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}, doi = {10.1098/rspa.2019.0038}, 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. Fluids1, 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. A3790, 1144-1148. (doi:10.1016/j.physleta.2015.02.025); Nedic et al. 2017 Phys. Rev. Fluids2, 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. Fluids23, 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. Fluids23, 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 = {}, number = {}, pages = {}, doi = {10.1016/j.cbpa.2019.06.013}, pmid = {31229600}, issn = {1531-4332}, 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}, 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 = {}, doi = {10.3390/mi10060398}, pmid = {31207995}, issn = {2072-666X}, support = {20180550950//Natural Science Foundation of Liaoning/ ; }, 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 modelling.}, journal = {Indoor air}, volume = {}, number = {}, pages = {}, doi = {10.1111/ina.12579}, pmid = {31206776}, issn = {1600-0668}, 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 1.105 and 3.104 . Results are presented and analysed to highlight the main determinants of exposure and to determine if 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 particles diameter (-8% to +16%) was observed between scenarios in correlation with the AER and with the source position, presumably largely attributable to aggregation. This article is protected by copyright. All rights reserved.}, } @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}, doi = {10.1063/1.5092718}, 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}, abstract = {Elemental mercury (Hg0) 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, Hg0-rich amalgamation tailings are often discharged into nearby aquatic systems where the Hg0 droplets settle in bottom sediment and sediment-water interfaces. Hg0 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 Hg0 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 Hg0 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 R2 = 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 Hg0 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 Hg0 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 = {}, doi = {10.3390/mi10060373}, 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}, doi = {10.1038/s41598-019-40464-2}, 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 {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 {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 104 to 106, 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 = {}, doi = {10.3390/mi10050317}, 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}, support = {51875544//National Science Foundation of China/ ; 51675503//National Science Foundation of China/ ; 61805230//National Science Foundation of China/ ; 51805508//National Science Foundation of China/ ; 51805509//National Science Foundation of China/ ; WK2090000011//Fundamental Research Funds for the Central Universities/ ; WK2090090012//Fundamental Research Funds for the Central Universities/ ; WK2090000013//Fundamental Research Funds for the Central Universities/ ; WK2480000002//Fundamental Research Funds for the Central Universities/ ; WK2090090021//Fundamental Research Funds for the Central Universities/ ; 2017495//Youth Innovation Promotion Association CAS/ ; YZ201566//Chinese Academy of Sciences Instrument/ ; 2017YFB1104303//National Key R&D Program of China/ ; 2018YFB1105400//National Key R&D Program of China/ ; }, 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 {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 {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 × 104. 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 = {}, number = {}, pages = {}, doi = {10.1007/s10439-019-02275-4}, pmid = {31037445}, issn = {1573-9686}, support = {R01 HL135505/HL/NHLBI NIH HHS/United States ; R01HL119824//National Institutes of Health/ ; 19POST34380804//American Heart Association/ ; }, 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 cm2 (less than 1 cm2 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 (R2 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}, 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}, doi = {10.1016/j.heliyon.2019.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}, doi = {10.1098/rspa.2018.0591}, 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 = {}, doi = {10.3390/mi10040262}, 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 = {}, number = {}, pages = {}, doi = {10.1113/EP087597}, pmid = {30993773}, issn = {1469-445X}, support = {DG #238819-13//Natural Sciences and Engineering Research Council/ ; }, 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}, doi = {10.1016/j.mex.2019.03.003}, 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 = {}, doi = {10.3390/polym11040596}, pmid = {30960580}, issn = {2073-4360}, support = {No.51576210//National Natural Science Foundation of China (NSFC)/ ; }, 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}, doi = {10.1098/rsif.2018.0448}, pmid = {30958231}, issn = {1742-5662}, 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}, doi = {10.1098/rsif.2018.0776}, pmid = {30958200}, issn = {1742-5662}, 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}, doi = {10.1098/rsif.2018.0736}, pmid = {30958167}, issn = {1742-5662}, 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}, doi = {10.1098/rsif.2018.0478}, pmid = {30958164}, issn = {1742-5662}, 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}, doi = {10.1098/rsif.2018.0630}, pmid = {30958143}, issn = {1742-5662}, 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}, 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}, doi = {10.1007/s13239-019-00410-9}, pmid = {30937853}, issn = {1869-4098}, support = {644798//Horizon 2020 Framework Programme/ ; G086917N//Fonds Wetenschappelijk Onderzoek (BE)/ ; }, 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 {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}, doi = {10.1126/sciadv.aau7765}, 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}, doi = {10.1016/j.heliyon.2019.