Effect of adiabatic index on Richtmyer-Meshkov flows induced by strong shocks

Richtmyer-Meshkov Instability is an instability that develops at the interface between fluids of distinct acoustic impedance when impacted by a shock wave. Its applications include inertial confinement fusion, supernovae explosions, and the evolution of blast waves. We systematically study the effect of the adiabatic index of the fluids on the dynamics of strong-shock-driven flows, particularly the amount of shock energy available for interfacial mixing. Only limited information is currently available about the dynamic properties of matter at these extreme regimes. We employ smooth particle hydrodynamics simulations to ensure accurate shock capturing and interface tracking. A range of adiabatic indexes is considered, approaching limits which, to the best of the author's knowledge, have never been considered before. We analyze the effect of the adiabatic indexes on the interface speed and growth rate immediately after the shock passage. The simulation results are compared wherever possible with rigorous theories, achieving good quantitative and qualitative agreement. We find that the more challenging cases for simulations arise where the adiabatic indexes are further apart, and that the initial growth rate is a non-monotone function of the initial perturbation amplitude, which holds across all adiabatic indexes of the fluids considered. The applications of these findings on experiment design are discussed.