The transition to turbulence in rarefaction-driven Rayleigh–Taylor mixing: Effects of diffuse interface

Abstract

Effects of interface diffusion on the transition to turbulence in rarefaction-driven flows are numerically investigated via Implicit Large-Eddy simulation. Three-dimensional, multimode perturbations are imposed on the diffuse interface between Air and SF6, with various diffusion layer thicknesses. A non-constant acceleration ranging from 103g0 to 104g0, where g0 is the acceleration due to gravity, is generated by the interaction between the interface and a rarefaction wave. Evolution of first- and second-order statistics, instantaneous flow structures, and the power spectrum of turbulent kinetic energy as well as spatial distributions of energy budget are evaluated, in order to confirm the accuracy and robustness of the mixed mass transition criterion proposed here. Meanwhile, it turns out that transitional behaviors are mainly governed by Reynolds normal stresses in the plane perpendicular to the streamwise direction. Furthermore, as interface diffuses, the decrease in peak values of pressure and advection components dominated in the laminar regimes, particularly at the bubble tips, eventually leads to transition delay.