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}, doi = {10.1140/epje/i2019-11791-1}, 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}, 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}, doi = {10.1007/s12182-018-0276-4}, 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}, doi = {10.1063/1.5050201}, 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 = {}, doi = {10.3390/mi10030176}, 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}, doi = {10.1007/s12551-019-00511-8}, 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 = {}, doi = {10.3390/mi10030175}, pmid = {30845732}, issn = {2072-666X}, support = {61703392//National Natural Science Foundation of China(NSFC) for Young Scholar with 223 the Project/ ; U1713201//the joint Research Fund between the NSFC and Shenzhen/ ; JCYJ20170413152640731//Fundamental Research and 224 Discipline Layout project/ ; 2018YFC0115200//National Key R&D Program of China/ ; }, 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 = {}, doi = {10.3390/ma12050765}, pmid = {30845671}, issn = {1996-1944}, support = {51675371//National Natural Science Foundation of China/ ; }, 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}, doi = {10.1038/s41598-019-39704-2}, pmid = {30842437}, issn = {2045-2322}, support = {20160953008//Aeronautical Science Foundation of China (Aeronautic Science Foundation of China)/ ; }, 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 = {}, number = {}, pages = {}, doi = {10.1002/elps.201900029}, pmid = {30830969}, issn = {1522-2683}, support = {CBET-135064//National Science Foundation/ ; }, 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, Pe t = U a / D , and rotation, Pe r = Ω a 2 / 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 Pe t and Pe r 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 F lift = L (κ a) (ε a 3 ζ 2 / D 2) U × Ω [ 1 + O (Pe t , Pe r) ] . Here, ε is the permittivity of the electrolyte; κ - 1 is the Debye length; and L (κ a) is a negative function that decreases in magnitude with increasing κ a . 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 = {}, doi = {10.3390/mi10030171}, pmid = {30823482}, issn = {2072-666X}, support = {643095//Horizon 2020 Framework Programme/ ; }, 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 {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 = {}, doi = {10.3390/mi10030161}, 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}, doi = {10.1371/journal.pone.0212239}, pmid = {30811449}, issn = {1932-6203}, 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}, doi = {10.1038/s41467-019-08916-5}, 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}, 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}, doi = {10.1098/rsos.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}, 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~104) 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}, 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 = {}, doi = {10.3390/nano9020267}, pmid = {30781378}, issn = {2079-4991}, support = {ENE2014-55489-C2-1/2-R; ENE2017-86425-C2-1/2-R//Ministerio de Economía, Industria y Competitividad, Gobierno de España/ ; }, 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 {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}, doi = {10.1007/s11356-019-04484-9}, pmid = {30771128}, issn = {1614-7499}, support = {Grant No. 51579061//National Natural Science Foundation of China/ ; }, 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}, 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}, doi = {10.1038/s41598-018-35907-1}, pmid = {30760794}, issn = {2045-2322}, support = {41506151//Guandong Natural Science Foundation/ ; }, 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 = {}, number = {}, pages = {}, doi = {10.1089/jamp.2018.1500}, pmid = {30759039}, issn = {1941-2703}, 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}, 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}, doi = {10.1126/sciadv.aau1532}, pmid = {30746446}, issn = {2375-2548}, 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 = {}, doi = {10.3390/mi10020110}, 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 = {}, doi = {10.3390/mi9110552}, 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 {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}, support = {IOS1354274//NSF/ ; IOS1754650//NSF/ ; 1354274//Division of Integrative Organismal Systems/ ; 1754650//Division of Integrative Organismal Systems/ ; }, 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 = {}, doi = {10.3390/mi10010056}, pmid = {30650659}, issn = {2072-666X}, support = {11502102//National Natural Science Foundation of China/ ; }, 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 {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}, 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 ∼ 105) 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}, 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}, support = {51406127//National Natural Science Foundation of China/ ; BK20140344//Natural Science Foundation of Jiangsu Province/ ; }, 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}, doi = {10.1016/j.heliyon.2018.