Hydrodynamic and Brownian fluctuations in sedimenting suspensions

The interplay between hydrodynamic and Brownian fluctuations during steady-state sedimentation of hard sphere particles for Peclet numbers (Pe) ranging from 0.1-15 was studied using a mesoscopic computer simulation. A stochastic rotation dynamics (SRD) to the problem of sedimenting HS was adapted to perform the simulations. It was shown that the hydrodynamic interactions (HI) induce backflow effects that dominate the reduction of the average sedimentation velocity with increasing particle packing fraction, even when the they were an order of magnitude weaker than Brownian forces. It was observed that the velocity fluctuations begin to show nonequilibrium hydrodynamic character for Pe>1