POF Nameplate
  • Volume/Page
  • Keyword
  • DOI
  • Citation
  • Advanced
   
 
 
 

Flickr Twitter iResearch App Facebook

Search Issue | RSS Feeds RSS
Previous Issue Next Issue

Sep 2008

Volume 20, Issue 9, Articles (09xxxx)

Issue Cover Spotlight Figure

Phys. Fluids 20, 091102 (2008); http://dx.doi.org/10.1063/1.2973206 (1 page)

M. Canals and G. Pawlak
Enlarge Image | Read More
Page 1 of 3 Pages Next Page | Jump to Page
back to top
RSS Feeds
FREE

Introduction: 25th Annual Gallery of Fluid Motion (Salt Lake City, Utah, 2007)

Todd B. Harman

Phys. Fluids 20, 091101 (2008); http://dx.doi.org/10.1063/1.2974812 (1 page)

Online Publication Date: 25 September 2008

Full Text: Read Online (HTML) | Download PDF

Abstract Unavailable
Show PACS
47.80.Jk Flow visualization and imaging
01.10.Hx Physics organizational activities
01.50.H- Computers in education
FREE

Topology and breakdown of Görtler vortices on an oscillating cylinder

M. Canals and G. Pawlak

Phys. Fluids 20, 091102 (2008); http://dx.doi.org/10.1063/1.2973206 (1 page)

Online Publication Date: 25 September 2008

Full Text: Read Online (HTML) | Download PDF

Abstract Unavailable
Show PACS
47.32.cd Vortex stability and breakdown
47.20.Ib Instability of boundary layers; separation
FREE

Spilling breakers and surfactants

Xinan Liu, James D. Diorio, and James H. Duncan

Phys. Fluids 20, 091103 (2008); http://dx.doi.org/10.1063/1.2973459 (1 page)

Online Publication Date: 25 September 2008

Full Text: Read Online (HTML) | Download PDF

multimedia

Abstract Unavailable
Show PACS
47.35.Jk Wave breaking
47.35.Pq Capillary waves
47.20.Ib Instability of boundary layers; separation
47.57.J- Colloidal systems
68.03.Cd Surface tension and related phenomena
FREE

Helical instability of a rotating liquid jet

J. P. Kubitschek and P. D. Weidman

Phys. Fluids 20, 091104 (2008); http://dx.doi.org/10.1063/1.2973479 (1 page) | Cited 2 times

Online Publication Date: 25 September 2008

Full Text: Read Online (HTML) | Download PDF

multimedia

Abstract Unavailable
Show PACS
47.20.Gv Viscous and viscoelastic instabilities
47.20.Dr Surface-tension-driven instability
47.20.Lz Secondary instabilities
47.32.Ef Rotating and swirling flows
47.60.Kz Flows and jets through nozzles
FREE

Digital particle image velocimetry of mammalian swimming

Paul Legac, Timothy Wei, Frank Fish, Terrie Williams, Russell Mark, and Sean Hutchison

Phys. Fluids 20, 091105 (2008); http://dx.doi.org/10.1063/1.2973663 (1 page)

Online Publication Date: 25 September 2008

Full Text: Read Online (HTML) | Download PDF

multimedia

Abstract Unavailable
Show PACS
87.85.gf Fluid mechanics and rheology
47.80.Jk Flow visualization and imaging
47.32.-y Vortex dynamics; rotating fluids
FREE

“Black hole” nucleation in a splash of milk

Laurent Courbin, James C. Bird, Andrew Belmonte, and Howard A. Stone

Phys. Fluids 20, 091106 (2008); http://dx.doi.org/10.1063/1.2973667 (1 page) | Cited 1 time

Online Publication Date: 25 September 2008

Full Text: Read Online (HTML) | Download PDF

multimedia

Abstract Unavailable
Show PACS
47.55.dr Interactions with surfaces
68.08.Bc Wetting
68.03.Cd Surface tension and related phenomena
FREE