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}, doi = {10.1098/rspa.2018.0281}, 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 = 103 (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 {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}, doi = {10.1089/jamp.2018.1490}, pmid = {30556777}, issn = {1941-2703}, 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}, support = {//German Research Foundation/ ; }, 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 = {2018}, author = {Sreenivasan, KR}, title = {Turbulent mixing: A perspective.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {}, number = {}, pages = {}, doi = {10.1073/pnas.1800463115}, 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}, 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}, 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 = {}, doi = {10.1098/rsif.2018.0592}, pmid = {30487240}, issn = {1742-5662}, 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}, doi = {10.1016/j.jtbi.2018.11.016}, pmid = {30465777}, issn = {1095-8541}, 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 = {}, doi = {10.1098/rsif.2018.0301}, pmid = {30464056}, issn = {1742-5662}, 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 {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}, 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}, support = {NRF-2015M2A2A4A02044826//National Research Foundation of Korea/ ; 10054488//Ministry of Trade, Industry & Energy (MOTIE, Korea)/ ; }, 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}, support = {NRF- 2016R1A2B4006987//National Research Foundation of Korea/ ; //Inha University/ ; }, 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}, support = {11402108//National Natural Science Foundation of China/ ; 11672163//National Natural Science Foundation of China/ ; 11571157//National Natural Science Foundation of China/ ; }, 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}, doi = {10.1038/s41598-018-34778-w}, 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}

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 = {2018}, 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 = {}, number = {}, pages = {1-15}, doi = {10.1080/09593330.2018.1531941}, pmid = {30280982}, issn = {1479-487X}, 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 m3 s-1, 8.33 × 10-6 m3 s-1 and 13.9 × 10-6 m3 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 Re0.50 Sc0.33) 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 m3 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}, support = {1505061//Division of Physics/ ; TG-CDA160015//Extreme Science and Engineering Discovery Environment/ ; TG-BIO170090//Extreme Science and Engineering Discovery Environment/ ; }, 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}, 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}, support = {Dartmouth College//Startup fund from Thayer School of Engineering at Dartmouth College/ ; Branco Weiss-Society in Science fellowship//Branco Weiss-Society in Science fellowship (administered by ETH Zürich)/ ; }, 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 = {2018}, author = {Molony, D and Park, J and Zhou, L and Fleischer, C and Sun, HY and Hu, X and Oshinski, J and Samady, H and Giddens, DP and Rezvan, A}, title = {Bulk Flow and Near Wall Hemodynamics of the Rabbit Aortic Arch: A 4D PC-MRI Derived CFD Study.}, journal = {Journal of biomechanical engineering}, volume = {}, number = {}, pages = {}, doi = {10.1115/1.4041222}, pmid = {30140921}, issn = {1528-8951}, 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 intra-species 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 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 co-localize 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<.05). Both traditional and statistical shape analysis 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}, 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 ; EU-H2020-BIOTEC-2014-2015-6335536//Horizon 2020 Framework Programme/ ; H2020-FET-OPEN-RIA-2017-1-766975//Horizon 2020 Framework Programme/ ; }, 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 {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}, doi = {10.1152/ajprenal.00219.2018}, pmid = {30089029}, issn = {1522-1466}, 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

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 ; 14GRNT19020017//American Heart Association/ ; R01HL121293//National Institutes of Health/ ; }, 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}, support = {EP/N014642/1//Engineering and Physical Sciences Research Council/ ; 11172200//National Natural Science Foundation of China/ ; 2013CB035042//National Basic Research Program of China/ ; RF-2015-510//Leverhulme Trust/ ; }, 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}, 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}, 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}, 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}, 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}, support = {DMS 0817529//National Science Foundation/ ; 1311974//National Science Foundation/ ; DMS1562176//National Science Foundation/ ; R01GM107264//National Institutes of Health/ ; }, 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 = {DMS 0817529//National Science Foundation/ ; 1311974//National Science Foundation/ ; #54-CA-210190//National Institutes of Health/ ; R01 GM029123/GM/NIGMS NIH HHS/United States ; U54 CA210190/CA/NCI NIH HHS/United States ; }, 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}, 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//Department of Health/United Kingdom ; }, 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 m2 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 nm2 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}, 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 = {}, doi = {10.1002/smll.201702724}, pmid = {29377529}, issn = {1613-6829}, support = {R01 HG004653/HG/NHGRI NIH HHS/United States ; R21 HG005077/HG/NHGRI NIH HHS/United States ; }, 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}, 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 × 103. 