Velocity correlations and diffusion during sedimentation - art. no. 061505

We study the dynamics of sedimenting non-Brownian particles under steady-st ate conditions in two-dimensional geometry. We concentrate on the autocorre lation functions of the velocity fluctuations and the corresponding memory functions and diffusion coefficients as functions of Phi (v) for small but finite Reynolds numbers. For the numerical simulations we have chosen the m odel of Schwarzer [Phys. Rev. E 52, 6461 (1995)] where a continuum liquid p hase is coupled through Stokesian friction to a discrete particle phase wit h volume fraction Phi (v). We find that the steady-state velocity fluctuati ons are spatially highly anisotropic and the correlation functions parallel to gravity have nonexponential time dependence similar to that of purely d issipative systems with strong interactions. The corresponding memory funct ions also show nontrivial behavior. Diffusion along the direction of gravit y is much faster than perpendicular to it, with the anisotropy decreasing a s either the Reynolds number or the volume fraction increases.