Decay of velocity fluctuations in a stably stratified suspension

The evolution of velocity fluctuations in a stably stratified suspension se ttling under the influence of gravity is studied. Based on a continuum mode l for sedimentation dynamics, decay of long-wave fluctuations in the partic le density is found. Substantial reduction in velocity fluctuations is an i mportant consequence. Specifically, the evolution of the particle density i n a stably stratified suspension immediately leads to particle distribution s, where the variance in the velocity is bounded as the container size grow s to infinity. This result is a possible explanation for why velocity fluct uations have been observed to depend on container size in numerical simulat ions but generally not in physical experiments. (C) 2000 American Institute of Physics. [S1070-6631(00)03006-3].