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Bibliography on: Reynolds Number

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ESP: PubMed Auto Bibliography 06 Dec 2019 at 01:33 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: 2019-12-05

Shah Z, Khan A, Khan W, et al (2019)

Micropolar gold blood nanofluid flow and radiative heat transfer between permeable channels.

Computer methods and programs in biomedicine, 186:105197 pii:S0169-2607(19)31672-4 [Epub ahead of print].

This article characterizes flow and heat transmission of blood that carries the micropolar nanofluid of gold in a permeable channel. The thermal radiations are also present in the channel while its walls are either moving or stationary. The base-fluid is considered as blood while micro polar nanofluid is taken as gold. By using similarity transformations along with dimensionless quantities the modeled equations of the problem are transmuted into a system of non-linear ODEs with a set of appropriate boundary conditions. The semi-analytical method, HAM is then applied to determine the solution of a set of resultant equations. The results obtained by HAM have also compared with numerical solutions. The influence of non-dimensional parameters like fractional parameter suction/injection β, Reynolds Number Re, Darcys Number Da, micropolar parameter K, Prandtl number Pr and Radiation parameter Rd etc., which provides physical interpretations of temperature, microrotation n and velocity fields are discussed in detail with the help of graphical representations. Nusselt number is calculated and presented through table. This study determined that the temperature of micropolar nanofluid augmented along with augmentation in the volume fraction. Radiation Rd augmented the heat transfer rate at the upper wall and reduce it at the lower wall. The suction/injection parameter 'β' reduces the heat transfer rate in case of β < 0 at the upper wall, where it is augmented at lower wall.

RevDate: 2019-12-05

Pandey R, Kumar M, Majdoubi J, et al (2019)

A review study on blood in human coronary artery: Numerical approach.

Computer methods and programs in biomedicine, 187:105243 pii:S0169-2607(19)31946-7 [Epub ahead of print].

Computational fluid dynamics (CFD) study of blood flow in human coronary artery is one of the emerging fields of Biomed- ical engineering. In present review paper, Finite Volume Method with governing equations and boundary conditions are briefly discussed for different coronary models. Many researchers have come up with astonishing results related to the various factors (blood viscosity, rate of blood flow, shear stress on the arterial wall, Reynolds number, etc.) affecting the hemodynamic of blood in the right/left coronary artery. The aim of this paper is to present an overview of all those work done by the researchers to justify their work related to factors which hampers proper functioning of heart and lead to Coronary Artery Disease (CAD). Governing equations like Navier-stokes equations, continuity equations etc. are widely used and are solved using CFD solver to get a clearer view of coronary artery blockage. Different boundary conditions and blood properties published in the last ten years are summarized in the tabulated form. This table will help new researchers to work on this area.

RevDate: 2019-12-04

Poehnl R, Popescu MN, W Uspal (2019)

Axisymmetric spheroidal squirmers and self-diffusiophoretic particles.

Journal of physics. Condensed matter : an Institute of Physics journal [Epub ahead of print].

We study, by means of an exact analytical solution, the motion of a spheroidal, axisymmetric squirmer in an unbounded fluid, as well as the low Reynolds number hydrodynamic flow associated to it. In contrast to the case of a spherical squirmer --- for which, e.g., the velocity of the squirmer and the magnitude of the stresslet associated with the flow induced by the squirmer are respectively determined by the amplitudes of the first two slip (``squirming'') modes --- for the spheroidal squirmer each squirming mode either contributes to the velocity, or contributes to the stresslet. The results are straightforwardly extended to the self-phoresis of axisymmetric, spheroidal, chemically active particles in the case when the phoretic slip approximation holds.

RevDate: 2019-12-04

Rajappan A, GH McKinley (2019)

Epidermal biopolysaccharides from plant seeds enable biodegradable turbulent drag reduction.

Scientific reports, 9(1):18263 pii:10.1038/s41598-019-54521-3.

The high cost of synthetic polymers has been a key impediment limiting the widespread adoption of polymer drag reduction techniques in large-scale engineering applications, such as marine drag reduction. To address consumable cost constraints, we investigate the use of high molar mass biopolysaccharides, present in the mucilaginous epidermis of plant seeds, as inexpensive drag reducers in large Reynolds number turbulent flows. Specifically, we study the aqueous mucilage extracted from flax seeds (Linum usitatissimum) and compare its drag reduction efficacy to that of poly(ethylene oxide) or PEO, a common synthetic polymer widely used as a drag reducing agent in aqueous flows. Macromolecular and rheological characterisation confirm the presence of high molar mass (≥2 MDa) polysaccharides in the extracted mucilage, with an acidic fraction comprising negatively charged chains. Frictional drag measurements, performed inside a bespoke Taylor-Couette apparatus, show that the as-extracted mucilage has comparable drag reduction performance under turbulent flow conditions as aqueous PEO solutions, while concurrently offering advantages in terms of raw material cost, availability, and bio-compatibility. Our results indicate that plant-sourced mucilage can potentially serve as a cost-effective and eco-friendly substitute for synthetic drag reducing polymers in large scale turbulent flow applications.

RevDate: 2019-12-01

Ibrahim M, M Ijaz Khan (2019)

Mathematical modeling and analysis of SWCNT-Water and MWCNT-Water flow over a stretchable sheet.

Computer methods and programs in biomedicine, 187:105222 pii:S0169-2607(19)31683-9 [Epub ahead of print].

In this article we focused on the mixed convection flow of SWCNT-Water and MWCNT-Water over a stretchable permeable sheet. The nanofluid occupied porous medium. Darcy's law is used to characterize porous medium. The impact of viscous dissipation is considered. Transformation procedure is adopted to transform the governing PDE's system into dimensionless form. In order to solve the dimensionless PDE's system we used numerical method known as Finite difference method. Effects of flow variables i.e porosity parameter, suction parameter, Grashof number and Reynolds number on velocity, skin friction, temperature and Nusselt number are described graphically. The obtained results shows that velocity is dominant in SWCNT-Water over MWCNT-Water. Temperature is dominant in MWCNT-Water over SWCNT-Water.

RevDate: 2019-12-02

Turkyilmazoglu M (2019)

Single phase nanofluids in fluid mechanics and their hydrodynamic linear stability analysis.

Computer methods and programs in biomedicine, 187:105171 pii:S0169-2607(19)31698-0 [Epub ahead of print].

BACKGROUND AND OBJECTIVE: The hydrodynamic stability of nanofluids of one phase is investigated in this paper based on linear stability theory. The overall thrust here is that the linear stability features of nanofluids can be estimated from their corresponding working fluid, at least in special circumstances.

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

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

CONCLUSION: The presented approach in this work serves us to understand the stabilizing/destabilizing effects of nanofluids as compared to the standard base fluids in terms of stability of viscous/inviscid and temporal/spatial senses. To illustrate, the critical Reynolds number in a traditional boundary layer flow is shown to be pushed to higher values with the dispersed nanoparticles in a working fluid, clearly implying the delay in transition from laminar to turbulent state.

RevDate: 2019-11-30

Chen J, He Y, Wang J, et al (2019)

Dynamics of nitrogen transformation and bacterial community with different aeration depths in malodorous river.

World journal of microbiology & biotechnology, 35(12):196 pii:10.1007/s11274-019-2773-z.

In this research, the dynamics of nitrogen transformation and bacterial community in malodorous river were investigated with different aeration depths. Computational flow dynamics (CFD) and Reynolds number (Re) were specially used to characterize the hydrodynamics condition under different aeration depths. The results indicated that aeration depth had vital impact on nitrogen transformation and bacterial community structure. It was found that a range of aeration depth (0.20-0.45 m above sediment-water interface) facilitated the removal of NH4+-N and TN with Re ranging between 6211 and 8930. Proteobacteria took over Firmicutes to become the predominant phylum (36-78%) under aeration, and the main subdivisions of γ-, β- and δ-Proteobacteria also varied greatly with different aeration depths. Interestingly, there was a marked shift of the inferentially identified dominant functional role within Proteobacteria from organic-matter degradation to nitrogen metabolism and then to sulfur metabolism as well as the coupling of nitrogen and sulfur with the increase of disturbance. The redundancy analysis (RDA) further confirmed the importance of aeration disturbance in shaping bacterial community. These findings help to gain improved understanding of endogenous N-behavior and aquatic microbial ecology, and underline the need for integrating the hydrodynamics factors with microbial community.

RevDate: 2019-12-02
CmpDate: 2019-12-02

Singh H, Bonnesoeur A, Besnard H, et al (2019)

A large thermal turbulent Taylor-Couette (THETACO) facility for investigation of turbulence induced by simultaneous action of rotation and radial temperature gradient.

The Review of scientific instruments, 90(11):115112.

A thermal turbulent Taylor-Couette facility has been designed to investigate turbulent flows generated by differential rotation and radial temperature gradient. It consists of a cylindrical annulus with a rotating inner cylinder and a fixed outer cylinder. The electric heating system is installed inside the inner cylinder, and the annulus is immersed in a large cylindrical container filled with cooling fluid. Temperature regulators independently control the temperature of the inner surface of the inner cylinder and that of the cooling fluid. The facility allows us to reach values of the Reynolds number (Re ∼ 5 × 105) and of the Rayleigh number (Ra ∼ 3 × 106) for water as the working fluid. The facility provides torque measurements, a full optical access at the side and from the bottom for velocity measurements using particle image velocimetry (2D, stereoscopic, and tomographic). Temperature measurements in the flow can be performed by thermochromic liquid crystals or laser induced fluorescence.

RevDate: 2019-12-01

Zhang X, Lam WA, MD Graham (2019)

Dynamics of deformable straight and curved prolate capsules in simple shear flow.

Physical review fluids, 4(4):.

This work investigates the motion of neutrally-buoyant, slightly deformable straight and curved prolate fluid-filled capsules in unbounded simple shear flow at zero Reynolds number using direct simulations. The curved capsules serve as a model for the typical crescent-shaped sickle red blood cells in sickle cell disease (SCD). The effects of deformability and curvature on the dynamics are revealed. We show that with low deformability, straight prolate spheroidal capsules exhibit tumbling in the shear plane as their unique asymptotically stable orbit. This result contrasts with that for rigid spheroids, where infinitely many neutrally stable Jeffery orbits exist. The dynamics of curved prolate capsules are more complicated due to a combined effect of deformability and curvature. At short times, depending on the initial orientation, slightly deformable curved prolate capsules exhibit either a Jeffery-like motion such as tumbling or kayaking, or a non-Jeffery-like behavior in which the director (end-to-end vector) of the capsule crosses the shear-gradient plane back and forth. At long times, however, a Jeffery-like quasiperiodic orbit is taken regardless of the initial orientation. We further show that the average of the long-time trajectory can be well approximated using the analytical solution for Jeffery orbits with an effective orbit constant Ceff and aspect ratio ℓeff. These parameters are useful for characterizing the dynamics of curved capsules as a function of given deformability and curvature. As the capsule becomes more deformable or curved, Ceff decreases, indicating a shift of the orbit towards log-rolling motion, while ℓeff increases weakly as the degree of curvature increases but shows negligible dependency on deformability. These features are not changed substantially as the viscosity ratio between the inner and outer fluids is changed from 1 to 5. As cell deformability, cell shape, and cell-cell interactions are all pathologically altered in blood disorders such as SCD, these results will have clear implications on improving our understanding of the pathophysiology of hematologic disease.

RevDate: 2019-11-29
CmpDate: 2019-11-29

Shan X (2019)

Central-moment-based Galilean-invariant multiple-relaxation-time collision model.

Physical review. E, 100(4-1):043308.

Aiming at systematically correcting the non-Galilean-invariant thermal diffusivity in the previous multiple-relaxation-time Boltzmann equation collision model [Shan and Chen, Int. J. Mod. Phys. C 18, 635 (2007)IJMPEO0129-183110.1142/S0129183107010887], we show that by separately relaxing the central moments of the distribution function, Chapman-Enskog calculation leads to the correct hydrodynamic equations with mutually independent and Galilean invariant viscosity and thermal diffusivity, provided the velocity-space discretization preserves moments up to the fourth order. By transforming the central moments back to the absolute reference frame and evaluating using fixed discrete velocities, the efficient and accurate streaming-collision time-stepping algorithm is preserved. The lattice Boltzmann model is found to have excellent numerical stability in high-Reynolds-number simulations.

RevDate: 2019-11-29
CmpDate: 2019-11-29

Berera A, D Clark (2019)

Information production in homogeneous isotropic turbulence.

Physical review. E, 100(4-1):041101.

We study the Reynolds number scaling of the Kolmogorov-Sinai entropy and attractor dimension for three-dimensional homogeneous isotropic turbulence through the use of direct numerical simulation. To do so, we obtain Lyapunov spectra for a range of different Reynolds numbers by following the divergence of a large number of orthogonal fluid trajectories. We find that the attractor dimension grows with the Reynolds number as Re^{2.35} with this exponent being larger than predicted by either dimensional arguments or intermittency models. The distribution of Lyapunov exponents is found to be finite around λ≈0 contrary to a possible divergence suggested by Ruelle. The relevance of the Kolmogorov-Sinai entropy and Lyapunov spectra in comparing complex physical systems is discussed.

RevDate: 2019-11-29
CmpDate: 2019-11-29

Chitsaz M, M Fathali (2019)

Impact of an initial random magnetic field on the evolution of two-dimensional shearless mixing layers.

Physical review. E, 100(4-1):043106.

The impact of an initial random magnetic field on the temporal evolution of a two-dimensional incompressible turbulent shearless mixing layer is investigated using direct numerical simulation. Different intensities of the initial random magnetic field are imposed with uniform probability distribution on an identical flow field. The initial flow field condition is the turbulent shearless mixing layer with different kinetic energy ratio (E_{H}/E_{L}=6.7) and identical integral length scale. Simulations are carried out in a moderate magnetic Reynolds number, which causes a two-way interaction between the velocity and magnetic fields. In order to analyze the effect of the initial random magnetic field on the mixing characteristics, the intermittency inside the mixing layer and the mixing evolution parameters are investigated. It is found that with small initial magnetic field intensity, the intermittency in both large and small scales are larger than those values in hydrodynamic flow. However, increasing the intensity of the initial magnetic field reduces the intermittency in the mixing region to lower values compared to the hydrodynamic flow. The mixing layer growth rate and the mixing efficiency both show reduction by increasing the initial magnetic field intensity, which is attributed to the reduction of the averaged Reynolds number of both homogenous isotropic turbulent regions due to the suppressing effect of the Lorentz force on the velocity fields of these regions.

RevDate: 2019-11-24

Ćmiel AM, Strużyński A, Wyrębek M, et al (2019)

Response of freshwater mussel recruitment to hydrological changes in a eutrophic floodplain lake.

The Science of the total environment pii:S0048-9697(19)35460-9 [Epub ahead of print].

Although eutrophication of freshwaters is a natural process, the human impact often leads to inland waters becoming overloaded with nutrients, impoverishing many valuable and vanishing habitats, such as floodplain lakes. These changes need to be reversed if the occurrence of endangered aquatic species is to be restored. In this paper we analyse the impact of a change in the water regime of a naturally eutrophic floodplain lake, which harbours a large diversity of Unionidae (large freshwater mussels), a globally threatened taxonomic group that provides important ecosystem functions and services. We found that a slight increase in the discharge from this waterbody, following the construction of an additional outflow pipe, positively influenced recruitment in three of the five mussel species inhabiting the lake. We also found that, after the construction of this additional outflow, the niches of juveniles of Anodonta cygnea and Unio spp. changed, revealing differences in their hydrological requirements. Our results suggest that, as in lotic habitats, complex hydraulic parameters are highly significant to unionid mussels in lentic conditions.

RevDate: 2019-11-20

Taheri RA, Goodarzi V, A Allahverdi (2019)

Mixing Performance of a Cost-effective Split-and-Recombine 3D Micromixer Fabricated by Xurographic Method.

Micromachines, 10(11): pii:mi10110786.

