Anomalous migration in simulated oscillatory pressure-driven flow of a concentrated suspension

Simulation by Stokesian dynamics of a suspension of noncolloidal spheres flowing in a monolayer channel under the action of a sinusoidally oscillating axial pressure gradient has been performed. The migration behavior is markedly different from the case of a unidirectional pressure-driven flow, where migration is to the centerline. For a range of the characteristic strain undergone by the suspension in a flow half-cycle, denoted S and defined as the mean axial distance traveled by the suspension divided by the channel half-width, particles are found to migrate away from the flow centerline. Strains of 0.1 <S <1.5 are found to yield migration toward the walls for phi (A,bulk)=0.4 and the two ratios of channel width (H) to particle radius (a) studied here, H/a=18.3 and H/a=30.5. A particle is found to interact with the same near neighbors throughout the flow when the migration is toward the walls. (C) 2001 American Institute of Physics.