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Bibliography on: Reynolds Number

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ESP: PubMed Auto Bibliography 24 Sep 2018 at 01:31 Created: 

Reynolds Number

It is well known that relative size greatly affects how organisms interact with the world. Less well known, at least among biologists, is that at sufficiently small sizes, mechanical interaction with the environment becomes difficult and then virtually impossible. In fluid dynamics, an important dimensionless parameter is the Reynolds Number (abbreviated Re), which is the ratio of inertial to viscous forces affecting the movement of objects in a fluid medium (or the movement of a fluid in a pipe). Since Re is determined mainly by the size of the object (pipe) and the properties (density and viscosity) of the fluid, organisms of different sizes exhibit significantly different Re values when moving through air or water. A fish, swimming at a high ratio of inertial to viscous forces, gives a flick of its tail and then glides for several body lengths. A bacterium, "swimming" in an environment dominated by viscosity, possesses virtually no inertia. When the bacterium stops moving its flagellum, the bacterium "coasts" for about a half of a microsecond, coming to a stop in a distance less than a tenth the diameter of a hydrogen atom. Similarly, the movement of molecules (nutrients toward, wastes away) in the vicinity of a bacterium is dominated by diffusion. Effective stirring — the generation of bulk flow through mechanical means — is impossible at very low Re. An understanding of the constraints imposed by life at low Reynolds numbers is essentially for understanding the prokaryotic biosphere.

Created with PubMed® Query: "reynolds number" NOT pmcbook NOT ispreviousversion

Citations The Papers (from PubMed®)

RevDate: 2018-09-22

Waldrop LD, He Y, S Khatri (2018)

What Can Computational Modeling Tell Us about the Diversity of Odor-Capture Structures in the Pancrustacea?.

Journal of chemical ecology pii:10.1007/s10886-018-1017-2 [Epub ahead of print].

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.

RevDate: 2018-09-14

Tripathi D, Akbar NS, Khan ZH, et al (2016)

Peristaltic transport of bi-viscosity fluids through a curved tube: A mathematical model for intestinal flow.

Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine, 230(9):817-828.

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.

RevDate: 2018-09-13

Fu Q, Chen H, Liao Q, et al (2018)

Drag reduction and shear-induced cells migration behavior of microalgae slurry in tube flow.

Bioresource technology, 270:38-45 pii:S0960-8524(18)31237-9 [Epub ahead of print].

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.

RevDate: 2018-09-13

Bergersen AW, Mortensen M, K Valen-Sendstad (2018)

The FDA Nozzle Benchmark: In Theory There Is No Difference Between Theory and Practice, But in Practice There Is.

International journal for numerical methods in biomedical engineering [Epub ahead of print].

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 5 and 10M simulation jets broke down in reasonable agreement with the experiments. However, the 17 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 (∼0.31%), much smaller than the reported flow asymmetry (∼3%) and model accuracy (∼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.

RevDate: 2018-09-11

Wan G, Jin C, Trase I, et al (2018)

Helical Structures Mimicking Chiral Seedpod Opening and Tendril Coiling.

Sensors (Basel, Switzerland), 18(9): pii:s18092973.

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.

RevDate: 2018-09-08

Daddi-Moussa-Ider A, Löwen H, S Gekle (2018)

Creeping motion of a solid particle inside a spherical elastic cavity⋆.

The European physical journal. E, Soft matter, 41(9):104 pii:10.1140/epje/i2018-11715-7.

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.

RevDate: 2018-09-03

Oosterhuis JP, Verbeek AA, Bühler S, et al (2017)

Flow Separation and Turbulence in Jet Pumps for Thermoacoustic Applications.

Flow, turbulence and combustion, 98(1):311-326.

The effect of flow separation and turbulence on the performance of a jet pump in oscillatory flows is investigated. A jet pump is a static device whose shape induces asymmetric hydrodynamic end effects when placed in an oscillatory flow. This will result in a time-averaged pressure drop which can be used to suppress acoustic streaming in closed-loop thermoacoustic devices. An experimental setup is used to measure the time-averaged pressure drop as well as the acoustic power dissipation across two different jet pump geometries in a pure oscillatory flow. The results are compared against published numerical results where flow separation was found to have a negative effect on the jet pump performance in a laminar flow. Using hot-wire anemometry the onset of flow separation is determined experimentally and the applicability of a critical Reynolds number for oscillatory pipe flows is confirmed for jet pump applications. It is found that turbulence can lead to a reduction of flow separation and hence, to an improvement in jet pump performance compared to laminar oscillatory flows.

RevDate: 2018-08-24

Andersen MC (1993)

DIASPORE MORPHOLOGY AND SEED DISPERSAL IN SEVERAL WIND-DISPERSED ASTERACEAE.

American journal of botany, 80(5):487-492.

I made measurements of morphology and settling velocity on seeds of 19 species of wind-dispersed Asteraceae. From the morphological measurements I calculated Reynolds numbers and approximate plume loadings for the species. Diaspore settling velocity increases linearly with the square root of plume loading. This relationship varies among species and among subfamilies, but not among life history types. Reynolds number is highly variable among subfamilies, less so within subfamilies. Diaspores with beaked achenes have significantly lower settling velocities than diaspores with unbeaked achenes, even though beaked and unbeaked achenes do not differ in plume loading or in Reynolds number. Reynolds numbers of all diaspores examined are well above the range in which Stokes' Law applies. I recommend that the use of formulae based on Stokes' Law be curtailed in studies of the relationship between plume loading and settling velocity. The results suggest that many seed characters may have evolved due to selection on dispersal ability. This is in spite of phyletic constraints on morphology reflected in the relative uniformity of Reynolds numbers within subfamilies.

RevDate: 2018-08-24

Molony D, Park J, Zhou L, et al (2018)

Bulk Flow and Near Wall Hemodynamics of the Rabbit Aortic Arch: A 4D PC-MRI Derived CFD Study.

Journal of biomechanical engineering pii:2698120 [Epub ahead of print].

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.

RevDate: 2018-08-23

Krastev VK, Amati G, Succi S, et al (2018)

On the effects of surface corrugation on the hydrodynamic performance of cylindrical rigid structures.

The European physical journal. E, Soft matter, 41(8):95 pii:10.1140/epje/i2018-11703-y.

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.

RevDate: 2018-08-22

Lee YJ, KB Lua (2018)

Wing-wake interaction: comparison of two- and three-dimensional flapping wings in hover.

Bioinspiration & biomimetics [Epub ahead of print].

The wing-wake interaction of flapping wings in hover has been investigated, with a focus on the difference in wing-wake interaction between two-dimensional (2D) and three-dimensional (3D) flapping wings. Numerical simulations are conducted at Reynolds number of 100, and the flapping configurations are divided into the 2D, quasi-3D, and 3D categories. Variations of 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 literature. On 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. On the mechanism of the closely attached LEV, the wake encourages the formation of a 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 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.