Viscous jet drawing air into a bath

Etienne Reyssat, Elise Lorenceau, Frédéric Restagno, and David Quéré

Phys. Fluids 20, 091107 (2008); http://dx.doi.org/10.1063/1.2973677 (1 page)

Online Publication Date: 25 September 2008

Full Text: Read Online (HTML) | Download PDF

Abstract Unavailable
Show PACS
47.15.Uv Laminar jets
66.20.-d Viscosity of liquids; diffusive momentum transport
47.55.db Drop and bubble formation
68.03.Cd Surface tension and related phenomena
47.55.Hd Stratified flows
FREE

Water bells created from below

Graeme J. Jameson, Claire Jenkins, Eleanor C. Button, and John E. Sader

Phys. Fluids 20, 091108 (2008); http://dx.doi.org/10.1063/1.2974790 (1 page)

Online Publication Date: 25 September 2008

Full Text: Read Online (HTML) | Download PDF

Abstract Unavailable
Show PACS
47.60.Kz Flows and jets through nozzles
47.55.-t Multiphase and stratified flows
FREE

Fractal Kelvin–Helmholtz breakups

Jérôme Fontane, Laurent Joly, and Jean N. Reinaud

Phys. Fluids 20, 091109 (2008); http://dx.doi.org/10.1063/1.2976423 (1 page)

Online Publication Date: 25 September 2008

Full Text: Read Online (HTML) | Download PDF

Abstract Unavailable
Show PACS
47.20.Ma Interfacial instabilities (e.g., Rayleigh-Taylor)
47.20.Lz Secondary instabilities
47.53.+n Fractals in fluid dynamics
47.55.Hd Stratified flows
47.32.Ef Rotating and swirling flows
47.11.-j Computational methods in fluid dynamics
FREE

Breakup of the tail of a bubble in a non-Newtonian fluid

Enrique Soto, Roberto Zenit, and Octavio Manero

Phys. Fluids 20, 091110 (2008); http://dx.doi.org/10.1063/1.2973481 (1 page)

Online Publication Date: 25 September 2008

Full Text: Read Online (HTML) | Download PDF

multimedia

Abstract Unavailable
Show PACS
47.55.df Breakup and coalescence
47.50.-d Non-Newtonian fluid flows
47.57.Ng Polymers and polymer solutions
FREE

The water-entry cavity formed by low Bond number impacts

Jeffrey M. Aristoff, Tadd T. Truscott, Alexandra H. Techet, and John W. M. Bush

Phys. Fluids 20, 091111 (2008); http://dx.doi.org/10.1063/1.2973662 (1 page)

Online Publication Date: 25 September 2008

Full Text: Read Online (HTML) | Download PDF

Abstract Unavailable
Show PACS
47.20.Ma Interfacial instabilities (e.g., Rayleigh-Taylor)
68.03.Cd Surface tension and related phenomena
47.60.Kz Flows and jets through nozzles
back to top
RSS Feeds
FREE

Modeling of the subfilter scalar dissipation rate using the concept of optimal estimators

G. Balarac, H. Pitsch, and V. Raman

Phys. Fluids 20, 091701 (2008); http://dx.doi.org/10.1063/1.2976818 (4 pages) | Cited 5 times

Online Publication Date: 5 September 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
In this work, modeling of the subfilter scalar dissipation rate is addressed. First, the best set of quantities to write a model is determined using the concept of optimal estimators. This study shows that the best approach is to assume a proportionality between the turbulent time scale and turbulent scalar mixing time scale. It is shown that the turbulent time scale should be defined by the subfilter kinetic energy. To define the coefficient appearing in this model, a dynamic determination based on a global subfilter equilibrium assumption between the dissipation and the production terms leads to the best results.
Show PACS
47.27.E- Turbulence simulation and modeling
FREE

A mathematical model of turbulent drag reduction by high-molecular-weight polymeric additives in a shear flow

Grigory Isaakovich Barenblatt

Phys. Fluids 20, 091702 (2008); http://dx.doi.org/10.1063/1.2979711 (4 pages)

