Instability of a heavy gas layer induced by a cylindrical convergent shock

Abstract

The instability of a heavy gas layer (SF6 sandwiched by air) induced by a cylindrical convergent shock is studied experimentally and numerically. The heavy gas layer is perturbed sinusoidally on its both interfaces, such that the shocked outer interface belongs to the standard Richtmyer–Meshkov instability (RMI) initiated by the interaction of a uniform shock with a perturbed interface, and the inner one belongs to the nonstandard RMI induced by a rippled shock impacting a perturbed interface. Results show that the development of the outer interface is evidently affected by the outgoing rarefaction wave generated at the inner interface, and such an influence relies on the layer thickness and the phase difference of the two interfaces. The development of the inner interface is insensitive (sensitive) to the layer thickness for in-phase (anti-phase) layers. Particularly, the inner interface of the anti-phase layers presents distinctly different morphologies from the in-phase counterparts at late stages. A theoretical model for the convergent nonstandard RMI is constructed by considering all the significant effects, including baroclinic vorticity, geometric convergence, nonuniform impact of a rippled shock, and the startup process, which reasonably predicts the present experimental and numerical results. The new model is demonstrated to be applicable to RMI induced by a uniform or rippled cylindrical shock.