microchannel prevented backflow in the closed state to ensure that the microchannel remained completely blocked in the closed state, but allowed forward flow in the open state. This microfluidic check valve was microfabricated using the combination of the soft lithography and the releasing methods with the use of a double photoresist layer to create microchannels and free-moving comb-shaped microstructures, respectively. As a result, the microfluidic check valves elicited average high-pressure differences as much as 10.75 kPa between the backward and forward flows at low Reynolds numbers of the order of 0.253, thus demonstrating efficient rectification of microfluids. This study supports the use of rectification systems for the development of biomedical devices, such as drug delivery, micropumps, and lab-on-a-chip, by allowing unidirectional flow.}, } @article {pmid30785756, year = {2019}, author = {Wang, P and Cilliers, JJ and Neethling, SJ and Brito-Parada, PR}, title = {Effect of Particle Size on the Rising Behavior of Particle-Laden Bubbles.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {35}, number = {10}, pages = {3680-3687}, doi = {10.1021/acs.langmuir.8b04112}, pmid = {30785756}, issn = {1520-5827}, abstract = {The rising behavior of bubbles, initially half and fully coated with glass beads of various sizes, was investigated. The bubble velocity, aspect ratio, and oscillation periods were determined using high-speed photography and image analysis. In addition, the acting forces, drag modification factor, and modified drag coefficient were calculated and interpreted. Results show that the aspect ratio oscillation of the rising bubbles is similar, irrespective of the attached particle size. As the particle size is increased, the rising bubbles have a lower velocity and aspect ratio amplitude, with the time from release to each aspect ratio peak increasing. Higher particle coverage is shown to decrease the bubble velocity and dampen the oscillations, reducing the number of aspect ratio peaks observed. The highest rise velocities correspond to the lowest aspect ratios and vice versa, whereas a constant aspect ratio yields a constant rise velocity, independent of the particle size. Force analysis shows that the particle drag modification factor increases with the increased particle size and is greatest for fully laden bubbles. The modified drag coefficient of particle-laden bubbles increases with the increased particle size, although it decreases with the increased Reynolds number independent of the particle size. The drag force exerted by the particles plays a more dominant role in decreasing bubble velocities as the particle size increases. The results and interpretation produced a quantitative description of the behavior of rising particle-laden bubbles and the development of correlations will enhance the modeling of industrial applications.}, } @article {pmid30781378, year = {2019}, author = {Álvarez-Regueiro, E and Vallejo, JP and Fernández-Seara, J and Fernández, J and Lugo, L}, title = {Experimental Convection Heat Transfer Analysis of a Nano-Enhanced Industrial Coolant.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {9}, number = {2}, pages = {}, pmid = {30781378}, issn = {2079-4991}, abstract = {Convection heat transfer coefficients and pressure drops of four functionalized graphene nanoplatelet nanofluids based on the commercial coolant Havoline[®] XLC Pre-mixed 50/50 were experimentally determined to assess its thermal performance. The potential heat transfer enhancement produced by nanofluids could play an important role in increasing the efficiency of cooling systems. Particularly in wind power, the increasing size of the wind turbines, up to 10 MW nowadays, requires sophisticated liquid cooling systems to keep the nominal temperature conditions and protect the components from temperature degradation and hazardous environment in off-shore wind parks. The effect of nanoadditive loading, temperature and Reynolds number in convection heat transfer coefficients and pressure drops is discussed. A dimensionless analysis of the results is carried out and empirical correlations for the Nusselt number and Darcy friction factor are proposed. A maximum enhancement in the convection heat transfer coefficient of 7% was found for the nanofluid with nanoadditive loading of 0.25 wt %. Contrarily, no enhancement was found for the nanofluids of higher functionalized graphene nanoplatelet mass fraction.}, } @article {pmid30780337, year = {2019}, author = {Lyu, YZ and Zhu, HJ and Sun, M}, title = {Flapping-mode changes and aerodynamic mechanisms in miniature insects.}, journal = {Physical review. E}, volume = {99}, number = {1-1}, pages = {012419}, doi = {10.1103/PhysRevE.99.012419}, pmid = {30780337}, issn = {2470-0053}, mesh = {*Air ; Animals ; Biomechanical Phenomena ; *Flight, Animal ; Insecta/*physiology ; }, abstract = {Miniature insects fly at very low Reynolds number (Re); low Re means large viscous effect. If flapping as larger insects, sufficient vertical force cannot be produced. We measure the wing kinematics for miniature-insect species of different sizes and compute the aerodynamic forces. The planar upstroke commonly used by larger insects changes to a U-shaped upstroke, which becomes deeper as size or Re decreases. For relatively large miniature insects, the U-shaped upstroke produces a larger vertical force than a planar upstroke by having a larger wing velocity and, for very small ones, the deep U-shaped upstroke produces a large transient drag directed upwards, providing the required vertical force.}, } @article {pmid30780316, year = {2019}, author = {Jiang, L and Sun, C and Calzavarini, E}, title = {Robustness of heat transfer in confined inclined convection at high Prandtl number.}, journal = {Physical review. E}, volume = {99}, number = {1-1}, pages = {013108}, doi = {10.1103/PhysRevE.99.013108}, pmid = {30780316}, issn = {2470-0053}, abstract = {We investigate the dependency of the magnitude of heat transfer in a convection cell as a function of its inclination by means of experiments and simulations. The study is performed with a working fluid of large Prandtl number, Pr≃480, and at Rayleigh numbers Ra≃10^{8} and Ra≃5×10^{8} in a quasi-two-dimensional rectangular cell with unit aspect ratio. By changing the inclination angle (β) of the convection cell, the character of the flow can be changed from moderately turbulent, for β=0^{∘}, to laminar and steady at β=90^{∘} . The global heat transfer is found to be insensitive to the drastic reduction of turbulent intensity, with maximal relative variations of the order of 20% at Ra≃10^{8} and 10% at Ra≃5×10^{8}, while the Reynolds number, based on the global root-mean-square velocity, is strongly affected with a decay of more than 85% occurring in the laminar regime. We show that the intensity of the heat flux in the turbulent regime can be only weakly enhanced by establishing a large-scale circulation flow by means of small inclinations. However, in the laminar regime the heat is transported solely by a slow large-scale circulation flow which exhibits large correlations between the velocity and temperature fields. For inclination angles close to the transition regime in-between the turbulentlike and laminar state, a quasiperiodic heat-flow bursting phenomenon is observed.}, } @article {pmid30780239, year = {2019}, author = {Suman, VK and Viknesh S, S and Tekriwal, MK and Bhaumik, S and Sengupta, TK}, title = {Grid sensitivity and role of error in computing a lid-driven cavity problem.}, journal = {Physical review. E}, volume = {99}, number = {1-1}, pages = {013305}, doi = {10.1103/PhysRevE.99.013305}, pmid = {30780239}, issn = {2470-0053}, abstract = {The investigation on grid sensitivity for the bifurcation problem of the canonical lid-driven cavity (LDC) flow results is reported here with very fine grids. This is motivated by different researchers presenting different first bifurcation critical Reynolds number (Re_{cr1} ), which appears to depend on the formulation, numerical method, and choice of grid. By using a very-high-accuracy parallel algorithm, and the same method with which sequential results were presented by Lestandi et al. [Comput. Fluids 166, 86 (2018)CPFLBI0045-793010.1016/j.compfluid.2018.01.038] [for (257 × 257) and (513 × 513) uniformly spaced grid], we present results using (1025×1025) and (2049×2049) grid points. Detailed results presented using these grids help us understand the computational physics of the numerical receptivity of the LDC flow, with and without explicit excitation. The mathematical physics of the investigated problem will become apparent when we identify the roles of numerical errors with the ambient omnipresent disturbances in real physical flows as interchangeable. In physical or in numerical setups, presence of disturbances cannot be ignored. In this context, the need for explicit excitation for the used compact scheme arises for a definitive threshold amplitude, below which the flow relaxes back to quiescent state after the excitation is removed in computations. We also implement the present parallel method to show the physical aspects of primary and secondary instabilities to be maintained for other numerical schemes, and we show the results to reflect the complex physics during multiple subcritical Hopf bifurcation. Also, we relate the various sources of errors during computations that is typical of such shear-driven flow. These results, with near spectral accuracy, constitute universal benchmark results for the solution of Navier-Stokes equation for LDC.}, } @article {pmid30780221, year = {2019}, author = {Takamure, K and Ozono, S}, title = {Relative importance of initial conditions on outflows from multiple fans.}, journal = {Physical review. E}, volume = {99}, number = {1-1}, pages = {013112}, doi = {10.1103/PhysRevE.99.013112}, pmid = {30780221}, issn = {2470-0053}, abstract = {Generation of homogeneous isotropic turbulence was attempted using an innovative "multifan wind tunnel" with 99 fans installed. The driving method used is based on a principle that the shear layers generated between outflows from the adjacent ducts lead to turbulent flow downstream. First, a signal composed of two frequency components is set, and then it is fed to all the fans for three kinds of arrangements of phases. Here, parameter N is introduced as the number of phases used for the 99 fans, which represents a variety of emanated shear layers. Furthermore, S is introduced as a measure of shear magnitude at the inlet of the test section. Relative importance of the initial conditions (N and S) in the development of turbulence was investigated. To estimate the contribution from naturally induced turbulence, we numerically decomposed the resulting velocity fluctuations into the periodic and nonperiodic component. Energy spectra for three values of N were calculated using nonperiodic data. The inertial subrange of a gradient of -5/3 widens with increasing N. The value S is the largest for N=2, but the turbulence intensity of the nonperiodic component is the largest for N=99. Hence, it might be suggested that the shear magnitude at the inlet of the test section is not as important as the variety of shear layers for effective generation of high-Reynolds-number turbulence.}, } @article {pmid33266906, year = {2019}, author = {Kurnia, JC and Lim, DC and Chen, L and Jiang, L and Sasmito, AP}, title = {Entropy Generation and Heat Transfer Performance in Microchannel Cooling.}, journal = {Entropy (Basel, Switzerland)}, volume = {21}, number = {2}, pages = {}, pmid = {33266906}, issn = {1099-4300}, abstract = {Owing to its relatively high heat transfer performance and simple configurations, liquid cooling remains the preferred choice for electronic cooling and other applications. In this cooling approach, channel design plays an important role in dictating the cooling performance of the heat sink. Most cooling channel studies evaluate the performance in view of the first thermodynamics aspect. This study is conducted to investigate flow behaviour and heat transfer performance of an incompressible fluid in a cooling channel with oblique fins with regards to first law and second law of thermodynamics. The effect of oblique fin angle and inlet Reynolds number are investigated. In addition, the performance of the cooling channels for different heat fluxes is evaluated. The results indicate that the oblique fin channel with 20° angle yields the highest figure of merit, especially at higher Re (250-1000). The entropy generation is found to be lowest for an oblique fin channel with 90° angle, which is about twice than that of a conventional parallel channel. Increasing Re decreases the entropy generation, while increasing heat flux increases the entropy generation.}, } @article {pmid30771128, year = {2019}, author = {Li, R and Xu, D and Yin, Q}, title = {Effects of channel morphology on nitrate retention in a headwater agricultural stream in Lake Chaohu Basin, China.}, journal = {Environmental science and pollution research international}, volume = {26}, number = {11}, pages = {10651-10661}, pmid = {30771128}, issn = {1614-7499}, mesh = {Agriculture ; China ; Environmental Monitoring/methods ; Lakes/*chemistry ; Nitrates/*analysis ; Rivers/chemistry ; Water Resources ; }, abstract = {Five field tracer experiments and relevant detailed investigations of physical characterizations were conducted to investigate the effects of channel geomorphic settings on nitrate uptake efficiency on a 310-m long geomorphically distinct stream reach in a headwater agricultural stream in Hefei District, Lake Chaohu Basin. The model-fitted parameters from the one-dimensional transport with inflow and storage model were used to estimate the transient storage metric ([Formula: see text]) and determine the total nitrate uptake coefficient (k) for the study reach. And then, a nutrient spiraling approach was applied to reach-scale nitrate uptake estimates (Sw, Vf, and U). The results showed that the main channel was the major contributor to nitrate uptake retention, and the higher geomorphic complexity might result in better nitrate uptake efficiency. The partial least squares regression (PLSR) analysis showed strong correlations between the independent variables as geomorphic settings, Reynolds number and transient storage, and the dependent variables as nitrate uptake metrics, which further underscored the importance of stream physical characteristics on measurement of stream nitrate uptake.}, } @article {pmid30770644, year = {2019}, author = {Morales-Acuna, F and Ochoa, L and Valencia, C and Gurovich, AN}, title = {Characterization of blood flow patterns and endothelial shear stress during flow-mediated dilation.}, journal = {Clinical physiology and functional imaging}, volume = {39}, number = {4}, pages = {240-245}, doi = {10.1111/cpf.12564}, pmid = {30770644}, issn = {1475-097X}, mesh = {Adolescent ; Adult ; Blood Flow Velocity ; Brachial Artery/diagnostic imaging/*physiology ; Endothelium, Vascular/diagnostic imaging/*physiology ; Female ; Healthy Volunteers ; Humans ; Male ; Models, Cardiovascular ; *Pulsatile Flow ; Regional Blood Flow ; Time Factors ; *Vasodilation ; Young Adult ; }, abstract = {INTRODUCTION: Endothelial dysfunction is considered the first step in the development of atherosclerosis. Flow-mediated dilation (FMD) has been the most common assessment of endothelial function in research but it has failed in obtaining a widespread use in clinical settings due to a lack of standardization and a large inter-subject variability. Normalization of FMD to endothelial shear stress (ESS) has been proposed to solve its technical limitations. However, studies have not considered the characteristic of the blood flow during FMD under pulsatile conditions in their ESS estimations.

METHODS: A total of 26 young healthy subjects (15 females and 11 males) underwent FMD testing. Microhematocrit measurement was used to determine blood viscosity (μ). ESS was calculated by Womersley's approximation, ESS = μ*2K*Velocity/Diameter, where K is a function of Womersley's parameter (α). Blood flow patterns were determined by critical Reynolds number. Statistical analysis included repeated measures ANOVA to detect ESS differences during FMD until peak dilation. Significance was established at P≤0.05.

RESULTS: The mean (SD) FMD% and time to peak dilation were 7·4 (3·1) % and 35 (9·3) seconds, respectively. ESS was significantly reduced during FMD until peak dilation (P<0·001). Turbulent blood flow was the only pattern observed until peak dilation in 96·15% of the sample.

CONCLUSION: Peak FMD dilation in a young healthy population is triggered mostly by high-ESS under turbulent flow conditions. Due to the pulsatile nature of blood flow and the appearance of a turbulent pattern during FMD, ESS should be estimated by Womersley's approximation rather than Poiseuille's law.}, } @article {pmid30760794, year = {2019}, author = {Tang, H and Hu, F and Xu, L and Dong, S and Zhou, C and Wang, X}, title = {Variations in hydrodynamic characteristics of netting panels with various twine materials, knot types, and weave patterns at small attack angles.}, journal = {Scientific reports}, volume = {9}, number = {1}, pages = {1923}, pmid = {30760794}, issn = {2045-2322}, abstract = {It is essential to conduct hydrodynamic experiments for fishing gear at small attack angles along the flow direction to better understand the hydrodynamic characteristics of netting and application of gear. The hydrodynamic characteristics of netting panels made of different materials at small attack angles were investigated by a self-designed setup; this is essential for the effective use of netting on different types of gears. As confirmed by experiments, the measured drag of designed frame without netting accounted for less than 20% of the total setup drag including experimental netting and remained in a steady state under various current speeds and small attack angles, indicating that the self-designed frame setup is suitable for such trials. The drag coefficient was determined by varying the attack angle, solidity ratio, Reynolds number, knot types, weave pattern, and twine materials at small attack angles. The results indicate that the drag coefficient increased as the attack angle increased, but decreased as the solidity ratio and Reynolds number increased. The drag generated by knot accounted for 21% of the total drag of nylon (PA) netting. For braided knotless netting, the drag coefficient of PA netting was about 8.4% lower than that of polythene netting (PE) and 7% lower than that of polyester netting (PES). Compared with twined netting, the braided netting exhibited a higher resistance to flow, corresponding to higher values of drag coefficient.}, } @article {pmid30759039, year = {2019}, author = {Sera, T and Kuninaga, H and Fukasaku, K and Yokota, H and Tanaka, M}, title = {The Effectiveness of An Averaged Airway Model in Predicting the Airflow and Particle Transport Through the Airway.}, journal = {Journal of aerosol medicine and pulmonary drug delivery}, volume = {32}, number = {5}, pages = {278-292}, doi = {10.1089/jamp.2018.1500}, pmid = {30759039}, issn = {1941-2703}, mesh = {Administration, Inhalation ; Adult ; Aerosols/*administration & dosage/pharmacokinetics ; Algorithms ; Biological Transport ; Computer Simulation ; Humans ; *Hydrodynamics ; Male ; Middle Aged ; *Models, Anatomic ; Respiratory System/*anatomy & histology ; Tissue Distribution ; }, abstract = {Background: In this study, we proposed an averaged airway model design based on four healthy subjects and numerically evaluated its effectiveness for predicting the airflow and particle transport through an airway. Methods: Direct-averaged models of the conducting airways of four subjects were restored by averaging the three-dimensional (3D) skeletons of four healthy airways, which were calculated using an inverse 3D thinning algorithm. We simulated the airflow and particle transport in the individual and the averaged airway models using computational fluid dynamics. Results: The bifurcation geometry differs even among healthy subjects, but the averaged model retains the typical geometrical characteristics of the airways. The Reynolds number of the averaged model varied within the range found in the individual subject models, and the averaged model had similar inspiratory flow characteristics as the individual subject models. The deposition fractions at almost all individual lobes ranged within the variation observed in the subjects, however, the deposition fraction was higher in only one lobe. The deposition distribution at the main bifurcation point differed among the healthy subjects, but the characteristics of the averaged model fell within the variation observed in the individual subject models. On the contrary, the deposition fraction of the averaged model was higher than that of the average of the individual subject models and deviated from the range observed in the subject models. Conclusion: These results indicate that the direct-averaged model may be useful for predicting the individual airflow and particle transport on a macroscopic scale.}, } @article {pmid30758910, year = {2019}, author = {Amer, M and Feng, Y and Ramsey, JD}, title = {Using CFD simulations and statistical analysis to correlate oxygen mass transfer coefficient to both geometrical parameters and operating conditions in a stirred-tank bioreactor.}, journal = {Biotechnology progress}, volume = {35}, number = {3}, pages = {e2785}, doi = {10.1002/btpr.2785}, pmid = {30758910}, issn = {1520-6033}, mesh = {Bioreactors ; Cell Culture Techniques/*instrumentation ; Gases/chemistry ; Hydrodynamics ; Kinetics ; Mathematical Computing ; Oxygen/*chemistry ; }, abstract = {Optimization of a bioreactor design can be an especially challenging process. For instance, testing different bioreactor vessel geometries and different impeller and sparger types, locations, and dimensions can lead to an exceedingly large number of configurations and necessary experiments. Computational fluid dynamics (CFD), therefore, has been widely used to model multiphase flow in stirred-tank bioreactors to minimize the number of optimization experiments. In this study, a multiphase CFD model with population balance equations are used to model gas-liquid mixing, as well as gas bubble distribution, in a 50 L single-use bioreactor vessel. The vessel is the larger chamber in an early prototype of a multichamber bioreactor for mammalian cell culture. The model results are validated with oxygen mass transfer coefficient (kL a) measurements within the prototype. The validated model is projected to predict the effect of using ring or pipe spargers of different sizes and the effect of varying the impeller diameter on kL a. The simulations show that ring spargers result in a superior kL a compared to pipe spargers, with an optimum sparger-to-impeller diameter ratio of 0.8. In addition, larger impellers are shown to improve kL a. A correlation of kL a is presented as a function of both the reactor geometry (i.e., sparger-to-impeller diameter ratio and impeller-to-vessel diameter ratio) and operating conditions (i.e., Reynolds number and gas flow rate). The resulting correlation can be used to predict kL a in a bioreactor and to optimize its design, geometry, and operating conditions.}, } @article {pmid30746446, year = {2019}, author = {Huang, HW and Uslu, FE and Katsamba, P and Lauga, E and Sakar, MS and Nelson, BJ}, title = {Adaptive locomotion of artificial microswimmers.}, journal = {Science advances}, volume = {5}, number = {1}, pages = {eaau1532}, pmid = {30746446}, issn = {2375-2548}, support = {743217/ERC_/European Research Council/International ; }, abstract = {Bacteria can exploit mechanics to display remarkable plasticity in response to locally changing physical and chemical conditions. Compliant structures play a notable role in their taxis behavior, specifically for navigation inside complex and structured environments. Bioinspired mechanisms with rationally designed architectures capable of large, nonlinear deformation present opportunities for introducing autonomy into engineered small-scale devices. This work analyzes the effect of hydrodynamic forces and rheology of local surroundings on swimming at low Reynolds number, identifies the challenges and benefits of using elastohydrodynamic coupling in locomotion, and further develops a suite of machinery for building untethered microrobots with self-regulated mobility. We demonstrate that coupling the structural and magnetic properties of artificial microswimmers with the dynamic properties of the fluid leads to adaptive locomotion in the absence of on-board sensors.}, } @article {pmid30736676, year = {2019}, author = {Waheed, W and Alazzam, A and Al-Khateeb, AN and Sung, HJ and Abu-Nada, E}, title = {Investigation of DPD transport properties in modeling bioparticle motion under the effect of external forces: Low Reynolds number and high Schmidt scenarios.}, journal = {The Journal of chemical physics}, volume = {150}, number = {5}, pages = {054901}, doi = {10.1063/1.5079835}, pmid = {30736676}, issn = {1089-7690}, abstract = {We have used a dissipative particle dynamics (DPD) model to study the movement of microparticles in a microfluidic device at extremely low Reynolds number (Re). The particles, immersed in a medium, are transported in the microchannel by a flow force and deflected transversely by an external force along the way. An in-house Fortran code is developed to simulate a two-dimensional fluid flow using DPD at Re ≥ 0.0005, which is two orders of magnitude less than the minimum Re value previously reported in the DPD literature. The DPD flow profile is verified by comparing it with the exact solution of Hagen-Poiseuille flow. A bioparticle based on a rigid spring-bead model is introduced in the DPD fluid, and the employed model is verified via comparing the velocity profile past a stationary infinite cylinder against the profile obtained via the finite element method. Moreover, the drag force and drag coefficient on the stationary cylinder are also computed and compared with the reported literature results. Dielectrophoresis (DEP) is investigated as a case study for the proposed DPD model to compute the trajectories of red blood cells in a microfluidic device. A mapping mechanism to scale the external deflecting force from the physical to DPD domain is performed. We designed and built our own experimental setup with the aim to compare the experimental trajectories of cells in a microfluidic device to validate our DPD model. These experimental results are used to investigate the dependence of the trajectory results on the Reynolds number and the Schmidt number. The numerical results agree well with the experiment results, and it is found that the Schmidt number is not a significant parameter for the current application; Reynolds numbers combined with the DEP-to-drag force ratio are the only important parameters influencing the behavior of particles inside the microchannel.}, } @article {pmid30736476, year = {2019}, author = {Tai, J and Lam, YC}, title = {Elastic Turbulence of Aqueous Polymer Solution in Multi-Stream Micro-Channel Flow.}, journal = {Micromachines}, volume = {10}, number = {2}, pages = {}, pmid = {30736476}, issn = {2072-666X}, abstract = {Viscous liquid flow in micro-channels is typically laminar because of the low Reynolds number constraint. However, by introducing elasticity into the fluids, the flow behavior could change drastically to become turbulent; this elasticity can be realized by dissolving small quantities of polymer molecules into an aqueous solvent. Our recent investigation has directly visualized the extension and relaxation of these polymer molecules in an aqueous solution. This elastic-driven phenomenon is known as 'elastic turbulence'. Hitherto, existing studies on elastic flow instability are mostly limited to single-stream flows, and a comprehensive statistical analysis of a multi-stream elastic turbulent micro-channel flow is needed to provide additional physical understanding. Here, we investigate the flow field characteristics of elastic turbulence in a 3-stream contraction-expansion micro-channel flow. By applying statistical analyses and flow visualization tools, we show that the flow field bares many similarities to that of inertia-driven turbulence. More interestingly, we observed regions with two different types of power-law dependence in the velocity power spectra at high frequencies. This is a typical characteristic of two-dimensional turbulence and has hitherto not been reported for elastic turbulent micro-channel flows.}, } @article {pmid30715051, year = {2018}, author = {Mehrdel, P and Karimi, S and Farré-Lladós, J and Casals-Terré, J}, title = {Novel Variable Radius Spiral[-]Shaped Micromixer: From Numerical Analysis to Experimental Validation.}, journal = {Micromachines}, volume = {9}, number = {11}, pages = {}, pmid = {30715051}, issn = {2072-666X}, abstract = {A novel type of spiral micromixer with expansion and contraction parts is presented in order to enhance the mixing quality in the low Reynolds number regimes for point-of-care tests (POCT). Three classes of micromixers with different numbers of loops and modified geometries were studied. Numerical simulation was performed to study the flow behavior and mixing performance solving the steady-state Navier[-]Stokes and the convection-diffusion equations in the Reynolds range of 0.1[-]10.0. Comparisons between the mixers with and without expansion parts were made to illustrate the effect of disturbing the streamlines on the mixing performance. Image analysis of the mixing results from fabricated micromixers was used to verify the results of the simulations. Since the proposed mixer provides up to 92% of homogeneity at Re 1.0, generating 442 Pa of pressure drop, this mixer makes a suitable candidate for research in the POCT field.}, } @article {pmid30714602, year = {2019}, author = {Schaaf, C and Rühle, F and Stark, H}, title = {A flowing pair of particles in inertial microfluidics.}, journal = {Soft matter}, volume = {15}, number = {9}, pages = {1988-1998}, doi = {10.1039/c8sm02476f}, pmid = {30714602}, issn = {1744-6848}, abstract = {A flowing pair of particles in inertial microfluidics gives important insights into understanding and controlling the collective dynamics of particles like cells or droplets in microfluidic devices. They are applied in medical cell analysis and engineering. We study the dynamics of a pair of solid particles flowing through a rectangular microchannel using lattice Boltzmann simulations. We determine the inertial lift force profiles as a function of the two particle positions, their axial distance, and the Reynolds number. Generally, the profiles strongly differ between particles leading and lagging in flow and the lift forces are enhanced due to the presence of a second particle. At small axial distances, they are determined by viscous forces, while inertial forces dominate at large separations. We identify cross-streamline pairs as stable fixed points in the lift force profiles and argue that same-streamline configurations are only one-sided stable. Depending on the initial conditions, the two-particle lift forces in combination with the Poiseuille flow give rise to three types of unbound particle trajectories, called moving-apart, passing, and swapping, and one type of bound trajectory, where the particles perform damped oscillations towards the cross-stream line configuration. The damping rate scales with Reynolds number squared, since inertial forces are responsible for driving the particles to their steady-state positions.}, } @article {pmid30712849, year = {2019}, author = {Lippert, T and Bandelin, J and Schlederer, F and Drewes, JE and Koch, K}, title = {Impact of ultrasound-induced cavitation on the fluid dynamics of water and sewage sludge in ultrasonic flatbed reactors.}, journal = {Ultrasonics sonochemistry}, volume = {55}, number = {}, pages = {217-222}, doi = {10.1016/j.ultsonch.2019.01.024}, pmid = {30712849}, issn = {1873-2828}, abstract = {The fluid dynamics of water, thickened waste activated sludge (WAS, total solids concentration 4.4%) and digested sludge (DS, total solids concentration 2.5%) within a lab-scale ultrasonic flatbed reactor were experimentally investigated. For a visual observation of the opaque sludge flow, sewage sludges were approximated by transparent xanthan solutions with identical flow behavior. The visualization of the flow was realized by use of an ultrasonic reactor with a transparent panel and dye streams injected into the flow. Without ultrasonic treatment, xanthan solutions showed distinct laminar flow behavior (generalized Reynolds numbers < 1), at a flow rate of 100 L/h. In water, dye streams remained coherent as well, but with slightly unsteady features (Reynolds number ∼ 350). Activation of the ultrasound reactor caused strong fluid dynamic disturbance in the water flow and dye streams were dissolved instantly, thus indicating turbulent mixing. For the xanthan solutions, however, mixing was considerably less pronounced. The dye streams in the DS substitute (0.5% xanthan solution) remained overall in laminar shape, but exhibited an eruption-like branching and an increase in diameter with advancing treatment duration. For the solution resembling WAS (2.0% xanthan solution), only weak dye stream disruption was observed, thus indicating that WAS flow in flatbed reactors is nearly laminar during ultrasonic treatment.}, } @article {pmid30712603, year = {2019}, author = {Ibrahim, MG and Hasona, WM and ElShekhipy, AA}, title = {Concentration-dependent viscosity and thermal radiation effects on MHD peristaltic motion of Synovial Nanofluid: Applications to rheumatoid arthritis treatment.}, journal = {Computer methods and programs in biomedicine}, volume = {170}, number = {}, pages = {39-52}, doi = {10.1016/j.cmpb.2019.01.001}, pmid = {30712603}, issn = {1872-7565}, mesh = {Algorithms ; Arthritis, Rheumatoid/*physiopathology/*radiotherapy ; Humans ; Models, Statistical ; *Nanoparticles ; Peristalsis/*radiation effects ; Synovial Fluid/*radiation effects ; Viscosity/*radiation effects ; }, abstract = {BACKGROUND AND OBJECTIVE: The biomedical fluid which fills the Synovial joint cavity is called Synovial fluid which behaves as in the fluid classifications to Non-Newtonian fluids. Also it's described as a several micrometers thick layer among the interstitial cartilages with very low friction coefficient. Consequently, the present paper opts to investigate the influence of the concentration-dependent viscosity on Magnetohydrodynamic peristaltic flow of Synovial Nanofluid in an asymmetric channel in presence of thermal radiation effect.

METHOD: Our problem is solved for two models, in the first model which referred as Model-(I), viscosity is considered exponentially dependent on the concentration. Model-(2), Shear thinning index is considered as a function of concentration. Those models are introduced for the first time in peristaltic or Nanofluid flows literature. The governing problem is reformulated under the assumption of low Reynolds number and long wavelength. The resulting system of equations is solved numerically with the aid of Parametric ND Solve.

RESULTS: Detailed comparisons have been made between Model-(I) and Model-(2) and found unrealistic results between them. Results for velocity, temperature and nanoparticle concentration distributions as well as pressure gradient and pressure rise are offered graphically for different values of various physical parameters.

CONCLUSIONS: Such models are applicable to rheumatoid arthritis (RA) treatment. Rheumatoid arthritis patients can be treated by applying the magnetic field on an electrically conducting fluid, due to the movement of the ions within the cell which accelerates the metabolism of fluids.}, } @article {pmid33266845, year = {2019}, author = {Ries, F and Li, Y and Nishad, K and Janicka, J and Sadiki, A}, title = {Entropy Generation Analysis and Thermodynamic Optimization of Jet Impingement Cooling Using Large Eddy Simulation.}, journal = {Entropy (Basel, Switzerland)}, volume = {21}, number = {2}, pages = {}, pmid = {33266845}, issn = {1099-4300}, abstract = {In this work, entropy generation analysis is applied to characterize and optimize a turbulent impinging jet on a heated solid surface. In particular, the influence of plate inclinations and Reynolds numbers on the turbulent heat and fluid flow properties and its impact on the thermodynamic performance of such flow arrangements are numerically investigated. For this purpose, novel model equations are derived in the frame of Large Eddy Simulation (LES) that allows calculation of local entropy generation rates in a post-processing phase including the effect of unresolved subgrid-scale irreversibilities. From this LES-based study, distinctive features of heat and flow dynamics of the impinging fluid are detected and optimal operating designs for jet impingement cooling are identified. It turned out that (1) the location of the stagnation point and that of the maximal Nusselt number differ in the case of plate inclination; (2) predominantly the impinged wall acts as a strong source of irreversibility; and (3) a flow arrangement with a jet impinging normally on the heated surface allows the most efficient use of energy which is associated with lowest exergy lost. Furthermore, it is found that increasing the Reynolds number intensifies the heat transfer and upgrades the second law efficiency of such thermal systems. Thereby, the thermal efficiency enhancement can overwhelm the frictional exergy loss.}, } @article {pmid30671967, year = {2019}, author = {Tandler, T and Gellman, E and De La Cruz, D and Ellerby, DJ}, title = {Drag coefficient estimates from coasting bluegill sunfish Lepomis macrochirus.}, journal = {Journal of fish biology}, volume = {94}, number = {3}, pages = {532-534}, doi = {10.1111/jfb.13906}, pmid = {30671967}, issn = {1095-8649}, mesh = {Animals ; Biomechanical Phenomena ; Perciformes/*physiology ; *Swimming ; }, abstract = {The drag coefficient bluegill sunfish Lepomis macrochirus was estimated from coasting deceleration as (mean ± SD) 0.0154 ± 0.0070 at a Reynolds number of 41,000 ± 14,000. This was within the coasting range in other species and lower than values obtained from dead drag measurements in this species and others. Low momentum losses during coasting may allow its use during intermittent propulsion to modulate power output or maximize energy economy.}, } @article {pmid30657156, year = {2019}, author = {Haward, SJ and Kitajima, N and Toda-Peters, K and Takahashi, T and Shen, AQ}, title = {Flow of wormlike micellar solutions around microfluidic cylinders with high aspect ratio and low blockage ratio.}, journal = {Soft matter}, volume = {15}, number = {9}, pages = {1927-1941}, doi = {10.1039/c8sm02099j}, pmid = {30657156}, issn = {1744-6848}, abstract = {We employ time-resolved flow velocimetry and birefringence imaging methods to study the flow of a well-characterized shear-banding wormlike micellar solution around a novel glass-fabricated microfluidic circular cylinder. In contrast with typical microfluidic cylinders, our geometry is characterized by a high aspect ratio α = H/W = 5 and a low blockage ratio β = 2r/W = 0.1, where H and W are the channel height and width, and the cylinder radius r = 20 μm. The small cylinder radius allows access up to very high Weissenberg numbers 1.9 ≤ Wi = λMU/r ≤ 3750 (where λM is the Maxwell relaxation time) while inertial effects remain entirely negligible (Reynolds number, Re < 10-4). At low Wi values, the flow remains steady and symmetric and a birefringent region (indicating micellar alignment and tensile stress) develops downstream of the cylinder. Above a critical value Wic ≈ 60 the flow transitions to a steady asymmetric state, characterized as a supercritical pitchfork bifurcation, in which the fluid takes a preferential path around one side of the cylinder. At a second critical value Wic2 ≈ 130, the flow becomes time-dependent, with a characteristic frequency f0 ≈ 1/λM. This initial transition to time dependence has characteristics of a subcritical Hopf bifurcation. Power spectra of the measured fluctuations become complex as Wi is increased further, showing a gradual slowing down of the dynamics and emergence of harmonics. A final transition at very high Wic3 corresponds to the re-emergence of a single peak in the power spectrum but at much higher frequency. We discuss this in terms of possible flow-induced breakage of micelles into shorter species with a faster relaxation time.}, } @article {pmid30650659, year = {2019}, author = {Luo, L and He, Y}, title = {Magnetically Induced Flow Focusing of Non-Magnetic Microparticles in Ferrofluids under Inclined Magnetic Fields.}, journal = {Micromachines}, volume = {10}, number = {1}, pages = {}, pmid = {30650659}, issn = {2072-666X}, abstract = {The ability to focus biological particles into a designated position of a microchannel is vital for various biological applications. This paper reports particle focusing under vertical and inclined magnetic fields. We analyzed the effect of the angle of rotation (θ) of the permanent magnets and the critical Reynolds number (Rec) on the particle focusing in depth. We found that a rotation angle of 10° is preferred; a particle loop has formed when Re < Rec and Rec of the inclined magnetic field is larger than that of the vertical magnetic field. We also conducted experiments with polystyrene particles (10.4 μm in diameter) to prove the calculations. Experimental results show that the focusing effectiveness improved with increasing applied magnetic field strength or decreasing inlet flow rate.}, } @article {pmid30636127, year = {2018}, author = {Iyer, KP and Schumacher, J and Sreenivasan, KR and Yeung, PK}, title = {Steep Cliffs and Saturated Exponents in Three-Dimensional Scalar Turbulence.}, journal = {Physical review letters}, volume = {121}, number = {26}, pages = {264501}, doi = {10.1103/PhysRevLett.121.264501}, pmid = {30636127}, issn = {1079-7114}, abstract = {The intermittency of a passive scalar advected by three-dimensional Navier-Stokes turbulence at a Taylor-scale Reynolds number of 650 is studied using direct numerical simulations on a 4096^{3} grid; the Schmidt number is unity. By measuring scalar increment moments of high orders, while ensuring statistical convergence, we provide unambiguous evidence that the scaling exponents saturate to 1.2 for moment orders beyond about 12, indicating that scalar intermittency is dominated by the most singular shocklike cliffs in the scalar field. We show that the fractal dimension of the spatial support of steep cliffs is about 1.8, whose sum with the saturation exponent value of 1.2 adds up to the space dimension of 3, thus demonstrating a deep connection between the geometry and statistics in turbulent scalar mixing. The anomaly for the fourth and sixth order moments is comparable to that in the Kraichnan model for the roughness exponent of 4/3.}, } @article {pmid33266771, year = {2019}, author = {Zhu, Z and Wang, H and Peng, D and Dou, J}, title = {Modelling the Hindered Settling Velocity of a Falling Particle in a Particle-Fluid Mixture by the Tsallis Entropy Theory.}, journal = {Entropy (Basel, Switzerland)}, volume = {21}, number = {1}, pages = {}, pmid = {33266771}, issn = {1099-4300}, abstract = {The settling velocity of a sediment particle is an important parameter needed for modelling the vertical flux in rivers, estuaries, deltas and the marine environment. It has been observed that a particle settles more slowly in the presence of other particles in the fluid than in a clear fluid, and this phenomenon has been termed 'hindered settling'. The Richardson and Zaki equation has been a widely used expression for relating the hindered settling velocity of a particle with that in a clear fluid in terms of a concentration function and the power of the concentration function, and the power index is known as the exponent of reduction of the settling velocity. This study attempts to formulate the model for the exponent of reduction of the settling velocity by using the probability method based on the Tsallis entropy theory. The derived expression is a function of the volumetric concentration of the suspended particle, the relative mass density of the particle and the particle's Reynolds number. This model is tested against experimental data collected from the literature and against five existing deterministic models, and this model shows good agreement with the experimental data and gives better prediction accuracy than the other deterministic models. The derived Tsallis entropy-based model is also compared with the existing Shannon entropy-based model for experimental data, and the Tsallis entropy-based model is comparable to the Shannon entropy-based model for predicting the hindered settling velocity of a falling particle in a particle-fluid mixture. This study shows the potential of using the Tsallis entropy together with the principle of maximum entropy to predict the hindered settling velocity of a falling particle in a particle-fluid mixture.}, } @article {pmid33867572, year = {2019}, author = {Paredes, P and Choudhari, MM and Li, F}, title = {Instability wave-streak interactions in a hypersonic boundary layer at flight conditions.}, journal = {Journal of fluid mechanics}, volume = {858}, number = {}, pages = {474-499}, pmid = {33867572}, issn = {0022-1120}, support = {/ARMD/Aeronautics NASA/United States ; }, abstract = {The interaction of stationary streaks undergoing nonmodal growth with modally unstable instability waves in a hypersonic boundary-layer flow is studied using numerical computations. The geometry and flow conditions are selected to match a relevant trajectory location from the ascent phase of the HIFiRE-1 flight experiment; namely, a 7 degree half-angle, circular cone with 2.5 mm nose radius, freestream Mach number equal to 5.30, unit Reynolds number equal to 13.42 m[-1], and wall-to-adiabatic temperature ratio of approximately 0.35 over most of the vehicle. This paper investigates the nonlinear evolution of initially linear optimal disturbances that evolve into finite-amplitude streaks, followed by an analysis of the modal instability characteristics of the perturbed, streaky boundary-layer flow. The investigation is performed with stationary direct numerical simulations (DNS) and plane-marching parabolized stability equations (PSE), in conjunction with partial-differential-equation-based planar eigenvalue analysis. The overall effect of streaks is to reduce the peak amplification factors of instability waves, indicating a possible downstream shift in the onset of laminar-turbulent transition. The present study confirms previous findings that the mean flow distorsion of the nonlinear streak perturbation reduces the amplification rates of the Mack-mode instability. More importantly, however, the present results demonstrate that the spanwise varying component of the streak can produce a larger effect on the Mack-mode amplification. The study with selected azimuthal wavenumbers for the stationary streaks reveals that a wavenumber of approximately 1.4 times larger than the optimal wavenumber is more effective in stabilizing the planar Mack-mode instabilities. In the absence of unstable first-mode waves for the present cold-wall condition, transition onset is expected to be delayed until the peak streak amplitude increases to nearly 35 percent of the freestream velocity, when intrinsic instabilities of the boundary-layer streaks begin to dominate the transition process. For streak amplitudes below that limit a significant net stabilization is achieved, yielding a potential transition delay that can exceed 100 percent of the length of the laminar region in the uncontrolled case.}, } @article {pmid30624119, year = {2018}, author = {Caracappa, JC and Munroe, DM}, title = {Morphological Variability Among Broods of First-Stage Blue Crab (Callinectes sapidus) Zoeae.}, journal = {The Biological bulletin}, volume = {235}, number = {3}, pages = {123-133}, doi = {10.1086/699922}, pmid = {30624119}, issn = {1939-8697}, mesh = {Animals ; Biological Variation, Population ; Brachyura/*anatomy & histology ; Female ; Larva/anatomy & histology ; Models, Biological ; Swimming ; }, abstract = {External morphology has been shown to influence predation and locomotion of decapod larvae and is, therefore, directly related to their ability to survive and disperse. The first goal of this study was to characterize first-stage blue crab zoeal morphology and its variability across larval broods to test whether inter-brood differences in morphology exist. The second was to identify possible correlations between maternal characteristics and zoeal morphology. The offspring of 21 individuals were hatched in the laboratory, photographed, and measured. Zoeae exhibited substantial variability, with all metrics showing significant inter-brood differences. The greatest variability was seen in the zoeal abdomen, rostrum, and dorsal spine length. A principal component analysis showed no distinct clustering of broods, with variation generally driven by larger zoeae. Using observed morphology, models of drag induced by swimming and sinking also showed significant inter-brood differences, with a maximum twofold difference across broods. In contrast to trends in other decapod taxa, maternal characteristics (female carapace width and mass and egg sponge volume and mass) are not significant predictors of zoeal morphology. These results suggest that brood effects are present across a wide range of morphological characteristics and that future experiments involving Callinectes sapidus morphology or its functionality should explicitly account for inter-brood variation. Additionally, inter-brood morphological differences may result in differential predation mortality and locomotory abilities among broods.}, } @article {pmid30624117, year = {2018}, author = {Lamont, EI and Emlet, RB}, title = {Permanently Fused Setules Create Unusual Folding Fans Used for Swimming in Cyprid Larvae of Barnacles.}, journal = {The Biological bulletin}, volume = {235}, number = {3}, pages = {185-194}, doi = {10.1086/700084}, pmid = {30624117}, issn = {1939-8697}, mesh = {Animals ; Larva/anatomy & histology/ultrastructure ; *Swimming ; Thoracica/*anatomy & histology/ultrastructure ; }, abstract = {Many crustacean swimming appendages carry arrays of plumose setae-exoskeletal, feather-like structures of long bristles (setae) with short branches (setules) distributed along two sides. Although closely spaced, setae are not physically interconnected. Setal arrays function during swimming as drag-based leaky paddles that push the organism through water. Barnacle cyprids, the final, non-feeding larval stage, swim with six pairs of legs (thoracopods) that open and close setal arrays in alternating high-drag power strokes and low-drag recovery strokes. While studying cyprid swimming, we found that their thoracopods contained setae permanently cross-linked by fused setules. These cuticular connections would seem highly unlikely because setae are individually produced exoskeletal secretions, and the connections imply unknown processes for the production or modification of crustacean setae. We describe the morphology and function of plumose setae on cyprids of Balanus glandula and other species across the clade Cirripedia. Setules from adjacent plumose setae are seamlessly joined at their tips and occur in three distinct linkage patterns. Thoracopods lack muscles to open and close the array; interconnected setae are instead pulled apart, producing a paddle-like fan with high drag when appendages spread laterally during power strokes. Setules are spring-like, passively closing setae into tight bundles with low drag during recovery strokes. The linked setules occur in the three main clades of the Cirripedia. This cuticular arrangement is effective in swimming, may eliminate the need for muscles to close the setal array, and may represent a unique swimming structure within the Crustacea.}, } @article {pmid30606096, year = {2019}, author = {Kunze, E}, title = {Biologically Generated Mixing in the Ocean.}, journal = {Annual review of marine science}, volume = {11}, number = {}, pages = {215-226}, doi = {10.1146/annurev-marine-010318-095047}, pmid = {30606096}, issn = {1941-0611}, mesh = {Aquatic Organisms/*physiology ; Diffusion ; Gravitation ; Swimming ; Temperature ; *Water Movements ; Wind ; }, abstract = {This article assesses the contribution to ocean mixing by the marine biosphere at both high and low Reynolds numbers Re= uℓ/ ν. While back-of-the-envelope estimates have suggested that swimming marine organisms might generate as much high-Reynolds-number turbulence as deep-ocean tide- and wind-generated internal waves, and that turbulent dissipation rates of O(10[-5] W kg[-1]) (Re ∼ 10[5]) could be produced by aggregations of organisms ranging from O(0.01 m) krill to O(10 m) cetaceans, comparable to strong wind and buoyancy forcing near the surface, microstructure measurements do not find consistently elevated dissipation associated with diel vertically migrating krill. Elevated dissipation rates are associated with schools of O(0.1- 1 m) fish but with low mixing coefficients (γ ∼ 0.002-0.02, as compared with γ ∼ 0.2 for geophysical turbulence). Likewise, viscously induced drift at low Reynolds numbers produces little mixing of temperature, solutes, dissolved nutrients, and gases when realistic swimmers and molecular scalar diffusion are taken into account. The conclusion is that, while the marine biosphere can generate turbulence, it contributes little ocean mixing compared with breaking internal gravity waves.}, } @article {pmid30605404, year = {2019}, author = {Itzhak, N and Greenblatt, D}, title = {Aerodynamic factors affecting rebreathing in infants.}, journal = {Journal of applied physiology (Bethesda, Md. : 1985)}, volume = {126}, number = {4}, pages = {952-964}, doi = {10.1152/japplphysiol.00784.2018}, pmid = {30605404}, issn = {1522-1601}, mesh = {Carbon Dioxide/metabolism ; Humans ; Infant, Newborn ; Oxygen/metabolism ; Prone Position/*physiology ; Respiration ; Risk Factors ; Sleep/*physiology ; Sudden Infant Death/*prevention & control ; Temperature ; Tidal Volume/physiology ; }, abstract = {The rebreathing of expire air, with high carbon dioxide and low oxygen concentrations, has long been implicated in unexplained Sudden Infant Death Syndrome (SIDS) when infants are placed to sleep in a prone (facedown) position. This study elucidates the effect of the aerodynamic parameters Reynolds number, Strouhal number, and Froude number on the percentage of expired air that is reinspired (rebreathed). A nasal module was designed that served as a simplified geometric representation of infant nostrils and placed above a hard, flat surface. Quantitative and flow visualization experiments were performed to measure rebreathing, using water as the working medium, under conditions of dynamic similarity. Different anatomic (e.g., tidal volume, nostril diameter), physiological (e.g., breathing frequency), and environmental (e.g., temperature, distance from the surface) factors were considered. Increases in Strouhal number (simultaneously faster and shallower breathing) always produced higher rebreathed percentages, because rolled-up vortices in the vicinity of the nostrils had less time to move away by self-induction. Positively and negatively buoyant flows resulted in significant rebreathing. In the latter case, consistent with a warm environment and a high percentage of rebreathed CO2, denser gas pooled in the vicinity of the nostrils. Reynolds numbers below 200 also dramatically increased rebreathing because the expired gas pooled much closer to the nostrils. These results clearly elucidated how the prone position dramatically increases rebreathing by a number of different mechanisms. Furthermore, the results offer plausible explanations of why a high-temperature environment and low birthweight are SIDS risk factors. NEW & NOTEWORTHY A fundamentally new aerodynamics-based approach to the study of rebreathing of expired air in infants is presented. Rebreathing is implicated in unexplained Sudden Infant Death Syndrome (SIDS) when infants sleep in a prone position. This is the first time that aerodynamic parameters are systematically varied and their effects on rebreathing quantified. The study provides us with a deeper understanding of the effects of breathing frequency, tidal volume (birthweight) and environmental conditions.}, } @article {pmid30604300, year = {2019}, author = {Wu, P and Gao, Q and Hsu, PL}, title = {On the representation of effective stress for computing hemolysis.}, journal = {Biomechanics and modeling in mechanobiology}, volume = {18}, number = {3}, pages = {665-679}, doi = {10.1007/s10237-018-01108-y}, pmid = {30604300}, issn = {1617-7940}, mesh = {Animals ; Capillaries/physiopathology ; Heart-Assist Devices ; *Hemolysis ; Humans ; Hydrodynamics ; *Models, Cardiovascular ; Pressure ; *Stress, Mechanical ; United States ; United States Food and Drug Administration ; }, abstract = {Hemolysis is a major concern in blood-circulating devices, which arises due to hydrodynamic loading on red blood cells from ambient flow environment. Hemolysis estimation models have often been used to aid hemocompatibility design. The preponderance of hemolysis models was formulated on the basis of laminar flows. However, flows in blood-circulating devices are rather complex and can be laminar, transitional or turbulent. It is an extrapolation to apply these models to turbulent flows. For the commonly used power-law models, effective stress has often been represented using Reynolds stresses for estimating hemolysis in turbulent flows. This practice tends to overpredict hemolysis. This study focused on the representation of effective stress in power-law models. Through arithmetic manipulations from Navier-Stokes equation, we showed that effective stress can be represented in terms of energy dissipation, which can be readily obtained from CFD simulations. Three cases were tested, including a capillary tube, the FDA benchmark cases of nozzle model and blood pump. The results showed that the representation of effective stress in terms of energy dissipation greatly improved the prediction of hemolysis for a wide range of flow conditions. The improvement increases as Reynolds number increases; the overprediction of hemolysis was reduced by up to two orders of magnitude.}, } @article {pmid30603681, year = {2018}, author = {Szaszák, N and Roloff, C and Bordás, R and Bencs, P and Szabó, S and Thévenin, D}, title = {A novel type of semi-active jet turbulence grid.}, journal = {Heliyon}, volume = {4}, number = {12}, pages = {e01026}, pmid = {30603681}, issn = {2405-8440}, abstract = {This article describes a novel approach to generate increased turbulence levels in an incoming flow. It relies on a cost-effective and robust semi-active jet grid, equipped with flexible tubes as moving elements attached onto tube connections placed at the intersections of a fixed, regular grid. For the present study, these flexible tubes are oriented in counter-flow direction in a wind tunnel. Tube motion is governed by multiple interactions between the main flow and the jets exiting the tubes, resulting in chaotic velocity fluctuations and high turbulence intensities in the test section. After describing the structure of the turbulence generator, the turbulent properties of the airflow downstream of the grid in both passive and active modes are measured by hot-wire anemometry and compared with one another. When activating the turbulence generator, turbulence intensity, turbulent kinetic energy, and the Taylor Reynolds number are noticeably increased in comparison with the passive mode (corresponding to simple grid turbulence). Furthermore, the inertial subrange of the turbulent energy spectrum becomes wider and closely follows Kolmogorov's -5/3 law. These results show that the semi-active grid, in contrast to passive systems, is capable of producing high turbulence levels, even at low incoming flow velocity. Compared to alternatives based on actuators driven by servo-motors, the production and operation costs of the semi-active grid are very moderate and its robustness is much higher.}, } @article {pmid30602925, year = {2018}, author = {Garcia, F and Stefani, F}, title = {Continuation and stability of rotating waves in the magnetized spherical Couette system: secondary transitions and multistability.}, journal = {Proceedings. Mathematical, physical, and engineering sciences}, volume = {474}, number = {2220}, pages = {20180281}, pmid = {30602925}, issn = {1364-5021}, abstract = {Rotating waves (RW) bifurcating from the axisymmetric basic magnetized spherical Couette (MSC) flow are computed by means of Newton-Krylov continuation techniques for periodic orbits. In addition, their stability is analysed in the framework of Floquet theory. The inner sphere rotates while the outer is kept at rest and the fluid is subjected to an axial magnetic field. For a moderate Reynolds number Re = 10[3] (measuring inner rotation), the effect of increasing the magnetic field strength (measured by the Hartmann number Ha) is addressed in the range Ha∈(0, 80) corresponding to the working conditions of the HEDGEHOG experiment at Helmholtz-Zentrum Dresden-Rossendorf. The study reveals several regions of multistability of waves with azimuthal wavenumber m = 2, 3, 4, and several transitions to quasi-periodic flows, i.e modulated rotating waves. These nonlinear flows can be classified as the three different instabilities of the radial jet, the return flow and the shear layer, as found in the previous studies. These two flows are continuously linked, and part of the same branch, as the magnetic forcing is increased. Midway between the two instabilities, at a certain critical Ha, the non-axisymmetric component of the flow is maximum.}, } @article {pmid30602310, year = {2018}, author = {Murphy, EAK and Barros, JM and Schultz, MP and Flack, KA and Steppe, CN and Reidenbach, MA}, title = {Roughness effects of diatomaceous slime fouling on turbulent boundary layer hydrodynamics.}, journal = {Biofouling}, volume = {34}, number = {9}, pages = {976-988}, doi = {10.1080/08927014.2018.1517867}, pmid = {30602310}, issn = {1029-2454}, mesh = {Biofilms/*growth & development ; Biofouling/*prevention & control ; Friction ; *Hydrodynamics ; Rheology ; *Ships ; Stress, Mechanical ; Surface Properties ; }, abstract = {Biofilm fouling significantly impacts ship performance. Here, the impact of biofilm on boundary layer structure at a ship-relevant, low Reynolds number was investigated. Boundary layer measurements were performed over slime-fouled plates using high resolution particle image velocimetry (PIV). The velocity profile over the biofilm showed a downward shift in the log-law region (ΔU[+]), resulting in an effective roughness height (ks) of 8.8 mm, significantly larger than the physical thickness of the biofilm (1.7 ± 0.5 mm) and generating more than three times as much frictional drag as the smooth-wall. The skin-friction coefficient, Cf, of the biofilm was 9.0 × 10[-3] compared with 2.9 × 10[-3] for the smooth wall. The biofilm also enhances turbulent kinetic energy (tke) and Reynolds shear stress, which are more heterogeneous in the streamwise direction than smooth-wall flows. This suggests that biofilms increase drag due to high levels of momentum transport, likely resulting from protruding streamers and surface compliance.}, } @article {pmid32625002, year = {2019}, author = {Pérez-Hernández, J and Nicasio-Torres, MDP and Sarmiento-López, LG and Rodríguez-Monroy, M}, title = {Production of anti-inflammatory compounds in Sphaeralcea angustifolia cell suspension cultivated in stirred tank bioreactor.}, journal = {Engineering in life sciences}, volume = {19}, number = {3}, pages = {196-205}, pmid = {32625002}, issn = {1618-0240}, abstract = {Sphaeralcea angustifolia is a plant used for the treatment of inflammatory processes. Scopoletin, tomentin, and sphaeralcic acid were identified as the compounds with anti-inflammatory and immunomodulatory effects. Successful establishment of the cell culture in Erlenmeyer flasks has been reported previously. The aim of this study was to evaluate the ability of cells in suspension from S. angustifolia grown in a stirred tank bioreactor and demonstrate their capacity to produce bioactive compounds. Cells in suspension grown at 200 rpm reached a maximal cell biomass in dry weight at 19.11 g/L and produced 3.47 mg/g of sphaeralcic acid. The mixture of scopoletin and tomentin was only detected at the beginning of the culture (12.13 μg/g). Considering that the profile of dissolved oxygen during the cultures was lesser than 15%, it is possible that the low growth at 100 rpm could be due to oxygen limitations or to cell sedimentation. At 400 rpm, a negative effect on cell viability could be caused by the increase in the hydrodynamic stress, including the impeller tip, average shear rate, and Reynolds number. The sphaeralcic acid content in the cell suspension of S. angustifolia obtained in the bioreactor was two orders of magnitude greater than that reported for the culture grown in Erlenmeyer flasks.}, } @article {pmid32116345, year = {2019}, author = {Mensch, AE and Cleary, TG}, title = {Measurements and predictions of thermophoretic soot deposition.}, journal = {International journal of heat and mass transfer}, volume = {143}, number = {}, pages = {}, pmid = {32116345}, issn = {0017-9310}, support = {9999-NIST/ImNIST/Intramural NIST DOC/United States ; }, abstract = {A thin laminar flow channel with a transverse temperature gradient was used to examine thermophoretic deposition of soot aerosol particles in experiments and modeled in Fire Dynamics Simulator (FDS) simulations. Conditions investigated included three flowrates, with nominal Reynolds number based on the hydraulic diameter of 55, 115 and 230, and two applied temperature gradients, nominally 10 °C/mm and 20 °C/mm, with repeats. Soot was generated from a propene diffusion flame. The burner exhaust was mixed with dilution air, and most large agglomerates greater than 1 μm aerodynamic diameter were removed prior to the channel inlet. The expected thermophoretic velocity of the aerosol was calculated from the applied temperature gradient. A calculated deposition velocity was determined from the mass of deposition, the channel inlet soot concentration, and the exposure time. Uniform soot deposition allowed targets to be used to measure the mass of deposition on the cold side of the channel. The mass of deposition was also determined by subtracting the mass of soot exiting the channel from the mass of soot entering the channel during the exposure time. The deposition velocities from these two methods generally agreed with the thermophoretic velocity and with each other. The deposition mass predicted by the FDS model also compared well with the experiments in most cases. The disagreements for the lowest flow rate cases are attributed to buoyant flow effects adding uncertainty to the actual temperature gradients present in the channel. (The opinions, findings, and conclusions expressed in this paper are the authors' and do not represent the views or policies of NIST or the United States Government.).}, } @article {pmid33266740, year = {2018}, author = {Wang, W and Pan, C and Wang, J}, title = {Wall-Normal Variation of Spanwise Streak Spacing in Turbulent Boundary Layer With Low-to-Moderate Reynolds Number.}, journal = {Entropy (Basel, Switzerland)}, volume = {21}, number = {1}, pages = {}, pmid = {33266740}, issn = {1099-4300}, abstract = {Low-speed streaks in wall-bounded turbulence are the dominant structures in the near-wall turbulent self-sustaining cycle. Existing studies have well characterized their spanwise spacing in the buffer layer and below. Recent studies suggested the existence of these small-scale structures in the higher layer where large-scale structures usually receive more attention. The present study is thus devoted to extending the understanding of the streak spacing to the log layer. An analysis is taken on two-dimensional (2D) wall-parallel velocity fields in a smooth-wall turbulent boundary layer with R e τ = 440∼2400, obtained via either 2D Particle Image Velocimetry (PIV) measurement taken here or public Direct Numerical Simulation (DNS). Morphological-based streak identification analysis yields a R e -independent log-normal distribution of the streak spacing till the upper bound of the log layer, based on which an empirical model is proposed to account for its wall-normal growth. The small-scale part of the spanwise spectra of the streamwise fluctuating velocity below y + = 100 is reasonably restored by a synthetic simulation that distributes elementary streak units based on the proposed empirical streak spacing model, which highlights the physical significance of streaks in shaping the small-scale part of the velocity spectra beyond the buffer layer.}, } @article {pmid30584714, year = {2018}, author = {Wang, WX and Wang, WL and Kang, HL and Guo, MM and Yang, B and Chen, ZX and Zhao, M}, title = {Effect of naturally restored grassland on the ephemeral gully erosion in the loess hilly and gully region.}, journal = {Ying yong sheng tai xue bao = The journal of applied ecology}, volume = {29}, number = {12}, pages = {3891-3899}, doi = {10.13287/j.1001-9332.201812.016}, pmid = {30584714}, issn = {1001-9332}, mesh = {Agriculture ; China ; *Conservation of Natural Resources ; Environmental Monitoring ; *Grassland ; *Soil ; }, abstract = {Ephemeral gully erosion is an important erosion type in hilly and gully regions of Loess Plateau. While previous studies mainly focused on ephemeral gullies in agricultural land, little is known about the effects of naturally restored grassland on ephemeral gully erosion. In this study, taking the bare ephemeral gullies as the baseline, we conducted in-situ flushing tests to explore runoff and sediment yield characteristics and erosion mechanism of grassland ephemeral gullies under the runoff conditions of 5, 10, 15, 20 and 25 L·min[-1]. Compared to the bare ephemeral gully, average flow velocity, stable runoff rate, Reynolds number and Froude number of grassland ephe-meral gullies was reduced by 25.4%-67.3%, 8.4%-26.6%, 54.9%-80.5%, 18.6%-65.1%, respectively, whereas resistance coefficient was increased by 0.09-7.18 folds. Compared to the bare ephemeral gully, the maximum sediment yield rate, stable sediment yield rate, average sediment yield rate of grassland ephemeral gullies was decreased by 55.1%-90.9%, 61.8%-95.4%, and 64.8%-92.4%, respectively. The sediment yield reduction benefit of the naturally restored grassland under the discharge flow rate of 5-25 L·min[-1] could reach 65.9%-88.8%, which decreased with increasing discharge flow rate. Compared to the bare ephemeral gully, average stream power and average shear stress of grassland ephemeral gullies was reduced by 54.9%-80.5% and 12.4%-51.1%, respectively, whereas the critical stream power and critical shear stress was increased by 1.43 folds and 33.7%, respectively. The average sediment yield of grassland and bare ephemeral gullies was signifi-cantly linearly related to average stream power and shear stress. Naturally restored grassland significantly increased the erosion resistance and reduced runoff erosion potential of ephemeral gullies.}, } @article {pmid30576199, year = {2018}, author = {Gabbana, A and Polini, M and Succi, S and Tripiccione, R and Pellegrino, FMD}, title = {Prospects for the Detection of Electronic Preturbulence in Graphene.}, journal = {Physical review letters}, volume = {121}, number = {23}, pages = {236602}, doi = {10.1103/PhysRevLett.121.236602}, pmid = {30576199}, issn = {1079-7114}, abstract = {Based on extensive numerical simulations, accounting for electrostatic interactions and dissipative electron-phonon scattering, we propose experimentally realizable geometries capable of sustaining electronic preturbulence in graphene samples. In particular, preturbulence is predicted to occur at experimentally attainable values of the Reynolds number between 10 and 50, over a broad spectrum of frequencies between 10 and 100 GHz.}, } @article {pmid30556777, year = {2019}, author = {Bass, K and Boc, S and Hindle, M and Dodson, K and Longest, W}, title = {High-Efficiency Nose-to-Lung Aerosol Delivery in an Infant: Development of a Validated Computational Fluid Dynamics Method.}, journal = {Journal of aerosol medicine and pulmonary drug delivery}, volume = {32}, number = {3}, pages = {132-148}, pmid = {30556777}, issn = {1941-2703}, support = {R01 HD087339/HD/NICHD NIH HHS/United States ; R01 HL139673/HL/NHLBI NIH HHS/United States ; }, mesh = {Administration, Inhalation ; Administration, Intranasal ; Aerosols/*administration & dosage/pharmacokinetics ; Computer Simulation ; *Drug Delivery Systems ; Equipment Design ; Humans ; *Hydrodynamics ; Infant ; Lung/metabolism ; *Models, Biological ; Particle Size ; }, abstract = {Background: Computational fluid dynamics (CFD) provides a powerful tool for developing new high-efficiency aerosol delivery strategies, such as nose-to-lung (N2L) aerosol administration to infants and children using correctly sized aerosols. The objective of this study was to establish numerically efficient CFD solution methods and guidelines for simulating N2L aerosol administration to an infant based on comparisons with concurrent in vitro experiments. Materials and Methods: N2L administration of a micrometer-sized aerosol (mass median aerodynamic diameter [MMAD] = 1.4 μm) was evaluated using concurrent CFD simulations and in vitro experiments. Aerosol transport and deposition was assessed in a new nasal airway geometry of a 6-month-old infant with a streamlined nasal cannula interface, which was constructed as a CFD mesh and three-dimensionally printed to form an identical physical prototype. CFD meshes explored were a conventional tetrahedral approach with near-wall (NW) prism elements and a new polyhedral mesh style with an equally refined NW layer. The presence of turbulence in the model was evaluated using a highly efficient low-Reynolds number (LRN) k-ω turbulence model, with previously established NW corrections that accounted for anisotropic wall-normal turbulence as well as improved NW velocity interpolations and hydrodynamic particle damping. Results: Use of the new polyhedral mesh was found to improve numerical efficiency by providing more rapid convergence and requiring fewer control volumes. Turbulent flow was found in the nasal geometry, generated by the inlet jets from the nasal cannula interface. However, due to the small particle size, turbulent dispersion was shown to have little effect on deposition. Good agreement was established between the CFD predictions using the numerically efficient LRN k-ω model with appropriate NW corrections and in vitro deposition data. Aerosol transmission efficiencies through the delivery tube, nasal cannula, and infant nasal model, based on experimental and CFD predictions, were 93.0% and 91.5%, respectively. Conclusions: A numerically efficient CFD approach was established to develop transnasal aerosol administration to infants and children. Small particle aerosols with aerodynamic diameters of ∼1.5 μm were confirmed to have low inertial depositional loss, and have low deposition from turbulent dispersion, making them ideal for high-efficiency lung delivery through an infant nasal cannula interface.}, } @article {pmid30548194, year = {2019}, author = {Enders, A and Siller, IG and Urmann, K and Hoffmann, MR and Bahnemann, J}, title = {3D Printed Microfluidic Mixers-A Comparative Study on Mixing Unit Performances.}, journal = {Small (Weinheim an der Bergstrasse, Germany)}, volume = {15}, number = {2}, pages = {e1804326}, doi = {10.1002/smll.201804326}, pmid = {30548194}, issn = {1613-6829}, abstract = {One of the basic operations in microfluidic systems for biological and chemical applications is the rapid mixing of different fluids. However, flow profiles in microfluidic systems are laminar, which means molecular diffusion is the only mixing effect. Therefore, mixing structures are crucial to enable more efficient mixing in shorter times. Since traditional microfabrication methods remain laborious and expensive, 3D printing has emerged as a potential alternative for the fabrication of microfluidic devices. In this work, five different passive micromixers known from literature are redesigned in comparable dimensions and manufactured using high-definition MultiJet 3D printing. Their mixing performance is evaluated experimentally, using sodium hydroxide and phenolphthalein solutions, and numerically via computational fluid dynamics. Both experimental and numerical analysis results show that HC and Tesla-like mixers achieve complete mixing after 0.99 s and 0.78 s, respectively, at the highest flow rate (Reynolds number (Re) = 37.04). In comparison, Caterpillar mixers exhibit a lower mixing rate with complete mixing after 1.46 s and 1.9 s. Furthermore, the HC mixer achieves very good mixing performances over all flow rates (Re = 3.7 to 37.04), while other mixers show improved mixing only at higher flow rates.}, } @article {pmid30545916, year = {2019}, author = {Sreenivasan, KR}, title = {Turbulent mixing: A perspective.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {116}, number = {37}, pages = {18175-18183}, pmid = {30545916}, issn = {1091-6490}, abstract = {Mixing of initially distinct substances plays an important role in our daily lives as well as in ecological and technological worlds. From the continuum point of view, which we adopt here, mixing is complete when the substances come together across smallest flow scales determined in part by molecular mechanisms, but important stages of the process occur via the advection of substances by an underlying flow. We know how smooth flows enable mixing but less well the manner in which a turbulent flow influences it; but the latter is the more common occurrence on Earth and in the universe. We focus here on turbulent mixing, with more attention paid to the postmixing state than to the transient process of initiation. In particular, we examine turbulent mixing when the substance is a scalar (i.e., characterized only by the scalar property of its concentration), and the mixing process does not influence the flow itself (i.e., the scalar is "passive"). This is the simplest paradigm of turbulent mixing. Within this paradigm, we discuss how a turbulently mixed state depends on the flow Reynolds number and the Schmidt number of the scalar (the ratio of fluid viscosity to the scalar diffusivity), point out some fundamental aspects of turbulent mixing that render it difficult to be addressed quantitatively, and summarize a set of ideas that help us appreciate its physics in diverse circumstances. We consider the so-called universal and anomalous features and summarize a few model studies that help us understand them both.}, } @article {pmid30523914, year = {2018}, author = {Bodling, A and Sharma, A}, title = {Numerical investigation of low-noise airfoils inspired by the down coat of owls.}, journal = {Bioinspiration & biomimetics}, volume = {14}, number = {1}, pages = {016013}, doi = {10.1088/1748-3190/aaf19c}, pmid = {30523914}, issn = {1748-3190}, mesh = {Animals ; Computer Simulation ; Flight, Animal/*physiology ; Models, Biological ; Noise ; Pressure ; Rotation ; Strigiformes/*physiology ; Wings, Animal/physiology ; }, abstract = {Numerical analysis of airfoil geometries inspired by the down coat of the night owl is presented. The bioinspired geometry consists of an array of 'finlet fences', which is placed near the trailing edge of the baseline (NACA 0012) airfoil. Two fences with maximum nondimensional heights, [Formula: see text] and [Formula: see text] are investigated, where [Formula: see text] is the displacement thickness at 2.9% chord upstream of the airfoil trailing edge. Wall-resolved large eddy simulations are performed at chord-based Reynolds number, [Formula: see text], flow Mach number, [Formula: see text], and angle of attack, [Formula: see text]. The simulation results show significant reductions in unsteady surface pressure and farfield radiated noise with the fences, in agreement with the measurements available in the literature. Analysis of the results reveals that the fences increase the distance between the boundary layer turbulence (source) and the airfoil trailing (scattering) edge, which is identified to be the mechanism behind high-frequency noise reduction. These reductions are larger for the taller fence as the source-scattering edge separation is greater. Two-point correlations show that the fences reduce the spanwise coherence at low frequencies for separation distances greater than a fence pitch (distance between two adjacent fences) and increase the coherence for smaller distances, the increase being higher for the taller fence. This increase in coherence and the reduced obliqueness of the leading edge of the fence are hypothesized to be responsible for the small increase in farfield noise at low frequencies observed in the simulations with the taller fence.}, } @article {pmid30522876, year = {2019}, author = {Paxman, T and Noga, M and Finlay, WH and Martin, AR}, title = {Experimental evaluation of pressure drop for flows of air and heliox through upper and central conducting airway replicas of 4- to 8-year-old children.}, journal = {Journal of biomechanics}, volume = {82}, number = {}, pages = {134-141}, doi = {10.1016/j.jbiomech.2018.10.028}, pmid = {30522876}, issn = {1873-2380}, mesh = {*Air ; *Airway Resistance ; Child ; Child, Preschool ; Female ; *Helium ; Humans ; Inhalation ; Male ; Models, Biological ; *Oxygen ; *Pressure ; *Respiratory Physiological Phenomena ; }, abstract = {Airway resistance describes the ratio between pressure drop and flow rate through the conducting respiratory airways. Analytical models of airway resistance for tracheobronchial airways have previously been developed and assessed without upper airways positioned upstream of the trachea. This work investigated pressure drop as a function of flow rate and gas properties for upper and central airway replicas of 10 child subjects, ages 4-8. Replica geometries were built based on computed tomography scan data and included airways from the nose through 3-5 distal branching airway generations. Pressure drop through the replicas was measured for constant inspiratory flows of air and heliox. For both the nose-throat and branching airways, the relationship between non-dimensional coefficient of friction, CF, with Reynolds number, Re, was found to resemble the turbulent Blasius equation for pipe flow, where CF∝Re[-0.25]. Additionally, pressure drop ratios between heliox and air were consistent with analytical predictions for turbulent flow. The presence of turbulence in the branching airways likely resulted from convection of turbulence produced upstream in the nose and throat. An airway resistance model based on the Blasius pipe friction correlation for turbulent flow was proposed for prediction of pressure drop through the branching bronchial airways downstream from the upper airway.}, } @article {pmid30522286, year = {2018}, author = {Acconcia, CN and Wright, A and Goertz, DE}, title = {Translational dynamics of individual microbubbles with millisecond scale ultrasound pulses.}, journal = {The Journal of the Acoustical Society of America}, volume = {144}, number = {5}, pages = {2859}, doi = {10.1121/1.5063353}, pmid = {30522286}, issn = {1520-8524}, abstract = {It is established that radiation forces can be used to transport ultrasound contrast agents, particularly for molecular imaging applications. However, the ability to model and control this process in the context of therapeutic ultrasound is limited by a paucity of data on the translational dynamics of encapsulated microbubbles under the influence of longer pulses. In this work, the translation of individual microbubbles, isolated with optical tweezers, was experimentally investigated over a range of diameters (1.8-8.8 μm, n = 187) and pressures (25, 50, 100, 150, and 200 kPa) with millisecond pulses. Data were compared with theoretical predictions of the translational dynamics, assessing the role of shell and history force effects. A pronounced feature of the displacement curves was an effective threshold size, below which there was only minimal translation. At higher pressures (≥150 kPa) a noticeable structure emerged where multiple local maxima occurred as a function of bubble size. The ability to accurately capture these salient features depended on the encapsulation model employed. In low Reynolds number conditions (i.e., low pressures, or high pressures, off-resonance) the inclusion of history force more accurately fit the data. After pulse cessation, bubbles exhibited substantial displacements consistent with the influence of history effects.}, } @article {pmid30511712, year = {2018}, author = {Jeon, W and Kim, T and Kim, SM and Baik, S}, title = {Fast mass transport-assisted convective heat transfer through a multi-walled carbon nanotube array.}, journal = {Nanoscale}, volume = {10}, number = {48}, pages = {23103-23112}, doi = {10.1039/c8nr07529h}, pmid = {30511712}, issn = {2040-3372}, abstract = {The recently reported fast mass transport through nanochannels provides a unique opportunity to explore nanoscale energy transport. Here we experimentally investigated the convective heat transport of air through vertically aligned multi-walled carbon nanotubes (VAMWNTs). The flow through the unit cell, defined as an interstitial space among four adjacent nanotubes (hydraulic diameter = 84.9 nm), was in the transition (0.62 ≤ Knudsen number ≤ 0.78) and creeping flow (3.83 × 10-5 ≤ Reynolds number (Re) ≤ 1.55 × 10-4) regime. The constant heat flux (0.102 or 0.286 W m-2) was supplied by a single-mode microwave (2.45 GHz) instantly heating the VAMWNTs. The volume flow rate was two orders of magnitude greater than the Hagen-Poiseuille theory value. The experimentally determined convective heat transfer coefficient (h, 3.70 × 10-4-4.01 × 10-3 W m-2 K-1) and Nusselt number (Nu, 1.17 × 10-9-1.26 × 10-8) were small partly due to the small Re. A further increase in Re (2.12 × 10-3) with the support of a polytetrafluoroethylene mesh significantly increased h (5.48 × 10-2 W m-2 K-1) and Nu (2.37 × 10-7). A large number of nanochannels in a given cross-section of heat sinks may enhance the heat dissipation significantly.}, } @article {pmid30511653, year = {2018}, author = {Wang, C and Tang, H}, title = {Influence of complex driving motion on propulsion performance of a heaving flexible foil.}, journal = {Bioinspiration & biomimetics}, volume = {14}, number = {1}, pages = {016011}, doi = {10.1088/1748-3190/aaf17a}, pmid = {30511653}, issn = {1748-3190}, mesh = {Animals ; Biomechanical Phenomena/physiology ; Biomimetics/*methods ; Fishes/physiology ; Models, Biological ; Motion ; Movement/*physiology ; Swimming/physiology ; }, abstract = {This study explores the effects of complex driving motion on the propulsion performance of a flexible foil heaving in the flight regimes of natural flyers. Such a fluid-structure interaction problem is numerically studied using an immersed boundary lattice Boltzmann method (IBLBM) based numerical framework. It is found that, at the Reynolds number 200 and when the foil's bending stiffness and mass ratio are moderate, adding an extra driving motion of doubled frequency to a purely harmonic motion on the foil's leading edge can enhance the thrust and propulsive efficiency by about 860% and 70%, respectively. The improvement in thrust increases with the extra-driving-motion amplitude. When the extra-driving-motion amplitude is fixed, there exists an optimal extra-driving-motion phase angle. As the foil becomes much stiffer or lighter, the improvement in the propulsion performance turns less. On the other hand, as the foil becomes much more flexible or heavier, drag instead of thrust is generated, and extra driving motion brings no improvement. Although the extra driving motion can improve the foil's propulsion performance in flows of different Reynolds numbers, the increasing rate of the thrust reduces with the Reynolds number. Through this study, details about the competitions among various forces exerted on the foil and their roles in the foil's dynamics are also revealed.}, } @article {pmid30487240, year = {2018}, author = {Kamal, A and Keaveny, EE}, title = {Enhanced locomotion, effective diffusion and trapping of undulatory micro-swimmers in heterogeneous environments.}, journal = {Journal of the Royal Society, Interface}, volume = {15}, number = {148}, pages = {}, pmid = {30487240}, issn = {1742-5662}, mesh = {Helicobacter/*physiology ; Locomotion/*physiology ; *Models, Biological ; Plasmodium/*physiology ; }, abstract = {Swimming cells and microorganisms must often move through complex fluids that contain an immersed microstructure such as polymer molecules or filaments. In many important biological processes, such as mammalian reproduction and bacterial infection, the size of the immersed microstructure is comparable to that of the swimming cells. This leads to discrete swimmer-microstructure interactions that alter the swimmer's path and speed. In this paper, we use a combination of detailed simulation and data-driven stochastic models to examine the motion of a planar undulatory swimmer in an environment of spherical obstacles tethered via linear springs to random points in the plane of locomotion. We find that, depending on environmental parameters, the interactions with the obstacles can enhance swimming speeds or prevent the swimmer from moving at all. We also show how the discrete interactions produce translational and angular velocity fluctuations that over time lead to diffusive behaviour primarily due to the coupling of swimming and rotational diffusion. Our results demonstrate that direct swimmer-microstructure interactions can produce changes in swimmer motion that may have important implications for the spreading of cell populations in or the trapping of harmful pathogens by complex fluids.}, } @article {pmid30467607, year = {2018}, author = {Grosjean, G and Hubert, M and Collard, Y and Pillitteri, S and Vandewalle, N}, title = {Surface swimmers, harnessing the interface to self-propel.}, journal = {The European physical journal. E, Soft matter}, volume = {41}, number = {11}, pages = {137}, pmid = {30467607}, issn = {1292-895X}, abstract = {In the study of microscopic flows, self-propulsion has been particularly topical in recent years, with the rise of miniature artificial swimmers as a new tool for flow control, low Reynolds number mixing, micromanipulation or even drug delivery. It is possible to take advantage of interfacial physics to propel these microrobots, as demonstrated by recent experiments using the proximity of an interface, or the interface itself, to generate propulsion at low Reynolds number. This paper discusses how a nearby interface can provide the symmetry breaking necessary for propulsion. An overview of recent experiments illustrates how forces at the interface can be used to generate locomotion. Surface swimmers ranging from the microscopic scale to typically the capillary length are covered. Two systems are then discussed in greater detail. The first is composed of floating ferromagnetic spheres that assemble through capillarity into swimming structures. Two previously studied configurations, triangular and collinear, are discussed and contrasted. A new interpretation for the triangular swimmer is presented. Then, the non-monotonic influence of surface tension and viscosity is evidenced in the collinear case. Finally, a new system is introduced. It is a magnetically powered, centimeter-sized piece that swims similarly to water striders.}, } @article {pmid30465777, year = {2019}, author = {Walker, BJ and Wheeler, RJ and Ishimoto, K and Gaffney, EA}, title = {Boundary behaviours of Leishmania mexicana: A hydrodynamic simulation study.}, journal = {Journal of theoretical biology}, volume = {462}, number = {}, pages = {311-320}, pmid = {30465777}, issn = {1095-8541}, mesh = {Animals ; Biophysical Phenomena ; *Hydrodynamics ; Insect Vectors/parasitology ; Leishmania mexicana/*physiology ; Life Cycle Stages ; Psychodidae/*parasitology ; Swimming ; }, abstract = {It is well established that the parasites of the genus Leishmania exhibit complex surface interactions with the sandfly vector midgut epithelium, but no prior study has considered the details of their hydrodynamics. Here, the boundary behaviours of motile Leishmania mexicana promastigotes are explored in a computational study using the boundary element method, with a model flagellar beating pattern that has been identified from digital videomicroscopy. In particular a simple flagellar kinematics is observed and quantified using image processing and mode identification techniques, suggesting a simple mechanical driver for the Leishmania beat. Phase plane analysis and long-time simulation of a range of Leishmania swimming scenarios demonstrate an absence of stable boundary motility for an idealised model promastigote, with behaviours ranging from boundary capture to deflection into the bulk both with and without surface forces between the swimmer and the boundary. Indeed, the inclusion of a short-range repulsive surface force results in the deflection of all surface-bound promastigotes, suggesting that the documented surface detachment of infective metacyclic promastigotes may be the result of their particular morphology and simple hydrodynamics. Further, simulation elucidates a remarkable morphology-dependent hydrodynamic mechanism of boundary approach, hypothesised to be the cause of the well-established phenomenon of tip-first epithelial attachment of Leishmania promastigotes to the sandfly vector midgut.}, } @article {pmid30464056, year = {2018}, author = {Digumarti, KM and Conn, AT and Rossiter, J}, title = {EuMoBot: replicating euglenoid movement in a soft robot.}, journal = {Journal of the Royal Society, Interface}, volume = {15}, number = {148}, pages = {}, pmid = {30464056}, issn = {1742-5662}, mesh = {Euglenida/*physiology ; *Locomotion ; *Robotics ; }, abstract = {Swimming is employed as a form of locomotion by many organisms in nature across a wide range of scales. Varied strategies of shape change are employed to achieve fluidic propulsion at different scales due to changes in hydrodynamics. In the case of microorganisms, the small mass, low Reynolds number and dominance of viscous forces in the medium, requires a change in shape that is non-invariant under time reversal to achieve movement. The Euglena family of unicellular flagellates evolved a characteristic type of locomotion called euglenoid movement to overcome this challenge, wherein the body undergoes a giant change in shape. It is believed that these large deformations enable the organism to move through viscous fluids and tiny spaces. The ability to drastically change the shape of the body is particularly attractive in robots designed to move through constrained spaces and cluttered environments such as through the human body for invasive medical procedures or through collapsed rubble in search of survivors. Inspired by the euglenoids, we present the design of EuMoBot, a multi-segment soft robot that replicates large body deformations to achieve locomotion. Two robots have been fabricated at different sizes operating with a constant internal volume, which exploit hyperelasticity of fluid-filled elastomeric chambers to replicate the motion of euglenoids. The smaller robot moves at a speed of [Formula: see text] body lengths per cycle (20 mm min[-1] or 2.2 cycles min[-1]) while the larger one attains a speed of [Formula: see text] body lengths per cycle (4.5 mm min[-1] or 0.4 cycles min[-1]). We show the potential for biomimetic soft robots employing shape change to both replicate biological motion and act as a tool for studying it. In addition, we present a quantitative method based on elliptic Fourier descriptors to characterize and compare the shape of the robot with that of its biological counterpart. Our results show a similarity in shape of 85% and indicate that this method can be applied to understand the evolution of shape in other nonlinear, dynamic soft robots where a model for the shape does not exist.}, } @article {pmid33266619, year = {2018}, author = {Abdollahzadeh Jamalabadi, MY}, title = {Optimal Design of Nanoparticle Enhanced Phan-Thien-Tanner Flow of a Viscoelastic Fluid in a Microchannel.}, journal = {Entropy (Basel, Switzerland)}, volume = {20}, number = {12}, pages = {}, pmid = {33266619}, issn = {1099-4300}, abstract = {The excellent thermal characteristics of nanoparticles have increased their application in the field of heat transfer. In this paper, a thermophysical and geometrical parameter study is performed to minimize the total entropy generation of the viscoelastic flow of nanofluid. Entropy generation with respect to volume fraction (<0.04), the Reynolds number (20,000-100,000), and the diameter of the microchannel (20-20,000 μm) with the circular cross-section under constant flux are calculated. As is shown, most of the entropy generation owes to heat transfer and by increasing the diameter of the channel, the Bejan number increases. The contribution of heat entropy generation in the microchannel is very poor and the major influence of entropy generation is attributable to friction. The maximum quantity of in-channel entropy generation happens in nanofluids with TiO2, CuO, Cu, and Ag nanoparticles, in turn, despite the fact in the microchannel this behavior is inverted, the minimum entropy generation occurs in nanofluids with CuO, Cu, Ag, and TiO2 nanoparticles, in turn. In the channel and microchannel for all nanofluids except water-TiO2, increasing the volume fraction of nanoparticles decreases entropy generation. In the channel and microchannel the total entropy generation increases by augmentation the Reynolds number.}, } @article {pmid30457929, year = {2019}, author = {Huang, HW and Tibbitt, MW and Huang, TY and Nelson, BJ}, title = {Matryoshka-Inspired Micro-Origami Capsules to Enhance Loading, Encapsulation, and Transport of Drugs.}, journal = {Soft robotics}, volume = {6}, number = {1}, pages = {150-159}, doi = {10.1089/soro.2018.0028}, pmid = {30457929}, issn = {2169-5180}, support = {/ERC_/European Research Council/International ; }, mesh = {Capsules/*chemistry ; Drug Delivery Systems/*methods ; Hydrogel, Polyethylene Glycol Dimethacrylate/chemistry ; Hydrogels/chemistry ; Russia ; Technology, Pharmaceutical/*methods ; Temperature ; }, abstract = {Stimuli-responsive hydrogels are promising candidates for use in the targeted delivery of drugs using microrobotics. These devices enable the delivery and sustained release of quantities of drugs several times greater than their dry weight and are responsive to external stimuli. However, existing systems have two major drawbacks: (1) severe drug leakage before reaching the targeted areas within the body and (2) impeded locomotion through liquids due to the inherent hydrophilicity of hydrogels. This article outlines an approach to the assembly of hydrogel-based microcapsules in which one device is assembled within another to prevent drug leakage during transport. Inspired by the famous Russian stacking dolls (Matryoshka), the proposed scheme not only improves drug-loading efficiency but also facilitates the movement of hydrogel-based microcapsules driven by an external magnetic field. At room temperature, drug leakage from the hydrogel matrix is 90%. However, at body temperature the device folds up and assembles to encapsulate the drug, thereby reducing leakage to a mere 6%. The Matryoshka-inspired micro-origami capsule (MIMC) can disassemble autonomously when it arrives at a targeted site, where the temperature is slightly above body temperature. Up to 30% of the encapsulated drug was shown to diffuse from the hydrogel matrix within 1 h when it unfolds and disassembles. The MIMC is also shown to enhance the movement of magnetically driven microcapsules while navigating through media with a low Reynolds number. The translational velocity of the proposed MIMC (four hydrogel-based microcapsules) driven by magnetic gradients is more than three times greater than that of a conventional (single) hydrogel-based microcapsule.}, } @article {pmid30425950, year = {2018}, author = {Rigatelli, G and Zuin, M and Dell'Avvocata, F and Nanjundappa, A and Daggubati, R and Nguyen, T}, title = {Non-invasive Evaluation of Fluid Dynamic of Aortoiliac Atherosclerotic Disease: Impact of Bifurcation Angle and Different Stent Configurations.}, journal = {Journal of translational internal medicine}, volume = {6}, number = {3}, pages = {138-145}, pmid = {30425950}, issn = {2450-131X}, abstract = {OBJECTIVES: To non-invasively evaluate by computational fluid dynamic (CFD) analysis the physiology and rheology of aortoiliac bifurcation disease at different angles and different stent configurations.

MATERIAL AND METHODS: For the analysis, we considered a physiologic model of abdominal aorta with an iliac bifurcation set at 30°, 45° and 70° without stenosis. Subsequently, a bilateral ostial common iliac stenosis of 80% was considered for each type of bifurcation. For the stent simulation, we reconstructed Zilver vascular self-expanding (Zilver; Cook, Bloomington, MN) and Palmaz Genesis Peripheral (Cordis, Miami, FL) stents.

RESULTS: The physiologic model, across the different angles, static pressure, Reynolds number and stream function, were lower for the 30° bifurcation angle with a gradient from 70° to 30° angles, whereas all the other parameters were inversely higher. After stenting, all the fluid parameters decreased homogenously independent of the stent type, maintaining a gradient in favour of 30° compared to 45° and 70° angles. The absolute greater deviation from physiology was observed for low kissing when self-expandable stents were used across all angles; in particular, the wall shear stress was high at at 45° angle.

CONCLUSION: Bifurcation angle deeply impacts the physiology of aortoiliac bifurcations, which are used to predict the fluid dynamic profile after stenting. CFD, having the potential to be derived both from computed tomography scan or invasive angiography, appears to be an ideal tool to predict fluid dynamic profile before and after stenting in aortoiliac bifurcation.}, } @article {pmid30424640, year = {2018}, author = {Sadri, M and Hejranfar, K and Ebrahimi, M}, title = {Prediction of fluid flow and acoustic field of a supersonic jet using vorticity confinement.}, journal = {The Journal of the Acoustical Society of America}, volume = {144}, number = {3}, pages = {1521}, doi = {10.1121/1.5055215}, pmid = {30424640}, issn = {1520-8524}, abstract = {In this study, the numerical simulation of the fluid flow and acoustic field of a supersonic jet is performed by using high-order discretization and the vorticity confinement (VC) method on coarse grids. The three-dimensional Navier-Stokes equations are considered in the generalized curvilinear coordinate system and the high-order compact finite-difference scheme is applied for the space discretization, and the time integration is performed by the fourth-order Runge-Kutta scheme. A low-pass high-order filter is applied to stabilize the numerical solution. The non-reflecting boundary conditions are adopted for all the free boundaries, and the Kirchhoff surface integration is utilized to obtain the far-field sound pressure levels in a number of observer locations. Comparisons of the jet mean flow and jet aeroacoustics results with the other numerical and experimental data at similar flow conditions are made and show a reasonable agreement. The study shows that the proposed solution methodology based on the high-order compact finite-difference scheme in conjunction with the VC method can reasonably predict the near-field flow and the far-field noise of high Reynolds number jets with a fairly coarser grid than that used in the large eddy simulations and, thus, the computational cost can be significantly decreased.}, } @article {pmid30424188, year = {2018}, author = {Jung, BJ and Kim, J and Kim, JA and Jang, H and Seo, S and Lee, W}, title = {PDMS-Parylene Hybrid, Flexible Microfluidics for Real-Time Modulation of 3D Helical Inertial Microfluidics.}, journal = {Micromachines}, volume = {9}, number = {6}, pages = {}, pmid = {30424188}, issn = {2072-666X}, abstract = {Inertial microfluidics has drawn much attention for its applications for circulating tumor cell separations from blood. The fluid flows and the inertial particle focusing in inertial microfluidic systems are highly dependent on the channel geometry and structure. Flexible microfluidic systems can have adjustable 3D channel geometries by curving planar 2D channels into 3D structures, which will enable tunable inertial separation. We present a poly(dimethylsiloxane) (PDMS)-parylene hybrid thin-film microfluidic system that can provide high flexibility for 3D channel shaping while maintaining the channel cross-sectional shape. The PDMS-parylene hybrid microfluidic channels were fabricated by a molding and bonding technique using initiated chemical vapor deposition (iCVD) bonding. We constructed 3D helical inertial microfluidic channels by coiling a straight 2D channel and studied the inertial focusing while varying radius of curvature and Reynolds number. This thin film structure allows for high channel curvature and high Dean numbers which leads to faster inertial particle focusing and shorter channel lengths than 2D spiral channels. Most importantly, the focusing positions of particles and cells in the microchannel can be tuned in real time by simply modulating the channel curvature. The simple mechanical modulation of these 3D structure microfluidic systems is expected to provide unique advantages of convenient tuning of cell separation thresholds with a single device.}, } @article {pmid30424137, year = {2018}, author = {Ansari, MA and Kim, KY and Kim, SM}, title = {Numerical and Experimental Study on Mixing Performances of Simple and Vortex Micro T-Mixers.}, journal = {Micromachines}, volume = {9}, number = {5}, pages = {}, pmid = {30424137}, issn = {2072-666X}, abstract = {Vortex flow increases the interface area of fluid streams by stretching along with providing continuous stirring action to the fluids in micromixers. In this study, experimental and numerical analyses on a design of micromixer that creates vortex flow were carried out, and the mixing performance was compared with a simple micro T-mixer. In the vortex micro T-mixer, the height of the inlet channels is half of the height of the main mixing channel. The inlet channel connects to the main mixing channel (micromixer) at the one end at an offset position in a fashion that creates vortex flow. In the simple micro T-mixer, the height of the inlet channels is equal to the height of the channel after connection (main mixing channel). Mixing of fluids and flow field have been analyzed for Reynolds numbers in a range from 1[-]80. The study has been further extended to planar serpentine microchannels, which were combined with a simple and a vortex T-junction, to evaluate and verify their mixing performances. The mixing performance of the vortex T-mixer is higher than the simple T-mixer and significantly increases with the Reynolds number. The design is promising for efficiently increasing mixing simply at the T-junction and can be applied to all micromixers.}, } @article {pmid30424044, year = {2018}, author = {Raza, W and Ma, SB and Kim, KY}, title = {Multi-Objective Optimizations of a Serpentine Micromixer with Crossing Channels at Low and High Reynolds Numbers.}, journal = {Micromachines}, volume = {9}, number = {3}, pages = {}, pmid = {30424044}, issn = {2072-666X}, abstract = {In order to maximize the mixing performance of a micromixer with an integrated three-dimensional serpentine and split-and-recombination configuration, multi-objective optimizations were performed at two different Reynolds numbers, 1 and 120, based on numerical simulation. Numerical analyses of fluid flow and mixing in the micromixer were performed using three-dimensional Navier-Stokes equations and convection-diffusion equation. Three dimensionless design variables that were related to the geometry of the micromixer were selected as design variables for optimization. Mixing index at the exit and pressure drop through the micromixer were employed as two objective functions. A parametric study was carried out to explore the effects of the design variables on the objective functions. Latin hypercube sampling method as a design-of-experiment technique has been used to select design points in the design space. Surrogate modeling of the objective functions was performed by using radial basis neural network. Concave Pareto-optimal curves comprising of Pareto-optimal solutions that represents the trade-off between the objective functions were obtained using a multi-objective genetic algorithm at Re = 1 and 120. Through the optimizations, maximum enhancements of 18.8% and 6.0% in mixing index were achieved at Re = 1 and 120, respectively.}, } @article {pmid30411937, year = {2018}, author = {Galitski, V and Kargarian, M and Syzranov, S}, title = {Dynamo Effect and Turbulence in Hydrodynamic Weyl Metals.}, journal = {Physical review letters}, volume = {121}, number = {17}, pages = {176603}, doi = {10.1103/PhysRevLett.121.176603}, pmid = {30411937}, issn = {1079-7114}, abstract = {The dynamo effect is a class of macroscopic phenomena responsible for generating and maintaining magnetic fields in astrophysical bodies. It hinges on the hydrodynamic three-dimensional motion of conducting gases and plasmas that achieve high hydrodynamic and/or magnetic Reynolds numbers due to the large length scales involved. The existing laboratory experiments modeling dynamos are challenging and involve large apparatuses containing conducting fluids subject to fast helical flows. Here we propose that electronic solid-state materials-in particular, hydrodynamic metals-may serve as an alternative platform to observe some aspects of the dynamo effect. Motivated by recent experimental developments, this Letter focuses on hydrodynamic Weyl semimetals, where the dominant scattering mechanism is due to interactions. We derive Navier-Stokes equations along with equations of magnetohydrodynamics that describe the transport of a Weyl electron-hole plasma appropriate in this regime. We estimate the hydrodynamic and magnetic Reynolds numbers for this system. The latter is a key figure of merit of the dynamo mechanism. We show that it can be relatively large to enable observation of the dynamo-induced magnetic field bootstrap in an experiment. Finally, we generalize the simplest dynamo instability model-the Ponomarenko dynamo-to the case of a hydrodynamic Weyl semimetal and show that the chiral anomaly term reduces the threshold magnetic Reynolds number for the dynamo instability.}, } @article {pmid30400531, year = {2017}, author = {Guo, X and Qi, H}, title = {Analytical Solution of Electro-Osmotic Peristalsis of Fractional Jeffreys Fluid in a Micro-Channel.}, journal = {Micromachines}, volume = {8}, number = {12}, pages = {}, pmid = {30400531}, issn = {2072-666X}, abstract = {The electro-osmotic peristaltic flow of a viscoelastic fluid through a cylindrical micro-channel is studied in this paper. The fractional Jeffreys constitutive model, including the relaxation time and retardation time, is utilized to describe the viscoelasticity of the fluid. Under the assumptions of long wavelength, low Reynolds number, and Debye-Hückel linearization, the analytical solutions of pressure gradient, stream function and axial velocity are explored in terms of Mittag-Leffler function by Laplace transform method. The corresponding solutions of fractional Maxwell fluid and generalized second grade fluid are also obtained as special cases. The numerical analysis of the results are depicted graphically, and the effects of electro-osmotic parameter, external electric field, fractional parameters and viscoelastic parameters on the peristaltic flow are discussed.}, } @article {pmid30397239, year = {2018}, author = {Nourazar, SS and Nazari-Golshan, A and Soleymanpour, F}, title = {On the expedient solution of the magneto-hydrodynamic Jeffery-Hamel flow of Casson fluid.}, journal = {Scientific reports}, volume = {8}, number = {1}, pages = {16358}, pmid = {30397239}, issn = {2045-2322}, abstract = {The equation of magneto-hydrodynamic Jeffery-Hamel flow of non-Newtonian Casson fluid in a stretching/shrinking convergent/divergent channel is derived and solved using a new modified Adomian decomposition method (ADM). So far in all problems where semi-analytical methods are used the boundary conditions are not satisfied completely. In the present research, a hybrid of the Fourier transform and the Adomian decomposition method (FTADM), is presented in order to incorporate all boundary conditions into our solution of magneto-hydrodynamic Jeffery-Hamel flow of non-Newtonian Casson fluid in a stretching/shrinking convergent/divergent channel flow. The effects of various emerging parameters such as channel angle, stretching/shrinking parameter, Casson fluid parameter, Reynolds number and Hartmann number on velocity profile are considered. The results using the FTADM are compared with the results of ADM and numerical Range-Kutta fourth-order method. The comparison reveals that, for the same number of components of the recursive sequences over a wide range of spatial domain, the relative errors associated with the new method, FTADM, are much less than the ADM. The results of the new method show that the method is an accurate and expedient approximate analytic method in solving the third-order nonlinear equation of Jeffery-Hamel flow of non-Newtonian Casson fluid.}, } @article {pmid30393471, year = {2018}, author = {Shahzad, K and Aeken, WV and Mottaghi, M and Kamyab, VK and Kuhn, S}, title = {Aggregation and clogging phenomena of rigid microparticles in microfluidics: Comparison of a discrete element method (DEM) and CFD-DEM coupling method.}, journal = {Microfluidics and nanofluidics}, volume = {22}, number = {9}, pages = {104}, pmid = {30393471}, issn = {1613-4982}, abstract = {We developed a numerical tool to investigate the phenomena of aggregation and clogging of rigid microparticles suspended in a Newtonian fluid transported through a straight microchannel. In a first step, we implement a time-dependent one-way coupling Discrete Element Method (DEM) technique to simulate the movement and effect of adhesion on rigid microparticles in two- and three-dimensional computational domains. The Johnson-Kendall-Roberts (JKR) theory of adhesion is applied to investigate the contact mechanics of particle-particle and particle-wall interactions. Using the one-way coupled solver, the agglomeration, aggregation and deposition behavior of the microparticles is studied by varying the Reynolds number and the particle adhesion. In a second step, we apply a two-way coupling CFD-DEM approach, which solves the equation of motion for each particle, and transfers the force field corresponding to particle-fluid interactions to the CFD toolbox OpenFOAM. Results for the one-way (DEM) and two-way (CFD-DEM) coupling techniques are compared in terms of aggregate size, aggregate percentages, spatial and temporal evaluation of aggregates in 2D and 3D. We conclude that two-way coupling is the more realistic approach, which can accurately capture the particle-fluid dynamics in microfluidic applications.}, } @article {pmid30393363, year = {2018}, author = {Ma, N and Duan, Z and Ma, H and Su, L and Liang, P and Ning, X and He, B and Zhang, X}, title = {Lattice Boltzmann Simulation of the Hydrodynamic Entrance Region of Rectangular Microchannels in the Slip Regime.}, journal = {Micromachines}, volume = {9}, number = {2}, pages = {}, pmid = {30393363}, issn = {2072-666X}, abstract = {Developing a three-dimensional laminar flow in the entrance region of rectangular microchannels has been investigated in this paper. When the hydrodynamic development length is the same magnitude as the microchannel length, entrance effects have to be taken into account, especially in relatively short ducts. Simultaneously, there are a variety of non-continuum or rarefaction effects, such as velocity slip and temperature jump. The available data in the literature appearing on this issue is quite limited, the available study is the semi-theoretical approximate model to predict pressure drop of developing slip flow in rectangular microchannels with different aspect ratios. In this paper, we apply the lattice Boltzmann equation method (LBE) to investigate the developing slip flow through a rectangular microchannel. The effects of the Reynolds number (1 < Re < 1000), channel aspect ratio (0 < ε < 1), and Knudsen number (0.001 < Kn < 0.1) on the dimensionless hydrodynamic entrance length, and the apparent friction factor, and Reynolds number product, are examined in detail. The numerical solution of LBM can recover excellent agreement with the available data in the literature, which proves its accuracy in capturing fundamental fluid characteristics in the slip-flow regime.}, } @article {pmid30393335, year = {2018}, author = {Afzal, MJ and Ashraf, MW and Tayyaba, S and Hossain, MK and Afzulpurkar, N}, title = {Sinusoidal Microchannel with Descending Curves for Varicose Veins Implantation.}, journal = {Micromachines}, volume = {9}, number = {2}, pages = {}, pmid = {30393335}, issn = {2072-666X}, abstract = {Approximately 26% of adult people, mostly females, are affected by varicose veins in old age. It is a common reason for distress, loss of efficiency, and worsening living conditions. Several traditional treatment techniques (sclerotherapy and foam sclerotherapy of large veins, laser surgeries and radiofrequency ablation, vein ligation and stripping, ambulatory phlebectomy, and endoscopic vein surgery) have failed to handle this disease effectively. Herein, authors have presented an alternative varicose vein implant method-the descending sinusoidal microchannel (DSMC). DSMC was simulated by Fuzzy logic MATLAB (The MathWorks, Natick, MA, USA) and ANSYS (ANSYS 18.2, perpetual license purchased by Ibadat Education Trust, The University of Lahore, Pakistan) with real and actual conditions. After simulations of DSMC, fabrication and testing were performed. The silver DSMC was manufactured by utilizing a micromachining procedure. The length, width, and depth of the silver substrate were 51 mm, 25 mm, and 1.1 mm, respectively. The measurements of the DSMC channel in the silver wafer substrate were 0.9 mm in width and 0.9 mm in depth. The three descending curves of the DSMC were 7 mm, 6 mm, and 5 mm in height. For pressure, actual conditions were carefully taken as 1.0 kPa to 1.5 kPa for varicose veins. For velocity, actual conditions were carefully taken as 0.02 m/s to 0.07 m/s for these veins. These are real and standard values used in simulations and experiments. At Reynolds number 323, the flow rate and velocity were determined as 1001.0 (0.1 nL/s), 11.4 cm/s and 1015.3 (0.1 nL/s), 12.19 cm/s by MATLAB (The MathWorks, Natick, MA, USA) and ANSYS simulations, respectively. The flow rate and velocity were determined to be 995.3 (0.1 nL/s) and 12.2 cm/s, respectively, at the same Reynolds number (323) in the experiment. Moreover, the Dean number was also calculated to observe Dean vortices. All simulated and experimental results were in close agreement. Consequently, DSMC can be implanted in varicose veins as a new treatment to preserve excellent blood flow in human legs from the original place to avoid tissue damage and other problems.}, } @article {pmid30389406, year = {2019}, author = {Amiri Delouei, A and Sajjadi, H and Mohebbi, R and Izadi, M}, title = {Experimental study on inlet turbulent flow under ultrasonic vibration: Pressure drop and heat transfer enhancement.}, journal = {Ultrasonics sonochemistry}, volume = {51}, number = {}, pages = {151-159}, doi = {10.1016/j.ultsonch.2018.10.032}, pmid = {30389406}, issn = {1873-2828}, abstract = {This experimental study examines the impact of ultrasonic vibration on pressure drop and heat transfer enhancement of inlet turbulent flows. A stainless steel tube connected to an ultrasonic transducer and immersed in a constant temperature two-phase fluid was considered as the test section. Regarding the designed configuration, the ultrasonic transducer utilized had an acoustic frequency of 28 kHz and two different power levels of 75 W and 100 W. The experiments were conducted for different ultrasonic power levels, inlet temperatures, and flow rates. The accuracy of measurements was successfully validated via the existing empirical correlations. The results indicate that the effect of ultrasonic vibration on pressure drop and heat transfer enhancement diminishes with the growth of both Reynolds number and inlet temperature. Based on previously reported results on inlet flows with a laminar flow regime, the effect of ultrasonic vibration is very trivial in current turbulent inlet flows (up to 7.28% for heat convection enhancement). The results of the present study will be beneficial for future investigations on designing vibrating heat exchangers.}, } @article {pmid30387646, year = {2018}, author = {Falkovich, G and Vladimirova, N}, title = {Turbulence Appearance and Nonappearance in Thin Fluid Layers.}, journal = {Physical review letters}, volume = {121}, number = {16}, pages = {164501}, doi = {10.1103/PhysRevLett.121.164501}, pmid = {30387646}, issn = {1079-7114}, abstract = {Flows in fluid layers are ubiquitous in industry, geophysics, and astrophysics. Large-scale flows in thin layers can be considered two dimensional with bottom friction added. Here we find that the properties of such flows depend dramatically on the way they are driven. We argue that a wall-driven (Couette) flow cannot sustain turbulence, no matter how small the viscosity and friction. Direct numerical simulations (DNSs) up to the Reynolds number Re=10^{6} confirm that all perturbations die in a plane Couette flow. On the contrary, for sufficiently small viscosity and friction, perturbations destroy the pressure-driven laminar (Poiseuille) flow. What appears instead is a traveling wave in the form of a jet slithering between wall vortices. For 5×10^{3} 1117, total stress (i.e., τ total = laminar + turbulent) was also calculated using a computational fluid dynamics (CFD) solver, Converge CFD (Converge Science Inc., Madison, WI, USA). Inhibition of ADAMTS13 with different concentration of EDTA (5 mM and 10 mM) was also performed to investigate the mechanism of cleavage in terms of mechanical and enzymatic aspects. Degradation of HMWM with CTD was negligible at all given testing conditions. Although no degradation of HMWM was observed with TCD at Re < 1117 (τ total = 1012 dyne/cm[2]), increase in degradation of HMWM was observed beyond Re of 1117 for all given exposure times. At Re ~ 2500 (τ total = 3070 dyne/cm[2]) with texp = 60 s, a severe degradation of HMWM (90.7 ± 3.8%, abnormal) was observed, and almost complete degradation of HMWM (96.1 ± 1.9%, abnormal) was observed with texp = 600 s. The inhibition studies with 5 mM EDTA at Re ~ 2500 showed that loss of HMWM was negligible (<10%, normal) for all given exposure times except for texp = 10 min (39.5 ± 22.3%, borderline-abnormal). With 10 mM EDTA, no degradation of HMWM was observed (11.1 ± 4.4%, normal) even for texp = 10 min. This study investigated the effect of shear stress and exposure time on the HMWM of vWF in laminar and turbulent flows. The inhibition study by EDTA confirms that degradation of HMWM is initiated by shear-induced unfolding followed by enzymatic cleavage at given conditions. Determination of magnitude of each mechanism needs further investigation. It is also important to note that the degradation of vWF is highly dependent on turbulence regardless of the time exposed within our testing conditions.}, } @article {pmid30362460, year = {2018}, author = {Kim, H and Kim, J and Choi, H}, title = {Flow structure modifications by leading-edge tubercles on a 3D wing.}, journal = {Bioinspiration & biomimetics}, volume = {13}, number = {6}, pages = {066011}, doi = {10.1088/1748-3190/aae6fc}, pmid = {30362460}, issn = {1748-3190}, mesh = {Animals ; Biomechanical Phenomena/physiology ; Flight, Animal/physiology ; Humpback Whale/*physiology ; Hydrodynamics ; Models, Biological ; Rheology/methods ; Wings, Animal/*physiology ; }, abstract = {Leading-edge tubercles on a humpback whale flipper are known to enhance its hydrodynamic performance at post-stall angles of attack (Miklosovic et al 2004 Phys. Fluids 16 39-42). We investigate vortical structures above a three-dimensional wing with tubercles using surface-oil-flow visualization and particle image velocimetry measurement. Two wing models with and without tubercles, previously studied by Miklosovic et al (2004 Phys. Fluids 16 39-42), are considered at the Reynolds number of 180 000 based on the free-stream velocity and mean chord length. At this Reynolds number, tubercles delay the stall angle by 7° and increase the maximum lift coefficient by about 22%. At a low angle of attack, flow separation first occurs near the tip region for both wing models. While flow separation rapidly progresses inboard (toward the wing root) for the model without tubercles with increasing angle of attack, tubercles produce two types of vortical motions and block the inboard progression of flow separation, resulting in delayed stall from α = 8° to 15°. One of these two vortical structures is pairs of counter-rotating streamwise vortices evolving from hemi-spherical separation bubbles near the leading-edge troughs at pre-, near-, and post-stall angles of attack, and the other is asymmetric pairs of streamwise vortices evolving from separated flow regions after the mid-chord region at near-stall angle of attack. At a post-stall angle of attack (α = 16°), strong clockwise and counter-clockwise streamwise vortices are generated from foci at the root and tip near the trailing edge, respectively, and delay flow separation in the mid-span, resulting in a higher lift coefficient than that without tubercles.}, } @article {pmid30349146, year = {2018}, author = {Bass, K and Longest, PW}, title = {Recommendations for Simulating Microparticle Deposition at Conditions Similar to the Upper Airways with Two-Equation Turbulence Models.}, journal = {Journal of aerosol science}, volume = {119}, number = {}, pages = {31-50}, pmid = {30349146}, issn = {0021-8502}, support = {R01 HD087339/HD/NICHD NIH HHS/United States ; R01 HL107333/HL/NHLBI NIH HHS/United States ; }, abstract = {The development of a CFD model, from initial geometry to experimentally validated result with engineering insight, can be a time-consuming process that often requires several iterations of meshing and solver set-up. Applying a set of guidelines in the early stages can help to streamline the process and improve consistency between different models. The objective of this study was to determine both mesh and CFD solution parameters that enable the accurate simulation of microparticle deposition under flow conditions consistent with the upper respiratory airways including turbulent flow. A 90° bend geometry was used as a characteristic model that occurs throughout the airways and for which high-quality experimental aerosol deposition data is available in the transitional and turbulent flow regimes. Four meshes with varying degrees of near-wall resolution were compared, and key solver settings were applied to determine the parameters that minimize sensitivity to the near-wall (NW) mesh. The Low Reynolds number (LRN) k-ω model was used to resolve the turbulence field, which is a numerically efficient two-equation turbulence model, but has recently been considered overly simplistic. Some recent studies have used more complex turbulence models, such as Large Eddy Simulation (LES), to overcome the perceived weaknesses of two-equation models. Therefore, the secondary objective was to determine whether the more computationally efficient LRN k-ω model was capable of providing deposition results that were comparable to LES. Results show how NW mesh sensitivity is reduced through application of the Green-Gauss Node-based gradient discretization scheme and physically realistic near-wall corrections. Using the newly recommended meshing parameters and solution guidelines gives an excellent match to experimental data. Furthermore, deposition data from the LRN k-ω model compares favorably with LES results for the same characteristic geometry. In summary, this study provides a set of meshing and solution guidelines for simulating aerosol deposition in transitional and turbulent flows found in the upper respiratory airways using the numerically efficient LRN k-ω approach.}, } @article {pmid30348646, year = {2018}, author = {Karakas, F and D'Oliveira, D and Maas, AE and Murphy, DW}, title = {Using a shell as a wing: pairing of dissimilar appendages in atlantiid heteropod swimming.}, journal = {The Journal of experimental biology}, volume = {221}, number = {Pt 23}, pages = {}, doi = {10.1242/jeb.192062}, pmid = {30348646}, issn = {1477-9145}, mesh = {Animal Fins/*physiology ; *Animal Shells ; Animals ; Biomechanical Phenomena ; Gastropoda/*physiology ; Swimming/*physiology ; Video Recording/methods ; Zooplankton ; }, abstract = {Atlantiid heteropods are zooplanktonic marine snails which have a calcium carbonate shell and single swimming fin. They actively swim to hunt prey and vertically migrate. Previous accounts of atlantiid heteropod swimming described these animals sculling with the swimming fin while the shell passively hung beneath the body. Here, we show, via high-speed stereophotogrammetric measurements of body, fin and shell kinematics, that the atlantiid heteropod Atlanta selvagensis actively flaps both the swimming fin and shell in a highly coordinated wing-like manner in order to swim in the intermediate Reynolds number regime (Re=10-100). The fin and shell kinematics indicate that atlantiid heteropods use unsteady hydrodynamic mechanisms such as clap-and-fling and delayed stall. Unique features of atlantiid heteropod swimming include the coordinated pairing of dissimilar appendages, use of the clap and fling mechanism twice during each stroke cycle, and the fin's extremely large stroke amplitude, which exceeds 180 deg.}, } @article {pmid30346731, year = {2018}, author = {Astumian, RD}, title = {Trajectory and Cycle-Based Thermodynamics and Kinetics of Molecular Machines: The Importance of Microscopic Reversibility.}, journal = {Accounts of chemical research}, volume = {51}, number = {11}, pages = {2653-2661}, doi = {10.1021/acs.accounts.8b00253}, pmid = {30346731}, issn = {1520-4898}, abstract = {A molecular machine is a nanoscale device that provides a mechanism for coupling energy from two (or more) processes that in the absence of the machine would be independent of one another. Examples include walking of a protein in one direction along a polymeric track (process 1, driving "force" X1 = - F⃗· l⃗) and hydrolyzing ATP (process 2, driving "force" X2 = ΔμATP); or synthesis of ATP (process 1, X1 = -ΔμATP) and transport of protons from the periplasm to the cytoplasm across a membrane (process 2, X2 = ΔμH[+]); or rotation of a flagellum (process 1, X1 = -torque) and transport of protons across a membrane (process 2, X2 = ΔμH[+]). In some ways, the function of a molecular machine is similar to that of a macroscopic machine such as a car that couples combustion of gasoline to translational motion. However, the low Reynolds number regime in which molecular machines operate is very different from that relevant for macroscopic machines. Inertia is negligible in comparison to viscous drag, and omnipresent thermal noise causes the machine to undergo continual transition among many states even at thermodynamic equilibrium. Cyclic trajectories among the states of the machine that result in a change in the environment can be broken into two classes: those in which process 1 in either the forward or backward direction ([Formula: see text]) occurs and which thereby exchange work [Formula: see text] with the environment; and those in which process 2 in either the forward or backward direction ([Formula: see text]) occurs and which thereby exchange work [Formula: see text] with the evironment. These two types of trajectories, [Formula: see text] and [Formula: see text], overlap, i.e., there are some trajectories in which both process 1 and process 2 occur, and for which the work exchanged is [Formula: see text]. The four subclasses of overlap trajectories [(+1,+2), (+1,-2), (-1,+2), (-1,-2)] are the coupled processes. The net probabilities for process 1 and process 2 are designated π+2 - π-2 and π+1 - π-1, respectively. The probabilities [Formula: see text] for any single trajectory [Formula: see text] and [Formula: see text] for its microscopic reverse [Formula: see text] are related by microscopic reversibility (MR), [Formula: see text], an equality that holds arbitrarily far from thermodynamic equilibrium, i.e., irrespective of the magnitudes of X1 and X2, and where [Formula: see text]. Using this formalism, we arrive at a remarkably simple and general expression for the rates of the processes, [Formula: see text], i = 1, 2, where the angle brackets indicate an average over the ensemble of all microscopic reverse trajectories. Stochastic description of coupling is doubtless less familiar than typical mechanical depictions of chemical coupling in terms of ATP induced violent kicks, judo throws, force generation and power-strokes. While the mechanical description of molecular machines is comforting in its familiarity, conclusions based on such a phenomenological perspective are often wrong. Specifically, a "power-stroke" model (i.e., a model based on energy driven "promotion" of a molecular machine to a high energy state followed by directional relaxation to a lower energy state) that has been the focus of mechanistic discussions of biomolecular machines for over a half century is, for catalysis driven molecular machines, incorrect. Instead, the key principle by which catalysis driven motors work is kinetic gating by a mechanism known as an information ratchet. Amazingly, this same principle is that by which catalytic molecular systems undergo adaptation to new steady states while facilitating an exergonic chemical reaction.}, } @article {pmid33265887, year = {2018}, author = {Qiang, Y and Wei, L and Luo, X and Jian, H and Wang, W and Li, F}, title = {Heat Transfer and Flow Structures of Laminar Confined Slot Impingement Jet with Power-Law Non-Newtonian Fluid.}, journal = {Entropy (Basel, Switzerland)}, volume = {20}, number = {10}, pages = {}, pmid = {33265887}, issn = {1099-4300}, abstract = {Heat transfer performances and flow structures of laminar impinging slot jets with power-law non-Newtonian fluids and corresponding typical industrial fluids (Carboxyl Methyl Cellulose (CMC) solutions and Xanthangum (XG) solutions) have been studied in this work. Investigations are performed for Reynolds number Re less than 200, power-law index n ranging from 0.5 to 1.5 and consistency index K varying from 0.001 to 0.5 to explore heat transfer and flow structure of shear-thinning fluid and shear-thickening fluid. Results indicate that with the increase of n, K for a given Re, wall Nusselt number increases mainly attributing to the increase of inlet velocity U. For a given inlet velocity, wall Nusselt number decreases with the increase of n and K, which mainly attributes to the increase of apparent viscosity and the reduction of momentum diffusion. For the same Re, U and Pr, wall Nusselt number decreases with the increase of n. Among the study of industrial power-law shear-thinning fluid, CMC solution with 100 ppm shows the best heat transfer performance at a given velocity. Moreover, new correlation of Nusselt number about industrial fluid is proposed. In general, for the heat transfer of laminar confined impinging jet, it is best to use the working fluid with low viscosity.}, } @article {pmid30327167, year = {2019}, author = {Zhang, H and Liu, C and Ou, Y and Chen, T and Yang, L and Hu, Z}, title = {Development of a helical coagulation reactor for harvesting microalgae.}, journal = {Journal of bioscience and bioengineering}, volume = {127}, number = {4}, pages = {447-450}, doi = {10.1016/j.jbiosc.2018.09.012}, pmid = {30327167}, issn = {1347-4421}, mesh = {Biomass ; *Bioreactors ; Cell Culture Techniques/instrumentation/methods ; Chemical Precipitation ; Flocculation ; Hydrodynamics ; Mechanical Phenomena ; Microalgae/*chemistry/*cytology/metabolism ; *Scenedesmus/cytology/metabolism ; Specimen Handling/instrumentation/methods ; }, abstract = {In this study, an innovative helical coagulation reactor (HCR) was developed for harvesting microalgae by sedimentation with polyaluminium chloride (PAC). The effects of construction and hydrodynamic characteristics on harvesting performance were investigated. Results showed that a higher harvesting efficiency, 96.37%, was achieved for the large and compact flocs generated by the HCR, and the settling rate of flocs was substantially influenced by the velocity gradient (G) and the Reynolds number (Re). When the Reynolds number closed to the transition between laminar and turbulent flow (4000), the flocs settled faster (20.51 m h[-1]), although settling slowed as the Reynolds number increased further because of ruptured flocs. The settling rate of flocs could be further improved to 23.27 m h[-1] by a pulse flow field, mainly due to larger and more compact flocs forming in the plug pipe flow. Furthermore, a comparative investigation of a mechanically agitated vessel and the HCR with the same Camp number (Gt) showed that the HCR achieved higher settling rates and a shorter residence time than those with a mechanical agitator. The HCR provided a uniform dissipation of energy and high velocity gradient while avoiding electrical and mechanical energy consumption, suggesting this reactor is an efficient and economic option for microalgae harvesting.}, } @article {pmid30327024, year = {2019}, author = {Hong, W and Shi, H and Huang, Z and Long, M and Xu, H and Liu, Z}, title = {Design and Simulation of a Passive Micromixer with Gourd-Shaped Channel.}, journal = {Journal of nanoscience and nanotechnology}, volume = {19}, number = {1}, pages = {206-212}, doi = {10.1166/jnn.2019.16431}, pmid = {30327024}, issn = {1533-4880}, abstract = {A gourd-shaped contraction-expansion design is proposed for a passive planar micromixer in this study. The mixing performance of the micromixer is analyzed numerically and compared with a T-shaped planar micromixer. The gourd-shaped contraction-expansion structure can enhance the vortex-formation and mixing abilities of the micromixer. The numerical simulation reveals that the gourd-shaped structure can improved vortex generation and mixing efficiency within a high Reynolds number range. The micromixer with an optimized waist width of 50 μm reaches a mixing efficiency of approximately 83.25% and maintains a moderate pressure drop of 4860 Pa at Re = 100. This study can shed light on the design of new 2D micromixers from the point view of bionics.}, } @article {pmid30326635, year = {2018}, author = {Sun, B and Wang, P and Luo, J and Deng, J and Guo, S and Ma, B}, title = {A Flexible Hot-Film Sensor Array for Underwater Shear Stress and Transition Measurement.}, journal = {Sensors (Basel, Switzerland)}, volume = {18}, number = {10}, pages = {}, pmid = {30326635}, issn = {1424-8220}, abstract = {A flexible hot-film sensor array for wall shear stress, flow separation, and transition measurement has been fabricated and implemented in experiments. Parylene C waterproof layer is vapor phase deposited to encapsulate the sensor. Experimental studies of shear stress and flow transition on a flat plate have been undertaken in a water tunnel with the sensor array. Compared with the shear stress derived from velocity profile and empirical formulas, the measuring errors of the hot-film sensors are less than 5%. In addition, boundary layer transition of the flat plate has also been detected successfully. Ensemble-averaged mean, normalized root mean square, and power spectra of the sensor output voltage indicate that the Reynolds number when transition begins at where the sensor array located is 1.82 × 10[5], 50% intermittency transition is 2.52 × 10[5], and transition finishes is 3.96 × 10[5]. These results have a good agreement with the transition Reynolds numbers, as measured by the Laser Doppler Velocimetry (LDV) system.}, } @article {pmid30302623, year = {2019}, author = {Tiwari, A and Chauhan, SS}, title = {Effect of Varying Viscosity on Two-Fluid Model of Blood Flow through Constricted Blood Vessels: A Comparative Study.}, journal = {Cardiovascular engineering and technology}, volume = {10}, number = {1}, pages = {155-172}, doi = {10.1007/s13239-018-00379-x}, pmid = {30302623}, issn = {1869-4098}, mesh = {Arterial Occlusive Diseases/*blood/physiopathology ; Arteries/*physiopathology ; Blood Flow Velocity ; *Blood Viscosity ; *Computer Simulation ; *Erythrocytes ; Humans ; *Models, Cardiovascular ; *Pulsatile Flow ; Regional Blood Flow ; }, abstract = {PURPOSE: Most of the previously studied non-Newtonian blood flow models considered blood viscosity to be constant but for correct measurement of flow rate and flow resistance, the hematocrit dependent viscosity will be better as various literature suggested the variable nature of blood viscosity. Present work concerns the steady and pulsatile nature of blood flow through constricted blood vessels. Two-fluid model for blood is considered with the suspension of all the RBCs (erythrocytes) in the core region as a non-Newtonian (Herschel-Bulkley) fluid and the plasma in the cell free region near wall as a Newtonian fluid. No slip condition on the wall and radially varying viscosity has been taken.

METHODS: For steady flow the analytical approach has been taken to obtain the exact solution. Regular perturbation expansion method has been used to solve the governing equations for pulsatile flow up to first order of approximation by assuming the pulsatile Reynolds number to be very small (much less than unity).

RESULTS: Flow rate, wall shear stress and velocity profile have been graphically analyzed and compared with constant viscosity model. A noteworthy observation of the present study is that rise in viscosity index leads to decay in velocity, velocity of plug flow region, flow rate while flow resistance increases with rising viscosity index (m). The results for Power-law fluid (PL), Bingham-plastic fluid (BP), Newtonian fluid (NF) are found as special cases from this model. Like the constant viscosity model, it has been also observed that the velocity, flow rate and plug core velocity of two-fluid model are higher than the single-fluid model for variable viscosity.

CONCLUSIONS: The two-phase fluid model is more significant than the single-fluid model. Effect of viscosity parameter on various hemodynamical quantities has been obtained. It is also concluded that a rising viscosity parameter (varying nature of viscosity) significantly distinguishes the single and two-fluid models in terms of changes in blood flow resistance. The outcome of present study may leave a significant impact on analyzing blood flow through small blood vessels with constriction, where correct measurement of flow rate and flow resistance for medical treatment is very important.}, } @article {pmid30297857, year = {2018}, author = {Karathanassis, IK and Trickett, K and Koukouvinis, P and Wang, J and Barbour, R and Gavaises, M}, title = {Illustrating the effect of viscoelastic additives on cavitation and turbulence with X-ray imaging.}, journal = {Scientific reports}, volume = {8}, number = {1}, pages = {14968}, pmid = {30297857}, issn = {2045-2322}, abstract = {The effect of viscoelastic additives on the topology and dynamics of the two-phase flow arising within an axisymmetric orifice with a flow path constriction along its main axis has been investigated employing high-flux synchrotron radiation. X-ray Phase Contrast Imaging (XPCI) has been conducted to visualise the cavitating flow of different types of diesel fuel within the orifice. An additised blend containing Quaternary Ammonium Salt (QAS) additives with a concentration of 500 ppm has been comparatively examined against a pure (base) diesel compound. A high-flux, 12 keV X-ray beam has been utilised to obtain time resolved radiographs depicting the vapour extent within the orifice from two views (side and top) with reference to its main axis. Different test cases have been examined for both fuel types and for a range of flow conditions characterised by Reynolds number of 35500 and cavitation numbers (CN) lying in the range 3.0-7.7. It has been established that the behaviour of viscoelastic micelles in the regions of shear flow is not consistent depending on the cavitation regimes encountered. Namely, viscoelastic effects enhance vortical (string) cavitation, whereas hinder cloud cavitation. Furthermore, the use of additised fuel has been demonstrated to suppress the level of turbulence within the orifice.}, } @article {pmid30280982, year = {2020}, author = {de Matos, DB and Barbosa, MPR and Leite, OM and Steter, JR and Lima, NS and Torres, NH and Marques, MN and de Alsina, OLS and Cavalcanti, EB}, title = {Characterization of a tubular electrochemical reactor for the degradation of the commercial diuron herbicide.}, journal = {Environmental technology}, volume = {41}, number = {10}, pages = {1307-1321}, doi = {10.1080/09593330.2018.1531941}, pmid = {30280982}, issn = {1479-487X}, mesh = {Diuron ; Electrodes ; *Herbicides ; Hydrogen Peroxide ; Oxidation-Reduction ; *Water Pollutants, Chemical ; }, abstract = {After designing and constructing an electrochemical reactor with concentric electrodes and tangential feed (RECT), it is necessary to characterize it and to study its performance. The experimental study of the residence time distribution (RTD) was conducted for flow rates of 2.78 × 10[-6] m[3] s[-1], 8.33 × 10[-6] m[3] s[-1] and 13.9 × 10[-6] m[3] s[-1]. According to the values obtained from the Pe number (0.67-1.52), the RECT fits as tubular with great dispersion. The determined empirical correlation (Sh = 18.16 Re[0.50] Sc[0.33]) showed a laminar flow behavior in the range of Reynolds number (Re) between 23 and 117. In order to use RECT in effluent treatment, an electrochemical oxidation study of the Diuron model molecule (Nortox[®]) was performed to analyze reactor performance in a closed system with total reflux. A decay kinetics of pseudo-first order was associated with the decay of the concentration of diuron and 30% mineralization in 180 min of process were obtained, having a total volume of 4 × 10[-3] m[3] and an initial concentration of commercial Diuron in 215.83 mg dm[-3]. Eleven by-products were identified by HPLC-MS analysis and, from this, it was possible to propose a route of degradation of the diuron. From these observations, it can be inferred that the studied electrochemical reactor had applicability in the degradation of recalcitrant compounds, as is the case of commercial diuron. Make some changes in the electrochemical reactor studied and other advanced oxidative processes, such as electro-Fenton, can be associated with the studied system to achieve a better conversion efficiency.}, } @article {pmid30242545, year = {2018}, author = {Waldrop, LD and He, Y and Khatri, S}, title = {What Can Computational Modeling Tell Us about the Diversity of Odor-Capture Structures in the Pancrustacea?.}, journal = {Journal of chemical ecology}, volume = {44}, number = {12}, pages = {1084-1100}, pmid = {30242545}, issn = {1573-1561}, mesh = {Air ; Animals ; Arthropod Antennae/metabolism ; Biological Evolution ; *Models, Theoretical ; *Odorants/analysis ; Water/chemistry ; }, abstract = {A major transition in the history of the Pancrustacea was the invasion of several lineages of these animals onto land. We investigated the functional performance of odor-capture organs, antennae with olfactory sensilla arrays, through the use of a computational model of advection and diffusion of odorants to olfactory sensilla while varying three parameters thought to be important to odor capture (Reynolds number, gap-width-to-sensillum-diameter ratio, and angle of the sensilla array with respect to oncoming flow). We also performed a sensitivity analysis on these parameters using uncertainty quantification to analyze their relative contributions to odor-capture performance. The results of this analysis indicate that odor capture in water and in air are fundamentally different. Odor capture in water and leakiness of the array are highly sensitive to Reynolds number and moderately sensitive to angle, whereas odor capture in air is highly sensitive to gap widths between sensilla and moderately sensitive to angle. Leakiness is not a good predictor of odor capture in air, likely due to the relative importance of diffusion to odor transport in air compared to water. We also used the sensitivity analysis to make predictions about morphological and kinematic diversity in extant groups of aquatic and terrestrial crustaceans. Aquatic crustaceans will likely exhibit denser arrays and induce flow within the arrays, whereas terrestrial crustaceans will rely on more sparse arrays with wider gaps and little-to-no animal-induced currents.}, } @article {pmid30212772, year = {2018}, author = {Fu, Q and Chen, H and Liao, Q and Huang, Y and Xia, A and Zhu, X and Xiao, C and Reungsang, A and Liu, Z}, title = {Drag reduction and shear-induced cells migration behavior of microalgae slurry in tube flow.}, journal = {Bioresource technology}, volume = {270}, number = {}, pages = {38-45}, doi = {10.1016/j.biortech.2018.08.133}, pmid = {30212772}, issn = {1873-2976}, mesh = {*Chlorella ; Physical Phenomena ; }, abstract = {To optimize the designing of microalgae slurry pumping system and enhance the efficiency of microalgae products production, the flow characteristics of microalgae slurries (Chlorella pyrenoidosa) in tube flow were for the first time investigated combining experiments and numerical simulation. The drag reduction behavior of microalgae slurry in the fully developed laminar flow regime was studied. In addition, the transition Reynolds number of microalgae slurries from laminar flow to turbulent flow was about 1000-1300, which was similar to the expression of two-phase flow. To provide a further understanding of flow feature of microalgae slurries in tube, a two-phase mixture model was proposed by considering the heterogeneity of concentration due to the shear-induced microalgae cells migration behavior. Simulation results revealed that the heterogeneous distribution of concentration was affected by average velocity and volume fraction of microalgae slurries, significantly affecting the flow resistance and flow stability of microalgae slurry in the tube flow.}, } @article {pmid30211982, year = {2019}, author = {Bergersen, AW and Mortensen, M and Valen-Sendstad, K}, title = {The FDA nozzle benchmark: "In theory there is no difference between theory and practice, but in practice there is".}, journal = {International journal for numerical methods in biomedical engineering}, volume = {35}, number = {1}, pages = {e3150}, doi = {10.1002/cnm.3150}, pmid = {30211982}, issn = {2040-7947}, mesh = {*Benchmarking ; Computer Simulation ; *Hydrodynamics ; United States ; United States Food and Drug Administration ; }, abstract = {The utility of flow simulations relies on the robustness of computational fluid dynamics (CFD) solvers and reproducibility of results. The aim of this study was to validate the Oasis CFD solver against in vitro experimental measurements of jet breakdown location from the FDA nozzle benchmark at Reynolds number 3500, which is in the particularly challenging transitional regime. Simulations were performed on meshes consisting of 5, 10, 17, and 28 million (M) tetrahedra, with Δt = 10[-5] seconds. The 5M and 10M simulation jets broke down in reasonable agreement with the experiments. However, the 17M and 28M simulation jets broke down further downstream. But which of our simulations are "correct"? From a theoretical point of view, they are all wrong because the jet should not break down in the absence of disturbances. The geometry is axisymmetric with no geometrical features that can generate angular velocities. A stable flow was supported by linear stability analysis. From a physical point of view, a finite amount of "noise" will always be present in experiments, which lowers transition point. To replicate noise numerically, we prescribed minor random angular velocities (approximately 0.31%), much smaller than the reported flow asymmetry (approximately 3%) and model accuracy (approximately 1%), at the inlet of the 17M simulation, which shifted the jet breakdown location closer to the measurements. Hence, the high-resolution simulations and "noise" experiment can potentially explain discrepancies in transition between sometimes "sterile" CFD and inherently noisy "ground truth" experiments. Thus, we have shown that numerical simulations can agree with experiments, but for the wrong reasons.}, } @article {pmid30200611, year = {2018}, author = {Wan, G and Jin, C and Trase, I and Zhao, S and Chen, Z}, title = {Helical Structures Mimicking Chiral Seedpod Opening and Tendril Coiling.}, journal = {Sensors (Basel, Switzerland)}, volume = {18}, number = {9}, pages = {}, pmid = {30200611}, issn = {1424-8220}, mesh = {Biomimetic Materials/*chemistry ; *Biomimetics ; Elastomers/chemistry ; Hydrogels/chemistry ; Liquid Crystals/chemistry ; *Plant Physiological Phenomena ; Plants/*anatomy & histology ; Polymers/chemistry ; }, abstract = {Helical structures are ubiquitous in natural and engineered systems across multiple length scales. Examples include DNA molecules, plants' tendrils, sea snails' shells, and spiral nanoribbons. Although this symmetry-breaking shape has shown excellent performance in elastic springs or propulsion generation in a low-Reynolds-number environment, a general principle to produce a helical structure with programmable geometry regardless of length scales is still in demand. In recent years, inspired by the chiral opening of Bauhinia variegata's seedpod and the coiling of plant's tendril, researchers have made significant breakthroughs in synthesizing state-of-the-art 3D helical structures through creating intrinsic curvatures in 2D rod-like or ribbon-like precursors. The intrinsic curvature results from the differential response to a variety of external stimuli of functional materials, such as hydrogels, liquid crystal elastomers, and shape memory polymers. In this review, we give a brief overview of the shape transformation mechanisms of these two plant's structures and then review recent progress in the fabrication of biomimetic helical structures that are categorized by the stimuli-responsive materials involved. By providing this survey on important recent advances along with our perspectives, we hope to solicit new inspirations and insights on the development and fabrication of helical structures, as well as the future development of interdisciplinary research at the interface of physics, engineering, and biology.}, } @article {pmid30194679, year = {2018}, author = {Daddi-Moussa-Ider, A and Löwen, H and Gekle, S}, title = {Creeping motion of a solid particle inside a spherical elastic cavity[⋆].}, journal = {The European physical journal. E, Soft matter}, volume = {41}, number = {9}, pages = {104}, pmid = {30194679}, issn = {1292-895X}, abstract = {On the basis of the linear hydrodynamic equations, we present an analytical theory for the low-Reynolds-number motion of a solid particle moving inside a larger spherical elastic cavity which can be seen as a model system for a fluid vesicle. In the particular situation where the particle is concentric with the cavity, we use the stream function technique to find exact analytical solutions of the fluid motion equations on both sides of the elastic cavity. In this particular situation, we find that the solution of the hydrodynamic equations is solely determined by membrane shear properties and that bending does not play a role. For an arbitrary position of the solid particle within the spherical cavity, we employ the image solution technique to compute the axisymmetric flow field induced by a point force (Stokeslet). We then obtain analytical expressions of the leading-order mobility function describing the fluid-mediated hydrodynamic interactions between the particle and the confining elastic cavity. In the quasi-steady limit of vanishing frequency, we find that the particle self-mobility function is higher than that predicted inside a rigid no-slip cavity. Considering the cavity motion, we find that the pair-mobility function is determined only by membrane shear properties. Our analytical predictions are supplemented and validated by fully resolved boundary integral simulations where a very good agreement is obtained over the whole range of applied forcing frequencies.}, } @article {pmid30140921, year = {2019}, author = {Molony, DS and Park, J and Zhou, L and Fleischer, CC and Sun, HY and Hu, XP and Oshinski, JN and Samady, H and Giddens, DP and Rezvan, A}, title = {Bulk Flow and Near Wall Hemodynamics of the Rabbit Aortic Arch and Descending Thoracic Aorta: A 4D PC-MRI Derived Computational Fluid Dynamics Study.}, journal = {Journal of biomechanical engineering}, volume = {141}, number = {1}, pages = {0110031-01100311}, pmid = {30140921}, issn = {1528-8951}, support = {HHSN268201000043C/HL/NHLBI NIH HHS/United States ; }, abstract = {Animal models offer a flexible experimental environment for studying atherosclerosis. The mouse is the most commonly used animal, however, the underlying hemodynamics in larger animals such as the rabbit are far closer to that of humans. The aortic arch is a vessel with complex helical flow and highly heterogeneous shear stress patterns which may influence where atherosclerotic lesions form. A better understanding of intraspecies flow variation and the impact of geometry on flow may improve our understanding of where disease forms. In this work, we use magnetic resonance angiography (MRA) and 4D phase contrast magnetic resonance imaging (PC-MRI) to image and measure blood velocity in the rabbit aortic arch. Measured flow rates from the PC-MRI were used as boundary conditions in computational fluid dynamics (CFD) models of the arches. Helical flow, cross flow index (CFI), and time-averaged wall shear stress (TAWSS) were determined from the simulated flow field. Both traditional geometric metrics and shape modes derived from statistical shape analysis were analyzed with respect to flow helicity. High CFI and low TAWSS were found to colocalize in the ascending aorta and to a lesser extent on the inner curvature of the aortic arch. The Reynolds number was linearly associated with an increase in helical flow intensity (R = 0.85, p < 0.05). Both traditional and statistical shape analyses correlated with increased helical flow symmetry. However, a stronger correlation was obtained from the statistical shape analysis demonstrating its potential for discerning the role of shape in hemodynamic studies.}, } @article {pmid30136131, year = {2018}, author = {Krastev, VK and Amati, G and Succi, S and Falcucci, G}, title = {On the effects of surface corrugation on the hydrodynamic performance of cylindrical rigid structures.}, journal = {The European physical journal. E, Soft matter}, volume = {41}, number = {8}, pages = {95}, pmid = {30136131}, issn = {1292-895X}, mesh = {Computer Simulation ; *Hydrodynamics ; Kinetics ; Surface Properties ; }, abstract = {In this work, we perform fully three-dimensional numerical simulations of the flow field surrounding cylindrical structures characterized by different types of corrugated surface. The simulations are carried out using the Lattice Boltzmann Method (LBM), considering a flow regime with a Reynolds number [Formula: see text]. The fluid-dynamic wake structure and stability are investigated by means of PSD analyses of the velocity components and by visual inspection of the vortical coherent structure evolution. Moreover, the energy dissipation of the flow is assessed by considering an equivalent discharge coefficient [Formula: see text], which measures the total pressure losses of the flow moving around the various layout under investigation. Outcomes from our study demonstrate that the helical ridges augment energy dissipation, but might also have a role in the passive control of the characteristic frequencies of the unsteady wake flow.}, } @article {pmid30132443, year = {2018}, author = {Lee, YJ and Lua, KB}, title = {Wing-wake interaction: comparison of 2D and 3D flapping wings in hover flight.}, journal = {Bioinspiration & biomimetics}, volume = {13}, number = {6}, pages = {066003}, doi = {10.1088/1748-3190/aadc31}, pmid = {30132443}, issn = {1748-3190}, mesh = {Animals ; Biomechanical Phenomena/physiology ; Biomimetics/methods ; Flight, Animal/*physiology ; Models, Biological ; Wings, Animal/*physiology ; }, abstract = {The wing-wake interaction of flapping wings while hovering has been investigated, with the focus on the difference in wing-wake interaction between 2D and 3D flapping wings. Numerical simulations are conducted at a Reynolds number of 100, and the flapping configurations are divided into the 2D, quasi-3D and 3D categories. Variations of the aspect ratio and Rossby number allow the flapping configuration to morph gradually between categories. The wing-wake interaction mechanisms are identified and the effect of three-dimensionality on these mechanisms is discussed. Three-dimensionality affects wing-wake interaction through four primary aerodynamic mechanisms, namely, induced jet, downwash/upwash, leading-edge vortex (LEV) shedding due to vortex pairing, and the formation of a closely attached LEV. The first two mechanisms are well-established in the literature. With regard to the LEV shedding mechanism, it is revealed that the interaction between the LEV and the residue vortex from the previous stroke plays an important role in the early vortex shedding of 2D flapping wings. This effect diminishes with increasing three-dimensionality. With regard to the mechanism of the closely attached LEV, the wake encourages the formation of an LEV that is closely attached to the wing's top surface, which is beneficial to lift generation. This closely attached LEV mechanism accounts for most of the lift enhancement that arises from wake effects. Three-dimensionality alters the efficacy of the different aerodynamic mechanisms. Consequently, the dual peak lift coefficient pattern typically seen on 2D flapping wings transforms into the single peak lift coefficient pattern of the 3D flapping wing. It is also demonstrated that the mean lift enhancement due to wing-wake interaction diminishes rapidly when three-dimensionality is introduced. Results suggest that, for wings with parameters close to those of natural flyers, wing-wake interaction yields marginal lift enhancement and a small increase in energy consumption.}, } @article {pmid30132198, year = {2018}, author = {Espeso, DR and Martínez-García, E and Carpio, A and de Lorenzo, V}, title = {Dynamics of Pseudomonas putida biofilms in an upscale experimental framework.}, journal = {Journal of industrial microbiology & biotechnology}, volume = {45}, number = {10}, pages = {899-911}, pmid = {30132198}, issn = {1476-5535}, support = {ERC-2012-ADG-322797//European Research Council/International ; }, mesh = {Algorithms ; Biofilms/*growth & development ; Culture Media ; Equipment Design ; Hydrodynamics ; Image Processing, Computer-Assisted ; Industrial Microbiology/methods ; Polycarboxylate Cement/chemistry ; Pseudomonas putida/*growth & development ; Software ; }, abstract = {Exploitation of biofilms for industrial processes requires them to adopt suitable physical structures for rendering them efficient and predictable. While hydrodynamics could be used to control material features of biofilms of the platform strain Pseudomonas putida KT2440 there is a dearth of experimental data on surface-associated growth behavior in such settings. Millimeter scale biofilm patterns formed by its parental strain P. putida mt-2 under different Reynolds numbers (Re) within laminar regime were analyzed using an upscale experimental continuous cultivation assembly. A tile-scan image acquisition process combined with a customized image analysis revealed patterns of dense heterogeneous structures at Re = 1000, but mostly flattened coverings sparsely patched for Re < 400. These results not only fix the somewhat narrow hydrodynamic regime under which P. putida cells form stable coatings on surfaces destined for large-scale processes, but also provide useful sets of parameters for engineering catalytic biofilms based on this important bacterium as a cell factory.}, } @article {pmid30123895, year = {2018}, author = {Lee, J and Estlack, Z and Somaweera, H and Wang, X and Lacerda, CMR and Kim, J}, title = {A microfluidic cardiac flow profile generator for studying the effect of shear stress on valvular endothelial cells.}, journal = {Lab on a chip}, volume = {18}, number = {19}, pages = {2946-2954}, doi = {10.1039/c8lc00545a}, pmid = {30123895}, issn = {1473-0189}, mesh = {Aortic Valve/*cytology/physiology ; Endothelial Cells/*metabolism ; Equipment Design ; *Lab-On-A-Chip Devices ; *Shear Strength ; *Stress, Mechanical ; }, abstract = {To precisely investigate the mechanobiological responses of valvular endothelial cells, we developed a microfluidic flow profile generator using a pneumatically-actuated micropump consisting of microvalves of various sizes. By controlling the closing pressures and the actuation times of these microvalves, we modulated the magnitude and frequency of the shear stress to mimic mitral and aortic inflow profiles with frequencies in the range of 0.8-2 Hz and shear stresses up to 20 dyn cm-2. To demonstrate this flow profile generator, aortic inflow with an average of 5.9 dyn cm-2 shear stress at a frequency of 1.2 Hz with a Reynolds number of 2.75, a Womersley number of 0.27, and an oscillatory shear index (OSI) value of 0.2 was applied to porcine aortic valvular endothelial cells (PAVECs) for mechanobiological studies. The cell alignment, cell elongation, and alpha-smooth muscle actin (αSMA) expression of PAVECs under perfusion, steady flow, and aortic inflow conditions were analyzed to determine their shear-induced cell migration and trans-differentiation. In this morphological and immunocytochemical study, we found that the PAVECs elongated and aligned themselves perpendicular to the directions of the steady flow and the aortic inflow. In contrast, under perfusion with a fluidic shear stress of 0.47 dyn cm-2, the PAVECs elongated and aligned themselves parallel to the direction of flow. The PAVECs exposed to the aortic inflow upregulated their αSMA-protein expression to a greater degree than those exposed to perfusion and steady flow. By comparing these results to those of previous studies of pulsatile flow, we also found that the ratio of positive to negative shear stress plays an important role in determining PAVECs' trans-differentiation and adaptation to flow. This microfluidic cardiac flow profile generator will enable future valvular mechanobiological studies to determine the roles of magnitude and frequency of shear stresses.}, } @article {pmid33265465, year = {2018}, author = {Mathur, A and Seddighi, M and He, S}, title = {Transition of Transient Channel Flow with High Reynolds Number Ratios.}, journal = {Entropy (Basel, Switzerland)}, volume = {20}, number = {5}, pages = {}, pmid = {33265465}, issn = {1099-4300}, abstract = {Large-eddy simulations of turbulent channel flow subjected to a step-like acceleration have been performed to investigate the effect of high Reynolds number ratios on the transient behaviour of turbulence. It is shown that the response of the flow exhibits the same fundamental characteristics described in He & Seddighi (J. Fluid Mech., vol. 715, 2013, pp. 60-102 and vol. 764, 2015, pp. 395-427)-a three-stage response resembling that of the bypass transition of boundary layer flows. The features of transition are seen to become more striking as the Re-ratio increases-the elongated streaks become stronger and longer, and the initial turbulent spot sites at the onset of transition become increasingly sparse. The critical Reynolds number of transition and the transition period Reynolds number for those cases are shown to deviate from the trends of He & Seddighi (2015). The high Re-ratio cases show double peaks in the transient response of streamwise fluctuation profiles shortly after the onset of transition. Conditionally-averaged turbulent statistics based on a λ_2-criterion are used to show that the two peaks in the fluctuation profiles are due to separate contributions of the active and inactive regions of turbulence generation. The peak closer to the wall is attributed to the generation of "new" turbulence in the active region, whereas the peak farther away from the wall is attributed to the elongated streaks in the inactive region. In the low Re-ratio cases, the peaks of these two regions are close to each other during the entire transient, resulting in a single peak in the domain-averaged profile.}, } @article {pmid31831915, year = {2018}, author = {Coleman, GN and Rumsey, CL and Spalart, PR}, title = {Numerical study of turbulent separation bubbles with varying pressure gradient and Reynolds number.}, journal = {Journal of fluid mechanics}, volume = {847}, number = {}, pages = {28-70}, doi = {10.1017/jfm.2018.257}, pmid = {31831915}, issn = {0022-1120}, support = {/LaRC/Langley Research Center NASA/United States ; N-999999/ImNASA/Intramural NASA/United States ; }, abstract = {A family of cases each containing a small separation bubble is treated by direct numerical simulation (DNS), varying two parameters: the severity of the pressure gradients, generated by suction and blowing across the opposite boundary, and the Reynolds number. Each flow contains a well-developed entry region with essentially zero pressure gradient, and all are adjusted to have the same value for the momentum thickness, extrapolated from the entry region to the centre of the separation bubble. Combined with fully defined boundary conditions this will make comparisons with other simulations and turbulence models rigorous; we present results for a set of eight Reynolds-averaged Navier-Stokes turbulence models. Even though the largest Reynolds number is approximately 5.5 times higher than in a similar DNS study we presented in 1997, the models have difficulties matching the DNS skin friction very closely even in the zero pressure gradient, which complicates their assessment. In the rest of the domain, the separation location per se is not particularly difficult to predict, and the most definite disagreement between DNS and models is near reattachment. Curiously, the better models tend to cluster together in their predictions of pressure and skin friction even when they deviate from the DNS, although their eddy-viscosity levels are widely different in the outer region near the bubble (or they do not rely on an eddy viscosity). Stratford's square-root law is satisfied by the velocity profiles, both at separation and reattachment. The Reynolds-number range covers a factor of two, with the Reynolds number based on the extrapolated momentum thickness equal to approximately 1500 and 3000. This allows tentative estimates of the improvements that even higher values will bring to the model comparisons. The solutions are used to assess models through pressure, skin friction and other measures; the flow fields are also used to produce effective eddy-viscosity targets for the models, thus guiding turbulence-modelling work in each region of the flow.}, } @article {pmid31631904, year = {2018}, author = {Yang, XIA and Abkar, M}, title = {A hierarchical random additive model for passive scalars in wall-bounded flows at high Reynolds numbers.}, journal = {Journal of fluid mechanics}, volume = {842}, number = {}, pages = {354-380}, pmid = {31631904}, issn = {0022-1120}, support = {NNX15AU93A//NASA/United States ; }, abstract = {The kinematics of a fully developed passive scalar is modelled using the hierarchical random additive process (HRAP) formalism. Here, 'a fully developed passive scalar' refers to a scalar field whose instantaneous fluctuations are statistically stationary, and the 'HRAP formalism' is a recently proposed interpretation of the Townsend attached eddy hypothesis. The HRAP model was previously used to model the kinematics of velocity fluctuations in wall turbulence: u = ∑ i = 1 N z a i , where the instantaneous streamwise velocity fluctuation at a generic wall-normal location z is modelled as a sum of additive contributions from wall-attached eddies (a i) and the number of addends is N z ~ log(δ/z). The HRAP model admits generalized logarithmic scalings including 〈ϕ [2]〉~log(δ/z), 〈ϕ(x)ϕ(x+r x)〉 ~ log(δ/r x), 〈(ϕ(x) - ϕ(x+r x))[2]〉 ~ log(r x /z), where ϕ is the streamwise velocity fluctuation, δ is an outer length scale, r x is the two-point displacement in the streamwise direction and 〈·〉 denotes ensemble averaging. If the statistical behaviours of the streamwise velocity fluctuation and the fluctuation of a passive scalar are similar, we can expect first that the above mentioned scalings also exist for passive scalars (i.e. for ϕ being fluctuations of scalar concentration) and second that the instantaneous fluctuations of a passive scalar can be modelled using the HRAP model as well. Such expectations are confirmed using large-eddy simulations. Hence the work here presents a framework for modelling scalar turbulence in high Reynolds number wall-bounded flows.}, } @article {pmid32372770, year = {2018}, author = {Chen, H and Yao, M}, title = {A high-flow portable biological aerosol trap (HighBioTrap) for rapid microbial detection.}, journal = {Journal of aerosol science}, volume = {117}, number = {}, pages = {212-223}, pmid = {32372770}, issn = {0021-8502}, abstract = {Bioaerosols exposure can lead to many adverse health effects and even result in death if highly infectious agents involved. Apparently, there is a great need for rapid detection of bioaerosols, for which air sampling often is the first critical step. However, currently available samplers often either require an external power and/or with low sampling flow rate, thus falling short of providing a practical solution when response time is of great concern. Here, we have designed and evaluated a new portable high volume bioaerosol sampler named as HighBioTrap through optimizing its operating parameters. The sampler was operated at a sampling flow rate of 1200 L/min, with an impaction velocity of about 10.2 m/s (S/W = 1.5, T/W = 1), while the weight of the sampler is about 1.9 kg. The performances of the HighBioTrap sampler were tested both in lab controlled and natural environments (outdoor and indoor environments in a university building) along with the reference sampler-the BioStage impactor using aerosolized Polystyrene (PS) uniform microspheres of various sizes, aerosolized bacteria and also ambient air particles. The microbial community structures of collected culturable bacterial aerosol particles both by the HighBioTrap and the BioStage impactor in the natural environments were analyzed using gene sequence method. Experimental results with PS particles showed the HighBioTrap has a cutoff size of ~ 2 µm. The widely used impactor design equation was found to be not applicable for predicting the performance of the HighBioTrap due to its large Reynolds number. When sampling aerosolized individual Pseudomonas fluorescens and Bacillus subtilis bacterial particles, the HighBioTrap had physical collection efficiencies of 10% and 20%, respectively. Despite the higher desiccation effects introduced by higher flow rate, the HighBioTrap was shown to obtain a higher microbial diversity than the BioStage impactor for both in outdoor and indoor environments given the same sampling time (p < 0.01). Our data also showed that most of the desiccation effects might have occurred between 3 and 5 min of the sampling and an impaction velocity of around 10 m/s might be a close-to-optimal impaction velocity for collecting most environmental bacterial aerosols while maximally preserving their culturability. This work contributes to our understanding of microbial sampling stress (impaction velocity and sampling time), while developing a portable high volume sampler. The HighBioTrap sampler could find its great efficiencies in qualitative microbial aerosol detection and analysis, such as investigation of microbial aerosol diversity for a particular environment, or when the low level of pathogens is present and detection time is of great concern.}, } @article {pmid31631915, year = {2018}, author = {Bose, ST and Park, GI}, title = {Wall-Modeled Large-Eddy Simulation for Complex Turbulent Flows.}, journal = {Annual review of fluid mechanics}, volume = {50}, number = {}, pages = {535-561}, pmid = {31631915}, issn = {0066-4189}, support = {NNX15AU93A//NASA/United States ; }, abstract = {Large-eddy simulation (LES) has proven to be a computationally tractable approach to simulate unsteady turbulent flows. However, prohibitive resolution requirements induced by near-wall eddies in high-Reynolds number boundary layers necessitate the use of wall models or approximate wall boundary conditions. We review recent investigations in wall-modeled LES, including the development of novel approximate boundary conditions and the application of wall models to complex flows (e.g., boundary-layer separation, shock/boundary-layer interactions, transition). We also assess the validity of underlying assumptions in wall-model derivations to elucidate the accuracy of these investigations, and offer suggestions for future studies.}, } @article {pmid30996402, year = {2018}, author = {Ricco, P and Hicks, PD}, title = {Streamwise-travelling viscous waves in channel flows.}, journal = {Journal of engineering mathematics}, volume = {111}, number = {1}, pages = {23-49}, pmid = {30996402}, issn = {0022-0833}, abstract = {The unsteady viscous flow induced by streamwise-travelling waves of spanwise wall velocity in an incompressible laminar channel flow is investigated. Wall waves belonging to this category have found important practical applications, such as microfluidic flow manipulation via electro-osmosis and surface acoustic forcing and reduction of wall friction in turbulent wall-bounded flows. An analytical solution composed of the classical streamwise Poiseuille flow and a spanwise velocity profile described by the parabolic cylinder function is found. The solution depends on the bulk Reynolds number R, the scaled streamwise wavelength λ , and the scaled wave phase speed U. Numerical solutions are discussed for various combinations of these parameters. The flow is studied by the boundary-layer theory, thereby revealing the dominant physical balances and quantifying the thickness of the near-wall spanwise flow. The Wentzel-Kramers-Brillouin-Jeffreys (WKBJ) theory is also employed to obtain an analytical solution, which is valid across the whole channel. For positive wave speeds which are smaller than or equal to the maximum streamwise velocity, a turning-point behaviour emerges through the WKBJ analysis. Between the wall and the turning point, the wall-normal viscous effects are balanced solely by the convection driven by the wall forcing, while between the turning point and the centreline, the Poiseuille convection balances the wall-normal diffusion. At the turning point, the Poiseuille convection and the convection from the wall forcing cancel each other out, which leads to a constant viscous stress and to the break down of the WKBJ solution. This flow regime is analysed through a WKBJ composite expansion and the Langer method. The Langer solution is simpler and more accurate than the WKBJ composite solution, while the latter quantifies the thickness of the turning-point region. We also discuss how these waves can be generated via surface acoustic forcing and electro-osmosis and propose their use as microfluidic flow mixing devices. For the electro-osmosis case, the Helmholtz-Smoluchowski velocity at the edge of the Debye-Hückel layer, which drives the bulk electrically neutral flow, is obtained by matched asymptotic expansion.}, } @article {pmid30965982, year = {2017}, author = {Bhambri, P and Narain, R and Fleck, B}, title = {Drag Reduction Using Polysaccharides in a Taylor[-]Couette Flow.}, journal = {Polymers}, volume = {9}, number = {12}, pages = {}, pmid = {30965982}, issn = {2073-4360}, abstract = {Three different polysaccharides, aloe vera, Tamarind powder and pineapple fibers, are utilized as drag reducing agents in a turbulent flow. Using a Taylor[-]Couette setup, consisting of a rotating inner cylinder, for measuring the drag reduction, a range of Reynolds numbers from 4 × 10[4] to 3 × 10[5] has been explored in this study. The results are in good agreement with previous studies on polysaccharides conducted in a pipe/channel flow and a maximum drag reduction of 35% has been observed. Further, novel additives such as cellulose nanocrystals (CNC), surfactants and CNC grafted with surfactants are also examined in this study for drag reduction. CNC due to its rigid rod structure reduced the drag by 30%. Surfactant, due to its unique micelle formation showed maximum drag reduction of 80% at low Re. Further, surfactant was grafted on CNC and was examined for drag reduction. However, drag reduction property of surfactant was observed to be significantly reduced after grafting on CNC. The effect of Reynolds number on drag reduction is studied for all the additives investigated in this study.}, } @article {pmid31631889, year = {2017}, author = {Park, GI}, title = {Wall-Modeled Large-Eddy Simulation of a High Reynolds Number Separating and Reattaching Flow.}, journal = {AIAA journal. American Institute of Aeronautics and Astronautics}, volume = {55}, number = {11}, pages = {}, pmid = {31631889}, issn = {1533-385X}, support = {NNX15AU93A//NASA/United States ; }, abstract = {The performance of two wall models based on Reynolds-averaged Navier-Stokes is compared in large-eddy simulation of a high Reynolds number separating and reattaching flow over the NASA wall-mounted hump. Wall modeling significantly improves flow prediction on a coarse grid where the large-eddy simulation with the no-slip wall boundary condition fails. Low-order statistics from the wall-modeled large-eddy simulation are in good agreement with the experiment. Wall-pressure fluctuations from the resolved-scale solution are in good agreement with the experiment, whereas wall shear-stress fluctuations modeled entirely through the wall models appear to be significantly underpredicted. Although the two wall models produce comparable results in the upstream attached flow region, the nonequilibrium wall model outperforms the equilibrium wall model in the separation bubble and recovery region where the key assumptions in the equilibrium model are shown to be invalid.}, } @article {pmid30400469, year = {2017}, author = {Afzal, MJ and Tayyaba, S and Ashraf, MW and Hossain, MK and Uddin, MJ and Afzulpurkar, N}, title = {Simulation, Fabrication and Analysis of Silver Based Ascending Sinusoidal Microchannel (ASMC) for Implant of Varicose Veins.}, journal = {Micromachines}, volume = {8}, number = {9}, pages = {}, pmid = {30400469}, issn = {2072-666X}, abstract = {Bioengineered veins can benefit humans needing bypass surgery, dialysis, and now, in the treatment of varicose veins. The implant of this vein in varicose veins has significant advantages over the conventional treatment methods. Deep vein thrombosis (DVT), vein patch repair, pulmonary embolus, and tissue-damaging problems can be solved with this implant. Here, the authors have proposed biomedical microdevices as an alternative for varicose veins. MATLAB and ANSYS Fluent have been used for simulations of blood flow for bioengineered veins. The silver based microchannel has been fabricated by using a micromachining process. The dimensions of the silver substrates are 51 mm, 25 mm, and 1.1 mm, in length, width, and depth respectively. The dimensions of microchannels grooved in the substrates are 0.9 mm in width and depth. The boundary conditions for pressure and velocity were considered, from 1.0 kPa to 1.50 kPa, and 0.02 m/s to 0.07 m/s, respectively. These are the actual values of pressure and velocity in varicose veins. The flow rate of 5.843 (0.1 nL/s) and velocity of 5.843 cm/s were determined at Reynolds number 164.88 in experimental testing. The graphs and results from simulations and experiments are in close agreement. These microchannels can be inserted into varicose veins as a replacement to maintain the excellent blood flow in human legs.}, } @article {pmid31631903, year = {2017}, author = {Yang, XIA and Lozano-Durán, A}, title = {A multifractal model for the momentum transfer process in wall-bounded flows.}, journal = {Journal of fluid mechanics}, volume = {824}, number = {}, pages = {}, pmid = {31631903}, issn = {0022-1120}, support = {NNX15AU93A//NASA/United States ; }, abstract = {The cascading process of turbulent kinetic energy from large-scale fluid motions to small-scale and lesser-scale fluid motions in isotropic turbulence may be modelled as a hierarchical random multiplicative process according to the multifractal formalism. In this work, we show that the same formalism might also be used to model the cascading process of momentum in wall-bounded turbulent flows. However, instead of being a multiplicative process, the momentum cascade process is additive. The proposed multifractal model is used for describing the flow kinematics of the low-pass filtered streamwise wall-shear stress fluctuation τ l ' , where l is the filtering length scale. According to the multifractal formalism, 〈 τ ' 2 〉 ~ log (R e τ) and 〈 exp (p τ l ') 〉 ~ (L / l) ζ p in the log-region, where Re τ is the friction Reynolds number, p is a real number, L is an outer length scale and ζ p is the anomalous exponent of the momentum cascade. These scalings are supported by the data from a direct numerical simulation of channel flow at Re τ = 4200.}, } @article {pmid31832014, year = {2017}, author = {Coleman, GN and Pirozzoli, S and Quadrio, M and Spalart, PR}, title = {Direct Numerical Simulation and Theory of a Wall-Bounded Flow with Zero Skin Friction.}, journal = {Flow, turbulence and combustion}, volume = {99}, number = {3-4}, pages = {553-564}, doi = {10.1007/s10494-017-9834-x}, pmid = {31832014}, issn = {1573-1987}, support = {/LaRC/Langley Research Center NASA/United States ; N-999999/ImNASA/Intramural NASA/United States ; }, abstract = {We study turbulent plane Couette-Poiseuille (CP) flows in which the conditions (relative wall velocity ΔU w ≡ 2U w , pressure gradient dP/dx and viscosity ν) are adjusted to produce zero mean skin friction on one of the walls, denoted by APG for adverse pressure gradient. The other wall, FPG for favorable pressure gradient, provides the friction velocity uτ , and h is the half-height of the channel. This leads to a one-dimensional family of flows of varying Reynolds number Re ≡ U w h/ν. We apply three codes, and cover three Reynolds numbers stepping by a factor of 2 each time. The agreement between codes is very good, and the Reynolds-number range is sizable. The theoretical questions revolve around Reynolds-number independence in both the core region (free of local viscous effects) and the two wall regions. The core region follows Townsend's hypothesis of universal behavior for the velocity and shear stress, when they are normalized with uτ and h; universality is not observed for all the Reynolds stresses, any more than it is in Poiseuille flow or boundary layers. The behavior at very high Re is unknown. The FPG wall region obeys the classical law of the wall, again for velocity and shear stress, but could suggest a low value for the Karman constant κ, possibly near 0.37. For the APG wall region, Stratford conjectured universal behavior when normalized with the pressure gradient, leading to a square-root law for the velocity. The literature, also covering other flows with zero skin friction, is ambiguous. Our results are very consistent with both of Stratford's conjectures, suggesting that at least in this idealized flow geometry the theory is successful like it was for the classical law of the wall. We appear to know the constants of the law within a 10% bracket. On the other hand, again that does not extend to Reynolds stresses other than the shear stress, but these stresses are passive in the momentum equation.}, } @article {pmid30400388, year = {2017}, author = {Wang, Q and Yuan, D and Li, W}, title = {Analysis of Hydrodynamic Mechanism on Particles Focusing in Micro-Channel Flows.}, journal = {Micromachines}, volume = {8}, number = {7}, pages = {}, pmid = {30400388}, issn = {2072-666X}, abstract = {In this paper, the hydrodynamic mechanism of moving particles in laminar micro-channel flows was numerically investigated. A hydrodynamic criterion was proposed to determine whether particles in channel flows can form a focusing pattern or not. A simple formula was derived to demonstrate how the focusing position varies with Reynolds number and particle size. Based on this proposed criterion, a possible hydrodynamic mechanism was discussed as to why the particles would not be focused if their sizes were too small or the channel Reynolds number was too low. The Re-λ curve (Re, λ respectively represents the channel-based Reynolds number and the particle's diameter scaled by the channel) was obtained using the data fitting with a least square method so as to obtain a parameter range of the focusing pattern. In addition, the importance of the particle rotation to the numerical modeling for the focusing of particles was discussed in view of the hydrodynamics. This research is expected to deepen the understanding of the particle transport phenomena in bounded flow, either in micro or macro fluidic scope.}, } @article {pmid30174548, year = {2017}, author = {Oosterhuis, JP and Verbeek, AA and Bühler, S and Wilcox, D and van der Meer, TH}, title = {Flow Separation and Turbulence in Jet Pumps for Thermoacoustic Applications.}, journal = {Flow, turbulence and combustion}, volume = {98}, number = {1}, pages = {311-326}, pmid = {30174548}, issn = {1573-1987}, abstract = {The effect of flow separation and turbulence on the performance of a jet pump in oscillatory flows is investigated. A jet pump is a static device whose shape induces asymmetric hydrodynamic end effects when placed in an oscillatory flow. This will result in a time-averaged pressure drop which can be used to suppress acoustic streaming in closed-loop thermoacoustic devices. An experimental setup is used to measure the time-averaged pressure drop as well as the acoustic power dissipation across two different jet pump geometries in a pure oscillatory flow. The results are compared against published numerical results where flow separation was found to have a negative effect on the jet pump performance in a laminar flow. Using hot-wire anemometry the onset of flow separation is determined experimentally and the applicability of a critical Reynolds number for oscillatory pipe flows is confirmed for jet pump applications. It is found that turbulence can lead to a reduction of flow separation and hence, to an improvement in jet pump performance compared to laminar oscillatory flows.}, } @article {pmid30404389, year = {2016}, author = {Zhou, T and Wang, H and Shi, L and Liu, Z and Joo, SW}, title = {An Enhanced Electroosmotic Micromixer with an Efficient Asymmetric Lateral Structure.}, journal = {Micromachines}, volume = {7}, number = {12}, pages = {}, pmid = {30404389}, issn = {2072-666X}, abstract = {Homogeneous and rapid mixing in microfluidic devices is difficult to accomplish, owing to the low Reynolds number associated with most flows in microfluidic channels. Here, an efficient electroosmotic micromixer based on a carefully designed lateral structure is demonstrated. The electroosmotic flow in this mixer with an asymmetrical structure induces enhanced disturbance in the micro channel, helping the fluid streams' folding and stretching, thereby enabling appreciable mixing. Quantitative analysis of the mixing efficiency with respect to the potential applied and the flow rate suggests that the electroosmotic microfluidic mixer developed in the present work can achieve efficient mixing with low applied potential.}, } @article {pmid30271109, year = {2016}, author = {Poroseva, SV and Colmenares F, JD and Murman, SM}, title = {On the accuracy of RANS simulations with DNS data.}, journal = {Physics of fluids (Woodbury, N.Y. : 1994)}, volume = {28}, number = {11}, pages = {}, doi = {10.1063/1.4966639}, pmid = {30271109}, issn = {1070-6631}, support = {NNX12AJ61A//NASA/United States ; }, abstract = {Simulation results conducted for incompressible planar wall-bounded turbulent flows with the Reynolds-Averaged Navier-Stokes (RANS) equations with no modeling involved are presented. Instead, all terms but the molecular diffusion are represented by the data from direct numerical simulation (DNS). In simulations, the transport equations for velocity moments through the second order (and the fourth order where the data are available) are solved in a zero-pressure gradient boundary layer over a flat plate and in a fully-developed channel flow in a wide range of Reynolds numbers using DNS data from Sillero et al. (2013), Lee & Moser (2015), and Jeyapaul et al. (2015). The results obtained demonstrate that DNS data are the significant and dominant source of uncertainty in such simulations (hereafter, RANS-DNS simulations). Effects of the Reynolds number, flow geometry, and the velocity moment order as well as an uncertainty quantification technique used to collect the DNS data on the results of RANS-DNS simulations are analyzed. New criteria for uncertainty quantification in statistical data collected from DNS are proposed to guarantee the data accuracy sufficient for their use in RANS equations and for the turbulence model validation.}, } @article {pmid30404361, year = {2016}, author = {Salieb-Beugelaar, GB and Gonçalves, D and Wolf, MP and Hunziker, P}, title = {Microfluidic 3D Helix Mixers.}, journal = {Micromachines}, volume = {7}, number = {10}, pages = {}, pmid = {30404361}, issn = {2072-666X}, abstract = {Polymeric microfluidic systems are well suited for miniaturized devices with complex functionality, and rapid prototyping methods for 3D microfluidic structures are increasingly used. Mixing at the microscale and performing chemical reactions at the microscale are important applications of such systems and we therefore explored feasibility, mixing characteristics and the ability to control a chemical reaction in helical 3D channels produced by the emerging thread template method. Mixing at the microscale is challenging because channel size reduction for improving solute diffusion comes at the price of a reduced Reynolds number that induces a strictly laminar flow regime and abolishes turbulence that would be desired for improved mixing. Microfluidic 3D helix mixers were rapidly prototyped in polydimethylsiloxane (PDMS) using low-surface energy polymeric threads, twisted to form 2-channel and 3-channel helices. Structure and flow characteristics were assessed experimentally by microscopy, hydraulic measurements and chromogenic reaction, and were modeled by computational fluid dynamics. We found that helical 3D microfluidic systems produced by thread templating allow rapid prototyping, can be used for mixing and for controlled chemical reaction with two or three reaction partners at the microscale. Compared to the conventional T-shaped microfluidic system used as a control device, enhanced mixing and faster chemical reaction was found to occur due to the combination of diffusive mixing in small channels and flow folding due to the 3D helix shape. Thus, microfluidic 3D helix mixers can be rapidly prototyped using the thread template method and are an attractive and competitive method for fluid mixing and chemical reactions at the microscale.}, } @article {pmid31534303, year = {2016}, author = {Thurman, D and Culley, D and Poinsatte, P and Raghu, S and Ameri, A and Shyam, V}, title = {INVESTIGATION OF SPIRAL AND SWEEPING HOLES.}, journal = {Journal of turbomachinery}, volume = {138}, number = {9}, pages = {}, pmid = {31534303}, issn = {0889-504X}, support = {//Glenn Research Center NASA/United States ; N-999999//Intramural NASA/United States ; }, abstract = {Surface infrared thermography, hotwire anemometry, and thermocouple surveys were performed on two new film cooling hole geometries: spiral/rifled holes and fluidic sweeping holes. The spiral holes attempt to induce large-scale vorticity to the film cooling jet as it exits the hole to prevent the formation of the kidney shaped vortices commonly associated with film cooling jets. The fluidic sweeping hole uses a passive in-hole geometry to induce jet sweeping at frequencies that scale with blowing ratios. The spiral hole performance is compared to that of round holes with and without compound angles. The fluidic hole is of the diffusion class of holes and is therefore compared to a 777 hole and Square holes. A patent-pending spiral hole design showed the highest potential of the non-diffusion type hole configurations. Velocity contours and flow temperature were acquired at discreet cross-sections of the downstream flow field. The passive fluidic sweeping hole shows the most uniform cooling distribution but suffers from low span-averaged effectiveness levels due to enhanced mixing. The data was taken at a Reynolds number of 11,000 based on hole diameter and freestream velocity. Infrared thermography was taken for blowing ratios of 1.0, 1.5, 2.0, and 2.5 at a density ratio of 1.05. The flow inside the fluidic sweeping hole was studied using 3D unsteady RANS.}, } @article {pmid30213252, year = {2016}, author = {Tripathi, D and Akbar, NS and Khan, ZH and Bég, OA}, title = {Peristaltic transport of bi-viscosity fluids through a curved tube: A mathematical model for intestinal flow.}, journal = {Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine}, volume = {230}, number = {9}, pages = {817-828}, doi = {10.1177/0954411916658318}, pmid = {30213252}, issn = {2041-3033}, abstract = {The human intestinal tract is a long, curved tube constituting the final section of the digestive system in which nutrients and water are mostly absorbed. Motivated by the dynamics of chyme in the intestine, a mathematical model is developed to simulate the associated transport phenomena via peristaltic transport. Rheology of chyme is modelled using the Nakamura-Sawada bi-viscosity non-Newtonian formulation. The intestinal tract is considered as a curved tube geometric model. Low Reynolds number (creeping hydrodynamics) and long wavelength approximations are taken into consideration. Analytical solutions of the moving boundary value problem are derived for velocity field, pressure gradient and pressure rise. Streamline flow visualization is achieved with Mathematica symbolic software. Peristaltic pumping phenomenon and trapping of the bolus are also examined. The influence of curvature parameter, apparent viscosity coefficient (rheological parameter) and volumetric flow rate on flow characteristics is described. Validation of analytical solutions is achieved with a MAPLE17 numerical quadrature algorithm. The work is relevant to improving understanding of gastric hydrodynamics and provides a benchmark for further computational fluid dynamic simulations.}, } @article {pmid35607219, year = {2016}, author = {Mao, C and Kong, M and Yang, Q and Li, G and Huang, Y}, title = {Vorticity Deformation in Polymeric Emulsions Induced by Anisotropic Ellipsoids.}, journal = {ACS macro letters}, volume = {5}, number = {8}, pages = {900-903}, doi = {10.1021/acsmacrolett.6b00456}, pmid = {35607219}, issn = {2161-1653}, abstract = {We study the influence of particle shape on shear-induced droplet deformation in polymeric emulsions. During shearing, droplets become elongated and rotate periodically about their major axes while aligning along the vorticity direction in ellipsoid-filled emulsions, while similar behavior is not observed in the pristine, microsphere-filled or ellipsoid-filled inverse systems. Based on the Jeffery orbit theory, the formation of anisotropic droplets with extremely small Reynolds number due to arrested coalescence in Newtonian matrix and strong confinement effect are suggested to be responsible for the vorticity alignment of droplets during slow shearing.}, } @article {pmid30404299, year = {2016}, author = {Lee, SJ and Kwon, K and Jeon, TJ and Kim, SM and Kim, D}, title = {Quantification of Vortex Generation Due to Non-Equilibrium Electrokinetics at the Micro/Nanochannel Interface: Particle Tracking Velocimetry.}, journal = {Micromachines}, volume = {7}, number = {7}, pages = {}, pmid = {30404299}, issn = {2072-666X}, abstract = {We describe a quantitative study of vortex generation due to non-equilibrium electrokinetics near a micro/nanochannel interface. The microfluidic device is comprised of a microchannel with a set of nanochannels. These perm-selective nanochannels induce flow instability and thereby produce strong vortex generation. We performed tracking visualization of fluorescent microparticles to obtain velocity fields. Particle tracking enables the calculation of an averaged velocity field and the velocity fluctuations. We characterized the effect of applied voltages and electrolyte concentrations on vortex formation. The experimental results show that an increasing voltage or decreasing concentration results in a larger vortex region and a strong velocity fluctuation. We calculate the normalized velocity fluctuation-whose meaning is comparable to turbulent intensity-and we found that it is as high as 0.12. This value is indicative of very efficient mixing, albeit with a small Reynolds number.}, } @article {pmid30404283, year = {2016}, author = {Lee, SJ and Jeon, TJ and Kim, SM and Kim, D}, title = {Quantification of Vortex Generation Due to Non-Equilibrium Electrokinetics at the Micro/Nanochannel Interface: Spectral Analysis.}, journal = {Micromachines}, volume = {7}, number = {7}, pages = {}, pmid = {30404283}, issn = {2072-666X}, abstract = {We report on our investigation of a low Reynolds number non-equilibrium electrokinetic flow in a micro/nanochannel platform. Non-equilibrium electrokinetic phenomena include so-called concentration polarization in a moderate electric field and vortex formation in a high electric field. We conducted a spectral analysis of non-equilibrium electrokinetic vortices at a micro/nanochannel interface. We found that periodic vortices are formed while the frequency varies with the applied voltages and solution concentrations. At a frequency as high as 60 Hz, vortex generation was obtained with the strongest electric field and the lowest concentration. The power spectra show increasing frequency with increasing voltage or decreasing concentration. We expect that our spectral analysis results will be useful for micromixer developers in the micromachine research field.}, } @article {pmid34434625, year = {2016}, author = {Kedzierski, MA}, title = {Diesel Adsorption to Polyvinyl Chloride and Iron During Contaminated Water Flow and Flushing Tests.}, journal = {Journal of research of the National Institute of Standards and Technology}, volume = {121}, number = {}, pages = {314-341}, pmid = {34434625}, issn = {1044-677X}, abstract = {This paper presents an experimental and theoretical study of aqueous diesel contamination and decontamination of a polyvinyl chloride (PVC) surface and an iron (Fe) surface. A test apparatus designed for the purpose of studying adsorption of diesel from a flowing dilute diesel/water mixture was used to measure the mass of diesel adsorbed per unit surface area (the excess surface density) and the bulk concentration of the diesel in the flow using a fluorescence based measurement technique. Both bulk composition and the excess surface density measurements were achieved via a traverse of the fluorescent measurement probe perpendicular to the test surface. The diesel adsorption to each test surface was examined for three different Reynolds numbers between zero and 7000. Measurements for a given condition were made over a period of approximately 200 h for a diesel mass fraction of approximately 0.15 % in tap water. For a Reynolds number of approximately 7000, the largest excess layer thickness was approximately 4.4 μm, which was measured on a PVC surface. Averaging over all contaminating flow rates and exposure times, the excess layer thickness on the PVC surface was approximately 2.0 μm. Reynolds number had little or no effect on the accumulation of diesel on an iron surface, which was approximately 0.71 μm. The adsorbed diesel on the PVC and iron surfaces was removed by flushing with tap water. Models to predict excess layer thickness during flushing and contamination were developed. The models predict flushing times to within 7 h and predict the influence of pipe surface on contamination level.}, } @article {pmid33154603, year = {2016}, author = {Goldstein, ME and Sescu, A and Duck, PW and Choudhari, M}, title = {Nonlinear wakes behind a row of elongated roughness elements.}, journal = {Journal of fluid mechanics}, volume = {796}, number = {}, pages = {516-557}, doi = {10.1017/jfm.2016.269}, pmid = {33154603}, issn = {0022-1120}, support = {/ARMD/Aeronautics NASA/United States ; }, abstract = {This paper is concerned with the high Reynolds number flow over a spanwise-periodic array of roughness elements with interelement spacing of the order of the local boundary-layer thickness. While earlier work by Goldstein et al. (J. Fluid Mech., vol. 644, 2010, pp. 123-163) and Goldstein et al. (J. Fluid Mech., vol. 668, 2011, pp. 236-266) was mainly concerned with smaller roughness heights that produced relatively weak distortions of the downstream flow, the focus here is on extending the analysis to larger roughness heights and streamwise elongated planform shapes that together produce a qualitatively different, nonlinear behaviour of the downstream wakes. The roughness scale flow now has a novel triple-deck structure that is somewhat different from related studies that have previously appeared in the literature. The resulting flow is formally nonlinear in the intermediate wake region, where the streamwise distance is large compared to the roughness dimensions but small compared to the downstream distance from the leading edge, as well as in the far wake region where the streamwise length scale is of the order of the downstream distance from the leading edge. In contrast, the flow perturbations in both of these wake regions were strictly linear in the earlier work by Goldstein et al. (2010, 2011). This is an important difference because the nonlinear wake flow in the present case provides an appropriate basic state for studying the secondary instability and eventual breakdown into turbulence.}, } @article {pmid32802012, year = {2016}, author = {Yu, T and Qiu, H and Yang, J and Shao, Y and Tao, L}, title = {Mixing at double-Tee junctions with unequal pipe sizes in water distribution systems.}, journal = {Water science & technology, water supply}, volume = {16}, number = {6}, pages = {1595-1602}, pmid = {32802012}, issn = {1607-0798}, support = {EPA999999/ImEPA/Intramural EPA/United States ; }, abstract = {Pipe flow mixing with various solute concentrations and flow rates at pipe junctions is investigated. The degree of mixing affects contaminant spread in a water distribution system, and many studies have focused on mixing at the cross junctions; however, only a few have focused on double-Tee junctions of unequal pipe diameters. To investigate the solute mixing at such junctions, a series of experiments was conducted in a turbulent regime (Re = 12,500-50,000) with different Reynolds number ratios and connecting pipe lengths. Dimensionless outlet concentrations were found to depend on mixing mechanism at the impinging interface of junctions, where junctions with a larger pipe diameter ratio were associated with more complete mixing. Further, the inlet Reynolds number ratio affected mixing more strongly than the outlet Reynolds number ratio. Finally, the dimensionless connecting pipe length in a double-Tee played an important and complicated role in the flow mixing. The results were used to develop two-dimensional isopleth maps for the calculation of normalized north outlet concentrations.}, } @article {pmid30514019, year = {2014}, author = {Mendoza, U and Candella, RN and Assad, LPF and Castillo, FV and Azevedo, L and Knoppers, BA and Albuquerque, ALS}, title = {A Model Analysis for the Design and Deployment of an Eulerian Sediment Trap Mooring Array in a Western Boundary Upwelling System from Southeast Brazil.}, journal = {Anais da Academia Brasileira de Ciencias}, volume = {86}, number = {2}, pages = {589-600}, pmid = {30514019}, issn = {1678-2690}, abstract = {This work addresses the design and configuration of a Eulerian sediment trap mooring array, which was deployed at the shelf edge (zm ≈ 140 m) 80 km off Cabo Frio, SE- Brazil (23° S). The site was subject to interplay between the Tropical Waters (TW) of the Brazil Current (BC), intrusions from the South Atlantic Central Waters (SACW), which are the source of upwelling in the region, and other oceanographic processes. Detailed computations were used to optimize the total weight, buoyancy balance, and maximum acceptable tilt to avoid hydrodynamic bias in the trapping efficiency and array adaptation to the local oceanographic conditions with the assistance of Matlab and Muringa programs and Modular Ocean Model 4.0 (MOM; i.e., to assert the vertical distribution of the meridional current component). The velocity range of the current component was determined by short term measurements to be between 0.1 and 0.5 m/s. Projections led to a resulting minimum anchor weight of 456 kg. The necessary line tension was ascertained by using the appropriate distribution of a series of buoys along the array, which finally attained a high vertical load of 350 kg because of the attached oceanographic equipment. Additional flotation devices resulted in a stable mooring array as reflected by their low calculated tilt (2.6° ± 0.6°). A low drag of 16 N was computed for the maximum surface current velocity of 0.5 m/s. The Reynolds number values ranged from 4 × 104 to 2 × 105 and a cone-trap aspect ratio of 1.75 was used to assess the trap sampling efficiency upon exposure to different current velocities.}, } @article {pmid30245535, year = {2014}, author = {Poroseva, SV}, title = {The Effect of a Pressure-Containing Correlation Model on Near-Wall Flow Simulations with RST Models.}, journal = {Journal of fluids engineering}, volume = {136}, number = {6}, pages = {}, doi = {10.1115/1.4025936}, pmid = {30245535}, issn = {0098-2202}, support = {NNX12AJ61A//NASA/United States ; }, abstract = {It is accustomed to think that turbulence models based on solving the Reynolds-Averaged Navier-Stokes equations require empirical functions to accurately reproduce the behavior of flow characteristics of interest, particularly near a wall. The current paper analyzes how choosing a model for pressure-strain correlations in second-order closures affects the need for introducing empirical functions in model equations to reproduce the flow behavior near a wall correctly. An axially-rotating pipe flow is used as a test flow for the analysis. Results of simulations demonstrate that by using more physics-based models to represent pressure-strain correlations, one can eliminate wall functions associated with such models. The higher the Reynolds number or the strength of imposed rotation on a flow, the less need there is for empirical functions regardless of the choice of a pressure-strain correlation model.}, } @article {pmid32646073, year = {2005}, author = {Nisisako, T and Okushima, S and Torii, T}, title = {Controlled formulation of monodisperse double emulsions in a multiple-phase microfluidic system.}, journal = {Soft matter}, volume = {1}, number = {1}, pages = {23-27}, doi = {10.1039/b501972a}, pmid = {32646073}, issn = {1744-6848}, abstract = {This paper gives an overview of our recent work on the use of microfluidic devices to formulate double emulsions. Key issues in the controlled encapsulation of highly monodisperse drops include: (a) regular periodicity in the formation of micro droplets due to the interplay between viscous shearing and interfacial tension in low Reynolds number streams; (b) serially connected hydrophobic and hydrophilic microchannels to form aqueous and organic drops consecutively. Water-in-oil-in-water emulsions and oil-in-water-in-oil emulsions can both be produced by reversing the order of hydrophobic and hydrophilic junctions. Alternating formation of aqueous droplets at a cross junction has enabled the production of organic droplets that encase two aqueous droplets of differing compositions.}, } @article {pmid30139156, year = {1993}, author = {Andersen, MC}, title = {DIASPORE MORPHOLOGY AND SEED DISPERSAL IN SEVERAL WIND-DISPERSED ASTERACEAE.}, journal = {American journal of botany}, volume = {80}, number = {5}, pages = {487-492}, doi = {10.1002/j.1537-2197.1993.tb13830.x}, pmid = {30139156}, issn = {1537-2197}, abstract = {I made measurements of morphology and settling velocity on seeds of 19 species of wind-dispersed Asteraceae. From the morphological measurements I calculated Reynolds numbers and approximate plume loadings for the species. Diaspore settling velocity increases linearly with the square root of plume loading. This relationship varies among species and among subfamilies, but not among life history types. Reynolds number is highly variable among subfamilies, less so within subfamilies. Diaspores with beaked achenes have significantly lower settling velocities than diaspores with unbeaked achenes, even though beaked and unbeaked achenes do not differ in plume loading or in Reynolds number. Reynolds numbers of all diaspores examined are well above the range in which Stokes' Law applies. I recommend that the use of formulae based on Stokes' Law be curtailed in studies of the relationship between plume loading and settling velocity. The results suggest that many seed characters may have evolved due to selection on dispersal ability. This is in spite of phyletic constraints on morphology reflected in the relative uniformity of Reynolds numbers within subfamilies.}, } @article {pmid31071803, year = {1992}, author = {Goff, HD and Davidson, VJ}, title = {Flow Characteristics and Holding Time Calculations of Ice Cream Mixes in HTST Holding Tubes.}, journal = {Journal of food protection}, volume = {55}, number = {1}, pages = {34-37}, doi = {10.4315/0362-028X-55.1.34}, pmid = {31071803}, issn = {1944-9097}, abstract = {In order to determine the potential for development of laminar flow and consequential underholding in the holding tubes of HTST pasteurizers, a study on the relationship between ice cream mix viscosity and shear rate at 80°C has been conducted. Typical shear rates at the wall were calculated for HTST holding tubes of standard industry sizes and flow rates. Shear rates in the holding tube were found to vary from 50 to 180 s[-1], depending on the conditions. Viscosity of ice cream mixes as a function of shear rate, stabilizer type, and stabilizer concentration were measured. Ice cream mix was found to be non-Newtonian and pseudoplastic. Viscosities ranged from 8.7 cP in an unstabilized mix at high shear rate (relative to the inside of the holding tube) to 103 cP for 0.25% carboxymethyl cellulose at low shear rate. Generalized Reynolds numbers inside the holding tubes varied from 100 to 1700, indicating a strong potential for the development of laminar flow. The apparent viscosities required to result in a minimum generalized Reynolds number of 2100 are very near to or less than the actual viscosities of stabilized ice cream mixes, and thus the potential for a laminar flow pattern within the holding tube needs to be addressed in determining holding tube lengths for a required holding time.}, } @article {pmid33327683, year = {1981}, author = {Wegener, WA}, title = {Diffusion coefficients for rigid macromolecules with irregular shapes that allow rotational-translational coupling.}, journal = {Biopolymers}, volume = {20}, number = {2}, pages = {303-326}, doi = {10.1002/bip.1981.360200205}, pmid = {33327683}, issn = {1097-0282}, abstract = {We consider six-dimensional diffusion and frictional tensors for a rigid macromolecule immersed in a viscous fluid at low Reynolds number. Our treatment allows for screwlike properties which couple rotational and translational movements. We show that the center of diffusion of a screwlike body can be distinct from its hydrodynamic center of reaction. Symmetry conditions which ensure coincidence are examined. The center of diffusion is found to be the point of a body with the slowest diffusive movements, while rotations about the center of reaction encounter the least average resistance. The macroscopic translational diffusion coefficient is evaluated from a perturbation analysis of the six-dimensional diffusion equation. We show that methodologies which ignore translational-rotational coupling will necessarily underestimate the diffusion rate of screwlike particles. A procedural framework is presented to calculate diffusion coefficients of complicated bodies. As an example we treat a long bent rod.}, } @article {pmid32196167, year = {1960}, author = {Sherlin, GC}, title = {Behavior of Isolated Disturbances Superimposed on Laminar Flow in a Rectangular Pipe.}, journal = {Journal of research of the National Bureau of Standards. Section A, Physics and chemistry}, volume = {64A}, number = {4}, pages = {281-289}, doi = {10.6028/jres.064A.027}, pmid = {32196167}, issn = {0022-4332}, abstract = {An investigation was conducted in a horizontal transparent rectangular pipe to study the behavior, in laminar flow, of an isolated turbulent-like disturbance produced by injecting a quantity of dye into the pipe 39 feet from the entrance. As the resulting mass of colored water moved downstream, time-distance measurements were made for the front of the dye mass and for the rear of the disturbance. The experimental setup, which is described in some detail, permitted reasonable control over the mean flow rate from which Reynolds number was calculated. The utilization of the data unfolded a functional relationship among three quantities: The ratio of the velocity of the rear of the disturbance to the velocity of the front of the dye UR/UF ; the distance from the origin, XF ; and the Reynolds number R. The similarity of this work to that being done by Lindgren in Stockholm is mentioned.}, } @article {pmid30119494, year = {2018}, author = {Gao, J and Katz, J}, title = {Self-calibrated microscopic dual-view tomographic holography for 3D flow measurements.}, journal = {Optics express}, volume = {26}, number = {13}, pages = {16708-16725}, doi = {10.1364/OE.26.016708}, pmid = {30119494}, issn = {1094-4087}, abstract = {This paper introduces the application of microscopic dual-view tomographic holography (M-DTH) to measure the 3D position and motion of micro-particles located in dense suspensions. Pairing of elongated traces of the same particle in the two inclined reconstructed fields requires precise matching of the entire sample volume that accounts for the inherent distortions in each view. It is achieved by an iterative volumetric self-calibration method, consisting of mapping one view onto the next, dividing the sample volume into slabs, and cross-correlating the two views. Testing of the procedures using synthetic particle fields with imposed distortion and realistic errors in particle locations shows that the self-calibration method achieves a 3D uncertainty of about 1µm, a third of the particle diameter. Multiplying the corrected intensity fields is used for truncating the elongated traces, whose centers are located within 1µm of the exact value. Without correction, only a small fraction of the traces even overlap. The distortion correction also increases the number of intersecting traces in experimental data along with their intensity. Application of this method for 3D velocity measurements is based on the centroids of the truncated/shortened particle traces. Matching of these traces in successive fields is guided by several criteria, including results of volumetric cross-correlation of the multiplied intensity fields. The resulting 3D velocity distribution is substantially more divergence-free, i.e., satisfies conservation of mass, compared to analysis performed using single-view data. Sample application of the new method shows the 3D flow structure around a pair of cubic roughness elements embedded in the inner part of a high Reynolds number turbulent boundary layer.}, } @article {pmid30118276, year = {2018}, author = {Mathai, V and Huisman, SG and Sun, C and Lohse, D and Bourgoin, M}, title = {Dispersion of Air Bubbles in Isotropic Turbulence.}, journal = {Physical review letters}, volume = {121}, number = {5}, pages = {054501}, doi = {10.1103/PhysRevLett.121.054501}, pmid = {30118276}, issn = {1079-7114}, abstract = {Bubbles play an important role in the transport of chemicals and nutrients in many natural and industrial flows. Their dispersion is crucial to understanding the mixing processes in these flows. Here we report on the dispersion of millimetric air bubbles in a homogeneous and isotropic turbulent flow with a Taylor Reynolds number from 110 to 310. We find that the mean squared displacement (MSD) of the bubbles far exceeds that of fluid tracers in turbulence. The MSD shows two regimes. At short times, it grows ballistically (∝τ^{2} ), while at larger times, it approaches the diffusive regime where the MSD∝τ. Strikingly, for the bubbles, the ballistic-to-diffusive transition occurs one decade earlier than for the fluid. We reveal that both the enhanced dispersion and the early transition to the diffusive regime can be traced back to the unsteady wake-induced motion of the bubbles. Further, the diffusion transition for bubbles is not set by the integral timescale of the turbulence (as it is for fluid tracers and microbubbles), but instead, by a timescale of eddy crossing of the rising bubbles. The present findings provide a Lagrangian perspective towards understanding mixing in turbulent bubbly flows.}, } @article {pmid30118271, year = {2018}, author = {Oettinger, D and Ault, JT and Stone, HA and Haller, G}, title = {Invisible Anchors Trap Particles in Branching Junctions.}, journal = {Physical review letters}, volume = {121}, number = {5}, pages = {054502}, doi = {10.1103/PhysRevLett.121.054502}, pmid = {30118271}, issn = {1079-7114}, abstract = {We combine numerical simulations and an analytic approach to show that the capture of finite, inertial particles during flow in branching junctions is due to invisible, anchor-shaped three-dimensional flow structures. These Reynolds-number-dependent anchors define trapping regions that confine particles to the junction. For a wide range of Stokes numbers, these structures occupy a large part of the flow domain. For flow in a V-shaped junction, at a critical Stokes number, we observe a topological transition due to the merger of two anchors into one. From a stability analysis, we identify the parameter region of particle sizes and densities where capture due to anchors occurs.}, } @article {pmid30117966, year = {2018}, author = {Karaminejad, S and Askari, MH and Ashjaee, M}, title = {Temperature field investigation of hydrogen/air and syngas/air axisymmetric laminar flames using Mach-Zehnder interferometry.}, journal = {Applied optics}, volume = {57}, number = {18}, pages = {5057-5067}, doi = {10.1364/AO.57.005057}, pmid = {30117966}, issn = {1539-4522}, abstract = {In this study, the optical method of Mach-Zehnder interferometry (MZI) is utilized in order to explore the flame structure and temperature field of syngas/air and hydrogen/air flames. Two axisymmetric burners with inner diameters of 4 mm and 6 mm are used for temperature field measurement of hydrogen and syngas, respectively. The effects of fuel composition, equivalence ratio, and Reynolds number (Re) are investigated at ambient condition (P=0.87 bar, T=300 K). Three different H2/CO fuel compositions with hydrogen fractions of 30%, 50%, and 100% are studied. Temperature profiles are reported at four different sections above the burner tip. Measured temperatures using the interferometry method are compared with thermocouple data and good agreement between them is observed. The results obtained in this investigation indicated that the MZI can be applied for accurate determination of flame front and temperature field, especially for high-temperature flames where other methods cannot be properly utilized. Analyses of the data reduction method revealed that the exact determination of the refractive index distribution and reference temperature is critical for accurate determination of the temperature field. The results indicated that by increasing the Re, the maximum flame temperature is enhanced. Increasing the equivalence ratio leads to expansion of the flame radial distribution (at the same distance from the burner tip). At higher distances from the burner tip, temperature increases uniformly from the flame boundary toward the flame axis, while at lower heights it shows reduction at the burner axis. By increasing the CO content of fuel, the maximum flame temperature increases at all equivalence ratios except at the stoichiometric condition, where SH100 illustrates the highest maximum flame temperature.}, } @article {pmid30109056, year = {2018}, author = {Bhat, SS and Zhao, J and Sheridan, J and Hourigan, K and Thompson, MC}, title = {The leading-edge vortex on a rotating wing changes markedly beyond a certain central body size.}, journal = {Royal Society open science}, volume = {5}, number = {7}, pages = {172197}, pmid = {30109056}, issn = {2054-5703}, abstract = {Stable attachment of a leading-edge vortex (LEV) plays a key role in generating the high lift on rotating wings with a central body. The central body size can affect the LEV structure broadly in two ways. First, an overall change in the size changes the Reynolds number, which is known to have an influence on the LEV structure. Second, it may affect the Coriolis acceleration acting across the wing, depending on the wing-offset from the axis of rotation. To investigate this, the effects of Reynolds number and the wing-offset are independently studied for a rotating wing. The three-dimensional LEV structure is mapped using a scanning particle image velocimetry technique. The rapid acquisition of images and their correlation are carefully validated. The results presented in this paper show that the LEV structure changes mainly with the Reynolds number. The LEV-split is found to be only minimally affected by changing the central body radius in the range of small offsets, which interestingly includes the range for most insects. However, beyond this small offset range, the LEV-split is found to change dramatically.}, } @article {pmid30089029, year = {2018}, author = {Gilmer, GG and Deshpande, VG and Chou, CL and Knepper, M}, title = {Flow resistance along the rat renal tubule.}, journal = {American journal of physiology. Renal physiology}, volume = {315}, number = {5}, pages = {F1398-F1405}, pmid = {30089029}, issn = {1522-1466}, support = {ZIA HL001285/HL/NHLBI NIH HHS/United States ; ZIA HL006129/HL/NHLBI NIH HHS/United States ; }, mesh = {Animals ; *Diuresis ; *Glomerular Filtration Rate ; Hydrostatic Pressure ; Kidney Tubules/anatomy & histology/*physiology ; *Models, Biological ; Rats ; Time Factors ; *Urodynamics ; Viscosity ; }, abstract = {The Reynolds number in the renal tubule is extremely low, consistent with laminar flow. Consequently, luminal flow can be described by the Hagen-Poiseuille laminar flow equation. This equation calculates the volumetric flow rate from the axial pressure gradient and flow resistance, which is dependent on the length and diameter of each renal tubule segment. Our goal was to calculate the pressure drop along each segment of the renal tubule and to determine the points of highest resistance. When the Hagen-Poiseuille equation was used for rat superficial nephrons based on known tubule flow rates, lengths, and diameters, it was found that the maximum pressure drop occurred in two segments: the thin descending limbs of Henle and the inner medullary collecting ducts. The high resistance in the thin descending limbs is due to their small diameters. The steep pressure drop observed in the inner medullary collecting ducts is due to the convergent structure of the tubules, which channels flow into fewer and fewer tubules toward the papillary tip. For short-looped nephrons, the calculated glomerular capsular pressure matched measured values, even with the high collecting duct flow rates seen in water diuresis, provided that tubule compliance was taken into account. In long-looped nephrons, the greater length of thin limb segments is likely compensated for by a larger luminal diameter. Simulation of the effect of proximal diuretics, namely acetazolamide or type 2 sodium-glucose transporter inhibitors, predicts a substantial back pressure in Bowman's capsule, which may contribute to observed decreases in glomerular filtration rate.}, } @article {pmid30088905, year = {2018}, author = {Mateos-Maroto, A and Guerrero-Martínez, A and Rubio, RG and Ortega, F and Martínez-Pedrero, F}, title = {Magnetic Biohybrid Vesicles Transported by an Internal Propulsion Mechanism.}, journal = {ACS applied materials & interfaces}, volume = {10}, number = {35}, pages = {29367-29377}, doi = {10.1021/acsami.8b09862}, pmid = {30088905}, issn = {1944-8252}, mesh = {*Hydrodynamics ; *Lipids ; *Magnetics ; *Models, Biological ; Rotation ; Transport Vesicles/metabolism ; }, abstract = {Some biological microorganisms can crawl or swim due to coordinated motions of their cytoskeleton or the flagella located inside their bodies, which push the cells forward through intracellular forces. To date, there is no demonstration of synthetic systems propelling at low Reynolds number via the precise actuation of the material confined within an enclosing lipid membrane. Here, we report lipid vesicles and other more complex self-assembled biohybrid structures able to propel due to the advection flows generated by the actuated rotation of the superparamagnetic particles they contain. The proposed swimming and release strategies, based on cooperative hydrodynamic mechanisms and near-infrared laser pulse-triggered destabilization of the phospholipid membranes, open new possibilities for the on-command transport of minute quantities of drugs, fluid or nano-objects. The lipid membranes protect the confined substances from the outside environment during transportation, thus enabling them to work in physiological conditions.}, } @article {pmid30083106, year = {2018}, author = {Vidal, EAG and Zeidberg, LD and Buskey, EJ}, title = {Development of Swimming Abilities in Squid Paralarvae: Behavioral and Ecological Implications for Dispersal.}, journal = {Frontiers in physiology}, volume = {9}, number = {}, pages = {954}, pmid = {30083106}, issn = {1664-042X}, abstract = {This study investigates the development of swimming abilities and its relationship with morphology, growth, and nourishment of reared Doryteuthis opalescens paralarvae from hatching to 60 days of age. Paralarvae (2.5-11 mm mantle length - ML) were videotaped, and their behavior quantified throughout development using computerized motion analysis. Hatchlings swim dispersed maintaining large nearest neighbor distances (NND, 8.7 ML), with swimming speeds (SS) of 3-8 mm s[-1] and paths with long horizontal displacements, resulting in high net to gross displacement ratios (NGDR). For 15-day-old paralarvae, swimming paths are more consistent between jets, growth of fins, length, and mass increases. The swimming pattern of 18-day-old paralarvae starved for 72 h exhibited a significant reduction in mean SS and inability to perform escape jets. A key morphological, behavioral, and ecological transition occurs at about 6 mm ML (>35-day old), when there is a clear change in body shape, swimming performance, and behavior, paths are more regularly repeated and directional swimming is evident, suggesting that morphological changes incur in swimming performance. These squid are able to perform sustained swimming and hover against a current at significantly closer NND (2.0 ML), as path displacement is reduced and maneuverability increases. As paralarvae reach 6-7 mm ML, they are able to attain speeds up to 562 mm s[-1] and to form schools. Social feeding interactions (kleptoparasitism) are often observed prior to the formation of schools. Schools are always formed within areas of high flow gradient in the tanks and are dependent on squid size and current speed. Fin development is a requisite for synchronized and maneuverable swimming of schooling early juveniles. Although average speeds of paralarvae are within intermediate Reynolds numbers (Re < 100), they make the transition to the inertia-dominated realm during escape jets of high propulsion (Re > 3200), transitioning from plankton to nekton after their first month of life. The progressive development of swimming capabilities and social interactions enable juvenile squid to school, while also accelerates learning, orientation and cognition. These observations indicate that modeling of the lifecycle should include competency to exert influence over small currents and dispersal patterns after the first month of life.}, } @article {pmid30072230, year = {2018}, author = {Gritti, F}, title = {High-resolution turbulent flow chromatography.}, journal = {Journal of chromatography. A}, volume = {1570}, number = {}, pages = {135-147}, doi = {10.1016/j.chroma.2018.07.059}, pmid = {30072230}, issn = {1873-3778}, mesh = {Benz(a)Anthracenes/*analysis/chemistry/isolation & purification ; Carbon Dioxide/*chemistry ; Chromatography, High Pressure Liquid/*methods ; Chromatography, Supercritical Fluid/*methods ; Molecular Weight ; Polycyclic Compounds/*analysis/chemistry/isolation & purification ; }, abstract = {The resolution power of turbulent flow chromatography using carbon dioxide as the mobile phase and coated (crosslinked methyl phenyl polysiloxane) open tube columns (OTCs) as the stationary phase was investigated under retentive conditions (0 ∼10[-1]). Using this technique, we demonstrated that synthetic particles as small as 500 nm and a submicron bacterium, Staphylococcus aureus, can be inertially focused. Furthermore, we characterized the physics of inertial microfluidics in this newly enabled particle size and Rep range using a Peclet-like dimensionless number (α). We experimentally observed that α >> 1 is required to overcome diffusion and be able to inertially manipulate particles.}, } @article {pmid29987441, year = {2018}, author = {Musacchio, S and Cencini, M and Plan, ELCVM and Vincenzi, D}, title = {Enhancement of mixing by rodlike polymers.}, journal = {The European physical journal. E, Soft matter}, volume = {41}, number = {7}, pages = {84}, pmid = {29987441}, issn = {1292-895X}, abstract = {We study the mixing of a passive scalar field dispersed in a solution of rodlike polymers in two dimensions, by means of numerical simulations of a rheological model for the polymer solution. The flow is driven by a parallel sinusoidal force (Kolmogorov flow). Although the Reynolds number is lower than the critical value for inertial instabilities, the rotational dynamics of the polymers generates a chaotic flow similar to the so-called elastic-turbulence regime observed in extensible polymer solutions. The temporal decay of the variance of the scalar field and its gradients shows that this chaotic flow strongly enhances mixing.}, } @article {pmid29974859, year = {2018}, author = {Bell, GRR and Collins, SR}, title = {"Rho"ing a Cellular Boat with Rearward Membrane Flow.}, journal = {Developmental cell}, volume = {46}, number = {1}, pages = {1-3}, doi = {10.1016/j.devcel.2018.06.008}, pmid = {29974859}, issn = {1878-1551}, support = {DP2 HD094656/HD/NICHD NIH HHS/United States ; }, mesh = {Cell Movement ; rho-Associated Kinases ; *rhoA GTP-Binding Protein ; }, abstract = {The physicist Edward Purcell wrote in 1977 about mechanisms that cells could use to propel themselves in a low Reynolds number environment. Reporting in Developmental Cell, O'Neill et al. (2018) provide direct evidence for one of these mechanisms by optogenetically driving the migration of cells suspended in liquid through RhoA activation.}, } @article {pmid29974114, year = {2018}, author = {Bukowicki, M and Ekiel-Jeżewska, ML}, title = {Different bending models predict different dynamics of sedimenting elastic trumbbells.}, journal = {Soft matter}, volume = {14}, number = {28}, pages = {5786-5799}, doi = {10.1039/c8sm00604k}, pmid = {29974114}, issn = {1744-6848}, abstract = {The main goal of this paper is to examine theoretically and numerically the impact of a chosen bending model on the dynamics of elastic filaments settling in a viscous fluid under gravity at low-Reynolds-number. We use the bead-spring approximation of a filament and the Rotne-Prager mobility matrix to describe hydrodynamic interactions between the beads. We analyze the dynamics of trumbbells, for which bending angles are typically larger than for thin and long filaments. Each trumbbell is made of three beads connected by springs and it exhibits a bending resistance, described by the harmonic or - alternatively - by the 'cosine' (also called the Kratky-Porod) bending models, both often used in the literature. Using the harmonic bending potential, and coupling it to the spring potential by the Young's modulus, we find simple benchmark solutions: stable stationary configurations of a single elastic trumbbell and attraction of two elastic trumbbells towards a periodic long-lasting orbit. As the most significant result of this paper, we show that for very elastic trumbbells at the same initial conditions, the Kratky-Porod bending potential can lead to qualitatively and quantitatively different spurious dynamics, with artificially large bending angles and unrealistic shapes. We point out that for the bead models of an elastic filament, the range of applicability of the Kratky-Porod model might not go beyond bending angles smaller than π/2 for touching beads and beyond an even much lower value for beads well-separated from each other. The existence of stable stationary configurations of elastic trumbbells and a family of periodic oscillations of two elastic trumbbells are very important findings on their own.}, } @article {pmid29957007, year = {2018}, author = {Kawata, T and Alfredsson, PH}, title = {Inverse Interscale Transport of the Reynolds Shear Stress in Plane Couette Turbulence.}, journal = {Physical review letters}, volume = {120}, number = {24}, pages = {244501}, doi = {10.1103/PhysRevLett.120.244501}, pmid = {29957007}, issn = {1079-7114}, abstract = {Interscale interaction between small-scale structures near the wall and large-scale structures away from the wall plays an increasingly important role with increasing Reynolds number in wall-bounded turbulence. While the top-down influence from the large- to small-scale structures is well known, it has been unclear whether the small scales near the wall also affect the large scales away from the wall. In this Letter we show that the small-scale near-wall structures indeed play a role to maintain the large-scale structures away from the wall, by showing that the Reynolds shear stress is transferred from small to large scales throughout the channel. This is in contrast to the turbulent kinetic energy transport which is from large to small scales. Such an "inverse" interscale transport of the Reynolds shear stress eventually supports the turbulent energy production at large scales.}, } @article {pmid29925578, year = {2018}, author = {Jardin, T and Colonius, T}, title = {On the lift-optimal aspect ratio of a revolving wing at low Reynolds number.}, journal = {Journal of the Royal Society, Interface}, volume = {15}, number = {143}, pages = {}, pmid = {29925578}, issn = {1742-5662}, mesh = {Animals ; Birds/*physiology ; *Computer Simulation ; Flight, Animal/*physiology ; Insecta/*physiology ; *Models, Biological ; Wings, Animal/*physiology ; }, abstract = {Lentink & Dickinson (2009 J. Exp. Biol.212, 2705-2719. (doi:10.1242/jeb.022269)) showed that rotational acceleration stabilized the leading-edge vortex on revolving, low aspect ratio (AR) wings and hypothesized that a Rossby number of around 3, which is achieved during each half-stroke for a variety of hovering insects, seeds and birds, represents a convergent high-lift solution across a range of scales in nature. Subsequent work has verified that, in particular, the Coriolis acceleration plays a key role in LEV stabilization. Implicit in these results is that there exists an optimal AR for wings revolving about their root, because it is otherwise unclear why, apart from possible morphological reasons, the convergent solution would not occur for an even lower Rossby number. We perform direct numerical simulations of the flow past revolving wings where we vary the AR and Rossby numbers independently by displacing the wing root from the axis of rotation. We show that the optimal lift coefficient represents a compromise between competing trends with competing time scales where the coefficient of lift increases monotonically with AR, holding Rossby number constant, but decreases monotonically with Rossby number, when holding AR constant. For wings revolving about their root, this favours wings of AR between 3 and 4.}, } @article {pmid29907430, year = {2018}, author = {Maldaner, CH and Quinn, PM and Cherry, JA and Parker, BL}, title = {Improving estimates of groundwater velocity in a fractured rock borehole using hydraulic and tracer dilution methods.}, journal = {Journal of contaminant hydrology}, volume = {214}, number = {}, pages = {75-86}, doi = {10.1016/j.jconhyd.2018.05.003}, pmid = {29907430}, issn = {1873-6009}, mesh = {*Groundwater ; Models, Theoretical ; Porosity ; *Water Movements ; *Water Supply ; }, abstract = {A straddle-packer system for use in boreholes in fractured rock was modified to investigate the average linear groundwater velocity (v¯f) in fractures under ambient flow conditions. This packer system allows two different tests to be conducted in the same interval between packers without redeploying the system: (1) forced gradient hydraulic tests to determine the interval transmissivity (T), and (2) borehole dilution experiments to determine the groundwater flow rate (Qt) across the test interval. The constant head step test method provides assurance that flow is Darcian when determining T for each interval and identifies the flow rate at the onset of non-Darcian flow. The critical Reynolds number method uses this flow rate to provide the number of hydraulically active fractures (N) in each interval, the average hydraulic aperture for the test interval and the effective bulk fracture porosity. The borehole dilution method provides Qt values for the interval at the time of the test, and v¯f can be estimated from Qt using the flow area derived from the hydraulic tests. The method was assessed by application to seven test intervals in a borehole 73 m deep in a densely fractured dolostone aquifer used for municipal water supply. The critical Reynolds number method identified one or two fractures in each test interval (1.1 m long), which provided v¯f values in the range of 10 to 8000 m/day. This velocity range is consistent with values reported in the literature for ambient flow in this aquifer. However, when hydraulically active fractures in each interval is identified and measured from acoustic and optical televiewer logs, the calculated v¯f values are unreasonably low as are the calculated values of the hydraulic gradient needed to provide the Qt value for each tested interval. The combination of hydraulic and dilution tests in the same interval is an improved method to obtain values of groundwater velocity in fractured rock aquifers.}, } @article {pmid29906944, year = {2018}, author = {Ngoma, J and Philippe, P and Bonelli, S and Radjaï, F and Delenne, JY}, title = {Two-dimensional numerical simulation of chimney fluidization in a granular medium using a combination of discrete element and lattice Boltzmann methods.}, journal = {Physical review. E}, volume = {97}, number = {5-1}, pages = {052902}, doi = {10.1103/PhysRevE.97.052902}, pmid = {29906944}, issn = {2470-0053}, abstract = {We present here a numerical study dedicated to the fluidization of a submerged granular medium induced by a localized fluid injection. To this end, a two-dimensional (2D) model is used, coupling the lattice Boltzmann method (LBM) with the discrete element method (DEM) for a relevant description of fluid-grains interaction. An extensive investigation has been carried out to analyze the respective influences of the different parameters of our configuration, both geometrical (bed height, grain diameter, injection width) and physical (fluid viscosity, buoyancy). Compared to previous experimental works, the same qualitative features are recovered as regards the general phenomenology including transitory phase, stationary states, and hysteretic behavior. We also present quantitative findings about transient fluidization, for which several dimensionless quantities and scaling laws are proposed, and about the influence of the injection width, from localized to homogeneous fluidization. Finally, the impact of the present 2D geometry is discussed, by comparison to the real three-dimensional (3D) experiments, as well as the crucial role of the prevailing hydrodynamic regime within the expanding cavity, quantified through a cavity Reynolds number, that can presumably explain some substantial differences observed regarding upward expansion process of the fluidized zone when the fluid viscosity is changed.}, } @article {pmid29906164, year = {2018}, author = {Baker, NT and Pothérat, A and Davoust, L and Debray, F}, title = {Inverse and Direct Energy Cascades in Three-Dimensional Magnetohydrodynamic Turbulence at Low Magnetic Reynolds Number.}, journal = {Physical review letters}, volume = {120}, number = {22}, pages = {224502}, doi = {10.1103/PhysRevLett.120.224502}, pmid = {29906164}, issn = {1079-7114}, abstract = {This experimental study analyzes the relationship between the dimensionality of turbulence and the upscale or downscale nature of its energy transfers. We do so by forcing low-Rm magnetohydrodynamic turbulence in a confined channel, while precisely controlling its dimensionality by means of an externally applied magnetic field. We first identify a specific length scale l[over ^]_{⊥} ^{c} that separates smaller 3D structures from larger quasi-2D ones. We then show that an inverse energy cascade of horizontal kinetic energy along horizontal scales is always observable at large scales, and that it extends well into the region of 3D structures. At the same time, a direct energy cascade confined to the smallest and strongly 3D scales is observed. These dynamics therefore appear not to be simply determined by the dimensionality of individual scales, nor by the forcing scale, unlike in other studies. In fact, our findings suggest that the relationship between kinematics and dynamics is not universal and may strongly depend on the forcing and dissipating mechanisms at play.}, } @article {pmid29900314, year = {2018}, author = {Parise, JAR and Saboya, FEM}, title = {Experimental data on transport coefficients for developing laminar flow in isosceles triangular ducts using the naphthalene sublimation technique.}, journal = {Data in brief}, volume = {18}, number = {}, pages = {1350-1359}, pmid = {29900314}, issn = {2352-3409}, abstract = {The data presented in this article are related to the research article entitled "Transport coefficients for developing laminar flow in isosceles triangular ducts" (Parise and Saboya, 1999) [1]. The article describes an experiment involving the determination of transport coefficients in the laminar entrance region of 30°, 45°, 60° and 90° isosceles triangular ducts. Data were obtained by application of the naphthalene sublimation technique in conjunction with the heat to mass transfer analogy. Experimental conditions (duct sides made of naphthalene and base made of metal) simulated developing velocity and temperature fields in an isosceles triangular duct with isothermal lateral walls and adiabatic base. The Reynolds number ranged from 100 to 1800 and the duct length to hydraulic diameter ratio, from 2 to 40. The experiment consisted of mounting a test section (triangular duct) with the lateral walls made of naphthalene. Air was forced past the test section and naphthalene walls were weighed prior and after each data run, providing the rate of mass transfer for given flow conditions. Raw data, for a total of 77 experimental runs, include: test section geometry, air flow and mass transfer conditions. Processed data comprise the relevant non-dimensional groups, namely: Reynolds, non-dimensional axial duct length and Sherwood numbers.}, } @article {pmid29897806, year = {2018}, author = {McCombe, D and Ackerman, JD}, title = {Collector Motion Affects Particle Capture in Physical Models and in Wind Pollination.}, journal = {The American naturalist}, volume = {192}, number = {1}, pages = {81-93}, doi = {10.1086/697551}, pmid = {29897806}, issn = {1537-5323}, mesh = {*Models, Theoretical ; Phleum/*physiology ; *Pollination ; *Wind ; }, abstract = {Particle capture is important for ecological processes in aquatic and terrestrial ecosystems. The current model is based on a stationary collector for which predictions about capture efficiency (η; flux of captured particles ∶ flux of particles) are based on the collector flow environment (i.e., collector Reynolds number, Rec; inertial force ∶ viscous force). This model does not account for the movement of collectors in nature. We examined the effect of collector motion (transverse and longitudinal to the flow) on η using a cylindrical model in the lab and the grass species Phleum pratense in the field. Collector motion increased η (up to 400% and 20% in the lab and field, respectively) and also affected the spatial distribution of particles on collectors, especially at low Rec. The effect was greatest for collectors moving transversely at large magnitude, which encountered more particles with higher relative momentum. These results, which differ from the stationary model, can be predicted by considering both Rec and the particle dynamics given by the Stokes number (Stk; particle stopping distance ∶ collector radius) and helped to resolve an existing controversy about pollination mechanisms. Collector motion should be considered in wind pollination and other ecological processes involving particle capture.}, } @article {pmid29891403, year = {2018}, author = {Gritti, F and Fogwill, M}, title = {Molecular dispersion in pre-turbulent and sustained turbulent flow of carbon dioxide.}, journal = {Journal of chromatography. A}, volume = {1564}, number = {}, pages = {176-187}, doi = {10.1016/j.chroma.2018.06.005}, pmid = {29891403}, issn = {1873-3778}, mesh = {Acetonitriles/chemistry ; Carbon Dioxide/*chemistry ; Diffusion ; Molecular Weight ; Polycyclic Compounds/chemistry ; Pressure ; *Rheology ; Silicon Dioxide ; Viscosity ; }, abstract = {The average dispersion coefficients, Da¯, of two small molecules (acetonitrile and coronene) were measured under laminar, transient, and sustained turbulent flow regimes along fused silica open tubular capillary (OTC) columns (180 μm inner diameter by 20 m length). Carbon dioxide was used as the mobile phase at room temperature (296 K) and at average pressures in the range from 1500 to 2700 psi. The Reynolds number (Re) was increased from 600 to 5000. The measurement of Da¯ is based on the observed plate height of the non-retained analytes as a function of the applied Reynolds number. Da¯ values are directly estimated from the best fit of the general Golay HETP equation to the experimental plate height curves. The experimental data revealed that under a pre-turbulent flow regime (Re < 2000), Da¯ is 2-6 times larger (3.5 × 10[-4] cm[2]/s) than the bulk diffusion coefficients Dm of the analyte (1.6 × 10[-4] and 5.8 × 10[-5] cm[2]/s for acetonitrile and coronene, respectively). This result was explained by the random formation of decaying or vanishing turbulent puffs under pre-turbulent flow regime. Yet, the peak width remains controlled exclusively by the slow mass transfer in the mobile phase across the inner diameter (i.d.) of the OTC. Under sustained turbulent flow regime (Re > 2500), Da¯ is about four to five orders of magnitude larger than Dm. The experimental data slightly overestimated the turbulent dispersion coefficients predicted by Flint-Eisenklam model (Da¯=4 cm[2]/s). The discrepancy is explained by the approximate nature of the general Golay equation, which assumes that Da¯ is strictly uniform across the entire i.d. of the OTC. In fact, both the viscous and buffer wall layers, in which viscous effects dominate inertial effects, cannot be considered as fully developed turbulent regions. Remarkably, the mass transfer mechanism in OTC under sustained turbulent flow regime is not only controlled by longitudinal dispersion but also by a slow mass transfer in the mobile phase across the thick buffer layer and the thin viscous layer. Altogether, these layers occupy as much as 35% of the OTC volume at Re = 4000. From a theoretical viewpoint, the general Golay HETP equation is only an approximate model which should be refined based on the actual profile of the analyte dispersion coefficient across the OTC i.d. In practice, the measured plate height of non-retained analytes under sustained turbulent flow of carbon dioxide are two orders of magnitude smaller than those expected under hypothetical laminar flow regime.}, } @article {pmid29863665, year = {2018}, author = {Kaiser, SC and Werner, S and Jossen, V and Blaschczok, K and Eibl, D}, title = {Power Input Measurements in Stirred Bioreactors at Laboratory Scale.}, journal = {Journal of visualized experiments : JoVE}, volume = {}, number = {135}, pages = {}, pmid = {29863665}, issn = {1940-087X}, mesh = {*Bioreactors ; Cell Culture Techniques/*methods ; Laboratories/*standards ; }, abstract = {The power input in stirred bioreactors is an important scaling-up parameter and can be measured through the torque that acts on the impeller shaft during rotation. However, the experimental determination of the power input in small-scale vessels is still challenging due to relatively high friction losses inside typically used bushings, bearings and/or shaft seals and the accuracy of commercially available torque meters. Thus, only limited data for small-scale bioreactors, in particular single-use systems, is available in the literature, making comparisons among different single-use systems and their conventional counterparts difficult. This manuscript provides a protocol on how to measure power inputs in benchtop scale bioreactors over a wide range of turbulence conditions, which can be described by the dimensionless Reynolds number (Re). The aforementioned friction losses are effectively reduced by the use of an air bearing. The procedure on how to set up, conduct and evaluate a torque-based power input measurement, with special focus on cell culture typical agitation conditions with low to moderate turbulence (100 < Re < 2·10[4]), is described in detail. The power input of several multi-use and single-use bioreactors is provided by the dimensionless power number (also called Newton number, P0), which is determined to be in the range of P0 ≈ 0.3 and P0 ≈ 4.5 for the maximum Reynolds numbers in the different bioreactors.}, } @article {pmid29861812, year = {2018}, author = {Herbig, BA and Yu, X and Diamond, SL}, title = {Using microfluidic devices to study thrombosis in pathological blood flows.}, journal = {Biomicrofluidics}, volume = {12}, number = {4}, pages = {042201}, pmid = {29861812}, issn = {1932-1058}, support = {R01 HL103419/HL/NHLBI NIH HHS/United States ; T32 HL007954/HL/NHLBI NIH HHS/United States ; }, abstract = {Extreme flows can exist within pathological vessel geometries or mechanical assist devices which create complex forces and lead to thrombogenic problems associated with disease. Turbulence and boundary layer separation are difficult to obtain in microfluidics due to the low Reynolds number flow in small channels. However, elongational flows, extreme shear rates and stresses, and stagnation point flows are possible using microfluidics and small perfusion volumes. In this review, a series of microfluidic devices used to study pathological blood flows are described. In an extreme stenosis channel pre-coated with fibrillar collagen that rapidly narrows from 500 μm to 15 μm, the plasma von Willebrand Factor (VWF) will elongate and assemble into thick fiber bundles on the collagen. Using a micropost-impingement device, plasma flow impinging on the micropost generates strong elongational and wall shear stresses that trigger the growth of a VWF bundle around the post (no collagen required). Using a stagnation-point device to mimic the zone near flow reattachment, blood can be directly impinged upon a procoagulant surface of collagen and the tissue factor. Clots formed at the stagnation point of flow impingement have a classic core-shell architecture where the core is highly activated (P-selectin positive platelets and fibrin rich). Finally, within occlusive clots that fill a microchannel, the Darcy flow driven by ΔP/L > 70 mm-Hg/mm-clot is sufficient to drive NETosis of entrapped neutrophils, an event not requiring either thrombin or fibrin. Novel microfluidic devices are powerful tools to access physical environments that exist in human disease.}, } @article {pmid29791262, year = {2018}, author = {Montoya Segnini, J and Bocanegra Evans, H and Castillo, L}, title = {Flow Recirculation in Cartilaginous Ring Cavities of Human Trachea Model.}, journal = {Journal of aerosol medicine and pulmonary drug delivery}, volume = {}, number = {}, pages = {}, doi = {10.1089/jamp.2017.1435}, pmid = {29791262}, issn = {1941-2703}, abstract = {BACKGROUND: Despite the prevailing assumption of "smooth trachea walls" in respiratory fluid dynamics research, recent investigations have demonstrated that cartilaginous rings in the trachea and main bronchi have a significant effect on the flow behavior and in particle deposition. However, there is not enough detailed information about the underlying physics of the interaction between the cartilage rings and the flow.