This paper presents experimental and numerical investigations of a novel passive micromixer based on the lamination of fluid layers. Lamination-based mixers benefit from increasing the contact surface between two fluid phases by enhancing molecular diffusion to achieve a faster mixing. Novel three-dimensional split and recombine (SAR) structures are proposed to generate fluid laminations. Numerical simulations were conducted to model the mixer performance. Furthermore, experiments were conducted using dyes to observe fluid laminations and evaluate the proposed mixer's characteristics. Mixing quality was experimentally obtained by means of image-based mixing index (MI) measurement. The multi-layer device was fabricated utilizing the Xurography method, which is a simple and low-cost method to fabricate 3D microfluidic devices. Mixing indexes of 96% and 90% were obtained at Reynolds numbers of 0.1 and 1, respectively. Moreover, the device had an MI value of 67% at a Reynolds number of 10 (flow rate of 116 µL/min for each inlet). The proposed micromixer, with its novel design and fabrication method, is expected to benefit a wide range of lab-on-a-chip applications, due to its high efficiency, low cost, high throughput and ease of fabrication.

RevDate: 2019-11-18

Shaikh MM, Massan SU, AI Wagan (2019)

A sixteen decimal places' accurate Darcy friction factor database using non-linear Colebrook's equation with a million nodes: A way forward to the soft computing techniques.

Data in brief, 27:104733 pii:104733.

The Colebrook's equation is considered as an empirical model to accurately compute the Darcy friction factor in pipes under fully-developed turbulent flow. Due to non-linearity and implicitness of the Colebrook's equation, one needs to use numerical methods to acquire reasonably good approximation to the true friction factor values. However, such idea is not preferred by practitioners as it demands use of computers - also more computational time and effort. To overcome this, explicit equations that can describe Darcy friction factor directly in terms of the Reynolds number and relative roughness are essential. Using Fixed point iteration method in the MATLAB software, we have developed a 16 decimal places' accurate friction factor database for the Darcy friction factor for a 1000 by 1000 mesh of Reynolds number and relative roughness values. The accurate dataset described in this work will serve to be basis for the construction of new and more reliable explicit equations using regression modeling, artificial intelligence techniques and other soft computing methods.

RevDate: 2019-11-18

Papageorgiou DT, S Tanveer (2019)

Analysis and computations of a non-local thin-film model for two-fluid shear driven flows.

Proceedings. Mathematical, physical, and engineering sciences, 475(2230):20190367.

This paper is concerned with analysis and computations of a non-local thin-film model developed in Kalogirou & Papageorgiou (J. Fluid Mech.802, 5-36, 2016) for a perturbed two-layer Couette flow when the thickness of the more viscous fluid layer next to the stationary wall is small compared to the thickness of the less viscous fluid. Travelling wave solutions and their stability are determined numerically, and secondary bifurcation points are identified in the process. We also determine regions in parameter space where bistability is observed with two branches being linearly stable at the same time. The travelling wave solutions are mathematically justified through a quasi-solution analysis in a neighbourhood of an empirically constructed approximate solution. This relies in part on precise asymptotics of integrals of Airy functions for large wave numbers. The primary bifurcation about the trivial state is shown rigorously to be supercritical, and the dependence of bifurcation points, as a function of Reynolds number R and the primary wavelength 2πν-1/2 of the disturbance, is determined analytically.

RevDate: 2019-12-02

Farooq S, Hayat T, Khan MI, et al (2019)

Entropy generation minimization (EGM) in magneto peristalsis with variable properties.

Computer methods and programs in biomedicine, 186:105045 pii:S0169-2607(19)30711-4 [Epub ahead of print].

OBJECTIVE AND BACKGROUND: This article featuring the peristaltic transport of viscous material with variable properties (i.e. temperature dependent viscosity and thermal conductivity) through curved configuration. Fluid saturating through porous channel walls of uniform space. Entropy generation consideration here is to analyze irreversibility aspects. Channel boundaries retain the velocity and thermal slip conditions.

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

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

CONCLUSION: Variable characteristics of viscosity has opposite impact on velocity and temperature is observed. It is also noticed small irreversibility effects are obtained for higher varying viscosity and thermal conductivity near the vicinity of the channel walls.

RevDate: 2019-11-20

Ying Y, Y Lin (2019)

Inertial Focusing and Separation of Particles in Similar Curved Channels.

Scientific reports, 9(1):16575.

Inertial particle focusing in curved channels has enormous potential for lab-on-a-chip applications. This paper compares a zigzag channel, which has not been used previously for inertial focusing studies, with a serpentine channel and a square wave channel to explore their differences in terms of focusing performance and separation possibilities. The particle trajectories and fluid fields in the curved channels are studied by a numerical simulation. The effects of different conditions (structure, Reynolds number, and particle size) on the competition between forces and the focusing performance are studied. The results indicate that the zigzag channel has the best focusing effect at a high Reynolds number and that the serpentine channel is second in terms of performance. Regarding the particle separation potential, the zigzag channel has a good performance in separating 5 μm and 10 μm particles at ReC = 62.5. In addition, the pressure drop of the channel is also considered to evaluate the channel performance, which has not been taken into account in the literature on inertial microfluidics. This result is expected to be instructive for the selection and optimization of inertial microchannel structures.

RevDate: 2019-11-26

Zhang Z, P Zhang (2019)

Numerical Interpretation to the Roles of Liquid Viscosity in Droplet Spreading at Small Weber Numbers.

Langmuir : the ACS journal of surfaces and colloids [Epub ahead of print].

Droplet impacting a free-slip plane at small Weber numbers (We < 30) was numerically investigated by a front tracking method, with particular emphasis on clarifying the roles of the liquid viscosity and the "left-over" internal kinetic energy in droplet spreading. The most interesting discovery is that there exists a certain range of We in which the maximum diameter rate, D̃m, shows a nonmonotonic variation with the Reynolds number, Re. This non-monotonic variation is owing to the dual role of liquid viscosity in influencing droplet spreading. Specifically, when the initial surface energy is comparable to the initial kinetic energy (the corresponding We is around 10-30), the high strain rates of the droplet internal flow dominate its viscous dissipation at a relatively large Re, while the liquid viscosity dominates the viscous dissipation at a relatively small Re. Furthermore, to unravel the influence of droplet attachment and detachment on droplet spreading, we considered two limiting situations such as full attachment (with no gas film throughout droplet spreading) and full detachment (with a gas film throughout droplet spreading). The results show that the droplet with a gas film tends to generate a stronger vortical motion in its rim, results in a larger left-over kinetic energy, and hence causes a smaller spreading.

RevDate: 2019-11-13

Kottmeier J, Wullenweber M, Blahout S, et al (2019)

Accelerated Particle Separation in a DLD Device at Re > 1 Investigated by Means of µPIV.

Micromachines, 10(11): pii:mi10110768.

A pressure resistant and optically accessible deterministic lateral displacement (DLD) device was designed and microfabricated from silicon and glass for high-throughput fractionation of particles between 3.0 and 7.0 µm comprising array segments of varying tilt angles with a post size of 5 µm. The design was supported by computational fluid dynamic (CFD) simulations using OpenFOAM software. Simulations indicated a change in the critical particle diameter for fractionation at higher Reynolds numbers. This was experimentally confirmed by microparticle image velocimetry (µPIV) in the DLD device with tracer particles of 0.86 µm. At Reynolds numbers above 8 an asymmetric flow field pattern between posts could be observed. Furthermore, the new DLD device allowed successful fractionation of 2 µm and 5 µm fluorescent polystyrene particles at Re = 0.5-25.

RevDate: 2019-11-20

Di D, Qu X, Liu C, et al (2019)

Continuous production of celecoxib nanoparticles using a three-dimensional-coaxial-flow microfluidic platform.

International journal of pharmaceutics pii:S0378-5173(19)30876-2 [Epub ahead of print].

Increasing the dissolution rate of water insoluble drugs by decreasing the particle size of the drugs into nano-size is a well-known strategy. However, continuous production of drug nanoparticles with uniform particle size is critical for clinical application of the strategy. Here we report a simple microfluidic mixing method that can achieve continuous production of celecoxib nanoparticles with uniform particle size and high dissolution rate. A three-dimensional (3D) coaxial-flow microfluidic device was fabricated by assembling two coaxial aligned borosilicate glass capillaries on a glass slide, and a tapered glass capillary was inserted into another bigger cylindrical one with coaxial alignment. Celecoxib nanoparticles were prepared by the microfluidic device under the turbulent jet regime. The 3D-coaxial-flow pattern and high Reynolds number ensured the extremely short mixing time, consequently, resulted in the high throughput production of drug nanoparticles with uniform particle size. The obtained nanoparticles were spherical in shape, and showed superior dissolution rate compared with the coarse powder both in sink and non-sink conditions. The bioavailability of the water insoluble drug was also significantly improved by the reduction of particle size into nano-size.

RevDate: 2019-11-10

Herrmann N, Neubauer P, M Birkholz (2019)

Spiral microfluidic devices for cell separation and sorting in bioprocesses.

Biomicrofluidics, 13(6):061501.

Inertial microfluidic systems have been arousing interest in medical applications due to their simple and cost-efficient use. However, comparably small sample volumes in the microliter and milliliter ranges have so far prevented efficient applications in continuous bioprocesses. Nevertheless, recent studies suggest that these systems are well suited for cell separation in bioprocesses because of their facile adaptability to various reactor sizes and cell types. This review will discuss potential applications of inertial microfluidic cell separation systems in downstream bioprocesses and depict recent advances in inertial microfluidics for bioprocess intensification. This review thereby focusses on spiral microchannels that separate particles at a moderate Reynolds number in a laminar flow (Re < 2300) according to their size by applying lateral hydrodynamic forces. Spiral microchannels have already been shown to be capable of replacing microfilters, extracting dead cells and debris in perfusion processes, and removing contaminant microalgae species. Recent advances in parallelization made it possible to process media on a liter-scale, which might pave the way toward industrial applications.

RevDate: 2019-11-25

Sharzehee M, Chang Y, Song JP, et al (2019)

Hemodynamic effects of myocardial bridging in patients with hypertrophic cardiomyopathy.

American journal of physiology. Heart and circulatory physiology, 317(6):H1282-H1291.

Myocardial bridging (MB) is linked to angina and myocardial ischemia and may lead to sudden cardiac death in patients with hypertrophic cardiomyopathy (HCM). However, it remains unclear how MB affect the coronary blood flow in HCM patients. The aim of this study was to assess the effects of MB on coronary hemodynamics in HCM patients. Fifteen patients with MB (7 HCM and 8 non-HCM controls) in their left anterior descending (LAD) coronary artery were chosen. Transient computational fluid dynamics (CFD) simulations were conducted in anatomically realistic models of diseased (with MB) and virtually healthy (without MB) LAD from these patients, reconstructed from biplane angiograms. Our CFD simulation results demonstrated that dynamic compression of MB led to diastolic flow disturbances and could significantly reduce the coronary flow in HCM patients as compared with non-HCM group (P < 0.01). The pressure drop coefficient was remarkably higher (P < 0.05) in HCM patients. The flow rate change is strongly correlated with both upstream Reynolds number and MB compression ratio, while the MB length has less impact on coronary flow. The hemodynamic results and clinical outcomes revealed that HCM patients with an MB compression ratio higher than 65% required a surgical intervention. In conclusion, the transient MB compression can significantly alter the diastolic flow pattern and wall shear stress distribution in HCM patients. HCM patients with severe MB may need a surgical intervention.NEW & NOTEWORTHY In this study, the hemodynamic significance of myocardial bridging (MB) in patients with hypertrophic cardiomyopathy (HCM) was investigated to provide valuable information for surgical decision-making. Our results illustrated that the transient MB compression led to complex flow patterns, which can significantly alter the diastolic flow and wall shear stress distribution. The hemodynamic results and clinical outcomes demonstrated that patients with HCM and an MB compression ratio higher than 65% required a surgical intervention.

RevDate: 2019-11-01

Shanko ES, van de Burgt Y, Anderson PD, et al (2019)

Microfluidic Magnetic Mixing at Low Reynolds Numbers and in Stagnant Fluids.

Micromachines, 10(11): pii:mi10110731.

Microfluidic mixing becomes a necessity when thorough sample homogenization is required in small volumes of fluid, such as in lab-on-a-chip devices. For example, efficient mixing is extraordinarily challenging in capillary-filling microfluidic devices and in microchambers with stagnant fluids. To address this issue, specifically designed geometrical features can enhance the effect of diffusion and provide efficient mixing by inducing chaotic fluid flow. This scheme is known as "passive" mixing. In addition, when rapid and global mixing is essential, "active" mixing can be applied by exploiting an external source. In particular, magnetic mixing (where a magnetic field acts to stimulate mixing) shows great potential for high mixing efficiency. This method generally involves magnetic beads and external (or integrated) magnets for the creation of chaotic motion in the device. However, there is still plenty of room for exploiting the potential of magnetic beads for mixing applications. Therefore, this review article focuses on the advantages of magnetic bead mixing along with recommendations on improving mixing in low Reynolds number flows (Re ≤ 1) and in stagnant fluids.

RevDate: 2019-12-02

Ijaz Khan M, Ali A, Hayat T, et al (2019)

Entropy optimized dissipative CNTs based flow with probable error and statistical declaration.

Computer methods and programs in biomedicine, 185:105137 pii:S0169-2607(19)31706-7 [Epub ahead of print].

BACKGROUND: CNTs are categorized subject to their structures i.e., SWCNTs (single wall nanotubes), DWCNTs (double wall nanotubes) and MWCNTs (multi-wall nanotubes). The various structures have distinct characteristics that make the nanotubes suitable for various physical applications. It is due their unique electrical, mechanical and thermal attributes CNTs present thrilling opportunities for mechanical engineering, industrial, scientific research and commercial applications. There is fruitful potential for carbon nanotubes in the composites business and industry. Today, CNTs find utilization in frequent various products, and analyst continue to explore new applications. Currently applications comprise wind turbines, bicycle components, scanning probe microscopes, flat panel displays, marine paints, sensing devices, electronics, batteries with longer lifetime and electrical circuitry etc. Such applications in mind, entropy optimized dissipative CNTs based flow of nanomaterial by a stretched surface. Flow is caused due to stretching phenomenon and studied in 3D coordinates. Both types of CNTs are studied i.e., SWCNTs and MWCNTs. CNTs are considered for nanoparticles and water for continuous phase fluid. Special consideration is given to the analysis of statistical declaration and probable error for skin friction and Nusselt number. Furthermore, entropy rate is calculated. Entropy rate is discussed in the presence of four main irreversibilities i.e., heat transfer, Joule heating, porosity and dissipation.

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

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

CONCLUSIONS: Results for entropy rate is calculated in the presence of various sundry variable through implementation of second law of thermodynamics. It is examined from the results that velocity decreases for both CNTs via higher magnetic, inertia coefficient and porosity parameters. Secondary velocity i.e., velocity in g-direction boosts up versus rotation parameter while it declines for larger slip parameter for both CNTs. thermal field intensifies for both CNTs via larger heat generation/absorption parameter. Concentration which shows the mass transfer of species increases subject to higher homogeneous parameter and Schmidt number in case of both CNTs. Entropy rate in more for larger magnetic, Reynolds number and slip parameter. Bejan number boosts up for higher Reynold number and slip parameter while it declines for magnetic parameter.

RevDate: 2019-10-28

Dincau B, Dressaire E, A Sauret (2019)

Pulsatile Flow in Microfluidic Systems.

Small (Weinheim an der Bergstrasse, Germany) [Epub ahead of print].

This review describes the current knowledge and applications of pulsatile flow in microfluidic systems. Elements of fluid dynamics at low Reynolds number are first described in the context of pulsatile flow. Then the practical applications in microfluidic processes are presented: the methods to generate a pulsatile flow, the generation of emulsion droplets through harmonic flow rate perturbation, the applications in mixing and particle separation, and the benefits of pulsatile flow for clog mitigation. The second part of the review is devoted to pulsatile flow in biological applications. Pulsatile flows can be used for mimicking physiological systems, to alter or enhance cell cultures, and for bioassay automation. Pulsatile flows offer unique advantages over a steady flow, especially in microfluidic systems, but also require some new physical insights and more rigorous investigation to fully benefit future applications.

RevDate: 2019-11-01

Folkersma M, Schmehl R, A Viré (2019)

Boundary layer transition modeling on leading edge inflatable kite airfoils.

Wind energy (Chichester, England), 22(7):908-921.

