Microscopic Richtmyer–Meshkov instability under strong shock

Abstract

The microscopic-scale Richtmyer–Meshkov instability (RMI) of a single-mode dense-gas interface is studied by the molecular dynamics approach. Physically realistic evolution processes involving the non-equilibrium effects such as diffusion, dissipation, and thermal conduction are examined for different shock strengths. Different dependence of the perturbation growth on the shock strength is found for the first time. Specifically, the amplitude growths for cases with relatively lower shock Mach numbers (Ma = 1.9, 2.4, 2.9) exhibit an evident discrepancy from a very early stage, whereas for cases with higher Mach numbers (Ma = 4.9, 9.0, 16.0), their amplitude variations with time match quite well during the whole simulation time. Such different behaviors are ascribed to the viscosity effect that plays a crucial role in the microscale RMI. The compressible linear theory of Yang et al. [“Small amplitude theory of Richtmyer–Meshkov instability,” Phys. Fluids 6(5), 1856–1873 (1994)] accounting for the viscosity dissipation provides a reasonable prediction of the simulated linear growth rate. Furthermore, a modified compressible nonlinear model [Q. Zhang et al., “Quantitative theory for the growth rate and amplitude of the compressible Richtmyer–Meshkov instability at all density ratios,” Phys. Rev. Lett. 121, 174502 (2018)] considering both the viscosity effect and the corrected linear growth rate is proposed, which gives an excellent forecast of the linear and nonlinear growths of the present microscale RMI.