Investigation of the initial perturbation amplitude for the inclined interface Richtmyer-Meshkov instability

A simulation studying the effects of inclination angle and incident shock Mach number on the inclined interface Richtmyer-Meshkov instability is presented. Interface inclination angle is varied from 30 degrees to 85 degrees, with incident shock Mach numbers of 1.5, 2.0 and 2.5 for an air over SF6 interface. The simulations were performed in support of experiments to be performed in the Texas A&M shock tube facility, and were created with the ARES code developed at Lawrence Livermore National Laboratory. The parametric cases are separated by inclination angle into nonlinear and linear initial perturbation cases. A linear initial perturbation is defined as when the interface amplitude over wavelength is less than 0.1. Density, pressure gradient and vorticity plots are presented for a nonlinear and a linear case to highlight the differences in the flow field evolution. It is shown that the nonlinear case contains strong secondary compressible effects which reverberate through the interface until late times, while in the linear case these waves are almost completely absent. The inclined interface scaling method presented in previous work (McFarland et al 2011 Phys. Rev. E 84 026303) is tested for its ability to scale the mixing width growth rate for linear initial perturbation cases. This model was shown in the previous work to collapse data well for varying Mach numbers and nonlinear inclination angles. The scaled data is presented to show that a regime change occurs in the mixing width growth rate near an inclination angle of 80 degrees which corresponds to the transition from a linear to nonlinear initial perturbation.