High-amplitude effect on single-mode Richtmyer–Meshkov instability of a light–heavy interface

Abstract

The high-amplitude effect on the Richtmyer–Meshkov instability flow characteristics is investigated by examining the interaction of a planar shock with a single-mode air–SF6 interface both experimentally and numerically. In our experiments, the soap–film technique is adopted to generate well-defined initial interfaces, and the shocked flows are recorded by high-speed schlieren photography. Numerical simulations are performed to highlight the effects of wave patterns on interface movements at the early stage. For cases with high initial amplitudes, a cavity is formed at each spike tip. The cavity formation is ascribed to the vorticity deposition on the slip lines resulting from the Mach reflection of the transmitted shock wave. A series of transverse shocks introduce the secondary compression effect, which changes the interface morphology and causes the failure of the impulsive model in predicting the amplitude linear growth rate. Those modified linear models considering a reduction factor are also found incapable of accurately predicting the linear growth rate. Moreover, a non-monotone dependence of linear growth rate on initial amplitude is observed. Although similar observations were reported in previous numerical simulations, they have never been reported in experiments before. According to the pressure and velocity distributions, the effects of shock–shock interaction on the movements of the interface peak and trough are demonstrated, and the mechanism of non-monotone dependence is discussed. The validity of the existing nonlinear model proposed for predicting the development of a single-mode interface is further tested. It is shown that the applicability of the model worsens as the initial amplitude or dimensionless time increases.