RevDate: 2018-08-22

Espeso DR, Martínez-García E, Carpio A, et al (2018)

Dynamics of Pseudomonas putida biofilms in an upscale experimental framework.

Journal of industrial microbiology & biotechnology pii:10.1007/s10295-018-2070-0 [Epub ahead of print].

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.

RevDate: 2018-08-20

Lee J, Estlack Z, Somaweera H, et al (2018)

A microfluidic cardiac flow profile generator for studying the effect of shear stress on valvular endothelial cells.

Lab on a chip [Epub ahead of print].

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.

RevDate: 2018-08-18

Gao J, J Katz (2018)

Self-calibrated microscopic dual-view tomographic holography for 3D flow measurements.

Optics express, 26(13):16708-16725.

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.

RevDate: 2018-08-17

Mathai V, Huisman SG, Sun C, et al (2018)

Dispersion of Air Bubbles in Isotropic Turbulence.

Physical review letters, 121(5):054501.

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.

RevDate: 2018-08-17

Oettinger D, Ault JT, Stone HA, et al (2018)

Invisible Anchors Trap Particles in Branching Junctions.

Physical review letters, 121(5):054502.

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.

RevDate: 2018-08-17

Karaminejad S, Askari MH, M Ashjaee (2018)

Temperature field investigation of hydrogen/air and syngas/air axisymmetric laminar flames using Mach-Zehnder interferometry.

Applied optics, 57(18):5057-5067.

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.

RevDate: 2018-08-15

Bhat SS, Zhao J, Sheridan J, et al (2018)

The leading-edge vortex on a rotating wing changes markedly beyond a certain central body size.

Royal Society open science, 5(7):172197 pii:rsos172197.

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.

RevDate: 2018-08-08

Gilmer GG, Deshpande V, Chou CL, et al (2018)

Flow Resistance along the Rat Renal Tubule.

American journal of physiology. Renal physiology [Epub ahead of print].

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 values of 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 determine the points of highest resistance. When the Hagen-Poiseuille equation was used for rat superficial nephrons based on known flow rates, tubule lengths, and diameters for each renal tubule segment, it was found that 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, providing that tubule compliance was taken into account. In long-looped nephrons, the greater length of thin limb segments is compensated for by a larger luminal diameter. Simulation of the effect of proximal diuretics, viz. acetazolamide or SGLT2-inhibitors, predicts a substantial back pressure in Bowman's capsule, which may contribute to observed decreases in glomerular filtration rate.

RevDate: 2018-08-08

Mateos-Maroto A, Guerrero-Martínez A, Rubio RG, et al (2018)

Magnetic Biohybrid Vesicles Transported by an Internal Propulsion Mechanism.

ACS applied materials & interfaces [Epub ahead of print].

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 a biomimetic self-propelled swimmer operating at a low Reynolds number due to internal movements within an enclosing 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 capsules separate the confined substances from the outside environment, protecting them from the surroundings. The proposed swimming and release strategies, based on near infrared laser pulse-triggered destabilization of the phospholipid membranes, open new possibilities for the on-command transport of minute quantities of drugs, fluids or nano-objects. The lipid membranes protect the confined substances from the outside environment during transportation, thus enabling to work in physiological conditions.

RevDate: 2018-08-07

Vidal EAG, Zeidberg LD, EJ Buskey (2018)

Development of Swimming Abilities in Squid Paralarvae: Behavioral and Ecological Implications for Dispersal.

Frontiers in physiology, 9:954.

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.

RevDate: 2018-08-03

Gritti F (2018)

High-resolution turbulent flow chromatography.

Journal of chromatography. A pii:S0021-9673(18)30943-9 [Epub ahead of print].

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

RevDate: 2018-08-02

Sengupta U, Nemati H, Boersma BJ, et al (2017)

Fully Compressible Low-Mach Number Simulations of Carbon-dioxide at Supercritical Pressures and Trans-critical Temperatures.

Flow, turbulence and combustion, 99(3):909-931.

This work investigates fully developed turbulent flows of carbon-dioxide close to its vapour-liquid critical point in a channel with a hot and a cold wall. Two direct numerical simulations are performed at low Mach numbers, with the trans-critical transition near the channel centre and the cold wall, respectively. An additional simulation with constant transport properties is used to selectively investigate the effect of the non-linear equation of state on turbulence. Compared to the case where the pseudo-critical transition occurs in the channel center, the case with the pseudo-critical transition close to the cold wall reveals that compressibility effects can exist in the near-wall region even at low Mach numbers. An analysis of the velocity streaks near the hot and the cold walls also indicates a greater degree of streak coherence near the cold wall. A comparison between the constant and variable viscosity cases at the same Reynolds number, Mach number and having the same isothermal wall boundary conditions reveals that variable viscosity increases turbulence near the cold wall and also causes higher velocity gradients near the hot wall. We also show that the extended van Driest transformation results in a better agreement of the velocity profile with the log-law of the wall compared to the standard van Driest transformation. The semi-locally scaled turbulent velocity fluctuations and the turbulent kinetic energy budgets on the hot and the cold sides of the channel collapse on top of each other, thereby establishing the validity of Morkovin's hypothesis.

RevDate: 2018-08-02

Sanmiguel Vila C, Örlü R, Vinuesa R, et al (2017)

Adverse-Pressure-Gradient Effects on Turbulent Boundary Layers: Statistics and Flow-Field Organization.

Flow, turbulence and combustion, 99(3):589-612.

RevDate: 2018-08-02

Rosti ME, Omidyeganeh M, A Pinelli (2018)

Numerical Simulation of a Passive Control of the Flow Around an Aerofoil Using a Flexible, Self Adaptive Flaplet.

Flow, turbulence and combustion, 100(4):1111-1143.

RevDate: 2018-08-02

Vernet JA, Örlü R, Söderblom D, et al (2018)

Plasma Streamwise Vortex Generators for Flow Separation Control on Trucks: A Proof-of-concept Experiment.

Flow, turbulence and combustion, 100(4):1101-1109.

An experimental study of the effect of Dielectric Barrier Discharge plasma actuators on the flow separation on the A-pillar of a modern truck under cross-wind conditions has been carried out. The experiments were done in a wind tunnel with a 1:6 scale model of a tractor-trailer combination. The actuators were used as vortex generators positioned on the A-pillar on the leeward side of the tractor and the drag force was measured with a wind-tunnel balance. The results show that the effect at the largest yaw angle (9 degrees) can give a drag reduction of about 20% and that it results in a net power reduction. At lower yaw angles the reduction was smaller. The present results were obtained at a lower Reynolds number and a lower speed than for real driving conditions so it is still not yet confirmed if a similar positive result can be obtained in full scale.

RevDate: 2018-08-02

Ahmadi S, Roccon A, Zonta F, et al (2018)

Turbulent Drag Reduction by a Near Wall Surface Tension Active Interface.