We present a computational fluid dynamic analysis of boundary layer transition on leading edge inflatable kite airfoils used for airborne wind energy generation. Because of the operation in pumping cycles, the airfoil is generally subject to a wide range of Reynolds numbers. The analysis is based on the combination of the shear stress transport turbulence model with the γ - R ˜ e θ t transition model, which can handle the laminar boundary layer and its transition to turbulence. The implementation of both models in OpenFOAM is described. We show a validation of the method for a sailwing (ie, a wing with a membrane) airfoil and an application to a leading edge inflatable kite airfoil. For the sailwing airfoil, the results computed with transition model agree well with the existing low Reynolds number experiment over the whole range of angles of attack. For the leading edge inflatable kite airfoil, the transition modeling has both favorable and unfavorable effects on the aerodynamics. On the one hand, the aerodynamics suffer from the laminar separation. But, on the other hand, the laminar boundary layer thickens slower than the turbulent counterpart, which, in combination with transition, delays the separation. The results also indicate that the aerodynamics of the kite airfoil could be improved by delaying the boundary layer transition during the traction phase and tripping the transition in the retraction phase.

RevDate: 2019-10-25

Ozden K, Sert C, Y Yazicioglu (2019)

Numerical investigation of wall pressure fluctuations downstream of concentric and eccentric blunt stenosis models.

Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine [Epub ahead of print].

Pressure fluctuations that cause acoustic radiation from vessel models with concentric and eccentric blunt stenoses are investigated. Large eddy simulations of non-pulsatile flow condition are performed using OpenFOAM. Calculated amplitude and spatial-spectral distribution of acoustic pressures at the post-stenotic region are compared with previous experimental and theoretical results. It is found that increasing the Reynolds number does not change the location of the maximum root mean square wall pressure, but causes a general increase in the spectrum level, although the change in the shape of the spectrum is not significant. On the contrary, compared to the concentric model at the same Reynolds number, eccentricity leads to an increase both at the distance of the location of the maximum root mean square wall pressure from the stenosis exit and the spectrum level. This effect becomes more distinct when radial eccentricity of the stenosis increases. Both the flow rate and the eccentricity of the stenosis shape are evaluated to be clinically important parameters in diagnosing stenosis.

RevDate: 2019-11-26

Su L, Duan Z, He B, et al (2019)

Thermally Developing Flow and Heat Transfer in Elliptical Minichannels with Constant Wall Temperature.

Micromachines, 10(10):.

Laminar convective heat transfer of elliptical minichannels is investigated for hydrodynamically fully developed but thermal developing flow with no-slip condition. A three-dimensional numerical model is developed in different elliptical geometries with the aspect ratio varying from 0.2 to 1. The effect of Reynolds number (25 ≤ Re ≤ 2000) on the local Nusselt number is examined in detail. The results indicate that the local Nusselt number is a decreasing function of Reynolds number and it is sensitive to Reynolds number especially for Re less than 250. The effect of aspect ratio on local Nusselt number is small when compared with the effect of Reynolds number on local Nusselt number. The local Nusselt number is independent of cross-section geometry at the inlet. The maximum effect of aspect ratio on local Nusselt number arises at the transition section rather than the fully developed region. However, the non-dimensional thermal entrance length is a monotonic decreasing concave function of aspect ratio but a weak function of Reynolds number. Correlations for the local Nusselt number and the thermal developing length for elliptical channels are developed with good accuracy, which may provide guidance for design and optimization of elliptical minichannel heat sinks.

RevDate: 2019-11-26

Raza W, Ma SB, KY Kim (2019)

Single and Multi-Objective Optimization of a Three-Dimensional Unbalanced Split-and-Recombine Micromixer.

Micromachines, 10(10):.

The three-dimensional geometry of a micromixer with an asymmetrical split-and-recombine mechanism was optimized to enhance the fluid-mixing capability at a Reynolds number of 20. Single and multi-objective optimizations were carried out by using particle swarm optimization and a genetic algorithm on a modeled surrogate surface. Surrogate modeling was performed using the computational results for the mixing. Mixing and flow analyses were carried out by solving the convection-diffusion equation in combination with the three-dimensional continuity and momentum equations. The optimization was carried out with two design variables related to dimensionless geometric parameters. The mixing effectiveness was chosen as the objective function for the single-objective optimization, and the pressure drop and mixing index at the outlet were chosen for the multi-objective optimization. The sampling points in the design space were determined using a design of experiment technique called Latin hypercube sampling. The surrogates for the objective functions were developed using a Kriging model. The single-objective optimization resulted in 58.9% enhancement of the mixing effectiveness compared to the reference design. The multi-objective optimization provided Pareto-optimal solutions that showed a maximum increase of 48.5% in the mixing index and a maximum decrease of 55.0% in the pressure drop in comparison to the reference design.

RevDate: 2019-10-28
CmpDate: 2019-10-28

Basu A, JK Bhattacharjee (2019)

Kolmogorov or Bolgiano-Obukhov scaling: Universal energy spectra in stably stratified turbulent fluids.

Physical review. E, 100(3-1):033117.

We set up the scaling theory for stably stratified turbulent fluids. For a system having infinite extent in the horizontal directions, but with a finite width in the vertical direction, this theory predicts that the inertial range can display three possible scaling behavior, which are essentially parametrized by the buoyancy frequency N, or dimensionless horizontal Froude number F_{h}, and the vertical length scale l_{v} that sets the scale of variation of the velocity field in the vertical direction for a fixed Reynolds number. For very low N or very high Re_{b} or F_{h}, and with l_{v}≫l_{h}, the typical horizontal length scale, buoyancy forces are irrelevant and hence, unsurprisingly, the kinetic energy spectra show the well-known K41 scaling in the inertial range. In this regime, the local temperature behaves as a passively advected scalar, without any effect on the flow fields. For intermediate ranges of values of N,F_{h}∼O(1), corresponding to moderate stratification, buoyancy forces are important enough to affect the scaling. This leads to the Bolgiano-Obukhov scaling which is isotropic, when l_{v}∼l_{h}. Finally, for very large N, corresponding to strong stratification, together with a very small l_{v}, the inertial-range flow fields effectively two-dimensionalize. The kinetic energy spectra are predicted to be anisotropic with only the horizontal part of the kinetic energy spectra following the K41 scaling. This suggests an intriguing re-entrant K41 scaling, as a function of stratification, for the horizontal components of the velocity field in this regime. The scaling theory further predicts the scaling of the thermal energy in each of these three scaling regimes. Our theory can be tested in large-scale simulations and appropriate laboratory-based experiments.

RevDate: 2019-10-26

Bae HJ, Lozano-Durán A, Bose ST, et al (2019)

Dynamic slip wall model for large-eddy simulation.

Journal of fluid mechanics, 859:400-432.

Wall modelling in large-eddy simulation (LES) is necessary to overcome the prohibitive near-wall resolution requirements in high-Reynolds-number turbulent flows. Most existing wall models rely on assumptions about the state of the boundary layer and require a priori prescription of tunable coefficients. They also impose the predicted wall stress by replacing the no-slip boundary condition at the wall with a Neumann boundary condition in the wall-parallel directions while maintaining the no-transpiration condition in the wall-normal direction. In the present study, we first motivate and analyse the Robin (slip) boundary condition with transpiration (non-zero wall-normal velocity) in the context of wall-modelled LES. The effect of the slip boundary condition on the one-point statistics of the flow is investigated in LES of turbulent channel flow and a flat-plate turbulent boundary layer. It is shown that the slip condition provides a framework to compensate for the deficit or excess of mean momentum at the wall. Moreover, the resulting non-zero stress at the wall alleviates the well-known problem of the wall-stress under-estimation by current subgrid-scale (SGS) models (Jiménez & Moser, AIAA J., vol. 38 (4), 2000, pp. 605-612). Second, we discuss the requirements for the slip condition to be used in conjunction with wall models and derive the equation that connects the slip boundary condition with the stress at the wall. Finally, a dynamic procedure for the slip coefficients is formulated, providing a dynamic slip wall model free of a priori specified coefficients. The performance of the proposed dynamic wall model is tested in a series of LES of turbulent channel flow at varying Reynolds numbers, non-equilibrium three-dimensional transient channel flow and a zero-pressure-gradient flat-plate turbulent boundary layer. The results show that the dynamic wall model is able to accurately predict one-point turbulence statistics for various flow configurations, Reynolds numbers and grid resolutions.

RevDate: 2019-10-26

Lozano-Durán A, HJ Bae (2019)

Error scaling of large-eddy simulation in the outer region of wall-bounded turbulence.

Journal of computational physics, 392:532-555.

We study the error scaling properties of large-eddy simulation (LES) in the outer region of wall-bounded turbulence at moderately high Reynolds numbers. In order to avoid the additional complexity of wall-modeling, we perform LES of turbulent channel flows in which the no-slip condition at the wall is replaced by a Neumann condition supplying the exact mean wall-stress. The statistics investigated are the mean velocity profile, turbulence intensities, and kinetic energy spectra. The errors follow (Δ / L) α R e τ γ , where Δ is the characteristic grid resolution, Reτ is the friction Reynolds number, and L is the meaningful length-scale to normalize Δ in order to collapse the errors across the wall-normal distance. We show that Δ can be expressed as the L2-norm of the grid vector and that L is well represented by the ratio of the friction velocity and mean shear. The exponent α is estimated from theoretical arguments for each statistical quantity of interest and shown to roughly match the values computed by numerical simulations. For the mean profile and kinetic energy spectra, α ≈ 1, whereas the turbulence intensities converge at a slower rate α < 1. The exponent γ is approximately 0, i.e. the LES solution is independent of the Reynolds number. The expected behavior of the turbulence intensities at high Reynolds numbers is also derived and shown to agree with the classic log-layer profiles for grid resolutions lying within the inertial range. Further examination of the LES turbulence intensities and spectra reveals that both quantities resemble their filtered counterparts from direct numerical simulation (DNS) data, but that the mechanism responsible for this similarity is related to the balance between the input power and dissipation rather than to filtering.

RevDate: 2019-11-11

Hayat T, Waqar Ahmad M, Ijaz Khan M, et al (2019)

Entropy optimization in CNTs based nanomaterial flow induced by rotating disks: A study on the accuracy of statistical declaration and probable error.

Computer methods and programs in biomedicine, 184:105105 pii:S0169-2607(19)31590-1 [Epub ahead of print].

BACKGROUND: CNTs (Carbon nanotubes) being allotropes of carbon, made of graphene and diameters of single and multi-walls carbon nanotubes are typically 0.8 to 2 nm and 5 to 20 mn, although diameter of MWCNTs can exceed 100 nm. Carbon nanotubes lengths range from less than 100 nm to 0.5 m. Their impressive structural, electronic and mechanical attributes subject to their small size and mass, their high electrical and thermal conductivities, and their strong mechanical potency. CNTs based materials are successfully applied in medicine and pharmacy subject to their huge surface area that is proficient of conjugating or adsorbing with a wide variety of genes, drugs, antibodies, vaccines and biosensors etc. Therefore, we have presented a theoretical study about mathematical modeling of CNTs based viscous material flow between two rotating disks. Both types of nanotubes i.e., SWCNTs and MWCNTs are considered. Xue model is used for the mathematical modeling. Fluid flow is due to rotating disks. Main focus here is given to probable error and statistical declaration. Entropy is calculated for both single and multi-walls nanotubes.

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

RESULTS AND CONCLUSION: Statistical declaration and probable error for skin friction and Nusselt number are numerically computed and discussed through Tables. From obtained outcomes it is concluded that magnitude of skin friction increases at both disks surface for higher values of Reynolds number, lower stretching parameter and porosity parameter while it decays for both of disks versus larger rotation parameter. Nusselt number or heat transfer rate also enhances at both disks in the presence of radiation and Reynolds number while it decays against Eckert number.

RevDate: 2019-12-02
CmpDate: 2019-12-02

Bukowicki M, ML Ekiel-Jeżewska (2019)

Sedimenting pairs of elastic microfilaments.

Soft matter, 15(46):9405-9417.

The dynamics of two identical elastic filaments settling under gravity in a viscous fluid in the low Reynolds number regime is investigated numerically. A large family of initial configurations symmetric with respect to a vertical plane is considered, as well as their non-symmetric perturbations. The behaviour of the filaments is primarily governed by the elasto-gravitational number, which depends on the filament's length and flexibility, and the strength of the external force. Flexible filaments usually converge toward horizontal and parallel orientation. We explain this phenomenon and show that it occurs also for curved rigid particles of similar shapes. Once aligned, the two fibres either converge toward a stationary, flexibility-dependent distance, or tend to collide or continuously repel each other. Rigid and straight rods perform periodic motions while settling down. Apart from very stiff particles, the dynamics is robust to non-symmetric perturbations.

RevDate: 2019-10-23

Holdenried-Chernoff D, Chen L, A Jackson (2019)

A trio of simple optimized axisymmetric kinematic dynamos in a sphere.

Proceedings. Mathematical, physical, and engineering sciences, 475(2229):20190308.

Planetary magnetic fields are generated by the motion of conductive fluid in the planet's interior. Complex flows are not required for dynamo action; simple flows have been shown to act as efficient kinematic dynamos, whose physical characteristics are more straightforward to study. Recently, Chen et al. (2018, J. Fluid Mech.839, 1-32. (doi:10.1017/jfm.2017.924)) found the optimal, unconstrained kinematic dynamo in a sphere, which, despite being of theoretical importance, is of limited practical use. We extend their work by restricting the optimization to three simple two-mode axisymmetric flows based on the kinematic dynamos of Dudley & James (1989, Proc. R. Soc. Lond. A425, 407-429. (doi:10.1098/rspa.1989.0112)). Using a Lagrangian optimization, we find the smallest critical magnetic Reynolds number for each flow type, measured using an enstrophy-based norm. A Galerkin method is used, in which the spectral coefficients of the fluid flow and magnetic field are updated in order to maximize the final magnetic energy. We consider the t01s01, t01s02 and t02s02 flows and find enstrophy-based critical magnetic Reynolds numbers of 107.7, 142.4 and 125.5 (13.7, 19.6 and 16.4, respectively, with the energy-based definition). These are up to four times smaller than the original flows. These simple and efficient flows may be used as benchmarks in future studies.

RevDate: 2019-10-11

Browne CA, Shih A, SS Datta (2019)

Pore-Scale Flow Characterization of Polymer Solutions in Microfluidic Porous Media.

Small (Weinheim an der Bergstrasse, Germany) [Epub ahead of print].

Polymer solutions are frequently used in enhanced oil recovery and groundwater remediation to improve the recovery of trapped nonaqueous fluids. However, applications are limited by an incomplete understanding of the flow in porous media. The tortuous pore structure imposes both shear and extension, which elongates polymers; moreover, the flow is often at large Weissenberg numbers, Wi, at which polymer elasticity in turn strongly alters the flow. This dynamic elongation can even produce flow instabilities with strong spatial and temporal fluctuations despite the low Reynolds number, Re. Unfortunately, macroscopic approaches are limited in their ability to characterize the pore-scale flow. Thus, understanding how polymer conformations, flow dynamics, and pore geometry together determine these nontrivial flow patterns and impact macroscopic transport remains an outstanding challenge. This review describes how microfluidic tools can shed light on the physics underlying the flow of polymer solutions in porous media at high Wi and low Re. Specifically, microfluidic studies elucidate how steady and unsteady flow behavior depends on pore geometry and solution properties, and how polymer-induced effects impact nonaqueous fluid recovery. This work thus provides new insights for polymer dynamics, non-Newtonian fluid mechanics, and applications such as enhanced oil recovery and groundwater remediation.

RevDate: 2019-10-23

Houba T, Dasgupta A, Gopalakrishnan S, et al (2019)

Supersonic turbulent flow simulation using a scalable parallel modal discontinuous Galerkin numerical method.

Scientific reports, 9(1):14442 pii:10.1038/s41598-019-50546-w.

The scalability and efficiency of numerical methods on parallel computer architectures is of prime importance as we march towards exascale computing. Classical methods like finite difference schemes and finite volume methods have inherent roadblocks in their mathematical construction to achieve good scalability. These methods are popularly used to solve the Navier-Stokes equations for fluid flow simulations. The discontinuous Galerkin family of methods for solving continuum partial differential equations has shown promise in realizing parallel efficiency and scalability when approaching petascale computations. In this paper an explicit modal discontinuous Galerkin (DG) method utilizing Implicit Large Eddy Simulation (ILES) is proposed for unsteady turbulent flow simulations involving the three-dimensional Navier-Stokes equations. A study of the method was performed for the Taylor-Green vortex case at a Reynolds number ranging from 100 to 1600. The polynomial order P = 2 (third order accurate) was found to closely match the Direct Navier-Stokes (DNS) results for all Reynolds numbers tested outside of Re = 1600, which had a normalized RMS error of 3.43 × 10-4 in the dissipation rate for a 603 element mesh. The scalability and performance study of the method was then conducted for a Reynolds number of 1600 for polynomials orders from P = 2 to P = 6. The highest order polynomial that was tested (P = 6) was found to have the most efficient scalability using both the MPI and OpenMP implementations.

