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May 2009

Volume 21, Issue 5, Articles (05xxxx)

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Phys. Fluids 21, 056602 (2009); http://dx.doi.org/10.1063/1.3140002 (10 pages)

R. D. Wordsworth
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back to top Particulate, Multiphase, and Granular Flows

Peristaltic particle transport using the lattice Boltzmann method

Kevin Connington, Qinjun Kang, Hari Viswanathan, Amr Abdel-Fattah, and Shiyi Chen

Phys. Fluids 21, 053301 (2009); http://dx.doi.org/10.1063/1.3111782 (16 pages) | Cited 10 times

Online Publication Date: 6 May 2009

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Peristaltic transport refers to a class of internal fluid flows where the periodic deformation of flexible containing walls elicits a non-negligible fluid motion. It is a mechanism used to transport fluid and immersed solid particles in a tube or channel when it is ineffective or impossible to impose a favorable pressure gradient or desirous to avoid contact between the transported mixture and mechanical moving parts. Peristaltic transport occurs in many physiological situations and has myriad industrial applications. We focus our study on the peristaltic transport of a macroscopic particle in a two-dimensional channel using the lattice Boltzmann method. We systematically investigate the effect of variation of the relevant dimensionless parameters of the system on the particle transport. We find, among other results, a case where an increase in Reynolds number can actually lead to a slight increase in particle transport, and a case where, as the wall deformation increases, the motion of the particle becomes non-negative only. We examine the particle behavior when the system exhibits the peculiar phenomenon of fluid trapping. Under these circumstances, the particle may itself become trapped where it is subsequently transported at the wave speed, which is the maximum possible transport in the absence of a favorable pressure gradient. Finally, we analyze how the particle presence affects stress, pressure, and dissipation in the fluid in hopes of determining preferred working conditions for peristaltic transport of shear-sensitive particles. We find that the levels of shear stress are most hazardous near the throat of the channel. We advise that shear-sensitive particles should be transported under conditions where trapping occurs as the particle is typically situated in a region of innocuous shear stress levels.
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47.60.Dx Flows in ducts and channels
47.57.Gc Granular flow
47.11.Qr Lattice gas

Particle migration and suspension structure in steady and oscillatory plane Poiseuille flow

K. Yapici, R. L. Powell, and R. J. Phillips

Phys. Fluids 21, 053302 (2009); http://dx.doi.org/10.1063/1.3119802 (16 pages) | Cited 11 times

Online Publication Date: 13 May 2009

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A structure-tensor-based model is used to compute the microstructure and velocity field of concentrated suspensions of hard spheres in a fully developed, pressure-driven channel flow. The model is comprised of equations governing conservation of mass and momentum in the bulk suspension, conservation of particles, and conservation of momentum in the particle phase. The equations governing the relation between structure and stress in hard-sphere suspensions were developed previously and were shown to reproduce quantitatively results obtained by Stokesian dynamics simulations of linear shear flows. In nonhomogeneous, pressure-driven flows, the divergence of the particle contribution to the stress is nonzero and acts as a body force that causes particles to migrate across streamlines. Under steady conditions, the model predicts that the resulting migration causes particles to move to the center of the channel, where the concentration approaches the maximum packing for hard-sphere suspensions. In oscillatory flow, the behavior depends strongly on the amplitude of the strain. For oscillations with large strains, the particles migrate to the channel center. However, when the strain is small, the maximum concentration is located either at a position between the channel center and walls or, in the limit of very small strains, at the wall. The migration to the wall induced by small-strain oscillation occurs in conjunction with the suspension microstructure becoming ordered. This behavior agrees qualitatively with experimental observations reported in the literature. However, the predicted rate of migration toward the wall in the simulations is significantly slower than what is observed experimentally.
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47.60.Dx Flows in ducts and channels
47.57.E- Suspensions
47.11.-j Computational methods in fluid dynamics

Dissipative-particle dynamics simulations of flow over a stationary sphere in compliant channels

Harinath Reddy and John Abraham

Phys. Fluids 21, 053303 (2009); http://dx.doi.org/10.1063/1.3134044 (10 pages)

Online Publication Date: 13 May 2009

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Dissipative-particle dynamics (DPD), a particle-based fluid-simulation approach, is employed to simulate isothermal pressure-driven flow across a sphere in compliant cylindrical channels. The sphere is represented by frozen DPD particles, while the surrounding fluid is modeled using simple fluid particles. The channel walls are made up of interconnected finite extensible nonlinear elastic bead-spring chains. The wall particles at the inlet and outlet ends of the channel are frozen so as to hinge the channel. The model is assessed for accuracy by computing the drag coefficient CD in shear flow past a uniform sphere in unbounded flow, and comparing the results with those from correlations in literature. The effect of the aspect ratio λ of the channel, i.e., the ratio of the sphere diameter d to the channel diameter D, on the drag force FD on the sphere is investigated, and it is found that FD decreases as λ decreases toward the values predicted by the correlations as λ approaches zero. The effect of the elasticity of the wall is also studied. It is observed that as the wall becomes more elastic, there is a decrease in FD on the sphere.
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47.60.Dx Flows in ducts and channels
47.50.Cd Modeling
47.11.-j Computational methods in fluid dynamics
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