Experiments of gravitational instabilities at particle suspension-fluid interface

Experiments are conducted to understand the gravitational instabilities that occur at the interface of an overlying suspension of granular particles and a clear fluid, utilizing a sealed Hele–Shaw cell. Attention is paid to the influences of particle Reynolds number and particle packing on the growth of the interfacial disturbances. At the intersection of the fluid and densely packed particles, perturbations take on an asymmetrical cusp-like structure. In contrast, at the interface where the fluid meets loosely packed particles, the perturbations initially form a symmetrical, sinusoidal pattern, similar to the typical Rayleigh–Taylor instability. The growth rate of both types of instabilities is found to increase with the particle Reynolds number. Notably, symmetrical perturbations grow faster than their asymmetrical counterparts at equivalent Reynolds numbers. The experimental data are also viewed through the lens of linear stability analysis for single-phase fluids to test the latter's applicability to the two-phase problem.