Sedimentation instability : A numerical and experimental study

Abstract

In this thesis the dynamics of the granular Rayleigh-Taylor is studied in a rectangular Hele-Shaw cell. The affect of the interstitial fluid properties on the mixing of the grains is studied in experiments and well matched simulations. The numerical model was modified to account for fluid compressibility fluid inertia and viscous forces which lead to a hydrodynamic particle-particle coupling and a coupling between the fluid flow and the confining plates. In addition the model also includes solid friction between the particles and the plates. To verify the numerical model and its simplifications it was compared to well matched experiments. This test showed excellent agreement between the numerical model and the experiments. In regard of the mixing the compressibility of the interstitial fluid affects the dynamical patterns and the particle mixing much less than the viscosity. Depending on the viscosity the initial dynamics could be classified into two regimes. For low viscosities a ballistic particle pair separation was measured and for high fluid viscosity turbulent-dispersive particle pair separation was observed. In a further work it will be of interest to study the dependency on system parameters of this transition from the ballistic to the turbulent-dispersive behavior.