Flow, turbulence and combustion, 100(4):979-993.

RevDate: 2018-08-02

Sundstrom LRJ, MJ Cervantes (2018)

On the Similarity of Pulsating and Accelerating Turbulent Pipe Flows.

Flow, turbulence and combustion, 100(2):417-436.

RevDate: 2018-07-25

Dey KK (2018)

Dynamic Coupling at Low Reynolds Number.

Angewandte Chemie (International ed. in English) [Epub ahead of print].

Collective and emergent behaviors of active colloidal assemblies provide useful insights into the statistical physics of out-of-equilibrium systems. Colloidal suspensions containing microscopic active swimmers have recently been studied with much vigor to understand principles of energy transfer at low Reynolds number conditions. Using molecules of active enzymes and ångström sized organometallic catalysts it has further been demonstrated that energy can be transferred even by molecules to their surroundings, influencing substantially the overall dynamics of the systems. Monitoring the diffusion of non-reacting tracers dispersed in active solutions, it has been shown that the nature of energy transfer in systems containing different swimmers is surprisingly similar - irrespective of their differences in sizes, modes of energy transduction and propulsion strategies. These observations provide motivation not only to characterize reaction generated force fields under complex fluidic environment but also to look for possible similarity in their behavior across multiple length scales. This review discusses research results obtained so far in this direction, highlighting the common features observed regarding dynamic coupling of swimmers with their surroundings. Activity-induced force generation and its collective effects are expected to find wide importance in transport and organization of materials at smaller length scales. Underscoring the nature of reaction generated perturbations, especially under crowded cytosolic conditions, is further likely to advance our knowledge of intracellular mechanics of small molecules during various metabolic processes and chemical transformations.

RevDate: 2018-07-24

Oh S, H Choi (2018)

A predictive model of the drag coefficient for a revolving wing at low Reynolds number.

Bioinspiration & biomimetics [Epub ahead of print].

A predictive model of the drag coefficient for a revolving wing at low Reynolds number is suggested. Unlike the previous model (Wang et al 2016), the present model includes a viscous drag on the wing from laminar boundary layer theory and thus predicts the drag force more accurately at low angles of attack and low Reynolds numbers. Also, in determining the model constants, we consider the attack angle of π/4 at which the resultant force on the wing is assumed to be perpendicular to the wing chord. The present aerodynamic model more accurately predicts drag forces of four different revolving wings than the existing ones.

RevDate: 2018-07-18

Dai L, He GW, Zhang X, et al (2018)

Intermittent locomotion of a fish-like swimmer driven by passive elastic mechanism.

Bioinspiration & biomimetics [Epub ahead of print].

The intermittent locomotion performance of a fish-like elastic swimmer is studied numerically in this paper. The actuation is imposed only at the head and the locomotion is indirectly driven by passive elastic mechanism. For intermittent swimming, certain time durations of passive coasting are interspersed between two half-periods of active bursting. To facilitate the comparison of energy efficiencies in continuous and intermittent swimming at the same cruising speed, we consider both intermittent swimming at various duty cycles and also continuous swimming at reduced actuation frequencies. The result indicates that the intermittent style is more economical than the continuous style only when the cruising Reynolds number is sufficiently large and the duty cycle is moderate. We also explore the passive tail-beating pattern and wake structure for intermittent swimming. It is found that the kinematics of the tail contains a preparatory burst phase which lies in between the active bursting and the passive coasting phases. Three vortex streets are found in the wake structure behind the intermittent swimmers. The two oblique streets consist of strong vortex dipoles and the horizontal street is made up of weak vortices. The results of this study can provide some insight into the burst-and-coast swimming of fish and also inform the design of efficient bio-mimetic under-water vehicles.

RevDate: 2018-07-17

Tang Y, Zhu DZ, B van Duin (2018)

Note on sediment removal efficiency in oil-grit separators.

Water science and technology : a journal of the International Association on Water Pollution Research, 2017(3):729-735.

Oil-grit separators (OGSs) are one type of best management practice, designed to remove oil and grit from stormwater runoff (e.g., from parking lots and paved roads). This note examines scaling parameters for OGS removal efficiency. Three dimensionless parameters are chosen as scaling parameters: Hazen number (Ha), Reynolds number (Re) and Froude number (Fr). The Hazen number is a ratio of hydraulic residence time to particle settling time. The Reynolds number measures the surrounding turbulence effects on sediment removal efficiency. The Froude number represents the ratio of inertial and gravitational forces, which indicates the influence of gravity on fluid motion. The collected data from the literature on sediment removal in OGSs can be represented by a single curve when the Hazen, Reynolds, and Froude numbers are combined into a new scaling parameter (HRF = Ha(Re/Fr)). A general form is proposed to correlate the sediment removal efficiency with this new parameter. This generalized prediction method can be used as a preliminary performance indicator for OGS units. The obtained curve can also be used to adjust raw laboratory and field measurement data to improve the evaluation of the performance of various OGSs.

RevDate: 2018-07-20
CmpDate: 2018-07-20

Fraternale F, Domenicale L, Staffilani G, et al (2018)

Internal waves in sheared flows: Lower bound of the vorticity growth and propagation discontinuities in the parameter space.

Physical review. E, 97(6-1):063102.

This study provides sufficient conditions for the temporal monotonic decay of enstrophy for two-dimensional perturbations traveling in the incompressible, viscous, plane Poiseuille, and Couette flows. Extension of Synge's procedure [J. L. Synge, Proc. Fifth Int. Congress Appl. Mech. 2, 326 (1938); Semicentenn. Publ. Am. Math. Soc. 2, 227 (1938)] to the initial-value problem allow us to find the region of the wave-number-Reynolds-number map where the enstrophy of any initial disturbance cannot grow. This region is wider than that of the kinetic energy. We also show that the parameter space is split into two regions with clearly distinct propagation and dispersion properties.

RevDate: 2018-07-11

Mutlu BR, Edd JF, M Toner (2018)

Oscillatory inertial focusing in infinite microchannels.

Proceedings of the National Academy of Sciences of the United States of America pii:1721420115 [Epub ahead of print].

RevDate: 2018-07-12
CmpDate: 2018-07-10

Musacchio S, Cencini M, Plan ELCVM, et al (2018)

Enhancement of mixing by rodlike polymers.

The European physical journal. E, Soft matter, 41(7):84 pii:10.1140/epje/i2018-11692-9.

We study the mixing of a passive scalar field dispersed in a solution of rodlike polymers in two dimensions, by means of numerical simulations of a rheological model for the polymer solution. The flow is driven by a parallel sinusoidal force (Kolmogorov flow). Although the Reynolds number is lower than the critical value for inertial instabilities, the rotational dynamics of the polymers generates a chaotic flow similar to the so-called elastic-turbulence regime observed in extensible polymer solutions. The temporal decay of the variance of the scalar field and its gradients shows that this chaotic flow strongly enhances mixing.