MATERIALS AND METHODS: This study presents an experimental observation of a simplified Weibel-based model of the human trachea and bronchi with cartilaginous rings. A transparent model and refractive index-matching methods were used to observe the flow, particularly near the wall. The flow was seeded with tracers to perform particle image velocimetry and particle tracking velocimetry to quantify the effect the rings have on the flow near the trachea and bronchi walls. The experiments were carried out with a flow rate comparable with a resting state (trachea-based Reynolds number of ReD = 2650).

RESULTS: The results present a previously unknown phenomenon in the cavities between the cartilaginous rings: a small recirculation is observed in the upstream side of the cavities throughout the trachea. This recirculation is due to the adverse pressure gradient created by the expansion, which traps particles within the ring cavity, thus affecting the treatment of patients suffering from lung disease and other respiratory conditions.

CONCLUSIONS: The detection of recirculation zones in the cartilage ring cavities sheds light on the particle deposition mechanism and helps explain results from previous studies that have observed an enhancement of particle deposition in models with cartilage rings. These results bring to light the importance of including cartilage rings in experimental, numerical, and theoretical models to better understand particle deposition in the trachea and bronchi. In addition, the results provide scientists and medical staff with new insights for improving drug delivery.}, } @article {pmid29786774, year = {2018}, author = {Bordones, AD and Leroux, M and Kheyfets, VO and Wu, YA and Chen, CY and Finol, EA}, title = {Computational Fluid Dynamics Modeling of the Human Pulmonary Arteries with Experimental Validation.}, journal = {Annals of biomedical engineering}, volume = {46}, number = {9}, pages = {1309-1324}, pmid = {29786774}, issn = {1573-9686}, support = {R01 HL121293/HL/NHLBI NIH HHS/United States ; }, mesh = {Computer Simulation ; Humans ; Hydrodynamics ; *Models, Cardiovascular ; Phantoms, Imaging ; Printing, Three-Dimensional ; Pulmonary Artery/*physiology ; Rheology ; }, abstract = {Pulmonary hypertension (PH) is a chronic progressive disease characterized by elevated pulmonary arterial pressure, caused by an increase in pulmonary arterial impedance. Computational fluid dynamics (CFD) can be used to identify metrics representative of the stage of PH disease. However, experimental validation of CFD models is often not pursued due to the geometric complexity of the model or uncertainties in the reproduction of the required flow conditions. The goal of this work is to validate experimentally a CFD model of a pulmonary artery phantom using a particle image velocimetry (PIV) technique. Rapid prototyping was used for the construction of the patient-specific pulmonary geometry, derived from chest computed tomography angiography images. CFD simulations were performed with the pulmonary model with a Reynolds number matching those of the experiments. Flow rates, the velocity field, and shear stress distributions obtained with the CFD simulations were compared to their counterparts from the PIV flow visualization experiments. Computationally predicted flow rates were within 1% of the experimental measurements for three of the four branches of the CFD model. The mean velocities in four transversal planes of study were within 5.9 to 13.1% of the experimental mean velocities. Shear stresses were qualitatively similar between the two methods with some discrepancies in the regions of high velocity gradients. The fluid flow differences between the CFD model and the PIV phantom are attributed to experimental inaccuracies and the relative compliance of the phantom. This comparative analysis yielded valuable information on the accuracy of CFD predicted hemodynamics in pulmonary circulation models.}, } @article {pmid29776113, year = {2018}, author = {Zhu, B and Ji, Z and Lou, Z and Qian, P}, title = {Torque scaling in small-gap Taylor-Couette flow with smooth or grooved wall.}, journal = {Physical review. E}, volume = {97}, number = {3-1}, pages = {033110}, doi = {10.1103/PhysRevE.97.033110}, pmid = {29776113}, issn = {2470-0053}, abstract = {The torque in the Taylor-Couette flow for radius ratios η≥0.97, with smooth or grooved wall static outer cylinders, is studied experimentally, with the Reynolds number of the inner cylinder reaching up to Re_{i} =2×10^{5}, corresponding to the Taylor number up to Ta=5×10^{10} . The grooves are perpendicular to the mean flow, and similar to the structure of a submersible motor stator. It is found that the dimensionless torque G, at a given Re_{i} and η, is significantly greater for grooved cases than smooth cases. We compare our experimental torques for the smooth cases to the fit proposed by Wendt [F. Wendt, Ing.-Arch. 4, 577 (1993)10.1007/BF02084936] and the fit proposed by Bilgen and Boulos [E. Bilgen and R. Boulos, J Fluids Eng. 95, 122 (1973)10.1115/1.3446944], which shows both fits are outside their range for small gaps. Furthermore, an additional dimensionless torque (angular velocity flux) Nu_{ω} in the smooth cases exhibits an effective scaling of Nu_{ω} ∼Ta^{0.39} in the ultimate regime, which occurs at a lower Taylor number, Ta≈3.5×10^{7}, than the well-explored η=0.714 case (at Ta≈3×10^{8} ). The same effective scaling exponent, 0.39, is also evident in the grooved cases, but for η=0.97 and 0.985, there is a peak before this exponent appears.}, } @article {pmid29776082, year = {2018}, author = {Liang, H and Xu, J and Chen, J and Wang, H and Chai, Z and Shi, B}, title = {Phase-field-based lattice Boltzmann modeling of large-density-ratio two-phase flows.}, journal = {Physical review. E}, volume = {97}, number = {3-1}, pages = {033309}, doi = {10.1103/PhysRevE.97.033309}, pmid = {29776082}, issn = {2470-0053}, abstract = {In this paper, we present a simple and accurate lattice Boltzmann (LB) model for immiscible two-phase flows, which is able to deal with large density contrasts. This model utilizes two LB equations, one of which is used to solve the conservative Allen-Cahn equation, and the other is adopted to solve the incompressible Navier-Stokes equations. A forcing distribution function is elaborately designed in the LB equation for the Navier-Stokes equations, which make it much simpler than the existing LB models. In addition, the proposed model can achieve superior numerical accuracy compared with previous Allen-Cahn type of LB models. Several benchmark two-phase problems, including static droplet, layered Poiseuille flow, and spinodal decomposition are simulated to validate the present LB model. It is found that the present model can achieve relatively small spurious velocity in the LB community, and the obtained numerical results also show good agreement with the analytical solutions or some available results. Lastly, we use the present model to investigate the droplet impact on a thin liquid film with a large density ratio of 1000 and the Reynolds number ranging from 20 to 500. The fascinating phenomena of droplet splashing is successfully reproduced by the present model and the numerically predicted spreading radius exhibits to obey the power law reported in the literature.}, } @article {pmid29776043, year = {2018}, author = {Oyama, N and Teshigawara, K and Molina, JJ and Yamamoto, R and Taniguchi, T}, title = {Reynolds-number-dependent dynamical transitions on hydrodynamic synchronization modes of externally driven colloids.}, journal = {Physical review. E}, volume = {97}, number = {3-1}, pages = {032611}, doi = {10.1103/PhysRevE.97.032611}, pmid = {29776043}, issn = {2470-0053}, abstract = {The collective dynamics of externally driven N_{p} -colloidal systems (1≤N_{p} ≤4) in a confined viscous fluid have been investigated using three-dimensional direct numerical simulations with fully resolved hydrodynamics. The dynamical modes of collective particle motion are studied by changing the particle Reynolds number as determined by the strength of the external driving force and the confining wall distance. For a system with N_{p} =3, we found that at a critical Reynolds number a dynamical mode transition occurs from the doublet-singlet mode to the triplet mode, which has not been reported experimentally. The dynamical mode transition was analyzed in detail from the following two viewpoints: (1) spectrum analysis of the time evolution of a tagged particle velocity and (2) the relative acceleration of the doublet cluster with respect to the singlet particle. For a system with N_{p} =4, we found similar dynamical mode transitions from the doublet-singlet-singlet mode to the triplet-singlet mode and further to the quartet mode.}, } @article {pmid29772223, year = {2018}, author = {Markwalter, CE and Prud'homme, RK}, title = {Design of a Small-Scale Multi-Inlet Vortex Mixer for Scalable Nanoparticle Production and Application to the Encapsulation of Biologics by Inverse Flash NanoPrecipitation.}, journal = {Journal of pharmaceutical sciences}, volume = {107}, number = {9}, pages = {2465-2471}, pmid = {29772223}, issn = {1520-6017}, mesh = {Biological Products/*chemical synthesis/metabolism ; *Chemical Precipitation ; Chemistry, Pharmaceutical/*instrumentation/methods ; Equipment Design/*instrumentation/methods ; Hydrophobic and Hydrophilic Interactions ; Nanoparticles/*chemistry/metabolism ; Particle Size ; }, abstract = {Flash NanoPrecipitation is a scalable approach to generate polymeric nanoparticles using rapid micromixing in specially designed geometries such as a confined impinging jets mixer or a Multi-Inlet Vortex Mixer (MIVM). A major limitation of formulation screening using the MIVM is that a single run requires tens of milligrams of the therapeutic. To overcome this, we have developed a scaled-down version of the MIVM, requiring as little as 0.2 mg of therapeutic, for formulation screening. The redesigned mixer can then be attached to pumps for scale-up of the identified formulation. It was shown that Reynolds number allowed accurate scaling between the 2 MIVM designs. The utility of the small-scale MIVM for formulation development was demonstrated through the encapsulation of a number of hydrophilic macromolecules using inverse Flash NanoPrecipitation with target loadings as high as 50% by mass.}, } @article {pmid29758688, year = {2018}, author = {Sanjeevi, SKP and Zarghami, A and Padding, JT}, title = {Choice of no-slip curved boundary condition for lattice Boltzmann simulations of high-Reynolds-number flows.}, journal = {Physical review. E}, volume = {97}, number = {4-1}, pages = {043305}, doi = {10.1103/PhysRevE.97.043305}, pmid = {29758688}, issn = {2470-0053}, abstract = {Various curved no-slip boundary conditions available in literature improve the accuracy of lattice Boltzmann simulations compared to the traditional staircase approximation of curved geometries. Usually, the required unknown distribution functions emerging from the solid nodes are computed based on the known distribution functions using interpolation or extrapolation schemes. On using such curved boundary schemes, there will be mass loss or gain at each time step during the simulations, especially apparent at high Reynolds numbers, which is called mass leakage. Such an issue becomes severe in periodic flows, where the mass leakage accumulation would affect the computed flow fields over time. In this paper, we examine mass leakage of the most well-known curved boundary treatments for high-Reynolds-number flows. Apart from the existing schemes, we also test different forced mass conservation schemes and a constant density scheme. The capability of each scheme is investigated and, finally, recommendations for choosing a proper boundary condition scheme are given for stable and accurate simulations.}, } @article {pmid29758634, year = {2018}, author = {Mahalinkam, R and Gong, F and Khair, AS}, title = {Reduced-order model for inertial locomotion of a slender swimmer.}, journal = {Physical review. E}, volume = {97}, number = {4-1}, pages = {043102}, doi = {10.1103/PhysRevE.97.043102}, pmid = {29758634}, issn = {2470-0053}, abstract = {The inertial locomotion of an elongated model swimmer in a Newtonian fluid is quantified, wherein self-propulsion is achieved via steady tangential surface treadmilling. The swimmer has a length 2l and a circular cross section of longitudinal profile aR(z), where a is the characteristic width of the cross section, R(z) is a dimensionless shape function, and z is a dimensionless coordinate, normalized by l, along the centerline of the body. It is assumed that the swimmer is slender, ε=a/l≪1. Hence, we utilize slender-body theory to analyze the Navier-Stokes equations that describe the flow around the swimmer. Therefrom, we compute an asymptotic approximation to the swimming speed, U, as U/u_{s} =1-β[V(Re)-1/2∫_{-1} ^{1} zlnR(z)dz]/ln(1/ε)+O[1/ln^{2} (1/ε)], where u_{s} is the characteristic speed of the surface treadmilling, Re is the Reynolds number based on the body length, and β is a dimensionless parameter that differentiates between "pusher" (propelled from the rear, β<0) and "puller" (propelled from the front, β>0) -type swimmers. The function V(Re) increases monotonically with increasing Re; hence, fluid inertia causes an increase (decrease) in the swimming speed of a pusher (puller). Next, we demonstrate that the power expenditure of the swimmer increases monotonically with increasing Re. Further, the power expenditures of a puller and pusher with the same value of |β| are equal. Therefore, pushers are superior in inertial locomotion as compared to pullers, in that they achieve a faster swimming speed for the same power expended. Finally, it is demonstrated that the flow structure predicted from our reduced-order model is consistent with that from direct numerical simulation of swimmers at intermediate Re.}, } @article {pmid29757157, year = {2018}, author = {Daddi-Moussa-Ider, A and Lisicki, M and Mathijssen, AJTM and Hoell, C and Goh, S and Bławzdziewicz, J and Menzel, AM and Löwen, H}, title = {State diagram of a three-sphere microswimmer in a channel.}, journal = {Journal of physics. Condensed matter : an Institute of Physics journal}, volume = {30}, number = {25}, pages = {254004}, doi = {10.1088/1361-648X/aac470}, pmid = {29757157}, issn = {1361-648X}, abstract = {Geometric confinements are frequently encountered in soft matter systems and in particular significantly alter the dynamics of swimming microorganisms in viscous media. Surface-related effects on the motility of microswimmers can lead to important consequences in a large number of biological systems, such as biofilm formation, bacterial adhesion and microbial activity. On the basis of low-Reynolds-number hydrodynamics, we explore the state diagram of a three-sphere microswimmer under channel confinement in a slit geometry and fully characterize the swimming behavior and trajectories for neutral swimmers, puller- and pusher-type swimmers. While pushers always end up trapped at the channel walls, neutral swimmers and pullers may further perform a gliding motion and maintain a stable navigation along the channel. We find that the resulting dynamical system exhibits a supercritical pitchfork bifurcation in which swimming in the mid-plane becomes unstable beyond a transition channel height while two new stable limit cycles or fixed points that are symmetrically disposed with respect to the channel mid-height emerge. Additionally, we show that an accurate description of the averaged swimming velocity and rotation rate in a channel can be captured analytically using the method of hydrodynamic images, provided that the swimmer size is much smaller than the channel height.}, } @article {pmid29749100, year = {2018}, author = {Tottori, S and Nelson, BJ}, title = {Controlled Propulsion of Two-Dimensional Microswimmers in a Precessing Magnetic Field.}, journal = {Small (Weinheim an der Bergstrasse, Germany)}, volume = {14}, number = {24}, pages = {e1800722}, doi = {10.1002/smll.201800722}, pmid = {29749100}, issn = {1613-6829}, abstract = {Magnetically actuated micro-/nanoswimmers can potentially be used in noninvasive biomedical applications, such as targeted drug delivery and micromanipulation. Herein, two-dimensional (2D) rigid ferromagnetic microstructures are shown to be capable of propelling themselves in three dimensions at low Reynolds numbers in a precessing field. Importantly, the above propulsion relies neither on soft structure deformation nor on the geometrical chirality of swimmers, but is rather driven by the dynamic chirality generated by field precession, which allows an almost unconstrained choice of materials and fabrication methods. Therefore, the swimming performance is systematically investigated as a function of precession angle and geometric design. One disadvantage of the described propulsion method is that the fabricated 2D swimmers are achiral, which means that the forward/backward swimming direction cannot be controlled. However, it has been found that asymmetric 2D swimmers always propel themselves toward their longer arm, which implies that dynamic chirality can be constrained to be either right-handed or left-handed by permanent magnetization. Thus, the simplicity of fabrication and possibility of dynamic chirality control make the developed method ideal for applications and fundamental studies that require a large number of swimmers.}, } @article {pmid29745778, year = {2018}, author = {Perrin, A and Herbelin, P and Jorand, FPA and Skali-Lami, S and Mathieu, L}, title = {Design of a rotating disk reactor to assess the colonization of biofilms by free-living amoebae under high shear rates.}, journal = {Biofouling}, volume = {34}, number = {4}, pages = {368-377}, doi = {10.1080/08927014.2018.1444756}, pmid = {29745778}, issn = {1029-2454}, mesh = {Amoeba/*physiology ; *Bacteria ; Bacterial Physiological Phenomena ; *Biofilms ; Fresh Water ; Hydrodynamics ; Locomotion ; Stainless Steel ; }, abstract = {The present study was aimed at designing and optimizing a rotating disk reactor simulating high hydrodynamic shear rates (γ), which are representative of cooling circuits. The characteristics of the hydrodynamic conditions in the reactor and the complex approach used to engineer it are described. A 60 l tank was filled with freshwater containing free-living amoebae (FLA) and bacteria. Adhesion of the bacteria and formation of a biofilm on the stainless steel coupons were observed. FLA were able to establish in these biofilms under γ as high as 85,000 s[-1]. Several physical mechanisms (convection, diffusion, sedimentation) could explain the accumulation of amoeboid cells on surfaces, but further research is required to fully understand and model the fine mechanisms governing such transport under γ similar to those encountered in the industrial environment. This technological advance may enable research into these topics.}, } @article {pmid29744606, year = {2018}, author = {Zhang, S and Luo, X and Cai, Z}, title = {Three-dimensional flows in a hyperelastic vessel under external pressure.}, journal = {Biomechanics and modeling in mechanobiology}, volume = {17}, number = {4}, pages = {1187-1207}, doi = {10.1007/s10237-018-1022-y}, pmid = {29744606}, issn = {1617-7940}, mesh = {Algorithms ; Arteries/anatomy & histology/*physiology ; Biomechanical Phenomena ; Blood Flow Velocity/*physiology ; Computer Simulation ; Elasticity ; Finite Element Analysis ; Humans ; Models, Anatomic ; Models, Cardiovascular ; Pressure ; Rheology ; Veins/anatomy & histology/*physiology ; Viscosity ; }, abstract = {We study the collapsible behaviour of a vessel conveying viscous flows subject to external pressure, a scenario that could occur in many physiological applications. The vessel is modelled as a three-dimensional cylindrical tube of nonlinear hyperelastic material. To solve the fully coupled fluid-structure interaction, we have developed a novel approach based on the Arbitrary Lagrangian-Eulerian (ALE) method and the frontal solver. The method of rotating spines is used to enable an automatic mesh adaptation. The numerical code is verified extensively with published results and those obtained using the commercial packages in simpler cases, e.g. ANSYS for the structure with the prescribed flow, and FLUENT for the fluid flow with prescribed structure deformation. We examine three different hyperelastic material models for the tube for the first time in this context and show that at the small strain, all three material models give similar results. However, for the large strain, results differ depending on the material model used. We further study the behaviour of the tube under a mode-3 buckling and reveal its complex flow patterns under various external pressures. To understand these flow patterns, we show how energy dissipation is associated with the boundary layers created at the narrowest collapsed section of the tube, and how the transverse flow forms a virtual sink to feed a strong axial jet. We found that the energy dissipation associated with the recirculation does not coincide with the flow separation zone itself, but overlaps with the streamlines that divide the three recirculation zones. Finally, we examine the bifurcation diagrams for both mode-3 and mode-2 collapses and reveal that multiple solutions exist for a range of the Reynolds number. Our work is a step towards modelling more realistic physiological flows in collapsible arteries and veins.}, } @article {pmid29732048, year = {2018}, author = {Zhou, Y and Lee, C and Wang, J}, title = {The Computational Fluid Dynamics Analyses on Hemodynamic Characteristics in Stenosed Arterial Models.}, journal = {Journal of healthcare engineering}, volume = {2018}, number = {}, pages = {4312415}, pmid = {29732048}, issn = {2040-2295}, mesh = {Arterial Occlusive Diseases/*physiopathology ; Computer Simulation ; Hemodynamics/*physiology ; Humans ; *Models, Cardiovascular ; Rheology ; }, abstract = {Arterial stenosis plays an important role in the progressions of thrombosis and stroke. In the present study, a standard axisymmetric tube model of the stenotic artery is introduced and the degree of stenosis η is evaluated by the area ratio of the blockage to the normal vessel. A normal case (η = 0) and four stenotic cases of η = 0.25, 0.5, 0.625, and 0.75 with a constant Reynolds number of 300 are simulated by computational fluid dynamics (CFD), respectively, with the Newtonian and Carreau models for comparison. Results show that for both models, the poststenotic separation vortex length increases exponentially with the growth of stenosis degree. However, the vortex length of the Carreau model is shorter than that of the Newtonian model. The artery narrowing accelerates blood flow, which causes high blood pressure and wall shear stress (WSS). The pressure drop of the η = 0.75 case is nearly 8 times that of the normal value, while the WSS peak at the stenosis region of η = 0.75 case even reaches up to 15 times that of the normal value. The present conclusions are of generality and contribute to the understanding of the dynamic mechanisms of artery stenosis diseases.}, } @article {pmid29729406, year = {2018}, author = {García-Salazar, G and de la Luz Zambrano-Zaragoza, M and Quintanar-Guerrero, D}, title = {Preparation of nanodispersions by solvent displacement using the Venturi tube.}, journal = {International journal of pharmaceutics}, volume = {545}, number = {1-2}, pages = {254-260}, doi = {10.1016/j.ijpharm.2018.05.005}, pmid = {29729406}, issn = {1873-3476}, mesh = {Acetone/*chemistry ; Drug Compounding ; Dynamic Light Scattering ; Equipment and Supplies ; Excipients/chemistry ; *Nanoparticles ; Nanotechnology ; Particle Size ; Polyesters/*chemistry ; Solvents/*chemistry ; Technology, Pharmaceutical/*instrumentation/methods ; }, abstract = {The Venturi tube (VT) is an apparatus that produces turbulence which is taken advantage of to produce nanoparticles (NP) by solvent displacement. The objective of this study was to evaluate the potential of this device for preparing NP of poly-ε-caprolactone. Response Surface Methodology was used to determine the effect of the operating conditions and optimization. The NP produced by VT were characterized by Dynamic Light-Scattering to determine their particle size distribution (PS) and polydispersity index (PDI). Results showed that the Reynolds number (Re) has a strong effect on both PS and process yield (PY).The turbulence regime is key to the efficient formation of NP. The optimal conditions for obtaining NP were a polymer concentration of 1.6 w/v, a recirculation rate of 4.8 L/min, and a stabilizer concentration of 1.1 w/v. The predicted response of the PY was 99.7%, with a PS of 333 nm, and a PDI of 0.2. Maintaining the same preparation conditions will make it possible to obtain NP using other polymers with similar properties. Our results show that VT is a reproducible and versatile method for manufacturing NP, and so may be a feasible method for industrial-scale nanoprecipitation production.}, } @article {pmid29710732, year = {2018}, author = {Sandeep, N and Kumaran, G and Saleem, S}, title = {The influence of cross diffusion on magnetohydrodynamic flow of Carreau liquid in the presence of buoyancy force.}, journal = {Journal of integrative neuroscience}, volume = {17}, number = {3-4}, pages = {525-546}, doi = {10.3233/JIN-180086}, pmid = {29710732}, issn = {0219-6352}, abstract = {The flow of magnetohydrodynamic Carreau liquid with the Brownian moment, thermophoresis and cross diffusion effects is investigated numerically. The buoyancy persuades on the flow is contemplated in such a way that the surface is neither perpendicular/horizontal nor wedge/cone. This is very helpful in the design of jet-engine. The equations govern the flow are transmuted using acceptable similarity variables and numerically solved by recruiting Runge-Kutta based Newtons method. The graphical results are obtained to discuss the stimulus of flow, thermal and concentration fields for different parameters of interest. The wall friction, local Nusselt and Sherwood numbers are examined with the assistance of tables. It is noticed that the parabolic flow is controlled by the buoyant forces developed by the temperature difference. Since the flow is laminar, the Reynolds number considered as <1000. This study has applicable in man-made products and various industries like pumps and oil purification, petroleum production, power engineering and chemical engineering processes.}, } @article {pmid29708343, year = {2018}, author = {Gao, S and Liao, Q and Liu, W and Liu, Z}, title = {Nanodroplets Impact on Rough Surfaces: A Simulation and Theoretical Study.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {34}, number = {20}, pages = {5910-5917}, doi = {10.1021/acs.langmuir.8b00480}, pmid = {29708343}, issn = {1520-5827}, abstract = {Impact of droplets is widespread in life, and modulating the dynamics of impinging droplets is a significant problem in production. However, on textured surfaces, the micromorphologic change and mechanism of impinging nanodroplets are not well-understood; furthermore, the accuracy of the theoretical model for nanodroplets needs to be improved. Here, considering the great challenge of conducting experiments on nanodroplets, a molecular dynamics simulation is performed to visualize the impact process of nanodroplets on nanopillar surfaces. Compared with macroscale droplets, apart from the similar relation of restitution coefficient with the Weber number, we found some distinctive results: the maximum spreading time is described as a power law of impact velocity, and the relation of maximum spreading factor with impact velocity or the Reynolds number is exponential. Moreover, the roughness of substrates plays a prominent role in the dynamics of impact nanodroplets, and on surfaces with lower solid fraction, the lower attraction force induces an easier rebound of impact nanodroplets. At last, on the basis of the energy balance, through modifying the estimation of viscous dissipation and surface energy terms, we proposed an improved model for the maximum spreading factor, which shows greater accuracy for nanodroplets, especially in the low-to-moderate velocity range. The outcome of this study demonstrates that a distinctive dynamical behavior of impinging nanodroplets, the fundamental insight, and more accurate prediction are very useful in the improvement of the hydrodynamic behavior of the nanodroplets.}, } @article {pmid29670984, year = {2018}, author = {Vilfan, M and Osterman, N and Vilfan, A}, title = {Magnetically driven omnidirectional artificial microswimmers.}, journal = {Soft matter}, volume = {14}, number = {17}, pages = {3415-3422}, doi = {10.1039/c8sm00230d}, pmid = {29670984}, issn = {1744-6848}, abstract = {We present an experimental realisation of two new artificial microswimmers that swim at low Reynolds number. The swimmers are externally driven with a periodically modulated magnetic field that induces an alternating attractive/repulsive interaction between the swimmer parts. The field sequence also modulates the drag on the swimmer components, making the working cycle non-reciprocal. The resulting net translational displacement leads to velocities of up to 2 micrometers per second. The swimmers can be made omnidirectional, meaning that the same magnetic field sequence can drive swimmers in any direction in the sample plane. Although the direction of their swimming is determined by the momentary orientation of the swimmer, their motion can be guided by solid boundaries. We demonstrate their omnidirectionality by letting them travel through a circular microfluidic channel. We use simple scaling arguments as well as more detailed numerical simulations to explain the measured velocity as a function of the actuation frequency.}, } @article {pmid29670148, year = {2018}, author = {Govindarajan, V and Mousel, J and Udaykumar, HS and Vigmostad, SC and McPherson, DD and Kim, H and Chandran, KB}, title = {Synergy between Diastolic Mitral Valve Function and Left Ventricular Flow Aids in Valve Closure and Blood Transport during Systole.}, journal = {Scientific reports}, volume = {8}, number = {1}, pages = {6187}, pmid = {29670148}, issn = {2045-2322}, support = {R01 HL109597/HL/NHLBI NIH HHS/United States ; UL1 TR000371/TR/NCATS NIH HHS/United States ; }, mesh = {Algorithms ; Atrial Function ; Blood Flow Velocity ; *Diastole ; Heart Atria/diagnostic imaging ; Heart Ventricles/diagnostic imaging ; *Hemodynamics ; Humans ; Imaging, Three-Dimensional ; Magnetic Resonance Imaging/methods ; Mitral Valve/diagnostic imaging/*physiology ; *Models, Cardiovascular ; *Systole ; Ventricular Function ; }, abstract = {Highly resolved three-dimensional (3D) fluid structure interaction (FSI) simulation using patient-specific echocardiographic data can be a powerful tool for accurately and thoroughly elucidating the biomechanics of mitral valve (MV) function and left ventricular (LV) fluid dynamics. We developed and validated a strongly coupled FSI algorithm to fully characterize the LV flow field during diastolic MV opening under physiologic conditions. Our model revealed that distinct MV deformation and LV flow patterns developed during different diastolic stages. A vortex ring that strongly depended on MV deformation formed during early diastole. At peak E wave, the MV fully opened, with a local Reynolds number of ~5500, indicating that the flow was in the laminar-turbulent transitional regime. Our results showed that during diastasis, the vortex structures caused the MV leaflets to converge, thus increasing mitral jet's velocity. The vortex ring became asymmetrical, with the vortex structures on the anterior side being larger than on the posterior side. During the late diastolic stages, the flow structures advected toward the LV outflow tract, enhancing fluid transport to the aorta. This 3D-FSI study demonstrated the importance of leaflet dynamics, their effect on the vortex ring, and their influence on MV function and fluid transport within the LV during diastole.}, } @article {pmid29657749, year = {2018}, author = {Li, H and Guo, S}, title = {Aerodynamic efficiency of a bioinspired flapping wing rotor at low Reynolds number.}, journal = {Royal Society open science}, volume = {5}, number = {3}, pages = {171307}, pmid = {29657749}, issn = {2054-5703}, abstract = {This study investigates the aerodynamic efficiency of a bioinspired flapping wing rotor kinematics which combines an active vertical flapping motion and a passive horizontal rotation induced by aerodynamic thrust. The aerodynamic efficiencies for producing both vertical lift and horizontal thrust of the wing are obtained using a quasi-steady aerodynamic model and two-dimensional (2D) CFD analysis at Reynolds number of 2500. The calculated efficiency data show that both efficiencies (propulsive efficiency-ηp, and efficiency for producing lift-Pf) of the wing are optimized at Strouhal number (St) between 0.1 and 0.5 for a range of wing pitch angles (upstroke angle of attack αu less than 45°); the St for high Pf (St = 0.1 ∼ 0.3) is generally lower than for high ηp (St = 0.2 ∼ 0.5), while the St for equilibrium rotation states lies between the two. Further systematic calculations show that the natural equilibrium of the passive rotating wing automatically converges to high-efficiency states: above 85% of maximum Pf can be obtained for a wide range of prescribed wing kinematics. This study provides insight into the aerodynamic efficiency of biological flyers in cruising flight, as well as practical applications for micro air vehicle design.}, } @article {pmid29648545, year = {2018}, author = {Wang, C and Tang, H}, title = {Enhancement of aerodynamic performance of a heaving airfoil using synthetic-jet based active flow control.}, journal = {Bioinspiration & biomimetics}, volume = {13}, number = {4}, pages = {046005}, doi = {10.1088/1748-3190/aabdb9}, pmid = {29648545}, issn = {1748-3190}, mesh = {Air ; Air Movements ; *Aircraft ; Animals ; Biomechanical Phenomena ; *Biomimetic Materials ; Biomimetics ; Computer Simulation ; Equipment Design ; Flight, Animal/physiology ; Models, Biological ; Physical Phenomena ; Wings, Animal/physiology ; }, abstract = {In this study, we explore the use of synthetic jet (SJ) in manipulating the vortices around a rigid heaving airfoil, so as to enhance its aerodynamic performance. The airfoil heaves at two fixed pitching angles, with the Strouhal number, reduced frequency and Reynolds number chosen as St = 0.3, k = 0.25 and Re = 100, respectively, all falling in the ranges for natural flyers. As such, the vortex force plays a dominant role in determining the airfoil's aerodynamic performance. A pair of in-phase SJs is implemented on the airfoil's upper and lower surfaces, operating with the same strength but in opposite directions. Such a fluid-structure interaction problem is numerically solved using a lattice Boltzmann method based numerical framework. It is found that, as the airfoil heaves with zero pitching angle, its lift and drag can be improved concurrently when the SJ phase angle [Formula: see text] relative to the heave motion varies between [Formula: see text] and [Formula: see text]. But this concurrent improvement does not occur as the airfoil heaves with [Formula: see text] pitching angle. Detailed inspection of the vortex evolution and fluid stress over the airfoil surface reveals that, if at good timing, the suction and blowing strokes of the SJ pair can effectively delay or promote the shedding of leading edge vortices, and mitigate or even eliminate the generation of trailing edge vortices, so as to enhance the airfoil's aerodynamic performance. Based on these understandings, an intermittent operation of the SJ pair is then proposed to realize concurrent lift and drag improvement for the heaving airfoil with [Formula: see text] pitching angle.}, } @article {pmid29633848, year = {2018}, author = {Bordbar, A and Taassob, A and Khojasteh, D and Marengo, M and Kamali, R}, title = {Maximum Spreading and Rebound of a Droplet Impacting onto a Spherical Surface at Low Weber Numbers.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {34}, number = {17}, pages = {5149-5158}, doi = {10.1021/acs.langmuir.8b00625}, pmid = {29633848}, issn = {1520-5827}, abstract = {The spreading and rebound patterns of low-viscous droplets upon impacting spherical solid surfaces are investigated numerically. The studied cases consider a droplet impinging onto hydrophobic and superhydrophobic surfaces with various parameters varied throughout the study, and their effects on the postimpingement behavior are discussed. These parameters include impact Weber number (through varying the surface tension and impingement velocity), the size ratio of the droplet to the solid surface, and the surface contact angle. According to the findings, the maximum spreading diameter increases with the impact velocity, with an increase of the sphere diameter, with a lower surface wettability, and with a lower surface tension. Typical outcomes of the impact include (1) complete rebound, (2) splash, and (3) a final deposition stage after a series of spreading and recoiling phases. Finally, a novel, practical model is proposed, which can reasonably predict the maximum deformation of low Reynolds number impact of droplets onto hydrophobic or superhydrophobic spherical solid surfaces.}, } @article {pmid29608886, year = {2018}, author = {Hopgood, M and Reynolds, G and Barker, R}, title = {Using Computational Fluid Dynamics to Compare Shear Rate and Turbulence in the TIM-Automated Gastric Compartment With USP Apparatus II.}, journal = {Journal of pharmaceutical sciences}, volume = {107}, number = {7}, pages = {1911-1919}, doi = {10.1016/j.xphs.2018.03.019}, pmid = {29608886}, issn = {1520-6017}, mesh = {Chemistry, Pharmaceutical/instrumentation ; Drug Development/instrumentation ; Humans ; *Hydrodynamics ; Models, Biological ; Solubility ; Stomach/anatomy & histology/*physiology ; Surface Properties ; Tablets/chemistry/*metabolism ; }, abstract = {We use computational fluid dynamics to compare the shear rate and turbulence in an advanced in vitro gastric model (TIMagc) during its simulation of fasted state Migrating Motor Complex phases I and II, with the United States Pharmacopeia paddle dissolution apparatus II (USPII). A specific focus is placed on how shear rate in these apparatus affects erosion-based solid oral dosage forms. The study finds that tablet surface shear rates in TIMagc are strongly time dependant and fluctuate between 0.001 and 360 s[-1]. In USPII, tablet surface shear rates are approximately constant for a given paddle speed and increase linearly from 9 s[-1] to 36 s[-1] as the paddle speed is increased from 25 to 100 rpm. A strong linear relationship is observed between tablet surface shear rate and tablet erosion rate in USPII, whereas TIMagc shows highly variable behavior. The flow regimes present in each apparatus are compared to in vivo predictions using Reynolds number analysis. Reynolds numbers for flow in TIMagc lie predominantly within the predicted in vivo bounds (0.01-30), whereas Reynolds numbers for flow in USPII lie above the predicted upper bound when operating with paddle speeds as low as 25 rpm (33).}, } @article {pmid29596861, year = {2018}, author = {Prakash, J and Ramesh, K and Tripathi, D and Kumar, R}, title = {Numerical simulation of heat transfer in blood flow altered by electroosmosis through tapered micro-vessels.}, journal = {Microvascular research}, volume = {118}, number = {}, pages = {162-172}, doi = {10.1016/j.mvr.2018.03.009}, pmid = {29596861}, issn = {1095-9319}, mesh = {Blood Flow Velocity ; *Computer Simulation ; *Electroosmosis ; Energy Transfer ; Humans ; Microvessels/anatomy & histology/*physiology ; *Models, Cardiovascular ; Numerical Analysis, Computer-Assisted ; Peristalsis ; Pulsatile Flow ; Regional Blood Flow ; *Temperature ; }, abstract = {A numerical simulation is presented to study the heat and flow characteristics of blood flow altered by electroosmosis through the tapered micro-vessels. Blood is assumed as non-Newtonian (micropolar) nanofluids. The flow regime is considered as asymmetric diverging (tapered) microchannel for more realistic micro-vessels which is produced by choosing the peristaltic wave train on the walls to have different amplitudes and phase. The Rosseland approximation is employed to model the radiation heat transfer and temperatures of the walls are presumed constants. The mathematical formulation of the present problem is simplified under the long-wavelength, low-Reynolds number and Debye-Hückel linearization approximations. The influence of various dominant physical parameters are discussed for axial velocity, microrotation distribution, thermal temperature distribution and nanoparticle volume fraction field. However, our foremost emphasis is to determine the effects of thermal radiation and coupling number on the axial velocity and microrotation distribution beneath electroosmotic environment. This analysis places a significant observation on the thermal radiation and coupling number which plays an influential role in hearten fluid velocity. This study is encouraged by exploring the nanofluid-dynamics in peristaltic transport as symbolized by heat transport in biological flows and also in novel pharmacodynamics pumps and gastro-intestinal motility enhancement.}, } @article {pmid29594300, year = {2018}, author = {Jing, H and Das, S}, title = {Theory of diffusioosmosis in a charged nanochannel.}, journal = {Physical chemistry chemical physics : PCCP}, volume = {20}, number = {15}, pages = {10204-10212}, doi = {10.1039/c8cp01091a}, pmid = {29594300}, issn = {1463-9084}, abstract = {We probe the diffusioosmotic transport in a charged nanofluidic channel in the presence of an applied tangential salt concentration gradient. Ionic salt gradient driven diffusioosmosis or ionic diffusioosmosis (IDO) is characterized by the generation of an induced tangential electric field and a diffusioosmotic velocity (DOSV) that is a combination of an electroosmotic velocity (EOSV) triggered by this electric field and a chemiosmotic velocity (COSV) triggered by an induced tangential pressure gradient. We explain that unlike the existing theories on IDO, it is more appropriate to apply the zero net current conditions (formulation F2) and not more restrictive zero net local flux conditions (formulation F1) particularly for the case where one considers a nanochannel connected to two reservoirs. We pinpoint limitations in the existing literature in correctly predicting the diffusioosmotic behavior even for the case where formulation F1 is used. We address these limitations and establish that (a) the induced electric field is an interplay of the differences in ionic diffusivity, the EDL-induced imbalance in ion concentrations, and the advection effects, (b) formulation F1 may overpredict or underpredict the electric field and the EOSV leading to an overprediction/underprediction of the DOSV and (c) formulation F2 demonstrates remarkable fluid physics of localized backflows owing to a dominant local influence of the COSV, which is missed by formulation F1. We anticipate that our theory will provide the first rigorous understanding of nanofluidic IDO with applications in multiple areas of low Reynolds number transport such as biofluidics, microfluidic separation, and colloidal transport.}, } @article {pmid29589515, year = {2018}, author = {Rigatelli, G and Zuin, M and Dell'Avvocata, F and Nguyen, T}, title = {Rheolytic effects of left main mid-shaft/distal stenting: a computational flow dynamic analysis.}, journal = {Therapeutic advances in cardiovascular disease}, volume = {12}, number = {6}, pages = {161-168}, pmid = {29589515}, issn = {1753-9455}, mesh = {Aged ; Aged, 80 and over ; Angioplasty, Balloon, Coronary/*instrumentation ; Cardiovascular Agents/administration & dosage ; Computed Tomography Angiography ; Coronary Artery Disease/diagnostic imaging/physiopathology/*therapy ; *Coronary Circulation ; Coronary Stenosis/diagnostic imaging/physiopathology/*therapy ; Coronary Vessels/diagnostic imaging/*physiopathology ; *Drug-Eluting Stents ; Everolimus/administration & dosage ; Female ; Humans ; Male ; Middle Aged ; *Models, Cardiovascular ; *Patient-Specific Modeling ; Prosthesis Design ; Retrospective Studies ; Rheology ; Treatment Outcome ; }, abstract = {Background The aim of this study was to evaluate the rheolytic effects of stenting a mid-shaft/distal left main coronary artery (LMCA) lesion with and without ostial coverage. Stenting of the LMCA has emerged as a valid alternative in place of traditional coronary bypass graft surgery. However, in case of mid-shaft/distal lesion, there is no consensus regarding the extension of the strut coverage up to the ostium or to stent only the culprit lesion. Methods We reconstructed a left main-left descending coronary artery (LM-LCA)-left circumflex (LCX) bifurcation after analysing 100 consecutive patients (mean age 71.4 ± 9.3, 49 males) with LM mid-shaft/distal disease. The mean diameter of proximal LM, left anterior descending (LAD) and LCX, evaluated with quantitative coronary angiography (QCA) was 4.62 ± 0.86 mm, 3.31 ± 0.92 mm, and 2.74 ± 0.93 mm, respectively. For the stent simulation, a third-generation, everolimus-eluting stent was virtually reconstructed. Results After virtual stenting, the net area averaged wall shear stress (WSS) of the model and the WSS at the LCA-LCX bifurcation resulted higher when the stent covered the culprit mid-shaft lesion only compared with the extension of the stent covering the ostium (3.68 versus 2.06 Pa, p = 0.01 and 3.97 versus 1.98 Pa, p < 0.001, respectively. Similarly, the static pressure and the Reynolds number were significantly higher after stent implantation covering up the ostium. At the ostium, the flow resulted more laminar when stenting only the mid-shaft lesion than including the ostium. Conclusions Although these findings cannot be translated directly into real practice our brief study suggests that stenting lesion 1:1 or extending the stent to cover the LM ostium impacts differently the rheolytic properties of LMCA bifurcation with potential insights for restenosis or thrombosis.}, } @article {pmid29584651, year = {2018}, author = {Xi, J and Hu, Q and Zhao, L and Si, XA}, title = {Molecular Binding Contributes to Concentration Dependent Acrolein Deposition in Rat Upper Airways: CFD and Molecular Dynamics Analyses.}, journal = {International journal of molecular sciences}, volume = {19}, number = {4}, pages = {}, pmid = {29584651}, issn = {1422-0067}, mesh = {Acrolein/*chemistry ; Animals ; Humans ; Hydrogen Bonding ; Male ; Models, Anatomic ; Molecular Dynamics Simulation ; Particle Size ; Rats ; Rats, Sprague-Dawley ; Trachea/anatomy & histology/*chemistry ; Water/*chemistry ; }, abstract = {Existing in vivo experiments show significantly decreased acrolein uptake in rats with increasing inhaled acrolein concentrations. Considering that high-polarity chemicals are prone to bond with each other, it is hypothesized that molecular binding between acrolein and water will contribute to the experimentally observed deposition decrease by decreasing the effective diffusivity. The objective of this study is to quantify the probability of molecular binding for acrolein, as well as its effects on acrolein deposition, using multiscale simulations. An image-based rat airway geometry was used to predict the transport and deposition of acrolein using the chemical species model. The low Reynolds number turbulence model was used to simulate the airflows. Molecular dynamic (MD) simulations were used to study the molecular binding of acrolein in different media and at different acrolein concentrations. MD results show that significant molecular binding can happen between acrolein and water molecules in human and rat airways. With 72 acrolein embedded in 800 water molecules, about 48% of acrolein compounds contain one hydrogen bond and 10% contain two hydrogen bonds, which agreed favorably with previous MD results. The percentage of hydrogen-bonded acrolein compounds is higher at higher acrolein concentrations or in a medium with higher polarity. Computational dosimetry results show that the size increase caused by the molecular binding reduces the effective diffusivity of acrolein and lowers the chemical deposition onto the airway surfaces. This result is consistent with the experimentally observed deposition decrease at higher concentrations. However, this size increase can only explain part of the concentration-dependent variation of the acrolein uptake and acts as a concurrent mechanism with the uptake-limiting tissue ration rate. Intermolecular interactions and associated variation in diffusivity should be considered in future dosimetry modeling of high-polarity chemicals such as acrolein.}, } @article {pmid29557508, year = {2018}, author = {Gupta, A and Clercx, HJH and Toschi, F}, title = {Computational study of radial particle migration and stresslet distributions in particle-laden turbulent pipe flow.}, journal = {The European physical journal. E, Soft matter}, volume = {41}, number = {3}, pages = {34}, pmid = {29557508}, issn = {1292-895X}, abstract = {Particle-laden turbulent flows occur in a variety of industrial applications as well as in naturally occurring flows. While the numerical simulation of such flows has seen significant advances in recent years, it still remains a challenging problem. Many studies investigated the rheology of dense suspensions in laminar flows as well as the dynamics of point-particles in turbulence. Here we employ a fully-resolved numerical simulation based on a lattice Boltzmann scheme, to investigate turbulent flow with large neutrally buoyant particles in a pipe flow at low Reynolds number and in dilute regimes. The energy input is kept fixed resulting in a Reynolds number based on the friction velocity around 250. Two different particle radii were used giving a particle-pipe diameter ratio of 0.05 and 0.075. The number of particles is kept constant resulting in a volume fraction of 0.54% and 1.83%, respectively. We investigated Eulerian and Lagrangian statistics along with the stresslet exerted by the fluid on the spherical particles. It was observed that the high particle-to-fluid slip velocity close to the wall corresponds locally to events of high energy dissipation, which are not present in the single-phase flow. The migration of particles from the inner to the outer region of the pipe, the dependence of the stresslet on the particle radial positions and a proxy for the fragmentation rate of the particles computed using the stresslet have been investigated.}, } @article {pmid29557347, year = {2018}, author = {Bayiz, Y and Ghanaatpishe, M and Fathy, H and Cheng, B}, title = {Hovering efficiency comparison of rotary and flapping flight for rigid rectangular wings via dimensionless multi-objective optimization.}, journal = {Bioinspiration & biomimetics}, volume = {13}, number = {4}, pages = {046002}, doi = {10.1088/1748-3190/aab801}, pmid = {29557347}, issn = {1748-3190}, mesh = {Algorithms ; Animals ; Biomechanical Phenomena ; Biomimetics ; Computer Simulation ; Flight, Animal/*physiology ; Insecta/physiology ; *Models, Biological ; Torque ; Wings, Animal/*physiology ; }, abstract = {In this work, a multi-objective optimization framework is developed for optimizing low Reynolds number ([Formula: see text]) hovering flight. This framework is then applied to compare the efficiency of rigid revolving and flapping wings with rectangular shape under varying [Formula: see text] and Rossby number ([Formula: see text], or aspect ratio). The proposed framework is capable of generating sets of optimal solutions and Pareto fronts for maximizing the lift coefficient and minimizing the power coefficient in dimensionless space, explicitly revealing the trade-off between lift generation and power consumption. The results indicate that revolving wings are more efficient when the required average lift coefficient [Formula: see text] is low (<1 for [Formula: see text] and <1.6 for [Formula: see text]), while flapping wings are more efficient in achieving higher [Formula: see text]. With the dimensionless power loading as the single-objective performance measure to be maximized, rotary flight is more efficient than flapping wings for [Formula: see text] regardless of the amount of energy storage assumed in the flapping wing actuation mechanism, while flapping flight is more efficient for [Formula: see text]. It is observed that wings with low [Formula: see text] perform better when higher [Formula: see text] is needed, whereas higher [Formula: see text] cases are more efficient at [Formula: see text] regions. However, for the selected geometry and [Formula: see text], the efficiency is weakly dependent on [Formula: see text] when the dimensionless power loading is maximized.}, } @article {pmid29555806, year = {2018}, author = {Margolin, LG}, title = {Scale matters.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {376}, number = {2118}, pages = {}, pmid = {29555806}, issn = {1471-2962}, abstract = {The applicability of Navier-Stokes equations is limited to near-equilibrium flows in which the gradients of density, velocity and energy are small. Here I propose an extension of the Chapman-Enskog approximation in which the velocity probability distribution function (PDF) is averaged in the coordinate phase space as well as the velocity phase space. I derive a PDF that depends on the gradients and represents a first-order generalization of local thermodynamic equilibrium. I then integrate this PDF to derive a hydrodynamic model. I discuss the properties of that model and its relation to the discrete equations of computational fluid dynamics.This article is part of the theme issue 'Hilbert's sixth problem'.}, } @article {pmid29553536, year = {2018}, author = {Agudo, JR and Han, J and Park, J and Kwon, S and Loekman, S and Luzi, G and Linderberger, C and Delgado, A and Wierschem, A}, title = {Visually Based Characterization of the Incipient Particle Motion in Regular Substrates: From Laminar to Turbulent Conditions.}, journal = {Journal of visualized experiments : JoVE}, volume = {}, number = {132}, pages = {}, pmid = {29553536}, issn = {1940-087X}, mesh = {Computer Simulation ; Motion ; Nonlinear Dynamics ; *Stress, Mechanical ; }, abstract = {Two different experimental methods for determining the threshold of particle motion as a function of geometrical properties of the bed from laminar to turbulent flow conditions are presented. For that purpose, the incipient motion of a single bead is studied on regular substrates that consist of a monolayer of fixed spheres of uniform size that are regularly arranged in triangular and quadratic symmetries. The threshold is characterized by the critical Shields number. The criterion for the onset of motion is defined as the displacement from the original equilibrium position to the neighboring one. The displacement and the mode of motion are identified with an imaging system. The laminar flow is induced using a rotational rheometer with a parallel disk configuration. The shear Reynolds number remains below 1. The turbulent flow is induced in a low-speed wind tunnel with open jet test section. The air velocity is regulated with a frequency converter on the blower fan. The velocity profile is measured with a hot wire probe connected to a hot film anemometer. The shear Reynolds number ranges between 40 and 150. The logarithmic velocity law and the modified wall law presented by Rotta are used to infer the shear velocity from the experimental data. The latter is of special interest when the mobile bead is partially exposed to the turbulent flow in the so-called hydraulically transitional flow regime. The shear stress is estimated at onset of motion. Some illustrative results showing the strong impact of the angle of repose, and the exposure of the bead to shear flow are represented in both regimes.}, } @article {pmid29548174, year = {2018}, author = {Kawamura, Y and Tsubaki, R}, title = {Phase reduction approach to elastohydrodynamic synchronization of beating flagella.}, journal = {Physical review. E}, volume = {97}, number = {2-1}, pages = {022212}, doi = {10.1103/PhysRevE.97.022212}, pmid = {29548174}, issn = {2470-0053}, mesh = {Flagella/*metabolism ; *Hydrodynamics ; *Models, Biological ; }, abstract = {We formulate a theory for the phase reduction of a beating flagellum. The theory enables us to describe the dynamics of a beating flagellum in a systematic manner using a single variable called the phase. The theory can also be considered as a phase reduction method for the limit-cycle solutions in infinite-dimensional dynamical systems, namely, the limit-cycle solutions to partial differential equations representing beating flagella. We derive the phase sensitivity function, which quantifies the phase response of a beating flagellum to weak perturbations applied at each point and at each time. Using the phase sensitivity function, we analyze the phase synchronization between a pair of beating flagella through hydrodynamic interactions at a low Reynolds number.}, } @article {pmid29548159, year = {2018}, author = {Rolland, J}, title = {Extremely rare collapse and build-up of turbulence in stochastic models of transitional wall flows.}, journal = {Physical review. E}, volume = {97}, number = {2-1}, pages = {023109}, doi = {10.1103/PhysRevE.97.023109}, pmid = {29548159}, issn = {2470-0053}, abstract = {This paper presents a numerical and theoretical study of multistability in two stochastic models of transitional wall flows. An algorithm dedicated to the computation of rare events is adapted on these two stochastic models. The main focus is placed on a stochastic partial differential equation model proposed by Barkley. Three types of events are computed in a systematic and reproducible manner: (i) the collapse of isolated puffs and domains initially containing their steady turbulent fraction; (ii) the puff splitting; (iii) the build-up of turbulence from the laminar base flow under a noise perturbation of vanishing variance. For build-up events, an extreme realization of the vanishing variance noise pushes the state from the laminar base flow to the most probable germ of turbulence which in turn develops into a full blown puff. For collapse events, the Reynolds number and length ranges of the two regimes of collapse of laminar-turbulent pipes, independent collapse or global collapse of puffs, is determined. The mean first passage time before each event is then systematically computed as a function of the Reynolds number r and pipe length L in the laminar-turbulent coexistence range of Reynolds number. In the case of isolated puffs, the faster-than-linear growth with Reynolds number of the logarithm of mean first passage time T before collapse is separated in two. One finds that ln(T)=A_{p} r-B_{p}, with A_{p} and B_{p} positive. Moreover, A_{p} and B_{p} are affine in the spatial integral of turbulence intensity of the puff, with the same slope. In the case of pipes initially containing the steady turbulent fraction, the length L and Reynolds number r dependence of the mean first passage time T before collapse is also separated. The author finds that T≍exp[L(Ar-B)] with A and B positive. The length and Reynolds number dependence of T are then discussed in view of the large deviations theoretical approaches of the study of mean first passage times and multistability, where ln(T) in the limit of small variance noise is studied. Two points of view, local noise of small variance and large length, can be used to discuss the exponential dependence in L of T. In particular, it is shown how a T≍exp[L(A^{'} R-B^{'} )] can be derived in a conceptual two degrees of freedom model of a transitional wall flow proposed by Dauchot and Manneville. This is done by identifying a quasipotential in low variance noise, large length limit. This pinpoints the physical effects controlling collapse and build-up trajectories and corresponding passage times with an emphasis on the saddle points between laminar and turbulent states. This analytical analysis also shows that these effects lead to the asymmetric probability density function of kinetic energy of turbulence.}, } @article {pmid29548094, year = {2018}, author = {Nemoto, T and Alexakis, A}, title = {Method to measure efficiently rare fluctuations of turbulence intensity for turbulent-laminar transitions in pipe flows.}, journal = {Physical review. E}, volume = {97}, number = {2-1}, pages = {022207}, doi = {10.1103/PhysRevE.97.022207}, pmid = {29548094}, issn = {2470-0053}, abstract = {The fluctuations of turbulence intensity in a pipe flow around the critical Reynolds number is difficult to study but important because they are related to turbulent-laminar transitions. We here propose a rare-event sampling method to study such fluctuations in order to measure the time scale of the transition efficiently. The method is composed of two parts: (i) the measurement of typical fluctuations (the bulk part of an accumulative probability function) and (ii) the measurement of rare fluctuations (the tail part of the probability function) by employing dynamics where a feedback control of the Reynolds number is implemented. We apply this method to a chaotic model of turbulent puffs proposed by Barkley and confirm that the time scale of turbulence decay increases super exponentially even for high Reynolds numbers up to Re =2500, where getting enough statistics by brute-force calculations is difficult. The method uses a simple procedure of changing Reynolds number that can be applied even to experiments.}, } @article {pmid29542932, year = {2018}, author = {Song, F and Ju, D and Gu, F and Liu, Y and Ji, Y and Ren, Y and He, X and Sha, B and Li, BQ and Yang, Q}, title = {Parametric Study on Electric Field-Induced Micro-/Nanopatterns in Thin Polymer Films.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {34}, number = {14}, pages = {4188-4198}, doi = {10.1021/acs.langmuir.8b00007}, pmid = {29542932}, issn = {1520-5827}, abstract = {Electric field-induced micro-/nanopatterns in thin polymer films, sometimes referred as electrohydrodynamic patterning, is a promising technique to fabricate micro-/nanostructures. Extensive attention has been attracted because of its advantages in microcontact (easy demolding) and low cost. Although considerable work has been done on this technique, including both experimental and theoretical ones, there still appears a requirement for understanding the mechanism of electrohydrodynamic patterning. Thus, we systematically studied the effect of different parameters on electrohydrodynamic patterning with a numerical phase field model. Previous researchers usually employed lubrication approximation (i.e., long-wave approximation) to simplify the numerical model. However, this approximation would lose its validity if the structure height is on the same scale or larger than the wavelength, which occurs in most cases. Thus, we abandoned the lubrication approximation and solved the full governing equations for fluid flow and electric field. In this model, the deformation of polymer film is described by the phase field model. As to the electric field, the leaky dielectric model is adopted in which both electrical permittivity and conductivity are considered. The fluid flow together with electric field is coupled together in the framework of phase field. By this model, the effect of physical parameters, such as external voltage, template structure height, and polymer conductivity, is studied in detail. After that, the governing equations are nondimesionalized to analyze the relationship between different parameters. A dimensionless parameter, electrical Reynolds number ER, is defined, for which, a large value would simplify the electric field to perfect dielectric model and a small value leads it to steady leaky model. These findings and results may enhance our understanding of electrohydrodynamic patterning and may be a meaningful guide for experiments.}, } @article {pmid29542796, year = {2018}, author = {Du, D and Hilou, E and Biswal, SL}, title = {Reconfigurable paramagnetic microswimmers: Brownian motion affects non-reciprocal actuation.}, journal = {Soft matter}, volume = {14}, number = {18}, pages = {3463-3470}, doi = {10.1039/c8sm00069g}, pmid = {29542796}, issn = {1744-6848}, abstract = {Swimming at low Reynolds number is typically dominated by a large viscous drag, therefore microscale swimmers require non-reciprocal body deformation to generate locomotion. Purcell described a simple mechanical swimmer at the microscale consisting of three rigid components connected together with two hinges. Here we present a simple microswimmer consisting of two rigid paramagnetic particles with different sizes. When placed in an eccentric magnetic field, this simple microswimmer exhibits non-reciprocal body motion and its swimming locomotion can be directed in a controllable manner. Additional components can be added to create a multibody microswimmer, whereby the particles act cooperatively and translate in a given direction. For some multibody swimmers, the stochastic thermal forces fragment the arm, which therefore modifies the swimming strokes and changes the locomotive speed. This work offers insight into directing the motion of active systems with novel time-varying magnetic fields. It also reveals that Brownian motion not only affects the locomotion of reciprocal swimmers that are subject to the Scallop theorem, but also affects that of non-reciprocal swimmers.}, } @article {pmid29542373, year = {2018}, author = {Oota-Ishigaki, A and Masuzawa, T and Nagayama, K}, title = {Analysis of the effect of the size of three-dimensional micro-geometric structures on physical adhesion phenomena using microprint technique.}, journal = {The International journal of artificial organs}, volume = {41}, number = {5}, pages = {277-283}, doi = {10.1177/0391398818763264}, pmid = {29542373}, issn = {1724-6040}, mesh = {Biocompatible Materials ; Heart-Assist Devices/*adverse effects ; Humans ; Hydrodynamics ; Surface Properties ; Thrombosis/*etiology ; }, abstract = {Thrombus formation on biomaterial surfaces with microstructures is complex and not fully understood. We have studied the micro-secondary flow around microstructures that causes components of blood to adhere physically in a low Reynolds number region. The purpose of this study was to investigate the effect of micro-column size on the adhesion phenomena and show a quantitative relationship between the micro-secondary flow and physical adhesion phenomena, considering microstructures of various sizes. The flow simulation and quantitative assessment of adhesion rates around micro-columns was conducted using four sizes of micro-columns. This study also calculated the vectors of micro-secondary flow and average shear rate around a micro-column using a computational fluid dynamics analysis. The simulation showed the micro-secondary flow toward the bottom surface at upstream side and low shear rate distribution generated around a micro-column. Furthermore, physical adhesion tests were conducted using microbeads and a perfusion circuit to examine the size effect of the micro-columns on the physical adhesion. The results showed that the average adhesion rate around the micro-column increases with the associated size increase of the micro-column. Our results indicate that quantification of micro-secondary flow on a material surface with microstructures of several sizes and shapes (such as in a rough surface) is important for the evaluation of the adhesion phenomenon even though the surface roughness value on the material surface is small.}, } @article {pmid29535341, year = {2018}, author = {Rubol, S and Ling, B and Battiato, I}, title = {Universal scaling-law for flow resistance over canopies with complex morphology.}, journal = {Scientific reports}, volume = {8}, number = {1}, pages = {4430}, pmid = {29535341}, issn = {2045-2322}, abstract = {Flow resistance caused by vegetation is a key parameter to properly assess flood management and river restoration. However, quantifying the friction factor or any of its alternative metrics, e.g. the drag coefficient, in canopies with complex geometry has proven elusive. We explore the effect of canopy morphology on vegetated channels flow structure and resistance by treating the canopy as a porous medium characterized by an effective permeability, a property that describes the ease with which water can flow through the canopy layer. We employ a two-domain model for flow over and within the canopy, which couples the log-law in the free layer to the Darcy-Brinkman equation in the vegetated layer. We validate the model analytical solutions for the average velocity profile within and above the canopy, the volumetric discharge and the friction factor against data collected across a wide range of canopy morphologies encountered in riverine systems. Results indicate agreement between model predictions and data for both simple and complex plant morphologies. For low submergence canopies, we find a universal scaling law that relates friction factor with canopy permeability and a rescaled bulk Reynolds number. This provides a valuable tool to assess habitats sustainability associated with hydro-dynamical conditions.}, } @article {pmid29527067, year = {2017}, author = {Yang, J and Wang, X and Krane, M and Zhang, LT}, title = {Fully-coupled aeroelastic simulation with fluid compressibility - For application to vocal fold vibration.}, journal = {Computer methods in applied mechanics and engineering}, volume = {315}, number = {}, pages = {584-606}, pmid = {29527067}, issn = {0045-7825}, support = {R01 DC005642/DC/NIDCD NIH HHS/United States ; }, abstract = {In this study, a fully-coupled fluid-structure interaction model is developed for studying dynamic interactions between compressible fluid and aeroelastic structures. The technique is built based on the modified Immersed Finite Element Method (mIFEM), a robust numerical technique to simulate fluid-structure interactions that has capabilities to simulate high Reynolds number flows and handles large density disparities between the fluid and the solid. For accurate assessment of this intricate dynamic process between compressible fluid, such as air and aeroelastic structures, we included in the model the fluid compressibility in an isentropic process and a solid contact model. The accuracy of the compressible fluid solver is verified by examining acoustic wave propagations in a closed and an open duct, respectively. The fully-coupled fluid-structure interaction model is then used to simulate and analyze vocal folds vibrations using compressible air interacting with vocal folds that are represented as layered viscoelastic structures. Using physiological geometric and parametric setup, we are able to obtain a self-sustained vocal fold vibration with a constant inflow pressure. Parametric studies are also performed to study the effects of lung pressure and vocal fold tissue stiffness in vocal folds vibrations. All the case studies produce expected airflow behavior and a sustained vibration, which provide verification and confidence in our future studies of realistic acoustical studies of the phonation process.}, } @article {pmid29513310, year = {2018}, author = {Marson, RL and Huang, Y and Huang, M and Fu, T and Larson, RG}, title = {Inertio-capillary cross-streamline drift of droplets in Poiseuille flow using dissipative particle dynamics simulations.}, journal = {Soft matter}, volume = {14}, number = {12}, pages = {2267-2280}, doi = {10.1039/c7sm02294h}, pmid = {29513310}, issn = {1744-6848}, abstract = {We find using dissipative particle dynamics (DPD) simulations that a deformable droplet sheared in a narrow microchannel migrates to steady-state position that depends upon the dimensionless particle capillary number , which controls the droplet deformability (with Vmax the centerline velocity, μf the fluid viscosity, Γ the surface tension, R the droplet radius, and H the gap), the droplet (particle) Reynolds number , which controls inertia, where ρ is the fluid density, as well as on the viscosity ratio of the droplet to the suspending fluid κ = μd/μf. We find that when the Ohnesorge number is around 0.06, so that inertia is stronger than capillarity, at small capillary number Cap < 0.1, the droplet migrates to a position close to that observed for hard spheres by Segre and Silberberg, around 60% of the distance from the centerline to the wall, while for increasing Cap the droplet steady-state position moves smoothly towards the centerline, reaching around 20% of the distance from centerline to the wall when Cap reaches 0.5 or so. For higher Oh, the droplet position is much less sensitive to Cap, and remains at around 30% of the distance from centerline to the wall over the whole accessible range of Cap. The results are insensitive to viscosity ratios from unity to the highest value studied here, around 13, and the drift towards the centerline for increasing Cap is observed for ratios of droplet diameter to gap size ranging from 0.1 to 0.3. We also find consistency between our predictions and existing perturbation theory for small droplet or particle size, as well as with experimental data. Additionally, we assess the accuracy of the DPD method and conclude that with current computer resources and methods DPD is not readily able to predict cross-stream-line drift for small particle Reynolds number (much less than unity), or for droplets that are less than one tenth the gap size, owing to excessive noise and inadequate numbers of DPD particles per droplet.}, } @article {pmid29512658, year = {2018}, author = {Hadikhani, P and Hashemi, SMH and Balestra, G and Zhu, L and Modestino, MA and Gallaire, F and Psaltis, D}, title = {Inertial manipulation of bubbles in rectangular microfluidic channels.}, journal = {Lab on a chip}, volume = {18}, number = {7}, pages = {1035-1046}, doi = {10.1039/c7lc01283g}, pmid = {29512658}, issn = {1473-0189}, abstract = {Inertial microfluidics is an active field of research that deals with crossflow positioning of the suspended entities in microflows. Until now, the majority of the studies have focused on the behavior of rigid particles in order to provide guidelines for microfluidic applications such as sorting and filtering. Deformable entities such as bubbles and droplets are considered in fewer studies despite their importance in multiphase microflows. In this paper, we show that the trajectory of bubbles flowing in rectangular and square microchannels can be controlled by tuning the balance of forces acting on them. A T-junction geometry is employed to introduce bubbles into a microchannel and analyze their lateral equilibrium position in a range of Reynolds (1 < Re < 40) and capillary numbers (0.1 < Ca < 1). We find that the Reynolds number (Re), the capillary number (Ca), the diameter of the bubble (D[combining macron]), and the aspect ratio of the channel are the influential parameters in this phenomenon. For instance, at high Re, the flow pushes the bubble towards the wall while large Ca or D[combining macron] moves the bubble towards the center. Moreover, in the shallow channels, having aspect ratios higher than one, the bubble moves towards the narrower sidewalls. One important outcome of this study is that the equilibrium position of bubbles in rectangular channels is different from that of solid particles. The experimental observations are in good agreement with the performed numerical simulations and provide insights into the dynamics of bubbles in laminar flows which can be utilized in the design of flow based multiphase flow reactors.}, } @article {pmid29505991, year = {2018}, author = {Martínez-Pedrero, F and Tierno, P}, title = {Advances in colloidal manipulation and transport via hydrodynamic interactions.}, journal = {Journal of colloid and interface science}, volume = {519}, number = {}, pages = {296-311}, doi = {10.1016/j.jcis.2018.02.062}, pmid = {29505991}, issn = {1095-7103}, abstract = {In this review article, we highlight many recent advances in the field of micromanipulation of colloidal particles using hydrodynamic interactions (HIs), namely solvent mediated long-range interactions. At the micrsocale, the hydrodynamic laws are time reversible and the flow becomes laminar, features that allow precise manipulation and control of colloidal matter. We focus on different strategies where externally operated microstructures generate local flow fields that induce the advection and motion of the surrounding components. In addition, we review cases where the induced flow gives rise to hydrodynamic bound states that may synchronize during the process, a phenomenon essential in different systems such as those that exhibit self-assembly and swarming.}, } @article {pmid29497820, year = {2018}, author = {Wang, Q and Othmer, HG}, title = {Analysis of a model microswimmer with applications to blebbing cells and mini-robots.}, journal = {Journal of mathematical biology}, volume = {76}, number = {7}, pages = {1699-1763}, pmid = {29497820}, issn = {1432-1416}, mesh = {Animals ; Biophysical Phenomena ; Cell Membrane/physiology ; Cell Movement/*physiology ; Computational Biology ; Computer Simulation ; Humans ; Hydrodynamics ; Mathematical Concepts ; *Models, Biological ; Robotics ; Viscosity ; }, abstract = {Recent research has shown that motile cells can adapt their mode of propulsion depending on the environment in which they find themselves. One mode is swimming by blebbing or other shape changes, and in this paper we analyze a class of models for movement of cells by blebbing and of nano-robots in a viscous fluid at low Reynolds number. At the level of individuals, the shape changes comprise volume exchanges between connected spheres that can control their separation, which are simple enough that significant analytical results can be obtained. Our goal is to understand how the efficiency of movement depends on the amplitude and period of the volume exchanges when the spheres approach closely during a cycle. Previous analyses were predicated on wide separation, and we show that the speed increases significantly as the separation decreases due to the strong hydrodynamic interactions between spheres in close proximity. The scallop theorem asserts that at least two degrees of freedom are needed to produce net motion in a cyclic sequence of shape changes, and we show that these degrees can reside in different swimmers whose collective motion is studied. We also show that different combinations of mode sharing can lead to significant differences in the translation and performance of pairs of swimmers.}, } @article {pmid29487930, year = {2018}, author = {Bao, L and Spandan, V and Yang, Y and Dyett, B and Verzicco, R and Lohse, D and Zhang, X}, title = {Flow-induced dissolution of femtoliter surface droplet arrays.}, journal = {Lab on a chip}, volume = {18}, number = {7}, pages = {1066-1074}, doi = {10.1039/c7lc01321c}, pmid = {29487930}, issn = {1473-0189}, abstract = {The dissolution of liquid nanodroplets is a crucial step in many applied processes, such as separation and dispersion in the food industry, crystal formation of pharmaceutical products, concentrating and analysis in medical diagnosis, and drug delivery in aerosols. In this work, using both experiments and numerical simulations, we quantitatively study the dissolution dynamics of femtoliter surface droplets in a highly ordered array under a uniform flow. Our results show that the dissolution of femtoliter droplets strongly depends on their spatial positions relative to the flow direction, drop-to-drop spacing in the array, and the imposed flow rate. In some particular cases, the droplet at the edge of the array can dissolve about 30% faster than the ones located near the centre. The dissolution rate of the droplet increases by 60% as the inter-droplet spacing is increased from 2.5 μm to 20 μm. Moreover, the droplets close to the front of the flow commence to shrink earlier than those droplets in the center of the array. The average dissolution rate is faster for the faster flow. As a result, the dissolution time (Ti) decreases with the Reynolds number (Re) of the flow as Ti ∝ Re-3/4. The experimental results are in good agreement with the numerical simulations where the advection-diffusion equation for the concentration field is solved and the concentration gradient on the surface of the drop is computed. The findings suggest potential approaches to manipulate nanodroplet sizes in droplet arrays simply by dissolution controlled by an external flow. The obtained droplets with varying curvatures may serve as templates for generating multifocal microlenses in one array.}, } @article {pmid29481162, year = {2018}, author = {Nissan, A and Berkowitz, B}, title = {Inertial Effects on Flow and Transport in Heterogeneous Porous Media.}, journal = {Physical review letters}, volume = {120}, number = {5}, pages = {054504}, doi = {10.1103/PhysRevLett.120.054504}, pmid = {29481162}, issn = {1079-7114}, abstract = {We investigate the effects of high fluid velocities on flow and tracer transport in heterogeneous porous media. We simulate fluid flow and advective transport through two-dimensional pore-scale matrices with varying structural complexity. As the Reynolds number increases, the flow regime transitions from linear to nonlinear; this behavior is controlled by the medium structure, where higher complexity amplifies inertial effects. The result is, nonintuitively, increased homogenization of the flow field, which leads in the context of conservative chemical transport to less anomalous behavior. We quantify the transport patterns via a continuous time random walk, using the spatial distribution of the kinetic energy within the fluid as a characteristic measure.}, } @article {pmid29481155, year = {2018}, author = {Cerbus, RT and Liu, CC and Gioia, G and Chakraborty, P}, title = {Laws of Resistance in Transitional Pipe Flows.}, journal = {Physical review letters}, volume = {120}, number = {5}, pages = {054502}, doi = {10.1103/PhysRevLett.120.054502}, pmid = {29481155}, issn = {1079-7114}, abstract = {As everyone knows who has opened a kitchen faucet, pipe flow is laminar at low flow velocities and turbulent at high flow velocities. At intermediate velocities, there is a transition wherein plugs of laminar flow alternate along the pipe with "flashes" of a type of fluctuating, nonlaminar flow that remains poorly understood. In the 19th century, Osborne Reynolds sought to connect these states of flow with quantitative "laws of resistance," whereby the fluid friction is determined as a function of the Reynolds number. While he succeeded for laminar and turbulent flows, the laws for transitional flows eluded him and remain unknown to this day. By properly distinguishing between laminar plugs and flashes in the transitional regime, we show experimentally and numerically that the law of resistance for laminar plugs corresponds to the laminar law and the law of resistance for flashes is identical to that of turbulence.}, } @article {pmid29480329, year = {2018}, author = {Wu, H and de León, MAP and Othmer, HG}, title = {Getting in shape and swimming: the role of cortical forces and membrane heterogeneity in eukaryotic cells.}, journal = {Journal of mathematical biology}, volume = {77}, number = {3}, pages = {595-626}, pmid = {29480329}, issn = {1432-1416}, support = {R01 GM029123/GM/NIGMS NIH HHS/United States ; #54-CA-210190/NH/NIH HHS/United States ; DMS 0817529//National Science Foundation/International ; U54 CA210190/CA/NCI NIH HHS/United States ; 1311974//National Science Foundation/International ; }, mesh = {Algorithms ; Animals ; Biophysical Phenomena ; Cell Membrane/physiology ; Cell Movement/*physiology ; Cell Polarity/physiology ; Cell Shape/*physiology ; Cellular Microenvironment/physiology ; Computer Simulation ; Eukaryotic Cells/physiology ; Extracellular Matrix/physiology ; Humans ; Mathematical Concepts ; *Models, Biological ; }, abstract = {Recent research has shown that motile cells can adapt their mode of propulsion to the mechanical properties of the environment in which they find themselves-crawling in some environments while swimming in others. The latter can involve movement by blebbing or other cyclic shape changes, and both highly-simplified and more realistic models of these modes have been studied previously. Herein we study swimming that is driven by membrane tension gradients that arise from flows in the actin cortex underlying the membrane, and does not involve imposed cyclic shape changes. Such gradients can lead to a number of different characteristic cell shapes, and our first objective is to understand how different distributions of membrane tension influence the shape of cells in an inviscid quiescent fluid. We then analyze the effects of spatial variation in other membrane properties, and how they interact with tension gradients to determine the shape. We also study the effect of fluid-cell interactions and show how tension leads to cell movement, how the balance between tension gradients and a variable bending modulus determine the shape and direction of movement, and how the efficiency of movement depends on the properties of the fluid and the distribution of tension and bending modulus in the membrane.}, } @article {pmid29466251, year = {2018}, author = {Arranz, G and Moriche, M and Uhlmann, M and Flores, O and García-Villalba, M}, title = {Kinematics and dynamics of the auto-rotation of a model winged seed.}, journal = {Bioinspiration & biomimetics}, volume = {13}, number = {3}, pages = {036011}, doi = {10.1088/1748-3190/aab144}, pmid = {29466251}, issn = {1748-3190}, mesh = {Biomechanical Phenomena ; Biomimetics ; Computer Simulation ; *Models, Biological ; Motion ; Rotation ; Seeds/*anatomy & histology/*physiology ; Wind ; }, abstract = {Numerical simulations of the auto-rotation of a model winged seed are presented. The calculations are performed by solving simultaneously the Navier-Stokes equations for the flow surrounding the seed and the rigid-body equations for the motion of the seed. The Reynolds number based on the descent speed and a characteristic chord length is varied in the range 80-240. Within this range, the seed attains an asymptotic state with finite amplitude auto-rotation, while for smaller values of the Reynolds number no auto-rotation is observed. The motion of the seed is characterized by the coning and pitch angles, the angular velocity and the horizontal translation of the seed. The values obtained for these quantities are qualitatively similar to those reported in the literature in experiments with real winged seeds. When increasing the Reynolds number, the seed tends to rotate at higher speeds, with less inclination with respect to the horizontal plane, and with a larger translation velocity. With respect to the aerodynamic forces, it is observed that, with increasing Reynolds number, the horizontal components decrease in magnitude while the vertical component increases. The force distribution along the wing span is characterized using both global and local characteristic speeds and chord lengths for the non-dimensionalisation of the force coefficients. It is found that the vertical component does not depend on the Reynolds number when using local scaling, while the chordwise component of the force does.}, } @article {pmid29462624, year = {2018}, author = {Ishimoto, K and Gadêlha, H and Gaffney, EA and Smith, DJ and Kirkman-Brown, J}, title = {Human sperm swimming in a high viscosity mucus analogue.}, journal = {Journal of theoretical biology}, volume = {446}, number = {}, pages = {1-10}, doi = {10.1016/j.jtbi.2018.02.013}, pmid = {29462624}, issn = {1095-8541}, support = {HCS SCL-2014-05-001/DH_/Department of Health/United Kingdom ; }, mesh = {Humans ; Male ; *Models, Biological ; Mucus/metabolism ; Sperm Motility/*physiology ; Spermatozoa/cytology/*physiology ; }, abstract = {Remarkably, mammalian sperm maintain a substantive proportion of their progressive swimming speed within highly viscous fluids, including those of the female reproductive tract. Here, we analyse the digital microscopy of a human sperm swimming in a highly viscous, weakly elastic mucus analogue. We exploit principal component analysis to simplify its flagellar beat pattern, from which boundary element calculations are used to determine the time-dependent flow field around the sperm cell. The sperm flow field is further approximated in terms of regularised point forces, and estimates of the mechanical power consumption are determined, for comparison with analogous low viscosity media studies. This highlights extensive differences in the structure of the flows surrounding human sperm in different media, indicating how the cell-cell and cell-boundary hydrodynamic interactions significantly differ with the physical microenvironment. The regularised point force decomposition also provides cell-level information that may ultimately be incorporated into sperm population models. We further observe indications that the core feature in explaining the effectiveness of sperm swimming in high viscosity media is the loss of cell yawing, which is related with a greater density of regularised point force singularities along the axis of symmetry of the flagellar beat to represent the flow field. In turn this implicates a reduction of the wavelength of the distal beat pattern - and hence dynamical wavelength selection of the flagellar beat - as the dominant feature governing the effectiveness of sperm swimming in highly viscous media.}, } @article {pmid29454239, year = {2018}, author = {Ren, LF and Adeel, M and Li, J and Xu, C and Xu, Z and Zhang, X and Shao, J and He, Y}, title = {Phenol separation from phenol-laden saline wastewater by membrane aromatic recovery system-like membrane contactor using superhydrophobic/organophilic electrospun PDMS/PMMA membrane.}, journal = {Water research}, volume = {135}, number = {}, pages = {31-43}, doi = {10.1016/j.watres.2018.02.011}, pmid = {29454239}, issn = {1879-2448}, mesh = {Dimethylpolysiloxanes/chemistry ; Equipment Design ; *Membranes, Artificial ; Methacrylates/chemistry ; Phenol/*isolation & purification ; Polymethyl Methacrylate/chemistry ; Sodium Chloride ; Waste Disposal, Fluid/instrumentation/*methods ; Waste Water/chemistry ; Water Pollutants, Chemical/*isolation & purification ; Water Purification/instrumentation/methods ; }, abstract = {Phenol recovery from phenol-laden saline wastewater plays an important role in the waste reclamation and pollution control. A membrane aromatic recovery system-like membrane contactor (MARS-like membrane contactor) was set up in this study using electrospun polydimethylsiloxane/polymethyl methacrylate (PDMS/PMMA) membrane with 0.0048 m[2] effective area to separate phenol from saline wastewater. Phenol and water contact angles of 0° and 162° were achieved on this membrane surface simultaneously, indicating its potential in the separation of phenol and water-soluble salt. Feed solution (500 mL) of 0.90 L/h and receiving solution (500 mL) of 1.26 L/h were investigated to be the optimum conditions for phenol separation, which corresponds to the employed Reynolds number of 14.6 and 20.5. During 108-h continuous separation for feed solution (2.0 g/L phenol, 10.0 g/L NaCl) under room temperature (20 °C), 42.6% of phenol was recycled in receiving solution with a salt rejection of 99.95%. Meanwhile, the mean phenol mass transfer coefficient (Kov) was 6.7 × 10[-7] m s[-1]. As a membrane-based process, though the permeated phenol increased with the increase of phenol concentration in feed solution, the phenol recovery ratio was determined by the membrane properties rather than the pollutant concentrations. Phenol was found to permeate this membrane via adsorption, diffusion and desorption, and therefore, the membrane fouling generated from pore blockage in other membrane separation processes was totally avoided.}, } @article {pmid29448779, year = {2018}, author = {Fang, C and Wu, X and Yang, F and Qiao, R}, title = {Flow of quasi-two dimensional water in graphene channels.}, journal = {The Journal of chemical physics}, volume = {148}, number = {6}, pages = {064702}, doi = {10.1063/1.5017491}, pmid = {29448779}, issn = {1089-7690}, abstract = {When liquids confined in slit channels approach a monolayer, they become two-dimensional (2D) fluids. Using molecular dynamics simulations, we study the flow of quasi-2D water confined in slit channels featuring pristine graphene walls and graphene walls with hydroxyl groups. We focus on to what extent the flow of quasi-2D water can be described using classical hydrodynamics and what are the effective transport properties of the water and the channel. First, the in-plane shearing of quasi-2D water confined between pristine graphene can be described using the classical hydrodynamic equation, and the viscosity of the water is ∼50% higher than that of the bulk water in the channel studied here. Second, the flow of quasi-2D water around a single hydroxyl group is perturbed at a position of tens of cluster radius from its center, as expected for low Reynolds number flows. Even though water is not pinned at the edge of the hydroxyl group, the hydroxyl group screens the flow greatly, with a single, isolated hydroxyl group rendering drag similar to ∼90 nm[2] pristine graphene walls. Finally, the flow of quasi-2D water through graphene channels featuring randomly distributed hydroxyl groups resembles the fluid flow through porous media. The effective friction factor of the channel increases linearly with the hydroxyl groups' area density up to 0.5 nm[-2] but increases nonlinearly at higher densities. The effective friction factor of the channel can be fitted to a modified Carman equation at least up to a hydroxyl area density of 2.0 nm[-2]. These findings help understand the liquid transport in 2D material-based nanochannels for applications including desalination.}, } @article {pmid29445037, year = {2018}, author = {Godoy-Diana, R and Thiria, B}, title = {On the diverse roles of fluid dynamic drag in animal swimming and flying.}, journal = {Journal of the Royal Society, Interface}, volume = {15}, number = {139}, pages = {}, pmid = {29445037}, issn = {1742-5662}, mesh = {Animals ; Biomechanical Phenomena ; *Hydrodynamics ; *Models, Biological ; Swimming/*physiology ; }, abstract = {Questions of energy dissipation or friction appear immediately when addressing the problem of a body moving in a fluid. For the most simple problems, involving a constant steady propulsive force on the body, a straightforward relation can be established balancing this driving force with a skin friction or form drag, depending on the Reynolds number and body geometry. This elementary relation closes the full dynamical problem and sets, for instance, average cruising velocity or energy cost. In the case of finite-sized and time-deformable bodies though, such as flapping flyers or undulatory swimmers, the comprehension of driving/dissipation interactions is not straightforward. The intrinsic unsteadiness of the flapping and deforming animal bodies complicates the usual application of classical fluid dynamic forces balance. One of the complications is because the shape of the body is indeed changing in time, accelerating and decelerating perpetually, but also because the role of drag (more specifically the role of the local drag) has two different facets, contributing at the same time to global dissipation and to driving forces. This causes situations where a strong drag is not necessarily equivalent to inefficient systems. A lot of living systems are precisely using strong sources of drag to optimize their performance. In addition to revisiting classical results under the light of recent research on these questions, we discuss in this review the crucial role of drag from another point of view that concerns the fluid-structure interaction problem of animal locomotion. We consider, in particular, the dynamic subtleties brought by the quadratic drag that resists transverse motions of a flexible body or appendage performing complex kinematics, such as the phase dynamics of a flexible flapping wing, the propagative nature of the bending wave in undulatory swimmers, or the surprising relevance of drag-based resistive thrust in inertial swimmers.}, } @article {pmid29435817, year = {2018}, author = {Walait, A and Siddiqui, AM and Rana, MA}, title = {Analysis of a self-propelling sheet with heat transfer through non-isothermal fluid in an inclined human cervical canal.}, journal = {Journal of biological physics}, volume = {44}, number = {3}, pages = {273-300}, pmid = {29435817}, issn = {1573-0689}, mesh = {*Biophysical Phenomena ; *Cervical Vertebrae ; Computer Simulation ; *Hot Temperature ; Humans ; *Models, Theoretical ; *Numerical Analysis, Computer-Assisted ; Pressure ; *Rheology ; }, abstract = {The present theoretical analysis deals with biomechanics of the self-propulsion of a swimming sheet with heat transfer through non-isothermal fluid filling an inclined human cervical canal. Partial differential equations arising from the mathematical modeling of the proposed model are solved analytically. Flow variables like pressure gradient, propulsive velocity, fluid velocity, time mean flow rate, fluid temperature, and heat-transfer coefficients are analyzed for the pertinent parameters. Striking features of the pumping characteristics are explored. Propulsive velocity of the swimming sheet becomes faster for lower Froude number, higher Reynolds number, and for a vertical channel. Temperature and peak value of the heat-transfer coefficients below the swimming sheet showed an increase by the increment of Brinkmann number, inclination, pressure difference over wavelength, and Reynolds number whereas these quantities decrease with increasing Froude number. Aforesaid parameters have shown opposite effects on the peak value of the heat-transfer coefficients below and above the swimming sheet. Relevance of the current results to the spermatozoa transport with heat transfer through non-isothermal cervical mucus filling an inclined human cervical canal is also explored.}, } @article {pmid29429719, year = {2018}, author = {Dehbani, M and Rahimi, M}, title = {Introducing ultrasonic falling film evaporator for moderate temperature evaporation enhancement.}, journal = {Ultrasonics sonochemistry}, volume = {42}, number = {}, pages = {689-696}, doi = {10.1016/j.ultsonch.2017.12.016}, pmid = {29429719}, issn = {1873-2828}, abstract = {In the present study, Ultrasonic Falling Film (USFF), as a novel technique has been proposed to increase the evaporation rate of moderate temperature liquid film. It is a proper method for some applications which cannot be performed at high temperature, such as foodstuff industry, due to their sensitivity to high temperatures. Evaporation rate of sodium chloride solution from an USFF on an inclined flat plate compared to that for Falling Film without ultrasonic irradiation (FF) at various temperatures was investigated. The results revealed that produced cavitation bubbles have different effects on evaporation rate at different temperatures. At lower temperatures, size fluctuation and collapse of bubbles and in consequence induced physical effects of cavitation bubbles resulted in more turbulency and evaporation rate enhancement. At higher temperatures, the behavior was different. Numerous created bubbles joined together and cover the plate surface, so not only decreased the ultrasound vibrations but also reduced the evaporation rate in comparison with FF. The highest evaporation rate enhancement of 353% was obtained at 40 °C at the lowest Reynolds number of 250. In addition, the results reveal that at temperature of 40 °C, USFF has the highest efficiency compared to FF.}, } @article {pmid29420569, year = {2018}, author = {Tang, H and Xu, L and Hu, F}, title = {Hydrodynamic characteristics of knotted and knotless purse seine netting panels as determined in a flume tank.}, journal = {PloS one}, volume = {13}, number = {2}, pages = {e0192206}, doi = {10.1371/journal.pone.0192206}, pmid = {29420569}, issn = {1932-6203}, mesh = {*Hydrodynamics ; Models, Theoretical ; *Nylons ; }, abstract = {Nylon (PA) netting is widely used in purse seines and other fishing gears due to its high strength and good sinking performance. However, hydrodynamic properties of nylon netting of different characteristics are poorly understood. This study investigated hydrodynamic characteristics of nylon netting of different knot types and solidity ratios under different attack angles and flow velocities. It was found that the hydrodynamic coefficient of netting panels was related to Reynolds number, solidity ratio, attack angle, knot type and twine construction. The solidity ratio was found to positively correlate with drag coefficient when the netting was normal to the flow (CD90), but not the case when the netting was parallel to the flow (CD0). For netting panels inclined to the flow, the inclined drag coefficient had a negative relationship with the solidity ratio for attack angles between 0° and 50°, but a positive relationship for attack angles between 50° and 90°. The lift coefficient increased with the attack angle, reaching the culminating point at an attack angle of 50°, before subsequent decline. We found that the drag generated by knot accounted for 15-25% of total drag, and the knotted netting with higher solidity ratio exhibited a greater CD0, but it was not the case for the knotless netting. Compared to knotless polyethylene (PE) netting, the drag coefficients of knotless PA netting were dominant at higher Reynolds number (Re>2200).}, } @article {pmid29407276, year = {2018}, author = {Mojahed, A and Rajabi, M}, title = {Self-motile swimmers: Ultrasound driven spherical model.}, journal = {Ultrasonics}, volume = {86}, number = {}, pages = {1-5}, doi = {10.1016/j.ultras.2018.01.006}, pmid = {29407276}, issn = {1874-9968}, abstract = {The concept of ultrasound acoustic driven self-motile swimmers which is the source of autonomous propulsion is the acoustic field generated by the swimmer due to the partial oscillation of its surface is investigated. Limiting the subject to a body with simple spherical geometry, it is analytically shown that the generated acoustic radiation force due to induction by asymmetric acoustic field in host medium is non-zero, which propels the device. Assuming low Reynolds number condition, the frequency-dependent swimming velocity is calculated as a function of design parameters and optimum operating condition is obtained. The proposed methodology will open a new path towards the micro- or molecular-sized self propulsive machines or mechanism with great applications in engineering, medicine and biology.}, } @article {pmid29404782, year = {2018}, author = {Huang, JJ and Wu, J and Huang, H}, title = {An alternative method to implement contact angle boundary condition and its application in hybrid lattice-Boltzmann finite-difference simulations of two-phase flows with immersed surfaces.}, journal = {The European physical journal. E, Soft matter}, volume = {41}, number = {2}, pages = {17}, pmid = {29404782}, issn = {1292-895X}, abstract = {We propose an alternative method to implement the contact angle boundary condition on a solid wall and apply it in hybrid lattice-Boltzmann finite-difference simulations of two-phase flows with immersed surfaces in which the flow equations are solved by the lattice-Boltzmann method and the interface equations are solved by the finite-difference method. Using the hyperbolic tangent profile of the order parameter across an interface in phase-field theory, we were able to obtain its unknown value at a ghost point from the information at only one point in the fluid domain. This is in contrast with existing approaches relying on interpolations involving several points. The special feature allows it to be more easily implemented on immersed surfaces cutting through the grid lines. It was properly incorporated into the framework of the hybrid lattice-Boltzmann finite-difference simulation, and applied successfully for several problems with different levels of complexity. First, the equilibrium shapes of a droplet on a sphere with different contact angles and radii were studied under cylindrical geometry and a good agreement with theoretical predictions was found. Preliminary studies on a three-dimensional droplet spreading on a sphere were also performed and the results agreed well with the corresponding axisymmetric results. Second, the spreading of a two-dimensional drop on an embedded inclined wall with a given contact angle was investigated and the results matched those on a flat wall at the domain boundary under the same condition. Third, capillary filling in a cylindrical tube was studied and the speed of the interface in the tube was found to follow Washburn's law. Fourth, a droplet impacting on a sphere was investigated and several different outcomes were captured depending on the Reynolds number, the viscosity ratio, and the wettability and radius of the sphere. Finally, the proposed method was shown to be capable of studying even more complicated problems involving the interaction between a droplet and multiple objects of different sizes and contact angles.}, } @article {pmid29395261, year = {2018}, author = {Mehrabian, S and Letendre, F and Cameron, CB}, title = {The mechanisms of filter feeding on oil droplets: Theoretical considerations.}, journal = {Marine environmental research}, volume = {135}, number = {}, pages = {29-42}, doi = {10.1016/j.marenvres.2018.01.006}, pmid = {29395261}, issn = {1879-0291}, mesh = {Animals ; *Feeding Behavior ; Filtration ; Hydrocarbons ; Models, Theoretical ; Water ; }, abstract = {Filter feeding animals capture food particles and oil droplets from the fluid environment using cilia or appendages composed of arrays of fibers. Here we review the theoretical models that have provided a foundation for observations on the efficiency of particle capture. We then provide the mathematical theoretical framework to characterize the efficient filtration of oil droplets. In the aquatic and marine environments oil droplets are released from the decay of organisms or as hydrocarbons. Droplet size and flow velocity, oil-to-water viscosity ratio, oil-water interfacial tension, oil and water density difference, and the surface wettability, or surface texture, of the filter fiber are the key parameters for oil droplet capture. Following capture, capillary force maintains the droplet at its location due to the oil-water interfacial tension. If the oil-coated fiber is subject to any external force such as viscous or gravitational forces, it may deform and separate from the fiber and re-enter the fluid stream. We show oil droplet capture in Daphnia and the barnacle Balanus glandula, and outline some of the ecological unknowns regarding oil capture in the oceans. Awareness of these mechanisms and their interrelationships will provide a foundation for investigations into the efficiency of various modes of filter feeding on oil droplets.}, } @article {pmid29390777, year = {2018}, author = {Karthik, K and Vengadesan, S and Bhattacharyya, SK}, title = {Prediction of flow induced sound generated by cross flow past finite length circular cylinders.}, journal = {The Journal of the Acoustical Society of America}, volume = {143}, number = {1}, pages = {260}, doi = {10.1121/1.5021243}, pmid = {29390777}, issn = {1520-8524}, abstract = {The paper presents aeroacoustic results for the flow around finite-length circular cylinders at Reynolds number 84 770 for various length-to-diameter (L/D) ratios (= 3, 9, 20, 25, 30, and 35). The incompressible Navier-Stokes equations are solved using the large eddy simulation model of turbulence followed by acoustic predictions in the far field using Ffwocs Williams and Hawkings method. The comparisons of numerical and anechoic wind tunnel measurements show good agreement in terms of the aerodynamic forces and acoustic parameters such as tonal frequency, tonal sound pressure level, and overall sound pressure level. The cylinder L/D ratio was observed to be a significant parameter that controls vortex shedding and consequently the flow induced sound generation.}, } @article {pmid29390714, year = {2018}, author = {Mastracci, B and Guo, W}, title = {An apparatus for generation and quantitative measurement of homogeneous isotropic turbulence in He ii.}, journal = {The Review of scientific instruments}, volume = {89}, number = {1}, pages = {015107}, doi = {10.1063/1.4997735}, pmid = {29390714}, issn = {1089-7623}, abstract = {The superfluid phase of helium-4, known as He ii, exhibits extremely small kinematic viscosity and may be a useful tool for economically producing and studying high Reynolds number turbulent flow. Such applications are not currently possible because a comprehensive understanding of the complex two-fluid behavior of He ii is lacking. This situation could be remedied by a systematic investigation of simple, well controlled turbulence that can be directly compared with theoretical models. To this end, we have developed a new apparatus that combines flow visualization with second sound attenuation to study turbulence in the wake of a mesh grid towed through a He ii filled channel. One of three mesh grids (mesh number M = 3, 3.75, or 5 mm) can be pulled at speeds between 0.1 and 60 cm/s through a cast acrylic flow channel which has a 16 mm × 16 mm cross section and measures 330 mm long. The motion of solidified deuterium tracer particles, with diameter of the order 1 μm, in the resulting flow is captured by a high speed camera, and a particle tracking velocimetry algorithm resolves the Lagrangian particle trajectories through the turbulent flow field. A pair of oscillating superleak second sound transducers installed in the channel allows complementary measurement of vortex line density in the superfluid throughout the turbulent decay process. Success in early experiments demonstrates the effectiveness of both probes, and preliminary analysis of the data shows that both measurements strongly correlate with each other. Further investigations will provide comprehensive information that can be used to address open questions about turbulence in He ii and move toward the application of this fluid to high Reynolds number fluid research.}, } @article {pmid29390681, year = {2018}, author = {Sajjadi, S and Buelna, X and Eloranta, J}, title = {Application of time-resolved shadowgraph imaging and computer analysis to study micrometer-scale response of superfluid helium.}, journal = {The Review of scientific instruments}, volume = {89}, number = {1}, pages = {013102}, doi = {10.1063/1.5002564}, pmid = {29390681}, issn = {1089-7623}, abstract = {Application of inexpensive light emitting diodes as backlight sources for time-resolved shadowgraph imaging is demonstrated. The two light sources tested are able to produce light pulse sequences in the nanosecond and microsecond time regimes. After determining their time response characteristics, the diodes were applied to study the gas bubble formation around laser-heated copper nanoparticles in superfluid helium at 1.7 K and to determine the local cavitation bubble dynamics around fast moving metal micro-particles in the liquid. A convolutional neural network algorithm for analyzing the shadowgraph images by a computer is presented and the method is validated against the results from manual image analysis. The second application employed the red-green-blue light emitting diode source that produces light pulse sequences of the individual colors such that three separate shadowgraph frames can be recorded onto the color pixels of a charge-coupled device camera. Such an image sequence can be used to determine the moving object geometry, local velocity, and acceleration/deceleration. These data can be used to calculate, for example, the instantaneous Reynolds number for the liquid flow around the particle. Although specifically demonstrated for superfluid helium, the technique can be used to study the dynamic response of any medium that exhibits spatial variations in the index of refraction.}, } @article {pmid29388556, year = {2018}, author = {Lynch, M and Mandadzhiev, B and Wissa, A}, title = {Bioinspired wingtip devices: a pathway to improve aerodynamic performance during low Reynolds number flight.}, journal = {Bioinspiration & biomimetics}, volume = {13}, number = {3}, pages = {036003}, doi = {10.1088/1748-3190/aaac53}, pmid = {29388556}, issn = {1748-3190}, mesh = {Animals ; Biomechanical Phenomena ; Biomimetic Materials ; *Biomimetics ; Computer Simulation ; Feathers/anatomy & histology/physiology ; Flight, Animal/*physiology ; Hawks/anatomy & histology/physiology ; Models, Anatomic ; *Models, Biological ; Wings, Animal/anatomy & histology/*physiology ; }, abstract = {Birds are highly capable and maneuverable fliers, traits not currently shared with current small unmanned aerial vehicles. They are able to achieve these flight capabilities by adapting the shape of their wings during flight in a variety of complex manners. One feature of bird wings, the primary feathers, separate to form wingtip gaps at the distal end of the wing. This paper presents bio-inspired wingtip devices with varying wingtip gap sizes, defined as the chordwise distance between wingtip devices, for operation in low Reynolds number conditions of Re = 100 000, where many bird species operate. Lift and drag data was measured for planar and nonplanar wingtip devices with the total wingtip gap size ranging from 0% to 40% of the wing's mean chord. For a planar wing with a gap size of 20%, the mean coefficient of lift in the pre-stall region is increased by 7.25%, and the maximum coefficient of lift is increased by 5.6% compared to a configuration with no gaps. The nonplanar wingtip device was shown to reduce the induced drag. The effect of wingtip gap sizes is shown to be independent of the planarity/nonplanarity of the wingtip device, thereby allowing designers to decouple the wingtip parameters to tune the desired lift and drag produced.}, } @article {pmid29377529, year = {2018}, author = {Lee, J and Burns, MA}, title = {One-Way Particle Transport Using Oscillatory Flow in Asymmetric Traps.}, journal = {Small (Weinheim an der Bergstrasse, Germany)}, volume = {14}, number = {9}, pages = {}, pmid = {29377529}, issn = {1613-6829}, support = {R01 HG004653/HG/NHGRI NIH HHS/United States ; R21 HG005077/HG/NHGRI NIH HHS/United States ; }, mesh = {Lab-On-A-Chip Devices ; Microfluidic Analytical Techniques/*methods ; Particle Size ; }, abstract = {One challenge of integrating of passive, microparticles manipulation techniques into multifunctional microfluidic devices is coupling the continuous-flow format of most systems with the often batch-type operation of particle separation systems. Here, a passive fluidic technique-one-way particle transport-that can conduct microparticle operations in a closed fluidic circuit is presented. Exploiting pass/capture interactions between microparticles and asymmetric traps, this technique accomplishes a net displacement of particles in an oscillatory flow field. One-way particle transport is achieved through four kinds of trap-particle interactions: mechanical capture of the particle, asymmetric interactions between the trap and the particle, physical collision of the particle with an obstacle, and lateral shift of the particle into a particle-trapping stream. The critical dimensions for those four conditions are found by numerically solving analytical mass balance equations formulated using the characteristics of the flow field in periodic obstacle arrays. Visual observation of experimental trap-particle dynamics in low Reynolds number flow (<0.01) confirms the validity of the theoretical predictions. This technique can transport hundreds of microparticles across trap rows in only a few fluid oscillations (<500 ms per oscillation) and separate particles by their size differences.}, } @article {pmid29376688, year = {2018}, author = {Berera, A and Ho, RDJG}, title = {Chaotic Properties of a Turbulent Isotropic Fluid.}, journal = {Physical review letters}, volume = {120}, number = {2}, pages = {024101}, doi = {10.1103/PhysRevLett.120.024101}, pmid = {29376688}, issn = {1079-7114}, abstract = {By tracking the divergence of two initially close trajectories in phase space in an Eulerian approach to forced turbulence, the relation between the maximal Lyapunov exponent λ and the Reynolds number Re is measured using direct numerical simulations, performed on up to 2048^{3} collocation points. The Lyapunov exponent is found to solely depend on the Reynolds number with λ∝Re^{0.53} and that after a transient period the divergence of trajectories grows at the same rate at all scales. Finally a linear divergence is seen that is dependent on the energy forcing rate. Links are made with other chaotic systems.}, } @article {pmid29376342, year = {2018}, author = {Lee, D and Nam, SM and Kim, JA and Di Carlo, D and Lee, W}, title = {Active Control of Inertial Focusing Positions and Particle Separations Enabled by Velocity Profile Tuning with Coflow Systems.}, journal = {Analytical chemistry}, volume = {90}, number = {4}, pages = {2902-2911}, doi = {10.1021/acs.analchem.7b05143}, pmid = {29376342}, issn = {1520-6882}, abstract = {Inertial microfluidics has drawn much attention not only for its diverse applications but also for counterintuitive new fluid dynamic behaviors. Inertial focusing positions are determined by two lift forces, that is, shear gradient and wall-induced lift forces, that are generally known to be opposite in direction in the flow through a channel. However, the direction of shear gradient lift force can be reversed if velocity profiles are shaped properly. We used coflows of two liquids with different viscosities to produce complex velocity profiles that lead to inflection point focusing and alteration of inertial focusing positions; the number and the locations of focusing positions could be actively controlled by tuning flow rates and viscosities of the liquids. Interestingly, 3-inlet coflow systems showed focusing mode switching between inflection point focusing and channel face focusing depending on Reynolds number and particle size. The focusing mode switching occurred at a specific size threshold, which was easily adjustable with the viscosity ratio of the coflows. This property led to different-sized particles focusing at completely different focusing positions and resulted in highly efficient particle separation of which the separation threshold was tunable. Passive separation techniques, including inertial microfluidics, generally have a limitation in the control of separation parameters. Coflow systems can provide a simple and versatile platform for active tuning of velocity profiles and subsequent inertial focusing characteristics, which was demonstrated by active control of the focusing mode using viscosity ratio tuning and temperature changes of the coflows.}, } @article {pmid29372888, year = {2018}, author = {Fu, J and Liu, X and Shyy, W and Qiu, H}, title = {Effects of flexibility and aspect ratio on the aerodynamic performance of flapping wings.}, journal = {Bioinspiration & biomimetics}, volume = {13}, number = {3}, pages = {036001}, doi = {10.1088/1748-3190/aaaac1}, pmid = {29372888}, issn = {1748-3190}, mesh = {Animals ; Biological Mimicry ; Biomechanical Phenomena ; Compliance/physiology ; Computer Simulation ; Flight, Animal/*physiology ; Insecta/anatomy & histology/physiology ; *Models, Biological ; Wings, Animal/anatomy & histology/*physiology ; }, abstract = {In the current study, we experimentally investigated the flexibility effects on the aerodynamic performance of flapping wings and the correlation with aspect ratio at angle of attack α = 45°. The Reynolds number based on the chord length and the wing tip velocity is maintained at Re = 5.3 × 10[3]. Our result for compliant wings with an aspect ratio of 4 shows that wing flexibility can offer improved aerodynamic performance compared to that of a rigid wing. Flexible wings are found to offer higher lift-to-drag ratios; in particular, there is significant reduction in drag with little compromise in lift. The mechanism of the flexibility effects on the aerodynamic performance is addressed by quantifying the aerodynamic lift and drag forces, the transverse displacement on the wings and the flow field around the wings. The regime of the effective stiffness that offers improved aerodynamic performance is quantified in a range of about 0.5-10 and it matches the stiffness of insect wings with similar aspect ratios. Furthermore, we find that the aspect ratio of the wing is the predominant parameter determining the flexibility effects of compliant wings. Compliant wings with an aspect ratio of two do not demonstrate improved performance compared to their rigid counterparts throughout the entire stiffness regime investigated. The correlation between wing flexibility effects and the aspect ratio is supported by the stiffness of real insect wings.}, } @article {pmid29367420, year = {2018}, author = {Bocanegra Evans, H and Hamed, AM and Gorumlu, S and Doosttalab, A and Aksak, B and Chamorro, LP and Castillo, L}, title = {Engineered bio-inspired coating for passive flow control.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {115}, number = {6}, pages = {1210-1214}, pmid = {29367420}, issn = {1091-6490}, abstract = {Flow separation and vortex shedding are some of the most common phenomena experienced by bluff bodies under relative motion with the surrounding medium. They often result in a recirculation bubble in regions with adverse pressure gradient, which typically reduces efficiency in vehicles and increases loading on structures. Here, the ability of an engineered coating to manipulate the large-scale recirculation region was tested in a separated flow at moderate momentum thickness Reynolds number, [Formula: see text] We show that the coating, composed of uniformly distributed cylindrical pillars with diverging tips, successfully reduces the size of, and shifts downstream, the separation bubble. Despite the so-called roughness parameter, [Formula: see text], falling within the hydrodynamic smooth regime, the coating is able to modulate the large-scale recirculating motion. Remarkably, this modulation does not induce noticeable changes in the near-wall turbulence levels. Supported with experimental data and theoretical arguments based on the averaged equations of motion, we suggest that the inherent mechanism responsible for the bubble modulation is essentially unsteady suction and blowing controlled by the increasing cross-section of the tips. The coating can be easily fabricated and installed and works under dry and wet conditions, increasing its potential impact on a diverse range of applications.}, } @article {pmid29347793, year = {2017}, author = {Zhao, Y and Tao, J and Xiong, X}, title = {Instabilities of an annulus flow between rotating cylinders in a helical magnetic field.}, journal = {Physical review. E}, volume = {96}, number = {5-1}, pages = {053101}, doi = {10.1103/PhysRevE.96.053101}, pmid = {29347793}, issn = {2470-0053}, abstract = {The stabilities of an annulus flow between the rotating inner and outer cylinders with an external helical magnetic field are studied by using the quasistatic approximation. It is shown numerically that for the spiral base flow with a zero axial pressure gradient, the helical magnetic field yields a helical traveling wave at a critical Reynolds number. This wave mode is revealed to be the most unstable mode by linear stability analysis. At higher Reynolds numbers, the first wave mode is superposed by a second antisymmetric helical wave mode, which travels with a higher phase velocity than the first mode. When the Reynolds number is increased further, the flow becomes turbulent, but the key features of the flow structure are still dominated by the first and the second wave modes. Furthermore, when a finite axial pressure gradient is applied to guarantee a zero axial flow rate, the annulus flow is found to be more unstable than the case with zero axial pressure gradient.}, } @article {pmid29347758, year = {2017}, author = {Elperin, T and Kleeorin, N and Liberman, M and Lipatnikov, AN and Rogachevskii, I and Yu, R}, title = {Turbulent diffusion of chemically reacting flows: Theory and numerical simulations.}, journal = {Physical review. E}, volume = {96}, number = {5-1}, pages = {053111}, doi = {10.1103/PhysRevE.96.053111}, pmid = {29347758}, issn = {2470-0053}, abstract = {The theory of turbulent diffusion of chemically reacting gaseous admixtures developed previously [T. Elperin et al., Phys. Rev. E 90, 053001 (2014)PLEEE81539-375510.1103/PhysRevE.90.053001] is generalized for large yet finite Reynolds numbers and the dependence of turbulent diffusion coefficient on two parameters, the Reynolds number and Damköhler number (which characterizes a ratio of turbulent and reaction time scales), is obtained. Three-dimensional direct numerical simulations (DNSs) of a finite-thickness reaction wave for the first-order chemical reactions propagating in forced, homogeneous, isotropic, and incompressible turbulence are performed to validate the theoretically predicted effect of chemical reactions on turbulent diffusion. It is shown that the obtained DNS results are in good agreement with the developed theory.}, } @article {pmid29347655, year = {2017}, author = {Plan, ELCVM and Musacchio, S and Vincenzi, D}, title = {Emergence of chaos in a viscous solution of rods.}, journal = {Physical review. E}, volume = {96}, number = {5-1}, pages = {053108}, doi = {10.1103/PhysRevE.96.053108}, pmid = {29347655}, issn = {2470-0053}, abstract = {It is shown that the addition of small amounts of microscopic rods in a viscous fluid at low Reynolds number causes a significant increase of the flow resistance. Numerical simulations of the dynamics of the solution reveal that this phenomenon is associated to a transition from laminar to chaotic flow. Polymer stresses give rise to flow instabilities which, in turn, perturb the alignment of the rods. This coupled dynamics results in the activation of a wide range of scales, which enhances the mixing efficiency of viscous flows.}, } @article {pmid29347433, year = {2017}, author = {Fouxon, I and Ge, Z and Brandt, L and Leshansky, A}, title = {Integral representation of channel flow with interacting particles.}, journal = {Physical review. E}, volume = {96}, number = {6-1}, pages = {063110}, doi = {10.1103/PhysRevE.96.063110}, pmid = {29347433}, issn = {2470-0053}, abstract = {We construct a boundary integral representation for the low-Reynolds-number flow in a channel in the presence of freely suspended particles (or droplets) of arbitrary size and shape. We demonstrate that lubrication theory holds away from the particles at horizontal distances exceeding the channel height and derive a multipole expansion of the flow which is dipolar to the leading approximation. We show that the dipole moment of an arbitrary particle is a weighted integral of the stress and the flow at the particle surface, which can be determined numerically. We introduce the equation of motion that describes hydrodynamic interactions between arbitrary, possibly different, distant particles, with interactions determined by the product of the mobility matrix and the dipole moment. Further, the problem of three identical interacting spheres initially aligned in the streamwise direction is considered and the experimentally observed "pair exchange" phenomenon is derived analytically and confirmed numerically. For nonaligned particles, we demonstrate the formation of a configuration with one particle separating from a stable pair. Our results suggest that in a dilute initially homogenous particulate suspension flowing in a channel the particles will eventually separate into singlets and pairs.}, } @article {pmid29347297, year = {2017}, author = {Hiruta, Y and Toh, S}, title = {Intermittent direction reversals of moving spatially localized turbulence observed in two-dimensional Kolmogorov flow.}, journal = {Physical review. E}, volume = {96}, number = {6-1}, pages = {063112}, doi = {10.1103/PhysRevE.96.063112}, pmid = {29347297}, issn = {2470-0053}, abstract = {We have found that in two-dimensional Kolmogorov flow a spatially localized turbulent state (SLT) exists stably and travels with a constant speed on average switching the moving direction randomly and intermittently for moderate values of the control parameters: Reynolds number and the flow rate. We define the coarse-grained position and velocity of an SLT and separate the motion of the SLT from its internal turbulent dynamics by introducing a co-moving frame. The switching process of an SLT represented by the coarse-grained velocity seems to be a random telegraph signal. Focusing on the asymmetry of the internal turbulence we introduce two coarse-grained variables characterizing the internal dynamics. These quantities follow the switching process reasonably. This suggests that the twin attracting invariant sets each of which corresponds to a one-way traveling SLT are embedded in the attractor of the moving SLT and the connection of the two sets is too complicated to be represented by a few degrees of freedom but the motion of an SLT is correlated with the internal turbulent dynamics.}, } @article {pmid29347290, year = {2017}, author = {Schilling, O and Mueschke, NJ}, title = {Turbulent transport and mixing in transitional Rayleigh-Taylor unstable flow: A priori assessment of gradient-diffusion and similarity modeling.}, journal = {Physical review. E}, volume = {96}, number = {6-1}, pages = {063111}, doi = {10.1103/PhysRevE.96.063111}, pmid = {29347290}, issn = {2470-0053}, abstract = {Data from a 1152×760×1280 direct numerical simulation [N. J. Mueschke and O. Schilling, Phys. Fluids 21, 014106 (2009)PHFLE61070-663110.1063/1.3064120] of a Rayleigh-Taylor mixing layer modeled after a small-Atwood-number water-channel experiment is used to investigate the validity of gradient diffusion and similarity closures a priori. The budgets of the mean flow, turbulent kinetic energy, turbulent kinetic energy dissipation rate, heavy-fluid mass fraction variance, and heavy-fluid mass fraction variance dissipation rate transport equations across the mixing layer were previously analyzed [O. Schilling and N. J. Mueschke, Phys. Fluids 22, 105102 (2010)PHFLE61070-663110.1063/1.3484247] at different evolution times to identify the most important transport and mixing mechanisms. Here a methodology is introduced to systematically estimate model coefficients as a function of time in the closures of the dynamically significant terms in the transport equations by minimizing the L_{2} norm of the difference between the model and correlations constructed using the simulation data. It is shown that gradient-diffusion and similarity closures used for the turbulent kinetic energy K, turbulent kinetic energy dissipation rate ε, heavy-fluid mass fraction variance S, and heavy-fluid mass fraction variance dissipation rate χ equations capture the shape of the exact, unclosed profiles well over the nonlinear and turbulent evolution regimes. Using order-of-magnitude estimates [O. Schilling and N. J. Mueschke, Phys. Fluids 22, 105102 (2010)PHFLE61070-663110.1063/1.3484247] for the terms in the exact transport equations and their closure models, it is shown that several of the standard closures for the turbulent production and dissipation (destruction) must be modified to include Reynolds-number scalings appropriate for Rayleigh-Taylor flow at small to intermediate Reynolds numbers. The late-time, large Reynolds number coefficients are determined to be different from those used in shear flow applications and largely adopted in two-equation Reynolds-averaged Navier-Stokes (RANS) models of Rayleigh-Taylor turbulent mixing. In addition, it is shown that the predictions of the Boussinesq model for the Reynolds stress agree better with the data when additional buoyancy-related terms are included. It is shown that an unsteady RANS paradigm is needed to predict the transitional flow dynamics from early evolution times, analogous to the small Reynolds number modifications in RANS models of wall-bounded flows in which the production-to-dissipation ratio is far from equilibrium. Although the present study is specific to one particular flow and one set of initial conditions, the methodology could be applied to calibrations of other Rayleigh-Taylor flows with different initial conditions (which may give different results during the early-time, transitional flow stages, and perhaps asymptotic stage). The implications of these findings for developing high-fidelity eddy viscosity-based turbulent transport and mixing models of Rayleigh-Taylor turbulence are discussed.}, } @article {pmid29347258, year = {2017}, author = {Adebayo, I and Xie, Z and Che, Z and Matar, OK}, title = {Doubly excited pulse waves on thin liquid films flowing down an inclined plane: An experimental and numerical study.}, journal = {Physical review. E}, volume = {96}, number = {1-1}, pages = {013118}, doi = {10.1103/PhysRevE.96.013118}, pmid = {29347258}, issn = {2470-0053}, abstract = {The interaction patterns between doubly excited pulse waves on thin liquid films flowing down an inclined plane are studied both experimentally and numerically. The effect of varying the film flow rate, interpulse interval, and substrate inclination angle on the pulse interaction patterns is examined. Our results show that different interaction patterns exist for these binary pulses, which include solitary wave behavior, partial or complete pulse coalescence, and pulse noncoalescence. A regime map of these patterns is plotted for each inclination angle examined, parametrized by the film Reynolds number and interpulse interval. Finally, the individual effect of the system parameters mentioned above on the coalescence distance of binary pulses in the "complete pulse coalescence" mode is studied; the results are compared to numerical simulations of the two-dimensional Navier-Stokes equations yielding good agreement.}, } @article {pmid29347222, year = {2017}, author = {Huang, Y and Wang, L and Schmitt, FG and Zheng, X and Jiang, N and Liu, Y}, title = {Extremal-point density of scaling processes: From fractional Brownian motion to turbulence in one dimension.}, journal = {Physical review. E}, volume = {96}, number = {1-1}, pages = {012215}, doi = {10.1103/PhysRevE.96.012215}, pmid = {29347222}, issn = {2470-0053}, abstract = {In recent years several local extrema-based methodologies have been proposed to investigate either the nonlinear or the nonstationary time series for scaling analysis. In the present work, we study systematically the distribution of the local extrema for both synthesized scaling processes and turbulent velocity data from experiments. The results show that for the fractional Brownian motion (fBm) without intermittency correction the measured extremal-point-density (EPD) agrees well with a theoretical prediction. For a multifractal random walk (MRW) with the lognormal statistics, the measured EPD is independent of the intermittency parameter μ, suggesting that the intermittency correction does not change the distribution of extremal points but changes the amplitude. By introducing a coarse-grained operator, the power-law behavior of these scaling processes is then revealed via the measured EPD for different scales. For fBm the scaling exponent ξ(H) is found to be ξ(H)=H, where H is Hurst number, while for MRW ξ(μ) shows a linear relation with the intermittency parameter μ. Such EPD approach is further applied to the turbulent velocity data obtained from a wind tunnel flow experiment with the Taylor scale λ-based Reynolds number Re_{λ} =720, and a turbulent boundary layer with the momentum thickness θ based Reynolds number Re_{θ} =810. A scaling exponent ξ≃0.37 is retrieved for the former case. For the latter one, the measured EPD shows clearly four regimes, which agrees well with the corresponding sublayer structures inside the turbulent boundary layer.}, } @article {pmid29347180, year = {2017}, author = {Saito, S and Abe, Y and Koyama, K}, title = {Lattice Boltzmann modeling and simulation of liquid jet breakup.}, journal = {Physical review. E}, volume = {96}, number = {1-1}, pages = {013317}, doi = {10.1103/PhysRevE.96.013317}, pmid = {29347180}, issn = {2470-0053}, abstract = {A three-dimensional color-fluid lattice Boltzmann model for immiscible two-phase flows is developed in the framework of a three-dimensional 27-velocity (D3Q27) lattice. The collision operator comprises the D3Q27 versions of three suboperators: a multiple-relaxation-time (MRT) collision operator, a generalized Liu-Valocchi-Kang perturbation operator, and a Latva-Kokko-Rothman recoloring operator. A D3Q27 version of an enhanced equilibrium distribution function is also incorporated into this model to improve the Galilean invariance. Three types of numerical tests, namely, a static droplet, an oscillating droplet, and the Rayleigh-Taylor instability, show a good agreement with analytical solutions and numerical simulations. Following these numerical tests, this model is applied to liquid-jet-breakup simulations. The simulation conditions are matched to the conditions of the previous experiments. In this case, numerical stability is maintained throughout the simulation, although the kinematic viscosity for the continuous phase is set as low as 1.8×10^{-4}, in which case the corresponding Reynolds number is 3.4×10^{3} ; the developed lattice Boltzmann model based on the D3Q27 lattice enables us to perform the simulation with parameters directly matched to the experiments. The jet's liquid column transitions from an asymmetrical to an axisymmetrical shape, and entrainment occurs from the side of the jet. The measured time history of the jet's leading-edge position shows a good agreement with the experiments. Finally, the reproducibility of the regime map for liquid-liquid systems is assessed. The present lattice Boltzmann simulations well reproduce the characteristics of predicted regimes, including varicose breakup, sinuous breakup, and atomization.}, } @article {pmid29346972, year = {2017}, author = {Coreixas, C and Wissocq, G and Puigt, G and Boussuge, JF and Sagaut, P}, title = {Recursive regularization step for high-order lattice Boltzmann methods.}, journal = {Physical review. E}, volume = {96}, number = {3-1}, pages = {033306}, doi = {10.1103/PhysRevE.96.033306}, pmid = {29346972}, issn = {2470-0053}, abstract = {A lattice Boltzmann method (LBM) with enhanced stability and accuracy is presented for various Hermite tensor-based lattice structures. The collision operator relies on a regularization step, which is here improved through a recursive computation of nonequilibrium Hermite polynomial coefficients. In addition to the reduced computational cost of this procedure with respect to the standard one, the recursive step allows to considerably enhance the stability and accuracy of the numerical scheme by properly filtering out second- (and higher-) order nonhydrodynamic contributions in under-resolved conditions. This is first shown in the isothermal case where the simulation of the doubly periodic shear layer is performed with a Reynolds number ranging from 10^{4} to 10^{6}, and where a thorough analysis of the case at Re=3×10^{4} is conducted. In the latter, results obtained using both regularization steps are compared against the Bhatnagar-Gross-Krook LBM for standard (D2Q9) and high-order (D2V17 and D2V37) lattice structures, confirming the tremendous increase of stability range of the proposed approach. Further comparisons on thermal and fully compressible flows, using the general extension of this procedure, are then conducted through the numerical simulation of Sod shock tubes with the D2V37 lattice. They confirm the stability increase induced by the recursive approach as compared with the standard one.}, } @article {pmid29346921, year = {2017}, author = {Maleki, M and Martinuzzi, RJ and Herzog, W and Federico, S}, title = {Orthotropic hydraulic permeability of arrays of parallel cylinders.}, journal = {Physical review. E}, volume = {96}, number = {3-1}, pages = {033112}, doi = {10.1103/PhysRevE.96.033112}, pmid = {29346921}, issn = {2470-0053}, abstract = {Approximate analytical methods are presented to calculate the overall orthotropic hydraulic permeability of a flow with low Reynolds number, passing through a bundle of parallel circular cylinders. Two particular distributions are considered: (i) arrays with ordered rectangular lattices and (ii) irregular nonrandom distributions for which the unit cell cross sections are elliptical. The standard unit cell models, originally developed by Happel and Kuwabara for a random distribution of cylinders, are adapted to the case of nonrandom distributions. The drag force on a representative cylinder in a direction perpendicular to its axis is obtained based on the standard unit cell model: the actual unit cell of rectangular or elliptical cross section is replaced with an "equivalent" cylindrical unit cell of diameter equal to the maximum width of the actual unit cell. Using the obtained drag forces and referring back to the original geometry of the unit cell, closed-form approximate expressions for the overall permeabilities in the perpendicular directions are obtained. Numerical comparisons with more sophisticated approaches confirm the good efficiency of the presented approach, especially in the range of low solid volume fraction, i.e., of high porosity. Previous studies have revealed that, for the parallel fluid flow, the variation of permeability with aspect ratio (or in general the lateral arrangement) of parallel cylinders is generally weak. These observations suggest that Happel's model for parallel permeability in a random distribution of cylinders could be a good approximation for parallel permeabilities in nonrandom distributions with the same volume fraction.}, } @article {pmid29346864, year = {2017}, author = {Yu, Z and Lin, Z and Shao, X and Wang, LP}, title = {Effects of particle-fluid density ratio on the interactions between the turbulent channel flow and finite-size particles.}, journal = {Physical review. E}, volume = {96}, number = {3-1}, pages = {033102}, doi = {10.1103/PhysRevE.96.033102}, pmid = {29346864}, issn = {2470-0053}, abstract = {A parallel direct-forcing fictitious domain method is employed to perform fully resolved numerical simulations of turbulent channel flow laden with finite-size particles. The effects of the particle-fluid density ratio on the turbulence modulation in the channel flow are investigated at the friction Reynolds number of 180, the particle volume fraction of 0.84%, and the particle-fluid density ratio ranging from 1 to 104.2. The results show that the variation of the flow drag with the particle-fluid density ratio is not monotonic, with a larger flow drag for the density ratio of 10.42, compared to those of unity and 104.2. A significant drag reduction by the particles is observed for large particle-fluid density ratios during the transient stage, but not at the statistically stationary stage. The intensity of particle velocity fluctuations generally decreases with increasing particle inertia, except that the particle streamwise root-mean-square velocity and streamwise-transverse velocity correlation in the near-wall region are largest at the density ratio of the order of 10. The averaged momentum equations are derived with the spatial averaging theorem and are used to analyze the mechanisms for the effects of the particles on the flow drag. The results indicate that the drag-reduction effect due to the decrease in the fluid Reynolds shear stress is counteracted by the drag-enhancement effect due to the increase in the total particle stress or the interphase drag force for the large particle-inertia case. The sum of the total Reynolds stress and particle inner stress contributions to the flow drag is largest at the density ratio of the order of 10, which is the reason for the largest flow drag at this density ratio. The interphase drag force obtained from the averaged momentum equation (the balance theory) is significantly smaller than (but agrees qualitatively with) that from the empirical drag formula based on the phase-averaged slip velocity for large density ratios. For the neutrally buoyant case, the balance theory predicts a positive interphase force on the particles arising from the negative gradient of the particle inner stress, which cannot be predicted by the drag formula based on the phase-averaged slip velocity. In addition, our results show that both particle collision and particle-turbulence interaction play roles in the formation of the inhomogeneous distribution of the particles at the density ratio of the order of 10.}, } @article {pmid29343852, year = {2018}, author = {Hamilton, JK and Bryan, MT and Gilbert, AD and Ogrin, FY and Myers, TO}, title = {A new class of magnetically actuated pumps and valves for microfluidic applications.}, journal = {Scientific reports}, volume = {8}, number = {1}, pages = {933}, pmid = {29343852}, issn = {2045-2322}, abstract = {We propose a new class of magnetically actuated pumps and valves that could be incorporated into microfluidic chips with no further external connections. The idea is to repurpose ferromagnetic low Reynolds number swimmers as devices capable of generating fluid flow, by restricting the swimmers' translational degrees of freedom. We experimentally investigate the flow structure generated by a pinned swimmer in different scenarios, such as unrestricted flow around it as well as flow generated in straight, cross-shaped, Y-shaped and circular channels. This demonstrates the feasibility of incorporating the device into a channel and its capability of acting as a pump, valve and flow splitter. Different regimes could be selected by tuning the frequency and amplitude of the external magnetic field driving the swimmer, or by changing the channel orientation with respect to the field. This versatility endows the device with varied functionality which, together with the robust remote control and reproducibility, makes it a promising candidate for several applications.}, } @article {pmid29341736, year = {2017}, author = {Yakhot, V and Donzis, D}, title = {Emergence of Multiscaling in a Random-Force Stirred Fluid.}, journal = {Physical review letters}, volume = {119}, number = {4}, pages = {044501}, doi = {10.1103/PhysRevLett.119.044501}, pmid = {29341736}, issn = {1079-7114}, abstract = {We consider the transition to strong turbulence in an infinite fluid stirred by a Gaussian random force. The transition is defined as a first appearance of anomalous scaling of normalized moments of velocity derivatives (dissipation rates) emerging from the low-Reynolds-number Gaussian background. It is shown that, due to multiscaling, strongly intermittent rare events can be quantitatively described in terms of an infinite number of different "Reynolds numbers" reflecting a multitude of anomalous scaling exponents. The theoretically predicted transition disappears at R_{λ} ≤3. The developed theory is in quantitative agreement with the outcome of large-scale numerical simulations.}, } @article {pmid29333202, year = {2017}, author = {Raffiee, AH and Dabiri, S and Ardekani, AM}, title = {Elasto-inertial migration of deformable capsules in a microchannel.}, journal = {Biomicrofluidics}, volume = {11}, number = {6}, pages = {064113}, pmid = {29333202}, issn = {1932-1058}, abstract = {In this paper, we study the dynamics of deformable cells in a channel flow of Newtonian and polymeric fluids and unravel the effects of deformability, elasticity, inertia, and size on the cell motion. We investigate the role of polymeric fluids on the cell migration behavior and the performance of inertial microfluidic devices. Our results show that the equilibrium position of the cell is on the channel diagonal, in contrast to that of rigid particles, which is on the center of the channel faces for the same range of Reynolds number. A constant-viscosity polymeric fluid, modeled using an Oldroyd-B constitutive equation, drives the cells toward the channel centerline, while a shear-thinning polymeric fluid, modeled using a Giesekus constitutive equation, pushes the cells toward the channel wall. The findings of this paper suggest that the addition of polymers in microfluidic devices can be used to enhance the throughput of cell focusing and separation devices at a low cost. This study provides an insight on the role of rheological properties of the fluid and the ways that they can be tuned to control the focal position of the cells.}, } @article {pmid29323150, year = {2018}, author = {Mrokowska, MM}, title = {Stratification-induced reorientation of disk settling through ambient density transition.}, journal = {Scientific reports}, volume = {8}, number = {1}, pages = {412}, pmid = {29323150}, issn = {2045-2322}, abstract = {Settling due to gravity force is a basic transport mechanism of solid particles in fluids in the Earth. A large portion of particles occurring in nature and used in technical applications are non-spherical. Settling of particles is usually studied in homogeneous ambient conditions, however, stratification is inherent of natural fluids. It has been acknowledged that stratification modifies the velocity of settling spheres and amorphous aggregates. However, the effect of particle shape on the dynamics of settling through density-stratified ambient fluid has not been recognized well enough. Here I show experimental evidence that continuous density transition markedly modifies the settling dynamics of a disk in terms of settling velocity and orientation of a particle. Settling dynamics of a disk are more complex than dynamics of spheres and aggregates studied previously. I found that in a two-layer ambient with density transition, a disk settling in a low Reynolds number regime undergoes five phases of settling with the orientation varying from horizontal to vertical, and it may achieve two local minimum settling velocities in the density transition layer. Moreover, I found that the settling dynamics depends on a density difference between upper and lower homogeneous layers, stratification strength and thickness of density transition.}, } @article {pmid29291432, year = {2018}, author = {Ranjit, NK and Shit, GC and Tripathi, D}, title = {Joule heating and zeta potential effects on peristaltic blood flow through porous micro vessels altered by electrohydrodynamic.}, journal = {Microvascular research}, volume = {117}, number = {}, pages = {74-89}, doi = {10.1016/j.mvr.2017.12.004}, pmid = {29291432}, issn = {1095-9319}, mesh = {Blood Flow Velocity ; *Computer Simulation ; *Electromagnetic Fields ; Electroosmosis ; Energy Transfer ; Hot Temperature ; Humans ; Hydrodynamics ; *Microcirculation ; Microvessels/*physiology ; *Models, Cardiovascular ; Porosity ; *Pulsatile Flow ; Regional Blood Flow ; }, abstract = {In most of the medical therapies, electromagnetic field plays important role to modulate the blood flow and to reduce the pain of human body. With this fact, this paper presents a mathematical model to study the peristaltic blood flow through porous microvessels in the presence of electrohydrodynamics. The effects of Joule heating and different zeta potential are also considered. Darcy law is employed for porous medium. The mathematical analysis is carried out in the form of electroosmosis, flow analysis and heat transfer analysis. Velocity slip conditions are imposed to solve momentum equation and thermal energy equation. Time dependent volumetric flow rate is considered which varies exponentially. Closed form solutions for potential function is obtained under Debye-Hückel approximation and velocity and temperature fields are obtained under low Reynolds number and large wavelength approximations. The influence of Hartmann number, electroosmotic parameter, slip parameters, Zeta potential, and couple stress parameter on flow characteristics, pumping characteristics and trapping phenomenon is computed. The effects of thermal slip parameters, Joule heating parameter, and Brinkman number on heat transfer characteristics are also presented graphically. Finally, the effect of Brinkman number on a graph between Nusselt number and Joule heating parameter is examined.}, } @article {pmid29289052, year = {2017}, author = {Hamilton, E and Bruot, N and Cicuta, P}, title = {The chimera state in colloidal phase oscillators with hydrodynamic interaction.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {27}, number = {12}, pages = {123108}, doi = {10.1063/1.4989466}, pmid = {29289052}, issn = {1089-7682}, abstract = {The chimera state is the incongruous situation where coherent and incoherent populations coexist in sets of identical oscillators. Using driven non-linear oscillators interacting purely through hydrodynamic forces at low Reynolds number, previously studied as a simple model of motile cilia supporting waves, we find concurrent incoherent and synchronised subsets in small arrays. The chimeras seen in simulation display a "breathing" aspect, reminiscent of uniformly interacting phase oscillators. In contrast to other systems where chimera has been observed, this system has a well-defined interaction metric, and we know that the emergent dynamics inherit the symmetry of the underlying Oseen tensor eigenmodes. The chimera state can thus be connected to a superposition of eigenstates, whilst considering the mean interaction strength within and across subsystems allows us to make a connection to more generic (and abstract) chimeras in populations of Kuramoto phase oscillators. From this work, we expect the chimera state to emerge in experimental observations of oscillators coupled through hydrodynamic forces.}, } @article {pmid29286796, year = {2017}, author = {Djellouli, A and Marmottant, P and Djeridi, H and Quilliet, C and Coupier, G}, title = {Buckling Instability Causes Inertial Thrust for Spherical Swimmers at All Scales.}, journal = {Physical review letters}, volume = {119}, number = {22}, pages = {224501}, doi = {10.1103/PhysRevLett.119.224501}, pmid = {29286796}, issn = {1079-7114}, abstract = {Microswimmers, and among them aspirant microrobots, generally have to cope with flows where viscous forces are dominant, characterized by a low Reynolds number (Re). This implies constraints on the possible sequences of body motion, which have to be nonreciprocal. Furthermore, the presence of a strong drag limits the range of resulting velocities. Here, we propose a swimming mechanism which uses the buckling instability triggered by pressure waves to propel a spherical, hollow shell. With a macroscopic experimental model, we show that a net displacement is produced at all Re regimes. An optimal displacement caused by nontrivial history effects is reached at intermediate Re. We show that, due to the fast activation induced by the instability, this regime is reachable by microscopic shells. The rapid dynamics would also allow high-frequency excitation with standard traveling ultrasonic waves. Scale considerations predict a swimming velocity of order 1 cm/s for a remote-controlled microrobot, a suitable value for biological applications such as drug delivery.}, } @article {pmid29286719, year = {2017}, author = {Atif, M and Kolluru, PK and Thantanapally, C and Ansumali, S}, title = {Essentially Entropic Lattice Boltzmann Model.}, journal = {Physical review letters}, volume = {119}, number = {24}, pages = {240602}, doi = {10.1103/PhysRevLett.119.240602}, pmid = {29286719}, issn = {1079-7114}, abstract = {The entropic lattice Boltzmann model (ELBM), a discrete space-time kinetic theory for hydrodynamics, ensures nonlinear stability via the discrete time version of the second law of thermodynamics (the H theorem). Compliance with the H theorem is numerically enforced in this methodology and involves a search for the maximal discrete path length corresponding to the zero dissipation state by iteratively solving a nonlinear equation. We demonstrate that an exact solution for the path length can be obtained by assuming a natural criterion of negative entropy change, thereby reducing the problem to solving an inequality. This inequality is solved by creating a new framework for construction of Padé approximants via quadrature on appropriate convex function. This exact solution also resolves the issue of indeterminacy in case of nonexistence of the entropic involution step. Since our formulation is devoid of complex mathematical library functions, the computational cost is drastically reduced. To illustrate this, we have simulated a model setup of flow over the NACA-0012 airfoil at a Reynolds number of 2.88×10^{6} .}, } @article {pmid29271639, year = {2018}, author = {Kim, JA and Lee, JR and Je, TJ and Jeon, EC and Lee, W}, title = {Size-Dependent Inertial Focusing Position Shift and Particle Separations in Triangular Microchannels.}, journal = {Analytical chemistry}, volume = {90}, number = {3}, pages = {1827-1835}, doi = {10.1021/acs.analchem.7b03851}, pmid = {29271639}, issn = {1520-6882}, abstract = {A recent study of inertial microfluidics within nonrectangular cross-section channels showed that the inertial focusing positions changes with cross-sectional shapes; therefore, the cross-sectional shape can be a useful control parameter for microfluidic particle manipulations. Here, we conducted detail investigation on unique focusing position shift phenomena, which occurs strongly in channels with the cross-sectional shape of the isosceles right triangle. The top focusing positions shift along the channel walls to the direction away from the apex with increasing Reynolds number and decreasing particle size. A larger particle with its center further away from the side walls experiences shear gradient lift toward the apex, which leads to an opposite result with changes of Reynolds and particle size. The focusing position shift and the subsequent stabilization of corner focusing lead to changes in the number of focusing positions, which enables a novel method for microparticle separations with high efficiency (>95%) and resolution (<2 μm). The separation method based on equilibrium focusing; therefore, the operation is simple and no complex separation optimization is needed. Moreover, the separation threshold can be easily modulated with flow rate adjustment. Rare cell separation from blood cell was successfully demonstrated with spiked MCF-7 cells in blood by achieving the yield of ∼95% and the throughput of ∼10[6] cells/min.}, } @article {pmid29264667, year = {2018}, author = {Oakes, JM and Roth, SC and Shadden, SC}, title = {Airflow Simulations in Infant, Child, and Adult Pulmonary Conducting Airways.}, journal = {Annals of biomedical engineering}, volume = {46}, number = {3}, pages = {498-512}, doi = {10.1007/s10439-017-1971-9}, pmid = {29264667}, issn = {1573-9686}, mesh = {Adolescent ; Adult ; Aging/*physiology ; Child ; Child, Preschool ; Female ; Humans ; Infant ; Infant, Newborn ; Lung/anatomy & histology/*physiology ; Male ; *Models, Biological ; Pulmonary Ventilation/*physiology ; Respiratory Mechanics/*physiology ; Trachea/anatomy & histology/*physiology ; }, abstract = {The airway structure continuously evolves from birth to adulthood, influencing airflow dynamics and respiratory mechanics. We currently know very little about how airflow patterns change throughout early life and its impact on airway resistance, namely because of experimental limitations. To uncover differences in respiratory dynamics between age groups, we performed subject-specific airflow simulations in an infant, child, and adult conducting airways. Airflow throughout the respiration cycle was calculated by coupling image-based models of the conducting airways to the global respiratory mechanics, where flow was driven by a pressure differential. Trachea diameter was 19, 9, and 4.5 mm for the adult (36 years, female), child (6 years, male), and infant (0.25 years, female), respectively. Mean Reynolds number within the trachea was nearly the same for each subject (1100) and Womersley number was above unity for all three subjects and largest for the adult, highlighting the significance of transient effects. In general, air speeds and airway resistances within the conducting airways were inversely correlated with age; the 3D pressure drop was highest in the infant model. These simulations provide new insight into age-dependent flow dynamics throughout the respiration cycle within subject-specific airways.}, } @article {pmid29258534, year = {2017}, author = {Sass, LR and Khani, M and Natividad, GC and Tubbs, RS and Baledent, O and Martin, BA}, title = {A 3D subject-specific model of the spinal subarachnoid space with anatomically realistic ventral and dorsal spinal cord nerve rootlets.}, journal = {Fluids and barriers of the CNS}, volume = {14}, number = {1}, pages = {36}, pmid = {29258534}, issn = {2045-8118}, support = {P20 GM103408/GM/NIGMS NIH HHS/United States ; R44 MH112210/MH/NIMH NIH HHS/United States ; U54 GM104944/GM/NIGMS NIH HHS/United States ; }, mesh = {Adult ; Female ; Humans ; Imaging, Three-Dimensional ; Magnetic Resonance Imaging ; *Models, Anatomic ; *Models, Neurological ; Spinal Cord/*anatomy & histology/diagnostic imaging ; Spinal Nerve Roots/*anatomy & histology/diagnostic imaging ; Subarachnoid Space/*anatomy & histology/diagnostic imaging ; Young Adult ; }, abstract = {BACKGROUND: The spinal subarachnoid space (SSS) has a complex 3D fluid-filled geometry with multiple levels of anatomic complexity, the most salient features being the spinal cord and dorsal and ventral nerve rootlets. An accurate anthropomorphic representation of these features is needed for development of in vitro and numerical models of cerebrospinal fluid (CSF) dynamics that can be used to inform and optimize CSF-based therapeutics.

METHODS: A subject-specific 3D model of the SSS was constructed based on high-resolution anatomic MRI. An expert operator completed manual segmentation of the CSF space with detailed consideration of the anatomy. 31 pairs of semi-idealized dorsal and ventral nerve rootlets (NR) were added to the model based on anatomic reference to the magnetic resonance (MR) imaging and cadaveric measurements in the literature. Key design criteria for each NR pair included the radicular line, descending angle, number of NR, attachment location along the spinal cord and exit through the dura mater. Model simplification and smoothing was performed to produce a final model with minimum vertices while maintaining minimum error between the original segmentation and final design. Final model geometry and hydrodynamics were characterized in terms of axial distribution of Reynolds number, Womersley number, hydraulic diameter, cross-sectional area and perimeter.

RESULTS: The final model had a total of 139,901 vertices with a total CSF volume within the SSS of 97.3 cm[3]. Volume of the dura mater, spinal cord and NR was 123.1, 19.9 and 5.8 cm[3]. Surface area of these features was 318.52, 112.2 and 232.1 cm[2] respectively. Maximum Reynolds number was 174.9 and average Womersley number was 9.6, likely indicating presence of a laminar inertia-dominated oscillatory CSF flow field.