Online Publication Date: 18 September 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Drag reduction, or the mean velocity increase in a turbulent flow at a fixed pressure drop through the addition of tiny amounts (several parts per million) of high-molecular-weight polymers (Thoms effect), has been known already for more than 60 years. Long ago it was understood that this effect is related to supramolecular structures formed in the flow. Recent experiments by Chu, Shaqfeh, and associates, where the motion of supramolecular structures was directly observed, made it possible to understand and quantify the dynamic interaction of the polymeric structures with the solvent (water) flow. These results lead to the construction of a mathematical model of the Thoms effect, based on the Kolmogorov (1942)–Prandtl (1945) semiempirical theory of shear flow turbulence. This is the subject of the present letter.
Show PACS
47.27.W- Boundary-free shear flow turbulence
47.50.-d Non-Newtonian fluid flows
47.10.A- Mathematical formulations
47.85.lb Drag reduction
47.57.Ng Polymers and polymer solutions
back to top
RSS Feeds
back to top Interfacial Flows
FREE

Multimode analysis of bubble growth in saturated film boiling

G. Tomar, G. Biswas, A. Sharma, and S. W. J. Welch

Phys. Fluids 20, 092101 (2008); http://dx.doi.org/10.1063/1.2976764 (7 pages) | Cited 3 times

Online Publication Date: 2 September 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The bubble formation sites in film boiling are the nodes of the instability occurring at the liquid-vapor interface. We perform a linear stability analysis with a time dependent base state, accounting for the growth of the film due to evaporation, in order to identify the most dominant wavelength. Choosing a domain size of five times the wavelength predicted by Berenson [ASME J. Heat Transfer 83, 351 (1961) ] and an initial liquid-vapor interface profile having a spectrum of wave numbers, we perform numerical simulations to address the effects of decay and growth of the wave numbers on bubble spacing. Numerical simulations have been performed using a coupled level set and volume of fluid algorithm.
Show PACS
47.55.D- Drops and bubbles
64.70.fh Boiling and bubble dynamics
64.70.F- Liquid-vapor transitions
FREE

Flow and transport in brush-coated capillaries: A molecular dynamics simulation

D. I. Dimitrov, L. I. Klushin, A. Milchev, and K. Binder

Phys. Fluids 20, 092102 (2008); http://dx.doi.org/10.1063/1.2975840 (8 pages) | Cited 8 times

Online Publication Date: 4 September 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We apply an efficient method of forced imbibition to (nano-)capillaries, coated internally with a polymer brush, to derive the change in permeability and suction force, corresponding to different grafting densities and lengths of the polymer chains. While the fluid is modeled by simple point particles interacting with Lennard-Jones forces, the (end-grafted, fully flexible) polymers, which form the brush coating, are described by a standard bead-spring model. Our computer experiments reveal a significant increase in the suction force (by a factor of 4, as compared to the case of a capillary with bare walls) when the brush width approaches the tube radius. A similar growth in the suction force is found when the grafting density of the brush is systematically increased. Even though the permeability of the tube is found to decline with both growing brush width and grafting density, the combined effect on the overall fluid influx into the capillary turns out to be weak, i.e., the total fluid uptake under spontaneous imbibition decreases only moderately. Thus we demonstrate that one may transport the fluid in vertical brush-coated capillaries to a much larger height than in an equivalent capillary with bare walls. Eventually, we also study the spreading of tracer particles transported by the uptaking fluid in brush-coated capillaries with regard to the grafting density of the brush and the length of the polymers. The observed characteristic asymmetric concentration profiles of the tracers and their evolution with elapsed time are interpreted in terms of a drift-diffusion equation with a reflecting boundary that moves with the fluid front. The resulting theoretical density profiles of the tracer particles are found to be in good agreement with those observed in the computer experiment.
Show PACS
47.55.nb Capillary and thermocapillary flows
47.60.Dx Flows in ducts and channels
47.56.+r Flows through porous media
FREE

Quantifying the linear stability of a flowing electrified two-fluid layer in a channel for fast electric times for normal and parallel electric fields

