Multi-mode compressible Rayleigh-Taylor instability under strong isothermal background stratification

This study explores the compressibility effects of the background isothermal stratification strength on multi-mode two-dimensional Rayleigh–Taylor instability (RTI) using fully compressible multi-species direct numerical simulations. Cases with three different isothermal Mach numbers are investigated to explore weakly, moderately, and strongly stratified compressible RTI at an Atwood number of 0.04. Unlike incompressible RTI, an increase in the flow compressibility through the background stratification strength can suppress the RTI growth and can lead to a saturation of the RTI mixing layer growth with highly molecularly mixed fluids. Our findings show that even at the chosen relatively low Atwood number, variable-density effects can be significantly increased with the background stratification strength for the compressible RTI, especially different spatial profiles become more asymmetric across the mixing layer for the strongly stratified case. Furthermore, the chaotic behavior of the cases is studied with the transport of the turbulent kinetic energy and the vortex dynamics.