Specific features of Richtmyer?Meshkov instability growth with 2D and 3D initial perturbation geometry

This paper addresses features of hydrodynamic instability growth on shock arrival at a free surface of condensed matter with deterministic initial perturbations. Richtmyer–Meshkov instability growth processes with initial two-dimensional (2D) and 3D perturbations are considered. Experimental diagnostics included pulsed radiography and a two-piston shock-tube technique. It is shown experimentally that the growth of perturbations strongly depends on material compression in the shock tube. In the hydrodynamic approximation, when the shock Mach number is M>1, the growth rate of initial 2D and 3D perturbations is the same. Under weak shock compression conditions (M~1), it may happen that initial 3D perturbations will not grow at all. Our results conflict with theoretical concepts of perturbation growth associated with Richtmyer–Meshkov instability, according to which the growth rate of initial 3D perturbations at the nonlinear stage should always be higher than the growth rate of 2D perturbations for the same a/λ ratios. A computational physics model of the process of interest was developed based on LEGAK simulations.