RTI dynamics in various Knudsen - Mach parameter regimes.

Rayleigh-Taylor instability (RTI) is important in a variety of flows, including inertial confinement fusion (ICF). In ICF, RTI is known to occur over a range of Knudsen and Mach numbers. At low Knudsen numbers and high Mach numbers, RTI exhibits canonical growth on both bubble and spike sides. At high Knudsen and low Mach numbers, RTI xhibits diffusive growth on both bubble and spike sides. The objective of this study is to examine the transition from classical to diffusive behavior as Knudsen and Mach numbers are varied. Toward this end, we perform simulations using the Unified Gas Kinetic scheme (UGKS) to investigate RTI dynamics from the continuum regime to highly rarefied regime (Kn ~ 1). The simulation results reveal the various stages of transition from advective instability to diffusive transport. Additionally, the characteristics underlying the transitional advective-diffusive region in between 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 in practically relevant regimes.