RevDate: 2018-07-10

Bell GRR, SR Collins (2018)

"Rho"ing a Cellular Boat with Rearward Membrane Flow.

Developmental cell, 46(1):1-3.

The physicist Edward Purcell wrote in 1977 about mechanisms that cells could use to propel themselves in a low Reynolds number environment. Reporting in Developmental Cell, O'Neill et al. (2018) provide direct evidence for one of these mechanisms by optogenetically driving the migration of cells suspended in liquid through RhoA activation.

RevDate: 2018-07-20
CmpDate: 2018-07-20

Bukowicki M, ML Ekiel-Jeżewska (2018)

Different bending models predict different dynamics of sedimenting elastic trumbbells.

Soft matter, 14(28):5786-5799.

The main goal of this paper is to examine theoretically and numerically the impact of a chosen bending model on the dynamics of elastic filaments settling in a viscous fluid under gravity at low-Reynolds-number. We use the bead-spring approximation of a filament and the Rotne-Prager mobility matrix to describe hydrodynamic interactions between the beads. We analyze the dynamics of trumbbells, for which bending angles are typically larger than for thin and long filaments. Each trumbbell is made of three beads connected by springs and it exhibits a bending resistance, described by the harmonic or - alternatively - by the 'cosine' (also called the Kratky-Porod) bending models, both often used in the literature. Using the harmonic bending potential, and coupling it to the spring potential by the Young's modulus, we find simple benchmark solutions: stable stationary configurations of a single elastic trumbbell and attraction of two elastic trumbbells towards a periodic long-lasting orbit. As the most significant result of this paper, we show that for very elastic trumbbells at the same initial conditions, the Kratky-Porod bending potential can lead to qualitatively and quantitatively different spurious dynamics, with artificially large bending angles and unrealistic shapes. We point out that for the bead models of an elastic filament, the range of applicability of the Kratky-Porod model might not go beyond bending angles smaller than π/2 for touching beads and beyond an even much lower value for beads well-separated from each other. The existence of stable stationary configurations of elastic trumbbells and a family of periodic oscillations of two elastic trumbbells are very important findings on their own.

RevDate: 2018-07-02
CmpDate: 2018-07-02

Kawata T, PH Alfredsson (2018)

Inverse Interscale Transport of the Reynolds Shear Stress in Plane Couette Turbulence.

Physical review letters, 120(24):244501.

Interscale interaction between small-scale structures near the wall and large-scale structures away from the wall plays an increasingly important role with increasing Reynolds number in wall-bounded turbulence. While the top-down influence from the large- to small-scale structures is well known, it has been unclear whether the small scales near the wall also affect the large scales away from the wall. In this Letter we show that the small-scale near-wall structures indeed play a role to maintain the large-scale structures away from the wall, by showing that the Reynolds shear stress is transferred from small to large scales throughout the channel. This is in contrast to the turbulent kinetic energy transport which is from large to small scales. Such an "inverse" interscale transport of the Reynolds shear stress eventually supports the turbulent energy production at large scales.

RevDate: 2018-07-17

Jardin T, T Colonius (2018)

On the lift-optimal aspect ratio of a revolving wing at low Reynolds number.

Journal of the Royal Society, Interface, 15(143):.

Lentink & Dickinson (2009 J. Exp. Biol.212, 2705-2719. (doi:10.1242/jeb.022269)) showed that rotational acceleration stabilized the leading-edge vortex on revolving, low aspect ratio (AR) wings and hypothesized that a Rossby number of around 3, which is achieved during each half-stroke for a variety of hovering insects, seeds and birds, represents a convergent high-lift solution across a range of scales in nature. Subsequent work has verified that, in particular, the Coriolis acceleration plays a key role in LEV stabilization. Implicit in these results is that there exists an optimal AR for wings revolving about their root, because it is otherwise unclear why, apart from possible morphological reasons, the convergent solution would not occur for an even lower Rossby number. We perform direct numerical simulations of the flow past revolving wings where we vary the AR and Rossby numbers independently by displacing the wing root from the axis of rotation. We show that the optimal lift coefficient represents a compromise between competing trends with competing time scales where the coefficient of lift increases monotonically with AR, holding Rossby number constant, but decreases monotonically with Rossby number, when holding AR constant. For wings revolving about their root, this favours wings of AR between 3 and 4.

RevDate: 2018-06-19

Maldaner CH, Quinn PM, Cherry JA, et al (2018)

Improving estimates of groundwater velocity in a fractured rock borehole using hydraulic and tracer dilution methods.

Journal of contaminant hydrology, 214:75-86.

A straddle-packer system for use in boreholes in fractured rock was modified to investigate the average linear groundwater velocity (v¯f) in fractures under ambient flow conditions. This packer system allows two different tests to be conducted in the same interval between packers without redeploying the system: (1) forced gradient hydraulic tests to determine the interval transmissivity (T), and (2) borehole dilution experiments to determine the groundwater flow rate (Qt) across the test interval. The constant head step test method provides assurance that flow is Darcian when determining T for each interval and identifies the flow rate at the onset of non-Darcian flow. The critical Reynolds number method uses this flow rate to provide the number of hydraulically active fractures (N) in each interval, the average hydraulic aperture for the test interval and the effective bulk fracture porosity. The borehole dilution method provides Qt values for the interval at the time of the test, and v¯f can be estimated from Qt using the flow area derived from the hydraulic tests. The method was assessed by application to seven test intervals in a borehole 73 m deep in a densely fractured dolostone aquifer used for municipal water supply. The critical Reynolds number method identified one or two fractures in each test interval (1.1 m long), which provided v¯f values in the range of 10 to 8000 m/day. This velocity range is consistent with values reported in the literature for ambient flow in this aquifer. However, when hydraulically active fractures in each interval is identified and measured from acoustic and optical televiewer logs, the calculated v¯f values are unreasonably low as are the calculated values of the hydraulic gradient needed to provide the Qt value for each tested interval. The combination of hydraulic and dilution tests in the same interval is an improved method to obtain values of groundwater velocity in fractured rock aquifers.

RevDate: 2018-07-10
CmpDate: 2018-07-10

Ngoma J, Philippe P, Bonelli S, et al (2018)

Two-dimensional numerical simulation of chimney fluidization in a granular medium using a combination of discrete element and lattice Boltzmann methods.

Physical review. E, 97(5-1):052902.