A. Kerem Uguz and N. Aubry

Phys. Fluids 20, 092103 (2008); http://dx.doi.org/10.1063/1.2976137 (10 pages) | Cited 11 times

Online Publication Date: 9 September 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Motivated by the destabilization of a two-fluid layer flowing in a microchannel for efficient mixing or droplet formation, we study quantitatively the linear stability of the interface between two liquids subjected to an electric field parallel or normal to the flat interface. In the case of fast electric charge relaxation times, the equations for the perturbation can be significantly reduced [ A. K. Uguz, O. Ozen, and N. Aubry, Phys. Fluids 20, 031702 (2008) ]. Using a simple argument and without solving the equations, Uguz et al. determined the range of parameters over which the electric field is destabilizing, which is narrower for the parallel compared to the normal electric field. However, the argument of Uguz et al. was not amenable to the calculation of growth rates and neutral stability curves. In this paper, by solving the equations, we not only confirm the previous findings but also determine the quantitative linear stability properties, namely, the growth rates and neutral stability curves. Depending on the value of the physical parameters and when both the normal and parallel electric fields lead to instability, it is found that for the same electric potential gradient either the normal or the parallel electric field leads to the largest maximum growth rate. This result should be of interest for experimental purposes.
Show PACS
47.60.Dx Flows in ducts and channels
47.20.-k Flow instabilities
07.10.Cm Micromechanical devices and systems
FREE

Rupture of radially spreading liquid films

Rajeev Dhiman and Sanjeev Chandra

Phys. Fluids 20, 092104 (2008); http://dx.doi.org/10.1063/1.2978186 (9 pages) | Cited 6 times

Online Publication Date: 10 September 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The rupture of thin water films (thickness of ∼ 100 μm) spreading radially outward on a solid surface was studied experimentally. Circular water films were produced by directing a 1 mm diameter water jet onto a flat horizontal plate for 10 ms. Jet impact velocity was varied from 1.6 to 6.1 m/s, giving Reynolds numbers from 1600 to 6100. Three different plates were used (glass, Plexiglas, and wax) to vary substrate wettability. Both rough and smooth wax surfaces were tested. Water films did not rupture on glass and Plexiglas plates, but holes formed and expanded in films spreading on wax, which had the highest liquid-solid contact angle. Tests in which the spreading film was not supported on a surface, but spread after impact on a pin to simulate a perfectly nonwetting surface, did not show formation of holes. A thermodynamic stability analysis predicted film rupture behavior by showing that films would be stable at very small or very large contact angle but unstable in between. Film rupture was also found to be promoted by increasing surface roughness or decreasing film thickness.
Show PACS
68.15.+e Liquid thin films
47.55.N- Interfacial flows
47.27.Cn Transition to turbulence
47.15.Fe Stability of laminar flows
FREE

Electrokinetic flows over inhomogeneously slipping surfaces

Todd M. Squires

Phys. Fluids 20, 092105 (2008); http://dx.doi.org/10.1063/1.2978954 (10 pages) | Cited 28 times

