Numerical study of initial perturbation effects on Richtmyer-Meshkov instability in nonuniform flows

The effects of an initial perturbation on Richtmyer-Meshkov instability are numerically studied by simulating the process of incident shock (Ma=1.27) impacting different groups of initial multimode cosine interfaces formed by different amplitudes in initially nonuniform flows whose density is a Gaussian function. The numerical results indicate that the evolution of the interface with a large initial amplitude in a low-density nonuniform area grows fastest, while that with a small initial amplitude in a high-density nonuniform area grows slowly. Further analysis of vorticity and circulation illustrates these phenomena. The interface with a large initial amplitude in a low-density zone possesses a larger density gradient, which results in a larger amount of vorticity and circulation, leading to the fast-changing evolution of the interface. Distinctive evolution mechanisms of Richtmyer-Meshkov instability between the nonuniform flows and the uniform flows are analyzed in detail.