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Jul 2007

Volume 19, Issue 7, Articles (07xxxx)

Issue Cover Spotlight Figure

Phys. Fluids 19, 076601 (2007); http://dx.doi.org/10.1063/1.2742728 (6 pages)

Chia-Shun Yih

Cover photograph © 1994 Greg Stumpf.

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back to top Laminar Flows

Shear flow over a rotating porous plate subjected to suction or blowing

M. Reza and A. S. Gupta

Phys. Fluids 19, 073601 (2007); http://dx.doi.org/10.1063/1.2749522 (10 pages)

Online Publication Date: 13 July 2007

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An analysis is made of the steady shear flow of an incompressible viscous fluid past a uniformly rotating infinite porous flat plate subjected to uniform suction or blowing. Inside the boundary layer, the pressure gradient dominates the momentum transfer of the outer shear flow. Therefore, the shear-induced component of the free-stream shear flow inside the boundary layer is less than its inviscid value. This results in flow reversal in the absence of suction. It is observed that the zone of reverse flow becomes smaller and smaller with an increase in suction, and when the suction parameter exceeds a certain critical value, no reverse flow occurs at all. The axial velocity toward the plate increases with an increase in suction but decreases with an increase in blowing. It turns out that a torque is exerted in a direction opposite to the direction of rotation of the plate, and the magnitude of the torque is an increasing function of suction. Further, this torque is not influenced by the shear in the external flow. The drag on the plate in the direction of free stream shear flow is always positive when the suction at the plate exceeds a certain critical value. However, in the case of blowing at the plate, this drag may be opposite to the direction of external flow for sufficiently high shear.
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47.32.Ef Rotating and swirling flows
47.56.+r Flows through porous media
47.20.Ft Instability of shear flows (e.g., Kelvin-Helmholtz)

Shear-induced diffusion in dilute suspensions of spherical or nonspherical particles: Effects of irreversibility and symmetry breaking

Mauricio Lopez and Michael D. Graham

Phys. Fluids 19, 073602 (2007); http://dx.doi.org/10.1063/1.2750525 (10 pages) | Cited 5 times

Online Publication Date: 17 July 2007

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Using Stokesian dynamics simulations, the shear-induced diffusivities due to pair collisions of identical spherical or nonspherical particles are considered, with the purpose to evaluate the effects of irreversibility and symmetry breaking. Results are compared to an approximate upper bound found by assuming that the particles leave the collision at their maximum separation. For spherical particles, the effects of surface roughness and a short-range repulsive force are considered. For nonspherical particles, a short-range repulsive force is used and effects of shape are considered. In general, it is found that at small repulsion (range of repulsive force, rc, equal to 10−6 the particle radius R), the shape of the particle has a large impact on the shear-induced diffusivity, so particles with broken symmetry have diffusivities that are up to five orders of magnitude larger than those of spheres. At high repulsion (rc = 10−1R), however, the effect on the particle shape on the diffusivity is not as strong and all particles have diffusivities with the same order of magnitude.
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47.57.eb Diffusion and aggregation
82.70.Kj Emulsions and suspensions
47.55.-t Multiphase and stratified flows
47.11.-j Computational methods in fluid dynamics
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