Non-equilibrium thermo-hydrodynamic effects on the Rayleigh-Taylor instability in compressible flows

A discrete Boltzmann model (DBM) is developed to investigate the Rayleigh-Taylor instability (RTI) in compressible flows. Compressibility effects are investigated by inspecting the interplay between thermodynamic and hydrodynamic non-equilibrium manifestations (TNE, HNE, respectively) and their impact on the dynamics of the bubble and the spike at the interface between the heavy and the light fluid. To this purpose, two effective approaches are presented, one tracking the \emph{local} TNE manifestations and the other focussing on the mean temperature of the flow. Both compressibility effect and the \emph{global} TNE intensity show different trends in the initial and the later stages of the instability. Compressibility is found to retard the initial stage of the RTI and accelerate the later one. It is also found that TNE effects are generally enhanced by compressibility, especially in the later stage of the instability.