Coupled Effects of Iso-thermal Stratification Strength and Atwood Number on 2D Single-Mode Compressible Rayleigh-Taylor Instability

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The coupled effects of the variable-density and background stratification strength on the growth of the fully compressible single-mode two-fluids Rayleigh-Taylor instability (RTI) are examined using direct numerical simulations (DNS) with varying Atwood and background isothermal Mach number values. The Hydrodynamics Adaptive Mesh Refinement Simulator (HAMeRS) framework with adaptive mesh refinement is utilized to solve the fully compressible Navier--Stokes equations with low and intermediate Atwood numbers (A = 0.04 and A = 0.25) for the weakly, moderately, and strongly stratified cases with a single-mode initial perturbation. At the low Atwood number, similar to the previous studies, it is observed that the growth of the interface slows down and is even suppressed with stronger background stratification, and the light fluid penetration remains similar (symmetrical) to the heavy fluid penetration with different iso-thermal stratification strengths. However, at the intermediate Atwood number, the interface growth is more persistent for the moderate background stratification case compared to the case with a low Atwood number. In addition, an increase in the background stratification strength eliminates the vortical structures on the bubble side where light fluid penetrates into the heavy fluid, whereas the effects are weaker on the spike side where the heavy fluid penetrates into the light fluid. Hence, even with the intermediate Atwood number, A = 0.25, the time evolution of the bubble and spike become highly asymmetric under certain strength of background stratification.