Numerical study of Richtmyer-Meshkov instability of a flat interface driven by perturbed and reflected shock waves

In this paper, the Richtmyer-Meshkov instability of a flat gas interface driven by perturbed and reflected shock waves is numerically investigated. The flat gas interface evolves into a "lambda "-shaped structure with a central N-2 cavity and steps on both sides, due to the impaction of the perturbed shock wave. After the secondary collision of the reflected shock wave from the high-density region to the low-density region, the gas interface first undergoes phase inversion, and the "lambda " interface then evolves into a bubble and spike structure. Three cases of different Atwood numbers, N-2/SF6, N-2/Kr, and N-2/CO2, are studied. The collision time and position of the reflected shock wave and the interface, the induced spikes, bubbles and gas mixing, are compared in detail. The formation of the spike and bubble is related to the RM instability developed by the collision of the reflected shock wave and the perturbed interface, in which the effect of baroclinic vorticity is highlighted. With the increase in the Atwood number, the density gradient and the baroclinic vorticity become larger, which induces more vortex along the interface. Kelvin Helmholtz unstable vortices are generated on the "legs " of the spikes due to shearing. The main spike structure is stretched and broken with the effect of the vortex, forming a turbulent mixing zone.