RevDate: 2019-10-08

Porteous R, Moreau DJ, CJ Doolan (2019)

The effect of the incoming boundary layer thickness on the aeroacoustics of finite wall-mounted square cylinders.

The Journal of the Acoustical Society of America, 146(3):1808.

This paper is concerned with the influence of the incoming wall boundary layer thickness on the noise produced by a square finite wall-mounted cylinder in cross-flow. Acoustic and near wake velocity measurements have been taken in an anechoic wind tunnel for a cylinder in two different near-zero-pressure gradient turbulent boundary layers with thicknesses of 130% and 370% of the cylinder width, W. The cylinders have an aspect ratio of 0.29≤L/W≤22.9 (where L is the cylinder span) and were examined at a Reynolds number, based on width, of ReW = 1.4 × 104. The results presented in this paper demonstrate that increasing the height of the boundary layer delays the production of acoustic tones to higher aspect ratios. The height of the boundary layer changes the balance between upwash and downwash across the cylinder span, resulting in a delayed onset of the shedding regimes and correspondingly, the production of acoustic tones.

RevDate: 2019-11-26

Kawaguchi M, Fukui T, Funamoto K, et al (2019)

Viscosity Estimation of a Suspension with Rigid Spheres in Circular Microchannels Using Particle Tracking Velocimetry.

Micromachines, 10(10):.

Suspension flows are ubiquitous in industry and nature. Therefore, it is important to understand the rheological properties of a suspension. The key to understanding the mechanism of suspension rheology is considering changes in its microstructure. It is difficult to evaluate the influence of change in the microstructure on the rheological properties affected by the macroscopic flow field for non-colloidal particles. In this study, we propose a new method to evaluate the changes in both the microstructure and rheological properties of a suspension using particle tracking velocimetry (PTV) and a power-law fluid model. Dilute suspension (0.38%) flows with fluorescent particles in a microchannel with a circular cross section were measured under low Reynolds number conditions (Re ≈ 10-4). Furthermore, the distribution of suspended particles in the radial direction was obtained from the measured images. Based on the power-law index and dependence of relative viscosity on the shear rate, we observed that the non-Newtonian properties of the suspension showed shear-thinning. This method will be useful in revealing the relationship between microstructural changes in a suspension and its rheology.

RevDate: 2019-10-02
CmpDate: 2019-10-02

Singh G, R Lakkaraju (2019)

Wall-mounted flexible plates in a two-dimensional channel trigger early flow instabilities.

Physical review. E, 100(2-1):023109.

A high level of mixing by passive means is a desirable feature in microchannels for various applications, and use of flexible obstacles (or plates) is one of the prime choices in that regard. To gain further insight, we carry out two-dimensional numerical simulations for flow past one or two flexible plates anchored to a channel's opposite walls using a fluid-structure interaction framework. For the inlet flow Reynolds number vs the Strouhal number plane, we observe a sudden flow change from a laminar to a time-periodic vortex shedding state when flexible plates are present in the channel. We found the critical Reynolds number to be Re_{cr}≈370 when a single plate is anchored on the channel wall and Re_{cr}≈290 or even lower when two plates are anchored. With an increase in the inlet flow Reynolds number (up to 3200), we found that vortices detach regularly at the plates' tips, which causes the flow to meander in the channel. In a two-plate anchored configuration, primary vortices generated at the first plate are constrained by the second plate and result in an energetic secondary vortex generation in the downstream side. The overall flow features and the energy dissipation in the channel are mainly controlled by the separation gap between the plates. At high-inlet-flow Reynolds numbers (≥1600), the probability density function (F) of the kinetic energy dissipation in a flexible plate configuration shows a stretched exponential shape in the form F(Z)∼1/sqrt[Z]e^{-pZ^{q}}, where Z is the normalized kinetic energy dissipation and the constants p=0.89 and q=0.86. The observed increase in energy dissipation comes at the cost of an increase in pressure loss in the channel, and we found that the loss is inversely related to the plates' separation gap. From our simulations, we found that if high mixing levels are desired, then two flexible plates anchored to the channel walls is a better choice than a channel flow without obstacles or flow past a single plate. The two-plate configuration with zero separation gap between the plates is best suited to achieve a high mixing level.

RevDate: 2019-10-02
CmpDate: 2019-10-02

Feng Y, Boivin P, Jacob J, et al (2019)

Hybrid recursive regularized lattice Boltzmann simulation of humid air with application to meteorological flows.

Physical review. E, 100(2-1):023304.

An extended version of the hybrid recursive regularized lattice-Boltzmann model which incorporates external force is developed to simulate humid air flows with phase change mechanisms under the Boussinesq approximation. Mass and momentum conservation equations are solved by a regularized lattice Boltzmann approach well suited for high Reynolds number flows, whereas the energy and humidity related equations are solved by a finite volume approach. Two options are investigated to account for cloud formation in atmospheric flow simulations. The first option considers a single conservation equation for total water and an appropriate invariant variable of temperature. In the other approach, liquid and vapor are considered via two separated equations, and phase transition is accounted for via a relaxation procedure. The obtained models are then systematically validated on four well-established benchmark problems including a double diffusive Rayleigh Bénard convection of humid air, two- and three-dimensional thermal moist rising bubble under convective atmospheric environment, as well as a shallow cumulus convection in the framework of large-eddy simulation.

RevDate: 2019-10-02
CmpDate: 2019-10-02

Topayev S, Nouar C, Bernardin D, et al (2019)

Taylor-vortex flow in shear-thinning fluids.

Physical review. E, 100(2-1):023117.

This paper deals with the Taylor-Couette flow of shear-thinning fluids. It focuses on the first principles understanding of the influence of the viscosity stratification and the nonlinear variation of the effective viscosity μ with the shear rate γ[over ̇] on the flow structure in the Taylor-vortex flow regime. A wide gap configuration (η=0.4) is mainly considered. A weakly nonlinear analysis, using the amplitude expansion method at high order, is adopted as a first approach to study nonlinear effects. For the numerical computation, the shear-thinning behavior is described by the Carreau model. The rheological parameters are varied in a wide range. The results indicate that the flow field undergoes a significant change as shear-thinning effects increase. First, vortices are squeezed against the inner wall and the center of the patterns is shifted axially toward the radial outflow boundaries (z=0,z/λ_{z}=1). This axial shift leads to increasing concentration of vorticity at these positions. The outflow becomes stronger than the inflow and the extent of the inflow zone where the vorticity is low increases acoordingly. Nevertheless, the strength of the vortices relative to the velocity of the inner cylinder is weaker. Second, the pseudo-Nusselt number, ratio of the torque to that obtained in the laminar flow, decreases. Third, higher harmonics become more relevant and grow faster with Reynolds number. Finally, the modification of the viscosity field is described.

RevDate: 2019-10-02
CmpDate: 2019-10-02

Krämer A, Wilde D, Küllmer K, et al (2019)

Pseudoentropic derivation of the regularized lattice Boltzmann method.

Physical review. E, 100(2-1):023302.

The lattice Boltzmann method (LBM) facilitates efficient simulations of fluid turbulence based on advection and collision of local particle distribution functions. To ensure stable simulations on underresolved grids, the collision operator must prevent drastic deviations from local equilibrium. This can be achieved by various methods, such as the multirelaxation time, entropic, quasiequilibrium, regularized, and cumulant schemes. Complementing a part of a unified theoretical framework of these schemes, the present work presents a derivation of the regularized lattice Boltzmann method (RLBM), which follows a recently introduced entropic multirelaxation time LBM by Karlin, Bösch, and Chikatamarla (KBC). It is shown that both methods can be derived by locally maximizing a quadratic Taylor expansion of the entropy function. While KBC expands around the local equilibrium distribution, the RLBM is recovered by expanding entropy around a global equilibrium. Numerical tests were performed to elucidate the role of pseudoentropy maximization in these models. Simulations of a two-dimensional shear layer show that the RLBM successfully reproduces the largest eddies even on a 16×16 grid, while the conventional LBM becomes unstable for grid resolutions of 128×128 and lower. The RLBM suppresses spurious vortices more effectively than KBC. In contrast, simulations of the three-dimensional Taylor-Green and Kida vortices show that KBC performs better in resolving small scale vortices, outperforming the RLBM by a factor of 1.8 in terms of the effective Reynolds number.

RevDate: 2019-10-02

Morris RG, M Rao (2019)

Active morphogenesis of epithelial monolayers.

Physical review. E, 100(2-1):022413.

During typical early-stage embryo development, single-cell-thick tissues of tightly bound epithelial cells autonomously generate profound changes in their shape, forming the basis of organism anatomy. We report on a (covariant) active-hydrodynamic theory of such monolayer morphogenesis that is closed under its shape-changing dynamics-i.e., the degrees of freedom that encode monolayer geometry appear properly as broken-symmetry variables. In our theory, the salient physics of tissue-scale deformations emerges from a balance between the displacement and/or shear of a low-Reynolds-number embedding fluid (the "yolk") and cell-autonomous stresses, themselves a result of combining apical contractile stresses with an elastic-like mechanical response under the constraint of constant cell volume. The leading-order hydrodynamic instabilities include both passive constrained-buckling and active deformation, which can be further categorized by cell shape changes that are either "squamous to columnar" or "regular-prism to truncated-pyramid." The deformations resulting from the latter qualitatively reproduce in vivo observations of the onset of both mesoderm and posterior midgut invaginations, which take place during gastrulation in the model organism Drosophila melanogaster.

RevDate: 2019-11-19

Phuong NL, Quang TV, Khoa ND, et al (2020)

CFD analysis of the flow structure in a monkey upper airway validated by PIV experiments.

Respiratory physiology & neurobiology, 271:103304.

Inhalation exposure to airborne contaminants has adverse effects on humans; however, related research is typically conducted using in vivo/in vitro tests on animals. Extrapolating the test results is complicated by anatomical and physiological differences between animals and humans and a lack of understanding of the transport mechanism inside their respective respiratory tracts. This study determined the detailed air-flow structure in the upper airway of a monkey. A steady computational fluid dynamics simulation, which was validated by previous particle image velocimetry measurements, was adopted for flow rates of 4 L/min and 10 L/min to analyze the flow structure from the nasal/oral cavities to the trachea region in a monkey airway model. The low Reynolds number type k-ε model provided a reasonably accurate prediction of the airflow in a monkey upper airway. Furthermore, it was confirmed that large velocity gradients were generated in the nasal vestibule and larynx regions, as well as increased turbulent air kinetic energy and wall sheer stress.

RevDate: 2019-10-22

Shi L, Wu J, Krenn HW, et al (2020)

Temporal model of fluid-feeding mechanisms in a long proboscid orchid bee compared to the short proboscid honey bee.

Journal of theoretical biology, 484:110017.

Bees (Apidae) are flower-visiting insects that possess highly efficient mouthparts for the ingestion of nectar and other sucrose fluids. Their mouthparts are composed of mandibles and a tube-like proboscis. The proboscis forms a food canal, which encompasses a protrusible and hairy tongue to load and imbibe nectar, representing a fluid-feeding technique with a low Reynolds number. The western honey bee, Apis mellifera ligustica, can rhythmically erect the tongue microtrichia to regulate the glossal shape, achieving a tradeoff between nectar intake rate and viscous drag. Neotropical orchid bees (Euglossa imperialis) possess a proboscis longer than the body and combines this lapping-sucking mode of fluid-feeding with suction feeding. This additional technique of nectar uptake may have different biophysics. In order to reveal the effect of special structures of mouthparts in terms of feeding efficiency, we build a temporal model for orchid bees considering fluid transport in multi-states including active suction, tongue protraction and viscous dipping. Our model indicates that the dipping technique employed by honey bees can contribute to more than seven times the volumetric and energetic intake rate at a certain nectar concentration compared with the combined mode used by orchid bees. The high capability of the honey bee's proboscis to ingest nectar may inspire micropumps for transporting viscous liquid with higher efficiency.

RevDate: 2019-11-09

Onyiriuka EJ, Ighodaro OO, Adelaja AO, et al (2019)

A numerical investigation of the heat transfer characteristics of water-based mango bark nanofluid flowing in a double-pipe heat exchanger.

Heliyon, 5(9):e02416.

In this study, the heat transfer characteristics of a new class of nanofluids made from mango bark was numerically simulated and studied during turbulent flow through a double pipe heat exchanger. A range of volume fractions was considered for a particle size of 100 nm. A two-phase flow was considered using the mixture model. The mixture model governing equations of continuity, momentum, energy and volume fraction were solved using the finite-volume method. The results showed an increase of the Nusselt number by 68% for a Reynolds number of 5,000 and 45% for a Reynolds number of 13 000, and the heat transfer coefficient of the nanofluid was about twice that of the base fluid. In addition, the Nusselt number decreased by an average value of 0.76 with an increase of volume fraction by 1%. It was also found that there was a range of Reynolds numbers in which the trend of the average heat transfer coefficient of the nanofluid was completely reversed, and several plots showing zones of higher heat transfer which if taken advantage of in design will lead to higher heat transfer while avoiding other zones that have low heat transfer. It is hoped that these results will influence the thermal design of new heat exchangers.

RevDate: 2019-09-22

Blumenthal BT, Elmiligui AA, Geiselhart KA, et al (2019)

Computational Investigation of a Boundary-Layer Ingesting Propulsion System for the Common Research Model.

Journal of aircraft, 55(3):1141-1153.

The present paper examines potential propulsive and aerodynamic benefits of integrating a Boundary-Layer Ingestion (BLI) propulsion system into the Common Research Model (CRM) geometry and the NASA Tetrahedral Unstructured Software System (TetrUSS). The Numerical Propulsion System Simulation (NPSS) environment is used to generate engine conditions for Computational Fluid Dynamics (CFD) analyses. Improvements to the BLI geometry are made using the Constrained Direct Iterative Surface Curvature (CDISC) design method. Potential benefits of the BLI system relating to cruise propulsive power are quantified using a power balance method, and a comparison to the baseline case is made. Iterations of the BLI geometric design are shown, and improvements between subsequent BLI designs are presented. Simulations are conducted for a cruise flight condition of Mach 0.85 at an altitude of 38,500 feet, with Reynolds number of 40 million based on mean aerodynamic chord and an angle of attack of 2° for all geometries. Results indicate an 8% reduction in engine power requirements at cruise for the BLI configuration compared to the baseline geometry. Small geometric alterations of the aft portion of the fuselage using CDISC has been shown to marginally increase the benefit from boundary-layer ingestion further, resulting in an 8.7% reduction in power requirements for cruise, as well as a drag reduction of approximately twelve counts over the baseline geometry.

RevDate: 2019-11-01

Wang R, Wang J, W Yuan (2019)

Analysis and Optimization of a Microchannel Heat Sink with V-Ribs Using Nanofluids for Micro Solar Cells.

Micromachines, 10(9):.

It is crucial to control the temperature of solar cells for enhancing efficiency with the increasing power intensity of multiple photovoltaic systems. In order to improve the heat transfer efficiency, a microchannel heat sink (MCHS) with V-ribs using a water-based nanofluid as a coolant for micro solar cells was designed. Numerical simulations were carried out to investigate the flows and heat transfers in the MCHS when the Reynolds number ranges from 200 to 1000. The numerical results showed that the periodically arranged V-ribs can interrupt the thermal boundary, induce chaotic convection, increase heat transfer area, and subsequently improve the heat transfer performance of a MCHS. In addition, the preferential values of the geometric parameters of V-ribs and the physical parameters of the nanofluid were obtained on the basis of the Nusselt numbers at identical pump power. For MCHS with V-ribs on both the top and bottom wall, preferential values of V-rib are rib width d / W = 1 , flare angle α = 75 ° , rib height h r / H = 0.3 , and ratio of two slant sides b / a = 0.75 , respectively. This can provide sound foundations for the design of a MCHS in micro solar cells.

