On the Aspects of a Convergent Shock Wave Impinging a Perturbed Density Interface

The detailed characterization of a fluid flow following a convergent shock wave impinging a perturbed density interface is an extremely complex task as this flow combines geometry effects, compressibility effects and turbulence. Nonetheless, more understanding is necessary to be able to develop models that help accurately predict the flow behavior when occurring in engineering applications. Such an application is Inertial Confinement Fusion (ICF), where turbulent mixing induced by the interaction of the shock wave with the fuel pellet is detrimental to the fusion process. This interaction triggers mixing due to baroclinic vorticity deposition at the density interface in a phenomenon known as the Richtmyer-Meshkov Instability (RM). Next, the Rayleigh-Taylor Instability (RT) is driving the final growth of the mixing layer limited by secondary instabilities such as the Kelvin-Helmholtz Instability (KH). These classical hydrodynamic instabilities (HI) trigger the mixing process that leads ultimately to a highly-mixed fluid layer. For this study, we simulate a cylindrical Sulfur hexafluoride (SF₆) target immersed into an air medium. The incident shock wave is regarded as a Chisnell-type converging shock wave impinging into a perturbed cylindrical density discontinuity generated with a wave-like spatial perturbation spectra. Parameters of interest are the growth rate and width of the mixing layer at the density discontinuity. This study aims at describing and quantifying relevant aspects of these flows coupling mixing layer growth with perturbation modes.