We present here a numerical study dedicated to the fluidization of a submerged granular medium induced by a localized fluid injection. To this end, a two-dimensional (2D) model is used, coupling the lattice Boltzmann method (LBM) with the discrete element method (DEM) for a relevant description of fluid-grains interaction. An extensive investigation has been carried out to analyze the respective influences of the different parameters of our configuration, both geometrical (bed height, grain diameter, injection width) and physical (fluid viscosity, buoyancy). Compared to previous experimental works, the same qualitative features are recovered as regards the general phenomenology including transitory phase, stationary states, and hysteretic behavior. We also present quantitative findings about transient fluidization, for which several dimensionless quantities and scaling laws are proposed, and about the influence of the injection width, from localized to homogeneous fluidization. Finally, the impact of the present 2D geometry is discussed, by comparison to the real three-dimensional (3D) experiments, as well as the crucial role of the prevailing hydrodynamic regime within the expanding cavity, quantified through a cavity Reynolds number, that can presumably explain some substantial differences observed regarding upward expansion process of the fluidized zone when the fluid viscosity is changed.

RevDate: 2018-06-22
CmpDate: 2018-06-22

Baker NT, Pothérat A, Davoust L, et al (2018)

Inverse and Direct Energy Cascades in Three-Dimensional Magnetohydrodynamic Turbulence at Low Magnetic Reynolds Number.

Physical review letters, 120(22):224502.

This experimental study analyzes the relationship between the dimensionality of turbulence and the upscale or downscale nature of its energy transfers. We do so by forcing low-Rm magnetohydrodynamic turbulence in a confined channel, while precisely controlling its dimensionality by means of an externally applied magnetic field. We first identify a specific length scale l[over ^]_{⊥}^{c} that separates smaller 3D structures from larger quasi-2D ones. We then show that an inverse energy cascade of horizontal kinetic energy along horizontal scales is always observable at large scales, and that it extends well into the region of 3D structures. At the same time, a direct energy cascade confined to the smallest and strongly 3D scales is observed. These dynamics therefore appear not to be simply determined by the dimensionality of individual scales, nor by the forcing scale, unlike in other studies. In fact, our findings suggest that the relationship between kinematics and dynamics is not universal and may strongly depend on the forcing and dissipating mechanisms at play.

RevDate: 2018-06-26

Parise JAR, FEM Saboya (2018)

Experimental data on transport coefficients for developing laminar flow in isosceles triangular ducts using the naphthalene sublimation technique.

Data in brief, 18:1350-1359 pii:S2352-3409(18)30303-2.

The data presented in this article are related to the research article entitled "Transport coefficients for developing laminar flow in isosceles triangular ducts" (Parise and Saboya, 1999) [1]. The article describes an experiment involving the determination of transport coefficients in the laminar entrance region of 30°, 45°, 60° and 90° isosceles triangular ducts. Data were obtained by application of the naphthalene sublimation technique in conjunction with the heat to mass transfer analogy. Experimental conditions (duct sides made of naphthalene and base made of metal) simulated developing velocity and temperature fields in an isosceles triangular duct with isothermal lateral walls and adiabatic base. The Reynolds number ranged from 100 to 1800 and the duct length to hydraulic diameter ratio, from 2 to 40. The experiment consisted of mounting a test section (triangular duct) with the lateral walls made of naphthalene. Air was forced past the test section and naphthalene walls were weighed prior and after each data run, providing the rate of mass transfer for given flow conditions. Raw data, for a total of 77 experimental runs, include: test section geometry, air flow and mass transfer conditions. Processed data comprise the relevant non-dimensional groups, namely: Reynolds, non-dimensional axial duct length and Sherwood numbers.

RevDate: 2018-06-13

McCombe D, JD Ackerman (2018)

Collector Motion Affects Particle Capture in Physical Models and in Wind Pollination.

The American naturalist, 192(1):81-93.

Particle capture is important for ecological processes in aquatic and terrestrial ecosystems. The current model is based on a stationary collector for which predictions about capture efficiency (η; flux of captured particles ∶ flux of particles) are based on the collector flow environment (i.e., collector Reynolds number, Rec; inertial force ∶ viscous force). This model does not account for the movement of collectors in nature. We examined the effect of collector motion (transverse and longitudinal to the flow) on η using a cylindrical model in the lab and the grass species Phleum pratense in the field. Collector motion increased η (up to 400% and 20% in the lab and field, respectively) and also affected the spatial distribution of particles on collectors, especially at low Rec. The effect was greatest for collectors moving transversely at large magnitude, which encountered more particles with higher relative momentum. These results, which differ from the stationary model, can be predicted by considering both Rec and the particle dynamics given by the Stokes number (Stk; particle stopping distance ∶ collector radius) and helped to resolve an existing controversy about pollination mechanisms. Collector motion should be considered in wind pollination and other ecological processes involving particle capture.

RevDate: 2018-07-07

Gritti F, M Fogwill (2018)

Molecular dispersion in pre-turbulent and sustained turbulent flow of carbon dioxide.

Journal of chromatography. A, 1564:176-187.

The average dispersion coefficients, Da¯, of two small molecules (acetonitrile and coronene) were measured under laminar, transient, and sustained turbulent flow regimes along fused silica open tubular capillary (OTC) columns (180 μm inner diameter by 20 m length). Carbon dioxide was used as the mobile phase at room temperature (296 K) and at average pressures in the range from 1500 to 2700 psi. The Reynolds number (Re) was increased from 600 to 5000. The measurement of Da¯ is based on the observed plate height of the non-retained analytes as a function of the applied Reynolds number. Da¯ values are directly estimated from the best fit of the general Golay HETP equation to the experimental plate height curves. The experimental data revealed that under a pre-turbulent flow regime (Re < 2000), Da¯ is 2-6 times larger (3.5 × 10-4 cm2/s) than the bulk diffusion coefficients Dm of the analyte (1.6 × 10-4 and 5.8 × 10-5 cm2/s for acetonitrile and coronene, respectively). This result was explained by the random formation of decaying or vanishing turbulent puffs under pre-turbulent flow regime. Yet, the peak width remains controlled exclusively by the slow mass transfer in the mobile phase across the inner diameter (i.d.) of the OTC. Under sustained turbulent flow regime (Re > 2500), Da¯ is about four to five orders of magnitude larger than Dm. The experimental data slightly overestimated the turbulent dispersion coefficients predicted by Flint-Eisenklam model (Da¯=4 cm2/s). The discrepancy is explained by the approximate nature of the general Golay equation, which assumes that Da¯ is strictly uniform across the entire i.d. of the OTC. In fact, both the viscous and buffer wall layers, in which viscous effects dominate inertial effects, cannot be considered as fully developed turbulent regions. Remarkably, the mass transfer mechanism in OTC under sustained turbulent flow regime is not only controlled by longitudinal dispersion but also by a slow mass transfer in the mobile phase across the thick buffer layer and the thin viscous layer. Altogether, these layers occupy as much as 35% of the OTC volume at Re = 4000. From a theoretical viewpoint, the general Golay HETP equation is only an approximate model which should be refined based on the actual profile of the analyte dispersion coefficient across the OTC i.d. In practice, the measured plate height of non-retained analytes under sustained turbulent flow of carbon dioxide are two orders of magnitude smaller than those expected under hypothetical laminar flow regime.