RevDate: 2019-10-28

Tang L, Pan X, Feng J, et al (2019)

Experimental Investigation on the Relationship Between COD Degradation and Hydrodynamic Conditions in Urban Rivers.

International journal of environmental research and public health, 16(18): pii:ijerph16183447.

Due to extensive pollution and the relatively weak flow replacement in urban rivers, determining how to fully utilize the self-purification abilities of water bodies for water quality protection has been a complex and popular topic of research and social concern. Organic pollution is an important type of urban river pollution, and COD (chemical oxygen demand) is one of the key pollution factors. Currently, there is a lack of research on the relationship between COD degradation and the flow characteristics of urban rivers. In this paper, COD degradation experiments were conducted in an annular flume with Jinjiang River water at controlled flow velocities and the COD degradation coefficients under different hydraulic conditions were analyzed. A good correlation was observed between the degradation coefficient and hydraulic conditions. According to dimensional analysis, the relationship between the COD degradation coefficient and hydraulic conditions such as the flow velocity, water depth, Reynolds number (Re), and Froude number (Fr) was established as K COD = 86400 u h F r 0.8415 R e - 1.2719 + 0.258 . The COD degradation coefficients of the Chishui River in Guizhou Province ranged from 0.175-0.373 1/d based on this formula, and the field-measured values varied from 0.234-0.463 1/d. The error in the formula ranged from 5.4-25.3%. This study provides a scientific basis for the prediction of the COD degradation coefficients of urban rivers.

RevDate: 2019-11-29

Wang C, Ren F, H Tang (2019)

Enhancing propulsion performance of a flexible heaving foil through dynamically adjusting its flexibility.

Bioinspiration & biomimetics, 14(6):064002.

This study investigates how dynamically adjusting the bending stiffness of a heaving foil affects its propulsion performance in a flow of Reynolds number 200. The foil is forced to oscillate sinusoidally at the leading edge, and its bending stiffness is tuned in a square-wave manner. Such a fluid-structure interaction (FSI) problem is explored using an immersed boundary lattice Boltzmann method (IBLBM) based numerical framework. The results reveal that when the lower and upper bounds of the foil's time-dependent bending stiffness are moderate, the net thrust can be evidently enhanced compared to those in the corresponding constant-bending-stiffness cases, while the propulsion efficiency is not apparently ameliorated. The most significant enhancement is observed when the bending stiffness has lower and upper bounds of the same duration (i.e. a duty cycle of 1/2) and also it remains at the lower bound during stroke reversals (corresponding to an actuation phase angle of [Formula: see text]). When the two bounds simultaneously increase or decrease, however, dynamically adjusting the bending stiffness fails to improve the net thrust. Through this study, competitions among various forces/moments, including the inertial force, tension force, bending moment and fluid loading, acting on the foil and their influences on the foil's dynamics are also unveiled.

RevDate: 2019-11-18

Acosta-Avalos D, E Rodrigues (2019)

On the motion of magnetotactic bacteria: theoretical predictions and experimental observations.

European biophysics journal : EBJ, 48(8):691-700.

The movement of magnetotactic bacteria is done in a viscous media in the low Reynolds number regime. In the present research, the simple model for magnetotactic bacteria motion, proposed by Nogueira and Lins de Barros (Eur Biophys J 24:13-21, 1995), was used to numerically simulate their trajectory. The model was done considering a spherical bacterium with a single flagellum and a magnetic moment positioned in the sphere center and parallel to the flagella. The numerical solution shows that the trajectory is a cylindrical helix and that the body Euler angles have linear dependencies on time. Using that information, analytical expressions were obtained for the first time for the center-of-mass coordinates, showing that the trajectories are helixes oriented to the magnetic field direction. They also show that the magnetic moment does not align to the magnetic field, but it precesses around it, being fully oriented only for very high magnetic fields. The analytical solution obtained permits to relate for the first time the flagellar force to the axial velocity and helical radius. Trajectories of uncultivated magnetotactic bacteria were registered in video and the coordinates were obtained for several bacteria in different magnetic fields. The trajectories showed to be a complex mixture of two oscillating functions: one with frequency lower than 5 Hz and the other one with frequency higher than 10 Hz. The simple model of Nogueira and Lins de Barros shows to be incomplete, because is unable to explain the trajectories composed of two oscillating functions observed in uncultivated magnetotactic bacteria.

RevDate: 2019-09-11
CmpDate: 2019-09-11

Falsaperla P, Giacobbe A, G Mulone (2019)

Nonlinear stability results for plane Couette and Poiseuille flows.

Physical review. E, 100(1-1):013113.

We prove that the plane Couette and Poiseuille flows are nonlinearly stable if the Reynolds number is less than Re_{Orr}(2π/(λsinθ))/sinθ when a perturbation is a tilted perturbation in the direction x^{'} which forms an angle θ∈(0,π/2] with the direction i of the basic motion and does not depend on x^{'}. Re_{Orr} is the critical Orr-Reynolds number for spanwise perturbations which is computed for wave number 2π/(λsinθ), with λ being any positive wavelength. By taking the minimum with respect to λ, we obtain the critical energy Reynolds number for a fixed inclination angle and any wavelength: for plane Couette flow, it is Re_{Orr}=44.3/sinθ, and for plane Poiseuille flow, it is Re_{Orr}=87.6/sinθ (in particular, for θ=π/2 we have the classical values Re_{Orr}=44.3 for plane Couette flow and Re_{Orr}=87.6 for plane Poiseuille flow). Here the nondimensional interval between the planes bounding the channel is [-1,1]. In particular, these results improve those obtained by Joseph, who found for streamwise perturbations a critical nonlinear value of 20.65 in the plane Couette case, and those obtained by Joseph and Carmi who found the value 49.55 for plane Poiseuille flow for streamwise perturbations. If we fix some wavelengths from the experimental data and the numerical simulations, the critical Reynolds numbers that we obtain are in a very good agreement both with the the experiments and the numerical simulation. These results partially solve the Couette-Sommerfeld paradox.

RevDate: 2019-11-24

Shah F, Khan MI, Hayat T, et al (2019)

Theoretical and mathematical analysis of entropy generation in fluid flow subject to aluminum and ethylene glycol nanoparticles.

Computer methods and programs in biomedicine, 182:105057.

BACKGROUND: Here we have conducted a magnetohydrodynamic (MHD) flow of viscous material with alumina water and ethylene glycol over a stretched surface. The flow is discussed with and without effective Prandtl number. MHD liquid is considered. Electric field is absent. Effect of uniform magnetic field is taken in the vertical direction to the surface. Influence of thermal radiation as well as Joule heating are taken into account for both aluminum oxide-water and aluminum oxide-Ethylene glycol nanofluids. Velocity slip and melting heat effects are considered.

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

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

CONCLUSIONS: Impact of magnetic and slip parameters on the velocity field show decreasing behavior for both effective and without effective Prandtl number. Temperature field increases for both effective and without effective Prandtl number for higher values of magnetic and radiative parameters. Entropy number is an increasing function of Reynolds number while Bejan number shows opposite impact against Reynolds number. Moreover, heat transfer rate upsurges versus larger melting and radiative parameter.

RevDate: 2019-09-04

DeJonckere P, J Lebacq (2019)

Intraglottal Aerodynamics at Vocal Fold Vibration Onset.

Journal of voice : official journal of the Voice Foundation pii:S0892-1997(19)30237-1 [Epub ahead of print].

The most frequently observed type of voice onset in spontaneous speech in normal subjects is the soft onset, and it may be considered as the "physiological" onset. It starts from an immobile narrow glottal slit crossed by a continuous airflow, and then a few oscillations (even a single one in some cases) precede the first glottal closure. It is a transient event, during which the acting forces, lung pressure, intraglottal pressure, myoelastic tension of the vocal fold (VF) oscillator and inertance of the supraglottal vocal tract, interact to progressively reach the steady state of a sustained oscillation. Combined measurements of flow, area, and pressure provide a detailed qualitative and quantitative analysis of the intraglottal mechanical events at the precise moment of starting oscillation in a physiological (soft or soft/breathy) onset. Our in vivo measurements of airflow and glottal area show that the very first oscillation occurs exactly at the time when turbulence appears at the level of the glottal narrowing, ie, when the Reynolds number reaches its critical value. The turbulence may be assumed to trigger an oscillator consisting in the ensemble of the VFs and the air of the vocal tract, which is known to be weakly damped. Turbulence can act here as an aspecific flick, triggering the oscillator, the frequency of oscillation being determined by its mechanical properties. Furthermore, the first noticeable glottal oscillations are sinusoidal: the VFs are neither steeply sucked together by a negative Bernoulli pressure, nor burst apart by the lung pressure. Our measurements show that, at the critical time, the rising positive lung pressure is balanced by the rising negative Bernoulli pressure generated by the transglottal flow.

RevDate: 2019-11-01

Tsai CD, XY Lin (2019)

Experimental Study on Microfluidic Mixing with Different Zigzag Angles.

Micromachines, 10(9):.

This paper presents experimental investigations of passive mixing in a microfluidic channel with different zigzag angles. Zigzag channel is commonly used for microfluidic mixing because it does not need an additional control unit and can be easily implemented in a lab-on-a-chip system. In this work, microfluidic channels with six different zigzag angles, from θ = 0° to θ = 75°, are tested under ten different flow rates corresponding to Reynolds number from 0.309 to 309. Two colored liquids are mixed with the zigzag channels and mixing performance is evaluated based on the color of the pixels on the region of interest from captured images. According to the results, we found that the mixing performance is almost independent of the zigzag angle in the low-speed regime where its Reynolds number is less than 4. The mixing became very much depending on the zigzag angle in the high-speed regime where its Reynolds number is greater than 100. Microfluidic mixing is needed for Lab-on-a-chip applications in both low flow speed, such as medium perfusion for cell culture, and high flow speed, such as high-speed sensing on a point-of-care device. This work is aimed to provide practical information on zigzag mixing for chip design and applications.

RevDate: 2019-09-01

Waheed W, Alazzam A, Al-Khateeb AN, et al (2019)

Dissipative particle dynamics for modeling micro-objects in microfluidics: application to dielectrophoresis.

Biomechanics and modeling in mechanobiology pii:10.1007/s10237-019-01216-3 [Epub ahead of print].

The dissipative particle dynamics (DPD) technique is employed to model the trajectories of micro-objects in a practical microfluidic device. The simulation approach is first developed using an in-house Fortran code to model Stokes flow at Reynolds number of 0.01. The extremely low Reynolds number is achieved by adjusting the DPD parameters, such as force coefficients, thermal energies of the particles, and time steps. After matching the numerical flow profile with the analytical results, the technique is developed further to simulate the deflection of micro-objects under the effect of a deflecting external force in a rectangular microchannel. A mapping algorithm is introduced to establish the scaling relationship for the deflecting force between the physical device and the DPD domain. Dielectrophoresis is studied as a case study for the deflecting force, and the trajectory of a single red blood cell under the influence of the dielectrophoretic force is simulated. The device is fabricated using standard microfabrication techniques, and the experiments involving a dilute sample of red blood cells are performed at two different cases of the actuation voltage. Good agreement between the numerical and experimental results is achieved.

RevDate: 2019-09-23

Chaput R, Majoris JE, Buston PM, et al (2019)

Hydrodynamic and biological constraints on group cohesion in plankton.

Journal of theoretical biology, 482:109987.

The dynamics of plankton in the ocean are determined by biophysical interactions. Although physics and biotic behaviors are known to influence the observed patchiness of planktonic populations, it is still unclear how much, and if, group behavior contributes to this biophysical interaction. Here, we demonstrate how simple rules of behavior can enhance or inhibit active group cohesion in plankton in a turbulent environment. In this study, we used coral-reef fish larvae as a model to investigate the interaction between microscale turbulence and planktonic organisms. We synthesized available information on the swimming speeds and sizes of reef fish larvae, and developed a set of equations to investigate the effects of viscosity and turbulence on larvae dispersion. We then calculated the critical dispersion rates for three different swimming strategies - cruise, random-walk, and pause-travel - to determine which strategies could facilitate group cohesion during dispersal. Our results indicate that swimming strategies and migration to low-turbulence regions are the key to maintaining group cohesion, suggesting that many reef fish species have the potential to remain together, from hatching to settlement. In addition, larvae might change their swimming strategies to maintain group cohesion, depending on environmental conditions and/or their ontogenic stage. This study provides a better understanding of the hydrodynamic and biological constraints on group formation and cohesion in planktonic organisms, and reveals a wide range of conditions under which group formation may occur.

RevDate: 2019-09-23

Zhang C, Sanjose M, S Moreau (2019)

Aeolian noise of a cylinder in the critical regime.

The Journal of the Acoustical Society of America, 146(2):1404.

The noise from the flow around a circular cylinder in the critical regime is investigated by combining a compressible wall-resolved large eddy simulation and a Ffowcs Williams and Hawkings analogy on solid and porous surfaces. This simulation is validated by comparing several flow parameters with previous experimental and numerical data in the same flow regime. Significantly reduced drag and increased vortex shedding Strouhal number (0.33) are observed. Two slightly asymmetric laminar separation bubbles (LSBs) on the cylinder surface at about 100° are shown to trigger turbulence through Kelvin-Helmholtz (KH) shear-layer instability. The latter contributes to a narrowband hump in the wall-pressure fluctuations with a tone at a Strouhal number of 27, which can be as intense as the dominant vortex shedding tone. The ratio of the corresponding Strouhal numbers is consistent with the proposed variation with the Reynolds number by Prasad and Williamson [(1997). J. Fluid Mech. 333, 375-402]. The dominant far-field noise source is still the vortex shedding dipolar tone radiating mostly at 90°. Yet, two additional broadband noise sources are evidenced in the wake, one at low frequencies caused by the wake oscillation and another one at high frequencies caused by the KH instability mostly directly toward the LSB locations.

RevDate: 2019-09-01

Gholampour S, Bahmani M, A Shariati (2019)

Comparing the Efficiency of Two Treatment Methods of Hydrocephalus: Shunt Implantation and Endoscopic Third Ventriculostomy.

Basic and clinical neuroscience, 10(3):185-198.

Introduction: Hydrocephalus is one of the most common diseases in children, and its treatment requires brain operation. However, the pathophysiology of the disease is very complicated and still unknown.

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

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

Conclusion: In infants with hydrocephalus, initial treatment by ETV was more reasonable than implanting the shunt. In adult with hydrocephalus, the initial failure in ETV occurred sooner compared to shunt therapy; however, ETV was more efficient.

RevDate: 2019-08-25

Foo YY, Pant S, Tay HS, et al (2019)

4D modelling of fluid mechanics in the zebrafish embryonic heart.

Biomechanics and modeling in mechanobiology pii:10.1007/s10237-019-01205-6 [Epub ahead of print].

Abnormal blood flow mechanics can result in pathological heart malformation, underlining the importance of understanding embryonic cardiac fluid mechanics. In the current study, we performed image-based computational fluid dynamics simulation of the zebrafish embryonic heart ventricles and characterized flow mechanics, organ dynamics, and energy dynamics in detail. 4D scans of 5 days post-fertilization embryonic hearts with GFP-labelled myocardium were acquired using line-scan focal modulation microscopy. This revealed that the zebrafish hearts exhibited a wave-like contractile/relaxation motion from the inlet to the outlet during both systole and diastole, which we showed to be an energy efficient configuration. No impedance pumping effects of pressure and velocity waves were observed. Due to its tube-like configuration, inflow velocities were higher near the inlet and smaller at the outlet and vice versa for outflow velocities. This resulted in an interesting spatial wall shear stress (WSS) pattern where WSS waveforms near the inlet and those near the outlet were out of phase. There was large spatial variability in WSS magnitudes. Peak WSS was in the range of 47.5-130 dyne/cm2 at the inflow and outflow tracts, but were much smaller, in the range of 4-11 dyne/cm2, in the mid-ventricular segment. Due to very low Reynolds number and the highly viscous environment, intraventricular pressure gradients were high, suggesting substantial energy losses of flow through the heart.

RevDate: 2019-08-23

Rackus DG, Riedel-Kruse IH, N Pamme (2019)

"Learning on a chip:" Microfluidics for formal and informal science education.

Biomicrofluidics, 13(4):041501 pii:017903BMF.