Online Publication Date: 11 September 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Recent measurements and theory suggest that some solid/liquid surfaces can exhibit slip, at times to a surprising degree. Proposed mechanisms for slip include both intrinsic molecular slip as well as “effective” slip over complex and multiphase interfaces (i.e., covered with “lubricating” nanobubbles or trapped gas pockets). Electrokinetic flow velocities can be significantly enhanced over slipping surfaces as the high shear rates within the double layer drive high slip velocities at the interface. It is not clear, however, that surfaces whose effective slip results from a macroscale average of microscopically inhomogeneous slip will exhibit the same effective slip in an electrokinetically driven system. As well, since the surface charge density is generally set by surface chemistry, one might reasonably expect the ζ potential over “slipping” regions to be different than that over nonslip surfaces. Here, we consider electrokinetic flows over inhomogeneously slipping and inhomogeneously charged surfaces that exhibit a macroscopic effective slip. Using the Lorentz reciprocal theorem for the Stokes flow, we derive general relations for the electrokinetic slip velocity and flow rates over effectively slipping surfaces in the thin double-layer limit. We place particular emphasis on surfaces that consist of discrete slip and no-slip regions, which are meant to model either geometrically rough superhydrophobic surfaces or surfaces with nanobubbles. We derive several surprising results: (i) electro-osmotic flows with uniformly charged (i.e., constant ζ) liquids over an arbitrarily slipping surface are enhanced by precisely the same amount as would be found by naively assuming the (macroscopic) effective slip length to apply homogeneously; (ii) surfaces whose “slip” regions are uncharged (as one might expect should be the case) show no enhancement due to slip, instead giving precisely the same electro-osmotic flow as though the surface were nonslip and homogeneously charged. Our results have clear implications for the practical implementation of electrokinetic effects over effective slip surfaces and give an additional “handle” to probe the properties of surfaces that exhibit effective slip. We briefly discuss the effects of inhomogeneous slip upon electrokinetic pumps, surface conduction, and streaming currents.
Show PACS
47.57.jd Electrokinetic effects
47.65.-d Magnetohydrodynamics and electrohydrodynamics
68.90.+g Other topics in structure, and nonelectronic properties of surfaces and interfaces; thin films and low-dimensional structures (restricted to new topics in section 68)
FREE

Boundary integral simulations of liquid emptying from a model gravure cell

Nazish Hoda and Satish Kumar

Phys. Fluids 20, 092106 (2008); http://dx.doi.org/10.1063/1.2980035 (12 pages) | Cited 5 times

Online Publication Date: 24 September 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We perform boundary integral simulations to understand the removal of Newtonian liquids from a model gravure cell. Two different configurations are considered. In the first configuration, there is a free surface and an outlet boundary, and the liquid is driven out of a cavity by a combination of horizontal substrate motion and an imposed pressure gradient; a similar model was used by Powell et al. [Trans. IChemeE, Part C 78, 61 (2000) ]. The percentage of liquid remaining in the cavity Vr is influenced by the capillary number Ca, cavity depth D, and contact angle θ. We found that Vr decreases with a decrease in Ca or D, consistent with prior studies, and for a shallow enough cavity, almost all of the liquid can be removed. Additionally, Vr decreases with an increase in θ. In the second configuration, there are two free surfaces, and the liquid is driven out of the cavity by moving the substrate both horizontally and vertically. Our simulations suggest that Vr decreases with an increase in the extensional velocity V, and in some cases the entire cavity can be emptied when V is greater than a critical value. The present work sheds light on the roles that surface wettability, cavity size, substrate kinematics, and free-surface dynamics play in surface-tension-driven liquid emptying from tiny cavities.
Show PACS
47.10.A- Mathematical formulations
47.55.nb Capillary and thermocapillary flows
68.08.Bc Wetting
FREE

Chaotic motions of a forced droplet-droplet oscillator

D. M. Slater, C. A. López, A. H. Hirsa, and P. H. Steen

Phys. Fluids 20, 092107 (2008); http://dx.doi.org/10.1063/1.2982372 (8 pages) | Cited 7 times

Online Publication Date: 24 September 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A model for the motion of two coupled spherical-cap droplets subject to periodic forcing is studied. The inviscid unforced model is a conservative second-order system, similar to Duffing’s equation. Surface tension resists the inertia of deformations from the spherical shape. Steady states of the system are parametrized by the total combined volume of the two droplet caps. The family of equilibria exhibits a classical pitchfork bifurcation, where a single lenslike symmetric steady state bifurcates into two dropletlike asymmetric states. The existence of homoclinic orbits in the unforced system suggests the possibility of chaotic dynamics in a forced, damped system. The forced damped extension is investigated for chaotic dynamics using Melnikov’s method and by calculating Lyapunov exponents. Observations are compared qualitatively to experimental results, confirming the existence of chaotic motions.
Show PACS
47.52.+j Chaos in fluid dynamics
47.55.D- Drops and bubbles
47.20.Ky Nonlinearity, bifurcation, and symmetry breaking
68.03.Cd Surface tension and related phenomena
FREE

