This problem considers two immiscible fluids, implemented through the Shan-Chen model. The red fluid is initially located in a layer on top of the blue fluid, and feels the action of gravity. As a way of modeling a large density difference between the fluids, the blue fluid is assumed to be unaware of gravity. After some time, a Rayleigh-Taylor instability occurs, and the red fluid penetrates the blue one.

Animation: AVI file / Animated GIF

2D Rayleigh-Taylor instability