Microfluidics is a technique for the handling of small volumes of liquids on the order of picoliters to nanoliters and has impact for miniaturized biomedical science and fundamental research. Because of its multi- and interdisciplinary nature (i.e., combining the fields of biology, chemistry, physics, and engineering), microfluidics offers much potential for educational applications, both at the university level as well as primary and secondary education. Microfluidics is also an ideal "tool" to enthuse and educate members of the general public about the interdisciplinary aspects of modern sciences, including concepts of science, technology, engineering, and mathematics subjects such as (bio)engineering, chemistry, and biomedical sciences. Here, we provide an overview of approaches that have been taken to make microfluidics accessible for formal and informal learning. We also point out future avenues and desired developments. At the extreme ends, we can distinguish between projects that teach how to build microfluidic devices vs projects that make various microscopic phenomena (e.g., low Reynolds number hydrodynamics, microbiology) accessible to learners and the general public. Microfluidics also enables educators to make experiments low-cost and scalable, and thereby widely accessible. Our goal for this review is to assist academic researchers working in the field of microfluidics and lab-on-a-chip technologies as well as educators with translating research from the laboratory into the lecture hall, teaching laboratory, or public sphere.

RevDate: 2019-09-18

Hayat T, Aslam N, Ijaz Khan M, et al (2019)

MHD peristaltic motion of Johnson-Segalman fluid in an inclined channel subject to radiative flux and convective boundary conditions.

Computer methods and programs in biomedicine, 180:104999.

BACKGROUND: In abundant of a digestive tract like smooth muscle tissue, human gastrointestinal tract contracts in sequence to generate a peristaltic wave, which pushes a food along the tract. The peristaltic motion contains circular relaxation smooth muscles, then their shrinkage (contraction) behind the chewed material to keep it from moving backward, then longitudinal contraction to shove it ahead. Therefore, we have conducted a theoretical investigation on peristaltic transport in flow of Johnson-Segalman liquid subject to inclined magnetic field. The energy equation is developed with extra heat transport assumptions like thermal radiative flux and dissipation. The channel walls are heated convectively.

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

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

CONCLUSIONS: The impact of complaint walls on radiative peristaltic transport of Johnson-Segalman liquid in symmetric channel subject to inclined angle. The influence of Johnson-Segalman variable on the velocity field shows decreasing behavior. Velocity also declines against larger Hartman number. Temperature and heat transfer rate boosts through rising values of E1 E2 while decays versus larger E3. Furthermore, reduction in heat transfer coefficient is observed when the values of α and Br are increased.

RevDate: 2019-09-18

Tanveer A, Khan M, Salahuddin T, et al (2019)

Numerical simulation of electroosmosis regulated peristaltic transport of Bingham nanofluid.

Computer methods and programs in biomedicine, 180:105005.

The effects of slip condition and Joule heating on the peristaltic flow of Bingham nanofluid are investigated. The flow is taken in a porous channel with elastic walls. Mathematical formulation is presented under the assumption of long wavelength and small Reynolds number. The transformed equations for the flow are solved to seek values for the nanoparticles velocity, concentration and temperature along the channel length. Graphs are plotted to evaluate the behavior of various physical parameters on flow quantities in both slip and no-slip cases. The main features of the physical parameters are highlighted on the inclined non uniform channel. The results show an increment in velocity with rise in inclination and porosity while it reduces with magnetic field. Moreover, nanofluid favors the heat transfer and decline the concentration.

RevDate: 2019-08-18

Lambert WB, Stanek MJ, Gurka R, et al (2019)

Leading-edge vortices over swept-back wings with varying sweep geometries.

Royal Society open science, 6(7):190514 pii:rsos190514.

Micro air vehicles are used in a myriad of applications, such as transportation and surveying. Their performance can be improved through the study of wing designs and lift generation techniques including leading-edge vortices (LEVs). Observation of natural fliers, e.g. birds and bats, has shown that LEVs are a major contributor to lift during flapping flight, and the common swift (Apus apus) has been observed to generate LEVs during gliding flight. We hypothesize that nonlinear swept-back wings generate a vortex in the leading-edge region, which can augment the lift in a similar manner to linear swept-back wings (i.e. delta wing) during gliding flight. Particle image velocimetry experiments were performed in a water flume to compare flow over two wing geometries: one with a nonlinear sweep (swift-like wing) and one with a linear sweep (delta wing). Experiments were performed at three spanwise planes and three angles of attack at a chord-based Reynolds number of 26 000. Streamlines, vorticity, swirling strength, and Q-criterion were used to identify LEVs. The results show similar LEV characteristics for delta and swift-like wing geometries. These similarities suggest that sweep geometries other than a linear sweep (i.e. delta wing) are capable of creating LEVs during gliding flight.

RevDate: 2019-08-15

Brown AI, DA Sivak (2019)

Theory of Nonequilibrium Free Energy Transduction by Molecular Machines.

Chemical reviews [Epub ahead of print].

Biomolecular machines are protein complexes that convert between different forms of free energy. They are utilized in nature to accomplish many cellular tasks. As isothermal nonequilibrium stochastic objects at low Reynolds number, they face a distinct set of challenges compared with more familiar human-engineered macroscopic machines. Here we review central questions in their performance as free energy transducers, outline theoretical and modeling approaches to understand these questions, identify both physical limits on their operational characteristics and design principles for improving performance, and discuss emerging areas of research.

RevDate: 2019-08-13

Berg O, Singh K, Hall MR, et al (2019)

Thermodynamics of the bladderwort feeding strike-suction power from elastic energy storage.

Integrative and comparative biology pii:5548213 [Epub ahead of print].

The carnivorous plant bladderwort exemplifies the use of accumulated elastic energy to power motion: respiration-driven pumps slowly load the walls of its suction traps with elastic energy (~1 h). During a feeding strike, this energy is released suddenly to accelerate water (~ 1 ms). However, due to the traps' small size and concomitant low Reynolds number, a significant fraction of the stored energy may be dissipated as viscous friction. Such losses and the mechanical reversibility of Stokes flow are thought to degrade the feeding success of other suction feeders in this size range, such as larval fish. In contrast, triggered bladderwort traps are generally successful. By mapping the energy budget of a bladderwort feeding strike, we illustrate how this smallest of suction feeders can perform like an adult fish. The elastic energy stored in loaded bladders-pressure-volume work performed during the loading process-is in the range of 1 µJ, as measured via the volume evacuated during loading, and literature values of internal pressure. We determined the kinetic energy present in the fluid during suction events from flow fields obtained by Particle Image Velocimetry. Such observations are confounded by the difficult-to-resolve timescale and internal flows, so we obtained independent estimates from mathematical and mechanical models. At the beginning of a feeding strike, we find that 0.5 mW of power are delivered by the elastic recoil mechanism, and the same amount appears as kinetic energy in the flow field. A power deficit would represent viscous dissipation heating the fluid by friction. Approximate solution of the Navier-Stokes equations for an idealized bladderwort strike suggests that less than 20% of energy is lost to friction on the timescale relevant to prey capture. This discrepancy would indeed be difficult to detect experimentally. However, even this upper limit is small in comparison with the 60% losses calculated for fish larvae of similar size, the suction of which is assumed to be muscle powered (and for which elastic energy accumulation has not been demonstrated). Our estimates of elastic energy storage and frictional losses during suction events support the hypothesis that small suction feeders convert a large proportion of the elastic energy stored in the trap walls into kinetic energy of the inspired water, with little energy thermalized due to friction.

RevDate: 2019-10-23

Alazzam A, Al-Khaleel M, Riahi MK, et al (2019)

Dielectrophoresis Multipath Focusing of Microparticles through Perforated Electrodes in Microfluidic Channels.

Biosensors, 9(3):.

This paper presents focusing of microparticles in multiple paths within the direction of the flow using dielectrophoresis. The focusing of microparticles is realized through partially perforated electrodes within the microchannel. A continuous electrode on the top surface of the microchannel is considered, while the bottom side is made of a circular meshed perforated electrode. For the mathematical model of this microfluidic channel, inertia, buoyancy, drag and dielectrophoretic forces are brought up in the motion equation of the microparticles. The dielectrophoretic force is accounted for through a finite element discretization taking into account the perforated 3D geometry within the microchannel. An ordinary differential equation is solved to track the trajectories of the microparticles. For the case of continuous electrodes using the same mathematical model, the numerical simulation shows a very good agreement with the experiments, and this confirms the validation of focusing of microparticles within the proposed perforated electrode microchannel. Microparticles of silicon dioxide and polystyrene are used for this analysis. Their initial positions and radius, the Reynolds number, and the radius of the pore in perforated electrodes mainly conduct microparticles trajectories. Moreover, the radius of the pore of perforated electrode is the dominant factor in the steady state levitation height.

RevDate: 2019-08-07

Samanta T, Tian H, VM Nakariakov (2019)

Evidence for Vortex Shedding in the Sun's Hot Corona.

Physical review letters, 123(3):035102.

Vortex shedding is an oscillating flow that is commonly observed in fluids due to the presence of a blunt body in a flowing medium. Numerical simulations have shown that the phenomenon of vortex shedding could also develop in the magnetohydrodynamic (MHD) domain. The dimensionless Strouhal number, the ratio of the blunt body diameter to the product of the period of vortex shedding and the speed of a flowing medium, is a robust indicator for vortex shedding, and, generally of the order of 0.2 for a wide range of Reynolds number. Using an observation from the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory, we report a wavelike or oscillating plasma flow propagating upward against the Sun's gravitational force. A newly formed shrinking loop in the postflare region possibly generates the oscillation of the upflow in the wake of the hot and dense loop through vortex shedding. The computed Strouhal number is consistent with the prediction from previous MHD simulations. Our observation suggests the possibility of vortex shedding in the solar corona.

RevDate: 2019-09-11

Yu X, Li Y, Liu Y, et al (2019)

Flow Patterns of Viscoelastic Fracture Fluids in Porous Media: Influence of Pore-Throat Structures.

Polymers, 11(8): pii:polym11081291.

Viscoelastic surfactant (VES) fluid and hydrolyzed polyacryamide (HPAM) solution are two of the most common fracturing fluids used in the hydraulic fracturing development of unconventional reservoirs. The filtration of fracturing fluids in porous media is mainly determined by the flow patterns in pore-throat structures. In this paper, three different microdevices analogue of porous media allow access to a large range of Deborah number (De) and concomitantly low Reynolds number (Re). Continuous pore-throat structures were applied to study the feedback effect of downstream structure on upstream flow of VES fluid and HPAM solution with Deborah (De) number from 1.11 to 146.4. In the infinite straight channel, flow patterns between VES fluids and HPAM solution were similar. However, as pore length shortened to 800 μm, flow field of VES fluid exhibited the triangle shape with double-peaks velocity patterns. The flow field of HPAM solution presented stable and centralized streamlines when Re was larger than 4.29 × 10-2. Additionally, when the pore length was further shortened to 400 μm, double-peaks velocity patterns were vanished for VES fluid and the stable convergent flow characteristic of HPAM solution was observed with all flow rates.

RevDate: 2019-08-20

Feng X, Ren Y, Hou L, et al (2019)

Tri-fluid mixing in a microchannel for nanoparticle synthesis.

Lab on a chip, 19(17):2936-2946.

It is becoming more difficult to use bulk mixing and bi-fluid micromixing in multi-step continuous-flow reactions, multicomponent reactions, and nanoparticle synthesis because they typically involve multiple reactants. To date, most micromixing studies, both passive and active, have focused on how to efficiently mix two fluids, while micromixing of three or more fluids together (multi-fluid mixing) has been rarely explored. This study is the first on tri-fluid mixing in microchannels. We investigated tri-fluid mixing in three microchannel models: a straight channel, a classical staggered herringbone mixing (SHM) channel, and a three-dimensional (3D) X-crossing microchannel. Numerical simulations and experiments were jointly conducted. A two-step experimental process was performed to determine the tri-fluid mixing efficiencies of these microchannels. We found that the SHM cannot significantly enhance mixing of three streams especially for a Reynolds number (Re) higher than 10. However, the 3D X-crossing channel based on splitting-and-recombination (SAR) showed effective tri-mixing performance over a wide Re range up to 275 (with a corresponding flow rate of 1972.5 μL min-1), thereby enabling high microchannel throughput. Furthermore, this tri-fluid micromixing process was used to synthesize a kind of Si-based nanoparticle. This achieved a narrower particle size distribution than traditional bulk mixing. Therefore, SAR-based tri-fluid mixing is an alternative for chemical and biochemical reactions where three reactants need to be mixed.

RevDate: 2019-09-11

Henein C, Awwad S, Ibeanu N, et al (2019)

Hydrodynamics of Intravitreal Injections into Liquid Vitreous Substitutes.

Pharmaceutics, 11(8): pii:pharmaceutics11080371.

Intravitreal injections have become the cornerstone of retinal care and one of the most commonly performed procedures across all medical specialties. The impact of hydrodynamic forces of intravitreal solutions when injected into vitreous or vitreous substitutes has not been well described. While computational models do exist, they tend to underestimate the starting surface area of an injected bolus of a drug. Here, we report the dispersion profile of a dye bolus (50 µL) injected into different vitreous substitutes of varying viscosities, surface tensions, and volumetric densities. A novel 3D printed in vitro model of the vitreous cavity of the eye was designed to visualize the dispersion profile of solutions when injected into the following vitreous substitutes-balanced salt solution (BSS), sodium hyaluronate (HA), and silicone oils (SO)-using a 30G needle with a Reynolds number (Re) for injection ranging from approximately 189 to 677. Larger bolus surface areas were associated with faster injection speeds, lower viscosity of vitreous substitutes, and smaller difference in interfacial surface tensions. Boluses exhibited buoyancy when injected into standard S1000. The hydrodynamic properties of liquid vitreous substitutes influence the initial injected bolus dispersion profile and should be taken into account when simulating drug dispersion following intravitreal injection at a preclinical stage of development, to better inform formulations and performance.

RevDate: 2019-08-05

Gvozdić B, Dung OY, van Gils DPM, et al (2019)

Twente mass and heat transfer water tunnel: Temperature controlled turbulent multiphase channel flow with heat and mass transfer.

The Review of scientific instruments, 90(7):075117.

A new vertical water tunnel with global temperature control and the possibility for bubble and local heat and mass injection has been designed and constructed. The new facility offers the possibility to accurately study heat and mass transfer in turbulent multiphase flow (gas volume fraction up to 8%) with a Reynolds-number range from 1.5 × 104 to 3 × 105 in the case of water at room temperature. The tunnel is made of high-grade stainless steel permitting the use of salt solutions in excess of 15% mass fraction. The tunnel has a volume of 300 l. The tunnel has three interchangeable measurement sections of 1 m height but with different cross sections (0.3 × 0.04 m2, 0.3 × 0.06 m2, and 0.3 × 0.08 m2). The glass vertical measurement sections allow for optical access to the flow, enabling techniques such as laser Doppler anemometry, particle image velocimetry, particle tracking velocimetry, and laser-induced fluorescent imaging. Local sensors can be introduced from the top and can be traversed using a built-in traverse system, allowing, for example, local temperature, hot-wire, or local phase measurements. Combined with simultaneous velocity measurements, the local heat flux in single phase and two phase turbulent flows can thus be studied quantitatively and precisely.

RevDate: 2019-08-01

O'Neill G, NS Tolley (2019)

The Complexities of Nasal Airflow - Theory and Practice.

Journal of applied physiology (Bethesda, Md. : 1985) [Epub ahead of print].

The objective of this study was to investigate the effects of nasal valve area, valve stiffness and turbinate region cross-sectional area on airflowrate, nasal resistance, flow limitation and inspiratory 'hysteresis' by the use of a mathematical model of nasal airflow. The model of O'Neill and Tolley (1988) describing the effects of valve area and stiffness on the nasal pressure-flow relationship was improved by the incorporation of additional terms involving i) airflow through the turbinate region, ii) the dependency of the flow coefficients for the valve and turbinate region on the Reynolds number and iii) effects of unsteady flow. The model was found to provide a good fit for normal values for nasal resistance and for pressure-flow curves reported in the literature for both congested and decongested states. Also, by showing the relative contribution of the nasal valve and turbinate region to nasal resistance, the model sheds light in explaining the generally poor correlation between nasal resistance measurements and the results from acoustic rhinometry. Furthermore, by proposing different flow conditions for the acceleration and deceleration phases of inspiration, the model produces an inspiratory loop (commonly referred to as 'hysteresis') consistent with those reported in the literature. With simulation of nasal flaring, the magnitude of the loop, the nasal resistance and flow limitation all show a similar change as observed in the experimental results.

