Development of the Rayleigh-Taylor instability at the boundary of a friable medium layer accelerated by a compressed air flow

Abstract

The results of experiments with a friable medium layer driven by a compressed gas flow are reported. A layer of polypropylene particles was accelerated in a square channel under the action of air pressure. The initial perturbation on the unstable layer boundary had a nearly sinusoidal shape. Since the medium possesses no tensile strength (and exhibits no surface tension), the unbound particles occurring in the protruding front regions (spikes) of the unstable layer boundary fall into the gas. In the depressed front regions (bubbles), the medium probably exhibits a certain densification and the resulting compressive strength hinders the bubble growth in the initial stage of instability development. The gas penetrating into the layer leads to expansion and fluidization of the layer.