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 {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}, doi = {10.1007/s10665-018-9953-y}, 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 {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 ∼106 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 = {1R44MH112210-01A1//National Institute of Mental Health/ ; 4U54GM104944-04TBD//National Institute of General Medical Sciences/ ; P20GM1033408//National Institute of General Medical Sciences/ ; P20 GM103408/GM/NIGMS NIH HHS/United States ; Vandal Ideas Project//University of Idaho/ ; 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 cm3. Volume of the dura mater, spinal cord and NR was 123.1, 19.9 and 5.8 cm3. Surface area of these features was 318.52, 112.2 and 232.1 cm2 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 {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 = {}, doi = {10.3390/polym9120683}, 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 × 10⁴ to 3 × 10⁵ 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 {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/m3 (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 = {}, doi = {10.1115/1.4038431}, pmid = {29131890}, issn = {1528-8951}, 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//Department of Health/United Kingdom ; }, 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}, 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 {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 {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 (Ca2+), the spasmoneme showcases Ca2+-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}, 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}, 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 {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 {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 1-104 Pa s where the higher end (greater than or equal to 102 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 105 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//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 {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 = {}, 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 N3.85. 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 ui3.85 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 ≃103 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 × 103 to 6.6 × 104. 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 3.8×104 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}, 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 = {}, doi = {10.1098/rsta.2016.0089}, 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 {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=107 and Taylor-Couette flow at shear Reynolds number ReS=2×104 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 × 104 to 1.5 × 105. 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 (~103-104mg/m3/day) than those with single main vortex as H/W=1-4 (~101-102mg/m3/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 (0.1

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 {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}, support = {NRP62//Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung/ ; 160178//Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung/ ; }, 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 {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 ; Asian Continental Ancestry Group ; 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}, doi = {10.1371/journal.pone.0163799}, 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 {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 {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}, doi = {10.1186/s40064-016-2666-7}, 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}, doi = {10.1098/rspa.2015.0850}, 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 {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}, support = {NRF 2014R1A2A2A01003618//National Research Foundation of Korea/ ; NRF-2016R1A2B4006987//National Research Foundation of Korea/ ; }, 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 {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}, 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}, doi = {10.1186/s40064-016-2361-8}, 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 {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}, support = {2009-0083501//National Research Foundation of Korea/ ; NRF-2012-0009578//National Research Foundation of Korea/ ; Research Grant//Inha University/ ; }, 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 {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 ; Kinesin/*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}, doi = {10.1371/journal.pone.0153755}, 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}, 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 ; }, ab