Atwood number effects on the isothermally stratified compressible Rayleigh-Taylor instability

The coupled effects of the variable-density and background stratification strength on the growth of the fully compressible 2D single-mode two-fluids Rayleigh-Taylor instability (RTI) are examined using direct numerical simulations (DNS) with varying Atwood and background isothermal Mach numbers. Compared to small Mach number (weakly stratified) case, at larger Mach number (strongly stratified) cases, we observe more asymmetric growth rates between the bubble side, regions with light fluid penetrating into heavy fluid, and spike side, regions with heavy fluid penetrating to the light fluid, for increasing Atwood number. This finding suggests that the asymmetric growth of the RTI mixing layer is enhanced by the compressibility and variable-density effects become observable at relatively small Atwood number under strong background stratification. We also analyze the combined Atwood and Mach number effects on the vortical dynamics and mixing of 2D compressible RTI.