RevDate: 2019-07-31

R Ferreira R, Fukui H, Chow R, et al (2019)

The cilium as a force sensor-myth versus reality.

Journal of cell science, 132(14): pii:132/14/jcs213496.

Cells need to sense their mechanical environment during the growth of developing tissues and maintenance of adult tissues. The concept of force-sensing mechanisms that act through cell-cell and cell-matrix adhesions is now well established and accepted. Additionally, it is widely believed that force sensing can be mediated through cilia. Yet, this hypothesis is still debated. By using primary cilia sensing as a paradigm, we describe the physical requirements for cilium-mediated mechanical sensing and discuss the different hypotheses of how this could work. We review the different mechanosensitive channels within the cilium, their potential mode of action and their biological implications. In addition, we describe the biological contexts in which cilia are acting - in particular, the left-right organizer - and discuss the challenges to discriminate between cilium-mediated chemosensitivity and mechanosensitivity. Throughout, we provide perspectives on how quantitative analysis and physics-based arguments might help to better understand the biological mechanisms by which cells use cilia to probe their mechanical environment.

RevDate: 2019-08-03

Jain K (2019)

Transition to turbulence in an oscillatory flow through stenosis.

Biomechanics and modeling in mechanobiology pii:10.1007/s10237-019-01199-1 [Epub ahead of print].

Onset of flow transition in a sinusoidally oscillating flow through a rigid, constant area circular pipe with a smooth sinusoidal obstruction in the center of the pipe is studied by performing direct numerical simulations, with resolutions close to the Kolmogorov microscales. The studied pipe is stenosed in the center with a 75% reduction in area in two distinct configurations-one that is symmetric to the axis of the parent pipe and the other that is offset by 0.05 diameters to introduce an eccentricity, which disturbs the flow thereby triggering the onset of flow transition. The critical Reynolds number at which the flow transitions to turbulence for a zero-mean oscillatory flow through a stenosis is shown to be nearly tripled in comparison with studies of pulsating unidirectional flow through the same stenosis. The onset of transition is further explored with three different flow pulsation frequencies resulting in a total of 90 simulations conducted on a supercomputer. It is found that the critical Reynolds number at which the oscillatory flow transitions is not affected by the pulsation frequencies. The locations of flow breakdown and re-stabilization post-stenosis are, however, respectively shifted closer to the stenosis throat with increasing pulsation frequencies. The results show that oscillatory physiological flows, while more stable, exhibit fluctuations due to geometric complexity and have implications in studies of dispersion and solute transport in the cerebrospinal fluid flow and understanding of pathological conditions.

RevDate: 2019-08-12

Krishnam U, Sharma V, PK Jha (2019)

The Reynolds number modulated low frequency dynamical modes of aqueous medium embedded spherical virus and implications to detecting and killing viruses.

Journal of biomolecular structure & dynamics [Epub ahead of print].

RevDate: 2019-11-29

Liu G, Xue Q, X Zheng (2019)

Phase-difference on seal whisker surface induces hairpin vortices in the wake to suppress force oscillation.

Bioinspiration & biomimetics, 14(6):066001.

Seals are able to use their uniquely shaped whiskers to track hydrodynamic trails generated 30 s ago and detect hydrodynamic velocities as low as 245 [Formula: see text]m s-1. The high sensibility has long thought to be related to the wavy shape of the whiskers. This work revisited the hydrodynamics of a seal whisker model in a uniform flow, and discovered a new mechanism of seal whiskers in reducing self-induced noises, which is different from the long thought-of effect of the wavy shape. It was reported that the major and minor axes of the elliptical cross-sections of seal whisker are out of phase by approximately 180 degrees. Three-dimensional numerical simulations of laminar flow (Reynolds number range: 150-500) around seal-whisker-like cylinders were performed to examine the effect of the phase-difference on hydrodynamic forces and wake structures. It was found that the phase-difference induced hairpin vortices in the wake over a wide range of geometric and flow parameters (wavelength, wavy amplitude and Reynolds number), therefore substantially reducing lift-oscillations and self-induced noises. The formation mechanism of the hairpin vortices was analyzed and is discussed in details. The results provide valuable insights into an innovative vibration reduction and hydrodynamic sensing mechanism.

RevDate: 2019-07-24

Jian X, Zhang W, Deng Q, et al (2019)

Turbulent lithosphere deformation in the Tibetan Plateau.

Physical review. E, 99(6-1):062122.

In this work, we show that the Tibetan Plateau deformation demonstrates turbulence-like statistics, e.g., spatial invariance across continuous scales. A dual-power-law behavior is evident to show the existence of two possible conservation laws for the enstrophy-like cascade in the range 500≲r≲2000km and kinetic-energy-like cascade in the range 50≲r≲500km. The measured second-order structure-function scaling exponents ζ(2) are similar to their counterparts in the Fourier scaling exponents observed in the atmosphere, where in the latter case the earth's rotation is relevant. The turbulent statistics observed here for nearly zero-Reynolds-number flow can be interpreted by the geostrophic turbulence theory. Moreover, the intermittency correction is recognized with an intensity close to that of the hydrodynamic turbulence of high-Reynolds-number turbulent flows, implying a universal scaling feature of very different turbulent flows. Our results not only shed new light on the debate regarding the mechanism of the Tibetan Plateau deformation but also lead to new challenges for the geodynamic modeling using Newton or non-Newtonian models because the observed turbulence-like features have to be taken into account.

RevDate: 2019-07-18

Dölger J, Kiørboe T, A Andersen (2019)

Dense Dwarfs versus Gelatinous Giants: The Trade-Offs and Physiological Limits Determining the Body Plan of Planktonic Filter Feeders.

The American naturalist, 194(2):E30-E40.

Most marine plankton have a high energy (carbon) density, but some are gelatinous with approximately 100 times more watery bodies. How do those distinctly different body plans emerge, and what are the trade-offs? We address this question by modeling the energy budget of planktonic filter feeders across life-forms, from micron-sized unicellular microbes such as choanoflagellates to centimeter-sized gelatinous tunicates such as salps. We find two equally successful strategies, one being small with high energy density (dense dwarf) and the other being large with low energy density (gelatinous giant). The constraint that forces large-but not small-filter feeders to be gelatinous is identified as a lower limit to the size-specific filter area, below which the energy costs lead to starvation. A further limit is found from the maximum size-specific motor force that restricts the access to optimum strategies. The quantified constraints are discussed in the context of other resource-acquisition strategies. We argue that interception feeding strategies can be accessed by large organisms only if they are gelatinous. On the other hand, organisms that use remote prey sensing do not need to be gelatinous, even if they are large.

RevDate: 2019-08-10

Samson JE, Miller LA, Ray D, et al (2019)

A novel mechanism of mixing by pulsing corals.

The Journal of experimental biology, 222(Pt 15): pii:jeb.192518.

The dynamic pulsation of xeniid corals is one of the most fascinating phenomena observed in coral reefs. We quantify for the first time the flow near the tentacles of these soft corals, the active pulsations of which are thought to enhance their symbionts' photosynthetic rates by up to an order of magnitude. These polyps are approximately 1 cm in diameter and pulse at frequencies between approximately 0.5 and 1 Hz. As a result, the frequency-based Reynolds number calculated using the tentacle length and pulse frequency is on the order of 10 and rapidly decays as with distance from the polyp. This introduces the question of how these corals minimize the reversibility of the flow and bring in new volumes of fluid during each pulse. We estimate the Péclet number of the bulk flow generated by the coral as being on the order of 100-1000 whereas the flow between the bristles of the tentacles is on the order of 10. This illustrates the importance of advective transport in removing oxygen waste. Flow measurements using particle image velocimetry reveal that the individual polyps generate a jet of water with positive vertical velocities that do not go below 0.1 cm s-1 and with average volumetric flow rates of approximately 0.71 cm3 s-1 Our results show that there is nearly continual flow in the radial direction towards the polyp with only approximately 3.3% back flow. 3D numerical simulations uncover a region of slow mixing between the tentacles during expansion. We estimate that the average flow that moves through the bristles of the tentacles is approximately 0.03 cm s-1 The combination of nearly continual flow towards the polyp, slow mixing between the bristles, and the subsequent ejection of this fluid volume into an upward jet ensures the polyp continually samples new water with sufficient time for exchange to occur.

RevDate: 2019-09-04

Liao P, Xing L, Zhang S, et al (2019)

Magnetically Driven Undulatory Microswimmers Integrating Multiple Rigid Segments.

Small (Weinheim an der Bergstrasse, Germany), 15(36):e1901197.

Mimicking biological locomotion strategies offers important possibilities and motivations for robot design and control methods. Among bioinspired microrobots, flexible microrobots exhibit remarkable efficiency and agility. These microrobots traditionally rely on soft material components to achieve undulatory propulsion, which may encounter challenges in design and manufacture including the complex fabrication processes and the interfacing of rigid and soft components. Herein, a bioinspired magnetically driven microswimmer that mimics the undulatory propulsive mechanism is proposed. The designed microswimmer consists of four rigid segments, and each segment is connected to the succeeding segment by joints. The microswimmer is fabricated integrally by 3D laser lithography without further assembly, thereby simplifying microrobot fabrication while enhancing structural integrity. Experimental results show that the microswimmer can successfully swim forward along guided directions via undulatory locomotion in the low Reynolds number (Re) regime. This work demonstrates for the first time that the flexible characteristic of microswimmers can be emulated by 3D structures with multiple rigid segments, which broadens possibilities in microrobot design. The proposed magnetically driven microswimmer can potentially be used in biomedical applications, such as medical diagnosis and treatment in precision medicine.

RevDate: 2019-07-18

Hoell C, Löwen H, Menzel AM, et al (2019)

Creeping motion of a solid particle inside a spherical elastic cavity: II. Asymmetric motion.

The European physical journal. E, Soft matter, 42(7):89 pii:10.1140/epje/i2019-11853-4.

An analytical method is proposed for computing the low-Reynolds-number hydrodynamic mobility function of a small colloidal particle asymmetrically moving inside a large spherical elastic cavity, the membrane of which is endowed with resistance toward shear and bending. In conjunction with the results obtained in the first part (A. Daddi-Moussa-Ider, H. Löwen, S. Gekle, Eur. Phys. J. E 41, 104 (2018)), in which the axisymmetric motion normal to the surface of an elastic cavity is investigated, the general motion for an arbitrary force direction can now be addressed. The elastohydrodynamic problem is formulated and solved using the classic method of images through expressing the hydrodynamic flow fields as a multipole expansion involving higher-order derivatives of the free-space Green's function. In the quasi-steady limit, we demonstrate that the particle self-mobility function of a particle moving tangent to the surface of the cavity is larger than that predicted inside a rigid stationary cavity of equal size. This difference is justified by the fact that a stationary rigid cavity introduces additional hindrance to the translational motion of the encapsulated particle, resulting in a reduction of its hydrodynamic mobility. Furthermore, the motion of the cavity is investigated, revealing that the translational pair (composite) mobility, which linearly couples the velocity of the elastic cavity to the force exerted on the solid particle, is solely determined by membrane shear properties. Our analytical predictions are favorably compared with fully-resolved computer simulations based on a completed-double-layer boundary integral method.

RevDate: 2019-08-27

Novelli GL, Ferrari LA, Vargas GG, et al (2019)

A synergistic analysis of drag reduction on binary polymer mixtures containing guar gum.

International journal of biological macromolecules, 137:1121-1129.

Drag reduction by the addition of polymer additives has been widely studied. However, there are only a few studies on binary polymer mixtures, here named blends. In this work, xanthan gum, polyacrylamide and poly(ethylene oxide) were associated with guar gum and drag reduction was used as a parameter to determine the synergistic interaction between polymers. The aim was to verify the relation of the synergy with the rigidity of the polymeric chains, the molecular weights and the magnitude of the molecular interactions between the studied polymers. To that end, several ratios of mixtures were tested at different Reynolds numbers in a rotational rheometer with double-gap concentric cylinders geometry. Finally, experiments were done to verify the behaviour of the blends over time at a fixed Reynolds number. From all these tests, it was documented that blends containing rigid chain polymers show positive synergism in the interaction in at least one of the ratios and that this interaction is more pronounced when the molecular weights are closer and intermolecular forces are stronger. It was also noted that, in general, blends are great substitutes for solutions containing only one type of polymer.

RevDate: 2019-07-24

Mazinani S, Al-Shimmery A, Chew YMJ, et al (2019)

3D Printed Fouling-Resistant Composite Membranes.

ACS applied materials & interfaces, 11(29):26373-26383.

Fouling remains a long-standing unsolved problem that hinders the widespread use of membrane applications in industry. This article reports the use of numerical simulations coupled with extensive material synthesis and characterization to fabricate fouling-resistant 3D printed composite membranes. The membranes consist of a thin polyethersulfone selective layer deposited onto a 3D printed flat and double sinusoidal (wavy) support. Fouling and cleaning of the composite membranes were tested by using bovine serum albumin solution in a cross-flow ultrafiltration setup. The transmembrane pressure was regulated at 1 bar and the cross-flow Reynolds number (Re) varied between 400 and 1000. In comparison to the flat membrane, the wavy membrane showed superior performance in terms of pure water permeance (PWP) (10% higher) and permeance recovery ratio (87% vs 53%) after the first filtration cycle at Re = 1000. Prolong testing showed that the wavy membrane could retain approximately 87% of its initial PWP after 10 complete filtration cycles. This impressive fouling-resistant behavior is attributed to the localized fluid turbulence induced by the 3D printed wavy structure. These results show that not only the lifetime of membrane operations could be favorably extended but also the operational costs and environmental damage of membrane-based processes could also be significantly reduced.

RevDate: 2019-07-09

Chajwa R, Menon N, S Ramaswamy (2019)

Kepler Orbits in Pairs of Disks Settling in a Viscous Fluid.

Physical review letters, 122(22):224501.

We show experimentally that a pair of disks settling at negligible Reynolds number (∼10^{-4}) displays two classes of bound periodic orbits, each with transitions to scattering states. We account for these dynamics, at leading far-field order, through an effective Hamiltonian in which gravitational driving endows orientation with the properties of momentum. This treatment is successfully compared against the measured properties of orbits and critical parameters of transitions between types of orbits. We demonstrate a precise correspondence with the Kepler problem of planetary motion for a wide range of initial conditions, find and account for a family of orbits with no Keplerian analog, and highlight the role of orientation as momentum in the many-disk problem.

RevDate: 2019-09-09
CmpDate: 2019-09-09

Ren Z, Hu W, Dong X, et al (2019)

Multi-functional soft-bodied jellyfish-like swimming.

Nature communications, 10(1):2703 pii:10.1038/s41467-019-10549-7.

The functionalities of the untethered miniature swimming robots significantly decrease as the robot size becomes smaller, due to limitations of feasible miniaturized on-board components. Here we propose an untethered jellyfish-inspired soft millirobot that could realize multiple functionalities in moderate Reynolds number by producing diverse controlled fluidic flows around its body using its magnetic composite elastomer lappets, which are actuated by an external oscillating magnetic field. We particularly investigate the interaction between the robot's soft body and incurred fluidic flows due to the robot's body motion, and utilize such physical interaction to achieve different predation-inspired object manipulation tasks. The proposed lappet kinematics can inspire other existing jellyfish-like robots to achieve similar functionalities at the same length and time scale. Moreover, the robotic platform could be used to study the impacts of the morphology and kinematics changing in ephyra jellyfish.

RevDate: 2019-08-30

Klusak E, NJ Quinlan (2019)

High-Resolution Measurements of Leakage Flow Inside the Hinge of a Large-scale Bileaflet Mechanical Heart Valve Hinge Model.

Cardiovascular engineering and technology, 10(3):469-481.

PURPOSE: It is believed that non-physiological leakage flow through hinge gaps during diastole contributes to thrombus formation in Bileaflet Mechanical Heart Valves (BMHVs). Because of the small scale and difficulty of experimental access, fluid dynamics inside the hinge cavity has not yet been characterised in detail. The objective is to investigate small-scale structure inside the hinge experimentally, and gain insight into its role in stimulating cellular responses.

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

CONCLUSIONS: The scale-up approach provided new insight into the nature of the hinge flow and enhanced understanding of its complexity. This study revealed flow features that may induce blood element damage.