Selection of the divergence waves on a model viscoelastic coating under a potential flow

V. P. Reutov and G. V. Rybushkina

Phys. Fluids 20, 092108 (2008); http://dx.doi.org/10.1063/1.2982389 (13 pages) | Cited 1 time

Online Publication Date: 24 September 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The paper is concerned with the established regimes of generation of the divergence (quasistatic) waves on a model viscoelastic coating under a potential flow of an incompressible liquid. Parameters of the effective coating that consists of a strongly damped flexible plate supported by an extended spring foundation are evaluated using the condition of modeling the deformation of the viscoelastic layer of a rubberlike material in the available experiments. The local nonlinearity due to the dependence of a stiffness coefficient of the spring foundation on surface displacement is taken into account together with the generalized Karman nonlinearity. The system of equations and boundary conditions of the problem are simplified and reduced to the dimensionless form in the limit of large losses in the plate. The perturbed potential flow is found to be quasistationary. A system of coupled equations describing the resonant and nonresonant (energetic) interactions of multiple harmonics of the surface displacement is derived for weak bending of the surface and small perturbation of flow velocity potential. Conditions for the selection of the period of the established waves are elucidated in this approximation. For the description of large amplitude divergence waves observed experimentally, the numerical procedure is elaborated based on the usage of an orthogonal curvilinear coordinate system following the surface bending. The onset of the essentially nonsinusoidal large amplitude divergence waves and the selection of their period are simulated numerically.
Show PACS
47.50.Cd Modeling
47.20.-k Flow instabilities
47.11.-j Computational methods in fluid dynamics
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
FREE

The influence of gravity on the steady propagation of a semi-infinite bubble into a flexible channel

Andrew L. Hazel and Matthias Heil

Phys. Fluids 20, 092109 (2008); http://dx.doi.org/10.1063/1.2982520 (13 pages) | Cited 3 times

Online Publication Date: 25 September 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Motivated by discrepancies between recent bench-top experiments [ A. Juel and A. Heap, J. Fluid Mech. 572, 287 (2007) ] and numerical simulations [ A. L. Hazel and M. Heil, ASME J. Biomech. Eng. 128, 573 (2006) ] we employ computational methods to examine the effects of transverse gravity on the steady propagation of a semi-infinite, inviscid air finger into a two-dimensional elastic channel filled with a Newtonian fluid. The special case of propagation in a rigid channel is also discussed in Appendix B. The coupled free-surface, fluid-structure-interaction problem is solved numerically using the object-oriented multiphysics finite-element library OOMPH-LIB. In the absence of gravity the relationship between the applied pressure and the propagation speed of the finger is nonmonotonic, with a turning point at small values of the propagation speed. We demonstrate that the turning point disappears when a modest gravitational force is applied and conjecture that it is this effect of gravity rather than any instability of the zero-gravity solution, as postulated in previous studies, that explains why the turning point has never been observed in experiments. At large propagation speeds, the presence of transverse gravity is shown to increase the pressure required to drive the air finger at a given speed, which is consistent with the observed discrepancies between previous zero-gravity simulations and the experimental results. Finally, we briefly discuss the possible implications of our results for the physiological problem of pulmonary airway reopening.
Show PACS
47.55.dd Bubble dynamics
47.35.Bb Gravity waves
47.35.Lf Wave-structure interactions
47.60.Dx Flows in ducts and channels
47.11.Fg Finite element methods
02.70.Dh Finite-element and Galerkin methods
FREE

Evolution of neutral and charged droplets in an electric field

M. A. Fontelos, U. Kindelán, and O. Vantzos

Phys. Fluids 20, 092110 (2008); http://dx.doi.org/10.1063/1.2980030 (12 pages) | Cited 2 times

