Atwood number effects on isothermally stratified compressible single-mode Rayleigh-Taylor instability*

The coupled effects of variable density and background isothermal stratification strength on the growth of the fully compressible single-mode two-fluid Rayleigh–Taylor instability (RTI) is examined using two-dimensional direct numerical simulations (DNS). Varying Atwood numbers and background isothermal Mach numbers are used to differentiate between cases. The Hydrodynamics Adaptive Mesh Refinement Simulator (HAMeRS) is used to solve the fully compressible, multi-species Navier–Stokes equations in the DNS of single-mode RTI cases at low, intermediate, and high Atwood numbers, which are cases under weak, moderate, and strong stratifications. At the low Atwood number, it is observed that the growth of the heavy (spike) and light (bubble) fluid penetration regions remains nearly symmetric, and this growth begins to experience suppression as the stratification strength is increased. At higher Atwood numbers, the asymmetry between the growth rates of the spikes and bubbles becomes evident. As stratification strength increases, the bubbles experience more growth suppression while spikes grow for a longer time and retain more small-scale vortical structures. These findings suggest that the asymmetry in the growth of the RT unstable interface and the vortical dynamics are highly related to the coupled effects of Atwood and isothermal Mach numbers.