Scale-to-scale energy transfer in rarefaction-driven Rayleigh-Taylor instability-induced transitional mixing

The rarefaction-driven Rayleigh-Taylor instability-induced mixing flow is numerically investigated via large eddy simulation. Prior analyses of interfacial diffusion are conducted to clarify the scale-to-scale transfer of kinetic energy during the laminar-to-turbulent transition. The statistical characteristics, including subgrid-scale (SGS) turbulent kinetic energy and SGS stresses, are outlined and highlight the mechanical production as well as pressure-related effects. Further inspection reveals that the relative intensity of SGS backscatter is somewhat noticeable, particularly for the transition onset, and the large-scale pressure-dilatation work is regulated through volumetric compression and expansion. Joint probability density function and the conditional averaging approaches both manifest that SGS backscatter is extremely associated with properties of the surrounding flow expansion induced by quadrupolar vortex structures. Furthermore, investigations on the effects of SGS backscatter on eddy viscosity are performed, and a regime classification, illustrating the relationship between various energy conversion modes and signs of the eddy viscosity, is provided. It is found that there is a significantly strong correlation between SGS backscatter and negative eddy viscosity; meanwhile, the volumetric compression and expansion tend to modulate the scale-to-scale energy transfer throughout the transitional process.