CONCLUSIONS: This study details an anatomically realistic anthropomorphic 3D model of the SSS based on high-resolution MR imaging of a healthy human adult female. The model is provided for re-use under the Creative Commons Attribution-ShareAlike 4.0 International license (CC BY-SA 4.0) and can be used as a tool for development of in vitro and numerical models of CSF dynamics for design and optimization of intrathecal therapeutics.}, } @article {pmid29244030, year = {2018}, author = {Shidhore, TC and Christov, IC}, title = {Static response of deformable microchannels: a comparative modelling study.}, journal = {Journal of physics. Condensed matter : an Institute of Physics journal}, volume = {30}, number = {5}, pages = {054002}, doi = {10.1088/1361-648X/aaa226}, pmid = {29244030}, issn = {1361-648X}, abstract = {We present a comparative modelling study of fluid-structure interactions in microchannels. Through a mathematical analysis based on plate theory and the lubrication approximation for low-Reynolds-number flow, we derive models for the flow rate-pressure drop relation for long shallow microchannels with both thin and thick deformable top walls. These relations are tested against full three-dimensional two-way-coupled fluid-structure interaction simulations. Three types of microchannels, representing different elasticity regimes and having been experimentally characterized previously, are chosen as benchmarks for our theory and simulations. Good agreement is found in most cases for the predicted, simulated and measured flow rate-pressure drop relationships. The numerical simulations performed allow us to also carefully examine the deformation profile of the top wall of the microchannel in any cross section, showing good agreement with the theory. Specifically, the prediction that span-wise displacement in a long shallow microchannel decouples from the flow-wise deformation is confirmed, and the predicted scaling of the maximum displacement with the hydrodynamic pressure and the various material and geometric parameters is validated.}, } @article {pmid29239446, year = {2018}, author = {Denn, MM and Morris, JF and Bonn, D}, title = {Shear thickening in concentrated suspensions of smooth spheres in Newtonian suspending fluids.}, journal = {Soft matter}, volume = {14}, number = {2}, pages = {170-184}, doi = {10.1039/c7sm00761b}, pmid = {29239446}, issn = {1744-6848}, abstract = {Shear thickening is a phenomenon in which the viscosity of a suspension increases with increasing stress or shear rate, sometimes in a discontinuous fashion. While the phenomenon, when observed in suspensions of corn starch in water, or Oobleck, is popular as a science experiment for children, shear thickening is actually of considerable importance for technological applications and exhibited by far simpler systems. Concentrated suspensions of smooth hard spheres will exhibit shear thickening, and understanding this behavior has required a fundamental change in the paradigm of describing low-Reynolds-number solid-fluid flows, in which contact forces have traditionally been absent. Here, we provide an overview of our understanding of shear thickening and the methods that have been developed to describe it, as well as outstanding questions.}, } @article {pmid29219534, year = {2017}, author = {Reeves, MT and Billam, TP and Yu, X and Bradley, AS}, title = {Enstrophy Cascade in Decaying Two-Dimensional Quantum Turbulence.}, journal = {Physical review letters}, volume = {119}, number = {18}, pages = {184502}, doi = {10.1103/PhysRevLett.119.184502}, pmid = {29219534}, issn = {1079-7114}, abstract = {We report evidence for an enstrophy cascade in large-scale point-vortex simulations of decaying two-dimensional quantum turbulence. Devising a method to generate quantum vortex configurations with kinetic energy narrowly localized near a single length scale, the dynamics are found to be well characterized by a superfluid Reynolds number Re_{s} that depends only on the number of vortices and the initial kinetic energy scale. Under free evolution the vortices exhibit features of a classical enstrophy cascade, including a k^{-3} power-law kinetic energy spectrum, and constant enstrophy flux associated with inertial transport to small scales. Clear signatures of the cascade emerge for N≳500 vortices. Simulating up to very large Reynolds numbers (N=32 768 vortices), additional features of the classical theory are observed: the Kraichnan-Batchelor constant is found to converge to C^{'} ≈1.6, and the width of the k^{-3} range scales as Re_{s} ^{1/2} .}, } @article {pmid29219520, year = {2017}, author = {Matsunaga, D and Meng, F and Zöttl, A and Golestanian, R and Yeomans, JM}, title = {Focusing and Sorting of Ellipsoidal Magnetic Particles in Microchannels.}, journal = {Physical review letters}, volume = {119}, number = {19}, pages = {198002}, doi = {10.1103/PhysRevLett.119.198002}, pmid = {29219520}, issn = {1079-7114}, abstract = {We present a simple method to control the position of ellipsoidal magnetic particles in microchannel Poiseuille flow at low Reynolds number using a static uniform magnetic field. The magnetic field is utilized to pin the particle orientation, and the hydrodynamic interactions between ellipsoids and channel walls allow control of the transverse position of the particles. We employ a far-field hydrodynamic theory and simulations using the boundary element method and Brownian dynamics to show how magnetic particles can be focused and segregated by size and shape. This is of importance for particle manipulation in lab-on-a-chip devices.}, } @article {pmid29201603, year = {2017}, author = {Wang, Q and Yang, L and Yu, J and Zhang, L}, title = {Characterizing dynamic behaviors of three-particle paramagnetic microswimmer near a solid surface.}, journal = {Robotics and biomimetics}, volume = {4}, number = {1}, pages = {20}, pmid = {29201603}, issn = {2197-3768}, abstract = {Particle-based magnetically actuated microswimmers have the potential to act as microrobotic tools for biomedical applications. In this paper, we report the dynamic behaviors of a three-particle paramagnetic microswimmer. Actuated by a rotating magnetic field with different frequencies, the microswimmer exhibits simple rotation and propulsion. When the input frequency is below 8 Hz, it exhibits simple rotation on the substrate, whereas it shows propulsion with varied poses when subjected to a frequency between 8 and 15 Hz. Furthermore, a solid surface that enhances swimming velocity was observed as the microswimmer is actuated near a solid surface. Our simulation results testify that the surface-enhanced swimming near a solid surface is because of the induced pressure difference in the surrounding fluid of the microagent.}, } @article {pmid29195661, year = {2018}, author = {Tarafder, A}, title = {A study on the onset of turbulent conditions with supercritical fluid chromatography mobile-phases.}, journal = {Journal of chromatography. A}, volume = {1532}, number = {}, pages = {182-190}, doi = {10.1016/j.chroma.2017.11.056}, pmid = {29195661}, issn = {1873-3778}, mesh = {Carbon Dioxide/chemistry ; Chromatography, Supercritical Fluid/*methods ; Pressure ; *Rheology ; Solvents/*chemistry ; Temperature ; Viscosity ; }, abstract = {Following a recent publication [1], the topic of turbulent flow in SFC has generated both interest and questions. Liquid-like density, coupled with significantly low viscosity of CO2-based mobile-phases may result in high Reynolds number (Re) - higher than what represents laminar flow conditions, reaching the so-called turbulent regions. Although such turbulent flows can form only in the connecting tubings, thus not directly affecting the chromatographic process, it is important to know under many situations, whether the flow inside the tubing is laminar or turbulent. In this report a comprehensive guideline to identify the possibilities of turbulent flow conditions is provided through a series of charts. Flow properties depend on state conditions (composition, pressure and temperature) and also on the tubing material and geometry. Here guidelines to detect the onset of turbulent conditions is provided for cylindrical stainless-steel tubings of different internal diameters (i.d.) under a wide range of SFC mobile-phase conditions.}, } @article {pmid29195464, year = {2017}, author = {Zhao, S and Cheng, E and Qiu, X and Burnett, I and Liu, JC}, title = {Wind noise spectra in small Reynolds number turbulent flows.}, journal = {The Journal of the Acoustical Society of America}, volume = {142}, number = {5}, pages = {3227}, doi = {10.1121/1.5012740}, pmid = {29195464}, issn = {1520-8524}, abstract = {Wind noise spectra caused by wind from fans in indoor environments have been found to be different from those measured in outdoor atmospheric conditions. Although many models have been developed to predict outdoor wind noise spectra under the assumption of large Reynolds number [Zhao, Cheng, Qiu, Burnett, and Liu (2016). J. Acoust. Soc. Am. 140, 4178-4182, and the references therein], they cannot be applied directly to the indoor situations because the Reynolds number of wind from fans in indoor environments is usually much smaller than that experienced in atmospheric turbulence. This paper proposes a pressure structure function model that combines the energy-containing and dissipation ranges so that the pressure spectrum for small Reynolds number turbulent flows can be calculated. The proposed pressure structure function model is validated with the experimental results in the literature, and then the obtained pressure spectrum is verified with the numerical simulation and experiment results. It is demonstrated that the pressure spectrum obtained from the proposed pressure structure function model can be utilized to estimate wind noise spectra caused by turbulent flows with small Reynolds numbers.}, } @article {pmid29183943, year = {2017}, author = {Boselli, F and Steed, E and Freund, JB and Vermot, J}, title = {Anisotropic shear stress patterns predict the orientation of convergent tissue movements in the embryonic heart.}, journal = {Development (Cambridge, England)}, volume = {144}, number = {23}, pages = {4322-4327}, pmid = {29183943}, issn = {1477-9129}, mesh = {Animals ; Anisotropy ; Biomechanical Phenomena ; Endocardial Cushions/cytology/embryology ; Endothelial Cells/cytology/physiology ; Erythrocytes/physiology ; Heart/*embryology ; Hemodynamics ; Hydrodynamics ; Imaging, Three-Dimensional ; *Models, Cardiovascular ; Organogenesis/physiology ; Shear Strength ; Stress, Mechanical ; Zebrafish/*embryology ; }, abstract = {Myocardial contractility and blood flow provide essential mechanical cues for the morphogenesis of the heart. In general, endothelial cells change their migratory behavior in response to shear stress patterns, according to flow directionality. Here, we assessed the impact of shear stress patterns and flow directionality on the behavior of endocardial cells, the specialized endothelial cells of the heart. At the early stages of zebrafish heart valve formation, we show that endocardial cells are converging to the valve-forming area and that this behavior depends upon mechanical forces. Quantitative live imaging and mathematical modeling allow us to correlate this tissue convergence with the underlying flow forces. We predict that tissue convergence is associated with the direction of the mean wall shear stress and of the gradient of harmonic phase-averaged shear stresses, which surprisingly do not match the overall direction of the flow. This contrasts with the usual role of flow directionality in vascular development and suggests that the full spatial and temporal complexity of the wall shear stress should be taken into account when studying endothelial cell responses to flow in vivo.}, } @article {pmid29181289, year = {2017}, author = {Li, K and Jing, D and Hu, J and Ding, X and Yao, Z}, title = {Numerical investigation of the tribological performance of micro-dimple textured surfaces under hydrodynamic lubrication.}, journal = {Beilstein journal of nanotechnology}, volume = {8}, number = {}, pages = {2324-2338}, pmid = {29181289}, issn = {2190-4286}, abstract = {Surface texturing is an important approach for controlling the tribological behavior of friction pairs used in mechanical and biological engineering. In this study, by utilizing the method of three-dimensional computational fluid dynamics (CFD) simulation, the lubrication model of a friction pair with micro-dimple array was established based on the Navier-Stokes equations. The typical pressure distribution of the lubricant film was analyzed. It was found that a positive hydrodynamic pressure is generated in the convergent part of the micro-dimple, while a negative hydrodynamic pressure is generated in the divergent part. With suitable parameters, the total integration of the pressure is positive, which can increase the load-carrying capacity of a friction pair. The effects of the micro-dimple parameters as well as fluid properties on tribological performance were investigated. It was concluded that under the condition of hydrodynamic lubrication, the main mechanism for the improvement in the tribological performance is the combined effects of wedging and recirculation. Within the range of parameters investigated in this study, the optimum texture density is 13%, while the optimum aspect ratio varies with the Reynolds number. For a given Reynolds number, there exists a combination of texture density and aspect ratio at which the optimum tribological performance could be obtained. Conclusions from this study could be helpful for the design of texture parameters in mechanical friction components and even in artificial joints.}, } @article {pmid29178057, year = {2017}, author = {Goldobin, DS}, title = {Existence of the passage to the limit of an inviscid fluid.}, journal = {The European physical journal. E, Soft matter}, volume = {40}, number = {11}, pages = {103}, doi = {10.1140/epje/i2017-11594-4}, pmid = {29178057}, issn = {1292-895X}, mesh = {Computer Simulation ; *Hydrodynamics ; *Viscosity ; }, abstract = {In the dynamics of a viscous fluid, the case of vanishing kinematic viscosity is actually equivalent to the Reynolds number tending to infinity. Hence, in the limit of vanishing viscosity the fluid flow is essentially turbulent. On the other hand, the Euler equation, which is conventionally adopted for the description of the flow of an inviscid fluid, does not possess proper turbulent behaviour. This raises the question of the existence of the passage to the limit of an inviscid fluid for real low-viscosity fluids. To address this question, one should employ the theory of turbulent boundary layer near an inflexible boundary (e.g., rigid wall). On the basis of this theory, one can see how the solutions to the Euler equation become relevant for the description of the flow of low-viscosity fluids, and obtain the small parameter quantifying accuracy of this description for real fluids.}, } @article {pmid29167371, year = {2017}, author = {De Canio, G and Lauga, E and Goldstein, RE}, title = {Spontaneous oscillations of elastic filaments induced by molecular motors.}, journal = {Journal of the Royal Society, Interface}, volume = {14}, number = {136}, pages = {}, pmid = {29167371}, issn = {1742-5662}, mesh = {Actin Cytoskeleton/*chemistry/physiology ; Biomechanical Phenomena ; *Models, Biological ; Molecular Motor Proteins/*physiology ; }, abstract = {It is known from the wave-like motion of microtubules in motility assays that the piconewton forces that motors produce can be sufficient to bend the filaments. In cellular phenomena such as cytosplasmic streaming, molecular motors translocate along cytoskeletal filaments, carrying cargo which entrains fluid. When large numbers of such forced filaments interact through the surrounding fluid, as in particular stages of oocyte development in Drosophila melanogaster, complex dynamics are observed, but the detailed mechanics underlying them has remained unclear. Motivated by these observations, we study here perhaps the simplest model for these phenomena: an elastic filament, pinned at one end, acted on by a molecular motor treated as a point force. Because the force acts tangential to the filament, no matter what its shape, this 'follower-force' problem is intrinsically non-variational, and thereby differs fundamentally from Euler buckling, where the force has a fixed direction, and which, in the low-Reynolds-number regime, ultimately leads to a stationary, energy-minimizing shape. Through a combination of linear stability theory, analytical study of a solvable simplified 'two-link' model and numerical studies of the full elastohydrodynamic equations of motion, we elucidate the Hopf bifurcation that occurs with increasing forcing of a filament, leading to flapping motion analogous to the high-Reynolds-number oscillations of a garden hose with a free end.}, } @article {pmid29144304, year = {2017}, author = {Wang, Z and Dong, W and Hu, X and Sun, T and Wang, T and Sun, Y}, title = {Low energy consumption vortex wave flow membrane bioreactor.}, journal = {Water science and technology : a journal of the International Association on Water Pollution Research}, volume = {76}, number = {9-10}, pages = {2465-2472}, doi = {10.2166/wst.2017.400}, pmid = {29144304}, issn = {0273-1223}, mesh = {Bioreactors ; Membranes, Artificial ; Waste Water/*chemistry ; Water Pollutants, Chemical/chemistry ; Water Purification/instrumentation/*methods ; }, abstract = {In order to reduce the energy consumption and membrane fouling of the conventional membrane bioreactor (MBR), a kind of low energy consumption vortex wave flow MBR was exploited based on the combination of biofilm process and membrane filtration process, as well as the vortex wave flow technique. The experimental results showed that the vortex wave flow state in the membrane module could be formed when the Reynolds number (Re) of liquid was adjusted between 450 and 1,050, and the membrane flux declined more slowly in the vortex wave flow state than those in the laminar flow state and turbulent flow state. The MBR system was used to treat domestic wastewater under the condition of vortex wave flow state for 30 days. The results showed that the removal efficiency for CODcr and NH3-N was 82% and 98% respectively, and the permeate quality met the requirement of 'Water quality standard for urban miscellaneous water consumption (GB/T 18920-2002)'. Analysis of the energy consumption of the MBR showed that the average energy consumption was 1.90 ± 0.55 kWh/m[3] (permeate), which was only two thirds of conventional MBR energy consumption.}, } @article {pmid29131890, year = {2018}, author = {Gamage, PPT and Khalili, F and Khurshidul Azad, MD and Mansy, HA}, title = {Modeling Inspiratory Flow in a Porcine Lung Airway.}, journal = {Journal of biomechanical engineering}, volume = {140}, number = {6}, pages = {0610031-06100311}, pmid = {29131890}, issn = {1528-8951}, support = {R01 EB012142/EB/NIBIB NIH HHS/United States ; R43 HL099053/HL/NHLBI NIH HHS/United States ; }, mesh = {Animals ; Biomechanical Phenomena ; Bronchi/physiology ; Humans ; *Inhalation ; Lung/*physiology ; *Models, Biological ; Pressure ; Swine ; Trachea/physiology ; }, abstract = {Inspiratory flow in a multigeneration pig lung airways was numerically studied at a steady inlet flow rate of 3.2 × 10-4 m3/s corresponding to a Reynolds number of 1150 in the trachea. The model was validated by comparing velocity distributions with previous measurements and simulations in simplified airway geometries. Simulation results provided detailed maps of the axial and secondary flow patterns at different cross sections of the airway tree. The vortex core regions in the airways were visualized using absolute helicity values and suggested the presence of secondary flow vortices where two counter-rotating vortices were observed at the main bifurcation and in many other bifurcations. Both laminar and turbulent flows were considered. Results showed that axial and secondary flows were comparable in the laminar and turbulent cases. Turbulent kinetic energy (TKE) vanished in the more distal airways, which indicates that the flow in these airways approaches laminar flow conditions. The simulation results suggested viscous pressure drop values comparable to earlier studies. The monopodial asymmetric nature of airway branching in pigs resulted in airflow patterns that are different from the less asymmetric human airways. The major daughters of the pig airways tended to have high airflow ratios, which may lead to different particle distribution and sound generation patterns. These differences need to be taken into consideration when interpreting the results of animal studies involving pigs before generalizing these results to humans.}, } @article {pmid29128680, year = {2018}, author = {Han, X and Fang, H and He, G and Reible, D}, title = {Effects of roughness and permeability on solute transfer at the sediment water interface.}, journal = {Water research}, volume = {129}, number = {}, pages = {39-50}, doi = {10.1016/j.watres.2017.10.049}, pmid = {29128680}, issn = {1879-2448}, mesh = {Computer Simulation ; Friction ; *Geologic Sediments ; Models, Theoretical ; Permeability ; Solutions ; Water ; *Water Movements ; }, abstract = {Understanding the mechanisms of solute transfer across the sediment-water interface plays a crucial role in water quality prediction and management. In this study, different arranged particles are used to form typical rough and permeable beds. Large Eddy Simulation (LES) is used to model the solute transfer from the overlying water to sediment beds. Three rough wall turbulence regimes, i.e., smooth, transitional and rough regime, are separately considered and the effects of bed roughness on solute transfer are quantitatively analyzed. Results show that the classic laws related to Schmidt numbers can well reflect the solute transfer under the smooth regime with small roughness Reynolds numbers. Under the transitional regime, the solute transfer coefficient (KL[+]) is enhanced and the effect of Schmidt number is weakened by increasing roughness Reynolds number. Under the rough regime, the solute transfer is suppressed by the transition layer (Brinkman layer) and controlled by the bed permeability. Moreover, it is found that water depth, friction velocity and bed permeability can be used to estimate the solute transfer velocity (KL) under the completely rough regime.}, } @article {pmid29117039, year = {2018}, author = {Korakianitis, T and Rezaienia, MA and Paul, G and Avital, E and Rothman, M and Mozafari, S}, title = {Optimization of Axial Pump Characteristic Dimensions and Induced Hemolysis for Mechanical Circulatory Support Devices.}, journal = {ASAIO journal (American Society for Artificial Internal Organs : 1992)}, volume = {64}, number = {6}, pages = {727-734}, pmid = {29117039}, issn = {1538-943X}, support = {II-LB-1111-20007/DH_/Department of Health/United Kingdom ; }, mesh = {*Computer Simulation ; *Equipment Design ; *Heart-Assist Devices ; Hemolysis ; Humans ; Stress, Mechanical ; }, abstract = {The application of axial pumps as ventricular assist devices (VADs) requires significant modifications to the size and characteristics of industrial pumps due to the difference in flow fields of industrial and medical pumps. Industrial pumps operate in the region of Reynolds number Re = 10, whereas axial blood pumps operate in Re < 10. The common pump design technique is to rely on the performance of previously designed pumps using the concept of fluid dynamic similarity. Such data are available for industrial pumps as specific speed-specific diameter (ns-ds) graphs. The difference between the flow fields of industrial and medical pumps makes the industrial ns-ds graphs unsuitable for medical pumps and consequently several clinically available axial blood pumps operate with low efficiencies. In this article, numerical and experimental techniques were used to design 62 axial pump impellers with different design characteristics suitable for VADs and mechanical circulatory support devices (MCSDs). The impellers were manufactured and experimentally tested in various operating conditions of flow, pressure, and rotational speed. The hemocompatibility of the impellers was numerically investigated by modeling shear stress and hemolysis. The highest efficiency of each pump impeller was plotted on an ns-ds diagram. The nondimensional results presented in this article enable preliminary design of efficient and hemocompatible axial flow pumps for VADs and MCSDs.}, } @article {pmid29104418, year = {2017}, author = {Luo, K and Hu, C and Wu, F and Fan, J}, title = {Direct numerical simulation of turbulent boundary layer with fully resolved particles at low volume fraction.}, journal = {Physics of fluids (Woodbury, N.Y. : 1994)}, volume = {29}, number = {5}, pages = {053301}, pmid = {29104418}, issn = {1070-6631}, abstract = {In the present work, a direct numerical simulation (DNS) of dilute particulate flow in a turbulent boundary layer has been conducted, containing thousands of finite-sized solid rigid particles. The particle surfaces are resolved with the multi-direct forcing immersed-boundary method. This is, to the best of the authors' knowledge, the first DNS study of a turbulent boundary layer laden with finite-sized particles. The particles have a diameter of approximately 11.3 wall units, a density of 3.3 times that of the fluid, and a solid volume fraction of 1/1000. The simulation shows that the onset and the completion of the transition processes are shifted earlier with the inclusion of the solid phase and that the resulting streamwise mean velocity of the boundary layer in the particle-laden case is almost consistent with the results of the single-phase case. At the same time, relatively stronger particle movements are observed in the near-wall regions, due to the driving of the counterrotating streamwise vortexes. As a result, increased levels of dissipation occur on the particle surfaces, and the root mean square of the fluctuating velocities of the fluid in the near-wall regions is decreased. Under the present parameters, including the particle Stokes number St[+] = 24 and the particle Reynolds number Rep = 33 based on the maximum instantaneous fluid-solid velocity lag, no vortex shedding behind the particle is observed. Lastly, a trajectory analysis of the particles shows the influence of turbophoresis on particle wall-normal concentration, and the particles that originated between y[+] = 60 and 2/3 of the boundary-layer thickness are the most influenced.}, } @article {pmid29061390, year = {2017}, author = {Watson, DJ and Sazonov, I and Zawieja, DC and Moore, JE and van Loon, R}, title = {Integrated geometric and mechanical analysis of an image-based lymphatic valve.}, journal = {Journal of biomechanics}, volume = {64}, number = {}, pages = {172-179}, pmid = {29061390}, issn = {1873-2380}, support = {U01 HL123420/HL/NHLBI NIH HHS/United States ; }, mesh = {Algorithms ; Biomechanical Phenomena ; Compliance ; Computer Simulation ; Humans ; Image Processing, Computer-Assisted ; Lymph/physiology ; Lymphatic Vessels/anatomy & histology/*physiology ; Microscopy, Confocal ; Models, Biological ; Pressure ; }, abstract = {Lymphatic valves facilitate the lymphatic system's role in maintaining fluid homeostasis. Malformed valves are found in several forms of primary lymphœdema, resulting in incurable swelling of the tissues and immune dysfunction. Their experimental study is complicated by their small size and operation in low pressure and low Reynolds number environments. Mathematical models of these structures can give insight and complement experimentation. In this work, we present the first valve geometry reconstructed from confocal imagery and used in the construction of a subject-specific model in a closing mode. A framework is proposed whereby an image is converted into a valve model. An FEA study was performed to identify the significance of the shear modulus, the consequences of smoothing the leaflet surface and the effect of wall motion on valve behaviour. Smoothing is inherent to any analysis from imagery. The nature of the image, segmentation and meshing all cause attenuation of high-frequency features. Smoothing not only causes loss of surface area but also the loss of high-frequency geometric features which may reduce stiffness. This work aimed to consider these effects and inform studies by taking a manual reconstruction and through manifold harmonic analysis, attenuating higher frequency features to replicate lower resolution images or lower degree-of-freedom reconstructions. In conclusion, two metrics were considered: trans-valvular pressure required to close the valve, ΔPc, and the retrograde volume displacement after closure. The higher ΔPc, the greater the volume of lymph that will pass through the valve during closure. Retrograde volume displacement after closure gives a metric of compliance of the valve and for the quality of the valve seal. In the case of the image-specific reconstructed valve, removing features with a wavelength longer than four μm caused changes in ΔPc. Varying the shear modulus from 10 kPa to 60 kPa caused a 3.85-fold increase in the retrograde volume displaced. The inclusion of a non-rigid wall caused ΔPc to increase from 1.56 to 2.52 cmH2O.}, } @article {pmid29054787, year = {2018}, author = {Chen, Y and Li, Y and Valocchi, AJ and Christensen, KT}, title = {Lattice Boltzmann simulations of liquid CO2 displacing water in a 2D heterogeneous micromodel at reservoir pressure conditions.}, journal = {Journal of contaminant hydrology}, volume = {212}, number = {}, pages = {14-27}, doi = {10.1016/j.jconhyd.2017.09.005}, pmid = {29054787}, issn = {1873-6009}, mesh = {Carbon Dioxide/*chemistry ; *Computer Simulation ; *Microfluidics ; Porosity ; Pressure ; Viscosity ; Water/*chemistry ; }, abstract = {We employed the color-fluid lattice Boltzmann multiphase model to simulate liquid CO2 displacing water documented in experiments in a 2D heterogeneous micromodel at reservoir pressure conditions. The main purpose is to investigate whether lattice Boltzmann simulation can reproduce the CO2 invasion patterns observed in these experiments for a range of capillary numbers. Although the viscosity ratio used in the simulation matches the experimental conditions, the viscosity of the fluids in the simulation is higher than that of the actual fluids used in the experiments. Doing so is required to enhance numerical stability, and is a common strategy employed in the literature when using the lattice Boltzmann method to simulate CO2 displacing water. The simulations reproduce qualitatively similar trends of changes in invasion patterns as the capillary number is increased. However, the development of secondary CO2 pathways, a key feature of the invasion patterns in the simulations and experiments, is found to occur at a much higher capillary number in the simulations compared with the experiments. Additional numerical simulations were conducted to investigate the effect of the absolute value of viscosity on the invasion patterns while maintaining the viscosity ratio and capillary number fixed. These results indicate that the use of a high viscosity (which significantly reduces the inertial effect in the simulations) suppresses the development of secondary CO2 pathways, leading to a different fluid distribution compared with corresponding experiments at the same capillary number. Therefore, inertial effects are not negligible in drainage process with liquid CO2 and water despite the low Reynolds number based on the average velocity, as the local velocity can be much higher due to Haines jump events. These higher velocities, coupled with the low viscosity of CO2, further amplifies the inertial effect. Therefore, we conclude that caution should be taken when using proxy fluids that only rely on the capillary number and viscosity ratio in both experiment and simulation.}, } @article {pmid29052556, year = {2017}, author = {Chen, D and Kolomenskiy, D and Nakata, T and Liu, H}, title = {Forewings match the formation of leading-edge vortices and dominate aerodynamic force production in revolving insect wings.}, journal = {Bioinspiration & biomimetics}, volume = {13}, number = {1}, pages = {016009}, doi = {10.1088/1748-3190/aa94d7}, pmid = {29052556}, issn = {1748-3190}, mesh = {Animals ; Bees/*physiology ; Biomechanical Phenomena ; Drosophila melanogaster/*physiology ; Manduca/*physiology ; *Models, Biological ; Wings, Animal/anatomy & histology/*physiology ; }, abstract = {In many flying insects, forewings and hindwings are coupled mechanically to achieve flapping flight synchronously while being driven by action of the forewings. How the forewings and hindwings as well as their morphologies contribute to aerodynamic force production and flight control remains unclear. Here we address the point that the forewings can produce most of the aerodynamic forces even with the hindwings removed through a computational fluid dynamic study of three revolving insect wing models, which are identical to the wing morphologies and Reynolds numbers of hawkmoth (Manduca sexta), bumblebee (Bombus ignitus) and fruitfly (Drosophila melanogaster). We find that the forewing morphologies match the formation of leading-edge vortices (LEV) and are responsible for generating sufficient lift forces at the mean angles of attack and the Reynolds numbers where the three representative insects fly. The LEV formation and pressure loading keep almost unchanged with the hindwing removed, and even lead to some improvement in power factor and aerodynamic efficiency. Moreover, our results indicate that the size and strength of the LEVs can be well quantified with introduction of a conical LEV angle, which varies remarkably with angles of attack and Reynolds numbers but within the forewing region while showing less sensitivity to the wing morphologies. This implies that the forewing morphology very likely plays a dominant role in achieving low-Reynolds number aerodynamic performance in natural flyers as well as in revolving and/or flapping micro air vehicles.}, } @article {pmid29036075, year = {2017}, author = {Prasad, S}, title = {Extended Taylor frozen-flow hypothesis and statistics of optical phase in aero-optics.}, journal = {Journal of the Optical Society of America. A, Optics, image science, and vision}, volume = {34}, number = {6}, pages = {931-942}, doi = {10.1364/JOSAA.34.000931}, pmid = {29036075}, issn = {1520-8532}, abstract = {We present an extended Taylor frozen-flow model for the statistics of the spatiotemporal disturbances of the index of refraction of air and the phase of an optical beam propagated through the turbulent boundary and shear layers in a high-Reynolds-number flow. By incorporating rapid random fluctuations of the flow velocity about a mean convection velocity and an anisotropic spatial power spectrum for the index of refraction, we calculate both the short-delay temporal structure function and the power spectral density of these disturbances. We discuss the predicted scaling behaviors for these quantities in the context of existing experimental observations, showing specifically the agreement of these predictions with some optical phase data obtained by the Airborne Aero-Optical Laboratory.}, } @article {pmid29027922, year = {2017}, author = {Song, Y and Zhao, K and Zuo, J and Wang, C and Li, Y and Miao, X and Zhao, X}, title = {The Detection of Water Flow in Rectangular Microchannels by Terahertz Time Domain Spectroscopy.}, journal = {Sensors (Basel, Switzerland)}, volume = {17}, number = {10}, pages = {}, pmid = {29027922}, issn = {1424-8220}, abstract = {Flow characteristics of water were tested in a rectangular microchannel for Reynolds number (Re) between 0 and 446 by terahertz time domain spectroscopy (THz-TDS). Output THz peak trough intensities and the calculated absorbances of the flow were analyzed theoretically. The results show a rapid change for Re < 250 and a slow change as Re increases, which is caused by the early transition from laminar to transition flow beginning nearly at Re = 250. Then this finding is confirmed in the plot of the flow resistant. Our results demonstrate that the THz-TDS could be a valuable tool to monitor and character the flow performance in microscale structures.}, } @article {pmid29027748, year = {2018}, author = {Middleton, K and Kondiboyina, A and Borrett, M and Cui, Y and Mei, X and You, L}, title = {Microfluidics approach to investigate the role of dynamic similitude in osteocyte mechanobiology.}, journal = {Journal of orthopaedic research : official publication of the Orthopaedic Research Society}, volume = {36}, number = {2}, pages = {663-671}, doi = {10.1002/jor.23773}, pmid = {29027748}, issn = {1554-527X}, support = {//CIHR/Canada ; }, mesh = {*Adaptation, Physiological ; Animals ; Biomechanical Phenomena ; Female ; Microfluidic Analytical Techniques ; Osteocytes/*physiology ; *Osteogenesis ; Rats, Sprague-Dawley ; Stress, Mechanical ; }, abstract = {Fluid flow is an important regulator of cell function and metabolism in many tissues. Fluid shear stresses have been used to level the mechanical stimuli applied in vitro with what occurs in vivo. However, these experiments often lack dynamic similarity, which is necessary to ensure the validity of the model. For interstitial fluid flow, the major requirement for dynamic similarity is the Reynolds number (Re), the ratio of inertial to viscous forces, is the same between the system and model. To study the necessity of dynamic similarity for cell mechanotransduction studies, we investigated the response of osteocyte-like MLO-Y4 cells to different Re flows at the same level of fluid shear stress. Osteocytes were chosen for this study as flows applied in vitro and in vivo have Re that are orders of magnitude different. We hypothesize that osteocytes' response to fluid flow is Re dependent. We observed that cells exposed to lower and higher Re flows developed rounded and triangular morphologies, respectively. Lower Re flows also reduced apoptosis rates compared to higher Re flows. Furthermore, MLO-Y4 cells exposed to higher Re flows had stronger calcium responses compared to lower Re flows. However, by also controlling for flow rate, the lower Re flows induced a stronger calcium response; while degradation of components of the osteocyte glycocalyx reversed this effect. This work suggests that osteocytes are highly sensitive to differences in Re, independent of just shear stresses, supporting the need for improved in vitro flow platforms that better recapitulate the physiological environment. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:663-671, 2018.}, } @article {pmid28989310, year = {2017}, author = {Manikantan, H and Squires, TM}, title = {Irreversible particle motion in surfactant-laden interfaces due to pressure-dependent surface viscosity.}, journal = {Proceedings. Mathematical, physical, and engineering sciences}, volume = {473}, number = {2205}, pages = {20170346}, pmid = {28989310}, issn = {1364-5021}, abstract = {The surface shear viscosity of an insoluble surfactant monolayer often depends strongly on its surface pressure. Here, we show that a particle moving within a bounded monolayer breaks the kinematic reversibility of low-Reynolds-number flows. The Lorentz reciprocal theorem allows such irreversibilities to be computed without solving the full nonlinear equations, giving the leading-order contribution of surface pressure-dependent surface viscosity. In particular, we show that a disc translating or rotating near an interfacial boundary experiences a force in the direction perpendicular to that boundary. In unbounded monolayers, coupled modes of motion can also lead to non-intuitive trajectories, which we illustrate using an interfacial analogue of the Magnus effect. This perturbative approach can be extended to more complex geometries, and to two-dimensional suspensions more generally.}, } @article {pmid28982172, year = {2017}, author = {Khan, NB and Ibrahim, Z and Nguyen, LTT and Javed, MF and Jameel, M}, title = {Numerical investigation of the vortex-induced vibration of an elastically mounted circular cylinder at high Reynolds number (Re = 104) and low mass ratio using the RANS code.}, journal = {PloS one}, volume = {12}, number = {10}, pages = {e0185832}, pmid = {28982172}, issn = {1932-6203}, mesh = {*Elasticity ; Models, Theoretical ; *Vibration ; }, abstract = {This study numerically investigates the vortex-induced vibration (VIV) of an elastically mounted rigid cylinder by using Reynolds-averaged Navier-Stokes (RANS) equations with computational fluid dynamic (CFD) tools. CFD analysis is performed for a fixed-cylinder case with Reynolds number (Re) = 104 and for a cylinder that is free to oscillate in the transverse direction and possesses a low mass-damping ratio and Re = 104. Previously, similar studies have been performed with 3-dimensional and comparatively expensive turbulent models. In the current study, the capability and accuracy of the RANS model are validated, and the results of this model are compared with those of detached eddy simulation, direct numerical simulation, and large eddy simulation models. All three response branches and the maximum amplitude are well captured. The 2-dimensional case with the RANS shear-stress transport k-w model, which involves minimal computational cost, is reliable and appropriate for analyzing the characteristics of VIV.}, } @article {pmid28981539, year = {2017}, author = {Islam, S and Nazeer, G and Ying, ZC and Islam, Z and Manzoor, R}, title = {Transitions in the flow patterns and aerodynamic characteristics of the flow around staggered rows of cylinders.}, journal = {PloS one}, volume = {12}, number = {10}, pages = {e0184169}, pmid = {28981539}, issn = {1932-6203}, mesh = {Computer Simulation ; *Models, Theoretical ; *Physical Phenomena ; }, abstract = {A two-dimensional numerical study of flow across rows of identical square cylinders arranged in staggered fashion is carried out. This study will unreveal complex flow physics depending upon the Reynolds number (Re) and gap spacing (g) between the cylinders. The combined effect of Reynolds number and gap spacing on the flow physics around staggered rows of cylinders are numerically studied for 20 ≤ Re ≤ 140 and 1 ≤ g ≤ 6. We use the lattice Boltzmann method for numerical computations. It is found that with increase in gap spacing between the cylinders the critical Reynolds number for the onset of vortex shedding also increases. We observed a strong effect of Reynolds number at g = 2 and 4. Secondary cylinder interaction frequency disappears for large Reynolds number at g = 6 and 5 and the flow around cylinders are fully dominated by the primary vortex shedding frequency. This ensures that at large gap spacing with an increase in the Reynolds number the wakes interaction between and behind the cylinders is weaken. Furthermore, it also ensures that the wake interaction behind the cylinders is strongly influenced by the jets in the gap spacing between the cylinders. We also found that g = 2 is the critical gap spacing for flow across rows of staggered square cylinders for the considered range of Reynolds number. Depending on the Reynolds number we observed; synchronous, quasi-periodic-I, quasi-periodic-II, and chaotic flow patterns. In synchronous flow pattern, an in-phase and anti-phase characteristics of consecutive cylinders has been observed. The important physical parameters are also analyzed and discussed in detail.}, } @article {pmid28949715, year = {2017}, author = {Boffetta, G and Musacchio, S}, title = {Chaos and Predictability of Homogeneous-Isotropic Turbulence.}, journal = {Physical review letters}, volume = {119}, number = {5}, pages = {054102}, doi = {10.1103/PhysRevLett.119.054102}, pmid = {28949715}, issn = {1079-7114}, abstract = {We study the chaoticity and the predictability of a turbulent flow on the basis of high-resolution direct numerical simulations at different Reynolds numbers. We find that the Lyapunov exponent of turbulence, which measures the exponential separation of two initially close solutions of the Navier-Stokes equations, grows with the Reynolds number of the flow, with an anomalous scaling exponent, larger than the one obtained on dimensional grounds. For large perturbations, the error is transferred to larger, slower scales, where it grows algebraically generating an "inverse cascade" of perturbations in the inertial range. In this regime, our simulations confirm the classical predictions based on closure models of turbulence. We show how to link chaoticity and predictability of a turbulent flow in terms of a finite size extension of the Lyapunov exponent.}, } @article {pmid28905060, year = {2017}, author = {Baber, R and Mazzei, L and Thanh, NTK and Gavriilidis, A}, title = {An engineering approach to synthesis of gold and silver nanoparticles by controlling hydrodynamics and mixing based on a coaxial flow reactor.}, journal = {Nanoscale}, volume = {9}, number = {37}, pages = {14149-14161}, doi = {10.1039/c7nr04962e}, pmid = {28905060}, issn = {2040-3372}, abstract = {In this work we present a detailed study of flow technology approaches that could open up new possibilities for nanoparticle synthesis. The synthesis of gold and silver nanoparticles (NPs) in a flow device based on a coaxial flow reactor (CFR) was investigated. The CFR comprised of an outer glass tube of 2 mm inner diameter (I.D.) and an inner glass tube whose I.D. varied between 0.142 and 0.798 mm. A split and recombine (SAR) mixer and coiled flow inverter (CFI) were further employed to alter the mixing conditions after the CFR. The 'Turkevich' method was used to synthesize gold NPs, with a CFR followed by a CFI. This assembly allows control over nucleation and growth through variation of residence time. Increasing the total flow rate from 0.25 ml min[-1] to 3 ml min[-1] resulted initially in a constant Au NP size, and beyond 1 ml min[-1] to a size increase of Au NPs from 17.9 ± 2.1 nm to 23.9 ± 4.7 nm. The temperature was varied between 60-100 °C and a minimum Au NP size of 17.9 ± 2.1 nm was observed at 80 °C. Silver NPs were synthesized in a CFR followed by a SAR mixer, using sodium borohydride to reduce silver nitrate in the presence of trisodium citrate. The SAR mixer provided an enhancement of the well-controlled laminar mixing in the CFR. Increasing silver nitrate concentration resulted in a decrease in Ag NP size from 5.5 ± 2.4 nm to 3.4 ± 1.4 nm. Different hydrodynamic conditions were studied in the CFR operated in isolation for silver NP synthesis. Increasing the Reynolds number from 132 to 530 in the inner tube created a vortex flow resulting in Ag NPs in the size range between 5.9 ± 1.5 nm to 7.7 ± 3.4 nm. Decreasing the inner tube I.D. from 0.798 mm to 0.142 mm resulted in a decrease in Ag NP size from 10.5 ± 4.0 nm to 4.7 ± 1.4 nm. Thus, changing the thickness of the inner stream enabled control over size of the Ag NPs.}, } @article {pmid28878968, year = {2017}, author = {Muir, RE and Arredondo-Galeana, A and Viola, IM}, title = {The leading-edge vortex of swift wing-shaped delta wings.}, journal = {Royal Society open science}, volume = {4}, number = {8}, pages = {170077}, pmid = {28878968}, issn = {2054-5703}, abstract = {Recent investigations on the aerodynamics of natural fliers have illuminated the significance of the leading-edge vortex (LEV) for lift generation in a variety of flight conditions. A well-documented example of an LEV is that generated by aircraft with highly swept, delta-shaped wings. While the wing aerodynamics of a manoeuvring aircraft, a bird gliding and a bird in flapping flight vary significantly, it is believed that this existing knowledge can serve to add understanding to the complex aerodynamics of natural fliers. In this investigation, a model non-slender delta-shaped wing with a sharp leading edge is tested at low Reynolds number, along with a delta wing of the same design, but with a modified trailing edge inspired by the wing of a common swift Apus apus. The effect of the tapering swift wing on LEV development and stability is compared with the flow structure over the unmodified delta wing model through particle image velocimetry. For the first time, a leading-edge vortex system consisting of a dual or triple LEV is recorded on a swift wing-shaped delta wing, where such a system is found across all tested conditions. It is shown that the spanwise location of LEV breakdown is governed by the local chord rather than Reynolds number or angle of attack. These findings suggest that the trailing-edge geometry of the swift wing alone does not prevent the common swift from generating an LEV system comparable with that of a delta-shaped wing.}, } @article {pmid28869874, year = {2017}, author = {Xiang, J and Liu, K and Li, D and Du, J}, title = {Effects of micro-structure on aerodynamics of Coccinella septempunctata elytra (ladybird) in forward flight as assessed via electron microscopy.}, journal = {Micron (Oxford, England : 1993)}, volume = {102}, number = {}, pages = {21-34}, doi = {10.1016/j.micron.2017.08.003}, pmid = {28869874}, issn = {1878-4291}, mesh = {Animals ; Biomechanical Phenomena/*physiology ; Coleoptera/*physiology ; Flight, Animal/*physiology ; Hydrodynamics ; Microscopy, Electron ; Models, Biological ; Wings, Animal/*ultrastructure ; }, abstract = {The effects of micro-structure on aerodynamics of Coccinella septempunctata (Coleoptera: Coccinellidae) elytra in forward flight were investigated. The micro-structure was examined by a scanning electron microscope and a digital microscope. Based on the experimental results, five elytron models were constructed to separately investigate the effects of the camber and the local corrugation in both leading edge and trailing edge on aerodynamics. Computational fluid dynamic simulations of five elytron models were conducted by solving the Reynolds-Averaged Navier-Stokes equations with the Reynolds number of 245. The results show that camber and the local corrugation in the leading edge play significant roles in improving the aerodynamic performance, while the local corrugation in the trailing edge has little effect on aerodynamics.}, } @article {pmid28862154, year = {2017}, author = {Chung, EG and Ryu, S}, title = {Stalk-length-dependence of the contractility of Vorticella convallaria.}, journal = {Physical biology}, volume = {14}, number = {6}, pages = {066002}, doi = {10.1088/1478-3975/aa89b8}, pmid = {28862154}, issn = {1478-3975}, mesh = {Biomechanical Phenomena ; Calcium/*metabolism ; Energy Metabolism ; Oligohymenophorea/*physiology ; Stress, Mechanical ; }, abstract = {Vorticella convallaria is a sessile protozoan of which the spasmoneme contracts on a millisecond timescale. Because this contraction is induced and powered by the binding of calcium ions (Ca[2+]), the spasmoneme showcases Ca[2+]-powered cellular motility. Because the isometric tension of V. convallaria increases linearly with its stalk length, it is hypothesized that the contractility of V. convallaria during unhindered contraction depends on the stalk length. In this study, the contractile force and energetics of V. convallaria cells of different stalk lengths were evaluated using a fluid dynamic drag model which accounts for the unsteadiness and finite Reynolds number of the water flow caused by contracting V. convallaria and the wall effect of the no-slip substrate. It was found that the contraction displacement, peak contraction speed, peak contractile force, total mechanical work, and peak power depended on the stalk length. The observed stalk-length-dependencies were simulated using a damped spring model, and the model estimated that the average spring constant of the contracting stalk was 1.34 nN µm[-1]. These observed length-dependencies of Vorticella's key contractility parameters reflect the biophysical mechanism of the spasmonemal contraction, and thus they should be considered in developing a theoretical model of the Vorticella spasmoneme.}, } @article {pmid28852432, year = {2017}, author = {Malvar, S and Gontijo, RG and Carmo, BS and Cunha, FR}, title = {On the kinematics-wave motion of living particles in suspension.}, journal = {Biomicrofluidics}, volume = {11}, number = {4}, pages = {044112}, pmid = {28852432}, issn = {1932-1058}, abstract = {This work presents theoretical and experimental analyses on the kinematics-wave motion of suspended active particles in a biological fluid. The fluid is an active suspension of nematodes immersed in a gel-like biological structure, moving at a low Reynolds number. The nematode chosen for the study is Caenorhabditis elegans. Its motion is subjected to the time reversibility of creeping flows. We investigate how this worm reacts to this reversibility condition in order to break the flow symmetry and move in the surrounding fluid. We show that the relationship between the length of an individual nematode and the wavelength of its motion is linear and can be fitted by a theoretical prediction proposed in this work. We provide a deep discussion regarding the propulsion mechanics based on a scaling analysis that identifies three major forces acting on an individual nematode. These forces are a viscous force, a yield stress force due to gelification of agar molecules in the gel-like medium, and a bending force associated with the muscular tension imposed by the nematodes in the medium. By the scalings, we identify the most relevant physical parameters of the nematode's motion. In order to examine and quantify the motion, dynamical system tools such as FFT are used in the present analysis. The motion characterization is performed by examining (or studying) two different populations: (i) in the absence of food with starving nematodes and (ii) with well-fed nematodes. In addition, several kinematic quantities of the head, center of mass, and tail for a sample of nematodes are also investigated: their slip velocities, wavelengths, trajectories, frequency spectra, and mean curvatures. The main findings of this work are the confirmation of a linear relationship between the nematode's physical length and its motion wavelength, the identification of secondary movements in high frequencies that helps breaking the time-reversibility in which the worms are bonded, and the observation and interpretation of a systematic difference between the individual motion of well-fed and starving nematodes.}, } @article {pmid28850622, year = {2017}, author = {Aftab, SMA and Ahmad, KA}, title = {CFD study on NACA 4415 airfoil implementing spherical and sinusoidal Tubercle Leading Edge.}, journal = {PloS one}, volume = {12}, number = {8}, pages = {e0183456}, pmid = {28850622}, issn = {1932-6203}, mesh = {Animal Structures/*anatomy & histology ; Animals ; *Computer Simulation ; *Humpback Whale ; *Models, Biological ; }, abstract = {The Humpback whale tubercles have been studied for more than a decade. Tubercle Leading Edge (TLE) effectively reduces the separation bubble size and helps in delaying stall. They are very effective in case of low Reynolds number flows. The current Computational Fluid Dynamics (CFD) study is on NACA 4415 airfoil, at a Reynolds number 120,000. Two TLE shapes are tested on NACA 4415 airfoil. The tubercle designs implemented on the airfoil are sinusoidal and spherical. A parametric study is also carried out considering three amplitudes (0.025c, 0.05c and 0.075c), the wavelength (0.25c) is fixed. Structured mesh is utilized to generate grid and Transition SST turbulence model is used to capture the flow physics. Results clearly show spherical tubercles outperform sinusoidal tubercles. Furthermore experimental study considering spherical TLE is carried out at Reynolds number 200,000. The experimental results show that spherical TLE improve performance compared to clean airfoil.}, } @article {pmid28837786, year = {2017}, author = {Narla, VK and Prasad, KM and Ramana Murthy, JV}, title = {Time-dependent peristaltic analysis in a curved conduit: Application to chyme movement through intestine.}, journal = {Mathematical biosciences}, volume = {293}, number = {}, pages = {21-28}, doi = {10.1016/j.mbs.2017.08.005}, pmid = {28837786}, issn = {1879-3134}, mesh = {*Gastrointestinal Contents ; *Gastrointestinal Transit ; Intestinal Mucosa/*metabolism ; Magnetic Fields ; *Models, Biological ; *Peristalsis ; Time Factors ; Viscosity ; }, abstract = {A theoretical model of time-dependent peristaltic viscous fluid flow through a curved channel in the presence of an applied magnetic field is investigated. The results for stream function, pressure distribution and mechanical efficiency are obtained under the assumptions of long wavelength and low Reynolds number approximation. Pressure fluctuations due to an integral and a non-integral number of waves along the channel length are discussed under influence of channel curvature and magnetic parameter. Two inherent characteristics of peristaltic flow regimes (trapping and reflux) are discussed numerically. The mechanical efficiency of curved magnetohydrodynamic peristaltic pumping is also examined. The magnitude of pressure increases with an increasing channel curvature and magnetic parameter. Reflex phenomenon is analyzed in the Lagrangian frame of reference. It is observed that reflex in the curved channel is higher than in the straight channel. The trapped fluid in a curved channel is studied in the Eulerian frame of reference and it contains two asymmetric boluses. The size of the lower bolus grows and the upper bolus decreases with increasing effect of magnetic strength. Pumping efficiency of the peristaltic pump is low for curved channel flow than for straight channel flow. Also, the pumping efficiency is comparatively low at the high effect of the magnetic parameter.}, } @article {pmid28836761, year = {2017}, author = {de Anda, J and Lee, EY and Lee, CK and Bennett, RR and Ji, X and Soltani, S and Harrison, MC and Baker, AE and Luo, Y and Chou, T and O'Toole, GA and Armani, AM and Golestanian, R and Wong, GCL}, title = {High-Speed "4D" Computational Microscopy of Bacterial Surface Motility.}, journal = {ACS nano}, volume = {11}, number = {9}, pages = {9340-9351}, pmid = {28836761}, issn = {1936-086X}, support = {R37 AI083256/AI/NIAID NIH HHS/United States ; T32 GM008042/GM/NIGMS NIH HHS/United States ; U54 CA193417/CA/NCI NIH HHS/United States ; R01 AI102584/AI/NIAID NIH HHS/United States ; T32 GM008185/GM/NIGMS NIH HHS/United States ; }, mesh = {Cell Tracking/methods ; Finite Element Analysis ; Flagella/metabolism ; Hydrodynamics ; Imaging, Three-Dimensional/*methods ; Microscopy/methods ; Pseudomonas aeruginosa/*cytology/metabolism ; Single-Cell Analysis/methods ; }, abstract = {Bacteria exhibit surface motility modes that play pivotal roles in early-stage biofilm community development, such as type IV pili-driven "twitching" motility and flagellum-driven "spinning" and "swarming" motility. Appendage-driven motility is controlled by molecular motors, and analysis of surface motility behavior is complicated by its inherently 3D nature, the speed of which is too fast for confocal microscopy to capture. Here, we combine electromagnetic field computation and statistical image analysis to generate 3D movies close to a surface at 5 ms time resolution using conventional inverted microscopes. We treat each bacterial cell as a spherocylindrical lens and use finite element modeling to solve Maxwell's equations and compute the diffracted light intensities associated with different angular orientations of the bacterium relative to the surface. By performing cross-correlation calculations between measured 2D microscopy images and a library of computed light intensities, we demonstrate that near-surface 3D movies of Pseudomonas aeruginosa translational and rotational motion are possible at high temporal resolution. Comparison between computational reconstructions and detailed hydrodynamic calculations reveals that P. aeruginosa act like low Reynolds number spinning tops with unstable orbits, driven by a flagellum motor with a torque output of ∼2 pN μm. Interestingly, our analysis reveals that P. aeruginosa can undergo complex flagellum-driven dynamical behavior, including precession, nutation, and an unexpected taxonomy of surface motility mechanisms, including upright-spinning bacteria that diffuse laterally across the surface, and horizontal bacteria that follow helicoidal trajectories and exhibit superdiffusive movements parallel to the surface.}, } @article {pmid28815228, year = {2017}, author = {Kim, J and Hong, SO and Shim, TS and Kim, JM}, title = {Inertio-elastic flow instabilities in a 90° bent microchannel.}, journal = {Soft matter}, volume = {13}, number = {34}, pages = {5656-5664}, doi = {10.1039/c7sm01355h}, pmid = {28815228}, issn = {1744-6848}, abstract = {Biological samples having viscoelastic properties are frequently tested using microfluidic devices. In addition, viscoelastic fluids such as polymer solutions have been used as a suspending medium to spatially focus particles in microchannels. The occurrence of flow instability even at low Reynolds number is a unique property of viscoelastic fluids. In this study, we report the instability in viscoelastic flow for a channel having a 90° bent geometry, which is a characteristic of many microfluidic devices. Interestingly, we observed that the flow instability in aqueous poly(ethylene oxide) (PEO) solution occurs when the concentration of PEO is as low as 50 ppm. We systematically investigated the effects of the polymer concentration, flow rate, and elasticity number on the flow instability. The results show that the flow is stabilized in shear-thinning fluids, whereas the flow instability is amplified when both elastic and inertial effects are pronounced. We believe that this study is useful to design microfluidic devices such as cell-deformability measurement devices based on viscoelastic particle focusing.}, } @article {pmid28809710, year = {2017}, author = {Zhao, Q and Yan, S and Yuan, D and Zhang, J and Du, H and Alici, G and Li, W}, title = {Double-Mode Microparticle Manipulation by Tunable Secondary Flow in Microchannel With Arc-Shaped Groove Arrays.}, journal = {IEEE transactions on biomedical circuits and systems}, volume = {11}, number = {6}, pages = {1406-1412}, doi = {10.1109/TBCAS.2017.2722012}, pmid = {28809710}, issn = {1940-9990}, mesh = {Microfluidic Analytical Techniques/*methods ; Particle Size ; }, abstract = {In this paper, we proposed a microparticle manipulation approach, by which particles are able to be guided to different equilibrium positions through modulating the Reynolds number. In the microchannel with arc-shaped groove arrays, secondary flow vortex arisen due to the pressure gradient varies in the aspects of both magnitude and shape with the increase of Reynolds number. And the variation of secondary flow vortex brings about different focusing modes of microparticles in the microchannel. We investigated the focusing phenomenon experimentally and analyzed the mechanism through numerical simulations. At a high Reynolds number (Re = 127.27), the geometry-induced secondary flow rotates constantly along a direction, and most particles are guided to the equilibrium position near one side of the microchannel. However, at a low Reynolds number (Re = 2.39), the shapes of geometry-induced secondary flow vortices are obviously different, forming a variant Dean-like vortex that consists of two asymmetric counter-rotating streams in cross sections of the straight channel. Because of the periodical effects, suspended particles are concentrated at another equilibrium position on the opposite side of the microchannel. Meanwhile, the effects of particle size influence both the focusing position and quality in regimes.}, } @article {pmid28805871, year = {2017}, author = {Hanasoge, S and Ballard, M and Hesketh, PJ and Alexeev, A}, title = {Asymmetric motion of magnetically actuated artificial cilia.}, journal = {Lab on a chip}, volume = {17}, number = {18}, pages = {3138-3145}, doi = {10.1039/c7lc00556c}, pmid = {28805871}, issn = {1473-0189}, mesh = {*Artificial Cells ; Biomechanical Phenomena ; Cilia/*physiology ; Equipment Design ; *Magnets ; *Microfluidics/instrumentation/methods ; *Models, Biological ; Motion ; Rotation ; Viscosity ; }, abstract = {Most microorganisms use hair-like cilia with asymmetric beating to perform vital bio-physical processes. In this paper, we demonstrate a novel fabrication method for creating magnetic artificial cilia capable of such a biologically inspired asymmetric beating pattern essential for inducing microfluidic transport at low Reynolds number. The cilia are fabricated using a lithographic process in conjunction with deposition of magnetic nickel-iron permalloy to create flexible filaments that can be manipulated by varying an external magnetic field. A rotating permanent magnet is used to actuate the cilia. We examine the kinematics of a cilium and demonstrate that the cilium motion is defined by an interplay among elastic, magnetic, and viscous forces. Specifically, the forward stroke is induced by the rotation of the magnet which bends the cilium, whereas the recovery stroke is defined by the straightening of the deformed cilium, releasing accumulated elastic potential energy. This difference in dominating forces acting during the forward stroke and the recovery stroke leads to an asymmetric beating pattern of the cilium. Such magnetic cilia can find applications in microfluidic pumping, mixing, and other fluid handling processes.}, } @article {pmid28772551, year = {2017}, author = {Ng, WL and Yeong, WY and Naing, MW}, title = {Polyvinylpyrrolidone-Based Bio-Ink Improves Cell Viability and Homogeneity during Drop-On-Demand Printing.}, journal = {Materials (Basel, Switzerland)}, volume = {10}, number = {2}, pages = {}, pmid = {28772551}, issn = {1996-1944}, abstract = {Drop-on-demand (DOD) bioprinting has attracted huge attention for numerous biological applications due to its precise control over material volume and deposition pattern in a contactless printing approach. 3D bioprinting is still an emerging field and more work is required to improve the viability and homogeneity of printed cells during the printing process. Here, a general purpose bio-ink was developed using polyvinylpyrrolidone (PVP) macromolecules. Different PVP-based bio-inks (0%-3% w/v) were prepared and evaluated for their printability; the short-term and long-term viability of the printed cells were first investigated. The Z value of a bio-ink determines its printability; it is the inverse of the Ohnesorge number (Oh), which is the ratio between the Reynolds number and a square root of the Weber number, and is independent of the bio-ink velocity. The viability of printed cells is dependent on the Z values of the bio-inks; the results indicated that the cells can be printed without any significant impairment using a bio-ink with a threshold Z value of ≤9.30 (2% and 2.5% w/v). Next, the cell output was evaluated over a period of 30 min. The results indicated that PVP molecules mitigate the cell adhesion and sedimentation during the printing process; the 2.5% w/v PVP bio-ink demonstrated the most consistent cell output over a period of 30 min. Hence, PVP macromolecules can play a critical role in improving the cell viability and homogeneity during the bioprinting process.}, } @article {pmid28754380, year = {2018}, author = {Grosjean, G and Hubert, M and Vandewalle, N}, title = {Magnetocapillary self-assemblies: Locomotion and micromanipulation along a liquid interface.}, journal = {Advances in colloid and interface science}, volume = {255}, number = {}, pages = {84-93}, doi = {10.1016/j.cis.2017.07.019}, pmid = {28754380}, issn = {1873-3727}, abstract = {This paper presents an overview and discussion of magnetocapillary self-assemblies. New results are presented, in particular concerning the possible development of future applications. These self-organizing structures possess the notable ability to move along an interface when powered by an oscillatory, uniform magnetic field. The system is constructed as follows. Soft magnetic particles are placed on a liquid interface, and submitted to a magnetic induction field. An attractive force due to the curvature of the interface around the particles competes with an interaction between magnetic dipoles. Ordered structures can spontaneously emerge from these conditions. Furthermore, time-dependent magnetic fields can produce a wide range of dynamic behaviours, including non-time-reversible deformation sequences that produce translational motion at low Reynolds number. In other words, due to a spontaneous breaking of time-reversal symmetry, the assembly can turn into a surface microswimmer. Trajectories have been shown to be precisely controllable. As a consequence, this system offers a way to produce microrobots able to perform different tasks. This is illustrated in this paper by the capture, transport and release of a floating cargo, and the controlled mixing of fluids at low Reynolds number.}, } @article {pmid28749743, year = {2017}, author = {Morley, ST and Walsh, MT and Newport, DT}, title = {Opportunities for Studying the Hydrodynamic Context for Breast Cancer Cell Spread Through Lymph Flow.}, journal = {Lymphatic research and biology}, volume = {15}, number = {3}, pages = {204-219}, doi = {10.1089/lrb.2017.0005}, pmid = {28749743}, issn = {1557-8585}, mesh = {Animals ; Breast Neoplasms/diagnostic imaging/*pathology ; Cell Adhesion ; *Cell Movement ; Female ; Humans ; *Hydrodynamics ; Lymph Nodes/diagnostic imaging/pathology ; Lymphatic Metastasis ; Lymphatic System/diagnostic imaging/*pathology ; Lymphatic Vessels/diagnostic imaging/physiology ; Models, Biological ; Tumor Microenvironment ; }, abstract = {The lymphatic system serves as the primary route for the metastatic spread of breast cancer cells (BCCs). A scarcity of information exists with regard to the advection of BCCs in lymph flow and a fundamental understanding of the response of BCCs to the forces in the lymphatics needs to be established. This review summarizes the flow environment metastatic BCCs are exposed to in the lymphatics. Special attention is paid to the behavior of cells/particles in microflows in an attempt to elucidate the behavior of BCCs under lymph flow conditions (Reynolds number <1).}, } @article {pmid28732945, year = {2017}, author = {Bulliard-Sauret, O and Ferrouillat, S and Vignal, L and Memponteil, A and Gondrexon, N}, title = {Heat transfer enhancement using 2MHz ultrasound.}, journal = {Ultrasonics sonochemistry}, volume = {39}, number = {}, pages = {262-271}, doi = {10.1016/j.ultsonch.2017.04.021}, pmid = {28732945}, issn = {1873-2828}, abstract = {The present work focuses on possible heat transfer enhancement from a heating plate towards tap water in forced convection by means of 2MHz ultrasound. The thermal approach allows to observe the increase of local convective heat transfer coefficients in the presence of ultrasound and to deduce a correlation between ultrasound power and Nusselt number. Heat transfer coefficient under ultrasound remains constant while heat transfer coefficient under silent conditions increases with Reynolds number from 900 up to 5000. Therefore, heat transfer enhancement factor ranges from 25% up to 90% for the same energy conditions (supplied ultrasonic power=110W and supplied thermal power=450W). In the same time cavitational activity due to 2MHz ultrasound emission was characterized from mechanical and chemical viewpoints without significant results. At least, Particle Image Velocimetry (PIV) measurements have been performed in order to investigate hydrodynamic modifications due to the presence of 2MHz ultrasound. It was therefore possible to propose a better understanding of heat transfer enhancement mechanism with high frequency ultrasound.}, } @article {pmid28726415, year = {2017}, author = {Zhao, X and Dey, KK and Jeganathan, S and Butler, PJ and Córdova-Figueroa, UM and Sen, A}, title = {Enhanced Diffusion of Passive Tracers in Active Enzyme Solutions.}, journal = {Nano letters}, volume = {17}, number = {8}, pages = {4807-4812}, doi = {10.1021/acs.nanolett.7b01618}, pmid = {28726415}, issn = {1530-6992}, mesh = {Catalysis ; Diffusion ; Energy Transfer ; Enzymes/*chemistry ; Fluorescent Dyes/chemistry ; Kinetics ; Microspheres ; Particle Size ; Rhodamines/chemistry ; Spectrometry, Fluorescence ; Thermodynamics ; Urease/chemistry ; }, abstract = {Colloidal suspensions containing microscopic swimmers have been the focus of recent studies aimed at understanding the principles of energy transfer in fluidic media at low Reynolds number conditions. Going down in scale, active enzymes have been shown to be force-generating, nonequilibrium systems, thus offering opportunity to examine energy transfer at the ultralow Reynolds number regime. By monitoring the change of diffusion of inert tracers dispersed in active enzyme solutions, we demonstrate that the nature of energy transfer in these systems is similar to that reported for larger microscopic active systems, despite the large differences in scale, modes of energy transduction, and propulsion. Additionally, even an enzyme that catalyzes an endothermic reaction behaves analogously, suggesting that heat generation is not the primary factor for the observed enhanced tracer diffusion. Our results provide new insights into the mechanism of energy transfer at the molecular level.}, } @article {pmid28725740, year = {2016}, author = {Darr, S and Dong, J and Glikin, N and Hartwig, J and Majumdar, A and Leclair, A and Chung, J}, title = {The effect of reduced gravity on cryogenic nitrogen boiling and pipe chilldown.}, journal = {NPJ microgravity}, volume = {2}, number = {}, pages = {16033}, doi = {10.1038/npjmgrav.2016.33}, pmid = {28725740}, issn = {2373-8065}, abstract = {Manned deep space exploration will require cryogenic in-space propulsion. Yet, accurate prediction of cryogenic pipe flow boiling heat transfer is lacking, due to the absence of a cohesive reduced gravity data set covering the expected flow and thermodynamic parameter ranges needed to validate cryogenic two-phase heat transfer models. This work provides a wide range of cryogenic chilldown data aboard an aircraft flying parabolic trajectories to simulate reduced gravity. Liquid nitrogen is used to quench a 1.27 cm diameter tube from room temperature. The pressure, temperature, flow rate, and inlet conditions are reported from 10 tests covering liquid Reynolds number from 2,000 to 80,000 and pressures from 80 to 810 kPa. Corresponding terrestrial gravity tests were performed in upward, downward, and horizontal flow configurations to identify gravity and flow direction effects on chilldown. Film boiling heat transfer was lessened by up to 25% in reduced gravity, resulting in longer time and more liquid to quench the pipe to liquid temperatures. Heat transfer was enhanced by increasing the flow rate, and differences between reduced and terrestrial gravity diminished at high flow rates. The new data set will enable the development of accurate and robust heat transfer models of cryogenic pipe chilldown in reduced gravity.}, } @article {pmid28709337, year = {2017}, author = {Gürcan, ÖD}, title = {Nested polyhedra model of turbulence.}, journal = {Physical review. E}, volume = {95}, number = {6-1}, pages = {063102}, doi = {10.1103/PhysRevE.95.063102}, pmid = {28709337}, issn = {2470-0053}, abstract = {A discretization of the wave-number space is proposed, using nested polyhedra, in the form of alternating dodecahedra and icosahedra that are self-similarly scaled. This particular choice allows the possibility of forming triangles using only discretized wave vectors when the scaling between two consecutive dodecahedra is equal to the golden ratio and the icosahedron between the two dodecahedra is the dual of the inner dodecahedron. Alternatively, the same discretization can be described as a logarithmically spaced (with a scaling equal to the golden ratio), nested dodecahedron-icosahedron compounds. A wave vector which points from the origin to a vertex of such a mesh, can always find two other discretized wave vectors that are also on the vertices of the mesh (which is not true for an arbitrary mesh). Thus, the nested polyhedra grid can be thought of as a reduction (or decimation) of the Fourier space using a particular set of self-similar triads arranged approximately in a spherical form. For each vertex (i.e., discretized wave vector) in this space, there are either 9 or 15 pairs of vertices (i.e., wave vectors) with which the initial vertex can interact to form a triangle. This allows the reduction of the convolution integral in the Navier-Stokes equation to a sum over 9 or 15 interaction pairs, transforming the equation in Fourier space to a network of "interacting" nodes that can be constructed as a numerical model, which evolves each component of the velocity vector on each node of the network. This model gives the usual Kolmogorov spectrum of k^{-5/3} . Since the scaling is logarithmic, and the number of nodes for each scale is constant, a very large inertial range (i.e., a very high Reynolds number) with a much lower number of degrees of freedom can be considered. Incidentally, by assuming isotropy and a certain relation between the phases, the model can be used to systematically derive shell models.}, } @article {pmid28709335, year = {2017}, author = {Dorschner, B and Chikatamarla, SS and Karlin, IV}, title = {Entropic multirelaxation-time lattice Boltzmann method for moving and deforming geometries in three dimensions.}, journal = {Physical review. E}, volume = {95}, number = {6-1}, pages = {063306}, doi = {10.1103/PhysRevE.95.063306}, pmid = {28709335}, issn = {2470-0053}, abstract = {Entropic lattice Boltzmann methods have been developed to alleviate intrinsic stability issues of lattice Boltzmann models for under-resolved simulations. Its reliability in combination with moving objects was established for various laminar benchmark flows in two dimensions in our previous work [B. Dorschner, S. Chikatamarla, F. Bösch, and I. Karlin, J. Comput. Phys. 295, 340 (2015)JCTPAH0021-999110.1016/j.jcp.2015.04.017] as well as for three-dimensional one-way coupled simulations of engine-type geometries in B. Dorschner, F. Bösch, S. Chikatamarla, K. Boulouchos, and I. Karlin [J. Fluid Mech. 801, 623 (2016)JFLSA70022-112010.1017/jfm.2016.448] for flat moving walls. The present contribution aims to fully exploit the advantages of entropic lattice Boltzmann models in terms of stability and accuracy and extends the methodology to three-dimensional cases, including two-way coupling between fluid and structure and then turbulence and deforming geometries. To cover this wide range of applications, the classical benchmark of a sedimenting sphere is chosen first to validate the general two-way coupling algorithm. Increasing the complexity, we subsequently consider the simulation of a plunging SD7003 airfoil in the transitional regime at a Reynolds number of Re=40000 and, finally, to access the model's performance for deforming geometries, we conduct a two-way coupled simulation of a self-propelled anguilliform swimmer. These simulations confirm the viability of the new fluid-structure interaction lattice Boltzmann algorithm to simulate flows of engineering relevance.}, } @article {pmid28698630, year = {2017}, author = {Castillo-Orozco, E and Kar, A and Kumar, R}, title = {Electrospray mode transition of microdroplets with semiconductor nanoparticle suspension.}, journal = {Scientific reports}, volume = {7}, number = {1}, pages = {5144}, pmid = {28698630}, issn = {2045-2322}, abstract = {Electrosprays operate in several modes depending on the flow rate and electric potential. This allows the deposition of droplets containing nanoparticles into discrete nanodot arrays to fabricate various electronic devices. In this study, seven different suspensions with varying properties were investigated. In the dripping mode, the normalized dropsize decreases linearly with electric capillary number, Ca e , (ratio of electric to surface tension forces) up to Ca e ≈ 1.0. The effect of viscous forces is found to be negligible in the dripping mode since the capillary number is small. For flow rates with low Reynolds number, the mode changes to microdripping mode, and then to a planar oscillating microdripping mode as Ca e increases. The normalized dropsize remains nearly constant at 0.07 for Ca e > 3.3. The microdripping mode which is important for depositing discrete array of nanodots is found to occur in the range, 2 ≤ Ca e ≤ 2.5. The droplet frequency increases steadily from dripping to microdripping mode, but stays roughly constant in the oscillating microdripping mode. This work provides a physical basis by which the flow rate and the voltage can be chosen for any nanosuspension to precisely operate in the microdripping mode at a predetermined dropsize and droplet frequency.}, } @article {pmid28690413, year = {2017}, author = {Marques, F and Meseguer, A and Mellibovsky, F and Weidman, PD}, title = {Extensional channel flow revisited: a dynamical systems perspective.}, journal = {Proceedings. Mathematical, physical, and engineering sciences}, volume = {473}, number = {2202}, pages = {20170151}, pmid = {28690413}, issn = {1364-5021}, abstract = {Extensional self-similar flows in a channel are explored numerically for arbitrary stretching-shrinking rates of the confining parallel walls. The present analysis embraces time integrations, and continuations of steady and periodic solutions unfolded in the parameter space. Previous studies focused on the analysis of branches of steady solutions for particular stretching-shrinking rates, although recent studies focused also on the dynamical aspects of the problems. We have adopted a dynamical systems perspective, analysing the instabilities and bifurcations the base state undergoes when increasing the Reynolds number. It has been found that the base state becomes unstable for small Reynolds numbers, and a transitional region including complex dynamics takes place at intermediate Reynolds numbers, depending on the wall acceleration values. The base flow instabilities are constitutive parts of different codimension-two bifurcations that control the dynamics in parameter space. For large Reynolds numbers, the restriction to self-similarity results in simple flows with no realistic behaviour, but the flows obtained in the transition region can be a valuable tool for the understanding of the dynamics of realistic Navier-Stokes solutions.}, } @article {pmid28688478, year = {2017}, author = {Akbar, NS and Butt, AW and Tripathi, D}, title = {Biomechanically driven unsteady non-uniform flow of Copper water and Silver water nanofluids through finite length channel.}, journal = {Computer methods and programs in biomedicine}, volume = {146}, number = {}, pages = {1-9}, doi = {10.1016/j.cmpb.2017.04.016}, pmid = {28688478}, issn = {1872-7565}, mesh = {Copper/*analysis ; Nanostructures/*analysis ; Pressure ; *Rheology ; Silver/*analysis ; Water/*analysis ; }, abstract = {BACKGROUND AND OBJECTIVES: This paper aims to investigate the unsteady flow of two types of nanofluids i.e Copper water nanofluids and Silver water nanofluids) through finite length non-uniform channel driven by peristaltic sinusoidal wave propagations.

METHODS: The governing equations are reduced in linear form using dimensional analysis and considering the low Reynolds number and large wavelength approximations. The time dependent temperature field, axial velocity, transverse velocity and pressure difference are obtained analytically in closed form solution. Trapping phenomenon is also discussed with the help of contour plots of stream function. A comparative study of pure water (Newtonian fluid), Copper water nanofluids and Silver water nanofluids under the influence of relevant physical parameters is made in graphical form and also discussed. The effects of absorption parameter and Grashof number on velocity profiles, temperature profiles and pressure distribution along the length of channel are examined.

RESULTS CONCLUSIONS: The computational results reveal that the velocity profile is maximum for Silver water nanofluids however, it is least for Copper water nanofluids. It is also concluded the temperature profile is more for pure water in comparison to Silver water and Copper water nanofluids. This model is applicable to design, micro-peristaltic pumps which help in Nanoparticle-based targeted drug delivery and to transport the sensitive or corrosive fluids, sanitary fluids, slurries and noxious fluids in nuclear industry.}, } @article {pmid28670352, year = {2017}, author = {Zhou, J and Ryu, S and Admiraal, D}, title = {Flow and transport effect caused by the stalk contraction cycle of Vorticella convallaria.}, journal = {Biomicrofluidics}, volume = {11}, number = {3}, pages = {034119}, pmid = {28670352}, issn = {1932-1058}, abstract = {Vorticella convallaria is a protozoan attached to a substrate by a stalk which can contract in less than 10 ms, translating the zooid toward the substrate with a maximum Reynolds number of ∼1. Following contraction, the stalk slowly relaxes, moving the zooid away from the substrate, which results in creeping flow. Although Vorticella has long been believed to contract to evade danger, it has been suggested that its stalk may contract to enhance food transport near the substrate. To elucidate how Vorticella utilizes its contraction-relaxation cycle, we investigated water flow caused by the cycle, using a computational fluid dynamics model validated with an experimental scale model and particle tracking velocimetry. The simulated flow was visualized and analyzed by tracing virtual particles around the Vorticella. It is observed that one cycle can displace particles up to ∼190 μm with the maximum net vertical displacement of 3-4 μm and that the net transport effect becomes more evident over repeated cycles. This transport effect appears to be due to asymmetry of the contraction and relaxation phases of the flow field, and it can be more effective on motile food particles than non-motile ones. Therefore, our Vorticella model enabled investigating the fluid dynamics principle and ecological role of the transport effects of Vorticella's stalk contraction.}, } @article {pmid28665292, year = {2017}, author = {Kazemi, A and Van de Riet, K and Curet, OM}, title = {Hydrodynamics of mangrove-type root models: the effect of porosity, spacing ratio and flexibility.}, journal = {Bioinspiration & biomimetics}, volume = {12}, number = {5}, pages = {056003}, doi = {10.1088/1748-3190/aa7ccf}, pmid = {28665292}, issn = {1748-3190}, mesh = {*Biomimetic Materials ; Ecosystem ; Equipment Design ; *Hydrodynamics ; Plant Roots/*anatomy & histology/*physiology ; *Porosity ; Rhizophoraceae/*anatomy & histology/*physiology ; }, abstract = {Mangrove trees play a prominent role in coastal tropic and subtropical regions, providing habitats for many organisms and protecting shorelines against high energy flows. In particular, the species Rhizophora mangle (red mangrove) exhibits complex cluster roots interacting with different hydrological flow conditions. To better understand the resilience of mangrove trees, we modeled the roots as a collection of cylinders with a circular pattern subject to unidirectional flow. We investigated the effect of porosity and spacing ratio between roots by varying both the diameter of the patch, D, and inset cylinders, d. In addition, we modeled hanging roots of red mangroves as cantilevered rigid cylinders on a hinge. Force and velocity measurements were performed in a water tunnel (Reynolds numbers from 2200 to 11 000). Concurrently, we performed 2D flow visualization using a flowing soap film. We found that the frequency of the vortex shedding increases as the diameter of the small cylinders decreases while the patch diameter is constant, therefore increasing the Strouhal number, [Formula: see text]. By comparing the change of Strouhal numbers with a single solid cylinder, we introduced a new length scale, the effective diameter. The effective diameter of the patch decreases as the porosity increases. In addition, we found that patch drag scales linearly with the patch diameter but decreases linearly as the spacing ratio increases. After a spacing ratio of ([Formula: see text]), the force scales linearly with the free stream velocity, and the mean velocity behind the patch is independent of the Reynolds number and the patch effect disappears. For flexible cylinders, we found that a decrease in stiffness increases both patch drag and the wake deficit behind the patch in a similar fashion as increasing the blockage of the patch. This information has the potential to help in the development of methods to design resilient bio-inspired coastline structures.}, } @article {pmid28658586, year = {2017}, author = {Qamar, A and Warnez, M and Valassis, DT and Guetzko, ME and Bull, JL}, title = {Small-bubble transport and splitting dynamics in a symmetric bifurcation.}, journal = {Computer methods in biomechanics and biomedical engineering}, volume = {20}, number = {11}, pages = {1182-1194}, doi = {10.1080/10255842.2017.1340466}, pmid = {28658586}, issn = {1476-8259}, support = {R01 EB006476/EB/NIBIB NIH HHS/United States ; }, mesh = {Arteries/physiology ; Embolization, Therapeutic ; Friction ; Humans ; *Microbubbles ; *Models, Theoretical ; Numerical Analysis, Computer-Assisted ; Skin ; Stress, Mechanical ; }, abstract = {Simulations of small bubbles traveling through symmetric bifurcations are conducted to garner information pertinent to gas embolotherapy, a potential cancer treatment. Gas embolotherapy procedures use intra-arterial bubbles to occlude tumor blood supply. As bubbles pass through bifurcations in the blood stream nonhomogeneous splitting and undesirable bioeffects may occur. To aid development of gas embolotherapy techniques, a volume of fluid method is used to model the splitting process of gas bubbles passing through artery and arteriole bifurcations. The model reproduces the variety of splitting behaviors observed experimentally, including the bubble reversal phenomenon. Splitting homogeneity and maximum shear stress along the vessel walls is predicted over a variety of physical parameters. Small bubbles, having initial length less than twice the vessel diameter, were found unlikely to split in the presence of gravitational asymmetry. Maximum shear stresses were found to decrease exponentially with increasing Reynolds number. Vortex-induced shearing near the bifurcation is identified as a possible mechanism for endothelial cell damage.}, } @article {pmid28658585, year = {2017}, author = {Qamar, A and Bull, JL}, title = {Transport and flow characteristics of an oscillating cylindrical fiber for total artificial lung application.}, journal = {Computer methods in biomechanics and biomedical engineering}, volume = {20}, number = {11}, pages = {1195-1211}, doi = {10.1080/10255842.2017.1340467}, pmid = {28658585}, issn = {1476-8259}, mesh = {*Artificial Organs ; Biological Transport ; Humans ; Numerical Analysis, Computer-Assisted ; Reproducibility of Results ; *Rheology ; Stress, Mechanical ; Time Factors ; }, abstract = {Mass transport and fluid dynamics characteristics in the vicinity of an oscillating cylindrical fiber with an imposed pulsatile inflow condition are computationally investigated in the present study. The work is motivated by a recently proposed design modification to the Total Artificial Lung (TAL) device, which is expected to provide better gas exchange. Navier-Stokes computations, coupled with convection-diffusion equation are performed to assess flow dynamics and mass transport behavior around the oscillating fiber. The oscillations and the pulsatile free stream velocity are represented by two sinusoidal functions. The resulting non-dimensional parameters are Keulegan-Carpenter number (KC), Schmidt number (Sc), Reynolds number (Re), pulsatile inflow amplitude ([Formula: see text]), and amplitude of cylinder oscillation ([Formula: see text]). Results are computed for [Formula: see text], Sc = 1000, Re = 5 and 10, [Formula: see text] and 0.7 and 0.25 [Formula: see text][Formula: see text][Formula: see text] 5.25. The pulsatile inflow parameters correspond to the flow velocities found in human pulmonary artery while matching the operating TAL Reynolds number. Mass transport from the surface of the cylinder to the bulk fluid is found to be primarily dependent on the size of surface vortices created by the movement of the cylinder. Time-averaged surface Sherwood number (Sh) is dependent on the amplitude and KC of cylinder oscillation. Compared to the fixed cylinder case, a significant gain up to 380% in Sh is achieved by oscillating the cylinder even at the small displacement amplitude (AD = 0.75D). Moreover, with decrease in KC the oscillating cylinder exhibits a lower drag amplitude compared with the fixed cylinder case. Inflow pulsation amplitude has minor effects on the mass transport characteristics. However, an increase in [Formula: see text] results in an increase in the amplitude of the periodic drag force on the cylinder. This rise in the drag amplitude is similar to that measured for the fixed cylinder case. Quantifications of shear stress distribution in the bulk fluid suggest that the physiological concerns of platelet activation and injury to red blood cells due to cylinder oscillation are negligible.}, } @article {pmid28652683, year = {2017}, author = {Qi, TY and Liu, C and Ni, MJ and Yang, JC}, title = {The linear stability of Hunt-Rayleigh-Bénard flow.}, journal = {Physics of fluids (Woodbury, N.Y. : 1994)}, volume = {29}, number = {6}, pages = {064103}, pmid = {28652683}, issn = {1070-6631}, abstract = {The stability of a pressure driven flow in a duct heated from below and subjected to a vertical magnetic field (Hunt-Rayleigh-Bénard flow) is studied. We use the Chebyshev collocation approach to solve the eigenvalue problem for the small-amplitude perturbations. It is demonstrated that the magnetic field can stabilize the flow, while the temperature field can disturb the flow. There exists a threshold for the Hartmann number below which the growth rate changes with the Prandtl number non-monotonously (first increases and then decreases) with a critical Prandtl number for the maximum growth rate. By comparing the [Formula: see text] neutral curves at different Rayleigh numbers, we find that the critical Reynolds number decreases with the increase in the Rayleigh number, which has an obvious influence on the long-wave instability and a little influence on the short-wave instability. The dominant mode of the long-wave instability changes from the boundary layer instability to the inflectional instability with the increase in the growth rate, which forms a new flow map. We also compare the [Formula: see text] curves and find that the critical Rayleigh number decreases with the increase in the Reynolds number. The obtained results gain an insight into the flow stability affected by the temperature field and the magnetic field.}, } @article {pmid28619665, year = {2017}, author = {Tripathi, D and Borode, A and Jhorar, R and Bég, OA and Tiwari, AK}, title = {Computer modelling of electro-osmotically augmented three-layered microvascular peristaltic blood flow.}, journal = {Microvascular research}, volume = {114}, number = {}, pages = {65-83}, doi = {10.1016/j.mvr.2017.06.004}, pmid = {28619665}, issn = {1095-9319}, mesh = {Animals ; Biomimetics/methods ; Blood Viscosity ; *Computer Simulation ; *Electroosmosis ; Humans ; *Microcirculation ; Microvessels/anatomy & histology/*physiology ; *Models, Cardiovascular ; *Pulsatile Flow ; Time Factors ; }, abstract = {A theoretical study is presented here for the electro-osmosis modulated peristaltic three-layered capillary flow of viscous fluids with different viscosities in the layers. The layers considered here are the core layer, the intermediate layer and the peripheral layer. The analysis has been carried out under a number of physical restrictions viz. Debye-Hückel linearization (i.e. wall zeta potential ≤25mV) is assumed sufficiently small, thin electric double layer limit (i.e. the peripheral layer is much thicker than the electric double layer thickness), low Reynolds number and large wavelength approximations. A non-dimensional analysis is used to linearize the boundary value problem. Fluid-fluid interfaces, peristaltic pumping characteristics, and trapping phenomenon are simulated. Present study also evaluates the responses of interface, pressure rise, time-averaged volume flow rate, maximum pressure rise, and the influence of Helmholtz-Smoluchowski velocity on the mechanical efficiency (with two different cases of the viscosity of fluids between the intermediate and the peripheral layer). Trapping phenomenon along with bolus dynamics evolution with thin EDL effects are analyzed. The findings of this study may ultimately be useful to control the microvascular flow during the fractionation of blood into plasma (in the peripheral layer), buffy coat (intermediate layer) and erythrocytes (core layer). This work may also contributes in electrophoresis, hematology, electrohydrodynamic therapy and, design and development of biomimetic electro-osmotic pumps.}, } @article {pmid28618644, year = {2017}, author = {Wang, L and Huang, Y}, title = {Intrinsic flow structure and multifractality in two-dimensional bacterial turbulence.}, journal = {Physical review. E}, volume = {95}, number = {5-1}, pages = {052215}, doi = {10.1103/PhysRevE.95.052215}, pmid = {28618644}, issn = {2470-0053}, abstract = {The active interaction between the bacteria and fluid generates turbulent structures even at zero Reynolds number. The velocity of such a flow obtained experimentally has been quantitatively investigated based on streamline segment analysis. There is a clear transition at about 16 times the organism body length separating two different scale regimes, which may be attributed to the different influence of the viscous effect. Surprisingly the scaling extracted from the streamline segment indicates the existence of scale similarity even at the zero Reynolds number limit. Moreover, the multifractal feature can be quantitatively described via a lognormal formula with the Hurst number H=0.76 and the intermittency parameter μ=0.20, which is coincidentally in agreement with the three-dimensional hydrodynamic turbulence result. The direction of cascade is measured via the filter-space technique. An inverse energy cascade is confirmed. For the enstrophy, a forward cascade is observed when r/R≤3, and an inverse one is observed when r/R>3, where r and R are the separation distance and the bacteria body size, respectively. Additionally, the lognormal statistics is verified for the coarse-grained energy dissipation and enstrophy, which supports the lognormal formula to fit the measured scaling exponent.}, } @article {pmid28618575, year = {2017}, author = {True, AC and Crimaldi, JP}, title = {Hydrodynamics of viscous inhalant flows.}, journal = {Physical review. E}, volume = {95}, number = {5-1}, pages = {053107}, doi = {10.1103/PhysRevE.95.053107}, pmid = {28618575}, issn = {2470-0053}, abstract = {Inhalant flows draw fluid into an orifice from a reservoir and are ubiquitous in engineering and biology. Surprisingly, there is a lack of quantitative information on viscous inhalant flows. We consider here laminar flows (Reynolds number Re≤100) developing after impulsive inhalation begins. We implement finite element simulations of flows with varying Re and extraction height h (orifice height above a bottom bed). Numerical results are experimentally validated using particle image velocimetry measurements in a physical model for a representative flow case in the middle of the Re-h parameter space. We use two metrics to characterize the flow in space and time: regions of influence (ROIs), which describe the spatial extent of the flow field, and inhalation volumes, which describe the initial distribution of inhaled fluid. The transient response for all Re features an inviscid sinklike component at early times followed by a viscous diffusive component. At lower Re, diffusion entrains an increasing volume of fluid over time, enlarging the ROI indefinitely. In some geometries, these flows spatially bifurcate, with some fluid being inhaled through the orifice and some bypassing into recirculation. At higher Re, inward advection dominates outward viscous diffusion and the flow remains trapped in a sinklike state. Both ROIs and inhalation volumes are strongly dependent on Re and extraction height, suggesting that organisms or engineers could tune these parameters to achieve specific inhalation criteria.}, } @article {pmid28618505, year = {2017}, author = {Puljiz, M and Menzel, AM}, title = {Forces and torques on rigid inclusions in an elastic environment: Resulting matrix-mediated interactions, displacements, and rotations.}, journal = {Physical review. E}, volume = {95}, number = {5-1}, pages = {053002}, doi = {10.1103/PhysRevE.95.053002}, pmid = {28618505}, issn = {2470-0053}, abstract = {Embedding rigid inclusions into elastic matrix materials is a procedure of high practical relevance, for instance, for the fabrication of elastic composite materials. We theoretically analyze the following situation. Rigid spherical inclusions are enclosed by a homogeneous elastic medium under stick boundary conditions. Forces and torques are directly imposed from outside onto the inclusions or are externally induced between them. The inclusions respond to these forces and torques by translations and rotations against the surrounding elastic matrix. This leads to elastic matrix deformations, and in turn results in mutual long-ranged matrix-mediated interactions between the inclusions. Adapting a well-known approach from low-Reynolds-number hydrodynamics, we explicitly calculate the displacements and rotations of the inclusions from the externally imposed or induced forces and torques. Analytical expressions are presented as a function of the inclusion configuration in terms of displaceability and rotateability matrices. The role of the elastic environment is implicitly included in these relations. That is, the resulting expressions allow a calculation of the induced displacements and rotations directly from the inclusion configuration, without having to explicitly determine the deformations of the elastic environment. In contrast to the hydrodynamic case, compressibility of the surrounding medium is readily taken into account. We present the complete derivation based on the underlying equations of linear elasticity theory. In the future, the method will, for example, be helpful to characterize the behavior of externally tunable elastic composite materials, to accelerate numerical approaches, as well as to improve the quantitative interpretation of microrheological results.}, } @article {pmid28618504, year = {2017}, author = {Altmeyer, S and Lueptow, RM}, title = {Wave propagation reversal for wavy vortices in wide-gap counter-rotating cylindrical Couette flow.}, journal = {Physical review. E}, volume = {95}, number = {5-1}, pages = {053103}, doi = {10.1103/PhysRevE.95.053103}, pmid = {28618504}, issn = {2470-0053}, abstract = {We present a numerical study of wavy supercritical cylindrical Couette flow between counter-rotating cylinders in which the wavy pattern propagates either prograde with the inner cylinder or retrograde opposite the rotation of the inner cylinder. The wave propagation reversals from prograde to retrograde and vice versa occur at distinct values of the inner cylinder Reynolds number when the associated frequency of the wavy instability vanishes. The reversal occurs for both twofold and threefold symmetric wavy vortices. Moreover, the wave propagation reversal only occurs for sufficiently strong counter-rotation. The flow pattern reversal appears to be intrinsic in the system as either periodic boundary conditions or fixed end wall boundary conditions for different system sizes always result in the wave propagation reversal. We present a detailed bifurcation sequence and parameter space diagram with respect to retrograde behavior of wavy flows. The retrograde propagation of the instability occurs when the inner Reynolds number is about two times the outer Reynolds number. The mechanism for the retrograde propagation is associated with the inviscidly unstable region near the inner cylinder and the direction of the global average azimuthal velocity. Flow dynamics, spatio-temporal behavior, global mean angular velocity, and torque of the flow with the wavy pattern are explored.}, } @article {pmid28613306, year = {2017}, author = {Khojah, R and Stoutamore, R and Di Carlo, D}, title = {Size-tunable microvortex capture of rare cells.}, journal = {Lab on a chip}, volume = {17}, number = {15}, pages = {2542-2549}, doi = {10.1039/c7lc00355b}, pmid = {28613306}, issn = {1473-0189}, mesh = {Blood Cells/cytology ; Cell Line, Tumor ; Cell Separation/*instrumentation/*methods ; Cell Size ; Humans ; Image Processing, Computer-Assisted/methods ; MCF-7 Cells ; Microfluidic Analytical Techniques/*instrumentation ; Microscopy, Fluorescence ; }, abstract = {Inertial separation of particles and cells based on their size has advanced significantly over the last decade. However, size-based inertial separation methods require precise tuning of microfluidic device geometries to adjust the separation size of particles or cells. Here, we show a passive capture method that targets a wide size range of cells by controlling the flow conditions in a single device geometry. This multimodal capture device is designed to generate laminar vortices in lateral cavities that branch from long rectangular channels. Micro-vortices generated at lower Reynolds numbers capture and stabilize large particles in equilibrium orbits or limit cycles near the vortex core. Other smaller particles or cells orbit near the vortex boundaries and they are susceptible to exiting the cavity flow. In the same cavity, however, at higher Reynolds number, we observe small particles migrating inward. This evolution in limit cycle trajectories led to a corresponding evolution in the average size of captured particles, indicating that the outermost orbits are less stable. We identify three phases of capture as a function of Reynolds number that give rise to unique particle orbit trajectories. Flow-based switching overcomes a major engineering challenge to automate capture and release of polydisperse cell subpopulations. The approach can expand clinical applications of label free trapping in isolating and processing a larger subset of rare cells like circulating tumor cells (CTCs) from blood and other body fluids.}, } @article {pmid28613157, year = {2017}, author = {Ferreira, RR and Vilfan, A and Jülicher, F and Supatto, W and Vermot, J}, title = {Physical limits of flow sensing in the left-right organizer.}, journal = {eLife}, volume = {6}, number = {}, pages = {}, pmid = {28613157}, issn = {2050-084X}, mesh = {Animals ; *Body Patterning ; Cilia/*physiology ; Embryo, Nonmammalian/cytology/*physiology ; Functional Laterality ; Gene Expression Regulation, Developmental ; Hydrodynamics ; Signal Transduction ; Zebrafish/embryology/*physiology ; Zebrafish Proteins/metabolism ; }, abstract = {Fluid flows generated by motile cilia are guiding the establishment of the left-right asymmetry of the body in the vertebrate left-right organizer. Competing hypotheses have been proposed: the direction of flow is sensed either through mechanosensation, or via the detection of chemical signals transported in the flow. We investigated the physical limits of flow detection to clarify which mechanisms could be reliably used for symmetry breaking. We integrated parameters describing cilia distribution and orientation obtained in vivo in zebrafish into a multiscale physical study of flow generation and detection. Our results show that the number of immotile cilia is too small to ensure robust left and right determination by mechanosensing, given the large spatial variability of the flow. However, motile cilia could sense their own motion by a yet unknown mechanism. Finally, transport of chemical signals by the flow can provide a simple and reliable mechanism of asymmetry establishment.}, } @article {pmid28582613, year = {2017}, author = {Chu, X and Yu, X and Greenstein, J and Aydin, F and Uppaladadium, G and Dutt, M}, title = {Flow-Induced Shape Reconfiguration, Phase Separation, and Rupture of Bio-Inspired Vesicles.}, journal = {ACS nano}, volume = {11}, number = {7}, pages = {6661-6671}, doi = {10.1021/acsnano.7b00753}, pmid = {28582613}, issn = {1936-086X}, mesh = {1,2-Dipalmitoylphosphatidylcholine/*chemistry ; Biomimetic Materials/*chemistry ; Cell Shape ; Cholesterol/chemistry ; Computer Simulation ; Dimyristoylphosphatidylcholine/*chemistry ; Drug Carriers/*chemistry ; Erythrocytes/chemistry/cytology ; Glycolipids/chemistry ; Hydrodynamics ; Liposomes/chemistry ; Models, Molecular ; *Phase Transition ; Polyethylene Glycols/*chemistry ; }, abstract = {The structural integrity of red blood cells and drug delivery carriers through blood vessels is dependent upon their ability to adapt their shape during their transportation. Our goal is to examine the role of the composition of bio-inspired multicomponent and hairy vesicles on their shape during their transport through in a channel. Through the dissipative particle dynamics simulation technique, we apply Poiseuille flow in a cylindrical channel. We investigate the effect of flow conditions and concentration of key molecular components on the shape, phase separation, and structural integrity of the bio-inspired multicomponent and hairy vesicles. Our results show the Reynolds number and molecular composition of the vesicles impact their flow-induced deformation, phase separation on the outer monolayer due to the Marangoni effect, and rupture. The findings from this study could be used to enhance the design of drug delivery and tissue engineering systems.}, } @article {pmid28577022, year = {2017}, author = {Huang, Y and Wang, HL and Chen, YQ and Zhang, YH and Yang, Q and Bai, ZS and Ma, L}, title = {Liquid-liquid extraction intensification by micro-droplet rotation in a hydrocyclone.}, journal = {Scientific reports}, volume = {7}, number = {1}, pages = {2678}, pmid = {28577022}, issn = {2045-2322}, abstract = {The previous literature reports that using a hydrocyclone as an extractor intensifies the mass transfer and largely reduces the consumption of extractant from 1800-2000 kg h[-1] to 30-90 kg h[-1]. However, the intensification mechanism has not been clear. This paper presents experimental and numerical methods to study the multi-scale motion of particles in hydrocyclones. In addition to the usually considered translational behavior, the high-speed rotation of dispersed micro-spheres caused by the anisotropic swirling shear flow is determined. The rotation speeds of the tested micro-spheres are above 1000 rad s[-1], which are much larger than the instantaneous rotation speed in isotropic turbulence. Due to the conical structure of a hydrocyclone, the rotation speed maintains stability along the axial direction. Numerical results show that the particle Reynolds number of micro-droplets in a hydrocyclone is equal to that in conventional extractors, but the particles have high rotation speeds of up to 10,000 rad s[-1] and long mixing lengths of more than 1000 mm. Both the rotation of micro-droplets along the spiral trajectories and the intense eddy diffusion in a hydrocyclone contribute to the extraction intensification.}, } @article {pmid28573002, year = {2017}, author = {Petford, N and Mirhadizadeh, S}, title = {Image-based modelling of lateral magma flow: the Basement Sill, Antarctica.}, journal = {Royal Society open science}, volume = {4}, number = {5}, pages = {161083}, pmid = {28573002}, issn = {2054-5703}, abstract = {The McMurdo Dry Valleys magmatic system, Antarctica, provides a world-class example of pervasive lateral magma flow on a continental scale. The lowermost intrusion (Basement Sill) offers detailed sections through the now frozen particle microstructure of a congested magma slurry. We simulated the flow regime in two and three dimensions using numerical models built on a finite-element mesh derived from field data. The model captures the flow behaviour of the Basement Sill magma over a viscosity range of 1-10[4] Pa s where the higher end (greater than or equal to 10[2] Pa s) corresponds to a magmatic slurry with crystal fractions varying between 30 and 70%. A novel feature of the model is the discovery of transient, low viscosity (less than or equal to 50 Pa s) high Reynolds number eddies formed along undulating contacts at the floor and roof of the intrusion. Numerical tracing of particle orbits implies crystals trapped in eddies segregate according to their mass density. Recovered shear strain rates (10[-3]-10[-5] s[-1]) at viscosities equating to high particle concentrations (around more than 40%) in the Sill interior point to shear-thinning as an explanation for some types of magmatic layering there. Model transport rates for the Sill magmas imply a maximum emplacement time of ca 10[5] years, consistent with geochemical evidence for long-range lateral flow. It is a theoretically possibility that fast-flowing magma on a continental scale will be susceptible to planetary-scale rotational forces.}, } @article {pmid28555615, year = {2017}, author = {Stieger, T and Agha, H and Schoen, M and Mazza, MG and Sengupta, A}, title = {Hydrodynamic cavitation in Stokes flow of anisotropic fluids.}, journal = {Nature communications}, volume = {8}, number = {}, pages = {15550}, pmid = {28555615}, issn = {2041-1723}, abstract = {Cavitation, the nucleation of vapour in liquids, is ubiquitous in fluid dynamics, and is often implicated in a myriad of industrial and biomedical applications. Although extensively studied in isotropic liquids, corresponding investigations in anisotropic liquids are largely lacking. Here, by combining liquid crystal microfluidic experiments, nonequilibrium molecular dynamics simulations and theoretical arguments, we report flow-induced cavitation in an anisotropic fluid. The cavitation domain nucleates due to sudden pressure drop upon flow past a cylindrical obstacle within a microchannel. For an anisotropic fluid, the inception and growth of the cavitation domain ensued in the Stokes regime, while no cavitation was observed in isotropic liquids flowing under similar hydrodynamic parameters. Using simulations we identify a critical value of the Reynolds number for cavitation inception that scales inversely with the order parameter of the fluid. Strikingly, the critical Reynolds number for anisotropic fluids can be 50% lower than that of isotropic fluids.}, } @article {pmid28529384, year = {2017}, author = {Rosti, ME and Kamps, L and Bruecker, C and Omidyeganeh, M and Pinelli, A}, title = {The PELskin project-part V: towards the control of the flow around aerofoils at high angle of attack using a self-activated deployable flap.}, journal = {Meccanica}, volume = {52}, number = {8}, pages = {1811-1824}, pmid = {28529384}, issn = {0025-6455}, abstract = {During the flight of birds, it is often possible to notice that some of the primaries and covert feathers on the upper side of the wing pop-up under critical flight conditions, such as the landing approach or when stalking their prey (see Fig. 1) . It is often conjectured that the feathers pop up plays an aerodynamic role by limiting the spread of flow separation . A combined experimental and numerical study was conducted to shed some light on the physical mechanism determining the feathers self actuation and their effective role in controlling the flow field in nominally stalled conditions. In particular, we have considered a NACA0020 aerofoil, equipped with a flexible flap at low chord Reynolds numbers. A parametric study has been conducted on the effects of the length, natural frequency, and position of the flap. A configuration with a single flap hinged on the suction side at 70 % of the chord size c (from the leading edge), with a length of [Formula: see text] matching the shedding frequency of vortices at stall condition has been found to be optimum in delivering maximum aerodynamic efficiency and lift gains. Flow evolution both during a ramp-up motion (incidence angle from [Formula: see text] to [Formula: see text] with a reduced frequency of [Formula: see text], [Formula: see text] being the free stream velocity magnitude), and at a static stalled condition ([Formula: see text]) were analysed with and without the flap. A significant increase of the mean lift after a ramp-up manoeuvre is observed in presence of the flap. Stall dynamics (i.e., lift overshoot and oscillations) are altered and the simulations reveal a periodic re-generation cycle composed of a leading edge vortex that lift the flap during his passage, and an ejection generated by the relaxing of the flap in its equilibrium position. The flap movement in turns avoid the interaction between leading and trailing edge vortices when lift up and push the trailing edge vortex downstream when relaxing back. This cyclic behaviour is clearly shown by the periodic variation of the lift about the average value, and also from the periodic motion of the flap. A comparison with the experiments shows a similar but somewhat higher non-dimensional frequency of the flap oscillation. By assuming that the cycle frequency scales inversely with the boundary layer thickness, one can explain the higher frequencies observed in the experiments which were run at a Reynolds number about one order of magnitude higher than in the simulations. In addition, in experiments the periodic re-generation cycle decays after 3-4 periods ultimately leading to the full stall of the aerofoil. In contrast, the 2D simulations show that the cycle can become self-sustained without any decay when the flap parameters are accurately tuned.}, } @article {pmid28508858, year = {2017}, author = {Doostmohammadi, A and Shendruk, TN and Thijssen, K and Yeomans, JM}, title = {Onset of meso-scale turbulence in active nematics.}, journal = {Nature communications}, volume = {8}, number = {}, pages = {15326}, pmid = {28508858}, issn = {2041-1723}, support = {291234/ERC_/European Research Council/International ; }, abstract = {Meso-scale turbulence is an innate phenomenon, distinct from inertial turbulence, that spontaneously occurs at low Reynolds number in fluidized biological systems. This spatiotemporal disordered flow radically changes nutrient and molecular transport in living fluids and can strongly affect the collective behaviour in prominent biological processes, including biofilm formation, morphogenesis and cancer invasion. Despite its crucial role in such physiological processes, understanding meso-scale turbulence and any relation to classical inertial turbulence remains obscure. Here we show how the motion of active matter along a micro-channel transitions to meso-scale turbulence through the evolution of locally disordered patches (active puffs) from an ordered vortex-lattice flow state. We demonstrate that the stationary critical exponents of this transition to meso-scale turbulence in a channel coincide with the directed percolation universality class. This finding bridges our understanding of the onset of low-Reynolds-number meso-scale turbulence and traditional scale-invariant turbulence in confinement.}, } @article {pmid28505752, year = {2017}, author = {Tasaka, Y and Iima, M}, title = {Surface switching statistics of rotating fluid: Disk-rim gap effects.}, journal = {Physical review. E}, volume = {95}, number = {4-1}, pages = {043113}, doi = {10.1103/PhysRevE.95.043113}, pmid = {28505752}, issn = {2470-0053}, abstract = {We examined the influence of internal noise on the irregular switching of the shape of the free surface of fluids in an open cylindrical vessel driven by a bottom disk rotating at constant speed [Suzuki, Iima, and Hayase, Phys. Fluids 18, 101701 (2006)PHFLE61070-663110.1063/1.2359740]. A slight increase in the disk-rim gap (less than 3% of the disk radius) was established experimentally to cause significant changes in this system, specifically, frequent appearance of the surface descending event connecting a nonaxisymmetric shape in strong mixing flow (turbulent flow) and an axisymmetric shape in laminar flow, as well as a shift in critical Reynolds number that define the characteristic states. The physical mechanism underlying the change is analyzed in terms of flow characteristics in the disk-rim gap, which acts as a noise source, and a mathematical model established from measurements of the surface height fluctuations with noise term.}, } @article {pmid28479987, year = {2017}, author = {Tank, J and Smith, L and Spedding, GR}, title = {Correction to 'On the possibility (or lack thereof) of agreement between experiment and computation of flows over wings at moderate Reynolds number'.}, journal = {Interface focus}, volume = {7}, number = {3}, pages = {20170024}, doi = {10.1098/rsfs.2017.0024}, pmid = {28479987}, issn = {2042-8898}, abstract = {[This corrects the article DOI: 10.1098/rsfs.2016.0076.].}, } @article {pmid28479086, year = {2017}, author = {Moroni, M and Lupo, E and La Marca, F}, title = {Hydraulic separation of plastic wastes: Analysis of liquid-solid interaction.}, journal = {Waste management (New York, N.Y.)}, volume = {66}, number = {}, pages = {13-22}, doi = {10.1016/j.wasman.2017.04.045}, pmid = {28479086}, issn = {1879-2456}, mesh = {*Plastics ; Polymers ; *Recycling ; Refuse Disposal ; }, abstract = {The separation of plastic wastes in mechanical recycling plants is the process that ensures high-quality secondary raw materials. An innovative device employing a wet technology for particle separation is presented in this work. Due to the combination of the characteristic flow pattern developing within the apparatus and density, shape and size differences among two or more polymers, it allows their separation into two products, one collected within the instrument and the other one expelled through its outlet ducts. The kinematic investigation of the fluid flowing within the apparatus seeded with a passive tracer was conducted via image analysis for different hydraulic configurations. The two-dimensional turbulent kinetic energy results strictly connected to the apparatus separation efficacy. Image analysis was also employed to study the behaviour of mixtures of passive tracer and plastic particles with different physical characteristics in order to understand the coupling regime between fluid and solid phases. The two-dimensional turbulent kinetic energy analysis turned out to be fundamental to this aim. For the tested operating conditions, two-way coupling takes place, i.e., the fluid exerts an influence on the plastic particle and the opposite occurs too. Image analysis confirms the outcomes from the investigation of the two-phase flow via non-dimensional numbers (particle Reynolds number, Stokes number and solid phase volume fraction).}, } @article {pmid28470538, year = {2017}, author = {Hosseinzadegan, H and Tafti, DK}, title = {Prediction of Thrombus Growth: Effect of Stenosis and Reynolds Number.}, journal = {Cardiovascular engineering and technology}, volume = {8}, number = {2}, pages = {164-181}, doi = {10.1007/s13239-017-0304-3}, pmid = {28470538}, issn = {1869-4098}, mesh = {Algorithms ; Heparin/*metabolism ; Humans ; Models, Theoretical ; Platelet Activation ; Platelet Adhesiveness ; Platelet Aggregation ; Shear Strength ; Thrombosis/*physiopathology ; }, abstract = {Shear stresses play a major role in platelet-substrate interactions and thrombus formation and growth in blood flow, where under both pathological and physiological conditions platelet adhesion and accumulation occur. In this study, a shear-dependent continuum model for platelet activation, adhesion and aggregation is presented. The model was first verified under three different shear conditions and at two heparin levels. Three-dimensional simulations were then carried out to evaluate the performance of the model for severely damaged (stripped) aortas with mild and severe stenosis degrees in laminar flow regime. For these cases, linear shear-dependent functions were developed for platelet-surface and platelet-platelet adhesion rates. It was confirmed that the platelet adhesion rate is not only a function of Reynolds number (or wall shear rate) but also the stenosis severity of the vessel. General correlations for adhesion rates of platelets as functions of stenosis and Reynolds number were obtained based on these cases. Finally using the new platelet adhesion rates, the model was applied to different experimental systems and shown to agree well with measured platelet deposition.}, } @article {pmid28462417, year = {2017}, author = {Khani, M and Xing, T and Gibbs, C and Oshinski, JN and Stewart, GR and Zeller, JR and Martin, BA}, title = {Nonuniform Moving Boundary Method for Computational Fluid Dynamics Simulation of Intrathecal Cerebrospinal Flow Distribution in a Cynomolgus Monkey.}, journal = {Journal of biomechanical engineering}, volume = {139}, number = {8}, pages = {0810051-08100512}, pmid = {28462417}, issn = {1528-8951}, support = {P20 GM103408/GM/NIGMS NIH HHS/United States ; R44 MH112210/MH/NIMH NIH HHS/United States ; U54 GM104944/GM/NIGMS NIH HHS/United States ; }, mesh = {Animals ; Cerebrospinal Fluid/diagnostic imaging/*physiology ; *Computer Simulation ; *Hydrodynamics ; Macaca fascicularis ; Magnetic Resonance Imaging ; Male ; }, abstract = {A detailed quantification and understanding of cerebrospinal fluid (CSF) dynamics may improve detection and treatment of central nervous system (CNS) diseases and help optimize CSF system-based delivery of CNS therapeutics. This study presents a computational fluid dynamics (CFD) model that utilizes a nonuniform moving boundary approach to accurately reproduce the nonuniform distribution of CSF flow along the spinal subarachnoid space (SAS) of a single cynomolgus monkey. A magnetic resonance imaging (MRI) protocol was developed and applied to quantify subject-specific CSF space geometry and flow and define the CFD domain and boundary conditions. An algorithm was implemented to reproduce the axial distribution of unsteady CSF flow by nonuniform deformation of the dura surface. Results showed that maximum difference between the MRI measurements and CFD simulation of CSF flow rates was <3.6%. CSF flow along the entire spine was laminar with a peak Reynolds number of ∼150 and average Womersley number of ∼5.4. Maximum CSF flow rate was present at the C4-C5 vertebral level. Deformation of the dura ranged up to a maximum of 134 μm. Geometric analysis indicated that total spinal CSF space volume was ∼8.7 ml. Average hydraulic diameter, wetted perimeter, and SAS area were 2.9 mm, 37.3 mm and 27.24 mm2, respectively. CSF pulse wave velocity (PWV) along the spine was quantified to be 1.2 m/s.}, } @article {pmid28452782, year = {2017}, author = {Carrera, L and Springer, F and Lipeme-Kouyi, G and Buffiere, P}, title = {Sulfide emissions in sewer networks: focus on liquid to gas mass transfer coefficient.}, journal = {Water science and technology : a journal of the International Association on Water Pollution Research}, volume = {75}, number = {7-8}, pages = {1899-1908}, doi = {10.2166/wst.2017.070}, pmid = {28452782}, issn = {0273-1223}, mesh = {Gases/chemistry ; Gravitation ; Models, Theoretical ; Phase Transition ; Sewage/*chemistry ; Sulfides/*chemistry ; Water Pollutants, Chemical/*chemistry ; }, abstract = {H2S emission dynamics in sewers are conditioned by the mass transfer coefficient at the interface. This work aims at measuring the variation of the mass transfer coefficient with the hydraulic characteristics, with the objective of estimating H2S emission in gravity pipes, and collecting data to establish models independent of the system geometry. The ratio between the H2S and O2 mass transfer coefficient was assessed in an 8 L mixed reactor under different experimental conditions. Then, oxygen mass transfer measurements were performed in a 10 m long gravity pipe. The following ranges of experimental conditions were investigated: velocity flow [0-0.61 m.s[-1]], Reynolds number [0-23,333]. The hydrodynamic parameters at the liquid/gas interface were calculated by computational fluid dynamics (CFD). In the laboratory-scale reactor, the O2 mass transfer coefficient was found to depend on the stirring rate (rph) as follows: KL,O2 = 0.016 + 0.025 N[3.85]. A KL,H2S/KL,O2 ratio of 0.64 ± 0.24 was found, in accordance with previously published data. CFD results helped in refining this correlation: the mass transfer coefficient depends on the local interface velocity ui (m.h[-1]): KL,O2 = 0.016 + 1.02 × 10[-5] ui[3.85] In the gravity pipe device, KL,O2 also exponentially increased with the mean flow velocity. These trends were found to be consistent with the increasing level of turbulence.}, } @article {pmid28446697, year = {2017}, author = {China, V and Levy, L and Liberzon, A and Elmaliach, T and Holzman, R}, title = {Hydrodynamic regime determines the feeding success of larval fish through the modulation of strike kinematics.}, journal = {Proceedings. Biological sciences}, volume = {284}, number = {1853}, pages = {}, pmid = {28446697}, issn = {1471-2954}, mesh = {Animals ; Biomechanical Phenomena ; *Feeding Behavior ; Hydrodynamics ; Larva/physiology ; Sea Bream/*physiology ; }, abstract = {Larval fishes experience extreme mortality rates, with 99% of a cohort perishing within days after starting to actively feed. While recent evidence suggests that hydrodynamic factors contribute to constraining larval feeding during early ontogeny, feeding is a complex process that involves numerous interacting behavioural and biomechanical components. How these components change throughout ontogeny and how they contribute to feeding remain unclear. Using 339 observations of larval feeding attempts, we quantified the effects of morphological and behavioural traits on feeding success of Sparus aurata larvae during early ontogeny. Feeding success was determined using high-speed videography, under both natural and increased water viscosity treatments. Successful strikes were characterized by Reynolds numbers that were an order of magnitude higher than those of failed strikes. The pattern of increasing strike success with increasing age was driven by the ontogeny of traits that facilitate the transition to higher Reynolds numbers. Hence, the physical growth of a larva plays an important role in its transition to a hydrodynamic regime of higher Reynolds numbers, in which suction feeding is more effective.}, } @article {pmid28443874, year = {2017}, author = {Schaaf, C and Stark, H}, title = {Inertial migration and axial control of deformable capsules.}, journal = {Soft matter}, volume = {13}, number = {19}, pages = {3544-3555}, doi = {10.1039/c7sm00339k}, pmid = {28443874}, issn = {1744-6848}, abstract = {The mechanical deformability of single cells is an important indicator for various diseases such as cancer, blood diseases and inflammation. Lab-on-a-chip devices allow to separate such cells from healthy cells using hydrodynamic forces. We perform hydrodynamic simulations based on the lattice-Boltzmann method and study the behavior of an elastic capsule in a microfluidic channel flow in the inertial regime. While inertial lift forces drive the capsule away from the channel center, its deformability favors migration in the opposite direction. Balancing both migration mechanisms, a deformable capsule assembles at a specific equilibrium distance depending on its size and deformability. We find that this equilibrium distance is nearly independent of the channel Reynolds number and falls on a single master curve when plotted versus the Laplace number. We identify a similar master curve for varying particle radius. In contrast, the actual deformation of a capsule strongly depends on the Reynolds number. The lift-force profiles behave in a similar manner as those for rigid particles. Using the Saffman effect, the capsule's equilibrium position can be controlled by an external force along the channel axis. While rigid particles move to the center when slowed down, very soft capsules show the opposite behavior. Interestingly, for a specific control force particles are focused on the same equilibrium position independent of their deformability.}, } @article {pmid28434714, year = {2017}, author = {Gritti, F and Fogwill, M}, title = {Speed-resolution advantage of turbulent supercritical fluid chromatography in open tubular columns: II - Theoretical and experimental evidences.}, journal = {Journal of chromatography. A}, volume = {1501}, number = {}, pages = {142-150}, doi = {10.1016/j.chroma.2017.04.032}, pmid = {28434714}, issn = {1873-3778}, mesh = {Benzene Derivatives/chemistry ; Carbon Dioxide/chemistry ; Chromatography, Supercritical Fluid/*instrumentation/methods ; Kinetics ; Models, Theoretical ; Pressure ; Silicon Dioxide/chemistry ; Temperature ; }, abstract = {The potential advantage of turbulent supercritical fluid chromatography (TSFC) in open tubular columns (OTC) was evaluated on both theoretical and practical viewpoints. First, the dispersion model derived by Golay in 1958 and recently extended from laminar to turbulent flow regime is used for the predictions of the speed-resolution performance in TSFC. The average dispersion coefficient of matter in the turbulent flow regime was taken from the available experimental data over a range of Reynolds number from 2000 to 6000. Kinetic plots are built at constant pressure drop (ΔP=4500psi) and Schmidt number (Sc=15) for four inner diameters (10, 30, 100, and 300μm) of the OTC and for three retention factors (0, 1, and 10). Accordingly, in turbulent flow regime, for a Reynolds number of 4000 and a retention factor of 1 (the stationary film thickness is assumed to be negligible with respect to the OTC diameter), the theory projects that a 300μm i.d. OTC has the same speed-resolution power (200,000 theoretical plates; 2.4min hold-up time) as that of a 10μm i.d. OTC operated in laminar flow regime. Secondly, the experimental plate heights of n-butylbenzene are measured in laminar and turbulent flow regimes for a 180μm×4.8m fused silica capillary column using pure carbon dioxide as the mobile phase. The back pressure regulator was set at 1500psi, the temperature was uniform at 297K, and the flow rate was increased step-wise from 0.50 to 3.60mL/min so that the experimental Reynolds number increases from 700 to 5400. The experiments are in good agreement with the plate heights projected in TSFC at high flow rates and with those expected at low flow rates in a laminar flow regime.}, } @article {pmid28429018, year = {2017}, author = {Menzel, AM}, title = {Force-induced elastic matrix-mediated interactions in the presence of a rigid wall.}, journal = {Soft matter}, volume = {13}, number = {18}, pages = {3373-3384}, doi = {10.1039/c7sm00459a}, pmid = {28429018}, issn = {1744-6848}, abstract = {We consider a soft elastic matrix that contains particulate inclusions and is bounded by a rigid wall, e.g., the substrate. Such a situation arises in elastic composite materials. They may serve as soft actuators when forces are imposed on or induced between the embedded particles. We investigate how the presence of the rigid wall affects the interactions between the inclusions. First, for no-slip boundary conditions, we transfer Blake's derivation of a corresponding Green's function from low-Reynolds-number hydrodynamics to the linearly elastic case. Then, we list the general expressions to describe the situation for point-like particles in the presence of no-slip and free-slip surface conditions. To compare the effect of the different surface conditions to each other and to the bulk behavior, we address the example situation of pairwise interactions between two embedded particles. The axis through both particle centers is either aligned parallel or perpendicular to the surface. Our results suggest that walls with free-slip surface conditions are preferred when they serve as substrates for soft actuators made from elastic composite materials. As we further demonstrate, the presence of a rigid wall can qualitatively change the interactions between the inclusions. In effect, it can switch attractive interactions into repulsive ones (and vice versa). It should be straightforward to observe the effects in future experiments and to combine our results, e.g., with the modeling of biological cells and tissue on rigid surfaces.}, } @article {pmid28415285, year = {2017}, author = {Fan, WL and Pak, OS and Sandoval, M}, title = {Ellipsoidal Brownian self-driven particles in a magnetic field.}, journal = {Physical review. E}, volume = {95}, number = {3-1}, pages = {032605}, doi = {10.1103/PhysRevE.95.032605}, pmid = {28415285}, issn = {2470-0053}, abstract = {We study the two-dimensional Brownian dynamics of an ellipsoidal paramagnetic microswimmer moving at a low Reynolds number and subject to a magnetic field. Its corresponding mean-square displacement, showing the effect of a particles's shape, activity, and magnetic field on the microswimmer's diffusion, is analytically obtained. Comparison between analytical and computational results shows good agreement. In addition, the effect of self-propulsion on the transition time from anisotropic to isotropic diffusion of the ellipse is investigated.}, } @article {pmid28415282, year = {2017}, author = {Shen, X and Marcos, and Fu, HC}, title = {Traction reveals mechanisms of wall effects for microswimmers near boundaries.}, journal = {Physical review. E}, volume = {95}, number = {3-1}, pages = {033105}, doi = {10.1103/PhysRevE.95.033105}, pmid = {28415282}, issn = {2470-0053}, abstract = {The influence of a plane boundary on low-Reynolds-number swimmers has frequently been studied using image systems for flow singularities. However, the boundary effect can also be expressed using a boundary integral representation over the traction on the boundary. We show that examining the traction pattern on the boundary caused by a swimmer can yield physical insights into determining when far-field multipole models are accurate. We investigate the swimming velocities and the traction of a three-sphere swimmer initially placed parallel to an infinite planar wall. In the far field, the instantaneous effect of the wall on the swimmer is well approximated by that of a multipole expansion consisting of a force dipole and a force quadrupole. On the other hand, the swimmer close to the wall must be described by a system of singularities reflecting its internal structure. We show that these limits and the transition between them can be independently identified by examining the traction pattern on the wall, either using a quantitative correlation coefficient or by visual inspection. Last, we find that for nonconstant propulsion, correlations between swimming stroke motions and internal positions are important and not captured by time-averaged traction on the wall, indicating that care must be taken when applying multipole expansions to study boundary effects in cases of nonconstant propulsion.}, } @article {pmid28413338, year = {2017}, author = {Aurnou, JM and King, EM}, title = {The cross-over to magnetostrophic convection in planetary dynamo systems.}, journal = {Proceedings. Mathematical, physical, and engineering sciences}, volume = {473}, number = {2199}, pages = {20160731}, pmid = {28413338}, issn = {1364-5021}, abstract = {Global scale magnetostrophic balance, in which Lorentz and Coriolis forces comprise the leading-order force balance, has long been thought to describe the natural state of planetary dynamo systems. This argument arises from consideration of the linear theory of rotating magnetoconvection. Here we test this long-held tenet by directly comparing linear predictions against dynamo modelling results. This comparison shows that dynamo modelling results are not typically in the global magnetostrophic state predicted by linear theory. Then, in order to estimate at what scale (if any) magnetostrophic balance will arise in nonlinear dynamo systems, we carry out a simple scaling analysis of the Elsasser number Λ, yielding an improved estimate of the ratio of Lorentz and Coriolis forces. From this, we deduce that there is a magnetostrophic cross-over length scale, [Formula: see text], where Λo is the linear (or traditional) Elsasser number, Rmo is the system scale magnetic Reynolds number and D is the length scale of the system. On scales well above [Formula: see text], magnetostrophic convection dynamics should not be possible. Only on scales smaller than [Formula: see text] should it be possible for the convective behaviours to follow the predictions for the magnetostrophic branch of convection. Because [Formula: see text] is significantly smaller than the system scale in most dynamo models, their large-scale flows should be quasi-geostrophic, as is confirmed in many dynamo simulations. Estimating Λo ≃1 and Rmo ≃10[3] in Earth's core, the cross-over scale is approximately 1/1000 that of the system scale, suggesting that magnetostrophic convection dynamics exists in the core only on small scales below those that can be characterized by geomagnetic observations.}, } @article {pmid28413332, year = {2017}, author = {Ferrari, A}, title = {Fluid dynamics of acoustic and hydrodynamic cavitation in hydraulic power systems.}, journal = {Proceedings. Mathematical, physical, and engineering sciences}, volume = {473}, number = {2199}, pages = {20160345}, pmid = {28413332}, issn = {1364-5021}, abstract = {Cavitation is the transition from a liquid to a vapour phase, due to a drop in pressure to the level of the vapour tension of the fluid. Two kinds of cavitation have been reviewed here: acoustic cavitation and hydrodynamic cavitation. As acoustic cavitation in engineering systems is related to the propagation of waves through a region subjected to liquid vaporization, the available expressions of the sound speed are discussed. One of the main effects of hydrodynamic cavitation in the nozzles and orifices of hydraulic power systems is a reduction in flow permeability. Different discharge coefficient formulae are analysed in this paper: the Reynolds number and the cavitation number result to be the key fluid dynamical parameters for liquid and cavitating flows, respectively. The latest advances in the characterization of different cavitation regimes in a nozzle, as the cavitation number reduces, are presented. The physical cause of choked flows is explained, and an analogy between cavitation and supersonic aerodynamic flows is proposed. The main approaches to cavitation modelling in hydraulic power systems are also reviewed: these are divided into homogeneous-mixture and two-phase models. The homogeneous-mixture models are further subdivided into barotropic and baroclinic models. The advantages and disadvantages of an implementation of the complete Rayleigh-Plesset equation are examined.}, } @article {pmid28399142, year = {2017}, author = {Potvin, J and Werth, AJ}, title = {Oral cavity hydrodynamics and drag production in Balaenid whale suspension feeding.}, journal = {PloS one}, volume = {12}, number = {4}, pages = {e0175220}, pmid = {28399142}, issn = {1932-6203}, mesh = {Animals ; Balaenoptera/*physiology ; *Feeding Behavior ; *Hydrodynamics ; Mouth/*physiology ; }, abstract = {Balaenid whales feed on large aggregates of small and slow-moving prey (predominantly copepods) through a filtration process enabled by baleen. These whales exhibit continuous filtration, namely, with the mouth kept partially opened and the baleen exposed to oncoming prey-laden waters while fluking. The process is an example of crossflow filtration (CFF) in which most of the particulates (prey) are separated from the substrate (water) without ever coming into contact with the filtering surface (baleen). This paper discusses the simulation of baleen filtration hydrodynamics based on a type of hydraulic circuit modeling commonly used in microfluidics, but adapted to the much higher Reynolds number flows typical of whale hydrodynamics. This so-called Baleen Hydraulic Circuit (BHC) model uses as input the basic characteristics of the flows moving through a section of baleen observed in a previous flume study by the authors. The model has low-spatial resolution but incorporates the effects of fluid viscosity, which doubles or more a whale's total body drag in comparison to non-feeding travel. Modeling viscous friction is crucial here since exposing the baleen system to the open ocean ends up tripling a whale's total wetted surface area. Among other findings, the BHC shows how CFF is enhanced by a large filtration surface and hence large body size; how it is carried out via the establishment of rapid anteroposterior flows transporting most of the prey-water slurry towards the oropharyngeal wall; how slower intra-baleen flows manage to transfer most of the substrate out of the mouth, all the while contributing only a fraction to overall oral cavity drag; and how these anteroposterior and intra-baleen flows lose speed as they approach the oropharyngeal wall.}, } @article {pmid28397936, year = {2017}, author = {Reigh, SY and Zhu, L and Gallaire, F and Lauga, E}, title = {Swimming with a cage: low-Reynolds-number locomotion inside a droplet.}, journal = {Soft matter}, volume = {13}, number = {17}, pages = {3161-3173}, doi = {10.1039/c6sm01636g}, pmid = {28397936}, issn = {1744-6848}, abstract = {Inspired by recent experiments using synthetic microswimmers to manipulate droplets, we investigate the low-Reynolds-number locomotion of a model swimmer (a spherical squirmer) encapsulated inside a droplet of a comparable size in another viscous fluid. Meditated solely by hydrodynamic interactions, the encaged swimmer is seen to be able to propel the droplet, and in some situations both remain in a stable co-swimming state. The problem is tackled using both an exact analytical theory and a numerical implementation based on a boundary element method, with a particular focus on the kinematics of the co-moving swimmer and the droplet in a concentric configuration, and we obtain excellent quantitative agreement between the two. The droplet always moves slower than a swimmer which uses purely tangential surface actuation but when it uses a particular combination of tangential and normal actuations, the squirmer and droplet are able to attain the same velocity and stay concentric for all times. We next employ numerical simulations to examine the stability of their concentric co-movement, and highlight several stability scenarios depending on the particular gait adopted by the swimmer. Furthermore, we show that the droplet reverses the nature of the far-field flow induced by the swimmer: a droplet cage turns a pusher swimmer into a puller, and vice versa. Our work sheds light on the potential development of droplets as self-contained carriers of both chemical content and self-propelled devices for controllable and precise drug deliveries.}, } @article {pmid28388112, year = {2017}, author = {Dyer, OT and Ball, RC}, title = {Wavelet Monte Carlo dynamics: A new algorithm for simulating the hydrodynamics of interacting Brownian particles.}, journal = {The Journal of chemical physics}, volume = {146}, number = {12}, pages = {124111}, doi = {10.1063/1.4978808}, pmid = {28388112}, issn = {1089-7690}, abstract = {We develop a new algorithm for the Brownian dynamics of soft matter systems that evolves time by spatially correlated Monte Carlo moves. The algorithm uses vector wavelets as its basic moves and produces hydrodynamics in the low Reynolds number regime propagated according to the Oseen tensor. When small moves are removed, the correlations closely approximate the Rotne-Prager tensor, itself widely used to correct for deficiencies in Oseen. We also include plane wave moves to provide the longest range correlations, which we detail for both infinite and periodic systems. The computational cost of the algorithm scales competitively with the number of particles simulated, N, scaling as N In N in homogeneous systems and as N in dilute systems. In comparisons to established lattice Boltzmann and Brownian dynamics algorithms, the wavelet method was found to be only a factor of order 1 times more expensive than the cheaper lattice Boltzmann algorithm in marginally semi-dilute simulations, while it is significantly faster than both algorithms at large N in dilute simulations. We also validate the algorithm by checking that it reproduces the correct dynamics and equilibrium properties of simple single polymer systems, as well as verifying the effect of periodicity on the mobility tensor.}, } @article {pmid28373015, year = {2017}, author = {Miguel, AF}, title = {Penetration of inhaled aerosols in the bronchial tree.}, journal = {Medical engineering & physics}, volume = {44}, number = {}, pages = {25-31}, doi = {10.1016/j.medengphy.2017.03.004}, pmid = {28373015}, issn = {1873-4030}, mesh = {Aerosols ; Bronchi/*anatomy & histology/*metabolism/physiology ; Humans ; *Inhalation ; *Models, Anatomic ; Particle Size ; }, abstract = {It has long been recognized that the pattern of particle deposition in the respiratory tree affects how far aerosols penetrate into the deeper zones of the arterial tree, and hence contribute to either their pathogenic potential or therapeutic benefit. In this paper, we introduce an anatomically-inspired model of the human respiratory tree featuring the generations 0-7 in the Weibel model of respiratory tree (i.e., the conducting zone). This model is used to study experimentally the dynamics of inhaled aerosol particles (0.5-20µm aerodynamic diameter), in terms of the penetration fraction of particles (i.e., the fraction of inflowing particles that leave the flow system) during typical breathing patterns. Our study underline important modifications in the penetration patterns for coarse particles compared to fine particles. Our experiments suggest a significant decrease of particle penetration for large-sized particles and higher respiratory frequencies. Dimensionless numbers are also introduced to further understand the particle penetration into the respiratory tree. A decline is seen in the penetration fraction with decreasing Reynolds number and increasing Stokes number. A simple conceptual framework is presented to provide additional insights into the findings obtained.}, } @article {pmid28364770, year = {2017}, author = {Smaoui, N and Zribi, M}, title = {On the control of the chaotic attractors of the 2-d Navier-Stokes equations.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {27}, number = {3}, pages = {033111}, doi = {10.1063/1.4978682}, pmid = {28364770}, issn = {1089-7682}, abstract = {The control problem of the chaotic attractors of the two dimensional (2-d) Navier-Stokes (N-S) equations is addressed in this paper. First, the Fourier Galerkin method based on a reduced-order modelling approach developed by Chen and Price is applied to the 2-d N-S equations to construct a fifth-order system of nonlinear ordinary differential equations (ODEs). The dynamics of the fifth-order system was studied by analyzing the system's attractor for different values of Reynolds number, Re. Then, control laws are proposed to drive the states of the ODE system to a desired attractor. Finally, an adaptive controller is designed to synchronize two reduced order ODE models having different Reynolds numbers and starting from different initial conditions. Simulation results indicate that the proposed control schemes work well.}, } @article {pmid28342532, year = {2017}, author = {Gülan, U and Binter, C and Kozerke, S and Holzner, M}, title = {Shear-scaling-based approach for irreversible energy loss estimation in stenotic aortic flow - An in vitro study.}, journal = {Journal of biomechanics}, volume = {56}, number = {}, pages = {89-96}, doi = {10.1016/j.jbiomech.2017.03.006}, pmid = {28342532}, issn = {1873-2380}, mesh = {Aorta/physiopathology ; Aortic Valve Stenosis/*physiopathology ; Blood Flow Velocity/physiology ; Constriction, Pathologic/physiopathology ; Humans ; Magnetic Resonance Imaging/methods ; Models, Cardiovascular ; Phantoms, Imaging ; Rheology/methods ; }, abstract = {Today, the functional and risk assessment of stenosed arteries is mostly based on ultrasound Doppler blood flow velocity measurements or catheter pressure measurements, which rely on several assumptions. Alternatively, blood velocity including turbulent kinetic energy (TKE) may be measured using MRI. The aim of the present study is to validate a TKE-based approach that relies on the fact that turbulence production is dominated by the flow's shear to determine the total irreversible energy loss from MRI scans. Three-dimensional particle tracking velocimetry (3D-PTV) and phase-contrast magnetic resonance imaging (PC-MRI) simulations were performed in an anatomically accurate, compliant, silicon aortic phantom. We found that measuring only the laminar viscous losses does not reflect the true losses of stenotic flows since the contribution of the turbulent losses to the total loss become more dominant for more severe stenosis types (for example, the laminar loss is 0.0094±0.0015W and the turbulent loss is 0.0361±0.0015W for the Remax=13,800 case, where Remax is the Reynolds number based on the velocity in the vena-contracta). We show that the commonly used simplified and modified Bernoulli's approaches overestimate the total loss, while the new TKE-based method proposed here, referred to as "shear scaling" approach, results in a good agreement between 3D-PTV and simulated PC-MRI (mean error is around 10%). In addition, we validated the shear scaling approach on a geometry with post-stenotic dilatation using numerical data by Casas et al. (2016). The shear scaling-based method may hence be an interesting alternative for irreversible energy loss estimation to replace traditional approaches for clinical use. We expect that our results will evoke further research, in particular patient studies for clinical implementation of the new method.}, } @article {pmid28337415, year = {2017}, author = {Nijp, JJ and Metselaar, K and Limpens, J and Gooren, HP and van der Zee, SE}, title = {A modification of the constant-head permeameter to measure saturated hydraulic conductivity of highly permeable media.}, journal = {MethodsX}, volume = {4}, number = {}, pages = {134-142}, pmid = {28337415}, issn = {2215-0161}, abstract = {The saturated hydraulic conductivity (Ks) is a key characteristic of porous media, describing the rate of water flow through saturated porous media. It is an indispensable parameter in a broad range of simulation models that quantify saturated and/or unsaturated water flow. The constant-head permeameter test is a common laboratory method to determine Ks on undisturbed soil samples collected from the field. In this paper we show that the application of this conventional method may result in a biased Ks in the case of highly permeable media, such as the top layer of Sphagnum peat and gravel. Tubes in the conventional permeameter, that collect water under the sample, introduce a hydraulic head-dependent resistance for highly permeable media and result in an underestimation of Ks . We present a simple and low-budget alternative of the constant-head permeameter test that overcomes the disadvantages of conventional permeameters. The new method was successfully tested on intact highly permeable peatmoss collected from a northern peatland. •Conventional constant-head permeameters underestimate Ks of highly permeable media due to flow resistance in tubing systems•We developed the low-resistance permeameter to overcome this disadvantage.•Testing of the low-resistance permeameter demonstrated no systematic bias and successful application for highly permeable media.}, } @article {pmid28325440, year = {2017}, author = {Hayat, T and Farooq, S and Alsaedi, A}, title = {Mixed convection peristaltic motion of copper-water nanomaterial with velocity slip effects in a curved channel.}, journal = {Computer methods and programs in biomedicine}, volume = {142}, number = {}, pages = {117-128}, doi = {10.1016/j.cmpb.2017.02.006}, pmid = {28325440}, issn = {1872-7565}, mesh = {Computer Simulation ; Convection ; Copper/*chemistry ; Drug Delivery Systems ; Hot Temperature ; Metal Nanoparticles ; Models, Theoretical ; Motion ; Nanostructures/*chemistry ; *Peristalsis ; Pressure ; Rheology ; Software ; Viscosity ; Water/*chemistry ; }, abstract = {BACKGROUND AND OBJECTIVE: The primary objective of present analysis is to model the peristalsis of copper-water based nanoliquid in the presence of first order velocity and thermal slip conditions in a curved channel. Mixed convection, viscous dissipation and heat generation/absorption are also accounted.

METHOD: Mathematical formulation is simplified under the assumption of small Reynolds number and large wavelength. Regular perturbation technique is employed to find the solution of the resulting equations in terms of series for small Brinkman number. The final expression for pressure gradient, pressure rise, stream function, velocity and temperature are obtained and discussed through graphs. Mathematica software is utilized to compute the solution of the system of equations and to plot the graphical results.

RESULTS: Results indicates that insertion of 30% copper nanoparticles in the basefluid (water) velocity and temperature reduces by almost 3% and 40% respecively. Moreover it is seen that size of the trapped bolus also reduces almost 20% with the insertion of 20% nanoparticles (copper) in the basefluid (water).

CONCLUSION: It is noted that velocity and temperature are decreasing functions of nanoparticle volume fraction. Moreover the temperature rises when heat generation parameter and Brinkman number are enhanced.}, } @article {pmid28297984, year = {2017}, author = {Hejranfar, K and Saadat, MH and Taheri, S}, title = {High-order weighted essentially nonoscillatory finite-difference formulation of the lattice Boltzmann method in generalized curvilinear coordinates.}, journal = {Physical review. E}, volume = {95}, number = {2-1}, pages = {023314}, doi = {10.1103/PhysRevE.95.023314}, pmid = {28297984}, issn = {2470-0053}, abstract = {In this work, a high-order weighted essentially nonoscillatory (WENO) finite-difference lattice Boltzmann method (WENOLBM) is developed and assessed for an accurate simulation of incompressible flows. To handle curved geometries with nonuniform grids, the incompressible form of the discrete Boltzmann equation with the Bhatnagar-Gross-Krook (BGK) approximation is transformed into the generalized curvilinear coordinates and the spatial derivatives of the resulting lattice Boltzmann equation in the computational plane are solved using the fifth-order WENO scheme. The first-order implicit-explicit Runge-Kutta scheme and also the fourth-order Runge-Kutta explicit time integrating scheme are adopted for the discretization of the temporal term. To examine the accuracy and performance of the present solution procedure based on the WENOLBM developed, different benchmark test cases are simulated as follows: unsteady Taylor-Green vortex, unsteady doubly periodic shear layer flow, steady flow in a two-dimensional (2D) cavity, steady cylindrical Couette flow, steady flow over a 2D circular cylinder, and steady and unsteady flows over a NACA0012 hydrofoil at different flow conditions. Results of the present solution are compared with the existing numerical and experimental results which show good agreement. To show the efficiency and accuracy of the solution methodology, the results are also compared with the developed second-order central-difference finite-volume lattice Boltzmann method and the compact finite-difference lattice Boltzmann method. It is shown that the present numerical scheme is robust, efficient, and accurate for solving steady and unsteady incompressible flows even at high Reynolds number flows.}, } @article {pmid28297968, year = {2017}, author = {de Graaf, J and Stenhammar, J}, title = {Lattice-Boltzmann simulations of microswimmer-tracer interactions.}, journal = {Physical review. E}, volume = {95}, number = {2-1}, pages = {023302}, doi = {10.1103/PhysRevE.95.023302}, pmid = {28297968}, issn = {2470-0053}, abstract = {Hydrodynamic interactions in systems composed of self-propelled particles, such as swimming microorganisms and passive tracers, have a significant impact on the tracer dynamics compared to the equivalent "dry" sample. However, such interactions are often difficult to take into account in simulations due to their computational cost. Here, we perform a systematic investigation of swimmer-tracer interaction using an efficient force-counterforce-based lattice-Boltzmann (LB) algorithm [De Graaf et al., J. Chem. Phys. 144, 134106 (2016)JCPSA60021-960610.1063/1.4944962] in order to validate its ability to capture the relevant low-Reynolds-number physics. We show that the LB algorithm reproduces far-field theoretical results well, both in a system with periodic boundary conditions and in a spherical cavity with no-slip walls, for which we derive expressions here. The force-lattice coupling of the LB algorithm leads to a "smearing out" of the flow field, which strongly perturbs the tracer trajectories at close swimmer-tracer separations, and we analyze how this effect can be accurately captured using a simple renormalized hydrodynamic theory. Finally, we show that care must be taken when using LB algorithms to simulate systems of self-propelled particles, since its finite momentum transport time can lead to significant deviations from theoretical predictions based on Stokes flow. These insights should prove relevant to the future study of large-scale microswimmer suspensions using these methods.}, } @article {pmid28297886, year = {2017}, author = {Iyer, KP and Sreenivasan, KR and Yeung, PK}, title = {Reynolds number scaling of velocity increments in isotropic turbulence.}, journal = {Physical review. E}, volume = {95}, number = {2-1}, pages = {021101}, doi = {10.1103/PhysRevE.95.021101}, pmid = {28297886}, issn = {2470-0053}, abstract = {Using the largest database of isotropic turbulence available to date, generated by the direct numerical simulation (DNS) of the Navier-Stokes equations on an 8192^{3} periodic box, we show that the longitudinal and transverse velocity increments scale identically in the inertial range. By examining the DNS data at several Reynolds numbers, we infer that the contradictory results of the past on the inertial-range universality are artifacts of low Reynolds number and residual anisotropy. We further show that both longitudinal and transverse velocity increments scale on locally averaged dissipation rate, just as postulated by Kolmogorov's refined similarity hypothesis, and that, in isotropic turbulence, a single independent scaling adequately describes fluid turbulence in the inertial range.}, } @article {pmid28289562, year = {2017}, author = {Cheng, X and Sun, M}, title = {Aerodynamic forces and flows of the full and partial clap-fling motions in insects.}, journal = {PeerJ}, volume = {5}, number = {}, pages = {e3002}, pmid = {28289562}, issn = {2167-8359}, abstract = {Most of the previous studies on Weis-Fogh clap-fling mechanism have focused on the vortex structures and velocity fields. Detailed pressure distribution results are provided for the first time in this study to reveal the differences between the full and the partial clap-fling motions. The two motions are studied by numerically solving the Navier-Stokes equations in moving overset grids. The Reynolds number is set to 20, relevant to the tiny flying insects. The following has been shown: (1) During the clap phase, the wings clap together and create a high pressure region in the closing gap between wings, greatly increasing the positive pressure on the lower surface of wing, while pressure on the upper surface is almost unchanged by the interaction; during the fling phase, the wings fling apart and create a low pressure region in the opening gap between wings, greatly increasing the suction pressure on the upper surface of wing, while pressure on the lower surface is almost unchanged by the interaction; (2) The interference effect between wings is most severe at the end of clap phase and the start of the fling phase: two sharp force peaks (8-9 times larger than that of the one-winged case) are generated. But the total force peaks are manifested mostly as drag and barely as lift of the wing, owing to the vertical orientation of the wing section; (3) The wing-wing interaction effect in the partial clap-fling case is much weaker than that in the full clap-fling case, avoiding the generation of huge drag. Compared with a single wing flapping with the same motion, mean lift in the partial case is enhanced by 12% without suffering any efficiency degradation, indicating that partial clap-fling is a more practical choice for tiny insects to employ.}, } @article {pmid28270051, year = {2017}, author = {Zeinoddini, M and Bakhtiari, A and Schoefs, F and Zandi, AP}, title = {Towards an understanding of marine fouling effects on the vortex-induced vibrations of circular cylinders: partial coverage issue.}, journal = {Biofouling}, volume = {33}, number = {3}, pages = {268-280}, doi = {10.1080/08927014.2017.1291803}, pmid = {28270051}, issn = {1029-2454}, mesh = {Animals ; Biofilms/*growth & development ; Biofouling/*prevention & control ; *Hydrodynamics ; *Models, Theoretical ; Thoracica/*physiology ; *Vibration ; }, abstract = {The results of in-water vortex-induced vibration (VIV) experiments on circular cylinders artificially covered with barnacles are reported. The paper focusses on the effects of the partial coverage and the shape of the fouling elements. An artificial barnacle typical of marine fouling was synthesised using 3-D printing. Coverage ratios of 80, 50 and 30% were examined and the results compared with those from a smooth cylinder. The Reynolds number ranged from 5.8 × 10[3] to 6.6 × 10[4]. The experimental results show that the fouling reduced the peak VIV amplitude, narrowed the synchronisation region and lowered the hydrodynamic force coefficients such as the coefficients of lift force RMS, the mean drag force and the fluctuating drag force RMS. The shape of the artificial barnacles had little effect on the maximum oscillation amplitude. The coverage ratio appeared to have a lower impact on the lift force than those on the amplitude and the frequency responses.}, } @article {pmid28267999, year = {2017}, author = {Gritti, F}, title = {Extension of Golay's plate height equation from laminar to turbulent flow I - Theory.}, journal = {Journal of chromatography. A}, volume = {1492}, number = {}, pages = {129-135}, doi = {10.1016/j.chroma.2017.02.044}, pmid = {28267999}, issn = {1873-3778}, mesh = {Algorithms ; Chromatography, Supercritical Fluid ; *Models, Theoretical ; Temperature ; }, abstract = {The reduced plate height (RPH) equation of Golay derived in 1958 for open tubular columns (OTC) is extended from laminar to turbulent-like flow. The mass balance equation is solved under near-equilibrium conditions in the mobile phase for changing shapes of the velocity profile across the OTC diameter. The final expression of the general RPH equation is: [Formula: see text] where ν is the reduced linear velocity, k is the retention factor, Dm is the bulk diffusion coefficient in the mobile phase, Da¯ is the average axial dispersion coefficient, Dr¯ is the average radial dispersion coefficient, Ds is the diffusion coefficient of the analyte in the stationary film of thickness df, D is the OTC inner diameter, and n≥2 is a positive number controlling the shape of the flow profile (polynomial of degree n). The correctness of the derived RPH equation is verified for Poiseuille (n=2), turburlent-like (n=10), and uniformly flat (n→∞) flow profiles. The derived RPH equation is applied to predict the gain in speed-resolution of a 180μm i.d.×20m OTC (df=2μm) from laminar to turbulent flow in supercritical fluid chromatography. Using pure carbon dioxide as the mobile phase at 297K, k=1, and increasing the Reynolds number from 2000 (laminar) to 4000 (turbulent), the OTC efficiency is expected to increase from 125 to 670 (×5.4) while the hold-up time decreases from 19 to 9s (×0.5). Despite the stronger resistance to mass transfer in the stationary phase, the projected improvement of the column performance in turbulent flow is explained by the quasi-elimination of the resistance to mass transfer in the mobile phase while axial dispersion remains negligible.}, } @article {pmid28267159, year = {2017}, author = {Peng, Z and Elfring, GJ and Pak, OS}, title = {Maximizing propulsive thrust of a driven filament at low Reynolds number via variable flexibility.}, journal = {Soft matter}, volume = {13}, number = {12}, pages = {2339-2347}, doi = {10.1039/c6sm02880b}, pmid = {28267159}, issn = {1744-6848}, abstract = {At low Reynolds numbers the locomotive capability of a body can be dramatically hindered by the absence of inertia. In this work, we show how propulsive performance in this regime can be significantly enhanced by employing spatially varying flexibility. As a prototypical example, we consider the propulsive thrust generated by a filament periodically driven at one end. The rigid case leads to zero propulsion, as so constrained by Purcell's scallop theorem, while for uniform filaments there exists a bending stiffness maximizing the propulsive force at a given frequency; here we demonstrate explicitly how considerable further improvement can be achieved by simply varying the stiffness along the filament. The optimal flexibility distribution is strongly configuration-dependent: while increasing the flexibility towards the tail-end enhances the propulsion of a clamped filament, for a hinged filament decreasing the flexibility towards the tail-end is instead favorable. The results reveal new design principles for maximizing propulsion at low Reynolds numbers, potentially useful for developing synthetic micro-swimmers requiring large propulsive force for various biomedical applications.}, } @article {pmid28253673, year = {2017}, author = {Van Blitterswyk, J and Rocha, J}, title = {An experimental study of the wall-pressure fluctuations beneath low Reynolds number turbulent boundary layers.}, journal = {The Journal of the Acoustical Society of America}, volume = {141}, number = {2}, pages = {1257}, doi = {10.1121/1.4976341}, pmid = {28253673}, issn = {1520-8524}, abstract = {A more complete understanding of the physical relationships, between wall-pressure and turbulence, is required for modeling flow-induced noise and developing noise reduction strategies. In this study, the wall-pressure fluctuations, induced by low Reynolds number turbulent boundary layers, are experimentally studied using a high-resolution microphone array. Statistical characteristics obtained using traditional cross-correlation and cross-spectra analyses are complimented with wall-pressure-velocity cross-spectra and wavelet cross-correlations. Wall-pressure-velocity correlations revealed that turbulent activity in the buffer layer contributes at least 40% of the energy to the wall-pressure spectrum at all measured frequencies. As Reynolds number increases, the low-frequency energy shifts from the buffer layer to the logarithmic layer, as expected for regions of uniform streamwise momentum formed by hairpin packets. Conditional cross-spectra suggests that the majority of broadband wall-pressure energy is concentrated within the packets, with the pressure signatures of individual hairpin vortices estimated to decay on average within traveling ten displacement thicknesses, and the packet signature is retained for up to seven boundary layer thicknesses on average.}, } @article {pmid28234274, year = {2017}, author = {Qin, Y and Wu, J and Hu, Q and Ghista, DN and Wong, KK}, title = {Computational evaluation of smoothed particle hydrodynamics for implementing blood flow modelling through CT reconstructed arteries.}, journal = {Journal of X-ray science and technology}, volume = {25}, number = {2}, pages = {213-232}, doi = {10.3233/XST-17255}, pmid = {28234274}, issn = {1095-9114}, mesh = {Arterial Occlusive Diseases/diagnostic imaging/pathology/physiopathology ; Blood Flow Velocity/*physiology ; *Computer Simulation ; Humans ; Hydrodynamics ; Image Processing, Computer-Assisted/*methods ; *Models, Cardiovascular ; Tomography, X-Ray Computed/*methods ; }, abstract = {Simulation of blood flow in a stenosed artery using Smoothed Particle Hydrodynamics (SPH) is a new research field, which is a particle-based method and different from the traditional continuum modelling technique such as Computational Fluid Dynamics (CFD). Both techniques harness parallel computing to process hemodynamics of cardiovascular structures. The objective of this study is to develop and test a new robust method for comparison of arterial flow velocity contours by SPH with the well-established CFD technique, and the implementation of SPH in computed tomography (CT) reconstructed arteries. The new method was developed based on three-dimensional (3D) straight and curved arterial models of millimeter range with a 25% stenosis in the middle section. In this study, we employed 1,000 to 13,000 particles to study how the number of particles influences SPH versus CFD deviation for blood-flow velocity distribution. Because further increasing the particle density has a diminishing effect on this deviation, we have determined a critical particle density of 1.45 particles/mm2 based on Reynolds number (Re = 200) at the inlet for an arterial flow simulation. Using this critical value of particle density can avoid unnecessarily big computational expenses that have no further effect on simulation accuracy. We have particularly shown that the SPH method has a big potential to be used in the virtual surgery system, such as to simulate the interaction between blood flow and the CT reconstructed vessels, especially those with stenosis or plaque when encountering vasculopathy, and for employing the simulation results output in clinical surgical procedures.}, } @article {pmid28231298, year = {2017}, author = {Hayat, T and Aziz, A and Muhammad, T and Alsaedi, A}, title = {A revised model for Jeffrey nanofluid subject to convective condition and heat generation/absorption.}, journal = {PloS one}, volume = {12}, number = {2}, pages = {e0172518}, pmid = {28231298}, issn = {1932-6203}, mesh = {Algorithms ; Computer Simulation ; *Convection ; *Hot Temperature ; *Hydrodynamics ; Magnetic Fields ; Models, Chemical ; Motion ; Nanoparticles/*chemistry ; Nanotechnology ; Surface Properties ; }, abstract = {Here magnetohydrodynamic (MHD) boundary layer flow of Jeffrey nanofluid by a nonlinear stretching surface is addressed. Heat generation/absorption and convective surface condition effects are considered. Novel features of Brownian motion and thermophoresis are present. A non-uniform applied magnetic field is employed. Boundary layer and small magnetic Reynolds number assumptions are employed in the formulation. A newly developed condition with zero nanoparticles mass flux is imposed. The resulting nonlinear systems are solved. Convergence domains are explicitly identified. Graphs are analyzed for the outcome of sundry variables. Further local Nusselt number is computed and discussed. It is observed that the effects of Hartman number on the temperature and concentration distributions are qualitatively similar. Both temperature and concentration distributions are enhanced for larger Hartman number.}, } @article {pmid28222160, year = {2017}, author = {Hayat, T and Zahir, H and Tanveer, A and Alsaedi, A}, title = {Soret and Dufour effects on MHD peristaltic transport of Jeffrey fluid in a curved channel with convective boundary conditions.}, journal = {PloS one}, volume = {12}, number = {2}, pages = {e0164854}, pmid = {28222160}, issn = {1932-6203}, mesh = {Convection ; Diffusion ; Electric Conductivity ; Equipment Design ; Magnetic Fields ; Osmolar Concentration ; Peristalsis ; *Rheology ; Solutions ; *Temperature ; }, abstract = {The purpose of present article is to examine the peristaltic flow of Jeffrey fluid in a curved channel. An electrically conducting fluid in the presence of radial applied magnetic field is considered. Analysis of heat and mass transfer is carried out. More generalized realistic constraints namely the convective conditions are utilized. Soret and Dufour effects are retained. Problems formulation is given for long wavelength and low Reynolds number assumptions. The expressions of velocity, temperature, heat transfer coefficient, concentration and stream function are computed. Effects of emerging parameters arising in solutions are analyzed in detail. It is found that velocity is not symmetric about centreline for curvature parameter. Also maximum velocity decreases with an increase in the strength of magnetic field. Further it is noticed that Soret and Dufour numbers have opposite behavior for temperature and concentration.}, } @article {pmid28208335, year = {2017}, author = {Walchli, B and Thornber, B}, title = {Reynolds number effects on the single-mode Richtmyer-Meshkov instability.}, journal = {Physical review. E}, volume = {95}, number = {1-1}, pages = {013104}, doi = {10.1103/PhysRevE.95.013104}, pmid = {28208335}, issn = {2470-0053}, abstract = {The Reynolds number effects on the nonlinear growth rates of the Richtmyer-Meshkov instability are investigated using two-dimensional numerical simulations. A decrease in Reynolds number gives an increased time to reach nonlinear saturation, with Reynolds number effects only significant in the range Re<256. Within this range there is a sharp change in instability properties. The bubble and spike amplitudes move towards equal size at lower Reynolds numbers and the bubble velocities decay faster than predicted by Sohn's model [S.-I. Sohn, Phys. Rev. E 80, 055302 (2009)PLEEE81539-375510.1103/PhysRevE.80.055302]. Predicted amplitudes show reasonable agreement with the existing theory of Carles and Popinet [P. Carles and S. Popinet, Phys. Fluids Lett. 13, 1833 (2001)10.1063/1.1377863; Eur. J. Mech. B 21, 511 (2002)EJBFEV0997-754610.1016/S0997-7546(02)01199-8] and Mikaelian [K. O. Mikaelian, Phys. Rev. E 47, 375 (1993)1063-651X10.1103/PhysRevE.47.375; K. O. Mikaelian, Phys. Rev. E 87, 031003 (2013)PLEEE81539-375510.1103/PhysRevE.87.031003], with the former being the closest match to the current computations.}, } @article {pmid28208331, year = {2017}, author = {Linkmann, M and Berera, A and Goldstraw, EE}, title = {Reynolds-number dependence of the dimensionless dissipation rate in homogeneous magnetohydrodynamic turbulence.}, journal = {Physical review. E}, volume = {95}, number = {1-1}, pages = {013102}, doi = {10.1103/PhysRevE.95.013102}, pmid = {28208331}, issn = {2470-0053}, abstract = {This paper examines the behavior of the dimensionless dissipation rate C_{ɛ} for stationary and nonstationary magnetohydrodynamic (MHD) turbulence in the presence of external forces. By combining with previous studies for freely decaying MHD turbulence, we obtain here both the most general model equation for C_{ɛ} applicable to homogeneous MHD turbulence and a comprehensive numerical study of the Reynolds number dependence of the dimensionless total energy dissipation rate at unity magnetic Prandtl number. We carry out a series of medium to high resolution direct numerical simulations of mechanically forced stationary MHD turbulence in order to verify the predictions of the model equation for the stationary case. Furthermore, questions of nonuniversality are discussed in terms of the effect of external forces as well as the level of cross- and magnetic helicity. The measured values of the asymptote C_{ɛ,∞} lie between 0.193≤C_{ɛ,∞} ≤0.268 for free decay, where the value depends on the initial level of cross- and magnetic helicities. In the stationary case we measure C_{ɛ,∞} =0.223.}, } @article {pmid28191582, year = {2017}, author = {Yasuda, S and Hayakawa, M and Onoe, H and Takinoue, M}, title = {Twisting microfluidics in a planetary centrifuge.}, journal = {Soft matter}, volume = {13}, number = {11}, pages = {2141-2147}, doi = {10.1039/c6sm02695h}, pmid = {28191582}, issn = {1744-6848}, abstract = {This paper reports a twisting microfluidic method utilising a centrifuge-based fluid extruding system in a planetary centrifuge which simultaneously generates an orbital rotation and an axial spin. In this method, fluid extrusion from a micro-scale capillary to an 'open-space' solution or air enables release of the fluid from the capillary-based microchannel, which physically means that there is a release of fluids from a confined low-Reynolds-number environment to an open non-low-Reynolds-number environment. As a result, the extruded fluids are separated from the axial spin of the capillary, and the difference in the angular rates of the axial spin between the capillary and the extruded fluids produces the 'twisting' of the fluid. In this study, we achieve control of the twist of highly viscous fluids, and we construct a simple physical model for the fluid twist. In addition, we demonstrate the formation of twisted hydrogel microstructures (stripe-patterned microbeads and multi-helical microfibres) with control over the stripe pattern and the helical pitch length. We believe that this method will enable the generation of more sophisticated microstructures which cannot easily be formed by usual channel-based microfluidic devices. This method can also provide advanced control of microfluids, as in the case of rapid mixing of highly viscous fluids. This method can contribute to a wide range of applications in materials science, biophysics, biomedical science, and microengineering in the future.}, } @article {pmid28187884, year = {2017}, author = {Shahzadi, I and Sadaf, H and Nadeem, S and Saleem, A}, title = {Bio-mathematical analysis for the peristaltic flow of single wall carbon nanotubes under the impact of variable viscosity and wall properties.}, journal = {Computer methods and programs in biomedicine}, volume = {139}, number = {}, pages = {137-147}, doi = {10.1016/j.cmpb.2016.10.016}, pmid = {28187884}, issn = {1872-7565}, mesh = {*Nanotubes, Carbon ; *Peristalsis ; *Viscosity ; }, abstract = {OBJECTIVE: The main objective of this paper is to study the Bio-mathematical analysis for the peristaltic flow of single wall carbon nanotubes under the impact of variable viscosity and wall properties.

DESIGN/APPROACH: The right and the left walls of the curved channel possess sinusoidal wave that is travelling along the outer boundary. The features of the peristaltic motion are determined by using long wavelength and low Reynolds number approximation. Exact solutions are determined for the axial velocity and for the temperature profile.

FINDINGS: Graphical results have been presented for velocity profile, temperature and stream function for various physical parameters of interest. Symmetry of the curved channel is disturbed for smaller values of the curvature parameter. It is found that the altitude of the velocity profile increases for larger values of variable viscosity parameter for both the cases (pure blood as well as single wall carbon nanotubes). It is detected that velocity profile increases with increasing values of rigidity parameter. It is due to the fact that an increase in rigidity parameter decreases tension in the walls of the blood vessels which speeds up the blood flow for pure blood as well as single wall carbon nanotubes. Increase in Grashof number decreases the fluid velocity. This is due to the reason that viscous forces play a prominent role that's why increase in Grashof number decreases the velocity profile. It is also found that temperature drops for increasing values of nanoparticle volume fraction. Basically, higher thermal conductivity of the nanoparticles plays a key role for quick heat dissipation, and this justifies the use of the single wall carbon nanotubes in different situations as a coolant.

CONCLUSIONS: Exact solutions are calculated for the temperature and the velocity profile. Symmetry of the curved channel is destroyed due to the curvedness for velocity, temperature and contour plots. Addition of single wall carbon nanotubes shows a decrease in fluid temperature. Trapping phenomena show that the size of the trapped bolus is smaller for pure blood case as compared to the single wall carbon nanotubes.}, } @article {pmid28176897, year = {2017}, author = {Guiffant, G and Flaud, P and Royon, L and Burnet, E and Merckx, J}, title = {Mechanical characteristics of plastic base Ports and impact on flushing efficacy.}, journal = {Medical devices (Auckland, N.Z.)}, volume = {10}, number = {}, pages = {11-15}, pmid = {28176897}, issn = {1179-1470}, abstract = {BACKGROUND: Three types of totally implantable venous access devices, Ports, are currently in use: titanium, plastic (polyoxymethylene, POM), and mixed (titanium base with a POM shell). Physics theory suggests that the interaction between a non-coring needle (NCN, made of stainless steel) and a plastic base would lead to the stronger material (steel) altering the more malleable material (plastic).

OBJECTIVES: To investigate whether needle impacts can alter a plastic base's surface, thus potentially reducing flushing efficacy.

STUDY DESIGN AND METHODS: A Port made of POM was punctured 200 times with a 19-gauge NCN. Following the existing guidelines, the needle tip pricked the base with each puncture. The Port's base was then examined using a two-dimensional optical instrument, and a bi-dimensional numerical simulation using COMSOL[®] was performed to investigate potential surface irregularities and their impact on fluid flow.

RESULTS: Each needle impact created a hole (mean depth, 0.12 mm) with a small bump beside it (mean height, 0.02 mm) the Reynolds number Rek≈10. A numerical simulation of the one hole/bump set showed that the flushing efficacy was 60% that of flushing along a flat surface.

DISCUSSION: In clinical practice, the number of times a Port is punctured depends on patient and treatment characteristics, but each needle impact on the plastic base may increase the risk of decreased flushing effectiveness. Therefore, the more a plastic Port is accessed, the greater the risk of microorganisms, blood products, and medication accumulation.

