Effects of container walls on the velocity fluctuations of sedimenting spheres

Simulations describing the settling of suspensions of solid particles bounded by a rigid container are presented. Results are compared with previous simulations of homogeneous suspensions with periodic boundary conditions. Velocity fluctuations in vertically inhomogeneous suspensions are found to saturate under conditions similar to those found in laboratory experiments, while in vertically homogeneous suspensions, with or without side walls, the velocity fluctuations diverge. A mechanism for the establishment of a correlation length in sedimenting suspensions is proposed.