Finger-like patterns in sedimenting water-sand suspensions

The temporal evolution of a water-sand interface driven by gravity is exper imentally investigated. By means of a Fourier analysis of the evolving inte rface the growth rates are determined for the different modes appearing in the developing front. To model the observed behavior we apply the idea of t he Rayleigh-Taylor instability for two stratified fluids. Carrying out a li near stability analysis we calculate the growth rates from the correspondin g dispersion relations for finite and infinite cell sizes and compose those results with the experimental data. Alternatively, the situation of the se dimenting sand can be modeled by a two-dimensional cellular automaton. A qu alitative similarity between that model and the experimental situation is o btained. (C) 2000 Elsevier Science B.V. All rights reserved.