CONCLUSIONS: Multiple needle impacts created an irregular surface on the Port's base, which decreased flushing efficacy. Clinical investigation is needed to determine whether plastic base Ports are associated with an increased risk of Port infection and occlusion compared to titanium base Ports.}, } @article {pmid28167586, year = {2017}, author = {Örlü, R and Fiorini, T and Segalini, A and Bellani, G and Talamelli, A and Alfredsson, PH}, title = {Reynolds stress scaling in pipe flow turbulence-first results from CICLoPE.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {375}, number = {2089}, pages = {}, pmid = {28167586}, issn = {1364-503X}, abstract = {This paper reports the first turbulence measurements performed in the Long Pipe Facility at the Center for International Cooperation in Long Pipe Experiments (CICLoPE). In particular, the Reynolds stress components obtained from a number of straight and boundary-layer-type single-wire and X-wire probes up to a friction Reynolds number of 3.8×10[4] are reported. In agreement with turbulent boundary-layer experiments as well as with results from the Superpipe, the present measurements show a clear logarithmic region in the streamwise variance profile, with a Townsend-Perry constant of A2≈1.26. The wall-normal variance profile exhibits a Reynolds-number-independent plateau, while the spanwise component was found to obey a logarithmic scaling over a much wider wall-normal distance than the other two components, with a slope that is nearly half of that of the Townsend-Perry constant, i.e. A2,w≈A2/2. The present results therefore provide strong support for the scaling of the Reynolds stress tensor based on the attached-eddy hypothesis. Intriguingly, the wall-normal and spanwise components exhibit higher amplitudes than in previous studies, and therefore call for follow-up studies in CICLoPE, as well as other large-scale facilities.This article is part of the themed issue 'Toward the development of high-fidelity models of wall turbulence at large Reynolds number'.}, } @article {pmid28167585, year = {2017}, author = {Klewicki, JC and Chini, GP and Gibson, JF}, title = {Prospectus: towards the development of high-fidelity models of wall turbulence at large Reynolds number.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {375}, number = {2089}, pages = {}, pmid = {28167585}, issn = {1364-503X}, abstract = {Recent and on-going advances in mathematical methods and analysis techniques, coupled with the experimental and computational capacity to capture detailed flow structure at increasingly large Reynolds numbers, afford an unprecedented opportunity to develop realistic models of high Reynolds number turbulent wall-flow dynamics. A distinctive attribute of this new generation of models is their grounding in the Navier-Stokes equations. By adhering to this challenging constraint, high-fidelity models ultimately can be developed that not only predict flow properties at high Reynolds numbers, but that possess a mathematical structure that faithfully captures the underlying flow physics. These first-principles models are needed, for example, to reliably manipulate flow behaviours at extreme Reynolds numbers. This theme issue of Philosophical Transactions of the Royal Society A provides a selection of contributions from the community of researchers who are working towards the development of such models. Broadly speaking, the research topics represented herein report on dynamical structure, mechanisms and transport; scale interactions and self-similarity; model reductions that restrict nonlinear interactions; and modern asymptotic theories. In this prospectus, the challenges associated with modelling turbulent wall-flows at large Reynolds numbers are briefly outlined, and the connections between the contributing papers are highlighted.This article is part of the themed issue 'Toward the development of high-fidelity models of wall turbulence at large Reynolds number'.}, } @article {pmid28167584, year = {2017}, author = {Dogan, E and Hearst, RJ and Ganapathisubramani, B}, title = {Modelling high Reynolds number wall-turbulence interactions in laboratory experiments using large-scale free-stream turbulence.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {375}, number = {2089}, pages = {}, pmid = {28167584}, issn = {1364-503X}, support = {277472/ERC_/European Research Council/International ; }, abstract = {A turbulent boundary layer subjected to free-stream turbulence is investigated in order to ascertain the scale interactions that dominate the near-wall region. The results are discussed in relation to a canonical high Reynolds number turbulent boundary layer because previous studies have reported considerable similarities between these two flows. Measurements were acquired simultaneously from four hot wires mounted to a rake which was traversed through the boundary layer. Particular focus is given to two main features of both canonical high Reynolds number boundary layers and boundary layers subjected to free-stream turbulence: (i) the footprint of the large scales in the logarithmic region on the near-wall small scales, specifically the modulating interaction between these scales, and (ii) the phase difference in amplitude modulation. The potential for a turbulent boundary layer subjected to free-stream turbulence to 'simulate' high Reynolds number wall-turbulence interactions is discussed. The results of this study have encouraging implications for future investigations of the fundamental scale interactions that take place in high Reynolds number flows as it demonstrates that these can be achieved at typical laboratory scales.This article is part of the themed issue 'Toward the development of high-fidelity models of wall turbulence at large Reynolds number'.}, } @article {pmid28167583, year = {2017}, author = {Chini, GP and Montemuro, B and White, CM and Klewicki, J}, title = {A self-sustaining process model of inertial layer dynamics in high Reynolds number turbulent wall flows.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {375}, number = {2089}, pages = {}, pmid = {28167583}, issn = {1364-503X}, abstract = {Field observations and laboratory experiments suggest that at high Reynolds numbers Re the outer region of turbulent boundary layers self-organizes into quasi-uniform momentum zones (UMZs) separated by internal shear layers termed 'vortical fissures' (VFs). Motivated by this emergent structure, a conceptual model is proposed with dynamical components that collectively have the potential to generate a self-sustaining interaction between a single VF and adjacent UMZs. A large-Re asymptotic analysis of the governing incompressible Navier-Stokes equation is performed to derive reduced equation sets for the streamwise-averaged and streamwise-fluctuating flow within the VF and UMZs. The simplified equations reveal the dominant physics within-and isolate possible coupling mechanisms among-these different regions of the flow.This article is part of the themed issue 'Toward the development of high-fidelity models of wall turbulence at large Reynolds number'.}, } @article {pmid28167582, year = {2017}, author = {Sharma, AS and Moarref, R and McKeon, BJ}, title = {Scaling and interaction of self-similar modes in models of high Reynolds number wall turbulence.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {375}, number = {2089}, pages = {}, pmid = {28167582}, issn = {1364-503X}, abstract = {Previous work has established the usefulness of the resolvent operator that maps the terms nonlinear in the turbulent fluctuations to the fluctuations themselves. Further work has described the self-similarity of the resolvent arising from that of the mean velocity profile. The orthogonal modes provided by the resolvent analysis describe the wall-normal coherence of the motions and inherit that self-similarity. In this contribution, we present the implications of this similarity for the nonlinear interaction between modes with different scales and wall-normal locations. By considering the nonlinear interactions between modes, it is shown that much of the turbulence scaling behaviour in the logarithmic region can be determined from a single arbitrarily chosen reference plane. Thus, the geometric scaling of the modes is impressed upon the nonlinear interaction between modes. Implications of these observations on the self-sustaining mechanisms of wall turbulence, modelling and simulation are outlined.This article is part of the themed issue 'Toward the development of high-fidelity models of wall turbulence at large Reynolds number'.}, } @article {pmid28167581, year = {2017}, author = {Cossu, C and Hwang, Y}, title = {Self-sustaining processes at all scales in wall-bounded turbulent shear flows.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {375}, number = {2089}, pages = {}, pmid = {28167581}, issn = {1364-503X}, abstract = {We collect and discuss the results of our recent studies which show evidence of the existence of a whole family of self-sustaining motions in wall-bounded turbulent shear flows with scales ranging from those of buffer-layer streaks to those of large-scale and very-large-scale motions in the outer layer. The statistical and dynamical features of this family of self-sustaining motions, which are associated with streaks and quasi-streamwise vortices, are consistent with those of Townsend's attached eddies. Motions at each relevant scale are able to sustain themselves in the absence of forcing from larger- or smaller-scale motions by extracting energy from the mean flow via a coherent lift-up effect. The coherent self-sustaining process is embedded in a set of invariant solutions of the filtered Navier-Stokes equations which take into full account the Reynolds stresses associated with the residual smaller-scale motions.This article is part of the themed issue 'Toward the development of high-fidelity models of wall turbulence at large Reynolds number'.}, } @article {pmid28167580, year = {2017}, author = {Hellström, LH and Smits, AJ}, title = {Structure identification in pipe flow using proper orthogonal decomposition.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {375}, number = {2089}, pages = {}, pmid = {28167580}, issn = {1364-503X}, abstract = {The energetic motions in direct numerical simulations of turbulent pipe flow at Reτ=685 are investigated using proper orthogonal decomposition. The procedure is extended such that a pressure component is identified in addition to the three-component velocity field for each mode. The pressure component of the modes is shown to align with the streamwise velocity component associated with the large-scale motions, where positive pressure coincides with positive streamwise velocity, and vice versa. The streamwise evolution of structures is then visualized using a conditional mode, which exhibit a strong similarity to the large-scale, low-momentum motions. A low-pressure region is present in the downstream section of the structure, and a high-pressure region is present in the upstream section.This article is part of the themed issue 'Toward the development of high-fidelity models of wall turbulence at large Reynolds number'.}, } @article {pmid28167579, year = {2017}, author = {Morrill-Winter, C and Philip, J and Klewicki, J}, title = {Statistical evidence of anasymptotic geometric structure to the momentum transporting motions in turbulent boundary layers.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {375}, number = {2089}, pages = {}, pmid = {28167579}, issn = {1364-503X}, abstract = {The turbulence contribution to the mean flow is reflected by the motions producing the Reynolds shear stress (〈-uv〉) and its gradient. Recent analyses of the mean dynamical equation, along with data, evidence that these motions asymptotically exhibit self-similar geometric properties. This study discerns additional properties associated with the uv signal, with an emphasis on the magnitudes and length scales of its negative contributions. The signals analysed derive from high-resolution multi-wire hot-wire sensor data acquired in flat-plate turbulent boundary layers. Space-filling properties of the present signals are shown to reinforce previous observations, while the skewness of uv suggests a connection between the size and magnitude of the negative excursions on the inertial domain. Here, the size and length scales of the negative uv motions are shown to increase with distance from the wall, whereas their occurrences decrease. A joint analysis of the signal magnitudes and their corresponding lengths reveals that the length scales that contribute most to 〈-uv〉 are distinctly larger than the average geometric size of the negative uv motions. Co-spectra of the streamwise and wall-normal velocities, however, are shown to exhibit invariance across the inertial region when their wavelengths are normalized by the width distribution, W(y), of the scaling layer hierarchy, which renders the mean momentum equation invariant on the inertial domain.This article is part of the themed issue 'Toward the development of high-fidelity models of wall turbulence at large Reynolds number'.}, } @article {pmid28167578, year = {2017}, author = {Schmid, PJ and Sayadi, T}, title = {Low-dimensional representation of near-wall dynamics in shear flows, with implications to wall-models.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {375}, number = {2089}, pages = {}, doi = {10.1098/rsta.2016.0082}, pmid = {28167578}, issn = {1364-503X}, abstract = {The dynamics of coherent structures near the wall of a turbulent boundary layer is investigated with the aim of a low-dimensional representation of its essential features. Based on a triple decomposition into mean, coherent and incoherent motion and a dynamic mode decomposition to recover statistical information about the incoherent part of the flow field, a driven linear system coupling first- and second-order moments of the coherent structures is derived and analysed. The transfer function for this system, evaluated for a wall-parallel plane, confirms a strong bias towards streamwise elongated structures, and is proposed as an 'impedance' boundary condition which replaces the bulk of the transport between the coherent velocity field and the coherent Reynolds stresses, thus acting as a wall model for large-eddy simulations (LES). It is interesting to note that the boundary condition is non-local in space and time. The extracted model is capable of reproducing the principal Reynolds stress components for the pretransitional, transitional and fully turbulent boundary layer.This article is part of the themed issue 'Toward the development of high-fidelity models of wall turbulence at large Reynolds number'.}, } @article {pmid28167577, year = {2017}, author = {Farrell, BF and Gayme, DF and Ioannou, PJ}, title = {A statistical state dynamics approach to wall turbulence.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {375}, number = {2089}, pages = {}, pmid = {28167577}, issn = {1364-503X}, abstract = {This paper reviews results obtained using statistical state dynamics (SSD) that demonstrate the benefits of adopting this perspective for understanding turbulence in wall-bounded shear flows. The SSD approach used in this work employs a second-order closure that retains only the interaction between the streamwise mean flow and the streamwise mean perturbation covariance. This closure restricts nonlinearity in the SSD to that explicitly retained in the streamwise constant mean flow together with nonlinear interactions between the mean flow and the perturbation covariance. This dynamical restriction, in which explicit perturbation-perturbation nonlinearity is removed from the perturbation equation, results in a simplified dynamics referred to as the restricted nonlinear (RNL) dynamics. RNL systems, in which a finite ensemble of realizations of the perturbation equation share the same mean flow, provide tractable approximations to the SSD, which is equivalent to an infinite ensemble RNL system. This infinite ensemble system, referred to as the stochastic structural stability theory system, introduces new analysis tools for studying turbulence. RNL systems provide computationally efficient means to approximate the SSD and produce self-sustaining turbulence exhibiting qualitative features similar to those observed in direct numerical simulations despite greatly simplified dynamics. The results presented show that RNL turbulence can be supported by as few as a single streamwise varying component interacting with the streamwise constant mean flow and that judicious selection of this truncated support or 'band-limiting' can be used to improve quantitative accuracy of RNL turbulence. These results suggest that the SSD approach provides new analytical and computational tools that allow new insights into wall turbulence.This article is part of the themed issue 'Toward the development of high-fidelity models of wall turbulence at large Reynolds number'.}, } @article {pmid28167576, year = {2017}, author = {Duvvuri, S and McKeon, B}, title = {Phase relations in a forced turbulent boundary layer: implications for modelling of high Reynolds number wall turbulence.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {375}, number = {2089}, pages = {}, pmid = {28167576}, issn = {1364-503X}, abstract = {Phase relations between specific scales in a turbulent boundary layer are studied here by highlighting the associated nonlinear scale interactions in the flow. This is achieved through an experimental technique that allows for targeted forcing of the flow through the use of a dynamic wall perturbation. Two distinct large-scale modes with well-defined spatial and temporal wavenumbers were simultaneously forced in the boundary layer, and the resulting nonlinear response from their direct interactions was isolated from the turbulence signal for the study. This approach advances the traditional studies of large- and small-scale interactions in wall turbulence by focusing on the direct interactions between scales with triadic wavenumber consistency. The results are discussed in the context of modelling high Reynolds number wall turbulence.This article is part of the themed issue 'Toward the development of high-fidelity models of wall turbulence at large Reynolds number'.}, } @article {pmid28167575, year = {2017}, author = {Brauckmann, HJ and Eckhardt, B and Schumacher, J}, title = {Heat transport in Rayleigh-Bénard convection and angular momentum transport in Taylor-Couette flow: a comparative study.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {375}, number = {2089}, pages = {}, pmid = {28167575}, issn = {1364-503X}, abstract = {Rayleigh-Bénard convection and Taylor-Couette flow are two canonical flows that have many properties in common. We here compare the two flows in detail for parameter values where the Nusselt numbers, i.e. the thermal transport and the angular momentum transport normalized by the corresponding laminar values, coincide. We study turbulent Rayleigh-Bénard convection in air at Rayleigh number Ra=10[7] and Taylor-Couette flow at shear Reynolds number ReS=2×10[4] for two different mean rotation rates but the same Nusselt numbers. For individual pairwise related fields and convective currents, we compare the probability density functions normalized by the corresponding root mean square values and taken at different distances from the wall. We find one rotation number for which there is very good agreement between the mean profiles of the two corresponding quantities temperature and angular momentum. Similarly, there is good agreement between the fluctuations in temperature and velocity components. For the heat and angular momentum currents, there are differences in the fluctuations outside the boundary layers that increase with overall rotation and can be related to differences in the flow structures in the boundary layer and in the bulk. The study extends the similarities between the two flows from global quantities to local quantities and reveals the effects of rotation on the transport.This article is part of the themed issue 'Toward the development of high-fidelity models of wall turbulence at large Reynolds number'.}, } @article {pmid28167574, year = {2017}, author = {Deguchi, K and Hall, P}, title = {The relationship between free-stream coherent structures and near-wall streaks at high Reynolds numbers.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {375}, number = {2089}, pages = {}, pmid = {28167574}, issn = {1364-503X}, abstract = {The present work is based on our recent discovery of a new class of exact coherent structures generated near the edge of quite general boundary layer flows. The structures are referred to as free-stream coherent structures and were found using a large Reynolds number asymptotic approach to describe equilibrium solutions of the Navier-Stokes equations. In this paper, first we present results for a new family of free-stream coherent structures existing at relatively large wavenumbers. The new results are consistent with our earlier theoretical result that such structures can generate larger amplitude wall streaks if and only if the local spanwise wavenumber is sufficiently small. In a Blasius boundary layer, the local wavenumber increases in the streamwise direction so the wall streaks can typically exist only over a finite interval. However, here it is shown that they can interact with wall curvature to produce exponentially growing Görtler vortices through the receptivity process by a novel nonparallel mechanism. The theoretical predictions found are confirmed by a hybrid numerical approach. In contrast with previous receptivity investigations, it is shown that the amplitude of the induced vortex is larger than the structures in the free-stream which generate it.This article is part of the themed issue 'Toward the development of high-fidelity models of wall turbulence at large Reynolds number'.}, } @article {pmid28167573, year = {2017}, author = {Baars, WJ and Hutchins, N and Marusic, I}, title = {Reynolds number trend of hierarchies and scale interactions in turbulent boundary layers.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {375}, number = {2089}, pages = {}, pmid = {28167573}, issn = {1364-503X}, abstract = {Small-scale velocity fluctuations in turbulent boundary layers are often coupled with the larger-scale motions. Studying the nature and extent of this scale interaction allows for a statistically representative description of the small scales over a time scale of the larger, coherent scales. In this study, we consider temporal data from hot-wire anemometry at Reynolds numbers ranging from Reτ≈2800 to 22 800, in order to reveal how the scale interaction varies with Reynolds number. Large-scale conditional views of the representative amplitude and frequency of the small-scale turbulence, relative to the large-scale features, complement the existing consensus on large-scale modulation of the small-scale dynamics in the near-wall region. Modulation is a type of scale interaction, where the amplitude of the small-scale fluctuations is continuously proportional to the near-wall footprint of the large-scale velocity fluctuations. Aside from this amplitude modulation phenomenon, we reveal the influence of the large-scale motions on the characteristic frequency of the small scales, known as frequency modulation. From the wall-normal trends in the conditional averages of the small-scale properties, it is revealed how the near-wall modulation transitions to an intermittent-type scale arrangement in the log-region. On average, the amplitude of the small-scale velocity fluctuations only deviates from its mean value in a confined temporal domain, the duration of which is fixed in terms of the local Taylor time scale. These concentrated temporal regions are centred on the internal shear layers of the large-scale uniform momentum zones, which exhibit regions of positive and negative streamwise velocity fluctuations. With an increasing scale separation at high Reynolds numbers, this interaction pattern encompasses the features found in studies on internal shear layers and concentrated vorticity fluctuations in high-Reynolds-number wall turbulence.This article is part of the themed issue 'Toward the development of high-fidelity models of wall turbulence at large Reynolds number'.}, } @article {pmid28163876, year = {2017}, author = {Phillips, N and Knowles, K and Bomphrey, RJ}, title = {Petiolate wings: effects on the leading-edge vortex in flapping flight.}, journal = {Interface focus}, volume = {7}, number = {1}, pages = {20160084}, pmid = {28163876}, issn = {2042-8898}, abstract = {The wings of many insect species including crane flies and damselflies are petiolate (on stalks), with the wing planform beginning some distance away from the wing hinge, rather than at the hinge. The aerodynamic impact of flapping petiolate wings is relatively unknown, particularly on the formation of the lift-augmenting leading-edge vortex (LEV): a key flow structure exploited by many insects, birds and bats to enhance their lift coefficient. We investigated the aerodynamic implications of petiolation P using particle image velocimetry flow field measurements on an array of rectangular wings of aspect ratio 3 and petiolation values of P = 1-3. The wings were driven using a mechanical device, the 'Flapperatus', to produce highly repeatable insect-like kinematics. The wings maintained a constant Reynolds number of 1400 and dimensionless stroke amplitude Λ* (number of chords traversed by the wingtip) of 6.5 across all test cases. Our results showed that for more petiolate wings the LEV is generally larger, stronger in circulation, and covers a greater area of the wing surface, particularly at the mid-span and inboard locations early in the wing stroke cycle. In each case, the LEV was initially arch-like in form with its outboard end terminating in a focus-sink on the wing surface, before transitioning to become continuous with the tip vortex thereafter. In the second half of the wing stroke, more petiolate wings exhibit a more detached LEV, with detachment initiating at approximately 70% and 50% span for P = 1 and 3, respectively. As a consequence, lift coefficients based on the LEV are higher in the first half of the wing stroke for petiolate wings, but more comparable in the second half. Time-averaged LEV lift coefficients show a general rise with petiolation over the range tested.}, } @article {pmid28163871, year = {2017}, author = {Widmann, A and Tropea, C}, title = {Reynolds number influence on the formation of vortical structures on a pitching flat plate.}, journal = {Interface focus}, volume = {7}, number = {1}, pages = {20160079}, pmid = {28163871}, issn = {2042-8898}, abstract = {The impact of chord-based Reynolds number on the formation of leading-edge vortices (LEVs) on unsteady pitching flat plates is investigated. The influence of secondary flow structures on the shear layer feeding the LEV and the subsequent topological change at the leading edge as the result of viscous processes are demonstrated. Time-resolved velocity fields are measured using particle image velocimetry simultaneously in two fields of view to correlate local and global flow phenomena in order to identify unsteady boundary-layer separation and the subsequent flow structures. Finally, the Reynolds number is identified as a parameter that is responsible for the transition in mechanisms leading to LEV detachment from an aerofoil, as it determines the viscous response of the boundary layer in the vortex-wall interaction.}, } @article {pmid28163870, year = {2017}, author = {Wagner, H and Weger, M and Klaas, M and Schröder, W}, title = {Features of owl wings that promote silent flight.}, journal = {Interface focus}, volume = {7}, number = {1}, pages = {20160078}, pmid = {28163870}, issn = {2042-8898}, abstract = {Owls are an order of birds of prey that are known for the development of a silent flight. We review here the morphological adaptations of owls leading to silent flight and discuss also aerodynamic properties of owl wings. We start with early observations (until 2005), and then turn to recent advances. The large wings of these birds, resulting in low wing loading and a low aspect ratio, contribute to noise reduction by allowing slow flight. The serrations on the leading edge of the wing and the velvet-like surface have an effect on noise reduction and also lead to an improvement of aerodynamic performance. The fringes at the inner feather vanes reduce noise by gliding into the grooves at the lower wing surface that are formed by barb shafts. The fringed trailing edge of the wing has been shown to reduce trailing edge noise. These adaptations to silent flight have been an inspiration for biologists and engineers for the development of devices with reduced noise production. Today several biomimetic applications such as a serrated pantograph or a fringed ventilator are available. Finally, we discuss unresolved questions and possible future directions.}, } @article {pmid28163869, year = {2017}, author = {Tank, J and Smith, L and Spedding, GR}, title = {On the possibility (or lack thereof) of agreement between experiment and computation of flows over wings at moderate Reynolds number.}, journal = {Interface focus}, volume = {7}, number = {1}, pages = {20160076}, pmid = {28163869}, issn = {2042-8898}, abstract = {The flight of many birds and bats, and their robotic counterparts, occurs over a range of chord-based Reynolds numbers from 1 × 10[4] to 1.5 × 10[5]. It is precisely over this range where the aerodynamics of simple, rigid, fixed wings becomes extraordinarily sensitive to small changes in geometry and the environment, with two sets of consequences. The first is that practical lifting devices at this scale will likely not be simple, rigid, fixed wings. The second is that it becomes non-trivial to make baseline comparisons for experiment and computation, when either one can be wrong. Here we examine one ostensibly simple case of the NACA 0012 aerofoil and make careful comparison between the technical literature, and new experiments and computations. The agreement (or lack thereof) will establish one or more baseline results and some sensitivities around them. The idea is that the diagnostic procedures will help to guide comparisons and predictions in subsequent more complex cases.}, } @article {pmid28163357, year = {2017}, author = {Wang, CY and Mercer, E and Kamranvand, F and Williams, L and Kolios, A and Parker, A and Tyrrel, S and Cartmell, E and McAdam, EJ}, title = {Tube-side mass transfer for hollow fibre membrane contactors operated in the low Graetz range.}, journal = {Journal of membrane science}, volume = {523}, number = {}, pages = {235-246}, pmid = {28163357}, issn = {0376-7388}, abstract = {Transformation of the tube-side mass transfer coefficient derived in hollow fibre membrane contactors (HFMC) of different characteristic length scales (equivalent diameter and fibre length) has been studied when operated in the low Graetz range (Gz<10). Within the low Gz range, mass transfer is generally described by the Graetz problem (Sh=3.67) which assumes that the concentration profile comprises a constant shape over the fibre radius. In this study, it is experimentally evidenced that this assumption over predicts mass transfer within the low Graetz range. Furthermore, within the low Gz range (below 2), a proportional relationship between the experimentally determined mass transfer coefficient (Kov) and the Graetz number has been identified. For Gz numbers below 2, the experimental Sh number approached unity, which suggests that mass transfer is strongly dependent upon diffusion. However, within this diffusion controlled region of mass transfer, tube-side fluid velocity remained important. For Gz numbers above 2, Sh could be satisfactorily described by extension to the Lévêque solution, which can be ascribed to the constrained growth of the concentration boundary layer adjacent to the fibre wall. Importantly this study demonstrates that whilst mass transfer in the low Graetz range does not explicitly conform to either the Graetz problem or classical Lévêque solution, it is possible to transform the experimentally derived overall mass transfer coefficient (Kov) between characteristic length scales (dh and L). T h is was corroborated by comparison of the empirical relationship determined in this study (Sh=0.36Gz) with previously published studies operated in the low Gz range. This analysis provides important insight for process design when slow tube-side flows, or low Schmidt numbers (coincident with gases) constrain operation of hollow fibre membrane contactors to the low Gz range.}, } @article {pmid28161594, year = {2017}, author = {Tanveer, A and Hayat, T and Alsaadi, F and Alsaedi, A}, title = {Mixed convection peristaltic flow of Eyring-Powell nanofluid in a curved channel with compliant walls.}, journal = {Computers in biology and medicine}, volume = {82}, number = {}, pages = {71-79}, doi = {10.1016/j.compbiomed.2017.01.015}, pmid = {28161594}, issn = {1879-0534}, mesh = {Animals ; Computer Simulation ; Elastic Modulus/*physiology ; Humans ; *Models, Biological ; Peristalsis/*physiology ; Rheology/*methods ; Temperature ; }, abstract = {The novel features of nanofluids made them potentially significant in heat transfer mechanism occurring in medical and industrial processes like microelectronics, pharmaceutical processes, hybrid engines, thermal management of vehicles, refrigerator, chiller, gas temperature reduction and so forth. These processes bear tendency to enhance thermal conductivity and the convective heat transfer more efficiently than base fluid. This unique aspect made nanofluids the topic of interest in recent time via different fluid flow models. The problem in hand is one such application of nanofluids in peristaltic flow through curved channel. Thus peristalsis of Eyring-Powell nanofluid followed through conservation principles of mass, momentum, energy and concentration has been modeled. The whole system is made coupled via viscous dissipation, mixed convection, thermophoresis and Brownian motion. The complexity of system has been executed through a numerical approach after utilizing small Reynolds number and large wavelength concepts. A striking feature of this study is the activation of velocity and temperature with larger Brownian diffusion, whereas reduction is noticed with advancement in thermophoresis. Moreover the numerically obtained results for compliant walls are compatible with those obtained through other techniques.}, } @article {pmid28152457, year = {2017}, author = {He, L and Hang, J and Wang, X and Lin, B and Li, X and Lan, G}, title = {Numerical investigations of flow and passive pollutant exposure in high-rise deep street canyons with various street aspect ratios and viaduct settings.}, journal = {The Science of the total environment}, volume = {584-585}, number = {}, pages = {189-206}, doi = {10.1016/j.scitotenv.2017.01.138}, pmid = {28152457}, issn = {1879-1026}, mesh = {Air Pollutants/*analysis ; *Cities ; Environmental Exposure/*analysis ; Humans ; Models, Theoretical ; Noise ; Vehicle Emissions/*analysis ; Wind ; }, abstract = {Vehicular pollutant exposure of residents and pedestrians in high-rise deep street canyons with viaducts and noise barriers requires special concerns because the ventilation capacity is weak and the literature reported inconsistent findings on flow patterns as aspect ratios (building height/street width, H/W) are larger than 2. By conducting computational fluid dynamics (CFD) simulations coupled with the intake fraction iF and the daily pollutant exposure Et, this paper investigates the impact of street aspect ratios, viaducts and noise barriers on the flow and vehicular passive pollutant exposure in full-scale street canyons (H/W=1-6, W=24m). iF represents the fraction of total emissions inhaled by a population (1ppm=10[-6]), while Et means the extent of human beings' contact with pollutants within one day. CFD methodologies of passive pollutant dispersion modeling are successfully validated by wind tunnel data in Meroney et al. (1996). As a novelty, the two-main-vortex pattern start appearing in full-scale street canyons as H/W changes from 4 to 5, however previous studies using wind-tunnel-scale models (H=6cm) reported two to five vortexes as H/W=2-5. This finding is validated by both smoke visualization in scale-model outdoor field experiments (H=1.2m, W=0.6m) and CFD simulations of Reynolds number independence. Cases with two main vortexes (H/W=5-6) experience much larger daily pollutant exposure (~10[3]-10[4]mg/m[3]/day) than those with single main vortex as H/W=1-4 (~10[1]-10[2]mg/m[3]/day). Moreover leeward-side pollutant exposures are much larger than windward-side as H/W=1-4 while oppositely as H/W=5-6. Assuming a general population density, the total iF is 485-803ppm as H/W=1, 2020-12051ppm as H/W=2-4, and 51112-794026ppm as H/W=5-6. With a single elevated pollutant source, cases with viaducts experience significantly smaller pollutant exposures than cases without viaducts. Road barriers slightly increase pollutant exposure in near-road buildings with H/W=1 while reduce a little as H/W=3 and 5. Two-source cases can experience 2.60-5.52 times pollutant exposure as great as single-source cases.}, } @article {pmid28151968, year = {2017}, author = {Tanveer, A and Hayat, T and Alsaedi, A and Ahmad, B}, title = {Numerical simulation for peristalsis of Carreau-Yasuda nanofluid in curved channel with mixed convection and porous space.}, journal = {PloS one}, volume = {12}, number = {2}, pages = {e0170029}, pmid = {28151968}, issn = {1932-6203}, mesh = {Computer Simulation ; Convection ; Hot Temperature ; Humans ; *Hydrodynamics ; *Models, Theoretical ; Nanoparticles ; *Peristalsis/physiology ; Porosity ; Rheology ; Thermal Conductivity ; }, abstract = {Main theme of present investigation is to model and analyze the peristaltic activity of Carraeu-Yasuda nanofluid saturating porous space in a curved channel. Unlike the traditional approach, the porous medium effects are characterized by employing modified Darcy's law for Carreau-Yasuda fluid. To our knowledge this is first attempt in this direction for Carreau-Yasuda fluid. Heat and mass transfer are further considered. Simultaneous effects of heat and mass transfer are examined in presence of mixed convection, viscous dissipation and thermal radiation. The compliant characteristics for channel walls are taken into account. The resulting complex mathematical system has been discussed for small Reynolds number and large wavelength concepts. Numerical approximation to solutions are thus plotted in graphs and the physical description is presented. It is concluded that larger porosity in a medium cause an enhancement in fluid velocity and reduction in concentration.}, } @article {pmid28141804, year = {2017}, author = {Wheeler, RJ}, title = {Use of chiral cell shape to ensure highly directional swimming in trypanosomes.}, journal = {PLoS computational biology}, volume = {13}, number = {1}, pages = {e1005353}, pmid = {28141804}, issn = {1553-7358}, support = {103261/Z/13/Z//Wellcome Trust/United Kingdom ; }, mesh = {Adaptation, Physiological/*physiology ; Cell Movement/*physiology ; *Cell Size ; Cell Tracking ; Computer Simulation ; Friction ; Hydrodynamics ; Microscopy, Video ; *Models, Biological ; Swimming/physiology ; Trypanosoma/*cytology/*physiology ; Viscosity ; }, abstract = {Swimming cells typically move along a helical path or undergo longitudinal rotation as they swim, arising from chiral asymmetry in hydrodynamic drag or propulsion bending the swimming path into a helix. Helical paths are beneficial for some forms of chemotaxis, but why asymmetric shape is so prevalent when a symmetric shape would also allow highly directional swimming is unclear. Here, I analyse the swimming of the insect life cycle stages of two human parasites; Trypanosoma brucei and Leishmania mexicana. This showed quantitatively how chirality in T. brucei cell shape confers highly directional swimming. High speed videomicrographs showed that T. brucei, L. mexicana and a T. brucei RNAi morphology mutant have a range of shape asymmetries, from wild-type T. brucei (highly chiral) to L. mexicana (near-axial symmetry). The chiral cells underwent longitudinal rotation while swimming, with more rapid longitudinal rotation correlating with swimming path directionality. Simulation indicated hydrodynamic drag on the chiral cell shape caused rotation, and the predicted geometry of the resulting swimming path matched the directionality of the observed swimming paths. This simulation of swimming path geometry showed that highly chiral cell shape is a robust mechanism through which microscale swimmers can achieve highly directional swimming at low Reynolds number. It is insensitive to random variation in shape or propulsion (biological noise). Highly symmetric cell shape can give highly directional swimming but is at risk of giving futile circular swimming paths in the presence of biological noise. This suggests the chiral T. brucei cell shape (associated with the lateral attachment of the flagellum) may be an adaptation associated with the bloodstream-inhabiting lifestyle of this parasite for robust highly directional swimming. It also provides a plausible general explanation for why swimming cells tend to have strong asymmetries in cell shape or propulsion.}, } @article {pmid28117769, year = {2017}, author = {Kulkarni, AA and Patel, RK and Friedman, C and Leftwich, MC}, title = {A Robotic Platform to Study the Foreflipper of the California Sea Lion.}, journal = {Journal of visualized experiments : JoVE}, volume = {}, number = {119}, pages = {}, pmid = {28117769}, issn = {1940-087X}, mesh = {Animals ; Biomechanical Phenomena ; Extremities ; Female ; *Robotics ; Sea Lions/*anatomy & histology ; *Swimming ; }, abstract = {The California sea lion (Zalophus californianus), is an agile and powerful swimmer. Unlike many successful swimmers (dolphins, tuna), they generate most of their thrust with their large foreflippers. This protocol describes a robotic platform designed to study the hydrodynamic performance of the swimming California sea lion (Zalophus californianus). The robot is a model of the animal's foreflipper that is actuated by motors to replicate the motion of its propulsive stroke (the 'clap'). The kinematics of the sea lion's propulsive stroke are extracted from video data of unmarked, non-research sea lions at the Smithsonian Zoological Park (SNZ). Those data form the basis of the actuation motion of the robotic flipper presented here. The geometry of the robotic flipper is based a on high-resolution laser scan of a foreflipper of an adult female sea lion, scaled to about 60% of the full-scale flipper. The articulated model has three joints, mimicking the elbow, wrist and knuckle joint of the sea lion foreflipper. The robotic platform matches dynamics properties-Reynolds number and tip speed-of the animal when accelerating from rest. The robotic flipper can be used to determine the performance (forces and torques) and resulting flowfields.}, } @article {pmid28085475, year = {2016}, author = {Mo, CJ and Qin, LZ and Zhao, F and Yang, LJ}, title = {Application of the dissipative particle dynamics method to the instability problem of a liquid thread.}, journal = {Physical review. E}, volume = {94}, number = {6-1}, pages = {063113}, doi = {10.1103/PhysRevE.94.063113}, pmid = {28085475}, issn = {2470-0053}, abstract = {We investigate the application of the dissipative particle dynamics method to the instability problem of a long liquid thread surrounded by another fluid. The dispersion curves obtained from simulations are compared with classic theoretical predictions. The results from standard dissipative particle dynamics (DPD) simulations at first have a tendency of gradually approaching to Tomotika's Stokes flow prediction when the Reynolds number is decreased. But they then abnormally deviate again when the viscosity is very large. The same phenomenon is also confirmed in droplet retraction simulations when also compared with theoretical Stokes flow results. On the other hand, when a hard-core DPD model is used, with the decrease of the Reynolds number the simulation results did finally approach Tomotika's predictions when Re≈0.1. A combined presentation of the hard-core DPD results and the standard DPD results, excluding the abnormal ones, demonstrates that they are approximately on a continuum when labeled with Reynolds number. These results suggest that the standard DPD method is a suitable method for investigation of the instability problem of immersed liquid thread in the inertioviscous regime (0.13, where k_{max} is the maximum resolved wave number and η is the flow Kolmogorov length. This resolution requirement can be contrasted with the requirements of k_{max} η>1 for the pseudospectral method and k_{max} η>2 for the LBE. It should be emphasized that although more validations should be conducted before the DUGKS can be called a viable tool for DNS of turbulent flows, the present work contributes to the overall assessment of the DUGKS, and it provides a basis for further applications of DUGKS in studying the physics of turbulent flows.}, } @article {pmid27841548, year = {2016}, author = {Bhattacharya, A and Kesarkar, T}, title = {Numerical simulation of particulate flows using a hybrid of finite difference and boundary integral methods.}, journal = {Physical review. E}, volume = {94}, number = {4-1}, pages = {043309}, doi = {10.1103/PhysRevE.94.043309}, pmid = {27841548}, issn = {2470-0053}, abstract = {A combination of finite difference (FD) and boundary integral (BI) methods is used to formulate an efficient solver for simulating unsteady Stokes flow around particles. The two-dimensional (2D) unsteady Stokes equation is being solved on a Cartesian grid using a second order FD method, while the 2D steady Stokes equation is being solved near the particle using BI method. The two methods are coupled within the viscous boundary layer, a few FD grid cells away from the particle, where solutions from both FD and BI methods are valid. We demonstrate that this hybrid method can be used to accurately solve for the flow around particles with irregular shapes, even though radius of curvature of the particle surface is not resolved by the FD grid. For dilute particle concentrations, we construct a virtual envelope around each particle and solve the BI problem for the flow field located between the envelope and the particle. The BI solver provides velocity boundary condition to the FD solver at "boundary" nodes located on the FD grid, adjacent to the particles, while the FD solver provides the velocity boundary condition to the BI solver at points located on the envelope. The coupling between FD method and BI method is implicit at every time step. This method allows us to formulate an O(N) scheme for dilute suspensions, where N is the number of particles. For semidilute suspensions, where particles may cluster, an envelope formation method has been formulated and implemented, which enables solving the BI problem for each individual particle cluster, allowing efficient simulation of hydrodynamic interaction between particles even when they are in close proximity. The method has been validated against analytical results for flow around a periodic array of cylinders and for Jeffrey orbit of a moving ellipse in shear flow. Simulation of multiple force-free irregular shaped particles in the presence of shear in a 2D slit flow has been conducted to demonstrate the robustness of the FD-BI scheme. This method can also be used to solve the full Navier-Stokes equations around particles. In this case, it is shown that, below a threshold particle Reynolds number, which in turn depends on the required resolution of the particle surface, the FD-BI scheme will be more computationally efficient than a pure FD scheme solved on a multiblock grid.}, } @article {pmid27841514, year = {2016}, author = {Kogan, E}, title = {Lift force due to odd Hall viscosity.}, journal = {Physical review. E}, volume = {94}, number = {4-1}, pages = {043111}, doi = {10.1103/PhysRevE.94.043111}, pmid = {27841514}, issn = {2470-0053}, abstract = {We study the problem of flow of a neutral gas past an infinite cylinder at right angle to its axis at low Reynolds number when the fluid is characterized by broken time-reversal invariance, and hence by odd viscosity in addition to the normal even one. We solve the Oseen approximation to Navier-Stokes equation and calculate the lift force which appears due to the odd viscosity.}, } @article {pmid27841488, year = {2016}, author = {Suresha, S and Sujith, RI and Emerson, B and Lieuwen, T}, title = {Nonlinear dynamics and intermittency in a turbulent reacting wake with density ratio as bifurcation parameter.}, journal = {Physical review. E}, volume = {94}, number = {4-1}, pages = {042206}, doi = {10.1103/PhysRevE.94.042206}, pmid = {27841488}, issn = {2470-0053}, abstract = {The flame or flow behavior of a turbulent reacting wake is known to be fundamentally different at high and low values of flame density ratio (ρ_{u} /ρ_{b} ), as the flow transitions from globally stable to unstable. This paper analyzes the nonlinear dynamics present in a bluff-body stabilized flame, and identifies the transition characteristics in the wake as ρ_{u} /ρ_{b} is varied over a Reynolds number (based on the bluff-body lip velocity) range of 1000-3300. Recurrence quantification analysis (RQA) of the experimentally obtained time series of the flame edge fluctuations reveals that the time series is highly aperiodic at high values of ρ_{u} /ρ_{b} and transitions to increasingly correlated or nearly periodic behavior at low values. From the RQA of the transverse velocity time series, we observe that periodicity in the flame oscillations are related to periodicity in the flow. Therefore, we hypothesize that this transition from aperiodic to nearly periodic behavior in the flame edge time series is a manifestation of the transition in the flow from globally stable, convective instability to global instability as ρ_{u} /ρ_{b} decreases. The recurrence analysis further reveals that the transition in periodicity is not a sudden shift; rather it occurs through an intermittent regime present at low and intermediate ρ_{u} /ρ_{b} . During intermittency, the flow behavior switches between aperiodic oscillations, reminiscent of a globally stable, convective instability, and periodic oscillations, reminiscent of a global instability. Analysis of the distribution of the lengths of the periodic regions in the intermittent time series and the first return map indicate the presence of type-II intermittency.}, } @article {pmid27841461, year = {2016}, author = {Leclercq, C and Nguyen, F and Kerswell, RR}, title = {Connections between centrifugal, stratorotational, and radiative instabilities in viscous Taylor-Couette flow.}, journal = {Physical review. E}, volume = {94}, number = {4-1}, pages = {043103}, doi = {10.1103/PhysRevE.94.043103}, pmid = {27841461}, issn = {2470-0053}, abstract = {The "Rayleigh line" μ=η^{2}, where μ=Ω_{o} /Ω_{i} and η=r_{i} /r_{o} are respectively the rotation and radius ratios between inner (subscript i) and outer (subscript o) cylinders, is regarded as marking the limit of centrifugal instability (CI) in unstratified inviscid Taylor-Couette flow, for both axisymmetric and nonaxisymmetric modes. Nonaxisymmetric stratorotational instability (SRI) is known to set in for anticyclonic rotation ratios beyond that line, i.e., η^{2} <μ<1 for axially stably stratified Taylor-Couette flow, but the competition between CI and SRI in the range μ<η^{2} has not yet been addressed. In this paper, we establish continuous connections between the two instabilities at finite Reynolds number Re, as previously suggested by Le Bars and Le Gal [Phys. Rev. Lett. 99, 064502 (2007)PRLTAO0031-900710.1103/PhysRevLett.99.064502], making them indistinguishable at onset. Both instabilities are also continuously connected to the radiative instability at finite Re. These results demonstrate the complex impact viscosity has on the linear stability properties of this flow. Several other qualitative differences with inviscid theory were found, among which are the instability of a nonaxisymmetric mode localized at the outer cylinder without stratification and the instability of a mode propagating against the inner cylinder rotation with stratification. The combination of viscosity and stratification can also lead to a "collision" between (axisymmetric) Taylor vortex branches, causing the axisymmetric oscillatory state already observed in past experiments. Perhaps more surprising is the instability of a centrifugal-like helical mode beyond the Rayleigh line, caused by the joint effects of stratification and viscosity. The threshold μ=η^{2} seems to remain, however, an impassable instability limit for axisymmetric modes, regardless of stratification, viscosity, and even disturbance amplitude.}, } @article {pmid27840656, year = {2016}, author = {Tian, FB}, title = {Deformation of a Capsule in a Power-Law Shear Flow.}, journal = {Computational and mathematical methods in medicine}, volume = {2016}, number = {}, pages = {7981386}, pmid = {27840656}, issn = {1748-6718}, mesh = {Algorithms ; *Blood Flow Velocity ; Computer Simulation ; Elasticity ; Erythrocytes/cytology ; Humans ; Models, Theoretical ; Motion ; Rheology/*methods ; Shear Strength ; Stress, Mechanical ; }, abstract = {An immersed boundary-lattice Boltzmann method is developed for fluid-structure interactions involving non-Newtonian fluids (e.g., power-law fluid). In this method, the flexible structure (e.g., capsule) dynamics and the fluid dynamics are coupled by using the immersed boundary method. The incompressible viscous power-law fluid motion is obtained by solving the lattice Boltzmann equation. The non-Newtonian rheology is achieved by using a shear rate-dependant relaxation time in the lattice Boltzmann method. The non-Newtonian flow solver is then validated by considering a power-law flow in a straight channel which is one of the benchmark problems to validate an in-house solver. The numerical results present a good agreement with the analytical solutions for various values of power-law index. Finally, we apply this method to study the deformation of a capsule in a power-law shear flow by varying the Reynolds number from 0.025 to 0.1, dimensionless shear rate from 0.004 to 0.1, and power-law index from 0.2 to 1.8. It is found that the deformation of the capsule increases with the power-law index for different Reynolds numbers and nondimensional shear rates. In addition, the Reynolds number does not have significant effect on the capsule deformation in the flow regime considered. Moreover, the power-law index effect is stronger for larger dimensionless shear rate compared to smaller values.}, } @article {pmid27830719, year = {2016}, author = {Kurzthaler, C and Leitmann, S and Franosch, T}, title = {Intermediate scattering function of an anisotropic active Brownian particle.}, journal = {Scientific reports}, volume = {6}, number = {}, pages = {36702}, pmid = {27830719}, issn = {2045-2322}, mesh = {*Algorithms ; *Anisotropy ; Diffusion ; Escherichia coli/physiology ; Kinetics ; *Models, Theoretical ; *Motion ; Movement ; Particle Size ; }, abstract = {Various challenges are faced when animalcules such as bacteria, protozoa, algae, or sperms move autonomously in aqueous media at low Reynolds number. These active agents are subject to strong stochastic fluctuations, that compete with the directed motion. So far most studies consider the lowest order moments of the displacements only, while more general spatio-temporal information on the stochastic motion is provided in scattering experiments. Here we derive analytically exact expressions for the directly measurable intermediate scattering function for a mesoscopic model of a single, anisotropic active Brownian particle in three dimensions. The mean-square displacement and the non-Gaussian parameter of the stochastic process are obtained as derivatives of the intermediate scattering function. These display different temporal regimes dominated by effective diffusion and directed motion due to the interplay of translational and rotational diffusion which is rationalized within the theory. The most prominent feature of the intermediate scattering function is an oscillatory behavior at intermediate wavenumbers reflecting the persistent swimming motion, whereas at small length scales bare translational and at large length scales an enhanced effective diffusion emerges. We anticipate that our characterization of the motion of active agents will serve as a reference for more realistic models and experimental observations.}, } @article {pmid27824053, year = {2016}, author = {Irajizad, P and Hasnain, M and Farokhnia, N and Sajadi, SM and Ghasemi, H}, title = {Magnetic slippery extreme icephobic surfaces.}, journal = {Nature communications}, volume = {7}, number = {}, pages = {13395}, pmid = {27824053}, issn = {2041-1723}, abstract = {Anti-icing surfaces have a critical footprint on daily lives of humans ranging from transportation systems and infrastructure to energy systems, but creation of these surfaces for low temperatures remains elusive. Non-wetting surfaces and liquid-infused surfaces have inspired routes for the development of icephobic surfaces. However, high freezing temperature, high ice adhesion strength, and high cost have restricted their practical applications. Here we report new magnetic slippery surfaces outperforming state-of-the-art icephobic surfaces with a ice formation temperature of -34 °C, 2-3 orders of magnitude higher delay time in ice formation, extremely low ice adhesion strength (≈2 Pa) and stability in shear flows up to Reynolds number of 10[5]. In these surfaces, we exploit the magnetic volumetric force to exclude the role of solid-liquid interface in ice formation. We show that these inexpensive surfaces are universal and can be applied to all types of solids (no required micro/nano structuring) with no compromise to their unprecedented properties.}, } @article {pmid27816870, year = {2017}, author = {Berry, JD and Dagastine, RR}, title = {Mapping coalescence of micron-sized drops and bubbles.}, journal = {Journal of colloid and interface science}, volume = {487}, number = {}, pages = {513-522}, doi = {10.1016/j.jcis.2016.10.040}, pmid = {27816870}, issn = {1095-7103}, abstract = {Emulsion formulation, solvent extraction and multiphase microfluidics are all examples of processes that require precise control of drop or bubble collision stability. We use a previously validated numerical model to map the exact conditions under which micron-sized drops or bubbles undergo coalescence in the presence of colloidal forces and hydrodynamic effects relevant to Brownian motion and low Reynolds number flows. We demonstrate that detailed understanding of how the equilibrium surface forces vary with film thickness can be applied to make accurate predictions of the outcome of a drop or bubble collision when hydrodynamic effects are negligible. In addition, we illuminate the parameter space (i.e. interaction velocity, drop deformation, interfacial tension, etc.) at which hydrodynamic effects can stabilise collisions that are unstable at equilibrium. Further, we determine conditions for which drop or bubble collisions become unstable upon separation, caused by negative hydrodynamic pressure in the film. Lastly, we show that scaling analyses are not applicable for constant force collisions where the approach timescale is comparable to the coalescence timescale, and demonstrate that initial conditions under these circumstances cannot be ignored.}, } @article {pmid27815242, year = {2016}, author = {Yanase, K and Saarenrinne, P}, title = {Boundary layer control by a fish: Unsteady laminar boundary layers of rainbow trout swimming in turbulent flows.}, journal = {Biology open}, volume = {5}, number = {12}, pages = {1853-1863}, pmid = {27815242}, issn = {2046-6390}, abstract = {The boundary layers of rainbow trout, Oncorhynchus mykiss [0.231±0.016 m total body length (L) (mean±s.d.); N=6], swimming at 1.6±0.09 L s[-1] (N=6) in an experimental flow channel (Reynolds number, Re=4×10[5]) with medium turbulence (5.6% intensity) were examined using the particle image velocimetry technique. The tangential flow velocity distributions in the pectoral and pelvic surface regions (arc length from the rostrum, lx=71±8 mm, N=3, and lx=110±13 mm, N=4, respectively) were approximated by a laminar boundary layer model, the Falkner-Skan equation. The flow regime over the pectoral and pelvic surfaces was regarded as a laminar flow, which could create less skin-friction drag than would be the case with turbulent flow. Flow separation was postponed until vortex shedding occurred over the posterior surface (lx=163±22 mm, N=3). The ratio of the body-wave velocity to the swimming speed was in the order of 1.2. This was consistent with the condition of the boundary layer laminarization that had been confirmed earlier using a mechanical model. These findings suggest an energy-efficient swimming strategy for rainbow trout in a turbulent environment.}, } @article {pmid27814386, year = {2016}, author = {Kwak, TJ and Nam, YG and Najera, MA and Lee, SW and Strickler, JR and Chang, WJ}, title = {Convex Grooves in Staggered Herringbone Mixer Improve Mixing Efficiency of Laminar Flow in Microchannel.}, journal = {PloS one}, volume = {11}, number = {11}, pages = {e0166068}, pmid = {27814386}, issn = {1932-6203}, mesh = {Computer Simulation ; Equipment Design/methods ; Microfluidic Analytical Techniques/*methods ; Microfluidics/*methods ; }, abstract = {The liquid streams in a microchannel are hardly mixed to form laminar flow, and the mixing issue is well described by a low Reynolds number scheme. The staggered herringbone mixer (SHM) using repeated patterns of grooves in the microchannel have been proved to be an efficient passive micro-mixer. However, only a negative pattern of the staggered herringbone mixer has been used so far after it was first suggested, to the best of our knowledge. In this study, the mixing efficiencies from negative and positive staggered herringbone mixer patterns as well as from opposite flow directions were tested to investigate the effect of the micro-structure geometry on the surrounding laminar flow. The positive herringbone pattern showed better mixing efficiency than the conventionally used negative pattern. Also, generally used forward flow gives better mixing efficiency than reverse flow. The mixing was completed after two cycles of staggered herringbone mixer with both forward and reverse flow in a positive pattern. The traditional negative pattern showed complete mixing after four and five cycles in forward and reverse flow direction, respectively. The mixing effect in all geometries was numerically simulated, and the results confirmed more efficient mixing in the positive pattern than the negative. The results can further enable the design of a more efficient microfluidic mixer, as well as in depth understanding of the phenomena of positive and negative patterns existing in nature with regards to the surrounding fluids.}, } @article {pmid27810627, year = {2016}, author = {Hayat, T and Zahir, H and Tanveer, A and Alsaedi, A}, title = {Numerical study for MHD peristaltic flow in a rotating frame.}, journal = {Computers in biology and medicine}, volume = {79}, number = {}, pages = {215-221}, doi = {10.1016/j.compbiomed.2016.09.021}, pmid = {27810627}, issn = {1879-0534}, mesh = {*Computer Simulation ; Hot Temperature ; Hydrodynamics ; Magnetic Fields ; *Models, Theoretical ; *Peristalsis ; Rotation ; }, abstract = {The aim of present investigation is to model and analyze the magnetohydrodynamic (MHD) peristaltic transport of Prandtl fluid in a channel with flexible walls. The whole system consisting of fluid and channel are in a rotating frame of reference with uniform angular velocity. Viscous dissipation in thermal equation is not ignored. The channel boundaries satisfy the convective conditions in terms of temperature. The arising complicated problems are reduced in solvable form using large wavelength and small Reynolds number assumptions. Numerical solution for axial and secondary velocities, temperature and heat transfer coefficient are presented. Main emphasis is given to the outcome of rotation and material parameters of Prandtl fluid on the physical quantities of interest.}, } @article {pmid27806284, year = {2016}, author = {Guillou, L and Dahl, JB and Lin, JG and Barakat, AI and Husson, J and Muller, SJ and Kumar, S}, title = {Measuring Cell Viscoelastic Properties Using a Microfluidic Extensional Flow Device.}, journal = {Biophysical journal}, volume = {111}, number = {9}, pages = {2039-2050}, pmid = {27806284}, issn = {1542-0086}, support = {R01 NS074831/NS/NINDS NIH HHS/United States ; R21 CA174573/CA/NCI NIH HHS/United States ; R21 EB016359/EB/NIBIB NIH HHS/United States ; T32 GM098218/GM/NIGMS NIH HHS/United States ; }, mesh = {Animals ; Biomechanical Phenomena ; Cell Line, Tumor ; *Elasticity ; Glioblastoma/pathology ; *Lab-On-A-Chip Devices ; Mice ; NIH 3T3 Cells ; Viscosity ; }, abstract = {The quantification of cellular mechanical properties is of tremendous interest in biology and medicine. Recent microfluidic technologies that infer cellular mechanical properties based on analysis of cellular deformations during microchannel traversal have dramatically improved throughput over traditional single-cell rheological tools, yet the extraction of material parameters from these measurements remains quite complex due to challenges such as confinement by channel walls and the domination of complex inertial forces. Here, we describe a simple microfluidic platform that uses hydrodynamic forces at low Reynolds number and low confinement to elongate single cells near the stagnation point of a planar extensional flow. In tandem, we present, to our knowledge, a novel analytical framework that enables determination of cellular viscoelastic properties (stiffness and fluidity) from these measurements. We validated our system and analysis by measuring the stiffness of cross-linked dextran microparticles, which yielded reasonable agreement with previously reported values and our micropipette aspiration measurements. We then measured viscoelastic properties of 3T3 fibroblasts and glioblastoma tumor initiating cells. Our system captures the expected changes in elastic modulus induced in 3T3 fibroblasts and tumor initiating cells in response to agents that soften (cytochalasin D) or stiffen (paraformaldehyde) the cytoskeleton. The simplicity of the device coupled with our analytical model allows straightforward measurement of the viscoelastic properties of cells and soft, spherical objects.}, } @article {pmid27766329, year = {2016}, author = {Li, M and Muñoz, HE and Schmidt, A and Guo, B and Lei, C and Goda, K and Di Carlo, D}, title = {Inertial focusing of ellipsoidal Euglena gracilis cells in a stepped microchannel.}, journal = {Lab on a chip}, volume = {16}, number = {22}, pages = {4458-4465}, doi = {10.1039/c6lc01118g}, pmid = {27766329}, issn = {1473-0189}, mesh = {Euglena gracilis/*cytology/genetics ; *Lab-On-A-Chip Devices ; Mutation ; }, abstract = {Euglena gracilis (E. gracilis) has recently been attracting attention as a potential renewable source for the production of biofuels, livestock feed, cosmetics, and dietary supplements. Research has focused on strain isolation, productivity improvement, nutrient and resource allocation, and co-product production, key steps that ultimately determine the economic viability and compatibility of the biomass produced. To achieve these characteristics, approaches to select E. gracilis mutants with desirable properties, such as high wax ester content, high growth rate, and high environmental tolerance for biodiesel and biomass production, are needed. Flow-based analysis and sorting can be rapid and highly automated but calls for techniques that can precisely control the position of E. gracilis with varying sizes and shapes in a tightly focused stream in a high-throughput manner. In this work, we use a stepped microchannel consisting of a low-aspect-ratio straight channel and a series of expansion regions along the channel height. We study horizontal and vertical focusing, orientation, rotational, and translational behaviors of E. gracilis as a function of aspect ratio (AR) and channel Reynolds number (Re). By making use of inertial focusing and local secondary flows, E. gracilis with diverse shapes are directed to a single equilibrium position in a single focal stream. As an application of on-chip flow cytometry, we integrate a focusing microchip with a custom laser-two-focus (L2F) optical system and demonstrate the detection of chlorophyll autofluorescence as well as the measurement of the velocity of E. gracilis cells flowing through the microchannel.}, } @article {pmid27791257, year = {2016}, author = {Lee, J and Kim, S and Kim, SM and Song, R and Kim, HK and Park, JS and Park, SC}, title = {Assessing radiocephalic wrist arteriovenous fistulas of obtuse anastomosis using computational fluid dynamics and clinical application.}, journal = {The journal of vascular access}, volume = {17}, number = {6}, pages = {512-520}, doi = {10.5301/jva.5000607}, pmid = {27791257}, issn = {1724-6032}, mesh = {*Arteriovenous Shunt, Surgical/adverse effects ; Blood Flow Velocity ; *Computer Simulation ; Female ; Finite Element Analysis ; Graft Occlusion, Vascular/etiology/physiopathology ; *Hemodynamics ; Humans ; Hydrodynamics ; Kaplan-Meier Estimate ; Kidney Failure, Chronic/diagnosis/*therapy ; Male ; Middle Aged ; *Models, Cardiovascular ; Numerical Analysis, Computer-Assisted ; Radial Artery/physiopathology/*surgery ; Regional Blood Flow ; *Renal Dialysis ; Retrospective Studies ; Risk Factors ; Software ; Stress, Mechanical ; Thrombosis/etiology/physiopathology ; Time Factors ; Treatment Outcome ; Vascular Patency ; Vascular Stiffness ; Veins/physiopathology/*surgery ; Wrist/*blood supply ; }, abstract = {INTRODUCTION: A radiocephalic arteriovenous fistula (AVF) is the best choice for achieving vascular access (VA) for hemodialysis, but this AVF has high rates of early failure due to juxta-anastomotic stenosis, making it impossible to use for dialysis. Low hemodynamic shear stress contributes to the pathophysiology of VA failure due to secondary thrombosis, stenosis, and re-occlusion after percutaneous intervention.

METHODS: We used a computational fluid dynamics (CFDs) approach to evaluate the shear stress distribution and minimize its effects under various conditions including changes in the anastomosis angle. A three-dimensional computational domain was designed for arteriovenous end-to-side anastomosis based on anastomosis angles of 45°, 90° and including 135° angle of an obtuse anastomosis using three-dimensional design software. COMSOL Multiphysics® simulation software was used to identify the hemodynamic factors influencing wall shear stress at the anastomosis site using a low Reynolds number k-ε turbulence model that included non-Newtonian blood flow characteristics, the complete cardiac pulse cycle, and distention of blood vessels. In preliminary clinical study, all 201 patients who received a radiocephalic wrist AVF from January 2009 to February 2014 were divided into classic and obtuse angle groups.

RESULTS: The CFD results showed that the largest anastomosis angle (135°) resulted in lower shear stress, which would help reduce AVF failures. This obtuse angle was preferred, as it minimized the development of anastomotic stenosis and tended to favor primary and primary-assisted patency in clinical study.

CONCLUSIONS: An obtuse radiocephalic wrist AVF shows more favorable patency compared to a classic radiocephalic AVF. Surgeons establishing a radiocephalic wrist AVF would be better to consider an AVF with an obtuse anastomosis.}, } @article {pmid27789458, year = {2016}, author = {Miyagawa, T and Imai, Y and Ishida, S and Ishikawa, T}, title = {Relationship between gastric motility and liquid mixing in the stomach.}, journal = {American journal of physiology. Gastrointestinal and liver physiology}, volume = {311}, number = {6}, pages = {G1114-G1121}, doi = {10.1152/ajpgi.00346.2016}, pmid = {27789458}, issn = {1522-1547}, mesh = {*Computer Simulation ; *Gastric Emptying ; *Gastrointestinal Transit ; Humans ; Muscle Contraction ; Pylorus/*physiology ; }, abstract = {The relationship between gastric motility and the mixing of liquid food in the stomach was investigated with a numerical analysis. Three parameters of gastric motility were considered: the propagation velocity, frequency, and terminal acceleration of peristaltic contractions. We simulated gastric flow with an anatomically realistic geometric model of the stomach, considering free surface flow and moving boundaries. When a peristaltic contraction approaches the pylorus, retropulsive flow is generated in the antrum. Flow separation then occurs behind the contraction. The extent of flow separation depends on the Reynolds number (Re), which quantifies the inertial forces due to the peristaltic contractions relative to the viscous forces of the gastric contents; no separation is observed at low Re, while an increase in reattachment length is observed at high Re. While mixing efficiency is nearly constant for low Re, it increases with Re for high Re because of flow separation. Hence, the effect of the propagation velocity, frequency, or terminal acceleration of peristaltic contractions on mixing efficiency increases with Re.}, } @article {pmid27722471, year = {2016}, author = {Zhao, Y and Shen, AQ and Haward, SJ}, title = {Flow of wormlike micellar solutions around confined microfluidic cylinders.}, journal = {Soft matter}, volume = {12}, number = {42}, pages = {8666-8681}, doi = {10.1039/c6sm01597b}, pmid = {27722471}, issn = {1744-6848}, abstract = {Wormlike micellar (WLM) solutions are frequently used in enhanced oil and gas recovery applications in porous rock beds where complex microscopic geometries result in mixed flow kinematics with strong shear and extensional components. Experiments with WLM solutions through model microfluidic porous media have revealed a variety of complex flow phenomena, including the formation of stable gel-like structures known as a Flow-Induced Structured Phase (FISP), which undoubtedly play an important role in applications of WLM fluids, but are still poorly understood. A first step in understanding flows of WLM fluids through porous media can be made by examining the flow around a single micro-scale cylinder aligned on the flow axis. Here we study flow behavior of an aqueous WLM solution consisting of cationic surfactant cetyltrimethylammonium bromide (CTAB) and a stable hydrotropic salt 3-hydroxy naphthalene-2-carboxylate (SHNC) in microfluidic devices with three different cylinder blockage ratios, β. We observe a rich sequence of flow instabilities depending on β as the Weissenberg number (Wi) is increased to large values while the Reynolds number (Re) remains low. Instabilities upstream of the cylinder are associated with high stresses in fluid that accelerates into the narrow gap between the cylinder and the channel wall; vortex growth upstream is reminiscent of that seen in microfluidic contraction geometries. Instability downstream of the cylinder is associated with stresses generated at the trailing stagnation point and the resulting flow modification in the wake, coupled with the onset of time-dependent flow upstream and the asymmetric division of flow around the cylinder.}, } @article {pmid27780156, year = {2016}, author = {Lu, H and Lua, KB and Lee, YJ and Lim, TT and Yeo, KS}, title = {Ground effect on the aerodynamics of three-dimensional hovering wings.}, journal = {Bioinspiration & biomimetics}, volume = {11}, number = {6}, pages = {066003}, doi = {10.1088/1748-3190/11/5/066003}, pmid = {27780156}, issn = {1748-3190}, mesh = {Animals ; Aviation ; Biomechanical Phenomena ; *Biomimetic Materials ; Biomimetics/*methods ; Computer Simulation ; Flight, Animal/*physiology ; Models, Biological ; Wings, Animal/*physiology ; }, abstract = {This paper reports the results of combined experimental and numerical studies on the ground effect on a pair of three-dimensional (3D) hovering wings. Parameters investigated include hovering kinematics, wing shapes, and Reynolds numbers (Re). The results are consistent with the observation by another study (Gao and Lu, 2008 Phys. Fluids, 20 087101) which shows that the cycle-averaged aerodynamic forces generated by two-dimensional (2D) wings in close proximity to the ground can be broadly categorized into three regimes with respect to the ground clearance; force enhancement, force reduction, and force recovery. However, the ground effect on a 3D wing is not as significant as that on a 2D flapping wing reported in (Lu et al 2014 Exp. Fluids, 55 1787); this could be attributed to a weaker wake capture effect on 3D wings. Also, unlike a 2D wing, the leading edge vortex (LEV) remains attached on a 3D wing regardless of ground clearance. For all the wing kinematics considered, the three above-mentioned regimes are closely correlated to a non-monotonic trend in the strength of downwash due to the restriction of root and tip vortex formation, and a positional shift of wake vortices. The root vortices in interaction with the ground induce an up-wash in-between the two wings, causing a strong 'fountain effect' (Maeda and Liu, 2013 J. Biomech. Sci. Eng., 8 344) that may increase the body lift of insects. The present study further shows that changes in wing planform have insignificant influence on the overall trend of ground effect except for a parallel shift in force magnitude, which is caused mainly by the difference in aspect ratio and leading edge pivot point. On the two Reynolds numbers investigated, the results for the low Re case of 100 do not deviate significantly from those of a higher Re = 5000 except for the difference in force magnitudes, since low Reynolds number generates lower downwash, weaker LEV, and lower rotational circulation. Additionally, lower Re leads to a weaker fountain effect.}, } @article {pmid27778306, year = {2016}, author = {Qureshi, MZ and Rubbab, Q and Irshad, S and Ahmad, S and Aqeel, M}, title = {Heat and Mass Transfer Analysis of MHD Nanofluid Flow with Radiative Heat Effects in the Presence of Spherical Au-Metallic Nanoparticles.}, journal = {Nanoscale research letters}, volume = {11}, number = {1}, pages = {472}, pmid = {27778306}, issn = {1931-7573}, abstract = {Energy generation is currently a serious concern in the progress of human civilization. In this regard, solar energy is considered as a significant source of renewable energy. The purpose of the study is to establish a thermal energy model in the presence of spherical Au-metallic nanoparticles. It is numerical work which studies unsteady magnetohydrodynamic (MHD) nanofluid flow through porous disks with heat and mass transfer aspects. Shaped factor of nanoparticles is investigated using small values of the permeable Reynolds number. In order to scrutinize variation of thermal radiation effects, a dimensionless Brinkman number is introduced. The results point out that heat transfer significantly escalates with the increase of Brinkman number. Partial differential equations that govern this study are reduced into nonlinear ordinary differential equations by means of similarity transformations. Then using a shooting technique, a numerical solution of these equations is constructed. Radiative effects on temperature and mass concentration are quite opposite. Heat transfer increases in the presence of spherical Au-metallic nanoparticles.}, } @article {pmid27771858, year = {2016}, author = {Daniels, DR}, title = {Curvature correction to the mobility of fluid membrane inclusions.}, journal = {The European physical journal. E, Soft matter}, volume = {39}, number = {10}, pages = {96}, pmid = {27771858}, issn = {1292-895X}, abstract = {Using rigorous low-Reynolds-number hydrodynamic theory on curved surfaces, we provide, via a Stokeslet-type approach, a general and concise expression for the leading-order curvature correction to the canonical, planar, Saffman-Delbrück value of the diffusion constant for a small inclusion embedded in an arbitrarily (albeit weakly) curved fluid membrane. In order to demonstrate the efficacy and utility of this general result, we apply our theory to the specific case of calculating the diffusion coefficient of a locally curvature inducing membrane inclusion. By including both the effects of inclusion and membrane elasticity, as well as their respective thermal shape fluctuations, excellent agreement is found with recently published experimental data on the surface tension dependent mobility of membrane bound inclusions.}, } @article {pmid27643464, year = {2016}, author = {Bhatti, MM and Zeeshan, A and Ellahi, R}, title = {Endoscope analysis on peristaltic blood flow of Sisko fluid with Titanium magneto-nanoparticles.}, journal = {Computers in biology and medicine}, volume = {78}, number = {}, pages = {29-41}, doi = {10.1016/j.compbiomed.2016.09.007}, pmid = {27643464}, issn = {1879-0534}, mesh = {Endoscopy/*methods ; Hemorheology/*physiology ; Humans ; Magnetic Fields ; Magnetite Nanoparticles/*chemistry ; *Models, Biological ; Peristalsis/*physiology ; Titanium/chemistry ; }, abstract = {In this article, endoscope analysis on peristaltic blood flow of Sisko fluid having Titanium magneto-nanoparticles through a uniform tube has been analyzed. The governing flow problem consists of continuity, linear momentum and thermal energy equations. The effect of magnetic field is also taken into account with the help of ohm's law. With the help of long wavelength and zero Reynolds number approximation, the governing equations are simplified. The reduced resulting nonlinear coupled equations are solved analytically with the help of Homotopy perturbation method (HPM). The impact of all the emerging parameters is discussed with the help of graphs for pressure rise, friction forces for outer and inner tube, velocity profile, temperature profile and pressure gradient. Moreover, numerical computation has been used to evaluate the expression for pressure rise and friction forces. Trapping phenomena is also presented with the help of streamlines. The present study depicts many interesting results that provide further study on different blood flow problems.}, } @article {pmid27757417, year = {2016}, author = {Saranadhi, D and Chen, D and Kleingartner, JA and Srinivasan, S and Cohen, RE and McKinley, GH}, title = {Sustained drag reduction in a turbulent flow using a low-temperature Leidenfrost surface.}, journal = {Science advances}, volume = {2}, number = {10}, pages = {e1600686}, pmid = {27757417}, issn = {2375-2548}, abstract = {Skin friction drag contributes a major portion of the total drag for small and large water vehicles at high Reynolds number (Re). One emerging approach to reducing drag is to use superhydrophobic surfaces to promote slip boundary conditions. However, the air layer or "plastron" trapped on submerged superhydrophobic surfaces often diminishes quickly under hydrostatic pressure and/or turbulent pressure fluctuations. We use active heating on a superhydrophobic surface to establish a stable vapor layer or "Leidenfrost" state at a relatively low superheat temperature. The continuous film of water vapor lubricates the interface, and the resulting slip boundary condition leads to skin friction drag reduction on the inner rotor of a custom Taylor-Couette apparatus. We find that skin friction can be reduced by 80 to 90% relative to an unheated superhydrophobic surface for Re in the range 26,100 ≤ Re ≤ 52,000. We derive a boundary layer and slip theory to describe the hydrodynamics in the system and show that the plastron thickness is h = 44 ± 11 μm, in agreement with expectations for a Leidenfrost surface.}, } @article {pmid27749870, year = {2016}, author = {Longhi, S}, title = {PT-symmetric mode-locking.}, journal = {Optics letters}, volume = {41}, number = {19}, pages = {4518-4521}, doi = {10.1364/OL.41.004518}, pmid = {27749870}, issn = {1539-4794}, abstract = {Parity-time (PT) symmetry is one of the most important accomplishments in optics over the past decade. Here the concept of PT mode-locking (ML) of a laser is introduced, in which active phase-locking of cavity axial modes is realized by asymmetric mode coupling in a complex time crystal. PT ML shows a transition from single- to double-pulse emission as the PT symmetry breaking point is crossed. The transition can show a turbulent behavior, depending on a dimensionless modulation parameter that plays the same role as the Reynolds number in hydrodynamic flows.}, } @article {pmid27742130, year = {2016}, author = {Li, P and Weng, L and Niu, H and Robinson, B and King, T and Conmy, R and Lee, K and Liu, L}, title = {Reynolds number scaling to predict droplet size distribution in dispersed and undispersed subsurface oil releases.}, journal = {Marine pollution bulletin}, volume = {113}, number = {1-2}, pages = {332-342}, doi = {10.1016/j.marpolbul.2016.10.005}, pmid = {27742130}, issn = {1879-3363}, mesh = {Alaska ; *Models, Theoretical ; Particle Size ; Petroleum/*analysis ; Petroleum Pollution/*analysis ; Viscosity ; Water Pollutants, Chemical/*analysis/*chemistry ; }, abstract = {This study was aimed at testing the applicability of modified Weber number scaling with Alaska North Slope (ANS) crude oil, and developing a Reynolds number scaling approach for oil droplet size prediction for high viscosity oils. Dispersant to oil ratio and empirical coefficients were also quantified. Finally, a two-step Rosin-Rammler scheme was introduced for the determination of droplet size distribution. This new approach appeared more advantageous in avoiding the inconsistency in interfacial tension measurements, and consequently delivered concise droplet size prediction. Calculated and observed data correlated well based on Reynolds number scaling. The relation indicated that chemical dispersant played an important role in reducing the droplet size of ANS under different seasonal conditions. The proposed Reynolds number scaling and two-step Rosin-Rammler approaches provide a concise, reliable way to predict droplet size distribution, supporting decision making in chemical dispersant application during an offshore oil spill.}, } @article {pmid27731461, year = {2016}, author = {Beauvier, E and Bodea, S and Pocheau, A}, title = {Front propagation in a vortex lattice: dependence on boundary conditions and vortex depth.}, journal = {Soft matter}, volume = {12}, number = {43}, pages = {8935-8941}, doi = {10.1039/c6sm01547f}, pmid = {27731461}, issn = {1744-6848}, abstract = {We experimentally address the propagation of reaction-diffusion fronts in vortex lattices by combining, in a Hele-Shaw cell and at low Reynolds number, forced electroconvective flows and an autocatalytic reaction in solution. We consider both vortex chains and vortex arrays, the former referring to mixed free/rigid boundary conditions for vortices and the latter to free boundary conditions. Varying the depth of the fluid layer, we observe no variation of the mean front velocities for vortex arrays and a noticeable variation for vortex chains. This questions the two-dimensional character of front propagation in low Reynolds number vortex lattices, as well as the mechanisms of this dependence.}, } @article {pmid27725841, year = {2016}, author = {Liu, X and Yan, W and Liu, Y and Choy, YS and Wei, Y}, title = {Numerical Investigation of Flow Characteristics in the Obstructed Realistic Human Upper Airway.}, journal = {Computational and mathematical methods in medicine}, volume = {2016}, number = {}, pages = {3181654}, pmid = {27725841}, issn = {1748-6718}, mesh = {Adult ; Airway Obstruction/diagnostic imaging/*physiopathology ; Asians ; Biomechanical Phenomena ; China ; Computer Simulation ; Humans ; Larynx/physiopathology ; Lung/diagnostic imaging ; Male ; Models, Statistical ; Models, Theoretical ; Mouth/physiopathology ; Nasal Cavity/physiopathology ; Pharynx/physiopathology ; Respiration ; Respiration Disorders/*diagnostic imaging/physiopathology ; Respiratory Mechanics ; Respiratory System/*physiopathology ; Tomography, X-Ray Computed ; Trachea/physiopathology ; }, abstract = {The flow characteristics in the realistic human upper airway (HUA) with obstruction that resulted from pharyngeal collapse were numerically investigated. The 3D anatomically accurate HUA model was reconstructed from CT-scan images of a Chinese male patient (38 years, BMI 25.7). The computational fluid dynamics (CFD) with the large eddy simulation (LES) method was applied to simulate the airflow dynamics within the HUA model in both inspiration and expiration processes. The laser Doppler anemometry (LDA) technique was simultaneously adopted to measure the airflow fields in the HUA model for the purpose of testifying the reliability of LES approach. In the simulations, the representative respiration intensities of 16.8 L/min (slight breathing), 30 L/min (moderate breathing), and 60 L/min (severe breathing) were conducted under continuous inspiration and expiration conditions. The airflow velocity field and static pressure field were obtained and discussed in detail. The results indicated the airflow experiences unsteady transitional/turbulent flow in the HUA model under low Reynolds number. The airflow fields cause occurrence of forceful injection phenomenon due to the narrowing of pharynx caused by the respiratory illness in inspiration and expiration. There also exist strong flow separation and back flow inside obstructed HUA owing to the vigorous jet flow effect in the pharynx. The present results would provide theoretical guidance for the treatment of obstructive respiratory disease.}, } @article {pmid27708761, year = {2016}, author = {Marth, W and Voigt, A}, title = {Collective migration under hydrodynamic interactions: a computational approach.}, journal = {Interface focus}, volume = {6}, number = {5}, pages = {20160037}, pmid = {27708761}, issn = {2042-8898}, abstract = {We consider a generic model for cell motility. Even if a comprehensive understanding of cell motility remains elusive, progress has been achieved in its modelling using a whole-cell physical model. The model takes into account the main mechanisms of cell motility, actin polymerization, actin-myosin dynamics and substrate mediated adhesion (if applicable), and combines them with steric cell-cell and hydrodynamic interactions. The model predicts the onset of collective cell migration, which emerges spontaneously as a result of inelastic collisions of neighbouring cells. Each cell here modelled as an active polar gel is accomplished with two vortices if it moves. Upon collision of two cells, the two vortices which come close to each other annihilate. This leads to a rotation of the cells and together with the deformation and the reorientation of the actin filaments in each cell induces alignment of these cells and leads to persistent translational collective migration. The effect for low Reynolds numbers is as strong as in the non-hydrodynamic model, but it decreases with increasing Reynolds number.}, } @article {pmid27703591, year = {2016}, author = {Lee, LM and Lee, JW and Chase, D and Gebrezgiabhier, D and Liu, AP}, title = {Development of an advanced microfluidic micropipette aspiration device for single cell mechanics studies.}, journal = {Biomicrofluidics}, volume = {10}, number = {5}, pages = {054105}, pmid = {27703591}, issn = {1932-1058}, support = {DP2 HL117748/HL/NHLBI NIH HHS/United States ; T32 EB005582/EB/NIBIB NIH HHS/United States ; }, abstract = {Various micro-engineered tools or platforms have been developed recently for cell mechanics studies based on acoustic, magnetic, and optical actuations. Compared with other techniques for single cell manipulations, microfluidics has the advantages with simple working principles and device implementations. In this work, we develop a multi-layer microfluidic pipette aspiration device integrated with pneumatically actuated microfluidic control valves. This configuration enables decoupling of cell trapping and aspiration, and hence causes less mechanical perturbation on trapped single cells before aspiration. A high trapping efficiency is achieved by the microfluidic channel design based on fluid resistance model and deterministic microfluidics. Compared to conventional micropipette aspiration, the suction pressure applied on the aspirating cells is highly stable due to the viscous nature of low Reynolds number flow. As a proof-of-concept of this novel microfluidic technology, we built a microfluidic pipette aspiration device with 2 × 13 trapping arrays and used this device to measure the stiffness of a human breast cancer cell line, MDA-MB-231, through the observation of cell deformations during aspiration. As a comparison, we studied the effect of Taxol, a FDA-approved anticancer drug on single cancer cell stiffness. We found that cancer cells treated with Taxol were less deformable with a higher Young's modulus. The multi-layer microfluidic pipette aspiration device is a scalable technology for single cell mechanophenotyping studies and drug discovery applications.}, } @article {pmid27688703, year = {2016}, author = {Dhanapal, C and Kamalakkannan, J and Prakash, J and Kothandapani, M}, title = {Analysis of Peristaltic Motion of a Nanofluid with Wall Shear Stress, Microrotation, and Thermal Radiation Effects.}, journal = {Applied bionics and biomechanics}, volume = {2016}, number = {}, pages = {4123741}, pmid = {27688703}, issn = {1176-2322}, abstract = {This paper analyzes the peristaltic flow of an incompressible micropolar nanofluid in a tapered asymmetric channel in the presence of thermal radiation and heat sources parameters. The rotation of the nanoparticles is incorporated in the flow model. The equations governing the nanofluid flow are modeled and exact solutions are managed under long wavelength and flow Reynolds number and long wavelength approximations. Explicit expressions of axial velocity, stream function, microrotation, nanoparticle temperature, and concentration have been derived. The phenomena of shear stress and trapping have also been discussed. Finally, the influences of various parameters of interest on flow variables have been discussed numerically and explained graphically. Besides, the results obtained in this paper will be helpful to those who are working on the development of various realms like fluid mechanics, the rotation, Brownian motion, thermophoresis, coupling number, micropolar parameter, and the nondimensional geometry parameters.}, } @article {pmid27686531, year = {2016}, author = {Salimi-Kenari, H and Imani, M and Nodehi, A and Abedini, H}, title = {An engineering approach to design of dextran microgels size fabricated by water/oil emulsification.}, journal = {Journal of microencapsulation}, volume = {33}, number = {6}, pages = {511-523}, doi = {10.1080/02652048.2016.1216188}, pmid = {27686531}, issn = {1464-5246}, mesh = {Dextrans/*chemistry ; Emulsions ; Gels/chemistry ; *Models, Chemical ; Oils/*chemistry ; Particle Size ; Water/*chemistry ; }, abstract = {A correlation, based on fluid mechanics, has been investigated for the mean particle diameter of crosslinked dextran microgels (CDMs) prepared via a water/oil emulsification methodology conducted in a single-stirred vessel. To this end, non-dimensional correlations were developed to predict the mean particle size of CDMs as a function of Weber number, Reynolds number and viscosity number similar to ones introduced for liquid-liquid dispersions. Moreover, a Rosin-Rammler distribution function has been successfully applied to the microgel particle size distributions. The correlations were validated using experimentally obtained mean particle sizes for CDMs prepared at different stirring conditions. The validated correlation is especially applicable to medical and pharmaceutical applications where strict control on the mean particle size and size distribution of CDMs are extremely essential. [Formula: see text].}, } @article {pmid27684076, year = {2016}, author = {Bachant, P and Wosnik, M and Gunawan, B and Neary, VS}, title = {Experimental Study of a Reference Model Vertical-Axis Cross-Flow Turbine.}, journal = {PloS one}, volume = {11}, number = {9}, pages = {e0163799}, pmid = {27684076}, issn = {1932-6203}, abstract = {The mechanical power, total rotor drag, and near-wake velocity of a 1:6 scale model (1.075 m diameter) of the US Department of Energy's Reference Model vertical-axis cross-flow turbine were measured experimentally in a towing tank, to provide a comprehensive open dataset for validating numerical models. Performance was measured for a range of tip speed ratios and at multiple Reynolds numbers by varying the rotor's angular velocity and tow carriage speed, respectively. A peak power coefficient CP = 0.37 and rotor drag coefficient CD = 0.84 were observed at a tip speed ratio λ0 = 3.1. A regime of weak linear Re-dependence of the power coefficient was observed above a turbine diameter Reynolds number ReD ≈ 106. The effects of support strut drag on turbine performance were investigated by covering the rotor's NACA 0021 struts with cylinders. As expected, this modification drastically reduced the rotor power coefficient. Strut drag losses were also measured for the NACA 0021 and cylindrical configurations with the rotor blades removed. For λ = λ0, wake velocity was measured at 1 m (x/D = 0.93) downstream. Mean velocity, turbulence kinetic energy, and mean kinetic energy transport were compared with results from a high solidity turbine acquired with the same test apparatus. Like the high solidity case, mean vertical advection was calculated to be the largest contributor to near-wake recovery. However, overall, lower levels of streamwise wake recovery were calculated for the RM2 case-a consequence of both the relatively low solidity and tapered blades reducing blade tip vortex shedding-responsible for mean vertical advection-and lower levels of turbulence caused by higher operating tip speed ratio and therefore reduced dynamic stall. Datasets, code for processing and visualization, and a CAD model of the turbine have been made publicly available.}, } @article {pmid27662761, year = {2016}, author = {de Camargo, CL and Shiroma, LS and Giordano, GF and Gobbi, AL and Vieira, LC and Lima, RS}, title = {Turbulence in microfluidics: Cleanroom-free, fast, solventless, and bondless fabrication and application in high throughput liquid-liquid extraction.}, journal = {Analytica chimica acta}, volume = {940}, number = {}, pages = {73-83}, doi = {10.1016/j.aca.2016.08.052}, pmid = {27662761}, issn = {1873-4324}, abstract = {This paper addresses an important breakthrough in the deployment of ultra-high adhesion strength microfluidic technologies to provide turbulence at harsh flow rate conditions. This paper is only, to our knowledge, the second reporting on the generation of high flow rate-assisted turbulence in microchannels. This flow solves a crucial bottleneck in microfluidics: the generation of high throughput homogeneous mixings. We focused on the fabrication of bulky polydimethylsiloxane (PDMS) microchips (without any interfaces) rather than the laborious surface modifications that were employed in the first reporting about turbulence-assisted microfluidics. The fabrication is cleanroom-free, simple, low-cost, fast, solventless, and bondless requiring only a laboratory oven. More specifically, our method relies on the shaping of a nylon scaffold, cure of PDMS with embedded nylon, and removal of this scaffold. The scaffold was obtained by manually wrapping nylon threads. The withdrawing out of the scaffold was completed in few seconds using only a plier. Such microchannels endured flow rates of up to 60.0 mL min(-1) with a strikingly low elastic deformation. The importance in producing turbulence into microscale channels was successfully shown in liquid-liquid extractions. The great energy dissipation rate relative to the turbulence created high throughput and efficient extractions in microfluidics for the first time. The residence time was only 0.01 s at 25.0 mL min(-1) (total flow rate of the immiscible phases). In addition, the partition coefficient determined in a single run was similar to that obtained by the conventional batch shake-flask method that was realized in triplicate.}, } @article {pmid27661694, year = {2016}, author = {Vakarelski, IU and Berry, JD and Chan, DY and Thoroddsen, ST}, title = {Leidenfrost Vapor Layers Reduce Drag without the Crisis in High Viscosity Liquids.}, journal = {Physical review letters}, volume = {117}, number = {11}, pages = {114503}, doi = {10.1103/PhysRevLett.117.114503}, pmid = {27661694}, issn = {1079-7114}, abstract = {The drag coefficient C_{D} of a solid smooth sphere moving in a fluid is known to be only a function of the Reynolds number Re and diminishes rapidly at the drag crisis around Re∼3×10^{5} . A Leidenfrost vapor layer on a hot sphere surface can trigger the onset of the drag crisis at a lower Re. By using a range of high viscosity perfluorocarbon liquids, we show that the drag reduction effect can occur over a wide range of Re, from as low as ∼600 to 10^{5} . The Navier slip model with a viscosity dependent slip length can fit the observed drag reduction and wake shape.}, } @article {pmid27635104, year = {2016}, author = {Chandler, ID and Guymer, I and Pearson, JM and van Egmond, R}, title = {Vertical variation of mixing within porous sediment beds below turbulent flows.}, journal = {Water resources research}, volume = {52}, number = {5}, pages = {3493-3509}, pmid = {27635104}, issn = {0043-1397}, abstract = {River ecosystems are influenced by contaminants in the water column, in the pore water and adsorbed to sediment particles. When exchange across the sediment-water interface (hyporheic exchange) is included in modeling, the mixing coefficient is often assumed to be constant with depth below the interface. Novel fiber-optic fluorometers have been developed and combined with a modified EROSIMESS system to quantify the vertical variation in mixing coefficient with depth below the sediment-water interface. The study considered a range of particle diameters and bed shear velocities, with the permeability Péclet number, PeK between 1000 and 77,000 and the shear Reynolds number, Re*, between 5 and 600. Different parameterization of both an interface exchange coefficient and a spatially variable in-sediment mixing coefficient are explored. The variation of in-sediment mixing is described by an exponential function applicable over the full range of parameter combinations tested. The empirical relationship enables estimates of the depth to which concentrations of pollutants will penetrate into the bed sediment, allowing the region where exchange will occur faster than molecular diffusion to be determined.}, } @article {pmid27627416, year = {2016}, author = {Ren, F and Song, B and Sukop, MC and Hu, H}, title = {Improved lattice Boltzmann modeling of binary flow based on the conservative Allen-Cahn equation.}, journal = {Physical review. E}, volume = {94}, number = {2-1}, pages = {023311}, doi = {10.1103/PhysRevE.94.023311}, pmid = {27627416}, issn = {2470-0053}, abstract = {The primary and key task of binary fluid flow modeling is to track the interface with good accuracy, which is usually challenging due to the sharp-interface limit and numerical dispersion. This article concentrates on further development of the conservative Allen-Cahn equation (ACE) [Geier et al., Phys. Rev. E 91, 063309 (2015)10.1103/PhysRevE.91.063309] under the framework of the lattice Boltzmann method (LBM), with incorporation of the incompressible hydrodynamic equations [Liang et al., Phys. Rev. E 89, 053320 (2014)10.1103/PhysRevE.89.053320]. Utilizing a modified equilibrium distribution function and an additional source term, this model is capable of correctly recovering the conservative ACE through the Chapman-Enskog analysis. We also simulate four phase-tracking benchmark cases, including one three-dimensional case; all show good accuracy as well as low numerical dispersion. By coupling the incompressible hydrodynamic equations, we also simulate layered Poiseuille flow and the Rayleigh-Taylor instability, illustrating satisfying performance in dealing with complex flow problems, e.g., high viscosity ratio, high density ratio, and high Reynolds number situations. The present work provides a reliable and efficient solution for binary flow modeling.}, } @article {pmid27627415, year = {2016}, author = {Ba, Y and Liu, H and Li, Q and Kang, Q and Sun, J}, title = {Multiple-relaxation-time color-gradient lattice Boltzmann model for simulating two-phase flows with high density ratio.}, journal = {Physical review. E}, volume = {94}, number = {2-1}, pages = {023310}, doi = {10.1103/PhysRevE.94.023310}, pmid = {27627415}, issn = {2470-0053}, abstract = {In this paper we propose a color-gradient lattice Boltzmann (LB) model for simulating two-phase flows with high density ratio and high Reynolds number. The model applies a multirelaxation-time (MRT) collision operator to enhance the stability of the simulation. A source term, which is derived by the Chapman-Enskog analysis, is added into the MRT LB equation so that the Navier-Stokes equations can be exactly recovered. Also, a form of the equilibrium density distribution function is used to simplify the source term. To validate the proposed model, steady flows of a static droplet and the layered channel flow are first simulated with density ratios up to 1000. Small values of spurious velocities and interfacial tension errors are found in the static droplet test, and improved profiles of velocity are obtained by the present model in simulating channel flows. Then, two cases of unsteady flows, Rayleigh-Taylor instability and droplet splashing on a thin film, are simulated. In the former case, the density ratio of 3 and Reynolds numbers of 256 and 2048 are considered. The interface shapes and spike and bubble positions are in good agreement with the results of previous studies. In the latter case, the droplet spreading radius is found to obey the power law proposed in previous studies for the density ratio of 100 and Reynolds number up to 500.}, } @article {pmid27627229, year = {2016}, author = {Heidenreich, S and Dunkel, J and Klapp, SH and Bär, M}, title = {Hydrodynamic length-scale selection in microswimmer suspensions.}, journal = {Physical review. E}, volume = {94}, number = {2-1}, pages = {020601}, doi = {10.1103/PhysRevE.94.020601}, pmid = {27627229}, issn = {2470-0053}, abstract = {A universal characteristic of mesoscale turbulence in active suspensions is the emergence of a typical vortex length scale, distinctly different from the scale invariance of turbulent high-Reynolds number flows. Collective length-scale selection has been observed in bacterial fluids, endothelial tissue, and active colloids, yet the physical origins of this phenomenon remain elusive. Here, we systematically derive an effective fourth-order field theory from a generic microscopic model that allows us to predict the typical vortex size in microswimmer suspensions. Building on a self-consistent closure condition, the derivation shows that the vortex length scale is determined by the competition between local alignment forces, rotational diffusion, and intermediate-range hydrodynamic interactions. Vortex structures found in simulations of the theory agree with recent measurements in Bacillus subtilis suspensions. Moreover, our approach yields an effective viscosity enhancement (reduction), as reported experimentally for puller (pusher) microorganisms.}, } @article {pmid27610298, year = {2016}, author = {Maqbool, K and Shaheen, S and Mann, AB}, title = {Exact solution of cilia induced flow of a Jeffrey fluid in an inclined tube.}, journal = {SpringerPlus}, volume = {5}, number = {1}, pages = {1379}, pmid = {27610298}, issn = {2193-1801}, abstract = {The present study investigated the cilia induced flow of MHD Jeffrey fluid through an inclined tube. This study is carried out under the assumptions of long wavelength and low Reynolds number approximations. Exact solutions for the velocity profile, pressure rise, pressure gradient, volume flow rate and stream function are obtained. Effects of pertinent physical parameters on the computational results are presented graphically.}, } @article {pmid27608508, year = {2016}, author = {Li, J and Liu, W and Li, T and Rozen, I and Zhao, J and Bahari, B and Kante, B and Wang, J}, title = {Swimming Microrobot Optical Nanoscopy.}, journal = {Nano letters}, volume = {16}, number = {10}, pages = {6604-6609}, doi = {10.1021/acs.nanolett.6b03303}, pmid = {27608508}, issn = {1530-6992}, abstract = {Optical imaging plays a fundamental role in science and technology but is limited by the ability of lenses to resolve small features below the fundamental diffraction limit. A variety of nanophotonic devices, such as metamaterial superlenses and hyperlenses, as well as microsphere lenses, have been proposed recently for subdiffraction imaging. The implementation of these micro/nanostructured lenses as practical and efficient imaging approaches requires locomotive capabilities to probe specific sites and scan large areas. However, directed motion of nanoscale objects in liquids must overcome low Reynolds number viscous flow and Brownian fluctuations, which impede stable and controllable scanning. Here we introduce a new imaging method, named swimming microrobot optical nanoscopy, based on untethered chemically powered microrobots as autonomous probes for subdiffraction optical scanning and imaging. The microrobots are made of high-refractive-index microsphere lenses and powered by local catalytic reactions to swim and scan over the sample surface. Autonomous motion and magnetic guidance of microrobots enable large-area, parallel and nondestructive scanning with subdiffraction resolution, as illustrated using soft biological samples such as neuron axons, protein microtubulin, and DNA nanotubes. Incorporating such imaging capacities in emerging nanorobotics technology represents a major step toward ubiquitous nanoscopy and smart nanorobots for spectroscopy and imaging.}, } @article {pmid27588859, year = {2016}, author = {Ault, JT and Fani, A and Chen, KK and Shin, S and Gallaire, F and Stone, HA}, title = {Vortex-Breakdown-Induced Particle Capture in Branching Junctions.}, journal = {Physical review letters}, volume = {117}, number = {8}, pages = {084501}, doi = {10.1103/PhysRevLett.117.084501}, pmid = {27588859}, issn = {1079-7114}, abstract = {We show experimentally that a flow-induced, Reynolds number-dependent particle-capture mechanism in branching junctions can be enhanced or eliminated by varying the junction angle. In addition, numerical simulations are used to show that the features responsible for this capture have the signatures of classical vortex breakdown, including an approach flow aligned with the vortex axis and a pocket of subcriticality. We show how these recirculation regions originate and evolve and suggest a physical mechanism for their formation. Furthermore, comparing experiments and numerical simulations, the presence of vortex breakdown is found to be an excellent predictor of particle capture. These results inform the design of systems in which suspended particle accumulation can be eliminated or maximized.}, } @article {pmid27586487, year = {2016}, author = {Hayat, T and Ahmed, B and Abbasi, FM and Ahmad, B}, title = {Mixed convective peristaltic flow of carbon nanotubes submerged in water using different thermal conductivity models.}, journal = {Computer methods and programs in biomedicine}, volume = {135}, number = {}, pages = {141-150}, doi = {10.1016/j.cmpb.2016.07.030}, pmid = {27586487}, issn = {1872-7565}, mesh = {*Models, Theoretical ; *Nanotubes, Carbon ; Water/*chemistry ; }, abstract = {BACKGROUND AND OBJECTIVE: Single Walled Carbon Nanotubes (SWCNTs) are the advanced product of nanotechnology having notable mechanical and physical properties. Peristalsis of SWCNTs suspended in water through an asymmetric channel is examined. Such mechanism is studied in the presence of viscous dissipation, velocity slip, mixed convection, temperature jump and heat generation/absorption.

METHODS: Mathematical modeling is carried out under the low Reynolds number and long wavelength approximation. Resulting nonlinear system is solved using the perturbation technique for small Brinkman's number. Physical analysis and comparison of the results in light of three different thermal conductivity models is also provided.

CONCLUSIONS: It is reported that the heat transfer rate at the boundary increases with an increase in the nanotubes volume fraction. The addition of nanotubes affects the pressure gradient during the peristaltic flow. Moreover, the maximum velocity of the fluid decreases due to addition of the nanotubes.}, } @article {pmid27586475, year = {2016}, author = {Ramesh, K}, title = {Effects of slip and convective conditions on the peristaltic flow of couple stress fluid in an asymmetric channel through porous medium.}, journal = {Computer methods and programs in biomedicine}, volume = {135}, number = {}, pages = {1-14}, doi = {10.1016/j.cmpb.2016.07.001}, pmid = {27586475}, issn = {1872-7565}, mesh = {*Hydrodynamics ; Models, Theoretical ; Porosity ; *Stress, Mechanical ; }, abstract = {BACKGROUND: Assessment of the fluid flow pattern in a non-pregnant uterus is important for understanding embryo transport in the uterus. Fertilization occurs in the fallopian tube and the embryo enters the uterine cavity within three days of ovulation. In the uterus, the embryo is conveyed by the uterine fluid for another three to four days to a successful implantation site at the upper part of the uterus. The movements of fluid within the uterus may be induced by several mechanisms, but they seem to be dominated by myometrial contractions. The intrauterine fluid flow due to these myometrial contractions is peristaltic type motion in nature and the myometrial contractions may occur in both symmetric and asymmetric directions.

OBJECTIVE: The aim of the present article is to investigate the peristaltic transport of couple stress fluid in an asymmetric channel. The channel asymmetry is produced by choosing the peristaltic wave train on the walls to have different wave amplitudes and phase differences. The fluid is filled with a homogeneous porous medium. The effects of slip and convective boundary conditions are also taken into consideration.

METHOD: The flow is investigated in the wave frame of reference moving with constant velocity with the wave. Long wavelength and low Reynolds number approximations are utilized in problem formulation. Exact solutions are presented for the stream function, pressure gradient and temperature.

RESULTS: The graphical analysis is carried out to examine the effects of sundry parameters on flow quantities of interest. Comparative study is also made for couple stress fluid with Newtonian fluid.

CONCLUSIONS: The results revealed that the trapping fluid can be increased and the central line axial velocity can be raised to a considerable extent by increasing Darcy number. Increasing of slip parameter increases the velocity near the boundary of the walls and Brinkman number increases the temperature of the fluid.}, } @article {pmid27575234, year = {2016}, author = {Pareschi, G and Frapolli, N and Chikatamarla, SS and Karlin, IV}, title = {Conjugate heat transfer with the entropic lattice Boltzmann method.}, journal = {Physical review. E}, volume = {94}, number = {1-1}, pages = {013305}, doi = {10.1103/PhysRevE.94.013305}, pmid = {27575234}, issn = {2470-0053}, abstract = {A conjugate heat-transfer model is presented based on the two-population entropic lattice Boltzmann method. The present approach relies on the extension of Grad's boundary conditions to the two-population model for thermal flows, as well as on the appropriate exact conjugate heat-transfer condition imposed at the fluid-solid interface. The simplicity and efficiency of the lattice Boltzmann method (LBM), and in particular of the entropic multirelaxation LBM, are retained in the present approach, thus enabling simulations of turbulent high Reynolds number flows and complex wall boundaries. The model is validated by means of two-dimensional parametric studies of various setups, including pure solid conduction, conjugate heat transfer with a backward-facing step flow, and conjugate heat transfer with the flow past a circular heated cylinder. Further validations are performed in three dimensions for the case of a turbulent flow around a heated mounted cube.}, } @article {pmid27575221, year = {2016}, author = {Sahu, S and Shankar, V}, title = {Passive manipulation of free-surface instability by deformable solid bilayers.}, journal = {Physical review. E}, volume = {94}, number = {1-1}, pages = {013111}, doi = {10.1103/PhysRevE.94.013111}, pmid = {27575221}, issn = {2470-0053}, abstract = {This study deals with the elastohydrodynamic coupling that occurs in the flow of a liquid layer down an inclined plane lined with a deformable solid bilayer and its consequences on the stability of the free surface of the liquid layer. The fluid is Newtonian and incompressible, while the linear elastic constitutive relation has been considered for the deformable solid bilayer, and the densities of the fluid and the two solids are kept equal. A temporal linear stability analysis is carried out for this coupled solid-fluid system. A long-wave asymptotic analysis is employed to obtain an analytical expression for the complex wavespeed in the low wave-number regime, and a numerical shooting method is used to solve the coupled set of governing differential equations in order to obtain the stability criterion for arbitrary values of the wave number. In a previous work on plane Couette flow past an elastic bilayer, Neelmegam et al. [Phys. Rev. E 90, 043004 (2014)PLEEE81539-375510.1103/PhysRevE.90.043004] showed that the instability of the flow can be significantly influenced by the nature of the solid layer, which is adjacent to the liquid layer. In stark contrast, for free-surface flow past a bilayer, our long-wave asymptotic analysis demonstrates that the stability of the free-surface mode is insensitive to the nature of the solid adjacent to the liquid layer. Instead, it is the effective shear modulus of the bilayer G_{eff} (given by H/G_{eff} =H_{1} /G_{1} +H_{2} /G_{2}, where H=H_{1} +H_{2} is the total thickness of the solid bilayer, H_{1} and H_{2} are the thicknesses of the two solid layers, and G_{1} and G_{2} are the shear moduli of the two solid layers) that determines the stability of the free surface in the long-wave limit. We show that for a given Reynolds number, the free-surface instability is stabilized when G_{eff} decreases below a critical value. At finite wave numbers, our numerical solution indicates that additional instabilities at the free surface and the liquid-solid interface can be induced by wall deformability and inertia in the fluid and solid. Interestingly, the onset of these additional instabilities is sensitive to the relative placements of the two solid layers comprising the bilayer. We show that it is possible to delay the onset of these additional instabilities, while still suppressing the free-surface instability, by manipulating the ratio of the shear moduli and the thicknesses of the two solid layers in the bilayer. At moderate Reynolds number and finite wave number, we demonstrate that an exchange of modes occurs between the gas-liquid and liquid-solid interfacial modes as the solid bilayer becomes more deformable. We demonstrate further that dissipative effects in the individual solid layers have an important bearing on the stability of the system, and they could also be exploited in suppressing the instability. This study thus shows that the ability to passively manipulate and control interfacial instabilities increases substantially with the use of solid bilayers.}, } @article {pmid27575215, year = {2016}, author = {Swaminathan, RV and Ravichandran, S and Perlekar, P and Govindarajan, R}, title = {Dynamics of circular arrangements of vorticity in two dimensions.}, journal = {Physical review. E}, volume = {94}, number = {1-1}, pages = {013105}, doi = {10.1103/PhysRevE.94.013105}, pmid = {27575215}, issn = {2470-0053}, abstract = {The merger of two like-signed vortices is a well-studied problem, but in a turbulent flow, we may often have more than two like-signed vortices interacting. We study the merger of three or more identical corotating vortices initially arranged on the vertices of a regular polygon. At low to moderate Reynolds numbers, we find an additional stage in the merger process, absent in the merger of two vortices, where an annular vortical structure is formed and is long lived. Vortex merger is slowed down significantly due to this. Such annular vortices are known at far higher Reynolds numbers in studies of tropical cyclones, which have been noticed to a break down into individual vortices. In the preannular stage, vortical structures in a viscous flow are found here to tilt and realign in a manner similar to the inviscid case, but the pronounced filaments visible in the latter are practically absent in the former. Five or fewer vortices initially elongate radially, and then reorient their long axis closer to the azimuthal direction so as to form an annulus. With six or more vortices, the initial alignment is already azimuthal. Interestingly at higher Reynolds numbers, the merger of an odd number of vortices is found to proceed very differently from that of an even number. The former process is rapid and chaotic whereas the latter proceeds more slowly via pairing events. The annular vortex takes the form of a generalized Lamb-Oseen vortex (GLO), and diffuses inward until it forms a standard Lamb-Oseen vortex. For lower Reynolds number, the numerical (fully nonlinear) evolution of the GLO vortex follows exactly the analytical evolution until merger. At higher Reynolds numbers, the annulus goes through instabilities whose nonlinear stages show a pronounced difference between even and odd mode disturbances. Here again, the odd mode causes an early collapse of the annulus via decaying turbulence into a single central vortex, whereas the even mode disturbance causes a more orderly progression into a single vortex. Results from linear stability analysis agree with the nonlinear simulations, and predict the frequencies of the most unstable modes better than they predict the growth rates. It is hoped that the present findings, that multiple vortex merger is qualitatively different from the merger of two vortices, will motivate studies on how multiple vortex interactions affect the inverse cascade in two-dimensional turbulence.}, } @article {pmid27567769, year = {2016}, author = {Tabe, R and Ghalichi, F and Hossainpour, S and Ghasemzadeh, K}, title = {Laminar-to-turbulence and relaminarization zones detection by simulation of low Reynolds number turbulent blood flow in large stenosed arteries.}, journal = {Bio-medical materials and engineering}, volume = {27}, number = {2-3}, pages = {119-129}, doi = {10.3233/BME-161574}, pmid = {27567769}, issn = {1878-3619}, mesh = {Arterial Occlusive Diseases/*physiopathology ; Arteries/*physiopathology ; Blood Flow Velocity ; Computer Simulation ; Constriction, Pathologic/*physiopathology ; Humans ; Models, Cardiovascular ; Pulsatile Flow ; Stress, Mechanical ; }, abstract = {Laminar, turbulent, transitional, or combine areas of all three types of viscous flow can occur downstream of a stenosis depending upon the Reynolds number and constriction shape parameter. Neither laminar flow solver nor turbulent models for instance the k-ω (k-omega), k-ε (k-epsilon), RANS or LES are opportune for this type of flow. In the present study attention has been focused vigorously on the effect of the constriction in the flow field with a unique way. It means that the laminar solver was employed from entry up to the beginning of the turbulent shear flow. The turbulent model (k-ω SST Transitional Flows) was utilized from starting of turbulence to relaminarization zone while the laminar model was applied again with onset of the relaminarization district. Stenotic flows, with 50 and 75% cross-sectional area, were simulated at Reynolds numbers range from 500 to 2000 employing FLUENT (v6.3.17). The flow was considered to be steady, axisymmetric, and incompressible. Achieving results were reported as axial velocity, disturbance velocity, wall shear stress and the outcomes were compared with previously experimental and CFD computations. The analogy of axial velocity profiles shows that they are in acceptable compliance with the empirical data. As well as disturbance velocity and wall shear stresses anticipated by this new approach, part by part simulation, are reasonably valid with the acceptable experimental studies.}, } @article {pmid27552860, year = {2016}, author = {Maneshian, B and Javadi, Kh and Rahni, MT and Miller, R}, title = {Droplet dynamics in rotating flows.}, journal = {Advances in colloid and interface science}, volume = {236}, number = {}, pages = {63-82}, doi = {10.1016/j.cis.2016.07.005}, pmid = {27552860}, issn = {1873-3727}, abstract = {This paper deals with investigations of droplet dynamics in rotating flows. In many previous studies droplet dynamics was analyzed in simple unidirectional flows. To fill this gap, the focus of this study is an overview on investigations of droplet dynamics in a complex rotating flow. A Lattice Boltzmann Method with high potential in simulation of two-phase unsteady flows is applied to simulate the physics of the problem in a lid-driven cavity. In spite of its simple geometry, there is a complex rotating flow field containing different vortices and shear regions. The Reynolds number based on the cavity length scale and the upper wall velocity, ReL, is considered to be 1000. We discuss here effects of different parameters such as: density ratios (1, 5, 10, 100, and 1000), droplet sizes (D/L=0.097, 0.114, 0.131 and 0.2), and droplet initial positions (1/8, 2/8, and 3/8 of the cavity length, L, out of center). The results are discussed in terms of global flow physics and its interaction with the droplet, drop deformation during its motion along with the main flow, and droplet trajectories. It is shown that there are strong interactions between the droplet and the main carrying flow. During motion, the droplets pass through different flow regions containing acceleration/deceleration zones. Consequently, the droplets experience different shear forces resulting in stretching, shrinking, rotating and dilatation which all contribute to the dynamics of the droplet.}, } @article {pmid27528780, year = {2016}, author = {Liu, H and Ravi, S and Kolomenskiy, D and Tanaka, H}, title = {Biomechanics and biomimetics in insect-inspired flight systems.}, journal = {Philosophical transactions of the Royal Society of London. Series B, Biological sciences}, volume = {371}, number = {1704}, pages = {}, pmid = {27528780}, issn = {1471-2970}, mesh = {*Aircraft ; Animals ; Biomechanical Phenomena ; *Biomimetics ; *Flight, Animal ; Insecta/*physiology ; }, abstract = {Insect- and bird-size drones-micro air vehicles (MAV) that can perform autonomous flight in natural and man-made environments are now an active and well-integrated research area. MAVs normally operate at a low speed in a Reynolds number regime of 10(4)-10(5) or lower, in which most flying animals of insects, birds and bats fly, and encounter unconventional challenges in generating sufficient aerodynamic forces to stay airborne and in controlling flight autonomy to achieve complex manoeuvres. Flying insects that power and control flight by flapping wings are capable of sophisticated aerodynamic force production and precise, agile manoeuvring, through an integrated system consisting of wings to generate aerodynamic force, muscles to move the wings and a control system to modulate power output from the muscles. In this article, we give a selective review on the state of the art of biomechanics in bioinspired flight systems in terms of flapping and flexible wing aerodynamics, flight dynamics and stability, passive and active mechanisms in stabilization and control, as well as flapping flight in unsteady environments. We further highlight recent advances in biomimetics of flapping-wing MAVs with a specific focus on insect-inspired wing design and fabrication, as well as sensing systems.This article is part of the themed issue 'Moving in a moving medium: new perspectives on flight'.}, } @article {pmid27518455, year = {2016}, author = {Li, F and Jian, Y and Chang, L and Zhao, G and Yang, L}, title = {Alternating current electroosmotic flow in polyelectrolyte-grafted nanochannel.}, journal = {Colloids and surfaces. B, Biointerfaces}, volume = {147}, number = {}, pages = {234-241}, doi = {10.1016/j.colsurfb.2016.07.064}, pmid = {27518455}, issn = {1873-4367}, mesh = {Electricity ; *Electrochemistry ; Electroosmosis/*instrumentation ; *Nanotechnology ; Polyelectrolytes/*chemistry ; Static Electricity ; }, abstract = {In this work, we investigate the time periodic electroosmotic flow (EOF) of an electrolyte solution through a slit polyelectrolyte-grafted (PE-grafted) nanochannel under applied alternating current (AC) electrical field. The PE-grafted nanochannel is represented by a rigid surface covered by a polyelectrolyte layer (PEL) in a brush-like configuration. Under Debye-Hückel approximation, we obtain analytical solutions of electrical potential in decoupled regime of PE-grafted nanochannel, where the thickness of PEL is independent of the electrostatic effects triggered by polyelectrolyte charges. Based upon the electrical potential obtained above, we calculate EOF velocities with uniform and non-uniform drag coefficients for PE-grafted nanochannel and compare their results. The effects of pertinent dimensionless parameters on EOF velocity amplitude are discussed in detail. Moreover, the amplitude of EOF velocity in a PE-grafted nanochannel is compared with that in a rigid one. It is shown that larger EOF velocity and volume flow rate are found for a PE-grafted nanochannel. In addition, AC EOF velocity is further investigated. The oscillation of velocity reduces and is restricted within the region near the PEL-electrolyte interface for higher oscillating Reynolds number Re.}, } @article {pmid27507620, year = {2016}, author = {Farutin, A and Piasecki, T and Słowicka, AM and Misbah, C and Wajnryb, E and Ekiel-Jeżewska, ML}, title = {Dynamics of flexible fibers and vesicles in Poiseuille flow at low Reynolds number.}, journal = {Soft matter}, volume = {12}, number = {35}, pages = {7307-7323}, doi = {10.1039/c6sm00819d}, pmid = {27507620}, issn = {1744-6848}, abstract = {The dynamics of flexible fibers and vesicles in unbounded planar Poiseuille flow at low Reynolds number is shown to exhibit similar basic features, when their equilibrium (moderate) aspect ratio is the same and vesicle viscosity contrast is relatively high. Tumbling, lateral migration, accumulation and shape evolution of these two types of flexible objects are analyzed numerically. The linear dependence of the accumulation position on relative bending rigidity, and other universal scalings are derived from the local shear flow approximation.}, } @article {pmid27501748, year = {2016}, author = {Daghooghi, M and Borazjani, I}, title = {Self-propelled swimming simulations of bio-inspired smart structures.}, journal = {Bioinspiration & biomimetics}, volume = {11}, number = {5}, pages = {056001}, doi = {10.1088/1748-3190/11/5/056001}, pmid = {27501748}, issn = {1748-3190}, mesh = {Animals ; Biomechanical Phenomena ; *Biomimetic Materials ; Eels/*physiology ; Locomotion ; Models, Biological ; Perciformes/*physiology ; Swimming/*physiology ; }, abstract = {This paper presents self-propelled swimming simulations of a foldable structure, whose folded configuration is a box. For self-locomotion through water the structure unfolds and undulates. To guide the design of the structure and understand how it should undulate to achieve either highest speed or maximize efficiency during locomotion, several kinematic parameters were systematically varied in the simulations: the wave type (standing wave versus traveling wave), the smoothness of undulations (smooth undulations versus undulations of rigid links), the mode of undulations (carangiform: mackerel-like versus anguilliform: eel-like undulations), and the maximum amplitude of undulations. We show that the swimmers with standing wave are slow and inefficient because they are not able to produce thrust using the added-mass mechanism. Among the tested types of undulation at low Reynolds number (Re) regime of [Formula: see text] (Strouhal number of about 1.0), structures that employ carangiform undulations can swim faster, whereas anguilliform swimmers are more economic, i.e., using less power they can swim a longer distance. Another finding of our simulations is that structures which are made of rigid links are typically less efficient (lower propulsive and power efficiencies and also lower swimming speed) compared with smoothly undulating ones because a higher added-mass force is generated by smooth undulations. The wake of all the swimmers bifurcated at the low Re regime because of the higher lateral relative to the axial velocity (high Strouhal number) that advects the vortices laterally creating a double row of vortices in the wake. In addition, we show that the wake cannot be used to predict the performance of the swimmers because the net force in each cycle is zero for self-propelled bodies and the pressure term is not negligible compared to the other terms.}, } @article {pmid27493565, year = {2016}, author = {Smith, FT and Johnson, ER}, title = {Movement of a finite body in channel flow.}, journal = {Proceedings. Mathematical, physical, and engineering sciences}, volume = {472}, number = {2191}, pages = {20160164}, pmid = {27493565}, issn = {1364-5021}, abstract = {A body of finite size is moving freely inside, and interacting with, a channel flow. The description of this unsteady interaction for a comparatively dense thin body moving slowly relative to flow at medium-to-high Reynolds number shows that an inviscid core problem with vorticity determines much, but not all, of the dominant response. It is found that the lift induced on a body of length comparable to the channel width leads to differences in flow direction upstream and downstream on the body scale which are smoothed out axially over a longer viscous length scale; the latter directly affects the change in flow directions. The change is such that in any symmetric incident flow the ratio of slopes is found to be [Formula: see text], i.e. approximately 0.900969, independently of Reynolds number, wall shear stresses and velocity profile. The two axial scales determine the evolution of the body and the flow, always yielding instability. This unusual evolution and linear or nonlinear instability mechanism arise outside the conventional range of flow instability and are influenced substantially by the lateral positioning, length and axial velocity of the body.}, } @article {pmid27475199, year = {2016}, author = {Padois, T and Laffay, P and Idier, A and Moreau, S}, title = {Tonal noise of a controlled-diffusion airfoil at low angle of attack and Reynolds number.}, journal = {The Journal of the Acoustical Society of America}, volume = {140}, number = {1}, pages = {EL113}, doi = {10.1121/1.4958916}, pmid = {27475199}, issn = {1520-8524}, abstract = {The acoustic signature of a controlled-diffusion airfoil immersed in a flow is experimentally characterized. Acoustic measurements have been carried out in an anechoic open-jet-wind-tunnel for low Reynolds numbers (from 5 × 10(4) to 4.3 × 10(5)) and several angles of attack. As with the NACA0012, the acoustic spectrum is dominated by discrete tones. These tonal behaviors are divided into three different regimes. The first one is characterized by a dominant primary tone which is steady over time, surrounded by secondary peaks. The second consists of two unsteady primary tones associated with secondary peaks and the third consists of a hump dominated by several small peaks. A wavelet study allows one to identify an amplitude modulation of the acoustic signal mainly for the unsteady tonal regime. This amplitude modulation is equal to the frequency interval between two successive tones. Finally, a bispectral analysis explains the presence of tones at higher frequencies.}, } @article {pmid27462481, year = {2016}, author = {Zhang, W and Jiang, Y and Li, L and Chen, G}, title = {Effects of wall suction/blowing on two-dimensional flow past a confined square cylinder.}, journal = {SpringerPlus}, volume = {5}, number = {1}, pages = {985}, pmid = {27462481}, issn = {2193-1801}, abstract = {A numerical simulation is conducted to study the laminar flow past a square cylinder confined in a channel (the ratio of side length of the square to channel width is fixed at 1/4) subjected to a locally uniform blowing/suction speed placed at the top and bottom channel walls. Governing equations with boundary conditions are resolved using a finite volume method in pressure-velocity formulation. The flow patterns relevant to the critical spacing values are investigated. Numerical results show that wall blowing has a stabilizing effect on the flow, and the corresponding critical Reynolds number increases monotonically with increasing blowing velocity. Remarkably, steady asymmetric solutions and hysteretic mode transitions exist in a certain range of parameters (Reynolds number and suction speed) in the case of suction.}, } @article {pmid27447509, year = {2016}, author = {Mathai, V and Calzavarini, E and Brons, J and Sun, C and Lohse, D}, title = {Microbubbles and Microparticles are Not Faithful Tracers of Turbulent Acceleration.}, journal = {Physical review letters}, volume = {117}, number = {2}, pages = {024501}, doi = {10.1103/PhysRevLett.117.024501}, pmid = {27447509}, issn = {1079-7114}, abstract = {We report on the Lagrangian statistics of acceleration of small (sub-Kolmogorov) bubbles and tracer particles with Stokes number St≪1 in turbulent flow. At a decreasing Reynolds number, the bubble accelerations show deviations from that of tracer particles; i.e., they deviate from the Heisenberg-Yaglom prediction and show a quicker decorrelation despite their small size and minute St. Using direct numerical simulations, we show that these effects arise due the drift of these particles through the turbulent flow. We theoretically predict this gravity-driven effect for developed isotropic turbulence, with the ratio of Stokes to Froude number or equivalently the particle drift velocity governing the enhancement of acceleration variance and the reductions in correlation time and intermittency. Our predictions are in good agreement with experimental and numerical results. The present findings are relevant to a range of scenarios encompassing tiny bubbles and droplets that drift through the turbulent oceans and the atmosphere. They also question the common usage of microbubbles and microdroplets as tracers in turbulence research.}, } @article {pmid27436965, year = {2016}, author = {Muralidhar, SD and Pier, B and Scott, JF and Govindarajan, R}, title = {Flow around a rotating, semi-infinite cylinder in an axial stream.}, journal = {Proceedings. Mathematical, physical, and engineering sciences}, volume = {472}, number = {2190}, pages = {20150850}, pmid = {27436965}, issn = {1364-5021}, abstract = {This paper concerns steady, high-Reynolds-number flow around a semi-infinite, rotating cylinder placed in an axial stream and uses boundary-layer type of equations which apply even when the boundary-layer thickness is comparable to the cylinder radius, as indeed it is at large enough downstream distances. At large rotation rates, it is found that a wall jet appears over a certain range of downstream locations. This jet strengthens with increasing rotation, but first strengthens then weakens as downstream distance increases, eventually disappearing, so the flow recovers a profile qualitatively similar to a classical boundary layer. The asymptotic solution at large streamwise distances is obtained as an expansion in inverse powers of the logarithm of the distance. It is found that the asymptotic radial and axial velocity components are the same as for a non-rotating cylinder, to all orders in this expansion.}, } @article {pmid27427674, year = {2016}, author = {Kristiawan, B and Kamal, S and Yanuar, }, title = {Thermo-Hydraulic Characteristics of Anatase Titania Nanofluids Flowing Through a Circular Conduit.}, journal = {Journal of nanoscience and nanotechnology}, volume = {16}, number = {6}, pages = {6078-6085}, doi = {10.1166/jnn.2016.10902}, pmid = {27427674}, issn = {1533-4880}, mesh = {*Hydrodynamics ; *Nanotechnology ; *Rheology ; *Temperature ; Titanium/*chemistry ; }, abstract = {The thermo-hydraulic characteristics of anatase titanium dioxide dispersed into distilled water with particle concentration of 0.1, 0.3, and 0.5 vol.% were investigated experimentally in this work. The influence of rheological behavior on hydrodynamic and convective heat transfer characteristics was evaluated under both laminar and turbulent flow conditions in a plain conduit and with twisted tape insert for twist ratio of 7. The nanofluids exhibited a strong shear-thinning behavior at low shear rate particularly higher particle concentration. The non-Newtonian titania nanofluids have also demonstrated a drag reduction phenomena in turbulent flow. At equal Reynolds number, the values of performance evaluation criterion in a conduit inserted a twisted tape were lower than those of in a plain conduit. It implies the unfavourable energy budget for twisted tape insert. The convective heat transfer coefficient does not gradually enhance with an increase of particle concentration. The flow features due mainly to the rheology of colloidal dispersions might be a reason for this phenomenon.}, } @article {pmid27415315, year = {2016}, author = {Apaza, L and Sandoval, M}, title = {Ballistic behavior and trapping of self-driven particles in a Poiseuille flow.}, journal = {Physical review. E}, volume = {93}, number = {6}, pages = {062602}, doi = {10.1103/PhysRevE.93.062602}, pmid = {27415315}, issn = {2470-0053}, abstract = {We study the two- and three-dimensional dynamics of a Brownian self-driven particle at low Reynolds number in a Poiseuille flow. A deterministic analysis is also performed and we find that under certain conditions the swimmer becomes trapped, thus performing closed orbits as observed in related experiments. Further analysis enables us to provide an analytic expression to achieve this trapping phenomenon. We then turn to Brownian dynamics simulations, where we show the effect of a Poiseuille flow, self-propulsion, and confinement on the diffusion of the swimmer in both two and three dimensions. It is found that for long times the mean-square displacement (MSD) along the flow direction is always quadratic in time, whereas for shorter times (before the particle reaches the walls) its MSD has also a quartic time behavior. It is also found that self-propelled particles will spread less in a Poiseuille flow than passive ones under the same circumstances.}, } @article {pmid27404898, year = {2016}, author = {Cole, BC and Marcus, GG and Parsa, S and Kramel, S and Ni, R and Voth, GA}, title = {Methods for Measuring the Orientation and Rotation Rate of 3D-printed Particles in Turbulence.}, journal = {Journal of visualized experiments : JoVE}, volume = {}, number = {112}, pages = {}, pmid = {27404898}, issn = {1940-087X}, mesh = {Anisotropy ; *Printing, Three-Dimensional ; }, abstract = {Experimental methods are presented for measuring the rotational and translational motion of anisotropic particles in turbulent fluid flows. 3D printing technology is used to fabricate particles with slender arms connected at a common center. Shapes explored are crosses (two perpendicular rods), jacks (three perpendicular rods), triads (three rods in triangular planar symmetry), and tetrads (four arms in tetrahedral symmetry). Methods for producing on the order of 10,000 fluorescently dyed particles are described. Time-resolved measurements of their orientation and solid-body rotation rate are obtained from four synchronized videos of their motion in a turbulent flow between oscillating grids with Rλ = 91. In this relatively low-Reynolds number flow, the advected particles are small enough that they approximate ellipsoidal tracer particles. We present results of time-resolved 3D trajectories of position and orientation of the particles as well as measurements of their rotation rates.}, } @article {pmid27390636, year = {2016}, author = {Wang, B and Li, H}, title = {POD analysis of flow over a backward-facing step forced by right-angle-shaped plasma actuator.}, journal = {SpringerPlus}, volume = {5}, number = {1}, pages = {795}, pmid = {27390636}, issn = {2193-1801}, abstract = {PURPOSE: This study aims to present flow control over the backward-facing step with specially designed right-angle-shaped plasma actuator and analyzed the influence of various scales of flow structures on the Reynolds stress through snapshot proper orthogonal decomposition (POD).

METHODS: 2D particle image velocimetry measurements were conducted on region (x/h = 0-2.25) and reattachment zone in the x-y plane over the backward-facing step at a Reynolds number of Re h  = 27,766 (based on step height [Formula: see text] and free stream velocity [Formula: see text]. The separated shear layer was excited by specially designed right-angle-shaped plasma actuator under the normalized excitation frequency St h  ≈ 0.345 along the 45° direction. The spatial distribution of each Reynolds stress component was reconstructed using an increasing number of POD modes.

RESULTS: The POD analysis indicated that the flow dynamic downstream of the step was dominated by large-scale flow structures, which contributed to streamwise Reynolds stress and Reynolds shear stress. The intense Reynolds stress localized to a narrow strip within the shear layer was mainly affected by small-scale flow structures, which were responsible for the recovery of the Reynolds stress peak. With plasma excitation, a significant increase was obtained in the vertical Reynolds stress peak.

CONCLUSIONS: Under the dimensionless frequencies St h  ≈ 0.345 and [Formula: see text] which are based on the step height and momentum thickness, the effectiveness of the flow control forced by the plasma actuator along the 45° direction was ordinary. Only the vertical Reynolds stress was significantly affected.}, } @article {pmid27390635, year = {2016}, author = {Hossain, S and Kim, KY}, title = {Parametric investigation on mixing in a micromixer with two-layer crossing channels.}, journal = {SpringerPlus}, volume = {5}, number = {1}, pages = {794}, pmid = {27390635}, issn = {2193-1801}, abstract = {This work presents a parametric investigation on flow and mixing in a chaotic micromixer consisting of two-layer crossing channels proposed by Xia et al. (Lab Chip 5: 748-755, 2005). The flow and mixing performance were numerically analyzed using commercially available software ANSYS CFX-15.0, which solves the Navier-Stokes and mass conservation equations with a diffusion-convection model in a Reynolds number range from 0.2 to 40. A mixing index based on the variance of the mass fraction of the mixture was employed to evaluate the mixing performance of the micromixer. The flow structure in the channel was also investigated to identify the relationship with mixing performance. The mixing performance and pressure-drop were evaluated with two dimensionless geometric parameters, i.e., ratios of the sub-channel width to the main channel width and the channels depth to the main channel width. The results revealed that the mixing index at the exit of the micromixer increases with increase in the channel depth-to-width ratio, but decreases with increase in the sub-channel width to main channel width ratio. And, it was found that the mixing index could be increased up to 0.90 with variations of the geometric parameters at Re = 0.2, and the pressure drop was very sensitive to the geometric parameters.}, } @article {pmid27378067, year = {2016}, author = {Manica, R and Klaseboer, E and Chan, DYC}, title = {The hydrodynamics of bubble rise and impact with solid surfaces.}, journal = {Advances in colloid and interface science}, volume = {235}, number = {}, pages = {214-232}, doi = {10.1016/j.cis.2016.06.010}, pmid = {27378067}, issn = {1873-3727}, abstract = {A bubble smaller than 1mm in radius rises along a straight path in water and attains a constant speed due to the balance between buoyancy and drag force. Depending on the purity of the system, within the two extreme limits of tangentially immobile or mobile boundary conditions at the air-water interface considerably different terminal speeds are possible. When such a bubble impacts on a horizontal solid surface and bounces, interesting physics can be observed. We study this physical phenomenon in terms of forces, which can be of colloidal, inertial, elastic, surface tension and viscous origins. Recent advances in high-speed photography allow for the observation of phenomena on the millisecond scale. Simultaneous use of such cameras to visualize both rise/deformation and the dynamics of the thin film drainage through interferometry are now possible. These experiments confirm that the drainage process obeys lubrication theory for the spectrum of micrometre to millimetre-sized bubbles that are covered in this review. We aim to bridge the colloidal perspective at low Reynolds numbers where surface forces are important to high Reynolds number fluid dynamics where the effect of the surrounding flow becomes important. A model that combines a force balance with lubrication theory allows for the quantitative comparison with experimental data under different conditions without any fitting parameter.}, } @article {pmid27377152, year = {2016}, author = {Dogra, N and Izadi, H and Vanderlick, TK}, title = {Micro-motors: A motile bacteria based system for liposome cargo transport.}, journal = {Scientific reports}, volume = {6}, number = {}, pages = {29369}, pmid = {27377152}, issn = {2045-2322}, mesh = {Bacteria/metabolism ; *Bacterial Physiological Phenomena ; Biological Transport ; Fluorescence Resonance Energy Transfer ; Lipid Bilayers/*metabolism ; Unilamellar Liposomes/*metabolism ; }, abstract = {Biological micro-motors (microorganisms) have potential applications in energy utilization and nanotechnology. However, harnessing the power generated by such motors to execute desired work is extremely difficult. Here, we employ the power of motile bacteria to transport small, large, and giant unilamellar vesicles (SUVs, LUVs, and GUVs). Furthermore, we demonstrate bacteria-bilayer interactions by probing glycolipids inside the model membrane scaffold. Fluorescence Resonance Energy Transfer (FRET) spectroscopic and microscopic methods were utilized for understanding these interactions. We found that motile bacteria could successfully propel SUVs and LUVs with a velocity of 28 μm s(-1) and 13 μm s(-1), respectively. GUVs, however, displayed Brownian motion and could not be propelled by attached bacteria. Bacterial velocity decreased with the larger loaded cargo, which agrees with our calculations of loaded bacteria swimming at low Reynolds number.}, } @article {pmid27370893, year = {2016}, author = {Takasugi, Y and Futagawa, K and Kazuhara, K and Morishita, S and Okuda, T}, title = {Roles of endotracheal tubes and slip joints in respiratory pressure loss: a laboratory study.}, journal = {Journal of anesthesia}, volume = {30}, number = {5}, pages = {789-795}, pmid = {27370893}, issn = {1438-8359}, mesh = {*Airway Resistance ; Humans ; Intubation, Intratracheal/*instrumentation ; Pressure ; }, abstract = {PURPOSE: The endotracheal tube (ETT) constitutes a significant component of total airway resistance. However, a discrepancy between measured and theoretical values has been reported in airway resistance through ETTs. The causes of the discrepancy were estimated by physical and rheological simulations.

METHODS: The pressure losses through total lengths of ETTs and slip joints under a volumetric flow rate of 30 L/min were measured, and the pressure losses through the tubular parts of ETTs with internal diameters (IDs) of 6.0-, 6.5-, 7.0-, 7.5-, and 8.0 mm were measured. The Reynolds number of each setting was calculated, and the pressure losses through the total length of the ETT, the tubular part, and the slip joint of each size of tube were estimated.

RESULTS: The Reynolds numbers were >5000 in all sizes of ETTs. Measured pressure losses were larger in small sized ETTs than in large sized ETTs-520.9 Pascals (Pa) in 6.0-mm ID and 136.4 Pa in 8.0-mm ID tubes. The measured pressure losses through the tubular part were comparable to the predicted values. The measured pressure losses through the slip joints were larger than the predicted values, and they accounted for approximately 25-40% of total pressure losses of the ETTs.

CONCLUSION: Especially in small sized tubes, the pressure loss through the slip joint accounts for a large percentage of the total pressure loss through the ETT. The pressure loss through the slip joint may play a role in the discrepancy between measured and theoretical pressure losses through ETTs.}, } @article {pmid27344122, year = {2016}, author = {Yang, T and Wang, Q and Wu, L and Zhang, P and Zhao, G and Liu, Y}, title = {A mathematical model for the transfer of soil solutes to runoff under water scouring.}, journal = {The Science of the total environment}, volume = {569-570}, number = {}, pages = {332-341}, doi = {10.1016/j.scitotenv.2016.06.094}, pmid = {27344122}, issn = {1879-1026}, abstract = {The transfer of nutrients from soil to runoff often causes unexpected pollution in water bodies. In this study, a mathematical model that relates to the detachment of soil particles by water flow and the degree of mixing between overland flow and soil nutrients was proposed. The model assumes that the mixing depth is an integral of average water flow depth, and it was evaluated by experiments with three water inflow rates to bare soil surfaces and to surfaces with eight treatments of different stone coverages. The model predicted outflow rates were compared with the experimentally observed data to test the accuracy of the infiltration parameters obtained by curve fitting the models to the data. Further analysis showed that the comprehensive mixing coefficient (ke) was linearly correlated with Reynolds' number Re (R(2)>0.9), and this relationship was verified by comparing the simulated potassium concentration and cumulative mass with observed data, respectively. The best performance with the bias error analysis (Nash Sutcliffe coefficient of efficiency (NS), relative error (RE) and the coefficient of determination (R(2))) showed that the predicted data by the proposed model was in good agreement with the measured data. Thus the model can be used to guide soil-water and fertilization management to minimize nutrient runoff from cropland.}, } @article {pmid27319152, year = {2016}, author = {Hahn, T and Klemm, A and Ziesse, P and Harms, K and Wach, W and Rupp, S and Hirth, T and Zibek, S}, title = {Optimization and Scale-up of Inulin Extraction from Taraxacum kok-saghyz roots.}, journal = {Natural product communications}, volume = {11}, number = {5}, pages = {689-692}, pmid = {27319152}, issn = {1934-578X}, mesh = {Chemical Fractionation/*methods ; Inulin/*isolation & purification ; Plant Roots/chemistry ; Taraxacum/*chemistry ; }, abstract = {The optimization and scale-up of inulin extraction from Taraxacum kok-saghyz Rodin was successfully performed. Evaluating solubility investigations, the extraction temperature was fixed at 85 degrees C. The inulin stability regarding degradation or hydrolysis could be confirmed by extraction in the presence of model inulin. Confirming stability at the given conditions the isolation procedure was transferred from a 1 L- to a 1 m3-reactor. The Reynolds number was selected as the relevant dimensionless number that has to remain constant in both scales. The stirrer speed in the large scale was adjusted to 3.25 rpm regarding a 300 rpm stirrer speed in the 1 L-scale and relevant physical and process engineering parameters. Assumptions were confirmed by approximately homologous extraction kinetics in both scales. Since T. kok-saghyz is in the focus of research due to its rubber content side-product isolation from residual biomass it is of great economic interest. Inulin is one of these additional side-products that can be isolated in high quantity (- 35% of dry mass) and with a high average degree of polymerization (15.5) in large scale with a purity of 77%.}, } @article {pmid27307513, year = {2016}, author = {Secchi, E and Rusconi, R and Buzzaccaro, S and Salek, MM and Smriga, S and Piazza, R and Stocker, R}, title = {Intermittent turbulence in flowing bacterial suspensions.}, journal = {Journal of the Royal Society, Interface}, volume = {13}, number = {119}, pages = {}, pmid = {27307513}, issn = {1742-5662}, mesh = {Bacillus subtilis/*physiology ; Gastrointestinal Microbiome/physiology ; Humans ; Locomotion/*physiology ; Suspensions ; }, abstract = {Dense suspensions of motile bacteria, possibly including the human gut microbiome, exhibit collective dynamics akin to those observed in classic, high Reynolds number turbulence with important implications for chemical and biological transport, yet this analogy has remained primarily qualitative. Here, we present experiments in which a dense suspension of Bacillus subtilis bacteria was flowed through microchannels and the velocity statistics of the flowing suspension were quantified using a recently developed velocimetry technique coupled with vortex identification methods. Observations revealed a robust intermittency phenomenon, whereby the average velocity profile of the suspension fluctuated between a plug-like flow and a parabolic flow profile. This intermittency is a hallmark of the onset of classic turbulence and Lagrangian tracking revealed that it here originates from the presence of transient vortices in the active, collective motion of the bacteria locally reinforcing the externally imposed flow. These results link together two entirely different manifestations of turbulence and show the potential of the microfluidic approach to mimic the environment characteristic of certain niches of the human microbiome.}, } @article {pmid27300988, year = {2016}, author = {Lagubeau, G and Grosjean, G and Darras, A and Lumay, G and Hubert, M and Vandewalle, N}, title = {Statics and dynamics of magnetocapillary bonds.}, journal = {Physical review. E}, volume = {93}, number = {5}, pages = {053117}, doi = {10.1103/PhysRevE.93.053117}, pmid = {27300988}, issn = {2470-0053}, abstract = {When ferromagnetic particles are suspended at an interface under magnetic fields, dipole-dipole interactions compete with capillary attraction. This combination of forces has recently given promising results towards controllable self-assemblies as well as low-Reynolds-number swimming systems. The elementary unit of these assemblies is a pair of particles. Although equilibrium properties of this interaction are well described, the dynamics remain unclear. In this paper, the properties of magnetocapillary bonds are determined by probing them with magnetic perturbations. Two deformation modes are evidenced and discussed. These modes exhibit resonances whose frequencies can be detuned to generate nonreciprocal motion. A model is proposed that can become the basis for elaborate collective behaviors.}, } @article {pmid27300987, year = {2016}, author = {Verjus, R and Angilella, JR}, title = {Critical Stokes number for the capture of inertial particles by recirculation cells in two-dimensional quasisteady flows.}, journal = {Physical review. E}, volume = {93}, number = {5}, pages = {053116}, doi = {10.1103/PhysRevE.93.053116}, pmid = {27300987}, issn = {2470-0053}, abstract = {Inertial particles are often observed to be trapped, temporarily or permanently, by recirculation cells which are ubiquitous in natural or industrial flows. In the limit of small particle inertia, determining the conditions of trapping is a challenging task, as it requires a large number of numerical simulations or experiments to test various particle sizes or densities. Here, we investigate this phenomenon analytically and numerically in the case of heavy particles (e.g., aerosols) at low Reynolds number, to derive a trapping criterion that can be used both in analytical and numerical velocity fields. The resulting criterion allows one to predict the characteristics of trapped particles as soon as single-phase simulations of the flow are performed. Our analysis is valid for two-dimensional particle-laden flows in the vertical plane, in the limit where the particle inertia, the free-fall terminal velocity, and the flow unsteadiness can be treated as perturbations. The weak unsteadiness of the flow generally induces a chaotic tangle near heteroclinic or homoclinic cycles if any, leading to the apparent diffusion of fluid elements through the boundary of the cell. The critical particle Stokes number St_{c} below which aerosols also enter and exit the cell in a complex manner has been derived analytically, in terms of the flow characteristics. It involves the nondimensional curvature-weighted integral of the squared velocity of the steady fluid flow along the dividing streamline of the recirculation cell. When the flow is unsteady and St>St_{c}, a regular motion takes place due to gravity and centrifugal effects, like in the steady case. Particles driven towards the interior of the cell are trapped permanently. In contrast, when the flow is unsteady and St
METHODS: In the present work, the onset of turbulent transition during pulsatile flow through coronary arteries for varying degree of stenosis (i.e., 0%, 30%, 50% and 70%) is quantitatively analyzed by calculating the turbulent parameters distal to the stenosis. Also, the effect of turbulence transition on hemodynamic parameters such as WSS and oscillatory shear index (OSI) for varying degree of stenosis is quantified. The validated transitional shear stress transport (SST) k-ω model used in the present investigation is the best suited Reynolds averaged Navier-Stokes turbulence model to capture the turbulent transition. The arterial wall is assumed to be rigid and the dynamic curvature effect due to myocardial contraction on the blood flow has been neglected.

RESULTS: Our observations shows that for stenosis 50% and above, the WSSavg, WSSmax and OSI calculated using turbulence model deviates from laminar by more than 10% and the flow disturbances seems to significantly increase only after 70% stenosis. Our model shows reliability and completely validated.

CONCLUSIONS: Blood flow through stenosed coronary arteries seems to be turbulent in nature for area stenosis above 70% and the transition to turbulent flow begins from 50% stenosis.}, } @article {pmid27190567, year = {2016}, author = {Zhou, R and Wang, C}, title = {Multiphase ferrofluid flows for micro-particle focusing and separation.}, journal = {Biomicrofluidics}, volume = {10}, number = {3}, pages = {034101}, pmid = {27190567}, issn = {1932-1058}, abstract = {Ferrofluids have demonstrated great potential for a variety of manipulations of diamagnetic (or non-magnetic) micro-particles/cells in microfluidics, including sorting, focusing, and enriching. By utilizing size dependent magnetophoresis velocity, most of the existing techniques employ single phase ferrofluids to push the particles towards the channel walls. In this work, we demonstrate a novel strategy for focusing and separating diamagnetic micro-particles by using the laminar fluid interface of two co-flowing fluids-a ferrofluid and a non-magnetic fluid. Next to the microfluidic channel, microscale magnets are fabricated to generate strong localized magnetic field gradients and forces. Due to the magnetic force, diamagnetic particles suspended in the ferrofluid phase migrate across the ferrofluid stream at the size-dependent velocities. Because of the low Reynolds number and high Péclet number associated with the flow, the fluid interface is sharp and stable. When the micro-particles migrate to the interface, they are accumulated near the interface, resulting in effective focusing and separation of particles. We investigated several factors that affect the focusing and separation efficiency, including susceptibility of the ferrofluid, distance between the microfluidic channel and microscale magnet, and width of the microfluidic channel. This concept can be extended to multiple fluid interfaces. For example, a complete separation of micro-particles was demonstrated by using a three-stream multiphase flow configuration.}, } @article {pmid27183101, year = {2016}, author = {Wada, Y and Koyama, D and Nakamura, K}, title = {Numerical simulation of compressible fluid flow in an ultrasonic suction pump.}, journal = {Ultrasonics}, volume = {70}, number = {}, pages = {191-198}, doi = {10.1016/j.ultras.2016.05.005}, pmid = {27183101}, issn = {1874-9968}, abstract = {Characteristics of an ultrasonic suction pump that uses a vibrating piston surface and a pipe are numerically simulated and compared with experimental results. Fluid analysis based on the finite-difference time-domain (FDTD) routine is performed, where the nonlinear term and the moving fluid-surface boundary condition are considered. As a result, the suction mechanism of the pump is found to be similar to that of a check valve, where the gap is open during the inflow phase, and it is nearly closed during the outflow phase. The effects of Reynolds number, vibration amplitude and gap thickness on the pump performance are analyzed. The calculated result is in good agreement with the previously measured results.}, } @article {pmid27176524, year = {2016}, author = {Maiden, MD and Lowman, NK and Anderson, DV and Schubert, ME and Hoefer, MA}, title = {Observation of Dispersive Shock Waves, Solitons, and Their Interactions in Viscous Fluid Conduits.}, journal = {Physical review letters}, volume = {116}, number = {17}, pages = {174501}, doi = {10.1103/PhysRevLett.116.174501}, pmid = {27176524}, issn = {1079-7114}, abstract = {Dispersive shock waves and solitons are fundamental nonlinear excitations in dispersive media, but dispersive shock wave studies to date have been severely constrained. Here, we report on a novel dispersive hydrodynamic test bed: the effectively frictionless dynamics of interfacial waves between two high viscosity contrast, miscible, low Reynolds number Stokes fluids. This scenario is realized by injecting from below a lighter, viscous fluid into a column filled with high viscosity fluid. The injected fluid forms a deformable pipe whose diameter is proportional to the injection rate, enabling precise control over the generation of symmetric interfacial waves. Buoyancy drives nonlinear interfacial self-steepening, while normal stresses give rise to the dispersion of interfacial waves. Extremely slow mass diffusion and mass conservation imply that the interfacial waves are effectively dissipationless. This enables high fidelity observations of large amplitude dispersive shock waves in this spatially extended system, found to agree quantitatively with a nonlinear wave averaging theory. Furthermore, several highly coherent phenomena are investigated including dispersive shock wave backflow, the refraction or absorption of solitons by dispersive shock waves, and the multiphase merging of two dispersive shock waves. The complex, coherent, nonlinear mixing of dispersive shock waves and solitons observed here are universal features of dissipationless, dispersive hydrodynamic flows.}, } @article {pmid27176410, year = {2016}, author = {Mandal, S and Bandopadhyay, A and Chakraborty, S}, title = {Effect of surface charge convection and shape deformation on the dielectrophoretic motion of a liquid drop.}, journal = {Physical review. E}, volume = {93}, number = {}, pages = {043127}, doi = {10.1103/PhysRevE.93.043127}, pmid = {27176410}, issn = {2470-0053}, abstract = {The dielectrophoretic motion and shape deformation of a Newtonian liquid drop in an otherwise quiescent Newtonian liquid medium in the presence of an axisymmetric nonuniform dc electric field consisting of uniform and quadrupole components is investigated. The theory put forward by Feng [J. Q. Feng, Phys. Rev. E 54, 4438 (1996)10.1103/PhysRevE.54.4438] is generalized by incorporating the following two nonlinear effects-surface charge convection and shape deformation-towards determining the drop velocity. This two-way coupled moving boundary problem is solved analytically by considering small values of electric Reynolds number (ratio of charge relaxation time scale to the convection time scale) and electric capillary number (ratio of electrical stress to the surface tension) under the framework of the leaky dielectric model. We focus on investigating the effects of charge convection and shape deformation for different drop-medium combinations. A perfectly conducting drop suspended in a leaky (or perfectly) dielectric medium always deforms to a prolate shape and this kind of shape deformation always augments the dielectrophoretic drop velocity. For a perfectly dielectric drop suspended in a perfectly dielectric medium, the shape deformation leads to either increase (for prolate shape) or decrease (for oblate shape) in the dielectrophoretic drop velocity. Both surface charge convection and shape deformation affect the drop motion for leaky dielectric drops. The combined effect of these can significantly increase or decrease the dielectrophoretic drop velocity depending on the electrohydrodynamic properties of both the liquids and the relative strength of the electric Reynolds number and electric capillary number. Finally, comparison with the existing experiments reveals better agreement with the present theory.}, } @article {pmid27176408, year = {2016}, author = {Koens, L and Lauga, E}, title = {Rotation of slender swimmers in isotropic-drag media.}, journal = {Physical review. E}, volume = {93}, number = {}, pages = {043125}, doi = {10.1103/PhysRevE.93.043125}, pmid = {27176408}, issn = {2470-0053}, abstract = {The drag anisotropy of slender filaments is a critical physical property allowing swimming in low-Reynolds number flows, and without it linear translation is impossible. Here we show that, in contrast, net rotation can occur under isotropic drag. We first demonstrate this result formally by considering the consequences of the force- and torque-free conditions on swimming bodies and we then illustrate it with two examples (a simple swimmers made of three rods and a model bacterium with two helical flagellar filaments). Our results highlight the different role of hydrodynamic forces in generating translational versus rotational propulsion.}, } @article {pmid27176402, year = {2016}, author = {Hawkins, C and Angheluta, L and Krotkiewski, M and Jamtveit, B}, title = {Reynolds-number dependence of the longitudinal dispersion in turbulent pipe flow.}, journal = {Physical review. E}, volume = {93}, number = {}, pages = {043119}, doi = {10.1103/PhysRevE.93.043119}, pmid = {27176402}, issn = {2470-0053}, abstract = {In Taylor's theory, the longitudinal dispersion in turbulent pipe flows approaches, on long time scales, a diffusive behavior with a constant diffusivity K_{L}, which depends empirically on the Reynolds number Re. We show that the dependence on Re can be determined from the turbulent energy spectrum. By using the intimate connection between the friction factor and the longitudinal dispersion in wall-bounded turbulence, we predict different asymptotic scaling laws of K_{L} (Re) depending on the different turbulent cascades in two-dimensional turbulence. We also explore numerically the K_{L} (Re) dependence in turbulent channel flows with smooth and rough walls using a lattice Boltzmann method.}, } @article {pmid27176396, year = {2016}, author = {Cappanera, L and Guermond, JL and Léorat, J and Nore, C}, title = {Two spinning ways for precession dynamo.}, journal = {Physical review. E}, volume = {93}, number = {}, pages = {043113}, doi = {10.1103/PhysRevE.93.043113}, pmid = {27176396}, issn = {2470-0053}, abstract = {It is numerically demonstrated by means of a magnetohydrodynamic code that precession can trigger dynamo action in a cylindrical container. Fixing the angle between the spin and the precession axis to be 1/2π, two limit configurations of the spinning axis are explored: either the symmetry axis of the cylinder is parallel to the spin axis (this configuration is henceforth referred to as the axial spin case), or it is perpendicular to the spin axis (this configuration is referred to as the equatorial spin case). In both cases, the centro-symmetry of the flow breaks when the kinetic Reynolds number increases. Equatorial spinning is found to be more efficient in breaking the centro-symmetry of the flow. In both cases, the average flow in the reference frame of the mantle converges to a counter-rotation with respect to the spin axis as the Reynolds number grows. We find a scaling law for the average kinetic energy in term of the Reynolds number in the axial spin case. In the equatorial spin case, the unsteady asymmetric flow is shown to be capable of sustaining dynamo action in the linear and nonlinear regimes. The magnetic field is mainly dipolar in the equatorial spin case, while it is is mainly quadrupolar in the axial spin case.}, } @article {pmid27176354, year = {2016}, author = {Goldfriend, T and Diamant, H and Witten, TA}, title = {Hydrodynamic interactions between two forced objects of arbitrary shape. II. Relative translation.}, journal = {Physical review. E}, volume = {93}, number = {}, pages = {042609}, doi = {10.1103/PhysRevE.93.042609}, pmid = {27176354}, issn = {2470-0053}, abstract = {We study the relative translation of two arbitrarily shaped objects, caused by their hydrodynamic interaction as they are forced through a viscous fluid in the limit of zero Reynolds number. It is well known that in the case of two rigid spheres in an unbounded fluid, the hydrodynamic interaction does not produce relative translation. More generally, such an effective pair-interaction vanishes in configurations with spatial inversion symmetry; for example, an enantiomorphic pair in mirror image positions has no relative translation. We show that the breaking of inversion symmetry by boundaries of the system accounts for the interactions between two spheres in confined geometries, as observed in experiments. The same general principle also provides new predictions for interactions in other object configurations near obstacles. We examine the time-dependent relative translation of two self-aligning objects, extending the numerical analysis of our preceding publication [Goldfriend, Diamant, and Witten, Phys. Fluids 27, 123303 (2015)]PHFLE61070-663110.1063/1.4936894. The interplay between the orientational interaction and the translational one, in most cases, leads over time to repulsion between the two objects. The repulsion is qualitatively different for self-aligning objects compared to the more symmetric case of uniform prolate spheroids. The separation between the two objects increases with time t as t^{1/3} in the former case, and more strongly, as t, in the latter.}, } @article {pmid27168523, year = {2016}, author = {Cheng, X and Sun, M}, title = {Wing-kinematics measurement and aerodynamics in a small insect in hovering flight.}, journal = {Scientific reports}, volume = {6}, number = {}, pages = {25706}, pmid = {27168523}, issn = {2045-2322}, mesh = {Animals ; Biomechanical Phenomena ; Diptera/*physiology ; Flight, Animal/*physiology ; Time Factors ; Wings, Animal/anatomy & histology/*physiology ; }, abstract = {Wing-motion of hovering small fly Liriomyza sativae was measured using high-speed video and flows of the wings calculated numerically. The fly used high wingbeat frequency (≈265 Hz) and large stroke amplitude (≈182°); therefore, even if its wing-length (R) was small (R ≈ 1.4 mm), the mean velocity of wing reached ≈1.5 m/s, the same as that of an average-size insect (R ≈ 3 mm). But the Reynolds number (Re) of wing was still low (≈40), owing to the small wing-size. In increasing the stroke amplitude, the outer parts of the wings had a "clap and fling" motion. The mean-lift coefficient was high, ≈1.85, several times larger than that of a cruising airplane. The partial "clap and fling" motion increased the lift by ≈7%, compared with the case of no aerodynamic interaction between the wings. The fly mainly used the delayed stall mechanism to generate the high-lift. The lift-to-drag ratio is only 0.7 (for larger insects, Re being about 100 or higher, the ratio is 1-1.2); that is, although the small fly can produce enough lift to support its weight, it needs to overcome a larger drag to do so.}, } @article {pmid27166813, year = {2016}, author = {Monteith, CE and Brunner, ME and Djagaeva, I and Bielecki, AM and Deutsch, JM and Saxton, WM}, title = {A Mechanism for Cytoplasmic Streaming: Kinesin-Driven Alignment of Microtubules and Fast Fluid Flows.}, journal = {Biophysical journal}, volume = {110}, number = {9}, pages = {2053-2065}, pmid = {27166813}, issn = {1542-0086}, support = {R01 GM046295/GM/NIGMS NIH HHS/United States ; }, mesh = {Biomechanical Phenomena ; *Cytoplasmic Streaming ; *Hydrodynamics ; Kinesins/*metabolism ; *Mechanical Phenomena ; Microtubules/*metabolism ; *Models, Biological ; Movement ; Oocytes/cytology ; }, abstract = {The transport of cytoplasmic components can be profoundly affected by hydrodynamics. Cytoplasmic streaming in Drosophila oocytes offers a striking example. Forces on fluid from kinesin-1 are initially directed by a disordered meshwork of microtubules, generating minor slow cytoplasmic flows. Subsequently, to mix incoming nurse cell cytoplasm with ooplasm, a subcortical layer of microtubules forms parallel arrays that support long-range, fast flows. To analyze the streaming mechanism, we combined observations of microtubule and organelle motions with detailed mathematical modeling. In the fast state, microtubules tethered to the cortex form a thin subcortical layer and undergo correlated sinusoidal bending. Organelles moving in flows along the arrays show velocities that are slow near the cortex and fast on the inward side of the subcortical microtubule layer. Starting with fundamental physical principles suggested by qualitative hypotheses, and with published values for microtubule stiffness, kinesin velocity, and cytoplasmic viscosity, we developed a quantitative coupled hydrodynamic model for streaming. The fully detailed mathematical model and its simulations identify key variables that can shift the system between disordered (slow) and ordered (fast) states. Measurements of array curvature, wave period, and the effects of diminished kinesin velocity on flow rates, as well as prior observations on f-actin perturbation, support the model. This establishes a concrete mechanistic framework for the ooplasmic streaming process. The self-organizing fast phase is a result of viscous drag on kinesin-driven cargoes that mediates equal and opposite forces on cytoplasmic fluid and on microtubules whose minus ends are tethered to the cortex. Fluid moves toward plus ends and microtubules are forced backward toward their minus ends, resulting in buckling. Under certain conditions, the buckling microtubules self-organize into parallel bending arrays, guiding varying directions for fast plus-end directed fluid flows that facilitate mixing in a low Reynolds number regime.}, } @article {pmid27145450, year = {2016}, author = {Xi, J and Si, XA and Kim, J and Zhang, Y and Jacob, RE and Kabilan, S and Corley, RA}, title = {Anatomical Details of the Rabbit Nasal Passages and Their Implications in Breathing, Air Conditioning, and Olfaction.}, journal = {Anatomical record (Hoboken, N.J. : 2007)}, volume = {299}, number = {7}, pages = {853-868}, pmid = {27145450}, issn = {1932-8494}, support = {R01 HL073598/HL/NHLBI NIH HHS/United States ; }, mesh = {*Air Conditioning ; Animals ; Computer Simulation ; Female ; Magnetic Resonance Imaging ; Nasal Cavity/*anatomy & histology/*physiology ; Pulmonary Ventilation ; Rabbits ; *Respiration ; Smell/*physiology ; }, abstract = {The rabbit is commonly used as a laboratory animal for inhalation toxicology tests and detail knowledge of the rabbit airway morphometry is needed for outcome analysis or theoretical modeling. The objective of this study is to quantify the morphometric dimension of the nasal airway of a New Zealand white rabbit and to relate the morphology and functions through analytical and computational methods. Images of high-resolution MRI scans of the rabbit were processed to measure the axial distribution of the cross-sectional areas, perimeter, and complexity level. The lateral recess, which has functions other than respiration or olfaction, was isolated from the nasal airway and its dimension was quantified separately. A low Reynolds number turbulence model was implemented to simulate the airflow, heat transfer, vapor transport, and wall shear stress. Results of this study provide detailed morphological information of the rabbit that can be used in the studies of olfaction, inhalation toxicology, drug delivery, and physiology-based pharmacokinetics modeling. For the first time, we reported a spiral nasal vestibule that splits into three paths leading to the dorsal meatus, maxilloturbinate, and ventral meatus, respectively. Both non-dimensional functional analysis and CFD simulations suggested that the airflow in the rabbit nose is laminar and the unsteady effect is only significantly during sniffing. Due to the large surface-to-volume ratio, the maxilloturbinate is highly effective in warming and moistening the inhaled air to body conditions. The unique anatomical structure and respiratory airflow pattern may have important implications for designing new odorant detectors or electronic noses. Anat Rec, 299:853-868, 2016. © 2016 Wiley Periodicals, Inc.}, } @article {pmid27136099, year = {2016}, author = {Li, S and Huai, W}, title = {United Formula for the Friction Factor in the Turbulent Region of Pipe Flow.}, journal = {PloS one}, volume = {11}, number = {5}, pages = {e0154408}, pmid = {27136099}, issn = {1932-6203}, mesh = {*Friction ; *Models, Theoretical ; }, abstract = {Friction factor is an important element in both flow simulations and river engineering. In hydraulics, studies on the friction factor in turbulent regions have been based on the concept of three flow regimes, namely, the fully smooth regime, the fully rough regime, and the transitional regime, since the establishment of the Nikuradze's chart. However, this study further demonstrates that combining the friction factor with Reynolds number yields a united formula that can scale the entire turbulent region. This formula is derived by investigating the correlation between friction in turbulent pipe flow and its influencing factors, i.e., Reynolds number and relative roughness. In the present study, the formulae of Blasius and Stricklerare modified to rearrange the implicit model of Tao. In addition, we derive a united explicit formula that can compute the friction factor in the entire turbulent regimes based on the asymptotic behavior of the improved Tao's model. Compared with the reported formulae of Nikuradze, the present formula exhibits higher computational accuracy for the original pipe experiment data of Nikuradze.}, } @article {pmid27131850, year = {2016}, author = {Bocanegra Evans, H and Castillo, L}, title = {Index-matched measurements of the effect of cartilaginous rings on tracheobronchial flow.}, journal = {Journal of biomechanics}, volume = {49}, number = {9}, pages = {1601-1606}, doi = {10.1016/j.jbiomech.2016.03.043}, pmid = {27131850}, issn = {1873-2380}, mesh = {Bronchi/*physiology ; Cartilage/*anatomy & histology ; Humans ; Hydrodynamics ; Rheology ; Trachea/*physiology ; }, abstract = {We present a comparison of the flow characteristics in an idealized smooth trachea model and a second model which has a roughness simulating cartilaginous rings. We use refractive index-matched particle image velocimetry (PIV) to measure the velocity field in a two-generation model of the trachea and main bronchi. The flow rate has a trachea-based Reynolds number Re=2800, which is comparable to a resting state. Our results show considerable differences between both cases, the most important of which is the size and magnitude of recirculation zones at the inlet of both bronchi. The smooth case shows a larger separation bubble at the bronchi entrance, which may retain aerosols and have different effects on particles of different sizes. Furthermore, the smooth case displays a higher vorticity along the bottom walls of the bronchi, while a higher vorticity is seen along the trachea walls in the ׳ringed׳ model. These findings suggest that modeling the trachea and main bronchi as smooth tubes may not be justified, since the flow conditions in lower generations will be affected by these differences.}, } @article {pmid27127498, year = {2016}, author = {Brkić, D and Ćojbašić, Ž}, title = {Intelligent Flow Friction Estimation.}, journal = {Computational intelligence and neuroscience}, volume = {2016}, number = {}, pages = {5242596}, pmid = {27127498}, issn = {1687-5273}, mesh = {*Friction ; *Hydrodynamics ; *Neural Networks, Computer ; }, abstract = {Nowadays, the Colebrook equation is used as a mostly accepted relation for the calculation of fluid flow friction factor. However, the Colebrook equation is implicit with respect to the friction factor (λ). In the present study, a noniterative approach using Artificial Neural Network (ANN) was developed to calculate the friction factor. To configure the ANN model, the input parameters of the Reynolds Number (Re) and the relative roughness of pipe (ε/D) were transformed to logarithmic scales. The 90,000 sets of data were fed to the ANN model involving three layers: input, hidden, and output layers with, 2, 50, and 1 neurons, respectively. This configuration was capable of predicting the values of friction factor in the Colebrook equation for any given values of the Reynolds number (Re) and the relative roughness (ε/D) ranging between 5000 and 10(8) and between 10(-7) and 0.1, respectively. The proposed ANN demonstrates the relative error up to 0.07% which had the high accuracy compared with the vast majority of the precise explicit approximations of the Colebrook equation.}, } @article {pmid27121547, year = {2016}, author = {Lee, YJ and Lua, KB and Lim, TT and Yeo, KS}, title = {A quasi-steady aerodynamic model for flapping flight with improved adaptability.}, journal = {Bioinspiration & biomimetics}, volume = {11}, number = {3}, pages = {036005}, doi = {10.1088/1748-3190/11/3/036005}, pmid = {27121547}, issn = {1748-3190}, mesh = {Air ; Aircraft/*instrumentation ; Animals ; Biomimetics/*instrumentation/methods ; Computer Simulation ; *Computer-Aided Design ; Equipment Design ; Equipment Failure Analysis ; Friction ; Miniaturization ; *Models, Theoretical ; Oscillometry/*instrumentation/methods ; Rheology/*instrumentation/methods ; Shear Strength ; Stress, Mechanical ; }, abstract = {An improved quasi-steady aerodynamic model for flapping wings in hover has been developed. The purpose of this model is to yield rapid predictions of lift generation and efficiency during the design phase of flapping wing micro air vehicles. While most existing models are tailored for a specific flow condition, the present model is applicable over a wider range of Reynolds number and Rossby number. The effects of wing aspect ratio and taper ratio are also considered. The model was validated by comparing against numerical simulations and experimental measurements. Wings with different geometries undergoing distinct kinematics at varying flow conditions were tested during validation. Generally, model predictions of mean force coefficients were within 10% of numerical simulation results, while the deviations in power coefficients could be up to 15%. The deviation is partly due to the model not taking into consideration the initial shedding of the leading-edge vortex and wing-wake interaction which are difficult to account under quasi-steady assumption. The accuracy of this model is comparable to other models in literature, which had to be specifically designed or tuned to a narrow range of operation. In contrast, the present model has the advantage of being applicable over a wider range of flow conditions without prior tuning or calibration, which makes it a useful tool for preliminary performance evaluations.}, } @article {pmid27118897, year = {2016}, author = {Shyy, W and Kang, CK and Chirarattananon, P and Ravi, S and Liu, H}, title = {Aerodynamics, sensing and control of insect-scale flapping-wing flight.}, journal = {Proceedings. Mathematical, physical, and engineering sciences}, volume = {472}, number = {2186}, pages = {20150712}, pmid = {27118897}, issn = {1364-5021}, abstract = {There are nearly a million known species of flying insects and 13 000 species of flying warm-blooded vertebrates, including mammals, birds and bats. While in flight, their wings not only move forward relative to the air, they also flap up and down, plunge and sweep, so that both lift and thrust can be generated and balanced, accommodate uncertain surrounding environment, with superior flight stability and dynamics with highly varied speeds and missions. As the size of a flyer is reduced, the wing-to-body mass ratio tends to decrease as well. Furthermore, these flyers use integrated system consisting of wings to generate aerodynamic forces, muscles to move the wings, and sensing and control systems to guide and manoeuvre. In this article, recent advances in insect-scale flapping-wing aerodynamics, flexible wing structures, unsteady flight environment, sensing, stability and control are reviewed with perspective offered. In particular, the special features of the low Reynolds number flyers associated with small sizes, thin and light structures, slow flight with comparable wind gust speeds, bioinspired fabrication of wing structures, neuron-based sensing and adaptive control are highlighted.}, } @article {pmid27108375, year = {2016}, author = {Sultan, T}, title = {Numerical study of the effects of lamp configuration and reactor wall roughness in an open channel water disinfection UV reactor.}, journal = {Chemosphere}, volume = {155}, number = {}, pages = {170-179}, doi = {10.1016/j.chemosphere.2016.04.050}, pmid = {27108375}, issn = {1879-1298}, mesh = {Disinfection/*methods ; *Ultraviolet Rays ; Water Microbiology ; Water Purification/*instrumentation/methods ; }, abstract = {This article describes the assessment of a numerical procedure used to determine the UV lamp configuration and surface roughness effects on an open channel water disinfection UV reactor. The performance of the open channel water disinfection UV reactor was numerically analyzed on the basis of the performance indictor reduction equivalent dose (RED). The RED values were calculated as a function of the Reynolds number to monitor the performance. The flow through the open channel UV reactor was modelled using a k-ε model with scalable wall function, a discrete ordinate (DO) model for fluence rate calculation, a volume of fluid (VOF) model to locate the unknown free surface, a discrete phase model (DPM) to track the pathogen transport, and a modified law of the wall to incorporate the reactor wall roughness effects. The performance analysis was carried out using commercial CFD software (ANSYS Fluent 15.0). Four case studies were analyzed based on open channel UV reactor type (horizontal and vertical) and lamp configuration (parallel and staggered). The results show that lamp configuration can play an important role in the performance of an open channel water disinfection UV reactor. The effects of the reactor wall roughness were Reynolds number dependent. The proposed methodology is useful for performance optimization of an open channel water disinfection UV reactor.}, } @article {pmid27104354, year = {2016}, author = {Aftab, SM and Mohd Rafie, AS and Razak, NA and Ahmad, KA}, title = {Turbulence Model Selection for Low Reynolds Number Flows.}, journal = {PloS one}, volume = {11}, number = {4}, pages = {e0153755}, pmid = {27104354}, issn = {1932-6203}, mesh = {*Models, Theoretical ; Viscosity ; }, abstract = {One of the major flow phenomena associated with low Reynolds number flow is the formation of separation bubbles on an airfoil's surface. NACA4415 airfoil is commonly used in wind turbines and UAV applications. The stall characteristics are gradual compared to thin airfoils. The primary criterion set for this work is the capture of laminar separation bubble. Flow is simulated for a Reynolds number of 120,000. The numerical analysis carried out shows the advantages and disadvantages of a few turbulence models. The turbulence models tested were: one equation Spallart Allmars (S-A), two equation SST K-ω, three equation Intermittency (γ) SST, k-kl-ω and finally, the four equation transition γ-Reθ SST. However, the variation in flow physics differs between these turbulence models. Procedure to establish the accuracy of the simulation, in accord with previous experimental results, has been discussed in detail.}, } @article {pmid27078458, year = {2016}, author = {Johnson, PL and Meneveau, C}, title = {Large-deviation statistics of vorticity stretching in isotropic turbulence.}, journal = {Physical review. E}, volume = {93}, number = {3}, pages = {033118}, doi = {10.1103/PhysRevE.93.033118}, pmid = {27078458}, issn = {2470-0053}, abstract = {A key feature of three-dimensional fluid turbulence is the stretching and realignment of vorticity by the action of the strain rate. It is shown in this paper, using the cumulant-generating function, that the cumulative vorticity stretching along a Lagrangian path in isotropic turbulence obeys a large deviation principle. As a result, the relevant statistics can be described by the vorticity stretching Cramér function. This function is computed from a direct numerical simulation data set at a Taylor-scale Reynolds number of Re(λ)=433 and compared to those of the finite-time Lyapunov exponents (FTLE) for material deformation. As expected, the mean cumulative vorticity stretching is slightly less than that of the most-stretched material line (largest FTLE), due to the vorticity's preferential alignment with the second-largest eigenvalue of strain rate and the material line's preferential alignment with the largest eigenvalue. However, the vorticity stretching tends to be significantly larger than the second-largest FTLE, and the Cramér functions reveal that the statistics of vorticity stretching fluctuations are more similar to those of the largest FTLE. In an attempt to relate the vorticity stretching statistics to the vorticity magnitude probability density function in statistically stationary conditions, a model Kramers-Moyal equation is constructed using the statistics encoded in the Cramér function. The model predicts a stretched-exponential tail for the vorticity magnitude probability density function, with good agreement for the exponent but significant difference (35%) in the prefactor.}, } @article {pmid27078456, year = {2016}, author = {De Santi, F and Fraternale, F and Tordella, D}, title = {Dispersive-to-nondispersive transition and phase-velocity transient for linear waves in plane wake and channel flows.}, journal = {Physical review. E}, volume = {93}, number = {3}, pages = {033116}, doi = {10.1103/PhysRevE.93.033116}, pmid = {27078456}, issn = {2470-0053}, abstract = {In this study we analyze the phase and group velocity of three-dimensional linear traveling waves in two sheared flows: the plane channel and the wake flows. This was carried out by varying the wave number over a large interval of values at a given Reynolds number inside the ranges 20-100, 1000-8000, for the wake and channel flow, respectively. Evidence is given about the possible presence of both dispersive and nondispersive effects which are associated with the long and short ranges of wavelength. We solved the Orr-Sommerfeld and Squire eigenvalue problem and observed the least stable mode. It is evident that, at low wave numbers, the least stable eigenmodes in the left branch of the spectrum behave in a dispersive manner. By contrast, if the wave number is above a specific threshold, a sharp dispersive-to-nondispersive transition can be observed. Beyond this transition, the dominant mode belongs to the right branch of the spectrum. The transient behavior of the phase velocity of small three-dimensional traveling waves was also considered. Having chosen the initial conditions, we then show that the shape of the transient highly depends on the transition wavelength threshold value. We show that the phase velocity can oscillate with a frequency which is equal to the frequency width of the eigenvalue spectrum. Furthermore, evidence of intermediate self-similarity is given for the perturbation field.}, } @article {pmid27078455, year = {2016}, author = {Nedić, J and Tavoularis, S}, title = {Energy dissipation scaling in uniformly sheared turbulence.}, journal = {Physical review. E}, volume = {93}, number = {3}, pages = {033115}, doi = {10.1103/PhysRevE.93.033115}, pmid = {27078455}, issn = {2470-0053}, abstract = {The rate of turbulent kinetic energy dissipation in spatially developing, uniformly sheared turbulence is examined experimentally. In the far-downstream fully developed region of the flow, we confirm that the dissipation parameter C(ɛ) is constant. More importantly, however, we find two upstream regions where this parameter could be scaled with the local turbulent Reynolds number as C(ɛ)=ARe(λ)(α); the exponents in these two regions are, respectively, α=-0.6 and 0.5. The observed changes in scaling laws are explained by consideration of structural changes in the turbulence.}, } @article {pmid27078453, year = {2016}, author = {Liang, H and Li, QX and Shi, BC and Chai, ZH}, title = {Lattice Boltzmann simulation of three-dimensional Rayleigh-Taylor instability.}, journal = {Physical review. E}, volume = {93}, number = {3}, pages = {033113}, doi = {10.1103/PhysRevE.93.033113}, pmid = {27078453}, issn = {2470-0053}, abstract = {In this paper, the three-dimensional (3D) Rayleigh-Taylor instability (RTI) with low Atwood number (A(t)=0.15) in a long square duct (12W × W × W) is studied by using a multiple-relaxation-time lattice Boltzmann (LB) multiphase model. The effect of the Reynolds number on the interfacial dynamics and bubble and spike amplitudes at late time is investigated in detail. The numerical results show that at sufficiently large Reynolds numbers, a sequence of stages in the 3D immiscible RTI can be observed, which includes the linear growth, terminal velocity growth, reacceleration, and chaotic development stages. At late stage, the RTI induces a very complicated topology structure of the interface, and an abundance of dissociative drops are also observed in the system. The bubble and spike velocities at late stage are unstable and their values have exceeded the predictions of the potential flow theory [V. N. Goncharov, Phys. Rev. Lett. 88, 134502 (2002)]. The acceleration of the bubble front is also measured and it is found that the normalized acceleration at late time fluctuates around a constant value of 0.16. When the Reynolds number is reduced to small values, some later stages cannot be reached sequentially. The interface becomes relatively smoothed and the bubble velocity at late time is approximate to a constant value, which coincides with the results of the extended Layzer model [S.-I. Sohn, Phys. Rev. E 80, 055302(R) (2009)] and the modified potential theory [R. Banerjee, L. Mandal, S. Roy, M. Khan, and M. R. Guptae, Phys. Plasmas 18, 022109 (2011)]. In our simulations, the Graphics Processing Unit (GPU) parallel computing is also used to relieve the massive computational cost.}, } @article {pmid27078416, year = {2016}, author = {Jaju, SJ and Kumaran, V}, title = {Structure-rheology relationship in a sheared lamellar fluid.}, journal = {Physical review. E}, volume = {93}, number = {3}, pages = {032609}, doi = {10.1103/PhysRevE.93.032609}, pmid = {27078416}, issn = {2470-0053}, abstract = {The structure-rheology relationship in the shear alignment of a lamellar fluid is studied using a mesoscale model which provides access to the lamellar configurations and the rheology. Based on the equations and free energy functional, the complete set of dimensionless groups that characterize the system are the Reynolds number (ργL(2)/μ), the Schmidt number (μ/ρD), the Ericksen number (μγ/B), the interface sharpness parameter r, the ratio of the viscosities of the hydrophilic and hydrophobic parts μ(r), and the ratio of the system size and layer spacing (L/λ). Here, ρ and μ are the fluid density and average viscosity, γ is the applied strain rate, D is the coefficient of diffusion, B is the compression modulus, μ(r) is the maximum difference in the viscosity of the hydrophilic and hydrophobic parts divided by the average viscosity, and L is the system size in the cross-stream direction. The lattice Boltzmann method is used to solve the concentration and momentum equations for a two dimensional system of moderate size (L/λ=32) and for a low Reynolds number, and the other parameters are systematically varied to examine the qualitative features of the structure and viscosity evolution in different regimes. At low Schmidt numbers where mass diffusion is faster than momentum diffusion, there is fast local formation of randomly aligned domains with "grain boundaries," which are rotated by the shear flow to align along the extensional axis as time increases. This configuration offers a high resistance to flow, and the layers do not align in the flow direction even after 1000 strain units, resulting in a viscosity higher than that for an aligned lamellar phase. At high Schmidt numbers where momentum diffusion is fast, the shear flow disrupts layers before they are fully formed by diffusion, and alignment takes place by the breakage and reformation of layers by shear, resulting in defects (edge dislocations) embedded in a background of nearly aligned layers. At high Ericksen number where the viscous forces are large compared to the restoring forces due to layer compression and bending, shear tends to homogenize the concentration field, and the viscosity decreases significantly. At very high Ericksen number, shear even disrupts the layering of the lamellar phase. At low Ericksen number, shear results in the formation of well aligned layers with edge dislocations. However, these edge dislocations take a long time to anneal; the relatively small misalignment due to the defects results in a large increase in viscosity due to high layer stiffness and due to shear localization, because the layers between defects get pinned and move as a plug with no shear. An increase in the viscosity contrast between the hydrophilic and hydrophobic parts does not alter the structural characteristics during alignment. However, there is a significant increase in the viscosity, due to pinning of the layers between defects, which results in a plug flow between defects and a localization of the shear to a part of the domain.}, } @article {pmid27078282, year = {2016}, author = {Haward, SJ and Poole, RJ and Alves, MA and Oliveira, PJ and Goldenfeld, N and Shen, AQ}, title = {Tricritical spiral vortex instability in cross-slot flow.}, journal = {Physical review. E}, volume = {93}, number = {3}, pages = {031101}, doi = {10.1103/PhysRevE.93.031101}, pmid = {27078282}, issn = {2470-0053}, support = {307499/ERC_/European Research Council/International ; }, abstract = {We examine fluid flow through cross-slot devices with various depth to width ratios α. At low Reynolds number, Re, flow is symmetric and a sharp boundary exists between the two incoming fluid streams. Above an α-dependent critical value, Re(c)(α), a steady symmetry-breaking bifurcation occurs and a spiral vortex structure develops. Order parameters characterizing the instability grow according to a sixth-order Landau potential, and show a progression from second- to first-order transitions as α increases beyond a tricritical value of α ≈ 0.55. Flow simulations indicate the instability is driven by vortex stretching at the stagnation point.}, } @article {pmid27071538, year = {2016}, author = {Xiang, Y and Xue, Y and Lv, P and Li, D and Duan, H}, title = {Influence of fluid flow on the stability and wetting transition of submerged superhydrophobic surfaces.}, journal = {Soft matter}, volume = {12}, number = {18}, pages = {4241-4246}, doi = {10.1039/c6sm00302h}, pmid = {27071538}, issn = {1744-6848}, abstract = {Superhydrophobic surfaces have attracted great attention for drag reduction application. However, these surfaces are subject to instabilities, especially under fluid flow. In this work, we in situ examine the stability and wetting transition of underwater superhydrophobicity under laminar flow conditions by confocal microscopy. The absolute liquid pressure in the flow channel is regulated to acquire the pinned Cassie-Baxter and depinned metastable states. The subsequent dynamic evolution of the meniscus morphology in the two states under shear flow is monitored. It is revealed that fluid flow does not affect the pressure-mediated equilibrium states but accelerates the air exchange between entrapped air cavities and bulk water. A diffusion-based model with varying effective diffusion lengths is used to interpret the experimental data, which show a good agreement. The Sherwood number representing the convection-enhanced mass transfer coefficient is extracted from the data, and is found to follow a classic 1/3-power-law relation with the Reynolds number as has been discovered in channel flows with diffusive boundary conditions. The current work paves the way for designing durable superhydrophobic surfaces under flow conditions.}, } @article {pmid27063642, year = {2016}, author = {Ishimoto, K}, title = {Hydrodynamic evolution of sperm swimming: Optimal flagella by a genetic algorithm.}, journal = {Journal of theoretical biology}, volume = {399}, number = {}, pages = {166-174}, doi = {10.1016/j.jtbi.2016.03.041}, pmid = {27063642}, issn = {1095-8541}, mesh = {*Algorithms ; Animals ; *Biological Evolution ; Flagella/*physiology ; *Hydrodynamics ; Male ; Models, Biological ; Sperm Motility/*physiology ; Spermatozoa/*physiology ; }, abstract = {Swimming performance of spermatozoa is an important index for the success of fertilization. For many years, numerous studies have reported the optimal swimming of flagellar organisms. Nevertheless, there is still a question as to which is optimal among planar, circular helical and ellipsoidal helical beating. In this paper, we use a genetic algorithm to investigate the beat pattern with the best swimming efficiency based on hydrodynamic dissipation and internal torque exertion. For the parameters considered, our results show that the planar beat is optimal for small heads and the helical flagellum is optimum for a larger heads, while the ellipsoidal beat is never optimal. Also, the genetic optimization reveals that the wavenumber and shape of wave envelope are relevant parameters, whereas the wave shape and head geometry have relatively minor effects on efficiency. The optimal beat with respect to the efficiency based on the internal torque exertion of an active elastic flagellum is characterized by a small-wavenumber and large-amplitude wave in a lower-viscosity medium. The obtained results on the optimal waveform are consistent with observations for planar waveforms, but in many respects, the results suggest the necessity of a detailed flagellar structure-fluid interaction to address whether real spermatozoa exhibit hydrodynamically efficient swimming. The evolutional optimization approach used in this study has distinguished biologically important parameters, and the methodology can potentially be applicable to various swimmers.}, } @article {pmid27055766, year = {2016}, author = {Iasiello, M and Vafai, K and Andreozzi, A and Bianco, N}, title = {Analysis of non-Newtonian effects on Low-Density Lipoprotein accumulation in an artery.}, journal = {Journal of biomechanics}, volume = {49}, number = {9}, pages = {1437-1446}, doi = {10.1016/j.jbiomech.2016.03.017}, pmid = {27055766}, issn = {1873-2380}, mesh = {Arteries/*metabolism/physiology ; Diffusion ; Hemodynamics ; Humans ; Lipoproteins, LDL/*metabolism ; *Models, Cardiovascular ; Porosity ; Rheology ; Stress, Mechanical ; }, abstract = {In this work, non-Newtonian effects on Low-Density Lipoprotein (LDL) transport across an artery are analyzed with a multi-layer model. Four rheological models (Carreau, Carreau-Yasuda, power-law and Newtonian) are used for the blood flow through the lumen. For the non-Newtonian cases, the arterial wall is modeled with a generalized momentum equation. Convection-diffusion equation is used for the LDL transport through the lumen, while Staverman-Kedem-Katchalsky, combined with porous media equations, are used for the LDL transport through the wall. Results are presented in terms of filtration velocity, Wall Shear Stresses (WSS) and concentration profiles. It is shown that non-Newtonian effects on mass transport are negligible for a healthy intramural pressure value. Non-Newtonian effects increase slightly with intramural pressure, but Newtonian assumption can still be considered reliable. Effects of arterial size are also analyzed, showing that Newtonian assumption can be considered valid for both medium and large arteries, in predicting LDL deposition. Finally, non-Newtonian effects are also analyzed for an aorta-common iliac bifurcation, showing that Newtonian assumption is valid for mass transport at low Reynolds numbers. At a high Reynolds number, it has been shown that a non-Newtonian fluid model can have more impact due to the presence of flow recirculation.}, } @article {pmid27042817, year = {2016}, author = {Beier, S and Ormiston, JA and Webster, MW and Cater, JE and Norris, SE and Medrano-Gracia, P and Young, AA and Cowan, BR}, title = {Dynamically scaled phantom phase contrast MRI compared to true-scale computational modeling of coronary artery flow.}, journal = {Journal of magnetic resonance imaging : JMRI}, volume = {44}, number = {4}, pages = {983-992}, doi = {10.1002/jmri.25240}, pmid = {27042817}, issn = {1522-2586}, mesh = {Blood Flow Velocity/*physiology ; Computer Simulation ; Coronary Circulation/*physiology ; Coronary Vessels/*diagnostic imaging/*physiology ; Equipment Design ; Equipment Failure Analysis ; Humans ; Image Interpretation, Computer-Assisted/methods ; Magnetic Resonance Angiography/*instrumentation/methods ; *Models, Cardiovascular ; *Phantoms, Imaging ; Reproducibility of Results ; Sensitivity and Specificity ; }, abstract = {PURPOSE: To examine the feasibility of combining computational fluid dynamics (CFD) and dynamically scaled phantom phase-contrast magnetic resonance imaging (PC-MRI) for coronary flow assessment.

MATERIALS AND METHODS: Left main coronary bifurcations segmented from computed tomography with bifurcation angles of 33°, 68°, and 117° were scaled-up ∼7× and 3D printed. Steady coronary flow was reproduced in these phantoms using the principle of dynamic similarity to preserve the true-scale Reynolds number, using blood analog fluid and a pump circuit in a 3T MRI scanner. After PC-MRI acquisition, the data were segmented and coregistered to CFD simulations of identical, but true-scale geometries. Velocities at the inlet region were extracted from the PC-MRI to define the CFD inlet boundary condition.

RESULTS: The PC-MRI and CFD flow data agreed well, and comparison showed: 1) small velocity magnitude discrepancies (2-8%); 2) with a Spearman's rank correlation ≥0.72; and 3) a velocity vector correlation (including direction) of r(2) ≥ 0.82. The highest agreement was achieved for high velocity regions with discrepancies being located in slow or recirculating zones with low MRI signal-to-noise ratio (SNRv) in tortuous segments and large bifurcating vessels.

CONCLUSION: Characterization of coronary flow using a dynamically scaled PC-MRI phantom flow is feasible and provides higher resolution than current in vivo or true-scale in vitro methods, and may be used to provide boundary conditions for true-scale CFD simulations. J. MAGN. RESON. IMAGING 2016;44:983-992.}, } @article {pmid27037586, year = {2016}, author = {Barsanti, L and Coltelli, P and Evangelista, V and Frassanito, AM and Gualtieri, P}, title = {Swimming patterns of the quadriflagellate Tetraflagellochloris mauritanica (Chlamydomonadales, Chlorophyceae).}, journal = {Journal of phycology}, volume = {52}, number = {2}, pages = {209-218}, doi = {10.1111/jpy.12384}, pmid = {27037586}, issn = {1529-8817}, mesh = {Cell Tracking ; Flagella/*physiology/ultrastructure ; Movement ; Time Factors ; Volvocida/anatomy & histology/*physiology/ultrastructure ; }, abstract = {Chlamydomonadales are elective subjects for the investigation of the problems related to locomotion and transport in biological fluid dynamics, whose resolution could enhance searching efficiency and assist in the avoidance of dangerous environments. In this paper, we elucidate the swimming behavior of Tetraflagellochloris mauritanica, a unicellular-multicellular alga belonging to the order Chlamydomonadales. This quadriflagellate alga has a complex swimming motion consisting of alternating swimming phases connected by in-place random reorientations and resting phases. It is capable of both forward and backward swimming, both being normal modes of swimming. The complex swimming behavior resembles the run-and-tumble motion of peritrichous bacteria, with in-place reorientation taking the place of tumbles. In the forward swimming, T. mauritanica shows a very efficient flagellar beat, with undulatory retrograde waves that run along the flagella to their tip. In the backward swimming, the flagella show a nonstereotypical synchronization mode, with a pattern that does not fit any of the modes present in the other Chlamydomonadales so far investigated.}, } @article {pmid27036817, year = {2016}, author = {Liu, C and Du, L and Zhao, Z}, title = {A directional cylindrical anemometer with four sets of differential pressure sensors.}, journal = {The Review of scientific instruments}, volume = {87}, number = {3}, pages = {035105}, doi = {10.1063/1.4943222}, pmid = {27036817}, issn = {1089-7623}, abstract = {This paper presents a solid-state directional anemometer for simultaneously measuring the speed and direction of a wind in a plane in a speed range 1-40 m/s. This instrument has a cylindrical shape and works by detecting the pressure differences across diameters of the cylinder when exposed to wind. By analyzing our experimental data in a Reynolds number regime 1.7 × 10(3)-7 × 10(4), we figure out the relationship between the pressure difference distribution and the wind velocity. We propose a novel and simple solution based on the relationship and design an anemometer which composes of a circular cylinder with four sets of differential pressure sensors, tubes connecting these sensors with the cylinder's surface, and corresponding circuits. In absence of moving parts, this instrument is small and immune of friction. It has simple internal structures, and the fragile sensing elements are well protected. Prototypes have been fabricated to estimate performance of proposed approach. The power consumption of the prototype is less than 0.5 W, and the sample rate is up to 31 Hz. The test results in a wind tunnel indicate that the maximum relative speed measuring error is 5% and the direction error is no more than 5° in a speed range 2-40 m/s. In theory, it is capable of measuring wind up to 60 m/s. When the air stream goes slower than 2 m/s, the measuring errors of directions are slightly greater, and the performance of speed measuring degrades but remains in an acceptable range of ±0.2 m/s.}, } @article {pmid27036184, year = {2016}, author = {Smith, SA and Warrier, S}, title = {Reynolds number effects on mixing due to topological chaos.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {26}, number = {3}, pages = {033106}, doi = {10.1063/1.4943170}, pmid = {27036184}, issn = {1089-7682}, abstract = {Topological chaos has emerged as a powerful tool to investigate fluid mixing. While this theory can guarantee a lower bound on the stretching rate of certain material lines, it does not indicate what fraction of the fluid actually participates in this minimally mandated mixing. Indeed, the area in which effective mixing takes place depends on physical parameters such as the Reynolds number. To help clarify this dependency, we numerically simulate the effects of a batch stirring device on a 2D incompressible Newtonian fluid in the laminar regime. In particular, we calculate the finite time Lyapunov exponent (FTLE) field for three different stirring protocols, one topologically complex (pseudo-Anosov) and two simple (finite-order), over a range of viscosities. After extracting appropriate measures indicative of both the amount of mixing and the area of effective mixing from the FTLE field, we see a clearly defined Reynolds number range in which the relative efficacy of the pseudo-Anosov protocol over the finite-order protocols justifies the application of topological chaos. More unexpectedly, we see that while the measures of effective mixing area increase with increasing Reynolds number for the finite-order protocols, they actually exhibit non-monotonic behavior for the pseudo-Anosov protocol.}, } @article {pmid27033298, year = {2016}, author = {Winzen, A and Roidl, B and Schröder, W}, title = {Combined particle-image velocimetry and force analysis of the three-dimensional fluid-structure interaction of a natural owl wing.}, journal = {Bioinspiration & biomimetics}, volume = {11}, number = {2}, pages = {026005}, doi = {10.1088/1748-3190/11/2/026005}, pmid = {27033298}, issn = {1748-3190}, mesh = {Air ; Animals ; Biomimetics/*methods ; Computer Simulation ; Elastic Modulus/physiology ; Feathers/anatomy & histology/*physiology ; Flight, Animal/*physiology ; Friction ; *Models, Biological ; Rheology/methods ; Stress, Mechanical ; Strigiformes/anatomy & histology/*physiology ; Surface Properties ; Viscosity ; Wings, Animal/anatomy & histology/*physiology ; }, abstract = {Low-speed aerodynamics has gained increasing interest due to its relevance for the design process of small flying air vehicles. These small aircraft operate at similar aerodynamic conditions as, e.g. birds which therefore can serve as role models of how to overcome the well-known problems of low Reynolds number flight. The flight of the barn owl is characterized by a very low flight velocity in conjunction with a low noise emission and a high level of maneuverability at stable flight conditions. To investigate the complex three-dimensional flow field and the corresponding local structural deformation in combination with their influence on the resulting aerodynamic forces, time-resolved stereoscopic particle-image velocimetry and force and moment measurements are performed on a prepared natural barn owl wing. Several spanwise positions are measured via PIV in a range of angles of attack [Formula: see text] 6° and Reynolds numbers 40 000 [Formula: see text] 120 000 based on the chord length. Additionally, the resulting forces and moments are recorded for -10° ≤ α ≤ 15° at the same Reynolds numbers. Depending on the spanwise position, the angle of attack, and the Reynolds number, the flow field on the wing's pressure side is characterized by either a region of flow separation, causing large-scale vortical structures which lead to a time-dependent deflection of the flexible wing structure or wing regions showing no instantaneous deflection but a reduction of the time-averaged mean wing curvature. Based on the force measurements the three-dimensional fluid-structure interaction is assumed to considerably impact the aerodynamic forces acting on the wing leading to a strong mechanical loading of the interface between the wing and body. These time-depending loads which result from the flexibility of the wing should be taken into consideration for the design of future small flying air vehicles using flexible wing structures.}, } @article {pmid27030773, year = {2016}, author = {Chin, DD and Lentink, D}, title = {Flapping wing aerodynamics: from insects to vertebrates.}, journal = {The Journal of experimental biology}, volume = {219}, number = {Pt 7}, pages = {920-932}, doi = {10.1242/jeb.042317}, pmid = {27030773}, issn = {1477-9145}, mesh = {Animals ; Biomechanical Phenomena ; Birds/*physiology ; Chiroptera/*physiology ; Flight, Animal/*physiology ; Insecta/*physiology ; Models, Biological ; Wings, Animal/*physiology ; }, abstract = {More than a million insects and approximately 11,000 vertebrates utilize flapping wings to fly. However, flapping flight has only been studied in a few of these species, so many challenges remain in understanding this form of locomotion. Five key aerodynamic mechanisms have been identified for insect flight. Among these is the leading edge vortex, which is a convergent solution to avoid stall for insects, bats and birds. The roles of the other mechanisms - added mass, clap and fling, rotational circulation and wing-wake interactions - have not yet been thoroughly studied in the context of vertebrate flight. Further challenges to understanding bat and bird flight are posed by the complex, dynamic wing morphologies of these species and the more turbulent airflow generated by their wings compared with that observed during insect flight. Nevertheless, three dimensionless numbers that combine key flow, morphological and kinematic parameters - the Reynolds number, Rossby number and advance ratio - govern flapping wing aerodynamics for both insects and vertebrates. These numbers can thus be used to organize an integrative framework for studying and comparing animal flapping flight. Here, we provide a roadmap for developing such a framework, highlighting the aerodynamic mechanisms that remain to be quantified and compared across species. Ultimately, incorporating complex flight maneuvers, environmental effects and developmental stages into this framework will also be essential to advancing our understanding of the biomechanics, movement ecology and evolution of animal flight.}, } @article {pmid27009180, year = {2016}, author = {Li, G and Müller, UK and van Leeuwen, JL and Liu, H}, title = {Fish larvae exploit edge vortices along their dorsal and ventral fin folds to propel themselves.}, journal = {Journal of the Royal Society, Interface}, volume = {13}, number = {116}, pages = {}, pmid = {27009180}, issn = {1742-5662}, mesh = {Animal Fins/*physiology ; Animals ; Fishes/*physiology ; Locomotion/*physiology ; }, abstract = {Larvae of bony fish swim in the intermediate Reynolds number (Re) regime, using body- and caudal-fin undulation to propel themselves. They share a median fin fold that transforms into separate median fins as they grow into juveniles. The fin fold was suggested to be an adaption for locomotion in the intermediate Reynolds regime, but its fluid-dynamic role is still enigmatic. Using three-dimensional fluid-dynamic computations, we quantified the swimming trajectory from body-shape changes during cyclic swimming of larval fish. We predicted unsteady vortices around the upper and lower edges of the fin fold, and identified similar vortices around real larvae with particle image velocimetry. We show that thrust contributions on the body peak adjacent to the upper and lower edges of the fin fold where large left-right pressure differences occur in concert with the periodical generation and shedding of edge vortices. The fin fold enhances effective flow separation and drag-based thrust. Along the body, net thrust is generated in multiple zones posterior to the centre of mass. Counterfactual simulations exploring the effect of having a fin fold across a range of Reynolds numbers show that the fin fold helps larvae achieve high swimming speeds, yet requires high power. We conclude that propulsion in larval fish partly relies on unsteady high-intensity vortices along the upper and lower edges of the fin fold, providing a functional explanation for the omnipresence of the fin fold in bony-fish larvae.}, } @article {pmid26986414, year = {2016}, author = {Köhler, J and Friedrich, J and Ostendorf, A and Gurevich, EL}, title = {Characterization of azimuthal and radial velocity fields induced by rotors in flows with a low Reynolds number.}, journal = {Physical review. E}, volume = {93}, number = {2}, pages = {023108}, doi = {10.1103/PhysRevE.93.023108}, pmid = {26986414}, issn = {2470-0053}, abstract = {We theoretically and experimentally investigate the flow field that emerges from a rodlike microrotor rotating about its center in a nonaxisymmetric manner. A simple theoretical model is proposed that uses a superposition of two rotlets as a fundamental solution to the Stokes equation. The predictions of this model are compared to measurements of the azimuthal and radial microfluidic velocity field components that are induced by a rotor composed of fused microscopic spheres. The rotor is driven magnetically and the fluid flow is measured with the help of a probe particle fixed by an optical tweezer. We find considerable deviations of the mere azimuthal flow pattern induced by a single rotating sphere as it has been reported by Di Leonardo et al. [Phys. Rev. Lett. 96, 134502 (2006)]. Notably, the presence of a radial velocity component that manifests itself by an oscillation of the probe particle with twice the rotor frequency is observed. These findings open up a way to discuss possible radial transport in microfluidic devices.}, } @article {pmid26986411, year = {2016}, author = {Lavrenteva, O and Prakash, J and Nir, A}, title = {Effect of added mass on the interaction of bubbles in a low-Reynolds-number shear flow.}, journal = {Physical review. E}, volume = {93}, number = {2}, pages = {023105}, doi = {10.1103/PhysRevE.93.023105}, pmid = {26986411}, issn = {2470-0053}, mesh = {Hydrodynamics ; *Models, Theoretical ; Nonlinear Dynamics ; *Shear Strength ; }, abstract = {Equal size air bubbles that are entrapped by a Taylor vortex of the secondary flow in a Couette device, thereby defying buoyancy, slowly form a stable ordered ring with equal separation distances between all neighbors. We present two models of the process dynamics based on force balance on a bubble in the presence of other bubbles positioned on the same streamline in a simple shear flow. The forces taken into account are the viscous resistance, the added mass force, and the inertia-induced repulsing force between two bubbles in a low-Reynolds-number shear flow obtained in Prakash et al. [J. Prakash et al., Phys. Rev. E 87, 043002 (2013)]. The first model of the process assumes that each bubble interacts solely with its nearest neighbors. The second model takes into account pairwise interactions among all the bubbles in the ring. The performed dynamic simulations were compared to the experimental results reported in Prakash et al. [J. Prakash et al., Phys. Rev. E 87, 043002 (2013)] and to the results of quasistationary models (ignoring the added mass effect) suggested in that paper. It is demonstrated that taking into account the effect of added mass, the models describe the major effect of the bubbles' ordering, provide good estimation of the relaxation time, and also predict nonmonotonic behavior of the separation distance between the bubbles, which exhibit over- and undershooting of equilibrium separations. The latter effects were observed in experiments, but are not predicted by the quasistationary models.}, } @article {pmid26951951, year = {2016}, author = {Flamini, V and DeAnda, A and Griffith, BE}, title = {Immersed boundary-finite element model of fluid-structure interaction in the aortic root.}, journal = {Theoretical and computational fluid dynamics}, volume = {30}, number = {1}, pages = {139-164}, pmid = {26951951}, issn = {0935-4964}, support = {P50 GM071558/GM/NIGMS NIH HHS/United States ; R01 HL117063/HL/NHLBI NIH HHS/United States ; }, abstract = {It has long been recognized that aortic root elasticity helps to ensure efficient aortic valve closure, but our understanding of the functional importance of the elasticity and geometry of the aortic root continues to e-volve as increasingly detailed in vivo imaging data become available. Herein, we describe a fluid-structure interaction model of the aortic root, including the aortic valve leaflets, the sinsuses of Valsalva, the aortic annulus, and the sinotubular junction, that employs a version of Peskin's immersed boundary (IB) method with a finite element (FE) description of the structural elasticity. As in earlier work, we use a fiber-based model of the valve leaflets, but this study extends earlier IB models of the aortic root by employing an incompressible hyperelastic model of the mechanics of the sinuses and ascending aorta using a constitutive law fit to experimental data from human aortic root tissue. In vivo pressure loading is accounted for by a backward displacement method that determines the unloaded configurations of the root model. Our model yields realistic cardiac output at physiological pressures, with low transvalvular pressure differences during forward flow, minimal regurgitation during valve closure, and realistic pressure loads when the valve is closed during diastole. Further, results from high-resolution computations indicate that although the detailed leaflet and root kinematics show some grid sensitivity, our IB model of the aortic root nonetheless produces essentially grid-converged flow rates and pressures at practical grid spacings for the high-Reynolds number flows of the aortic root. These results thereby clarify minimum grid resolutions required by such models when used as stand-alone models of the aortic valve as well as when used to provide models of the outflow valves in models of left ventricular fluid dynamics.}, } @article {pmid26943538, year = {2016}, author = {Sadek, M and Alexakis, A and Fauve, S}, title = {Optimal Length Scale for a Turbulent Dynamo.}, journal = {Physical review letters}, volume = {116}, number = {7}, pages = {074501}, doi = {10.1103/PhysRevLett.116.074501}, pmid = {26943538}, issn = {1079-7114}, abstract = {We demonstrate that there is an optimal forcing length scale for low Prandtl number dynamo flows that can significantly reduce the required energy injection rate. The investigation is based on simulations of the induction equation in a periodic box of size 2πL. The flows considered are the laminar and turbulent ABC flows forced at different forcing wave numbers k_{f}, where the turbulent case is simulated using a subgrid turbulence model. At the smallest allowed forcing wave number k_{f} =k_{min} =1/L the laminar critical magnetic Reynolds number Rm_{c} ^{lam} is more than an order of magnitude smaller than the turbulent critical magnetic Reynolds number Rm_{c} ^{turb} due to the hindering effect of turbulent fluctuations. We show that this hindering effect is almost suppressed when the forcing wave number k_{f} is increased above an optimum wave number k_{f} L≃4 for which Rm_{c} ^{turb} is minimum. At this optimal wave number, Rm_{c} ^{turb} is smaller by more than a factor of 10 than the case forced in k_{f} =1. This leads to a reduction of the energy injection rate by 3 orders of magnitude when compared to the case where the system is forced at the largest scales and thus provides a new strategy for the design of a fully turbulent experimental dynamo.}, } @article {pmid26925504, year = {2016}, author = {Hervella, P and Parra, E and Needham, D}, title = {Encapsulation and retention of chelated-copper inside hydrophobic nanoparticles: Liquid cored nanoparticles show better retention than a solid core formulation.}, journal = {European journal of pharmaceutics and biopharmaceutics : official journal of Arbeitsgemeinschaft fur Pharmazeutische Verfahrenstechnik e.V}, volume = {102}, number = {}, pages = {64-76}, doi = {10.1016/j.ejpb.2016.02.015}, pmid = {26925504}, issn = {1873-3441}, mesh = {Chelating Agents/*chemistry ; Chemistry, Pharmaceutical/methods ; Copper/*chemistry ; Hydrophobic and Hydrophilic Interactions ; Lipids/chemistry ; Liposomes/chemistry ; Nanoparticles/*chemistry ; Particle Size ; Porphyrins/chemistry ; }, abstract = {MOTIVATION: In the field of imaging, (18)F-fluorodeoxyglucose (FDG) PET imaging allows evaluation of glucose metabolism and is the most widely used imaging agent clinically for metastatic cancer. While it can certainly detect the metastatic disease, in order to provide a more fully "individualized medicine" strategy of detection and pharmaceutical treatment, what is needed are additional imaging nanoparticles that resemble the subsequently-administered nanoparticle drug delivery system itself. Both of these nanoparticles must also be able to take advantage of what may well be a limited EPR effect in human tumors, which in and of itself still needs to be characterized in the clinic. Administration of FDG, followed by a nanoparticle imaging agent, followed by a therapeutic nanoparticle would constitute such an "individualized medicine strategy", especially for anti-metastasis approaches. It is here that our endogenous-inspired nanoparticle strategies for imaging and therapeutics are focused on encapsulating and retaining imaging ions such as copper inside novel hydrophobic nanoparticles. In this paper, we describe a new approach to label the core of hydrophobic nanoparticles composed of Glyceryl Trioleate (Triolein) with copper using the hydrophobic chelator Octaethyl porphyrin (OEP).

RESEARCH PLAN AND METHODS: The research plan for this study was to (1) Formulate nanoparticles and control nanoparticle size using a modification of the solvent injection technique, named fast ethanol injection; (2) Chelate copper into the octaethyl porphyrin; (3) Encapsulate OEP-Cu in nanoparticles: the encapsulation efficiency of copper into liquid nanoparticles (LNP), solid nanoparticles (SNP) and phospholipid liposomes (PL) was evaluated by UV-Vis and atomic absorption spectroscopy; (4) Retain the encapsulated OEP-Cu in the liquid or solid cores of the nanoparticles in the presence of a lipid sink.

