Experiments on the Richtmyer–Meshkov instability: Wall effects and wave phenomena

Abstract

Experiments examining the interaction of shock waves with an interface separating two gases of different densities are reported. Flow visualization by the schlieren method and x-ray densitometry reveals that important secondary effects are introduced by the experimental apparatus, especially at the walls of the shock tube from shock wave/boundary layer interaction below, above, and at the interface itself. These effects can impair the observation of the primary phenomenon under study and can lead to the overall deformation of the interface. In particular, the thickness of the viscous boundary layer at the interface is computed using a familiar shock tube turbulent boundary layer model and the occurrence of bifurcation of reflected waves below and above the interface is successfully predicted based on classical bifurcation arguments. The formation of wall vortical structures at the interface is explained in terms of baroclinic vorticity deposition resulting from the interaction of reflected waves with the interface distorted by the boundary layer. This mechanism of wall vortex formation can also explain observed test gas contamination in reflected shock tunnels when shock wave bifurcation is absent. In general, it is found that most of the side effects of the experimental investigation of the Richtmyer–Meshkov instability can be alleviated by performing experiments in large test sections near atmospheric initial pressure.