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

Experiments examining the interaction of shock waves with an interface sepa rating two gases of different densities are reported. Flow visualization by the schlieren method and x-ray densitometry reveals that important seconda ry effects are introduced by the experimental apparatus, especially at the walls of the shock tube from shock wave/boundary layer interaction below, a bove, and at the interface itself. These effects can impair the observation of the primary phenomenon under study and can lead to the overall deformat ion of the interface. In particular, the thickness of the viscous boundary layer at the interface is computed using a familiar shock tube turbulent bo undary layer model and the occurrence of bifurcation of reflected waves bel ow and above the interface is successfully predicted based on classical bif urcation arguments. The formation of wall vortical structures at the interf ace is explained in terms of baroclinic vorticity deposition resulting from the interaction of reflected waves with the interface distorted by the bou ndary layer. This mechanism of wall vortex formation can also explain obser ved test gas contamination in reflected shock tunnels when shock wave bifur cation is absent. In general, it is found that most of the side effects of the experimental investigation of the Richtmyer-Meskkov instability can be alleviated by performing experiments in large test sections near atmospheri c initial pressure. (C) 1999 American Institute of Physics; [S1070-6631(99) 01505-6].