RESULTS: (1) The size of the nanoparticles was found to be strongly dependent on the Reynolds number and the initial concentration of components for the fast injection technique. At high Reynolds number (2181), a minimum value for the particle diameter of ∼30nm was measured. (2) Copper was chelated by OEP in a 1:1mol ratio with an association constant of 2.57×10(5)M(-1). (3) The diameter of the nanoparticles was not significantly affected by the presence of OEP or OEP-Cu. The percentage of encapsulation of copper to nanoparticles was >95% at low OEP-Cu concentrations. In the absence of OEP, copper was not detected in nanoparticles demonstrating the role of the hydrophobic chelator OEP in the encapsulation of the otherwise water-soluble copper inside lipid nanoparticles. (4) The in vitro retention upon incubation at 37°C over a 48h period in the presence of a lipid sink showed a slow transfer of OEP-Cu into the lipid sink (t1/2=7.7h) for SNP; for PL there was an almost instantaneous transfer of OEP-Cu into the lipid sink (t1/2=0.5h), while for the LNP, all OEP-Cu was retained in the LNP over the full 48h period.

CONCLUSIONS: The main conclusion of this study was that a very hydrophilic ion such as Cu(2+) can indeed be solubilized and retained in the core of hydrophobic nanoparticles when a hydrophobic molecule (OEP) is used as a chelator. The fast-injection technique was shown to provide a very convenient method to formulate both liquid and solid nanoparticles labeled with Cu (well chelated by OEP), with diameters as small as 30nm, and encapsulation efficiencies higher than 95% when the concentration of OEP-Cu loaded into the nanoparticles was equal to or below 2.5mol%. This is expected to be sufficient for PET-imaging studies.}, } @article {pmid26889002, year = {2016}, author = {Murphy, DW and Adhikari, D and Webster, DR and Yen, J}, title = {Underwater flight by the planktonic sea butterfly.}, journal = {The Journal of experimental biology}, volume = {219}, number = {Pt 4}, pages = {535-543}, doi = {10.1242/jeb.129205}, pmid = {26889002}, issn = {1477-9145}, mesh = {Animals ; Biomechanical Phenomena ; Gastropoda/anatomy & histology/*physiology ; Hydrodynamics ; Swimming ; Wings, Animal/anatomy & histology/physiology ; Zooplankton ; }, abstract = {In a remarkable example of convergent evolution, we show that the zooplanktonic sea butterfly Limacina helicina 'flies' underwater in the same way that very small insects fly in the air. Both sea butterflies and flying insects stroke their wings in a characteristic figure-of-eight pattern to produce lift, and both generate extra lift by peeling their wings apart at the beginning of the power stroke (the well-known Weis-Fogh 'clap-and-fling' mechanism). It is highly surprising to find a zooplankter 'mimicking' insect flight as almost all zooplankton swim in this intermediate Reynolds number range (Re=10-100) by using their appendages as paddles rather than wings. The sea butterfly is also unique in that it accomplishes its insect-like figure-of-eight wing stroke by extreme rotation of its body (what we call 'hyper-pitching'), a paradigm that has implications for micro aerial vehicle (MAV) design. No other animal, to our knowledge, pitches to this extent under normal locomotion.}, } @article {pmid26887934, year = {2016}, author = {Wang, G and Yang, F and Zhao, W and Chen, CP}, title = {On micro-electrokinetic scalar turbulence in microfluidics at a low Reynolds number.}, journal = {Lab on a chip}, volume = {16}, number = {6}, pages = {1030-1038}, doi = {10.1039/c5lc01541c}, pmid = {26887934}, issn = {1473-0189}, abstract = {We recently demonstrated the direct observation of micro-electrokinetic turbulence in a microchannel at a low Reynolds number (Re) when a pressure-driven flow was forced electrokinetically. Here, we characterize the corresponding scalar turbulence and surprisingly find that the corresponding turbulent mixing has some typical and important features of scalar turbulence, such as the Obukhov-Corrsin (O-C) -5/3 spectrum of concentration fluctuation, which can commonly be realized only at high Re in macroflows. This discovery could provide a new perspective of scalar turbulence and an avenue for control of transport phenomena in lab-on-a-chip platforms. This will deepen our fundamental understanding of transport phenomena in microfluidics.}, } @article {pmid26886919, year = {2016}, author = {Hayat, T and Shafique, M and Tanveer, A and Alsaedi, A}, title = {Radiative Peristaltic Flow of Jeffrey Nanofluid with Slip Conditions and Joule Heating.}, journal = {PloS one}, volume = {11}, number = {2}, pages = {e0148002}, pmid = {26886919}, issn = {1932-6203}, mesh = {*Heating ; Models, Theoretical ; Nanoparticles/*chemistry ; *Peristalsis ; *Rheology ; }, abstract = {Mixed convection peristaltic flow of Jeffrey nanofluid in a channel with compliant walls is addressed here. The present investigation includes the viscous dissipation, thermal radiation and Joule heating. Whole analysis is performed for velocity, thermal and concentration slip conditions. Related problems through long wavelength and low Reynolds number are examined for stream function, temperature and concentration. Impacts of thermal radiation, Hartman number, Brownian motion parameter, thermophoresis, Joule heating and slip parameters are explored in detail. Clearly temperature is a decreasing function of Hartman number and radiation parameter.}, } @article {pmid26883291, year = {2016}, author = {Pinto, SI and Campos, JB}, title = {Numerical study of wall shear stress-based descriptors in the human left coronary artery.}, journal = {Computer methods in biomechanics and biomedical engineering}, volume = {19}, number = {13}, pages = {1443-1455}, doi = {10.1080/10255842.2016.1149575}, pmid = {26883291}, issn = {1476-8259}, mesh = {Computer Simulation ; Coronary Vessels/*physiopathology ; Hemorheology ; Humans ; Models, Cardiovascular ; *Numerical Analysis, Computer-Assisted ; Shear Strength ; *Stress, Mechanical ; Time Factors ; }, abstract = {The present work is about the application of wall shear stress descriptors - time averaged wall shear stress (TAWSS), oscillating shear index (OSI) and relative residence time (RRT) - to the study of blood flow in the left coronary artery (LCA). These descriptors aid the prediction of disturbed flow conditions in the vessels and play a significant role in the detection of potential zones of atherosclerosis development. Hemodynamic descriptors data were obtained, numerically, through ANSYS® software, for the LCA of a patient-specific geometry and for a 3D idealized model. Comparing both cases, the results are coherent, in terms of location and magnitude. Low TAWSS, high OSI and high RRT values are observed in the bifurcation - potential zone of atherosclerosis appearance. The dissimilarities observed in the TAWSS values, considering blood as a Newtonian or non-Newtonian fluid, releases the importance of the correct blood rheologic caracterization. Moreover, for a higher Reynolds number, the TAWSS values decrease in the bifurcation and along the LAD branch, increasing the probability of plaques deposition. Furthermore, for a stenotic LCA model, very low TAWSS and high RRT values in front and behind the stenosis are observed, indicating the probable extension, in the flow direction, of the lesion.}, } @article {pmid26871181, year = {2016}, author = {Tsai, CM and Chu, HY}, title = {Evolution of a plasma vortex in air.}, journal = {Physical review. E}, volume = {93}, number = {1}, pages = {013205}, doi = {10.1103/PhysRevE.93.013205}, pmid = {26871181}, issn = {2470-0053}, mesh = {*Air ; Equipment Design ; *Helium ; Models, Theoretical ; *Motion ; *Plasma Gases ; }, abstract = {We report the generation of a vortex-shaped plasma in air by using a capacitively coupled dielectric barrier discharge system. We show that a vortex-shaped plasma can be produced inside a helium gas vortex and is capable of propagating for 3 cm. The fluctuation of the plasma ring shows a scaling relation with the Reynolds number of the vortex. The transient discharge reveals the property of corona discharge, where the conducting channel within the gas vortex and the blur plasma emission are observed at each half voltage cycle.}, } @article {pmid26871163, year = {2016}, author = {Thiesset, F and Maurice, G and Halter, F and Mazellier, N and Chauveau, C and Gökalp, I}, title = {Geometrical properties of turbulent premixed flames and other corrugated interfaces.}, journal = {Physical review. E}, volume = {93}, number = {1}, pages = {013116}, doi = {10.1103/PhysRevE.93.013116}, pmid = {26871163}, issn = {2470-0053}, abstract = {This study focuses on the geometrical properties of turbulent flame fronts and other interfaces. Toward that end, we use an original tool based on proper orthogonal decomposition (POD), which is applied to the interface spatial coordinates. The focus is mainly on the degree of roughness of the flame front, which is quantified through the scale dependence of its coverage arclength. POD is first validated by comparing with the caliper technique. Fractal characteristics are extracted in an unambiguous fashion using a parametric expression which appears to be impressively well suited for representing Richardson plots. Then it is shown that, for the range of Reynolds numbers investigated here, the scale-by-scale contribution to the arclength does not comply with scale similarity, irrespectively of the type of similarity which is invoked. The finite ratios between large and small scales, referred to as finite Reynolds number effects, are likely to explain this observation. In this context, the Reynolds number that ought to be achieved for a proper inertial range to be discernible, and for scale similarity to be likely to apply, is calculated. Fractal characteristics of flame folding are compared to available predictions. It is confirmed that the inner cutoff satisfactorily correlates with the Kolmogorov scale while the outer cutoff appears to be proportional to the integral length scale. However, the scaling for the fractal dimension is much less obvious. It is argued that much higher Reynolds numbers have to be reached for drawing firm statements about the evolution (or constancy) of the fractal dimension with respect to flame and flow parameters. Finally, a heuristic phenomenology of corrugated interfaces is highlighted. The degree of generality of the latter phenomenology is confirmed by comparing the folding of different interfaces including a turbulent-nonturbulent interface, a liquid jet destabilized by a surrounding air jet, a cavitating flow, and an isoscalar evolving in a turbulent medium. The latter outcome is likely to have strong implications for modeling the corrugation of turbulent interfaces occurring in many physical situations.}, } @article {pmid26871162, year = {2016}, author = {Nie, D and Lin, J and Chen, R}, title = {Grouping behavior of coaxial settling particles in a narrow channel.}, journal = {Physical review. E}, volume = {93}, number = {1}, pages = {013114}, doi = {10.1103/PhysRevE.93.013114}, pmid = {26871162}, issn = {2470-0053}, abstract = {Using numerical simulations, we studied the grouping behaviors of particles settling along their line of centers in narrow channels having a Reynolds number range of 5 ≤ Re ≤ 50. The calculations are based on our previously developed lattice Boltzmann direct-forcing-fictitious-domain method. We report the grouping behavior and investigate the dependence on the number of particles n, the initial interparticle separation h_{0}, and the Reynolds number Re. In particular, the mode of grouping is found to be independent of the number of particles when the Reynolds numbers is small. The two lowermost particles always come together first and form a vertical doublet and then the next two lowest particles form another doublet, and so on. Therefore, we observe n/2 doublets or (n-1)/2 doublets when n is even or odd, respectively. The uppermost particle is always left behind when n is odd. Furthermore, the separation between these doublets remains constant, displaying a power-law dependence decreasing from top to bottom.}, } @article {pmid26871154, year = {2016}, author = {Wang, G and Yang, F and Zhao, W}, title = {Microelectrokinetic turbulence in microfluidics at low Reynolds number.}, journal = {Physical review. E}, volume = {93}, number = {1}, pages = {013106}, doi = {10.1103/PhysRevE.93.013106}, pmid = {26871154}, issn = {2470-0053}, mesh = {Fluorescein ; Fluorescent Dyes ; Kinetics ; Lab-On-A-Chip Devices ; *Microfluidics ; Models, Theoretical ; *Motion ; Pressure ; Solutions ; Static Electricity ; Water ; }, abstract = {There is commonly no turbulence in microfluidics, and the flows are believed to be either laminar or chaotic, since Reynolds number (Re) in microflows is usually on the order of unity or lower. However, we recently demonstrated that it is possible to achieve turbulence with low Re (based on the measured flow velocity and the width of the channel entrance) when a pressure-driven flow is electrokinetically forced in a quasi T-microchannel. To be able to measure high frequency velocity fluctuations in microchannels, a velocimeter with submicrometer spatial resolution and microsecond temporal resolution, called a laser-induced fluorescence photobleaching anemometer, is developed. Here we characterize the microelectrokinetic turbulence and observe some typical and important features of high Re flows, such as Kolmogorov -5/3 spectrum of velocity fluctuation, which usually can be realized only at very high Re in macroturbulent flows.}, } @article {pmid26853995, year = {2016}, author = {Kim, J and Lee, J and Wu, C and Nam, S and Di Carlo, D and Lee, W}, title = {Inertial focusing in non-rectangular cross-section microchannels and manipulation of accessible focusing positions.}, journal = {Lab on a chip}, volume = {16}, number = {6}, pages = {992-1001}, doi = {10.1039/c5lc01100k}, pmid = {26853995}, issn = {1473-0189}, abstract = {Inertial focusing in microfluidic channels has been extensively studied experimentally and theoretically, which has led to various applications including microfluidic separation and enrichment of cells. Inertial lift forces are strongly dependent on the flow velocity profile and the channel cross-sectional shape. However, the channel cross-sections studied have been limited to circles and rectangles. We studied inertial focusing in non-rectangular cross-section channels to manipulate the flow profile and thus the inertial focusing of microparticles. The location and number of focusing positions are analyzed with varying cross-sectional shapes and Reynolds number. We found that the broken symmetry of non-equilateral triangular channels leads to the shifting of focusing positions with varying Reynolds number. Non-rectangular channels have unique mapping of the focusing positions and the corresponding basins of attraction. By connecting channels with different cross-sectional shapes, we were able to manipulate the accessible focusing positions and achieve focusing of microparticles to a single stream with ∼99% purity.}, } @article {pmid26841796, year = {2016}, author = {Mathijssen, AJ and Doostmohammadi, A and Yeomans, JM and Shendruk, TN}, title = {Hotspots of boundary accumulation: dynamics and statistics of micro-swimmers in flowing films.}, journal = {Journal of the Royal Society, Interface}, volume = {13}, number = {115}, pages = {20150936}, pmid = {26841796}, issn = {1742-5662}, mesh = {*Bacteria ; *Bacterial Physiological Phenomena ; Flagella/*physiology ; Locomotion/*physiology ; *Models, Biological ; }, abstract = {Biological flows over surfaces and interfaces can result in accumulation hotspots or depleted voids of microorganisms in natural environments. Apprehending the mechanisms that lead to such distributions is essential for understanding biofilm initiation. Using a systematic framework, we resolve the dynamics and statistics of swimming microbes within flowing films, considering the impact of confinement through steric and hydrodynamic interactions, flow and motility, along with Brownian and run-tumble fluctuations. Micro-swimmers can be peeled off the solid wall above a critical flow strength. However, the interplay of flow and fluctuations causes organisms to migrate back towards the wall above a secondary critical value. Hence, faster flows may not always be the most efficacious strategy to discourage biofilm initiation. Moreover, we find run-tumble dynamics commonly used by flagellated microbes to be an intrinsically more successful strategy to escape from boundaries than equivalent levels of enhanced Brownian noise in ciliated organisms.}, } @article {pmid26830757, year = {2016}, author = {Rosenberg, D and Marino, R and Herbert, C and Pouquet, A}, title = {Variations of characteristic time scales in rotating stratified turbulence using a large parametric numerical study.}, journal = {The European physical journal. E, Soft matter}, volume = {39}, number = {1}, pages = {8}, pmid = {26830757}, issn = {1292-895X}, abstract = {We study rotating stratified turbulence (RST) making use of numerical data stemming from a large parametric study varying the Reynolds, Froude and Rossby numbers, Re, Fr and Ro in a broad range of values. The computations are performed using periodic boundary conditions on grids of 1024(3) points, with no modeling of the small scales, no forcing and with large-scale random initial conditions for the velocity field only, and there are altogether 65 runs analyzed in this paper. The buoyancy Reynolds number defined as R(B) = ReFr2 varies from negligible values to ≈ 10(5), approaching atmospheric or oceanic regimes. This preliminary analysis deals with the variation of characteristic time scales of RST with dimensionless parameters, focusing on the role played by the partition of energy between the kinetic and potential modes, as a key ingredient for modeling the dynamics of such flows. We find that neither rotation nor the ratio of the Brunt-Väisälä frequency to the inertial frequency seem to play a major role in the absence of forcing in the global dynamics of the small-scale kinetic and potential modes. Specifically, in these computations, mostly in regimes of wave turbulence, characteristic times based on the ratio of energy to dissipation of the velocity and temperature fluctuations, T(V) and T(P), vary substantially with parameters. Their ratio γ=T(V)/T(P) follows roughly a bell-shaped curve in terms of Richardson number Ri. It reaches a plateau - on which time scales become comparable, γ≈0.6 - when the turbulence has significantly strengthened, leading to numerous destabilization events together with a tendency towards an isotropization of the flow.}, } @article {pmid26824542, year = {2016}, author = {Shishkina, O and Wagner, S}, title = {Prandtl-Number Dependence of Heat Transport in Laminar Horizontal Convection.}, journal = {Physical review letters}, volume = {116}, number = {2}, pages = {024302}, doi = {10.1103/PhysRevLett.116.024302}, pmid = {26824542}, issn = {1079-7114}, abstract = {We report the Prandtl-number (Pr) and Rayleigh-number (Ra) dependencies of the Reynolds number (Re) and mean convective heat transport, measured by the Nusselt number (Nu), in horizontal convection (HC) systems, where the heat supply and removal are provided exclusively through a lower horizontal surface of a fluid layer. For laminar HC, we find that Re∼Ra^{2/5} Pr^{-4/5}, Nu∼Ra^{1/5} Pr^{1/10} with a transition to Re∼Ra^{1/2} Pr^{-1}, Nu∼Ra^{1/4} Pr^{0} for large Pr. The results are based on direct numerical simulations for Ra from 3×10^{8} to 5×10^{10} and Pr from 0.05 to 50 and are explained by applying the Grossmann-Lohse approach [J. Fluid Mech. 407, 27 (2000)] transferred from the case of Rayleigh-Bénard convection to the case of laminar HC.}, } @article {pmid26821214, year = {2016}, author = {Maier, AM and Weig, C and Oswald, P and Frey, E and Fischer, P and Liedl, T}, title = {Magnetic Propulsion of Microswimmers with DNA-Based Flagellar Bundles.}, journal = {Nano letters}, volume = {16}, number = {2}, pages = {906-910}, pmid = {26821214}, issn = {1530-6992}, mesh = {Biocompatible Materials/*chemistry ; DNA/*chemistry ; Magnetic Fields ; Magnetite Nanoparticles/*chemistry ; Robotics/instrumentation ; }, abstract = {We show that DNA-based self-assembly can serve as a general and flexible tool to construct artificial flagella of several micrometers in length and only tens of nanometers in diameter. By attaching the DNA flagella to biocompatible magnetic microparticles, we provide a proof of concept demonstration of hybrid structures that, when rotated in an external magnetic field, propel by means of a flagellar bundle, similar to self-propelling peritrichous bacteria. Our theoretical analysis predicts that flagellar bundles that possess a length-dependent bending stiffness should exhibit a superior swimming speed compared to swimmers with a single appendage. The DNA self-assembly method permits the realization of these improved flagellar bundles in good agreement with our quantitative model. DNA flagella with well-controlled shape could fundamentally increase the functionality of fully biocompatible nanorobots and extend the scope and complexity of active materials.}, } @article {pmid26802269, year = {2016}, author = {Sultan, T and Ahmad, S and Cho, J}, title = {Numerical study of the effects of surface roughness on water disinfection UV reactor.}, journal = {Chemosphere}, volume = {148}, number = {}, pages = {108-117}, doi = {10.1016/j.chemosphere.2016.01.005}, pmid = {26802269}, issn = {1879-1298}, mesh = {*Bioreactors ; *Construction Materials ; Disinfection/*methods ; Hydrodynamics ; *Models, Theoretical ; Surface Properties ; *Ultraviolet Rays ; Water Pollutants/isolation & purification ; Water Purification/*methods ; }, abstract = {UV reactors are an emerging choice as a big barrier against the pathogens present in drinking water. However, the precise role of reactor's wall roughness for cross flow ultraviolet (CF-UV) and axial flow ultraviolet (AF-UV) water disinfection reactors are unknown. In this paper, the influences of reactor's wall roughness were investigated with a view to identify their role on the performance factors namely dose distribution and reduction equivalent dose (RED). Herein, the relative effects of reactor's wall roughness on the performance of CF-UV and AF-UV reactors were also highlighted. This numerical study is a first step towards the comprehensive analysis of the effects of reactor's wall roughness for UV reactor. A numerical analysis was performed using ANSYS Fluent 15 academic version. The reactor's wall roughness has a significant effect on the RED. We found that the increase in RED is Reynolds number dependent (at lower value of turbulent Reynolds number the effects are remarkable). The effects of reactor's roughness were more pronounced for AF-UV reactor. The simulation results suggest that the study of reactor's wall roughness provides valuable insight to fully understand the effects of reactor's wall roughness and its impact on the flow behavior and other features of CF-UV and AF-UV water disinfection reactors.}, } @article {pmid26780177, year = {2016}, author = {Agbesi, MP and Naylor, S and Perkins, E and Borsuk, HS and Sykes, D and Maclaine, JS and Wang, Z and Cox, JP}, title = {Complex flow in the nasal region of guitarfishes.}, journal = {Comparative biochemistry and physiology. Part A, Molecular & integrative physiology}, volume = {193}, number = {}, pages = {52-63}, doi = {10.1016/j.cbpa.2015.12.007}, pmid = {26780177}, issn = {1531-4332}, mesh = {Animals ; Fishes/metabolism/*physiology ; Nasal Cavity/metabolism/*physiology ; Respiration ; Smell/*physiology ; Swimming/physiology ; Water/metabolism ; }, abstract = {Scent detection in an aquatic environment is dependent on the movement of water. We set out to determine the mechanisms for moving water through the olfactory organ of guitarfishes (Rhinobatidae, Chondrichthyes) with open nasal cavities. We found at least two. In the first mechanism, which we identified by observing dye movement in the nasal region of a life-sized physical model of the head of Rhinobatos lentiginosus mounted in a flume, olfactory flow is generated by the guitarfish's motion relative to water, e.g. when it swims. We suggest that the pressure difference responsible for motion-driven olfactory flow is caused by the guitarfish's nasal flaps, which create a region of high pressure at the incurrent nostril, and a region of low pressure in and behind the nasal cavity. Vortical structures in the nasal region associated with motion-driven flow may encourage passage of water through the nasal cavity and its sensory channels, and may also reduce the cost of swimming. The arrangement of vortical structures is reminiscent of aircraft wing vortices. In the second mechanism, which we identified by observing dye movement in the nasal regions of living specimens of Glaucostegus typus, the guitarfish's respiratory pump draws flow through the olfactory organ in a rhythmic (0.5-2 Hz), but continuous, fashion. Consequently, the respiratory pump will maintain olfactory flow whether the guitarfish is swimming or at rest. Based on our results, we propose a model for olfactory flow in guitarfishes with open nasal cavities, and suggest other neoselachians which this model might apply to.}, } @article {pmid26775865, year = {2015}, author = {Wang, Q and Othmer, HG}, title = {The performance of discrete models of low Reynolds number swimmers.}, journal = {Mathematical biosciences and engineering : MBE}, volume = {12}, number = {6}, pages = {1303-1320}, doi = {10.3934/mbe.2015.12.1303}, pmid = {26775865}, issn = {1551-0018}, support = {GM29123-36/GM/NIGMS NIH HHS/United States ; }, mesh = {Animals ; Cell Movement/physiology ; Cell Shape/physiology ; Computer Simulation ; Dictyostelium/cytology/physiology ; Humans ; Mathematical Concepts ; Melanoma/pathology/physiopathology ; *Models, Biological ; Movement/*physiology ; }, abstract = {Swimming by shape changes at low Reynolds number is widely used in biology and understanding how the performance of movement depends on the geometric pattern of shape changes is important to understand swimming of microorganisms and in designing low Reynolds number swimming models. The simplest models of shape changes are those that comprise a series of linked spheres that can change their separation and/or their size. Herein we compare the performance of three models in which these modes are used in different ways.}, } @article {pmid26764831, year = {2015}, author = {Ebrahimian, M and Yekehzare, M and Ejtehadi, MR}, title = {Low-Reynolds-number predator.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {6}, pages = {063035}, doi = {10.1103/PhysRevE.92.063035}, pmid = {26764831}, issn = {1550-2376}, abstract = {To generalize simple bead-linker model of swimmers to higher dimensions and to demonstrate the chemotaxis ability of such swimmers, here we introduce a low-Reynolds predator, using a two-dimensional triangular bead-spring model. Two-state linkers as mechanochemical enzymes expand as a result of interaction with particular activator substances in the environment, causing the whole body to translate and rotate. The concentration of the chemical stimulator controls expansion versus the contraction rate of each arm and so affects the ability of the body for diffusive movements; also the variation of activator substance's concentration in the environment breaks the symmetry of linkers' preferred state, resulting in the drift of the random walker along the gradient of the density of activators. External food or danger sources may attract or repel the body by producing or consuming the chemical activators of the organism's enzymes, inducing chemotaxis behavior. Generalization of the model to three dimensions is straightforward.}, } @article {pmid26764821, year = {2015}, author = {Iyer, KP and Sreenivasan, KR and Yeung, PK}, title = {Refined similarity hypothesis using three-dimensional local averages.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {6}, pages = {063024}, doi = {10.1103/PhysRevE.92.063024}, pmid = {26764821}, issn = {1550-2376}, abstract = {The refined similarity hypotheses of Kolmogorov, regarded as an important ingredient of intermittent turbulence, has been tested in the past using one-dimensional data and plausible surrogates of energy dissipation. We employ data from direct numerical simulations, at the microscale Reynolds number R(λ)∼650, on a periodic box of 4096(3) grid points to test the hypotheses using three-dimensional averages. In particular, we study the small-scale properties of the stochastic variable V=Δu(r)/(rε(r))(1/3), where Δu(r) is the longitudinal velocity increment and ε(r) is the dissipation rate averaged over a three-dimensional volume of linear size r. We show that V is universal in the inertial subrange. In the dissipation range, the statistics of V are shown to depend solely on a local Reynolds number.}, } @article {pmid26764819, year = {2015}, author = {Rosén, T and Einarsson, J and Nordmark, A and Aidun, CK and Lundell, F and Mehlig, B}, title = {Numerical analysis of the angular motion of a neutrally buoyant spheroid in shear flow at small Reynolds numbers.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {6}, pages = {063022}, doi = {10.1103/PhysRevE.92.063022}, pmid = {26764819}, issn = {1550-2376}, abstract = {We numerically analyze the rotation of a neutrally buoyant spheroid in a shear flow at small shear Reynolds number. Using direct numerical stability analysis of the coupled nonlinear particle-flow problem, we compute the linear stability of the log-rolling orbit at small shear Reynolds number Re(a). As Re(a)→0 and as the box size of the system tends to infinity, we find good agreement between the numerical results and earlier analytical predictions valid to linear order in Re(a) for the case of an unbounded shear. The numerical stability analysis indicates that there are substantial finite-size corrections to the analytical results obtained for the unbounded system. We also compare the analytical results to results of lattice Boltzmann simulations to analyze the stability of the tumbling orbit at shear Reynolds numbers of order unity. Theory for an unbounded system at infinitesimal shear Reynolds number predicts a bifurcation of the tumbling orbit at aspect ratio λ(c)≈0.137 below which tumbling is stable (as well as log rolling). The simulation results show a bifurcation line in the λ-Re(a) plane that reaches λ≈0.1275 at the smallest shear Reynolds number (Re(a)=1) at which we could simulate with the lattice Boltzmann code, in qualitative agreement with the analytical results.}, } @article {pmid26764810, year = {2015}, author = {Deng, J and Sun, L and Shao, X}, title = {Dynamical features of the wake behind a pitching foil.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {6}, pages = {063013}, doi = {10.1103/PhysRevE.92.063013}, pmid = {26764810}, issn = {1550-2376}, abstract = {As an extension of the previous study on the three-dimensional transition of the wake behind a pitching foil [Deng and Caulfield, Phys. Rev. E 91, 043017 (2015)], this investigation draws a comprehensive map on the pitching frequency-amplitude phase space. First, by fixing the Reynolds number at Re=1700 and varying the pitching frequency and amplitude, we identify three key dynamical features of the wake: first, the transition from Bénard-von Kármán (BvK) vortex streets to reverse BvK vortex streets, and second, the symmetry breaking of this reverse BvK wake leading to a deflected wake, and a further transition from two-dimensional (2D) wakes to three-dimensional (3D) wakes. The transition boundary between the 2D and 3D wakes lies top right of the wake deflection boundary, implying a correlation between the wake deflection and the 2D to 3D wake transition, confirming that this transition occurs after the wake deflection. This paper supports the previous extensive numerical studies under two-dimensional assumption at low Reynolds number, since it is indeed two dimensional except for the cases at very high pitching frequencies or large amplitudes. Furthermore, by three-dimensional direct numerical simulations (DNSs), we confirm the previous statement about the physical realizability of the short wavelength mode at β=30 (or λ(z)=0.21) for Re=1500. By comparing the three-dimensional vortical structures by DNSs with that from the reconstruction of Floquet modes, we find a good consistency between them, both exhibiting clear streamwise structures in the wake.}, } @article {pmid26764807, year = {2015}, author = {Allouche, MH and Millet, S and Botton, V and Henry, D and Ben Hadid, H and Rousset, F}, title = {Stability of a flow down an incline with respect to two-dimensional and three-dimensional disturbances for Newtonian and non-Newtonian fluids.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {6}, pages = {063010}, doi = {10.1103/PhysRevE.92.063010}, pmid = {26764807}, issn = {1550-2376}, abstract = {Squire's theorem, which states that the two-dimensional instabilities are more dangerous than the three-dimensional instabilities, is revisited here for a flow down an incline, making use of numerical stability analysis and Squire relationships when available. For flows down inclined planes, one of these Squire relationships involves the slopes of the inclines. This means that the Reynolds number associated with a two-dimensional wave can be shown to be smaller than that for an oblique wave, but this oblique wave being obtained for a larger slope. Physically speaking, this prevents the possibility to directly compare the thresholds at a given slope. The goal of the paper is then to reach a conclusion about the predominance or not of two-dimensional instabilities at a given slope, which is of practical interest for industrial or environmental applications. For a Newtonian fluid, it is shown that, for a given slope, oblique wave instabilities are never the dominant instabilities. Both the Squire relationships and the particular variations of the two-dimensional wave critical curve with regard to the inclination angle are involved in the proof of this result. For a generalized Newtonian fluid, a similar result can only be obtained for a reduced stability problem where some term connected to the perturbation of viscosity is neglected. For the general stability problem, however, no Squire relationships can be derived and the numerical stability results show that the thresholds for oblique waves can be smaller than the thresholds for two-dimensional waves at a given slope, particularly for large obliquity angles and strong shear-thinning behaviors. The conclusion is then completely different in that case: the dominant instability for a generalized Newtonian fluid flowing down an inclined plane with a given slope can be three dimensional.}, } @article {pmid26764803, year = {2015}, author = {Anbarlooei, HR and Cruz, DO and Ramos, F and Silva Freire, AP}, title = {Phenomenological Blasius-type friction equation for turbulent power-law fluid flows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {6}, pages = {063006}, doi = {10.1103/PhysRevE.92.063006}, pmid = {26764803}, issn = {1550-2376}, abstract = {We propose a friction formula for turbulent power-law fluid flows, a class of purely viscous non-Newtonian fluids commonly found in applications. Our model is derived through an extension of the friction factor analysis based on Kolmogorov's phenomenology, recently proposed by Gioia and Chakraborty. Tests against classical empirical data show excellent agreement over a significant range of Reynolds number. Limits of the model are also discussed.}, } @article {pmid26739143, year = {2016}, author = {Low, SC and Eshtiaghi, N and Slatter, P and Baudez, JC and Parthasarathy, R}, title = {Mixing characteristics of sludge simulant in a model anaerobic digester.}, journal = {Bioprocess and biosystems engineering}, volume = {39}, number = {3}, pages = {473-483}, doi = {10.1007/s00449-015-1530-4}, pmid = {26739143}, issn = {1615-7605}, mesh = {*Models, Chemical ; Sewage/*chemistry ; }, abstract = {This study aims to investigate the mixing characteristics of a transparent sludge simulant in a mechanically agitated model digester using flow visualisation technique. Video images of the flow patterns were obtained by recording the progress of an acid-base reaction and analysed to determine the active and inactive volumes as a function of time. The doughnut-shaped inactive region formed above and below the impeller in low concentration simulant decreases in size with time and disappears finally. The 'cavern' shaped active mixing region formed around the impeller in simulant solutions with higher concentrations increases with increasing agitation time and reaches a steady state equilibrium size, which is a function of specific power input. These results indicate that the active volume is jointly determined by simulant rheology and specific power input. A mathematical correlation is proposed to estimate the active volume as a function of simulant concentration in terms of yield Reynolds number.}, } @article {pmid26738932, year = {2016}, author = {Jawed, MK and Reis, PM}, title = {Deformation of a soft helical filament in an axial flow at low Reynolds number.}, journal = {Soft matter}, volume = {12}, number = {6}, pages = {1898-1905}, doi = {10.1039/c5sm02625c}, pmid = {26738932}, issn = {1744-6848}, mesh = {Bacterial Physiological Phenomena ; Biomechanical Phenomena ; *Elasticity ; Flagella/*chemistry/physiology ; Models, Theoretical ; Movement ; Rotation ; }, abstract = {We perform a numerical investigation of the deformation of a rotating helical filament subjected to an axial flow, under low Reynolds number conditions, motivated by the propulsion of bacteria using helical flagella. Given its slenderness, the helical rod is intrinsically soft and deforms due to the interplay between elastic forces and hydrodynamic loading. We make use of a previously developed and experimentally validated computational tool framework that models the elasticity of the filament using the discrete elastic rod method and the fluid forces are treated using Lighthill's slender body theory. Under axial flow, and in the absence of rotation, the initially helical rod is extended. Above a critical flow speed its configuration comprises a straight portion connected to a localized helix near the free end. When the rod is also rotated about its helical axis, propulsion is only possible in a finite range of angular velocity, with an upper bound that is limited by buckling of the soft helix arising due to viscous stresses. A systematic exploration of the parameter space allows us to quantify regimes for successful propulsion for a number of specific bacteria.}, } @article {pmid26736424, year = {2015}, author = {Nita, C and Itu, L and Mihalef, V and Sharma, P and Rapaka, S}, title = {GPU-accelerated model for fast, three-dimensional fluid-structure interaction computations.}, journal = {Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual International Conference}, volume = {2015}, number = {}, pages = {965-968}, doi = {10.1109/EMBC.2015.7318524}, pmid = {26736424}, issn = {2694-0604}, mesh = {*Computer Simulation ; }, abstract = {In this paper we introduce a methodology for performing one-way Fluid-Structure interaction (FSI), i.e. where the motion of the wall boundaries is imposed. We use a Graphics Processing Unit (GPU) accelerated Lattice-Boltzmann Method (LBM) implementation and present an efficient workflow for embedding the moving geometry, given as a set of polygonal meshes, in the LBM computation. The proposed method is first validated in a synthetic experiment: a vessel which is periodically expanding and contracting. Next, the evaluation focuses on the 3D Peristaltic flow problem: a fluid flows inside a flexible tube, where a periodic wave-like deformation produces a fluid motion along the centerline of the tube. Different geometry configurations are used and results are compared against previously published solutions. The efficient approach leads to an average execution time of approx. one hour per computation, whereas 50% of it is required for the geometry update operations. Finally, we also analyse the effect of changing the Reynolds number on the flow streamlines: the flow regime is significantly affected by the Reynolds number.}, } @article {pmid26730219, year = {2015}, author = {Huang, D and Chernyshenko, S and Goulart, P and Lasagna, D and Tutty, O and Fuentes, F}, title = {Sum-of-squares of polynomials approach to nonlinear stability of fluid flows: an example of application.}, journal = {Proceedings. Mathematical, physical, and engineering sciences}, volume = {471}, number = {2183}, pages = {20150622}, pmid = {26730219}, issn = {1364-5021}, abstract = {With the goal of providing the first example of application of a recently proposed method, thus demonstrating its ability to give results in principle, global stability of a version of the rotating Couette flow is examined. The flow depends on the Reynolds number and a parameter characterizing the magnitude of the Coriolis force. By converting the original Navier-Stokes equations to a finite-dimensional uncertain dynamical system using a partial Galerkin expansion, high-degree polynomial Lyapunov functionals were found by sum-of-squares of polynomials optimization. It is demonstrated that the proposed method allows obtaining the exact global stability limit for this flow in a range of values of the parameter characterizing the Coriolis force. Outside this range a lower bound for the global stability limit was obtained, which is still better than the energy stability limit. In the course of the study, several results meaningful in the context of the method used were also obtained. Overall, the results obtained demonstrate the applicability of the recently proposed approach to global stability of the fluid flows. To the best of our knowledge, it is the first case in which global stability of a fluid flow has been proved by a generic method for the value of a Reynolds number greater than that which could be achieved with the energy stability approach.}, } @article {pmid26723345, year = {2015}, author = {Phong, V and Papamoschou, D}, title = {Normal incidence acoustic insertion loss of perforated plates with bias flow.}, journal = {The Journal of the Acoustical Society of America}, volume = {138}, number = {6}, pages = {3907-3921}, doi = {10.1121/1.4937602}, pmid = {26723345}, issn = {1520-8524}, abstract = {The transmission of sound at normal incidence through perforated plates with bias flow is investigated experimentally and theoretically over a large parameter space. A specially designed experimental apparatus enabled the measurement of insertion loss with bias flow Mach number up to 0.25. A theoretical model for insertion loss was constructed based on inviscid, one-dimensional wave propagation with mean flow through a single contraction/expansion chamber. The mass end correction of the contraction is modified for hole interaction effects and mean flow. Hydrodynamic losses are modeled using a vena contracta coefficient dependent on both perforation geometry and Reynolds number. Losses in acoustic energy that occur in the mixing region downstream of the perforations are modeled as fluctuations in entropy. The proposed model was validated experimentally over a range of plate thickness, porosity, and hole size. The experimental results indicate an increase in insertion loss with increasing frequency, followed by saturation and decline as resonant conditions are established in the perforations. The insertion loss at low frequency increases with increasing Mach number through the perforation. The proposed model captures these trends and its predictions are shown to be more accurate than those of past models.}, } @article {pmid26718062, year = {2016}, author = {O Connor, J and Revell, A and Mandal, P and Day, P}, title = {Application of a lattice Boltzmann-immersed boundary method for fluid-filament dynamics and flow sensing.}, journal = {Journal of biomechanics}, volume = {49}, number = {11}, pages = {2143-2151}, doi = {10.1016/j.jbiomech.2015.11.057}, pmid = {26718062}, issn = {1873-2380}, mesh = {Cilia/metabolism ; Computer Simulation ; Cytoskeleton/metabolism ; Humans ; *Hydrodynamics ; Models, Biological ; Shear Strength ; Stress, Mechanical ; }, abstract = {Complex fluid-structure interactions between elastic filaments, or cilia, immersed in viscous flows are commonplace in nature and bear important roles. Some biological systems have evolved to interpret flow-induced motion into signals for the purpose of feedback response. Given the challenges associated with extracting meaningful experimental data at this scale, there has been particular focus on the numerical study of these effects. Porous models have proven useful where cilia arrangements are relatively dense, but for more sparse configurations the dynamic interactions of individual structures play a greater role and direct modelling becomes increasingly necessary. The present study reports efforts towards explicit modelling of regularly spaced wall-mounted cilia using a lattice Boltzmann-immersed boundary method. Both steady and forced unsteady 2D channel flows at different Reynolds numbers are investigated, with and without the presence of a periodic array of elastic inextensible filaments. It is demonstrated that the structure response depends significantly on Reynolds number. For low Reynolds flow, the recirculation vortex aft of successive filaments is small relative to the cilia spacing and does not fully bridge the gap, in which case the structure lags the flow. At higher Reynolds number, when this gap is fully bridged the structure and flow move in phase. The trapping of vortices between cilia is associated with relatively lower wall shear stress. At low to intermediate Reynolds, vortex bridging is incomplete and large deflection is still possible, which is reflected in the tip dynamics and wall shear stress profiles.}, } @article {pmid26705658, year = {2015}, author = {Klotsa, D and Baldwin, KA and Hill, RJ and Bowley, RM and Swift, MR}, title = {Propulsion of a Two-Sphere Swimmer.}, journal = {Physical review letters}, volume = {115}, number = {24}, pages = {248102}, doi = {10.1103/PhysRevLett.115.248102}, pmid = {26705658}, issn = {1079-7114}, mesh = {Biomechanical Phenomena ; Computer Simulation ; *Models, Theoretical ; *Swimming ; }, abstract = {We describe experiments and simulations demonstrating the propulsion of a neutrally buoyant swimmer that consists of a pair of spheres attached by a spring, immersed in a vibrating fluid. The vibration of the fluid induces relative motion of the spheres which, for sufficiently large amplitudes, can lead to motion of the center of mass of the two spheres. We find that the swimming speed obtained from both experiment and simulation agree and collapse onto a single curve if plotted as a function of the streaming Reynolds number, suggesting that the propulsion is related to streaming flows. There appears to be a critical onset value of the streaming Reynolds number for swimming to occur. We observe a change in the streaming flows as the Reynolds number increases, from that generated by two independent oscillating spheres to a collective flow pattern around the swimmer as a whole. The mechanism for swimming is traced to a strengthening of a jet of fluid in the wake of the swimmer.}, } @article {pmid26698964, year = {2015}, author = {Hay, RF and Gibson, GM and Simpson, SH and Padgett, MJ and Phillips, DB}, title = {'Lissajous-like' trajectories in optical tweezers.}, journal = {Optics express}, volume = {23}, number = {25}, pages = {31716-31727}, doi = {10.1364/OE.23.031716}, pmid = {26698964}, issn = {1094-4087}, abstract = {When a microscopic particle moves through a low Reynolds number fluid, it creates a flow-field which exerts hydrodynamic forces on surrounding particles. In this work we study the 'Lissajous-like' trajectories of an optically trapped 'probe' microsphere as it is subjected to time-varying oscillatory hydrodynamic flow-fields created by a nearby moving particle (the 'actuator'). We show a breaking of time-reversal symmetry in the motion of the probe when the driving motion of the actuator is itself time-reversal symmetric. This symmetry breaking results in a fluid-pumping effect, which arises due to the action of both a time-dependent hydrodynamic flow and a position-dependent optical restoring force, which together determine the trajectory of the probe particle. We study this situation experimentally, and show that the form of the trajectories observed is in good agreement with Stokesian dynamics simulations. Our results are related to the techniques of active micro-rheology and flow measurement, and also highlight how the mere presence of an optical trap can perturb the environment it is in place to measure.}, } @article {pmid26684120, year = {2015}, author = {Stepanov, R and Golbraikh, E and Frick, P and Shestakov, A}, title = {Hindered Energy Cascade in Highly Helical Isotropic Turbulence.}, journal = {Physical review letters}, volume = {115}, number = {23}, pages = {234501}, doi = {10.1103/PhysRevLett.115.234501}, pmid = {26684120}, issn = {1079-7114}, abstract = {The conventional approach to the turbulent energy cascade, based on Richardson-Kolmogorov phenomenology, ignores the topology of emerging vortices, which is related to the helicity of the turbulent flow. It is generally believed that helicity can play a significant role in turbulent systems, e.g., supporting the generation of large-scale magnetic fields, but its impact on the energy cascade to small scales has never been observed. We suggest, for the first time, a generalized phenomenology for isotropic turbulence with an arbitrary spectral distribution of the helicity. We discuss various scenarios of direct turbulent cascades with new helicity effect, which can be interpreted as a hindering of the spectral energy transfer. Therefore, the energy is accumulated and redistributed so that the efficiency of nonlinear interactions will be sufficient to provide a constant energy flux. We confirm our phenomenology by high Reynolds number numerical simulations based on a shell model of helical turbulence. The energy in our model is injected at a certain large scale only, whereas the source of helicity is distributed over all scales. In particular, we found that the helical bottleneck effect can appear in the inertial interval of the energy spectrum.}, } @article {pmid26671398, year = {2015}, author = {Zia, RN and Swan, JW and Su, Y}, title = {Pair mobility functions for rigid spheres in concentrated colloidal dispersions: Force, torque, translation, and rotation.}, journal = {The Journal of chemical physics}, volume = {143}, number = {22}, pages = {224901}, doi = {10.1063/1.4936664}, pmid = {26671398}, issn = {1089-7690}, abstract = {The formulation of detailed models for the dynamics of condensed soft matter including colloidal suspensions and other complex fluids requires accurate description of the physical forces between microstructural constituents. In dilute suspensions, pair-level interactions are sufficient to capture hydrodynamic, interparticle, and thermodynamic forces. In dense suspensions, many-body interactions must be considered. Prior analytical approaches to capturing such interactions such as mean-field approaches replace detailed interactions with averaged approximations. However, long-range coupling and effects of concentration on local structure, which may play an important role in, e.g., phase transitions, are smeared out in such approaches. An alternative to such approximations is the detailed modeling of hydrodynamic interactions utilizing precise couplings between moments of the hydrodynamic traction on a suspended particle and the motion of that or other suspended particles. For two isolated spheres, a set of these functions was calculated by Jeffrey and Onishi [J. Fluid Mech. 139, 261-290 (1984)] and Jeffrey [J. Phys. Fluids 4, 16-29 (1992)]. Along with pioneering work by Batchelor, these are the touchstone for low-Reynolds-number hydrodynamic interactions and have been applied directly in the solution of many important problems related to the dynamics of dilute colloidal dispersions [G. K. Batchelor and J. T. Green, J. Fluid Mech. 56, 375-400 (1972) and G. K. Batchelor, J. Fluid Mech. 74, 1-29 (1976)]. Toward extension of these functions to concentrated systems, here we present a new stochastic sampling technique to rapidly calculate an analogous set of mobility functions describing the hydrodynamic interactions between two hard spheres immersed in a suspension of arbitrary concentration, utilizing accelerated Stokesian dynamics simulations. These mobility functions provide precise, radially dependent couplings of hydrodynamic force and torque to particle translation and rotation, for arbitrary colloid volume fraction ϕ. The pair mobilities (describing entrainment of one particle by the disturbance flow created by another) decay slowly with separation distance: as 1/r, for volume fractions 0.05 ≤ ϕ ≤ 0.5. For the relative mobility, we find an initially rapid growth as a pair separates, followed by a slow, 1/r growth. Up to ϕ ≤ 0.4, the relative mobility does not reached the far-field value even beyond separations of many particle sizes. In the case of ϕ = 0.5, the far-field asymptote is reached but only at a separation of eight radii and after a slow 1/r growth. At these higher concentrations, the coefficients also reveal liquid-like structural effects on pair mobility at close separations. These results confirm that long-range many-body hydrodynamic interactions are an essential part of the dynamics of concentrated systems and that care must be taken when applying renormalization schemes.}, } @article {pmid26652667, year = {2015}, author = {Schultz, MP and Walker, JM and Steppe, CN and Flack, KA}, title = {Impact of diatomaceous biofilms on the frictional drag of fouling-release coatings.}, journal = {Biofouling}, volume = {31}, number = {9-10}, pages = {759-773}, doi = {10.1080/08927014.2015.1108407}, pmid = {26652667}, issn = {1029-2454}, mesh = {Biofilms/*growth & development ; Biofouling/*prevention & control ; *Friction ; Models, Theoretical ; *Paint ; *Ships ; Surface Properties ; }, abstract = {Skin-friction results are presented for fouling-release (FR) hull coatings in the unexposed, clean condition and after dynamic exposure to diatomaceous biofilms for 3 and 6 months. The experiments were conducted in a fully developed turbulent channel flow facility spanning a wide Reynolds number range. The results show that the clean FR coatings tested were hydraulically smooth over much of the Reynolds number range. Biofilms, however, resulted in an increase in skin-friction of up to 70%. The roughness functions for the biofilm-covered surfaces did not display universal behavior, but instead varied with the percentage coverage by the biofilm. The effect of the biofilm was observed to scale with its mean thickness and the square root of the percentage coverage. A new effective roughness length scale (keff) for biofilms based on these parameters is proposed. Boundary layer similarity-law scaling is used to predict the impact of these biofilms on the required shaft power for a mid-sized naval surface combatant at cruising speed. The increase in power is estimated to be between 1.5% and 10.1% depending on the biofilm thickness and percentage coverage.}, } @article {pmid26651792, year = {2015}, author = {Minier, JP and Profeta, C}, title = {Kinetic and dynamic probability-density-function descriptions of disperse turbulent two-phase flows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {5}, pages = {053020}, doi = {10.1103/PhysRevE.92.053020}, pmid = {26651792}, issn = {1550-2376}, abstract = {This article analyzes the status of two classical one-particle probability density function (PDF) descriptions of the dynamics of discrete particles dispersed in turbulent flows. The first PDF formulation considers only the process made up by particle position and velocity Z(p)=(x(p),U(p)) and is represented by its PDF p(t; y(p),V(p)) which is the solution of a kinetic PDF equation obtained through a flux closure based on the Furutsu-Novikov theorem. The second PDF formulation includes fluid variables into the particle state vector, for example, the fluid velocity seen by particles Z(p)=(x(p),U(p),U(s)), and, consequently, handles an extended PDF p(t; y(p),V(p),V(s)) which is the solution of a dynamic PDF equation. For high-Reynolds-number fluid flows, a typical formulation of the latter category relies on a Langevin model for the trajectories of the fluid seen or, conversely, on a Fokker-Planck equation for the extended PDF. In the present work, a new derivation of the kinetic PDF equation is worked out and new physical expressions of the dispersion tensors entering the kinetic PDF equation are obtained by starting from the extended PDF and integrating over the fluid seen. This demonstrates that, under the same assumption of a Gaussian colored noise and irrespective of the specific stochastic model chosen for the fluid seen, the kinetic PDF description is the marginal of a dynamic PDF one. However, a detailed analysis reveals that kinetic PDF models of particle dynamics in turbulent flows described by statistical correlations constitute incomplete stand-alone PDF descriptions and, moreover, that present kinetic-PDF equations are mathematically ill posed. This is shown to be the consequence of the non-Markovian characteristic of the stochastic process retained to describe the system and the use of an external colored noise. Furthermore, developments bring out that well-posed PDF descriptions are essentially due to a proper choice of the variables selected to describe physical systems and guidelines are formulated to emphasize the key role played by the notion of slow and fast variables.}, } @article {pmid26651790, year = {2015}, author = {Altmeyer, S and Do, Y and Lai, YC}, title = {Ring-bursting behavior en route to turbulence in narrow-gap Taylor-Couette flows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {5}, pages = {053018}, doi = {10.1103/PhysRevE.92.053018}, pmid = {26651790}, issn = {1550-2376}, abstract = {We investigate the Taylor-Couette system where the radius ratio is close to unity. Systematically increasing the Reynolds number, we observe a number of previously known transitions, such as one from the classical Taylor vortex flow (TVF) to wavy vortex flow (WVF) and the transition to fully developed turbulence. Prior to the onset of turbulence, we observe intermittent bursting patterns of localized turbulent patches, confirming the experimentally observed pattern of very short wavelength bursts (VSWBs). A striking finding is that, for a Reynolds number larger than that for the onset of VSWBs, a new type of intermittently bursting behavior emerges: patterns of azimuthally closed rings of various orders. We call them ring-bursting patterns, which surround the cylinder completely but remain localized and separated in the axial direction through nonturbulent wavy structures. We employ a number of quantitative measures including the cross-flow energy to characterize the ring-bursting patterns and to distinguish them from the background flow. These patterns are interesting because they do not occur in the wide-gap Taylor-Couette flow systems. The narrow-gap regime is less studied but certainly deserves further attention to gain deeper insights into complex flow dynamics in fluids.}, } @article {pmid26636667, year = {2016}, author = {Dey, KK and Pong, FY and Breffke, J and Pavlick, R and Hatzakis, E and Pacheco, C and Sen, A}, title = {Dynamic Coupling at the Ångström Scale.}, journal = {Angewandte Chemie (International ed. in English)}, volume = {55}, number = {3}, pages = {1113-1117}, doi = {10.1002/anie.201509237}, pmid = {26636667}, issn = {1521-3773}, abstract = {While momentum transfer from active particles to their immediate surroundings has been studied for both synthetic and biological micron-scale systems, a similar phenomenon was presumed unlikely to exist at smaller length scales due to the dominance of viscosity in the ultralow Reynolds number regime. Using diffusion NMR spectroscopy, we studied the motion of two passive tracers--tetramethylsilane and benzene--dissolved in an organic solution of active Grubbs catalyst. Significant enhancements in diffusion were observed for both the tracers and the catalyst as a function of reaction rate. A similar behavior was also observed for the enzyme urease in aqueous solution. Surprisingly, momentum transfer at the molecular scale closely resembles that reported for microscale systems and appears to be independent of swimming mechanism. Our work provides new insight into the role of active particles on advection and mixing at the Ångström scale.}, } @article {pmid26628288, year = {2015}, author = {Wang, S and Ardekani, AM}, title = {Biogenic mixing induced by intermediate Reynolds number swimming in stratified fluids.}, journal = {Scientific reports}, volume = {5}, number = {}, pages = {17448}, pmid = {26628288}, issn = {2045-2322}, mesh = {Animals ; Humans ; *Models, Theoretical ; *Swimming ; }, abstract = {We study fully resolved motion of interacting swimmers in density stratified fluids using an archetypal swimming model called "squirmer". The intermediate Reynolds number regime is particularly important, because the vast majority of organisms in the aphotic ocean (i.e. regions that are 200 m beneath the sea surface) are small (mm-cm) and their motion is governed by the balance of inertial and viscous forces. Our study shows that the mixing efficiency and the diapycnal eddy diffusivity, a measure of vertical mass flux, within a suspension of squirmers increases with Reynolds number. The mixing efficiency is in the range of O(0.0001-0.04) when the swimming Reynolds number is in the range of O(0.1-100). The values of diapycnal eddy diffusivity and Cox number are two orders of magnitude larger for vertically swimming cells compared to horizontally swimming cells. For a suspension of squirmers in a decaying isotropic turbulence, we find that the diapycnal eddy diffusivity enhances due to the strong viscous dissipation generated by squirmers as well as the interaction of squirmers with the background turbulence.}, } @article {pmid26621672, year = {2016}, author = {Avari, H and Savory, E and Rogers, KA}, title = {An In Vitro Hemodynamic Flow System to Study the Effects of Quantified Shear Stresses on Endothelial Cells.}, journal = {Cardiovascular engineering and technology}, volume = {7}, number = {1}, pages = {44-57}, doi = {10.1007/s13239-015-0250-x}, pmid = {26621672}, issn = {1869-4098}, support = {//Canadian Institutes of Health Research/Canada ; }, mesh = {Animals ; Biomechanical Phenomena/physiology ; Cells, Cultured ; Endothelial Cells/*physiology ; Endothelium, Vascular/cytology/*physiology ; Hemodynamics/*physiology ; Laser-Doppler Flowmetry ; *Models, Cardiovascular ; Stress, Mechanical ; Swine ; }, abstract = {Numerous in vitro systems have previously been developed and employed for studying the effects of hemodynamics on endothelial cell (EC) dysfunction. In the majority of that work, accurate flow quantification (e.g., uniformity of the flow over the ECs) remains elusive and wall shear stress (WSS) quantifications are determined using theoretical relationships (without considering the flow channel aspect ratio effects). In addition, those relationships are not applicable to flows other than steady laminar cases. The present work discusses the development of a novel hemodynamic flow system for studying the effects of various well-quantified flow regimes over ECs. The current work presents a novel hemodynamic flow system applying the concept of a parallel plate flow chamber (PPFC) with live microscopy access for studying the effects of quantified WSS on ECs. A range of steady laminar, pulsatile (carotid wave form) and low-Reynolds number turbulent WSSs were quantified through velocity field measurements by a laser Doppler velocimetry (LDV) system, to validate the functionality of the current hemodynamic flow system. Uniformity of the flow across the channel width can be analyzed with the current system (e.g., the flow was uniform across about 65-75% of the channel width for the steady cases). The WSS obtained from the experiments had higher values in almost all of the cases when compared to the most commonly-used theoretical solution (9% < error < 16%), whereas another relationship, which considers the channel dimensions, had better agreement with the experimental results (1% < error < 8%). Additionally, the latter relationship predicted the uniform flow region in the PPFC with an average difference of <5% when compared to the experimental results. The experimental data also showed that the WSS at various locations (D, E and F) at the test section differed by less than 4% for the laminar cases representing a fully developed flow. WSS was also determined for a low-Re (Re = 2750) turbulent flow using (1) the Reynolds shears stress and (2) the time-averaged velocity profile gradient at the wall, with a good agreement (differences <16%) between the two where the first method returned a higher value than the second. Porcine aortic endothelial cell (PAEC) viability in the system and morphological cell response to laminar WSS of about 11 dyne/cm(2), were observed. These results provide performance validation of this novel in vitro system with many improved features compared to previous similar prototypes for investigation of flow effects on ECs. The integration of the LDV technique in the current study and the comparison of the results with those from theory revealed that great care must be taken when using PPFCs since the commonly used theoretical relation for laminar steady flows is unable to predict the flow uniformity (which may introduce significant statistical bias in biological studies) and the predicted WSS was subjected to greater error when compared to a more comprehensive equation presented in the current work. Moreover, application of the LDV technique in the current system is essential for studies of more complex cases, such as disturbed flows, where the WSS cannot be predicted using theoretical or numerical modelling methods.}, } @article {pmid26598001, year = {2015}, author = {Gaddam, A and Agrawal, A and Joshi, SS and Thompson, MC}, title = {Utilization of Cavity Vortex To Delay the Wetting Transition in One-Dimensional Structured Microchannels.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {31}, number = {49}, pages = {13373-13384}, doi = {10.1021/acs.langmuir.5b03666}, pmid = {26598001}, issn = {1520-5827}, abstract = {Frictional resistance across rough surfaces depends on the existence of slip on the liquid-gas interface; therefore, prolonging the existence of liquid-gas interface becomes relevant. In this work, we explore manipulation of the cavity shape in order to delay the wetting transition. We propose that liquid-driven vortices generated in the air cavity dissipate sufficient energy to delay the Cassie-Wenzel transition. Toward this, we fabricated cavities on the side walls of a polydimethylsiloxane-based microchannel for easy visualization and analysis of the dynamics of the liquid-gas interface. Two distinct flow regimes are identified in the experimental envelope. In the first regime, the liquid-gas interface is found to be protruding into the flow field, thus increasing the pressure drop at low Reynolds number. In the second regime, flow rate and geometry-based wetting transitions are established at moderate to high Reynolds numbers. We then investigate the effect of different cavity shapes (square, trapezoidal, and U-shape) in delaying the wetting transition by manipulating liquid-driven vortices. Out of the shapes considered in this study, trapezoidal cavities perform better than cavities with vertical walls in delaying the wetting transition due to geometrical squeezing of vortices toward the liquid-gas interface. Numerical simulations corroborate the experimental findings in that cavities with inclined walls exert more force on the liquid-gas interface, thus delaying their wetting transition. The proposed method being passive in nature appears more attractive than previous active methods.}, } @article {pmid26593731, year = {2016}, author = {Sekhar, YR and Sharma, KV and Kamal, S}, title = {Nanofluid heat transfer under mixed convection flow in a tube for solar thermal energy applications.}, journal = {Environmental science and pollution research international}, volume = {23}, number = {10}, pages = {9411-9417}, doi = {10.1007/s11356-015-5715-9}, pmid = {26593731}, issn = {1614-7499}, mesh = {*Convection ; *Hot Temperature ; *Nanoparticles ; *Solar Energy ; Water ; }, abstract = {The solar flat plate collector operating under different convective modes has low efficiency for energy conversion. The energy absorbed by the working fluid in the collector system and its heat transfer characteristics vary with solar insolation and mass flow rate. The performance of the system is improved by reducing the losses from the collector. Various passive methods have been devised to aid energy absorption by the working fluid. Also, working fluids are modified using nanoparticles to improve the thermal properties of the fluid. In the present work, simulation and experimental studies are undertaken for pipe flow at constant heat flux boundary condition in the mixed convection mode. The working fluid at low Reynolds number in the mixed laminar flow range is undertaken with water in thermosyphon mode for different inclination angles of the tube. Local and average coefficients are determined experimentally and compared with theoretical values for water-based Al2O3 nanofluids. The results show an enhancement in heat transfer in the experimental range with Rayleigh number at higher inclinations of the collector tube for water and nanofluids.}, } @article {pmid26590151, year = {2015}, author = {Rolland, J}, title = {Stochastic analysis of the time evolution of laminar-turbulent bands of plane Couette flow.}, journal = {The European physical journal. E, Soft matter}, volume = {38}, number = {11}, pages = {121}, pmid = {26590151}, issn = {1292-895X}, abstract = {This article is concerned with the time evolution of the oblique laminar-turbulent bands of transitional plane Couette flow under the influence of turbulent noise. Our study is focused on the amplitude of modulation of turbulence (the bands). In order to guide the numerical study of the flow, we first perform an analytical and numerical analysis of a Stochastic Ginzburg-Landau (GL) equation for a complex order parameter. The modulus of this order parameter models the amplitude of modulation of turbulence. Firstly, we compute the autocorrelation function of said modulus once the band is established. Secondly, we perform a calculation of average and fluctuations around the exponential growth of the order parameter. This type of analysis is similar to the Stochastic Structural Stability Theory (S3T). We then perform numerical simulations of the Navier-Stokes equations in order to confront these predictions with the actual behaviour of the bands. Computation of the autocorrelation function of the modulation of turbulence shows quantitative agreement with the model: in the established band regime, the amplitude of modulation follows an Ornstein-Uhlenbeck process. In order to test the S3T predictions, we perform quench experiments, sudden decreases of the Reynolds number from uniform turbulence, in which modulation appears. We compute the average evolution of the amplitude of modulation and the fluctuations around it. We find good agreement between numerics and modeling. The average trajectory grows exponentially, at a rate clearly smaller than that of the formation of laminar holes. Meanwhile, the actual time evolution remains in a flaring envelope, centered on the average, and expanding at the same rate. These results provide further validation of the stochastic modeling for the time evolution of the bands for further studies. Besides, they stress on the difference between the oblique band formation and the formation of laminar holes.}, } @article {pmid26584257, year = {2016}, author = {Zhang, J and Yan, S and Yuan, D and Alici, G and Nguyen, NT and Ebrahimi Warkiani, M and Li, W}, title = {Fundamentals and applications of inertial microfluidics: a review.}, journal = {Lab on a chip}, volume = {16}, number = {1}, pages = {10-34}, doi = {10.1039/c5lc01159k}, pmid = {26584257}, issn = {1473-0189}, mesh = {Humans ; *Microfluidic Analytical Techniques ; Particle Size ; Surface Properties ; }, abstract = {In the last decade, inertial microfluidics has attracted significant attention and a wide variety of channel designs that focus, concentrate and separate particles and fluids have been demonstrated. In contrast to conventional microfluidic technologies, where fluid inertia is negligible and flow remains almost within the Stokes flow region with very low Reynolds number (Re ≪ 1), inertial microfluidics works in the intermediate Reynolds number range (~1 < Re < ~100) between Stokes and turbulent regimes. In this intermediate range, both inertia and fluid viscosity are finite and bring about several intriguing effects that form the basis of inertial microfluidics including (i) inertial migration and (ii) secondary flow. Due to the superior features of high-throughput, simplicity, precise manipulation and low cost, inertial microfluidics is a very promising candidate for cellular sample processing, especially for samples with low abundant targets. In this review, we first discuss the fundamental kinematics of particles in microchannels to familiarise readers with the mechanisms and underlying physics in inertial microfluidic systems. We then present a comprehensive review of recent developments and key applications of inertial microfluidic systems according to their microchannel structures. Finally, we discuss the perspective of employing fluid inertia in microfluidics for particle manipulation. Due to the superior benefits of inertial microfluidics, this promising technology will still be an attractive topic in the near future, with more novel designs and further applications in biology, medicine and industry on the horizon.}, } @article {pmid26577358, year = {2015}, author = {Clark, WD and Eslahpazir, BA and Argueta-Morales, IR and Kassab, AJ and Divo, EA and DeCampli, WM}, title = {Comparison Between Bench-Top and Computational Modelling of Cerebral Thromboembolism in Ventricular Assist Device Circulation.}, journal = {Cardiovascular engineering and technology}, volume = {6}, number = {3}, pages = {242-255}, doi = {10.1007/s13239-015-0230-1}, pmid = {26577358}, issn = {1869-4098}, mesh = {Carotid Arteries/*physiopathology ; Cerebral Cortex/*blood supply ; Coronary Artery Bypass/methods ; *Heart-Assist Devices ; Hydrodynamics ; Intracranial Thrombosis/*physiopathology ; *Models, Cardiovascular ; }, abstract = {Despite improvements in ventricular assist devices (VAD) design, VAD-induced stroke rates remain remarkably high at 14-47%. We previously employed computational fluid dynamics (CFD) to propose adjustment of VAD outflow graft (VAD-OG) implantation to reduce stoke. Herein, we present an in-vitro model of cerebral vessel embolization in VAD-assisted circulation, and compare benchtop results to CFD predictions. The benchtop flow-loop consists of a 3D printed aortic bed using Accura 60 polymer driven by a continuous-flow pump. Three hundred spherical particles simulating thrombi of 2, 3.5, and 5 mm diameters were injected at the mock VAD-OG inlet. A water and glycerin mixture (3.8 cP viscosity) synthetically mimicked blood. The flowrate was adjusted to match the CFD Reynolds number. Catch cans were used to capture and count particles reaching cerebral vessels. VAD-OG geometries were evaluated using comparison of means Z-score range of -1.96 ≤ Z ≤ 1.96 to demonstrate overall agreement between computational and in-vitro techniques. Z-scores were: (i) Z = -1.05 for perpendicular (0°), (ii) Z = 0.32 for intermediate (30°), and (iii) Z = -0.52 for shallow (60°) anastomosis and confirmed agreement for all geometries. This study confirmed added benefits of using a left carotid artery bypass-graft with percent embolization reduction: 22.6% for perpendicular, 21.2% for intermediate, and 11.9% for shallow anastomoses. The shallow anastomosis demonstrated lower degrees of aortic arch flow recirculation, consistent with steady-flow computations. Quantitatively and qualitatively, contemporary steady-flow computational models for predicting VAD-induced cerebral embolization can be achieved in-vitro to validate the CFD equivalent.}, } @article {pmid26565499, year = {2015}, author = {Gravish, N and Peters, JM and Combes, SA and Wood, RJ}, title = {Collective Flow Enhancement by Tandem Flapping Wings.}, journal = {Physical review letters}, volume = {115}, number = {18}, pages = {188101}, doi = {10.1103/PhysRevLett.115.188101}, pmid = {26565499}, issn = {1079-7114}, abstract = {We examine the fluid-mechanical interactions that occur between arrays of flapping wings when operating in close proximity at a moderate Reynolds number (Re≈100-1000). Pairs of flapping wings are oscillated sinusoidally at frequency f, amplitude θ_{M}, phase offset ϕ, and wing separation distance D^{*}, and outflow speed v^{*} is measured. At a fixed separation distance, v^{*} is sensitive to both f and ϕ, and we observe both constructive and destructive interference in airspeed. v^{*} is maximized at an optimum phase offset, ϕ_{max}, which varies with wing separation distance, D^{*} . We propose a model of collective flow interactions between flapping wings based on vortex advection, which reproduces our experimental data.}, } @article {pmid26565366, year = {2015}, author = {Bösch, F and Chikatamarla, SS and Karlin, IV}, title = {Entropic multirelaxation lattice Boltzmann models for turbulent flows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {4}, pages = {043309}, doi = {10.1103/PhysRevE.92.043309}, pmid = {26565366}, issn = {1550-2376}, abstract = {We present three-dimensional realizations of a class of lattice Boltzmann models introduced recently by the authors [I. V. Karlin, F. Bösch, and S. S. Chikatamarla, Phys. Rev. E 90, 031302(R) (2014)] and review the role of the entropic stabilizer. Both coarse- and fine-grid simulations are addressed for the Kida vortex flow benchmark. We show that the outstanding numerical stability and performance is independent of a particular choice of the moment representation for high-Reynolds-number flows. We report accurate results for low-order moments for homogeneous isotropic decaying turbulence and second-order grid convergence for most assessed statistical quantities. It is demonstrated that all the three-dimensional lattice Boltzmann realizations considered herein converge to the familiar lattice Bhatnagar-Gross-Krook model when the resolution is increased. Moreover, thanks to the dynamic nature of the entropic stabilizer, the present model features less compressibility effects and maintains correct energy and enstrophy dissipation. The explicit and efficient nature of the present lattice Boltzmann method renders it a promising candidate for both engineering and scientific purposes for highly turbulent flows.}, } @article {pmid26565347, year = {2015}, author = {Perrin, VE and Jonker, HJ}, title = {Relative velocity distribution of inertial particles in turbulence: A numerical study.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {4}, pages = {043022}, doi = {10.1103/PhysRevE.92.043022}, pmid = {26565347}, issn = {1550-2376}, abstract = {The distribution of relative velocities between particles provides invaluable information on the rates and characteristics of particle collisions. We show that the theoretical model of Gustavsson and Mehlig [K. Gustavsson and B. Mehlig, J. Turbul. 15, 34 (2014)], within its anticipated limits of validity, can predict the joint probability density function of relative velocities and separations of identical inertial particles in isotropic turbulent flows with remarkable accuracy. We also quantify the validity range of the model. The model matches two limits (or two types) of relative motion between particles: one where pair diffusion dominates (i.e., large coherence between particle motion) and one where caustics dominate (i.e., large velocity differences between particles at small separations). By using direct numerical simulation combined with Lagrangian particle tracking, we assess the model prediction in homogeneous and isotropic turbulence. We demonstrate that, when sufficient caustics are present at a given separation and the particle response time is significantly smaller than the integral time scales of the flow, the distribution exhibits the same universal power-law form dictated by the correlation dimension as predicted by the model of Gustavsson and Mehlig. In agreement with the model, no strong dependency on the Taylor-based Reynolds number is observed.}, } @article {pmid26565336, year = {2015}, author = {Kim, I and Wu, XL}, title = {Unified Strouhal-Reynolds number relationship for laminar vortex streets generated by different-shaped obstacles.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {4}, pages = {043011}, doi = {10.1103/PhysRevE.92.043011}, pmid = {26565336}, issn = {1550-2376}, abstract = {A structure-based Strouhal-Reynolds number relationship, St=1/(A+B/Re), has been recently proposed based on observations of laminar vortex shedding from circular cylinders in a flowing soap film. Since the new St-Re relation was derived from a general physical consideration, it raises the possibility that it may be applicable to vortex shedding from bodies other than circular ones. The work presented herein provides experimental evidence that this is the case. Our measurements also show that, in the asymptotic limit (Re→∞), St(∞)=1/A≃0.21 is constant independent of rod shapes, leaving B the only parameter that is shape dependent.}, } @article {pmid26565330, year = {2015}, author = {Edlund, EM and Ji, H}, title = {Reynolds number scaling of the influence of boundary layers on the global behavior of laboratory quasi-Keplerian flows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {4}, pages = {043005}, doi = {10.1103/PhysRevE.92.043005}, pmid = {26565330}, issn = {1550-2376}, abstract = {We present fluid velocity measurements in a modified Taylor-Couette device operated in the quasi-Keplerian regime, where it is observed that nearly ideal flows exhibit self-similarity under scaling of the Reynolds number. In contrast, nonideal flows show progressive departure from ideal Couette as the Reynolds number is increased. We present a model that describes the observed departures from ideal Couette rotation as a function of the fluxes of angular momentum across the boundaries, capturing the dependence on Reynolds number and boundary conditions.}, } @article {pmid26565328, year = {2015}, author = {Phillips, WR}, title = {Drift and pseudomomentum in bounded turbulent shear flows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {4}, pages = {043003}, doi = {10.1103/PhysRevE.92.043003}, pmid = {26565328}, issn = {1550-2376}, abstract = {This paper is concerned with the evaluation of two Lagrangian measures which arise in oscillatory or fluctuating shear flows when the fluctuating field is rotational and the spectrum of wave numbers which comprise it is continuous. The measures are the drift and pseudomomentum. Phillips [J. Fluid Mech. 430, 209 (2001)] has shown that the measures are, in such instances, succinctly expressed in terms of Lagrangian integrals of Eulerian space-time correlations. But they are difficult to interpret, and the present work begins by expressing them in a more insightful form. This is achieved by assuming the space-time correlations are separable as magnitude, determined by one-point velocity correlations, and spatial diminution. The measures then parse into terms comprised of the mean Eulerian velocity, one-point velocity correlations, and a family of integrals of spatial diminution, which in turn define a series of Lagrangian time and velocity scales. The pseudomomentum is seen to be strictly negative and related to the turbulence kinetic energy, while the drift is mixed and strongly influenced by the Reynolds stress. Both are calculated for turbulent channel flow for a range of Reynolds numbers and appear, as the Reynolds number increases, to approach a terminal form. At all Reynolds numbers studied, the pseudomomentum has a sole peak located in wall units in the low teens, while at the highest Reynolds number studied, Re(τ)=5200, the drift is negative in the vicinity of that peak, positive elsewhere, and largest near the rigid boundary. In contrast, the time and velocity scales grow almost logarithmically over much of the layer. Finally, the drift and pseudomomentum are discussed in the context of coherent wall layer structures with which they are intricately linked.}, } @article {pmid26565230, year = {2015}, author = {Clark, AH and Shattuck, MD and Ouellette, NT and O'Hern, CS}, title = {Onset and cessation of motion in hydrodynamically sheared granular beds.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {4}, pages = {042202}, doi = {10.1103/PhysRevE.92.042202}, pmid = {26565230}, issn = {1550-2376}, abstract = {We performed molecular dynamics simulations of granular beds driven by a model hydrodynamic shear flow to elucidate general grain-scale mechanisms that determine the onset and cessation of sediment transport. By varying the Shields number (the nondimensional shear stress at the top of the bed) and particle Reynolds number (the ratio of particle inertia to viscous damping), we explore how variations of the fluid flow rate, particle inertia, and fluid viscosity affect the onset and cessation of bed motion. For low to moderate particle Reynolds numbers, a critical boundary separates mobile and static states. Transition times between these states diverge as this boundary is approached both from above and below. At high particle Reynolds number, inertial effects become dominant, and particle motion can be sustained well below flow rates at which mobilization of a static bed occurs. We also find that the onset of bed motion (for both low and high particle Reynolds numbers) is described by Weibullian weakest-link statistics and thus is crucially dependent on the packing structure of the granular bed, even deep beneath the surface.}, } @article {pmid26563615, year = {2015}, author = {Tai, J and Lim, CP and Lam, YC}, title = {Visualization of polymer relaxation in viscoelastic turbulent micro-channel flow.}, journal = {Scientific reports}, volume = {5}, number = {}, pages = {16633}, pmid = {26563615}, issn = {2045-2322}, abstract = {In micro-channels, the flow of viscous liquids e.g. water, is laminar due to the low Reynolds number in miniaturized dimensions. An aqueous solution becomes viscoelastic with a minute amount of polymer additives; its flow behavior can become drastically different and turbulent. However, the molecules are typically invisible. Here we have developed a novel visualization technique to examine the extension and relaxation of polymer molecules at high flow velocities in a viscoelastic turbulent flow. Using high speed videography to observe the fluorescein labeled molecules, we show that viscoelastic turbulence is caused by the sporadic, non-uniform release of energy by the polymer molecules. This developed technique allows the examination of a viscoelastic liquid at the molecular level, and demonstrates the inhomogeneity of viscoelastic liquids as a result of molecular aggregation. It paves the way for a deeper understanding of viscoelastic turbulence, and could provide some insights on the high Weissenberg number problem. In addition, the technique may serve as a useful tool for the investigations of polymer drag reduction.}, } @article {pmid26553982, year = {2015}, author = {Ni, R and Michalski, MH and Brown, E and Doan, N and Zinter, J and Ouellette, NT and Shepherd, GM}, title = {Optimal directional volatile transport in retronasal olfaction.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {112}, number = {47}, pages = {14700-14704}, pmid = {26553982}, issn = {1091-6490}, support = {R01DC 00997701/DC/NIDCD NIH HHS/United States ; }, mesh = {Female ; Humans ; Middle Aged ; Models, Anatomic ; Nose/anatomy & histology/*physiology ; Smell/*physiology ; Time Factors ; Volatilization ; }, abstract = {The ability of humans to distinguish the delicate differences in food flavors depends mostly on retronasal smell, in which food volatiles entrained into the airway at the back of the oral cavity are transported by exhaled air through the nasal cavity to stimulate the olfactory receptor neurons. Little is known whether food volatiles are preferentially carried by retronasal flow toward the nasal cavity rather than by orthonasal flow into the lung. To study the differences between retronasal and orthonasal flow, we obtained computed tomography (CT) images of the orthonasal airway from a healthy human subject, printed an experimental model using a 3D printer, and analyzed the flow field inside the airway. The results show that, during inhalation, the anatomical structure of the oropharynx creates an air curtain outside a virtual cavity connecting the oropharynx and the back of the mouth, which prevents food volatiles from being transported into the main stream toward the lung. In contrast, during exhalation, the flow preferentially sweeps through this virtual cavity and effectively enhances the entrainment of food volatiles into the main retronasal flow. This asymmetrical transport efficiency is also found to have a nonmonotonic Reynolds number dependence: The asymmetry peaks at a range of an intermediate Reynolds number close to 800, because the air curtain effect during inhalation becomes strongest in this range. This study provides the first experimental evidence, to our knowledge, for adaptations of the geometry of the human oropharynx for efficient transport of food volatiles toward the olfactory receptors in the nasal cavity.}, } @article {pmid26550904, year = {2015}, author = {Jawed, MK and Khouri, NK and Da, F and Grinspun, E and Reis, PM}, title = {Propulsion and Instability of a Flexible Helical Rod Rotating in a Viscous Fluid.}, journal = {Physical review letters}, volume = {115}, number = {16}, pages = {168101}, doi = {10.1103/PhysRevLett.115.168101}, pmid = {26550904}, issn = {1079-7114}, mesh = {*Bacterial Physiological Phenomena ; Locomotion ; *Models, Biological ; Swimming ; Viscosity ; }, abstract = {We combine experiments with simulations to investigate the fluid-structure interaction of a flexible helical rod rotating in a viscous fluid, under low Reynolds number conditions. Our analysis takes into account the coupling between the geometrically nonlinear behavior of the elastic rod with a nonlocal hydrodynamic model for the fluid loading. We quantify the resulting propulsive force, as well as the buckling instability of the originally helical filament that occurs above a critical rotation velocity. A scaling analysis is performed to rationalize the onset of this instability. A universal phase diagram is constructed to map out the region of successful propulsion and the corresponding boundary of stability is established. Comparing our results with data for flagellated bacteria suggests that this instability may be exploited in nature for physiological purposes.}, } @article {pmid26542943, year = {2016}, author = {Ishimoto, K and Cosson, J and Gaffney, EA}, title = {A simulation study of sperm motility hydrodynamics near fish eggs and spheres.}, journal = {Journal of theoretical biology}, volume = {389}, number = {}, pages = {187-197}, doi = {10.1016/j.jtbi.2015.10.013}, pmid = {26542943}, issn = {1095-8541}, mesh = {Algorithms ; Animals ; Biophysical Phenomena ; Computer Simulation ; Female ; Flatfishes/*physiology ; Hydrodynamics ; Male ; Models, Theoretical ; Movement ; Oscillometry ; *Sperm Motility ; Sperm-Ovum Interactions/*physiology ; Spermatozoa/*physiology ; }, abstract = {For teleost fish fertilisation, sperm must proceed through a small opening on the egg surface, referred to as the micropyle. In this paper, we have used boundary element simulations to explore whether the hydrodynamic attraction between sperm and a fish egg can be a sperm guidance cue. Hydrodynamical egg-sperm interactions alone do not increase the chances of an egg encounter, nor do they induce surface swimming for virtual turbot fish sperm across smooth spheres with a diameter of 1mm, which is representative of a turbot fish egg. When a repulsive surface force between the virtual turbot sperm and the egg is introduced, as motivated by surface charge and van-der-Waals interactions for instance, we find that extended surface swimming of the virtual sperm across a model turbot egg occurs, but ultimately the sperm escapes from the egg. This is due to the small exit angle of the scattering associated with the initial sperm-egg interaction at the egg surface, leading to a weak drift away from the egg, in combination with a weak hydrodynamical attraction between both gametes, though the latter is not sufficient to prevent eventual escape. The resulting transience is not observed experimentally but is a detailed quantitative difference between theory and observation in that stable surface swimming is predicted for eggs with radii larger than about 1.8mm. Regardless, the extended sperm swimming trajectory across the egg constitutes a two-dimensional search for the micropyle and thus the egg is consistently predicted to provide a guidance cue for sperm once they are sufficiently close. In addition, the observation that the virtual turbot sperm swims stably next to a flat plane given repulsive surface interactions, but does not swim stably adjacent to a turbot-sized egg, which is extremely large by sperm-lengthscales, also highlights that the stability of sperm swimming near a boundary is very sensitive to geometry.}, } @article {pmid26538006, year = {2015}, author = {Grosjean, G and Lagubeau, G and Darras, A and Hubert, M and Lumay, G and Vandewalle, N}, title = {Remote control of self-assembled microswimmers.}, journal = {Scientific reports}, volume = {5}, number = {}, pages = {16035}, pmid = {26538006}, issn = {2045-2322}, abstract = {Physics governing the locomotion of microorganisms and other microsystems is dominated by viscous damping. An effective swimming strategy involves the non-reciprocal and periodic deformations of the considered body. Here, we show that a magnetocapillary-driven self-assembly, composed of three soft ferromagnetic beads, is able to swim along a liquid-air interface when powered by an external magnetic field. More importantly, we demonstrate that trajectories can be fully controlled, opening ways to explore low Reynolds number swimming. This magnetocapillary system spontaneously forms by self-assembly, allowing miniaturization and other possible applications such as cargo transport or solvent flows.}, } @article {pmid26528815, year = {2015}, author = {Ge, M and Fang, L and Tian, D}, title = {Influence of Reynolds Number on Multi-Objective Aerodynamic Design of a Wind Turbine Blade.}, journal = {PloS one}, volume = {10}, number = {11}, pages = {e0141848}, pmid = {26528815}, issn = {1932-6203}, mesh = {*Aviation ; *Models, Theoretical ; }, abstract = {At present, the radius of wind turbine rotors ranges from several meters to one hundred meters, or even more, which extends Reynolds number of the airfoil profile from the order of 105 to 107. Taking the blade for 3MW wind turbines as an example, the influence of Reynolds number on the aerodynamic design of a wind turbine blade is studied. To make the study more general, two kinds of multi-objective optimization are involved: one is based on the maximum power coefficient (CPopt) and the ultimate load, and the other is based on the ultimate load and the annual energy production (AEP). It is found that under the same configuration, the optimal design has a larger CPopt or AEP (CPopt//AEP) for the same ultimate load, or a smaller load for the same CPopt//AEP at higher Reynolds number. At a certain tip-speed ratio or ultimate load, the blade operating at higher Reynolds number should have a larger chord length and twist angle for the maximum Cpopt//AEP. If a wind turbine blade is designed by using an airfoil database with a mismatched Reynolds number from the actual one, both the load and Cpopt//AEP will be incorrectly estimated to some extent. In some cases, the assessment error attributed to Reynolds number is quite significant, which may bring unexpected risks to the earnings and safety of a wind power project.}, } @article {pmid26521001, year = {2015}, author = {Kumar, M and Tordjeman, P and Bergez, W and Cavaro, M}, title = {Note: Void effects on eddy current distortion in two-phase liquid metal.}, journal = {The Review of scientific instruments}, volume = {86}, number = {10}, pages = {106104}, doi = {10.1063/1.4932990}, pmid = {26521001}, issn = {1089-7623}, abstract = {A model based on the first order perturbation expansion of magnetic flux in a two-phase liquid metal flow has been developed for low magnetic Reynolds number Rem. This model takes into account the distortion of the induced eddy currents due to the presence of void in the conducting medium. Specific experiments with an eddy current flow meter have been realized for two periodic void distributions. The results have shown, in agreement with the model, that the effects of velocity and void on the emf modulation are decoupled. The magnitude of the void fraction and the void spatial frequency can be determined from the spectral density of the demodulated emf.}, } @article {pmid26519975, year = {2016}, author = {Adams, MC and Barbano, DM}, title = {Effect of ceramic membrane channel diameter on limiting retentate protein concentration during skim milk microfiltration.}, journal = {Journal of dairy science}, volume = {99}, number = {1}, pages = {167-182}, doi = {10.3168/jds.2015-9897}, pmid = {26519975}, issn = {1525-3198}, mesh = {Animals ; Blood Proteins/analysis ; Ceramics/*chemistry ; Computer Simulation ; *Filtration ; Food Handling ; Hydrodynamics ; *Membranes, Artificial ; Milk/*chemistry ; Milk Proteins/analysis ; Pilot Projects ; Viscosity ; }, abstract = {Our objective was to determine the effect of retentate flow channel diameter (4 or 6mm) of nongraded permeability 100-nm pore size ceramic membranes operated in nonuniform transmembrane pressure mode on the limiting retentate protein concentration (LRPC) while microfiltering (MF) skim milk at a temperature of 50°C, a flux of 55 kg · m(-2) · h(-1), and an average cross-flow velocity of 7 m · s(-1). At the above conditions, the retentate true protein concentration was incrementally increased from 7 to 11.5%. When temperature, flux, and average cross-flow velocity were controlled, ceramic membrane retentate flow channel diameter did not affect the LRPC. This indicates that LRPC is not a function of the Reynolds number. Computational fluid dynamics data, which indicated that both membranes had similar radial velocity profiles within their retentate flow channels, supported this finding. Membranes with 6-mm flow channels can be operated at a lower pressure decrease from membrane inlet to membrane outlet (ΔP) or at a higher cross-flow velocity, depending on which is controlled, than membranes with 4-mm flow channels. This implies that 6-mm membranes could achieve a higher LRPC than 4-mm membranes at the same ΔP due to an increase in cross-flow velocity. In theory, the higher LRPC of the 6-mm membranes could facilitate 95% serum protein removal in 2 MF stages with diafiltration between stages if no serum protein were rejected by the membrane. At the same flux, retentate protein concentration, and average cross-flow velocity, 4-mm membranes require 21% more energy to remove a given amount of permeate than 6-mm membranes, despite the lower surface area of the 6-mm membranes. Equations to predict skim milk MF retentate viscosity as a function of protein concentration and temperature are provided. Retentate viscosity, retentate recirculation pump frequency required to maintain a given cross-flow velocity at a given retentate viscosity, and retentate protein determination by mid-infrared spectrophotometry were all useful tools for monitoring the retentate protein concentration to ensure a sustainable MF process. Using 6-mm membranes instead of 4-mm membranes would be advantageous for processors who wish to reduce energy costs or maximize the protein concentration of a MF retentate.}, } @article {pmid26504982, year = {2015}, author = {Colla, L and Marinelli, L and Fedele, L and Bobbo, S and Manca, O}, title = {Characterization and Simulation of the Heat Transfer Behaviour of Water-Based ZnO Nanofluids.}, journal = {Journal of nanoscience and nanotechnology}, volume = {15}, number = {5}, pages = {3599-3609}, doi = {10.1166/jnn.2015.9864}, pmid = {26504982}, issn = {1533-4899}, abstract = {This paper deals with the characterization and modelling of water-based nanofluids containing zinc oxide (ZnO) nanoparticles in concentrations ranging between 1 and 10 wt%. Low concentrations were chosen to reduce fouling and excessive pressure drops. First of all, the stability was verified by means of an instrument, based on the dynamic light scattering (DLS) technique, measuring mean nanoparticle diameters and Zeta potential. Moreover, nanofluids pH was measured. Then, thermal conductivities and dynamic viscosities were measured, analysing their dependence on temperature and nanoparticle concentration. Thermal conductivity was measured by means of a hot disk apparatus in the temperature range between 10 and 70 degrees C, while viscosity was measured by a magnetic suspension rheometer in the same range of temperatures. Finally, the heat transfer capability of these fluids was studied measuring their heat transfer coefficients in a dedicated apparatus between 18 and 40 degrees C. Heat transfer coefficient was evaluated at different Reynolds number, in turbulent flow regime. Reynolds and Nusselt numbers were deduced by using previously measured thermal conductivity and viscosity values. Moreover, numerical simulations in two-dimensional turbulent and steady state flow were carried out. No increase in heat transfer coefficient in the temperature range between 18 and 40 degrees C was found. Comparison between experimental and numerical simulation data, in terms of wall temperature profiles, showed a good agreement.}, } @article {pmid26490629, year = {2015}, author = {Lenz, PH and Takagi, D and Hartline, DK}, title = {Choreographed swimming of copepod nauplii.}, journal = {Journal of the Royal Society, Interface}, volume = {12}, number = {112}, pages = {}, pmid = {26490629}, issn = {1742-5662}, mesh = {Animals ; Biomechanical Phenomena ; Copepoda/*physiology ; *Models, Biological ; Swimming/*physiology ; }, abstract = {Small metazoan paddlers, such as crustacean larvae (nauplii), are abundant, ecologically important and active swimmers, which depend on exploiting viscous forces for locomotion. The physics of micropaddling at low Reynolds number was investigated using a model of swimming based on slender-body theory for Stokes flow. Locomotion of nauplii of the copepod Bestiolina similis was quantified from high-speed video images to obtain precise measurements of appendage movements and the resulting displacement of the body. The kinematic and morphological data served as inputs to the model, which predicted the displacement in good agreement with observations. The results of interest did not depend sensitively on the parameters within the error of measurement. Model tests revealed that the commonly attributed mechanism of 'feathering' appendages during return strokes accounts for only part of the displacement. As important for effective paddling at low Reynolds number is the ability to generate a metachronal sequence of power strokes in combination with synchronous return strokes of appendages. The effect of feathering together with a synchronous return stroke is greater than the sum of each factor individually. The model serves as a foundation for future exploration of micropaddlers swimming at intermediate Reynolds number where both viscous and inertial forces are important.}, } @article {pmid26456297, year = {2015}, author = {Schwarz, US}, title = {Physical constraints for pathogen movement.}, journal = {Seminars in cell & developmental biology}, volume = {46}, number = {}, pages = {82-90}, doi = {10.1016/j.semcdb.2015.09.025}, pmid = {26456297}, issn = {1096-3634}, mesh = {Algorithms ; Amoeba/*physiology ; Animals ; Bacteria/*growth & development ; Host-Pathogen Interactions ; Humans ; Models, Biological ; Movement/physiology ; Plasmodium/*physiology ; Viruses/*growth & development ; }, abstract = {In this pedagogical review, we discuss the physical constraints that pathogens experience when they move in their host environment. Due to their small size, pathogens are living in a low Reynolds number world dominated by viscosity. For swimming pathogens, the so-called scallop theorem determines which kinds of shape changes can lead to productive motility. For crawling or gliding cells, the main resistance to movement comes from protein friction at the cell-environment interface. Viruses and pathogenic bacteria can also exploit intracellular host processes such as actin polymerization and motor-based transport, if they present the appropriate factors on their surfaces. Similar to cancer cells that also tend to cross various barriers, pathogens often combine several of these strategies in order to increase their motility and therefore their chances to replicate and spread.}, } @article {pmid26452005, year = {2015}, author = {Emetere, ME and Akinyemi, ML and Akin-Ojo, O}, title = {Parametric retrieval model for estimating aerosol size distribution via the AERONET, LAGOS station.}, journal = {Environmental pollution (Barking, Essex : 1987)}, volume = {207}, number = {}, pages = {381-390}, doi = {10.1016/j.envpol.2015.09.047}, pmid = {26452005}, issn = {1873-6424}, mesh = {Aerosols ; Air Pollutants/*analysis ; Atmosphere ; Environmental Monitoring/*methods ; *Models, Theoretical ; Nigeria ; Particle Size ; Particulate Matter/*analysis ; Seasons ; Weather ; Wind ; }, abstract = {The size characteristics of atmospheric aerosol over the tropical region of Lagos, Southern Nigeria were investigated using two years of continuous spectral aerosol optical depth measurements via the AERONET station for four major bands i.e. blue, green, red and infrared. Lagos lies within the latitude of 6.465°N and longitude of 3.406°E. Few systems of dispersion model was derived upon specified conditions to solve challenges on aerosols size distribution within the Stokes regime. The dispersion model was adopted to derive an aerosol size distribution (ASD) model which is in perfect agreement with existing model. The parametric nature of the formulated ASD model shows the independence of each band to determine the ASD over an area. The turbulence flow of particulates over the area was analyzed using the unified number (Un). A comparative study via the aid of the Davis automatic weather station was carried out on the Reynolds number, Knudsen number and the Unified number. The Reynolds and Unified number were more accurate to describe the atmospheric fields of the location. The aerosols loading trend in January to March (JFM) and August to October (ASO) shows a yearly 15% retention of aerosols in the atmosphere. The effect of the yearly aerosol retention can be seen to partly influence the aerosol loadings between October and February.}, } @article {pmid26451802, year = {2015}, author = {Phillips, N and Knowles, K and Bomphrey, RJ}, title = {The effect of aspect ratio on the leading-edge vortex over an insect-like flapping wing.}, journal = {Bioinspiration & biomimetics}, volume = {10}, number = {5}, pages = {056020}, doi = {10.1088/1748-3190/10/5/056020}, pmid = {26451802}, issn = {1748-3190}, mesh = {Animals ; Biomimetics/*instrumentation ; Computer Simulation ; Computer-Aided Design ; Equipment Failure Analysis ; Flight, Animal/*physiology ; Insecta/*physiology ; *Models, Biological ; Rheology/methods ; Robotics/*instrumentation ; Shear Strength/physiology ; Stress, Mechanical ; Viscosity ; Wings, Animal/*physiology ; }, abstract = {Insect wing shapes are diverse and a renowned source of inspiration for the new generation of autonomous flapping vehicles, yet the aerodynamic consequences of varying geometry is not well understood. One of the most defining and aerodynamically significant measures of wing shape is the aspect ratio, defined as the ratio of wing length (R) to mean wing chord (c). We investigated the impact of aspect ratio, AR, on the induced flow field around a flapping wing using a robotic device. Rigid rectangular wings ranging from AR = 1.5 to 7.5 were flapped with insect-like kinematics in air with a constant Reynolds number (Re) of 1400, and a dimensionless stroke amplitude of 6.5c (number of chords traversed by the wingtip). Pseudo-volumetric, ensemble-averaged, flow fields around the wings were captured using particle image velocimetry at 11 instances throughout simulated downstrokes. Results confirmed the presence of a high-lift, separated flow field with a leading-edge vortex (LEV), and revealed that the conical, primary LEV grows in size and strength with increasing AR. In each case, the LEV had an arch-shaped axis with its outboard end originating from a focus-sink singularity on the wing surface near the tip. LEV detachment was observed for AR > 1.5 around mid-stroke at ~70% span, and initiated sooner over higher aspect ratio wings. At AR > 3 the larger, stronger vortex persisted under the wing surface well into the next half-stroke leading to a reduction in lift. Circulatory lift attributable to the LEV increased with AR up to AR = 6. Higher aspect ratios generated proportionally less lift distally because of LEV breakdown, and also less lift closer to the wing root due to the previous LEV's continuing presence under the wing. In nature, insect wings go no higher than AR ~ 5, likely in part due to architectural and physiological constraints but also because of the reducing aerodynamic benefits of high AR wings.}, } @article {pmid26451559, year = {2015}, author = {Linkmann, MF and Morozov, A}, title = {Sudden Relaminarization and Lifetimes in Forced Isotropic Turbulence.}, journal = {Physical review letters}, volume = {115}, number = {13}, pages = {134502}, doi = {10.1103/PhysRevLett.115.134502}, pmid = {26451559}, issn = {1079-7114}, abstract = {We demonstrate an unexpected connection between isotropic turbulence and wall-bounded shear flows. We perform direct numerical simulations of isotropic turbulence forced at large scales at moderate Reynolds numbers and observe sudden transitions from a chaotic dynamics to a spatially simple flow, analogous to the laminar state in wall bounded shear flows. We find that the survival probabilities of turbulence are exponential and the typical lifetimes increase superexponentially with the Reynolds number. Our results suggest that both isotropic turbulence and wall-bounded shear flows qualitatively share the same phase-space dynamics.}, } @article {pmid26447541, year = {2015}, author = {Lucas, KN and Thornycroft, PJ and Gemmell, BJ and Colin, SP and Costello, JH and Lauder, GV}, title = {Effects of non-uniform stiffness on the swimming performance of a passively-flexing, fish-like foil model.}, journal = {Bioinspiration & biomimetics}, volume = {10}, number = {5}, pages = {056019}, doi = {10.1088/1748-3190/10/5/056019}, pmid = {26447541}, issn = {1748-3190}, mesh = {Animal Fins/*physiology ; Animals ; Biomimetics/*methods ; Computer Simulation ; Elastic Modulus/physiology ; Fishes/*physiology ; *Models, Biological ; Rheology/methods ; Robotics/*methods ; Shear Strength/physiology ; Stress, Mechanical ; Swimming/*physiology ; Viscosity ; }, abstract = {Simple mechanical models emulating fish have been used recently to enable targeted study of individual factors contributing to swimming locomotion without the confounding complexity of the whole fish body. Yet, unlike these uniform models, the fish body is notable for its non-uniform material properties. In particular, flexural stiffness decreases along the fish's anterior-posterior axis. To identify the role of non-uniform bending stiffness during fish-like propulsion, we studied four foil model configurations made by adhering layers of plastic sheets to produce discrete regions of high (5.5 × 10(-5) Nm(2)) and low (1.9 × 10(-5) Nm(2)) flexural stiffness of biologically-relevant magnitudes. This resulted in two uniform control foils and two foils with anterior regions of high stiffness and posterior regions of low stiffness. With a mechanical flapping foil controller, we measured forces and torques in three directions and quantified swimming performance under both heaving (no pitch) and constant 0° angle of attack programs. Foils self-propelled at Reynolds number 21 000-115 000 and Strouhal number ∼0.20-0.25, values characteristic of fish locomotion. Although previous models have emphasized uniform distributions and heaving motions, the combination of non-uniform stiffness distributions and 0° angle of attack pitching program was better able to reproduce the kinematics of freely-swimming fish. This combination was likewise crucial in maximizing swimming performance and resulted in high self-propelled speeds at low costs of transport and large thrust coefficients at relatively high efficiency. Because these metrics were not all maximized together, selection of the 'best' stiffness distribution will depend on actuation constraints and performance goals. These improved models enable more detailed, accurate analyses of fish-like swimming.}, } @article {pmid26446009, year = {2016}, author = {Martin, BA and Yiallourou, TI and Pahlavian, SH and Thyagaraj, S and Bunck, AC and Loth, F and Sheffer, DB and Kröger, JR and Stergiopulos, N}, title = {Inter-operator Reliability of Magnetic Resonance Image-Based Computational Fluid Dynamics Prediction of Cerebrospinal Fluid Motion in the Cervical Spine.}, journal = {Annals of biomedical engineering}, volume = {44}, number = {5}, pages = {1524-1537}, pmid = {26446009}, issn = {1573-9686}, support = {R13 NS063446/NS/NINDS NIH HHS/United States ; R15 NS071455/NS/NINDS NIH HHS/United States ; 492 1R15NS071455-01/NS/NINDS NIH HHS/United States ; }, mesh = {*Arnold-Chiari Malformation/diagnostic imaging/physiopathology ; *Cerebrospinal Fluid ; *Cervical Cord/diagnostic imaging/physiopathology ; Female ; Humans ; *Magnetic Resonance Imaging ; Male ; Motion ; Observer Variation ; }, abstract = {For the first time, inter-operator dependence of MRI based computational fluid dynamics (CFD) modeling of cerebrospinal fluid (CSF) in the cervical spinal subarachnoid space (SSS) is evaluated. In vivo MRI flow measurements and anatomy MRI images were obtained at the cervico-medullary junction of a healthy subject and a Chiari I malformation patient. 3D anatomies of the SSS were reconstructed by manual segmentation by four independent operators for both cases. CFD results were compared at nine axial locations along the SSS in terms of hydrodynamic and geometric parameters. Intraclass correlation (ICC) assessed the inter-operator agreement for each parameter over the axial locations and coefficient of variance (CV) compared the percentage of variance for each parameter between the operators. Greater operator dependence was found for the patient (0.19 < ICC < 0.99) near the craniovertebral junction compared to the healthy subject (ICC > 0.78). For the healthy subject, hydraulic diameter and Womersley number had the least variance (CV = ~2%). For the patient, peak diastolic velocity and Reynolds number had the smallest variance (CV = ~3%). These results show a high degree of inter-operator reliability for MRI-based CFD simulations of CSF flow in the cervical spine for healthy subjects and a lower degree of reliability for patients with Type I Chiari malformation.}, } @article {pmid26439225, year = {2015}, author = {Chen, H and Tang, T and Amirfazli, A}, title = {Fast Liquid Transfer between Surfaces: Breakup of Stretched Liquid Bridges.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {31}, number = {42}, pages = {11470-11476}, doi = {10.1021/acs.langmuir.5b03292}, pmid = {26439225}, issn = {1520-5827}, abstract = {In this work, a systematic experimental study was performed to understand the fast liquid transfer process between two surfaces. According to the value of the Reynolds number (Re), the fast transfer is divided into two different scenarios, one with negligible inertia effects (Re ≪ 1) and the other with significant inertia effects (Re > 1). For Re ≪ 1, the influences of the capillary number (Ca) and the dimensionless minimum separation (H(min)* = H(min)/V(1/3), where H(min) is the minimum separation between two surfaces and V is the volume of liquid) on the transfer ratio (α, the volume of liquid transferred to the acceptor surface over the total liquid volume) are discussed. On the basis of the roles of each physical parameter, an empirical equation is presented to predict the transfer ratio, α = f(Ca). This equation involves two coefficients which are affected only by the surface contact angles and H(min)* but not by the liquid viscosity or surface tension. When Re > 1, it is shown for the first time that the transfer ratio does not converge to 0.5 with the increase in the stretching speed.}, } @article {pmid26429038, year = {2015}, author = {Słowicka, AM and Wajnryb, E and Ekiel-Jeżewska, ML}, title = {Dynamics of flexible fibers in shear flow.}, journal = {The Journal of chemical physics}, volume = {143}, number = {12}, pages = {124904}, doi = {10.1063/1.4931598}, pmid = {26429038}, issn = {1089-7690}, abstract = {Dynamics of flexible non-Brownian fibers in shear flow at low-Reynolds-number are analyzed numerically for a wide range of the ratios A of the fiber bending force to the viscous drag force. Initially, the fibers are aligned with the flow, and later they move in the plane perpendicular to the flow vorticity. A surprisingly rich spectrum of different modes is observed when the value of A is systematically changed, with sharp transitions between coiled and straightening out modes, period-doubling bifurcations from periodic to migrating solutions, irregular dynamics, and chaos.}, } @article {pmid26428671, year = {2016}, author = {Costa, AP and Xu, X and Khan, MA and Burgess, DJ}, title = {Liposome Formation Using a Coaxial Turbulent Jet in Co-Flow.}, journal = {Pharmaceutical research}, volume = {33}, number = {2}, pages = {404-416}, pmid = {26428671}, issn = {1573-904X}, support = {HHSF223201310117C//PHS HHS/United States ; }, mesh = {Dynamic Light Scattering ; Equipment Design ; Ethanol/chemistry ; Lipids/chemistry ; Liposomes/*chemistry/*ultrastructure ; Particle Size ; Technology, Pharmaceutical/*instrumentation ; Water/chemistry ; }, abstract = {PURPOSE: Liposomes are robust drug delivery systems that have been developed into FDA-approved drug products for several pharmaceutical indications. Direct control in producing liposomes of a particular particle size and particle size distribution is extremely important since liposome size may impact cellular uptake and biodistribution.

METHODS: A device consisting of an injection-port was fabricated to form a coaxial turbulent jet in co-flow that produces liposomes via the ethanol injection method. By altering the injection-port dimensions and flow rates, a fluid flow profile (i.e., flow velocity ratio vs. Reynolds number) was plotted and associated with the polydispersity index of liposomes.

RESULTS: Certain flow conditions produced unilamellar, monodispersed liposomes and the mean particle size was controllable from 25 up to >465 nm. The mean liposome size is highly dependent on the Reynolds number of the mixed ethanol/aqueous phase and independent of the flow velocity ratio.

CONCLUSIONS: The significance of this work is that the Reynolds number is predictive of the liposome particle size, independent of the injection-port dimensions. In addition, a new model describing liposome formation is outlined. The significance of the model is that it relates fluid dynamic properties and lipid-molecule physical properties to the final liposome size.}, } @article {pmid26417381, year = {2015}, author = {Khalafvand, SS and Hung, TK and Ng, EY and Zhong, L}, title = {Kinematic, Dynamic, and Energy Characteristics of Diastolic Flow in the Left Ventricle.}, journal = {Computational and mathematical methods in medicine}, volume = {2015}, number = {}, pages = {701945}, pmid = {26417381}, issn = {1748-6718}, mesh = {Adult ; Biomechanical Phenomena ; Blood Flow Velocity ; Diastole ; Heart Ventricles/anatomy & histology ; Hemodynamics ; Humans ; Hydrodynamics ; Imaging, Three-Dimensional ; Magnetic Resonance Angiography ; Mitral Valve/physiology ; *Models, Cardiovascular ; *Ventricular Function, Left ; }, abstract = {Blood flow characteristics in the normal left ventricle are studied by using the magnetic resonance imaging, the Navier-Stokes equations, and the work-energy equation. Vortices produced during the mitral valve opening and closing are modeled in a two-dimensional analysis and correlated with temporal variations of the Reynolds number and pressure drop. Low shear stress and net pressures on the mitral valve are obtained for flow acceleration and deceleration. Bernoulli energy flux delivered to blood from ventricular dilation is practically balanced by the energy influx and the rate change of kinetic energy in the ventricle. The rates of work done by shear and energy dissipation are small. The dynamic and energy characteristics of the 2D results are comparable to those of a 3D model.}, } @article {pmid26413565, year = {2015}, author = {Prabu, PM and Padmanaban, KP}, title = {Laminar Wall Jet Flow and Heat Transfer over a Shallow Cavity.}, journal = {TheScientificWorldJournal}, volume = {2015}, number = {}, pages = {926249}, pmid = {26413565}, issn = {1537-744X}, abstract = {This paper presents the detailed simulation of two-dimensional incompressible laminar wall jet flow over a shallow cavity. The flow characteristics of wall jet with respect to aspect ratio (AR), step length (X u), and Reynolds number (Re) of the shallow cavity are expressed. For higher accuracy, third-order discretization is applied for momentum equation which is solved using QUICK scheme with SIMPLE algorithm for pressure-velocity coupling. Low Reynolds numbers 25, 50, 100, 200, 400, and 600 are assigned for simulation. Results are presented for streamline contour, velocity contour, and vorticity formation at wall and also velocity profiles are reported. The detailed study of vortex formation on shallow cavity region is presented for various AR, X u , and Re conditions which led to key findings as Re increases and vortex formation moves from leading edge to trailing edge of the wall. Distance between vortices increases when the step length (X u) increases. When Re increases, the maximum temperature contour distributions take place in shallow cavity region and highest convection heat transfer is obtained in heated walls. The finite volume code (FLUENT) is used for solving Navier-Stokes equations and GAMBIT for modeling and meshing.}, } @article {pmid26406780, year = {2015}, author = {Shimizu, Y and Ohta, M}, title = {Influence of plaque stiffness on deformation and blood flow patterns in models of stenosis.}, journal = {Biorheology}, volume = {52}, number = {3}, pages = {171-182}, doi = {10.3233/BIR-14016}, pmid = {26406780}, issn = {1878-5034}, mesh = {Arteries/chemistry/physiopathology ; Blood Flow Velocity ; Blood Pressure ; Constriction, Pathologic/*physiopathology ; Humans ; Models, Cardiovascular ; Pulsatile Flow ; Rheology ; *Vascular Stiffness ; }, abstract = {BACKGROUND: Blood flow in stenotic vessels strongly influences the progression of vascular diseases. Plaques in stenotic blood vessels vary in stiffness, which influences plaque behavior and deformation by pressure and flow. Concurrent changes in plaque geometry can, in turn, affect blood flow conditions. Thus, simultaneous studies of blood flow and plaque deformation are needed to fully understand these interactions.

OBJECTIVES: This study aims to identify the change of flow conditions attendant to plaque deformation in a model stenotic vessel.

METHODS: Three plaques of differing stiffness were constructed on a vessel wall using poly (vinyl alcohol) hydrogels (PVA-H) with defined stiffness to facilitate simultaneous observations of blood flow and plaque deformation. Flow patterns were observed using particle image velocimetry (PIV).

RESULTS: Decreases in Reynolds number (Re) with increased plaque deformation suggest that velocity decrease is more critical to establishment of the flow pattern than expansion of the model lumen. Upon exiting the stenosis, the location of the flow reattachment point, shifted further downstream in all models as plaque stiffness decreased and depended on the increase in upstream pressure.

CONCLUSIONS: These results suggest that in addition to luminal area, plaque stiffness should be considered as a measure of the severity of the pathology.}, } @article {pmid26406014, year = {2015}, author = {Wang, C and Si, X and Shen, Y and Zheng, L and Lin, P}, title = {The exterior unsteady viscous flow and heat transfer due to a porous expanding or contracting cylinder.}, journal = {Bio-medical materials and engineering}, volume = {26 Suppl 1}, number = {}, pages = {S279-85}, doi = {10.3233/BME-151315}, pmid = {26406014}, issn = {1878-3619}, mesh = {Body Fluids/*physiology ; Body Temperature/*physiology ; Computer Simulation ; Elastic Modulus/physiology ; Energy Transfer/*physiology ; Humans ; *Models, Biological ; Peristalsis/*physiology ; Porosity ; Pulsatile Flow/*physiology ; Rheology/methods ; Temperature ; Thermal Conductivity ; Viscosity ; }, abstract = {Since the vessels in the biological tissues are characterized by low seepage Reynolds numbers and contracting or expanding walls, more attention is paid on the viscous flow outside the porous pipe with small expansion or contraction. This paper presents a numerical solution of the flow and heat transfer outside an expanding or contracting porous cylinder. The coupled nonlinear similarity equations are solved by Bvp4c, which is a collocation method with MATLAB. The effects of the different physical parameters, namely the permeability Reynolds number,the expansion ratio and the Prandtl number, on the velocity and temperature distribution are obtained and the results are shown graphically.}, } @article {pmid26399987, year = {2016}, author = {Sharp, MK and Diem, AK and Weller, RO and Carare, RO}, title = {Peristalsis with Oscillating Flow Resistance: A Mechanism for Periarterial Clearance of Amyloid Beta from the Brain.}, journal = {Annals of biomedical engineering}, volume = {44}, number = {5}, pages = {1553-1565}, doi = {10.1007/s10439-015-1457-6}, pmid = {26399987}, issn = {1573-9686}, mesh = {*Alzheimer Disease/blood/pathology/physiopathology ; Amyloid beta-Peptides/*blood ; *Cerebral Arteries/metabolism/pathology/physiopathology ; *Cerebrovascular Circulation ; Humans ; *Models, Cardiovascular ; *Pulsatile Flow ; }, abstract = {Alzheimer's disease is characterized by accumulation of amyloid-β (Aβ) in the brain and in the walls of cerebral arteries. The focus of this work is on clearance of Aβ along artery walls, the failure of which may explain the accumulation of Aβ in Alzheimer's disease. Periarterial basement membranes form continuous channels from cerebral capillaries to major arteries on the surface of the brain. Arterial pressure pulses drive peristaltic flow in the basement membranes in the same direction as blood flow. Here we forward the hypothesis that flexible structures within the basement membrane, if oriented such they present greater resistance to forward than retrograde flow, may cause net reverse flow, advecting Aβ along with it. A solution was obtained for peristaltic flow with low Reynolds number, long wavelength compared to channel height and small channel height compared to vessel radius in a Darcy-Brinkman medium representing a square array of cylinders. Results show that retrograde flow is promoted by high cylinder volume fraction and low peristaltic amplitude. A decrease in cylinder concentration and/or an increase in amplitude, both of which may occur during ageing, can reduce retrograde flow or even cause a transition from retrograde to forward flow. Such changes may explain the accumulation of Aβ in the brain and in artery walls in Alzheimer's disease.}, } @article {pmid26396254, year = {2015}, author = {Ober, TJ and Foresti, D and Lewis, JA}, title = {Active mixing of complex fluids at the microscale.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {112}, number = {40}, pages = {12293-12298}, pmid = {26396254}, issn = {1091-6490}, abstract = {Mixing of complex fluids at low Reynolds number is fundamental for a broad range of applications, including materials assembly, microfluidics, and biomedical devices. Of these materials, yield stress fluids (and gels) pose the most significant challenges, especially when they must be mixed in low volumes over short timescales. New scaling relationships between mixer dimensions and operating conditions are derived and experimentally verified to create a framework for designing active microfluidic mixers that can efficiently homogenize a wide range of complex fluids. Active mixing printheads are then designed and implemented for multimaterial 3D printing of viscoelastic inks with programmable control of local composition.}, } @article {pmid26395149, year = {2015}, author = {Sousa, PC and Pinho, FT and Oliveira, MS and Alves, MA}, title = {Purely elastic flow instabilities in microscale cross-slot devices.}, journal = {Soft matter}, volume = {11}, number = {45}, pages = {8856-8862}, doi = {10.1039/c5sm01298h}, pmid = {26395149}, issn = {1744-6848}, abstract = {We present an experimental investigation of viscoelastic fluid flow in a cross-slot microgeometry under low Reynolds number flow conditions. By using several viscoelastic fluids, we investigate the effects of the microchannel bounding walls and the polymer solution concentration on the flow patterns. We demonstrate that for concentrated polymer solutions, the flow undergoes a bifurcation above a critical Weissenberg number (Wi) at which the flow becomes asymmetric but remains steady. The appearance of this elastic instability depends on the channel aspect ratio, defined as the ratio between the depth and the width of the channels. At high aspect ratios, when bounding wall effects are reduced, two types of elastic instabilities were observed, one in which the flow becomes asymmetric and steady, followed by a second instability at higher Wi, in which the flow becomes time-dependent. When the aspect ratio decreases, the bounding walls have a stabilizing effect, preventing the occurrence of steady asymmetric flow and postponing the transition to unsteady flow to higher Wi. For less concentrated solutions, the first elastic instability to steady asymmetric flow is absent and only the time-dependent flow instability is observed.}, } @article {pmid26383225, year = {2015}, author = {Vach, PJ and Fratzl, P and Klumpp, S and Faivre, D}, title = {Fast Magnetic Micropropellers with Random Shapes.}, journal = {Nano letters}, volume = {15}, number = {10}, pages = {7064-7070}, pmid = {26383225}, issn = {1530-6992}, abstract = {Studying propulsion mechanisms in low Reynolds number fluid has implications for many fields, ranging from the biology of motile microorganisms and the physics of active matter to micromixing in catalysis and micro- and nanorobotics. The propulsion of magnetic micropropellers can be characterized by a dimensionless speed, which solely depends on the propeller geometry for a given axis of rotation. However, this dependence has so far been only investigated for helical propeller shapes, which were assumed to be optimal. In order to explore a larger variety of shapes, we experimentally studied the propulsion properties of randomly shaped magnetic micropropellers. Surprisingly, we found that their dimensionless speeds are high on average, comparable to previously reported nanofabricated helical micropropellers. The highest dimensionless speed we observed is higher than that of any previously reported propeller moving in a low Reynolds number fluid, proving that physical random shape generation can be a viable optimization strategy.}, } @article {pmid26382522, year = {2015}, author = {Gruca, M and Bukowicki, M and Ekiel-Jeżewska, ML}, title = {Periodic and quasiperiodic motions of many particles falling in a viscous fluid.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {2}, pages = {023026}, doi = {10.1103/PhysRevE.92.023026}, pmid = {26382522}, issn = {1550-2376}, abstract = {The dynamics of regular clusters of many nontouching particles falling under gravity in a viscous fluid at low Reynolds number are analyzed within the point-particle model. The evolution of two families of particle configurations is determined: two or four regular horizontal polygons (called "rings") centered above or below each other. Two rings fall together and periodically oscillate. Four rings usually separate from each other with chaotic scattering. For hundreds of thousands of initial configurations, a map of the cluster lifetime is evaluated in which the long-lasting clusters are centered around periodic solutions for the relative motions, and they are surrounded by regions of chaotic scattering in a similar way to what was observed by Janosi et al. [Phys. Rev. E. 56, 2858 (1997)] for three particles only. These findings suggest that we should consider the existence of periodic orbits as a possible physical mechanism of the existence of unstable clusters of particles falling under gravity in a viscous fluid.}, } @article {pmid26382516, year = {2015}, author = {Takagi, D}, title = {Swimming with stiff legs at low Reynolds number.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {2}, pages = {023020}, doi = {10.1103/PhysRevE.92.023020}, pmid = {26382516}, issn = {1550-2376}, mesh = {Animals ; Crustacea/physiology ; Extremities/*physiology ; *Models, Biological ; Periodicity ; Swimming/*physiology ; Viscosity ; }, abstract = {Locomotion at low Reynolds number is not possible with cycles of reciprocal motion, an example being the oscillation of a single pair of rigid paddles or legs. Here, I demonstrate the possibility of swimming with two or more pairs of legs. They are assumed to oscillate collectively in a metachronal wave pattern in a minimal model based on slender-body theory for Stokes flow. The model predicts locomotion in the direction of the traveling wave, as commonly observed along the body of free-swimming crustaceans. The displacement of the body and the swimming efficiency depend on the number of legs, the amplitude, and the phase of oscillations. This study shows that paddling legs with distinct orientations and phases offers a simple mechanism for driving flow.}, } @article {pmid26382506, year = {2015}, author = {Schober, J and Schleicher, DR and Federrath, C and Bovino, S and Klessen, RS}, title = {Saturation of the turbulent dynamo.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {2}, pages = {023010}, doi = {10.1103/PhysRevE.92.023010}, pmid = {26382506}, issn = {1550-2376}, abstract = {The origin of strong magnetic fields in the Universe can be explained by amplifying weak seed fields via turbulent motions on small spatial scales and subsequently transporting the magnetic energy to larger scales. This process is known as the turbulent dynamo and depends on the properties of turbulence, i.e., on the hydrodynamical Reynolds number and the compressibility of the gas, and on the magnetic diffusivity. While we know the growth rate of the magnetic energy in the linear regime, the saturation level, i.e., the ratio of magnetic energy to turbulent kinetic energy that can be reached, is not known from analytical calculations. In this paper we present a scale-dependent saturation model based on an effective turbulent resistivity which is determined by the turnover time scale of turbulent eddies and the magnetic energy density. The magnetic resistivity increases compared to the Spitzer value and the effective scale on which the magnetic energy spectrum is at its maximum moves to larger spatial scales. This process ends when the peak reaches a characteristic wave number k☆ which is determined by the critical magnetic Reynolds number. The saturation level of the dynamo also depends on the type of turbulence and differs for the limits of large and small magnetic Prandtl numbers Pm. With our model we find saturation levels between 43.8% and 1.3% for Pm≫1 and between 2.43% and 0.135% for Pm≪1, where the higher values refer to incompressible turbulence and the lower ones to highly compressible turbulence.}, } @article {pmid26382503, year = {2015}, author = {Roisman, IV and Criscione, A and Tropea, C and Mandal, DK and Amirfazli, A}, title = {Dislodging a sessile drop by a high-Reynolds-number shear flow at subfreezing temperatures.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {2}, pages = {023007}, doi = {10.1103/PhysRevE.92.023007}, pmid = {26382503}, issn = {1550-2376}, mesh = {Air Movements ; *Models, Theoretical ; *Temperature ; Viscosity ; Wettability ; }, abstract = {The drop, exposed to an air flow parallel to the substrate, starts to dislodge when the air velocity reaches some threshold value, which depends on the substrate wetting properties and drop volume. In this study the critical air velocity is measured for different drop volumes, on substrates of various wettabilities. The substrate initial temperatures varied between the normal room temperature (24.5∘C) and subfreezing temperatures (-5∘C and -1∘C). The physics of the drop did not change at the subfreezing temperatures of the substrates, which clearly indicates that the drop does not freeze and remains liquid for a relatively long time. During this time solidification is not initiated, neither by the air flow nor by mechanical disturbances. An approximate theoretical model is proposed that allows estimation of the aerodynamic forces acting on the sessile drop. The model is valid for the case when the drop height is of the same order as the thickness of the viscous boundary in the airflow, but the inertial effects are still dominant. Such a situation, relevant to many practical applications, was never modeled before. The theoretical predictions for the critical velocity of drop dislodging agree well with the experimental data for both room temperature and lower temperatures of the substrates.}, } @article {pmid26382501, year = {2015}, author = {Nath, SK and Mukhopadhyay, B}, title = {Origin of nonlinearity and plausible turbulence by hydromagnetic transient growth in accretion disks: Faster growth rate than magnetorotational instability.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {2}, pages = {023005}, doi = {10.1103/PhysRevE.92.023005}, pmid = {26382501}, issn = {1550-2376}, abstract = {We investigate the evolution of hydromagnetic perturbations in a small section of accretion disks. It is known that molecular viscosity is negligible in accretion disks. Hence, it has been argued that a mechanism, known as magnetorotational instability (MRI), is responsible for transporting matter in the presence of a weak magnetic field. However, there are some shortcomings, which question the effectiveness of MRI. Now the question arises, whether other hydromagnetic effects, e.g., transient growth (TG), can play an important role in bringing nonlinearity into the system, even at weak magnetic fields. In addition, it should be determined whether MRI or TG is primarily responsible for revealing nonlinearity in order to make the flow turbulent. Our results prove explicitly that the flows with a high Reynolds number (Re), which is the case for realistic astrophysical accretion disks, exhibit nonlinearity via TG of perturbation modes faster than that by modes producing MRI. For a fixed wave vector, MRI dominates over transient effects only at low Re, lower than the value expected to be in astrophysical accretion disks, and low magnetic fields. This calls into serious question the (overall) persuasiveness of MRI in astrophysical accretion disks.}, } @article {pmid26382500, year = {2015}, author = {Man, Y and Lauga, E}, title = {Phase-separation models for swimming enhancement in complex fluids.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {2}, pages = {023004}, doi = {10.1103/PhysRevE.92.023004}, pmid = {26382500}, issn = {1550-2376}, mesh = {*Models, Biological ; Rheology ; *Swimming ; Viscosity ; }, abstract = {Swimming cells often have to self-propel through fluids displaying non-Newtonian rheology. While past theoretical work seems to indicate that stresses arising from complex fluids should systematically hinder low-Reynolds number locomotion, experimental observations suggest that locomotion enhancement is possible. In this paper we propose a physical mechanism for locomotion enhancement of microscopic swimmers in a complex fluid. It is based on the fact that microstructured fluids will generically phase-separate near surfaces, leading to the presence of low-viscosity layers, which promote slip and decrease viscous friction near the surface of the swimmer. We use two models to address the consequence of this phase separation: a nonzero apparent slip length for the fluid and then an explicit modeling of the change of viscosity in a thin layer near the swimmer. Considering two canonical setups for low-Reynolds number locomotion, namely the waving locomotion of a two-dimensional sheet and that of a three-dimensional filament, we show that phase-separation systematically increases the locomotion speeds, possibly by orders of magnitude. We close by confronting our predictions with recent experimental results.}, } @article {pmid26382498, year = {2015}, author = {Mandal, S and Bandopadhyay, A and Chakraborty, S}, title = {Effect of interfacial slip on the cross-stream migration of a drop in an unbounded Poiseuille flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {2}, pages = {023002}, doi = {10.1103/PhysRevE.92.023002}, pmid = {26382498}, issn = {1550-2376}, abstract = {We analyze the motion and deformation of a buoyant drop suspended in an unbounded fluid which is undergoing a quadratic shearing flow at small Reynolds number in the presence of slip at the interface of the drop. The boundary condition at the interface is accounted for by means of a simple Navier slip condition. Expressions for the velocity and the shape deformation of the drop are derived considering small but finite interface deformation, and results are presented for the specific cases of sedimentation, shear flow, and Poiseuille flow with previously reported results as the limiting cases of our general expressions. The presence of interfacial slip is found to markedly affect axial as well as cross-stream migration velocity of the drop in Poiseuille flow. The effect of slip is more prominent for drops with larger viscosity wherein the drop velocity increases. The presence of significant interface slippage always leads to migration of a deformed drop towards the centerline of the channel for any drop-to-medium viscosity ratio, which is in contrast to the case of no slip at the interface, which allows drop migration towards or away from the centerline depending on the viscosity ratio. We obtain the effect of slip on the cross-stream migration time scale, which quantifies the time required to reach a final steady radial position in the channel. The presence of slip at the drop interface leads to a decrease in the cross-stream migration time scale, which further results in faster motion of the drop in the cross-stream direction. Gravity in the presence of Poiseuille flow is shown to affect not only the axial motion, but also the cross-stream migration velocity of the drop; interfacial slip always increases the drop velocities.}, } @article {pmid26382497, year = {2015}, author = {Burnishev, Y and Steinberg, V}, title = {Turbulence and turbulent drag reduction in swirling flow: Inertial versus viscous forcing.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {2}, pages = {023001}, doi = {10.1103/PhysRevE.92.023001}, pmid = {26382497}, issn = {1550-2376}, abstract = {We report unexpected results of a drastic difference in the transition to fully developed turbulent and turbulent drag reduction (TDR) regimes and in their properties in a von Karman swirling flow with counter-rotating disks of water-based polymer solutions for viscous (by smooth disks) as well as inertial (by bladed disks) forcing and by tracking just torque Γ(t) and pressure p(t) . For the viscous forcing, just a single TDR regime is found with the transition values of the Reynolds number (Re) Re turb c =Re TDR c ≃(4.8±0.2)×10(5) independent of ϕ , whereas for the inertial forcing two turbulent regimes are revealed. The first transition is to fully developed turbulence, and the second one is to the TDR regime with both Re turb c and Re TDR c depending on polymer concentration ϕ . Both regimes differ by the values of C f and C p , by the scaling exponents of the fundamental turbulent characteristics, by the nonmonotonic dependencies of skewness and flatness of the pressure PDFs on Re, and by the different frequency power spectra of p with the different dependencies of the main vortex peak frequency in the p power spectra on ϕ and Re. Thus our experimental results show the transition to the TDR regime in a von Karman swirling flow for the viscous and inertial forcings in a sharp contrast to the recent experiments [Phys. Fluids 10, 426 (1998); Phys. Rev. E 47, R28(R) (1993); and J. Phys.: Condens. Matter 17, S1195 (2005)] where the transition to TDR is observed in the same swirling flow with counter-rotating disks only for the viscous forcing. The latter result has led its authors to the wrong conclusion that TDR is a solely boundary effect contrary to the inertial forcing associated with the bulk effect, and this conception is currently rather widely accepted in literature.}, } @article {pmid26382334, year = {2015}, author = {Piñeirua, M and Godoy-Diana, R and Thiria, B}, title = {Resistive thrust production can be as crucial as added mass mechanisms for inertial undulatory swimmers.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {2}, pages = {021001}, doi = {10.1103/PhysRevE.92.021001}, pmid = {26382334}, issn = {1550-2376}, abstract = {In this Rapid Communication, we address a crucial point regarding the description of moderate to high Reynolds numbers aquatic swimmers. For decades, swimming animals have been classified in two different families of propulsive mechanisms based on the Reynolds number: the resistive swimmers, using local friction to produce the necessary thrust force for locomotion at low Reynolds number, and the reactive swimmers, lying in the high Reynolds range, and using added mass acceleration (described by perfect fluid theory). However, inertial swimmers are also systems that dissipate energy, due to their finite size, therefore involving strong resistive contributions, even for high Reynolds numbers. Using a complete model for the hydrodynamic forces, involving both reactive and resistive contributions, we revisit here the physical mechanisms responsible for the thrust production of such swimmers. We show, for instance, that the resistive part of the force balance is as crucial as added mass effects in the modeling of the thrust force, especially for elongated species. The conclusions brought by this work may have significant contributions to the understanding of complex swimming mechanisms, especially for the future design of artificial swimmers.}, } @article {pmid26367403, year = {2015}, author = {Mekni, MA and Achour, W and Ben Hassen, A}, title = {New Robbins device to evaluate antimicrobial activity against bacterial biofilms on central venous catheters.}, journal = {La Tunisie medicale}, volume = {93}, number = {3}, pages = {153-157}, pmid = {26367403}, issn = {0041-4131}, mesh = {Anti-Bacterial Agents/*therapeutic use ; Bacteriological Techniques/*instrumentation ; Biofilms/*growth & development ; Central Venous Catheters/*microbiology ; Daptomycin/*therapeutic use ; Humans ; Staphylococcus epidermidis/*physiology ; }, abstract = {BACKGROUND: Layouts of biomedical devices were tightly related with the emergence of Staphylococcus epidermidis as a major cause of nosocomial infections because of its ability to form biofilm on the biomaterial surfaces. This fact led researchers to develop in-vitro models to simulate what is really happening during biofilm formation process in order to have a better understanding of this phenomena and then to control it and to resolve the associated problems. The aim of this paper was to develop a homemade dynamic device based on instruments used in clinical practice, easy to mount, with low coast and with no sophisticated features.

METHODS: used to evaluate this dispositive were hydrodynamic calculation and enumeration of bacterial cells on petri dishes and with real time polymerase chain reaction during simulation of Staphylococcus epidermidis biofilm eradication with daptomycin.

RESULTS: With hydrodynamic calculation, Reynolds number was estimated to be 26.62 corresponding to a perfect laminar flux giving suitable dynamic growth environment for such experiment. Data recovered from cell enumeration with the two methods showed that bacterial colonization of the tested catheter segment was significantly reduced after 24 and 48h of treatment with daptomycin (P<0.01) reflecting a considerable reliability of this device.

