Effect of a diffuse interface on the Richtmyer-Meshkov instability

The Richtmyer-Meshkov (RM) instability occurs when a shock wave interacts with a perturbed material interface separating two fluids of different densities, and is important in inertial confinement fusion (ICF) because of the material mixing it may lead to. ICF capsules are often subjected to material preheating causing the separating interface to expand and become a finite diffusion layer before shock arrival. In this work, we numerically investigate the role of the size of the initial diffusion layer on perturbation growth and fluid mixing in a simplified planar geometry. We simulate the interaction between a shock (shock Mach number Ms = 1.21) and a single-mode perturbation (wavelength λ ≈ 6 cm, amplitude a0 ≈ 0.2 cm) imposed on an air/SF6 diffuse interface. The size of the initial diffusion layer δ is varied by controlling the ratio 0.1 ≤ δ/λ ≤ 0.5. We quantify its effect on the flow dynamics by investigating the interface morphology, vorticity distribution, mixing layer width, and interface length. To understand its effect on late-time fluid mixing, we subject the interface to reshock and use a mix model to obtain turbulence quantities such as the turbulent kinetic energy and Reynolds stresses.

This work was supported by the U.S. Department of Energy through the Los Alamos National Laboratory. Los Alamos National Laboratory is operated by Triad National Security, LLC, for the National Nuclear Security Administration of U.S. Department of Energy (Contract No. 89233218CNA000001).