2D single-mode Richtmyer–Meshkov instability

We study the evolution of the single-mode Richtmyer–Meshkov instability for a wide range of Atwood numbers, shock strengths and perturbation amplitudes using Youngs’ hydrodynamical simulation code TURMOIL. We compare our results to previously published analytic models for the impulsively-driven growth rate, and propose a modification to them to treat the reduction of growth found at high initial perturbation amplitudes and high Mach numbers. It is known that the overall asymmetry between bubbles and spikes and their eventual deceleration can be interpreted as the result of nonlinear coupling to higher harmonic modes. However, we find that for light-to-heavy interfaces at moderate to high impinging shock Mach numbers, the shape of the growing bubbles varies in time, with the initial curved bubble surfaces flattening and inverting to generate a second low velocity jet. For high shock Mach numbers and low initial surface amplitudes, the process of inversion can recur on numerous occasions. We interpret this as being the result of vorticity deposited by the transmitted shock in the bulk of the heavy material, away from the initial interface.