CONCLUSION: the simple dispositive developed in this work has shown acceptable hydrodynamic proprieties and good reliability making research on biofilm easy to reach.}, } @article {pmid26362281, year = {2016}, author = {Wang, Q and Othmer, HG}, title = {Computational analysis of amoeboid swimming at low Reynolds number.}, journal = {Journal of mathematical biology}, volume = {72}, number = {7}, pages = {1893-1926}, pmid = {26362281}, issn = {1432-1416}, mesh = {Dictyostelium/*physiology ; *Models, Biological ; Swimming ; }, abstract = {Recent experimental work has shown that eukaryotic cells can swim in a fluid as well as crawl on a substrate. We investigate the swimming behavior of Dictyostelium discoideum amoebae who swim by initiating traveling protrusions at the front that propagate rearward. In our model we prescribe the velocity at the surface of the swimming cell, and use techniques of complex analysis to develop 2D models that enable us to study the fluid-cell interaction. Shapes that approximate the protrusions used by Dictyostelium discoideum can be generated via the Schwarz-Christoffel transformation, and the boundary-value problem that results for swimmers in the Stokes flow regime is then reduced to an integral equation on the boundary of the unit disk. We analyze the swimming characteristics of several varieties of swimming Dictyostelium discoideum amoebae, and discuss how the slenderness of the cell body and the shapes of the protrusion effect the swimming of these cells. The results may provide guidance in designing low Reynolds number swimming models.}, } @article {pmid26353555, year = {2015}, author = {Wang, J and Wang, Y and Chen, Z and Chen, K and Li, B}, title = {The Numerical Simulation of Liquid-Vapor Stratified Flow in Horizontal Metal-Foam Tubes.}, journal = {Journal of nanoscience and nanotechnology}, volume = {15}, number = {4}, pages = {3161-3167}, doi = {10.1166/jnn.2015.9626}, pmid = {26353555}, issn = {1533-4899}, abstract = {In this paper, a boiling stratified flow model in a metal-foam tube is proposed. First, based on Branuer non-equilibrium gas-liquid interface model, a force balance on the gas-liquid interface in metal-foam is calculated. The shape of the interface of upper gas phase and lower liquid phase in metal foam tube is obtained. As for the lower liquid phase, the energy conservation equations of liquid and metal foam are formulated, which account for porosity and fiber diameter of foam on the basis of non-local thermal equilibrium model (NTEM), respectively. Therefore, a profile of temperature difference between liquid and metal foam can be obtained. For the upper gas phase, an empirical correlation developed by other researchers is utilized to obtain temperature difference between gas phase and solid wall. In addition, the variation of the Reynolds number with increasing mass quality along the flow direction is acquired. Ultimately, an average circumference heat transfer coefficient is calculated. The results of circumference heat transfer coefficient agree well with available experimental data, showing the prediction of the proposed stratified flow model is feasible. The reason resulting in discrepancies between the prediction and experiment data is also illustrated.}, } @article {pmid26353536, year = {2015}, author = {Wei, B and Yang, M and Wang, Z and Xu, H and Zhang, Y}, title = {Flow and Thermal Performance of a Water-Cooled Periodic Transversal Elliptical Microchannel Heat Sink for Chip Cooling.}, journal = {Journal of nanoscience and nanotechnology}, volume = {15}, number = {4}, pages = {3061-3066}, doi = {10.1166/jnn.2015.9683}, pmid = {26353536}, issn = {1533-4899}, abstract = {Flow and thermal performance of transversal elliptical microchannels were investigated as a passive scheme to enhance the heat transfer performance of laminar fluid flow. The periodic transversal elliptical micro-channel is designed and its pressure drop and heat transfer characteristics in laminar flow are numerically investigated. Based on the comparison with a conventional straight micro- channel having rectangular cross section, it is found that periodic transversal elliptical microchannel not only has great potential to reduce pressure drop but also dramatically enhances heat transfer performance. In addition, when the Reynolds number equals to 192, the pressure drop of the transversal elliptical channel is 36.5% lower than that of the straight channel, while the average Nusselt number is 72.8% higher; this indicates that the overall thermal performance of the periodic transversal elliptical microchannel is superior to the conventional straight microchannel. It is suggested that such transversal elliptical microchannel are attractive candidates for cooling future electronic chips effectively with much lower pressure drop.}, } @article {pmid26347566, year = {2015}, author = {Berthé, R and Lehmann, FO}, title = {Body appendages fine-tune posture and moments in freely manoeuvring fruit flies.}, journal = {The Journal of experimental biology}, volume = {218}, number = {Pt 20}, pages = {3295-3307}, doi = {10.1242/jeb.122408}, pmid = {26347566}, issn = {1477-9145}, mesh = {Animals ; Behavior, Animal/physiology ; Biomechanical Phenomena ; Drosophila melanogaster/*physiology ; Extremities/physiology ; *Flight, Animal ; Posture ; Wings, Animal/physiology ; }, abstract = {The precise control of body posture by turning moments is key to elevated locomotor performance in flying animals. Although elevated moments for body stabilization are typically produced by wing aerodynamics, animals also steer using drag on body appendages, shifting their centre of body mass, and changing moments of inertia caused by active alterations in body shape. To estimate the instantaneous contribution of each of these components for posture control in an insect, we three-dimensionally reconstructed body posture and movements of body appendages in freely manoeuvring fruit flies (Drosophila melanogaster) by high-speed video and experimentally scored drag coefficients of legs and body trunk at low Reynolds number. The results show that the sum of leg- and abdomen-induced yaw moments dominates wing-induced moments during 17% of total flight time but is, on average, 7.2-times (roll, 3.4-times) smaller during manoeuvring. Our data reject a previous hypothesis on synergistic moment support, indicating that drag on body appendages and mass-shift inhibit rather than support turning moments produced by the wings. Numerical modelling further shows that hind leg extension alters the moments of inertia around the three main body axes of the animal by not more than 6% during manoeuvring, which is significantly less than previously reported for other insects. In sum, yaw, pitch and roll steering by body appendages probably fine-tune turning behaviour and body posture, without providing a significant advantage for posture stability and moment support. Motion control of appendages might thus be part of the insect's trimming reflexes, which reduce imbalances in moment generation caused by unilateral wing damage and abnormal asymmetries of the flight apparatus.}, } @article {pmid26347563, year = {2015}, author = {van Bokhorst, E and de Kat, R and Elsinga, GE and Lentink, D}, title = {Feather roughness reduces flow separation during low Reynolds number glides of swifts.}, journal = {The Journal of experimental biology}, volume = {218}, number = {Pt 20}, pages = {3179-3191}, doi = {10.1242/jeb.121426}, pmid = {26347563}, issn = {1477-9145}, mesh = {Animals ; Biomechanical Phenomena ; Birds/anatomy & histology/*physiology ; Feathers/*anatomy & histology ; *Flight, Animal ; *Models, Biological ; Wings, Animal/anatomy & histology/*physiology ; }, abstract = {Swifts are aerodynamically sophisticated birds with a small arm and large hand wing that provides them with exquisite control over their glide performance. However, their hand wings have a seemingly unsophisticated surface roughness that is poised to disturb flow. This roughness of about 2% chord length is formed by the valleys and ridges of overlapping primary feathers with thick protruding rachides, which make the wing stiffer. An earlier flow study of laminar-turbulent boundary layer transition over prepared swift wings suggested that swifts can attain laminar flow at a low angle of attack. In contrast, aerodynamic design theory suggests that airfoils must be extremely smooth to attain such laminar flow. In hummingbirds, which have similarly rough wings, flow measurements on a 3D printed model suggest that the flow separates at the leading edge and becomes turbulent well above the rachis bumps in a detached shear layer. The aerodynamic function of wing roughness in small birds is, therefore, not fully understood. Here, we performed particle image velocimetry and force measurements to compare smooth versus rough 3D-printed models of the swift hand wing. The high-resolution boundary layer measurements show that the flow over rough wings is indeed laminar at a low angle of attack and a low Reynolds number, but becomes turbulent at higher values. In contrast, the boundary layer over the smooth wing forms open laminar separation bubbles that extend beyond the trailing edge. The boundary layer dynamics of the smooth surface varies non-linearly as a function of angle of attack and Reynolds number, whereas the rough surface boasts more consistent turbulent boundary layer dynamics. Comparison of the corresponding drag values, lift values and glide ratios suggests, however, that glide performance is equivalent. The increased structural performance, boundary layer robustness and equivalent aerodynamic performance of rough wings might have provided small (proto) birds with an evolutionary window to high glide performance.}, } @article {pmid26337704, year = {2015}, author = {Lee, JS and Park, SJ and Lee, JH and Weon, BM and Fezzaa, K and Je, JH}, title = {Origin and dynamics of vortex rings in drop splashing.}, journal = {Nature communications}, volume = {6}, number = {}, pages = {8187}, pmid = {26337704}, issn = {2041-1723}, abstract = {A vortex is a flow phenomenon that is very commonly observed in nature. More than a century, a vortex ring that forms during drop splashing has caught the attention of many scientists due to its importance in understanding fluid mixing and mass transport processes. However, the origin of the vortices and their dynamics remain unclear, mostly due to the lack of appropriate visualization methods. Here, with ultrafast X-ray phase-contrast imaging, we show that the formation of vortex rings originates from the energy transfer by capillary waves generated at the moment of the drop impact. Interestingly, we find a row of vortex rings along the drop wall, as demonstrated by a phase diagram established here, with different power-law dependencies of the angular velocities on the Reynolds number. These results provide important insight that allows understanding and modelling any type of vortex rings in nature, beyond just vortex rings during drop splashing.}, } @article {pmid26328576, year = {2015}, author = {Huhn, F and van Rees, WM and Gazzola, M and Rossinelli, D and Haller, G and Koumoutsakos, P}, title = {Quantitative flow analysis of swimming dynamics with coherent Lagrangian vortices.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {25}, number = {8}, pages = {087405}, doi = {10.1063/1.4919784}, pmid = {26328576}, issn = {1089-7682}, abstract = {Undulatory swimmers flex their bodies to displace water, and in turn, the flow feeds back into the dynamics of the swimmer. At moderate Reynolds number, the resulting flow structures are characterized by unsteady separation and alternating vortices in the wake. We use the flow field from simulations of a two-dimensional, incompressible viscous flow of an undulatory, self-propelled swimmer and detect the coherent Lagrangian vortices in the wake to dissect the driving momentum transfer mechanisms. The detected material vortex boundary encloses a Lagrangian control volume that serves to track back the vortex fluid and record its circulation and momentum history. We consider two swimming modes: the C-start escape and steady anguilliform swimming. The backward advection of the coherent Lagrangian vortices elucidates the geometry of the vorticity field and allows for monitoring the gain and decay of circulation and momentum transfer in the flow field. For steady swimming, momentum oscillations of the fish can largely be attributed to the momentum exchange with the vortex fluid. For the C-start, an additionally defined jet fluid region turns out to balance the high momentum change of the fish during the rapid start.}, } @article {pmid26315920, year = {2015}, author = {Broderick, SP and Houston, JG and Walsh, MT}, title = {The influence of the instabilities in modelling arteriovenous junction haemodynamics.}, journal = {Journal of biomechanics}, volume = {48}, number = {13}, pages = {3591-3598}, doi = {10.1016/j.jbiomech.2015.07.038}, pmid = {26315920}, issn = {1873-2380}, mesh = {Arteriovenous Fistula/*physiopathology ; Biomechanical Phenomena ; Blood Pressure ; Computer Simulation ; Humans ; Hydrodynamics ; Models, Biological ; Regional Blood Flow ; }, abstract = {The arteriovenous junction is characterised by high flow rates, large pressure difference and typically a palpable thrill or audible bruit, associated with turbulent flow. However, the arteriovenous junction is frequently studied with the assumption of streamline flow. This assumption is based on the Reynolds number calculation, although other factors can contribute to turbulent generation. In this study, the presence of instabilities is examined and the influencing factors discussed. This was performed using a pseudo-realistic geometry with adapted graft angles, vein diameter, outflow split ratio and graft inlet velocity values. Correlation was performed between steady and unsteady averaged simulation cases with correlation performance ranked. Overall the arteriovenous junction is capable of possessing highly disturbed flows, in which strict modelling requirements are necessary to capture such instabilities and avoid erroneous conclusions. Vein diameter and flow split ratio contribute to turbulent generation, thus Reynolds number cannot be used as a sole turbulent criterion in the arteriovenous junction.}, } @article {pmid26314259, year = {2015}, author = {Krieger, MS and Dias, MA and Powers, TR}, title = {Minimal model for transient swimming in a liquid crystal.}, journal = {The European physical journal. E, Soft matter}, volume = {38}, number = {8}, pages = {94}, pmid = {26314259}, issn = {1292-895X}, mesh = {Elasticity ; *Hydrodynamics ; Liquid Crystals/*chemistry ; *Models, Theoretical ; Rotation ; Viscosity ; }, abstract = {When a microorganism begins swimming from rest in a Newtonian fluid such as water, it rapidly attains its steady-state swimming speed since changes in the velocity field spread quickly when the Reynolds number is small. However, swimming microorganisms are commonly found or studied in complex fluids. Because these fluids have long relaxation times, the time to attain the steady-state swimming speed can also be long. In this article we study the swimming startup problem in the simplest liquid crystalline fluid: a two-dimensional hexatic liquid crystal film. We study the dependence of startup time on anchoring strength and Ericksen number, which is the ratio of viscous to elastic stresses. For strong anchoring, the fluid flow starts up immediately but the liquid crystal field and swimming velocity attain their sinusoidal steady-state values after a time proportional to the relaxation time of the liquid crystal. When the Ericksen number is high, the behavior is the same as in the strong-anchoring case for any anchoring strength. We also find that the startup time increases with the ratio of the rotational viscosity to the shear viscosity, and then ultimately saturates once the rotational viscosity is much greater than the shear viscosity.}, } @article {pmid26314256, year = {2015}, author = {Felderhof, BU}, title = {Efficient swimming of an assembly of rigid spheres at low Reynolds number.}, journal = {The European physical journal. E, Soft matter}, volume = {38}, number = {8}, pages = {90}, pmid = {26314256}, issn = {1292-895X}, mesh = {*Hydrodynamics ; Microfluidics ; *Models, Theoretical ; Viscosity ; }, abstract = {The swimming of an assembly of rigid spheres immersed in a viscous fluid of infinite extent is studied in low-Reynolds-number hydrodynamics. The instantaneous swimming velocity and rate of dissipation are expressed in terms of the time-dependent displacements of sphere centers about their collective motion. For small-amplitude swimming with periodically oscillating displacements, optimization of the mean swimming speed at given mean power leads to an eigenvalue problem involving a velocity matrix and a power matrix. The corresponding optimal stroke permits generalization to large-amplitude motion in a model of spheres with harmonic interactions and corresponding actuating forces. The method allows straightforward calculation of the swimming performance of structures modeled as assemblies of interacting rigid spheres. A model of three collinear spheres with motion along the common axis is studied as an example.}, } @article {pmid26298765, year = {2015}, author = {Adams, MC and Hurt, EE and Barbano, DM}, title = {Effect of ceramic membrane channel geometry and uniform transmembrane pressure on limiting flux and serum protein removal during skim milk microfiltration.}, journal = {Journal of dairy science}, volume = {98}, number = {11}, pages = {7527-7543}, doi = {10.3168/jds.2015-9753}, pmid = {26298765}, issn = {1525-3198}, mesh = {Animals ; Blood Proteins/analysis ; Caseins/analysis ; Ceramics/*chemistry ; Filtration ; *Food Handling ; Hydrodynamics ; Hydrogen-Ion Concentration ; Membranes, Artificial ; Milk/*chemistry ; Milk Proteins/analysis ; }, abstract = {Our objectives were to determine the effects of a ceramic microfiltration (MF) membrane's retentate flow channel geometry (round or diamond-shaped) and uniform transmembrane pressure (UTP) on limiting flux (LF) and serum protein (SP) removal during skim milk MF at a temperature of 50°C, a retentate protein concentration of 8.5%, and an average cross-flow velocity of 7 m·s(-1). Performance of membranes with round and diamond flow channels was compared in UTP mode. Performance of the membrane with round flow channels was compared with and without UTP. Using UTP with round flow channel MF membranes increased the LF by 5% when compared with not using UTP, but SP removal was not affected by the use of UTP. Using membranes with round channels instead of diamond-shaped channels in UTP mode increased the LF by 24%. This increase was associated with a 25% increase in Reynolds number and can be explained by lower shear at the vertices of the diamond-shaped channel's surface. The SP removal factor of the diamond channel system was higher than the SP removal factor of the round channel system below the LF. However, the diamond channel system passed more casein into the MF permeate than the round channel system. Because only one batch of each membrane was tested in our study, it was not possible to determine if the differences in protein rejection between channel geometries were due to the membrane design or random manufacturing variation. Despite the lower LF of the diamond channel system, the 47% increase in membrane module surface area of the diamond channel system produced a modular permeate removal rate that was at least 19% higher than the round channel system. Consequently, using diamond channel membranes instead of round channel membranes could reduce some of the costs associated with ceramic MF of skim milk if fewer membrane modules could be used to attain the required membrane area.}, } @article {pmid26296866, year = {2015}, author = {Higuchi, M and Terada, K and Sugano, K}, title = {Coning phenomena under laminar flow.}, journal = {European journal of pharmaceutical sciences : official journal of the European Federation for Pharmaceutical Sciences}, volume = {80}, number = {}, pages = {53-55}, doi = {10.1016/j.ejps.2015.08.004}, pmid = {26296866}, issn = {1879-0720}, mesh = {Nuclear Proteins ; *Pharmacokinetics ; RNA-Binding Proteins ; *Rheology ; Rotation ; Technology, Pharmaceutical/*methods ; }, abstract = {The purpose of the present study was to investigate coning phenomena in the paddle dissolution test under laminar flow (Reynolds number <500). The minimum rotation speed at which the coning phenomena disappear (no coning rpm, NCrpm) was measured in viscous media (23 to 147mPa∙s) using various particles. The exponent values of particle size, density, and viscosity parameters in the Zwietering equation were found to be 0.066, 0.38, and 0.22, respectively. NCrpm was appropriately predicted by the Zwietering equation (average error: 8rpm). These values are very different from those for turbulent flow, suggesting that the main physical forces governing the motion of particles can be different between turbulent flow and laminar flow. This point should be taken into account when understanding the dissolution of drug products in viscous fluids representing the fed state.}, } @article {pmid26278133, year = {2015}, author = {Hassanpourfard, M and Nikakhtari, Z and Ghosh, R and Das, S and Thundat, T and Liu, Y and Kumar, A}, title = {Bacterial floc mediated rapid streamer formation in creeping flows.}, journal = {Scientific reports}, volume = {5}, number = {}, pages = {13070}, pmid = {26278133}, issn = {2045-2322}, mesh = {Bacteria/*metabolism ; Bacterial Adhesion/physiology ; Biofilms ; Elasticity ; Green Fluorescent Proteins/genetics/metabolism ; Microfluidic Analytical Techniques/instrumentation/*methods ; Microscopy, Fluorescence ; Microscopy, Video ; Pseudomonas fluorescens/physiology ; }, abstract = {One of the central puzzles concerning the interaction of low Reynolds number fluid transport with bacterial biomass is the formation of filamentous structures called streamers. In this manuscript, we report our discovery of a new kind of low Re bacterial streamers, which appear from pre-formed bacterial flocs. In sharp contrast to the biofilm-mediated streamers, these streamers form over extremely small timescales (less than a second). Our experiments, carried out in a microchannel with micropillars rely on fluorescence microscopy techniques to illustrate that floc-mediated streamers form when a freely-moving floc adheres to the micropillar wall and gets rapidly sheared by the background flow. We also show that at their inception the deformation of the flocs is dominated by recoverable large strains indicating significant elasticity. These strains subsequently increase tremendously to produce filamentous streamers. Interestingly, we find that these fully formed streamers are not static structures and show viscous response at time scales larger than their formation time scales. Finally, we show that such novel streamer formation can lead to rapid clogging of microfluidic devices.}, } @article {pmid26274284, year = {2015}, author = {Wedin, H and Cherubini, S and Bottaro, A}, title = {Effect of plate permeability on nonlinear stability of the asymptotic suction boundary layer.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {1}, pages = {013022}, doi = {10.1103/PhysRevE.92.013022}, pmid = {26274284}, issn = {1550-2376}, abstract = {The nonlinear stability of the asymptotic suction boundary layer is studied numerically, searching for finite-amplitude solutions that bifurcate from the laminar flow state. By changing the boundary conditions for disturbances at the plate from the classical no-slip condition to more physically sound ones, the stability characteristics of the flow may change radically, both for the linearized as well as the nonlinear problem. The wall boundary condition takes into account the permeability K̂ of the plate; for very low permeability, it is acceptable to impose the classical boundary condition (K̂=0). This leads to a Reynolds number of approximately Re(c)=54400 for the onset of linearly unstable waves, and close to Re(g)=3200 for the emergence of nonlinear solutions [F. A. Milinazzo and P. G. Saffman, J. Fluid Mech. 160, 281 (1985); J. H. M. Fransson, Ph.D. thesis, Royal Institute of Technology, KTH, Sweden, 2003]. However, for larger values of the plate's permeability, the lower limit for the existence of linear and nonlinear solutions shifts to significantly lower Reynolds numbers. For the largest permeability studied here, the limit values of the Reynolds numbers reduce down to Re(c)=796 and Re(g)=294. For all cases studied, the solutions bifurcate subcritically toward lower Re, and this leads to the conjecture that they may be involved in the very first stages of a transition scenario similar to the classical route of the Blasius boundary layer initiated by Tollmien-Schlichting (TS) waves. The stability of these nonlinear solutions is also investigated, showing a low-frequency main unstable mode whose growth rate decreases with increasing permeability and with the Reynolds number, following a power law Re(-ρ), where the value of ρ depends on the permeability coefficient K̂. The nonlinear dynamics of the flow in the vicinity of the computed finite-amplitude solutions is finally investigated by direct numerical simulations, providing a viable scenario for subcritical transition due to TS waves.}, } @article {pmid26274272, year = {2015}, author = {Zhou, L and Rauh, C and Delgado, A}, title = {Multifractal-cascade model for inertial and dissipation ranges based on the wavelet reconstruction method.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {1}, pages = {013010}, doi = {10.1103/PhysRevE.92.013010}, pmid = {26274272}, issn = {1550-2376}, abstract = {The discrete wavelet is introduced to construct the turbulent velocity fields. The simple binary cascade model p model is served as the inertial range model for velocity increments. The dissipation model, which follows Foias et al. [Phys. Fluids A 2, 464 (1990)] takes the form of exp(-gk). The length of inertial and dissipation ranges is computed according to the different construction levels. Based on the binary cascade theory and the proposed dissipation model, the Reynolds number regarding to the cascade process can be estimated. The dissipation rate calculated from the proposed model not only agrees with the existing experiment data, but also suggests that the dissipation rate is not an independent variable with respect to the Reynolds number.}, } @article {pmid26274266, year = {2015}, author = {Rorai, C and Mininni, PD and Pouquet, A}, title = {Stably stratified turbulence in the presence of large-scale forcing.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {1}, pages = {013003}, doi = {10.1103/PhysRevE.92.013003}, pmid = {26274266}, issn = {1550-2376}, abstract = {We perform two high-resolution direct numerical simulations of stratified turbulence for Reynolds number equal to Re≈25000 and Froude number, respectively, of Fr≈0.1 and Fr≈0.03. The flows are forced at large scale and discretized on an isotropic grid of 2048(3) points. Stratification makes the flow anisotropic and introduces two extra characteristic scales with respect to homogeneous isotropic turbulence: the buoyancy scale, L(B), and the Ozmidov scale, ℓ(oz). The former is related to the number of layers that the flow develops in the direction of gravity, and the latter is regarded as the scale at which isotropy is recovered. The values of L(B) and ℓ(oz) depend on the Froude number, and their absolute and relative amplitudes affect the repartition of energy among Fourier modes in ways that are not easy to predict. By contrasting the behavior of the two simulated flows we identify some surprising similarities: After an initial transient the two flows evolve towards comparable values of the kinetic and potential enstrophy and energy dissipation rate. This is the result of the Reynolds number being large enough in both flows for the Ozmidov scale to be resolved. When properly dimensionalized, the energy dissipation rate is compatible with atmospheric observations. Further similarities emerge at large scales: The same ratio between potential and total energy (≈0.1) is spontaneously selected by the flows, and slow modes grow monotonically in both regimes, causing a slow increase of the total energy in time. The axisymmetric total energy spectrum shows a wide variety of spectral slopes as a function of the angle between the imposed stratification and the wave vector. One-dimensional energy spectra computed in the direction parallel to gravity are flat from the forcing up to buoyancy scale. At intermediate scales a ∼k(-3) parallel spectrum develops for the Fr≈0.03 run, whereas for weaker stratification, the saturation spectrum does not have enough scales to develop and instead one observes a power law compatible with Kolmogorov scaling. Finally, the spectrum of helicity is flat until L(B), as observed in the nocturnal planetary boundary layer.}, } @article {pmid26269230, year = {2015}, author = {van Leeuwen, JL and Voesenek, CJ and Müller, UK}, title = {How body torque and Strouhal number change with swimming speed and developmental stage in larval zebrafish.}, journal = {Journal of the Royal Society, Interface}, volume = {12}, number = {110}, pages = {0479}, pmid = {26269230}, issn = {1742-5662}, mesh = {Animals ; Biomechanical Phenomena ; *Models, Biological ; Swimming/*physiology ; Zebrafish/*physiology ; }, abstract = {Small undulatory swimmers such as larval zebrafish experience both inertial and viscous forces, the relative importance of which is indicated by the Reynolds number (Re). Re is proportional to swimming speed (vswim) and body length; faster swimming reduces the relative effect of viscous forces. Compared with adults, larval fish experience relatively high (mainly viscous) drag during cyclic swimming. To enhance thrust to an equally high level, they must employ a high product of tail-beat frequency and (peak-to-peak) amplitude fAtail, resulting in a relatively high fAtail/vswim ratio (Strouhal number, St), and implying relatively high lateral momentum shedding and low propulsive efficiency. Using kinematic and inverse-dynamics analyses, we studied cyclic swimming of larval zebrafish aged 2-5 days post-fertilization (dpf). Larvae at 4-5 dpf reach higher f (95 Hz) and Atail (2.4 mm) than at 2 dpf (80 Hz, 1.8 mm), increasing swimming speed and Re, indicating increasing muscle powers. As Re increases (60 → 1400), St (2.5 → 0.72) decreases nonlinearly towards values of large swimmers (0.2-0.6), indicating increased propulsive efficiency with vswim and age. Swimming at high St is associated with high-amplitude body torques and rotations. Low propulsive efficiencies and large yawing amplitudes are unavoidable physical constraints for small undulatory swimmers.}, } @article {pmid26267247, year = {2015}, author = {Rashidi, MM and Freidoonimehr, N and Momoniat, E and Rostami, B}, title = {Study of Nonlinear MHD Tribological Squeeze Film at Generalized Magnetic Reynolds Numbers Using DTM.}, journal = {PloS one}, volume = {10}, number = {8}, pages = {e0135004}, pmid = {26267247}, issn = {1932-6203}, mesh = {*Models, Theoretical ; }, abstract = {In the current article, a combination of the differential transform method (DTM) and Padé approximation method are implemented to solve a system of nonlinear differential equations modelling the flow of a Newtonian magnetic lubricant squeeze film with magnetic induction effects incorporated. Solutions for the transformed radial and tangential momentum as well as solutions for the radial and tangential induced magnetic field conservation equations are determined. The DTM-Padé combined method is observed to demonstrate excellent convergence, stability and versatility in simulating the magnetic squeeze film problem. The effects of involved parameters, i.e. squeeze Reynolds number (N1), dimensionless axial magnetic force strength parameter (N2), dimensionless tangential magnetic force strength parameter (N3), and magnetic Reynolds number (Rem) are illustrated graphically and discussed in detail. Applications of the study include automotive magneto-rheological shock absorbers, novel aircraft landing gear systems and biological prosthetics.}, } @article {pmid26252657, year = {2015}, author = {Nabawy, MR and Crowthe, WJ}, title = {A Quasi-Steady Lifting Line Theory for Insect-Like Hovering Flight.}, journal = {PloS one}, volume = {10}, number = {8}, pages = {e0134972}, pmid = {26252657}, issn = {1932-6203}, mesh = {Animals ; Biomechanical Phenomena ; Computer Simulation ; Flight, Animal/*physiology ; Insecta/*physiology ; *Models, Biological ; Time Factors ; Wings, Animal/anatomy & histology/physiology ; }, abstract = {A novel lifting line formulation is presented for the quasi-steady aerodynamic evaluation of insect-like wings in hovering flight. The approach allows accurate estimation of aerodynamic forces from geometry and kinematic information alone and provides for the first time quantitative information on the relative contribution of induced and profile drag associated with lift production for insect-like wings in hover. The main adaptation to the existing lifting line theory is the use of an equivalent angle of attack, which enables capture of the steady non-linear aerodynamics at high angles of attack. A simple methodology to include non-ideal induced effects due to wake periodicity and effective actuator disc area within the lifting line theory is included in the model. Low Reynolds number effects as well as the edge velocity correction required to account for different wing planform shapes are incorporated through appropriate modification of the wing section lift curve slope. The model has been successfully validated against measurements from revolving wing experiments and high order computational fluid dynamics simulations. Model predicted mean lift to weight ratio results have an average error of 4% compared to values from computational fluid dynamics for eight different insect cases. Application of an unmodified linear lifting line approach leads on average to a 60% overestimation in the mean lift force required for weight support, with most of the discrepancy due to use of linear aerodynamics. It is shown that on average for the eight insects considered, the induced drag contributes 22% of the total drag based on the mean cycle values and 29% of the total drag based on the mid half-stroke values.}, } @article {pmid26252016, year = {2015}, author = {Zhang, C and Hedrick, TL and Mittal, R}, title = {Centripetal Acceleration Reaction: An Effective and Robust Mechanism for Flapping Flight in Insects.}, journal = {PloS one}, volume = {10}, number = {8}, pages = {e0132093}, pmid = {26252016}, issn = {1932-6203}, mesh = {*Acceleration ; Animals ; Biomechanical Phenomena ; Computer Simulation ; Flight, Animal/*physiology ; Models, Biological ; Moths/*physiology ; Time Factors ; Wings, Animal/*physiology ; }, abstract = {Despite intense study by physicists and biologists, we do not fully understand the unsteady aerodynamics that relate insect wing morphology and kinematics to lift generation. Here, we formulate a force partitioning method (FPM) and implement it within a computational fluid dynamic model to provide an unambiguous and physically insightful division of aerodynamic force into components associated with wing kinematics, vorticity, and viscosity. Application of the FPM to hawkmoth and fruit fly flight shows that the leading-edge vortex is the dominant mechanism for lift generation for both these insects and contributes between 72-85% of the net lift. However, there is another, previously unidentified mechanism, the centripetal acceleration reaction, which generates up to 17% of the net lift. The centripetal acceleration reaction is similar to the classical inviscid added-mass in that it depends only on the kinematics (i.e. accelerations) of the body, but is different in that it requires the satisfaction of the no-slip condition, and a combination of tangential motion and rotation of the wing surface. Furthermore, the classical added-mass force is identically zero for cyclic motion but this is not true of the centripetal acceleration reaction. Furthermore, unlike the lift due to vorticity, centripetal acceleration reaction lift is insensitive to Reynolds number and to environmental flow perturbations, making it an important contributor to insect flight stability and miniaturization. This force mechanism also has broad implications for flow-induced deformation and vibration, underwater locomotion and flows involving bubbles and droplets.}, } @article {pmid26244665, year = {2015}, author = {Yu, X and Sun, Z and Huang, R and Zhang, Y and Huang, Y}, title = {A Thermal Equilibrium Analysis of Line Contact Hydrodynamic Lubrication Considering the Influences of Reynolds Number, Load and Temperature.}, journal = {PloS one}, volume = {10}, number = {8}, pages = {e0134806}, doi = {10.1371/journal.pone.0134806}, pmid = {26244665}, issn = {1932-6203}, mesh = {Computer Simulation ; Convection ; Friction ; *Hydrodynamics ; *Lubrication ; Models, Chemical ; Temperature ; Weight-Bearing ; }, abstract = {Thermal effects such as conduction, convection and viscous dissipation are important to lubrication performance, and they vary with the friction conditions. These variations have caused some inconsistencies in the conclusions of different researchers regarding the relative contributions of these thermal effects. To reveal the relationship between the contributions of the thermal effects and the friction conditions, a steady-state THD analysis model was presented. The results indicate that the contribution of each thermal effect sharply varies with the Reynolds number and temperature. Convective effect could be dominant under certain conditions. Additionally, the accuracy of some simplified methods of thermo-hydrodynamic analysis is further discussed.}, } @article {pmid26226349, year = {2015}, author = {Maertens, AP and Triantafyllou, MS and Yue, DK}, title = {Efficiency of fish propulsion.}, journal = {Bioinspiration & biomimetics}, volume = {10}, number = {4}, pages = {046013}, doi = {10.1088/1748-3190/10/4/046013}, pmid = {26226349}, issn = {1748-3190}, mesh = {Animals ; Computer Simulation ; Energy Metabolism/*physiology ; Energy Transfer/*physiology ; Fishes/*physiology ; Friction ; *Models, Biological ; Rheology/*methods ; Shear Strength/physiology ; Stress, Mechanical ; Viscosity ; }, abstract = {The system efficiency of a self-propelled flexible body is ill-defined, hence we introduce the concept of quasi-propulsive efficiency, defined as the ratio of the power needed to tow a body in rigid-straight condition over the power it requires for self-propulsion, both measured for the same speed. Through examples we show that the quasi-propulsive efficiency is a rational non-dimensional metric of the propulsive fitness of fish and fish-like mechanisms, consistent with the goal to minimize fuel consumption under size and velocity constraints. We perform two-dimensional viscous simulations and apply the concept of quasi-propulsive efficiency to illustrate and discuss the efficiency of two-dimensional undulating foils employing first carangiform and then anguilliform kinematics. We show that low efficiency may be due to adverse body-propulsor hydrodynamic interactions, which cannot be accounted for by an increase in friction drag, as done previously, since at the Reynolds number Re = 5 000 considered in the simulations, pressure is a major contributor to both thrust and drag.}, } @article {pmid26196807, year = {2015}, author = {Linkmann, MF and Berera, A and McComb, WD and McKay, ME}, title = {Nonuniversality and Finite Dissipation in Decaying Magnetohydrodynamic Turbulence.}, journal = {Physical review letters}, volume = {114}, number = {23}, pages = {235001}, doi = {10.1103/PhysRevLett.114.235001}, pmid = {26196807}, issn = {1079-7114}, abstract = {A model equation for the Reynolds number dependence of the dimensionless dissipation rate in freely decaying homogeneous magnetohydrodynamic turbulence in the absence of a mean magnetic field is derived from the real-space energy balance equation, leading to Cϵ=Cϵ,∞+C/R-+O(1/R-(2)), where R- is a generalized Reynolds number. The constant Cϵ,∞ describes the total energy transfer flux. This flux depends on magnetic and cross helicities, because these affect the nonlinear transfer of energy, suggesting that the value of Cϵ,∞ is not universal. Direct numerical simulations were conducted on up to 2048(3) grid points, showing good agreement between data and the model. The model suggests that the magnitude of cosmological-scale magnetic fields is controlled by the values of the vector field correlations. The ideas introduced here can be used to derive similar model equations for other turbulent systems.}, } @article {pmid26195761, year = {2015}, author = {Wang, J and Li, Q and E, W}, title = {Study of the instability of the Poiseuille flow using a thermodynamic formalism.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {112}, number = {31}, pages = {9518-9523}, pmid = {26195761}, issn = {1091-6490}, mesh = {Friction ; Kinetics ; Magnetic Phenomena ; Models, Theoretical ; *Rheology ; Skin Physiological Phenomena ; Solutions ; Thermodynamics ; }, abstract = {The stability of the plane Poiseuille flow is analyzed using a thermodynamic formalism by considering the deterministic Navier-Stokes equation with Gaussian random initial data. A unique critical Reynolds number, Rec ≈ 2,332, at which the probability of observing puffs in the solution changes from 0 to 1, is numerically demonstrated to exist in the thermodynamic limit and is found to be independent of the noise amplitude. Using the puff density as the macrostate variable, the free energy of such a system is computed and analyzed. The puff density approaches zero as the critical Reynolds number is approached from above, signaling a continuous transition despite the fact that the bifurcation is subcritical for a finite-sized system. An action function is found for the probability of observing puffs in a small subregion of the flow, and this action function depends only on the Reynolds number. The strategy used here should be applicable to a wide range of other problems exhibiting subcritical instabilities.}, } @article {pmid26180066, year = {2015}, author = {Gemmell, BJ and Jiang, H and Buskey, EJ}, title = {A tale of the ciliate tail: investigation into the adaptive significance of this sub-cellular structure.}, journal = {Proceedings. Biological sciences}, volume = {282}, number = {1812}, pages = {20150770}, pmid = {26180066}, issn = {1471-2954}, mesh = {Biomechanical Phenomena ; Ciliophora/*physiology ; *Escape Reaction ; *Hydrodynamics ; Species Specificity ; Swimming ; Video Recording ; }, abstract = {Ciliates can form an important link between the microbial loop and higher trophic levels primarily through consumption by copepods. This high predation pressure has resulted in a number of ciliate species developing rapid escape swimming behaviour. Several species of these escaping ciliates also possess a long contractile tail for which the functionality remains unresolved. We use high-speed video, specialized optics and novel fluid visualization tools to evaluate the role of this contractile appendage in two free-swimming ciliates, Pseudotontonia sp. and Tontonia sp., and compare the performance to escape swimming behaviour of a non-tailed species, Strobilidium sp. Here, we show that 'tailed' species respond to hydrodynamic disturbances with extremely short response latencies (less than or equal to 0.89 ms) by rapidly contracting the tail which carries the cell body 2-4 cell diameters within a few milliseconds. This provides an advantage over non-tailed species during the critical first 10-30 ms of an escape. Two small, short-lived vortex rings are created during contraction of the tail. The flow imposed by the ciliate jumping can be described as two well-separated impulsive Stokeslets and the overall flow attenuates spatially as r(-3). The high initial velocities and spatio-temporal arrangement of vortices created by tail contractions appear to provide a means for rapid escape as well as hydrodynamic 'camouflage' against fast striking, mechanoreceptive predators such as copepods.}, } @article {pmid26179936, year = {2015}, author = {Murakami, R and Tsai, CH and Kaneko, M and Sakuma, S and Arai, F}, title = {Cell pinball: phenomenon and mechanism of inertia-like cell motion in a microfluidic channel.}, journal = {Lab on a chip}, volume = {15}, number = {16}, pages = {3307-3313}, doi = {10.1039/c5lc00535c}, pmid = {26179936}, issn = {1473-0189}, mesh = {Biomechanical Phenomena ; Cell Movement ; Erythrocytes/*cytology/metabolism ; Humans ; Microfluidic Analytical Techniques/instrumentation/*methods ; Microscopy, Confocal ; Microspheres ; Sodium Chloride/chemistry ; }, abstract = {An unexpected phenomenon of red blood cells bouncing back and forth between the walls inside a microfluidic channel was observed during experiments, and is presented as "Cell Pinball" in this paper. In general, cells in a microfluidic environment are supposed to move along the streamlines parallel to the channel walls when the Reynolds number is small, and the inertia of the cells becomes negligible. However, the cell pinball presented in this paper does not only move along the streamlines but also moves across the channel with the velocity component perpendicular to the streamlines while the Reynolds number is only 0.74. Furthermore, the motion in the direction perpendicular to the streamlines reverses when the cell pinball hits a wall as it "bounces" at the wall. This phenomenon caught our attention and is investigated with both microbead visualization and confocal microscopy. Consistent patterns of rotation with respect to the direction of motion are observed. A kinematic model is proposed to interpret the phenomenon, and it is believed that the phenomenon is caused by the separation of the centroid of the cell and the contact point. The model successfully interprets the features of cell pinball, and the estimated separation between the centroid and the contact point is presented.}, } @article {pmid26172798, year = {2015}, author = {Piedra, S and Ramos, E and Herrera, JR}, title = {Dynamics of two-dimensional bubbles.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {91}, number = {6}, pages = {063013}, doi = {10.1103/PhysRevE.91.063013}, pmid = {26172798}, issn = {1550-2376}, abstract = {The dynamics of two-dimensional bubbles ascending under the influence of buoyant forces is numerically studied with a one-fluid model coupled with the front-tracking technique. The bubble dynamics are described by recording the position, shape, and orientation of the bubbles as functions of time. The qualitative properties of the bubbles and their terminal velocities are described in terms of the Eötvos (ratio of buoyancy to surface tension) and Archimedes numbers (ratio of buoyancy to viscous forces). The terminal Reynolds number result from the balance of buoyancy and drag forces and, consequently, is not an externally fixed parameter. In the cases that yield small Reynolds numbers, the bubbles follow straight paths and the wake is steady. A more interesting behavior is found at high Reynolds numbers where the bubbles follow an approximately periodic zigzag trajectory and an unstable wake with properties similar to the Von Karman vortex street is formed. The dynamical features of the motion of single bubbles are compared to experimental observations of air bubbles ascending in a water-filled Hele-Shaw cell. Although the comparison is not strictly valid in the sense that the effect of the lateral walls is not incorporated in the model, most of the dynamical properties observed are in good qualitative agreement with the numerical calculations. Hele-Shaw cells with different gaps have been used to determine the degree of approximation of the numerical calculation. It is found that for the relation between the terminal Reynolds number and the Archimedes number, the numerical calculations are closer to the observations of bubble dynamics in Hele-Shaw cells of larger gaps.}, } @article {pmid26172790, year = {2015}, author = {Cadot, O and Evrard, A and Pastur, L}, title = {Imperfect supercritical bifurcation in a three-dimensional turbulent wake.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {91}, number = {6}, pages = {063005}, doi = {10.1103/PhysRevE.91.063005}, pmid = {26172790}, issn = {1550-2376}, abstract = {The turbulent wake of a square-back body exhibits a strong bimodal behavior. The wake randomly undergoes symmetry-breaking reversals between two mirror asymmetric steady modes [reflectional symmetry-breaking (RSB) modes]. The characteristic time for reversals is about 2 or 3 orders of magnitude larger than the natural time for vortex shedding. Studying the effects of the proximity of a ground wall together with the Reynolds number, it is shown that the bimodal behavior is the result of an imperfect pitchfork bifurcation. The RSB modes correspond to the two stable bifurcated branches resulting from an instability of the stable symmetric wake. An attempt to stabilize the unstable symmetric wake is investigated using a passive control technique. Although the controlled wake still exhibits strong fluctuations, the bimodal behavior is suppressed and the drag reduced. This promising experiment indicates the possible existence of an unstable solution branch corresponding to a reflectional symmetry preserved (RSP) mode. This work is encouraging to develop a control strategy based on a stabilization of this RSP mode to reduce mean drag and lateral force fluctuations.}, } @article {pmid26163996, year = {2016}, author = {Elcner, J and Lizal, F and Jedelsky, J and Jicha, M and Chovancova, M}, title = {Numerical investigation of inspiratory airflow in a realistic model of the human tracheobronchial airways and a comparison with experimental results.}, journal = {Biomechanics and modeling in mechanobiology}, volume = {15}, number = {2}, pages = {447-469}, doi = {10.1007/s10237-015-0701-1}, pmid = {26163996}, issn = {1617-7940}, mesh = {Biomechanical Phenomena ; Bronchi/*physiology ; Humans ; *Models, Biological ; *Numerical Analysis, Computer-Assisted ; Pulmonary Ventilation/*physiology ; *Respiration ; Time Factors ; Trachea/*physiology ; }, abstract = {In this article, the results of numerical simulations using computational fluid dynamics (CFD) and a comparison with experiments performed with phase Doppler anemometry are presented. The simulations and experiments were conducted in a realistic model of the human airways, which comprised the throat, trachea and tracheobronchial tree up to the fourth generation. A full inspiration/expiration breathing cycle was used with tidal volumes 0.5 and 1 L, which correspond to a sedentary regime and deep breath, respectively. The length of the entire breathing cycle was 4 s, with inspiration and expiration each lasting 2 s. As a boundary condition for the CFD simulations, experimentally obtained flow rate distribution in 10 terminal airways was used with zero pressure resistance at the throat inlet. CCM+ CFD code (Adapco) was used with an SST k-ω low-Reynolds Number RANS model. The total number of polyhedral control volumes was 2.6 million with a time step of 0.001 s. Comparisons were made at several points in eight cross sections selected according to experiments in the trachea and the left and right bronchi. The results agree well with experiments involving the oscillation (temporal relocation) of flow structures in the majority of the cross sections and individual local positions. Velocity field simulation in several cross sections shows a very unstable flow field, which originates in the tracheal laryngeal jet and propagates far downstream with the formation of separation zones in both left and right airways. The RANS simulation agrees with the experiments in almost all the cross sections and shows unstable local flow structures and a quantitatively acceptable solution for the time-averaged flow field.}, } @article {pmid26160306, year = {2015}, author = {Carugo, D and Capretto, L and Roy, B and Carboni, M and Caine, M and Lewis, AL and Hill, M and Chakraborty, S and Zhang, X}, title = {Spatiotemporal dynamics of doxorubicin elution from embolic beads within a microfluidic network.}, journal = {Journal of controlled release : official journal of the Controlled Release Society}, volume = {214}, number = {}, pages = {62-75}, doi = {10.1016/j.jconrel.2015.07.003}, pmid = {26160306}, issn = {1873-4995}, mesh = {Algorithms ; Antibiotics, Antineoplastic/*administration & dosage/*chemistry ; Capillaries/metabolism ; Chemoembolization, Therapeutic/*methods ; Doxorubicin/*administration & dosage/*chemistry ; Drug Delivery Systems ; Drug Design ; Injections, Intravenous ; Kinetics ; Lab-On-A-Chip Devices ; Microfluidics ; Microspheres ; Models, Biological ; Spectrometry, Fluorescence ; }, abstract = {Anticancer treatment using embolic drug-eluting beads (DEBs) has shown multifarious advantages compared to systemic chemotherapy. However, there is a growing need for a better understanding of the physical parameters governing drug-elution from embolic devices under physiologically relevant fluidic conditions. In the present study, we investigated the spatiotemporal dynamics of doxorubicin hydrochloride elution from drug-loaded hydrogel embolic beads within a microfluidic device consisting of a network of interconnected microchannels which replicates the architectural properties of microvascular systems. Drug-elution has been investigated experimentally at a single-bead level, using in-house developed microscopy- and spectrofluorimetry-based methods. Results demonstrated that the kinetics of drug-elution and the amount of eluted drug strongly depended on the location of the embolic event within the embolised channel (e.g. fractional amount of eluted drug after 3h was equal to ~0.2 and ~0.6 for completely-confined and partially-confined bead, respectively). Drug-elution from partially-confined bead showed a counterintuitive dependence on the local Reynolds number (and thus on the mean fluid velocity), as a result of dynamic changes in bead compressibility causing the displacement of the bead from the primary embolic site. Conversely, the kinetics of drug-elution from fully-confined bead was less affected by the local Reynolds number and bead displayed faster elution from the surface area exposed to the systemic flow, which was associated with the formation of fluid eddies nearby the bead post embolisation.}, } @article {pmid26158210, year = {2016}, author = {Ali, N and Javid, K and Sajid, M and Anwar Bég, O}, title = {Numerical simulation of peristaltic flow of a biorheological fluid with shear-dependent viscosity in a curved channel.}, journal = {Computer methods in biomechanics and biomedical engineering}, volume = {19}, number = {6}, pages = {614-627}, doi = {10.1080/10255842.2015.1055257}, pmid = {26158210}, issn = {1476-8259}, mesh = {Body Fluids/physiology ; Humans ; *Models, Theoretical ; Peristalsis/*physiology ; Reproducibility of Results ; Rheology ; Viscosity ; }, abstract = {Peristaltic motion of a non-Newtonian Carreau fluid is analyzed in a curved channel under the long wavelength and low Reynolds number assumptions, as a simulation of digestive transport. The flow regime is shown to be governed by a dimensionless fourth-order, nonlinear, ordinary differential equation subject to no-slip wall boundary conditions. A well-tested finite difference method based on an iterative scheme is employed for the solution of the boundary value problem. The important phenomena of pumping and trapping associated with the peristaltic motion are investigated for various values of rheological parameters of Carreau fluid and curvature of the channel. An increase in Weissenberg number is found to generate a small eddy in the vicinity of the lower wall of the channel, which is enhanced with further increase in Weissenberg number. For shear-thinning bio-fluids (power-law rheological index, n < 1) greater Weissenberg number displaces the maximum velocity toward the upper wall. For shear-thickening bio-fluids, the velocity amplitude is enhanced markedly with increasing Weissenberg number.}, } @article {pmid26154384, year = {2015}, author = {Arrieta, J and Cartwright, JH and Gouillart, E and Piro, N and Piro, O and Tuval, I}, title = {Geometric Mixing, Peristalsis, and the Geometric Phase of the Stomach.}, journal = {PloS one}, volume = {10}, number = {7}, pages = {e0130735}, pmid = {26154384}, issn = {1932-6203}, mesh = {Animals ; Computer Simulation ; Gastric Juice/*physiology ; Humans ; Models, Anatomic ; Models, Biological ; Nonlinear Dynamics ; Peristalsis/*physiology ; Stomach/*physiology ; }, abstract = {Mixing fluid in a container at low Reynolds number--in an inertialess environment--is not a trivial task. Reciprocating motions merely lead to cycles of mixing and unmixing, so continuous rotation, as used in many technological applications, would appear to be necessary. However, there is another solution: movement of the walls in a cyclical fashion to introduce a geometric phase. We show using journal-bearing flow as a model that such geometric mixing is a general tool for using deformable boundaries that return to the same position to mix fluid at low Reynolds number. We then simulate a biological example: we show that mixing in the stomach functions because of the "belly phase," peristaltic movement of the walls in a cyclical fashion introduces a geometric phase that avoids unmixing.}, } @article {pmid26135361, year = {2015}, author = {Alexandrov, DV and Galenko, PK}, title = {Thermo-solutal and kinetic regimes of an anisotropic dendrite growing under forced convective flow.}, journal = {Physical chemistry chemical physics : PCCP}, volume = {17}, number = {29}, pages = {19149-19161}, doi = {10.1039/c5cp03018h}, pmid = {26135361}, issn = {1463-9084}, abstract = {A thermo-diffusional problem of a free dendrite growing in a binary mixture is considered analytically. Effects of the anisotropy and convective flow on the stable mode of the dendrite with four-fold crystal symmetry are studied. Special analysis is given for the parabolic dendrite growing at arbitrary Péclet numbers and with small anisotropy of surface energy and atomic kinetics. The stable growth mode is analyzed through the solvability condition giving the stability criterion for the dendrite tip velocity V and dendrite tip diameter ρ as a function of growth Péclet number, Pg, flow Péclet number, Pf, and Reynolds number, Re. Using the obtained criterion of stability, a complete sequence of transitions in growth regimes (namely, from solute diffusion-limited to thermally controlled and further to kinetically-limited regimes) of the anisotropic dendrite is derived and revealed. Limiting cases to known criteria for small and high growth Péclet numbers of the solidifying system with and without convective fluid flow are found. Two-dimensional solidification regimes and scalings obtained are discussed for their extension to three-dimensional dendritic growth.}, } @article {pmid26133874, year = {2015}, author = {Huisman, SG and van der Veen, RC and Bruggert, GW and Lohse, D and Sun, C}, title = {The boiling Twente Taylor-Couette (BTTC) facility: Temperature controlled turbulent flow between independently rotating, coaxial cylinders.}, journal = {The Review of scientific instruments}, volume = {86}, number = {6}, pages = {065108}, doi = {10.1063/1.4923082}, pmid = {26133874}, issn = {1089-7623}, abstract = {A new Taylor-Couette system has been designed and constructed with precise temperature control. Two concentric independently rotating cylinders are able to rotate at maximum rates of f(i) = ± 20 Hz for the inner cylinder and f(o) = ± 10 Hz for the outer cylinder. The inner cylinder has an outside radius of r(i) = 75 mm, and the outer cylinder has an inside radius of r(o) = 105 mm, resulting in a gap of d = 30 mm. The height of the gap is L = 549 mm, giving a volume of V = 9.3 L. The geometric parameters are η = r(i)/r(o) = 0.714 and Γ = L/d = 18.3. With water as working fluid at room temperature, the Reynolds numbers that can be achieved are Re(i) = ω(i)r(i)(r(o) - r(i))/ν = 2.8 × 10(5) and Re(o) = ω(o)r(o)(r(o) - r(i))/ν = 2 × 10(5) or a combined Reynolds number of up to Re = (ω(i)r(i) - ω(o)r(o))(r(o) - r(i))/ν = 4.8 × 10(5). If the working fluid is changed to the fluorinated liquid FC-3284 with kinematic viscosity 0.42 cSt, the combined Reynolds number can reach Re = 1.1 × 10(6). The apparatus features precise temperature control of the outer and inner cylinders separately and is fully optically accessible from the side and top. The new facility offers the possibility to accurately study the process of boiling inside a turbulent flow and its effect on the flow.}, } @article {pmid26116202, year = {2015}, author = {Vasey, G and Lukeman, R and Wyeth, RC}, title = {Additional Navigational Strategies Can Augment Odor-Gated Rheotaxis for Navigation under Conditions of Variable Flow.}, journal = {Integrative and comparative biology}, volume = {55}, number = {3}, pages = {447-460}, doi = {10.1093/icb/icv073}, pmid = {26116202}, issn = {1557-7023}, mesh = {Animals ; *Chemotaxis ; Fishes/*physiology ; Invertebrates/*physiology ; Models, Biological ; *Movement ; *Odorants ; Rheology ; *Spatial Navigation ; }, abstract = {The navigation strategies animals use to find sources of odor depend on the olfactory stimuli, the properties of flowing fluids, and the locomotory capabilities of the animal. In high Reynolds number environments, animals typically use odor-gated rheotaxis to find the source of turbulent odor plumes. This strategy succeeds because, although turbulence creates an intermittent chemical cue, the animal follows the (continuous) directional cue created by the flow that is transporting the chemical. However, in nature, animals may lose all contact with an odor plume as variations in the direction of bulk flow cause the plume to be rotated away before the animal reaches the source of the odor. Our goal was to use a mathematical model to test the hypothesis that strategies that augment odor-gated rheotaxis would be beneficial for finding the source of an odor plume in such variable flow. The model links a stochastic variable-direction odor plume with a turbulence-based intermittent chemical signal and four different movement strategies, including: odor-gated rheotaxis alone (as a control), odor-gated rheotaxis augmented by further rheotaxis in the absence of odor, odor-gated rheotaxis augmented by a random walk, and odor-gated rheotaxis augmented by movement actively guided by the heading of the flow when the odor was still present. We found that any of the three augmented strategies could improve on strict odor-gated rheotaxis. Moreover, variations in performance caused the best strategy to depend on the speed of movement of the animal and the magnitude of the variation in flow, and more subtly on the duration over which the augmented strategy was performed. For most combinations of parameters in the model, either augmenting with a random walk or following the last-known heading were the best-performing strategies. Overall, our results suggest that marine animals that rely on odor cues to navigate in turbulent environments may augment odor-gated rheotaxis with additional movements that will increase the probability of finding the sources of odors. Moreover, we believe our approach to modeling odor plumes in variable flows is a valuable step toward mathematically capturing the key conditions experienced by animals navigating on the basis of odors carried by flows.}, } @article {pmid26100535, year = {2015}, author = {Mirbod, P and Meng, D}, title = {Analysis of bolus formation in micropipette ejection systems.}, journal = {The European physical journal. E, Soft matter}, volume = {38}, number = {6}, pages = {59}, pmid = {26100535}, issn = {1292-895X}, mesh = {*Hydrodynamics ; Injections/*instrumentation ; Microfluidics ; Models, Theoretical ; }, abstract = {The ejection of drugs from micropipettes is practiced frequently in biomedical research and clinical studies however, little is known about the dynamics of this process. The fundamentals of disperse fluid injection via a capillary into an ambient immiscible fluid have been investigated extensively. Here, we experimentally investigate the bolus formation in micropipette ejection systems, where the injection and ambient fluid are the same. We experimentally measure the temporal evolution of the bolus formation in the same fluid. There are three different bolus formation mechanisms that arise from different Re t regimes: a) a nearly spherical bolus, b) a pear-like bolus, and c) a large distortion or axial jet. We examine the scaled dimensions of the bolus, R b/D t, L b/D t, H/D t, and α, as a function of the dimensionless parameters such as tip Reynolds number, Re t, dimensionless value of g/(D t (.) V t), the dimensionless time, tV t/D t, and the distance between the edge of the micropipette and the free surface, D/D t. The bolus radius for 0.2 < Re t < 30 grows according to t (1/2) in the entire time range, which allows us to estimate the time for complete bolus formation.}, } @article {pmid26098511, year = {2015}, author = {Yadav, V and Duan, W and Butler, PJ and Sen, A}, title = {Anatomy of Nanoscale Propulsion.}, journal = {Annual review of biophysics}, volume = {44}, number = {}, pages = {77-100}, doi = {10.1146/annurev-biophys-060414-034216}, pmid = {26098511}, issn = {1936-1238}, mesh = {Animals ; Bacteria/chemistry/cytology ; Bacterial Physiological Phenomena ; Chemotaxis ; Cilia/physiology/ultrastructure ; Flagella/physiology ; Locomotion ; Molecular Motor Proteins/chemistry ; *Motion ; Nanotechnology/instrumentation/*methods ; }, abstract = {Nature supports multifaceted forms of life. Despite the variety and complexity of these forms, motility remains the epicenter of life. The applicable laws of physics change upon going from macroscales to microscales and nanoscales, which are characterized by low Reynolds number (Re). We discuss motion at low Re in natural and synthetic systems, along with various propulsion mechanisms, including electrophoresis, electrolyte diffusiophoresis, and nonelectrolyte diffusiophoresis. We also describe the newly uncovered phenomena of motility in non-ATP-driven self-powered enzymes and the directional movement of these enzymes in response to substrate gradients. These enzymes can also be immobilized to function as fluid pumps in response to the presence of their substrates. Finally, we review emergent collective behavior arising from interacting motile species, and we discuss the possible biomedical applications of the synthetic nanobots and microbots.}, } @article {pmid26084355, year = {2015}, author = {Pan, R and Geng, J and Cai, J and Tyree, MT}, title = {A comparison of two methods for measuring vessel length in woody plants.}, journal = {Plant, cell & environment}, volume = {38}, number = {12}, pages = {2519-2526}, doi = {10.1111/pce.12566}, pmid = {26084355}, issn = {1365-3040}, mesh = {Acer/*anatomy & histology ; Plant Stems/anatomy & histology ; Populus/*anatomy & histology ; Quercus/*anatomy & histology ; Vitis/*anatomy & histology ; Wood/anatomy & histology ; }, abstract = {Vessel lengths are important to plant hydraulic studies, but are not often reported because of the time required to obtain measurements. This paper compares the fast dynamic method (air injection method) with the slower but traditional static method (rubber injection method). Our hypothesis was that the dynamic method should yield a larger mean vessel length than the static method. Vessel length was measured by both methods in current year stems of Acer, Populus, Vitis and Quercus representing short- to long-vessel species. The hypothesis was verified. The reason for the consistently larger values of vessel length is because the dynamic method measures air flow rates in cut open vessels. The Hagen-Poiseuille law predicts that the air flow rate should depend on the product of number of cut open vessels times the fourth power of vessel diameter. An argument is advanced that the dynamic method is more appropriate because it measures the length of the vessels that contribute most to hydraulic flow. If all vessels had the same vessel length distribution regardless of diameter, then both methods should yield the same average length. This supports the hypothesis that large-diameter vessels might be longer than short-diameter vessels in most species.}, } @article {pmid26083027, year = {2015}, author = {Noreen, S and Qasim, M}, title = {Influence of Hall Current and Viscous Dissipation on Pressure Driven Flow of Pseudoplastic Fluid with Heat Generation: A Mathematical Study.}, journal = {PloS one}, volume = {10}, number = {6}, pages = {e0129588}, pmid = {26083027}, issn = {1932-6203}, mesh = {Body Fluids/*physiology ; Body Temperature ; Hot Temperature ; Humans ; Hydrodynamics ; Models, Biological ; Motion ; *Peristalsis ; Pressure ; *Rheology ; Viscosity ; }, abstract = {In this paper, we study the influence of heat sink (or source) on the peristaltic motion of pseudoplastic fluid in the presence of Hall current, where channel walls are non-conducting in nature. Flow analysis has been carried out under the approximations of a low Reynolds number and long wavelength. Coupled equations are solved using shooting method for numerical solution for the axial velocity function, temperature and pressure gradient distributions. We analyze the influence of various interesting parameters on flow quantities. The present study can be considered as a mathematical presentation of the dynamics of physiological organs with stones.}, } @article {pmid26066439, year = {2015}, author = {Bos, WJ and Kadoch, B and Schneider, K}, title = {Angular statistics of Lagrangian trajectories in turbulence.}, journal = {Physical review letters}, volume = {114}, number = {21}, pages = {214502}, doi = {10.1103/PhysRevLett.114.214502}, pmid = {26066439}, issn = {1079-7114}, abstract = {The angle between subsequent particle displacement increments is evaluated as a function of the time lag in isotropic turbulence. It is shown that the evolution of this angle contains two well-defined power laws, reflecting the multiscale dynamics of high-Reynolds number turbulence. The probability density function of the directional change is shown to be self-similar and well approximated by an analytically derived model assuming Gaussianity and independence of the velocity and the Lagrangian acceleration.}, } @article {pmid26066263, year = {2015}, author = {Low, R and Pothérat, A}, title = {Bounds on the attractor dimension for magnetohydrodynamic channel flow with parallel magnetic field at low magnetic Reynolds number.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {91}, number = {5}, pages = {053022}, doi = {10.1103/PhysRevE.91.053022}, pmid = {26066263}, issn = {1550-2376}, abstract = {We investigate aspects of low-magnetic-Reynolds-number flow between two parallel, perfectly insulating walls in the presence of an imposed magnetic field parallel to the bounding walls. We find a functional basis to describe the flow, well adapted to the problem of finding the attractor dimension and which is also used in subsequent direct numerical simulation of these flows. For given Reynolds and Hartmann numbers, we obtain an upper bound for the dimension of the attractor by means of known bounds on the nonlinear inertial term and this functional basis for the flow. Three distinct flow regimes emerge: a quasi-isotropic three-dimensional (3D) flow, a nonisotropic 3D flow, and a 2D flow. We find the transition curves between these regimes in the space parametrized by Hartmann number Ha and attractor dimension d(att). We find how the attractor dimension scales as a function of Reynolds and Hartmann numbers (Re and Ha) in each regime. We also investigate the thickness of the boundary layer along the bounding wall and find that in all regimes this scales as 1/Re, independently of the value of Ha, unlike Hartmann boundary layers found when the field is normal to the channel. The structure of the set of least dissipative modes is indeed quite different between these two cases but the properties of turbulence far from the walls (smallest scales and number of degrees of freedom) are found to be very similar.}, } @article {pmid26066258, year = {2015}, author = {Rosén, T and Do-Quang, M and Aidun, CK and Lundell, F}, title = {Effect of fluid and particle inertia on the rotation of an oblate spheroidal particle suspended in linear shear flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {91}, number = {5}, pages = {053017}, doi = {10.1103/PhysRevE.91.053017}, pmid = {26066258}, issn = {1550-2376}, mesh = {*Hydrodynamics ; *Mechanical Phenomena ; *Models, Theoretical ; Rheology ; *Rotation ; }, abstract = {This work describes the inertial effects on the rotational behavior of an oblate spheroidal particle confined between two parallel opposite moving walls, which generate a linear shear flow. Numerical results are obtained using the lattice Boltzmann method with an external boundary force. The rotation of the particle depends on the particle Reynolds number, Re(p)=Gd(2)ν(-1) (G is the shear rate, d is the particle diameter, ν is the kinematic viscosity), and the Stokes number, St=αRe(p) (α is the solid-to-fluid density ratio), which are dimensionless quantities connected to fluid and particle inertia, respectively. The results show that two inertial effects give rise to different stable rotational states. For a neutrally buoyant particle (St=Re(p)) at low Re(p), particle inertia was found to dominate, eventually leading to a rotation about the particle's symmetry axis. The symmetry axis is in this case parallel to the vorticity direction; a rotational state called log-rolling. At high Re(p), fluid inertia will dominate and the particle will remain in a steady state, where the particle symmetry axis is perpendicular to the vorticity direction and has a constant angle ϕ(c) to the flow direction. The sequence of transitions between these dynamical states were found to be dependent on density ratio α, particle aspect ratio r(p), and domain size. More specifically, the present study reveals that an inclined rolling state (particle rotates around its symmetry axis, which is not aligned in the vorticity direction) appears through a pitchfork bifurcation due to the influence of periodic boundary conditions when simulated in a small domain. Furthermore, it is also found that a tumbling motion, where the particle symmetry axis rotates in the flow-gradient plane, can be a stable motion for particles with high r(p) and low α.}, } @article {pmid26066247, year = {2015}, author = {Mishra, PK and Herault, J and Fauve, S and Verma, MK}, title = {Dynamics of reversals and condensates in two-dimensional Kolmogorov flows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {91}, number = {5}, pages = {053005}, doi = {10.1103/PhysRevE.91.053005}, pmid = {26066247}, issn = {1550-2376}, abstract = {We present numerical simulations of the different two-dimensional flow regimes generated by a constant spatially periodic forcing balanced by viscous dissipation and large-scale drag with a dimensionless damping rate 1/Rh. The linear response to the forcing is a 6×6 square array of counterrotating vortices, which is stable when the Reynolds number Re or Rh are small. After identifying the sequence of bifurcations that lead to a spatially and temporally chaotic regime of the flow when Re and Rh are increased, we study the transitions between the different turbulent regimes observed for large Re by varying Rh. A large-scale circulation at the box size (the condensate state) is the dominant mode in the limit of vanishing large-scale drag (Rh large). When Rh is decreased, the condensate becomes unstable and a regime with random reversals between two large-scale circulations of opposite signs is generated. It involves a bimodal probability density function of the large-scale velocity that continuously bifurcates to a Gaussian distribution when Rh is decreased further.}, } @article {pmid26066225, year = {2015}, author = {Joglekar, M and Feudel, U and Yorke, JA}, title = {Geometry of the edge of chaos in a low-dimensional turbulent shear flow model.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {91}, number = {5}, pages = {052903}, doi = {10.1103/PhysRevE.91.052903}, pmid = {26066225}, issn = {1550-2376}, abstract = {We investigate the geometry of the edge of chaos for a nine-dimensional sinusoidal shear flow model and show how the shape of the edge of chaos changes with increasing Reynolds number. Furthermore, we numerically compute the scaling of the minimum perturbation required to drive the laminar attracting state into the turbulent region. We find this minimum perturbation to scale with the Reynolds number as Re(-2).}, } @article {pmid26064617, year = {2015}, author = {Montenegro-Johnson, TD and Gadêlha, H and Smith, DJ}, title = {Spermatozoa scattering by a microchannel feature: an elastohydrodynamic model.}, journal = {Royal Society open science}, volume = {2}, number = {3}, pages = {140475}, pmid = {26064617}, issn = {2054-5703}, abstract = {Sperm traverse their microenvironment through viscous fluid by propagating flagellar waves; the waveform emerges as a consequence of elastic structure, internal active moments and low Reynolds number fluid dynamics. Engineered microchannels have recently been proposed as a method of sorting and manipulating motile cells; the interaction of cells with these artificial environments therefore warrants investigation. A numerical method is presented for large-amplitude elastohydrodynamic interaction of active swimmers with domain features. This method is employed to examine hydrodynamic scattering by a model microchannel backstep feature. Scattering is shown to depend on backstep height and the relative strength of viscous and elastic forces in the flagellum. In a 'high viscosity' parameter regime corresponding to human sperm in cervical mucus analogue, this hydrodynamic contribution to scattering is comparable in magnitude to recent data on contact effects, being of the order of 5°-10°. Scattering can be positive or negative depending on the relative strength of viscous and elastic effects, emphasizing the importance of viscosity on the interaction of sperm with their microenvironment. The modulation of scattering angle by viscosity is associated with variations in flagellar asymmetry induced by the elastohydrodynamic interaction with the boundary feature.}, } @article {pmid26037711, year = {2015}, author = {Krujatz, F and Illing, R and Krautwer, T and Liao, J and Helbig, K and Goy, K and Opitz, J and Cuniberti, G and Bley, T and Weber, J}, title = {Light-field-characterization in a continuous hydrogen-producing photobioreactor by optical simulation and computational fluid dynamics.}, journal = {Biotechnology and bioengineering}, volume = {112}, number = {12}, pages = {2439-2449}, doi = {10.1002/bit.25667}, pmid = {26037711}, issn = {1097-0290}, mesh = {*Chemical Phenomena ; *Hydrodynamics ; Hydrogen/*metabolism ; *Light ; Photobioreactors/*microbiology ; Rhodobacter sphaeroides/*growth & development/*metabolism ; }, abstract = {Externally illuminated photobioreactors (PBRs) are widely used in studies on the use of phototrophic microorganisms as sources of bioenergy and other photobiotechnology research. In this work, straightforward simulation techniques were used to describe effects of varying fluid flow conditions in a continuous hydrogen-producing PBR on the rate of photofermentative hydrogen production (rH2) by Rhodobacter sphaeroides DSM 158. A ZEMAX optical ray tracing simulation was performed to quantify the illumination intensity reaching the interior of the cylindrical PBR vessel. 24.2% of the emitted energy was lost through optical effects, or did not reach the PBR surface. In a dense culture of continuously producing bacteria during chemostatic cultivation, the illumination intensity became completely attenuated within the first centimeter of the PBR radius as described by an empirical three-parametric model implemented in Mathcad. The bacterial movement in chemostatic steady-state conditions was influenced by varying the fluid Reynolds number. The "Computational Fluid Dynamics" and "Particle Tracing" tools of COMSOL Multiphysics were used to visualize the fluid flow pattern and cellular trajectories through well-illuminated zones near the PBR periphery and dark zones in the center of the PBR. A moderate turbulence (Reynolds number = 12,600) and fluctuating illumination of 1.5 Hz were found to yield the highest continuous rH2 by R. sphaeroides DSM 158 (170.5 mL L(-1) h(-1)) in this study.}, } @article {pmid26030270, year = {2015}, author = {Walker, D and Kübler, M and Morozov, KI and Fischer, P and Leshansky, AM}, title = {Optimal Length of Low Reynolds Number Nanopropellers.}, journal = {Nano letters}, volume = {15}, number = {7}, pages = {4412-4416}, doi = {10.1021/acs.nanolett.5b01925}, pmid = {26030270}, issn = {1530-6992}, abstract = {Locomotion in fluids at the nanoscale is dominated by viscous drag. One efficient propulsion scheme is to use a weak rotating magnetic field that drives a chiral object. From bacterial flagella to artificial drills, the corkscrew is a universally useful chiral shape for propulsion in viscous environments. Externally powered magnetic micro- and nanomotors have been recently developed that allow for precise fuel-free propulsion in complex media. Here, we combine analytical and numerical theory with experiments on nanostructured screw-propellers to show that the optimal length is surprisingly short-only about one helical turn, which is shorter than most of the structures in use to date. The results have important implications for the design of artificial actuated nano- and micropropellers and can dramatically reduce fabrication times, while ensuring optimal performance.}, } @article {pmid26029795, year = {2015}, author = {Jang, B and Gutman, E and Stucki, N and Seitz, BF and Wendel-García, PD and Newton, T and Pokki, J and Ergeneman, O and Pané, S and Or, Y and Nelson, BJ}, title = {Undulatory Locomotion of Magnetic Multilink Nanoswimmers.}, journal = {Nano letters}, volume = {15}, number = {7}, pages = {4829-4833}, doi = {10.1021/acs.nanolett.5b01981}, pmid = {26029795}, issn = {1530-6992}, support = {336456/ERC_/European Research Council/International ; }, abstract = {Micro- and nanorobots operating in low Reynolds number fluid environments require specialized swimming strategies for efficient locomotion. Prior research has focused on designs mimicking the rotary corkscrew motion of bacterial flagella or the planar beating motion of eukaryotic flagella. These biologically inspired designs are typically of uniform construction along their flagellar axis. This work demonstrates for the first time planar undulations of composite multilink nanowire-based chains (diameter 200 nm) induced by a planar-oscillating magnetic field. Those chains comprise an elastic eukaryote-like polypyrrole tail and rigid magnetic nickel links connected by flexible polymer bilayer hinges. The multilink design exhibits a high swimming efficiency. Furthermore, the manufacturing process enables tuning the geometrical and material properties to specific applications.}, } @article {pmid26015833, year = {2015}, author = {Kim, H and Cheang, UK and Kim, D and Ali, J and Kim, MJ}, title = {Hydrodynamics of a self-actuated bacterial carpet using microscale particle image velocimetry.}, journal = {Biomicrofluidics}, volume = {9}, number = {2}, pages = {024121}, pmid = {26015833}, issn = {1932-1058}, abstract = {Microorganisms can effectively generate propulsive force at the microscale where viscous forces overwhelmingly dominate inertia forces; bacteria achieve this task through flagellar motion. When swarming bacteria, cultured on agar plates, are blotted onto the surface of a microfabricated structure, a monolayer of bacteria forms what is termed a "bacterial carpet," which generates strong flows due to the combined motion of their freely rotating flagella. Furthermore, when the bacterial carpet coated microstructure is released into a low Reynolds number fluidic environment, the propulsive force of the bacterial carpet is able to give the microstructure motility. In our previous investigations, we demonstrated motion control of these bacteria powered microbiorobots (MBRs). Without any external stimuli, MBRs display natural rotational and translational movements on their own; this MBR self-actuation is due to the coordination of flagella. Here, we investigate the flow fields generated by bacterial carpets, and compare this flow to the flow fields observed in the bulk fluid at a series of locations above the bacterial carpet. Using microscale particle image velocimetry, we characterize the flow fields generated from the bacterial carpets of MBRs in an effort to understand their propulsive flow, as well as the resulting pattern of flagella driven self-actuated motion. Comparing the velocities between the bacterial carpets on fixed and untethered MBRs, it was found that flow velocities near the surface of the microstructure were strongest, and at distances far above, the surface flow velocities were much smaller.}, } @article {pmid26005774, year = {2015}, author = {Lu, X and Xuan, X}, title = {Continuous Microfluidic Particle Separation via Elasto-Inertial Pinched Flow Fractionation.}, journal = {Analytical chemistry}, volume = {87}, number = {12}, pages = {6389-6396}, doi = {10.1021/acs.analchem.5b01432}, pmid = {26005774}, issn = {1520-6882}, mesh = {Chemical Fractionation ; *Microfluidic Analytical Techniques ; Particle Size ; }, abstract = {Many of the fluids encountered in chemical and biomedical applications exhibit non-Newtonian behavior. However, the majority of current particle separation methods have been demonstrated in Newtonian fluids only. This work presents an experimental study of continuous particle separation in viscoelastic solutions via a combined action of elastic and inertial lift forces, which we term elasto-inertial pinched flow fractionation (eiPFF). The parametric effects on eiPFF are systematically investigated in terms of dimensionless numbers. It is found that eiPFF offers much higher particle throughput and separation resolution than the traditional steric effects-based PFF. Moreover, eiPFF works most efficiently when the Reynolds number, Re, is of order 1 and hence fills perfectly into the gap of our recently proposed inertia-enhanced PFF (iPFF) technique (Anal. Chem. 2015, 87, 4560-4565) that favors Re of the order 10 or more. However, the particle separation via eiPFF does not increase monotonically with the elasticity number at higher polymer concentrations and is strongly affected by the aspect ratio of channel width to height, both of which have not been previously reported. More surprisingly, the elasto-inertial deflection of small particles can be even greater than that of large particles in a high-aspect-ratio channel for Re less than 1.}, } @article {pmid26004808, year = {2015}, author = {Hu, R and Li, F and Lv, J and He, Y and Lu, D and Yamada, T and Ono, N}, title = {Microfluidic analysis of pressure drop and flow behavior in hypertensive micro vessels.}, journal = {Biomedical microdevices}, volume = {17}, number = {3}, pages = {9959}, doi = {10.1007/s10544-015-9959-4}, pmid = {26004808}, issn = {1572-8781}, mesh = {Animals ; *Blood Flow Velocity ; Computer Simulation ; Humans ; Microcirculation ; Microfluidics/*methods ; Microvessels/*physiopathology ; *Models, Cardiovascular ; Retinal Artery/*physiopathology ; Retinal Artery Occlusion/*physiopathology ; }, abstract = {The retinal arterial network is the only source of the highly nutrient-consumptive retina, thus any insult on the arteries can impair the retinal oxygen and nutrient supply and affect its normal function. The aim of this work is to study the influences of vascular structure variation on the flow and pressure characteristics via microfluidic devices. Two sets of micro-channel were designed to mimic the stenosed microvessels and dichotomous branching structure in the retinal arteries. Three working fluids including red blood cell (RBC) suspension were employed to investigate the pressure drop in the stenosed channel. The flow behaviors of RBC suspensions inside the micro channels were observed using high speed camera system. Pressure drop of different working fluids and RBC velocity profiles in the stenosed channel were obtained. Moreover, hematocrit levels of RBC suspensions inside the bifurcated channels were analyzed from the sequential images of RBC flow. The results of the flow in the stenosed channel show that RBCs drift from the center of the channels, and RBC velocity is influenced not only by the inlet flow rate but also the interaction between RBCs. The measured pressure drops in the stenosed channel increase notably with the increase of fluid viscosity. Furthermore, the dimensionless pressure drop due to the stenosis decreases with Reynolds number. On the other hand, the results of flow through the bifurcated channels show that as the ratio of the daughter-branch width to the mother-channel width increases, the ratio of hematocrit in two connected branches (Ht/Hd) decreases, which is in favorable agreement with the available analysis results.}, } @article {pmid25998171, year = {2015}, author = {Dasgupta, R and Tomar, G and Govindarajan, R}, title = {Numerical study of laminar, standing hydraulic jumps in a planar geometry.}, journal = {The European physical journal. E, Soft matter}, volume = {38}, number = {5}, pages = {130}, doi = {10.1140/epje/i2015-15045-0}, pmid = {25998171}, issn = {1292-895X}, abstract = {We solve the two-dimensional, planar Navier-Stokes equations to simulate a laminar, standing hydraulic jump using a Volume-of-Fluid method. The geometry downstream of the jump has been designed to be similar to experimental conditions by including a pit at the edge of the platform over which liquid film flows. We obtain jumps with and without separation. Increasing the inlet Froude number pushes the jump downstream and makes the slope of the jump weaker, consistent with experimental observations of circular jumps, and decreasing the Reynolds number brings the jump upstream while making it steeper. We study the effect of the length of the domain and that of a downstream obstacle on the structure and location of the jump. The transient flow which leads to a final steady jump is described for the first time to our knowledge. In the moderate Reynolds number regime, we obtain steady undular jumps with a separated bubble underneath the first few undulations. Interestingly, surface tension leads to shortening of wavelength of these undulations. We show that the undulations can be explained using the inviscid theory of Benjamin and Lighthill (Proc. R. Soc. London, Ser. A, 1954). We hope this new finding will motivate experimental verification.}, } @article {pmid26001019, year = {2015}, author = {Henríquez Rivera, RG and Sinha, K and Graham, MD}, title = {Margination regimes and drainage transition in confined multicomponent suspensions.}, journal = {Physical review letters}, volume = {114}, number = {18}, pages = {188101}, doi = {10.1103/PhysRevLett.114.188101}, pmid = {26001019}, issn = {1079-7114}, mesh = {Blood ; *Blood Chemical Analysis ; Hydrodynamics ; *Models, Biological ; *Models, Chemical ; Suspensions/*chemistry ; }, abstract = {A mechanistic theory is developed to describe segregation in confined multicomponent suspensions such as blood. It incorporates the two key phenomena arising in these systems at low Reynolds number: hydrodynamic pair collisions and wall-induced migration. In simple shear flow, several regimes of segregation arise, depending on the value of a "margination parameter" M. Most importantly, there is a critical value of M below which a sharp "drainage transition" occurs: one component is completely depleted from the bulk flow to the vicinity of the walls. Direct simulations also exhibit this transition as the size or flexibility ratio of the components changes.}, } @article {pmid25990633, year = {2015}, author = {Montino, A and DeSimone, A}, title = {Three-sphere low-Reynolds-number swimmer with a passive elastic arm.}, journal = {The European physical journal. E, Soft matter}, volume = {38}, number = {5}, pages = {127}, pmid = {25990633}, issn = {1292-895X}, abstract = {One of the simplest model swimmers at low Reynolds number is the three-sphere swimmer by Najafi and Golestanian. It consists of three spheres connected by two rods which change their lengths periodically in non-reciprocal fashion. Here we investigate a variant of this model in which one rod is periodically actuated while the other is replaced by an elastic spring. We show that the competition between the elastic restoring force and the hydrodynamic drag produces a delay in the response of the passive elastic arm with respect to the active one. This leads to non-reciprocal shape changes and self-propulsion. After formulating the equations of motion, we study their solutions qualitatively and numerically. The leading-order term of the solution is computed analytically. We then address questions of optimization with respect to both actuation frequency and swimmer's geometry. Our results can provide valuable conceptual guidance in the engineering of robotic microswimmers.}, } @article {pmid25974595, year = {2015}, author = {Grafke, T and Frishman, A and Falkovich, G}, title = {Time irreversibility of the statistics of a single particle in compressible turbulence.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {91}, number = {4}, pages = {043022}, doi = {10.1103/PhysRevE.91.043022}, pmid = {25974595}, issn = {1550-2376}, abstract = {We investigate time irreversibility from the point of view of a single particle in Burgers turbulence. Inspired by the recent work for incompressible flows [Xu et al., Proc. Natl. Acad. Sci. USA 111, 7558 (2014)], we analyze the evolution of the kinetic energy for fluid markers and use the fluctuations of the instantaneous power as a measure of time irreversibility. For short times, starting from a uniform distribution of markers, we find the scaling 〈[E(t)-E(0)](n)〉∝t and 〈p(n)〉∝Re(n-1) for the power as a function of the Reynolds number. Both observations can be explained using the "flight-crash" model, suggested by Xu et al. Furthermore, we use a simple model for shocks that reproduces the moments of the energy difference, including the pre-factor for 〈E(t)-E(0)〉. To complete the single-particle picture for Burgers we compute the moments of the Lagrangian velocity difference and show that they are bifractal. This arises in a similar manner to the bifractality of Eulerian velocity differences. In the above setting, time irreversibility is directly manifest as particles eventually end up in shocks. We additionally investigate time irreversibility in the long-time limit when all particles are located inside shocks and the Lagrangian velocity statistics are stationary. We find the same scalings for the power and energy differences as at short times and argue that this is also a consequence of rare "flight-crash" events related to shock collisions.}, } @article {pmid25974591, year = {2015}, author = {Felderhof, BU}, title = {Stokesian spherical swimmers and active particles.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {91}, number = {4}, pages = {043018}, doi = {10.1103/PhysRevE.91.043018}, pmid = {25974591}, issn = {1550-2376}, abstract = {The net steady state flow pattern of a distorting sphere is studied in the framework of the bilinear theory of swimming at low Reynolds number. It is argued that the starting point of a theory of interacting active particles should be based on such a calculation, since any arbitrarily chosen steady state flow pattern is not necessarily the result of a swimming motion. Furthermore, it is stressed that as a rule the phase of stroke is relevant in hydrodynamic interactions, so that the net flow pattern must be used with caution.}, } @article {pmid25974590, year = {2015}, author = {Deng, J and Caulfield, CP}, title = {Three-dimensional transition after wake deflection behind a flapping foil.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {91}, number = {4}, pages = {043017}, doi = {10.1103/PhysRevE.91.043017}, pmid = {25974590}, issn = {1550-2376}, abstract = {We report the inherently three-dimensional linear instabilities of a propulsive wake, produced by a flapping foil, mimicking the caudal fin of a fish or the wing of a flying animal. For the base flow, three sequential wake patterns appear as we increase the flapping amplitude: Bénard-von Kármán (BvK) vortex streets; reverse BvK vortex streets; and deflected wakes. Imposing a three-dimensional spanwise periodic perturbation, we find that the resulting Floquet multiplier |μ| indicates an unstable "short wavelength" mode at wave number β=30, or wavelength λ=0.21 (nondimensionalized by the chord length) at sufficiently high flow Reynolds number Re=Uc/ν≃600, where U is the upstream flow velocity, c is the chord length, and ν is the kinematic viscosity of the fluid. Another, "long wavelength" mode at β=6 (λ=1.05) becomes critical at somewhat higher Reynolds number, although we do not expect that this mode would be observed physically because its growth rate is always less than the short wavelength mode, at least for the parameters we have considered. The long wavelength mode has certain similarities with the so-called mode A in the drag wake of a fixed bluff body, while the short wavelength mode appears to have a period of the order of twice that of the base flow, in that its structure seems to repeat approximately only every second cycle of the base flow. Whether it is appropriate to classify this mode as a truly subharmonic mode or as a quasiperiodic mode is still an open question however, worthy of a detailed parametric study with various flapping amplitudes and frequencies.}, } @article {pmid25974586, year = {2015}, author = {McComb, WD and Berera, A and Yoffe, SR and Linkmann, MF}, title = {Energy transfer and dissipation in forced isotropic turbulence.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {91}, number = {4}, pages = {043013}, doi = {10.1103/PhysRevE.91.043013}, pmid = {25974586}, issn = {1550-2376}, abstract = {A model for the Reynolds-number dependence of the dimensionless dissipation rate C(ɛ) was derived from the dimensionless Kármán-Howarth equation, resulting in C(ɛ)=C(ɛ,∞)+C/R(L)+O(1/R(L)(2)), where R(L) is the integral scale Reynolds number. The coefficients C and C(ɛ,∞) arise from asymptotic expansions of the dimensionless second- and third-order structure functions. This theoretical work was supplemented by direct numerical simulations (DNSs) of forced isotropic turbulence for integral scale Reynolds numbers up to R(L)=5875 (R(λ)=435), which were used to establish that the decay of dimensionless dissipation with increasing Reynolds number took the form of a power law R(L)(n) with exponent value n=-1.000±0.009 and that this decay of C(ɛ) was actually due to the increase in the Taylor surrogate U(3)/L. The model equation was fitted to data from the DNS, which resulted in the value C=18.9±1.3 and in an asymptotic value for C(ɛ) in the infinite Reynolds-number limit of C(ɛ,∞)=0.468±0.006.}, } @article {pmid25974583, year = {2015}, author = {Beaume, C and Chini, GP and Julien, K and Knobloch, E}, title = {Reduced description of exact coherent states in parallel shear flows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {91}, number = {4}, pages = {043010}, doi = {10.1103/PhysRevE.91.043010}, pmid = {25974583}, issn = {1550-2376}, abstract = {A reduced description of exact coherent structures in the transition regime of plane parallel shear flows is developed, based on the Reynolds number scaling of streamwise-averaged (mean) and streamwise-varying (fluctuation) velocities observed in numerical simulations. The resulting system is characterized by an effective unit Reynolds number mean equation coupled to linear equations for the fluctuations, regularized by formally higher-order diffusion. Stationary coherent states are computed by solving the resulting equations simultaneously using a robust numerical algorithm developed for this purpose. The algorithm determines self-consistently the amplitude of the fluctuations for which the associated mean flow is just such that the fluctuations neither grow nor decay. The procedure is used to compute exact coherent states of a flow introduced by Drazin and Reid [Hydrodynamic Stability (Cambridge University Press, Cambridge, UK, 1981)] and studied by Waleffe [Phys. Fluids 9, 883 (1997)]: a linearly stable, plane parallel shear flow confined between stationary stress-free walls and driven by a sinusoidal body force. Numerical continuation of the lower-branch states to lower Reynolds numbers reveals the presence of a saddle node; the saddle node allows access to upper-branch states that are, like the lower-branch states, self-consistently described by the reduced equations. Both lower- and upper-branch states are characterized in detail.}, } @article {pmid25974578, year = {2015}, author = {Chantry, M and Kerswell, RR}, title = {Localization in a spanwise-extended model of plane Couette flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {91}, number = {4}, pages = {043005}, doi = {10.1103/PhysRevE.91.043005}, pmid = {25974578}, issn = {1550-2376}, abstract = {We consider a nine-partial-differential-equation (1-space and 1-time) model of plane Couette flow in which the degrees of freedom are severely restricted in the streamwise and cross-stream directions to study spanwise localization in detail. Of the many steady Eckhaus (spanwise modulational) instabilities identified of global steady states, none lead to a localized state. Spatially localized, time-periodic solutions were found instead, which arise in saddle node bifurcations in the Reynolds number. These solutions appear global (domain filling) in narrow (small spanwise) domains yet can be smoothly continued out to fully spanwise-localized states in very wide domains. This smooth localization behavior, which has also been seen in fully resolved duct flow (S. Okino, Ph.D. thesis, Kyoto University, Kyoto, 2011), indicates that an apparently global flow structure does not have to suffer a modulational instability to localize in wide domains.}, } @article {pmid25974576, year = {2015}, author = {Cerbus, RT and Goldburg, WI}, title = {Predicting two-dimensional turbulence.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {91}, number = {4}, pages = {043003}, doi = {10.1103/PhysRevE.91.043003}, pmid = {25974576}, issn = {1550-2376}, abstract = {Prediction is a fundamental objective of science. It is more difficult for chaotic and complex systems like turbulence. Here we use information theory to quantify spatial prediction using experimental data from a turbulent soap film. At high Reynolds number, Re, where a cascade exists, turbulence becomes easier to predict as the inertial range broadens. The development of a cascade at low Re is also detected.}, } @article {pmid25974574, year = {2015}, author = {Verma, MK and Kumaran, V}, title = {Stability of the flow in a soft tube deformed due to an applied pressure gradient.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {91}, number = {4}, pages = {043001}, doi = {10.1103/PhysRevE.91.043001}, pmid = {25974574}, issn = {1550-2376}, abstract = {A linear stability analysis is carried out for the flow through a tube with a soft wall in order to resolve the discrepancy of a factor of 10 for the transition Reynolds number between theoretical predictions in a cylindrical tube and the experiments of Verma and Kumaran [J. Fluid Mech. 705, 322 (2012)]. Here the effect of tube deformation (due to the applied pressure difference) on the mean velocity profile and pressure gradient is incorporated in the stability analysis. The tube geometry and dimensions are reconstructed from experimental images, where it is found that there is an expansion and then a contraction of the tube in the streamwise direction. The mean velocity profiles at different downstream locations and the pressure gradient, determined using computational fluid dynamics, are found to be substantially modified by the tube deformation. The velocity profiles are then used in a linear stability analysis, where the growth rates of perturbations are calculated for the flow through a tube with the wall modeled as a neo-Hookean elastic solid. The linear stability analysis is carried out for the mean velocity profiles at different downstream locations using the parallel flow approximation. The analysis indicates that the flow first becomes unstable in the downstream converging section of the tube where the flow profile is more pluglike when compared to the parabolic flow in a cylindrical tube. The flow is stable in the upstream diverging section where the deformation is maximum. The prediction for the transition Reynolds number is in good agreement with experiments, indicating that the downstream tube convergence and the consequent modification in the mean velocity profile and pressure gradient could reduce the transition Reynolds number by an order of magnitude.}, } @article {pmid25974532, year = {2015}, author = {Andersen, A and Wadhwa, N and Kiørboe, T}, title = {Quiet swimming at low Reynolds number.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {91}, number = {4}, pages = {042712}, doi = {10.1103/PhysRevE.91.042712}, pmid = {25974532}, issn = {1550-2376}, mesh = {Animals ; Biomechanical Phenomena ; Chlamydomonas reinhardtii/physiology ; Ciliophora/physiology ; Copepoda/physiology ; Crustacea/physiology ; Flagella/physiology ; Hydrodynamics ; *Models, Biological ; *Swimming/physiology ; }, abstract = {The stresslet provides a simple model of the flow created by a small, freely swimming and neutrally buoyant aquatic organism and shows that the far field fluid disturbance created by such an organism in general decays as one over distance squared. Here we discuss a quieter swimming mode that eliminates the stresslet component of the flow and leads to a faster spatial decay of the fluid disturbance described by a force quadrupole that decays as one over distance cubed. Motivated by recent experimental results on fluid disturbances due to small aquatic organisms, we demonstrate that a three-Stokeslet model of a swimming organism which uses breast stroke type kinematics is an example of such a quiet swimmer. We show that the fluid disturbance in both the near field and the far field is significantly reduced by appropriately arranging the propulsion apparatus, and we find that the far field power laws are valid surprisingly close to the organism. Finally, we discuss point force models as a general framework for hypothesis generation and experimental exploration of fluid mediated predator-prey interactions in the planktonic world.}, } @article {pmid25967293, year = {2015}, author = {Mishra, GK and Kumar, A and Prakash, O and Biswal, R and Dixit, SK and Nakhe, SV}, title = {Flow and thermal characteristics of high Reynolds number (2800-17,000) dye cell: simulation and experiment.}, journal = {Applied optics}, volume = {54}, number = {11}, pages = {3106-3114}, doi = {10.1364/AO.54.003106}, pmid = {25967293}, issn = {1539-4522}, abstract = {This paper presents computational and experimental studies on wavelength/frequency fluctuation characteristics of a high pulse repetition rate (18 kHz) dye laser pumped by a frequency-doubled Nd:YAG laser (532 nm). The temperature gradient in the dye solution is found to be responsible for wavelength fluctuations of the dye laser at low flow rates (28000.1 μm by means of an electric discharge through a thin lubricating film. We discuss the implications of these findings on the charging of the particle and its subsequent dynamics.}, } @article {pmid25775552, year = {2015}, author = {Yuan, J and Raizen, DM and Bau, HH}, title = {Propensity of undulatory swimmers, such as worms, to go against the flow.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {112}, number = {12}, pages = {3606-3611}, pmid = {25775552}, issn = {1091-6490}, support = {5R03AG042690-02/AG/NIA NIH HHS/United States ; R01 NS088432/NS/NINDS NIH HHS/United States ; P40 OD010440/OD/NIH HHS/United States ; R01 NS064030/NS/NINDS NIH HHS/United States ; R03 AG042690/AG/NIA NIH HHS/United States ; R01NS064030/NS/NINDS NIH HHS/United States ; }, mesh = {Animals ; *Behavior, Animal ; Caenorhabditis elegans/*physiology ; Ecosystem ; Hydrodynamics ; Microfluidics ; *Orientation ; Rheology ; Swimming ; Temperature ; }, abstract = {The ability to orient oneself in response to environmental cues is crucial to the survival and function of diverse organisms. One such orientation behavior is the alignment of aquatic organisms with (negative rheotaxis) or against (positive rheotaxis) fluid current. The questions of whether low-Reynolds-number, undulatory swimmers, such as worms, rheotax and whether rheotaxis is a deliberate or an involuntary response to mechanical forces have been the subject of conflicting reports. To address these questions, we use Caenorhabditis elegans as a model undulatory swimmer and examine, in experiment and theory, the orientation of C. elegans in the presence of flow. We find that when close to a stationary surface the animal aligns itself against the direction of the flow. We elucidate for the first time to our knowledge the mechanisms of rheotaxis in worms and show that rheotaxis can be explained solely by mechanical forces and does not require sensory input or deliberate action. The interaction between the flow field induced by the swimmer and a nearby surface causes the swimmer to tilt toward the surface and the velocity gradient associated with the flow rotates the animal to face upstream. Fluid mechanical computer simulations faithfully mimic the behavior observed in experiments, supporting the notion that rheotaxis behavior can be fully explained by hydrodynamics. Our study highlights the important role of hydrodynamics in the behavior of small undulating swimmers and may assist in developing control strategies to affect the animals' life cycles.}, } @article {pmid25768609, year = {2015}, author = {Davoust, L and Achard, JL and Drazek, L}, title = {Low-to-moderate Reynolds number swirling flow in an annular channel with a rotating end wall.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {91}, number = {2}, pages = {023019}, doi = {10.1103/PhysRevE.91.023019}, pmid = {25768609}, issn = {1550-2376}, abstract = {This paper presents a new method for solving analytically the axisymmetric swirling flow generated in a finite annular channel from a rotating end wall, with no-slip boundary conditions along stationary side walls and a slip condition along the free surface opposite the rotating floor. In this case, the end-driven swirling flow can be described from the coupling between an azimuthal shear flow and a two-dimensional meridional flow driven by the centrifugal force along the rotating floor. A regular asymptotic expansion based on a small but finite Reynolds number is used to calculate centrifugation-induced first-order correction to the azimuthal Stokes flow obtained as the solution at leading order. For solving the first-order problem, the use of an integral boundary condition for the vorticity is found to be a convenient way to attribute boundary conditions in excess for the stream function to the vorticity. The annular geometry is characterized by both vertical and horizontal aspect ratios, whose respective influences on flow patterns are investigated. The vertical aspect ratio is found to involve nontrivial changes in flow patterns essentially due to the role of corner eddies located on the left and right sides of the rotating floor. The present analytical method can be ultimately extended to cylindrical geometries, irrespective of the surface opposite the rotating floor: a wall or a free surface. It can also serve as an analytical tool for monitoring confined rotating flows in applications related to surface viscosimetry or crystal growth from the melt.}, } @article {pmid25768597, year = {2015}, author = {Chokshi, P and Bhade, P and Kumaran, V}, title = {Wall-mode instability in plane shear flow of viscoelastic fluid over a deformable solid.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {91}, number = {2}, pages = {023007}, doi = {10.1103/PhysRevE.91.023007}, pmid = {25768597}, issn = {1550-2376}, mesh = {Computer Simulation ; Linear Models ; *Models, Theoretical ; Pliability ; Polymers/chemistry ; Solutions ; *Viscoelastic Substances/chemistry ; Viscosity ; }, abstract = {The linear stability analysis of a plane Couette flow of an Oldroyd-B viscoelastic fluid past a flexible solid medium is carried out to investigate the role of polymer addition in the stability behavior. The system consists of a viscoelastic fluid layer of thickness R, density ρ, viscosity η, relaxation time λ, and retardation time βλ flowing past a linear elastic solid medium of thickness HR, density ρ, and shear modulus G. The emphasis is on the high-Reynolds-number wall-mode instability, which has recently been shown in experiments to destabilize the laminar flow of Newtonian fluids in soft-walled tubes and channels at a significantly lower Reynolds number than that for flows in rigid conduits. For Newtonian fluids, the linear stability studies have shown that the wall modes become unstable when flow Reynolds number exceeds a certain critical value Re(c) which scales as Σ(3/4), where Reynolds number Re=ρVR/η,V is the top-plate velocity, and dimensionless parameter Σ=ρGR(2)/η(2) characterizes the fluid-solid system. For high-Reynolds-number flow, the addition of polymer tends to decrease the critical Reynolds number in comparison to that for the Newtonian fluid, indicating a destabilizing role for fluid viscoelasticity. Numerical calculations show that the critical Reynolds number could be decreased by up to a factor of 10 by the addition of small amount of polymer. The critical Reynolds number follows the same scaling Re(c)∼Σ(3/4) as the wall modes for a Newtonian fluid for very high Reynolds number. However, for moderate Reynolds number, there exists a narrow region in β-H parametric space, corresponding to very dilute polymer solution (0.9≲β<1) and thin solids (H≲1.1), in which the addition of polymer tends to increase the critical Reynolds number in comparison to the Newtonian fluid. Thus, Reynolds number and polymer properties can be tailored to either increase or decrease the critical Reynolds number for unstable modes, thus providing an additional degree of control over the laminar-turbulent transition.}, } @article {pmid25752537, year = {2015}, author = {Johansen, Ø and Reed, M and Bodsberg, NR}, title = {Natural dispersion revisited.}, journal = {Marine pollution bulletin}, volume = {93}, number = {1-2}, pages = {20-26}, doi = {10.1016/j.marpolbul.2015.02.026}, pmid = {25752537}, issn = {1879-3363}, mesh = {*Models, Chemical ; Norway ; Petroleum ; Petroleum Pollution/*statistics & numerical data ; Water Pollutants, Chemical/*analysis ; Water Pollution, Chemical/*statistics & numerical data ; }, abstract = {This paper presents a new semi-empirical model for oil droplet size distributions generated by single breaking wave events. Empirical data was obtained from laboratory experiments with different crude oils at different stages of weathering. The paper starts with a review of the most commonly used model for natural dispersion, which is followed by a presentation of the laboratory study on oil droplet size distributions formed by breaking waves conducted by SINTEF on behalf of the NOAA/UNH Coastal Response Research Center. The next section presents the theoretical and empirical foundation for the new model. The model is based on dimensional analysis and contains two non-dimensional groups; the Weber and Reynolds number. The model was validated with data from a full scale experimental oil spill conducted in the Haltenbanken area offshore Norway in July 1982, as described in the last section of the paper.}, } @article {pmid25750412, year = {2015}, author = {Yanase, K and Saarenrinne, P}, title = {Unsteady turbulent boundary layers in swimming rainbow trout.}, journal = {The Journal of experimental biology}, volume = {218}, number = {Pt 9}, pages = {1373-1385}, doi = {10.1242/jeb.108043}, pmid = {25750412}, issn = {1477-9145}, mesh = {Animals ; Biomechanical Phenomena ; Friction ; Oncorhynchus mykiss/*physiology ; Pressure ; Rheology ; *Swimming ; }, abstract = {The boundary layers of rainbow trout, Oncorhynchus mykiss, swimming at 1.02±0.09 L s(-1) (mean±s.d., N=4), were measured by the particle image velocimetry (PIV) technique at a Reynolds number of 4×10(5). The boundary layer profile showed unsteadiness, oscillating above and beneath the classical logarithmic law of the wall with body motion. Across the entire surface regions that were measured, local Reynolds numbers based on momentum thickness, which is the distance that is perpendicular to the fish surface through which the boundary layer momentum flows at free-stream velocity, were greater than the critical value of 320 for the laminar-to-turbulent transition. The skin friction was dampened on the convex surface while the surface was moving towards a free-stream flow and increased on the concave surface while retreating. These observations contradict the result of a previous study using different species swimming by different methods. Boundary layer compression accompanied by an increase in local skin friction was not observed. Thus, the overall results may not support absolutely the Bone-Lighthill boundary layer thinning hypothesis that the undulatory motions of swimming fish cause a large increase in their friction drag because of the compression of the boundary layer. In some cases, marginal flow separation occurred on the convex surface in the relatively anterior surface region, but the separated flow reattached to the fish surface immediately downstream. Therefore, we believe that a severe impact due to induced drag components (i.e. pressure drag) on the swimming performance, an inevitable consequence of flow separation, was avoided.}, } @article {pmid25750148, year = {2015}, author = {Launder, BE}, title = {First steps in modelling turbulence and its origins: a commentary on Reynolds (1895) 'On the dynamical theory of incompressible viscous fluids and the determination of the criterion'.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {373}, number = {2039}, pages = {}, pmid = {25750148}, issn = {1471-2962}, abstract = {Reynolds' paper sought to explain the change in character of flow through a pipe from laminar to turbulent that his earlier experiments had shown to occur when the dimensionless group that today bears his name exceeded approximately 2000. This he did by decomposing the velocity into mean and fluctuating components and noting how the average kinetic energy generation and dissipation rates changed with Reynolds number. The paper was only grudgingly accepted by two very distinguished referees and initially raised little external interest. As years went by, however, the averaged form of the equations of motion, known as the Reynolds equations (which were an intermediate stage in Reynolds' analysis) became the acknowledged starting point for computing turbulent flows. Moreover, some 50 years after his paper, a refinement of his strategy for predicting transition was also successfully taken up. For some engineering problems, the continual rapid growth of computing resources has meant that more detailed approaches for computing turbulent flow phenomena can nowadays be employed. However, this growth of computing power likewise makes possible a Reynolds-averaging strategy for complex flow systems in industry or the environment which formerly had to adopt less comprehensive analyses. Thus, Reynolds' approach may well remain in use throughout the present century. This commentary was written to celebrate the 350th anniversary of the journal Philosophical Transactions of the Royal Society.}, } @article {pmid25737365, year = {2015}, author = {Marschewski, J and Jung, S and Ruch, P and Prasad, N and Mazzotti, S and Michel, B and Poulikakos, D}, title = {Mixing with herringbone-inspired microstructures: overcoming the diffusion limit in co-laminar microfluidic devices.}, journal = {Lab on a chip}, volume = {15}, number = {8}, pages = {1923-1933}, doi = {10.1039/c5lc00045a}, pmid = {25737365}, issn = {1473-0189}, abstract = {Enhancing mixing is of uttermost importance in many laminar microfluidic devices, aiming at overcoming the severe performance limitation of species transport by diffusion alone. Here we focus on the significant category of microscale co-laminar flows encountered in membraneless redox flow cells for power delivery. The grand challenge is to achieve simultaneously convective mixing within each individual reactant, to thin the reaction depletion boundary layers, while maintaining separation of the co-flowing reactants, despite the absence of a membrane. The concept presented here achieves this goal with the help of optimized herringbone flow promoting microstructures with an integrated separation zone. Our electrochemical experiments using a model redox couple show that symmetric flow promoter designs exhibit laminar to turbulent flow behavior, the latter at elevated flow rates. This change in flow regime is accompanied by a significant change in scaling of the Sherwood number with respect to the Reynolds number from Sh ~ Re(0.29) to Sh ~ Re(0.58). The stabilized continuous laminar flow zone along the centerline of the channel allows operation in a co-laminar flow regime up to Re ~325 as we demonstrate by micro laser-induced fluorescence (μLIF) measurements. Micro particle image velocimetry (μPIV) proves the maintenance of a stratified flow along the centerline, mitigating reactant cross-over effectively. The present work paves the way toward improved performance in membraneless microfluidic flow cells for electrochemical energy conversion.}, } @article {pmid25711100, year = {2014}, author = {Filatova, OV and Sidorenko, AA and Skorobogatov, IuIu}, title = {[The study of hemodynamic parameters of human internal carotid arteries depending on the age considering the sex and the localization of the artery].}, journal = {Fiziologiia cheloveka}, volume = {40}, number = {5}, pages = {93-102}, pmid = {25711100}, issn = {0131-1646}, mesh = {Adolescent ; Adult ; *Age Factors ; Aged ; Aged, 80 and over ; Blood Flow Velocity/*physiology ; Carotid Artery, Internal/*physiology ; Child ; Child, Preschool ; Female ; *Hemodynamics ; Humans ; Infant ; Infant, Newborn ; Male ; Middle Aged ; Sex Characteristics ; }, abstract = {The research of the ultrasound diameter, linear velocity and the resistance of internal carotid arteries of 647 people of both sexes aged from one to 74 years was conducted. Additionally, shear stress and the Reynolds number were calculated. During the period from early childhood to adolescence and from the first mature to old age there is an increase in the diameter of the internal carotid arteries. The phases of increased vascular resistance by the first period of childhood, adolescence and old age are observed. Volumetric flow rate has relatively stable parameters till adolescence, then it declines by old age. The average linear velocity, shear stress, and the Reynolds number diminish progressively twice with age. Laminar blood flow with local twists in the early stages of postnatal ontogenesis is characteristic of internal carotid arteries. The diameter of internal carotid arteries, vascular resistance index, blood flow velocity are higher in males than in females during most age periods. Shear stress in both internal carotid arteries during the age periods studied is symmetrical and has no sex differences.}, } @article {pmid25680212, year = {2015}, author = {Nadeem, S and Sadaf, H}, title = {Theoretical Analysis of Cu-Blood Nanofluid for Metachronal Wave of Cilia Motion in a Curved Channel.}, journal = {IEEE transactions on nanobioscience}, volume = {14}, number = {4}, pages = {447-454}, doi = {10.1109/TNB.2015.2401972}, pmid = {25680212}, issn = {1558-2639}, abstract = {In this paper, the mechanism of cilia-induced flow is discussed through a mathematical model. In this study two dimensional flow of a viscous fluid in the presence of nanoparticles are observed in a curved channel with ciliated walls. Cilia have a distinctive pattern of motion by which they can set fluid into motion at low Reynolds number. The flow is modeled in both fixed and wave frame of reference. Exact solution is calculated for the velocity as well as for temperature profile and the flow properties for the Cu-blood nanofluid is determined as a function of the cilia and metachronal wave velocity. Results for temperature profile, velocity, pressure rise, pressure gradient and stream function are constructed and evaluated graphically.}, } @article {pmid25672601, year = {2015}, author = {Gibbs, JG and Fischer, P}, title = {Active colloidal microdrills.}, journal = {Chemical communications (Cambridge, England)}, volume = {51}, number = {20}, pages = {4192-4195}, doi = {10.1039/c5cc00565e}, pmid = {25672601}, issn = {1364-548X}, mesh = {Catalysis ; Colloids/*chemistry ; *Hydrodynamics ; Movement ; Platinum/chemistry ; Rotation ; Torque ; }, abstract = {We demonstrate a chemically driven, autonomous catalytic microdrill. An asymmetric distribution of catalyst causes the helical swimmer to twist while it undergoes directed propulsion. A driving torque and hydrodynamic coupling between translation and rotation at low Reynolds number leads to drill-like swimming behaviour.}, } @article {pmid25671438, year = {2015}, author = {You, JB and Kang, K and Tran, TT and Park, H and Hwang, WR and Kim, JM and Im, SG}, title = {PDMS-based turbulent microfluidic mixer.}, journal = {Lab on a chip}, volume = {15}, number = {7}, pages = {1727-1735}, doi = {10.1039/c5lc00070j}, pmid = {25671438}, issn = {1473-0189}, abstract = {Over the past decade, homogeneous mixing in microfluidic devices has been a critical challenge, because of the inherently low flow rates in microfluidic channels. Although several mixer designs have been suggested to achieve efficient mixing, most of them involve intricate structures requiring a series of laborious fabrication processes. Operation at high flow rates can greatly enhance mixing by induction of turbulence, but devices that can resist such a high pressure drop to induce turbulence in microfluidic channels are difficult to fabricate, especially for commonly used poly(dimethylsiloxane) (PDMS)-based microfluidic devices. We have developed a Y-shaped, turbulent microfluidic mixer made of PDMS and a glass substrate by strong bonding of the substrates to a nanoadhesive layer deposited via initiated chemical vapor deposition. The high bonding strength of the nanoadhesive layer enables safe operation of the PDMS/glass turbulent microfluidic mixer at a total water flow rate of 40 mL min(-1), corresponding to a Reynolds number, Re, of ~4423, one of the highest values achieved in a microfluidic channel. The turbulence generated as a result of the high Re allows rapid mixing of the input fluids on contact. Image analysis showed that mixing started as soon as the fluids were introduced into the mixer. The experimental results matched the numerical predictions well, demonstrating that convective mixing was dominant as a result of turbulence induced in the microfluidic channel. Using the turbulent microfluidic mixer, we have demonstrated high throughput formation of emulsions with narrower size distribution. It was shown that as the flow rate increases inside the microfluidic channel, the size distribution of resulting emulsions decreases owing to the increase in the turbulent energy dissipation. The turbulent microfluidic mixer developed in this work not only enables rapid mixing of streams, but also increases throughputs of microfluidic reactors.}, } @article {pmid25659002, year = {2015}, author = {Sinhuber, M and Bodenschatz, E and Bewley, GP}, title = {Decay of turbulence at high reynolds numbers.}, journal = {Physical review letters}, volume = {114}, number = {3}, pages = {034501}, doi = {10.1103/PhysRevLett.114.034501}, pmid = {25659002}, issn = {1079-7114}, abstract = {Turbulent motions in a fluid decay at a certain rate once stirring has stopped. The role of the most basic parameter in fluid mechanics, the Reynolds number, in setting the decay rate is not generally known. This Letter concerns the high-Reynolds-number limit of the process. In a classical grid-turbulence wind-tunnel experiment that both reaches higher Reynolds numbers than ever before and covers a wide range of them (10^{4}
METHODS: A 3D virtual stent with 90° curvature was modelled and the distribution of wall shear stress (WSS) and drug concentration in this model were numerically studied at Reynolds numbers of 200, 400, 600, 800.

RESULTS: The results showed that (1) the intensity of secondary flow at the 45° cross-section was stronger than that at the 90° cross-section; (2) As the Reynolds number increases, the WSS decreases. When the Reynolds number reaches 600, the low-WSS region only accounts for 3% of the total area. (3) The effects of Reynolds number on drug concentration in the vascular wall decreases in proportionally and then the blood velocity increased 4 times, the drug concentration in the vascular wall decreased by about 30%. (4) The size of the high drug concentration region is inversely proportional to the Reynolds number. As the blood velocity increases, the drug concentration in the DES decreases, especially at the outer bend.

CONCLUSIONS: It is beneficial for the patient to decrease vigorous activities and keep calm at the beginning of the stent implantation, because a substantial amount of the drug is released in the first two months of stent implantation, thus a calm status is conducive to drug release and absorption; Subsequently, appropriate exercise which increases the blood velocity is helpful in decreasing regions of low-WSS.}, } @article {pmid25598070, year = {2014}, author = {Bit, A and Chattopadhyay, H}, title = {Numerical investigations of pulsatile flow in stenosed artery.}, journal = {Acta of bioengineering and biomechanics}, volume = {16}, number = {4}, pages = {33-44}, pmid = {25598070}, issn = {1509-409X}, mesh = {Blood Flow Velocity ; Coronary Stenosis/pathology/*physiopathology ; Coronary Vessels/pathology/*physiopathology ; Humans ; Models, Cardiovascular ; *Numerical Analysis, Computer-Assisted ; Pressure ; Pulsatile Flow/*physiology ; Stress, Mechanical ; Time Factors ; }, abstract = {PURPOSE: Abnormalities in blood vessels by virtue of complex blood flow dynamics is being supported by non-Newtonian behavior of blood. Thus it becomes a focus of research to most of the researchers. Additionally, consideration of real life patient specific model of vessel as well as patient specific inlet flow boundary condition implementation was limited in literature. Thus a thorough implementation of these considerations was done here.

METHOD: In this work, a numerical investigation of hemodynamic flow in stenosed artery has been carried out with realistic pulsating profile at the inlet. Flow has been considered to be laminar due to arresting condition of cardiovascular state of the subject. Two non- Newtonian rheological models namely, Power Law viscosity model and Quemada viscosity model have been used. Two different patient- specific pulsatile profiles are considered at the inlet of a long stenosed artery with varying degree of stenoses from 25% to 80%.

RESULTS: Transient form of Navier-Stokes equation is solved in an axi-symmetric domain to calculate the detailed flow structure of the flow field. From the simulation data, temporal and time averaged wall shear stress, oscillatory shear index and pressure drop are calculated.

CONCLUSIONS: The results demonstrate that oscillatory shear index and wall shear stresses are extensively governed by the degree of stenoses. The position and movement of recirculation bubbles are found to vary with flow Reynolds number.}, } @article {pmid25573580, year = {2015}, author = {Ekiel-Jeżewska, ML and Felderhof, BU}, title = {Hydrodynamic interactions between a sphere and a number of small particles.}, journal = {The Journal of chemical physics}, volume = {142}, number = {1}, pages = {014904}, doi = {10.1063/1.4904981}, pmid = {25573580}, issn = {1089-7690}, abstract = {Exact expressions are derived for the pair and three-body hydrodynamic interactions between a sphere and a number of small particles immersed in a viscous incompressible fluid. The analysis is based on the Stokes equations of low Reynolds number hydrodynamics. The results follow by a combination of the solutions for flow about a sphere with no-slip boundary condition derived by Stokes and Kirchhoff and the result derived by Oseen for the Green tensor of Stokes equations in the presence of a fixed sphere.}, } @article {pmid25564849, year = {2015}, author = {Visser, CW and Gielen, MV and Hao, Z and Le Gac, S and Lohse, D and Sun, C}, title = {Quantifying cell adhesion through impingement of a controlled microjet.}, journal = {Biophysical journal}, volume = {108}, number = {1}, pages = {23-31}, pmid = {25564849}, issn = {1542-0086}, mesh = {*Cell Adhesion ; Computer Simulation ; Cytological Techniques/*instrumentation ; HeLa Cells ; Humans ; Microtechnology/*instrumentation/*methods ; Models, Biological ; Stress, Mechanical ; }, abstract = {The impingement of a submerged, liquid jet onto a cell-covered surface allows assessing cell attachment on surfaces in a straightforward and quantitative manner and in real time, yielding valuable information on cell adhesion. However, this approach is insufficiently characterized for reliable and routine use. In this work, we both model and measure the shear stress exerted by the jet on the impingement surface in the micrometer-domain, and subsequently correlate this to jet-induced cell detachment. The measured and numerically calculated shear stress data are in good agreement with each other, and with previously published values. Real-time monitoring of the cell detachment reveals the creation of a circular cell-free area upon jet impingement, with two successive detachment regimes: 1), a dynamic regime, during which the cell-free area grows as a function of both the maximum shear stress exerted by the jet and the jet diameter; followed by 2), a stationary regime, with no further evolution of the cell-free area. For the latter regime, which is relevant for cell adhesion strength assessment, a relationship between the jet Reynolds number, the cell-free area, and the cell adhesion strength is proposed. To illustrate the capability of the technique, the adhesion strength of HeLa cervical cancer cells is determined ((34 ± 14) N/m(2)). Real-time visualization of cell detachment in the dynamic regime shows that cells detach either cell-by-cell or by collectively (for which intact parts of the monolayer detach as cell sheets). This process is dictated by the cell monolayer density, with a typical threshold of (1.8 ± 0.2) × 10(9) cells/m(2), above which the collective behavior is mostly observed. The jet impingement method presents great promises for the field of tissue engineering, as the influence of both the shear stress and the surface characteristics on cell adhesion can be systematically studied.}, } @article {pmid25563524, year = {2015}, author = {Liu, C and Hu, G and Jiang, X and Sun, J}, title = {Inertial focusing of spherical particles in rectangular microchannels over a wide range of Reynolds numbers.}, journal = {Lab on a chip}, volume = {15}, number = {4}, pages = {1168-1177}, doi = {10.1039/c4lc01216j}, pmid = {25563524}, issn = {1473-0189}, mesh = {Equipment Design ; *Lab-On-A-Chip Devices ; Particle Size ; }, abstract = {Inertial microfluidics has emerged as an important tool for manipulating particles and cells. For a better design of inertial microfluidic devices, we conduct 3D direct numerical simulations (DNS) and experiments to determine the complicated dependence of focusing behaviour on the particle size, channel aspect ratio, and channel Reynolds number. We find that the well-known focusing of the particles at the two centers of the long channel walls occurs at a relatively low Reynolds number, whereas additional stable equilibrium positions emerge close to the short walls with increasing Reynolds number. Based on the numerically calculated trajectories of particles, we propose a two-stage particle migration which is consistent with experimental observations. We further present a general criterion to secure good focusing of particles for high flow rates. This work thus provides physical insight into the multiplex focusing of particles in rectangular microchannels with different geometries and Reynolds numbers, and paves the way for efficiently designing inertial microfluidic devices.}, } @article {pmid25554885, year = {2014}, author = {Lashgari, I and Picano, F and Breugem, WP and Brandt, L}, title = {Laminar, turbulent, and inertial shear-thickening regimes in channel flow of neutrally buoyant particle suspensions.}, journal = {Physical review letters}, volume = {113}, number = {25}, pages = {254502}, doi = {10.1103/PhysRevLett.113.254502}, pmid = {25554885}, issn = {1079-7114}, abstract = {The aim of this Letter is to characterize the flow regimes of suspensions of finite-size rigid particles in a viscous fluid at finite inertia. We explore the system behavior as a function of the particle volume fraction and the Reynolds number (the ratio of flow and particle inertia to viscous forces). Unlike single-phase flows, where a clear distinction exists between the laminar and the turbulent states, three different regimes can be identified in the presence of a particulate phase, with smooth transitions between them. At low volume fractions, the flow becomes turbulent when increasing the Reynolds number, transitioning from the laminar regime dominated by viscous forces to the turbulent regime characterized by enhanced momentum transport by turbulent eddies. At larger volume fractions, we identify a new regime characterized by an even larger increase of the wall friction. The wall friction increases with the Reynolds number (inertial effects) while the turbulent transport is weakly affected, as in a state of intense inertial shear thickening. This state may prevent the transition to a fully turbulent regime at arbitrary high speed of the flow.}, } @article {pmid25554059, year = {2014}, author = {Sikiö, P and Jalali, P}, title = {Study of turbulent energy dissipation rate of fluid flow in the vicinity of dispersed phase boundary using spatiotemporal tree model.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {24}, number = {4}, pages = {043139}, doi = {10.1063/1.4903818}, pmid = {25554059}, issn = {1089-7682}, abstract = {The hierarchical shell models of turbulence including a spatial dimension, namely, spatiotemporal tree models, reproduce the intermittent behavior of Navier-Stokes equations in both space and time dimensions corresponding to high Reynolds number turbulent flows. This model is used, for the first time in this paper, in a one-dimensional flow zone containing a dispersed-phase particle that can be used in the study of dispersed-phase flows. In this paper, a straightforward method has been used to introduce discrete phase into the spatiotemporal tree model that leads to an increased amount of turbulent energy dissipation rate in the vicinity of the discrete phase. The effects of particle insertion and particle size on the turbulent energy dissipation rate are demonstrated. Moreover, the space-scale behavior of the time-averaged turbulent energy dissipation rate in the presence of dispersed phase is demonstrated by means of continuous wavelet transform.}, } @article {pmid25553185, year = {2014}, author = {Song, J and Song, M and Kang, T and Kim, D and Lee, LP}, title = {Label-free density difference amplification-based cell sorting.}, journal = {Biomicrofluidics}, volume = {8}, number = {6}, pages = {064108}, pmid = {25553185}, issn = {1932-1058}, abstract = {The selective cell separation is a critical step in fundamental life sciences, translational medicine, biotechnology, and energy harvesting. Conventional cell separation methods are fluorescent activated cell sorting and magnetic-activated cell sorting based on fluorescent probes and magnetic particles on cell surfaces. Label-free cell separation methods such as Raman-activated cell sorting, electro-physiologically activated cell sorting, dielectric-activated cell sorting, or inertial microfluidic cell sorting are, however, limited when separating cells of the same kind or cells with similar sizes and dielectric properties, as well as similar electrophysiological phenotypes. Here we report a label-free density difference amplification-based cell sorting (dDACS) without using any external optical, magnetic, electrical forces, or fluidic activations. The conceptual microfluidic design consists of an inlet, hydraulic jump cavity, and multiple outlets. Incoming particles experience gravity, buoyancy, and drag forces in the separation chamber. The height and distance that each particle can reach in the chamber are different and depend on its density, thus allowing for the separation of particles into multiple outlets. The separation behavior of the particles, based on the ratio of the channel heights of the inlet and chamber and Reynolds number has been systematically studied. Numerical simulation reveals that the difference between the heights of only lighter particles with densities close to that of water increases with increasing the ratio of the channel heights, while decreasing Reynolds number can amplify the difference in the heights between the particles considered irrespective of their densities.}, } @article {pmid27057133, year = {2015}, author = {Ebrahimi, M and Abbaspour, M}, title = {A Comparative Numerical Study on the Performances and Vortical Patterns of Two Bioinspired Oscillatory Mechanisms: Undulating and Pure Heaving.}, journal = {Applied bionics and biomechanics}, volume = {2015}, number = {}, pages = {325934}, pmid = {27057133}, issn = {1176-2322}, abstract = {The hydrodynamics and energetics of bioinspired oscillating mechanisms have received significant attentions by engineers and biologists to develop the underwater and air vehicles. Undulating and pure heaving (or plunging) motions are two significant mechanisms which are utilized in nature to provide propulsive, maneuvering, and stabilization forces. This study aims to elucidate and compare the propulsive vortical signature and performance of these two important natural mechanisms through a systematic numerical study. Navier-Stokes equations are solved, by a pressure-based finite volume method solver, in an arbitrary Lagrangian-Eulerian (ALE) framework domain containing a 2D NACA0012 foil moving with prescribed kinematics. Some of the important findings are (1) the thrust production of the heaving foil begins at lower St and has a greater growing slope with respect to the St; (2) the undulating mechanism has some limitations to produce high thrust forces; (3) the undulating foil shows a lower power consumption and higher efficiency; (4) changing the Reynolds number (Re) in a constant St affects the performance of the oscillations; and (5) there is a distinguishable appearance of leading edge vortices in the wake of the heaving foil without observable ones in the wake of the undulating foil, especially at higher St.}, } @article {pmid27057132, year = {2015}, author = {Chaube, MK and Tripathi, D and Bég, OA and Sharma, S and Pandey, VS}, title = {Peristaltic Creeping Flow of Power Law Physiological Fluids through a Nonuniform Channel with Slip Effect.}, journal = {Applied bionics and biomechanics}, volume = {2015}, number = {}, pages = {152802}, pmid = {27057132}, issn = {1176-2322}, abstract = {A mathematical study on creeping flow of non-Newtonian fluids (power law model) through a nonuniform peristaltic channel, in which amplitude is varying across axial displacement, is presented, with slip effects included. The governing equations are simplified by employing the long wavelength and low Reynolds number approximations. The expressions for axial velocity, stream function, pressure gradient, and pressure difference are obtained. Computational and numerical results for velocity profile, pressure gradient, and trapping under the effects of slip parameter, fluid behavior index, angle between the walls, and wave number are discussed with the help of Mathematica graphs. The present model is applicable to study the behavior of intestinal flow (chyme movement from small intestine to large intestine). It is also relevant to simulations of biomimetic pumps conveying hazardous materials, polymers, and so forth.}, } @article {pmid27041980, year = {2015}, author = {Pandey, SK and Chaube, MK and Tripathi, D}, title = {Flow Characteristics of Distinctly Viscous Multilayered Intestinal Fluid Motion.}, journal = {Applied bionics and biomechanics}, volume = {2015}, number = {}, pages = {515241}, pmid = {27041980}, issn = {1176-2322}, abstract = {The goal of this investigation is to study the three layered (core layer, intermediate layer, and peripheral layer) tubular flow of power law fluids with variable viscosity by peristalsis in order to investigate the strength of the role played by an artificially generated intermediate layer to ease constipation. The solution is carried out under the long wavelength and low Reynolds number approximations in the wave frame of reference as the flow is creeping one. The stream functions for each layer such as core layer, intermediate layer, and peripheral layer are determined. The expressions for axial pressure gradient, interfaces, trapping, and reflux limits are obtained. The effects of power law index and viscosities on pressure across one wavelength, mechanical efficiency, and trapping are discussed numerically. It is found that the pressure required to restrain flow rates and the mechanical efficiency increase with the viscosities of the intermediate and peripheral layers as well as with the flow behaviour index. It is observed that the axisymmetric flow in intestines is less prone to constipation than two-dimensional flow and may be more easily overcome with introducing a viscous intermediate layer.}, } @article {pmid25527319, year = {2015}, author = {Wang, S and Vafai, K}, title = {Analysis of Low Density Lipoprotein (LDL) Transport Within a Curved Artery.}, journal = {Annals of biomedical engineering}, volume = {43}, number = {7}, pages = {1571-1584}, doi = {10.1007/s10439-014-1219-x}, pmid = {25527319}, issn = {1573-9686}, mesh = {Arteries/*anatomy & histology/*physiology ; Atherosclerosis/physiopathology ; Humans ; Lipoproteins, LDL/*physiology ; *Models, Cardiovascular ; }, abstract = {To elucidate the mechanism of the effect of LDL concentration on the thickening of intima in a curved artery, LDL transport in each layer of the curved arterial wall is studied analytically. A comprehensive concentration distribution expression of LDL in each layer of the curved artery wall is presented along with the characterization and estimation of the effect of curvature on the growth of atherosclerosis within the arterial wall. The effect of curvature on species concentration distribution is analyzed and the results are thoroughly benchmarked against prior pertinent works. The concentration at the interface of lumen and endothelium will directly affect the concentration profile inside the arterial wall layers. The results show that the average concentration in the circumferential direction is actually decreasing in the axial direction for a curved artery compared with a straight artery. Small radius ratio and Reynolds number will augment the LDL accumulation at the lumen endothelium interface. The increase in concentration at the lumen/endothelium interface in the axial direction has a minor effect on the concentration profile at the other wall interface layers.}, } @article {pmid25526130, year = {2014}, author = {Dennis, DJ and Sogaro, FM}, title = {Distinct organizational States of fully developed turbulent pipe flow.}, journal = {Physical review letters}, volume = {113}, number = {23}, pages = {234501}, doi = {10.1103/PhysRevLett.113.234501}, pmid = {25526130}, issn = {1079-7114}, abstract = {Organizational states of turbulence are identified through novel analysis of large scale pipe flow experiments at a Reynolds number of 35 000. The distinct states are revealed by an azimuthal decomposition of the two-point spatial correlation of the streamwise velocity fluctuation. States with dominant azimuthal wave numbers corresponding to k_{θ} =2,3,4,5,6 are discovered and their structure revealed as a series of alternately rotating quasistreamwise vortices. Such organizational states are highly reminiscent of the nonlinear traveling wave solutions previously identified at Reynolds numbers an order of magnitude lower.}, } @article {pmid25512586, year = {2015}, author = {Bourguet, R and Triantafyllou, MS}, title = {Vortex-induced vibrations of a flexible cylinder at large inclination angle.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {373}, number = {2033}, pages = {}, pmid = {25512586}, issn = {1471-2962}, abstract = {The free vibrations of a flexible circular cylinder inclined at 80° within a uniform current are investigated by means of direct numerical simulation, at Reynolds number 500 based on the body diameter and inflow velocity. In spite of the large inclination angle, the cylinder exhibits regular in-line and cross-flow vibrations excited by the flow through the lock-in mechanism, i.e. synchronization of body motion and vortex formation. A profound reconfiguration of the wake is observed compared with the stationary body case. The vortex-induced vibrations are found to occur under parallel, but also oblique vortex shedding where the spanwise wavenumbers of the wake and structural response coincide. The shedding angle and frequency increase with the spanwise wavenumber. The cylinder vibrations and fluid forces present a persistent spanwise asymmetry which relates to the asymmetry of the local current relative to the body axis, owing to its in-line bending. In particular, the asymmetrical trend of flow-body energy transfer results in a monotonic orientation of the structural waves. Clockwise and counter-clockwise figure eight orbits of the body alternate along the span, but the latter are found to be more favourable to structure excitation. Additional simulations at normal incidence highlight a dramatic deviation from the independence principle, which states that the system behaviour is essentially driven by the normal component of the inflow velocity.}, } @article {pmid25502616, year = {2015}, author = {Khodarahmi, I}, title = {Comparing velocity and fluid shear stress in a stenotic phantom with steady flow: phase-contrast MRI, particle image velocimetry and computational fluid dynamics.}, journal = {Magma (New York, N.Y.)}, volume = {28}, number = {4}, pages = {385-393}, pmid = {25502616}, issn = {1352-8661}, mesh = {Constriction, Pathologic ; Hydrodynamics ; In Vitro Techniques ; Magnetic Resonance Imaging/*methods ; Phantoms, Imaging ; Pulsatile Flow ; Reproducibility of Results ; Rheology/*methods ; }, abstract = {OBJECT: This study aims to validate phase-contrast magnetic resonance imaging (PC-MRI) measurements of a steady flow through a severe stenotic phantom using particle image velocimetry (PIV) and computational fluid dynamics (CFD).

MATERIALS AND METHODS: The study was performed in an axisymmetric 87 % area stenosis model using an inlet Reynolds number (Re) of 160, corresponding to a jet Re of 444. Velocity patterns and estimated fluid shear stresses from three modalities were analyzed and compared qualitatively and quantitatively.

RESULTS: Visual analysis via contour subtraction and Bland-Altman plots showed good agreement for flow velocities and less agreement for maximum shear stress (MSS). The Pearson's coefficients of correlation between PC-MRI and PIV were 0.97 for the velocity field and 0.82 for the MSS. The corresponding parameters between PC-MRI and CFD were 0.96 and 0.84, respectively.

CONCLUSION: Findings indicate that PC-MRI can be implemented to estimate velocity flow fields and MSS; however, this method is not sufficiently accurate to quantify the MSS at regions of high shear rate.}, } @article {pmid25497311, year = {2015}, author = {Ziffels, S and Bemelmans, NL and Durham, PG and Hickey, AJ}, title = {In vitro dry powder inhaler formulation performance considerations.}, journal = {Journal of controlled release : official journal of the Controlled Release Society}, volume = {199}, number = {}, pages = {45-52}, doi = {10.1016/j.jconrel.2014.11.035}, pmid = {25497311}, issn = {1873-4995}, mesh = {Albuterol/administration & dosage/pharmacokinetics ; Anti-Asthmatic Agents/administration & dosage/pharmacokinetics ; Budesonide/administration & dosage/pharmacokinetics ; Chemistry, Pharmaceutical/*methods ; Drug Carriers ; Drug Delivery Systems ; *Dry Powder Inhalers ; Excipients ; In Vitro Techniques ; Lactose ; Particle Size ; Powders ; }, abstract = {It has long been desired to match airflow conditions during formulation evaluation to those of relevance to lung deposition. In this context several strategies have been adopted involving sampling at different: flow rate (without consideration of flow conditions, e.g. shear, Reynolds number, work function); pressure drop (with and without consideration of flow conditions) and; flow rate and pressure drop. Performance testing has focused on the influence of these sampling conditions on delivered dose uniformity and aerodynamic particle size distribution. However, in order to be physiologically relevant it is also important to know when the drug was delivered with respect to initiation of airflow as variation in this parameter would influence lung deposition. A light obscuration method of detecting the dose delivered from a dry powder inhaler while sampling for aerodynamic particle size distributions (APSD) by inertial impaction has been developed. Four formulations of albuterol sulfate and budesonide in sieved and milled lactose, respectively, were dispersed and their rate of delivery monitored. The differences observed have the potential to impact the site of delivery in the lungs. The rate of delivery of drug is clearly an important companion measurement to delivered dose and APSD if the intent is to predict the similarity of in vivo performance of dry powder inhaler products.}, } @article {pmid25496731, year = {2015}, author = {Krick, J and Ackerman, JD}, title = {Adding ecology to particle capture models: numerical simulations of capture on a moving cylinder in crossflow.}, journal = {Journal of theoretical biology}, volume = {368}, number = {}, pages = {13-26}, doi = {10.1016/j.jtbi.2014.12.003}, pmid = {25496731}, issn = {1095-8541}, mesh = {Algorithms ; Computer Simulation ; *Ecological and Environmental Phenomena ; *Hydrodynamics ; *Models, Biological ; Particle Size ; Pollination ; Rheology/methods ; }, abstract = {The particle capture efficiency, η, of systems that remove suspended particles from ambient flow (e.g. suspension feeding, abiotic pollination) has been studied using static collectors in steady flows. Particle deposition on collectors moving due to fluid flow remains largely unknown, despite its ecological relevance. We used numerical modeling to simulate particle deposition on a 2D circular cylinder subject to flow-induced oscillation in a cross flow. Using parameter values relevant to wind pollination and other natural biological systems, we examined the influence of the direction, amplitude and frequency of the oscillation, the Stokes number (Stk=0.01-5, characterizing particle behavior), as well as the Reynolds number (Re=662 and 3309, characterizing flow regime) in steady and unsteady flow, on η. The numerical model was validated with empirical results for parts of the parameter space. Particle capture occurred via "inertial impaction", "direct interception" and "leeward deposition", as well as via a new mechanism, "collector chasing" for moving collectors. The η of an oscillating cylinder varied significantly relative to a static cylinder, depending on the parameters used, and on the magnitude of a numerical error that caused loss of particles. This variance of η was due to a change in relative momentum between the particle and the moving collector, which depends on Re, Stk and the oscillation parameters. Collector oscillation transverse to oncoming flow direction strongly increased η, whereas collector motion parallel to flow had little effect on capture efficiency. The oscillation also changed leeward capture significantly in some cases. For most conditions, however, leeward deposition was small. Results suggest that collector motion could have significant influence on the particle capture efficiency of natural systems, which indicates the need to incorporate these ecologically more relevant findings into current models. Empirical studies, however, are still necessary to validate these results and provide reliable data.}, } @article {pmid25493887, year = {2014}, author = {Felderhof, BU}, title = {Collinear swimmer propelling a cargo sphere at low Reynolds number.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {90}, number = {5-1}, pages = {053013}, doi = {10.1103/PhysRevE.90.053013}, pmid = {25493887}, issn = {1550-2376}, abstract = {The swimming velocity and rate of dissipation of a linear chain consisting of two or three little spheres and a big sphere is studied on the basis of low Reynolds number hydrodynamics. The big sphere is treated as a passive cargo, driven by the tail of little spheres via hydrodynamic and direct elastic interaction. The fundamental solution of Stokes equations in the presence of a sphere with a no-slip boundary condition, as derived by Oseen, is used to model the hydrodynamic interactions between the big sphere and the little spheres.}, } @article {pmid25493884, year = {2014}, author = {McComb, WD and Yoffe, SR and Linkmann, MF and Berera, A}, title = {Spectral analysis of structure functions and their scaling exponents in forced isotropic turbulence.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {90}, number = {5-1}, pages = {053010}, doi = {10.1103/PhysRevE.90.053010}, pmid = {25493884}, issn = {1550-2376}, abstract = {The pseudospectral method, in conjunction with a technique for obtaining scaling exponents ζ_{n} from the structure functions S_{n} (r), is presented as an alternative to the extended self-similarity (ESS) method and the use of generalized structure functions. We propose plotting the ratio |S_{n} (r)/S_{3} (r)| against the separation r in accordance with a standard technique for analyzing experimental data. This method differs from the ESS technique, which plots S_{n} (r) against S_{3} (r), with the assumption S_{3} (r)∼r. Using our method for the particular case of S_{2} (r) we obtain the result that the exponent ζ_{2} decreases as the Taylor-Reynolds number increases, with ζ_{2} →0.679±0.013 as R_{λ} →∞. This supports the idea of finite-viscosity corrections to the K41 prediction for S_{2}, and is the opposite of the result obtained by ESS. The pseudospectral method also permits the forcing to be taken into account exactly through the calculation of the energy input in real space from the work spectrum of the stirring forces.}, } @article {pmid25493880, year = {2014}, author = {Jalali, MA and Alam, MR and Mousavi, S}, title = {Versatile low-Reynolds-number swimmer with three-dimensional maneuverability.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {90}, number = {5-1}, pages = {053006}, doi = {10.1103/PhysRevE.90.053006}, pmid = {25493880}, issn = {1550-2376}, abstract = {We design and simulate the motion of a swimmer, the Quadroar, with three-dimensional translation and reorientation capabilities in low-Reynolds-number conditions. The Quadroar is composed of an I-shaped frame whose body link is a simple linear actuator and four disks that can rotate about the axes of flange links. The time symmetry is broken by a combination of disk rotations and the one-dimensional expansion or contraction of the body link. The Quadroar propels on forward and transverse straight lines and performs full three-dimensional reorientation maneuvers, which enable it to swim along arbitrary trajectories. We find continuous operation modes that propel the swimmer on planar and three-dimensional periodic and quasiperiodic orbits. Precessing quasiperiodic orbits consist of slow lingering phases with cardioid or multiloop turns followed by directional propulsive phases. Quasiperiodic orbits allow the swimmer to access large parts of its neighboring space without using complex control strategies. We also discuss the feasibility of fabricating a nanoscale Quadroar by photoactive molecular rotors.}, } @article {pmid25483750, year = {2014}, author = {Rossen, NS and Tarp, JM and Mathiesen, J and Jensen, MH and Oddershede, LB}, title = {Long-range ordered vorticity patterns in living tissue induced by cell division.}, journal = {Nature communications}, volume = {5}, number = {}, pages = {5720}, pmid = {25483750}, issn = {2041-1723}, mesh = {Biophysics ; Blood Flow Velocity ; *Cell Division ; Cytoplasm/metabolism ; Endothelial Cells/*cytology ; Fourier Analysis ; Hemodynamics ; Human Umbilical Vein Endothelial Cells ; Humans ; Hydrodynamics ; Microscopy, Phase-Contrast ; Models, Cardiovascular ; Models, Theoretical ; Stress, Mechanical ; }, abstract = {In healthy blood vessels with a laminar blood flow, the endothelial cell division rate is low, only sufficient to replace apoptotic cells. The division rate significantly increases during embryonic development and under halted or turbulent flow. Cells in barrier tissue are connected and their motility is highly correlated. Here we investigate the long-range dynamics induced by cell division in an endothelial monolayer under non-flow conditions, mimicking the conditions during vessel formation or around blood clots. Cell divisions induce long-range, well-ordered vortex patterns extending several cell diameters away from the division site, in spite of the system's low Reynolds number. Our experimental results are reproduced by a hydrodynamic continuum model simulating division as a local pressure increase corresponding to a local tension decrease. Such long-range physical communication may be crucial for embryonic development and for healing tissue, for instance around blood clots.}, } @article {pmid25480040, year = {2014}, author = {Van Hirtum, A and Fujiso, Y and Nozaki, K}, title = {The role of initial flow conditions for sibilant fricative production.}, journal = {The Journal of the Acoustical Society of America}, volume = {136}, number = {6}, pages = {2922}, doi = {10.1121/1.4900595}, pmid = {25480040}, issn = {1520-8524}, abstract = {Sibilant fricative sound production depends on the geometric and flow properties of the production system. Nevertheless, few studies deal with the potential impact of flow properties other than the inlet volume flow rate on the noise produced. In this work, an experimental study is presented using a replica based on a reconstructed oral cavity for the phoneme /s/. Initial flow conditions upstream from the sibilant groove are altered by varying the method of air supply. Statistical moments of the initial velocity distribution are characterized using hot-film anemometry and related to spectral features of the radiated acoustic pressure. Discrepancies in the dynamic amplitude (≤25%) and negative spectral slope (≤35%) observed at a constant Reynolds number but different initial upstream flow conditions are of the same order of magnitude as those previously reported in humans. This suggests that consideration of the upstream flow conditions is important in the study of sibilant fricative sound production.}, } @article {pmid25474212, year = {2014}, author = {Hina, S and Mustafa, M and Hayat, T}, title = {Peristaltic motion of Johnson-Segalman fluid in a curved channel with slip conditions.}, journal = {PloS one}, volume = {9}, number = {12}, pages = {e114168}, pmid = {25474212}, issn = {1932-6203}, mesh = {Body Fluids/*physiology ; Computer Graphics ; *Hydrodynamics ; *Models, Biological ; *Movement ; *Peristalsis ; Software ; }, abstract = {Slip effects on the peristaltic transport of Johnson-Segalman fluid through a curved channel have been addressed. The influence of wall properties is also analyzed. Long wavelength and low Reynolds number assumptions have been utilized in the mathematical formulation of the problem. The equations so formed have been solved numerically by shooting method through computational software Mathematica 8. In addition the analytic solution for small Weissenberg number (elastic parameter) is computed through a regular perturbation method. An excellent agreement is noticed between the two solutions. The results indicate an increase in the magnitude of velocity with an intensification in the slip effect. Moreover the size and circulation of the trapped boluses increase with an increase in the slip parameter. Unlike the planar channel, the profiles of axial velocity are not symmetric about the central line of the channel.}, } @article {pmid25460608, year = {2014}, author = {Hayat, T and Tanveer, A and Yasmin, H and Alsaedi, A}, title = {Homogeneous-heterogeneous reactions in peristaltic flow with convective conditions.}, journal = {PloS one}, volume = {9}, number = {12}, pages = {e113851}, pmid = {25460608}, issn = {1932-6203}, mesh = {*Convection ; Models, Theoretical ; *Peristalsis ; *Rheology ; Solutions ; Temperature ; }, abstract = {This article addresses the effects of homogeneous-heterogeneous reactions in peristaltic transport of Carreau fluid in a channel with wall properties. Mathematical modelling and analysis have been carried out in the presence of Hall current. The channel walls satisfy the more realistic convective conditions. The governing partial differential equations along with long wavelength and low Reynolds number considerations are solved. The results of temperature and heat transfer coefficient are analyzed for various parameters of interest.}, } @article {pmid25455807, year = {2015}, author = {Dukhin, SS and Kovalchuk, VI and Gochev, GG and Lotfi, M and Krzan, M and Malysa, K and Miller, R}, title = {Dynamics of Rear Stagnant Cap formation at the surface of spherical bubbles rising in surfactant solutions at large Reynolds numbers under conditions of small Marangoni number and slow sorption kinetics.}, journal = {Advances in colloid and interface science}, volume = {222}, number = {}, pages = {260-274}, doi = {10.1016/j.cis.2014.10.002}, pmid = {25455807}, issn = {1873-3727}, abstract = {On the surface of bubbles rising in a surfactant solution the adsorption process proceeds and leads to the formation of a so called Rear Stagnant Cap (RSC). The larger this RSC is the stronger is the retardation of the rising velocity. The theory of a steady RSC and steady retarded rising velocity, which sets in after a transient stage, has been generally accepted. However, a non-steady process of bubble rising starting from the initial zero velocity represents an important portion of the trajectory of rising, characterized by a local velocity profile (LVP). As there is no theory of RSC growth for large Reynolds numbers Re » 1 so far, the interpretation of LVPs measured in this regime was impossible. It turned out, that an analytical theory for a quasi-steady growth of RSC is possible for small Marangoni numbers Ma « 1, i.e. when the RSC is almost completely compressed, which means a uniform surface concentration Γ(θ)=Γ(∞) within the RSC. Hence, the RSC angle ψ(t) is obtained as a function of the adsorption isotherm parameters and time t. From the steady velocity v(st)(ψ), the dependence of non-steady velocity on time is obtained by employing v(st)[ψ(t)] via a quasi-steady approximation. The measurement of LVP creates a promising new opportunity for investigation of the RSC dynamics and adsorption kinetics. While adsorption and desorption happen at the same localization in the classical methods, in rising bubble experiments desorption occurs mainly within RSC while adsorption on the mobile part of the bubble surface. The desorption flux from RSC is proportional to αΓ(∞), while it is usually αΓ. The adsorption flux at the mobile surface above RSC can be assumed proportional to βC0, while it is usually βC0(1-Γ/Γ(∞)). These simplifications may become favorable in investigations of the adsorption kinetics for larger molecules, in particular for globular proteins, which essentially stay at an interface once adsorbed.}, } @article {pmid25434694, year = {2016}, author = {Chen, Z and Zhan, F and Ding, J and Zhang, X and Deng, X}, title = {A new stent with streamlined cross-section can suppress monocyte cell adhesion in the flow disturbance zones of the endovascular stent.}, journal = {Computer methods in biomechanics and biomedical engineering}, volume = {19}, number = {1}, pages = {60-66}, doi = {10.1080/10255842.2014.984701}, pmid = {25434694}, issn = {1476-8259}, mesh = {Cell Adhesion ; *Hemorheology ; Humans ; Monocytes/*cytology ; Perfusion ; *Stents ; Stress, Mechanical ; U937 Cells ; }, abstract = {We proposed a new stent with streamlined cross-sectional wires, which is different from the clinical coronary stents with square or round cross-sections. We believe the new stent might have better hemodynamic performance than the clinical metal stents. To test the hypothesis, we designed an experimental study to compare the performance of the new stent with the clinical stents in terms of monocyte (U-937 cells) adhesion. The results showed that when compared with the clinical stents, the adhesion of U-937 cells were much less in the new stent. The results also showed that, when Reynolds number increased from 180 (the rest condition for the coronary arteries) to 360 (the strenuous exercise condition for the coronary arteries), the flow disturbance zones in the clinical stents became larger, while they became smaller with the new stent. The present experimental study therefore suggests that the optimization of the cross-sectional shape of stent wires ought to be taken into consideration in the design of endovascular stents.}, } @article {pmid25430137, year = {2014}, author = {Krynkin, A and Horoshenkov, KV and Nichols, A and Tait, SJ}, title = {A non-invasive acoustical method to measure the mean roughness height of the free surface of a turbulent shallow water flow.}, journal = {The Review of scientific instruments}, volume = {85}, number = {11}, pages = {114902}, doi = {10.1063/1.4901932}, pmid = {25430137}, issn = {1089-7623}, abstract = {In this paper, the directivity of the airborne sound field scattered by a dynamically rough free flow surface in a flume is used to determine the mean roughness height for six hydraulic conditions in which the uniform depth of the turbulent flow. The nonlinear curve fitting method is used to minimize the error between the predicted directivity and directivity data. The data fitting algorithm is based on the averaged solution for the scattered sound pressure as a function of angle which is derived through the Kirchhoff integral and its approximations. This solution takes into account the directivity of the acoustic source. For the adopted source and receiver geometry and acoustic frequency it is shown that the contribution from the stationary phase point (single specular point on the rough surface) yields similar results to those which can be obtained through the full Kirchhoff's integral. The accuracy in the inverted mean roughness height is comparable to that achieved with an array of conductive wave probes. This method enables non-invasive estimation of the flow Reynolds number and uniform flow depth.}, } @article {pmid25410423, year = {2014}, author = {Das, S and Kumar, A}, title = {Formation and post-formation dynamics of bacterial biofilm streamers as highly viscous liquid jets.}, journal = {Scientific reports}, volume = {4}, number = {}, pages = {7126}, pmid = {25410423}, issn = {2045-2322}, mesh = {Biofilms/*growth & development ; Elasticity ; *Models, Statistical ; Pseudomonas aeruginosa/chemistry/*physiology ; Pseudomonas fluorescens/chemistry/*physiology ; Rheology ; Shear Strength ; Staphylococcus epidermidis/chemistry/*physiology ; Stress, Mechanical ; Viscosity ; }, abstract = {It has been recently reported that in presence of low Reynolds number (Re ≪ 1) transport, preformed bacterial biofilms, several hours after their formation, may degenerate in form of filamentous structures, known as streamers. In this work, we explain that such streamers form as the highly viscous liquid states of the intrinsically viscoelastic biofilms. Such "viscous liquid" state can be hypothesized by noting that the time of appearance of the streamers is substantially larger than the viscoelastic relaxation time scale of the biofilms, and this appearance is explained by the inability of a viscous liquid to withstand external shear. Further, by identifying the post formation dynamics of the streamers as that of a viscous liquid jet in a surrounding flow field, we can interpret several unexplained issues associated with the post-formation dynamics of streamers, such as the clogging of the flow passage or the exponential time growth of streamer dimensions. Overall our manuscript provides a biophysical basis for understanding the evolution of biofilm streamers in creeping flows.}, } @article {pmid25403834, year = {2014}, author = {Felderhof, BU}, title = {Swimming of an assembly of rigid spheres at low Reynolds number.}, journal = {The European physical journal. E, Soft matter}, volume = {37}, number = {11}, pages = {110}, pmid = {25403834}, issn = {1292-895X}, abstract = {A matrix formulation is derived for the calculation of the swimming speed and the power required for swimming of an assembly of rigid spheres immersed in a viscous fluid of infinite extent. The spheres may have arbitrary radii and may interact with elastic forces. The analysis is based on the Stokes mobility matrix of the set of spheres, defined in low Reynolds number hydrodynamics. For small amplitude, swimming optimization of the swimming speed at given power leads to an eigenvalue problem. The method allows straightforward calculation of the swimming performance of structures modeled as assemblies of interacting rigid spheres.}, } @article {pmid25381677, year = {2014}, author = {Han, JS and Chang, JW and Kim, ST}, title = {Reynolds number dependency of an insect-based flapping wing.}, journal = {Bioinspiration & biomimetics}, volume = {9}, number = {4}, pages = {046012}, doi = {10.1088/1748-3182/9/4/046012}, pmid = {25381677}, issn = {1748-3190}, mesh = {Aircraft/*instrumentation ; Animals ; Biological Clocks/physiology ; Biomimetics/*instrumentation/methods ; Computer Simulation ; Computer-Aided Design ; Equipment Design ; Equipment Failure Analysis ; Flight, Animal/*physiology ; Insecta/*physiology ; *Models, Biological ; Rheology/*methods ; Viscosity ; Wings, Animal/*physiology ; }, abstract = {Aerodynamic characteristics depending on Reynolds number (Re) ranges were studied to investigate the suitable design parameters of an insect-based micro air vehicle (MAV). The tests centered on the wing rotation timing and Re ranges, and were conducted to understand the lift augmentations and unsteady effects. A dynamically scaled-up flapping wing controlled by a pair of servos was installed underwater with a micro force/torque sensor. A high-speed camera and a laser sheet were also put in front of the water tank for the time-resolved digital particle image velocimetry (DPIV). The lift augmentations clearly appeared at low Re and were well reflected on the insect's flight range. In the case of the high Re, however, the peak standing for the wing–wake interaction was delayed, and the pitching-up rotation was not able to lead to another lift enhancement, i.e., rotational lift. In such Re, the mean CL and the L/D of the advanced rotation were substantially decreased from those of the other rotations. The DPIV results at high Re well described turbulent characteristics such as the irregular, unstable, and high-intensity vortex structures with a short temporal delay. In the advanced rotation, the LEV in the rotational phase could not maintain the attachment. Thus, the rotational lift was not able to work. On the contrary, the temporal response delay benefitted the wing in the delayed rotation. Therefore, the wing in the delayed rotation had both a similar level of the mean CL and a higher marked L/D than those of the advanced rotation. Such results indicate that the high Re could interrupt lift augmentation mechanisms, and these augmentations would not be suitable for a heavier MAV. In conclusion, using adequate wing kinematics to acquire estimations of the weight and range of the Re is highly recommended at the aerodynamic design step.}, } @article {pmid25379087, year = {2014}, author = {Shi, Y and Fox, RO and Olsen, MG}, title = {Micromixing visualization and quantification in a microscale multi-inlet vortex nanoprecipitation reactor using confocal-based reactive micro laser-induced fluorescence.}, journal = {Biomicrofluidics}, volume = {8}, number = {4}, pages = {044102}, pmid = {25379087}, issn = {1932-1058}, abstract = {A technique for visualizing and quantifying reactive mixing for laminar and turbulent flow in a microscale chemical reactor using confocal-based microscopic laser induced fluorescence (confocal μ-LIF) was demonstrated in a microscale multi-inlet vortex nanoprecipitation reactor. Unlike passive scalar μ-LIF, the reactive μ-LIF technique is able to visualize and quantify micromixing effects. The confocal imaging results indicated that the flow in the reactor was laminar and steady for inlet Reynolds numbers of 10, 53, and 93. Mixing and reaction were incomplete at each of these Reynolds numbers. The results also suggested that although mixing by diffusion was enhanced near the midplane of the reactor at Rej = 53 and 93 due to very thin bands of acidic and basic fluid forming as the fluid spiraled towards the center of the reactor, near the top, and bottom walls of the reactor, the lower velocities due to fluid friction with the walls hindered the formation of these thin bands, and, thus, resulted in large regions of unmixed and unreacted fluid. At Rej = 240, the flow was turbulent and unsteady. The mixing and reaction processes were still found to be incomplete even at this highest Reynolds number. At the reactor midplane, the flow images at Rej = 240 showed unmixed base fluid near the center of the reactor, suggesting that just as in the Rej = 53 and 93 cases, lower velocities near the top and bottom walls of the reactor hinder the mixing and rection of the acidic and basic streams. Ensemble averages of line-scan profiles for the Rej = 240 were then calculated to provide statistical quantification of the microscale mixing in the reactor. These results further demonstrate that even at this highest Reynolds number investigated, mixing and reaction are incomplete. Visualization and quantification of micromixing using this reactive μ-LIF technique can prove useful in the validation of computational fluid dynamics models of micromixing within microscale chemical reactors.}, } @article {pmid25378709, year = {2014}, author = {Huang, H and He, X}, title = {Interfacial tension based on-chip extraction of microparticles confined in microfluidic Stokes flows.}, journal = {Applied physics letters}, volume = {105}, number = {14}, pages = {143704}, pmid = {25378709}, issn = {0003-6951}, support = {R01 EB012108/EB/NIBIB NIH HHS/United States ; }, abstract = {Microfluidics involving two immiscible fluids (oil and water) has been increasingly used to produce hydrogel microparticles with wide applications. However, it is difficult to extract the microparticles out of the microfluidic Stokes flows of oil that have a Reynolds number (the ratio of inertia to viscous force) much less than one, where the dominant viscous force tends to drive the microparticles to move together with the surrounding oil. Here, we present a passive method for extracting hydrogel microparticles in microfluidic Stokes flow from oil into aqueous extracting solution on-chip by utilizing the intrinsic interfacial tension between oil and the microparticles. We further reveal that the thickness of an "extended confining layer" of oil next to the interface between oil and aqueous extracting solution must be smaller than the radius of microparticles for effective extraction. This method uses a simple planar merging microchannel design that can be readily fabricated and further integrated into a fluidic system to extract microparticles for wide applications.}, } @article {pmid25378268, year = {2014}, author = {Ishihara, D and Horie, T and Niho, T}, title = {An experimental and three-dimensional computational study on the aerodynamic contribution to the passive pitching motion of flapping wings in hovering flies.}, journal = {Bioinspiration & biomimetics}, volume = {9}, number = {4}, pages = {046009}, doi = {10.1088/1748-3182/9/4/046009}, pmid = {25378268}, issn = {1748-3190}, mesh = {Animals ; Biological Clocks/*physiology ; Biomimetics/*methods ; Computer Simulation ; Diptera/*physiology ; Flight, Animal/*physiology ; *Models, Biological ; Rheology/*methods ; Stress, Mechanical ; Wings, Animal/anatomy & histology/*physiology ; }, abstract = {The relative importance of the wing's inertial and aerodynamic forces is the key to revealing how the kinematical characteristics of the passive pitching motion of insect flapping wings are generated, which is still unclear irrespective of its importance in the design of insect-like micro air vehicles. Therefore, we investigate three species of flies in order to reveal this, using a novel fluid-structure interaction analysis that consists of a dynamically scaled experiment and a three-dimensional finite element analysis. In the experiment, the dynamic similarity between the lumped torsional flexibility model as a first approximation of the dipteran wing and the actual insect is measured by the Reynolds number Re, the Strouhal number St, the mass ratio M, and the Cauchy number Ch. In the computation, the three-dimension is important in order to simulate the stable leading edge vortex and lift force in the present Re regime over 254. The drawback of the present experiment is the difficulty in satisfying the condition of M due to the limitation of available solid materials. The novelty of the present analysis is to complement this drawback using the computation. We analyze the following two cases: (a) The equilibrium between the wing's elastic and fluid forces is dynamically similar to that of the actual insect, while the wing's inertial force can be ignored. (b) All forces are dynamically similar to those of the actual insect. From the comparison between the results of cases (a) and (b), we evaluate the contributions of the equilibrium between the aerodynamic and the wing's elastic forces and the wing's inertial force to the passive pitching motion as 80-90% and 10-20%, respectively. It follows from these results that the dipteran passive pitching motion will be based on the equilibrium between the wing's elastic and aerodynamic forces, while it will be enhanced by the wing's inertial force.}, } @article {pmid25375605, year = {2014}, author = {Yakhot, V}, title = {Reynolds number of transition and self-organized criticality of strong turbulence.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {90}, number = {4}, pages = {043019}, doi = {10.1103/PhysRevE.90.043019}, pmid = {25375605}, issn = {1550-2376}, abstract = {A turbulent flow is characterized by velocity fluctuations excited in an extremely broad interval of wave numbers k>Λf, where Λf is a relatively small set of the wave vectors where energy is pumped into fluid by external forces. Iterative averaging over small-scale velocity fluctuations from the interval Λf10 keV) central hot spot. Turbulence has been suggested as a mechanism for degrading the hot-spot conditions by altering transport properties, introducing colder, mixed material, or reducing the conversion of radially directed kinetic energy to hot-spot heating. We show, however, that the hot spot is very viscous, and the assumption of turbulent conditions in the hot spot is incorrect. This work presents the first high-resolution, three-dimensional simulations of National Ignition Facility (NIF) implosion experiments using detailed knowledge of implosion dynamics and instability seeds and including an accurate model of physical viscosity. We find that when viscous effects are neglected, the hot spot can exhibit a turbulent kinetic energy cascade. Viscous effects, however, are significant and strongly damp small-scale velocity structures, with a hot-spot Reynolds number in the range of only 10-100.}, } @article {pmid25353889, year = {2014}, author = {Honey, RE and Hershberger, R and Donnelly, RJ and Bolster, D}, title = {Oscillating-grid experiments in water and superfluid helium.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {89}, number = {5}, pages = {053016}, doi = {10.1103/PhysRevE.89.053016}, pmid = {25353889}, issn = {1550-2376}, abstract = {Passing a fluid through a grid is a well-known mechanism used to study the properties of turbulence. Oscillating a horizontal grid vertically in a tank has also been used extensively and is considered to be a source of almost homogenous isotropic turbulence. When the oscillating grid is turned on a turbulent flow is induced. A front translates into the experimental tank, behind which the flow is highly turbulent. Long predicted that the growth of such a front would grow diffusively as the square root of time (i.e., d ∼ sqrt[t]) and Dickinson and Long presented experimental evidence for the diffusive result at a low mesh Reynolds number of 555. This paper revisits these experiments and attempts a set of two models for the advancing front in both square and round tanks. We do not observe significant differences between runs in square and round tanks. The experiments in water reach mesh Reynolds numbers of order 30000. Using some data from superfluid helium experiments we are able to explore mesh Reynolds numbers to about 43000. We find the power law for the advancing front decreases weakly with the mesh Reynolds number. Using a very long tank we find that the turbulent front stops completely at a certain depth and attempt a simple explanation for that behavior. We study the propagation of the turbulent front into tubes of different diameters inserted into the main tank. We show that these tubes exclude wavelengths much larger than the tube diameter. We explore the variation of the position of the steady-state boundary H on tube diameter D and find that H = cD with c ∼ 2. We suggest this may be explained by saturation of the energy-containing length scale ℓ(e). We also report on the effect of plugging up just one hole of the grid. Finally, we recall some earlier oscillating grid experiments in superfluid (4)He in the light of the present results.}, } @article {pmid25353601, year = {2014}, author = {Nash, RW and Carver, HB and Bernabeu, MO and Hetherington, J and Groen, D and Krüger, T and Coveney, PV}, title = {Choice of boundary condition for lattice-Boltzmann simulation of moderate-Reynolds-number flow in complex domains.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {89}, number = {2}, pages = {023303}, doi = {10.1103/PhysRevE.89.023303}, pmid = {25353601}, issn = {1550-2376}, support = {//British Heart Foundation/United Kingdom ; }, mesh = {*Algorithms ; Animals ; Blood Flow Velocity/*physiology ; Blood Vessels/*physiology ; Blood Viscosity/physiology ; Computer Simulation ; Humans ; *Models, Cardiovascular ; *Numerical Analysis, Computer-Assisted ; Rheology/*methods ; }, abstract = {Modeling blood flow in larger vessels using lattice-Boltzmann methods comes with a challenging set of constraints: a complex geometry with walls and inlets and outlets at arbitrary orientations with respect to the lattice, intermediate Reynolds (Re) number, and unsteady flow. Simple bounce-back is one of the most commonly used, simplest, and most computationally efficient boundary conditions, but many others have been proposed. We implement three other methods applicable to complex geometries [Guo, Zheng, and Shi, Phys. Fluids 14, 2007 (2002); Bouzidi, Firdaouss, and Lallemand, Phys. Fluids 13, 3452 (2001); Junk and Yang, Phys. Rev. E 72, 066701 (2005)] in our open-source application hemelb. We use these to simulate Poiseuille and Womersley flows in a cylindrical pipe with an arbitrary orientation at physiologically relevant Re number (1-300) and Womersley (4-12) numbers and steady flow in a curved pipe at relevant Dean number (100-200) and compare the accuracy to analytical solutions. We find that both the Bouzidi-Firdaouss-Lallemand (BFL) and Guo-Zheng-Shi (GZS) methods give second-order convergence in space while simple bounce-back degrades to first order. The BFL method appears to perform better than GZS in unsteady flows and is significantly less computationally expensive. The Junk-Yang method shows poor stability at larger Re number and so cannot be recommended here. The choice of collision operator (lattice Bhatnagar-Gross-Krook vs multiple relaxation time) and velocity set (D3Q15 vs D3Q19 vs D3Q27) does not significantly affect the accuracy in the problems studied.}, } @article {pmid25353575, year = {2014}, author = {Taghavi, SM and Larson, RG}, title = {Regularized thin-fiber model for nanofiber formation by centrifugal spinning.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {89}, number = {2}, pages = {023011}, doi = {10.1103/PhysRevE.89.023011}, pmid = {25353575}, issn = {1550-2376}, abstract = {We propose a regularized thin-fiber (string) model that overcomes past numerical limitations and allows determination of the steady fiber velocity and diameter of a semi-infinite Newtonian viscous fiber emerging from a nozzle rotating about an axis in the presence of centrifugal, inertial, and viscous forces of arbitrary magnitudes. The results are controlled by two dimensionless groups, namely, the Rossby number Rb expressing the ratio of inertial to centrifugal forces and the Reynolds number Re, the ratio of inertial to viscous forces. We find that for Rb < 0.5 and Re < 1, regularization of the string-model equations is required to provide numerical stability, which we achieve. Solutions are thereby obtained in which viscosity reduces curvature in the fiber trajectory; these solutions asymptotically approach the inviscid solution at large distances along the spin line. Thus, long spin lines reach a diameter that is independent of viscosity, as long as the fiber is sufficiently long, a criterion that is made clear in the paper. At Rb > 0.5, regularization is not required, the curvature in fiber trajectory is increased by viscosity, and the solution at large distances along the spin line does not converge to the inviscid result. Regimes of behavior in the plane formed by Re and Rb are mapped out and example behavior is given for each regime.}, } @article {pmid25353568, year = {2014}, author = {Musacchio, S and Boffetta, G}, title = {Turbulent channel without boundaries: the periodic Kolmogorov flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {89}, number = {2}, pages = {023004}, doi = {10.1103/PhysRevE.89.023004}, pmid = {25353568}, issn = {1550-2376}, abstract = {The Kolmogorov flow provides an ideal instance of a virtual channel flow: It has no boundaries, but it possesses well defined mean flow in each half wavelength. We exploit this remarkable feature for the purpose of investigating the interplay between the mean flow and the turbulent drag of the bulk flow. By means of a set of direct numerical simulations at increasing Reynolds number, we show the dependence of the bulk turbulent drag on the amplitude of the mean flow. Further, we present a detailed analysis of the scale-by-scale energy balance, which describes how kinetic energy is redistributed among different regions of the flow while being transported toward small dissipative scales. Our results allow us to obtain an accurate prediction for the spatial energy transport at large scales.}, } @article {pmid25353409, year = {2014}, author = {Gupta, A and Vincenzi, D and Pandit, R}, title = {Elliptical tracers in two-dimensional, homogeneous, isotropic fluid turbulence: the statistics of alignment, rotation, and nematic order.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {89}, number = {2}, pages = {021001}, doi = {10.1103/PhysRevE.89.021001}, pmid = {25353409}, issn = {1550-2376}, abstract = {We study the statistical properties of orientation and rotation dynamics of elliptical tracer particles in two-dimensional, homogeneous, and isotropic turbulence by direct numerical simulations. We consider both the cases in which the turbulent flow is generated by forcing at large and intermediate length scales. We show that the two cases are qualitatively different. For large-scale forcing, the spatial distribution of particle orientations forms large-scale structures, which are absent for intermediate-scale forcing. The alignment with the local directions of the flow is much weaker in the latter case than in the former. For intermediate-scale forcing, the statistics of rotation rates depends weakly on the Reynolds number and on the aspect ratio of particles. In contrast with what is observed in three-dimensional turbulence, in two dimensions the mean-square rotation rate increases as the aspect ratio increases.}, } @article {pmid25338940, year = {2014}, author = {Bandyopadhyay, PR and Hellum, AM}, title = {Modeling how shark and dolphin skin patterns control transitional wall-turbulence vorticity patterns using spatiotemporal phase reset mechanisms.}, journal = {Scientific reports}, volume = {4}, number = {}, pages = {6650}, pmid = {25338940}, issn = {2045-2322}, mesh = {Animals ; Diffusion ; Dolphins/*physiology ; Movement/*physiology ; Nonlinear Dynamics ; Pigmentation/physiology ; Sharks/*physiology ; Skin Physiological Phenomena ; *Spatio-Temporal Analysis ; Zebrafish ; }, abstract = {Many slow-moving biological systems like seashells and zebrafish that do not contend with wall turbulence have somewhat organized pigmentation patterns flush with their outer surfaces that are formed by underlying autonomous reaction-diffusion (RD) mechanisms. In contrast, sharks and dolphins contend with wall turbulence, are fast swimmers, and have more organized skin patterns that are proud and sometimes vibrate. A nonlinear spatiotemporal analytical model is not available that explains the mechanism underlying control of flow with such proud patterns, despite the fact that shark and dolphin skins are major targets of reverse engineering mechanisms of drag and noise reduction. Comparable to RD, a minimal self-regulation model is given for wall turbulence regeneration in the transitional regime--laterally coupled, diffusively--which, although restricted to pre-breakdown durations and to a plane close and parallel to the wall, correctly reproduces many experimentally observed spatiotemporal organizations of vorticity in both laminar-to-turbulence transitioning and very low Reynolds number but turbulent regions. We further show that the onset of vorticity disorganization is delayed if the skin organization is treated as a spatiotemporal template of olivo-cerebellar phase reset mechanism. The model shows that the adaptation mechanisms of sharks and dolphins to their fluid environment have much in common.}, } @article {pmid25314537, year = {2014}, author = {Herault, J and Pétrélis, F}, title = {Optimum reduction of the dynamo threshold by a ferromagnetic layer located in the flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {90}, number = {3}, pages = {033015}, doi = {10.1103/PhysRevE.90.033015}, pmid = {25314537}, issn = {1550-2376}, mesh = {*Electromagnetic Phenomena ; *Magnets ; *Models, Theoretical ; Motion ; }, abstract = {We consider a fluid dynamo model generated by the flow on both sides of a moving layer. The magnetic permeability of the layer is larger than that of the flow. We show that there exists an optimum value of magnetic permeability for which the critical magnetic Reynolds number for dynamo onset is smaller than for a nonmagnetic material and also smaller than for a layer of infinite magnetic permeability. We present a mechanism that provides an explanation for recent experimental results. A similar effect occurs when the electrical conductivity of the layer is large.}, } @article {pmid25314534, year = {2014}, author = {Lee, W and Kim, Y and Olson, SD and Lim, S}, title = {Nonlinear dynamics of a rotating elastic rod in a viscous fluid.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {90}, number = {3}, pages = {033012}, doi = {10.1103/PhysRevE.90.033012}, pmid = {25314534}, issn = {1550-2376}, mesh = {*Elasticity ; Nonlinear Dynamics ; *Rotation ; *Viscosity ; }, abstract = {The dynamics of an elastic rod in a viscous fluid at zero Reynolds number is investigated when the bottom end of the rod is tethered at a point in space and rotates at a prescribed angular frequency, while the other part of the rod freely moves through the fluid. A rotating elastic rod, which is intrinsically straight, exhibits three dynamical motions: twirling, overwhirling, and whirling. The first two motions are stable, whereas the last motion is unstable. The stability of dynamical motions is determined by material and geometrical properties of the rod, fluid properties, and the angular frequency of the rod. We employ the regularized Stokes flow to describe the fluid motion and the Kirchhoff rod model to describe the elastic rod. Our simulation results display subcritical Hopf bifurcation diagrams indicating the bistability region. We also investigate the whirling motion generated by the rotation of an intrinsically bent rod. It is observed that the angular frequency determines the handedness of the whirling rod and thus the flow direction and that there is a critical frequency which separates the positive (upward) flow at frequencies above it from the negative (downward) flow at frequencies below it.}, } @article {pmid25314533, year = {2014}, author = {Aouane, O and Thiébaud, M and Benyoussef, A and Wagner, C and Misbah, C}, title = {Vesicle dynamics in a confined Poiseuille flow: from steady state to chaos.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {90}, number = {3}, pages = {033011}, doi = {10.1103/PhysRevE.90.033011}, pmid = {25314533}, issn = {1550-2376}, mesh = {Cell Shape ; Elasticity ; *Erythrocytes/cytology ; Lipid Bilayers ; *Models, Cardiovascular ; Motion ; Nonlinear Dynamics ; }, abstract = {Red blood cells (RBCs) are the major component of blood, and the flow of blood is dictated by that of RBCs. We employ vesicles, which consist of closed bilayer membranes enclosing a fluid, as a model system to study the behavior of RBCs under a confined Poiseuille flow. We extensively explore two main parameters: (i) the degree of confinement of vesicles within the channel and (ii) the flow strength. Rich and complex dynamics for vesicles are revealed, ranging from steady-state shapes (in the form of parachute and slipper shapes) to chaotic dynamics of shape. Chaos occurs through a cascade of multiple periodic oscillations of the vesicle shape. We summarize our results in a phase diagram in the parameter plane (degree of confinement and flow strength). This finding highlights the level of complexity of a flowing vesicle in the small Reynolds number where the flow is laminar in the absence of vesicles and can be rendered turbulent due to elasticity of vesicles.}, } @article {pmid25314529, year = {2014}, author = {Cheang, UK and Meshkati, F and Kim, D and Kim, MJ and Fu, HC}, title = {Minimal geometric requirements for micropropulsion via magnetic rotation.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {90}, number = {3}, pages = {033007}, doi = {10.1103/PhysRevE.90.033007}, pmid = {25314529}, issn = {1550-2376}, mesh = {Algorithms ; Elasticity ; Linear Models ; *Magnetic Phenomena ; Magnets ; Models, Theoretical ; Nanostructures ; Robotics ; *Rotation ; Swimming ; Torque ; }, abstract = {Controllable propulsion of microscale and nanoscale devices enhanced with additional functionality would enable the realization of miniaturized robotic swimmers applicable to transport and assembly, actuators, and drug delivery systems. Following biological examples, existing magnetically actuated microswimmers have been designed to use flexibility or chirality, presenting fabrication challenges. Here we show that, contrary to biomimetic expectations, magnetically actuated geometries with neither flexibility nor chirality can produce propulsion, through both experimental demonstration and a theoretical analysis, which elucidates the fundamental constraints on micropropulsion via magnetetic rotation. Our results advance existing paradigms of low-Reynolds-number propulsion, possibly enabling simpler fabrication and design of microswimmers and nanoswimmers.}, } @article {pmid25314388, year = {2014}, author = {Karlin, IV and Bösch, F and Chikatamarla, SS}, title = {Gibbs' principle for the lattice-kinetic theory of fluid dynamics.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {90}, number = {3}, pages = {031302}, doi = {10.1103/PhysRevE.90.031302}, pmid = {25314388}, issn = {1550-2376}, mesh = {*Hydrodynamics ; Kinetics ; Mechanical Phenomena ; *Models, Theoretical ; }, abstract = {Gibbs' seminal prescription for constructing optimal states by maximizing the entropy under pertinent constraints is used to derive a lattice kinetic theory for the computation of high Reynolds number flows. The notion of modifying the viscosity to stabilize subgrid simulations is challenged in this kinetic framework. A lattice Boltzmann model for direct simulation of turbulent flows is presented without any need for tunable parameters and turbulent viscosity. Simulations at very high Reynolds numbers demonstrate a major extension of the operation range for fluid dynamics.}, } @article {pmid25309949, year = {2014}, author = {Tisa, F and Raman, AA and Daud, WM}, title = {Simulation for supporting scale-up of a fluidized bed reactor for advanced water oxidation.}, journal = {TheScientificWorldJournal}, volume = {2014}, number = {}, pages = {348974}, pmid = {25309949}, issn = {1537-744X}, mesh = {Computer Simulation ; Hydrodynamics ; Hydrogen Peroxide/chemistry ; Kinetics ; Oxidation-Reduction ; Phenols/*chemistry/isolation & purification ; Waste Disposal, Fluid ; Waste Water/*chemistry ; Water Pollutants, Chemical/*chemistry/isolation & purification ; Water Purification/instrumentation/*methods ; }, abstract = {Simulation of fluidized bed reactor (FBR) was accomplished for treating wastewater using Fenton reaction, which is an advanced oxidation process (AOP). The simulation was performed to determine characteristics of FBR performance, concentration profile of the contaminants, and various prominent hydrodynamic properties (e.g., Reynolds number, velocity, and pressure) in the reactor. Simulation was implemented for 2.8 L working volume using hydrodynamic correlations, continuous equation, and simplified kinetic information for phenols degradation as a model. The simulation shows that, by using Fe(3+) and Fe(2+) mixtures as catalyst, TOC degradation up to 45% was achieved for contaminant range of 40-90 mg/L within 60 min. The concentration profiles and hydrodynamic characteristics were also generated. A subsequent scale-up study was also conducted using similitude method. The analysis shows that up to 10 L working volume, the models developed are applicable. The study proves that, using appropriate modeling and simulation, data can be predicted for designing and operating FBR for wastewater treatment.}, } @article {pmid25283952, year = {2014}, author = {Yeh, PH and Hsu, JP and Tseng, S}, title = {Influence of polyelectrolyte shape on its sedimentation behavior: effect of relaxation electric field.}, journal = {Soft matter}, volume = {10}, number = {44}, pages = {8864-8874}, doi = {10.1039/c4sm01351d}, pmid = {25283952}, issn = {1744-6848}, abstract = {The sedimentation of an isolated, charged polyelectrolyte (PE) subjected to an applied field is modeled theoretically, taking into account the variation of its shape. In particular, the effects of double-layer relaxation, effective charge density, and strength of the induced relaxation electric field are examined. We show that the interaction of these effects yields complex and interesting sedimentation behaviors. For example, the behavior of the electric force acting on a loosely structured PE can be different from that on a compactly structured one; the former is dominated mainly by the convective fluid flow. For thick double layers, electric force has a local maximum as the Reynolds number varies, but tends to increase monotonically with increasing Reynolds number if the layer is thin. The drag factor is found to behave differently from literature results. The shape of a PE significantly influences its sedimentation behavior by affecting the amount of counterions attracted to its interior and the associated local electric field. Interestingly, a more stretched PE has a higher effective charge density but experiences a weaker electric force.}, } @article {pmid25279733, year = {2014}, author = {Ismadi, MZ and Gupta, P and Fouras, A and Verma, P and Jadhav, S and Bellare, J and Hourigan, K}, title = {Flow characterization of a spinner flask for induced pluripotent stem cell culture application.}, journal = {PloS one}, volume = {9}, number = {10}, pages = {e106493}, pmid = {25279733}, issn = {1932-6203}, mesh = {Animals ; Batch Cell Culture Techniques ; Bioreactors ; Cell Culture Techniques/*instrumentation/*methods ; Cell Proliferation ; Induced Pluripotent Stem Cells/*cytology ; Mice ; Rheology ; }, abstract = {We present detailed quantitative measurement analyses for flow in a spinner flask with spinning rates between 20 to 45 RPM, utilizing the optical velocimetry measurement technique of Particle Image Velocimetry (PIV). A partial section of the impeller was immersed in the working fluid to reduce the shear forces induced on the cells cultured on microcarriers. Higher rotational speeds improved the mixing effect in the medium at the expense of a higher shear environment. It was found that the mouse induced pluripotent stem (iPS) cells achieved the optimum number of cells over 7 days in 25 RPM suspension culture. This condition translates to 0.0984 Pa of maximum shear stress caused by the interaction of the fluid flow with the bottom surface. However, inverse cell growth was obtained at 28 RPM culture condition. Such a narrow margin demonstrated that mouse iPS cells cultured on microcarriers are very sensitive to mechanical forces. This study provides insight to biomechanical parameters, specifically the shear stress distribution, for a commercially available spinner flask over a wide range of Reynolds number.}, } @article {pmid25278637, year = {2014}, author = {Jus, Y and Longatte, E and Chassaing, JC and Sagaut, P}, title = {Low Mass-Damping Vortex-Induced Vibrations of a Single Cylinder at Moderate Reynolds Number.}, journal = {Journal of pressure vessel technology}, volume = {136}, number = {5}, pages = {0513051-0513057}, pmid = {25278637}, issn = {0094-9930}, abstract = {The feasibility and accuracy of large eddy simulation is investigated for the case of three-dimensional unsteady flows past an elastically mounted cylinder at moderate Reynolds number. Although these flow problems are unconfined, complex wake flow patterns may be observed depending on the elastic properties of the structure. An iterative procedure is used to solve the structural dynamic equation to be coupled with the Navier-Stokes system formulated in a pseudo-Eulerian way. A moving mesh method is involved to deform the computational domain according to the motion of the fluid structure interface. Numerical simulations of vortex-induced vibrations are performed for a freely vibrating cylinder at Reynolds number 3900 in the subcritical regime under two low mass-damping conditions. A detailed physical analysis is provided for a wide range of reduced velocities, and the typical three-branch response of the amplitude behavior usually reported in the experiments is exhibited and reproduced by numerical simulation.}, } @article {pmid25273740, year = {2014}, author = {Bodenschatz, E and Bewley, GP and Nobach, H and Sinhuber, M and Xu, H}, title = {Variable density turbulence tunnel facility.}, journal = {The Review of scientific instruments}, volume = {85}, number = {9}, pages = {093908}, doi = {10.1063/1.4896138}, pmid = {25273740}, issn = {1089-7623}, abstract = {The Variable Density Turbulence Tunnel at the Max Planck Institute for Dynamics and Self-Organization in Göttingen, Germany, produces very high turbulence levels at moderate flow velocities, low power consumption, and adjustable kinematic viscosity between 10(-4) m(2)/s and 10(-7) m(2)/s. The Reynolds number can be varied by changing the pressure or flow rate of the gas or by using different non-flammable gases including air. The highest kinematic viscosities, and hence lowest Reynolds numbers, are reached with air or nitrogen at 0.1 bar. To reach the highest Reynolds numbers the tunnel is pressurized to 15 bars with the dense gas sulfur hexafluoride (SF6). Turbulence is generated at the upstream ends of two measurement sections with grids, and the evolution of this turbulence is observed as it moves down the length of the sections. We describe the instrumentation presently in operation, which consists of the tunnel itself, classical grid turbulence generators, and state-of-the-art nano-fabricated hot-wire anemometers provided by Princeton University [M. Vallikivi, M. Hultmark, S. C. C. Bailey, and A. J. Smits, Exp. Fluids 51, 1521 (2011)]. We report measurements of the characteristic scales of the flow and of turbulent spectra up to Taylor Reynolds number R(λ) ≈ 1600, higher than any other grid-turbulence experiment. We also describe instrumentation under development, which includes an active grid and a Lagrangian particle tracking system that moves down the length of the tunnel with the mean flow. In this configuration, the properties of the turbulence are adjustable and its structure is resolvable up to R(λ) ≈ 8000.}, } @article {pmid25266059, year = {2015}, author = {Zhou, D and Xu, Z and Wang, Y and Wang, J and Hou, D and Dong, S}, title = {Simultaneous removal of multi-pollutants in an intimate integrated flocculation-adsorption fluidized bed.}, journal = {Environmental science and pollution research international}, volume = {22}, number = {5}, pages = {3794-3802}, pmid = {25266059}, issn = {1614-7499}, mesh = {Adsorption ; Aluminum Chloride ; Aluminum Compounds ; Aluminum Silicates ; Charcoal ; Chlorides ; Clay ; Flocculation ; Kaolin ; Microscopy, Electron, Scanning ; Phenols ; Polymers ; Silicon Dioxide ; Waste Disposal, Fluid/*methods ; *Water Movements ; Water Pollutants, Chemical/analysis/*isolation & purification ; Water Purification/*methods ; }, abstract = {A novel intimate integrated flocculation-adsorption fluidized bed (IFAFB) was designed based on the hydraulic classification theory, and the operation, performance, characterization, and mechanisms of the novel process were developed. In this system, 150 mg · L(-1) kaolin clay and 100 mg · L(-1) phenol were used to simulate multi-pollutants in synthetic influent; resin beads and silica beads were the solid phases for the fluidized flocculator, and polymer aluminum chloride (PAC) and granular activated carbon were the flocculant and the adsorbent, respectively. The results showed that the Euler numeral was the most suitable dynamic parameter for flocculation in the fluidized bed when compared with the velocity gradient (G), Reynolds number (Re), and GRe (-1/2) . Additionally, the adsorption capacities of the fluidized regime were 8.77 and 24.70 mg · g(-1) greater than those of the fixed regime at superficial velocities of 6 and 8 mm · s(-1), respectively. In the IFAFB, the removal efficiencies of kaolin clay and phenol in the IFAFB reached 95 and 80 % simultaneously at total initial bed height of 35 mm. Flocs size, fractal dimension, and scanning electron microscopy (SEM) confirmed that the relationship of flocculation and adsorption in the IFAFB was mutually beneficial. Adsorption favored continuous growth of flocs and protected flocs from breakage, while flocculation removed fine particles as the first stage to prevent the adsorption of kaolin clay.}, } @article {pmid25254236, year = {2014}, author = {Yarmand, H and Gharehkhani, S and Kazi, SN and Sadeghinezhad, E and Safaei, MR}, title = {Numerical investigation of heat transfer enhancement in a rectangular heated pipe for turbulent nanofluid.}, journal = {TheScientificWorldJournal}, volume = {2014}, number = {}, pages = {369593}, pmid = {25254236}, issn = {1537-744X}, mesh = {*Algorithms ; Aluminum Oxide/chemistry ; Computer Simulation ; Copper/chemistry ; *Hot Temperature ; Hydrodynamics ; Models, Chemical ; Nanoparticles/*chemistry ; Silicon Dioxide/chemistry ; *Thermal Conductivity ; Water/*chemistry ; Zinc Oxide/chemistry ; }, abstract = {Thermal characteristics of turbulent nanofluid flow in a rectangular pipe have been investigated numerically. The continuity, momentum, and energy equations were solved by means of a finite volume method (FVM). The symmetrical rectangular channel is heated at the top and bottom at a constant heat flux while the sides walls are insulated. Four different types of nanoparticles Al2O3, ZnO, CuO, and SiO2 at different volume fractions of nanofluids in the range of 1% to 5% are considered in the present investigation. In this paper, effect of different Reynolds numbers in the range of 5000 < Re < 25000 on heat transfer characteristics of nanofluids flowing through the channel is investigated. The numerical results indicate that SiO2-water has the highest Nusselt number compared to other nanofluids while it has the lowest heat transfer coefficient due to low thermal conductivity. The Nusselt number increases with the increase of the Reynolds number and the volume fraction of nanoparticles. The results of simulation show a good agreement with the existing experimental correlations.}, } @article {pmid25252883, year = {2014}, author = {Bergmann, M and Iollo, A and Mittal, R}, title = {Effect of caudal fin flexibility on the propulsive efficiency of a fish-like swimmer.}, journal = {Bioinspiration & biomimetics}, volume = {9}, number = {4}, pages = {046001}, doi = {10.1088/1748-3182/9/4/046001}, pmid = {25252883}, issn = {1748-3190}, mesh = {Animal Fins/*physiology ; Animals ; Biomimetics/*instrumentation ; Computer Simulation ; Computer-Aided Design ; Elastic Modulus/physiology ; Energy Transfer/*physiology ; Equipment Design ; Equipment Failure Analysis ; *Models, Biological ; Physical Exertion/physiology ; Rheology/methods ; Robotics/*instrumentation ; *Ships ; Stress, Mechanical ; Swimming/*physiology ; }, abstract = {A computational model is used to examine the effect of caudal fin flexibility on the propulsive efficiency of a self-propelled swimmer. The computational model couples a penalization method based Navier-Stokes solver with a simple model of flow induced deformation and self-propelled motion at an intermediate Reynolds number of about 1000. The results indicate that a significant increase in efficiency is possible by careful choice of caudal fin rigidity. The flow-physics underlying this observation is explained through the use of a simple hydrodynamic force model and guidelines for bioinspired designs of flexible fin propulsors are proposed.}, } @article {pmid25250384, year = {2014}, author = {Wan Mohtar, WH and ElShafie, A}, title = {Characteristics of low reynolds number shear-free turbulence at an impermeable base.}, journal = {TheScientificWorldJournal}, volume = {2014}, number = {}, pages = {683537}, doi = {10.1155/2014/683537}, pmid = {25250384}, issn = {1537-744X}, mesh = {*Permeability ; Rheology/instrumentation/*methods ; *Shear Strength ; }, abstract = {Shear-free turbulence generated from an oscillating grid in a water tank impinging on an impermeable surface at varying Reynolds number 74 ≤ Re(l) ≤ 570 was studied experimentally, where the Reynolds number is defined based on the root-mean-square (r.m.s) horizontal velocity and the integral length scale. A particular focus was paid to the turbulence characteristics for low Re(l) < 150 to investigate the minimum limit of Re l obeying the profiles of rapid distortion theory. The measurements taken at near base included the r.m.s turbulent velocities, evolution of isotropy, integral length scales, and energy spectra. Statistical analysis of the velocity data showed that the anisotropic turbulence structure follows the theory for flows with Re(l) ≥ 117. At low Re(l) < 117, however, the turbulence profile deviated from the prediction where no amplification of horizontal velocity components was observed and the vertical velocity components were seen to be constant towards the tank base. Both velocity components sharply decreased towards zero at a distance of ≈ 1/3 of the integral length scale above the base due to viscous damping. The lower limit where Re(l) obeys the standard profile was found to be within the range 114 ≤ Re(l) ≤ 116.}, } @article {pmid25238401, year = {2014}, author = {Zizzari, A and Bianco, M and Miglietta, R and del Mercato, LL and Carraro, M and Sorarù, A and Bonchio, M and Gigli, G and Rinaldi, R and Viola, I and Arima, V}, title = {Catalytic oxygen production mediated by smart capsules to modulate elastic turbulence under a laminar flow regime.}, journal = {Lab on a chip}, volume = {14}, number = {22}, pages = {4391-4397}, doi = {10.1039/c4lc00791c}, pmid = {25238401}, issn = {1473-0189}, abstract = {Liquid flow in microchannels is completely laminar and uniaxial, with a very low Reynolds number regime and long mixing lengths. To increase fluid mixing and solubility of reactants, as well as to reduce reaction time, complex three-dimensional networks inducing chaotic advection have to be designed. Alternatively, turbulence in the liquid can be generated by active mixing methods (magnetic, acoustic waves, etc.) or adding small quantities of elastic materials to the working liquid. Here, polyelectrolyte multilayer capsules embodying a catalytic polyoxometalate complex have been suspended in an aqueous solution and used to create elastic turbulence and to propel fluids inside microchannels as an alternative to viscoelastic polymers. The overall effect is enhanced and controlled by feeding the polyoxometalate-modified capsules with hydrogen peroxide, H2O2, thus triggering an on-demand propulsion due to oxygen evolution resulting from H2O2 decomposition. The quantification of the process is done by analysing some structural parameters of motion such as speed, pressure, viscosity, and Reynolds and Weissenberg numbers, directly obtained from the capillary dynamics of the aqueous mixtures with different concentrations of H2O2. The increases in fluid speed as well as the capsule-induced turbulence effects are proportional to the H2O2 added and therefore dependent on the kinetics of H2O2 dismutation.}, } @article {pmid25226956, year = {2014}, author = {Ma, J and Xu, Y and Tian, F and Tang, X}, title = {IB-LBM study on cell sorting by pinched flow fractionation.}, journal = {Bio-medical materials and engineering}, volume = {24}, number = {6}, pages = {2547-2554}, doi = {10.3233/BME-141069}, pmid = {25226956}, issn = {1878-3619}, mesh = {Animals ; *Cell Physiological Phenomena ; Cell Separation/*instrumentation/methods ; Computer Simulation ; Equipment Design ; Equipment Failure Analysis ; Flow Cytometry/*instrumentation/methods ; Humans ; Microfluidic Analytical Techniques/*instrumentation/methods ; *Models, Biological ; }, abstract = {Separation of two categories of cells in pinched flow fractionation(PFF) device is simulated by employing IB-LBM. The separation performances at low Reynolds number (about 1) under different pinched segment widths, flow ratios, cell features, and distances between neighboring cells are studied and the results are compared with those predicted by the empirical formula. The simulation indicates that the diluent flow rate should approximate to or more than the flow rate of particle solution in order to get a relatively ideal separation performance. The discrepancy of outflow position between numerical simulation and the empirical prediction enlarges, when the cells become more flexible. Too short distance between two neighboring cells could lead to cell banding which would result in incomplete separation, and the relative position of two neighboring cells influences the banding of cells. The present study will probably provide some new applications of PFF, and make some suggestions on the design of PFF devices.}, } @article {pmid25226942, year = {2014}, author = {Yu, CH and Kwon, TK}, title = {Study of parameters for evaluating flow reduction with stents in a sidewall aneurysm phantom model.}, journal = {Bio-medical materials and engineering}, volume = {24}, number = {6}, pages = {2417-2424}, doi = {10.3233/BME-141055}, pmid = {25226942}, issn = {1878-3619}, mesh = {Biomimetics/instrumentation ; Blood Flow Velocity ; Blood Pressure ; *Blood Vessel Prosthesis ; *Cerebrovascular Circulation ; *Computer-Aided Design ; Equipment Design ; Equipment Failure Analysis ; Humans ; Intracranial Aneurysm/*physiopathology/*therapy ; Laser-Doppler Flowmetry ; Phantoms, Imaging ; Shear Strength ; *Stents ; Treatment Outcome ; }, abstract = {The effect of stent design parameters such as porosity, pore density, number of strands, and strut angle to the artery were studied in vitro using particle image velocimetry (PIV). Five mesh stents were implanted into a sidewall aneurysm model. The flow features in a sidewall aneurysm silicone phantom model were investigated at a Reynolds number of 300. It was found that the lowest porosity stent had the best value for velocity and vorticity reduction in an aneurysm pocket. The stent with higher pore density had a tendency to decrease the mean and maximum velocities, but it was not superior to the effects of porosity. In addition, investigation of the evaluation system confirmed that higher stent strut angles to the parent artery had a tendency to lower mean velocity, as shown by PIV and CFD. However, this effect was relatively smaller compared to porosity and pore density. Our evaluation system suggested the best combinations of parameters for the development of an ideal stent would be lower porosity, higher pore density, and higher strut angle. The results obtained in this study indicated that our evaluation system could be useful for various purposes related to evaluation of endovascular interventional devices.}, } @article {pmid25215821, year = {2014}, author = {Felderhof, BU and Jones, RB}, title = {Optimal translational swimming of a sphere at low Reynolds number.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {90}, number = {2}, pages = {023008}, doi = {10.1103/PhysRevE.90.023008}, pmid = {25215821}, issn = {1550-2376}, mesh = {*Models, Theoretical ; *Motion ; Swimming ; Viscosity ; }, abstract = {Swimming velocity and rate of dissipation of a sphere with surface distortions are discussed on the basis of the Stokes equations of low-Reynolds-number hydrodynamics. At first the surface distortions are assumed to cause an irrotational axisymmetric flow pattern. The efficiency of swimming is optimized within this class of flows. Subsequently, more general axisymmetric polar flows with vorticity are considered. This leads to a considerably higher maximum efficiency. An additional measure of swimming performance is proposed based on the energy consumption for given amplitude of stroke.}, } @article {pmid25189373, year = {2014}, author = {Yaniv, S and Elad, D and Holzman, R}, title = {Suction feeding across fish life stages: flow dynamics from larvae to adults and implications for prey capture.}, journal = {The Journal of experimental biology}, volume = {217}, number = {Pt 20}, pages = {3748-3757}, doi = {10.1242/jeb.104331}, pmid = {25189373}, issn = {1477-9145}, mesh = {Animals ; Biomechanical Phenomena ; Computer Simulation ; Feeding Behavior/*physiology ; Larva/growth & development/physiology ; Mouth/physiology ; Predatory Behavior ; Rheology ; Sea Bream/growth & development/*physiology ; Sucking Behavior/physiology ; Swimming/physiology ; }, abstract = {Suction feeding is thought to be the primary mode of prey capture in most larval fishes. Similar to adult suction feeders, larvae swim towards their prey while rapidly expanding their mouth cavity to generate an inward flow of water that draws the prey into the mouth. Although larvae are known to experience flows with lower Reynolds numbers than adults, it is unclear how the suction-induced flow field changes throughout ontogeny, and how such changes relate to prey capture performance. To address these questions, we determined mouth dimensions and opening speeds in Sparus aurata from first-feeding larvae to adults. We proceeded to develop a computational model of mouth expansion in order to analyze the scaling of suction flows under the observed parameters. Larval fish produced suction flows that were around two orders of magnitude slower than those of adults. Compared with adult fish, in which flow speed decays steeply with distance in front of the mouth, flow speed decayed more gradually in larval fish. This difference indicates that viscous forces in low Reynolds number flows modify the spatial distribution flow speed in front of the mouth. Consequently, simulated predator-prey encounters showed that larval fish could capture inert prey from a greater distance compared with adults. However, if prey attempted to escape then larval fish performed poorly: simulations inferred capture success in only weakly escaping prey immediately in front of the mouth. These ontogenetic changes in Reynolds number, suction-induced flow field and feeding performance could explain a widespread ontogenetic diet shift from passive prey at early life stages to evasive prey as larvae mature.}, } @article {pmid25170908, year = {2014}, author = {Abbasi, FM and Hayat, T and Ahmad, B and Chen, GQ}, title = {Slip effects on mixed convective peristaltic transport of copper-water nanofluid in an inclined channel.}, journal = {PloS one}, volume = {9}, number = {8}, pages = {e105440}, pmid = {25170908}, issn = {1932-6203}, mesh = {Copper/*chemistry ; Hot Temperature ; Metal Nanoparticles/*chemistry ; Models, Chemical ; Motion ; Rheology ; Water/*chemistry ; }, abstract = {Peristaltic transport of copper-water nanofluid in an inclined channel is reported in the presence of mixed convection. Both velocity and thermal slip conditions are considered. Mathematical modelling has been carried out using the long wavelength and low Reynolds number approximations. Resulting coupled system of equations is solved numerically. Quantities of interest are analyzed through graphs. Numerical values of heat transfer rate at the wall for different parameters are obtained and examined. Results showed that addition of copper nanoparticles reduces the pressure gradient, axial velocity at the center of channel, trapping and temperature. Velocity slip parameter has a decreasing effect on the velocity near the center of channel. Temperature of nanofluid increases with increase in the Grashoff number and channel inclination angle. It is further concluded that the heat transfer rate at the wall increases considerably in the presence of copper nanoparticles.}, } @article {pmid25152217, year = {2014}, author = {Sen, S and Voorheis, HP}, title = {Protein folding: understanding the role of water and the low Reynolds number environment as the peptide chain emerges from the ribosome and folds.}, journal = {Journal of theoretical biology}, volume = {363}, number = {}, pages = {169-187}, doi = {10.1016/j.jtbi.2014.07.025}, pmid = {25152217}, issn = {1095-8541}, mesh = {Hydrodynamics ; Hydrophobic and Hydrophilic Interactions ; *Models, Biological ; Peptides/*chemistry ; Protein Biosynthesis/*physiology ; *Protein Folding ; Water/*chemistry ; }, abstract = {The mechanism of protein folding during early stages of the process has three determinants. First, moving water molecules obey the rules of low Reynolds number physics without an inertial component. Molecular movement is instantaneous and size insensitive. Proteins emerging from the ribosome move and rotate without an external force if they change shape, forming and propagating helical structures that increases translocational efficiency. Forward motion ceases when the shape change or propelling force ceases. Second, application of quantum field theory to water structure predicts the spontaneous formation of low density coherent units of fixed size that expel dissolved atmospheric gases. Structured water layers with both coherent and non-coherent domains, form a sheath around the new protein. The surface of exposed hydrophobic amino acids is protected from water contact by small nanobubbles of dissolved atmospheric gases, 5 or 6 molecules on average, that vibrate, attracting even widely separated resonating nanobubbles. This force results from quantum effects, appearing only when the system is within and interacts with an oscillating electromagnetic field. The newly recognized quantum force sharply bends the peptide and is part of a dynamic field determining the pathway of protein folding. Third, the force initiating the tertiary folding of proteins arises from twists at the position of each hydrophobic amino acid, that minimizes surface exposure of the hydrophobic amino acids and propagates along the protein. When the total bend reaches 360°, the leading segment of water sheath intersects the trailing segment. This steric self-intersection expels water from overlapping segments of the sheath and by Newton׳s second law moves the polypeptide chain in an opposite direction. Consequently, with very few exceptions that we enumerate and discuss, tertiary structures are absent from proteins without hydrophobic amino acids, which control the early stages of protein folding and the overall shape of protein. Consequently, proteins only adopt a limited number of forms. The formation of quaternary structures is not necessarily prevented by the absence of hydrophobic amino acids.}, } @article {pmid25148210, year = {2014}, author = {Saini, R and Garg, A and Barz, DP}, title = {Streaming potential revisited: the influence of convection on the surface conductivity.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {30}, number = {36}, pages = {10950-10961}, doi = {10.1021/la501426c}, pmid = {25148210}, issn = {1520-5827}, abstract = {Electrokinetic phenomena play an important role in the electrical characterization of surfaces. In terms of planar or porous substrates, streaming potential and/or streaming current measurements can be used to determine the zeta potential of the substrates in contact with aqueous electrolytes. In this work, we perform electrical impedance spectroscopy measurements to infer the electrical resistance in a microchannel with the same conditions as for a streaming potential experiment. Novel correlations are derived to relate the streaming current and streaming potential to the Reynolds number of the channel flow. Our results not only quantify the influence of surface conductivity, and here especially the contribution of the stagnant layer, but also reveal that channel resistance and therefore zeta potential are influenced by the flow in the case of low ionic strengths. We conclude that convection can have a significant impact on the electrical double layer configuration which is reflected by changes in the surfaces conductivity.}, } @article {pmid25145564, year = {2014}, author = {De Pauw, R and Choikhet, K and Desmet, G and Broeckhoven, K}, title = {Occurrence of turbulent flow conditions in supercritical fluid chromatography.}, journal = {Journal of chromatography. A}, volume = {1361}, number = {}, pages = {277-285}, doi = {10.1016/j.chroma.2014.07.088}, pmid = {25145564}, issn = {1873-3778}, mesh = {Chromatography, Supercritical Fluid/instrumentation/*methods ; Diffusion ; Kinetics ; Pressure ; Time Factors ; Viscosity ; }, abstract = {Having similar densities as liquids but with viscosities up to 20 times lower (higher diffusion coefficients), supercritical CO2 is the ideal (co-)solvent for fast and/or highly efficient separations without mass-transfer limitations or excessive column pressure drops. Whereas in liquid chromatography the flow remains laminar in both the packed bed and tubing, except in extreme cases (e.g. in a 75 μm tubing, pure acetonitrile at 5 ml/min), a supercritical fluid can experience a transition from laminar to turbulent flow in more typical operation modes. Due to the significant lower viscosity, this transition for example already occurs at 1.3 ml/min for neat CO2 when using connection tubing with an ID of 127 μm. By calculating the Darcy friction factor, which can be plotted versus the Reynolds number in a so-called Moody chart, typically used in fluid dynamics, higher values are found for stainless steel than PEEK tubing, in agreement with their expected higher surface roughness. As a result turbulent effects are more pronounced when using stainless steel tubing. The higher than expected extra-column pressure drop limits the kinetic performance of supercritical fluid chromatography and complicates the optimization of tubing ID, which is based on a trade-off between extra-column band broadening and pressure drop. One of the most important practical consequences is the non-linear increase in extra-column pressure drop over the tubing downstream of the column which leads to an unexpected increase in average column pressure and mobile phase density, and thus decrease in retention. For close eluting components with a significantly different dependence of retention on density, the selectivity can significantly be affected by this increase in average pressure. In addition, the occurrence of turbulent flow is also observed in the detector cell and connection tubing. This results in a noise-increase by a factor of four when going from laminar to turbulent flow (e.g. going from 0.5 to 2.5 ml/min for neat CO2).}, } @article {pmid25122841, year = {2014}, author = {Maraj, EN and Akbar, NS and Nadeem, S}, title = {Biological analysis of Jeffrey nanofluid in a curved channel with heat dissipation.}, journal = {IEEE transactions on nanobioscience}, volume = {13}, number = {4}, pages = {431-437}, doi = {10.1109/TNB.2014.2338891}, pmid = {25122841}, issn = {1558-2639}, mesh = {Animals ; Computer Simulation ; *Energy Transfer ; Humans ; *Models, Biological ; Nanoparticles/*chemistry ; Peristalsis/*physiology ; Pressure ; Pulsatile Flow/*physiology ; Rheology/*methods ; }, abstract = {This study examines the peristaltic flow of Jeffrey nanofluid in a curved channel. The governing equations of Jeffrey nanofluid model for curved channel are derived including the effects of curvature. The highly nonlinear partial differential equations are simplified by using the long wave length and low Reynolds number assumptions. The reduced nonlinear partial differential equations are solved analytically with the help of homotopy perturbation method. The expression for pressure rise is computed through numerical integration. The physical features of pertinent parameters have been discussed by plotting the graphs of pressure rise, velocity, temperature, nanoparticle volume fraction and stream functions. It is observed that the curve-ness of the channel decreases the pressure rise in the peristaltic pumping region. Moreover, curve-ness of the channel effects the fluid flow by decreasing the fluid velocity near inner wall and increasing the velocity near the outer wall of the channel.}, } @article {pmid25122386, year = {2014}, author = {Parra-Rojas, C and Soto, R}, title = {Casimir effect in swimmer suspensions.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {90}, number = {1}, pages = {013024}, doi = {10.1103/PhysRevE.90.013024}, pmid = {25122386}, issn = {1550-2376}, mesh = {*Models, Theoretical ; *Motion ; Suspensions ; }, abstract = {We show that the Casimir effect can emerge in microswimmer suspensions. In principle, two effects conspire against the development of Casimir effects in swimmer suspensions. First, at low Reynolds number, the force on any closed volume vanishes, but here the relevant effect is the drag by the flow produced by the swimmers, which can be finite. Second, the fluid velocity and the pressure are linear on the swimmer force dipoles, and averaging over the swimmer orientations would lead to a vanishing effect. However, being that the suspension is a discrete system, the noise terms of the coarse-grained equations depend on the density, which itself fluctuates, resulting in effective nonlinear dynamics. Applying the tools developed for other nonequilibrium systems to general coarse-grained equations for swimmer suspensions, the Casimir drag is computed on immersed objects, and it is found to depend on the correlation function between the rescaled density and dipolar density fields. By introducing a model correlation function with medium-range order, explicit expressions are obtained for the Casimir drag on a body. When the correlation length is much larger than the microscopic cutoff, the average drag is independent of the correlation length, with a range that depends only on the size of the immersed bodies.}, } @article {pmid25122373, year = {2014}, author = {Jardin, T and David, L}, title = {Spanwise gradients in flow speed help stabilize leading-edge vortices on revolving wings.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {90}, number = {1}, pages = {013011}, doi = {10.1103/PhysRevE.90.013011}, pmid = {25122373}, issn = {1550-2376}, mesh = {Air ; Animals ; Biomechanical Phenomena ; Flight, Animal ; Kinetics ; *Mechanical Phenomena ; *Models, Biological ; *Wings, Animal/physiology ; }, abstract = {While a leading-edge vortex on an infinite translating wing is shed after a short distance of travel, its counterpart on a finite span revolving insect wing or maple seed membrane exhibits robust attachment. The latter explains the aerodynamic lift generated by such biological species. Here we analyze the mechanisms responsible for leading-edge vortex attachment. We compute the Navier-Stokes solution of the flow past a finite span wing (i) embedded in a uniform oncoming flow, (ii) embedded in a spanwise varying oncoming flow, and (iii) revolving about its root. We show that over flapping amplitudes typical of insect flight (ϕ = 120°), the spanwise gradient of the local wing speed may suffice in maintaining leading-edge vortex attachment. We correlate this result with the development of spanwise flow, driven by the spanwise gradient of pressure, and we evaluate the sensitivity of such a mechanism to the Reynolds number. It is noted, however, that leading-edge vortex attachment through the spanwise gradient of the local wing speed does not promote large lift, which ultimately arises from centrifugal and Coriolis effects.}, } @article {pmid25122372, year = {2014}, author = {Li, GJ and Ardekani, AM}, title = {Hydrodynamic interaction of microswimmers near a wall.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {90}, number = {1}, pages = {013010}, pmid = {25122372}, issn = {1550-2376}, support = {UL1 TR000006/TR/NCATS NIH HHS/United States ; UL1 TR001108/TR/NCATS NIH HHS/United States ; }, mesh = {*Hydrodynamics ; *Models, Theoretical ; Motion ; }, abstract = {The hydrodynamics of an archetypal low-Reynolds number swimmer, called "squirmer," near a wall has been numerically studied. For a single squirmer, depending on the swimming mechanism, three different modes are distinguished: (a) the squirmer escaping from the wall, (b) the squirmer swimming along the wall at a constant distance and orientation angle, and (c) the squirmer swimming near the wall in a periodic trajectory. The role of inertial effects on the near-wall motion of the squirmer is quantified. The dynamics of multiple squirmers swimming between two walls is found to be very different from a single squirmer. Near-wall accumulation of squirmers are observed. At a relatively small concentration c = 0.1, around 60-80% of the squirmers are accumulated near the walls and attraction of pushers and pullers toward the wall is stronger than neutral squirmers. Near-wall squirmers orient normal to the wall, while in the bulk region, the squirmers are mostly oriented parallel to the wall. At a high concentration c = 0.4, the percentage of the near-wall squirmers is around 40%. The orientation angle of squirmers in the bulk region is more uniformly distributed at high concentrations. In the near-wall region, pullers repel each other, while pushers are attracted to each other and form clusters.}, } @article {pmid25122366, year = {2014}, author = {Tilgner, A}, title = {Magnetic energy dissipation and mean magnetic field generation in planar convection-driven dynamos.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {90}, number = {1}, pages = {013004}, doi = {10.1103/PhysRevE.90.013004}, pmid = {25122366}, issn = {1550-2376}, mesh = {*Convection ; *Hydrodynamics ; *Magnetic Phenomena ; *Models, Theoretical ; Rotation ; }, abstract = {A numerical study of dynamos in rotating convecting plane layers is presented which focuses on magnetic energies and dissipation rates and the generation of mean fields (where the mean is taken over horizontal planes). The scaling of the magnetic energy with the flux Rayleigh number is different from the scaling proposed in spherical shells, whereas the same dependence of the magnetic dissipation length on the magnetic Reynolds number is found for the two geometries. Dynamos both with and without mean field exist in rapidly rotating convecting plane layers.}, } @article {pmid25122298, year = {2014}, author = {Risbud, SR and Drazer, G}, title = {Directional locking in deterministic lateral-displacement microfluidic separation systems.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {90}, number = {1}, pages = {012302}, doi = {10.1103/PhysRevE.90.012302}, pmid = {25122298}, issn = {1550-2376}, mesh = {*Microfluidics ; Models, Molecular ; Molecular Conformation ; }, abstract = {We analyze the trajectory of suspended spherical particles moving through a square array of obstacles, in the deterministic limit and at zero Reynolds number. We show that in the dilute approximation of widely separated obstacles, the average motion of the particles is equivalent to the trajectory followed by a point particle moving through an array of obstacles with an effective radius. The effective radius accounts for the hydrodynamic as well as short-range repulsive nonhydrodynamic interactions between the suspended particles and the obstacles, and is equal to the critical offset at which particle trajectories become irreversible. Using this equivalent system we demonstrate the presence of directional locking in the trajectory of the particles and derive an inequality that accurately describes the "devil's staircase" type of structure observed in the migration angle as a function of the forcing direction. We use these results to determine the optimum resolution in the fractionation of binary mixtures using deterministic lateral-displacement microfluidic separation systems as well as to comment on the collision frequencies when the arrays of posts are utilized as immunocapture devices.}, } @article {pmid25118607, year = {2014}, author = {Liangjie, M and Qingyou, L and Shouwei, Z}, title = {Experimental study of the vortex-induced vibration of drilling risers under the shear flow with the same shear parameter at the different Reynolds numbers.}, journal = {PloS one}, volume = {9}, number = {8}, pages = {e104806}, doi = {10.1371/journal.pone.0104806}, pmid = {25118607}, issn = {1932-6203}, mesh = {Computer Simulation ; Extraction and Processing Industry/*instrumentation ; *Models, Theoretical ; Oceans and Seas ; *Shear Strength ; *Vibration ; *Water Movements ; }, abstract = {A considerable number of studies for VIV under the uniform flow have been performed. However, research on VIV under shear flow is scarce. An experiment for VIV under the shear flow with the same shear parameter at the two different Reynolds numbers was conducted in a deep-water offshore basin. Various measurements were obtained by the fiber bragg grating strain sensors. Experimental data were analyzed by modal analysis method. Results show several valuable features. First, the corresponding maximum order mode of the natural frequency for shedding frequency is the maximum dominant vibration mode and multi-modal phenomenon is appeared in VIV under the shear flow, and multi-modal phenomenon is more apparent at the same shear parameter with an increasing Reynolds number under the shear flow effect. Secondly, the riser vibrates at the natural frequency and the dominant vibration frequency increases for the effect of the real-time tension amplitude under the shear flow and the IL vibration frequency is the similar with the CF vibration frequency at the Reynolds number of 1105 in our experimental condition and the IL dominant frequency is twice the CF dominant frequency with an increasing Reynolds number. In addition, the displacement trajectories at the different locations of the riser appear the same shape and the shape is changed at the same shear parameter with an increasing Reynolds number under the shear flow. The diagonal displacement trajectories are observed at the low Reynolds number and the crescent-shaped displacement trajectories appear with an increasing Reynolds number under shear flow in the experiment.}, } @article {pmid25110161, year = {2014}, author = {Arun, RK and Chaudhury, K and Ghosh, M and Biswas, G and Chanda, N and Chakraborty, S}, title = {Controlled splitting and focusing of a stream of nanoparticles in a converging-diverging microchannel.}, journal = {Lab on a chip}, volume = {14}, number = {19}, pages = {3800-3808}, doi = {10.1039/c4lc00542b}, pmid = {25110161}, issn = {1473-0189}, abstract = {We demonstrate the potential of a converging-diverging microchannel to split a stream of nanoparticles towards the interfacial region of the dispersed and the carrier phases, introduced through the middle inlet and through the remaining two inlets respectively, while maintaining a low Reynolds number limit (<10) for the flow of both phases. In addition to the splitting of passive tracer particles, such as polystyrene beads as used herein, the present setup has the potential to be utilized for a controlled reaction and thereby the separation of products towards an intended location, as observed from the experimentation with silver-nanoparticles and hydrogen-peroxide solution. Moreover, the microscale dimension of the channel allows controlled deposition of the reaction product over the bottom surface of the channel, allowing the possibility of bottom-up fabrication of microscale features. We unveil the underlying hydrodynamics that lead to such behaviours through numerical simulations, which are consistent with the experimental observations. The phenomenological features are found to be guided by the splitting of the intrinsic streamlines conforming to the flow geometry under consideration.}, } @article {pmid25109407, year = {2014}, author = {Maxwell, AD and Park, S and Vaughan, BL and Cain, CA and Grotberg, JB and Xu, Z}, title = {Trapping of embolic particles in a vessel phantom by cavitation-enhanced acoustic streaming.}, journal = {Physics in medicine and biology}, volume = {59}, number = {17}, pages = {4927-4943}, pmid = {25109407}, issn = {1361-6560}, support = {R01 EB008998/EB/NIBIB NIH HHS/United States ; }, mesh = {*Acoustics ; Embolism/*therapy ; Humans ; Phantoms, Imaging ; *Rheology ; Ultrasonic Therapy/*methods ; }, abstract = {Cavitation clouds generated by short, high-amplitude, focused ultrasound pulses were previously observed to attract, trap, and erode thrombus fragments in a vessel phantom. This phenomenon may offer a noninvasive method to capture and eliminate embolic fragments flowing through the bloodstream during a cardiovascular intervention. In this article, the mechanism of embolus trapping was explored by particle image velocimetry (PIV). PIV was used to examine the fluid streaming patterns generated by ultrasound in a vessel phantom with and without crossflow of blood-mimicking fluid. Cavitation enhanced streaming, which generated fluid vortices adjacent to the focus. The focal streaming velocity, uf, was as high as 120 cm/s, while mean crossflow velocities, uc, were imposed up to 14 cm/s. When a solid particle 3-4 mm diameter was introduced into crossflow, it was trapped near the focus. Increasing uf promoted particle trapping while increasing uc promoted particle escape. The maximum crossflow Reynolds number at which particles could be trapped, Rec, was approximately linear with focal streaming number, Ref, i.e. Rec = 0.25Ref + 67.44 (R(2) = 0.76) corresponding to dimensional velocities uc = 0.084uf + 3.122 for 20 < uf < 120 cm/s. The fluidic pressure map was estimated from PIV and indicated a negative pressure gradient towards the focus, trapping the embolus near this location.}, } @article {pmid25105872, year = {2014}, author = {Lázaro, GR and Hernández-Machado, A and Pagonabarraga, I}, title = {Rheology of red blood cells under flow in highly confined microchannels: I. effect of elasticity.}, journal = {Soft matter}, volume = {10}, number = {37}, pages = {7195-7206}, doi = {10.1039/c4sm00894d}, pmid = {25105872}, issn = {1744-6848}, mesh = {Biophysical Phenomena ; Elasticity ; Erythrocyte Membrane/metabolism ; Erythrocytes/*cytology ; Humans ; Models, Biological ; Oscillometry ; Rheology/*methods ; Stress, Mechanical ; Surface Properties ; Viscosity ; }, abstract = {We analyze the rheology of dilute red blood cell suspensions in pressure driven flows at low Reynolds number, in terms of the morphologies and elasticity of the cells. We focus on narrow channels of width similar to the cell diameter, when the interactions with the walls dominate the cell dynamics. The suspension presents a shear-thinning behaviour, with a Newtonian-behaviour at low shear rates, an intermediate region of strong decay of the suspension viscosity, and an asymptotic regime at high shear rates in which the effective viscosity converges to that of the solvent. We identify the relevant aspects of cell elasticity that contribute to the rheological response of blood at high confinement. In a second paper, we will explore the focusing of red blood cells while flowing at high shear rates and how this effect is controlled by the geometry of the channel.}, } @article {pmid25085867, year = {2014}, author = {Hall, CL and Calt, M}, title = {Computational modeling of thrombotic microparticle deposition in nonparallel flow regimes.}, journal = {Journal of biomechanical engineering}, volume = {136}, number = {11}, pages = {}, doi = {10.1115/1.4028134}, pmid = {25085867}, issn = {1528-8951}, mesh = {Biomechanical Phenomena ; *Blood Circulation ; Cell-Derived Microparticles/*pathology ; *Computer Simulation ; Constriction, Pathologic/pathology/physiopathology ; *Mechanical Phenomena ; Models, Biological ; Thrombosis/*pathology/*physiopathology ; }, abstract = {Thrombotic microparticles (MPs) released from cells and platelets in response to various stimuli are present in elevated numbers in various disease states that increase the risk for thrombotic events. In order to understand how particles of this size may localize in nonparallel flow regimes and increase thrombotic risk, a computational analysis of flow and MP deposition was performed for 3 deg of stenosis at moderate Reynolds number (20
OBJECTIVE: To systematically evaluate the effects of the facial interface on aerosol inhalability, nasal deposition and thoracic dose in a 5-year-old child airway model using a coupled imaging-computational fluid dynamics approach.

METHODS: A face-nose-throat model was developed from magnetic resonance imaging scans of a 5-year-old boy. Respiration airflows and particle transport were simulated with the low Reynolds number k-ω turbulence model and the Lagrangian tracking approach. Particles ranging from 1 to 70 µm were considered in a calm air.

RESULTS: Retaining the facial interface in the computational model induced substantial variations in flow dynamics, aerosol inhalability and thoracic doses. The nasal and thoracic deposition fractions were much lower with the facial interface due to the low inhalability into downward-facing nostrils and facial deposition losses. For a given inhalation rate of 10 L/min, including the facial interface reduced the thoracic dose by 5% for 2.5-µm particles and by 50% for 10 µm particles in the child model. Considering localized conditions, facial interface substantially increased depositions at the turbinate region and dorsal pharynx.