RevDate: 2018-06-07

Kaiser SC, Werner S, Jossen V, et al (2018)

Power Input Measurements in Stirred Bioreactors at Laboratory Scale.

Journal of visualized experiments : JoVE.

The power input in stirred bioreactors is an important scaling-up parameter and can be measured through the torque that acts on the impeller shaft during rotation. However, the experimental determination of the power input in small-scale vessels is still challenging due to relatively high friction losses inside typically used bushings, bearings and/or shaft seals and the accuracy of commercially available torque meters. Thus, only limited data for small-scale bioreactors, in particular single-use systems, is available in the literature, making comparisons among different single-use systems and their conventional counterparts difficult. This manuscript provides a protocol on how to measure power inputs in benchtop scale bioreactors over a wide range of turbulence conditions, which can be described by the dimensionless Reynolds number (Re). The aforementioned friction losses are effectively reduced by the use of an air bearing. The procedure on how to set up, conduct and evaluate a torque-based power input measurement, with special focus on cell culture typical agitation conditions with low to moderate turbulence (100 < Re < 2·104), is described in detail. The power input of several multi-use and single-use bioreactors is provided by the dimensionless power number (also called Newton number, P0), which is determined to be in the range of P0 ≈ 0.3 and P0 ≈ 4.5 for the maximum Reynolds numbers in the different bioreactors.

RevDate: 2018-06-07

Herbig BA, Yu X, SL Diamond (2018)

Using microfluidic devices to study thrombosis in pathological blood flows.

Biomicrofluidics, 12(4):042201 pii:001891BMF.

Extreme flows can exist within pathological vessel geometries or mechanical assist devices which create complex forces and lead to thrombogenic problems associated with disease. Turbulence and boundary layer separation are difficult to obtain in microfluidics due to the low Reynolds number flow in small channels. However, elongational flows, extreme shear rates and stresses, and stagnation point flows are possible using microfluidics and small perfusion volumes. In this review, a series of microfluidic devices used to study pathological blood flows are described. In an extreme stenosis channel pre-coated with fibrillar collagen that rapidly narrows from 500 μm to 15 μm, the plasma von Willebrand Factor (VWF) will elongate and assemble into thick fiber bundles on the collagen. Using a micropost-impingement device, plasma flow impinging on the micropost generates strong elongational and wall shear stresses that trigger the growth of a VWF bundle around the post (no collagen required). Using a stagnation-point device to mimic the zone near flow reattachment, blood can be directly impinged upon a procoagulant surface of collagen and the tissue factor. Clots formed at the stagnation point of flow impingement have a classic core-shell architecture where the core is highly activated (P-selectin positive platelets and fibrin rich). Finally, within occlusive clots that fill a microchannel, the Darcy flow driven by ΔP/L > 70 mm-Hg/mm-clot is sufficient to drive NETosis of entrapped neutrophils, an event not requiring either thrombin or fibrin. Novel microfluidic devices are powerful tools to access physical environments that exist in human disease.

RevDate: 2018-05-23

Montoya Segnini J, Bocanegra Evans H, L Castillo (2018)

Flow Recirculation in Cartilaginous Ring Cavities of Human Trachea Model.

Journal of aerosol medicine and pulmonary drug delivery [Epub ahead of print].

BACKGROUND: Despite the prevailing assumption of "smooth trachea walls" in respiratory fluid dynamics research, recent investigations have demonstrated that cartilaginous rings in the trachea and main bronchi have a significant effect on the flow behavior and in particle deposition. However, there is not enough detailed information about the underlying physics of the interaction between the cartilage rings and the flow.

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

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

CONCLUSIONS: The detection of recirculation zones in the cartilage ring cavities sheds light on the particle deposition mechanism and helps explain results from previous studies that have observed an enhancement of particle deposition in models with cartilage rings. These results bring to light the importance of including cartilage rings in experimental, numerical, and theoretical models to better understand particle deposition in the trachea and bronchi. In addition, the results provide scientists and medical staff with new insights for improving drug delivery.

RevDate: 2018-06-07

Bordones AD, Leroux M, Kheyfets VO, et al (2018)

Computational Fluid Dynamics Modeling of the Human Pulmonary Arteries with Experimental Validation.

Annals of biomedical engineering pii:10.1007/s10439-018-2047-1 [Epub ahead of print].

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.

RevDate: 2018-07-10
CmpDate: 2018-07-10

Zhu B, Ji Z, Lou Z, et al (2018)

Torque scaling in small-gap Taylor-Couette flow with smooth or grooved wall.

Physical review. E, 97(3-1):033110.

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.

RevDate: 2018-07-10
CmpDate: 2018-07-10

Liang H, Xu J, Chen J, et al (2018)

Phase-field-based lattice Boltzmann modeling of large-density-ratio two-phase flows.

Physical review. E, 97(3-1):033309.

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.

RevDate: 2018-07-10
CmpDate: 2018-07-10

Oyama N, Teshigawara K, Molina JJ, et al (2018)

Reynolds-number-dependent dynamical transitions on hydrodynamic synchronization modes of externally driven colloids.

Physical review. E, 97(3-1):032611.

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.

RevDate: 2018-06-24

Markwalter CE, RK Prud'homme (2018)

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 of pharmaceutical sciences pii:S0022-3549(18)30307-1 [Epub ahead of print].

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.

RevDate: 2018-07-10
CmpDate: 2018-07-10

Sanjeevi SKP, Zarghami A, JT Padding (2018)

Choice of no-slip curved boundary condition for lattice Boltzmann simulations of high-Reynolds-number flows.

Physical review. E, 97(4-1):043305.

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.

RevDate: 2018-07-10
CmpDate: 2018-07-10

Mahalinkam R, Gong F, AS Khair (2018)

Reduced-order model for inertial locomotion of a slender swimmer.

Physical review. E, 97(4-1):043102.

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.

RevDate: 2018-06-01

Daddi-Moussa-Ider A, Lisicki M, Mathijssen AJTM, et al (2018)

State diagram of a three-sphere microswimmer in a channel.

Journal of physics. Condensed matter : an Institute of Physics journal, 30(25):254004.

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.

RevDate: 2018-06-14

Tottori S, BJ Nelson (2018)

Controlled Propulsion of Two-Dimensional Microswimmers in a Precessing Magnetic Field.

Small (Weinheim an der Bergstrasse, Germany), 14(24):e1800722.

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.

RevDate: 2018-06-05

Perrin A, Herbelin P, Jorand FPA, et al (2018)

Design of a rotating disk reactor to assess the colonization of biofilms by free-living amoebae under high shear rates.

Biofouling, 34(4):368-377.

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.

RevDate: 2018-05-10

Zhang S, Luo X, Z Cai (2018)

Three-dimensional flows in a hyperelastic vessel under external pressure.

Biomechanics and modeling in mechanobiology pii:10.1007/s10237-018-1022-y [Epub ahead of print].

