Rayleigh-Taylor Instability : Bubble-Spike asymmetry in transitional regime

In Inertial confinement fusion (ICF) applications and astrophysical flows, Rayleigh Taylor instability (RTI) occurs over a wide range of Mach, Reynolds and Knudsen numbers. The objective of the current study is to establish RTI characteristics in the continuum-rarefied transitional regime at different Mach and Reynolds numbers. The Gas Kinetic Scheme is used to perform numerical simulations of RTI in the continuum and transitional regimes. At a given Mach number, decreasing Reynolds number results in increasing Knudsen number. At each Mach number, there exists a critical Reynolds number (Re_cr) below which flow is dominated by diffusive transport characteristic of rarefied flows. In the transitional regime (near

Re_cr), significant bubble-spike asymmetry is observed. It is shown that the spike side is dominated by diffusive transport, whereas the bubble side is advective in nature. The metrics characterizing the advective and diffusive domains in this transitional regime are identified. The results of this study can lead to a more comprehensive understanding of RTI over a wide range of Mach and Knudsen numbers.