RevDate: 2019-06-28

Cafiero G, JC Vassilicos (2019)

Non-equilibrium turbulence scalings and self-similarity in turbulent planar jets.

Proceedings. Mathematical, physical, and engineering sciences, 475(2225):20190038.

We study the self-similarity and dissipation scalings of a turbulent planar jet and the theoretically implied mean flow scalings. Unlike turbulent wakes where such studies have already been carried out (Dairay et al. 2015 J. Fluid Mech. 781, 166-198. (doi:10.1017/jfm.2015.493); Obligado et al. 2016 Phys. Rev. Fluids1, 044409. (doi:10.1103/PhysRevFluids.1.044409)), this is a boundary-free turbulent shear flow where the local Reynolds number increases with distance from inlet. The Townsend-George theory revised by (Dairay et al. 2015 J. Fluid Mech. 781, 166-198. (doi:10.1017/jfm.2015.493)) is applied to turbulent planar jets. Only a few profiles need to be self-similar in this theory. The self-similarity of mean flow, turbulence dissipation, turbulent kinetic energy and Reynolds stress profiles is supported by our experimental results from 18 to at least 54 nozzle sizes, the furthermost location investigated in this work. Furthermore, the non-equilibrium dissipation scaling found in turbulent wakes, decaying grid-generated turbulence, various instances of periodic turbulence and turbulent boundary layers (Dairay et al. 2015 J. Fluid Mech. 781, 166-198. (doi:10.1017/jfm.2015.493); Vassilicos 2015 Annu. Rev. Fluid Mech. 95, 114. (doi:10.1146/annurev-fluid-010814-014637); Goto & Vassilicos 2015 Phys. Lett. A3790, 1144-1148. (doi:10.1016/j.physleta.2015.02.025); Nedic et al. 2017 Phys. Rev. Fluids2, 032601. (doi:10.1103/PhysRevFluids.2.032601)) is also observed in the present turbulent planar jet and in the turbulent planar jet of (Antonia et al. 1980 Phys. Fluids23, 863055. (doi:10.1063/1.863055)). Given these observations, the theory implies new mean flow and jet width scalings which are found to be consistent with our data and the data of (Antonia et al. 1980 Phys. Fluids23, 863055. (doi:10.1063/1.863055)). In particular, it implies a hitherto unknown entrainment behaviour: the ratio of characteristic cross-stream to centreline streamwise mean flow velocities decays as the -1/3 power of streamwise distance in the region, where the non-equilibrium dissipation scaling holds.

RevDate: 2019-07-12

Garwood RJ, Behnsen J, Haysom HK, et al (2019)

Olfactory flow in the sturgeon is externally driven.

Comparative biochemistry and physiology. Part A, Molecular & integrative physiology, 235:211-225.

Fluid dynamics plays an important part in olfaction. Using the complementary techniques of dye visualisation and computational fluid dynamics (CFD), we investigated the hydrodynamics of the nasal region of the sturgeon Huso dauricus. H. dauricus offers several experimental advantages, including a well-developed, well-supported, radial array (rosette) of visible-by-eye olfactory sensory channels. We represented these features in an anatomically accurate rigid model derived from an X-ray scan of the head of a preserved museum specimen. We validated the results from the CFD simulation by comparing them with data from the dye visualisation experiments. We found that flow through both the nasal chamber and, crucially, the sensory channels could be induced by an external flow (caused by swimming in vivo) at a physiologically relevant Reynolds number. Flow through the nasal chamber arises from the anatomical arrangement of the incurrent and excurrent nostrils, and is assisted by the broad, cartilage-supported, inner wall of the incurrent nostril. Flow through the sensory channels arises when relatively high speed flow passing through the incurrent nostril encounters the circular central support of the olfactory rosette, decelerates, and is dispersed amongst the sensory channels. Vortices within the olfactory flow may assist odorant transport to the sensory surfaces. We conclude that swimming alone is sufficient to drive olfactory flow in H. dauricus, and consider the implications of our results for the three other extant genera of sturgeons (Acipenser, Pseudoscaphirhynchus and Scaphirhynchus), and for other fishes with olfactory rosettes.

RevDate: 2019-11-28
CmpDate: 2019-11-28

Man Y, E Kanso (2019)

Morphological transitions of axially-driven microfilaments.

Soft matter, 15(25):5163-5173.

The interactions of microtubules with motor proteins are ubiquitous in cellular and sub-cellular processes that involve motility and cargo transport. In vitro motility assays have demonstrated that motor-driven microtubules exhibit rich dynamical behaviors from straight to curved configurations. Here, we theoretically investigate the dynamic instabilities of elastic filaments, with free-ends, driven by single follower forces that emulate the action of molecular motors. Using the resistive force theory at low Reynolds number, and a combination of numerical techniques with linear stability analysis, we show the existence of four distinct regimes of filament behavior, including a novel buckled state with locked curvature. These successive instabilities recapitulate the full range of experimentally-observed microtubule behavior, implying that neither structural nor actuation asymmetry are needed to elicit this rich repertoire of motion.

RevDate: 2019-06-19

He G, Wang J, A Rinoshika (2019)

Orthogonal wavelet multiresolution analysis of the turbulent boundary layer measured with two-dimensional time-resolved particle image velocimetry.

Physical review. E, 99(5-1):053105.

The turbulent boundary layer flow measured by two-dimensional time-resolved particle image velocimetry is analyzed using the discrete orthogonal wavelet method. The Reynolds number of the turbulent boundary layer based on the friction velocity is Re_{τ}=235. The flow field is decomposed into a number of wavelet levels which have different characteristic scales. The velocity statistics and coherent structures at different wavelet levels are investigated. It is found that the fluctuation intensities and their peak locations differ for varying scales. The proper orthogonal decomposition (POD) of different wavelet components reveals a cascade of scales of coherent structures, especially the small-scale ones that are usually difficult to be identified in POD modes of the undecomposed flow field. The interactions among the scales are investigated in terms of large-scale amplitude modulations of the small-scale structures. In previous studies the velocity fluctuations are separated into two parts, the large scale and the small scale, divided usually by the boundary layer thickness. In the present study, however, the scales smaller than the boundary layer thickness are further separated. Therefore, the modulation analysis is a refined investigation that differentiates the modulation effects on separated small scales. The results reveal that the modulation effects vary among the small scales.

RevDate: 2019-06-19

Puljiz M, AM Menzel (2019)

Displacement field around a rigid sphere in a compressible elastic environment, corresponding higher-order Faxén relations, as well as higher-order displaceability and rotateability matrices.

Physical review. E, 99(5-1):053002.

An efficient route to the displacement field around a rigid spherical inclusion in an infinitely extended homogeneous elastic medium is presented in a slightly alternative way when compared to some common textbook methods. Moreover, two Faxén relations of next-higher order beyond the stresslet are calculated explicitly for compressible media. They quantify higher-order moments involving the force distribution on a rigid spherical particle in a deformed elastic medium. As a consequence, additional contributions to the distortions of the deformed elastic medium are identified that are absent to lower order. Furthermore, the displaceability and rotateability matrices for an ensemble of rigid spheres are calculated up to (including) sixth order in inverse particle separation distance. These matrices describe the interactions mediated between the rigid embedded particles by the elastic environment. In this way, additional coupling effects are identified that are absent to lower order, particularly when rotations and torques are involved. All methods and results can formally be transferred to the corresponding case of incompressible hydrodynamic low-Reynolds-number Stokes flow by considering the limit of an incompressible environment. The roles of compressibility of the embedding medium and of the here additionally derived higher-order contributions are highlighted by some selected example configurations.

RevDate: 2019-06-19

Nie D, J Lin (2019)

Discontinuity in the sedimentation system with two particles having different densities in a vertical channel.

Physical review. E, 99(5-1):053112.

The two-dimensional lattice Boltzmann method was used to numerically study a sedimentation system with two particles having different densities in a vertical channel for Galileo numbers in the range of 5≤Ga≤15 (resulting in a Reynolds number, based on the settling velocity, approximately ranging between 0.6 and 7). Two types of periodic motion, differing from each other in terms of the size of the limit cycle, the magnitude of the time period, and their changes upon increasing the density difference between particles, are identified depending on whether there is a wake effect. The most prominent features of this system are discontinuous changes in the settling velocity (6.7≤Ga<9.7) and time period of oscillation (10.5≤Ga≤15) at a critical value of the density difference between particles. The first discontinuity results in an abrupt increase in the Reynolds number, associated with a Hopf bifurcation without the presence of vortex shedding. The second discontinuity is accompanied by the disappearance of "abnormal rotation" (referring to the situation in which a particle appears to roll up a wall when settling) of the heavy particle, which directly results from a sharp increase in the amplitude of oscillation induced by the enhanced wake effect at another critical density difference between particles. The wall effects on these discontinuous changes were also examined.

RevDate: 2019-06-19

Wang L, FB Tian (2019)

Numerical simulation of flow over a parallel cantilevered flag in the vicinity of a rigid wall.

Physical review. E, 99(5-1):053111.

Flow over a parallel cantilevered flag in the vicinity of a rigid wall is numerically studied using an immersed boundary-lattice Boltzmann method (IB-LBM) in two-dimensional domain, where the dynamics of the fluid and structure are, respectively, solved by the LBM and a finite-element method (FEM), with a penalty IB to handle the fluid-structure interaction (FSI). Specifically, a benchmark case considering a plate attached to the downstream of a stationary cylinder is first conducted to validate the current solver. Then, the wall effects on the flag are systemically studied, considering the effects of off-wall distance, structure-to-fluid mass ratio, bending rigidity, and Reynolds number. Three flapping modes, including symmetrical flapping, asymmetrical flapping, and chaotic flapping, along with a steady state are observed in the simulations. It is found that the flag is vibrating or stable with a mean angle inclined in the fluid when it is mounted in the vicinity of a rigid wall. The mean inclined angle first increases in the steady state and then decreases in the unsteady state with the off-wall distance. In the unsteady regime, the dependency of the inclined angle on the off-wall distance is similar to that of the gradient of the fluid velocity. In addition, the rigid wall near the flag decreases the lift and drag generation and further stabilizes the flag-fluid system. Contrarily, the flag inertia destabilizes the flag, and large flag inertia induces chaotic vibrating modes.

RevDate: 2019-08-20

Zhang H, Li X, Chuai R, et al (2019)

Chaotic Micromixer Based on 3D Horseshoe Transformation.

Micromachines, 10(6): pii:mi10060398.

To improve the efficiency of mixing under laminar flow with a low Reynolds number (Re), a novel three-dimensional Horseshoe Transformation (3D HT) was proposed as the basis for the design of a micromixer. Compared with the classical HT, the Lyapunov exponent of the 3D HT, which was calculated based on a symbolic dynamic system, proved the chaotic enhancement. Based on the 3D HT, a micromixer with a mixing length of 12 mm containing six mixing units was obtained by sequentially applying "squeeze", "stretch", "twice fold", "inverse transformation", and "intersection" operations. Numerical simulation and Peclet Number (Pe) calculations indicated that when the squeeze amplitude 0 < α < 1/2, 0 < β < 1/2, the stretch amplitude γ > 4, and Re ≥ 1, the mass transfer in the mixer was dominated by convective diffusion induced by chaotic flow. When Re = 10, at the outlet of the mixing chamber, the simulated mixing index was 96.4%, which was far less than the value at Re = 0.1 (σ = 0.041). Microscope images of the mixing chamber and the curve trend of pH buffer solutions obtained from a mixing experiment were both consistent with the results of the simulation. When Re = 10, the average mixing index of the pH buffer solutions was 91.75%, which proved the excellent mixing efficiency of the mixer based on the 3D HT.

RevDate: 2019-10-07

Belut E, Sánchez Jiménez A, Meyer-Plath A, et al (2019)

Indoor dispersion of airborne nano and fine particles: Main factors affecting spatial and temporal distribution in the frame of exposure modeling.

Indoor air, 29(5):803-816.

A particle exposure experiment inside a large climate-controlled chamber was conducted. Data on spatial and temporal distribution of nanoscale and fine aerosols in the range of mobility diameters 8-600 nm were collected with high resolution, for sodium chloride, fluorescein sodium, and silica particles. Exposure scenarios studied included constant and intermittent source emissions, different aggregation conditions, high (10 h-1) and low (3.5 h-1) air exchange rates (AERs) corresponding to chamber Reynolds number, respectively, equal to 1 × 105 and 3 × 104 . Results are presented and analyzed to highlight the main determinants of exposure and to determine whether the assumptions underlying two-box models hold under various scenarios. The main determinants of exposure found were the source generation rate and the ventilation rate. The effect of particles nature was indiscernible, and the decrease of airborne total number concentrations attributable to surface deposition was estimated lower than 2% when the source was active. A near-field/far-field structure of aerosol concentration was always observed for the AER = 10 h-1 but for AER = 3.5 h-1 , a single-field structure was found. The particle size distribution was always homogeneous in space but a general shift of particle diameter (-8% to +16%) was observed between scenarios in correlation with the AER and with the source position, presumably largely attributable to aggregation.

RevDate: 2019-06-14

Aghilinejad A, Aghaamoo M, X Chen (2019)

On the transport of particles/cells in high-throughput deterministic lateral displacement devices: Implications for circulating tumor cell separation.

Biomicrofluidics, 13(3):034112 pii:012903BMF.

Deterministic lateral displacement (DLD), which takes advantage of the asymmetric bifurcation of laminar flow around the embedded microposts, has shown promising capabilities in separating cells and particles of different sizes. Growing interest in utilizing high-throughput DLD devices for practical applications, such as circulating tumor cell separation, necessitates employing higher flow rates in these devices, leading to operating in moderate to high Reynolds number (Re) regimes. Despite extensive research on DLD devices in the creeping regime, limited research has focused on the physics of flow, critical size of the device, and deformable cell behavior in DLD devices at moderate to high Re. In this study, the transport behavior of particles/cells is investigated in realistic high-throughput DLD devices with hundreds of microposts by utilizing multiphysics modeling. A practical formula is proposed for the prediction of the device critical size, which could serve as a design guideline for high-throughput DLD devices. Then, the complex hydrodynamic interactions between a deformable cell and DLD post arrays are investigated. A dimensionless index is utilized for comparing different post designs to quantify the cell-post interaction. It is shown that the separation performances in high-throughput devices are highly affected by Re as well as the micropost shapes. These findings can be utilized for the design and optimization of high-throughput DLD microfluidic devices.

RevDate: 2019-10-22
CmpDate: 2019-10-22

Tshumah-Mutingwende RRMS, F Takahashi (2019)

Physio-chemical effects of freshwaters on the dissolution of elementary mercury.

Environmental pollution (Barking, Essex : 1987), 252(Pt A):627-636.

Elemental mercury (Hg0) is widely used by Artisanal and small-scale gold miners (ASGMs) to extract gold from ore. Due to the unavailability of appropriate waste disposal facilities, Hg0-rich amalgamation tailings are often discharged into nearby aquatic systems where the Hg0 droplets settle in bottom sediment and sediment-water interfaces. Hg0 dissolution and following biogeochemical transformations to methylmercury (MeHg) have been concerned owing to its potential risk to human health and the ecosystem. For reliable estimates of Hg exposure to human bodies using pollutant environmental fate and transport models, knowledge of the Hg0 dissolution rate is important. However, only limited literature is available. Therefore, it was investigated in this study. Dissolution tests in a 'dark chamber' revealed that an increase in medium pH resulted in a decrease in the dissolution rate, whereas, a large Hg0 droplet surface area (SA) and high Reynolds number (Re) resulted in a faster dissolution. A multivariate first order dissolution model of the form:kˆ=-7.9×10-5[pH]+7.0×10-4[logRe]+7.9×10-4[SA]-2.5×10-3 was proposed (adjusted R2 = 0.99). The Breusch-Pagan and White heteroscedasticity tests revealed that the model residuals are homoscedastic (p-value = 0.05) at the 5% significance level. Parameter sensitivity analysis suggests that slow mercury dissolution from the Hg0 droplets to aquatic systems might mask emerging environmental risk of mercury. Even after mercury usage in ASGM is banned, mercury dissolution and following contamination will continue for about 40 years or longer owing to previously discharged Hg0 droplets.

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ESP Quick Facts

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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.

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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.

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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.

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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.

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Papers in Classical Genetics

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Digital Books

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Timelines

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Selected Bibliographies

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