CONCLUSION: This study highlighted the need to include facial interface in future numerical and in vitro studies. Findings of this study have practical implications in the design of aerosol samplers and interpretation of deposition data from studies without facial interfaces.}, } @article {pmid24987735, year = {2014}, author = {Xu, Y and Wu, Y and Sun, Q}, title = {Flow characteristics of the raw sewage for the design of sewage-source heat pump systems.}, journal = {TheScientificWorldJournal}, volume = {2014}, number = {}, pages = {503624}, doi = {10.1155/2014/503624}, pmid = {24987735}, issn = {1537-744X}, mesh = {Algorithms ; *Models, Theoretical ; *Rheology ; Sewage/*chemistry ; }, abstract = {The flow characteristics of raw sewage directly affect the technical and economic performance of sewage-source heat pump systems. The purpose of this research is to characterize the flow characteristics of sewage by experimental means. A sophisticated and flexible experimental apparatus was designed and constructed. Then the flow characteristics of the raw sewage were studied through laboratorial testing and theoretical analyses. Results indicated that raw sewage could be characterized as a power-law fluid with the rheological exponent n being 0.891 and the rheological coefficient k being 0.00175. In addition, the frictional loss factor formula in laminar flow for raw sewage was deduced by theoretical analysis of the power-law fluid. Furthermore, an explicit empirical formula for the frictional loss factor in turbulent flow was obtained through curve fitting of the experimental data. Finally, the equivalent viscosity of the raw sewage is defined in order to calculate the Reynolds number in turbulent flow regions; it was found that sewage had two to three times the viscosity of water at the same temperature. These results contributed to appropriate parameters of fluid properties when designing and operating sewage-source heat pump systems.}, } @article {pmid24985873, year = {2014}, author = {Venugopal, A and Agrawal, A and Prabhu, SV}, title = {Note: A vortex cross-correlation flowmeter with enhanced turndown ratio.}, journal = {The Review of scientific instruments}, volume = {85}, number = {6}, pages = {066109}, doi = {10.1063/1.4884078}, pmid = {24985873}, issn = {1089-7623}, abstract = {In the present study, a novel dual sensor vortex cross correlation technique is suggested and implemented to extend the lower operating range of the flowmeter. The first sensor located at an optimum streamwise location of 0.85 times the width of the bluff body is employed to compute the vortex shedding frequency under high Reynolds number conditions. Under low Reynolds number conditions, when the strength of the vortex signal is poor, the outputs from the two piezoelectric sensors are correlated to compute the vortex convection velocity. This vortex convection velocity is used to compute the volume flow rate. This novel dual flow rate estimation technique has demonstrated its robustness under low Reynolds number flow conditions with a remarkable turndown ratio of 1:66 as compared to 1:20 for conventional vortex flowmeters.}, } @article {pmid24984071, year = {2014}, author = {Alizadeh, A and Zhang, L and Wang, M}, title = {Mixing enhancement of low-Reynolds electro-osmotic flows in microchannels with temperature-patterned walls.}, journal = {Journal of colloid and interface science}, volume = {431}, number = {}, pages = {50-63}, doi = {10.1016/j.jcis.2014.05.070}, pmid = {24984071}, issn = {1095-7103}, mesh = {*Electroosmosis ; *Models, Chemical ; }, abstract = {Mixing becomes challenging in microchannels because of the low Reynolds number. This study aims to present a mixing enhancement method for electro-osmotic flows in microchannels using vortices caused by temperature-patterned walls. Since the fluid is non-isothermal, the conventional form of Nernst-Planck equation is modified by adding a new migration term which is dependent on both temperature and internal electric potential gradient. This term results in the so-called thermo-electrochemical migration phenomenon. The coupled Navier-Stokes, Poisson, modified Nernst-Planck, energy and advection-diffusion equations are iteratively solved by multiple lattice Boltzmann methods to obtain the velocity, internal electric potential, ion distribution, temperature and species concentration fields, respectively. To enhance the mixing, three schemes of temperature-patterned walls have been considered with symmetrical or asymmetrical arrangements of blocks with surface charge and temperature. Modeling results show that the asymmetric arrangement scheme is the most efficient scheme and enhances the mixing of species by 39% when the Reynolds number is on the order of 10(-3). Current results may help improve the design of micro-mixers at low Reynolds number.}, } @article {pmid24975756, year = {2015}, author = {Barbosa, TM and Morais, JE and Marques, MC and Silva, AJ and Marinho, DA and Kee, YH}, title = {Hydrodynamic profile of young swimmers: changes over a competitive season.}, journal = {Scandinavian journal of medicine & science in sports}, volume = {25}, number = {2}, pages = {e184-96}, doi = {10.1111/sms.12281}, pmid = {24975756}, issn = {1600-0838}, mesh = {Adolescent ; Athletic Performance/*physiology ; Biomechanical Phenomena ; Child ; Female ; Humans ; *Hydrodynamics ; Longitudinal Studies ; Male ; Models, Biological ; Seasons ; Swimming/*physiology ; }, abstract = {The aim of this study was to analyze the changes in the hydrodynamic profile of young swimmers over a competitive season and to compare the variations according to a well-designed training periodization. Twenty-five swimmers (13 boys and 12 girls) were evaluated in (a) October (M1); (b) March (M2); and (c) June (M3). Inertial and anthropometrical measures included body mass, swimmer's added water mass, height, and trunk transverse surface area. Swimming efficiency was estimated by the speed fluctuation, stroke index, and approximate entropy. Active drag was estimated with the velocity perturbation method and the passive drag with the gliding decay method. Hydrodynamic dimensionless numbers (Froude and Reynolds numbers) and hull velocity (i.e., speed at Froude number = 0.42) were also calculated. No variable presented a significant gender effect. Anthropometrics and inertial parameters plus dimensionless numbers increased over time. Swimming efficiency improved between M1 and M3. There was a trend for both passive and active drag increase from M1 to M2, but being lower at M3 than at M1. Intra-individual changes between evaluation moments suggest high between- and within-subject variations. Therefore, hydrodynamic changes over a season occur in a non-linear fashion way, where the interplay between growth and training periodization explain the unique path flow selected by each young swimmer.}, } @article {pmid24973704, year = {2014}, author = {Slominski, CG and Kraynik, AM and Brady, JF}, title = {The Einstein shear viscosity correction for non no-slip hyperspheres.}, journal = {Journal of colloid and interface science}, volume = {430}, number = {}, pages = {302-304}, doi = {10.1016/j.jcis.2014.05.052}, pmid = {24973704}, issn = {1095-7103}, abstract = {We calculate the effective shear viscosity of a dilute dispersion of n-dimensional non no-slip hyperspheres, first for hyperdrops, second for slippery hyperspheres, and third for porous hyperspheres.}, } @article {pmid24960397, year = {2014}, author = {Hong, J and Toloui, M and Chamorro, LP and Guala, M and Howard, K and Riley, S and Tucker, J and Sotiropoulos, F}, title = {Natural snowfall reveals large-scale flow structures in the wake of a 2.5-MW wind turbine.}, journal = {Nature communications}, volume = {5}, number = {}, pages = {4216}, doi = {10.1038/ncomms5216}, pmid = {24960397}, issn = {2041-1723}, abstract = {To improve power production and structural reliability of wind turbines, there is a pressing need to understand how turbines interact with the atmospheric boundary layer. However, experimental techniques capable of quantifying or even qualitatively visualizing the large-scale turbulent flow structures around full-scale turbines do not exist today. Here we use snowflakes from a winter snowstorm as flow tracers to obtain velocity fields downwind of a 2.5-MW wind turbine in a sampling area of ~36 × 36 m(2). The spatial and temporal resolutions of the measurements are sufficiently high to quantify the evolution of blade-generated coherent motions, such as the tip and trailing sheet vortices, identify their instability mechanisms and correlate them with turbine operation, control and performance. Our experiment provides an unprecedented in situ characterization of flow structures around utility-scale turbines, and yields significant insights into the Reynolds number similarity issues presented in wind energy applications.}, } @article {pmid24948628, year = {2014}, author = {Wadhwa, N and Andersen, A and Kiørboe, T}, title = {Hydrodynamics and energetics of jumping copepod nauplii and copepodids.}, journal = {The Journal of experimental biology}, volume = {217}, number = {Pt 17}, pages = {3085-3094}, doi = {10.1242/jeb.105676}, pmid = {24948628}, issn = {1477-9145}, mesh = {Animals ; Biomechanical Phenomena ; Copepoda/growth & development/*physiology ; *Hydrodynamics ; Larva ; Rheology ; *Swimming ; Video Recording ; Viscosity ; }, abstract = {Within its life cycle, a copepod goes through drastic changes in size, shape and swimming mode. In particular, there is a stark difference between the early (nauplius) and later (copepodid) stages. Copepods inhabit an intermediate Reynolds number regime (between ~1 and 100) where both viscosity and inertia are potentially important, and the Reynolds number changes by an order of magnitude during growth. Thus we expect the life stage related changes experienced by a copepod to result in hydrodynamic and energetic differences, ultimately affecting the fitness. To quantify these differences, we measured the swimming kinematics and fluid flow around jumping Acartia tonsa at different stages of its life cycle, using particle image velocimetry and particle tracking velocimetry. We found that the flow structures around nauplii and copepodids are topologically different, with one and two vortex rings, respectively. Our measurements suggest that copepodids cover a larger distance compared to their body size in each jump and are also hydrodynamically quieter, as the flow disturbance they create attenuates faster with distance. Also, copepodids are energetically more efficient than nauplii, presumably due to the change in hydrodynamic regime accompanied with a well-adapted body form and swimming stroke.}, } @article {pmid24936020, year = {2014}, author = {Scheichl, B}, title = {Gross separation approaching a blunt trailing edge as the turbulence intensity increases.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {372}, number = {2020}, pages = {}, doi = {10.1098/rsta.2014.0001}, pmid = {24936020}, issn = {1364-503X}, abstract = {A novel rational description of incompressible two-dimensional time-mean turbulent boundary layer (BL) flow separating from a bluff body at an arbitrarily large globally formed Reynolds number, Re, is devised. Partly in contrast to and partly complementing previous approaches, it predicts a pronounced delay of massive separation as the turbulence intensity level increases. This is bounded from above by a weakly decaying Re-dependent gauge function (hence, the BL approximation stays intact locally), and thus the finite intensity level characterizing fully developed turbulence. However, it by far exceeds the moderate level found in a preceding study which copes with the associated moderate delay of separation. Thus, the present analysis bridges this self-consistent and another forerunner theory, proposing extremely retarded separation by anticipating a fully attached external potential flow. Specifically, it is shown upon formulation of a respective distinguished limit at which rate the separation point and the attached-flow trailing edge collapse as [Formula: see text] and how on a short streamwise scale the typical small velocity deficit in the core region of the incident BL evolves to a large one. Hence, at its base, the separating velocity profile varies generically with the one-third power of the wall distance, and the classical triple-deck problem describing local viscous-inviscid interaction crucial for moderately retarded separation is superseded by a Rayleigh problem, governing separation of that core layer. Its targeted solution proves vital for understanding the separation process more close to the wall. Most importantly, the analysis does not resort to any specific turbulence closure. A first comparison with the available experimentally found positions of separation for the canonical flow past a circular cylinder is encouraging.}, } @article {pmid24936018, year = {2014}, author = {Rothmayer, AP}, title = {Magnetohydrodynamic channel flows with weak transverse magnetic fields.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {372}, number = {2020}, pages = {}, doi = {10.1098/rsta.2013.0344}, pmid = {24936018}, issn = {1364-503X}, abstract = {Magnetohydrodynamic flow of an incompressible fluid through a plane channel with slowly varying walls and a magnetic field applied transverse to the channel is investigated in the high Reynolds number limit. It is found that the magnetic field can first influence the hydrodynamic flow when the Hartmann number reaches a sufficiently large value. The magnetic field is found to suppress the steady and unsteady viscous flow near the channel walls unless the wall shapes become large.}, } @article {pmid24936016, year = {2014}, author = {Logue, RP and Gajjar, JS and Ruban, AI}, title = {Instability of supersonic compression ramp flow.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {372}, number = {2020}, pages = {}, doi = {10.1098/rsta.2013.0342}, pmid = {24936016}, issn = {1364-503X}, abstract = {The instability of supersonic compression ramp flow is investigated. It is assumed that the Reynolds number is large and that the governing equations are the unsteady triple-deck equations. The mean flow is first calculated by solving the steady equations for various scaled ramp angles α, and the numerical results suggest that there is no singularity for increasing ramp angles. The stability of the flow is investigated using two approaches, first by solving the linearized unsteady equations and looking for global modes proportional to e(λt). In the second approach, the linearized unsteady equations are solved numerically with various initial conditions. Whereas no globally unsteady modes could be found for the range of ramp angles studied, the numerical simulations show the formation of wavepacket type disturbances which grow and convect and reach large amplitudes. However, the numerical results show large variations with grid size even on very fine grids.}, } @article {pmid24936013, year = {2014}, author = {Braun, S and Scheichl, S}, title = {On recent developments in marginal separation theory.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {372}, number = {2020}, pages = {}, pmid = {24936013}, issn = {1364-503X}, abstract = {Thin aerofoils are prone to localized flow separation at their leading edge if subjected to moderate angles of attack α. Although 'laminar separation bubbles' at first do not significantly alter the aerofoil performance, they tend to 'burst' if α is increased further or if perturbations acting upon the flow reach a certain intensity. This then either leads to global flow separation (stall) or triggers the laminar-turbulent transition process within the boundary layer flow. This paper addresses the asymptotic analysis of the early stages of the latter phenomenon in the limit as the characteristic Reynolds number [Formula: see text], commonly referred to as marginal separation theory. A new approach based on the adjoint operator method is presented that enables the fundamental similarity laws of marginal separation theory to be derived and the analysis to be extended to higher order. Special emphasis is placed on the breakdown of the flow description, i.e. the formation of finite-time singularities (a manifestation of the bursting process), and on its resolution being based on asymptotic arguments. The passage to the subsequent triple-deck stage is described in detail, which is a prerequisite for carrying out a future numerical treatment of this stage in a proper way. Moreover, a composite asymptotic model is developed in order for the inherent ill-posedness of the Cauchy problems associated with the current flow description to be resolved.}, } @article {pmid24936012, year = {2014}, author = {Wu, X}, title = {On the role of acoustic feedback in boundary-layer instability.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {372}, number = {2020}, pages = {}, doi = {10.1098/rsta.2013.0347}, pmid = {24936012}, issn = {1364-503X}, abstract = {In this paper, the classical triple-deck formalism is employed to investigate two instability problems in which an acoustic feedback loop plays an essential role. The first concerns a subsonic boundary layer over a flat plate on which two well-separated roughness elements are present. A spatially amplifying Tollmien-Schlichting (T-S) wave between the roughness elements is scattered by the downstream roughness to emit a sound wave that propagates upstream and impinges on the upstream roughness to regenerate the T-S wave, thereby forming a closed feedback loop in the streamwise direction. Numerical calculations suggest that, at high Reynolds numbers and for moderate roughness heights, the long-range acoustic coupling may lead to absolute instability, which is characterized by self-sustained oscillations at discrete frequencies. The dominant peak frequency may jump from one value to another as the Reynolds number, or the distance between the roughness elements, is varied gradually. The second problem concerns the supersonic 'twin boundary layers' that develop along two well-separated parallel flat plates. The two boundary layers are in mutual interaction through the impinging and reflected acoustic waves. It is found that the interaction leads to a new instability that is absent in the unconfined boundary layer.}, } @article {pmid24936011, year = {2014}, author = {Cassel, KW and Conlisk, AT}, title = {Unsteady separation in vortex-induced boundary layers.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {372}, number = {2020}, pages = {}, doi = {10.1098/rsta.2013.0348}, pmid = {24936011}, issn = {1364-503X}, abstract = {This paper provides a brief review of the analytical and numerical developments related to unsteady boundary-layer separation, in particular as it relates to vortex-induced flows, leading up to our present understanding of this important feature in high-Reynolds-number, surface-bounded flows in the presence of an adverse pressure gradient. In large part, vortex-induced separation has been the catalyst for pulling together the theory, numerics and applications of unsteady separation. Particular attention is given to the role that Prof. Frank T. Smith, FRS, has played in these developments over the course of the past 35 years. The following points will be emphasized: (i) unsteady separation plays a pivotal role in a wide variety of high-Reynolds-number flows, (ii) asymptotic methods have been instrumental in elucidating the physics of both steady and unsteady separation, (iii) Frank T. Smith has served as a catalyst in the application of asymptotic methods to high-Reynolds-number flows, and (iv) there is still much work to do in articulating a complete theoretical understanding of unsteady boundary-layer separation.}, } @article {pmid24936010, year = {2014}, author = {Kluwick, A and Kornfeld, M}, title = {Triple-deck analysis of transonic high Reynolds number flow through slender channels.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {372}, number = {2020}, pages = {}, doi = {10.1098/rsta.2013.0346}, pmid = {24936010}, issn = {1364-503X}, abstract = {In this work, laminar transonic weakly three-dimensional flows at high Reynolds numbers in slender channels, as found in microsupersonic nozzles and turbomachines of micro-electro-mechanical systems, are considered. The channel height is taken so small that the viscous wall layers forming at the channel walls start to interact strongly rather than weakly with the inviscid core flow and, therefore, the classical boundary layer approach fails. The resulting viscous-inviscid interaction problem is formulated using matched asymptotic expansions and found to be governed by a triple-deck structure. As a consequence, the properties of the predominantly inviscid core region and the viscous wall layers have to be calculated simultaneously in the interaction region. Weakly three-dimensional effects caused by surface roughness, upstream propagating flow perturbations, boundary layer separation as well as bifurcating solutions are discussed. Representative results for subsonic as well as supersonic conditions are presented, and the importance of these flow phenomena in technical applications as, for example, a means to reduce shock losses through the use of deformed geometry is addressed.}, } @article {pmid24936008, year = {2014}, author = {Goldstein, ME}, title = {Effect of free-stream turbulence on boundary layer transition.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {372}, number = {2020}, pages = {}, doi = {10.1098/rsta.2013.0354}, pmid = {24936008}, issn = {1364-503X}, abstract = {This paper is concerned with the transition to turbulence in flat plate boundary layers due to moderately high levels of free-stream turbulence. The turbulence is assumed to be generated by an (idealized) grid and matched asymptotic expansions are used to analyse the resulting flow over a finite thickness flat plate located in the downstream region. The characteristic Reynolds number Rλ based on the mesh size λ and free-stream velocity is assumed to be large, and the turbulence intensity ε is assumed to be small. The asymptotic flow structure is discussed for the generic case where the turbulence Reynolds number εRλ and the plate thickness and are held fixed (at O(1) and O(λ), respectively) in the limit as [Formula: see text] and ε→0. But various limiting cases are considered in order to explain the relevant transition mechanisms. It is argued that there are two types of streak-like structures that can play a role in the transition process: (i) those that appear in the downstream region and are generated by streamwise vorticity in upstream flow and (ii) those that are concentrated near the leading edge and are generated by plate normal vorticity in upstream flow. The former are relatively unaffected by leading edge geometry and are usually referred to as Klebanoff modes while the latter are strongly affected by leading edge geometry and are more streamwise vortex-like in appearance.}, } @article {pmid24936006, year = {2014}, author = {Deguchi, K and Hall, P}, title = {Canonical exact coherent structures embedded in high Reynolds number flows.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {372}, number = {2020}, pages = {}, doi = {10.1098/rsta.2013.0352}, pmid = {24936006}, issn = {1364-503X}, abstract = {The applications and implications of two recently addressed asymptotic descriptions of exact coherent structures in shear flows are discussed. The first type of asymptotic framework to be discussed was introduced in a series of papers by Hall & Smith in the 1990s and was referred to as vortex-wave interaction theory (VWI). New results are given here for the canonical VWI problem in an infinite region; the results confirm and extend the results for the infinite problem inferred the recent VWI computation of plane Couette flow. The results given define for the first time exact coherent structures in unbounded flows. The second type of canonical structure described here is that recently found for asymptomatic suction boundary layer and corresponds to freestream coherent structures (FCS), in boundary layer flows. Here, it is shown that the FCS can also occur in flows such as Burgers vortex sheet. It is concluded that both canonical problems can be locally embedded in general shear flows and thus have widespread applicability.}, } @article {pmid24931649, year = {2014}, author = {Kozu, H and Kobayashi, I and Neves, MA and Nakajima, M and Uemura, K and Sato, S and Ichikawa, S}, title = {PIV and CFD studies on analyzing intragastric flow phenomena induced by peristalsis using a human gastric flow simulator.}, journal = {Food & function}, volume = {5}, number = {8}, pages = {1839-1847}, doi = {10.1039/c4fo00041b}, pmid = {24931649}, issn = {2042-650X}, mesh = {*Computer Simulation ; Humans ; *Models, Biological ; Peristalsis/*physiology ; *Rheology ; }, abstract = {This study quantitatively analyzed the flow phenomena in model gastric contents induced by peristalsis using a human gastric flow simulator (GFS). Major functions of the GFS include gastric peristalsis simulation by controlled deformation of rubber walls and direct observation of inner flow through parallel transparent windows. For liquid gastric contents (water and starch syrup solutions), retropulsive flow against the direction of peristalsis was observed using both particle image velocimetry (PIV) and computational fluid dynamics (CFD). The maximum flow velocity was obtained in the region occluded by peristalsis. The maximum value was 9 mm s(-1) when the standard value of peristalsis speed in healthy adults (UACW = 2.5 mm s(-1)) was applied. The intragastric flow-field was laminar with the maximum Reynolds number (Re = 125). The viscosity of liquid gastric contents hardly affected the maximum flow velocity in the applied range of this study (1 to 100 mPa s). These PIV results agreed well with the CFD results. The maximum shear rate in the liquid gastric contents was below 20 s(-1) at UACW = 2.5 mm s(-1). We also measured the flow-field in solid-liquid gastric contents containing model solid food particles (plastic beads). The direction of velocity vectors was influenced by the presence of the model solid food particle surface. The maximum flow velocity near the model solid food particles ranged from 8 to 10 mm s(-1) at UACW = 2.5 mm s(-1). The maximum shear rate around the model solid food particles was low, with a value of up to 20 s(-1).}, } @article {pmid24910525, year = {2014}, author = {Pihler-Puzović, D and Pedley, TJ}, title = {Flutter in a quasi-one-dimensional model of a collapsible channel.}, journal = {Proceedings. Mathematical, physical, and engineering sciences}, volume = {470}, number = {2166}, pages = {20140015}, pmid = {24910525}, issn = {1364-5021}, abstract = {The effects of wall inertia on instabilities in a collapsible channel with a long finite-length flexible wall containing a high Reynolds number flow of incompressible fluid are studied. Using the ideas of interactive boundary layer theory, the system is described by a one-dimensional model that couples inviscid flow outside the boundary layers formed on the channel walls with the deformation of the flexible wall. The observed instability is a form of flutter, which is superposed on the behaviour of the system when the wall mass is neglected. We show that the flutter has a positive growth rate because the fluid loading acts as a negative damping in the system. We discuss these findings in relation to other work on self-excited oscillations in collapsible channels.}, } @article {pmid24895466, year = {2013}, author = {Benmouhoub, D and Mataoui, A}, title = {Turbulent Heat Transfer From a Slot Jet Impinging on a Flat Plate.}, journal = {Journal of heat transfer}, volume = {135}, number = {10}, pages = {1022011-1022019}, pmid = {24895466}, issn = {0022-1481}, abstract = {The flow field and heat transfer of a plane impinging jet on a hot moving wall were investigated using one point closure turbulence model. Computations were carried out by means of a finite volume method. The evolutions of mean velocity components, vorticity, skin friction coefficient, Nusselt number and pressure coefficient are examined in this paper. Two parameters of this type of interaction are considered for a given impinging distance of 8 times the nozzle thickness (H/e = 8): the jet-surface velocity ratio and the jet exit Reynolds number. The flow field structure at a given surface-to-jet velocity ratio is practically independent to the jet exit Reynolds number. A slight modification of the flow field is observed for weak surface-to-jet velocity ratios while the jet is strongly driven for higher velocity ratio. The present results satisfactorily compare to the experimental data available in the literature for Rsj ≤ 1.The purpose of this paper is to investigate this phenomenon for higher Rsj values (0 ≤ Rsj ≤ 4). It follows that the variation of the mean skin friction and the Nusselt number can be correlated according to the surface-to-jet velocity ratios and the Reynolds numbers.}, } @article {pmid24864128, year = {2014}, author = {Odeleye, AO and Marsh, DT and Osborne, MD and Lye, GJ and Micheletti, M}, title = {On the fluid dynamics of a laboratory scale single-use stirred bioreactor.}, journal = {Chemical engineering science}, volume = {111}, number = {100}, pages = {299-312}, pmid = {24864128}, issn = {0009-2509}, abstract = {The commercial success of mammalian cell-derived recombinant proteins has fostered an increase in demand for novel single-use bioreactor (SUB) systems that facilitate greater productivity, increased flexibility and reduced costs (Zhang et al., 2010). These systems exhibit fluid flow regimes unlike those encountered in traditional glass/stainless steel bioreactors because of the way in which they are designed. With such disparate hydrodynamic environments between SUBs currently on the market, traditional scale-up approaches applied to stirred tanks should be revised. One such SUB is the Mobius[®] 3 L CellReady, which consists of an upward-pumping marine scoping impeller. This work represents the first experimental study of the flow within the CellReady using a Particle Image Velocimetry (PIV) approach, combined with a biological study into the impact of these fluid dynamic characteristics on cell culture performance. The PIV study was conducted within the actual vessel, rather than using a purpose-built mimic. PIV measurements conveyed a degree of fluid compartmentalisation resulting from the up-pumping impeller. Both impeller tip speed and fluid working volume had an impact upon the fluid velocities and spatial distribution of turbulence within the vessel. Cell cultures were conducted using the GS-CHO cell-line (Lonza) producing an IgG4 antibody. Disparity in cellular growth and viability throughout the range of operating conditions used (80-350 rpm and 1-2.4 L working volume) was not substantial, although a significant reduction in recombinant protein productivity was found at 350 rpm and 1 L working volume (corresponding to the highest Reynolds number tested in this work). The study shows promise in the use of PIV to improve understanding of the hydrodynamic environment within individual SUBs and allows identification of the critical hydrodynamic parameters under the different flow regimes for compatibility and scalability across the range of bioreactor platforms.}, } @article {pmid24855668, year = {2014}, author = {Ngo, V and McHenry, MJ}, title = {The hydrodynamics of swimming at intermediate Reynolds numbers in the water boatman (Corixidae).}, journal = {The Journal of experimental biology}, volume = {217}, number = {Pt 15}, pages = {2740-2751}, doi = {10.1242/jeb.103895}, pmid = {24855668}, issn = {1477-9145}, mesh = {Acceleration ; Animals ; Biomechanical Phenomena ; Extremities/physiology ; Heteroptera/*physiology ; *Hydrodynamics ; Models, Theoretical ; Swimming/*physiology ; Video Recording ; Viscosity ; }, abstract = {The fluid forces that govern propulsion determine the speed and energetic cost of swimming. These hydrodynamics are scale dependent and it is unclear what forces matter to the tremendous diversity of aquatic animals that are between a millimeter and a centimeter in length. Animals at this scale generally operate within the regime of intermediate Reynolds numbers, where both viscous and inertial fluid forces have the potential to play a role in propulsion. The present study aimed to resolve which forces create thrust and drag in the paddling of the water boatman (Corixidae), an animal that spans much of the intermediate regime (101 mm) and whole pulmonary arteries (r ≥0.004 mm), optimal x in the rigid model explained 2.7 in elastic-muscular (0.1 < r ≤1 mm) and 3.0 in peripheral resistive systemic arteries (0.004 ≤ r ≤0.1 mm), in agreement with data obtained from angiographic, cast-morphometric, and in vivo experimental studies in the literature. The least energy principle on the total energy basis provides an alternate concept of optimality relating to mammalian arterial fractal dimensions under α = 1.0.}, } @article {pmid24738015, year = {2014}, author = {Fan, LL and He, XK and Han, Y and Du, L and Zhao, L and Zhe, J}, title = {Continuous size-based separation of microparticles in a microchannel with symmetric sharp corner structures.}, journal = {Biomicrofluidics}, volume = {8}, number = {2}, pages = {024108}, pmid = {24738015}, issn = {1932-1058}, abstract = {A new microchannel with a series of symmetric sharp corner structures is reported for passive size-dependent particle separation. Micro particles of different sizes can be completely separated based on the combination of the inertial lift force and the centrifugal force induced by the sharp corner structures in the microchannel. At appropriate flow rate and Reynolds number, the centrifugal force effect on large particles, induced by the sharp corner structures, is stronger than that on small particles; hence after passing a series of symmetric sharp corner structures, large particles are focused to the center of the microchannel, while small particles are focused at two particle streams near the two side walls of the microchannel. Particles of different sizes can then be completely separated. Particle separation with this device was demonstrated using 7.32 μm and 15.5 μm micro particles. Experiments show that in comparison with the prior multi-orifice flow fractionation microchannel and multistage-multiorifice flow fractionation microchannel, this device can completely separate two-size particles with narrower particle stream band and larger separation distance between particle streams. In addition, it requires no sheath flow and complex multi-stage separation structures, avoiding the dilution of analyte sample and complex operations. The device has potentials to be used for continuous, complete particle separation in a variety of lab-on-a-chip and biomedical applications.}, } @article {pmid24736320, year = {2014}, author = {Hayat, T and Abbasi, FM and Ahmad, B and Alsaedi, A}, title = {Peristaltic transport of Carreau-Yasuda fluid in a curved channel with slip effects.}, journal = {PloS one}, volume = {9}, number = {4}, pages = {e95070}, pmid = {24736320}, issn = {1932-6203}, mesh = {Algorithms ; *Models, Theoretical ; }, abstract = {The wide occurrence of peristaltic pumping should not be surprising at all since it results physiologically from neuro-muscular properties of any tubular smooth muscle. Of special concern here is to predict the rheological effects on the peristaltic motion in a curved channel. Attention is focused to develop and simulate a nonlinear mathematical model for Carreau-Yasuda fluid. The progressive wave front of peristaltic flow is taken sinusoidal (expansion/contraction type). The governing problem is challenge since it has nonlinear differential equation and nonlinear boundary conditions even in the long wavelength and low Reynolds number regime. Numerical solutions for various flow quantities of interest are presented. Comparison for different flow situations is also made. Results of physical quantities are interpreted with particular emphasis to rheological characteristics.}, } @article {pmid24730943, year = {2014}, author = {Okamoto, N and Yoshimatsu, K and Schneider, K and Farge, M}, title = {Small-scale anisotropic intermittency in magnetohydrodynamic turbulence at low magnetic Reynolds numbers.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {89}, number = {3}, pages = {033013}, doi = {10.1103/PhysRevE.89.033013}, pmid = {24730943}, issn = {1550-2376}, abstract = {Small-scale anisotropic intermittency is examined in three-dimensional incompressible magnetohydrodynamic turbulence subjected to a uniformly imposed magnetic field. Orthonormal wavelet analyses are applied to direct numerical simulation data at moderate Reynolds number and for different interaction parameters. The magnetic Reynolds number is sufficiently low such that the quasistatic approximation can be applied. Scale-dependent statistical measures are introduced to quantify anisotropy in terms of the flow components, either parallel or perpendicular to the imposed magnetic field, and in terms of the different directions. Moreover, the flow intermittency is shown to increase with increasing values of the interaction parameter, which is reflected in strongly growing flatness values when the scale decreases. The scale-dependent anisotropy of energy is found to be independent of scale for all considered values of the interaction parameter. The strength of the imposed magnetic field does amplify the anisotropy of the flow.}, } @article {pmid24730940, year = {2014}, author = {Ding, Z and Wong, TN}, title = {Electrohydrodynamic instability in an annular liquid layer with radial conductivity gradients.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {89}, number = {3}, pages = {033010}, doi = {10.1103/PhysRevE.89.033010}, pmid = {24730940}, issn = {1550-2376}, abstract = {In this paper, the electrohydrodynamic stability in an annular liquid layer with a radial electrical conductivity gradient is investigated. A weak shear flow arises from a constant pressure gradient in the axial direction. In the radial direction, an electric field is applied. The three-dimensional linear instability analysis is implemented to study the influence of the inner radius, electrical conductivity gradient, shear flow, and ionic diffusion on the dynamics of the fluid layer. It is found that the critical unstable mode may either be oscillatory or stationary. The system becomes more unstable as the dimensionless inner radius a increases. When the inner radius a is small, the critical unstable mode is stationary, while it is given by three-dimensional oblique waves when a is large. When the conductivity gradient is small, the critical unstable mode is the three-dimensional oblique wave, while when the conductivity gradient is large, it would switch to the stationary mode rather than the oscillatory mode. The system becomes more unstable when the Reynolds number is slightly increased from zero. Additionally, it is found that the electrical Schmidt number has dual effects. The liquid layer becomes either more unstable or stable as the electric Schmidt number increases.}, } @article {pmid24730939, year = {2014}, author = {Rüdiger, G and Brandenburg, A}, title = {α effect in a turbulent liquid-metal plane Couette flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {89}, number = {3}, pages = {033009}, doi = {10.1103/PhysRevE.89.033009}, pmid = {24730939}, issn = {1550-2376}, abstract = {We calculate the mean electromotive force in plane Couette flows of a nonrotating conducting fluid under the influence of a large-scale magnetic field for driven turbulence. A vertical stratification of the turbulence intensity results in an α effect owing to the presence of horizontal shear. Here we discuss the possibility of an experimental determination of the components of the α tensor using both quasilinear theory and nonlinear numerical simulations. For magnetic Prandtl numbers of the order of unity, we find that in the high-conductivity limit the α effect in the direction of the flow clearly exceeds the component in spanwise direction. In this limit, α runs linearly with the magnetic Reynolds number Rm, while in the low-conductivity limit it runs with the product Rm·Re, where Re is the kinetic Reynolds number, so that for a given Rm the α effect grows with decreasing magnetic Prandtl number. For the small magnetic Prandtl numbers of liquid metals, a common value for the horizontal elements of the α tensor appears, which makes it unimportant whether the α effect is measured in the spanwise or the streamwise directions. The resulting effect should lead to an observable voltage of about 0.5 mV in both directions for magnetic fields of 1 kG and velocity fluctuations of about 1 m/s in a channel of 50-cm height (independent of its width).}, } @article {pmid24724653, year = {2014}, author = {du Puits, R and Li, L and Resagk, C and Thess, A and Willert, C}, title = {Turbulent boundary layer in high Rayleigh number convection in air.}, journal = {Physical review letters}, volume = {112}, number = {12}, pages = {124301}, doi = {10.1103/PhysRevLett.112.124301}, pmid = {24724653}, issn = {1079-7114}, abstract = {Flow visualizations and particle image velocimetry measurements in the boundary layer of a Rayleigh-Bénard experiment are presented for the Rayleigh number Ra=1.4×1010. Our visualizations indicate that the appearance of the flow structures is similar to ordinary (isothermal) turbulent boundary layers. Our particle image velocimetry measurements show that vorticity with both positive and negative sign is generated and that the smallest flow structures are 1 order of magnitude smaller than the boundary layer thickness. Additional local measurements using laser Doppler velocimetry yield turbulence intensities up to I=0.4 as in turbulent atmospheric boundary layers. From our observations, we conclude that the convective boundary layer becomes turbulent locally and temporarily although its Reynolds number Re≈200 is considerably smaller than the value 420 underlying existing phenomenological theories. We think that, in turbulent Rayleigh-Bénard convection, the transition of the boundary layer towards turbulence depends on subtle details of the flow field and is therefore not universal.}, } @article {pmid24721664, year = {2014}, author = {Phuntsho, S and Lotfi, F and Hong, S and Shaffer, DL and Elimelech, M and Shon, HK}, title = {Membrane scaling and flux decline during fertiliser-drawn forward osmosis desalination of brackish groundwater.}, journal = {Water research}, volume = {57}, number = {}, pages = {172-182}, doi = {10.1016/j.watres.2014.03.034}, pmid = {24721664}, issn = {1879-2448}, mesh = {Fertilizers/*analysis ; Groundwater/*chemistry ; Microscopy, Electron, Scanning ; *Osmosis ; *Salinity ; Spectrometry, X-Ray Emission ; Water Purification/*methods ; X-Ray Diffraction ; }, abstract = {Fertiliser-drawn forward osmosis (FDFO) desalination has been recently studied as one feasible application of forward osmosis (FO) for irrigation. In this study, the potential of membrane scaling in the FDFO process has been investigated during the desalination of brackish groundwater (BGW). While most fertilisers containing monovalent ions did not result in any scaling when used as an FO draw solution (DS), diammonium phosphate (DAP or (NH4)2HPO4) resulted in significant scaling, which contributed to severe flux decline. Membrane autopsy using scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDS), and x-ray diffraction (XRD) analysis indicated that the reverse diffusion of DAP from the DS to the feed solution was primarily responsible for scale formation during the FDFO process. Physical cleaning of the membrane with deionised water at varying crossflow velocities was employed to evaluate the reversibility of membrane scaling and the extent of flux recovery. For the membrane scaled using DAP as DS, 80-90% of the original flux was recovered when the crossflow velocity for physical cleaning was the same as the crossflow velocity during FDFO desalination. However, when a higher crossflow velocity or Reynolds number was used, the flux was recovered almost completely, irrespective of the DS concentration used. This study underscores the importance of selecting a suitable fertiliser for FDFO desalination of brackish groundwater to avoid membrane scaling and severe flux decline.}, } @article {pmid24718997, year = {2014}, author = {Anzai, H and Falcone, JL and Chopard, B and Hayase, T and Ohta, M}, title = {Optimization of strut placement in flow diverter stents for four different aneurysm configurations.}, journal = {Journal of biomechanical engineering}, volume = {136}, number = {6}, pages = {061006}, doi = {10.1115/1.4027411}, pmid = {24718997}, issn = {1528-8951}, mesh = {Algorithms ; *Blood Circulation ; Intracranial Aneurysm/pathology/*physiopathology ; Models, Anatomic ; *Prosthesis Design ; *Stents ; }, abstract = {A modern technique for the treatment of cerebral aneurysms involves insertion of a flow diverter stent. Flow stagnation, produced by the fine mesh structure of the diverter, is thought to promote blood clotting in an aneurysm. However, apart from its effect on flow reduction, the insertion of the metal device poses the risk of occlusion of a parent artery. One strategy for avoiding the risk of arterial occlusion is the use of a device with a higher porosity. To aid the development of optimal stents in the view point of flow reduction maintaining a high porosity, we used lattice Boltzmann flow simulations and simulated annealing optimization to investigate the optimal placement of stent struts. We constructed four idealized aneurysm geometries that resulted in four different inflow characteristics and employed a stent model with 36 unconnected struts corresponding to the porosity of 80%. Assuming intracranial flow, steady flow simulation with Reynolds number of 200 was applied for each aneurysm. Optimization of strut position was performed to minimize the average velocity in an aneurysm while maintaining the porosity. As the results of optimization, we obtained nonuniformed structure as optimized stent for each aneurysm geometry. And all optimized stents were characterized by denser struts in the inflow area. The variety of inflow patterns that resulted from differing aneurysm geometries led to unique strut placements for each aneurysm type.}, } @article {pmid24704879, year = {2014}, author = {Eltsov, V and Hänninen, R and Krusius, M}, title = {Quantum turbulence in superfluids with wall-clamped normal component.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {111 Suppl 1}, number = {Suppl 1}, pages = {4711-4718}, pmid = {24704879}, issn = {1091-6490}, abstract = {In Fermi superfluids, such as superfluid (3)He, the viscous normal component can be considered to be stationary with respect to the container. The normal component interacts with the superfluid component via mutual friction, which damps the motion of quantized vortex lines and eventually couples the superfluid component to the container. With decreasing temperature and mutual friction, the internal dynamics of the superfluid component becomes more important compared with the damping and coupling effects from the normal component. As a result profound changes in superfluid dynamics are observed: the temperature-dependent transition from laminar to turbulent vortex motion and the decoupling from the reference frame of the container at even lower temperatures.}, } @article {pmid24700264, year = {2014}, author = {Nason, F and Pennati, G and Dubini, G}, title = {Computational modeling of passive furrowed channel micromixers for lab-on-a-chip applications.}, journal = {Journal of applied biomaterials & functional materials}, volume = {12}, number = {3}, pages = {278-285}, doi = {10.5301/jabfm.5000191}, pmid = {24700264}, issn = {2280-8000}, mesh = {Computer Simulation ; Computer-Aided Design ; Equipment Design ; Equipment Failure Analysis ; Microfluidic Analytical Techniques/*instrumentation/methods ; *Models, Chemical ; Solutions/*chemistry ; }, abstract = {BACKGROUND: Effective micromixers represent essential components for micro total analysis systems or lab-on-a-chip. Indeed, mixing is a key process for the success of all chemical or biochemical reactions. Most microfluidic systems operate in a laminar flow regime dominated by molecular diffusion, which is not favorable to mixing. In the present work, numerical analyses of mixing in 3-dimensional channels with obstacles on the walls were performed to investigate mixing behavior and flow characteristics with geometric parameters as well as Reynolds number.

METHODS: Several channel wall geometries were numerically modeled, and the influence of obstacle height, phase shift between the walls, channel cross-section shape (aspect ratio) and Reynolds number on mixer performances was investigated. Wall geometries were evaluated comparatively in terms of index of mixing and pressure drops caused.

RESULTS: Results indicated that furrowed channels with proper triangle-shaped obstacles show good performances in terms of achieving complete mixing in a very short length of channel, and at the same time offer low pressure losses. Convective motions are the main influences responsible for successful mixing, and micromixers with triangle-shaped obstacles show an improvement in the mixing performances for increasing Reynolds numbers. Moreover, short times are required for the mixing process. Finally, depending on the Reynolds number that one works at, there is also some flexibility in the choice of the channel geometry, as the occurrence of effective chaotic advection was obtained for several conformations of the channels proposed in this study.

CONCLUSIONS: Mixing enhancement can be achieved by optimizing the shape of the furrowed channel.}, } @article {pmid24671449, year = {2014}, author = {Battiato, I}, title = {Effective medium theory for drag-reducing micro-patterned surfaces in turbulent flows.}, journal = {The European physical journal. E, Soft matter}, volume = {37}, number = {3}, pages = {19}, pmid = {24671449}, issn = {1292-895X}, abstract = {Many studies in the last decade have revealed that patterns at the microscale can reduce skin drag. Yet, the mechanisms and parameters that control drag reduction, e.g. Reynolds number and pattern geometry, are still unclear. We propose an effective medium representation of the micro-features, that treats the latter as a porous medium, and provides a framework to model turbulent flow over patterned surfaces. Our key result is a closed-form expression for the skin friction coefficient in terms of frictional Reynolds (or Kármán) number in turbulent regime, the viscosity ratio between the fluid in and above the features, and their geometrical properties. We apply the proposed model to turbulent flows over superhydrophobic ridged surfaces. The model predictions agree with laboratory experiments for Reynolds numbers ranging from 3000 to 10000.}, } @article {pmid24671019, year = {2014}, author = {Wickramarathna, LN and Noss, C and Lorke, A}, title = {Hydrodynamic trails produced by Daphnia: size and energetics.}, journal = {PloS one}, volume = {9}, number = {3}, pages = {e92383}, pmid = {24671019}, issn = {1932-6203}, mesh = {Animals ; Biomechanical Phenomena ; Daphnia/*physiology ; *Hydrodynamics ; Swimming ; Viscosity ; Zooplankton ; }, abstract = {This study focuses on quantifying hydrodynamic trails produced by freely swimming zooplankton. We combined volumetric tracking of swimming trajectories with planar observations of the flow field induced by Daphnia of different size and swimming in different patterns. Spatial extension of the planar flow field along the trajectories was used to interrogate the dimensions (length and volume) and energetics (dissipation rate of kinetic energy and total dissipated power) of the trails. Our findings demonstrate that neither swimming pattern nor size of the organisms affect the trail width or the dissipation rate. However, we found that the trail volume increases with increasing organism size and swimming velocity, more precisely the trail volume is proportional to the third power of Reynolds number. This increase furthermore results in significantly enhanced total dissipated power at higher Reynolds number. The biggest trail volume observed corresponds to about 500 times the body volume of the largest daphnids. Trail-averaged viscous dissipation rate of the swimming daphnids vary in the range of 1.8 x 10(-6) W/kg to 3.4 x 10(-6) W/kg and the observed magnitudes of total dissipated power between 1.3 x 10(-9) W and 1 x 10(-8) W, respectively. Among other zooplankton species, daphnids display the highest total dissipated power in their trails. These findings are discussed in the context of fluid mixing and transport by organisms swimming at intermediate Reynolds numbers.}, } @article {pmid24647804, year = {2014}, author = {Dey, R and Raj M, K and Bhandaru, N and Mukherjee, R and Chakraborty, S}, title = {Tunable hydrodynamic characteristics in microchannels with biomimetic superhydrophobic (lotus leaf replica) walls.}, journal = {Soft matter}, volume = {10}, number = {19}, pages = {3451-3462}, doi = {10.1039/c4sm00037d}, pmid = {24647804}, issn = {1744-6848}, mesh = {Biomimetic Materials/*chemistry ; *Hydrodynamics ; Hydrophobic and Hydrophilic Interactions ; Lotus/*chemistry ; Microscopy, Fluorescence ; Plant Leaves/chemistry ; Surface Properties ; }, abstract = {The present work comprehensively addresses the hydrodynamic characteristics through microchannels with lotus leaf replica (exhibiting low adhesion and superhydrophobic properties) walls. The lotus leaf replica is fabricated following an efficient, two-step, soft-molding process and is then integrated with rectangular microchannels. The inherent biomimetic, superhydrophobic surface-liquid interfacial hydrodynamics, and the consequential bulk flow characteristics, are critically analyzed by the micro-particle image velocimetry technique. It is observed that the lotus leaf replica mediated microscale hydrodynamics comprise of two distinct flow regimes even within the low Reynolds number paradigm, unlike the commonly perceived solely apparent slip-stick dominated flows over superhydrophobic surfaces. While the first flow regime is characterized by an apparent slip-stick flow culminating in an enhanced bulk throughput rate, the second flow regime exhibits a complete breakdown of the aforementioned laminar and uni-axial flow model, leading to a predominantly no-slip flow. Interestingly, the critical flow condition dictating the transition between the two hydrodynamic regimes is intrinsically dependent on the micro-confinement effect. In this regard, an energetically consistent theoretical model is also proposed to predict the alterations in the critical flow condition with varying microchannel configurations, by addressing the underlying biomimetic surface-liquid interfacial conditions. Hence, the present research endeavour provides a new design-guiding paradigm for developing multi-functional microfluidic devices involving biomimetic, superhydrophobic surfaces, by judicious exploitation of the tunable hydrodynamic characteristics in the two regimes.}, } @article {pmid24633506, year = {2014}, author = {Jachero, L and Ahumada, I and Richter, P}, title = {Rotating-disk sorptive extraction: effect of the rotation mode of the extraction device on mass transfer efficiency.}, journal = {Analytical and bioanalytical chemistry}, volume = {406}, number = {12}, pages = {2987-2992}, doi = {10.1007/s00216-014-7693-z}, pmid = {24633506}, issn = {1618-2650}, abstract = {The extraction device used in rotating-disk sorptive extraction consists of a Teflon disk in which a sorptive phase is fixed on one of its surfaces. Depending on the configuration, the rotation axis of the disk device can be either perpendicular or parallel to its radius, giving rise to two different mass transfer patterns when rotating-disk sorptive extraction is applied in liquid samples. In the perpendicular case (configuration 1), which is the typical configuration, the disk contains an embedded miniature stir bar that allows the disk rotation to be driven using a common laboratory magnetic stirrer. In the parallel case (configuration 2), the disk is driven by a rotary rod connected to an electric stirrer. In this study, triclosan and its degradation product methyl triclosan were used as analyte models to demonstrate the significant effect of the rotation configuration of the disk on the efficiency of analyte mass transfer from water to a sorptive phase of polydimethylsiloxane. Under the same experimental conditions and at a rotation velocity of 1,250 rpm, extraction equilibrium was reached at 80 min when the disk was rotated in configuration 1 and at 30 min when the disk was rotated in configuration 2. The extraction equilibration time decreased to 14 min when the rotation velocity was increased to 2,000 rpm in configuration 2. Because the rotation pattern affects the mass transfer efficiency, each rotation configuration was characterized through the Reynolds number; Re values of 6,875 and 16,361 were achieved with configurations 1 and 2, respectively, at 1,250 rpm.}, } @article {pmid24632825, year = {2014}, author = {Horstmann, JT and Henningsson, P and Thomas, AL and Bomphrey, RJ}, title = {Wake development behind paired wings with tip and root trailing vortices: consequences for animal flight force estimates.}, journal = {PloS one}, volume = {9}, number = {3}, pages = {e91040}, pmid = {24632825}, issn = {1932-6203}, support = {BB/J001244/2/BB_/Biotechnology and Biological Sciences Research Council/United Kingdom ; BB/J001244/1/BB_/Biotechnology and Biological Sciences Research Council/United Kingdom ; }, mesh = {Animals ; Flight, Animal/*physiology ; Models, Biological ; Rheology ; Wings, Animal/*physiology ; }, abstract = {Recent experiments on flapping flight in animals have shown that a variety of unrelated species shed a wake behind left and right wings consisting of both tip and root vortices. Here we present an investigation using Particle Image Velocimetry (PIV) of the behaviour and interaction of trailing vortices shed by paired, fixed wings that simplify and mimic the wake of a flying animal with a non-lifting body. We measured flow velocities at five positions downstream of two adjacent NACA 0012 aerofoils and systematically varied aspect ratio, the gap between the wings (corresponding to the width of a non-lifting body), angle of attack, and the Reynolds number. The range of aspect ratios and Reynolds number where chosen to be relevant to natural fliers and swimmers, and insect flight in particular. We show that the wake behind the paired wings deformed as a consequence of the induced flow distribution such that the wingtip vortices convected downwards while the root vortices twist around each other. Vortex interaction and wake deformation became more pronounced further downstream of the wing, so the positioning of PIV measurement planes in experiments on flying animals has an important effect on subsequent force estimates due to rotating induced flow vectors. Wake deformation was most severe behind wings with lower aspect ratios and when the distance between the wings was small, suggesting that animals that match this description constitute high-risk groups in terms of measurement error. Our results, therefore, have significant implications for experimental design where wake measurements are used to estimate forces generated in animal flight. In particular, the downstream distance of the measurement plane should be minimised, notwithstanding the animal welfare constraints when measuring the wake behind flying animals.}, } @article {pmid24632685, year = {2014}, author = {Sochol, RD and Lu, A and Lei, J and Iwai, K and Lee, LP and Lin, L}, title = {Microfluidic bead-based diodes with targeted circular microchannels for low Reynolds number applications.}, journal = {Lab on a chip}, volume = {14}, number = {9}, pages = {1585-1594}, doi = {10.1039/c3lc51069g}, pmid = {24632685}, issn = {1473-0189}, mesh = {Dimethylpolysiloxanes/chemistry ; Microfluidic Analytical Techniques/*instrumentation ; *Microspheres ; Models, Theoretical ; Pressure ; }, abstract = {Self-regulating fluidic components are critical to the advancement of microfluidic processors for chemical and biological applications, such as sample preparation on chip, point-of-care molecular diagnostics, and implantable drug delivery devices. Although researchers have developed a wide range of components to enable flow rectification in fluidic systems, engineering microfluidic diodes that function at the low Reynolds number (Re) flows and smaller scales of emerging micro/nanofluidic platforms has remained a considerable challenge. Recently, researchers have demonstrated microfluidic diodes that utilize high numbers of suspended microbeads as dynamic resistive elements; however, using spherical particles to block fluid flow through rectangular microchannels is inherently limited. To overcome this issue, here we present a single-layer microfluidic bead-based diode (18 μm in height) that uses a targeted circular-shaped microchannel for the docking of a single microbead (15 μm in diameter) to rectify fluid flow under low Re conditions. Three-dimensional simulations and experimental results revealed that adjusting the docking channel geometry and size to better match the suspended microbead greatly increased the diodicity (Di) performance. Arraying multiple bead-based diodes in parallel was found to adversely affect system efficacy, while arraying multiple diodes in series was observed to enhance device performance. In particular, systems consisting of four microfluidic bead-based diodes with targeted circular-shaped docking channels in series revealed average Di's ranging from 2.72 ± 0.41 to 10.21 ± 1.53 corresponding to Re varying from 0.1 to 0.6.}, } @article {pmid24605055, year = {2014}, author = {Salman, SD and Kadhum, AA and Takriff, MS and Mohamad, AB}, title = {Heat transfer enhancement of laminar nanofluids flow in a circular tube fitted with parabolic-cut twisted tape inserts.}, journal = {TheScientificWorldJournal}, volume = {2014}, number = {}, pages = {543231}, pmid = {24605055}, issn = {1537-744X}, mesh = {Algorithms ; *Models, Theoretical ; }, abstract = {Numerical investigation has been carried out on heat transfer and friction factor characteristics of copper-water nanofluid flow in a constant heat-fluxed tube with the existence of new configuration of vortex generator using Computational Fluid Dynamics (CFD) simulation. Two types of swirl flow generator: Classical twisted tape (CTT) and Parabolic-cut twisted tape (PCT) with a different twist ratio (y = 2.93, 3.91 and 4.89) and different cut depth (w = 0.5, 1.0 and 1.5 cm) with 2% and 4% volume concentration of CuO nanofluid were used for simulation. The effect of different parameters such as flow Reynolds number, twist ratio, cut depth and nanofluid were considered. The results show that the enhancement of heat transfer rate and the friction factor induced by the Classical (CTT) and Parabolic-cut (PCT) inserts increases with twist ratio and cut depth decreases. The results also revealed that the heat transfer enhancement increases with an increase in the volume fraction of the CuO nanoparticle. Furthermore, the twisted tape with twist ratio (y = 2.93) and cut depth w = 0.5 cm offered 10% enhancement of the average Nusselt number with significant increases in friction factor than those of Classical twisted tape.}, } @article {pmid24599543, year = {2014}, author = {Wang, GR and Yang, F and Zhao, W}, title = {There can be turbulence in microfluidics at low Reynolds number.}, journal = {Lab on a chip}, volume = {14}, number = {8}, pages = {1452-1458}, doi = {10.1039/c3lc51403j}, pmid = {24599543}, issn = {1473-0189}, mesh = {Diffusion ; *Hydrodynamics ; Kinetics ; *Microfluidics ; Pressure ; }, abstract = {Turbulence is commonly viewed as a type of macroflow, where the Reynolds number (Re) has to be sufficiently high. In microfluidics, when Re is below or on the order of 1 and fast mixing is required, so far only chaotic flow has been reported to enhance mixing based on previous publications since turbulence is believed not to be possible to generate in such a low Re microflow. There is even a lack of velocimeter that can measure turbulence in microchannels. In this work, we report a direct observation of the existence of turbulence in microfluidics with Re on the order of 1 in a pressure driven flow under electrokinetic forcing using a novel velocimeter having ultrahigh spatiotemporal resolution. The work could provide a new method to control flow and transport phenomena in lab-on-a-chip and a new perspective on turbulence.}, } @article {pmid24592153, year = {2014}, author = {Wu, PS and Tsai, ST and Jhuo, YH}, title = {Effect of turbulence intensity on cross-injection film cooling at a stepped or smooth endwall of a gas turbine vane passage.}, journal = {TheScientificWorldJournal}, volume = {2014}, number = {}, pages = {256136}, doi = {10.1155/2014/256136}, pmid = {24592153}, issn = {1537-744X}, mesh = {Liquid Crystals ; *Natural Gas ; Power Plants/*instrumentation ; Temperature ; }, abstract = {This study is concerned with a film cooling technique applicable to the protection of the endwalls of a gas turbine vane. In the experiments, cross-injection coolant flow from two-row, paired, inclined holes with nonintersecting centerlines was utilized. The test model is a scaled two-half vane. The levels of turbulence intensity used in the experiments are T.I. = 1.8%, 7%, and 12%. Other parameters considered in the film cooling experiments include three inlet Reynolds numbers (9.20 × 10(4), 1.24 × 10(5), and 1.50 × 10(5)), three blowing ratios (0.5, 1.0, and 2.0), and three endwall conditions (smooth endwall and stepped endwall with forward-facing or backward-facing step). Thermochromic liquid crystal (TLC) technique with steady-state heat transfer experiments was used to obtain the whole-field film cooling effectiveness. Results show that, at low turbulence intensity, increasing Reynolds number decreases the effectiveness in most of the vane passage. There is no monotonic trend of influence by Reynolds number at high turbulence intensity. The effect of blowing ratio on the effectiveness has opposite trends at low and high turbulence levels. Increasing turbulent intensity decreases the effectiveness, especially near the inlet of the vane passage. With a stepped endwall, turbulence intensity has only mild effect on the film cooling effectiveness.}, } @article {pmid24587561, year = {2014}, author = {Anupindi, K and Lai, W and Frankel, S}, title = {Characterization of oscillatory instability in lid driven cavity flows using lattice Boltzmann method.}, journal = {Computers & fluids}, volume = {92}, number = {}, pages = {7-21}, pmid = {24587561}, issn = {0045-7930}, support = {R01 HL098353/HL/NHLBI NIH HHS/United States ; }, abstract = {In the present work, lattice Boltzmann method (LBM) is applied for simulating flow in a three-dimensional lid driven cubic and deep cavities. The developed code is first validated by simulating flow in a cubic lid driven cavity at 1000 and 12000 Reynolds numbers following which we study the effect of cavity depth on the steady-oscillatory transition Reynolds number in cavities with depth aspect ratio equal to 1, 2 and 3. Turbulence modeling is performed through large eddy simulation (LES) using the classical Smagorinsky sub-grid scale model to arrive at an optimum mesh size for all the simulations. The simulation results indicate that the first Hopf bifurcation Reynolds number correlates negatively with the cavity depth which is consistent with the observations from two-dimensional deep cavity flow data available in the literature. Cubic cavity displays a steady flow field up to a Reynolds number of 2100, a delayed anti-symmetry breaking oscillatory field at a Reynolds number of 2300, which further gets restored to a symmetry preserving oscillatory flow field at 2350. Deep cavities on the other hand only attain an anti-symmetry breaking flow field from a steady flow field upon increase of the Reynolds number in the range explored. As the present work involved performing a set of time-dependent calculations for several Reynolds numbers and cavity depths, the parallel performance of the code is evaluated a priori by running the code on up to 4096 cores. The computational time required for these runs shows a close to linear speed up over a wide range of processor counts depending on the problem size, which establishes the feasibility of performing a thorough search process such as the one presently undertaken.}, } @article {pmid24584155, year = {2014}, author = {Tay, WB and van Oudheusden, BW and Bijl, H}, title = {Numerical simulation of X-wing type biplane flapping wings in 3D using the immersed boundary method.}, journal = {Bioinspiration & biomimetics}, volume = {9}, number = {3}, pages = {036001}, doi = {10.1088/1748-3182/9/3/036001}, pmid = {24584155}, issn = {1748-3190}, mesh = {Aircraft/*instrumentation ; Algorithms ; Animals ; Biological Clocks/physiology ; Biomimetics/*instrumentation ; Computer Simulation ; *Computer-Aided Design ; Equipment Design ; Equipment Failure Analysis ; Flight, Animal/*physiology ; *Models, Biological ; Movement/*physiology ; Numerical Analysis, Computer-Assisted ; Oscillometry/methods ; Wings, Animal/*physiology ; }, abstract = {The numerical simulation of an insect-sized 'X-wing' type biplane flapping wing configuration is performed in 3D using an immersed boundary method solver at Reynolds numbers equal to 1000 (1 k) and 5 k, based on the wing's root chord length. This X-wing type flapping configuration draws its inspiration from Delfly, a bio-inspired ornithopter MAV which has two pairs of wings flapping in anti-phase in a biplane configuration. The objective of the present investigation is to assess the aerodynamic performance when the original Delfly flapping wing micro-aerial vehicle (FMAV) is reduced to the size of an insect. Results show that the X-wing configuration gives more than twice the average thrust compared with only flapping the upper pair of wings of the X-wing. However, the X-wing's average thrust is only 40% that of the upper wing flapping at twice the stroke angle. Despite this, the increased stability which results from the smaller lift and moment variation of the X-wing configuration makes it more suited for sharp image capture and recognition. These advantages make the X-wing configuration an attractive alternative design for insect-sized FMAVS compared to the single wing configuration. In the Reynolds number comparison, the vorticity iso-surface plot at a Reynolds number of 5 k revealed smaller, finer vortical structures compared to the simulation at 1 k, due to vortices' breakup. In comparison, the force output difference is much smaller between Re = 1 k and 5 k. Increasing the body inclination angle generates a uniform leading edge vortex instead of a conical one along the wingspan, giving higher lift. Understanding the force variation as the body inclination angle increases will allow FMAV designers to optimize the thrust and lift ratio for higher efficiency under different operational requirements. Lastly, increasing the spanwise flexibility of the wings increases the thrust slightly but decreases the efficiency. The thrust result is similar to one of the spanwise studies, but the efficiency result contradicts it, indicating that other flapping parameters are involved as well. Results from this study provide a deeper understanding of the underlying aerodynamics of the X-wing type, which will help to improve the performance of insect-sized FMAVs using this unique configuration.}, } @article {pmid24580458, year = {2014}, author = {Kreilos, T and Eckhardt, B and Schneider, TM}, title = {Increasing lifetimes and the growing saddles of shear flow turbulence.}, journal = {Physical review letters}, volume = {112}, number = {4}, pages = {044503}, doi = {10.1103/PhysRevLett.112.044503}, pmid = {24580458}, issn = {1079-7114}, abstract = {In linearly stable shear flows, turbulence spontaneously decays with a characteristic lifetime that varies with Reynolds number. The lifetime sharply increases with Reynolds number so that a possible divergence marking the transition to sustained turbulence at a critical point has been discussed. We present a mechanism by which the lifetimes increase: in the system's state space, turbulent motion is supported by a chaotic saddle. Inside this saddle a locally attracting periodic orbit is created and undergoes a traditional bifurcation sequence generating chaos. The formed new "turbulent bubble" is initially an attractor supporting persistent chaotic dynamics. Soon after its creation, it collides with its own boundary, by which it becomes leaky and dynamically connected with the surrounding structures. The complexity of the chaotic saddle that supports transient turbulence hence increases by incorporating the remnant of a new bubble. As a a result, the time it takes for a trajectory to leave the saddle and decay to the laminar state is increased. We demonstrate this phenomenon in plane Couette flow and show that characteristic lifetimes vary nonsmoothly and nonmonotonically with Reynolds number.}, } @article {pmid24580356, year = {2014}, author = {Zhou, Y and Grinstein, FF and Wachtor, AJ and Haines, BM}, title = {Estimating the effective Reynolds number in implicit large-eddy simulation.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {89}, number = {1}, pages = {013303}, doi = {10.1103/PhysRevE.89.013303}, pmid = {24580356}, issn = {1550-2376}, abstract = {In implicit large-eddy simulation (ILES), energy-containing large scales are resolved, and physics capturing numerics are used to spatially filter out unresolved scales and to implicitly model subgrid scale effects. From an applied perspective, it is highly desirable to estimate a characteristic Reynolds number (Re)-and therefore a relevant effective viscosity-so that the impact of resolution on predicted flow quantities and their macroscopic convergence can usefully be characterized. We argue in favor of obtaining robust Re estimates away from the smallest scales of the simulated flow-where numerically controlled dissipation takes place and propose a theoretical basis and framework to determine such measures. ILES examples include forced turbulence as a steady flow case, the Taylor-Green vortex to address transition and decaying turbulence, and simulations of a laser-driven reshock experiment illustrating a fairly complex turbulence problem of current practical interest.}, } @article {pmid24580339, year = {2014}, author = {Niebling, MJ and Tallakstad, KT and Toussaint, R and Måløy, KJ}, title = {Direct velocity measurement of a turbulent shear flow in a planar Couette cell.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {89}, number = {1}, pages = {013026}, doi = {10.1103/PhysRevE.89.013026}, pmid = {24580339}, issn = {1550-2376}, abstract = {In a plane Couette cell a thin fluid layer consisting of water is sheared between the sides of a transparent band at Reynolds numbers ranging from 300 to 1400. The length of the cell's flow channel is large compared to the film separation. To extract the flow velocity in the experiments, a correlation image velocimetry method is used on pictures recorded with a high-speed camera. The flow is recorded at a resolution that allows us to analyze flow patterns similar in size to the film separation. The fluid flow is then studied by calculating flow velocity autocorrelation functions. The turbulent patterns that arise on this scale above a critical Reynolds number of Re=360 display characteristic patterns that are proven by use of the calculated velocity autocorrelation functions. The patterns are metastable and reappear at different positions and times throughout the experiments. Typically these patterns are turbulent rolls which are elongated in the stream direction, which is the direction in which the band is moving. Although the flow states are metastable they possess similarities to the steady Taylor vortices known to appear in circular Taylor Couette cells.}, } @article {pmid24580328, year = {2014}, author = {Joung, YS and Buie, CR}, title = {Scaling laws for drop impingement on porous films and papers.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {89}, number = {1}, pages = {013015}, doi = {10.1103/PhysRevE.89.013015}, pmid = {24580328}, issn = {1550-2376}, abstract = {This study investigates drop impingement on highly wetting porous films and papers. Experiments reveal previously unexplored impingement modes on porous surfaces designated as necking, spreading, and jetting. Dimensional analysis yields a nondimensional parameter, denoted the Washburn-Reynolds number, relating droplet kinetic energy and surface energy. The impingement modes correlate with Washburn-Reynolds number variations spanning four orders of magnitude and a corresponding energy conservation analysis for droplet spreading shows good agreement with the experimental results. The simple scaling laws presented will inform the investigation of dynamic interactions between porous surfaces and liquid drops.}, } @article {pmid24580325, year = {2014}, author = {Xu, M}, title = {Effect of soft-iron impellers on the von Kármán-sodium dynamo.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {89}, number = {1}, pages = {013012}, doi = {10.1103/PhysRevE.89.013012}, pmid = {24580325}, issn = {1550-2376}, abstract = {The explanation for the observed axisymmetric magnetic field in the von Kármán-sodium (VKS) dynamo experiment is still an unresolved question. In this paper, the integral equation approach is extended to investigate the VKS dynamo action by taking into account the discontinuity of the magnetic permeability and electrical conductivity in the conducting region. When the relative magnetic permeability of the soft-iron impellers is set to 65, a steady toroidal field that is apparently axisymmetric is excited at the critical magnetic Reynolds number, Rmc≈27.23, which is close to the experimental result, Rmc≈30. Our results show that the critical magnetic Reynolds number declines as the relative magnetic permeability of the impellers increases. Furthermore, when the relative magnetic permeability is not greater than 37, an equatorial magnetic field with an azimuthal wave number m=1 is the dominant mode, otherwise a steady toroidal field with an azimuthal wave number m=0 predominates the magnetic field generated by the VKS dynamo action.}, } @article {pmid24563612, year = {2013}, author = {Zhao, C and Oztekin, A and Cheng, X}, title = {Gravity-induced swirl of nanoparticles in microfluidics.}, journal = {Journal of nanoparticle research : an interdisciplinary forum for nanoscale science and technology}, volume = {15}, number = {}, pages = {1611}, pmid = {24563612}, issn = {1388-0764}, support = {R21 AI081638/AI/NIAID NIH HHS/United States ; }, abstract = {Parallel flows of two fluids in microfluidic devices are used for miniaturized chemistry, physics, biology and bioengineering studies, and the streams are often considered to remain parallel. However, as the two fluids do not always have the same density, interface reorientation induced by density stratification is unavoidable. In this paper, flow characteristics of an aqueous polystyrene nanofluid and a sucrose-densified aqueous solution flowing parallel in microchannels are examined. Nanoparticles 100 nm in diameter are used in the study. The motion of the nanoparticles is simulated using the Lagrangian description and directly observed by a confocal microscope. Matched results are obtained from computational and empirical analysis. Although solution density homogenizes rapidly resulting from a fast diffusion of sucrose in water, the nanofluid is observed to rotate for an extended period. Angular displacement of the nanofluid depends on the ratio of gravitational force to viscous force, Re/Fr[2], where Re is the Reynolds number and Fr is the Froude number. In the developing region at the steady state, the angular displacement is related to y/Dh, the ratio between distance from the inlet and the hydraulic diameter of the microfluidic channel. The development of nanofluid flow feature also depends on h/w, the ratio of microfluidic channel's height to width. The quantitative description of the angular displacement of nanofluid will aid rational designs of microfluidic devices utilizing multistream, multiphase flows.}, } @article {pmid24561349, year = {2014}, author = {Janiga, G}, title = {Large eddy simulation of the FDA benchmark nozzle for a Reynolds number of 6500.}, journal = {Computers in biology and medicine}, volume = {47}, number = {}, pages = {113-119}, doi = {10.1016/j.compbiomed.2014.01.004}, pmid = {24561349}, issn = {1879-0534}, mesh = {Computer Simulation/*standards ; *Hydrodynamics ; *Models, Theoretical ; }, abstract = {This work investigates the flow in a benchmark nozzle model of an idealized medical device proposed by the FDA using computational fluid dynamics (CFD). It was in particular shown that a proper modeling of the transitional flow features is particularly challenging, leading to large discrepancies and inaccurate predictions from the different research groups using Reynolds-averaged Navier-Stokes (RANS) modeling. In spite of the relatively simple, axisymmetric computational geometry, the resulting turbulent flow is fairly complex and non-axisymmetric, in particular due to the sudden expansion. The resulting flow cannot be well predicted with simple modeling approaches. Due to the varying diameters and flow velocities encountered in the nozzle, different typical flow regions and regimes can be distinguished, from laminar to transitional and to weakly turbulent. The purpose of the present work is to re-examine the FDA-CFD benchmark nozzle model at a Reynolds number of 6500 using large eddy simulation (LES). The LES results are compared with published experimental data obtained by Particle Image Velocimetry (PIV) and an excellent agreement can be observed considering the temporally averaged flow velocities. Different flow regimes are characterized by computing the temporal energy spectra at different locations along the main axis.}, } @article {pmid24532222, year = {2014}, author = {Whitfield, CA and Marenduzzo, D and Voituriez, R and Hawkins, RJ}, title = {Active polar fluid flow in finite droplets.}, journal = {The European physical journal. E, Soft matter}, volume = {37}, number = {2}, pages = {8}, pmid = {24532222}, issn = {1292-895X}, mesh = {Actin Cytoskeleton/*chemistry/metabolism ; Cell Movement ; *Models, Biological ; *Motion ; }, abstract = {We present a continuum level analytical model of a droplet of active contractile fluid consisting of filaments and motors. We calculate the steady state flows that result from a splayed polarisation of the filaments. We account for interaction with the external medium by imposing a viscous friction at the fixed droplet boundary. We then show that the droplet has non-zero force dipole and quadrupole moments, the latter of which is essential for self-propelled motion of the droplet at low Reynolds' number. Therefore, this calculation describes a simple mechanism for the motility of a droplet of active contractile fluid embedded in a three-dimensional environment, which is relevant to cell migration in confinement (for example, embedded within a gel or tissue). Our analytical results predict how the system depends on various parameters such as the effective friction coefficient, the phenomenological activity parameter and the splay of the imposed polarisation.}, } @article {pmid24529910, year = {2014}, author = {Helgeland, A and Mardal, KA and Haughton, V and Reif, BA}, title = {Numerical simulations of the pulsating flow of cerebrospinal fluid flow in the cervical spinal canal of a Chiari patient.}, journal = {Journal of biomechanics}, volume = {47}, number = {5}, pages = {1082-1090}, doi = {10.1016/j.jbiomech.2013.12.023}, pmid = {24529910}, issn = {1873-2380}, mesh = {Arnold-Chiari Malformation/*physiopathology ; Cerebrospinal Fluid/*physiology ; Cervical Vertebrae ; Computer Simulation ; Diastole ; Humans ; Male ; *Models, Biological ; *Pulsatile Flow ; Spinal Canal/*physiopathology ; Subarachnoid Space ; Systole ; }, abstract = {The flow of cerebrospinal fluid (CSF) in a patient-specific model of the subarachnoid space in a Chiari I patient was investigated using numerical simulations. The pulsating CSF flow was modeled using a time-varying velocity pulse based on peak velocity measurements (diastole and systole) derived from a selection of patients with Chiari I malformation. The present study introduces the general definition of the Reynolds number to provide a measure of CSF flow instability to give an estimate of the possibility of turbulence occurring in CSF flow. This was motivated by the fact that the combination of pulsating flow and the geometric complexity of the spinal canal may result in local Reynolds numbers that are significantly higher than the commonly used global measure such that flow instabilities may develop into turbulent flow in these regions. The local Reynolds number was used in combination with derived statistics to characterize the flow. The results revealed the existence of both local unstable regions and local regions with velocity fluctuations similar in magnitude to what is observed in fully turbulent flows. The results also indicated that the fluctuations were not self-sustained turbulence, but rather flow instabilities that may develop into turbulence. The case considered was therefore believed to represent a CSF flow close to transition.}, } @article {pmid24522785, year = {2014}, author = {Nabawy, MR and Crowther, WJ}, title = {On the quasi-steady aerodynamics of normal hovering flight part I: the induced power factor.}, journal = {Journal of the Royal Society, Interface}, volume = {11}, number = {93}, pages = {20131196}, pmid = {24522785}, issn = {1742-5662}, mesh = {Animals ; Flight, Animal/*physiology ; *Models, Biological ; Wings, Animal/*physiology ; }, abstract = {An analytical treatment to quantify the losses captured in the induced power factor, k, is provided for flapping wings in normal hover, including the effects of non-uniform downwash, tip losses and finite flapping amplitude. The method is based on a novel combination of actuator disc and lifting line blade theories that also takes into account the effect of advance ratio. The model has been evaluated against experimental results from the literature and qualitative agreement obtained for the effect of advance ratio on the lift coefficient of revolving wings. Comparison with quantitative experimental data for the circulation as a function of span for a fruitfly wing shows that the model is able to correctly predict the circulation shape of variation, including both the magnitude of the peak circulation and the rate of decay in circulation towards zero. An evaluation of the contributions to induced power factor in normal hover for eight insects is provided. It is also shown how Reynolds number can be accounted for in the induced power factor, and good agreement is obtained between predicted span efficiency as a function of Reynolds number and numerical results from the literature. Lastly, it is shown that for a flapping wing in hover k owing to the non-uniform downwash effect can be reduced to 1.02 using an arcsech chord distribution. For morphologically realistic wing shapes based on beta distributions, it is shown that a value of 1.07 can be achieved for a radius of first moment of wing area at 40% of wing length.}, } @article {pmid24520175, year = {2014}, author = {Moffatt, HK}, title = {Helicity and singular structures in fluid dynamics.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {111}, number = {10}, pages = {3663-3670}, pmid = {24520175}, issn = {1091-6490}, mesh = {*Hydrodynamics ; *Magnetic Fields ; Models, Theoretical ; Physics ; *Planets ; }, abstract = {Helicity is, like energy, a quadratic invariant of the Euler equations of ideal fluid flow, although, unlike energy, it is not sign definite. In physical terms, it represents the degree of linkage of the vortex lines of a flow, conserved when conditions are such that these vortex lines are frozen in the fluid. Some basic properties of helicity are reviewed, with particular reference to (i) its crucial role in the dynamo excitation of magnetic fields in cosmic systems; (ii) its bearing on the existence of Euler flows of arbitrarily complex streamline topology; (iii) the constraining role of the analogous magnetic helicity in the determination of stable knotted minimum-energy magnetostatic structures; and (iv) its role in depleting nonlinearity in the Navier-Stokes equations, with implications for the coherent structures and energy cascade of turbulence. In a final section, some singular phenomena in low Reynolds number flows are briefly described.}, } @article {pmid24511253, year = {2014}, author = {Namdeo, S and Khaderi, SN and Onck, PR}, title = {Numerical modelling of chirality-induced bi-directional swimming of artificial flagella.}, journal = {Proceedings. Mathematical, physical, and engineering sciences}, volume = {470}, number = {2162}, pages = {20130547}, pmid = {24511253}, issn = {1364-5021}, abstract = {Biomimetic micro-swimmers can be used for various medical applications, such as targeted drug delivery and micro-object (e.g. biological cells) manipulation, in lab-on-a-chip devices. Bacteria swim using a bundle of flagella (flexible hair-like structures) that form a rotating cork-screw of chiral shape. To mimic bacterial swimming, we employ a computational approach to design a bacterial (chirality-induced) swimmer whose chiral shape and rotational velocity can be controlled by an external magnetic field. In our model, we numerically solve the coupled governing equations that describe the system dynamics (i.e. solid mechanics, fluid dynamics and magnetostatics). We explore the swimming response as a function of the characteristic dimensionless parameters and put special emphasis on controlling the swimming direction. Our results provide fundamental physical insight on the chirality-induced propulsion, and it provides guidelines for the design of magnetic bi-directional micro-swimmers.}, } @article {pmid24503612, year = {2014}, author = {Bahraseman, H and Hassani, K and Khosravi, A and Navidbakhsh, M and Espino, D and Fatouraee, N and Kazemi-Saleh, D}, title = {Combining numerical and clinical methods to assess aortic valve hemodynamics during exercise.}, journal = {Perfusion}, volume = {29}, number = {4}, pages = {340-350}, doi = {10.1177/0267659114521103}, pmid = {24503612}, issn = {1477-111X}, abstract = {Computational simulations have the potential to aid understanding of cardiovascular hemodynamics under physiological conditions, including exercise. Therefore, blood hemodynamic parameters during different heart rates, rest and exercise have been investigated, using a numerical method. A model was developed for a healthy subject. Using geometrical data acquired by echo-Doppler, a two-dimensional model of the chamber of aortic sinus valsalva and aortic root was created. Systolic ventricular and aortic pressures were applied as boundary conditions computationally. These pressures were the initial physical conditions applied to the model to predict valve deformation and changes in hemodynamics. They were the clinically measured brachial pressures plus differences between brachial, central and left ventricular pressures. Echocardiographic imaging was also used to acquire different ejection times, necessary for pressure waveform equations of blood flow during exercise. A fluid-structure interaction simulation was performed, using an arbitrary Lagrangian-Eulerian mesh. During exercise, peak vorticity increased by 14.8%, peak shear rate by 15.8%, peak cell Reynolds number by 20%, peak leaflet tip velocity increased by 47% and the blood velocity increased by 3% through the leaflets, whereas full opening time decreased by 11%. Our results show that numerical methods can be combined with clinical measurements to provide good estimates of patient-specific hemodynamics at different heart rates.}, } @article {pmid24501132, year = {2014}, author = {Staaf, DJ and Gilly, WF and Denny, MW}, title = {Aperture effects in squid jet propulsion.}, journal = {The Journal of experimental biology}, volume = {217}, number = {Pt 9}, pages = {1588-1600}, doi = {10.1242/jeb.082271}, pmid = {24501132}, issn = {1477-9145}, mesh = {Animals ; Biomechanical Phenomena ; Decapodiformes/anatomy & histology/*physiology ; Models, Theoretical ; Swimming/*physiology ; }, abstract = {Squid are the largest jet propellers in nature as adults, but as paralarvae they are some of the smallest, faced with the inherent inefficiency of jet propulsion at a low Reynolds number. In this study we describe the behavior and kinematics of locomotion in 1 mm paralarvae of Dosidicus gigas, the smallest squid yet studied. They swim with hop-and-sink behavior and can engage in fast jets by reducing the size of the mantle aperture during the contraction phase of a jetting cycle. We go on to explore the general effects of a variable mantle and funnel aperture in a theoretical model of jet propulsion scaled from the smallest (1 mm mantle length) to the largest (3 m) squid. Aperture reduction during mantle contraction increases propulsive efficiency at all squid sizes, although 1 mm squid still suffer from low efficiency (20%) because of a limited speed of contraction. Efficiency increases to a peak of 40% for 1 cm squid, then slowly declines. Squid larger than 6 cm must either reduce contraction speed or increase aperture size to maintain stress within maximal muscle tolerance. Ecological pressure to maintain maximum velocity may lead them to increase aperture size, which reduces efficiency. This effect might be ameliorated by nonaxial flow during the refill phase of the cycle. Our model's predictions highlight areas for future empirical work, and emphasize the existence of complex behavioral options for maximizing efficiency at both very small and large sizes.}, } @article {pmid24500609, year = {2014}, author = {Dhital, S and Dolan, G and Stokes, JR and Gidley, MJ}, title = {Enzymatic hydrolysis of starch in the presence of cereal soluble fibre polysaccharides.}, journal = {Food & function}, volume = {5}, number = {3}, pages = {579-586}, doi = {10.1039/c3fo60506j}, pmid = {24500609}, issn = {2042-650X}, mesh = {Animals ; Biocatalysis ; Dietary Fiber/*analysis/metabolism ; Digestion ; Glucan 1,4-alpha-Glucosidase/*chemistry ; Hydrolysis ; Pancreatin/*chemistry ; Polysaccharides/*chemistry/metabolism ; Starch/*chemistry/metabolism ; Swine ; Viscosity ; Zea mays/*chemistry/metabolism ; }, abstract = {The in vitro amylolysis of both granular and cooked maize starch and the diffusion of glucose in the presence of 1% and 2% cereal soluble fibre polysaccharides (arabinoxylan and mixed linkage beta-glucan) were studied at various levels of shear mixing in order to identify potential molecular mechanisms underlying observed glycemia-reducing effects of soluble fibres in vivo. The presence of soluble fibres increased viscosity by ca. 10× and 100× for 1% and 2% concentrations respectively. Despite this large difference in viscosity, measured digestion and mass transfer coefficients were only reduced by a factor of 1.5 to 2.5 at the same mixing speed. In contrast, introduction of mixing in the digesting and diffusing medium significantly increased the rate of amylolytic starch digestion and mass transfer of glucose. This effect is such that mixing at high speeds negates the hindering effect of the 100× increased viscosity imparted by the presence of 2% soluble fibre; this is essentially captured by the Reynolds number (the ratio of inertial and viscous forces) that defines the flow kinematics. The modest reduction of in vitro starch hydrolysis and glucose diffusion at increased viscosity suggests that the established benefits of soluble fibres on post-prandial glycaemia, in terms of attenuation of the overall rate and extent of dietary starch conversion to blood glucose, are not primarily due to a direct effect of viscosity. Alternative hypotheses are proposed based on gastric emptying, restriction of turbulent flow, and/or stimulation of mucus turnover.}, } @article {pmid24483567, year = {2013}, author = {Dallas, V and Alexakis, A}, title = {Symmetry breaking of decaying magnetohydrodynamic Taylor-Green flows and consequences for universality.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {88}, number = {6}, pages = {063017}, doi = {10.1103/PhysRevE.88.063017}, pmid = {24483567}, issn = {1550-2376}, abstract = {We investigate the evolution and stability of a decaying magnetohydrodynamic Taylor-Green flow, using pseudospectral simulations with resolutions up to 2048(3). The chosen flow has been shown to result in a steep total energy spectrum with power law behavior k(-2). We study the symmetry breaking of this flow by exciting perturbations of different amplitudes. It is shown that for any finite amplitude perturbation there is a high enough Reynolds number for which the perturbation will grow enough at the peak of dissipation rate resulting in a nonlinear feedback into the flow and subsequently break the Taylor-Green symmetries. In particular, we show that symmetry breaking at large scales occurs if the amplitude of the perturbation is σ(crit)∼Re(-1) and at small scales occurs if σ(crit)∼Re(-3/2). This symmetry breaking modifies the scaling laws of the energy spectra at the peak of dissipation rate away from the k(-2) scaling and towards the classical k(-5/3) and k(-3/2) power laws.}, } @article {pmid24483558, year = {2013}, author = {Vosskuhle, M and Lévêque, E and Wilkinson, M and Pumir, A}, title = {Multiple collisions in turbulent flows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {88}, number = {6}, pages = {063008}, doi = {10.1103/PhysRevE.88.063008}, pmid = {24483558}, issn = {1550-2376}, abstract = {In turbulent suspensions, collision rates determine how rapidly particles coalesce or react with each other. To determine the collision rate, many numerical studies rely on the ghost collision approximation (GCA), which simply records how often pairs of point particles come within a threshold distance. In many applications, the suspended particles stick (or in the case of liquid droplets, coalesce) upon collision, and it is the frequency of first contact which is of interest. If a pair of "ghost" particles undergoes multiple collisions, the GCA may overestimate the true collision rate. Here, using fully resolved direct numerical simulations of turbulent flows at moderate Reynolds number (Re(λ)=130), we investigate the prevalence and properties of multiple collisions. We find the probability P(N(c)) for a given pair of ghost particles to collide N(c) times to be of the form P(N(c))=βα(N(c)) for N(c)>1, where α and β are coefficients which depend upon the particle inertia. We also investigate the statistics of the times that ghost particles remain in contact. We show that the probability density function of the contact time is different for the first collision. The difference is explained by the effect of caustics in the phase space of the suspended particles. We demonstrate that, as a result of multiple collisions, the GCA leads to a small, but systematic overestimate of the collision rate, which is of the order of ∼15% when the particle inertia is small, and slowly decreases when inertia increases.}, } @article {pmid24483556, year = {2013}, author = {Chen, P}, title = {Dynamics of finite-symmetry and general-shaped objects under shear and shear alignment of uniaxial objects at finite temperatures.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {88}, number = {6}, pages = {063006}, doi = {10.1103/PhysRevE.88.063006}, pmid = {24483556}, issn = {1550-2376}, abstract = {We prove that, for an object with a finitefold rotational symmetry (except for a twofold one) around an axis and mirror symmetries (such as a square rod or pentagonal slab, etc.), dynamics of the symmetry axis in low Reynolds number shear flow exactly follows the same form as that of a uniaxial object (e.g., a circular rod or symmetric ellipsoid) as the so-called Jeffery orbits. We use the formulation in which the dynamics of the rigid body follows first-order ordinary differential equations in time [Phys. Rev. E 84, 056309 (2011)]. Interaction between the object and the shear flow enters through a set of scalar coefficients, and the flow field does not need to be solved dynamically. Results of numerical simulations for general-shaped objects also are discussed. In the second part, Brownian dynamics of a uniaxial object is studied numerically. With D as the rotational diffusion constant, α as a parameter characterizing the aspect ratio, and γ as the shear rate, the object starts to align with the flow when the value of D/(γα) decreases near 1. At large α (the long object limit), the results suggest much lower flow alignment when D/(γα)>1.}, } @article {pmid24481172, year = {2014}, author = {Xi, J and Si, X and Longest, W}, title = {Electrostatic charge effects on pharmaceutical aerosol deposition in human nasal-laryngeal airways.}, journal = {Pharmaceutics}, volume = {6}, number = {1}, pages = {26-35}, pmid = {24481172}, issn = {1999-4923}, abstract = {Electrostatic charging occurs in most aerosol generation processes and can significantly influence subsequent particle deposition rates and patterns in the respiratory tract through the image and space forces. The behavior of inhaled aerosols with charge is expected to be most affected in the upper airways, where particles come in close proximity to the narrow turbinate surface, and before charge dissipation occurs as a result of high humidity. The objective of this study was to quantitatively evaluate the deposition of charged aerosols in an MRI-based nasal-laryngeal airway model. Particle sizes of 5 nm-30 µm and charge levels ranging from neutralized to ten times the saturation limit were considered. A well-validated low Reynolds number (LRN) k-ω turbulence model and a discrete Lagrangian tracking approach that accounted for electrostatic image force were employed to simulate the nasal airflow and aerosol dynamics. For ultrafine aerosols, electrostatic charge was observed to exert a discernible but insignificant effect. In contrast, remarkably enhanced depositions were observed for micrometer particles with charge, which could be one order of magnitude larger than no-charge depositions. The deposition hot spots shifted towards the anterior part of the upper airway as the charge level increased. Results of this study have important implications for evaluating nasal drug delivery devices and for assessing doses received from pollutants, which often carry a certain level of electric charges.}, } @article {pmid24477611, year = {2014}, author = {Holden, D and Socha, JJ and Cardwell, ND and Vlachos, PP}, title = {Aerodynamics of the flying snake Chrysopelea paradisi: how a bluff body cross-sectional shape contributes to gliding performance.}, journal = {The Journal of experimental biology}, volume = {217}, number = {Pt 3}, pages = {382-394}, doi = {10.1242/jeb.090902}, pmid = {24477611}, issn = {1477-9145}, mesh = {Animals ; Biomechanical Phenomena ; Colubridae/anatomy & histology/*physiology ; *Flight, Animal ; Rheology ; }, abstract = {A prominent feature of gliding flight in snakes of the genus Chrysopelea is the unique cross-sectional shape of the body, which acts as the lifting surface in the absence of wings. When gliding, the flying snake Chrysopelea paradisi morphs its circular cross-section into a triangular shape by splaying its ribs and flattening its body in the dorsoventral axis, forming a geometry with fore-aft symmetry and a thick profile. Here, we aimed to understand the aerodynamic properties of the snake's cross-sectional shape to determine its contribution to gliding at low Reynolds numbers. We used a straight physical model in a water tunnel to isolate the effects of 2D shape, analogously to studying the profile of an airfoil of a more typical flyer. Force measurements and time-resolved (TR) digital particle image velocimetry (DPIV) were used to determine lift and drag coefficients, wake dynamics and vortex-shedding characteristics of the shape across a behaviorally relevant range of Reynolds numbers and angles of attack. The snake's cross-sectional shape produced a maximum lift coefficient of 1.9 and maximum lift-to-drag ratio of 2.7, maintained increases in lift up to 35 deg, and exhibited two distinctly different vortex-shedding modes. Within the measured Reynolds number regime (Re=3000-15,000), this geometry generated significantly larger maximum lift coefficients than many other shapes including bluff bodies, thick airfoils, symmetric airfoils and circular arc airfoils. In addition, the snake's shape exhibited a gentle stall region that maintained relatively high lift production even up to the highest angle of attack tested (60 deg). Overall, the cross-sectional geometry of the flying snake demonstrated robust aerodynamic behavior by maintaining significant lift production and near-maximum lift-to-drag ratios over a wide range of parameters. These aerodynamic characteristics help to explain how the snake can glide at steep angles and over a wide range of angles of attack, but more complex models that account for 3D effects and the dynamic movements of aerial undulation are required to fully understand the gliding performance of flying snakes.}, } @article {pmid24476281, year = {2013}, author = {Li, CK and Ryutov, DD and Hu, SX and Rosenberg, MJ and Zylstra, AB and Séguin, FH and Frenje, JA and Casey, DT and Johnson, MG and Manuel, MJ and Rinderknecht, HG and Petrasso, RD and Amendt, PA and Park, HS and Remington, BA and Wilks, SC and Betti, R and Froula, DH and Knauer, JP and Meyerhofer, DD and Drake, RP and Kuranz, CC and Young, R and Koenig, M}, title = {Structure and dynamics of colliding plasma jets.}, journal = {Physical review letters}, volume = {111}, number = {23}, pages = {235003}, doi = {10.1103/PhysRevLett.111.235003}, pmid = {24476281}, issn = {1079-7114}, abstract = {Monoenergetic-proton radiographs of laser-generated, high-Mach-number plasma jets colliding at various angles shed light on the structures and dynamics of these collisions. The observations compare favorably with results from 2D hydrodynamic simulations of multistream plasma jets, and also with results from an analytic treatment of electron flow and magnetic field advection. In collisions of two noncollinear jets, the observed flow structure is similar to the analytic model's prediction of a characteristic feature with a narrow structure pointing in one direction and a much thicker one pointing in the opposite direction. Spontaneous magnetic fields, largely azimuthal around the colliding jets and generated by the well-known ∇T(e)×∇n(e) Biermann battery effect near the periphery of the laser spots, are demonstrated to be "frozen in" the plasma (due to high magnetic Reynolds number Re(M)∼5×10(4)) and advected along the jet streamlines of the electron flow. These studies provide novel insight into the interactions and dynamics of colliding plasma jets.}, } @article {pmid24461848, year = {2014}, author = {Dalili, A and Chandra, S and Mostaghimi, J and Fan, HT and Simmer, JC}, title = {Formation of liquid sheets by deposition of droplets on a surface.}, journal = {Journal of colloid and interface science}, volume = {418}, number = {}, pages = {292-299}, doi = {10.1016/j.jcis.2013.12.033}, pmid = {24461848}, issn = {1095-7103}, abstract = {Experiments were done to observe the coalescence of highly viscous liquid droplets (87 wt% glycerin-in-water solutions) deposited onto a flat, solid steel plate. Droplets were deposited sequentially in straight lines or square droplet arrays. Droplet center-to-center distance was varied and the final dimensions of lines and sheets measured from photographs. When overlapping droplets were deposited surface tension forces pulled impacting droplets towards those already on the surface, a phenomena known as drawback. A dimensionless drawback index, quantifying the extent of droplet displacement, was calculated from experimental measurements for different values of droplet overlap. At large overlaps droplets deposited in a line or square array coalesced to form a circular film. When the droplet center-to-center distance increased, leading to less interaction, long, thin lines and square sheets were formed. As overlap was further decreased lines and sheets became discontinuous. A simple model was developed to predict the conditions under which rupture occurred. The lowest droplet overlap ratio (defined as droplet overlap distance divided by droplet spread diameter) at which a continuous liquid film could be formed was λ=0.293. At large overlap ratios (λ>0.6) droplets deposited in a square array formed a circular film. The minimum thickness of a continuous film formed by coalescence of droplets was shown to vary from 5% to 70% of the initial droplet diameter while increasing impact Weber and Reynolds number reduced the film thickness.}, } @article {pmid24437742, year = {2014}, author = {Reyt, I and Bailliet, H and Valière, JC}, title = {Experimental investigation of acoustic streaming in a cylindrical wave guide up to high streaming Reynolds numbers.}, journal = {The Journal of the Acoustical Society of America}, volume = {135}, number = {1}, pages = {27-37}, doi = {10.1121/1.4837855}, pmid = {24437742}, issn = {1520-8524}, mesh = {*Acoustics ; Laser-Doppler Flowmetry ; *Models, Theoretical ; Motion ; Nonlinear Dynamics ; Pressure ; *Signal Processing, Computer-Assisted ; *Sound ; Sound Spectrography ; Time Factors ; }, abstract = {Measurements of streaming velocity are performed by means of Laser Doppler Velocimetry and Particle Image Velociimetry in an experimental apparatus consisting of a cylindrical waveguide having one loudspeaker at each end for high intensity sound levels. The case of high nonlinear Reynolds number ReNL is particularly investigated. The variation of axial streaming velocity with respect to the axial and to the transverse coordinates are compared to available Rayleigh streaming theory. As expected, the measured streaming velocity agrees well with the Rayleigh streaming theory for small ReNL but deviates significantly from such predictions for high ReNL. When the nonlinear Reynolds number is increased, the outer centerline axial streaming velocity gets distorted towards the acoustic velocity nodes until counter-rotating additional vortices are generated near the acoustic velocity antinodes. This kind of behavior is followed by outer streaming cells only and measurements in the near wall region show that inner streaming vortices are less affected by this substantial evolution of fast streaming pattern. Measurements of the transient evolution of streaming velocity provide an additional insight into the evolution of fast streaming.}, } @article {pmid24435099, year = {2014}, author = {Williams, BJ and Anand, SV and Rajagopalan, J and Saif, MT}, title = {A self-propelled biohybrid swimmer at low Reynolds number.}, journal = {Nature communications}, volume = {5}, number = {}, pages = {3081}, doi = {10.1038/ncomms4081}, pmid = {24435099}, issn = {2041-1723}, mesh = {Animals ; Biocompatible Materials ; Biomechanical Phenomena/physiology ; Cell Movement/*physiology ; Cells, Cultured ; *Dimethylpolysiloxanes ; Fibroblasts/cytology/physiology ; *Hydrodynamics ; *Models, Biological ; Myocytes, Cardiac/cytology/*physiology ; Rats ; Rats, Sprague-Dawley ; }, abstract = {Many microorganisms, including spermatozoa and forms of bacteria, oscillate or twist a hair-like flagella to swim. At this small scale, where locomotion is challenged by large viscous drag, organisms must generate time-irreversible deformations of their flagella to produce thrust. To date, there is no demonstration of a self propelled, synthetic flagellar swimmer operating at low Reynolds number. Here we report a microscale, biohybrid swimmer enabled by a unique fabrication process and a supporting slender-body hydrodynamics model. The swimmer consists of a polydimethylsiloxane filament with a short, rigid head and a long, slender tail on which cardiomyocytes are selectively cultured. The cardiomyocytes contract and deform the filament to propel the swimmer at 5-10 μm s(-1), consistent with model predictions. We then demonstrate a two-tailed swimmer swimming at 81 μm s(-1). This small-scale, elementary biohybrid swimmer can serve as a platform for more complex biological machines.}, } @article {pmid24430733, year = {2014}, author = {Boyd, DA and Adams, AA and Daniele, MA and Ligler, FS}, title = {Microfluidic fabrication of polymeric and biohybrid fibers with predesigned size and shape.}, journal = {Journal of visualized experiments : JoVE}, volume = {}, number = {83}, pages = {e50958}, pmid = {24430733}, issn = {1940-087X}, mesh = {Click Chemistry ; Hydrogels/chemistry ; Hydrophobic and Hydrophilic Interactions ; Liquid Crystals/chemistry ; Microfluidic Analytical Techniques/instrumentation/*methods ; Photochemical Processes ; Polymers/*chemistry ; Viscosity ; }, abstract = {A "sheath" fluid passing through a microfluidic channel at low Reynolds number can be directed around another "core" stream and used to dictate the shape as well as the diameter of a core stream. Grooves in the top and bottom of a microfluidic channel were designed to direct the sheath fluid and shape the core fluid. By matching the viscosity and hydrophilicity of the sheath and core fluids, the interfacial effects are minimized and complex fluid shapes can be formed. Controlling the relative flow rates of the sheath and core fluids determines the cross-sectional area of the core fluid. Fibers have been produced with sizes ranging from 300 nm to ~1 mm, and fiber cross-sections can be round, flat, square, or complex as in the case with double anchor fibers. Polymerization of the core fluid downstream from the shaping region solidifies the fibers. Photoinitiated click chemistries are well suited for rapid polymerization of the core fluid by irradiation with ultraviolet light. Fibers with a wide variety of shapes have been produced from a list of polymers including liquid crystals, poly(methylmethacrylate), thiol-ene and thiol-yne resins, polyethylene glycol, and hydrogel derivatives. Minimal shear during the shaping process and mild polymerization conditions also makes the fabrication process well suited for encapsulation of cells and other biological components.}, } @article {pmid24414062, year = {2014}, author = {Bermejo, J and Benito, Y and Alhama, M and Yotti, R and Martínez-Legazpi, P and Del Villar, CP and Pérez-David, E and González-Mansilla, A and Santa-Marta, C and Barrio, A and Fernández-Avilés, F and Del Álamo, JC}, title = {Intraventricular vortex properties in nonischemic dilated cardiomyopathy.}, journal = {American journal of physiology. Heart and circulatory physiology}, volume = {306}, number = {5}, pages = {H718-29}, pmid = {24414062}, issn = {1522-1539}, support = {1-R21-HL-108268-01/HL/NHLBI NIH HHS/United States ; }, mesh = {Adult ; Aged ; Biomechanical Phenomena ; Cardiomyopathy, Dilated/diagnostic imaging/*physiopathology ; Case-Control Studies ; Echocardiography, Doppler, Color ; Echocardiography, Doppler, Pulsed ; Female ; Heart Ventricles/diagnostic imaging/*physiopathology ; Humans ; Image Interpretation, Computer-Assisted ; Magnetic Resonance Imaging ; Male ; Middle Aged ; Models, Cardiovascular ; Predictive Value of Tests ; Stroke Volume ; Time Factors ; *Ventricular Function, Left ; Ventricular Pressure ; Ventricular Remodeling ; }, abstract = {Vortices may have a role in optimizing the mechanical efficiency and blood mixing of the left ventricle (LV). We aimed to characterize the size, position, circulation, and kinetic energy (KE) of LV main vortex cores in patients with nonischemic dilated cardiomyopathy (NIDCM) and analyze their physiological correlates. We used digital processing of color-Doppler images to study flow evolution in 61 patients with NIDCM and 61 age-matched control subjects. Vortex features showed a characteristic biphasic temporal course during diastole. Because late filling contributed significantly to flow entrainment, vortex KE reached its maximum at the time of the peak A wave, storing 26 ± 20% of total KE delivered by inflow (range: 1-74%). Patients with NIDCM showed larger and stronger vortices than control subjects (circulation: 0.008 ± 0.007 vs. 0.006 ± 0.005 m(2)/s, respectively, P = 0.02; KE: 7 ± 8 vs. 5 ± 5 mJ/m, P = 0.04), even when corrected for LV size. This helped confining the filling jet in the dilated ventricle. The vortex Reynolds number was also higher in the NIDCM group. By multivariate analysis, vortex KE was related to the KE generated by inflow and to chamber short-axis diameter. In 21 patients studied head to head, Doppler measurements of circulation and KE closely correlated with phase-contract magnetic resonance values (intraclass correlation coefficient = 0.82 and 0.76, respectively). Thus, the biphasic nature of filling determines normal vortex physiology. Vortex formation is exaggerated in patients with NIDCM due to chamber remodeling, and enlarged vortices are helpful for ameliorating convective pressure losses and facilitating transport. These findings can be accurately studied using ultrasound.}, } @article {pmid24404073, year = {2013}, author = {Yaginuma, T and Oliveira, MS and Lima, R and Ishikawa, T and Yamaguchi, T}, title = {Human red blood cell behavior under homogeneous extensional flow in a hyperbolic-shaped microchannel.}, journal = {Biomicrofluidics}, volume = {7}, number = {5}, pages = {54110}, pmid = {24404073}, issn = {1932-1058}, abstract = {It is well known that certain pathological conditions result in a decrease of red blood cells (RBCs) deformability and subsequently can significantly alter the blood flow in microcirculation, which may block capillaries and cause ischemia in the tissues. Microfluidic systems able to obtain reliable quantitative measurements of RBC deformability hold the key to understand and diagnose RBC related diseases. In this work, a microfluidic system composed of a microchannel with a hyperbolic-shaped contraction followed by a sudden expansion is presented. We provide a detailed quantitative description of the degree of deformation of human RBCs under a controlled homogeneous extensional flow field. We measured the deformation index (DI) as well as the velocity of the RBCs travelling along the centerline of the channel for four different flow rates and analyze the impact of the particle Reynolds number. The results show that human RBC deformation tends to reach a plateau value in the region of constant extensional rate, the value of which depends on the extension rate. Additionally, we observe that the presence of a sudden expansion downstream of the hyperbolic contraction modifies the spatial distribution of cells and substantially increases the cell free layer (CFL) downstream of the expansion plane similarly to what is seen in other expansion flows. Beyond a certain value of flow rate, there is only a weak effect of inlet flow rates on the enhancement of the downstream CFL. These in vitro experiments show the potential of using microfluidic systems with hyperbolic-shaped microchannels both for the separation of the RBCs from plasma and to assess changes in RBC deformability in physiological and pathological situations for clinical purposes. However, the selection of the geometry and the identification of the most suitable region to evaluate the changes on the RBC deformability under extensional flows are crucial if microfluidics is to be used as an in vitro clinical methodology to detect circulatory diseases.}, } @article {pmid24404068, year = {2013}, author = {Mbaye, S and Séchet, P and Pignon, F and Martins, JM}, title = {Influence of hydrodynamics on the growth kinetics of glass-adhering Pseudomonas putida cells through a parallel plate flow chamber.}, journal = {Biomicrofluidics}, volume = {7}, number = {5}, pages = {54105}, pmid = {24404068}, issn = {1932-1058}, abstract = {The objective of this work was to investigate the influence of hydrodynamics on the growth kinetics of surface-adhering Pseudomonas putida cells. The results showed in particular that under non substrate-limiting conditions, the early step of bacterial apparent growth rate is lower than those measured with suspended cells. Contrary to previously cited authors which explain this behavior to the different adhesive properties of the "daughter"-cells (which makes more probable the detachment of these daughter-cells), in our experimental conditions, that explanation does not hold and we show a clear dependence of growth kinetics with flow conditions, due to the formation of boundary layer concentration at low Reynolds number. These results revealed that using Monod law in the modeling of biofilm growth in fixed-biomass processes should be performed with care.}, } @article {pmid24404053, year = {2013}, author = {Geislinger, TM and Franke, T}, title = {Sorting of circulating tumor cells (MV3-melanoma) and red blood cells using non-inertial lift.}, journal = {Biomicrofluidics}, volume = {7}, number = {4}, pages = {44120}, pmid = {24404053}, issn = {1932-1058}, abstract = {We demonstrate the method of non-inertial lift induced cell sorting (NILICS), a continuous, passive, and label-free cell sorting approach in a simple single layer microfluidic device at low Reynolds number flow conditions. In the experiments, we exploit the non-inertial lift effect to sort circulating MV3-melanoma cells from red blood cell suspensions at different hematocrits as high as 9%. We analyze the separation process and the influence of hematocrit and volume flow rates. We achieve sorting efficiencies for MV3-cells up to EMV3 = 100% at Hct = 9% and demonstrate cell viability by recultivation of the sorted cells.}, } @article {pmid24399860, year = {2013}, author = {Boghosian, ME and Cassel, KW}, title = {A pressure-gradient mechanism for vortex shedding in constricted channels.}, journal = {Physics of fluids (Woodbury, N.Y. : 1994)}, volume = {25}, number = {12}, pages = {123603}, pmid = {24399860}, issn = {1070-6631}, support = {R01 DK090769/DK/NIDDK NIH HHS/United States ; }, abstract = {Numerical simulations of the unsteady, two-dimensional, incompressible Navier-Stokes equations are performed for a Newtonian fluid in a channel having a symmetric constriction modeled by a two-parameter Gaussian distribution on both channel walls. The Reynolds number based on inlet half-channel height and mean inlet velocity ranges from 1 to 3000. Constriction ratios based on the half-channel height of 0.25, 0.5, and 0.75 are considered. The results show that both the Reynolds number and constriction geometry have a significant effect on the behavior of the post-constriction flow field. The Navier-Stokes solutions are observed to experience a number of bifurcations: steady attached flow, steady separated flow (symmetric and asymmetric), and unsteady vortex shedding downstream of the constriction depending on the Reynolds number and constriction ratio. A sequence of events is described showing how a sustained spatially growing flow instability, reminiscent of a convective instability, leads to the vortex shedding phenomenon via a proposed streamwise pressure-gradient mechanism.}, } @article {pmid24397384, year = {2014}, author = {Dudani, JS and Go, DE and Gossett, DR and Tan, AP and Di Carlo, D}, title = {Mediating millisecond reaction time around particles and cells.}, journal = {Analytical chemistry}, volume = {86}, number = {3}, pages = {1502-1510}, doi = {10.1021/ac402920m}, pmid = {24397384}, issn = {1520-6882}, support = {//Howard Hughes Medical Institute/United States ; }, mesh = {Cell Survival ; Equipment Design ; HeLa Cells ; Humans ; MCF-7 Cells ; Microfluidic Analytical Techniques/instrumentation/*methods ; Permeability ; Staining and Labeling ; Time Factors ; }, abstract = {Precise spatiotemporal control of how particles and cells interact with reagents is critical for numerous laboratory and industrial processes. Novel tools for exerting this control at shorter time scales will enable development of new chemical processes and biomedical assays. Previously, we have developed a generalized approach to manipulate cells and particles across fluid streams termed rapid inertial solution exchange (RInSE), which utilizes inertial lift forces at finite Reynolds number and high Peclet number to transfer particles from an initial solution to another within a millisecond. Here, we apply these principles toward developing a continuous flow microfluidic platform that enables transient chemical treatments of cells and particles (on the order of 1 ms). We also demonstrate how the reactant stream can be employed as a diffusion barrier, preventing adverse reactions between coflowing solutions. In order to demonstrate the utility of the method, we applied it to various operations in molecular biology and automated cell staining including cell permeabilization, fluorescent staining, and molecular delivery to viable cells. We expect this method will enable previously unexplored studies of the dynamics of molecular events, improve uniformity of reactions carried on the surface of beads, and increase uniformity in cell-based assays through automation.}, } @article {pmid24396530, year = {2013}, author = {Feng, X and Ren, Y and Jiang, H}, title = {An effective splitting-and-recombination micromixer with self-rotated contact surface for wide Reynolds number range applications.}, journal = {Biomicrofluidics}, volume = {7}, number = {5}, pages = {54121}, pmid = {24396530}, issn = {1932-1058}, abstract = {It is difficult to mix two liquids on a microfluidic chip because the small dimensions and velocities effectively prevent the turbulence. This paper describes two 2-layer PDMS passive micromixers based on the concept of splitting and recombining the flow that exploits a self-rotated contact surface to increase the concentration gradients to obtain fast and efficient mixing. The designed micromixers were simulated and the mixing performance was assessed. The mixers have shown excellent mixing efficiency over a wide range of Reynolds number. The mixers were reasonably fabricated by multilayer soft lithography, and the experimental measurements were performed to qualify the mixing performance of the realized mixer. The results show that the mixing efficiency for one realized mixer is from 91.8% to 87.7% when the Reynolds number increases from 0.3 to 60, while the corresponding value for another mixer is from 89.4% to 72.9%. It is rather interesting that the main mechanism for the rapid mixing is from diffusion to chaotic advection when the flow rate increases, but the mixing efficiency has not obvious decline. The smart geometry of the mixers with total length of 10.25 mm makes it possible to be integrated with many microfluidic devices for various applications in μ-TAS and Lab-on-a-chip systems.}, } @article {pmid27355040, year = {2014}, author = {Srivastava, N}, title = {MHD Flow of the Micropolar Fluid between Eccentrically Rotating Disks.}, journal = {International scholarly research notices}, volume = {2014}, number = {}, pages = {317075}, pmid = {27355040}, issn = {2356-7872}, abstract = {This analytical investigation examines the magnetohydrodynamic flow problem of an incompressible micropolar fluid between the two eccentrically placed disks. Employing suitable transformations, the flow governing partial differential equations is reduced to ordinary differential equations. An exact solution representing the different flow characteristic of micropolar fluid has been derived by solving the ordinary differential equations. Analysis of the flow characteristics of the micropolar fluid has been done graphically by varying the Reynolds number and the Hartmann number. This analysis has been carried out for the weak and strong interactions.}, } @article {pmid24353347, year = {2012}, author = {Deng, M and Li, X and Liang, H and Caswell, B and Karniadakis, GE}, title = {Simulation and modelling of slip flow over surfaces grafted with polymer brushes and glycocalyx fibres.}, journal = {Journal of fluid mechanics}, volume = {711}, number = {}, pages = {}, pmid = {24353347}, issn = {0022-1120}, support = {R01 HL094270/HL/NHLBI NIH HHS/United States ; }, abstract = {Fabrication of functionalized surfaces using polymer brushes is a relatively simple process and parallels the presence of glycocalyx filaments coating the luminal surface of our vasculature. In this paper, we perform atomistic-like simulations based on dissipative particle dynamics (DPD) to study both polymer brushes and glycocalyx filaments subject to shear flow, and we apply mean-field theory to extract useful scaling arguments on their response. For polymer brushes, a weak shear flow has no effect on the brush density profile or its height, while the slip length is independent of the shear rate and is of the order of the brush mesh size as a result of screening by hydrodynamic interactions. However, for strong shear flow, the polymer brush is penetrated deeper and is deformed, with a corresponding decrease of the brush height and an increase of the slip length. The transition from the weak to the strong shear regime can be described by a simple 'blob' argument, leading to the scaling γ̇0 ∝ σ[3/2], where γ̇0 is the critical transition shear rate and σ is the grafting density. Furthermore, in the strong shear regime, we observe a cyclic dynamic motion of individual polymers, causing a reversal in the direction of surface flow. To study the glycocalyx layer, we first assume a homogeneous flow that ignores the discrete effects of blood cells, and we simulate microchannel flows at different flow rates. Surprisingly, we find that, at low Reynolds number, the slip length decreases with the mean flow velocity, unlike the behaviour of polymer brushes, for which the slip length remains constant under similar conditions. (The slip length and brush height are measured with respect to polymer mesh size and polymer contour length, respectively.) We also performed additional DPD simulations of blood flow in a tube with walls having a glycocalyx layer and with the deformable red blood cells modelled accurately at the spectrin level. In this case, a plasma cell-free layer is formed, with thickness more than three times the glycocalyx layer. We then find our scaling arguments based on the homogeneous flow assumption to be valid for this physiologically correct case as well. Taken together, our findings point to the opposing roles of conformational entropy and bending rigidity - dominant effects for the brush and glycocalyx, respectively - which, in turn, lead to different flow characteristics, despite the apparent similarity of the two systems.}, } @article {pmid24329356, year = {2013}, author = {Cerbus, RT and Goldburg, WI}, title = {Information content of turbulence.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {88}, number = {5}, pages = {053012}, doi = {10.1103/PhysRevE.88.053012}, pmid = {24329356}, issn = {1550-2376}, abstract = {We treat a turbulent velocity field as a message in the same way as a book or a picture. All messages can be described by their entropy per symbol h, defined as in Shannon's theory of communication. In a turbulent flow, as the Reynolds number Re increases, more correlated degrees of freedom are excited and participate in the turbulent cascade. Experiments in a turbulent soap film suggest that the spatial entropy density h is a decreasing function of Re, namely h[proportionality]-logRe + const. In the logistic map, also analyzed here, increasing the control parameter r increases h. A modified logistic map with additional coupling to past iterations suggests the significance of correlations.}, } @article {pmid24329355, year = {2013}, author = {Favier, B and Proctor, MR}, title = {Kinematic dynamo action in square and hexagonal patterns.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {88}, number = {5}, pages = {053011}, doi = {10.1103/PhysRevE.88.053011}, pmid = {24329355}, issn = {1550-2376}, abstract = {We consider kinematic dynamo action in rapidly rotating Boussinesq convection just above onset. The velocity is constrained to have either a square or a hexagonal pattern. For the square pattern, large-scale dynamo action is observed at onset, with most of the magnetic energy being contained in the horizontally averaged component. As the magnetic Reynolds number increases, small-scale dynamo action becomes possible, reducing the overall growth rate of the dynamo. For the hexagonal pattern, the breaking of symmetry between up and down flows results in an effective pumping velocity. For intermediate rotation rates, this additional effect can prevent the growth of any mean-field dynamo, so that only a small-scale dynamo is eventually possible at large enough magnetic Reynolds number. For very large rotation rates, this pumping term becomes negligible, and the dynamo properties of square and hexagonal patterns are qualitatively similar. These results hold for both perfectly conducting and infinite magnetic permeability boundary conditions.}, } @article {pmid24329354, year = {2013}, author = {Guervilly, C and Wood, TS and Brummell, NH}, title = {Effect of metallic walls on dynamos generated by laminar boundary-driven flow in a spherical domain.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {88}, number = {5}, pages = {053010}, doi = {10.1103/PhysRevE.88.053010}, pmid = {24329354}, issn = {1550-2376}, abstract = {We present a numerical study of dynamo action in a conducting fluid encased in a metallic spherical shell. Motions in the fluid are driven by differential rotation of the outer metallic shell, which we refer to as "the wall." The two hemispheres of the wall are held in counter-rotation, producing a steady, axisymmetric interior flow consisting of differential rotation and a two-cell meridional circulation with radial inflow in the equatorial plane. From previous studies, this type of flow is known to maintain a stationary equatorial dipole by dynamo action if the magnetic Reynolds number is larger than about 300 and if the outer boundary is electrically insulating. We vary independently the thickness, electrical conductivity, and magnetic permeability of the wall to determine their effect on the dynamo action. The main results are the following: (a) Increasing the conductivity of the wall hinders the dynamo by allowing eddy currents within the wall, which are induced by the relative motion of the equatorial dipole field and the wall. This processes can be viewed as a skin effect or, equivalently, as the tearing apart of the dipole by the differential rotation of the wall, to which the field lines are anchored by high conductivity. (b) Increasing the magnetic permeability of the wall favors dynamo action by constraining the magnetic field lines in the fluid to be normal to the wall, thereby decoupling the fluid from any induction in the wall. (c) Decreasing the wall thickness limits the amplitude of the eddy currents, and is therefore favorable for dynamo action, provided that the wall is thinner than the skin depth. We explicitly demonstrate these effects of the wall properties on the dynamo field by deriving an effective boundary condition in the limit of vanishing wall thickness.}, } @article {pmid24329353, year = {2013}, author = {Mizuta, A and Matsumoto, T and Toh, S}, title = {Transition of the scaling law in inverse energy cascade range caused by a nonlocal excitation of coherent structures observed in two-dimensional turbulent fields.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {88}, number = {5}, pages = {053009}, doi = {10.1103/PhysRevE.88.053009}, pmid = {24329353}, issn = {1550-2376}, abstract = {We numerically investigate the inverse energy cascade range of two-dimensional Navier-Stokes turbulence. Our focus is on the universality of the Kolmogorov's phenomenology. In our direct numerical simulations, two types of forcing processes, the random forcing and the deterministic forcing, are employed besides the systematically varied numerical parameters. We first calculate the two-dimensional Navier-Stokes equations and confirm that results in the quasi steady state are consistent with the classical phenomenology for both types of forcing processes. It is also found that the difference in forcing process appears after the inverse energy cascade range reaches the system size; the dipole coherent vortices emerge and grow only when the random forcing is adopted. Then we add a large-scale drag term to the Navier-Stokes equations to obtain the statistically stationary state. When the random forcing is used, the scaling exponent of the energy spectrum in the stationary state starts to differ from the predicted -5/3 in the inverse energy cascade range as the infrared Reynolds number Re(d) increases, where Re(d) is defined as k(f)/k(d) with the forcing wave number k(f) and the large-scale drag wave number k(d). That can be interpreted as a transition phenomenon in which the local maximum vorticity grows like an order parameter caused by excitation of strong coherent vortices. Strong coherent vortices emerge and grow after the quasi steady state and destroy the scaling law when Re(d) is over a critical value. These coherent vortices are not due to the finite-size effect, unlike the dipole coherent vortices. On the other hand, when the deterministic forcing is adopted, strong coherent vortices are hardly seen and the -5/3 scaling law holds independently of Re(d). We examine the cases of the combination of both types of forcing processes and find that formation of such coherent vortices is sensitive to the mechanism of the external forcing process as well as the numerical parameters. Several types of large-scale drag terms are also tested and their insignificant influence on these qualitative properties is revealed.}, } @article {pmid24329352, year = {2013}, author = {Huang, W and Liu, H and Wang, F and Wu, J and Zhang, HP}, title = {Experimetal study of a freely falling plate with an inhomogeneous mass distribution.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {88}, number = {5}, pages = {053008}, doi = {10.1103/PhysRevE.88.053008}, pmid = {24329352}, issn = {1550-2376}, abstract = {A homogeneous thin plate often flutters while falling through a fluid under gravity. The center of gravity of the plate moves back-and-forth horizontally and the plate tilting angle oscillates symmetrically from the horizontal. Here we show that such a scenario is qualitatively changed for a plate with noncoinciding centers of gravity and buoyancy due to an inhomogeneous mass distribution. Mismatch of the centers causes an external torque that breaks the symmetry of rotational motion, shifts the mean tilting position from the horizontal, and leads to a net horizontal plate displacement. In laboratory experiments with a Reynolds number around 1500, we found that the net horizontal displacement scales linearly with the separation between the centers up to a critical value, beyond which the plate falls vertically in an edge-on configuration with the heavier side downward. Experimental results are compared to predictions of a quasi-steady numerical model. Our work demonstrates that motion of freely moving objects in a fluid depends sensitively on external torques, which potentially can be used as an effective control method.}, } @article {pmid24329346, year = {2013}, author = {Samanta, A}, title = {Shear wave instability for electrified falling films.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {88}, number = {5}, pages = {053002}, doi = {10.1103/PhysRevE.88.053002}, pmid = {24329346}, issn = {1550-2376}, abstract = {The effect of an electric field on the shear wave instability pertaining to a gravity driven conducting liquid film is studied based on the Chebyshev-Tau method. The shear wave appears at very large values of the Reynolds number when the inclination angle is sufficiently small. The presence of an electric field shows peculiar behavior on the critical Reynolds number corresponding to the shear mode. It suppresses shear wave instability through the amplification of the critical Reynolds number and leads to a nontrivial stabilizing effect when inclination angle B≥3'. On the other hand, the reduction of the critical Reynolds number is found if the inclination angle is further lowered in magnitude.}, } @article {pmid24329198, year = {2013}, author = {Kraft, DJ and Wittkowski, R and ten Hagen, B and Edmond, KV and Pine, DJ and Löwen, H}, title = {Brownian motion and the hydrodynamic friction tensor for colloidal particles of complex shape.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {88}, number = {5}, pages = {050301}, doi = {10.1103/PhysRevE.88.050301}, pmid = {24329198}, issn = {1550-2376}, abstract = {We synthesize colloidal particles with various anisotropic shapes and track their orientationally resolved Brownian trajectories using confocal microscopy. An analysis of appropriate short-time correlation functions provides direct access to the hydrodynamic friction tensor of the particles revealing nontrivial couplings between the translational and rotational degrees of freedom. The results are consistent with calculations of the hydrodynamic friction tensor in the low-Reynolds-number regime for the experimentally determined particle shapes.}, } @article {pmid24312547, year = {2013}, author = {Sagong, W and Jeon, WP and Choi, H}, title = {Hydrodynamic characteristics of the sailfish (Istiophorus platypterus) and swordfish (Xiphias gladius) in gliding postures at their cruise speeds.}, journal = {PloS one}, volume = {8}, number = {12}, pages = {e81323}, pmid = {24312547}, issn = {1932-6203}, mesh = {Animals ; *Hydrodynamics ; Kinetics ; *Movement ; Perciformes/anatomy & histology/*physiology ; *Posture ; Skin/anatomy & histology ; }, abstract = {The sailfish and swordfish are known as the fastest sea animals, reaching their maximum speeds of around 100 km/h. In the present study, we investigate the hydrodynamic characteristics of these fishes in their cruise speeds of about 1 body length per second. We install a taxidermy specimen of each fish in a wind tunnel, and measure the drag on its body and boundary-layer velocity above its body surface at the Reynolds number corresponding to its cruising condition. The drag coefficients of the sailfish and swordfish based on the free-stream velocity and their wetted areas are measured to be 0.0075 and 0.0091, respectively, at their cruising conditions. These drag coefficients are very low and comparable to those of tuna and pike and smaller than those of dogfish and small-size trout. On the other hand, the long bill is one of the most distinguished features of these fishes from other fishes, and we study its role on the ability of drag modification. The drag on the fish without the bill or with an artificially-made shorter one is slightly smaller than that with the original bill, indicating that the bill itself does not contribute to any drag reduction at its cruise speed. From the velocity measurement near the body surface, we find that at the cruise speed flow separation does not occur over the whole body even without the bill, and the boundary layer flow is affected only at the anterior part of the body by the bill.}, } @article {pmid24307870, year = {2013}, author = {Guarendi, AN and Chandy, AJ}, title = {Magnetohydrodynamic simulations of hypersonic flow over a cylinder using axial- and transverse-oriented magnetic dipoles.}, journal = {TheScientificWorldJournal}, volume = {2013}, number = {}, pages = {438381}, doi = {10.1155/2013/438381}, pmid = {24307870}, issn = {1537-744X}, mesh = {*Air Movements ; Computer Simulation ; *Hydrodynamics ; Magnetics ; *Models, Theoretical ; *Spacecraft ; }, abstract = {Numerical simulations of magnetohydrodynamic (MHD) hypersonic flow over a cylinder are presented for axial- and transverse-oriented dipoles with different strengths. ANSYS CFX is used to carry out calculations for steady, laminar flows at a Mach number of 6.1, with a model for electrical conductivity as a function of temperature and pressure. The low magnetic Reynolds number (<<1) calculated based on the velocity and length scales in this problem justifies the quasistatic approximation, which assumes negligible effect of velocity on magnetic fields. Therefore, the governing equations employed in the simulations are the compressible Navier-Stokes and the energy equations with MHD-related source terms such as Lorentz force and Joule dissipation. The results demonstrate the ability of the magnetic field to affect the flowfield around the cylinder, which results in an increase in shock stand-off distance and reduction in overall temperature. Also, it is observed that there is a noticeable decrease in drag with the addition of the magnetic field.}, } @article {pmid24300568, year = {2014}, author = {Tripathi, D and Anwar Bég, O}, title = {Peristaltic propulsion of generalized Burgers' fluids through a non-uniform porous medium: a study of chyme dynamics through the diseased intestine.}, journal = {Mathematical biosciences}, volume = {248}, number = {}, pages = {67-77}, doi = {10.1016/j.mbs.2013.11.006}, pmid = {24300568}, issn = {1879-3134}, mesh = {Biophysical Phenomena ; Body Fluids/physiology ; Elasticity ; Gastrointestinal Contents ; Humans ; Intestinal Diseases/*physiopathology ; Mathematical Concepts ; *Models, Biological ; Peristalsis/*physiology ; Porosity ; Rheology ; Viscosity ; }, abstract = {A mathematical study of the peristaltic flow of complex rheological viscoelastic fluids using the generalized fractional Burgers' model through a non-uniform channel is presented. This model is designed to study the movement of chyme and undigested chyme (biophysical waste materials) through the small intestine to the large intestine. To simulate blockages and impedance of debris generated by cell shedding, infections, adhesions on the wall and undigested material, a drag force porous media model is utilized. This effectively mimicks resistance to chyme percolation generated by solid matrix particles in the regime. The conduit geometry is mathematically simulated as a sinusoidal propagation with linear increment in shape of the bolus along the length of channel. A modified Darcy-Brinkman model is employed to simulate the generalized flows through isotropic, homogenous porous media, a simplified but physically robust approximation to actual clinical situations. To model the rheological properties of chyme, a viscoelastic Burgers' fluid formulation is adopted. The governing equations are simplified by assuming long wavelength and low Reynolds number approximations. Numerical and approximate analytical solutions are obtained with two semi-numerical techniques, namely the homotopy perturbation method and the variational iteration method. Visualization of the results is achieved with Mathematica software. The influence of the dominant hydromechanical and geometric parameters such as fractional viscoelastic parameters, wave number, non-uniformity constant, permeability parameter, and material constants on the peristaltic flow characteristics are depicted graphically.}, } @article {pmid24292011, year = {2014}, author = {Tripathi, D and Bég, OA}, title = {Mathematical modelling of peristaltic propulsion of viscoplastic bio-fluids.}, journal = {Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine}, volume = {228}, number = {1}, pages = {67-88}, doi = {10.1177/0954411913511584}, pmid = {24292011}, issn = {2041-3033}, mesh = {Biomechanical Phenomena/*physiology ; Body Fluids ; Friction ; Humans ; *Models, Biological ; Peristalsis/*physiology ; Pressure ; Rheology/*methods ; Viscosity ; }, abstract = {This article studies theoretically the transportation of rheological viscoplastic fluids through physiological vessels by continuous muscle contraction and relaxation, that is, peristalsis. Both cases of planar and cylindrical physiological vessels are considered. A mathematical model is developed under long wavelength and low Reynolds number approximations. Expressions for axial velocity in core region, axial velocity in plug flow region, volume flow rate and pressure gradient in non-dimensional form are obtained. A comparative study of velocity profiles, pressure distribution, friction force and mechanical efficiency for different viscoplastic liquids is conducted. The influence of width of plug flow region, shear rate strain index and yield stress index on the pressure distribution, friction force and mechanical efficiency is elaborated. The study is relevant to gastric fluid mechanics and also non-Newtonian biomimetic pump hazardous waste systems exploiting peristaltic mechanisms.}, } @article {pmid24260130, year = {2013}, author = {Noreen, S}, title = {Mixed convection peristaltic flow of third order nanofluid with an induced magnetic field.}, journal = {PloS one}, volume = {8}, number = {11}, pages = {e78770}, pmid = {24260130}, issn = {1932-6203}, mesh = {*Magnetic Fields ; *Models, Theoretical ; Nanoparticles/*chemistry ; *Rheology ; }, abstract = {This research is concerned with the peristaltic flow of third order nanofluid in an asymmetric channel. The governing equations of third order nanofluid are modelled in wave frame of reference. Effect of induced magnetic field is considered. Long wavelength and low Reynolds number situation is tackled. Numerical solutions of the governing problem are computed and analyzed. The effects of Brownian motion and thermophoretic diffusion of nano particles are particularly emphasized. Physical quantities such as velocity, pressure rise, temperature, induced magnetic field and concentration distributions are discussed.}, } @article {pmid24237566, year = {2013}, author = {Pushkin, DO and Yeomans, JM}, title = {Fluid mixing by curved trajectories of microswimmers.}, journal = {Physical review letters}, volume = {111}, number = {18}, pages = {188101}, doi = {10.1103/PhysRevLett.111.188101}, pmid = {24237566}, issn = {1079-7114}, mesh = {Chlamydomonas reinhardtii/physiology ; Escherichia coli/physiology ; *Models, Biological ; *Swimming ; }, abstract = {We consider the tracer diffusion D(rr) that arises from the run-and-tumble motion of low Reynolds number swimmers, such as bacteria. Assuming a dilute suspension, where the bacteria move in uncorrelated runs of length λ, we obtain an exact expression for D(rr) for dipolar swimmers in three dimensions, hence explaining the surprising result that this is independent of λ. We compare D(rr) to the contribution to tracer diffusion from entrainment.}, } @article {pmid24229310, year = {2013}, author = {Najafi, A and Raad, SS and Yousefi, R}, title = {Self-propulsion in a low-Reynolds-number fluid confined by two walls of a microchannel.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {88}, number = {4}, pages = {045001}, doi = {10.1103/PhysRevE.88.045001}, pmid = {24229310}, issn = {1550-2376}, abstract = {The problem of hydrodynamic interactions with confining walls is examined for a model of a microswimmer composed of three connected beads. Two parallel walls of a narrow microfluidic channel confine the fluid flow. We show that different trajectories for this linear swimmer emerge because of long-range hydrodynamic interactions with the walls of the channel. The possibility of space-spanning trajectories for this swimmer can potentially introduce it as a candidate for constructing a mixing device for working at the laminar flow conditions in microfluidic channels.}, } @article {pmid24229281, year = {2013}, author = {Paul, MR and Clark, MT and Cross, MC}, title = {Coupled motion of microscale and nanoscale elastic objects in a viscous fluid.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {88}, number = {4}, pages = {043012}, doi = {10.1103/PhysRevE.88.043012}, pmid = {24229281}, issn = {1550-2376}, abstract = {We study the coupled dynamics of two closely spaced micron or nanoscale elastic objects immersed in a viscous fluid. The dynamics of the elastic objects are coupled through the motion of the surrounding viscous fluid. We consider two cases: (i) one object is driven externally by an imposed harmonic actuation force and the second object is passive and (ii) both objects are driven by a Brownian force to yield stochastic dynamics. Using a harmonic oscillator approximation for the elastic objects and the unsteady Stokes equations to describe the fluid dynamics, we develop analytical expressions for the amplitude and phase of the displacement of the oscillating objects. For the case of an imposed actuation we use an impulse in force to determine the resulting dynamics over all frequencies. For the Brownian-driven objects the stochastic dynamics are found using the fluctuation-dissipation theorem. We validate our theoretical expressions by comparison with results from finite-element numerical simulations of the complete fluid-solid interaction problem. Our results yield interesting features in the amplitude and phase of the displacement of the elastic objects due to the fluid motion. We find that the dynamics depend on the separation of the objects, a measure of the mass loading due to the fluid, and the frequency parameter which acts as a frequency-based Reynolds number. Our results are valid over the range of parameters typical of micron and nanoscale elastic objects in fluid. The range of dynamics found can be understood in terms of the interplay between the viscous and potential components of the fluid flow field described by the unsteady Stokes equation for an oscillating cylinder. For small values of the frequency parameter, typical of nanoscale elastic objects, the dynamics are overdamped due to the dominance of viscous forces over inertial forces. For moderate and large values of the frequency parameter, typical of micron-scale elastic objects, we find that the dynamics of the fluid-coupled objects exhibits an interesting mode splitting to yield a bimodal signature in the amplitude-frequency plots. We find that the mode splitting can be described using a normal mode analysis containing only potential fluid interactions between the cylinders.}, } @article {pmid24223445, year = {2013}, author = {Wang, X and Zhang, LT}, title = {Modified Immersed Finite Element Method For Fully-Coupled Fluid-Structure Interations.}, journal = {Computer methods in applied mechanics and engineering}, volume = {267}, number = {}, pages = {}, pmid = {24223445}, issn = {0045-7825}, support = {R01 DC005642/DC/NIDCD NIH HHS/United States ; }, abstract = {In this paper, we develop a "modified" immersed finite element method (mIFEM), a non-boundary-fitted numerical technique, to study fluid-structure interactions. Using this method, we can more precisely capture the solid dynamics by solving the solid governing equation instead of imposing it based on the fluid velocity field as in the original immersed finite element (IFEM). Using the IFEM may lead to severe solid mesh distortion because the solid deformation is been over-estimated, especially for high Reynolds number flows. In the mIFEM, the solid dynamics is solved using appropriate boundary conditions generated from the surrounding fluid, therefore produces more accurate and realistic coupled solutions. We show several 2-D and 3-D testing cases where the mIFEM has a noticeable advantage in handling complicated fluid-structure interactions when the solid behavior dominates the fluid flow.}, } @article {pmid24222752, year = {2013}, author = {Yadav, AS and Bhagoria, JL}, title = {Modeling and simulation of turbulent flows through a solar air heater having square-sectioned transverse rib roughness on the absorber plate.}, journal = {TheScientificWorldJournal}, volume = {2013}, number = {}, pages = {827131}, doi = {10.1155/2013/827131}, pmid = {24222752}, issn = {1537-744X}, mesh = {*Air ; Computer Simulation ; Heating/*instrumentation/methods ; *Hydrodynamics ; *Models, Theoretical ; *Solar Energy ; Thermodynamics ; }, abstract = {Solar air heater is a type of heat exchanger which transforms solar radiation into heat energy. The thermal performance of conventional solar air heater has been found to be poor because of the low convective heat transfer coefficient from the absorber plate to the air. Use of artificial roughness on a surface is an effective technique to enhance the rate of heat transfer. A CFD-based investigation of turbulent flow through a solar air heater roughened with square-sectioned transverse rib roughness has been performed. Three different values of rib-pitch (P) and rib-height (e) have been taken such that the relative roughness pitch (P/e = 14.29) remains constant. The relative roughness height, e/D, varies from 0.021 to 0.06, and the Reynolds number, Re, varies from 3800 to 18,000. The results predicted by CFD show that the average heat transfer, average flow friction, and thermohydraulic performance parameter are strongly dependent on the relative roughness height. A maximum value of thermohydraulic performance parameter has been found to be 1.8 for the range of parameters investigated. Comparisons with previously published work have been performed and found to be in excellent agreement.}, } @article {pmid24194551, year = {2013}, author = {Wilson, LG and Carter, LM and Reece, SE}, title = {High-speed holographic microscopy of malaria parasites reveals ambidextrous flagellar waveforms.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {110}, number = {47}, pages = {18769-18774}, pmid = {24194551}, issn = {1091-6490}, support = {082234MA//Wellcome Trust/United Kingdom ; }, mesh = {Animals ; Axoneme/physiology ; Biomechanical Phenomena ; Flagella/*physiology/*ultrastructure ; Germ Cells/*physiology ; Holography/*methods ; Male ; Microscopy/*methods ; *Models, Biological ; Plasmodium berghei/*cytology ; }, abstract = {Axonemes form the core of eukaryotic flagella and cilia, performing tasks ranging from transporting fluid in developing embryos to the propulsion of sperm. Despite their abundance across the eukaryotic domain, the mechanisms that regulate the beating action of axonemes remain unknown. The flagellar waveforms are 3D in general, but current understanding of how axoneme components interact stems from 2D data; comprehensive measurements of flagellar shape are beyond conventional microscopy. Moreover, current flagellar model systems (e.g., sea urchin, human sperm) contain accessory structures that impose mechanical constraints on movement, obscuring the "native" axoneme behavior. We address both problems by developing a high-speed holographic imaging scheme and applying it to the (male) microgametes of malaria (Plasmodium) parasites. These isolated flagella are a unique, mathematically tractable model system for the physics of microswimmers. We reveal the 3D flagellar waveforms of these microorganisms and map the differential shear between microtubules in their axonemes. Furthermore, we overturn claims that chirality in the structure of the axoneme governs the beat pattern [Hirokawa N, et al. (2009) Ann Rev Fluid Mech 41:53-72], because microgametes display a left- or right-handed character on alternate beats. This breaks the link between structural chirality in the axoneme and larger scale symmetry breaking (e.g., in developing embryos), leading us to conclude that accessory structures play a critical role in shaping the flagellar beat.}, } @article {pmid24187531, year = {2013}, author = {Zhou, J and Kasper, S and Papautsky, I}, title = {Enhanced size-dependent trapping of particles using microvortices.}, journal = {Microfluidics and nanofluidics}, volume = {15}, number = {5}, pages = {}, pmid = {24187531}, issn = {1613-4982}, support = {R01 DK060957/DK/NIDDK NIH HHS/United States ; }, abstract = {Inertial microfluidics has been attracting considerable interest for size-based separation of particles and cells. The inertial forces can be manipulated by expanding the microchannel geometry, leading to formation of microvortices which selectively isolate and trap particles or cells from a mixture. In this work, we aim to enhance our understanding of particle trapping in such microvortices by developing a model of selective particle trapping. Design and operational parameters including flow conditions, size of the trapping region, and target particle concentration are explored to elucidate their influence on trapping behavior. Our results show that the size dependence of trapping is characterized by a threshold Reynolds number, which governs the selective entry of particles into microvortices from the main flow. We show that concentration enhancement on the order of 100,000× and isolation of targets at concentrations in the 1/mL is possible. Ultimately, the insights gained from our systematic investigation suggest optimization solutions that enhance device performance (efficiency, size selectivity, and yield) and are applicable to selective isolation and trapping of large rare cells as well as other applications.}, } @article {pmid24182136, year = {2013}, author = {Si, J and Colgate, SA and Li, H and Martinic, J and Westpfahl, D}, title = {Data acquisition in a high-speed rotating frame for New Mexico Institute of Mining and Technology liquid sodium αω dynamo experiment.}, journal = {The Review of scientific instruments}, volume = {84}, number = {10}, pages = {104501}, doi = {10.1063/1.4825354}, pmid = {24182136}, issn = {1089-7623}, abstract = {New Mexico Institute of Mining and Technology liquid sodium αω-dynamo experiment models the magnetic field generation in the universe as discussed in detail by Colgate, Li, and Pariev [Phys. Plasmas 8, 2425 (2001)]. To obtain a quasi-laminar flow with magnetic Reynolds number R(m) ~ 120, the dynamo experiment consists of two co-axial cylinders of 30.5 cm and 61 cm in diameter spinning up to 70 Hz and 17.5 Hz, respectively. During the experiment, the temperature of the cylinders must be maintained to 110 °C to ensure that the sodium remains fluid. This presents a challenge to implement a data acquisition (DAQ) system in such high temperature, high-speed rotating frame, in which the sensors (including 18 Hall sensors, 5 pressure sensors, and 5 temperature sensors, etc.) are under the centrifugal acceleration up to 376g. In addition, the data must be transmitted and stored in a computer 100 ft away for safety. The analog signals are digitized, converted to serial signals by an analog-to-digital converter and a field-programmable gate array. Power is provided through brush/ring sets. The serial signals are sent through ring/shoe sets capacitively, then reshaped with cross-talk noises removed. A microcontroller-based interface circuit is used to decode the serial signals and communicate with the data acquisition computer. The DAQ accommodates pressure up to 1000 psi, temperature up to more than 130 °C, and magnetic field up to 1000 G. First physics results have been analyzed and published. The next stage of the αω-dynamo experiment includes the DAQ system upgrade.}, } @article {pmid24180752, year = {2013}, author = {Vladimirov, VA and Ilin, K}, title = {An asymptotic model in acoustics: acoustic drift equations.}, journal = {The Journal of the Acoustical Society of America}, volume = {134}, number = {5}, pages = {3419-3424}, doi = {10.1121/1.4821211}, pmid = {24180752}, issn = {1520-8524}, mesh = {*Acoustics ; *Models, Theoretical ; Motion ; *Sound ; Time Factors ; }, abstract = {A rigorous asymptotic procedure with the Mach number as a small parameter is used to derive the equations of mean flows which coexist and are affected by the background acoustic waves in the limit of very high Reynolds number.}, } @article {pmid24173367, year = {2013}, author = {Mendoza, M and Succi, S and Herrmann, HJ}, title = {Flow through randomly curved manifolds.}, journal = {Scientific reports}, volume = {3}, number = {}, pages = {3106}, pmid = {24173367}, issn = {2045-2322}, abstract = {We present a computational study of the transport properties of campylotic (intrinsically curved) media. It is found that the relation between the flow through a campylotic media, consisting of randomly located curvature perturbations, and the average Ricci scalar of the system, exhibits two distinct functional expressions, depending on whether the typical spatial extent of the curvature perturbation lies above or below the critical value maximizing the overall scalar of curvature. Furthermore, the flow through such systems as a function of the number of curvature perturbations is found to present a sublinear behavior for large concentrations, due to the interference between curvature perturbations leading to an overall less curved space. We have also characterized the flux through such media as a function of the local Reynolds number and the scale of interaction between impurities. For the purpose of this study, we have also developed and validated a new lattice Boltzmann model.}, } @article {pmid24160630, year = {2013}, author = {Leptos, KC and Wan, KY and Polin, M and Tuval, I and Pesci, AI and Goldstein, RE}, title = {Antiphase synchronization in a flagellar-dominance mutant of Chlamydomonas.}, journal = {Physical review letters}, volume = {111}, number = {15}, pages = {158101}, doi = {10.1103/PhysRevLett.111.158101}, pmid = {24160630}, issn = {1079-7114}, support = {BB/F021844/1/BB_/Biotechnology and Biological Sciences Research Council/United Kingdom ; /WT_/Wellcome Trust/United Kingdom ; }, mesh = {Chlamydomonas reinhardtii/genetics/*physiology ; Flagella/genetics/*physiology ; *Models, Biological ; Oscillometry ; Stochastic Processes ; }, abstract = {Groups of beating flagella or cilia often synchronize so that neighboring filaments have identical frequencies and phases. A prime example is provided by the unicellular biflagellate Chlamydomonas reinhardtii, which typically displays synchronous in-phase beating in a low-Reynolds number version of breaststroke swimming. We report the discovery that ptx1, a flagellar-dominance mutant of C. reinhardtii, can exhibit synchronization in precise antiphase, as in the freestyle swimming stroke. High-speed imaging shows that ptx1 flagella switch stochastically between in-phase and antiphase states, and that the latter has a distinct waveform and significantly higher frequency, both of which are strikingly similar to those found during phase slips that stochastically interrupt in-phase beating of the wild-type. Possible mechanisms underlying these observations are discussed.}, } @article {pmid26029774, year = {2013}, author = {Luo, ZY and Wang, SQ and He, L and Xu, F and Bai, BF}, title = {Inertia-dependent dynamics of three-dimensional vesicles and red blood cells in shear flow.}, journal = {Soft matter}, volume = {9}, number = {40}, pages = {9651-9660}, doi = {10.1039/c3sm51823j}, pmid = {26029774}, issn = {1744-6848}, mesh = {*Blood Viscosity ; Computer Simulation ; Elasticity ; Erythrocyte Membrane/physiology ; Erythrocytes/*physiology ; Humans ; Microfluidic Analytical Techniques ; Microscopy, Confocal ; Models, Biological ; *Shear Strength ; *Stress, Mechanical ; }, abstract = {A three-dimensional (3D) simulation study of the effect of inertia on the dynamics of vesicles and red blood cells (RBCs) has not been reported. Here, we developed a 3D model based on the front tracking method to investigate how inertia affects the dynamics of spherical/non-spherical vesicles and biconcave-shaped RBCs with the Reynolds number ranging from 0.1 to 10. The results showed that inertia induced non-spherical vesicles transitioned from tumbling to swinging, which was not observed in previous 2D models. The critical viscosity ratio of inner/outer fluids for the tumbling–swinging transition remarkably increased with an increasing Reynolds number. The deformation of vesicles was greatly enhanced by inertia, and the frequency of tumbling and tank-treading was significantly decreased by inertia. We also found that RBCs can transit from tumbling to steady tank-treading through the swinging regime when the Reynolds number increased from 0.1 to 10. These results indicate that inertia needs to be considered at moderate Reynolds number (Re ~ 1) in the study of blood flow in the human body and the flow of deformable particle suspension in inertial microfluidic devices. The developed 3D model provided new insights into the dynamics of RBCs under shear flow, thus holding great potential to better understand blood flow behaviors under normal/disease conditions.}, } @article {pmid24146013, year = {2013}, author = {Nevmerzhitskiy, NV}, title = {Some peculiarities of turbulent mixing growth and perturbations at hydrodynamic instabilities.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {371}, number = {2003}, pages = {20120291}, doi = {10.1098/rsta.2012.0291}, pmid = {24146013}, issn = {1364-503X}, abstract = {The author presents a review of some experimental works devoted to the research of evolution of large-scale perturbations and turbulent mixing (TM) in liquid and gaseous media during the growth of hydrodynamic instabilities. In particular, it is shown that growth of perturbations and TM in gases is sensitive to the Mach number of shock wave; character of gas front penetration into liquid is not changed as the Reynolds number of flow increases from 5×10(5) to 10(7); and change of the Atwood number sign from positive to negative causes stopping of gas front penetration into liquid, but mixing zone width is expanded under inertia.}, } @article {pmid24146005, year = {2013}, author = {Youngs, DL}, title = {The density ratio dependence of self-similar Rayleigh-Taylor mixing.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {371}, number = {2003}, pages = {20120173}, doi = {10.1098/rsta.2012.0173}, pmid = {24146005}, issn = {1364-503X}, abstract = {Previous research on self-similar mixing caused by Rayleigh-Taylor (RT) instability is summarized and a recent series of high resolution large eddy simulations is described. Mesh sizes of approximately 2000 ×1000 × 1000 are used to investigate the properties of high Reynolds number self-similar RT mixing at a range of density ratios from 1.5 : 1 to 20 : 1. In some cases, mixing evolves from 'small random perturbations'. In other cases, random long wavelength perturbations (k(-3) spectrum) are added to give self-similar mixing at an enhanced rate, more typical of that observed in experiments. The properties of the turbulent mixing zone (volume fraction distributions, turbulence kinetic energy, molecular mixing parameter, etc.) are related to the RT growth rate parameter, α. Comparisons are made with experimental data on the internal structure and the asymmetry of the mixing zone (spike distance/bubble distance). The main purpose of this series of simulations is to provide data for calibration of engineering models (e.g. Reynolds-averaged Navier-Stokes models). It is argued that the influence of initial conditions is likely to be significant in most applications and the implications of this for engineering modelling are discussed.}, } @article {pmid24145440, year = {2013}, author = {Geyer, VF and Jülicher, F and Howard, J and Friedrich, BM}, title = {Cell-body rocking is a dominant mechanism for flagellar synchronization in a swimming alga.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {110}, number = {45}, pages = {18058-18063}, pmid = {24145440}, issn = {1091-6490}, mesh = {Biomechanical Phenomena ; Chlamydomonas/*physiology ; Flagella/*physiology ; Hydrodynamics ; Locomotion/*physiology ; Microscopy, Video ; *Models, Biological ; }, abstract = {The unicellular green alga Chlamydomonas swims with two flagella that can synchronize their beat. Synchronized beating is required to swim both fast and straight. A long-standing hypothesis proposes that synchronization of flagella results from hydrodynamic coupling, but the details are not understood. Here, we present realistic hydrodynamic computations and high-speed tracking experiments of swimming cells that show how a perturbation from the synchronized state causes rotational motion of the cell body. This rotation feeds back on the flagellar dynamics via hydrodynamic friction forces and rapidly restores the synchronized state in our theory. We calculate that this "cell-body rocking" provides the dominant contribution to synchronization in swimming cells, whereas direct hydrodynamic interactions between the flagella contribute negligibly. We experimentally confirmed the two-way coupling between flagellar beating and cell-body rocking predicted by our theory.}, } @article {pmid24125344, year = {2013}, author = {Boi, S and Mazzino, A and Pralits, JO}, title = {Minimal model for zero-inertia instabilities in shear-dominated non-Newtonian flows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {88}, number = {3}, pages = {033007}, doi = {10.1103/PhysRevE.88.033007}, pmid = {24125344}, issn = {1550-2376}, abstract = {The emergence of fluid instabilities in the relevant limit of vanishing fluid inertia (i.e., arbitrarily close to zero Reynolds number) has been investigated for the well-known Kolmogorov flow. The finite-time shear-induced order-disorder transition of the non-Newtonian microstructure and the corresponding viscosity change from lower to higher values are the crucial ingredients for the instabilities to emerge. The finite-time low-to-high viscosity change for increasing shear characterizes the rheopectic fluids. The instability does not emerge in shear-thinning or -thickening fluids where viscosity adjustment to local shear occurs instantaneously. The lack of instabilities arbitrarily close to zero Reynolds number is also observed for thixotropic fluids, in spite of the fact that the viscosity adjustment time to shear is finite as in rheopectic fluids. Renormalized perturbative expansions (multiple-scale expansions), energy-based arguments (on the linearized equations of motion), and numerical results (of suitable eigenvalue problems from the linear stability analysis) are the main tools leading to our conclusions. Our findings may have important consequences in all situations where purely hydrodynamic fluid instabilities or mixing are inhibited due to negligible inertia, as in microfluidic applications. To trigger mixing in these situations, suitable (not necessarily viscoelastic) non-Newtonian fluid solutions appear as a valid answer. Our results open interesting questions and challenges in the field of smart (fluid) materials.}, } @article {pmid24125342, year = {2013}, author = {Chaudhuri, S and Wu, F and Law, CK}, title = {Scaling of turbulent flame speed for expanding flames with Markstein diffusion considerations.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {88}, number = {3}, pages = {033005}, doi = {10.1103/PhysRevE.88.033005}, pmid = {24125342}, issn = {1550-2376}, abstract = {In this paper we clarify the role of Markstein diffusivity, which is the product of the planar laminar flame speed and the Markstein length, on the turbulent flame speed and its scaling, based on experimental measurements on constant-pressure expanding turbulent flames. Turbulent flame propagation data are presented for premixed flames of mixtures of hydrogen, methane, ethylene, n-butane, and dimethyl ether with air, in near-isotropic turbulence in a dual-chamber, fan-stirred vessel. For each individual fuel-air mixture presented in this work and the recently published iso-octane data from Leeds, normalized turbulent flame speed data of individual fuel-air mixtures approximately follow a Re_{T,f} ^{0.5} scaling, for which the average radius is the length scale and thermal diffusivity is the transport property of the turbulence Reynolds number. At a given Re_{T,f} ^{}, it is experimentally observed that the normalized turbulent flame speed decreases with increasing Markstein number, which could be explained by considering Markstein diffusivity as the leading dissipation mechanism for the large wave number flame surface fluctuations. Consequently, by replacing thermal diffusivity with the Markstein diffusivity in the turbulence Reynolds number definition above, it is found that normalized turbulent flame speeds could be scaled by Re_{T,M} ^{0.5} irrespective of the fuel, equivalence ratio, pressure, and turbulence intensity for positive Markstein number flames.}, } @article {pmid24125340, year = {2013}, author = {Lovecchio, S and Marchioli, C and Soldati, A}, title = {Time persistence of floating-particle clusters in free-surface turbulence.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {88}, number = {3}, pages = {033003}, doi = {10.1103/PhysRevE.88.033003}, pmid = {24125340}, issn = {1550-2376}, abstract = {We study the dispersion of light particles floating on a flat shear-free surface of an open channel in which the flow is turbulent. This configuration mimics the motion of buoyant matter (e.g., phytoplankton, pollutants, or nutrients) in water bodies when surface waves and ripples are smooth or absent. We perform direct numerical simulation of turbulence coupled with Lagrangian particle tracking, considering different values of the shear Reynolds number (Re_{τ} =171 and 509) and of the Stokes number (0.06
OBJECTIVE: The aim of this study is to analyse the effect of lesion eccentricity on the transient flow behaviour in a model of a coronary artery and also to investigate the correlation between Reynolds number (Re) and the eccentricity effect on flow behaviour.

METHODS: A transient particle image velocimetry (PIV) experiment was implemented in two silicone based models with 70% diameter stenosis, one with eccentric stenosis and one with concentric stenosis.

RESULTS: At different times throughout the flow cycle, the eccentric model was always associated with a greater recirculation zone length, maximum shear strain rate and maximum axial velocity; however, the highest and lowest impacts of eccentricity were on the recirculation zone length and maximum shear strain rate, respectively. Analysis of the results revealed a negative correlation between the Reynolds number (Re) and the eccentricity effect on maximum axial velocity, maximum shear strain rate and recirculation zone length.

CONCLUSIONS: As Re number increases the eccentricity effect on the flow behavior becomes negligible.}, } @article {pmid23944553, year = {2013}, author = {Horne, E and Mininni, PD}, title = {Sign cancellation and scaling in the vertical component of velocity and vorticity in rotating turbulence.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {88}, number = {1}, pages = {013011}, doi = {10.1103/PhysRevE.88.013011}, pmid = {23944553}, issn = {1550-2376}, abstract = {We study sign changes and scaling laws in the Cartesian components of the velocity and vorticity of rotating turbulence, in the helicity, and in the components of vertically averaged fields. Data for the analysis are provided by high-resolution direct numerical simulations of rotating turbulence with different forcing functions, with up to 1536(3) grid points, with Reynolds numbers between ≈1100 and ≈5100, and with moderate Rossby numbers between ≈0.06 and ≈8. When rotation is negligible, all Cartesian components of the velocity show similar scaling, in agreement with the expected isotropy of the flow. However, in the presence of rotation, only the vertical components of the fields show clear scaling laws, with evidence of possible sign singularity in the limit of an infinite Reynolds number. Horizontal components of the velocity are smooth and do not display rapid fluctuations for arbitrarily small scales. The vertical velocity and vorticity, as well as the vertically averaged vertical velocity and vorticity, show the same scaling within error bars, in agreement with theories that predict that these quantities have the same dynamical equation for very strong rotation.}, } @article {pmid23944548, year = {2013}, author = {Marques, F and Mellibovsky, F and Meseguer, A}, title = {Fold-pitchfork bifurcation for maps with Z(2) symmetry in pipe flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {88}, number = {1}, pages = {013006}, doi = {10.1103/PhysRevE.88.013006}, pmid = {23944548}, issn = {1550-2376}, abstract = {This study aims to provide a better understanding of recently identified transition scenarios exhibited by traveling wave solutions in pipe flow. This particular family of solutions are invariant under certain reflectional symmetry transformations and they emerge from saddle-node bifurcations within a two-dimensional parameter space characterized by the length of the pipe and the Reynolds number. The present work precisely provides a detailed analysis of a codimension-two saddle-node bifurcation arising in discrete dynamical systems (maps) with Z(2) symmetry. Normal form standard techniques are applied in order to obtain the reduced map up to cubic order. All possible bifurcation scenarios exhibited by this normal form are analyzed in detail. Finally, a qualitative comparison of these scenarios with the ones observed in the aforementioned hydrodynamic problem is provided.}, } @article {pmid23944544, year = {2013}, author = {Miralles, S and Bonnefoy, N and Bourgoin, M and Odier, P and Pinton, JF and Plihon, N and Verhille, G and Boisson, J and Daviaud, F and Dubrulle, B}, title = {Dynamo threshold detection in the von Kármán sodium experiment.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {88}, number = {1}, pages = {013002}, doi = {10.1103/PhysRevE.88.013002}, pmid = {23944544}, issn = {1550-2376}, abstract = {Predicting dynamo self-generation in liquid metal experiments has been an ongoing question for many years. In contrast to simple dynamical systems for which reliable techniques have been developed, the ability to predict the dynamo capacity of a flow and the estimate of the corresponding critical value of the magnetic Reynolds number (the control parameter of the instability) has been elusive, partly due to the high level of turbulent fluctuations of flows in such experiments (with kinetic Reynolds numbers in excess of 10(6)). We address these issues here, using the von Kármán sodium experiment and studying its response to an externally applied magnetic field. We first show that a dynamo threshold can be estimated from analysis related to critical slowing down and susceptibility divergence, in configurations for which dynamo action is indeed observed. These approaches are then applied to flow configurations that have failed to self-generate magnetic fields within operational limits, and we quantify the dynamo capacity of these configurations.}, } @article {pmid23933985, year = {2013}, author = {Saha, S and Salin, D and Talon, L}, title = {Low Reynolds number suspension gravity currents.}, journal = {The European physical journal. E, Soft matter}, volume = {36}, number = {8}, pages = {85}, pmid = {23933985}, issn = {1292-895X}, mesh = {Extracellular Fluid/*chemistry ; *Gravitation ; *Hydrodynamics ; *Models, Chemical ; *Rheology ; Surface Properties ; Viscosity ; }, abstract = {The extension of a gravity current in a lock-exchange problem, proceeds as square root of time in the viscous-buoyancy phase, where there is a balance between gravitational and viscous forces. In the presence of particles however, this scenario is drastically altered, because sedimentation reduces the motive gravitational force and introduces a finite distance and time at which the gravity current halts. We investigate the spreading of low Reynolds number suspension gravity currents using a novel approach based on the Lattice-Boltzmann (LB) method. The suspension is modeled as a continuous medium with a concentration-dependent viscosity. The settling of particles is simulated using a drift flux function approach that enables us to capture sudden discontinuities in particle concentration that travel as kinematic shock waves. Thereafter a numerical investigation of lock-exchange flows between pure fluids of unequal viscosity, reveals the existence of wall layers which reduce the spreading rate substantially compared to the lubrication theory prediction. In suspension gravity currents, we observe that the settling of particles leads to the formation of two additional fronts: a horizontal front near the top that descends vertically and a sediment layer at the bottom which aggrandises due to deposition of particles. Three phases are identified in the spreading process: the final corresponding to the mutual approach of the two horizontal fronts while the laterally advancing front halts indicating that the suspension current stops even before all the particles have settled. The first two regimes represent a constant and a decreasing spreading rate respectively. Finally we conduct experiments to substantiate the conclusions of our numerical and theoretical investigation.}, } @article {pmid23931372, year = {2013}, author = {de Silva, CM and Philip, J and Chauhan, K and Meneveau, C and Marusic, I}, title = {Multiscale geometry and scaling of the turbulent-nonturbulent interface in high Reynolds number boundary layers.}, journal = {Physical review letters}, volume = {111}, number = {4}, pages = {044501}, doi = {10.1103/PhysRevLett.111.044501}, pmid = {23931372}, issn = {1079-7114}, abstract = {The scaling and surface area properties of the wrinkled surface separating turbulent from nonturbulent regions in open shear flows are important to our understanding of entrainment mechanisms at the boundaries of turbulent flows. Particle image velocimetry data from high Reynolds number turbulent boundary layers covering three decades in scale are used to resolve the turbulent-nonturbulent interface experimentally and, for the first time, determine unambiguously whether such surfaces exhibit fractal scaling. Box counting of the interface intersection with the measurement plane exhibits power-law scaling, with an exponent between -1.3 and -1.4. A complementary analysis based on spatial filtering of the velocity fields also shows power-law behavior of the coarse-grained interface length as a function of filter width, with an exponent between -0.3 and -0.4. These results establish that the interface is fractal-like with a multiscale geometry and fractal dimension of Df≈2.3-2.4.}, } @article {pmid23930807, year = {2013}, author = {Basiri Parsa, A and Rashidi, MM and Anwar Bég, O and Sadri, SM}, title = {Semi-computational simulation of magneto-hemodynamic flow in a semi-porous channel using optimal homotopy and differential transform methods.}, journal = {Computers in biology and medicine}, volume = {43}, number = {9}, pages = {1142-1153}, doi = {10.1016/j.compbiomed.2013.05.019}, pmid = {23930807}, issn = {1879-0534}, mesh = {Blood Flow Velocity ; *Blood Viscosity ; *Computer Simulation ; Humans ; *Magnetic Fields ; *Models, Cardiovascular ; Porosity ; }, abstract = {In this paper, the semi-numerical techniques known as the optimal homotopy analysis method (HAM) and Differential Transform Method (DTM) are applied to study the magneto-hemodynamic laminar viscous flow of a conducting physiological fluid in a semi-porous channel under a transverse magnetic field. The two-dimensional momentum conservation partial differential equations are reduced to ordinary form incorporating Lorentizian magnetohydrodynamic body force terms. These ordinary differential equations are solved by the homotopy analysis method, the differential transform method and also a numerical method (fourth-order Runge-Kutta quadrature with a shooting method), under physically realistic boundary conditions. The homotopy analysis method contains the auxiliary parameter ℏ, which provides us with a simple way to adjust and control the convergence region of solution series. The differential transform method (DTM) does not require an auxiliary parameter and is employed to compute an approximation to the solution of the system of nonlinear differential equations governing the problem. The influence of Hartmann number (Ha) and transpiration Reynolds number (mass transfer parameter, Re) on the velocity profiles in the channel are studied in detail. Interesting fluid dynamic characteristics are revealed and addressed. The HAM and DTM solutions are shown to both correlate well with numerical quadrature solutions, testifying to the accuracy of both HAM and DTM in nonlinear magneto-hemodynamics problems. Both these semi-numerical techniques hold excellent potential in modeling nonlinear viscous flows in biological systems.}, } @article {pmid23930806, year = {2013}, author = {Ghodsi, SR and Esfahanian, V and Shamsodini, R and Ghodsi, SM and Ahmadi, G}, title = {Blood flow vectoring control in aortic arch using full and partial clamps.}, journal = {Computers in biology and medicine}, volume = {43}, number = {9}, pages = {1134-1141}, doi = {10.1016/j.compbiomed.2013.05.016}, pmid = {23930806}, issn = {1879-0534}, mesh = {Aorta, Thoracic/pathology/*physiopathology ; Aortic Aneurysm/pathology/*physiopathology ; Blood Flow Velocity ; Humans ; *Models, Cardiovascular ; *Stress, Physiological ; }, abstract = {BACKGROUND: Early diagnosis and treatment of aneurysm plays an important role in reducing the mortality risk of rupture. The aneurysm is a complex phenomenon and caused by different reasons, such as arteriosclerosis and heredity. In addition, pressure and Wall Shear Stress are two known factors influencing the establishment of an aneurysm. The aim of this study is to investigate the effect of using a full or partial clamp to control the blood flow streamlines and hence the location of stress concentration in a clean configuration of aorta. The main question is how to control the stresses distribution in order to reduce the possibility of aneurysm growth with less negative effects on the other sides.

METHODS AND RESULTS: A simple form of aortic arch with three branches is considered to simulate the effect of changing blood flow streamlines directions. A parameter study has been performed on the main characteristics of clamp, i.e. size, location, and the percentage of coverage. The Shear Stress Transport model is employed to simulate steady-state Newtonian blood flow when the Reynolds number is about 6500. Simulations are conducted using the commercial CFD solver ANSYS Fluent. The obtained results show that the location of clamp is more effective than the size. It is also found that increasing the depth of clamp has a negative impact on mean velocity field and hence on stress concentration.

CONCLUSION: The present results demonstrate that the Blood Flow Vectoring Control (BFVC) can change the main form of flow streamlines and consequently the distributions of pressure and Wall Shear Stress. A partial clamp leads to better results.}, } @article {pmid23930803, year = {2013}, author = {Tian, FB and Zhu, L and Fok, PW and Lu, XY}, title = {Simulation of a pulsatile non-Newtonian flow past a stenosed 2D artery with atherosclerosis.}, journal = {Computers in biology and medicine}, volume = {43}, number = {9}, pages = {1098-1113}, doi = {10.1016/j.compbiomed.2013.05.023}, pmid = {23930803}, issn = {1879-0534}, mesh = {*Atherosclerosis/blood/pathology/physiopathology ; *Blood Viscosity ; Constriction, Pathologic/blood/pathology/physiopathology ; Endothelial Cells/metabolism/pathology ; Humans ; *Models, Cardiovascular ; Myocytes, Smooth Muscle/metabolism/pathology ; *Plaque, Atherosclerotic/blood/pathology/physiopathology ; *Pulsatile Flow ; *Stress, Physiological ; }, abstract = {Atherosclerotic plaque can cause severe stenosis in the artery lumen. Blood flow through a substantially narrowed artery may have different flow characteristics and produce different forces acting on the plaque surface and artery wall. The disturbed flow and force fields in the lumen may have serious implications on vascular endothelial cells, smooth muscle cells, and circulating blood cells. In this work a simplified model is used to simulate a pulsatile non-Newtonian blood flow past a stenosed artery caused by atherosclerotic plaques of different severity. The focus is on a systematic parameter study of the effects of plaque size/geometry, flow Reynolds number, shear-rate dependent viscosity and flow pulsatility on the fluid wall shear stress and its gradient, fluid wall normal stress, and flow shear rate. The computational results obtained from this idealized model may shed light on the flow and force characteristics of more realistic blood flow through an atherosclerotic vessel.}, } @article {pmid23911695, year = {2013}, author = {Tripathi, D and Anwar Bég, O}, title = {Transient magneto-peristaltic flow of couple stress biofluids: a magneto-hydro-dynamical study on digestive transport phenomena.}, journal = {Mathematical biosciences}, volume = {246}, number = {1}, pages = {72-83}, doi = {10.1016/j.mbs.2013.07.012}, pmid = {23911695}, issn = {1879-3134}, mesh = {Animals ; Biological Transport ; *Hydrodynamics ; Magnetic Fields ; *Models, Biological ; Peristalsis/*physiology ; Rheology/*statistics & numerical data ; }, abstract = {Magnetic fields are increasingly being utilized in endoscopy and gastric transport control. In this regard, the present study investigates the influence of a transverse magnetic field in the transient peristaltic rheological transport. An electrically-conducting couple stress non-Newtonian model is employed to accurately simulate physiological fluids in peristaltic flow through a sinusoidally contracting channel of finite length. This model is designed for computing the intra-bolus oesophageal and intestinal pressures during the movement of food bolus in the digestive system under magneto-hydro-dynamic effects. Long wavelength and low Reynolds number approximations have been employed to reduce the governing equations from nonlinear to linear form, this being a valid approach for creeping flows which characterizes physiological dynamics. Analytical approximate solutions for axial velocity, transverse velocity, pressure gradient, local wall shear stress and volumetric flow rate are obtained for the non-dimensional conservation equations subject to appropriate boundary conditions. The effects of couple stress parameter and transverse magnetic field on the velocity profile, pressure distribution, local wall shear stress and the averaged flow rate are discussed with the aid of computational results. The comparative study of non-integral and integral number of waves propagating along the finite length channel is also presented. Magnetic field and non-Newtonian properties are found to strongly influence peristaltic transport.}, } @article {pmid23909127, year = {2013}, author = {Park, YR and Kim, SJ and Kim, SJ and Kim, JS and Kang, HS and Kim, GB}, title = {A study on hemodynamic characteristics at the stenosed blood vessel using computational fluid dynamics simulations.}, journal = {Journal of biomedical nanotechnology}, volume = {9}, number = {7}, pages = {1137-1145}, doi = {10.1166/jbn.2013.1516}, pmid = {23909127}, issn = {1550-7033}, mesh = {Aneurysm, Ruptured/etiology/*physiopathology ; Animals ; Arterial Occlusive Diseases/complications/*physiopathology ; Arterial Pressure ; Arteries/*physiopathology ; Blood Flow Velocity ; Computer Simulation ; Humans ; *Models, Cardiovascular ; Rheology/*methods ; Shear Strength ; Vascular Resistance ; }, abstract = {In this study, we have used computational fluid dynamics to investigate the blood flow in the stenosed blood vessels. The numerical simulation using commercial software ADINA 8.6 were solved about the stenosed blood vessel according to the percent of stenosis and Reynolds number. The blood flow in the normal and stenosed blood vessel was grasped for the validity of the model. The characteristic of the pulsatile flow changed through the steady state flow and analysis of the pulsatile flow according to the time was grasped. The computational model with the characteristics of the fluid-structure interaction is introduced to investigate the wall shear stress, pressure distribution and axial flow velocity. The results show that axial flow velocity and wall shear stress in the region of stenosis was increased by increasing percent of stenosis and Reynolds number. Also, we can know that in the stenosed blood vessel the possibility of the generation of the aneurysm was increased by increasing Reynolds number and percent of stenosis.}, } @article {pmid23906281, year = {2013}, author = {Teodósio, JS and Silva, FC and Moreira, JM and Simões, M and Melo, LF and Alves, MA and Mergulhão, FJ}, title = {Flow cells as quasi-ideal systems for biofouling simulation of industrial piping systems.}, journal = {Biofouling}, volume = {29}, number = {8}, pages = {953-966}, doi = {10.1080/08927014.2013.821467}, pmid = {23906281}, issn = {1029-2454}, mesh = {*Biofilms ; Biofouling ; Environmental Monitoring/*methods ; Escherichia coli/*physiology ; *Hydrodynamics ; Models, Theoretical ; Plankton/physiology ; *Water Supply ; }, abstract = {Semi-circular flow cells are often used to simulate the formation of biofilms in industrial pipes with circular section because their planar surface allows easy sampling using coupons. Computational fluid dynamics was used to assess whether the flow in pipe systems can be emulated by the semi-circular flow cells that are used to study biofilm formation. The results show that this is the case for Reynolds numbers (Re) ranging from 10 to 1000 and 3500 to 10,000. A correspondence involving the friction factor was obtained in order to correlate any semi-circular flow cell to any circular pipe for Re between 10 and 100,000. The semi-circular flow cell was then used to assess experimentally the effect of Reynolds number (Re = 4350 and 6720) on planktonic cell concentration and biofilm formation using Escherichia coli JM109 (DE3). Lower planktonic cell concentrations and thicker biofilms (>1.2 mm) were obtained with the lower Re.}, } @article {pmid23897065, year = {2013}, author = {Haber, S and Clark, A and Tawhai, M}, title = {Blood flow in capillaries of the human lung.}, journal = {Journal of biomechanical engineering}, volume = {135}, number = {10}, pages = {101006-101011}, doi = {10.1115/1.4025092}, pmid = {23897065}, issn = {1528-8951}, mesh = {Blood Pressure ; Capillaries/*physiology/*physiopathology ; Emphysema/physiopathology ; Humans ; Lung/*blood supply ; Models, Biological ; *Regional Blood Flow ; }, abstract = {A novel model for the blood system is postulated focusing on the flow rate and pressure distribution inside the arterioles and venules of the pulmonary acinus. Based upon physiological data it is devoid of any ad hoc constants. The model comprises nine generations of arterioles, venules, and capillaries in the acinus, the gas exchange unit of the lung. Blood is assumed incompressible and Newtonian and the blood vessels are assumed inextensible. Unlike previous models of the blood system, the venules and arterioles open up to the capillary network in numerous locations along each generation. The large number of interconnected capillaries is perceived as a porous medium in which the flow is macroscopically unidirectional from arterioles to venules openings. In addition, the large number of capillaries extending from each arteriole and venule allows introduction of a continuum theory and formulation of a novel system of ordinary, nonlinear differential equations which governs the blood flow and pressure fields along the arterioles, venules, and capillaries. The solution of the differential equations is semianalytical and requires the inversion of three diagonal, 9 × 9 matrices only. The results for the total flow rate of blood through the acinus are within the ballpark of physiological observations despite the simplifying assumptions used in our model. The results also manifest that the contribution of the nonlinear convection term of the Navier-Stokes equations has little effect (less than 2%) on the total blood flow entering/leaving the acinus despite the fact that the Reynolds number is not much smaller than unity at the proximal generations. The model makes it possible to examine some pathological cases. Here, centri-acinar and distal emphysema were investigated yielding a reduction in inlet blood flow rate.}, } @article {pmid23893860, year = {2013}, author = {Rani, SD and Park, T and You, BH and Soper, SA and Murphy, MC and Nikitopoulos, DE}, title = {Modeling of misalignment effects in microfluidic interconnects for modular bio-analytical chip applications.}, journal = {Electrophoresis}, volume = {34}, number = {20-21}, pages = {2988-2995}, pmid = {23893860}, issn = {1522-2683}, support = {R24 EB002115/EB/NIBIB NIH HHS/United States ; NIH R24-EB002115/EB/NIBIB NIH HHS/United States ; }, mesh = {Computer Simulation ; Equipment Design ; Microfluidic Analytical Techniques/*instrumentation ; Models, Theoretical ; }, abstract = {Minimizing misalignments during the interconnection of microfluidic modules is extremely critical to develop a fully integrated microfluidic device. Misalignments arising during chip-to-chip or world-to-chip interconnections can be greatly detrimental to efficient functioning of microfluidic devices. To address this problem, we have performed numerical simulations to investigate the effect of misalignments arising in three types of interconnection methods: (i) end-to-end interconnection (ii) channel overlap when chips are stacked on top of each other, and (iii) tube-in-reservoir misalignment occurring due to the offset between the external tubing and the reservoir. For the case of end-to-end interconnection, the effect of misalignment was investigated for 0, 13, 50, 58, and 75% reduction in the available flow area at the location of geometrical misalignment. In the channel overlap interconnection method, various possible misalignment configurations were simulated by maintaining the same amount of misalignment (75% flow area reduction). The effect of misalignment in a tube-in-reservoir interconnection was investigated by positioning the tube at an offset of 164 μm from the reservoir center. All the results were evaluated in terms of the equivalent length of a straight pipe. The effect of Reynolds number (Re) was also taken into account by performing additional simulations of aforementioned cases at Re ranging between 0.075 ≤ Re ≤ 75. Correlations were developed and the results were interpreted in terms of equivalent length (Le). Equivalent length calculations revealed that the effect of misalignment in tube-in-reservoir interconnection method was the least significant when compared to the other two methods of interconnection.}, } @article {pmid23891174, year = {2013}, author = {Sayed Razavi, M and Shirani, E}, title = {Development of a general method for designing microvascular networks using distribution of wall shear stress.}, journal = {Journal of biomechanics}, volume = {46}, number = {13}, pages = {2303-2309}, doi = {10.1016/j.jbiomech.2013.06.005}, pmid = {23891174}, issn = {1873-2380}, mesh = {Blood Flow Velocity ; Computer Simulation ; Microvessels/*physiology ; *Models, Cardiovascular ; Rheology ; Stress, Mechanical ; Viscosity ; }, abstract = {In the present study, theoretical formulations for calculation of optimal bifurcation angle and relationship between the diameters of mother and daughter vessels using the power law model for non-Newtonian fluids are developed. The method is based on the distribution of wall shear stress in the mother and daughter vessels. Also, the effect of distribution of wall shear stress on the minimization of energy loss and flow resistance is considered. It is shown that constant wall shear stress in the mother and daughter vessels provides the minimum flow resistance and energy loss of biological flows. Moreover, the effects of different wall shear stresses in the mother and daughter branches, different lengths of daughter branches in the asymmetric bifurcations and non-Newtonian effect of biological fluid flows on the bifurcation angle and the relationship between the diameters of mother and daughter branches are considered. Using numerical simulations for non-Newtonian models such as power law and Carreau models, the effects of optimal bifurcation angle on the pressure drop and flow resistance of blood flow in the symmetric bifurcation are investigated. Numerical simulations show that optimal bifurcation angle decreases the pressure drop and flow resistance especially for bifurcations at large Reynolds number.}, } @article {pmid23887878, year = {2013}, author = {M'rabet Bensalah, K and Uehlinger, D and Kalicki, R and Czerwinska, J}, title = {Hemodynamic modeling of the intrarenal circulation.}, journal = {Annals of biomedical engineering}, volume = {41}, number = {12}, pages = {2630-2644}, doi = {10.1007/s10439-013-0865-8}, pmid = {23887878}, issn = {1573-9686}, mesh = {Arteries/physiology ; Computer Simulation ; Constriction, Pathologic/physiopathology ; Hemodynamics ; Humans ; Kidney/*blood supply ; *Models, Cardiovascular ; Renal Circulation ; Software ; Veins/physiology ; }, abstract = {Three dimensional, time dependent numerical simulations of healthy and pathological conditions in a model kidney were performed. Blood flow in a kidney is not commonly investigated by computational approach, in contrast for example, to the flow in a heart. The flow in a kidney is characterized by relatively small Reynolds number (100 < Re < 0.01-laminar regime). The presented results give insight into the structure of such flow, which is hard to measure in vivo. The simulations have suggested that venous thrombosis is more likely than arterial thrombosis-higher shear rate observed. The obtained maximum velocity, as a result of the simulations, agrees with the observed in vivo measurements. The time dependent simulations show separation regimes present in the vicinity of the maximum pressure value. The pathological constriction introduced to the arterial geometry leads to the changes in separation structures. The constriction of a single vessel affects flow in the whole kidney. Pathology results in different flow rate values in healthy and affected branches, as well as, different pulsate cycle characteristic for the whole system.}, } @article {pmid23886851, year = {2013}, author = {Imamoglu, E and Sukan, FV}, title = {Scale-up and kinetic modeling for bioethanol production.}, journal = {Bioresource technology}, volume = {144}, number = {}, pages = {311-320}, doi = {10.1016/j.biortech.2013.06.118}, pmid = {23886851}, issn = {1873-2976}, mesh = {*Biofuels ; Bioreactors ; Biotechnology/*methods ; Escherichia coli/metabolism ; Ethanol/*metabolism ; Glucose/analysis ; Kinetics ; Lactic Acid/biosynthesis ; *Models, Theoretical ; Oryza/chemistry ; Rheology ; Waste Products/analysis ; Xylose/analysis ; }, abstract = {Bioethanol was produced from acidic hydrolysate of rice hulls using recombinant Escherichia coli KO11. Two different issues (scale-up and kinetic modeling) were evaluated simultaneously and concomitantly for bioethanol production. During the step-wise scale-up process from 100 mL shaken flask to 10 L stirred-tank bioreactor, the constant Reynolds number and the constant impeller tip speed were evaluated as scale-up methodologies under laboratory conditions. It was determined that the volumetric bioethanol productivity was 88% higher in 10 L bioreactor in comparison to the value of 0.21 g L(-1) h(-1) in shaken flask. The modified Monod and Luedeking-Piret models provided an accurate approach for the modeling of the experimental data. Ethanol concentration reached the maximum level of 29.03 g/L, which was 5% higher than the value of model prediction in 10 L bioreactor. The findings of this research could contribute to the industrial scale productions especially from lignocellulosic raw materials.}, } @article {pmid23872180, year = {2013}, author = {Hadinoto, K and Sundaresan, A and Cheow, WS}, title = {Lipid-polymer hybrid nanoparticles as a new generation therapeutic delivery platform: a review.}, journal = {European journal of pharmaceutics and biopharmaceutics : official journal of Arbeitsgemeinschaft fur Pharmazeutische Verfahrenstechnik e.V}, volume = {85}, number = {3 Pt A}, pages = {427-443}, doi = {10.1016/j.ejpb.2013.07.002}, pmid = {23872180}, issn = {1873-3441}, mesh = {Animals ; *Drug Delivery Systems ; Drug Stability ; High-Throughput Screening Assays/methods ; Humans ; Lipids/*chemistry ; Liposomes ; *Nanoparticles ; Polyethylene Glycols/chemistry ; Polymers/*chemistry ; }, abstract = {Lipid-polymer hybrid nanoparticles (LPNs) are core-shell nanoparticle structures comprising polymer cores and lipid/lipid-PEG shells, which exhibit complementary characteristics of both polymeric nanoparticles and liposomes, particularly in terms of their physical stability and biocompatibility. Significantly, the LPNs have recently been demonstrated to exhibit superior in vivo cellular delivery efficacy compared to that obtained from polymeric nanoparticles and liposomes. Since their inception, the LPNs have advanced significantly in terms of their preparation strategy and scope of applications. Their preparation strategy has undergone a shift from the conceptually simple two-step method, involving preformed polymeric nanoparticles and lipid vesicles, to the more principally complex, yet easier to perform, one-step method, relying on simultaneous self-assembly of the lipid and polymer, which has resulted in better products and higher production throughput. The scope of LPNs' applications has also been extended beyond single drug delivery for anticancer therapy, to include combinatorial and active targeted drug deliveries, and deliveries of genetic materials, vaccines, and diagnostic imaging agents. This review details the current state of development for the LPNs preparation and applications from which we identify future research works needed to bring the LPNs closer to its clinical realization.}, } @article {pmid23870271, year = {2013}, author = {Bark, DL and Ku, DN}, title = {Platelet transport rates and binding kinetics at high shear over a thrombus.}, journal = {Biophysical journal}, volume = {105}, number = {2}, pages = {502-511}, pmid = {23870271}, issn = {1542-0086}, mesh = {Animals ; Blood Platelets/*physiology ; *Cell Movement ; Coronary Thrombosis/*pathology ; Erythrocytes/physiology ; Hemodynamics ; Humans ; Kinetics ; *Models, Biological ; *Platelet Adhesiveness ; *Platelet Aggregation ; }, abstract = {Thrombus formation over a ruptured atherosclerotic plaque cap can occlude an artery with fatal consequences. We describe a computational model of platelet transport and binding to interpret rate-limiting steps seen in experimental thrombus formation over a collagen-coated stenosis. The model is used to compute shear rates in stenoses with growing boundaries. In the model, moving erythrocytes influence platelet transport based on shear-dependent enhanced diffusivity and a nonuniform platelet distribution. Adhesion is modeled as platelet-platelet binding kinetics. The results indicate that observed thrombus growth rates are limited by platelet transport to the wall for shear rates up to 6000 s(-1). Above 7000 s(-1), the thrombus growth rate is likely limited by binding kinetics (10(-4) m/s). Thrombus growth computed from these rate-limiting steps match the thrombus location and occlusion times for experimental conditions if a lag time for platelet activation is included. Using fitted parameters, the model is then used to predict thrombus size and shape at a higher Reynolds number flow consistent with coronary artery disease.}, } @article {pmid23860724, year = {2014}, author = {Walther, C and Mayer, S and Trefilov, A and Sekot, G and Hahn, R and Jungbauer, A and Dürauer, A}, title = {Prediction of inclusion body solubilization from shaken to stirred reactors.}, journal = {Biotechnology and bioengineering}, volume = {111}, number = {1}, pages = {84-94}, doi = {10.1002/bit.24998}, pmid = {23860724}, issn = {1097-0290}, mesh = {Bioreactors/*microbiology ; *Biotechnology/instrumentation/methods ; Escherichia coli/metabolism ; High-Throughput Screening Assays/instrumentation/methods ; Inclusion Bodies/*chemistry/*metabolism ; Kinetics ; Solubility ; }, abstract = {Inclusion bodies (IBs) were solubilized in a µ-scale system using shaking microtiter plates or a stirred tank reactor in a laboratory setting. Characteristic dimensionless numbers for mixing, the Phase number Ph and Reynolds number Re did not correlate with the kinetics and equilibrium of protein solubilization. The solubilization kinetics was independent of the mixing system, stirring or shaking rate, shaking diameter, and energy input. Good agreement was observed between the solubilization kinetics and yield on the µ-scale and laboratory setting. We show that the IB solubilization process is controlled predominantly by pore diffusion. Thus, for the process it is sufficient to keep the IBs homogeneously suspended, and additional power input will not improve the process. The high-throughput system developed on the µ-scale can predict solubilization in stirred reactors up to a factor of 500 and can therefore be used to determine optimal solubilization conditions on laboratory and industrial scale.}, } @article {pmid23851658, year = {2013}, author = {Sobh, AM}, title = {Combined effect of couple stresses and heat and mass transfer on peristaltic flow with slip conditions in a tube.}, journal = {Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine}, volume = {227}, number = {10}, pages = {1073-1082}, doi = {10.1177/0954411913487852}, pmid = {23851658}, issn = {2041-3033}, mesh = {Animals ; Body Fluids/*physiology ; Computer Simulation ; Energy Transfer/*physiology ; Friction ; Hot Temperature ; Humans ; *Models, Biological ; Peristalsis/*physiology ; Rheology/*methods ; Shear Strength/physiology ; Stress, Mechanical ; Thermal Conductivity ; Thermodynamics ; }, abstract = {In this article, the influence of heat and mass transfer on peristaltic transport of a couple stress fluid in a uniform tube with slip conditions on the wall is studied. The problem can model the blood flow in living creatures. Under long wavelength approximation and zero Reynolds number, exact solutions for the axial velocity component, pressure gradient, and both temperature and concentration fields are derived. The pressure rise is computed numerically and explained graphically. Moreover, effects of various physical parameters of the problem on temperature distribution, concentration field, and trapping are studied and discussed graphically.}, } @article {pmid23848775, year = {2013}, author = {Wang, S and Ardekani, AM}, title = {Swimming of a model ciliate near an air-liquid interface.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {87}, number = {6}, pages = {063010}, doi = {10.1103/PhysRevE.87.063010}, pmid = {23848775}, issn = {1550-2376}, mesh = {Air ; Biological Clocks/*physiology ; Ciliophora/*physiology ; Computer Simulation ; Lubrication ; *Models, Biological ; Rheology/*methods ; Shear Strength/physiology ; Solutions ; Swimming/*physiology ; }, abstract = {In this work, the role of the hydrodynamic forces on a swimming microorganism near an air-liquid interface is studied. The lubrication theory is utilized to analyze hydrodynamic effects within the narrow gap between a flat interface and a small swimmer. By using an archetypal low-Reynolds-number swimming model called "squirmer," we find that the magnitude of the vertical swimming velocity is on the order of O(εlnε), where ε is the ratio of the gap width to the swimmer's body size. The reduced swimming velocity near an interface can explain experimental observations of the aggregation of microorganisms near a liquid interface.}, } @article {pmid23848693, year = {2013}, author = {Alexandrov, DV and Galenko, PK}, title = {Selection criterion of stable dendritic growth at arbitrary Péclet numbers with convection.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {87}, number = {6}, pages = {062403}, doi = {10.1103/PhysRevE.87.062403}, pmid = {23848693}, issn = {1550-2376}, mesh = {Computer Simulation ; Convection ; Crystallization/*methods ; Dendrimers/*chemical synthesis ; *Models, Chemical ; *Models, Molecular ; Nanoparticles/*chemistry/*ultrastructure ; }, abstract = {A free dendrite growth under forced fluid flow is analyzed for solidification of a nonisothermal binary system. Using an approach to dendrite growth developed by Bouissou and Pelcé [Phys. Rev. A 40, 6673 (1989)], the analysis is presented for the parabolic dendrite interface with small anisotropy of surface energy growing at arbitrary Péclet numbers. The stable growth mode is obtained from the solvability condition giving the stability criterion for the dendrite tip velocity V and dendrite tip radius ρ as a function of the growth Péclet number, flow Péclet number, and Reynolds number. In limiting cases, the obtained stability criterion presents known criteria for small and high growth Péclet numbers of the solidifying system with and without convective fluid flow.}, } @article {pmid23848659, year = {2013}, author = {Anvari, M and Aghamohammadi, C and Dashti-Naserabadi, H and Salehi, E and Behjat, E and Qorbani, M and Nezhad, MK and Zirak, M and Hadjihosseini, A and Peinke, J and Tabar, MR}, title = {Stochastic nature of series of waiting times.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {87}, number = {6}, pages = {062139}, doi = {10.1103/PhysRevE.87.062139}, pmid = {23848659}, issn = {1550-2376}, abstract = {Although fluctuations in the waiting time series have been studied for a long time, some important issues such as its long-range memory and its stochastic features in the presence of nonstationarity have so far remained unstudied. Here we find that the "waiting times" series for a given increment level have long-range correlations with Hurst exponents belonging to the interval 1/2
METHODS: The face-airway model was developed from computed tomography scans of a 7-month-old girl. Respiratory airflows and particle transport were simulated with the low Reynolds number κ-ω turbulence model and Lagrangian tracking approach. Three pharmaceutical aerosol sizes (1, 2.5, and 5 μm) via hood nebulization were considered under quiet breathing conditions (5 L/min).

RESULTS: Both head direction and breathing mode can noticeably affect aerosol inhalability and lung delivery efficiency. A maximum of 20% difference in inhalability is observed among the three head positions. Facial-ocular depositions are predominantly influenced by head position, but not breathing mode. The facial-ocular deposition rate with the face-up position is about threefold that with the sitting position for 5-μm particles. Nasal breathing gives about 17.8% lower lung deposition and about 65% higher facial-ocular deposition than the oronasal breathing.

CONCLUSION: The face-side position has less facial-ocular deposition than the face-up position, while still achieving similar lung delivery efficiency. Because aerosols deposited around the eyes may cause irritation to the eyes, the face-side position appears to be a better option than the face-up position for comfort and safety reasons.}, } @article {pmid23804440, year = {2013}, author = {Pennycuick, CJ and Åkesson, S and Hedenström, A}, title = {Air speeds of migrating birds observed by ornithodolite and compared with predictions from flight theory.}, journal = {Journal of the Royal Society, Interface}, volume = {10}, number = {86}, pages = {20130419}, pmid = {23804440}, issn = {1742-5662}, mesh = {Animal Migration/*physiology ; Animals ; Birds/*physiology ; Female ; Flight, Animal/*physiology ; Male ; *Models, Biological ; }, abstract = {We measured the air speeds of 31 bird species, for which we had body mass and wing measurements, migrating along the east coast of Sweden in autumn, using a Vectronix Vector 21 ornithodolite and a Gill WindSonic anemometer. We expected each species' average air speed to exceed its calculated minimum-power speed (Vmp), and to fall below its maximum-range speed (Vmr), but found some exceptions to both limits. To resolve these discrepancies, we first reduced the assumed induced power factor for all species from 1.2 to 0.9, attributing this to splayed and up-turned primary feathers, and then assigned body drag coefficients for different species down to 0.060 for small waders, and up to 0.12 for the mute swan, in the Reynolds number range 25 000-250 000. These results will be used to amend the default values in existing software that estimates fuel consumption in migration, energy heights on arrival and other aspects of flight performance, using classical aeronautical theory. The body drag coefficients are central to range calculations. Although they cannot be measured on dead bird bodies, they could be checked against wind tunnel measurements on living birds, using existing methods.}, } @article {pmid23802980, year = {2013}, author = {Reddig, S and Stark, H}, title = {Nonlinear dynamics of spherical particles in Poiseuille flow under creeping-flow condition.}, journal = {The Journal of chemical physics}, volume = {138}, number = {23}, pages = {234902}, doi = {10.1063/1.4809989}, pmid = {23802980}, issn = {1089-7690}, mesh = {Colloids/*chemistry ; Computer Simulation ; Hydrodynamics ; *Nonlinear Dynamics ; Solvents/*chemistry ; }, abstract = {We study the nonlinear dynamics of spherical colloids under the influence of a pressure driven flow at vanishing Reynolds number. The colloids are confined between two parallel planar walls with a distance comparable to the particle diameter and they interact hydrodynamically via the solvent. We show that the bounded Poiseuille flow gives rise to new classes of trajectories resulting in cross-streamline migration. Two particles moving on these new trajectories exhibit either bound or unbound states. In the first case they oscillate on closed trajectories in the center-of-mass frame. In the second case, they exhibit cross-swapping trajectories in addition to swapping trajectories which were already observed in unbounded or bounded linear shear flow. The different classes of trajectories occur depending on the initial positions of the two particles and their size. We present state diagrams in the lateral positions, where we categorize the trajectories and color code the oscillation frequencies of the bound states. Finally we discuss how the results on the two-particle system help to understand the stability of particle trains composed of several particles.}, } @article {pmid23781125, year = {2013}, author = {Yang, J and Wolgemuth, CW and Huber, G}, title = {Force and torque on a cylinder rotating in a narrow gap at low Reynolds number: Scaling and lubrication analyses.}, journal = {Physics of fluids (Woodbury, N.Y. : 1994)}, volume = {25}, number = {5}, pages = {51901}, pmid = {23781125}, issn = {1070-6631}, support = {R01 GM072004/GM/NIGMS NIH HHS/United States ; }, abstract = {The hydrodynamic forces and torques on a rotating cylinder in a narrow channel are investigated in this paper using lubrication analysis and scaling analysis. To explore the effect of the shape of the gap, three different geometries are considered. The force and torque expressions from lubrication analysis agree well with numerical solutions when the gap between cylinder and wall is small. The solutions from scaling analysis can be applied over a broader range, but only if the scaling coefficients are properly deduced from numerical solution or lubrication analysis. Self-similarity in the solutions is discussed as well.}, } @article {pmid23767651, year = {2013}, author = {Li, Q and Luo, KH and Li, XJ}, title = {Lattice Boltzmann modeling of multiphase flows at large density ratio with an improved pseudopotential model.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {87}, number = {5}, pages = {053301}, doi = {10.1103/PhysRevE.87.053301}, pmid = {23767651}, issn = {1550-2376}, mesh = {Computer Simulation ; *Membranes, Artificial ; *Models, Chemical ; *Models, Molecular ; Rheology/*methods ; Solutions/*chemistry ; }, abstract = {Owing to its conceptual simplicity and computational efficiency, the pseudopotential multiphase lattice Boltzmann (LB) model has attracted significant attention since its emergence. In this work, we aim to extend the pseudopotential LB model to simulate multiphase flows at large density ratio and relatively high Reynolds number. First, based on our recent work [Q. Li, K. H. Luo, and X. J. Li, Phys. Rev. E 86, 016709 (2012)], an improved forcing scheme is proposed for the multiple-relaxation-time pseudopotential LB model in order to achieve thermodynamic consistency and large density ratio in the model. Next, through investigating the effects of the parameter a in the Carnahan-Starling equation of state, we find that the interface thickness is approximately proportional to 1/√a. Using a smaller a will lead to a wider interface thickness, which can reduce the spurious currents and enhance the numerical stability of the pseudopotential model at large density ratio. Furthermore, it is found that a lower liquid viscosity can be gained in the pseudopotential model by increasing the kinematic viscosity ratio between the vapor and liquid phases. The improved pseudopotential LB model is numerically validated via the simulations of stationary droplet and droplet oscillation. Using the improved model as well as the above treatments, numerical simulations of droplet splashing on a thin liquid film are conducted at a density ratio in excess of 500 with Reynolds numbers ranging from 40 to 1000. The dynamics of droplet splashing is correctly reproduced and the predicted spread radius is found to obey the power law reported in the literature.}, } @article {pmid23767635, year = {2013}, author = {Parra-Rojas, C and Soto, R}, title = {Active temperature and velocity correlations produced by a swimmer suspension.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {87}, number = {5}, pages = {053022}, doi = {10.1103/PhysRevE.87.053022}, pmid = {23767635}, issn = {1550-2376}, mesh = {Animals ; Anisotropy ; Cell Movement/*physiology ; Computer Simulation ; Humans ; Microfluidics/*methods ; *Models, Biological ; Swimming/*physiology ; Temperature ; }, abstract = {The agitation produced in a fluid by a suspension of microswimmers in the low Reynolds number limit is studied. In this limit, swimmers are modeled as force dipoles all with equal strength. The agitation is characterized by the active temperature defined, as in kinetic theory, as the mean square velocity, and by the equal-time spatial correlations. Considering the phase in which the swimmers are homogeneously and isotropically distributed in the fluid, it is shown that the active temperature and velocity correlations depend on a single scalar correlation function of the dipole-dipole correlation function. By making a simple medium-range order model, in which the dipole-dipole correlation function is characterized by a single correlation length k(0)(-1) it is possible to make quantitative predictions. It is found that the active temperature depends on the system size, scaling as L(4-d) at large correlation lengths L<
Courtship songs were recorded using high-speed videography (2,000 fps) and audio recordings. The song consists of a long duration amplitude-modulated "buzz" followed by a series of pulsatile higher amplitude "boings," each decaying into a terminal buzz followed by a short inter-boing pause while wings are stationary. Boings have higher amplitude and lower frequency than buzz components. The lower frequency of the boing sound is due to greater wing displacement. The power spectrum is a harmonic series dominated by wing repetition rate ∼220 Hz, but the sound waveform indicates a higher frequency resonance ∼5 kHz. Sound is not generated by the wings contacting each other, the substrate, or the abdomen. The abdomen is elevated during the first several wing cycles of the boing, but its position is unrelated to sound amplitude. Unlike most sounds generated by volume velocity, the boing is generated at the termination of the wing down stroke when displacement is maximal and wing velocity is zero. Calculation indicates a low Reynolds number of ∼1000.

