Vortex dynamics of a twice-accelerated interface in an incompressible ideal fluid

We report on a direct numerical simulation (DNS) of the evolution of a two- dimensional sinusoidal density-stratified interface subjected to two sequen tial impulsive accelerations. The concepts and phenomena are immediately ap plicable to the "reshock" problem of the Richtmyer-Meshkov (RM) environment . The computational parameters and geometry are chosen such as to model the experimental results of the incompressible RM instability of Jacobs and Ni ederhaus performed with an impulsively reaccelerated free-falling tank. Our DNS results are in very good agreement with the experiment after the first impulse and in qualitative agreement with the short time evolution after t he second impulse. We explain the phenomena, including the rate of growth o f the interface, in terms of the evolving vortex layers and projected rate- of-strain tensor onto the interfacial vortex layer. In particular, the pres ence of nearby oppositely signed layers of vorticity after the second impul se contributes to the rapid turbulization of the region. The numerical meth od applied is based on the Contour Advection Semi-Lagrangian algorithm modi fied with the vortex-in-cell method for density interfaces in incompressibl e ideal fluids.