Online Publication Date: 30 September 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We study the evolution of drops of a very viscous and conducting fluid under the influence of an external electric field. The drops may be neutral or may be charged with some amount of electric charge. If both the external electric field and total drop charge are sufficiently small, then prolate spherical shapes develop according to Taylor’s observations. For sufficiently large charge and/or external field a self-similar conelike singularity develops in a mechanism different from Taylor’s prediction. The opening semiangle of the cones both for uncharged and charged drops in a constant electric field is typically around 30° with a very slight dependence on the viscosity ratio and independence from both total charge and external field. We also discuss the structure of electric and velocity fields near the tip.
Show PACS
47.55.df Breakup and coalescence
47.65.-d Magnetohydrodynamics and electrohydrodynamics
47.53.+n Fractals in fluid dynamics
back to top Particulate, Multiphase, and Granular Flows
FREE

History force on an asymmetrically rotating body in Poiseuille flow inducing particle migration across a slit pore

Sukalyan Bhattacharya

Phys. Fluids 20, 093301 (2008); http://dx.doi.org/10.1063/1.2974827 (16 pages) | Cited 3 times

Online Publication Date: 8 September 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Experimental evidence shows that suspended particles preferentially migrate away from confining boundaries due to the effect of a shear flow. In this paper, we consider an asymmetric particle in Poiseuille flow and determine an inertial lift force which can contribute to the particle migration. Under the influence of Poiseuille flow in a slit pore, an arbitrary particle undergoes periodic rotation which is described by Jeffery’s orbit [ G. Jeffery, Proc. R. Soc. London, Ser. A 102, 161 (1922) ]. In the absence of rotational symmetry, a rotating particle produces an unsteady scattered field. The fluid inertia due to the unsteadiness causes an inertial force on the rotating body if the Reynolds number Re and the temporal variation in viscous force on the particle are nonzero. The resulting effect of this force on the particle migration can be significant especially for microfluidic systems, where gravitational contribution is negligible. In this paper, we consider two systems where the Reynolds number is assumed to be small but finite. In the first problem, we analyze the inertial force on a body asymmetrically rotating around its fixed center. In the second case, we focus on a freely suspended heavy particle which is considerably denser than the solvent so that the product of Re and the particle-solvent density ratio is greater than unity. For both systems, the Reynolds number and the temporal variation in viscous force are significant enough to produce a considerable inertial force on the particle. Our results indicate that the mean of this inertial component perpendicular to the boundaries is nonzero and acts in the direction away from the wall. The magnitude of this force is relatively larger near the wall and gradually decays as the particle-wall distance increases. Hence, we conclude that the discussed effect influences the preferential particle migration in conjunction with other factors.
Show PACS
47.60.Dx Flows in ducts and channels
47.56.+r Flows through porous media
47.32.Ef Rotating and swirling flows
FREE

Dynamics of prolate ellipsoidal particles in a turbulent channel flow

P. H. Mortensen, H. I. Andersson, J. J. J. Gillissen, and B. J. Boersma

Phys. Fluids 20, 093302 (2008); http://dx.doi.org/10.1063/1.2975209 (14 pages) | Cited 14 times

Online Publication Date: 9 September 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The dynamical behavior of tiny elongated particles in a directly simulated turbulent flow field is investigated. The ellipsoidal particles are affected both by inertia and hydrodynamic forces and torques. The time evolution of the particle orientation and translational and rotational motions in a statistically steady channel flow is obtained for six different particle classes. The focus is on the influence of particle aspect ratio λ and the particle response time on the particle dynamics, i.e., distribution, orientation, translation, and rotation. Both ellipsoidal and spherical particles tend to accumulate in the viscous sublayer and preferentially concentrate in regions of low-speed fluid velocity. The translational motion is practically unaffected by the aspect ratio, whereas both mean and fluctuating spin components depend crucially on λ. The ellipsoids tend to align themselves with the mean flow direction and this tendency becomes more pronounced in the wall proximity when the lateral tilting of the elongated particles is suppressed.
Show PACS
47.27.N- Wall-bounded shear flow turbulence
47.55.-t Multiphase and stratified flows
47.60.Dx Flows in ducts and channels
47.20.-k Flow instabilities
Page 1 of 3 Pages Next Page | Jump to Page
Close

Google Calendar

ADVERTISEMENT

Go to AIP Home   © AIP Publishing LLC
close