CONCLUSIONS AND SIGNIFICANCE: Acoustic pressure is proportional to velocity for typical sound sources. Our finding that the boing sound was generated at maximal wing displacement coincident with cessation of wing motion indicates that it is caused by acceleration of the wing tips, consistent with a dipole source. The low Reynolds number requires a high wing flap rate for flight and predisposes wings of small insects for sound production.}, } @article {pmid23594696, year = {2013}, author = {Sidik, NA and Khakbaz, M and Jahanshaloo, L and Samion, S and Darus, AN}, title = {Simulation of forced convection in a channel with nanofluid by the lattice Boltzmann method.}, journal = {Nanoscale research letters}, volume = {8}, number = {1}, pages = {178}, pmid = {23594696}, issn = {1931-7573}, abstract = {This paper presents a numerical study of the thermal performance of fins mounted on the bottom wall of a horizontal channel and cooled with either pure water or an Al2O3-water nanofluid. The bottom wall of the channel is heated at a constant temperature and cooled by mixed convection of laminar flow at a relatively low temperature. The results of the numerical simulation indicate that the heat transfer rate of fins is significantly affected by the Reynolds number (Re) and the thermal conductivity of the fins. The influence of the solid volume fraction on the increase of heat transfer is more noticeable at higher values of the Re.}, } @article {pmid23592394, year = {2013}, author = {Miloh, T}, title = {Dipolophoresis of Janus nanoparticles in a microchannel.}, journal = {Electrophoresis}, volume = {34}, number = {13}, pages = {1939-1949}, doi = {10.1002/elps.201300037}, pmid = {23592394}, issn = {1522-2683}, mesh = {Electrophoresis/*instrumentation/methods ; Hydrodynamics ; Microfluidic Analytical Techniques/*instrumentation ; *Models, Chemical ; Nanoparticles/*chemistry ; Static Electricity ; }, abstract = {A nonlinear dipolophoretic analysis is applied to analytically explain the counterintuitive experimental results of Gangwal et al. that an uncharged micro/nanosize dielectric Janus particle is attracted to the wall of a microchannel when exposed to an AC-uniform electric field in the direction parallel to the no-slip boundaries. We employ the so-called "weak" field assumption and consider a metallodielectric Janus colloid comprising two semispheres of distinct dielectric properties subject to an oscillating-uniform electric field with moderate frequency (below the Maxwell-Wagner limit). The Debye scale (ratio of electric double layer thickness to particle size) is considered unrestricted. Under the low Reynolds number hypothesis, Faxén's theorem and the Green's function (Stokeslet) method of singularities, including appropriate images with respect to the no-slip boundary, are applied under the remote-field approximation to determine the dynamics and trajectory of a small colloid moving near a wall. When assuming maximum dielectric contrasts between hemispheres and relatively low Debye scale (compared to particle radius), a rather simple relation for the equilibrium position of the colloid (i.e. tilt angle and distance from the wall) is obtained and found to be in qualitative good agreement with the experimental observations of Gangwal et al. and the predictions of Kilic and Bazant.}, } @article {pmid25167273, year = {2013}, author = {Pacheco-Martinez, HA and Liao, L and Hill, RJ and Swift, MR and Bowley, RM}, title = {Spontaneous orbiting of two spheres levitated in a vibrated liquid.}, journal = {Physical review letters}, volume = {110}, number = {15}, pages = {154501}, doi = {10.1103/PhysRevLett.110.154501}, pmid = {25167273}, issn = {1079-7114}, abstract = {In the absence of gravity, particles can form a suspension in a liquid irrespective of the difference in density between the solid and the liquid. If such a suspension is subjected to vibration, there is relative motion between the particles and the fluid which can lead to self-organization and pattern formation. Here, we describe experiments carried out to investigate the behavior of two identical spheres suspended magnetically in a fluid, mimicking weightless conditions. Under vibration, the spheres mutually attract and, for sufficiently large vibration amplitudes, the spheres are observed to spontaneously orbit each other. The collapse of the experimental data onto a single curve indicates that the instability occurs at a critical value of the streaming Reynolds number. Simulations reproduce the observed behavior qualitatively and quantitatively, and are used to identify the features of the flow that are responsible for this instability.}, } @article {pmid23576069, year = {2013}, author = {Kim, J and Kim, HS and Han, S and Lee, JY and Oh, JE and Chung, S and Park, HD}, title = {Hydrodynamic effects on bacterial biofilm development in a microfluidic environment.}, journal = {Lab on a chip}, volume = {13}, number = {10}, pages = {1846-1849}, doi = {10.1039/c3lc40802g}, pmid = {23576069}, issn = {1473-0189}, mesh = {Biofilms/*growth & development ; Hydrodynamics ; *Microfluidic Analytical Techniques ; Models, Biological ; Pseudomonas aeruginosa/*physiology ; }, abstract = {In aquatic environments, microorganisms tend to form biofilms on surfaces to protect them from harsh conditions. The biofilms then accumulate into multilayered mat-like structures. In this study, we evaluated the effects of the hydrodynamic conditions on the ecology of biofilms produced by Pseudomonas aeruginosa (PA14). In microfluidic channels, we found that the development of biofilms was regulated by hydrodynamic conditions, but the developed biofilms also changed flow velocity by narrowing flow width. The coupled growing conditions were simplified by a new concept of consequent variables, and the dimensionless biofilm development (Ab/h(2) & Ab/w(cs)(2)) was successfully expressed by the Reynolds number (Re) and the dimension of the channel (r). At low Re, higher flow rates encouraged growth of biofilms, while higher flow rates with high Re suppressed growth of biofilms. These results provide a simple model as a theoretical basis for understanding development of biofilms in microfluidic channels.}, } @article {pmid23568531, year = {2013}, author = {Tanaka, Y and Koghure, T and Ueno, M and Sugiyama, H and Hamamoto, Y and Tamai, M and Taguchi, N and Sakamoto, H}, title = {Effects of flow patterns and hemodynamic force on vascular endothelium in the temporary arteriovenous shunt loop in rabbits.}, journal = {Journal of reconstructive microsurgery}, volume = {29}, number = {5}, pages = {331-340}, doi = {10.1055/s-0033-1343500}, pmid = {23568531}, issn = {1098-8947}, mesh = {Animals ; *Arteriovenous Shunt, Surgical/adverse effects ; Blood Flow Velocity ; Blood Viscosity ; Endothelium, Vascular/*physiopathology ; Femoral Artery/*physiopathology ; Hemodynamics/*physiology ; Heparin/pharmacology ; Male ; Rabbits ; Risk Factors ; Stress, Mechanical ; Thrombosis/*etiology ; Vascular Patency ; }, abstract = {The purpose of this study was to investigate whether there is a risk of thrombosis in the temporary arteriovenous shunt loop (TAVSL). The authors established a TAVSL model in the rabbit. Experimental groups were divided into non-heparin treated and heparin treated. The maximum blood flow volume, blood viscosity, and radius of curvature were measured, and the Reynolds number and the sheer stress were calculated. Computational fluid dynamics (CFD) was used to predict the flow pattern in the TAVSL, and these predicted data were compared with histological results. Early occlusion was noted in 70% (7/10) of the non-heparin-treated group and 22% (2/9) of the heparin-treated group. CFD analysis predicted a high shear stress at the arterial anastomosis region and the outer luminal surface of the curved section. The intimal structure at the luminal surface of the curved section was extensively lost histologically. In the patent group, severe stenosis of the lumen was noted at the apex of the loop due to an organized thrombus. Thus, thrombosis is likely to occur in the TAVSL due to endothelium injury caused by high shear stress, and this results in the formation of white thrombi at an early stage and an organized thrombus at a late stage.}, } @article {pmid23563437, year = {2013}, author = {Nunes, MA and Fernandes, PC and Ribeiro, MH}, title = {Microtiter plates versus stirred mini-bioreactors in biocatalysis: a scalable approach.}, journal = {Bioresource technology}, volume = {136}, number = {}, pages = {30-40}, doi = {10.1016/j.biortech.2013.02.057}, pmid = {23563437}, issn = {1873-2976}, mesh = {*Biocatalysis ; *Bioreactors ; Biotechnology/*instrumentation/*methods ; Enzymes, Immobilized/metabolism ; Flavanones/metabolism ; Hydrolysis ; Kinetics ; Multienzyme Complexes/metabolism ; Polyvinyl Alcohol/chemistry ; Rheology ; beta-Glucosidase/metabolism ; }, abstract = {To place the application of miniaturized vessels as microbioreactors on a firm footing, focus has been given to engineering characterization. Studies on this matter have mostly involved carrier-free biological systems, while support-based systems have been overlooked. The present work aims to contribute to fill in such gap. Thus, it intended to establish a robust scaled down approach to identify and optimize relevant operational conditions of naringin hydrolysis by naringinase in PVA lens-shaped particles. The influence of geometric and dynamic (viz. Reynolds number) parameters was evaluated. Naringin hydrolysis in round, flat bottom MTP proved more effective than in square, pyramidal bottom. The bioconversion at MTP and stirred tank reactors scales showed that, given the 12.5-fold scale difference was in agreement between the bioconversion rates. The external mass transfer resistances were negligible as deduced from Damkohler modulus ≤1. The bioconversion was effectively scaled-up 200-fold from shaken microtiter plates to stirred tank reactors.}, } @article {pmid23556981, year = {2013}, author = {Chekmarev, SF}, title = {Tendency to occupy a statistically dominant spatial state of the flow as a driving force for turbulent transition.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {23}, number = {1}, pages = {013144}, doi = {10.1063/1.4795279}, pmid = {23556981}, issn = {1089-7682}, mesh = {*Elementary Particles ; Entropy ; Hydrodynamics ; *Models, Statistical ; Motion ; Particle Size ; Rheology ; Time Factors ; Uncertainty ; Viscosity ; }, abstract = {The transition from laminar to turbulent fluid motion occurring at large Reynolds numbers is generally associated with the instability of the laminar flow. On the other hand, since the turbulent flow characteristically appears in the form of spatially localized structures (e.g., eddies) filling the flow field, a tendency to occupy such a structured state of the flow cannot be ruled out as a driving force for turbulent transition. To examine this possibility, we propose a simple analytical model that treats the flow as a collection of localized spatial structures, each of which consists of elementary cells in which the behavior of the particles (atoms or molecules) is uncorrelated. This allows us to introduce the Reynolds number, associating it with the ratio between the total phase volume for the system and that for the elementary cell. Using the principle of maximum entropy to calculate the most probable size distribution of the localized structures, we show that as the Reynolds number increases, the elementary cells group into the localized structures, which successfully explains turbulent transition and some other general properties of turbulent flows. An important feature of the present model is that a bridge between the spatial-statistical description of the flow and hydrodynamic equations is established. We show that the basic assumptions underlying the model, i.e., that the particles are indistinguishable and elementary volumes of phase space exist in which the state of the particles is uncertain, are involved in the derivation of the Navier-Stokes equation. Taking into account that the model captures essential features of turbulent flows, this suggests that the driving force for the turbulent transition is basically the same as in the present model, i.e., the tendency of the system to occupy a statistically dominant state plays a key role. The instability of the flow at high Reynolds numbers can then be a mechanism to initiate structural rearrangement of the flow to find this state.}, } @article {pmid25166810, year = {2013}, author = {Wadhwa, N and Vlachos, P and Jung, S}, title = {Noncoalescence in the oblique collision of fluid jets.}, journal = {Physical review letters}, volume = {110}, number = {12}, pages = {124502}, doi = {10.1103/PhysRevLett.110.124502}, pmid = {25166810}, issn = {1079-7114}, abstract = {When two jets of fluid collide, they can "bounce" off each other, due to a thin film of air which keeps them separated. We describe the phenomenon of stable noncoalescence between two jets of the same fluid, colliding obliquely with each other. Using a simple experimental setup, we carry out a parametric study of the bouncing jets by varying the jet diameter, velocity, angle of inclination, and fluid viscosity, which suggests that the contact time of bouncing jets scales as the square root of the normal Weber number We. A dimensionless parameter K = (We sqrt[Re]/sinα)(1/2), where Re is the normal Reynolds number and α the angle of inclination of the jets, quantitatively captures the transition of colliding jets from bouncing to coalescence. This parameter draws parallels between jet coalescence and droplet splashing and indicates that the transition is governed by a surface instability. Stable and continuous noncoalescence between fluid jets makes it a good platform for experimental studies of the interaction between fluid interfaces and the properties of the interfacial air films.}, } @article {pmid23496636, year = {2013}, author = {Fakhari, A and Lee, T}, title = {Multiple-relaxation-time lattice Boltzmann method for immiscible fluids at high Reynolds numbers.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {87}, number = {2}, pages = {023304}, doi = {10.1103/PhysRevE.87.023304}, pmid = {23496636}, issn = {1550-2376}, mesh = {*Algorithms ; Computer Simulation ; *Models, Theoretical ; Rheology/*methods ; }, abstract = {The lattice Boltzmann method for immiscible multiphase flows with large density ratio is extended to high Reynolds number flows using a multiple-relaxation-time (MRT) collision operator, and its stability and accuracy are assessed by simulating the Kelvin-Helmholtz instability. The MRT model is successful at damping high-frequency oscillations in the kinetic energy emerging from traveling waves generated by the inclusion of curvature. Numerical results are shown to be in good agreement with prior studies using adaptive mesh refinement techniques applied to the Navier-Stokes equations. Effects of viscosity and surface tension, as well as density ratio, are investigated in terms of the Reynolds and Weber numbers. It is shown that increasing the Reynolds number results in a more chaotic interface evolution and eventually shattering of the interface, while surface tension is shown to have a stabilizing effect.}, } @article {pmid23496617, year = {2013}, author = {Merbold, S and Brauckmann, HJ and Egbers, C}, title = {Torque measurements and numerical determination in differentially rotating wide gap Taylor-Couette flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {87}, number = {2}, pages = {023014}, doi = {10.1103/PhysRevE.87.023014}, pmid = {23496617}, issn = {1550-2376}, mesh = {Computer Simulation ; *Energy Transfer ; *Models, Theoretical ; Rheology/*methods ; Rotation ; Torque ; }, abstract = {We investigate experimentally and numerically turbulent Taylor-Couette flow with independently rotating cylinders and radius ratio η=0.5. The torque acting on the inner wall is measured to analyze the transverse current of azimuthal motion J(ω). The scaling of the torque with shear Reynolds number is determined for the outer cylinder at rest. For constant shear Reynolds number we investigate various ratios of angular velocities and find a torque maximum for counter-rotating cylinders that deviates from the prediction suggested by van Gils et al. [J. Fluid Mech. 706, 118 (2012)]. The direct comparison between the experiment and the numerical simulation shows a good agreement in the torques.}, } @article {pmid23496605, year = {2013}, author = {Ni, R and Xia, KQ}, title = {Kolmogorov constants for the second-order structure function and the energy spectrum.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {87}, number = {2}, pages = {023002}, doi = {10.1103/PhysRevE.87.023002}, pmid = {23496605}, issn = {1550-2376}, mesh = {Computer Simulation ; *Energy Transfer ; *Models, Theoretical ; Rheology/*methods ; }, abstract = {We examine the behavior of the Kolmogorov constants C(2), C(k), and C(k1), which are, respectively, the prefactors of the second-order longitudinal structure function and the three-dimensional and one-dimensional longitudinal energy spectrum in the inertial range. We show that their ratios, C(2)/C(k1) and C(k)/C(k1), exhibit clear dependence on the microscale Reynolds number R(λ), implying that they cannot all be independent of R(λ). In particular, it is found that (C(k1)/C(2)-0.25)=1.95R(λ)(-0.68). The study further reveals that the widely used relation C(2)=4.02C(k1) holds only asymptotically when R(λ)>/~10(5). It is also found that C(2) has much stronger R(λ) dependence than either C(k) or C(k1) if the latter indeed has a systematic dependence on R(λ). We further show that the varying dependence on R(λ) of these three numbers can be attributed to the difference of the inertial range in real- and wave-number space, with the inertial range in real-space known to be much shorter than that in wave-number space.}, } @article {pmid23487740, year = {2013}, author = {Gemmell, BJ and Sheng, J and Buskey, EJ}, title = {Compensatory escape mechanism at low Reynolds number.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {110}, number = {12}, pages = {4661-4666}, pmid = {23487740}, issn = {1091-6490}, mesh = {Animals ; Biomechanical Phenomena/physiology ; Copepoda/*physiology ; Locomotion/*physiology ; *Models, Biological ; Phytoplankton/physiology ; Predatory Behavior/*physiology ; Zooplankton/*physiology ; }, abstract = {Despite high predation pressure, planktonic copepods remain one of the most abundant groups on the planet. Their escape response provides one of most effective mechanisms to maximize evolutionary fitness. Owing to their small size (100 µm) compared with their predators (>1 mm), increasing viscosity is believed to have detrimental effects on copepods' fitness at lower temperature. Using high-speed digital holography we acquire 3D kinematics of the nauplius escape including both location and detailed appendage motion. By independently varying temperature and viscosity we demonstrate that at natural thermal extremes, contrary to conventional views, nauplii achieve equivalent escape distance while maintaining optimal velocity. Using experimental results and kinematic simulations from a resistive force theory propulsion model, we demonstrate that a shift in appendage timing creates an increase in power stroke duration relative to recovery stroke duration. This change allows the nauplius to limit losses in velocity and maintain distance during escapes at the lower bound of its natural thermal range. The shift in power stroke duration relative to recovery stroke duration is found to be regulated by the temperature dependence of swimming appendage muscle groups, not a dynamic response to viscosity change. These results show that copepod nauplii have natural adaptive mechanisms to compensate for viscosity variations with temperature but not in situations in which viscosity varies independent of temperature, such as in some phytoplankton blooms. Understanding the robustness of escapes in the wake of environmental changes such as temperature and viscosity has implications in assessing the future health of performance compensation.}, } @article {pmid23480363, year = {2013}, author = {Bukiet, F and Soler, T and Guivarch, M and Camps, J and Tassery, H and Cuisinier, F and Candoni, N}, title = {Factors affecting the viscosity of sodium hypochlorite and their effect on irrigant flow.}, journal = {International endodontic journal}, volume = {46}, number = {10}, pages = {954-961}, doi = {10.1111/iej.12086}, pmid = {23480363}, issn = {1365-2591}, mesh = {Hot Temperature ; *Root Canal Irrigants ; Sodium Hypochlorite/*chemistry ; Surface-Active Agents/chemistry ; *Viscosity ; }, abstract = {AIM: To assess the influence of concentration, temperature and surfactant addition to a sodium hypochlorite solution on its dynamic viscosity and to calculate the corresponding Reynolds number to determine the corresponding flow regimen.

METHODOLOGY: The dynamic viscosity of the irrigant was assessed using a rotational viscometer. Sodium hypochlorite with concentrations ranging from 0.6% to 9.6% was tested at 37 and 22 °C. A wide range of concentrations of three different surfactants was mixed in 2.4% sodium hypochlorite for viscosity measurements. The Reynolds number was calculated under each condition. Data were analysed using two-way anova.

RESULTS: There was a significant influence of sodium hypochlorite concentration (P < 0.001) and temperature (P < 0.001) on dynamic viscosity: the latter significantly increased with sodium hypochlorite concentration and decreased with temperature. A significant influence of surfactant concentration on dynamic viscosity (P < 0.001) occurred, especially for high surfactant concentrations: 6.25% for benzalkonium chloride, 15% for Tween 80 and 6.25% for Triton X-100. Reynolds number values calculated for a given flow rate (0.14 mL s(-1)), and root canal diameter (sizes 45 and 70) clearly qualified the irrigant flow regimen as laminar.

CONCLUSIONS: Dynamic viscosity increased with sodium hypochlorite and surfactant concentration but decreased with temperature. Under clinical conditions, all viscosities measured led to laminar flow. The transition between laminar and turbulent flow may be reached by modifying different parameters at the same time: increasing flow rate and temperature whilst decreasing irrigant viscosity by adding surfactants with a high value of critical micellar concentration.}, } @article {pmid23473153, year = {2013}, author = {Alexakis, A}, title = {Large-scale magnetic fields in magnetohydrodynamic turbulence.}, journal = {Physical review letters}, volume = {110}, number = {8}, pages = {084502}, doi = {10.1103/PhysRevLett.110.084502}, pmid = {23473153}, issn = {1079-7114}, abstract = {High Reynolds number magnetohydrodynamic turbulence in the presence of zero-flux large-scale magnetic fields is investigated as a function of the magnetic field strength. For a variety of flow configurations, the energy dissipation rate [symbol: see text] follows the scaling [Symbol: see text] proportional U(rms)(3)/ℓ even when the large-scale magnetic field energy is twenty times larger than the kinetic energy. A further increase of the magnetic energy showed a transition to the [Symbol: see text] proportional U(rms)(2) B(rms)/ℓ scaling implying that magnetic shear becomes more efficient at this point at cascading the energy than the velocity fluctuations. Strongly helical configurations form nonturbulent helicity condensates that deviate from these scalings. Weak turbulence scaling was absent from the investigation. Finally, the magnetic energy spectra support the Kolmogorov spectrum k(-5/3) while kinetic energy spectra are closer to the Iroshnikov-Kraichnan spectrum k(-3/2) as observed in the solar wind.}, } @article {pmid23464237, year = {2013}, author = {Hindasageri, V and Vedula, RP and Prabhu, SV}, title = {Thermocouple error correction for measuring the flame temperature with determination of emissivity and heat transfer coefficient.}, journal = {The Review of scientific instruments}, volume = {84}, number = {2}, pages = {024902}, doi = {10.1063/1.4790471}, pmid = {23464237}, issn = {1089-7623}, abstract = {Temperature measurement by thermocouples is prone to errors due to conduction and radiation losses and therefore has to be corrected for precise measurement. The temperature dependent emissivity of the thermocouple wires is measured by the use of thermal infrared camera. The measured emissivities are found to be 20%-40% lower than the theoretical values predicted from theory of electromagnetism. A transient technique is employed for finding the heat transfer coefficients for the lead wire and the bead of the thermocouple. This method does not require the data of thermal properties and velocity of the burnt gases. The heat transfer coefficients obtained from the present method have an average deviation of 20% from the available heat transfer correlations in literature for non-reacting convective flow over cylinders and spheres. The parametric study of thermocouple error using the numerical code confirmed the existence of a minimum wire length beyond which the conduction loss is a constant minimal. Temperature of premixed methane-air flames stabilised on 16 mm diameter tube burner is measured by three B-type thermocouples of wire diameters: 0.15 mm, 0.30 mm, and 0.60 mm. The measurements are made at three distances from the burner tip (thermocouple tip to burner tip/burner diameter = 2, 4, and 6) at an equivalence ratio of 1 for the tube Reynolds number varying from 1000 to 2200. These measured flame temperatures are corrected by the present numerical procedure, the multi-element method, and the extrapolation method. The flame temperatures estimated by the two-element method and extrapolation method deviate from numerical results within 2.5% and 4%, respectively.}, } @article {pmid23456695, year = {2013}, author = {Krishnakumar, S and Gaudana, SB and Viswanathan, GA and Pakrasi, HB and Wangikar, PP}, title = {Rhythm of carbon and nitrogen fixation in unicellular cyanobacteria under turbulent and highly aerobic conditions.}, journal = {Biotechnology and bioengineering}, volume = {110}, number = {9}, pages = {2371-2379}, doi = {10.1002/bit.24882}, pmid = {23456695}, issn = {1097-0290}, mesh = {Biotechnology ; Carbon/*metabolism ; Carbon Dioxide/metabolism ; Cell Culture Techniques/*methods ; Chemical Phenomena ; Cyanothece/genetics/metabolism/*physiology ; Glycogen/metabolism ; *Light ; Nitrogen/metabolism ; Nitrogen Fixation/*physiology ; Oxygen/metabolism ; Transcriptome/physiology ; }, abstract = {Nitrogen fixing cyanobacteria are being increasingly explored for nitrogenase-dependent hydrogen production. Commercial success however will depend on the ability to grow these cultures at high cell densities. Photo-limitation at high cell densities leads to hindered photoautotrophic growth while turbulent conditions, which simulate flashing light effect, can lead to oxygen toxicity to the nitrogenase enzyme. Cyanothece sp. strain ATCC 51142, a known hydrogen producer, is reported to grow and fix nitrogen under moderately oxic conditions in shake flasks. In this study, we explore the growth and nitrogen fixing potential of this organism under turbulent conditions with volumetric oxygen mass transfer coefficient (KL a) values that are up to 20-times greater than in shake flasks. In a stirred vessel, the organism grows well in turbulent regime possibly due to a simulated flashing light effect with optimal growth at Reynolds number of approximately 35,000. A respiratory burst lasting for about 4 h creates anoxic conditions intracellularly with near saturating levels of dissolved oxygen in the extracellular medium. This is concomitant with complete exhaustion of intracellular glycogen storage and upregulation of nifH and nifX, the genes encoding proteins of the nitrogenase complex. Further, the rhythmic oscillations in exhaust gas CO2 and O2 profiles synchronize faithfully with those in biochemical parameters and gene expression thereby serving as an effective online monitoring tool. These results will have important implications in potential commercial success of nitrogenase-dependent hydrogen production by cyanobacteria.}, } @article {pmid23430990, year = {2013}, author = {Salcedo, E and Treviño, C and Vargas, RO and Martínez-Suástegui, L}, title = {Stereoscopic particle image velocimetry measurements of the three-dimensional flow field of a descending autorotating mahogany seed (Swietenia macrophylla).}, journal = {The Journal of experimental biology}, volume = {216}, number = {Pt 11}, pages = {2017-2030}, doi = {10.1242/jeb.085407}, pmid = {23430990}, issn = {1477-9145}, mesh = {Biomechanical Phenomena ; Meliaceae/*anatomy & histology ; Models, Biological ; Rheology ; Seeds/*anatomy & histology ; Wind ; }, abstract = {An experimental investigation of near field aerodynamics of wind dispersed rotary seeds has been performed using stereoscopic digital particle image velocimetry (DPIV). The detailed three-dimensional flow structure of the leading-edge vortex (LEV) of autorotating mahogany seeds (Swietenia macrophylla) in a low-speed vertical wind tunnel is revealed for the first time. The results confirm that the presence of strong spanwise flow and strain produced by centrifugal forces through a spiral vortex are responsible for the attachment and stability of the LEV, with its core forming a cone pattern with a gradual increase in vortex size. The LEV appears at 25% of the wingspan, increases in size and strength outboard along the wing, and reaches its maximum stability and spanwise velocity at 75% of the wingspan. At a region between 90 and 100% of the wingspan, the strength and stability of the vortex core decreases and the LEV re-orientation/inflection with the tip vortex takes place. In this study, the instantaneous flow structure and the instantaneous velocity and vorticity fields measured in planes parallel to the free stream direction are presented as contour plots using an inertial and a non-inertial frame of reference. Results for the mean aerodynamic thrust coefficients as a function of the Reynolds number are presented to supplement the DPIV data.}, } @article {pmid23427919, year = {2013}, author = {Hoppe, TJ and Moorjani, SG and Shear, JB}, title = {Generating arbitrary chemical patterns for multipoint dosing of single cells.}, journal = {Analytical chemistry}, volume = {85}, number = {7}, pages = {3746-3751}, pmid = {23427919}, issn = {1520-6882}, support = {R21 GM078228/GM/NIGMS NIH HHS/United States ; R43 MH085396/MH/NIMH NIH HHS/United States ; 1R43MH085396-01/MH/NIMH NIH HHS/United States ; }, mesh = {Animals ; Cell Culture Techniques/methods ; Cell Line, Tumor ; Fluorescent Dyes/analysis ; Laser Therapy/methods ; Microfluidic Analytical Techniques/*methods ; Microscopy/*methods ; Single-Cell Analysis/*methods ; }, abstract = {Living cells reside within anisotropic microenvironments that orchestrate a broad range of polarized responses through physical and chemical cues. To unravel how localized chemical signals influence complex behaviors, tools must be developed for establishing patterns of chemical gradients that vary over subcellular dimensions. Here, we present a strategy for addressing this critical need in which an arbitrary number of chemically distinct, subcellular dosing streams are created in real time within a microfluidic environment. In this approach, cells are cultured on a thin polymer membrane that serves as a barrier between the cell-culture environment and a reagent chamber containing multiple reagent species flowing in parallel under low Reynolds number conditions. Focal ablation of the membrane creates pores that allow solution to flow from desired regions within this reagent pattern into the cell-culture chamber, resulting in narrow, chemically distinct dosing streams. Unlike previous dosing strategies, this system provides the capacity to tailor arbitrary patterns of reagents on the fly to suit the geometry and orientation of specific cells.}, } @article {pmid23427094, year = {2013}, author = {Yagi, T and Sato, A and Shinke, M and Takahashi, S and Tobe, Y and Takao, H and Murayama, Y and Umezu, M}, title = {Experimental insights into flow impingement in cerebral aneurysm by stereoscopic particle image velocimetry: transition from a laminar regime.}, journal = {Journal of the Royal Society, Interface}, volume = {10}, number = {82}, pages = {20121031}, pmid = {23427094}, issn = {1742-5662}, mesh = {Blood Flow Velocity ; Female ; Humans ; Intracranial Aneurysm/pathology/*physiopathology ; Middle Aged ; *Models, Cardiovascular ; Pulsatile Flow ; Rheology ; }, abstract = {This study experimentally investigated the instability of flow impingement in a cerebral aneurysm, which was speculated to promote the degradation of aneurysmal wall. A patient-specific, full-scale and elastic-wall replica of cerebral artery was fabricated from transparent silicone rubber. The geometry of the aneurysm corresponded to that found at 9 days before rupture. The flow in a replica was analysed by quantitative flow visualization (stereoscopic particle image velocimetry) in a three-dimensional, high-resolution and time-resolved manner. The mid-systolic and late-diastolic flows with a Reynolds number of 450 and 230 were compared. The temporal and spatial variations of near-wall velocity at flow impingement delineated its inherent instability at a low Reynolds number. Wall shear stress (WSS) at that site exhibited a combination of temporal fluctuation and spatial divergence. The frequency range of fluctuation was found to exceed significantly that of the heart rate. The high-frequency-fluctuating WSS appeared only during mid-systole and disappeared during late diastole. These results suggested that the flow impingement induced a transition from a laminar regime. This study demonstrated that the hydrodynamic instability of shear layer could not be neglected even at a low Reynolds number. No assumption was found to justify treating the aneurysmal haemodynamics as a fully viscous laminar flow.}, } @article {pmid23419503, year = {2013}, author = {Wagner, GL and Lauga, E}, title = {Crawling scallop: friction-based locomotion with one degree of freedom.}, journal = {Journal of theoretical biology}, volume = {324}, number = {}, pages = {42-51}, doi = {10.1016/j.jtbi.2013.01.021}, pmid = {23419503}, issn = {1095-8541}, mesh = {Animals ; Biomechanical Phenomena ; *Friction ; *Locomotion ; *Models, Biological ; }, abstract = {Fluid-based locomotion at low Reynolds number is subject to the constraints of the scallop theorem, which dictate that body kinematics identical under a time-reversal symmetry (in particular, those with a single degree of freedom) cannot display locomotion on average. The implications of the theorem naturally compel one to ask whether similar symmetry constraints exist for locomotion in different environments. In this work we consider locomotion along a surface where forces are described by isotropic Coulomb friction. To address whether motions with a single degree of freedom can lead to transport, we analyze a model system consisting of two bodies whose separation distance undergoes periodic time variations. The behavior of the two-body system is entirely determined by the kinematic specification of their separation, the friction forces, and the mass of each body. We show that the constraints of the scallop theorem can be escaped in frictional media if two asymmetry conditions are met at the same time: the frictional forces of each body against the surface must be distinct and the time-variation of the body-body separation must vary asymmetrically in time (so quick-slow or slow-quick in the extension-contraction phases). Our results are demonstrated numerically and interpreted using asymptotic expansions.}, } @article {pmid23410462, year = {2013}, author = {Clausen, JR}, title = {Entropically damped form of artificial compressibility for explicit simulation of incompressible flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {87}, number = {1}, pages = {013309}, doi = {10.1103/PhysRevE.87.013309}, pmid = {23410462}, issn = {1550-2376}, mesh = {*Algorithms ; Computer Simulation ; Elastic Modulus ; Energy Transfer ; *Models, Theoretical ; *Numerical Analysis, Computer-Assisted ; Rheology/*methods ; Viscosity ; }, abstract = {An alternative artificial compressibility (AC) scheme is proposed to allow the explicit simulation of the incompressible Navier-Stokes (INS) equations. Traditional AC schemes rely on an artificial equation of state that gives the pressure as a function of the density, which is known to enforce isentropic behavior. This behavior is nonideal, especially in viscously dominated flows. An alternative, the entropically damped artificial compressibility (EDAC) method, is proposed that employs a thermodynamic constraint to damp the pressure oscillations inherent to AC methods. The EDAC method converges to the INS in the low-Mach limit, and is consistent in both the low- and high-Reynolds-number limits, unlike standard AC schemes. The proposed EDAC method is discretized using a simple finite-difference scheme and is compared with traditional AC schemes as well as the lattice-Boltzmann method for steady lid-driven cavity flow and a transient traveling-wave problem. The EDAC method is shown to be beneficial in damping pressure and velocity-divergence oscillations when performing transient simulations. The EDAC method follows a similar derivation to the kinetically reduced local Navier-Stokes (KRLNS) method [Borok et al., Phys. Rev. E 76, 066704 (2007)]; however, the EDAC method does not rely on the grand potential as the thermodynamic variable, but instead uses the more common pressure-velocity system. Additionally, a term neglected in the KRLNS is identified that is important for accurately approximating the INS equations.}, } @article {pmid23410432, year = {2013}, author = {Bailey, PR and Abbá, A and Tordella, D}, title = {Pressure and kinetic energy transport across the cavity mouth in resonating cavities.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {87}, number = {1}, pages = {013013}, doi = {10.1103/PhysRevE.87.013013}, pmid = {23410432}, issn = {1550-2376}, mesh = {*Algorithms ; Computer Simulation ; *Energy Transfer ; Kinetics ; *Models, Theoretical ; Pressure ; Rheology/*methods ; }, abstract = {Basic properties of the incompressible fluid motion in a rectangular cavity located along one wall of a plane channel are considered. For Mach numbers of the order of 1×10(-3) and using the incompressible formulation, we look for observable properties that can be associated with acoustic emission, which is normally observed in this kind of flow beyond a critical value of Reynolds number. The focus is put on the energy dynamics, in particular on the accumulation of energy in the cavity which takes place in the form of pressure and kinetic energy. By increasing the external forcing, we observe that the pressure flow into the cavity increases very rapidly, then peaks. However, the flow of kinetic energy, which is many orders of magnitude lower than that of the pressure, slowly but continuously grows. This leads to the pressure-kinetic energy flows ratio reaching an asymptotic state around the value 1000 for the channel bulk speed Reynolds number. It is interesting to note that beyond this threshold when the channel flow is highly unsteady-a sort of coarse turbulent flow-a sequence of high and low pressure spots is seen to depart from the downward cavity step in the statistically averaged field. The set of spots forms a steady spatial structure, a sort of damped standing wave stretching along the spanwise direction. The line joining the centers of the spots has an inclination similar to the normal to the fronts of density or pressure waves, which are observed to propagate from the downstream cavity edge in compressible cavity flows (at Mach numbers of 1×10(2) to 1×10(3), larger than those considered here). The wavelength of the standing wave is of the order of 1/8 the cavity depth and observed at the channel bulk Reynolds number, Re~2900. In this condition, the measure of the maximum pressure differences in the cavity field shows values of the order of 1×10(-1) Pa. We interpret the presence of this sort of wave as the fingerprint of the noise emission spots which could be observed in simulations where the full compressible formulation is used. The flow is studied by means of a sequence of direct numerical simulations in the Reynolds number range 25-2900. This allows the study to span across the steady laminar regime up to a first coarse turbulent regime. These results are confirmed by the good agreement with a set of laboratory results obtained at a Reynolds number one order of magnitude larger in a different cavity geometry [M. Gharib and A. Roshko, J. Fluid Mech. 177, 501 (1987)]. This leaves room for a certain degree of qualitative universality to be associated with the present findings.}, } @article {pmid23368468, year = {2012}, author = {Soulard, O}, title = {Implications of the Monin-Yaglom relation for Rayleigh-Taylor turbulence.}, journal = {Physical review letters}, volume = {109}, number = {25}, pages = {254501}, doi = {10.1103/PhysRevLett.109.254501}, pmid = {23368468}, issn = {1079-7114}, abstract = {The aim of this letter is to assess existing theories for Rayleigh-Taylor small turbulent scales. For this purpose, we propose to adapt the Monin-Yaglom relation to the Rayleigh-Taylor turbulence context. A special emphasis is put on the inhomogeneity of the flow and on the effect of buoyancy forces. This relation is then used to show that, among existing theories, the standard Kolmogorov-Obukhov theory should apply to Rayleigh-Taylor turbulence in the limit of a large Reynolds number, large times, and small scales.}, } @article {pmid23368443, year = {2012}, author = {Willis, AP}, title = {Optimization of the magnetic dynamo.}, journal = {Physical review letters}, volume = {109}, number = {25}, pages = {251101}, doi = {10.1103/PhysRevLett.109.251101}, pmid = {23368443}, issn = {1079-7114}, abstract = {In stars and planets, magnetic fields are believed to originate from the motion of electrically conducting fluids in their interior, through a process known as the dynamo mechanism. In this Letter, an optimization procedure is used to simultaneously address two fundamental questions of dynamo theory: "Which velocity field leads to the most magnetic energy growth?" and "How large does the velocity need to be relative to magnetic diffusion?" In general, this requires optimization over the full space of continuous solenoidal velocity fields possible within the geometry. Here the case of a periodic box is considered. Measuring the strength of the flow with the root-mean-square amplitude, an optimal velocity field is shown to exist, but without limitation on the strain rate, optimization is prone to divergence. Measuring the flow in terms of its associated dissipation leads to the identification of a single optimal at the critical magnetic Reynolds number necessary for a dynamo. This magnetic Reynolds number is found to be only 15% higher than that necessary for transient growth of the magnetic field.}, } @article {pmid23368064, year = {2012}, author = {Schober, J and Schleicher, D and Bovino, S and Klessen, RS}, title = {Small-scale dynamo at low magnetic Prandtl numbers.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {86}, number = {6 Pt 2}, pages = {066412}, doi = {10.1103/PhysRevE.86.066412}, pmid = {23368064}, issn = {1550-2376}, abstract = {The present-day Universe is highly magnetized, even though the first magnetic seed fields were most probably extremely weak. To explain the growth of the magnetic field strength over many orders of magnitude, fast amplification processes need to operate. The most efficient mechanism known today is the small-scale dynamo, which converts turbulent kinetic energy into magnetic energy leading to an exponential growth of the magnetic field. The efficiency of the dynamo depends on the type of turbulence indicated by the slope of the turbulence spectrum v(ℓ)∝ℓ^{ϑ}, where v(ℓ) is the eddy velocity at a scale ℓ. We explore turbulent spectra ranging from incompressible Kolmogorov turbulence with ϑ=1/3 to highly compressible Burgers turbulence with ϑ=1/2. In this work, we analyze the properties of the small-scale dynamo for low magnetic Prandtl numbers Pm, which denotes the ratio of the magnetic Reynolds number, Rm, to the hydrodynamical one, Re. We solve the Kazantsev equation, which describes the evolution of the small-scale magnetic field, using the WKB approximation. In the limit of low magnetic Prandtl numbers, the growth rate is proportional to Rm^{(1-ϑ)/(1+ϑ)} . We furthermore discuss the critical magnetic Reynolds number Rm_{crit}, which is required for small-scale dynamo action. The value of Rm_{crit} is roughly 100 for Kolmogorov turbulence and 2700 for Burgers. Furthermore, we discuss that Rm_{crit} provides a stronger constraint in the limit of low Pm than it does for large Pm. We conclude that the small-scale dynamo can operate in the regime of low magnetic Prandtl numbers if the magnetic Reynolds number is large enough. Thus, the magnetic field amplification on small scales can take place in a broad range of physical environments and amplify week magnetic seed fields on short time scales.}, } @article {pmid23368052, year = {2012}, author = {Kim, Y and Lai, MC}, title = {Numerical study of viscosity and inertial effects on tank-treading and tumbling motions of vesicles under shear flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {86}, number = {6 Pt 2}, pages = {066321}, doi = {10.1103/PhysRevE.86.066321}, pmid = {23368052}, issn = {1550-2376}, mesh = {Biophysics/*methods ; Computer Simulation ; Models, Theoretical ; *Motion ; Movement ; Shear Strength ; Stress, Mechanical ; *Viscosity ; }, abstract = {An inextensible vesicle under shear flow experiences a tank-treading motion on its membrane if the viscosity contrast between the interior and exterior fluids is small. Above a critical threshold of viscosity contrast, the vesicle undergoes a tumbling bifurcation. In this paper, we extend our previous work [Kim and Lai, J. Comput. Phys. 229, 4840 (2010)] to the case of different viscosity and investigate the transition between the tank-treading and tumbling motions in detail. The present numerical results are in a good agreement with other numerical and theoretical studies qualitatively. In addition, we study the inertial effect on this transition and find that the inertial effect might inhibit the tumbling motion in favor of the tank-treading motion, which is observed recently in the literature. The critical viscosity contrast for the transition to the tumbling motion usually increases as the reduced area increases in the Stokes regime. However, we surprisingly observe that the critical viscosity contrast decreases as the reduced area increases to some point in the flow of slightly higher Reynolds number. Our numerical result also shows that the inertial effect has stronger inhibition to tumbling motion when the reduced area is small.}, } @article {pmid23368040, year = {2012}, author = {Brouwers, JJ}, title = {Statistical description of turbulent dispersion.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {86}, number = {6 Pt 2}, pages = {066309}, doi = {10.1103/PhysRevE.86.066309}, pmid = {23368040}, issn = {1550-2376}, abstract = {We derive a comprehensive statistical model for dispersion of passive or almost passive admixture particles such as fine particulate matter, aerosols, smoke, and fumes in turbulent flow. The model rests on the Markov limit for particle velocity. It is in accordance with the asymptotic structure of turbulence at large Reynolds number as described by Kolmogorov. The model consists of Langevin and diffusion equations in which the damping and diffusivity are expressed by expansions in powers of the reciprocal Kolmogorov constant C_{0} . We derive solutions of O(C_{0} ^{0} ) and O(C_{0} ^{-1} ). We truncate at O(C_{0} ^{-2} ) which is shown to result in an error of a few percentages in predicted dispersion statistics for representative cases of turbulent flow. We reveal analogies and remarkable differences between the solutions of classical statistical mechanics and those of statistical turbulence.}, } @article {pmid23363214, year = {2013}, author = {Kousera, CA and Wood, NB and Seed, WA and Torii, R and O'Regan, D and Xu, XY}, title = {A numerical study of aortic flow stability and comparison with in vivo flow measurements.}, journal = {Journal of biomechanical engineering}, volume = {135}, number = {1}, pages = {011003}, doi = {10.1115/1.4023132}, pmid = {23363214}, issn = {1528-8951}, mesh = {Adult ; Aorta/*physiology ; *Blood Circulation ; Female ; Humans ; *Hydrodynamics ; Models, Anatomic ; *Models, Biological ; Stress, Mechanical ; }, abstract = {The development of an engineering transitional turbulence model and its subsequent evaluation and validation for some diseased cardiovascular flows have been suggestive of its likely utility in normal aortas. The existence of experimental data from human aortas, acquired in the early 1970s with catheter-mounted hot film velocimeters, provided the opportunity to compare the performance of the model on such flows. A generic human aorta, derived from magnetic resonance anatomical and velocity images of a young volunteer, was used as the basis for varying both Reynolds number (Re) and Womersley parameter (α) to match four experimental data points from human ascending aortas, comprising two with disturbed flow and two with apparently undisturbed flow. Trials were made with three different levels of inflow turbulence intensity (Tu) to find if a single level could represent the four different cases with 4000 < Re < 10,000 and 17 < α < 26. A necessary boundary condition includes the inflow "turbulence" level, and convincing results were obtained for all four cases with inflow Tu = 1.0%, providing additional confidence in the application of the transitional model in flows in larger arteries. The Reynolds-averaged Navier-Stokes (RANS)-based shear stress transport (SST) transitional model is capable of capturing the correct flow state in the human aorta when low inflow turbulence intensity (1.0%) is specified.}, } @article {pmid23363125, year = {2013}, author = {Vaik, I and Paál, G}, title = {Flow simulations on an organ pipe foot model.}, journal = {The Journal of the Acoustical Society of America}, volume = {133}, number = {2}, pages = {1102-1110}, doi = {10.1121/1.4773861}, pmid = {23363125}, issn = {1520-8524}, mesh = {*Acoustics ; *Computer Simulation ; *Models, Theoretical ; Motion ; *Music ; *Numerical Analysis, Computer-Assisted ; Oscillometry ; *Sound ; Time Factors ; }, abstract = {The present paper shows numerical simulations of the flow responsible for the sound generation in an organ pipe. Only the foot model of the organ pipe (i.e., with the resonator detached) is investigated by two-dimensional incompressible CFD simulations. It is shown that in spite of the moderately high Reynolds number (Re≈2350) no turbulence modeling is necessary. Free jet simulation (foot model without the upper lip) showed that the jet oscillates due to its natural instability. The velocity profile, the centerline and the width of the jet is determined at different heights above the flue. Edge tone simulations (foot model with the upper lip) were carried out having the upper lip at a constant height but at different x positions. It was found that the strongest and most stable edge tone oscillation occurs if the lower left corner of the upper lip is in the centerline of the jet (optimum position). When the upper lip is far from its optimum position the oscillation of the jet is rather due to the natural instability of the jet than the edge tone phenomenon. The results agree well with the experimental results of Außerlechner et al. [J. Acoust. Soc. Am. 126, 878-886 (2009)] and Außerlechner (Ph.D. thesis, Universität Stuttgart, Stuttgart, Germany) and with former results of the authors [Paál and Vaik, Int. J. Heat Fluid Flow 28, 575-586 (2007); Paál and Vaik, in Conference on Modelling Fluid Flow (CMFF'09), Budapest, Hungary].}, } @article {pmid23363089, year = {2013}, author = {Lam, GC and Leung, RC and Tang, SK}, title = {Aeroacoustics of T-junction merging flow.}, journal = {The Journal of the Acoustical Society of America}, volume = {133}, number = {2}, pages = {697-708}, doi = {10.1121/1.4773351}, pmid = {23363089}, issn = {1520-8524}, mesh = {*Acoustics/instrumentation ; Computer Simulation ; Equipment Design ; *Models, Theoretical ; Motion ; Noise/prevention & control ; Numerical Analysis, Computer-Assisted ; Pressure ; Rheology ; *Sound ; Time Factors ; }, abstract = {This paper reports a numerical study of the aeroacoustics of merging flow at T-junction. The primary focus is to elucidate the acoustic generation by the flow unsteadiness. The study is conducted by performing direct aeroacoustic simulation approach, which solves the unsteady compressible Navier-Stokes equations and the perfect gas equation of state simultaneously using the conservation element and solution element method. For practical flows, the Reynolds number based on duct width is usually quite high (>10(5)). In order to properly account for the effects of flow turbulence, a large eddy simulation methodology together with a wall modeling derived from the classical logarithm wall law is adopted. The numerical simulations are performed in two dimensions and the acoustic generation physics at different ratios of side-branch to main duct flow velocities VR (=0.5,0.67,1.0,2.0) are studied. Both the levels of unsteady interactions of merging flow structures and the efficiency of acoustic generation are observed to increase with VR. Based on Curle's analogy, the major acoustic source is found to be the fluctuating wall pressure induced by the flow unsteadiness occurred in the downstream branch. A scaling between the wall fluctuating force and the efficiency of the acoustic generation is also derived.}, } @article {pmid23326222, year = {2013}, author = {Chindapol, N and Kaandorp, JA and Cronemberger, C and Mass, T and Genin, A}, title = {Modelling growth and form of the scleractinian coral Pocillopora verrucosa and the influence of hydrodynamics.}, journal = {PLoS computational biology}, volume = {9}, number = {1}, pages = {e1002849}, pmid = {23326222}, issn = {1553-7358}, mesh = {Animals ; Anthozoa/*growth & development ; Finite Element Analysis ; *Hydrodynamics ; *Models, Biological ; Tomography, X-Ray Computed ; }, abstract = {The growth of scleractinian corals is strongly influenced by the effect of water motion. Corals are known to have a high level of phenotypic variation and exhibit a diverse range of growth forms, which often contain a high level of geometric complexity. Due to their complex shape, simulation models represent an important option to complement experimental studies of growth and flow. In this work, we analyzed the impact of flow on coral's morphology by an accretive growth model coupled with advection-diffusion equations. We performed simulations under no-flow and uni-directional flow setup with the Reynolds number constant. The relevant importance of diffusion to advection was investigated by varying the diffusion coefficient, rather than the flow speed in Péclet number. The flow and transport equations were coupled and solved using COMSOL Multiphysics. We then compared the simulated morphologies with a series of Computed Tomography (CT) scans of scleractinian corals Pocillopora verrucosa exposed to various flow conditions in the in situ controlled flume setup. As a result, we found a similar trend associated with the increasing Péclet for both simulated forms and in situ corals; that is uni-directional current tends to facilitate asymmetrical growth response resulting in colonies with branches predominantly developed in the upstream direction. A closer look at the morphological traits yielded an interesting property about colony symmetry and plasticity induced by uni-directional flow. Both simulated and in situ corals exhibit a tendency where the degree of symmetry decreases and compactification increases in conjunction with the augmented Péclet thus indicates the significant importance of hydrodynamics.}, } @article {pmid23319607, year = {2013}, author = {Rodenborn, B and Chen, CH and Swinney, HL and Liu, B and Zhang, HP}, title = {Propulsion of microorganisms by a helical flagellum.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {110}, number = {5}, pages = {E338-47}, pmid = {23319607}, issn = {1091-6490}, mesh = {*Algorithms ; *Bacterial Physiological Phenomena ; Computer Simulation ; Flagella/*physiology ; *Models, Biological ; Movement/physiology ; Rotation ; Torque ; }, abstract = {The swimming of a bacterium or a biomimetic nanobot driven by a rotating helical flagellum is often interpreted using the resistive force theory developed by Gray and Hancock and by Lighthill, but this theory has not been tested for a range of physically relevant parameters. We test resistive force theory in experiments on macroscopic swimmers in a fluid that is highly viscous so the Reynolds number is small compared to unity, just as for swimming microorganisms. The measurements are made for the range of helical wavelengths λ, radii R, and lengths L relevant to bacterial flagella. The experiments determine thrust, torque, and drag, thus providing a complete description of swimming driven by a rotating helix at low Reynolds number. Complementary numerical simulations are conducted using the resistive force theories, the slender body theories of Lighthill and Johnson, and the regularized Stokeslet method. The experimental results differ qualitatively and quantitatively from the predictions of resistive force theory. The difference is especially large for and/or , parameter ranges common for bacteria. In contrast, the predictions of Stokeslet and slender body analyses agree with the laboratory measurements within the experimental uncertainty (a few percent) for all λ, R, and L. We present code implementing the slender body, regularized Stokeslet, and resistive force theories; thus readers can readily compute force, torque, and drag for any bacterium or nanobot driven by a rotating helical flagellum.}, } @article {pmid23315132, year = {2012}, author = {Uchida, N and Golestanian, R}, title = {Hydrodynamic synchronization between objects with cyclic rigid trajectories.}, journal = {The European physical journal. E, Soft matter}, volume = {35}, number = {12}, pages = {9813}, pmid = {23315132}, issn = {1292-895X}, mesh = {Cilia ; Flagella ; *Hydrodynamics ; *Models, Theoretical ; Rotation ; }, abstract = {Synchronization induced by long-range hydrodynamic interactions is attracting attention as a candidate mechanism behind coordinated beating of cilia and flagella. Here we consider a minimal model of hydrodynamic synchronization in the low Reynolds number limit. The model consists of rotors, each of which assumed to be a rigid bead making a fixed trajectory under periodically varying driving force. By a linear analysis, we derive the necessary and sufficient conditions for a pair of rotors to synchronize in phase. We also derive a non-linear evolution equation for their phase difference, which is reduced to minimization of an effective potential. The effective potential is calculated for a variety of trajectory shapes and geometries (either bulk or substrated), for which the stable and metastable states of the system are identified. Finite size of the trajectory induces asymmetry of the potential, which also depends sensitively on the tilt of the trajectory. Our results show that flexibility of cilia or flagella is not a requisite for their synchronized motion, in contrast to previous expectations. We discuss the possibility to directly implement the model and verify our results by optically driven colloids.}, } @article {pmid23293067, year = {2013}, author = {Kim, JW and Xi, J and Si, XA}, title = {Dynamic growth and deposition of hygroscopic aerosols in the nasal airway of a 5-year-old child.}, journal = {International journal for numerical methods in biomedical engineering}, volume = {29}, number = {1}, pages = {17-39}, doi = {10.1002/cnm.2490}, pmid = {23293067}, issn = {2040-7947}, mesh = {Administration, Intranasal ; Aerosols/*pharmacology ; Child, Preschool ; Humans ; Male ; *Models, Biological ; *Nasal Cavity ; }, abstract = {Hygroscopic growth within the human respiratory tract can be significant, which may notably alter the behavior and fate of the inhaled aerosols. The objective of this study is to evaluate the hygroscopic effects upon the transport and deposition of nasally inhaled fine-regime aerosols in children. A physiologically realistic nasal-laryngeal airway model was developed based on magnetic resonance imaging of a 5-year-old boy. Temperature and relative humidity field were simulated using the low Reynolds number k - ε turbulence model and chemical specie transport model under a spectrum of four thermo-humidity conditions. Particle growth and transport were simulated using a well validated Lagrangian tracking model coupled with a user-defined hygroscopic growth module. The subsequent aerosol depositions for the four inhalation scenarios were evaluated on a multiscale basis such as total, subregional, and cellular-level depositions. Results of this study show that a supersaturated humid environment is possible in the nasal turbinate region and can lead to significant condensation growth (d / d(0) > 10) of nasally inhaled aerosols. Depositions in the nasal airway can also be greatly enhanced by condensation growth with appropriate inhalation temperature and humidity. For subsaturated and mild inhalation conditions, the hygroscopic effects were found to be nonsignificant for total depositions, while exerting a large impact upon localized depositions.}, } @article {pmid23280552, year = {2013}, author = {Spruell, C and Baker, AB}, title = {Analysis of a high-throughput cone-and-plate apparatus for the application of defined spatiotemporal flow to cultured cells.}, journal = {Biotechnology and bioengineering}, volume = {110}, number = {6}, pages = {1782-1793}, pmid = {23280552}, issn = {1097-0290}, support = {DP2 OD008716/OD/NIH HHS/United States ; }, mesh = {Cell Culture Techniques/*instrumentation/*methods ; Cells, Cultured ; Computer Simulation ; Endothelial Cells/cytology ; High-Throughput Screening Assays/*instrumentation ; Humans ; Stress, Mechanical ; Viscosity ; }, abstract = {The shear stresses derived from blood flow regulate many aspects of vascular and immunobiology. In vitro studies on the shear stress-mediated mechanobiology of endothelial cells have been carried out using systems analogous to the cone-and-plate viscometer in which a rotating, low-angle cone applies fluid shear stress to cells grown on an underlying, flat culture surface. We recently developed a device that could perform high-throughput studies on shear-mediated mechanobiology through the rotation of cone-tipped shafts in a standard 96-well culture plate. Here, we present a model of the three-dimensional flow within the culture wells with a rotating, cone-tipped shaft. Using this model we examined the effects of modifying the design parameters of the system to allow the device to create a variety of flow profiles. We first examined the case of steady-state flow with the shaft rotating at constant angular velocity. By varying the angular velocity and distance of the cone from the underlying plate we were able to create flow profiles with controlled shear stress gradients in the radial direction within the plate. These findings indicate that both linear and non-linear spatial distributions in shear stress can be created across the bottom of the culture plate. In the transition and "parallel shaft" regions of the system, the angular velocities needed to provide high levels of physiological shear stress (5 Pa) created intermediate Reynolds number Taylor-Couette flow. In some cases, this led to the development of a flow regime in which stable helical vortices were created within the well. We also examined the system under oscillatory and pulsatile motion of the shaft and demonstrated minimal time lag between the rotation of the cone and the shear stress on the cell culture surface.}, } @article {pmid24957058, year = {2013}, author = {Ochando-Pulido, JM and Hodaifa, G and Victor-Ortega, MD and Martinez-Ferez, A}, title = {Performance modeling and cost analysis of a pilot-scale reverse osmosis process for the final purification of olive mill wastewater.}, journal = {Membranes}, volume = {3}, number = {4}, pages = {285-297}, pmid = {24957058}, issn = {2077-0375}, abstract = {A secondary treatment for olive mill wastewater coming from factories working with the two-phase olive oil production process (OMW-2) has been set-up on an industrial scale in an olive oil mill in the premises of Jaén (Spain). The secondary treatment comprises Fenton-like oxidation followed by flocculation-sedimentation and filtration through olive stones. In this work, performance modelization and preliminary cost analysis of a final reverse osmosis (RO) process was examined on pilot scale for ulterior purification of OMW-2 with the goal of closing the loop of the industrial production process. Reduction of concentration polarization on the RO membrane equal to 26.3% was provided upon increment of the turbulence over the membrane to values of Reynolds number equal to 2.6 × 104. Medium operating pressure (25 bar) should be chosen to achieve significant steady state permeate flux (21.1 L h-1 m-2) and minimize membrane fouling, ensuring less than 14.7% flux drop and up to 90% feed recovery. Under these conditions, irreversible fouling below 0.08 L h-2 m-2 bar-1 helped increase the longevity of the membrane and reduce the costs of the treatment. For 10 m3 day-1 OMW-2 on average, 47.4 m2 required membrane area and 0.87 € m-3 total costs for the RO process were estimated.}, } @article {pmid24891756, year = {2013}, author = {Siddique, W and El-Gabry, L and Shevchuk, IV and Fransson, TH}, title = {Validation and Analysis of Numerical Results for a Two-Pass Trapezoidal Channel With Different Cooling Configurations of Trailing Edge.}, journal = {Journal of turbomachinery}, volume = {135}, number = {1}, pages = {0110271-0110278}, pmid = {24891756}, issn = {0889-504X}, abstract = {High inlet temperatures in a gas turbine lead to an increase in the thermal efficiency of the gas turbine. This results in the requirement of cooling of gas turbine blades/vanes. Internal cooling of the gas turbine blade/vanes with the help of two-pass channels is one of the effective methods to reduce the metal temperatures. In particular, the trailing edge of a turbine vane is a critical area, where effective cooling is required. The trailing edge can be modeled as a trapezoidal channel. This paper describes the numerical validation of the heat transfer and pressure drop in a trapezoidal channel with and without orthogonal ribs at the bottom surface. A new concept of ribbed trailing edge has been introduced in this paper which presents a numerical study of several trailing edge cooling configurations based on the placement of ribs at different walls. The baseline geometries are two-pass trapezoidal channels with and without orthogonal ribs at the bottom surface of the channel. Ribs induce secondary flow which results in enhancement of heat transfer; therefore, for enhancement of heat transfer at the trailing edge, ribs are placed at the trailing edge surface in three different configurations: first without ribs at the bottom surface, then ribs at the trailing edge surface in-line with the ribs at the bottom surface, and finally staggered ribs. Heat transfer and pressure drop is calculated at Reynolds number equal to 9400 for all configurations. Different turbulent models are used for the validation of the numerical results. For the smooth channel low-Re k-ɛ model, realizable k-ɛ model, the RNG k-ω model, low-Re k-ω model, and SST k-ω models are compared, whereas for ribbed channel, low-Re k-ɛ model and SST k-ω models are compared. The results show that the low-Re k-ɛ model, which predicts the heat transfer in outlet pass of the smooth channels with difference of +7%, underpredicts the heat transfer by -17% in case of ribbed channel compared to experimental data. Using the same turbulence model shows that the height of ribs used in the study is not suitable for inducing secondary flow. Also, the orthogonal rib does not strengthen the secondary flow rotational momentum. The comparison between the new designs for trailing edge shows that if pressure drop is acceptable, staggered arrangement is suitable for the outlet pass heat transfer. For the trailing edge wall, the thermal performance for the ribbed trailing edge only was found about 8% better than other configurations.}, } @article {pmid23229757, year = {2012}, author = {Seto, R and Botet, R and Auernhammer, GK and Briesen, H}, title = {Restructuring of colloidal aggregates in shear flow: coupling interparticle contact models with Stokesian dynamics.}, journal = {The European physical journal. E, Soft matter}, volume = {35}, number = {12}, pages = {9805}, pmid = {23229757}, issn = {1292-895X}, abstract = {A method to couple interparticle contact models with Stokesian dynamics (SD) is introduced to simulate colloidal aggregates under flow conditions. The contact model mimics both the elastic and plastic behavior of the cohesive connections between particles within clusters. Owing to this, clusters can maintain their structures under low stress while restructuring or even breakage may occur under sufficiently high stress conditions. SD is an efficient method to deal with the long-ranged and many-body nature of hydrodynamic interactions for low Reynolds number flows. By using such a coupled model, the restructuring of colloidal aggregates under shear flows with stepwise increasing shear rates was studied. Irreversible compaction occurs due to the increase of hydrodynamic stress on clusters. Results show that the greater part of the fractal clusters are compacted to rod-shaped packed structures, while the others show isotropic compaction.}, } @article {pmid23224111, year = {2012}, author = {Leoni, M and Liverpool, TB}, title = {Translations and rotations at low Reynolds number: a study of simple model swimmers with finite amplitude strokes.}, journal = {The European physical journal. E, Soft matter}, volume = {35}, number = {12}, pages = {9803}, pmid = {23224111}, issn = {1292-895X}, mesh = {Humans ; *Models, Theoretical ; Rotation ; Swimming/*physiology ; }, abstract = {We present a simple dynamical model of self-propeller at low Reynolds number in which self-propulsion is achieved via rotary elements (rotors). In this model by changing the sense of rotation of the rotors, the self-propeller can switch between a "linear swimming" phase where it swims in a straight line and a "tumbling" phase in which it can change direction in a controllable way via a global rotation of its body. We study the dynamics of this propeller in detail. To do this we provide an analytic framework within which the non-perturbative aspects of the internal dynamics can be treated allowing us to study the swimming process for arbitrary values of the swimmer deformations. Using it, we compute the averages (over a deformation cycle) of a number of characteristic properties of the swimmer such as its self-propulsion velocity, the dissipated power, its efficiency and the fluid flow patterns it generates. We compare these results to the corresponding average quantities for another class of model swimmers, where self-propulsion is achieved via periodic translations. Finally, we provide an explanation of why non-perturbative results can be obtained for these models using the geometrical language of gauge theory.}, } @article {pmid23215676, year = {2013}, author = {Mattei, TA and Morris, M and Nowak, K and Smith, D and Yee, J and Goulart, CR and Zborowski, A and Lin, JJ}, title = {Addressing the siphoning effect in new shunt designs by decoupling the activation pressure and the pressure gradient across the valve.}, journal = {Journal of neurosurgery. Pediatrics}, volume = {11}, number = {2}, pages = {181-187}, doi = {10.3171/2012.10.PEDS11561}, pmid = {23215676}, issn = {1933-0715}, mesh = {*Cerebrospinal Fluid ; Cerebrospinal Fluid Shunts/*instrumentation/methods ; *Computer Simulation ; Equipment Design ; Humans ; Hydrocephalus/*physiopathology/*surgery ; *Hydrodynamics ; *Intracranial Pressure ; }, abstract = {OBJECT: Although several improvements have been observed in the past few years in shunt technology, currently available systems still present several associated problems. Among these, overdrainage along with its complications remains one of the great challenges for new shunt designs. To address the so-called siphoning effect, the authors provide a practical example of how it is possible to decouple the activation pressure and the pressure gradient across the valve through a 3-key component system. In this new shunt design, the flow is expected to depend only on the intracranial pressure and not on the pressure gradient across the valve, thus avoiding the so-called siphoning effect.

METHODS: The authors used computer models to theoretically evaluate the mechanical variables involved in the operation of the newly designed valve, such as the fluid's Reynolds number, proximal pressure, distal pressure, pressure gradient, actual flow rate, and expected flow rate. After fabrication of the first superscaled model, the authors performed benchmark tests to analyze the performance of the new shunt prototype, and the obtained data were compared with the results predicted by the previous mathematical models.

RESULTS: The final design of the new paddle wheel valve with the 3-key component antisiphoning system was tested in the hydrodynamics laboratory to prove that the siphoning effect did not occur. According to the calculations obtained using the LabVIEW program during the experiments, each time the distal pressure decreased without an increase in the proximal pressure (despite the range of the pressure gradient), the pin blocked the spinning of the paddle wheels, and the calculated fluid velocity through the system tended to zero. Such a situation was significantly different from the expected flow rate for such a pressure gradient in a siphoning situation without the new antisiphon system.

CONCLUSIONS: The design of this new prototype with a 3-key component antisiphoning system demonstrated that it is possible to decouple the activation pressure and the pressure gradient across the valve, avoiding the siphoning effect. Although further developments are necessary to provide a model compatible to clinical use, the authors believe that this new prototype illustrates the possibility of successfully addressing the siphoning effect by using a simple 3-key component system that is able to decouple the activation pressure and the pressure gradient across the valve by using a separate pressure chamber. It is expected that such proof of concept may significantly contribute to future shunt designs attempting to address the problem of overdrainage due to the siphoning effect.}, } @article {pmid23214882, year = {2012}, author = {Urzhumov, YA and Smith, DR}, title = {Flow stabilization with active hydrodynamic cloaks.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {86}, number = {5 Pt 2}, pages = {056313}, doi = {10.1103/PhysRevE.86.056313}, pmid = {23214882}, issn = {1550-2376}, mesh = {Computer Simulation ; *Hydrodynamics ; *Models, Theoretical ; Refractometry/*methods ; Rheology/*methods ; }, abstract = {We demonstrate that fluid flow cloaking solutions, based on active hydrodynamic metamaterials, exist for two-dimensional flows past a cylinder in a wide range of Reynolds numbers (Re's), up to approximately 200. Within the framework of the classical Brinkman equation for homogenized porous flow, we demonstrate using two different methods that such cloaked flows can be dynamically stable for Re's in the range of 5-119. The first highly efficient method is based on a linearization of the Brinkman-Navier-Stokes equation and finding the eigenfrequencies of the least stable eigenperturbations; the second method is a direct numerical integration in the time domain. We show that, by suppressing the von Kármán vortex street in the weakly turbulent wake, porous flow cloaks can raise the critical Reynolds number up to about 120 or five times greater than for a bare uncloaked cylinder.}, } @article {pmid23214877, year = {2012}, author = {Shi, L and Pan, TW and Glowinski, R}, title = {Lateral migration and equilibrium shape and position of a single red blood cell in bounded Poiseuille flows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {86}, number = {5 Pt 2}, pages = {056308}, doi = {10.1103/PhysRevE.86.056308}, pmid = {23214877}, issn = {1550-2376}, mesh = {Animals ; Blood Flow Velocity/*physiology ; Cell Movement/*physiology ; Cell Polarity ; Cell Size ; Cells, Cultured ; Computer Simulation ; Erythrocytes/*physiology ; Humans ; Membrane Fluidity/*physiology ; *Models, Cardiovascular ; Shear Strength/physiology ; }, abstract = {Lateral migration and equilibrium shape and position of a single red blood cell (RBC) in bounded two-dimensional Poiseuille flows are investigated by using an immersed boundary method. An elastic spring model is applied to simulate the skeleton structure of a RBC membrane. We focus on studying the properties of lateral migration of a single RBC in Poiseuille flows by varying the initial position, the initial angle, the swelling ratio (s), the membrane bending stiffness of RBC (k{b} ), the maximum velocity of fluid flow (u{max} ), and the degree of confinement. The combined effect of the deformability, the degree of confinement, and the shear gradient of the Poiseuille flow make the RBCs migrate toward a certain cross-sectional equilibrium position, which lies either on the center line of the channel or off center line. For s>0.8, the speed of the migration at the beginning decreases as one increases the swelling ratio s. But for s<0.8, the speed of the migration at the beginning is an increasing function of the swelling ratio s. Two motions of oscillation and vacillating breathing (swing) of RBCs are observed. The distance Y{d} between the cell mass center of the equilibrium position and the center line of the channel increases with increasing the Reynolds number Re and reaches a peak, then decreases with increasing Re. The peak of Re is a decreasing function of the swelling ratio (s<1.0). The cell membrane energy of the equilibrium position is an increasing function as Re increases. The slipper-shaped cell is more stable than the parachute-shaped one in the sense that the energy stored in the former is lower than that in the latter. For a given Re, the bigger the swelling ratio (s<1.0), the lower the cell membrane energy.}, } @article {pmid23214698, year = {2012}, author = {Wei, T and Livescu, D}, title = {Late-time quadratic growth in single-mode Rayleigh-Taylor instability.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {86}, number = {4 Pt 2}, pages = {046405}, doi = {10.1103/PhysRevE.86.046405}, pmid = {23214698}, issn = {1550-2376}, abstract = {The growth of the two-dimensional single-mode Rayleigh-Taylor instability (RTI) at low Atwood number (A=0.04) is investigated using Direct Numerical Simulations. The main result of the paper is that, at long times and sufficiently high Reynolds numbers, the bubble acceleration becomes stationary, indicating mean quadratic growth. This is contrary to the general belief that single-mode Rayleigh-Taylor instability reaches a constant bubble velocity at long times. At unity Schmidt number, the development of the instability is strongly influenced by the perturbation Reynolds number, defined as Rep≡λsqrt[Agλ/(1+A)]/ν. Thus, the instability undergoes different growth stages at low and high Rep. A new stage, chaotic development, was found at sufficiently high Rep values, after the reacceleration stage. During the chaotic stage, the instability experiences seemingly random acceleration and deceleration phases, as a result of complex vortical motions, with strong dependence on the initial perturbation shape (i.e., wavelength, amplitude, and diffusion thickness). Nevertheless, our results show that the mean acceleration of the bubble front becomes constant at late times, with little influence from the initial shape of the interface. As Rep is lowered to small values, the later instability stages, chaotic development, reacceleration, potential flow growth, and even the exponential growth described by linear stability theory, are subsequently no longer reached. Therefore, the results suggest a minimum Reynolds number and a minimum development time necessary to achieve all stages of single-mode RTI development, requirements which were not satisfied in the previous studies of single-mode RTI.}, } @article {pmid23214675, year = {2012}, author = {Huang, H and Wu, Y and Lu, X}, title = {Shear viscosity of dilute suspensions of ellipsoidal particles with a lattice Boltzmann method.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {86}, number = {4 Pt 2}, pages = {046305}, doi = {10.1103/PhysRevE.86.046305}, pmid = {23214675}, issn = {1550-2376}, abstract = {The intrinsic viscosities for prolate and oblate spheroidal suspensions in a dilute Newtonian fluid are studied using a three-dimensional lattice Boltzmann method. Through directly calculated viscous dissipation, the minimum and maximum intrinsic viscosities and the period of the tumbling state all agree well with the analytical solution for particles with different aspect ratios. This numerical test verifies the analysis on maximum and minimum intrinsic viscosities. Different behavior patterns of transient intrinsic viscosity in a period are analyzed in detail. A phase lag between the transient intrinsic viscosity and the orientation of the particle at finite Reynolds number (Re) is found and attributed to fluid and particle inertia. At lower Re, the phase lag increases with Re. There exists a critical Reynolds number Rea at which the phase lag begins to decrease with Re. The Rea depends on the aspect ratio of the particle. We found that both the intrinsic viscosity and the period change linearly with Re when ReRea (high-Re regime). In the high-Re regime, the dependence of the period on Re is consistent with a scaling law, and the dependence of the intrinsic viscosity on Re is well described by second-degree polynomial fits.}, } @article {pmid23214641, year = {2012}, author = {Castrejón-Pita, AA and Castrejón-Pita, JR and Hutchings, IM}, title = {Experimental observation of von Kármán vortices during drop impact.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {86}, number = {4 Pt 2}, pages = {045301}, doi = {10.1103/PhysRevE.86.045301}, pmid = {23214641}, issn = {1550-2376}, abstract = {The observation of von Kármán type vortices during the impact of water droplets onto a pool of water is reported. Shadowgraph imaging and laser-sheet visualization are used to document these events. The appearance of these vortices occurs within theoretically predicted regions in a Reynolds-splash number parameter space. In addition, and also in agreement with theoretical predictions, smooth splashing, with vortices absent, is found for smaller Reynolds number.}, } @article {pmid23205152, year = {2012}, author = {McCormick, SM and Seil, JT and Smith, DS and Tan, F and Loth, F}, title = {Transitional Flow in a Cylindrical Flow Chamber for Studies at the Cellular Level.}, journal = {Cardiovascular engineering and technology}, volume = {3}, number = {4}, pages = {439-449}, pmid = {23205152}, issn = {1869-4098}, support = {R01 HL055296/HL/NHLBI NIH HHS/United States ; }, abstract = {Fluid shear stress is an important regulator of vascular and endothelial cell (EC) functions. Its effect is dependent not only on magnitude but also on flow type. Although laminar flow predominates in the vasculature, transitional flow can occur and is thought to play a role in vascular diseases. While a great deal is known about the mechanisms and signaling cascades through which laminar shear stress regulates cells, little is known on how transitional shear stress regulates cells. To better understand the response of endothelial cells to transitional shear stress, a novel cylindrical flow chamber was designed to expose endothelial cells to a transitional flow environment similar to that found in vivo. The velocity profiles within the transitional flow chamber at Reynolds numbers 2200 and 3000 were measured using laser Doppler anemometry (LDA). At both Reynolds numbers, the velocity profiles are blunt (non-parabolic) with fluctuations larger than 5% of the velocity at the center of the pipe indicating the flows are transitional. Based on near wall velocity measurements and well established data for flow at these Reynolds numbers, the wall shear stress was estimated to be 3-4 and 5-6 dynes/cm(2) for Reynolds number 2200 and 3000, respectively. In contrast to laminar shear stress, no cell alignment was observed under transitional shear stress at both Reynolds numbers. However, transitional shear stress at the higher Reynolds number caused cell elongation similar to that of laminar shear stress at 3 dynes/cm(2). The fluctuating component of the wall shear stress may be responsible for these differences. The transitional flow chamber will facilitate cellular studies to identify the mechanisms through which transitional shear stress alters EC biology, which will assist in the development of vascular therapeutic treatments.}, } @article {pmid25552745, year = {2012}, author = {Attia, JA and McKinley, IM and Moreno-Magana, D and Pilon, L}, title = {Convective heat transfer in foams under laminar flow in pipes and tube bundles.}, journal = {International journal of heat and mass transfer}, volume = {55}, number = {25-26}, pages = {7823-7831}, pmid = {25552745}, issn = {0017-9310}, support = {R25 GM055052/GM/NIGMS NIH HHS/United States ; }, abstract = {The present study reports experimental data and scaling analysis for forced convection of foams and microfoams in laminar flow in circular and rectangular tubes as well as in tube bundles. Foams and microfoams are pseudoplastic (shear thinning) two-phase fluids consisting of tightly packed bubbles with diameters ranging from tens of microns to a few millimeters. They have found applications in separation processes, soil remediation, oil recovery, water treatment, food processes, as well as in fire fighting and in heat exchangers. First, aqueous solutions of surfactant Tween 20 with different concentrations were used to generate microfoams with various porosity, bubble size distribution, and rheological behavior. These different microfoams were flowed in uniformly heated circular tubes of different diameter instrumented with thermocouples. A wide range of heat fluxes and flow rates were explored. Experimental data were compared with analytical and semi-empirical expressions derived and validated for single-phase power-law fluids. These correlations were extended to two-phase foams by defining the Reynolds number based on the effective viscosity and density of microfoams. However, the local Nusselt and Prandtl numbers were defined based on the specific heat and thermal conductivity of water. Indeed, the heated wall was continuously in contact with a film of water controlling convective heat transfer to the microfoams. Overall, good agreement between experimental results and model predictions was obtained for all experimental conditions considered. Finally, the same approach was shown to be also valid for experimental data reported in the literature for laminar forced convection of microfoams in rectangular minichannels and of macrofoams across aligned and staggered tube bundles with constant wall heat flux.}, } @article {pmid23194395, year = {2013}, author = {Atlar, M and Unal, B and Unal, UO and Politis, G and Martinelli, E and Galli, G and Davies, C and Williams, D}, title = {An experimental investigation of the frictional drag characteristics of nanostructured and fluorinated fouling-release coatings using an axisymmetric body.}, journal = {Biofouling}, volume = {29}, number = {1}, pages = {39-52}, doi = {10.1080/08927014.2012.745856}, pmid = {23194395}, issn = {1029-2454}, mesh = {Biofouling/*prevention & control ; Dimethylpolysiloxanes/*chemistry ; Fluorine/chemistry ; Friction ; Hydrodynamics ; Laser-Doppler Flowmetry ; Nanostructures/*chemistry ; Polymers/*chemistry ; Surface Properties ; }, abstract = {The hydrodynamic performance of two, recently developed, nanostructured and fluorinated polymer coatings was explored in a systematic experimental study using the Newcastle University Cavitation Tunnel. The experiments consisted of testing the two coatings on an axisymmetric body apparatus to measure their boundary layer flow and frictional drag simultaneously. The tests also included a smooth reference surface as well as a state-of-the-art commercial fouling-release coating (Intersleek(®) 900). The boundary layer measurements were performed using a two-dimensional Laser Doppler Velocimetry (LDV) system whilst the direct frictional force measurements were taken using a special load cell installed in the testing body. Careful surface roughness measurements of the test surfaces were also performed including the use of a non-contact high precision laser profilometer. The tests and subsequent analysis of the data highlighted the exceptionally good frictional properties of all the coatings tested as well as some of the drag benefits of the new polymer coatings in the investigated Reynolds number range.}, } @article {pmid23192329, year = {2013}, author = {Mikhal, J and Geurts, BJ}, title = {Development and application of a volume penalization immersed boundary method for the computation of blood flow and shear stresses in cerebral vessels and aneurysms.}, journal = {Journal of mathematical biology}, volume = {67}, number = {6-7}, pages = {1847-1875}, pmid = {23192329}, issn = {1432-1416}, mesh = {Blood Flow Velocity/*physiology ; Brain/*blood supply ; Cerebral Arteries/*physiology ; Computer Simulation ; Hemodynamics/physiology ; Humans ; Intracranial Aneurysm/*physiopathology ; *Models, Cardiovascular ; }, abstract = {A volume-penalizing immersed boundary method is presented for the simulation of laminar incompressible flow inside geometrically complex blood vessels in the human brain. We concentrate on cerebral aneurysms and compute flow in curved brain vessels with and without spherical aneurysm cavities attached. We approximate blood as an incompressible Newtonian fluid and simulate the flow with the use of a skew-symmetric finite-volume discretization and explicit time-stepping. A key element of the immersed boundary method is the so-called masking function. This is a binary function with which we identify at any location in the domain whether it is 'solid' or 'fluid', allowing to represent objects immersed in a Cartesian grid. We compare three definitions of the masking function for geometries that are non-aligned with the grid. In each case a 'staircase' representation is used in which a grid cell is either 'solid' or 'fluid'. Reliable findings are obtained with our immersed boundary method, even at fairly coarse meshes with about 16 grid cells across a velocity profile. The validation of the immersed boundary method is provided on the basis of classical Poiseuille flow in a cylindrical pipe. We obtain first order convergence for the velocity and the shear stress, reflecting the fact that in our approach the solid-fluid interface is localized with an accuracy on the order of a grid cell. Simulations for curved vessels and aneurysms are done for different flow regimes, characterized by different values of the Reynolds number (Re). The validation is performed for laminar flow at Re = 250, while the flow in more complex geometries is studied at Re = 100 and Re = 250, as suggested by physiological conditions pertaining to flow of blood in the circle of Willis.}, } @article {pmid23188458, year = {2013}, author = {Beas-Catena, A and Sánchez-Mirón, A and García-Camacho, F and Contreras-Gómez, A and Molina-Grima, E}, title = {Adaptation of the Spodoptera exigua Se301 insect cell line to grow in serum-free suspended culture. Comparison of SeMNPV productivity in serum-free and serum-containing media.}, journal = {Applied microbiology and biotechnology}, volume = {97}, number = {8}, pages = {3373-3381}, doi = {10.1007/s00253-012-4576-0}, pmid = {23188458}, issn = {1432-0614}, mesh = {Animals ; Baculoviridae/*growth & development ; Cell Culture Techniques/*methods ; Cell Line ; Culture Media, Serum-Free ; *Genetic Vectors ; Spodoptera ; }, abstract = {Spodoptera exigua Se301 cells have been successfully adapted to two different commercial serum-free media (SFM; Ex-Cell 420 and Serum-Free Insect Medium-1) by gradually reducing the 10 %-added serum-containing medium content from 100 % to 0 % (v/v) in suspended cultures. Both direct adaptation to a serum-free medium and cell growth in the absence of protective additives against fluid dynamic stress [polyvinyl pyrrolidone and polyvinyl alcohol] and disaggregation [dextran sulfate] proved impossible. Cells grew reproducibly in both SFMs once the serum had been completely removed, although the use of Ex-Cell 420 resulted in higher growth rates and cell densities. Turbulence was sufficiently high to reduce growth rates and final cell densities at the highest Reynolds number investigated, although no clear influence of agitation was observed on virus productivity. Both attached and suspended Se301 cell cultures were successfully infected with the SeMNPV baculovirus. Cells adapted to different conditions (attached or suspended culture, serum-containing or serum-free medium) showed different occlusion bodies productivities at the two multiplicities of infection assayed (0.1 and 0.5).}, } @article {pmid23185060, year = {2013}, author = {Lozovatsky, ID and Fernando, HJ}, title = {Mixing efficiency in natural flows.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {371}, number = {1982}, pages = {20120213}, doi = {10.1098/rsta.2012.0213}, pmid = {23185060}, issn = {1364-503X}, abstract = {It is argued that the mixing efficiency of naturally occurring stratified shear flows, γ=Rf/(1-Rf), where Rf is the flux Richardson number, is dependent on at least two governing parameters: the gradient Richardson number Ri and the buoyancy Reynolds number Re(b)=ε/vN(2). It is found that, in the range approximately 0.031 and N≤Re(3/2)+Pr(-1)Rm(3/2) for Pr≤1. In three dimensions, on the other hand, N satisfies N≤(PrRe(3/2)+Rm(3/2))(3/2) for Pr>1 and N≤(Re(3/2)+Pr(-1)Rm(3/2))(3/2) for Pr≤1. In the limit Pr→0, Re(3/2) dominates Pr(-1)Rm(3/2), and the present estimate for N appropriately reduces to Re(9/4) as in the case of usual Navier-Stokes turbulence. For Pr≈1, our results imply the classical spectral scaling of the energy inertial range and dissipation wave number (in the form of upper bounds). These bounds are consistent with the existing predictions in the literature for turbulence with or without Alfvén wave effects. We discuss the possibility of solution regularity, with an emphasis on the two-dimensional case in the absence of either one or both of the dissipation terms.}, } @article {pmid23005217, year = {2012}, author = {Liu, R and Liu, QS}, title = {Nonmodal stability in Hagen-Poiseuille flow of a shear thinning fluid.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {85}, number = {6 Pt 2}, pages = {066318}, doi = {10.1103/PhysRevE.85.066318}, pmid = {23005217}, issn = {1550-2376}, mesh = {Computer Simulation ; *Models, Chemical ; Rheology/*methods ; Shear Strength ; Viscosity ; }, abstract = {Linear stability in Hagen-Poiseuille flow of a shear-thinning fluid is considered. The non-Newtonian viscosity is described by the Carreau rheological law. The effects of shear thinning on the stability are investigated using the energy method and the nonmodal stability theory. The energy analysis shows that the nonaxisymmetric disturbance with the azimuthal wave number m=1 has the lowest critical energy Reynolds number for both the Newtonian and shear-thinning cases. With the increase of shear thinning, the critical energy Reynolds number decreases for both the axisymmetric and nonaxisymmetric cases. For the nonmodal stability, we focus on two problems: response to external excitations and response to initial conditions. The former is studied by examining the ε pseudospectrum, and the latter by examining the energy growth function G(t). For both Newtonian and shear-thinning fluids, it is found that there can be a rather large transient growth even though the linear operator of the Hagen-Poiseuille flow has no unstable eigenvalue. For the problem of response to external excitations, the optimal response is achieved by disturbance with m=1 for both the Newtonian and non-Newtonian cases. For the problem of response to initial conditions, the optimal disturbance is in the form of streamwise uniform streaks. Being different from the Newtonian case, the azimuthal wave number of the optimal disturbance may be greater than 1 for strongly shear-thinning cases.}, } @article {pmid23005207, year = {2012}, author = {Tanino, Y and Moisy, F and Hulin, JP}, title = {Laminar-turbulent cycles in inclined lock-exchange flows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {85}, number = {6 Pt 2}, pages = {066308}, doi = {10.1103/PhysRevE.85.066308}, pmid = {23005207}, issn = {1550-2376}, mesh = {Computer Simulation ; *Models, Chemical ; Nonlinear Dynamics ; Rheology/*methods ; }, abstract = {We consider strongly confined, stably stratified shear flows generated as a lock exchange in a tube inclined at an angle of θ=45(∘). This paper focuses on a transitional regime, in which the flow alternates between two distinct states: laminar, parallel shear flow and intense transverse motion characteristic of turbulence. Laminar-turbulent cycles were captured at Atwood numbers At≡(ρ(2)-ρ(1))/(ρ(1)+ρ(2)) ranging from 2.45×10(-3) to 4.0×10(-3), where (ρ(1),ρ(2)) are the initial densities of the two fluids, with multiple cycles observed at At=2.55×10(-3). The evolution of the density and velocity fields in these flows was measured simultaneously using laser-induced fluorescence and particle image velocimetry. During each laminar-turbulent cycle, the axial velocity exhibits a distinctive ramp-cliff pattern, indicating that the flow accelerates as it relaminarizes, then decelerates rapidly as the Kelvin-Helmholtz billows break down. Within the range of experimental conditions, transverse stratification does not directly determine the onset of instability. Instead, the data suggest that a necessary criterion for the onset of instability is for the local Reynolds number to exceed 2200, with only a weak dependence on the Richardson number.}, } @article {pmid23005203, year = {2012}, author = {Setter, E and Bucher, I and Haber, S}, title = {Low-Reynolds-number swimmer utilizing surface traveling waves: analytical and experimental study.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {85}, number = {6 Pt 2}, pages = {066304}, doi = {10.1103/PhysRevE.85.066304}, pmid = {23005203}, issn = {1550-2376}, mesh = {Biomimetics/*methods ; Computer Simulation ; *Models, Theoretical ; Motion ; Rheology/*methods ; Robotics/*methods ; *Swimming ; }, abstract = {Microscale slender swimmers are frequently encountered in nature and are now used in microrobotic applications. The swimming mechanism examined in this paper is based on small transverse axisymmetric traveling wave deformations of a cylindrical long shell. The thin-shelled device is assumed to be inextensible at the middle surface and extensible at the surface wetted by the fluid. Assuming low-Reynolds-number hydrodynamics, an analytical solution is derived for waves of small amplitudes compared with the cylinder diameter. We show that swimming velocity increases with β(1) (the ratio of cylinder radius to wavelength) and that swimming velocity is linearly dependent on wave propagation velocity, increasing to leading order with the square of the ratio of wave amplitude to wavelength β(2) and decreasing with the wall thickness. A fourth-order correction in β(2) was also calculated and was found to have a negative effect on the swimming velocity. The results for a shell of negligible-wall thickness were compared with Taylor's solution for an inextensible two-dimensional flat membrane undergoing a waving motion and Felderhof's results [Phys. Fluids 22, 113604 (2010)] for an unbounded flow field and negligible-wall thickness. We show that Taylor's analytic solution is a particular limiting case of the present solution, assuming zero wall thickness and infinite values of β(1). The present mechanism was also compared with Taylor's well known solutions of waving planar and helical circular tails. We show that the present approach yields higher velocities as β(1) increases, whereas, the opposite occurs for waving tails. Indeed, in the region where β(1)>15, the present approach yields velocities nearly as fast as Taylor's helical waving tail while consuming less power and with a design that is considerably more compact. In this regime, the axisymmetric swimmer is twice as fast as Taylor's planar-tail swimmer for an additional investment of only one-third of the power. Experiments were conducted using a macroscale autonomous model immersed in highly viscous silicone fluid. We outlined how the proposed mechanism was realized to propel an elongated, yet finite, swimmer. Measured data demonstrate the effects of wave velocity and wavelength on swimming speed, showing good agreement with analytical results.}, } @article {pmid23005134, year = {2012}, author = {Farzin, M and Ronasi, K and Najafi, A}, title = {General aspects of hydrodynamic interactions between three-sphere low-Reynolds-number swimmers.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {85}, number = {6 Pt 1}, pages = {061914}, doi = {10.1103/PhysRevE.85.061914}, pmid = {23005134}, issn = {1550-2376}, mesh = {Animals ; Biological Clocks/*physiology ; Computer Simulation ; Humans ; *Models, Biological ; Rheology/*methods ; Stress, Mechanical ; Swimming/*physiology ; }, abstract = {We investigate hydrodynamic interactions between two three-sphere swimmers analytically and numerically. Hydrodynamic forces exerted on the swimmers as well as the translational and angular velocities of them are obtained in the far field regime. We demonstrate that the active term of the translational velocity is along the intrinsic direction of swimming (n) and has no component along the direction of relative positions of swimmers (r[over ̂]) as reported in previous papers. Using numerical simulations we investigate the long-time swimming paths of swimmers in two general situations of swimming in the same and opposite directions. The former reveals four swimming states for symmetric swimmers-attractive, repulsive, parallel, and oscillatory-and only three swimming states for asymmetric swimmers-attractive, repulsive, and contracting-oscillatory, confirming that the expanding-oscillatory state reported in previous papers is not stable. The latter shows that there are rotative bound states in hydrodynamic scattering of the swimmers.}, } @article {pmid23004865, year = {2012}, author = {Mohammadzadeh, A and Roohi, E and Niazmand, H and Stefanov, S and Myong, RS}, title = {Thermal and second-law analysis of a micro- or nanocavity using direct-simulation Monte Carlo.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {85}, number = {5 Pt 2}, pages = {056310}, doi = {10.1103/PhysRevE.85.056310}, pmid = {23004865}, issn = {1550-2376}, abstract = {In this study the direct-simulation Monte Carlo (DSMC) method is utilized to investigate thermal characteristics of micro- or nanocavity flow. The rarefied cavity flow shows unconventional behaviors which cannot be predicted by the Fourier law, the constitutive relation for the continuum heat transfer. Our analysis in this study confirms some recent observations and shows that the gaseous flow near the top-left corner of the cavity is in a strong nonequilibrium state even within the early slip regime, Kn=0.005. As we obtained slip velocity and temperature jump on the driven lid of the cavity, we reported meaningful discrepancies between the direct and macroscopic sampling of rarefied flow properties in the DSMC method due to existence of nonequilibrium effects in the corners of cavity. The existence of unconventional nonequilibrium heat transfer mechanisms in the middle of slip regime, Kn=0.05, results in the appearance of cold-to-hot heat transfer in the microcavity. In the current study we demonstrate that existence of such unconventional heat transfer is strongly dependent on the Reynolds number and it vanishes in the large values of the lid velocity. As we compared DSMC solution with the results of regularized 13 moments (R13) equations, we showed that the thermal characteristic of the microcavity obtained by the R13 method coincides with the DSMC prediction. Our investigation also includes the analysis of molecular entropy in the microcavity to explain the heat transfer mechanism with the aid of the second law of thermodynamics. To this aim, we obtained the two-dimensional velocity distribution functions to report the molecular-based entropy distribution, and show that the cold-to-hot heat transfer in the cavity is well in accordance with the second law of thermodynamics and takes place in the direction of increasing entropy. At the end we introduce the entropy density for the rarefied flow and show that it can accurately illustrate departure from the equilibrium state.}, } @article {pmid23004662, year = {2012}, author = {Or, Y}, title = {Asymmetry and stability of shape kinematics in microswimmers' motion.}, journal = {Physical review letters}, volume = {108}, number = {25}, pages = {258101}, doi = {10.1103/PhysRevLett.108.258101}, pmid = {23004662}, issn = {1079-7114}, mesh = {Biomechanical Phenomena ; Eukaryota/*physiology ; Flagella/chemistry/*physiology ; *Models, Biological ; Structure-Activity Relationship ; Swimming ; }, abstract = {Many swimming microorganisms governed by low Reynolds number hydrodynamics utilize flagellar undulations for self-propulsion. Most of the existing theoretical models assume that the shape kinematics is directly controlled, while in reality, eukaryotes actuate internal bending moments along their flagellum. Under this control, the shape is dynamically evolving and periodic gaits may become unstable. This Letter addresses the problem by revisiting Purcell's three-link swimmer model where joint torques are controlled, and the geometric symmetries underlying the dynamics of the swimmer are analyzed. It is found that one has to break the front-back symmetry of the swimmer's structure and/or actuation profile in order to induce stable shape kinematics. The results may explain why most of the flagellated eukaryotes swim with their head forward.}, } @article {pmid23004333, year = {2012}, author = {Hendrix, MH and Manica, R and Klaseboer, E and Chan, DY and Ohl, CD}, title = {Spatiotemporal evolution of thin liquid films during impact of water bubbles on glass on a micrometer to nanometer scale.}, journal = {Physical review letters}, volume = {108}, number = {24}, pages = {247803}, doi = {10.1103/PhysRevLett.108.247803}, pmid = {23004333}, issn = {1079-7114}, abstract = {Collisions between millimeter-size bubbles in water against a glass plate are studied using high-speed video. Bubble trajectory and shape are tracked simultaneously with laser interferometry between the glass and bubble surfaces that monitors spatial-temporal evolution of the trapped water film. Initial bubble bounces and the final attachment of the bubble to the surface have been quantified. While the global Reynolds number is large (∼10(2)), the film Reynolds number remains small and permits analysis with lubrication theory with tangentially immobile boundary condition at the air-water interface. Accurate predictions of dimple formation and subsequent film drainage are obtained.}, } @article {pmid23003602, year = {2012}, author = {Matsuda, K and Onishi, R and Kurose, R and Komori, S}, title = {Turbulence effect on cloud radiation.}, journal = {Physical review letters}, volume = {108}, number = {22}, pages = {224502}, doi = {10.1103/PhysRevLett.108.224502}, pmid = {23003602}, issn = {1079-7114}, abstract = {The effect of turbulent clustering of water droplets on radiative transfer is investigated by means of both a three-dimensional direct numerical simulation of particle-laden homogeneous isotropic turbulence and a radiative transfer simulation based on a Monte Carlo photon tracing method. The results show that turbulent clustering causes the formation of void regions of droplets and hence increases the direct transmittance. This effect decreases as the turbulent Reynolds number increases and is estimated to be negligibly small under the conditions in real clouds.}, } @article {pmid23003267, year = {2012}, author = {Valente, PC and Vassilicos, JC}, title = {Universal dissipation scaling for nonequilibrium turbulence.}, journal = {Physical review letters}, volume = {108}, number = {21}, pages = {214503}, doi = {10.1103/PhysRevLett.108.214503}, pmid = {23003267}, issn = {1079-7114}, abstract = {It is experimentally shown that the nonclassical high Reynolds number energy dissipation behavior, C(ε)≡εL/u(3)=f(Re(M))/Re(L), observed during the decay of fractal square grid-generated turbulence (where Re(M) is a global inlet Reynolds number and Re(L) is a local turbulence Reynolds number) is also manifested in decaying turbulence originating from various regular grids. For sufficiently high values of the global Reynolds numbers Re(M), f(Re(M))~Re(M).}, } @article {pmid22996450, year = {2013}, author = {Elimelech, Y and Ellington, CP}, title = {Analysis of the transitional flow field over a fixed hummingbird wing.}, journal = {The Journal of experimental biology}, volume = {216}, number = {Pt 2}, pages = {303-318}, doi = {10.1242/jeb.075341}, pmid = {22996450}, issn = {1477-9145}, mesh = {Animals ; Biomechanical Phenomena ; Birds/anatomy & histology/*physiology ; *Flight, Animal ; Male ; Models, Biological ; Wings, Animal/anatomy & histology/*physiology ; }, abstract = {We analyzed the flow fields characterized by chord-based Reynolds numbers of 5000 to 15,000 over a stationary model of a hummingbird (Calypte anna) wing. Utilizing two experimental techniques, constant-temperature anemometry and stereo particle image velocimetry, the high-fidelity results depict a laminar-to-turbulent transition process that develops over the wing. At both zero and non-zero angles of attack the spectrum of the velocity signals is wide. At non-zero angles of attack the flow separates from the wing surface and a shear layer forms. As a result, unsteady flow disturbances amplify at a chord-based Reynolds numbers as low as 5000. Nevertheless, only at a Reynolds number of 15,000 is the flow disturbance growth rate sufficient to bring enough momentum from the outer region of the boundary layer to reattach the flow to the wing surface. For a Reynolds number of 5000, a comparison between the observed growth rates and a theoretical approximation concludes that flow disturbances of a Strouhal number of unity (and above) are no longer two-dimensional. In view of these conclusions, this study could serve as the first step towards a better understanding of the flow mechanisms over steady revolving and periodically flapping wings at this Reynolds number regime.}, } @article {pmid22972227, year = {2012}, author = {DeSimone, A and Tatone, A}, title = {Crawling motility through the analysis of model locomotors: two case studies.}, journal = {The European physical journal. E, Soft matter}, volume = {35}, number = {9}, pages = {85}, pmid = {22972227}, issn = {1292-895X}, mesh = {Animals ; Bacteria/*cytology ; *Cell Movement ; Friction ; *Locomotion ; *Models, Theoretical ; Robotics ; Snails/*physiology ; }, abstract = {We study model locomotors on a substrate, which derive their propulsive capabilities from the tangential (viscous or frictional) resistance offered by the substrate. Our aim is to develop new tools and insight for future studies of cellular motility by crawling and of collective bacterial motion. The purely viscous case (worm) is relevant for cellular motility by crawling of individual cells. We re-examine some recent results on snail locomotion in order to assess the role of finely regulated adhesion mechanisms in crawling motility. Our main conclusion is that such regulation, although well documented in several biological systems, is not indispensable to accomplish locomotion driven by internal deformations, provided that the crawler may execute sufficiently large body deformations. Thus, there is no snail theorem. Namely, the crawling analog of the scallop theorem of low Reynolds number hydrodynamics does not hold for snail-like crawlers. The frictional case is obtained by assuming that the viscous coefficient governing tangential resistance forces, which act parallel and in the direction opposite to the velocity of the point to which they are applied, depends on the normal force acting at that point. We combine these surface interactions with inertial effects in order to investigate the mechanisms governing the motility of a bristle-robot. This model locomotor is easily manufactured and has been proposed as an effective tool to replicate and study collective bacterial motility.}, } @article {pmid22960952, year = {2012}, author = {Martel, S}, title = {Bacterial microsystems and microrobots.}, journal = {Biomedical microdevices}, volume = {14}, number = {6}, pages = {1033-1045}, doi = {10.1007/s10544-012-9696-x}, pmid = {22960952}, issn = {1572-8781}, mesh = {Bacteria/*metabolism ; Bacterial Adhesion ; Chemotaxis ; Microfluidics/methods ; Robotics/*instrumentation/methods ; Systems Biology/*methods ; }, abstract = {Microorganisms and specifically motile bacteria have been recently added to the list of micro-actuators typically considered for the implementation of microsystems and microrobots. Such trend has been motivated by the fact these microorganisms are self-powered actuators with overall sizes at the lower end of the micrometer range and which have proven to be extremely effective in low Reynolds number hydrodynamic regime of usually less than 10(-2). Furthermore, the various sensors or taxes in bacteria influencing their movements can also be exploited to perform tasks that were previously considered only for futuristic artificial microrobots. Bacterial implementations and related issues are not only reviewed, but this paper also proposes many techniques and approaches that can be considered as building blocks for the implementations of more sophisticated microsystems and microrobots.}, } @article {pmid22938326, year = {2012}, author = {Fonda, E and Sreenivasan, KR and Lathrop, DP}, title = {Liquid nitrogen in fluid dynamics: visualization and velocimetry using frozen particles.}, journal = {The Review of scientific instruments}, volume = {83}, number = {8}, pages = {085101}, doi = {10.1063/1.4739837}, pmid = {22938326}, issn = {1089-7623}, abstract = {High-Reynolds-number flows are common both in nature and industrial applications, but are difficult to attain in laboratory settings using standard test fluids such as air and water. To extend the Reynolds number range, water and air have been replaced at times by low-viscosity fluids such as pressurized air, sulfur hexafluoride, and cryogenic nitrogen gas, as well as liquid and gaseous helium. With a few exceptions, liquid nitrogen has been neglected despite the fact that it has a kinematic viscosity of about a fifth of that of water at room temperature. We explore the use of liquid nitrogen here. In particular, we study the use of frozen particles for flow visualization and velocimetry in liquid nitrogen. We create particles in situ by injecting a gaseous mixture of room-temperature nitrogen and an additional seeding gas into the flow. We present a systematic study of potential seeding gases to determine which create particles with the best fidelity and optical properties. The technique has proven capable of producing sub-micrometer sized tracers that allow particle tracking and particle image velocimetry. We review possible high-Reynolds-number experiments using this technique, and discuss the merits and challenges of using liquid nitrogen as a test fluid.}, } @article {pmid22926809, year = {2012}, author = {Prohm, C and Gierlak, M and Stark, H}, title = {Inertial microfluidics with multi-particle collision dynamics.}, journal = {The European physical journal. E, Soft matter}, volume = {35}, number = {8}, pages = {80}, pmid = {22926809}, issn = {1292-895X}, abstract = {Using the method of multi-particle collision dynamics (MPCD), we investigate inertial focussing in microfluidic channels that gives rise to the Segré-Silberberg effect. At intermediate Reynolds numbers, we model the motion of a spherical colloid in a circular microchannel under pressure-driven flow. We determine the radial distribution function and show how its width and the location of its maximum are strongly influenced by the colloid size and the Reynolds number of the Poiseuille flow. We demonstrate that MPCD is well suited for calculating mean values for the lift force acting on the colloid in the cross-sectional plane and for its mean axial velocity. We introduce a Langevin equation for the cross-sectional motion whose steady state is the Boltzmann distribution that contains the integrated lift force as potential energy. It perfectly coincides with the simulated radial distribution function.}, } @article {pmid22925874, year = {2012}, author = {de Cassia Feroni, R and Santos, JM and Reis, NC}, title = {Volatilization of hydrogen sulfide from a quiescent surface.}, journal = {Water science and technology : a journal of the International Association on Water Pollution Research}, volume = {66}, number = {9}, pages = {1991-1996}, doi = {10.2166/wst.2012.382}, pmid = {22925874}, issn = {0273-1223}, mesh = {Hydrogen Sulfide/*chemistry ; *Models, Theoretical ; Volatilization ; }, abstract = {Air-water mass transfer of hydrogen sulfide from a shallow tank with a quiescent surface under the influence of weak wind stress on the water surface was studied numerically using a two-dimensional model. The flow field in the tank was investigated using a computational code based on a finite volume, which is used to numerically solve momentum, mass and continuity conservation equations. The results show that water phase flow field is strongly dependent on the wind-induced surface velocity and the aspect ratio of the tank. Based on the numerical study, the liquid-side mass transfer coefficient is correlated with Reynolds number (R(e)), tank aspect ratio (AR) and Schmidt number (S(c)). Overall mass transfer coefficient (K(L)) values extend further downstream as the R(e) number increases.}, } @article {pmid22923592, year = {2012}, author = {Wang, W and Jiang, Z and Westermann, M and Ping, L}, title = {Three mutations in Escherichia coli that generate transformable functional flagella.}, journal = {Journal of bacteriology}, volume = {194}, number = {21}, pages = {5856-5863}, pmid = {22923592}, issn = {1098-5530}, mesh = {Escherichia coli/chemistry/*genetics/physiology ; Escherichia coli Proteins/chemistry/genetics/metabolism ; Flagella/chemistry/*genetics/physiology ; Flagellin ; *Locomotion ; Models, Molecular ; *Mutation, Missense ; *Point Mutation ; Protein Conformation ; }, abstract = {Hydrodynamics predicts that swimming bacteria generate a propulsion force when a helical flagellum rotates because rotating helices necessarily translate at a low Reynolds number. It is generally believed that the flagella of motile bacteria are semirigid helices with a fixed pitch determined by hydrodynamic principles. Here, we report the characterization of three mutations in laboratory strains of Escherichia coli that produce different steady-state flagella without losing cell motility. E. coli flagella rotate counterclockwise during forward swimming, and the normal form of the flagella is a left-handed helix. A single amino acid exchange A45G and a double mutation of A48S and S110A change the resting flagella to right-handed helices. The stationary flagella of the triple mutant were often straight or slightly curved at neutral pH. Deprotonation facilitates the helix formation of it. The helical and curved flagella can be transformed to the normal form by torsion upon rotation and thus propel the cell. These mutations arose in the long-term laboratory cultivation. However, flagella are under strong selection pressure as extracellular appendages, and similar transformable flagella would be common in natural environments.}, } @article {pmid22908251, year = {2012}, author = {Posner, JD and Pérez, CL and Santiago, JG}, title = {Electric fields yield chaos in microflows.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {109}, number = {36}, pages = {14353-14356}, pmid = {22908251}, issn = {1091-6490}, mesh = {Electric Conductivity ; Electrochemistry/*methods ; *Electromagnetic Fields ; *Hydrodynamics ; Microfluidics/*methods ; *Models, Chemical ; *Nonlinear Dynamics ; }, abstract = {We present an investigation of chaotic dynamics of a low Reynolds number electrokinetic flow. Electrokinetic flows arise due to couplings of electric fields and electric double layers. In these flows, applied (steady) electric fields can couple with ionic conductivity gradients outside electric double layers to produce flow instabilities. The threshold of these instabilities is controlled by an electric Rayleigh number, Ra(e). As Ra(e) increases monotonically, we show here flow dynamics can transition from steady state to a time-dependent periodic state and then to an aperiodic, chaotic state. Interestingly, further monotonic increase of Ra(e) shows a transition back to a well-ordered state, followed by a second transition to a chaotic state. Temporal power spectra and time-delay phase maps of low dimensional attractors graphically depict the sequence between periodic and chaotic states. To our knowledge, this is a unique report of a low Reynolds number flow with such a sequence of periodic-to-aperiodic transitions. Also unique is a report of strange attractors triggered and sustained through electric fluid body forces.}, } @article {pmid22907616, year = {2012}, author = {Passov, E and Or, Y}, title = {Dynamics of Purcell's three-link microswimmer with a passive elastic tail.}, journal = {The European physical journal. E, Soft matter}, volume = {35}, number = {8}, pages = {78}, pmid = {22907616}, issn = {1292-895X}, mesh = {*Elasticity ; *Microbiology ; *Models, Biological ; *Movement ; }, abstract = {One of the few possible mechanisms for self-propulsion at low Reynolds number is undulations of a passive elastic tail, as proposed in the classical work of Purcell (1977). This effect is studied here by investigating a variant of Purcell's three-link swimmer model where the front joint angle is periodically actuated while the rear joint is driven by a passive torsional spring. The dynamic equations of motion are formulated and explicit expressions for the leading-order solution are derived by using perturbation expansion. The dependence of the motion on the actuation amplitude and frequency is analyzed, and optimization with respect to the swimmer's geometry is conducted.}, } @article {pmid22901062, year = {2012}, author = {Abbas, F and Sudarsan, R and Eberl, HJ}, title = {Longtime behavior of one-dimensional biofilm models with shear dependent detachment rates.}, journal = {Mathematical biosciences and engineering : MBE}, volume = {9}, number = {2}, pages = {215-239}, doi = {10.3934/mbe.2012.9.215}, pmid = {22901062}, issn = {1551-0018}, mesh = {Bacteria/growth & development ; Bacterial Adhesion ; *Biofilms ; Bioreactors ; Computer Simulation ; Hydrodynamics ; *Models, Biological ; *Shear Strength ; *Stress, Mechanical ; }, abstract = {We investigate the role of non shear stress and shear stressed based detachment rate functions for the longterm behavior of one-dimensional biofilm models. We find that the particular choice of a detachment rate function can affect the model prediction of persistence or washout of the biofilm. Moreover, by comparing biofilms in three settings: (i) Couette flow reactors, (ii) Poiseuille flow with fixed flow rate and (iii) Poiseuille flow with fixed pressure drop, we find that not only the bulk flow Reynolds number but also the particular mechanism driving the flow can play a crucial role for longterm behavior. We treat primarily the single species-case that can be analyzed with elementary ODE techniques. But we show also how the results, to some extent, can be carried over to multi-species biofilm models, and to biofilm models that are embedded in reactor mass balances.}, } @article {pmid22891974, year = {2014}, author = {Xinhui, S and Liancun, Z and Xinxin, Z and Xinyi, S and Min, L}, title = {Asymmetric viscoelastic flow through a porous channel with expanding or contracting walls: a model for transport of biological fluids through vessels.}, journal = {Computer methods in biomechanics and biomedical engineering}, volume = {17}, number = {6}, pages = {623-631}, doi = {10.1080/10255842.2012.708341}, pmid = {22891974}, issn = {1476-8259}, mesh = {Biological Transport ; Body Fluids/*metabolism ; Elasticity ; *Models, Biological ; Porosity ; Viscosity ; }, abstract = {In this article, the asymmetric viscoelastic fluid in a rectangular domain bounded by two porous moving channels with expanding or contracting walls is investigated. The governing equations are reduced to an ordinary equation by using suitable similar transformations. Homotopy analysis method is used to obtain the expression for velocity fields. The analytical solutions are influenced by the permeation Reynolds number Re, the wall expansion ratio [Formula: see text] and viscoelastic parameter [Formula: see text]. Graphs are sketched and the effects of some values of parameters, especially the expansion ratio and viscoelastic parameter, on the velocity fields are discussed in detail.}, } @article {pmid22886565, year = {2012}, author = {Vilfan, A}, title = {Generic flow profiles induced by a beating cilium.}, journal = {The European physical journal. E, Soft matter}, volume = {35}, number = {8}, pages = {72}, pmid = {22886565}, issn = {1292-895X}, mesh = {Cilia/*metabolism ; *Hydrodynamics ; *Mechanical Phenomena ; Models, Biological ; }, abstract = {We describe a multipole expansion for the low-Reynolds-number fluid flows generated by a localized source embedded in a plane with a no-slip boundary condition. It contains 3 independent terms that fall quadratically with the distance and 6 terms that fall with the third power. Within this framework we discuss the flows induced by a beating cilium described in different ways: a small particle circling on an elliptical trajectory, a thin rod and a general ciliary beating pattern. We identify the flow modes present based on the symmetry properties of the ciliary beat.}, } @article {pmid22886515, year = {2012}, author = {Mitri, K and Vauthier, C and Huang, N and Menas, A and Ringard-Lefebvre, C and Anselmi, C and Stambouli, M and Rosilio, V and Vachon, JJ and Bouchemal, K}, title = {Scale-up of nanoemulsion produced by emulsification and solvent diffusion.}, journal = {Journal of pharmaceutical sciences}, volume = {101}, number = {11}, pages = {4240-4247}, doi = {10.1002/jps.23291}, pmid = {22886515}, issn = {1520-6017}, mesh = {Diffusion ; *Emulsions ; *Nanotechnology ; *Solvents ; Viscosity ; }, abstract = {The scale-up of nanoemulsions (NEs) produced by emulsification and solvent diffusion process was successfully achieved in the present work. Up to 1500 mL of NEs were produced with olive oil, castor oil, almond oil, or Arlamol™ E by using a Y-shaped mixer device. NE droplet sizes were significantly modulated from 290 to 185 nm by changing the process parameters without modification of the formulation composition. Smaller NE droplet sizes were obtained by (1) decreasing the internal diameter of the Y-mixer from 5 to 0.8 mm, (2) increasing the flow rates of the organic and the aqueous phases upon mixing, and (3) increasing the temperature of the experiment from 5°C to 40°C. All the results of NE diameters (d(sc)) expressed as a function of the Reynolds number (Re) and the shear rate inside the Y-mixer (\documentclass{article} \usepackage{amssymb} \begin{document} \pagestyle{empty} $\dot \gamma$\end{document} ) showed the existence of typical power-law relationships: d(sc) = 10(2.82) Re(- 0.14) and \documentclass{article} \usepackage{amssymb} \begin{document} \pagestyle{empty} $d_{{\rm sc} } = 10^{2.60} \dot \gamma ^{- 0.06} $\end{document}, respectively. The existence of these power-laws for NE formation by emulsification and solvent diffusion process has never been reported in the literature yet and constitutes a new finding in this work. We definitely proved that the high turbulences created upon NE formation are the most important parameter allowing to decrease droplet size.}, } @article {pmid22864542, year = {2012}, author = {Ledesma-Aguilar, R and Löwen, H and Yeomans, JM}, title = {A circle swimmer at low Reynolds number.}, journal = {The European physical journal. E, Soft matter}, volume = {35}, number = {8}, pages = {70}, pmid = {22864542}, issn = {1292-895X}, abstract = {Swimming in circles occurs in a variety of situations at low Reynolds number. Here we propose a simple model for a swimmer that undergoes circular motion, generalising the model of a linear swimmer proposed by Najafi and Golestanian (Phys. Rev. E 69, 062901 (2004)). Our model consists of three solid spheres arranged in a triangular configuration, joined by two links of time-dependent length. For small strokes, we discuss the motion of the swimmer as a function of the separation angle between its links. We find that swimmers describe either clockwise or anticlockwise circular motion depending on the tilting angle in a non-trivial manner. The symmetry of the swimmer leads to a quadrupolar decay of the far flow field. We discuss the potential extensions and experimental realisation of our model.}, } @article {pmid22817394, year = {2014}, author = {Tripathi, D and Pandey, SK and Siddiqui, A and Bég, OA}, title = {Non-steady peristaltic propulsion with exponential variable viscosity: a study of transport through the digestive system.}, journal = {Computer methods in biomechanics and biomedical engineering}, volume = {17}, number = {6}, pages = {591-603}, doi = {10.1080/10255842.2012.703660}, pmid = {22817394}, issn = {1476-8259}, mesh = {Body Fluids/metabolism ; Humans ; Intestines/physiology ; *Models, Biological ; *Peristalsis ; Pressure ; Stress, Mechanical ; Viscosity ; }, abstract = {A theoretical study is presented for transient peristaltic flow of an incompressible fluid with variable viscosity in a finite length cylindrical tube as a simulation of transport in physiological vessels and biomimetic peristaltic pumps. The current axisymmetric analysis is qualitatively similar to two-dimensional analysis but exhibits quantitative variations. The current analysis is motivated towards further elucidating the physiological migration of gastric suspensions (food bolus) in the human digestive system. It also applies to variable viscosity industrial fluid (waste) peristaltic pumping systems. First, an axisymmetric model is analysed in the limit of large wavelength ([Formula: see text]) and low Reynolds number ([Formula: see text]) for axial velocity, radial velocity, pressure, hydromechanical efficiency and stream function in terms of radial vibration of the wall ([Formula: see text]), amplitude of the wave ([Formula: see text]), averaged flow rate ([Formula: see text]) and variable viscosity ([Formula: see text]). Subsequently, the peristaltic flow of a fluid with an exponential viscosity model is examined, which is based on the analytical solutions for pressure, wall shear stress, hydromechanical efficiency and streamline patterns in the finite length tube. The results are found to correlate well with earlier studies using a constant viscosity formulation. This study reveals some important features in the flow characteristics including the observation that pressure as well as both number and size of lower trapped bolus increases. Furthermore, the study indicates that hydromechanical efficiency reduces with increasing magnitude of viscosity parameter.}, } @article {pmid22761309, year = {2012}, author = {Amini, H and Sollier, E and Weaver, WM and Di Carlo, D}, title = {Intrinsic particle-induced lateral transport in microchannels.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {109}, number = {29}, pages = {11593-11598}, pmid = {22761309}, issn = {1091-6490}, mesh = {Convection ; Microfluidics/*methods ; *Models, Chemical ; Particle Size ; Rheology/*methods ; }, abstract = {In microfluidic systems at low Reynolds number, the flow field around a particle is assumed to maintain fore-aft symmetry, with fluid diverted by the presence of a particle, returning to its original streamline downstream. This current model considers particles as passive components of the system. However, we demonstrate that at finite Reynolds number, when inertia is taken into consideration, particles are not passive elements in the flow but significantly disturb and modify it. In response to the flow field, particles translate downstream while rotating. The combined effect of the flow of fluid around particles, particle rotation, channel confinement (i.e., particle dimensions approaching those of the channel), and finite fluid inertia creates a net recirculating flow perpendicular to the primary flow direction within straight channels that resembles the well-known Dean flow in curved channels. Significantly, the particle generating this flow remains laterally fixed as it translates downstream and only the fluid is laterally transferred. Therefore, as the particles remain inertially focused, operations can be performed around the particles in a way that is compatible with downstream assays such as flow cytometry. We apply this particle-induced transfer to perform fluid switching and mixing around rigid microparticles as well as deformable cells. This transport phenomenon, requiring only a simple channel geometry with no external forces to operate, offers a practical approach for fluid transfer at high flow rates with a wide range of applications, including sample preparation, flow reaction, and heat transfer.}, } @article {pmid24910780, year = {2012}, author = {Ito, K and Li, Z and Qiao, Z}, title = {The Sensitivity Analysis for the Flow Past Obstacles Problem with Respect to the Reynolds Number.}, journal = {Advances in applied mathematics and mechanics}, volume = {4}, number = {1}, pages = {21-35}, doi = {10.4208/aamm.11-m1110}, pmid = {24910780}, issn = {2070-0733}, support = {R01 GM096195/GM/NIGMS NIH HHS/United States ; }, abstract = {In this paper, numerical sensitivity analysis with respect to the Reynolds number for the flow past obstacle problem is presented. To carry out such analysis, at each time step, we need to solve the incompressible Navier-Stokes equations on irregular domains twice, one for the primary variables; the other is for the sensitivity variables with homogeneous boundary conditions. The Navier-Stokes solver is the augmented immersed interface method for Navier-Stokes equations on irregular domains. One of the most important contribution of this paper is that our analysis can predict the critical Reynolds number at which the vortex shading begins to develop in the wake of the obstacle. Some interesting experiments are shown to illustrate how the critical Reynolds number varies with different geometric settings.}, } @article {pmid23956497, year = {2012}, author = {Scherr, T and Quitadamo, C and Tesvich, P and Park, DS and Tiersch, T and Hayes, D and Choi, JW and Nandakumar, K and Monroe, WT}, title = {A Planar Microfluidic Mixer Based on Logarithmic Spirals.}, journal = {Journal of micromechanics and microengineering : structures, devices, and systems}, volume = {22}, number = {5}, pages = {55019}, pmid = {23956497}, issn = {0960-1317}, support = {R24 OD010441/OD/NIH HHS/United States ; R24 RR023998/RR/NCRR NIH HHS/United States ; }, abstract = {A passive, planar micromixer design based on logarithmic spirals is presented. The device was fabricated using polydimethylsiloxane soft photolithography techniques, and mixing performance was characterized via numerical simulation and fluorescent microscopy. Mixing efficiency initially declined as Reynolds number increased, and this trend continued until a Reynolds number of 15 where a minimum was reached at 53%. Mixing efficiency then began to increase reaching a maximum mixing efficiency of 86% at Re = 67. Three-dimensional simulations of fluid mixing in this design were compared to other planar geometries such as the Archimedes spiral and Meandering-S mixers. The implementation of logarithmic curvature offers several unique advantages that enhance mixing, namely a variable cross-sectional area and a logarithmically varying radius of curvature that creates 3-D Dean vortices. These flow phenomena were observed in simulations with multilayered fluid folding and validated with confocal microscopy. This design provides improved mixing performance over a broader range of Reynolds numbers than other reported planar mixers, all while avoiding external force fields, more complicated fabrication processes, and the introduction of flow obstructions or cavities that may unintentionally affect sensitive or particulate-containing samples. Due to the planar design requiring only single-step lithographic features, this compact geometry could be easily implemented into existing micro-total analysis systems requiring effective rapid mixing.}, } @article {pmid23471191, year = {2012}, author = {Khanafer, K and Cook, K and Marafie, A}, title = {THE ROLE OF POROUS MEDIA IN MODELING FLUID FLOW WITHIN HOLLOW FIBER MEMBRANES OF THE TOTAL ARTIFICIAL LUNG.}, journal = {Journal of porous media}, volume = {15}, number = {2}, pages = {113-122}, pmid = {23471191}, issn = {1091-028X}, support = {R01 HL089043/HL/NHLBI NIH HHS/United States ; }, abstract = {A numerical study was conducted to analyze fluid flow within hollow fiber membranes of the artificial lungs. The hollow fiber bundle was approximated using a porous media model. In addition, the transport equations were solved using the finite-element formulation based on the Galerkin method of weighted residuals. Comparisons with previously published work on the basis of special cases were performed and found to be in excellent agreement. A Newtonian viscous fluid model for the blood was used. Different flow models for porous media, such as the Brinkman-extended Darcy model, Darcy's law model, and the generalized flow model, were considered. Results were obtained in terms of streamlines, velocity vectors, and pressure distribution for various Reynolds numbers and Darcy numbers. The results from this investigation showed that the pressure drop across the artificial lung device increased with an increase in the Reynolds number. In addition, the pressure drop was found to increase significantly for small Darcy numbers.}, } @article {pmid23555330, year = {2011}, author = {Barber, JO and Restrepo, JM and Secomb, TW}, title = {Simulated Red Blood Cell Motion in Microvessel Bifurcations: Effects of Cell-Cell Interactions on Cell Partitioning.}, journal = {Cardiovascular engineering and technology}, volume = {2}, number = {4}, pages = {349-360}, pmid = {23555330}, issn = {1869-4098}, support = {R01 HL034555/HL/NHLBI NIH HHS/United States ; }, abstract = {Partitioning of red blood cell (RBC) fluxes between the branches of a diverging microvessel bifurcation is generally not proportional to the flow rates, as RBCs preferentially enter the higher-flow branch. A two-dimensional model for RBC motion and deformation is used to investigate the effects of cell-cell mechanical interactions on RBC partitioning in bifurcations. The RBC membrane and cytoplasm are represented by sets of viscoelastic elements immersed in a low Reynolds number flow. Several types of two-cell interactions that can affect partitioning are found. In the most frequent interactions, a `trade-off' occurs, in which a cell entering one branch causes a following cell to enter the other branch. Other types of interactions include `herding,' where the leading cell is caused to enter the same branch as the following cell, and `following,' where the trailing cell is caused to enter the same branch as the leading cell. The combined effect of these cell-cell interactions is a tendency towards more uniform partitioning, which results from the trade-off effect but is reduced by the herding and following effects. With increasing hematocrit, the frequency of interactions increases, and more uniform partitioning results. This prediction is consistent with experimental observations on how hematocrit affects RBC partitioning.}, } @article {pmid27524855, year = {2011}, author = {Briguglio, A and Hohenegger, J}, title = {How to react to shallow water hydrodynamics: The larger benthic foraminifera solution.}, journal = {Marine micropaleontology}, volume = {81}, number = {1-2}, pages = {63-76}, pmid = {27524855}, issn = {0377-8398}, support = {P 23459/FWF_/Austrian Science Fund FWF/Austria ; }, abstract = {Symbiont-bearing larger benthic foraminifera inhabit the photic zone to provide their endosymbiotic algae with light. Because of the hydrodynamic conditions of shallow water environments, tests of larger foraminifera can be entrained and transported by water motion. To resist water motion, these foraminifera have to build a test able to avoid transport or have to develop special mechanisms to attach themselves to substrate or to hide their test below sediment grains. For those species which resist transport by the construction of hydrodynamic convenient shapes, the calculation of hydrodynamic parameters of their test defines the energetic input they can resist and therefore the scenario where they can live in. Measuring the density, size and shape of every test, combined with experimental data, helps to define the best mathematical approach for the settling velocity and Reynolds number of every shell. The comparison between water motion at the sediment-water interface and the specimen-specific settling velocity helps to calculate the water depths at which, for a certain test type, transport, deposition and accumulation may occur. The results obtained for the investigated taxa show that the mathematical approach gives reliable results and can discriminate the hydrodynamic behaviour of different shapes. Furthermore, the study of the settling velocities, calculated for all the investigated taxa, shows that several species are capable to resist water motion and therefore they appear to be functionally adapted to the hydrodynamic condition of its specific environment. The same study is not recommended on species which resist water motion by adopting hiding or anchoring strategies to avoid the effect of water motion.}, } @article {pmid28509944, year = {2010}, author = {Kumar, MS and Philominathan, P}, title = {The physics of flagellar motion of E. coli during chemotaxis.}, journal = {Biophysical reviews}, volume = {2}, number = {1}, pages = {13-20}, pmid = {28509944}, issn = {1867-2450}, abstract = {Flagellar motion has been an active area of study right from the discovery of bacterial chemotaxis in 1882. During chemotaxis, E. coli moves with the help of helical flagella in an aquatic environment. Helical flagella are rotated in clockwise or counterclockwise direction using reversible flagellar motors situated at the base of each flagellum. The swimming of E. coli is characterized by a low Reynolds number that is unique and time reversible. The random motion of E. coli is influenced by the viscosity of the fluid and the Brownian motion of molecules of fluid, chemoattractants, and chemorepellants. This paper reviews the literature about the physics involved in the propulsion mechanism of E. coli. Starting from the resistive-force theory, various theories on flagellar hydrodynamics are critically reviewed. Expressions for drag force, elastic force and velocity of flagellar elements are derived. By taking the elastic nature of flagella into account, linear and nonlinear equations of motions are derived and their solutions are presented.}, } @article {pmid22949744, year = {2009}, author = {Padaki, A and Ultman, JS and Borhan, A}, title = {Ozone Uptake During Inspiratory Flow in a Model of the Larynx, Trachea and Primary Bronchial Bifurcation.}, journal = {Chemical engineering science}, volume = {64}, number = {22}, pages = {4640-4648}, pmid = {22949744}, issn = {0009-2509}, support = {P01 ES011617/ES/NIEHS NIH HHS/United States ; P01 ES011617-04/ES/NIEHS NIH HHS/United States ; }, abstract = {Three-dimensional simulations of the transport and uptake of a reactive gas such as O(3) were compared between an idealized model of the larynx, trachea, and first bifurcation and a second "control" model in which the larynx was replaced by an equivalent, cylindrical, tube segment. The Navier-Stokes equations, Spalart-Allmaras turbulence equation, and convection-diffusion equation were implemented at conditions reflecting inhalation into an adult human lung. Simulation results were used to analyze axial velocity, turbulent viscosity, local fractional uptake, and regional uptake. Axial velocity data revealed a strong laryngeal jet with a reattachment point in the proximal trachea. Turbulent viscosity data indicated that jet turbulence occurred only at high Reynolds numbers and was attenuated by the first bifurcation. Local fractional uptake data affirmed hotspots previously reported at the first carina, and suggested additional hotspots at the glottal constriction and jet reattachment point in the proximal trachea. These laryngeal effects strongly depended on inlet Reynolds number, with maximal effects (approaching 15%) occurring at maximal inlet flow rates. While the increase in the regional uptake caused by the larynx subsided by the end of the model, the effect of the larynx on cumulative uptake persisted further downstream. These results suggest that with prolonged exposure to a reactive gas, entire regions of the larynx and proximal trachea could show signs of tissue injury.}, } @article {pmid23133151, year = {2009}, author = {Srivastava, A and Sood, A and Joy, SP and Woodcock, J}, title = {Principles of physics in surgery: the laws of flow dynamics physics for surgeons - Part 1.}, journal = {The Indian journal of surgery}, volume = {71}, number = {4}, pages = {182-187}, pmid = {23133151}, issn = {0972-2068}, abstract = {In the field of medicine and surgery many principles of physics find numerous applications. In this article we have summarized some prominent applications of the laws of fluid mechanics and hydrodynamics in surgery. Poiseuille's law sets the limits of isovolaemic haemodilution, enumerates limiting factors during fluid resuscitation and is a guiding principle in surgery for vascular stenoses. The equation of continuity finds use in non-invasive measurement of blood flow. Bernoulli's theorem explains the formation of post-stenotic dilatation. Reynolds number explains the origin of murmurs, haemolysis and airflow disturbances. Various forms of oxygen therapy are a direct application of the gas laws. Doppler effect is used in ultrasonography to find the direction and velocity of blood flow. In this first part of a series of articles we describe some applications of the laws of hydrodynamics governing the flow of blood and other body fluids.}, } @article {pmid23345732, year = {2001}, author = {Ramadan, QM and Hamid, O and Lim, KO}, title = {Steady flow visualization in a rigid model of the aortic bifurcation: application to atherosclerosis.}, journal = {Journal of biological physics}, volume = {27}, number = {1}, pages = {35-57}, pmid = {23345732}, issn = {0092-0606}, abstract = {Hemodynamics have long been implicated in atherogenesis. The studiesreported here seek to explain the mechanisms for the formation ofatherosclerotic plaque in an aortic bifurcation. Flow studies were made ina model constructed from plexiglass to represent an aortic bifurcation. Under steady flow conditions at inflow Reynolds numbers of 80-1250,the streamline flow patterns and the boundary layer separation zones wereinvestigated in relation to the location of atherosclerotic plaques clinicallyfound at regions in the human aortic bifurcation. The streamline flowswere visualized by a slow injection of dye over the cross section of the tubeentrance and along the tube walls. The studies revealed a complex flowfield where secondary flows, induced by the centrifugal and viscous forces,cause the fluid to move towards the inner walls of the aortic bifurcation. The effect was more clearly seen with increasing Reynolds number. Boundary layer separation zones were observed to occur at the outercorners of the branching. The nature of the separation zone formed wasfound to be dependent on Reynolds number. The residence time of fluidparticles within such a separation zone was estimated by measuring thewashout time of a bolus of dye injected at strategic locations along the tubewalls. The residence time was found to decrease exponentially withincreasing Reynolds number. These observations provide strong support forthe role of flow separation in the accumulation of LDL and plateletaggregation within the aortic bifurcation.}, } @article {pmid28868711, year = {1996}, author = {Tamagawa, M and Akamatsu, T and Saitoh, K}, title = {Prediction of Hemolysis in Turbulent Shear Orifice Flow.}, journal = {Artificial organs}, volume = {20}, number = {5}, pages = {553-559}, doi = {10.1111/j.1525-1594.1996.tb04479.x}, pmid = {28868711}, issn = {1525-1594}, abstract = {This study proposes a method of predicting hemolysis induced by turbulent shear stress (Reynolds stress) in a simplified orifice pipe flow. In developing centrifugal blood pumps, there has been a serious problem with hemolysis at the impeller or casing edge; because of flow separation and turbulence in these regions. In the present study, hemolysis caused by turbulent shear stress must occur at high shear stress levels in regions near the edge of an orifice pipe flow. We have computed turbulent shear flow using the low-Reynolds number k -ε model. We found that the computed turbulent shear stress near the edge was several hundreds times that of the laminar shear stress (molecular shear stress). The peak turbulent shear stress is much greater than that obtained in conventional hemolysis testing using a viscometer apparatus. Thus, these high turbulent shear stresses should not be ignored in estimating hemolysis in this blood flow. Using an integrated power by shear force, it is optimimal to determine the threshold of the turbulent shear stress by comparing computed stress levels with those of hemolysis experiments of pipe orifice blood flow.}, } @article {pmid29281382, year = {1994}, author = {Williams, TA}, title = {A Model of Rowing Propulsion and the Ontogeny of Locomotion in Artemia Larvae.}, journal = {The Biological bulletin}, volume = {187}, number = {2}, pages = {164-173}, doi = {10.2307/1542239}, pmid = {29281382}, issn = {1939-8697}, abstract = {Newly hatched Artemia larvae use one pair of limbs to locomote. During development they gradually add additional limbs along the elongating trunk. As larvae grow, body length increases from about 0.4 mm to 4 mm, mean swimming speed increases from 1.8 mm s-1 to 9.9 mm s-1, and frequency of antennal beat decreases from 9.5 to 6.7 Hz. As new limbs are added, they become active in the metachronal rhythm of pre-existing limbs. The body velocity oscillates as early larvae swim; later larvae swim without a cyclic acceleration and deceleration of the body. The change in the pattern of swimming is correlated with the addition of propulsors and a transition in the relative importance of viscous and inertial effects that determine the propulsion in subsequent stages. Reynolds number (based on body length) increases from 2 to 37. A theoretical analysis of rowing propulsion at these intermediate Reynolds numbers shows that initial development of new limbs in Artemia larvae is unimportant for propulsion. Rowing propulsion at the low Reynolds numbers is drag-based; as Reynolds number increases, inertial effects become more important, and unsteady forces on the body become significant in the balance between limb and body. A glide of the body develops at the end of the powerstroke, and relative limb velocity changes.}, } @article {pmid29281381, year = {1994}, author = {Williams, TA}, title = {Locomotion in Developing Artemia Larvae: Mechanical Analysis of Antennal Propulsors Based on Large-Scale Physical Models.}, journal = {The Biological bulletin}, volume = {187}, number = {2}, pages = {156-163}, doi = {10.2307/1542238}, pmid = {29281381}, issn = {1939-8697}, abstract = {A physical model of the swimming appendage (second antenna) of a larval Artemia was oscillated and translated through a tank of glycerine to determine how such a shape may be used to generate thrust at the intermediate Reynolds numbers at which it operates. Force on the model was measured by strain gauges and used to calculate coefficients of drag at a series of speeds and frequencies that represented flow regimes of different larval stages. Measured coefficients of drag (Cd) over this Reynolds number range ({approx} 1-10) suggest that an expression for a cylinder perpendicular to flow at intermediate Reynolds number (Cd = 1 + 10 Re-2/3) best represents the changes in drag coefficients for this geometry. Unsteady forces were found to be a negligible portion of the force on the model in spite of a high ratio of frequency of oscillation to forward translational velocity (i.e., Strouhal number). Comparison of the thrust generated by the model with its fan of setae rigidly fixed versus passively flexing suggests that passive extension of setae can be influenced by relative limb and body speed.}, } @article {pmid29303631, year = {1991}, author = {Patterson, MR}, title = {The Effects of Flow on Polyp-Level Prey Capture in an Octocoral, Alcyonium siderium.}, journal = {The Biological bulletin}, volume = {180}, number = {1}, pages = {93-102}, doi = {10.2307/1542432}, pmid = {29303631}, issn = {1939-8697}, abstract = {Particle capture by individual polyps and tentacles of the octocoral, Alcyonium siderium, was investigated in flows of different speed and turbulence intensity. In low flow (Umean = 2.7 cm/s; u' = 1.2 cm/s, where u' is the root mean square of the fluctuations from Umean), tentacles on the upstream side of a polyp capture the most prey. In intermediate flow (Umean = 12.2 cm/s; u' = 6.0 cm/s), downstream tentacles within a polyp catch the most prey. In high flow (Umean = 19.8 cm/s; u'= 4.0 cm/s), polyps are bent downstream, eddies form over the tentacular surfaces, and the capture distribution over tentacles becomes radially symmetric. At all flow speeds tested, particles are caught with increasing frequency nearer the tip of the tentacle relative to locations near the pharynx. At the highest flow speed tested, no particles are caught on the segment of each tentacle closest to the pharynx. The per polyp capture efficiency is low and drops markedly with increasing Reynolds number. The capture mechanism for this species appears to be direct interception; inertial impaction is shown to be unimportant. Flow modulation of particle capture by polyps is probably a general phenomenon among octocorals.}, } @article {pmid28312353, year = {1989}, author = {Statzner, B and Holm, TF}, title = {Morphological adaptation of shape to flow: Microcurrents around lotic macroinvertebrates with known Reynolds numbers at quasi-natural flow conditions.}, journal = {Oecologia}, volume = {78}, number = {2}, pages = {145-157}, pmid = {28312353}, issn = {1432-1939}, abstract = {Using Laser Doppler Anemometry we measured current velocities in the median plane around dead lotic macroinvertebrates in a flume which reproduced natural near bottom hydraulics. We investigated specimens of the gastropods Ancylus, Acroloxus, and Potamopyrgus, the amphipod Gammarus, and the larval caddisflies Anabolia, Micrasema, and Silo of various size, various alignment to the flow or which were otherwise manipulated in order to clarify certain questions of adaptation of shape or case building style to flow, or the effects of flow on field distribution patterns. The steepest velocity gradients close to the animals were found near areas of their bodies protruding furthest into the flow. In such regions the rates of potential diffusive exchange processes, the potential corrasion (abrasion through suspended solids), and, for larger specimens, the lift forces (directed towards the water surface) must be highest. Posterior of these areas growing boundary layers formed above those species whose upper contour was approximately parallel to the upstream-downstream direction of the flow. All specimens removed momentum from the flow and thus experience a drag force (directed downstream). From the complete data set we derived the following general conclusions about the physical effects of potential morphological adaptations, taking into consideration diffusion through boundary layers, corrasion, lift forces, friction and pressure drag forces: The physical significance of these five factors generally depends on the Reynolds number of an animal and is largely affected by flow separation, which was significantly related to the ratio of body length to height and the slope of the posterior contour. A simultaneous effective morphological adaptation to all five factors is physically impossible and, in addition, would have to change from life at low (e.g. a young, small specimen of a species) to life at high (e.g. a fully grown specimen of the same species) Reynolds number.}, } @article {pmid28310857, year = {1985}, author = {Gilbert, JJ}, title = {Escape response of the rotifer Polyarthra: a high-speed cinematographic analysis.}, journal = {Oecologia}, volume = {66}, number = {3}, pages = {322-331}, pmid = {28310857}, issn = {1432-1939}, abstract = {Cinefilms of unconstrained P. vulgaris at 17°C were taken at a low magnification (∼2x) and 120-200 fps to analyze body movements during swimming and escape responses mediated by movements of the 12 lateral, bladelike appendages or paddles. Cinefilms of partially constrained P. vulgaris and P. dolichoptera at 16°C were taken at a higher magnification (∼10x) and 300 fps, using interference contrast optics, to resolve paddle movements during escape responses. When swimming, P. vulgaris moved at a velocity of 0.348±0,025 (S.E.) mm·s[-1] (2.64 body lenghs·s[-1]), having a Reynolds number of 0.05. During escape responses, P. vulgaris traveled 1.947±0.124 (S.E.) mm (15 body lengths) during 0.0564±0.0038 (S.E.) s, continuously moving at a velocity of 35.7±1.2 (S.E.) mm·s[-1] (270 body lengths·s[-1]) and having a Reynolds number of 5. During these responses, P. vulgaris tumbled sinuously but mostly-88.9±2.3 (S.E.) %-in a constant direction; the angular change in direction from one frame to the next was 28±2 (S.E.) degrees, but the sign of the change in direction frequently alternated. Escape responses are caused by 1-3 cycles of paddle movements. In each cycle, the rigid paddles move up asynchronously until they are all directly overhead, and then they move downwards to their original resting positions, again asynchronously. Polyarthra's body moves along the flight path during all phases of this cycle. A single cycle may take as little as 26 ms, 13 ms for the paddles to elevate and 13 ms for them to descend. The asynchronous upward and downward movements of each of the 12 paddles explain why Polyarthra's body tumbles continuously through its low Reynolds number, viscous environment. Escape responses generally were initiated by contact with another rotifer. In one P. dolichoptera response, the time lag between such contact and the initiation of paddle elevation was about 7 ms. The very short lag time, great velocity, considerable displacement, and unpredictable directionality of Polyarthra's escape response make it a very effective defense against capture by some invertebrate predators.}, } @article {pmid28310572, year = {1983}, author = {Porter, KG and Feig, YS and Vetter, EF}, title = {Morphology, flow regimes, and filtering rates of Daphnia, Ceriodaphnia, and Bosmina fed natural bacteria.}, journal = {Oecologia}, volume = {58}, number = {2}, pages = {156-163}, pmid = {28310572}, issn = {1432-1939}, abstract = {Body size is the best overall indicator of the abilities of the cladocerans Daphnia magna, D. parvula, Ceriodaphnia lacustris and Bosmina longirostris to filter natural bacteria (<1.0 μm). However, species differences exist which cannot be inferred from differences in size, behavior, or morphology alone. The relationship between filtering rate (FR in ml animal[-1]h[-1]) and body length (L in mm) for the cladocerans studied can be described by the power function: [Formula: see text] In D. parvula, algal filtering rates are higher and increase more rapidly with increasing body size than do bacterial filtering rates which are 26 to 33% of algal rates. This suggests that different processes may be involved in the capture of these ultrafine particles and that ultrafine particle capture efficiency decreases with increasing body size within a species. Weight specific filtering rates (in μl μg dry wt[-1]h[-1]) have a strong negative relationship to body size and show species specific differences. Appendage beat rates intersetular distances, setule diameter, appendage, area, % open space on the filtering appendage, Reynolds number, and boundary layer thickness do not provide simple predictions of bacterial filtering rates for the cladocerans studied. Filtering rates on cultured laboratory bacteria and algae may not indicate filtering rates on natural bacterioplankton because of differences in bacterial size, motility, and surface properties. Uptake of ultrafine particles may be enhanced by the presence of larger, more readily filtered particles through a "piggybacking" phenomenon.}, } @article {pmid28310599, year = {1982}, author = {Kingsolver, JG and Moffat, RJ}, title = {Thermoregulation and the determinants of heat transfer in Colias butterflies.}, journal = {Oecologia}, volume = {53}, number = {1}, pages = {27-33}, pmid = {28310599}, issn = {1432-1939}, abstract = {As a means of exploring behavioral and morphological adaptations for thermoregulation in Colias butterflies, convective heat transfer coefficients of real and model butterflies were measured in a wind tunnel as a function of wind speed and body orientation (yaw angle). Results are reported in terms of a dimensionless heat transfer coefficient (Nusselt number, Nu) and a dimensionless wind speed (Reynolds number, Re), for a wind speed range typical of that experienced by basking Colias in the field. The resultant Nusselt-Reynolds (Nu-Re) plots thus indicate the rates of heat transfer by forced convection as a function of wind speed for particular model geometries.For Reynolds numbers throughout the measured range, Nusselt numbers for C. eurytheme butterflies are consistently lower than those for long cylinders, and are independent of yaw angle. There is significant variation among individual butterflies in heat transfer coefficients throughout the Re range. Model butterflies without artificial fur have Nu-Re relations similar to those for cylinders. Heat transfer in these models depends upon yaw angle, with higher heat transfer at intermediate yaw angles (30-60°); these yaw effects increase with increasing Reynolds number. Models with artificial fur, like real Colias, have Nusselt numbers which are consistently lower than those for models without fur at given Reynolds numbers throughout the Re range. Unlike real Colias, however, the models with fur do show yaw angle effects similar to those for models without fur.The independence of heat loss from yaw angle for real Colias is consistent with field observations indicating no behavioral orientation to wind direction. The presence of fur on the models reduces heat loss but does not affect yaw dependence. The large individual variation in heat transfer coefficients among butterflies is probably due to differences in fur characteristics rather than to differences in wing morphology.Finally, a physical model of a butterfly was constructed which accurately simulates the body temperatures of basking Colias in the field for a variety of radiation and wind velocity conditions. The success of the butterfly simulator in mimicking Colias thermal characteristics confirms our preliminary understanding of the physical bases for and heat transfer mechanisms underlying thermoregulatory adaptations in these butterflies.}, } @article {pmid22757491, year = {2012}, author = {Zheng, LY and Farnam, DS and Homentcovschi, D and Sammakia, BG}, title = {A porous elastic model for bacterial biofilms: application to the simulation of deformation of bacterial biofilms under microfluidic jet impingement.}, journal = {Journal of biomechanical engineering}, volume = {134}, number = {5}, pages = {051003}, doi = {10.1115/1.4006683}, pmid = {22757491}, issn = {1528-8951}, mesh = {Anti-Bacterial Agents/pharmacology ; *Biofilms/drug effects/growth & development ; Cell Line ; *Elasticity ; Extracellular Matrix/drug effects/metabolism ; *Microfluidic Analytical Techniques ; Models, Biological ; Porosity ; Pressure ; Streptococcus mutans/cytology/drug effects/*physiology ; }, abstract = {The presence of bacterial biofilms is detrimental in a wide range of healthcare situations especially wound healing. Physical debridement of biofilms is a method widely used to remove them. This study evaluates the use of microfluidic jet impingement to debride biofilms. In this case, a biofilm is treated as a saturated porous medium also having linear elastic properties. A numerical modeling approach is used to calculate the von Mises stress distribution within a porous medium under fluid-structure interaction (FSI) loading to determine the initial rupture of the biofilm structure. The segregated model first simulates the flow field to obtain the FSI interface loading along the fluid-solid interface and body force loading within the porous medium. A stress-strain model is consequently used to calculate the von Mises stress distribution to obtain the biofilm deformation. Under a vertical jet, 60% of the deformation of the porous medium can be accounted for by treating the medium as if it was an impermeable solid. However, the maximum deformation in the porous medium corresponds to the point of maximum shear stress which is a different position in the porous medium than that of the maximum normal stress in an impermeable solid. The study shows that a jet nozzle of 500 μm internal diameter (ID) with flow of Reynolds number (Re) of 200 can remove the majority of biofilm species.}, } @article {pmid22750570, year = {2012}, author = {Zhu, JH and Lee, HP and Lim, KM and Gordon, BR and Wang, de Y}, title = {Effect of accessory ostia on maxillary sinus ventilation: a computational fluid dynamics (CFD) study.}, journal = {Respiratory physiology & neurobiology}, volume = {183}, number = {2}, pages = {91-99}, doi = {10.1016/j.resp.2012.06.026}, pmid = {22750570}, issn = {1878-1519}, mesh = {Adult ; Air ; Female ; Humans ; *Hydrodynamics ; Imaging, Three-Dimensional ; Maxillary Sinus/diagnostic imaging/*physiopathology ; Models, Biological ; Rhinitis, Allergic ; Rhinitis, Allergic, Perennial/diagnostic imaging/physiopathology ; Sinusitis/diagnostic imaging/physiopathology ; Tomography, X-Ray Computed ; }, abstract = {We evaluated, by CFD simulation, effects of accessory ostium (AO) on maxillary sinus ventilation. A three-dimensional nasal model was constructed from an adult CT scan with two left maxillary AOs (sinus I) and one right AO (sinus II), then compared to an identical control model with all AOs sealed (sinuses III and IV). Transient simulations of quiet inspiration and expiration at 15 L/min, and nasal blow at 48 L/min, were calculated for both models using low-Reynolds-number turbulent analysis. At low flows, ventilation rates in sinuses with AOs (I ≈ 0.46 L/min, II ≈ 0.54 L/min), were both more than a magnitude higher than sinuses without AOs (II I ≈ 0.019 L/min, IV ≈ 0.020 L/min). Absence of AO almost completely prevented sinus ventilation. Increased ventilation of sinuses with AOs is complex. Under high flow conditions mimicking nose blowing, in sinuses II, III, and IV, the sinus flow rate increased. In contrast, the airflow direction through sinus I reversed between inspiration and expiration, while it remained almost constant throughout the respiration cycle in sinus II. CFD simulation demonstrated that AOs markedly increase maxillary sinus airflow rates and alter sinus air circulation patterns. Whether these airflow changes impact maxillary sinus physiology or pathophysiology is unknown.}, } @article {pmid22736305, year = {2012}, author = {Deng, Y and Liu, Z and Zhang, P and Liu, Y and Gao, Q and Wu, Y}, title = {A flexible layout design method for passive micromixers.}, journal = {Biomedical microdevices}, volume = {14}, number = {5}, pages = {929-945}, doi = {10.1007/s10544-012-9672-5}, pmid = {22736305}, issn = {1572-8781}, mesh = {Equipment Design ; Microfluidics/*instrumentation/*methods ; Models, Theoretical ; Software ; Spatial Analysis ; }, abstract = {This paper discusses a flexible layout design method of passive micromixers based on the topology optimization of fluidic flows. Being different from the trial and error method, this method obtains the detailed layout of a passive micromixer according to the desired mixing performance by solving a topology optimization problem. Therefore, the dependence on the experience of the designer is weaken, when this method is used to design a passive micromixer with acceptable mixing performance. Several design disciplines for the passive micromixers are considered to demonstrate the flexibility of the layout design method for passive micromixers. These design disciplines include the approximation of the real 3D micromixer, the manufacturing feasibility, the spacial periodic design, and effects of the Péclet number and Reynolds number on the designs obtained by this layout design method. The capability of this design method is validated by several comparisons performed between the obtained layouts and the optimized designs in the recently published literatures, where the values of the mixing measurement is improved up to 40.4% for one cycle of the micromixer.}, } @article {pmid22733254, year = {2012}, author = {Lagus, TP and Edd, JF}, title = {High throughput single-cell and multiple-cell micro-encapsulation.}, journal = {Journal of visualized experiments : JoVE}, volume = {}, number = {64}, pages = {e4096}, pmid = {22733254}, issn = {1940-087X}, mesh = {HL-60 Cells ; High-Throughput Screening Assays/*methods ; Humans ; Microfluidic Analytical Techniques/*methods ; Single-Cell Analysis/*methods ; }, abstract = {UNLABELLED: Microfluidic encapsulation methods have been previously utilized to capture cells in picoliter-scale aqueous, monodisperse drops, providing confinement from a bulk fluid environment with applications in high throughput screening, cytometry, and mass spectrometry. We describe a method to not only encapsulate single cells, but to repeatedly capture a set number of cells (here we demonstrate one- and two-cell encapsulation) to study both isolation and the interactions between cells in groups of controlled sizes. By combining drop generation techniques with cell and particle ordering, we demonstrate controlled encapsulation of cell-sized particles for efficient, continuous encapsulation. Using an aqueous particle suspension and immiscible fluorocarbon oil, we generate aqueous drops in oil with a flow focusing nozzle. The aqueous flow rate is sufficiently high to create ordering of particles which reach the nozzle at integer multiple frequencies of the drop generation frequency, encapsulating a controlled number of cells in each drop. For representative results, 9.9 μm polystyrene particles are used as cell surrogates. This study shows a single-particle encapsulation efficiency P(k=1) of 83.7% and a double-particle encapsulation efficiency P(k=2) of 79.5% as compared to their respective Poisson efficiencies of 39.3% and 33.3%, respectively. The effect of consistent cell and particle concentration is demonstrated to be of major importance for efficient encapsulation, and dripping to jetting transitions are also addressed.

INTRODUCTION: Continuous media aqueous cell suspensions share a common fluid environment which allows cells to interact in parallel and also homogenizes the effects of specific cells in measurements from the media. High-throughput encapsulation of cells into picoliter-scale drops confines the samples to protect drops from cross-contamination, enable a measure of cellular diversity within samples, prevent dilution of reagents and expressed biomarkers, and amplify signals from bioreactor products. Drops also provide the ability to re-merge drops into larger aqueous samples or with other drops for intercellular signaling studies. The reduction in dilution implies stronger detection signals for higher accuracy measurements as well as the ability to reduce potentially costly sample and reagent volumes. Encapsulation of cells in drops has been utilized to improve detection of protein expression, antibodies, enzymes, and metabolic activity for high throughput screening, and could be used to improve high throughput cytometry. Additional studies present applications in bio-electrospraying of cell containing drops for mass spectrometry and targeted surface cell coatings. Some applications, however, have been limited by the lack of ability to control the number of cells encapsulated in drops. Here we present a method of ordered encapsulation which increases the demonstrated encapsulation efficiencies for one and two cells and may be extrapolated for encapsulation of a larger number of cells. To achieve monodisperse drop generation, microfluidic "flow focusing" enables the creation of controllable-size drops of one fluid (an aqueous cell mixture) within another (a continuous oil phase) by using a nozzle at which the streams converge. For a given nozzle geometry, the drop generation frequency f and drop size can be altered by adjusting oil and aqueous flow rates Q(oil) and Q(aq). As the flow rates increase, the flows may transition from drop generation to unstable jetting of aqueous fluid from the nozzle. When the aqueous solution contains suspended particles, particles become encapsulated and isolated from one another at the nozzle. For drop generation using a randomly distributed aqueous cell suspension, the average fraction of drops D(k) containing k cells is dictated by Poisson statistics, where D(k) = λ(k) exp(-λ)/(k!) and λ is the average number of cells per drop. The fraction of cells which end up in the "correctly" encapsulated drops is calculated using P(k) = (k x D(k))/Σ(k' x D(k)'). The subtle difference between the two metrics is that D(k) relates to the utilization of aqueous fluid and the amount of drop sorting that must be completed following encapsulation, and P(k) relates to the utilization of the cell sample. As an example, one could use a dilute cell suspension (low λ) to encapsulate drops where most drops containing cells would contain just one cell. While the efficiency metric P(k) would be high, the majority of drops would be empty (low D(k)), thus requiring a sorting mechanism to remove empty drops, also reducing throughput. Combining drop generation with inertial ordering provides the ability to encapsulate drops with more predictable numbers of cells per drop and higher throughputs than random encapsulation. Inertial focusing was first discovered by Segre and Silberberg and refers to the tendency of finite-sized particles to migrate to lateral equilibrium positions in channel flow. Inertial ordering refers to the tendency of the particles and cells to passively organize into equally spaced, staggered, constant velocity trains. Both focusing and ordering require sufficiently high flow rates (high Reynolds number) and particle sizes (high Particle Reynolds number). Here, the Reynolds number Re =uD(h)/ν and particle Reynolds number Rep =Re(a/D(h))², where u is a characteristic flow velocity, D(h) [=2wh/(w+h)] is the hydraulic diameter, ν is the kinematic viscosity, a is the particle diameter, w is the channel width, and h is the channel height. Empirically, the length required to achieve fully ordered trains decreases as Re and Re(p) increase. Note that the high Re and Re(p) requirements (for this study on the order of 5 and 0.5, respectively) may conflict with the need to keep aqueous flow rates low to avoid jetting at the drop generation nozzle. Additionally, high flow rates lead to higher shear stresses on cells, which are not addressed in this protocol. The previous ordered encapsulation study demonstrated that over 90% of singly encapsulated HL60 cells under similar flow conditions to those in this study maintained cell membrane integrity. However, the effect of the magnitude and time scales of shear stresses will need to be carefully considered when extrapolating to different cell types and flow parameters. The overlapping of the cell ordering, drop generation, and cell viability aqueous flow rate constraints provides an ideal operational regime for controlled encapsulation of single and multiple cells. Because very few studies address inter-particle train spacing, determining the spacing is most easily done empirically and will depend on channel geometry, flow rate, particle size, and particle concentration. Nonetheless, the equal lateral spacing between trains implies that cells arrive at predictable, consistent time intervals. When drop generation occurs at the same rate at which ordered cells arrive at the nozzle, the cells become encapsulated within the drop in a controlled manner. This technique has been utilized to encapsulate single cells with throughputs on the order of 15 kHz, a significant improvement over previous studies reporting encapsulation rates on the order of 60-160 Hz. In the controlled encapsulation work, over 80% of drops contained one and only one cell, a significant efficiency improvement over Poisson (random) statistics, which predicts less than 40% efficiency on average. In previous controlled encapsulation work, the average number of particles per drop λ was tuned to provide single-cell encapsulation. We hypothesize that through tuning of flow rates, we can efficiently encapsulate any number of cells per drop when λ is equal or close to the number of desired cells per drop. While single-cell encapsulation is valuable in determining individual cell responses from stimuli, multiple-cell encapsulation provides information relating to the interaction of controlled numbers and types of cells. Here we present a protocol, representative results using polystyrene microspheres, and discussion for controlled encapsulation of multiple cells using a passive inertial ordering channel and drop generation nozzle.}, } @article {pmid22729901, year = {2012}, author = {Pandey, A and Simha, RA}, title = {Minimal polar swimmer at low Reynolds number.}, journal = {The European physical journal. E, Soft matter}, volume = {35}, number = {6}, pages = {52}, pmid = {22729901}, issn = {1292-895X}, abstract = {We propose a minimal model for a polar swimmer, consisting of two spheres connected by a rigid slender arm, at low Reynolds number. The propulsive velocity for the proposed model is the maximum for any swimming cycle with the same variations in its two degrees of freedom and its displacement in a cycle is achieved entirely in one step. The stroke averaged flow field generated by the contractile swimmer at large distances is found to be dipolar. In addition, the changing radius of one of the spheres generates the field of a potential doublet centered at its initial position.}, } @article {pmid22723904, year = {2012}, author = {Furlan, S and Comparini, D and Ciszak, M and Beccai, L and Mancuso, S and Mazzolai, B}, title = {Origin of polar order in dense suspensions of phototactic micro-swimmers.}, journal = {PloS one}, volume = {7}, number = {6}, pages = {e38895}, pmid = {22723904}, issn = {1932-6203}, mesh = {*Cyanobacteria ; Microfluidics ; *Models, Theoretical ; *Motion ; Rheology ; Suspensions ; }, abstract = {A main question for the study of collective motion in living organisms is the origin of orientational polar order, i.e., how organisms align and what are the benefits of such collective behaviour. In the case of micro-organisms swimming at a low Reynolds number, steric repulsion and long-range hydrodynamic interactions are not sufficient to explain a homogeneous polar order state in which the direction of motion is aligned. An external symmetry-breaking guiding field such as a mechanism of taxis appears necessary to understand this phonemonon. We have investigated the onset of polar order in the velocity field induced by phototaxis in a suspension of a motile micro-organism, the algae Chlamydomonas reinhardtii, for density values above the limit provided by the hydrodynamic approximation of a force dipole model. We show that polar order originates from a combination of both the external guiding field intensity and the population density. In particular, we show evidence for a linear dependence of a phototactic guiding field on cell density to determine the polar order for dense suspensions and demonstrate the existence of a density threshold for the origin of polar order. This threshold represents the density value below which cells undergoing phototaxis are not able to maintain a homogeneous polar order state and marks the transition to ordered collective motion. Such a transition is driven by a noise dominated phototactic reorientation where the noise is modelled as a normal distribution with a variance that is inversely proportional to the guiding field strength. Finally, we discuss the role of density in dense suspensions of phototactic micro-swimmers.}, } @article {pmid22716029, year = {2012}, author = {Kim, Y and Lee Chung, B and Ma, M and Mulder, WJ and Fayad, ZA and Farokhzad, OC and Langer, R}, title = {Mass production and size control of lipid-polymer hybrid nanoparticles through controlled microvortices.}, journal = {Nano letters}, volume = {12}, number = {7}, pages = {3587-3591}, pmid = {22716029}, issn = {1530-6992}, support = {HHSN268201000045C/HL/NHLBI NIH HHS/United States ; U54 CA151884/CA/NCI NIH HHS/United States ; R01 CA155432/CA/NCI NIH HHS/United States ; CA151884/CA/NCI NIH HHS/United States ; 268201000045C//PHS HHS/United States ; }, mesh = {Lipids/*chemistry ; *Microfluidic Analytical Techniques ; Molecular Weight ; Nanoparticles/*chemistry ; Particle Size ; Polymers/*chemistry ; Surface Properties ; }, abstract = {Lipid-polymer hybrid (LPH) nanoparticles can deliver a wide range of therapeutic compounds in a controlled manner. LPH nanoparticle syntheses using microfluidics improve the mixing process but are restricted by a low throughput. In this study, we present a pattern-tunable microvortex platform that allows mass production and size control of LPH nanoparticles with superior reproducibility and homogeneity. We demonstrate that by varying flow rates (i.e., Reynolds number (30-150)) we can control the nanoparticle size (30-170 nm) with high productivity (∼3 g/hour) and low polydispersity (∼0.1). Our approach may contribute to efficient development and optimization of a wide range of multicomponent nanoparticles for medical imaging and drug delivery.}, } @article {pmid22711456, year = {2012}, author = {Pennella, F and Rossi, M and Ripandelli, S and Rasponi, M and Mastrangelo, F and Deriu, MA and Ridolfi, L and Kähler, CJ and Morbiducci, U}, title = {Numerical and experimental characterization of a novel modular passive micromixer.}, journal = {Biomedical microdevices}, volume = {14}, number = {5}, pages = {849-862}, doi = {10.1007/s10544-012-9665-4}, pmid = {22711456}, issn = {1572-8781}, mesh = {Computer Simulation ; Equipment Design ; Microfluidic Analytical Techniques/*instrumentation/methods ; Microfluidics/*instrumentation/*methods ; Models, Theoretical ; }, abstract = {This paper reports a new low-cost passive microfluidic mixer design, based on a replication of identical mixing units composed of microchannels with variable curvature (clothoid) geometry. The micromixer presents a compact and modular architecture that can be easily fabricated using a simple and reliable fabrication process. The particular clothoid-based geometry enhances the mixing by inducing transversal secondary flows and recirculation effects. The role of the relevant fluid mechanics mechanisms promoting the mixing in this geometry were analysed using computational fluid dynamics (CFD) for Reynolds numbers ranging from 1 to 110. A measure of mixing potency was quantitatively evaluated by calculating mixing efficiency, while a measure of particle dispersion was assessed through the lacunarity index. The results show that the secondary flow arrangement and recirculation effects are able to provide a mixing efficiency equal to 80 % at Reynolds number above 70. In addition, the analysis of particles distribution promotes the lacunarity as powerful tool to quantify the dispersion of fluid particles and, in turn, the overall mixing. On fabricated micromixer prototypes the microscopic-Laser-Induced-Fluorescence (μLIF) technique was applied to characterize mixing. The experimental results confirmed the mixing potency of the microdevice.}, } @article {pmid22687444, year = {2012}, author = {Lorente, S and Cetkin, E and Bello-Ochende, T and Meyer, JP and Bejan, A}, title = {The constructal-law physics of why swimmers must spread their fingers and toes.}, journal = {Journal of theoretical biology}, volume = {308}, number = {}, pages = {141-146}, doi = {10.1016/j.jtbi.2012.05.033}, pmid = {22687444}, issn = {1095-8541}, mesh = {Animals ; Athletes ; Biomechanical Phenomena/physiology ; Computer Simulation ; Fingers/*physiology ; Humans ; Hydrodynamics ; *Models, Biological ; Swimming/*physiology ; Time Factors ; Toes/*physiology ; }, abstract = {Here we show theoretically that swimming animals and athletes gain an advantage in force and speed by spreading their fingers and toes optimally. The larger force means larger body mass lifted and greater speed, in accord with the constructal theory of all animal locomotion. The spacing between fingers must be twice the thickness of the boundary layer around one finger. This theoretical prediction is confirmed by computational fluid dynamics simulations of flow across two and four cylinders of diameter D. The optimal spacing is in the range 0.2D-0.4D, and decreases slightly as the Reynolds number (Re) increases from 20 to 100. For example, the total force exerted by two optimally spaced cylinders exceeds by 53% the total force of two cylinders with no spacing when Re=20. These design features hold for both time-dependent and steady-state flows.}, } @article {pmid22680576, year = {2012}, author = {Liu, H and Valocchi, AJ and Kang, Q}, title = {Three-dimensional lattice Boltzmann model for immiscible two-phase flow simulations.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {85}, number = {4 Pt 2}, pages = {046309}, doi = {10.1103/PhysRevE.85.046309}, pmid = {22680576}, issn = {1550-2376}, abstract = {We present an improved three-dimensional 19-velocity lattice Boltzmann model for immisicible binary fluids with variable viscosity and density ratios. This model uses a perturbation step to generate the interfacial tension and a recoloring step to promote phase segregation and maintain surfaces. A generalized perturbation operator is derived using the concept of a continuum surface force together with the constraints of mass and momentum conservation. A theoretical expression for the interfacial tension is determined directly without any additional analysis and assumptions. The recoloring algorithm proposed by Latva-Kokko and Rothman is applied for phase segregation, which minimizes the spurious velocities and removes lattice pinning. This model is first validated against the Laplace law for a stationary bubble. It is found that the interfacial tension is predicted well for density ratios up to 1000. The model is then used to simulate droplet deformation and breakup in simple shear flow. We compute droplet deformation at small capillary numbers in the Stokes regime and find excellent agreement with the theoretical Taylor relation for the segregation parameter β=0.7. In the limit of creeping flow, droplet breakup occurs at a critical capillary number 0.350, hydrodynamic interactions can lead to a homogeneous synchronized state. Numerical simulations for a finite number of oscillators confirm this and, when α<0, show the propagation of waves, reminiscent of metachronal coordination.}, } @article {pmid22671425, year = {2012}, author = {Berendsen, CW and Zeegers, JC and Kruis, GC and Riepen, M and Darhuber, AA}, title = {Rupture of thin liquid films induced by impinging air-jets.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {28}, number = {26}, pages = {9977-9985}, doi = {10.1021/la301353f}, pmid = {22671425}, issn = {1520-5827}, mesh = {*Air ; Models, Theoretical ; *Pressure ; *Surface-Active Agents ; Time Factors ; }, abstract = {Thin liquid films on partially wetting substrates are subjected to laminar axisymmetric air-jets impinging at normal incidence. We measured the time at which film rupture occurs and dewetting commences as a function of diameter and Reynolds number of the air-jet. We developed numerical models for the air flow as well as the height evolution of the thin liquid film. The experimental results were compared with numerical simulations based on the lubrication approximation and a phenomenological expression for the disjoining pressure. We achieved quantitative agreement for the rupture times. We found that the film thickness profiles were highly sensitive to the presence of minute quantities of surface-active contaminants.}, } @article {pmid22662054, year = {2011}, author = {Berry, JD and Davidson, MR and Bharti, RP and Harvie, DJ}, title = {Effect of wall permittivity on electroviscous flow through a contraction.}, journal = {Biomicrofluidics}, volume = {5}, number = {4}, pages = {44102-4410217}, pmid = {22662054}, issn = {1932-1058}, abstract = {The electroviscous flow at low Reynolds number through a two-dimensional slit contraction with electric double-layer overlap is investigated numerically for cases where the permittivity of the wall material is significant in comparison with the permittivity of the liquid. The liquid-solid interface is assumed to have uniform surface-charge density. It is demonstrated that a finite wall permittivity has a marked effect on the distribution of ions in and around the contraction, with a significant build-up of counter-ions observed at the back-step. The development length of the flow increases substantially as the wall permittivity becomes significant, meaning that the electric double-layers require a longer distance to develop within the contraction. Consequently, there is a corresponding decrease in the hydrodynamic and electro-potential resistance caused by the contraction. The effect of wall-region width on the flow characteristics is also quantified, demonstrating that the development length increases with increasing wall-region width for widths up to 5 channel widths.}, } @article {pmid22639553, year = {2012}, author = {Hao, J and Li, Z and Lubkin, SR}, title = {AN AUGMENTED IMMERSED INTERFACE METHOD FOR MOVING STRUCTURES WITH MASS.}, journal = {Discrete and continuous dynamical systems. Series B}, volume = {17}, number = {4}, pages = {1175-1184}, pmid = {22639553}, issn = {1531-3492}, support = {R01 GM096195/GM/NIGMS NIH HHS/United States ; R01 GM096195-02/GM/NIGMS NIH HHS/United States ; }, abstract = {We present an augmented immersed interface method for simulating the dynamics of a deformable structure with mass in an incompressible fluid. The fluid is modeled by the Navier-Stokes equations in two dimensions. The acceleration of the structure due to mass is coupled with the flow velocity and the pressure. The surface tension of the structure is assumed to be a constant for simplicity. In our method, we treat the unknown acceleration as the only augmented variable so that the augmented immersed interface method can be applied. We use a modified projection method that can enforce the pressure jump conditions corresponding to the unknown acceleration. The acceleration must match the flow acceleration along the interface. The proposed augmented method is tested against an exact solution with a stationary interface. It shows that the augmented method has a second order of convergence in space. The dynamics of a deformable circular structure with mass is also investigated. It shows that the fluid-structure system has bi-stability: a stationary state for a smaller Reynolds number and an oscillatory state for a larger Reynolds number. The observation agrees with those in the literature.}, } @article {pmid22616875, year = {2014}, author = {Tripathi, D and Bég, OA and Curiel-Sosa, JL}, title = {Homotopy semi-numerical simulation of peristaltic flow of generalised Oldroyd-B fluids with slip effects.}, journal = {Computer methods in biomechanics and biomedical engineering}, volume = {17}, number = {4}, pages = {433-442}, doi = {10.1080/10255842.2012.688109}, pmid = {22616875}, issn = {1476-8259}, mesh = {Body Fluids/*physiology ; Hydrodynamics ; *Models, Biological ; Peristalsis ; Pressure ; }, abstract = {This investigation deals with the peristaltic flow of generalised Oldroyd-B fluids (with the fractional model) through a cylindrical tube under the influence of wall slip conditions. The analysis is carried out under the assumptions of long wavelength and low Reynolds number. Analytical approximate solutions are obtained by using the highly versatile and rigorous semi-numerical procedure known as the homotopy analysis method. It is assumed that the cross section of the tube varies sinusoidally along the length of the tube. The effects of the dominant hydromechanical parameters, i.e. fractional parameters, material constants, slip parameter, time and amplitude on the pressure difference across one wavelength, are studied. Graphical plots reveal that the influence of both fractional parameters on pressure is opposite to each other. Interesting responses to a variation in the constants are obtained. Pressure is shown to be reduced by increasing the slip parameter. Furthermore, the pressure in the case of fractional models (fractional Oldroyd-B model and fractional Maxwell model) of viscoelastic fluids is considerably more substantial than that in the corresponding classical viscoelastic models (Oldroyd-B and Maxwell models). Applications of the study arise in biophysical food processing, embryology and gastro-fluid dynamics.}, } @article {pmid22587177, year = {2012}, author = {Du, J and Keener, JP and Guy, RD and Fogelson, AL}, title = {Low-Reynolds-number swimming in viscous two-phase fluids.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {85}, number = {3 Pt 2}, pages = {036304}, doi = {10.1103/PhysRevE.85.036304}, pmid = {22587177}, issn = {1550-2376}, mesh = {Elasticity ; *Hydrodynamics ; Models, Theoretical ; *Motion ; Viscosity ; }, abstract = {The fluid media surrounding many microorganisms are often mixtures of multiple materials with very different physical properties. The composition and rheology of the mixture may strongly affect the related locomotive behaviors. We study the classical Taylor's swimming sheet problem within a two-fluid model, which consists of two intermixed viscous fluids with different viscosities, with both numerical experiments and analysis. Our results indicate that both the swimming speed and efficiency may be decreased substantially relative to those for a single-phase fluid.}, } @article {pmid22549087, year = {2012}, author = {Nichols, JT and Krueger, PS}, title = {Effect of vehicle configuration on the performance of a submersible pulsed-jet vehicle at intermediate Reynolds number.}, journal = {Bioinspiration & biomimetics}, volume = {7}, number = {3}, pages = {036010}, doi = {10.1088/1748-3182/7/3/036010}, pmid = {22549087}, issn = {1748-3190}, mesh = {Animals ; Biomimetic Materials ; Biomimetics/*instrumentation ; Computer Simulation ; Computer-Aided Design ; Decapodiformes/*physiology ; Equipment Design ; Equipment Failure Analysis ; Immersion ; *Models, Biological ; Rheology/*instrumentation ; *Ships ; Swimming/*physiology ; }, abstract = {Recent results have demonstrated that pulsed-jet propulsion can achieve propulsive efficiency greater than that for steady jets when short, high frequency pulses are used, and the pulsed-jet advantage increases as Reynolds number decreases into the intermediate range (∼50). An important aspect of propulsive performance, however, is the vehicle configuration. The nozzle configuration influences the jet speed and, in the case of pulsed-jets, the formation of the vortex rings with each jet pulse, which have important effects on thrust. Likewise, the hull configuration influences the vehicle speed through its effect on drag. To investigate these effects, several flow inlet, nozzle, and hull tail configurations were tested on a submersible, self-propelled pulsed-jet vehicle ('Robosquid' for short) for jet pulse length-to-diameter ratios (L/D) in the range 0.5-6 and pulsing duty cycles (St(L)) of 0.2 and 0.5. For the configurations tested, the vehicle Reynolds number (Re(υ)) ranged from 25 to 110. In terms of propulsive efficiency, changing between forward and aft-facing inlets had little effect for the conditions considered, but changing from a smoothly tapered aft hull section to a blunt tail increased propulsive efficiency slightly due to reduced drag for the blunt tail at intermediate Re(υ). Sharp edged orifices also showed increased vehicle velocity and propulsive efficiency in comparison to smooth nozzles, which was associated with stronger vortex rings being produced by the flow contraction through the orifice. Larger diameter orifices showed additional gains in propulsive efficiency over smaller orifices if the rate of mass flow was matched with the smaller diameter cases, but using the same maximum jet velocity with the larger diameter decreased the propulsive efficiency relative to the smaller diameter cases.}, } @article {pmid22540703, year = {2012}, author = {Jakiela, S and Korczyk, PM and Makulska, S and Cybulski, O and Garstecki, P}, title = {Discontinuous transition in a laminar fluid flow: a change of flow topology inside a droplet moving in a micron-size channel.}, journal = {Physical review letters}, volume = {108}, number = {13}, pages = {134501}, doi = {10.1103/PhysRevLett.108.134501}, pmid = {22540703}, issn = {1079-7114}, abstract = {Even at moderate values of Reynolds number [e.g., Re=O(1)] a curved interface between liquids can induce an abrupt transition between topologically different configurations of laminar flow. Here we show for the first time direct evidence of a sharp transition in the speed of flow of a droplet upon a small increase of the value of the capillary number above a threshold and the associated change of topology of flow. The quantitative results on the dependence of the threshold capillary number on the contrast of viscosities and on the direction of transition cannot be explained by any of the existing theories and call for a new description.}, } @article {pmid22533995, year = {2012}, author = {Siddiqui, SW and Norton, IT}, title = {Oil-in-water emulsification using confined impinging jets.}, journal = {Journal of colloid and interface science}, volume = {377}, number = {1}, pages = {213-221}, doi = {10.1016/j.jcis.2012.03.062}, pmid = {22533995}, issn = {1095-7103}, mesh = {Emulsions/chemistry ; Hexoses/chemistry ; Lecithins/chemistry ; *Microfluidic Analytical Techniques ; Milk Proteins/chemistry ; Plant Oils/*chemistry ; Polysorbates/chemistry ; Sodium Dodecyl Sulfate/chemistry ; Sunflower Oil ; Water/chemistry ; Whey Proteins ; }, abstract = {A confined impinging jet mixing device has been used to investigate the continuous sunflower oil/water emulsification process under turbulent flow conditions with oil contents between 5% (v/v) and 10% (v/v). Various emulsifiers (Tween20, Span80, Whey Protein, Lecithin and Sodium Dodecylsulphate) varying in molecular weights have been studied. Mean droplet sizes varied with the emulsifiers used and smallest droplets were obtained under fully turbulent flow regime, i.e. at the highest jet flow rate and highest jet Reynolds Number conditions. Sodium Dodecylsulfate (SDS) produced droplets in the range of 3.8 μm while 6 μm droplets were obtained with Whey Protein. Similar droplet sizes were obtained under fully turbulent flow conditions (610 mL/min; Reynolds Number=13,000) for oil content varying between 5% (v/v) and 10% (v/v). To investigate the smallest droplet size possible in the device, the emulsion was passed through the geometry multiple times. Multi-pass emulsification resulted in reduction in droplet size indicating that longer residence in the flow field under high shear condition allowed for breakage of droplets as well as the time for the emulsifier to stabilize the newly formed droplets, decreasing the impact of coalescence. This was confirmed by timescale analysis of the involved process steps for the droplet data obtained via experiments. Dependence of mean droplet size on the o/w interfacial tension and peak energy dissipation was also investigated.}, } @article {pmid22531992, year = {2012}, author = {Valente, I and Stella, B and Marchisio, DL and Dosio, F and Barresi, AA}, title = {Production of PEGylated nanocapsules through solvent displacement in confined impinging jet mixers.}, journal = {Journal of pharmaceutical sciences}, volume = {101}, number = {7}, pages = {2490-2501}, doi = {10.1002/jps.23167}, pmid = {22531992}, issn = {1520-6017}, mesh = {Cyanoacrylates/chemistry ; Equipment Design ; Nanocapsules/*chemistry ; Nanotechnology/instrumentation ; Particle Size ; Polyethylene Glycols/*chemistry ; }, abstract = {The growth of importance of nanocapsules (and other particulate systems) in different fields requires fast and reproducible methods for their production. Confined impinging jet mixers were successfully used for the production of nanospheres and are now tested for the first time for the production of nanocapsules. This work focuses on the understanding of formation mechanisms and on the quantification of the effect of the most important operating parameters involved in their production. Solvent displacement is employed here for the assembly of the nanocapsules by using a PEGylated derivative of cyanoacrylate as copolymer. A comparison with nanospheres obtained under the same operating conditions is also reported. Results show that the oil-to-copolymer mass ratio (MR) is the main factor affecting the final size distribution and that small nanocapsules are obtained only at low oil-to-copolymer MR. The effect of mixing is significant, proving that mixing of solvent and antisolvent also affects the final size distribution; this depends mainly on the inlet jet velocity, but the size of the mixer is also important. The Reynolds number may be useful to take this into account for geometrically similar systems. Quenching by dilution allows to stabilize the nanocapsules, evidencing the role of aggregation and ripening.}, } @article {pmid22529933, year = {2012}, author = {Lichter, S and Rafferty, B and Flohr, Z and Martini, A}, title = {Protein high-force pulling simulations yield low-force results.}, journal = {PloS one}, volume = {7}, number = {4}, pages = {e34781}, pmid = {22529933}, issn = {1932-6203}, mesh = {Hydrodynamics ; *Molecular Dynamics Simulation ; Protein Conformation ; *Protein Unfolding ; Proteins/*chemistry ; }, abstract = {All-atom explicit-solvent molecular dynamics simulations are used to pull with extremely large constant force (750-3000 pN) on three small proteins. The introduction of a nondimensional timescale permits direct comparison of unfolding across all forces. A crossover force of approximately 1100 pN divides unfolding dynamics into two regimes. At higher forces, residues sequentially unfold from the pulling end while maintaining the remainder of the protein force-free. Measurements of hydrodynamic viscous stresses are made easy by the high speeds of unfolding. Using an exact low-Reynolds-number scaling, these measurements can be extrapolated to provide, for the first time, an estimate of the hydrodynamic force on low-force unfolding. Below 1100 pN, but surprisingly still at extremely large applied force, intermediate states and cooperative unfoldings as seen at much lower forces are observed. The force-insensitive persistence of these structures indicates that decomposition into unfolded fragments requires a large fluctuation. This finding suggests how proteins are constructed to resist transient high force. The progression of [Formula: see text] helix and [Formula: see text] sheet unfolding is also found to be insensitive to force. The force-insensitivity of key aspects of unfolding opens the possibility that numerical simulations can be accelerated by high applied force while still maintaining critical features of unfolding.}, } @article {pmid22517056, year = {2012}, author = {McFaul, SM and Lin, BK and Ma, H}, title = {Cell separation based on size and deformability using microfluidic funnel ratchets.}, journal = {Lab on a chip}, volume = {12}, number = {13}, pages = {2369-2376}, doi = {10.1039/c2lc21045b}, pmid = {22517056}, issn = {1473-0189}, support = {//Canadian Institutes of Health Research/Canada ; }, mesh = {Animals ; Cell Line, Tumor ; *Cell Separation ; Cell Size ; Humans ; Leukocytes, Mononuclear/*cytology ; Mice ; Microfluidic Analytical Techniques/*instrumentation/methods ; }, abstract = {The separation of biological cells by filtration through microstructured constrictions is limited by unpredictable variations of the filter hydrodynamic resistance as cells accumulate in the microstructure. Applying a reverse flow to unclog the filter will undo the separation and reduce filter selectivity because of the reversibility of low-Reynolds number flow. We introduce a microfluidic structural ratchet mechanism to separate cells using oscillatory flow. Using model cells and microparticles, we confirmed the ability of this mechanism to sort and separate cells and particles based on size and deformability. We further demonstrate that the spatial distribution of cells after sorting is repeatable and that the separation process is irreversible. This mechanism can be applied generally to separate cells that differ based on size and deformability.}, } @article {pmid22498691, year = {2012}, author = {Johnston, J and Gopalarathnam, A}, title = {Investigation of a bio-inspired lift-enhancing effector on a 2D airfoil.}, journal = {Bioinspiration & biomimetics}, volume = {7}, number = {3}, pages = {036003}, doi = {10.1088/1748-3182/7/3/036003}, pmid = {22498691}, issn = {1748-3190}, mesh = {*Aircraft ; Animals ; *Biomimetic Materials ; Biomimetics/*instrumentation ; Birds/*physiology ; Computer Simulation ; Computer-Aided Design ; Equipment Design ; Equipment Failure Analysis ; Flight, Animal/*physiology ; *Models, Biological ; Movement/*physiology ; Wings, Animal/*physiology ; }, abstract = {A flap mounted on the upper surface of an airfoil, called a 'lift-enhancing effector', has been shown in wind tunnel tests to have a similar function to a bird's covert feathers, which rise off the wing's surface in response to separated flows. The effector, fabricated from a thin Mylar sheet, is allowed to rotate freely about its leading edge. The tests were performed in the NCSU subsonic wind tunnel at a chord Reynolds number of 4 × 10(5). The maximum lift coefficient with the effector was the same as that for the clean airfoil, but was maintained over an angle-of-attack range from 12° to almost 20°, resulting in a very gentle stall behavior. To better understand the aerodynamics and to estimate the deployment angle of the free-moving effector, fixed-angle effectors fabricated out of stiff wood were also tested. A progressive increase in the stall angle of attack with increasing effector angle was observed, with diminishing returns beyond the effector angle of 60°. Drag tests on both the free-moving and fixed effectors showed a marked improvement in drag at high angles of attack. Oil flow visualization on the airfoil with and without the fixed-angle effectors proved that the effector causes the separation point to move aft on the airfoil, as compared to the clean airfoil. This is thought to be the main mechanism by which an effector improves both lift and drag. A comparison of the fixed-effector results with those from the free-effector tests shows that the free effector's deployment angle is between 30° and 45°. When operating at and beyond the clean airfoil's stall angle, the free effector automatically deploys to progressively higher angles with increasing angles of attack. This slows down the rapid upstream movement of the separation point and avoids the severe reduction in the lift coefficient and an increase in the drag coefficient that are seen on the clean airfoil at the onset of stall. Thus, the effector postpones the stall by 4-8° and makes the stall behavior more gentle. The benefits of using the effector could include care-free operations at high angles of attack during perching and maneuvering flight, especially in gusty conditions.}, } @article {pmid22463643, year = {2012}, author = {Hultmark, M and Vallikivi, M and Bailey, SC and Smits, AJ}, title = {Turbulent pipe flow at extreme Reynolds numbers.}, journal = {Physical review letters}, volume = {108}, number = {9}, pages = {094501}, doi = {10.1103/PhysRevLett.108.094501}, pmid = {22463643}, issn = {1079-7114}, abstract = {Both the inherent intractability and complex beauty of turbulence reside in its large range of physical and temporal scales. This range of scales is captured by the Reynolds number, which in nature and in many engineering applications can be as large as 10(5)-10(6). Here, we report turbulence measurements over an unprecedented range of Reynolds numbers using a unique combination of a high-pressure air facility and a new nanoscale anemometry probe. The results reveal previously unknown universal scaling behavior for the turbulent velocity fluctuations, which is remarkably similar to the well-known scaling behavior of the mean velocity distribution.}, } @article {pmid22463354, year = {2012}, author = {Li, Q and Luo, KH and Gao, YJ and He, YL}, title = {Additional interfacial force in lattice Boltzmann models for incompressible multiphase flows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {85}, number = {2 Pt 2}, pages = {026704}, doi = {10.1103/PhysRevE.85.026704}, pmid = {22463354}, issn = {1550-2376}, abstract = {The existing lattice Boltzmann models for incompressible multiphase flows are mostly constructed with two distribution functions: one is the order parameter distribution function, which is used to track the interface between different phases, and the other is the pressure distribution function for solving the velocity field. In this paper, it is shown that in these models the recovered momentum equation is inconsistent with the target one: an additional force is included in the recovered momentum equation. The additional force has the following features. First, it is proportional to the macroscopic velocity. Second, it is zero in every single-phase region but is nonzero in the interface. Therefore it can be interpreted as an interfacial force. To investigate the effects of the additional interfacial force, numerical simulations are carried out for the problem of Rayleigh-Taylor instability, droplet splashing on a thin liquid film, and the evolution of a falling droplet under gravity. Numerical results demonstrate that, with the increase of the velocity or the Reynolds number, the additional interfacial force will gradually have an important influence on the interface and affect the numerical accuracy.}, } @article {pmid22463328, year = {2012}, author = {Tamayol, A and Wong, KW and Bahrami, M}, title = {Effects of microstructure on flow properties of fibrous porous media at moderate Reynolds number.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {85}, number = {2 Pt 2}, pages = {026318}, doi = {10.1103/PhysRevE.85.026318}, pmid = {22463328}, issn = {1550-2376}, mesh = {*Hydrodynamics ; Microtechnology/*methods ; Models, Theoretical ; Porosity ; }, abstract = {In this study, effects of microstructure on the viscous permeability and Forchheimer coefficient of monodispersed fibers are investigated. The porous material is represented by a unit cell which is assumed to be repeated throughout the medium. Based on the orientation of the fibers in the space, fibrous media are divided into three categories: one-, two-, and three-directional (1D, 2D, and 3D) structures. Parallel and transverse flow through square arrangements of 1D fibers, simple 2D mats, and 3D simple cubic structures are solved numerically over a wide range of porosity (0.35 < ε < 0.95) and Reynolds number (0.01 < Re < 200). The results are used to calculate the permeability and the inertial coefficient of the considered geometries. An experimental study is performed; the flow coefficients of three different ordered tube banks in the moderate range of Reynolds number (0.001 < Re < 15) are determined. The numerical results are successfully compared with the present and the existing experimental data in the literature. The results suggest that the permeability and Forchheimer coefficient are functions of porosity and fiber orientation. A comparison of the experimental and numerical results with the Ergun equation reveals that this equation is not suitable for highly porous materials. As such, accurate correlations are proposed for determining the Forchheimer coefficient in fibrous porous media.}, } An unhandled exception occurred at $0000000000402653 : EAccessViolation : Access violation $0000000000402653 $0000000000404849