The bipolar behavior of the Richtmyer-Meshkov instability

A numerical study of the evolution of the multimode planar Richtmyer-Meshkov instability (RMI) in a light-heavy (air-SF 6 , Atwood number A =0.67) configuration involving a Mach number Ma =1.5 shock is carried out. Our results demonstrate that the initial material interface morphology controls the evolution characteristics of RMI (for fixed A , Ma ), and provide a significant basis to develop metrics for transition to turbulence. Depending on initial rms slope of the interface, RMI evolves into linear or nonlinear regimes, with distinctly different flow features and growth rates, turbulence statistics, and material mixing rates. We have called this the bipolar behavior of RMI. Some of our findings are not consistent with heuristic notions of mixing in equilibrium turbulence: more turbulent flow-as measured by spectral bandwidth, can be associated with higher material mixing but, paradoxically, to lower integral measures of turbulent kinetic energy and mixing layer width.