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.

RevDate: 2018-05-11

Zhou Y, Lee C, J Wang (2018)

The Computational Fluid Dynamics Analyses on Hemodynamic Characteristics in Stenosed Arterial Models.

Journal of healthcare engineering, 2018:4312415.

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.

RevDate: 2018-06-01

García-Salazar G, de la Luz Zambrano-Zaragoza M, D Quintanar-Guerrero (2018)

Preparation of nanodispersions by solvent displacement using the Venturi tube.

International journal of pharmaceutics, 545(1-2):254-260.

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.

RevDate: 2018-05-01

Sandeep N, Kumaran G, S Saleem (2018)

The influence of cross diffusion on magnetohydrodynamic flow of Carreau liquid in the presence of buoyancy force.

Journal of integrative neuroscience pii:JIN086 [Epub ahead of print].

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.

RevDate: 2018-05-22

Gao S, Liao Q, Liu W, et al (2018)

Nanodroplets Impact on Rough Surfaces: A Simulation and Theoretical Study.

Langmuir : the ACS journal of surfaces and colloids, 34(20):5910-5917.

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.

RevDate: 2018-05-02

Vilfan M, Osterman N, A Vilfan (2018)

Magnetically driven omnidirectional artificial microswimmers.

Soft matter, 14(17):3415-3422.

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.

RevDate: 2018-05-01

Govindarajan V, Mousel J, Udaykumar HS, et al (2018)

Synergy between Diastolic Mitral Valve Function and Left Ventricular Flow Aids in Valve Closure and Blood Transport during Systole.

Scientific reports, 8(1):6187 pii:10.1038/s41598-018-24469-x.

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.

RevDate: 2018-04-18

Li H, S Guo (2018)

Aerodynamic efficiency of a bioinspired flapping wing rotor at low Reynolds number.

Royal Society open science, 5(3):171307 pii:rsos171307.

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.

RevDate: 2018-05-25

Wang C, H Tang (2018)

Enhancement of aerodynamic performance of a heaving airfoil using synthetic-jet based active flow control.

Bioinspiration & biomimetics, 13(4):046005.

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.

RevDate: 2018-05-01

Bordbar A, Taassob A, Khojasteh D, et al (2018)

Maximum Spreading and Rebound of a Droplet Impacting onto a Spherical Surface at Low Weber Numbers.

Langmuir : the ACS journal of surfaces and colloids, 34(17):5149-5158.

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.

RevDate: 2018-06-15

Hopgood M, Reynolds G, R Barker (2018)

Using Computational Fluid Dynamics to Compare Shear Rate and Turbulence in the TIM-Automated Gastric Compartment With USP Apparatus II.

Journal of pharmaceutical sciences, 107(7):1911-1919.

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).

RevDate: 2018-05-09

Prakash J, Ramesh K, Tripathi D, et al (2018)

Numerical simulation of heat transfer in blood flow altered by electroosmosis through tapered micro-vessels.

Microvascular research, 118:162-172.

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.

RevDate: 2018-04-19
CmpDate: 2018-04-19

Jing H, S Das (2018)

Theory of diffusioosmosis in a charged nanochannel.

Physical chemistry chemical physics : PCCP, 20(15):10204-10212.

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.

RevDate: 2018-07-05

Rigatelli G, Zuin M, Dell'Avvocata F, et al (2018)

Rheolytic effects of left main mid-shaft/distal stenting: a computational flow dynamic analysis.

Therapeutic advances in cardiovascular disease, 12(6):161-168.

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.

RevDate: 2018-06-11

Xi J, Hu Q, Zhao L, et al (2018)

Molecular Binding Contributes to Concentration Dependent Acrolein Deposition in Rat Upper Airways: CFD and Molecular Dynamics Analyses.

International journal of molecular sciences, 19(4): pii:ijms19040997.

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.

RevDate: 2018-03-27
CmpDate: 2018-03-21

Gupta A, Clercx HJH, F Toschi (2018)

Computational study of radial particle migration and stresslet distributions in particle-laden turbulent pipe flow.

The European physical journal. E, Soft matter, 41(3):34 pii:10.1140/epje/i2018-11638-3.

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.

RevDate: 2018-05-08

Bayiz Y, Ghanaatpishe M, Fathy H, et al (2018)

Hovering efficiency comparison of rotary and flapping flight for rigid rectangular wings via dimensionless multi-objective optimization.

Bioinspiration & biomimetics, 13(4):046002.

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.

RevDate: 2018-03-29

Margolin LG (2018)

Scale matters.

Philosophical transactions. Series A, Mathematical, physical, and engineering sciences, 376(2118):.

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'.

RevDate: 2018-06-22
CmpDate: 2018-06-22

Agudo JR, Han J, Park J, et al (2018)

Visually Based Characterization of the Incipient Particle Motion in Regular Substrates: From Laminar to Turbulent Conditions.

Journal of visualized experiments : JoVE.

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.

RevDate: 2018-07-06

Kawamura Y, R Tsubaki (2018)

Phase reduction approach to elastohydrodynamic synchronization of beating flagella.

Physical review. E, 97(2-1):022212.

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.

RevDate: 2018-07-10
CmpDate: 2018-07-10

Rolland J (2018)

Extremely rare collapse and build-up of turbulence in stochastic models of transitional wall flows.

Physical review. E, 97(2-1):023109.

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.

RevDate: 2018-07-10
CmpDate: 2018-07-10

Nemoto T, A Alexakis (2018)

Method to measure efficiently rare fluctuations of turbulence intensity for turbulent-laminar transitions in pipe flows.

Physical review. E, 97(2-1):022207.

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.

RevDate: 2018-04-10

Song F, Ju D, Gu F, et al (2018)

Parametric Study on Electric Field-Induced Micro-/Nanopatterns in Thin Polymer Films.

Langmuir : the ACS journal of surfaces and colloids, 34(14):4188-4198.

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.

RevDate: 2018-05-10

Du D, Hilou E, SL Biswal (2018)

Reconfigurable paramagnetic microswimmers: Brownian motion affects non-reciprocal actuation.

Soft matter, 14(18):3463-3470.

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.

RevDate: 2018-05-09

Oota-Ishigaki A, Masuzawa T, K Nagayama (2018)

Analysis of the effect of the size of three-dimensional micro-geometric structures on physical adhesion phenomena using microprint technique.

The International journal of artificial organs, 41(5):277-283.

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.

RevDate: 2018-03-22

Rubol S, Ling B, I Battiato (2018)

Universal scaling-law for flow resistance over canopies with complex morphology.

Scientific reports, 8(1):4430 pii:10.1038/s41598-018-22346-1.

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.

RevDate: 2018-03-14

Yang J, Wang X, Krane M, et al (2017)

Fully-coupled aeroelastic simulation with fluid compressibility - For application to vocal fold vibration.

