Experiments and Direct Simulations of Fluid Particle Motions (original) (raw)

This paper and the accompanying video segment show how the motions of sedimenting particles may be simulated by direct computations based on the Navier-Stokes equations and the particles equations of motion. Sedimenting and fluidized particles are confined by closely spaced walls to move essentially in two dimensions under forces determined by three-dimensional motions of the fluidizing liquids. Attention is confined to the case when there are only few particles, not more than four. The experiments and simulations give rise to deterministic dynamics, to equilibrium positions and steady flows, to Hopf bifurcation and wavy fall trajectories and to more chaotic motions. It is shown that long bodies always turn to put their broadside perpendicular to the stream. The same mechanism which causes long bodies to turn broadside-on causes spherical bodies, which come into contact by wake interactions, to tumble, giving rise to a flow induced anisotropy in which across stream arrangements are favored. The numerical simulation, unlike the experiments, is strictly two-dimensional, but many of the observed features of the experiments are predicted by the simulation. The video segment on which this paper is based is a stand alone document. The paper gives additional information which is not conveniently expressed in a video format.