Vorticity generation and evolution in shock-accelerated density-stratified interfaces

The results of direct numerical simulations of inviscid planar shock-accelerated density-stratified interfaces in two dimensions are presented and compared with shock tube experiments of Haas [(private communication, 1988)] and Sturtevant [in Shock Tubes and Waves, edited by H. Gronig (VCH, Berlin, 1987), p. 89]. Heavy-to-light ("slow/fast or s/f) and light-to-heavy ("fast/slow," or f/s) gas interfaces are examined and early-time impulsive vorticity deposition and the evolution of coherent vortex structures are emphasized and quantified. The present second-order Godunov scheme yields excellent agreement with shock-polar analyses at early time. A more physical vortex interpretation explains the commonly used (i.e., linear paradigm) designations of "unstable" and "stable" for the f/s and s/f interfaces, respectively. The later time events are Rayleigh-Taylor-like and can be described in terms of the evolution of a vortex layer (large-scale translation and rotation): asymmetric tip vortex "roll-up" and "binding;" layer "instability;" convective mixing; and baroclinic vorticity generation from secondary shock-interface interactions.