Computer methods in applied mechanics and engineering, 315:584-606.

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.

RevDate: 2018-03-23

Marson RL, Huang Y, Huang M, et al (2018)

Inertio-capillary cross-streamline drift of droplets in Poiseuille flow using dissipative particle dynamics simulations.

Soft matter, 14(12):2267-2280.

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.

RevDate: 2018-05-18
CmpDate: 2018-05-18

Hadikhani P, Hashemi SMH, Balestra G, et al (2018)

Inertial manipulation of bubbles in rectangular microfluidic channels.

Lab on a chip, 18(7):1035-1046.

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.

RevDate: 2018-06-06
CmpDate: 2018-06-06

Martínez-Pedrero F, P Tierno (2018)

Advances in colloidal manipulation and transport via hydrodynamic interactions.

Journal of colloid and interface science, 519:296-311.

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.

RevDate: 2018-05-01

Wang Q, HG Othmer (2018)

Analysis of a model microswimmer with applications to blebbing cells and mini-robots.

Journal of mathematical biology, 76(7):1699-1763.

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.

RevDate: 2018-05-18
CmpDate: 2018-05-18

Bao L, Spandan V, Yang Y, et al (2018)

Flow-induced dissolution of femtoliter surface droplet arrays.

Lab on a chip, 18(7):1066-1074.

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.

RevDate: 2018-03-05
CmpDate: 2018-03-05

Nissan A, B Berkowitz (2018)

Inertial Effects on Flow and Transport in Heterogeneous Porous Media.

Physical review letters, 120(5):054504.

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.

RevDate: 2018-03-05
CmpDate: 2018-03-05

Cerbus RT, Liu CC, Gioia G, et al (2018)

Laws of Resistance in Transitional Pipe Flows.

Physical review letters, 120(5):054502.

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.

RevDate: 2018-03-18

Wu H, de León MAP, HG Othmer (2018)

Getting in shape and swimming: the role of cortical forces and membrane heterogeneity in eukaryotic cells.

Journal of mathematical biology pii:10.1007/s00285-018-1223-0 [Epub ahead of print].

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.

RevDate: 2018-04-18

Arranz G, Moriche M, Uhlmann M, et al (2018)

Kinematics and dynamics of the auto-rotation of a model winged seed.

Bioinspiration & biomimetics, 13(3):036011.

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.

RevDate: 2018-04-09

Ishimoto K, Gadêlha H, Gaffney EA, et al (2018)

Human sperm swimming in a high viscosity mucus analogue.

Journal of theoretical biology, 446:1-10.

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.

RevDate: 2018-04-10

Ren LF, Adeel M, Li J, et al (2018)

Phenol separation from phenol-laden saline wastewater by membrane aromatic recovery system-like membrane contactor using superhydrophobic/organophilic electrospun PDMS/PMMA membrane.

Water research, 135:31-43.

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.

RevDate: 2018-06-11
CmpDate: 2018-06-11

Fang C, Wu X, Yang F, et al (2018)

Flow of quasi-two dimensional water in graphene channels.

The Journal of chemical physics, 148(6):064702.

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.

RevDate: 2018-03-07

Godoy-Diana R, B Thiria (2018)

On the diverse roles of fluid dynamic drag in animal swimming and flying.

Journal of the Royal Society, Interface, 15(139):.

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.

RevDate: 2018-02-13

Walait A, Siddiqui AM, MA Rana (2018)

Analysis of a self-propelling sheet with heat transfer through non-isothermal fluid in an inclined human cervical canal.

Journal of biological physics pii:10.1007/s10867-018-9481-z [Epub ahead of print].

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.

RevDate: 2018-03-14
CmpDate: 2018-03-14

Dehbani M, M Rahimi (2018)

Introducing ultrasonic falling film evaporator for moderate temperature evaporation enhancement.

Ultrasonics sonochemistry, 42:689-696.

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.

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ESP Quick Facts

ESP Origins

In the early 1990's, Robert Robbins was a faculty member at Johns Hopkins, where he directed the informatics core of GDB — the human gene-mapping database of the international human genome project. To share papers with colleagues around the world, he set up a small paper-sharing section on his personal web page. This small project evolved into The Electronic Scholarly Publishing Project.

ESP Support

In 1995, Robbins became the VP/IT of the Fred Hutchinson Cancer Research Center in Seattle, WA. Soon after arriving in Seattle, Robbins secured funding, through the ELSI component of the US Human Genome Project, to create the original ESP.ORG web site, with the formal goal of providing free, world-wide access to the literature of classical genetics.

ESP Rationale

Although the methods of molecular biology can seem almost magical to the uninitiated, the original techniques of classical genetics are readily appreciated by one and all: cross individuals that differ in some inherited trait, collect all of the progeny, score their attributes, and propose mechanisms to explain the patterns of inheritance observed.

ESP Goal

In reading the early works of classical genetics, one is drawn, almost inexorably, into ever more complex models, until molecular explanations begin to seem both necessary and natural. At that point, the tools for understanding genome research are at hand. Assisting readers reach this point was the original goal of The Electronic Scholarly Publishing Project.

ESP Usage

Usage of the site grew rapidly and has remained high. Faculty began to use the site for their assigned readings. Other on-line publishers, ranging from The New York Times to Nature referenced ESP materials in their own publications. Nobel laureates (e.g., Joshua Lederberg) regularly used the site and even wrote to suggest changes and improvements.

ESP Content

When the site began, no journals were making their early content available in digital format. As a result, ESP was obliged to digitize classic literature before it could be made available. For many important papers — such as Mendel's original paper or the first genetic map — ESP had to produce entirely new typeset versions of the works, if they were to be available in a high-quality format.

ESP Help

Early support from the DOE component of the Human Genome Project was critically important for getting the ESP project on a firm foundation. Since that funding ended (nearly 20 years ago), the project has been operated as a purely volunteer effort. Anyone wishing to assist in these efforts should send an email to Robbins.

ESP Plans

With the development of methods for adding typeset side notes to PDF files, the ESP project now plans to add annotated versions of some classical papers to its holdings. We also plan to add new reference and pedagogical material. We have already started providing regularly updated, comprehensive bibliographies to the ESP.ORG site.

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Papers in Classical Genetics

The ESP began as an effort to share a handful of key papers from the early days of classical genetics. Now the collection has grown to include hundreds of papers, in full-text format.

Digital Books

Along with papers on classical genetics, ESP offers a collection of full-text digital books, including many works by Darwin (and even a collection of poetry — Chicago Poems by Carl Sandburg).

Timelines

ESP now offers a much improved and expanded collection of timelines, designed to give the user choice over subject matter and dates.

Biographies

Biographical information about many key scientists.

Selected Bibliographies

Bibliographies on several topics of potential interest to the ESP community are now being automatically maintained and generated on the ESP site.

ESP Picks from Around the Web (updated 07 JUL 2018 )