Simultaneous particle-image velocimetry–planar laser-induced fluorescence measurements of Richtmyer–Meshkov instability growth in a gas curtain with and without reshock

The structure of the concentration and velocity fields in a light-heavy-light fluid layer subjected to an impulsive acceleration by a shock wave (Richtmyer–Meshkov instability) is studied using simultaneous particle-image velocimetry and planar laser-induced fluorescence (PLIF) measurements (performed in such flows for the first time). The initial condition prior to shock impact is accurately characterized using calibrated PLIF measurements to enable comparisons of the evolving structure to numerical simulations. Experiments performed on a SF6 curtain in air (Atwood number, At=0.67), after single shock by a Mach 1.2 shock wave and reshock by the reflected wave, show that the reshock wave has a dramatic impact on the evolution of the unstable structure. After first shock and in the absence of reshock(s), the structure widths agree well with an analytical extension to the nonlinear point vortex model [J. W. Jacobs et al., “Nonlinear growth of the shock-accelerated instability of a thin fluid layer,” J. Fluid Mech. 295, 23 (1995)] that accounts for the nonuniform spacing of the row of counter-rotating vortices that drive the flow. However, upon reshock, the width deviates significantly from the singly shocked case, and a substantial rise in the growth rate is observed. Enhanced mixing, destruction of the ordered velocity field, and an increase in both the positive and negative circulations ensue. Large velocity fluctuations relative to the mean flow, and the advection of a wide spectrum of vortex scales combine to mix the flow well and create turbulent conditions in the reshocked structure.