Richtmyer-Meshkov instability of a flat interface subjected to a rippled shock wave.

The Richtmyer-Meshkov (RM) instability of a nominally flat interface (N_{2}/SF_{6}) subjected to a rippled shock, as the counterpart of a corrugated interface interacting with a planar shock, is studied experimentally in a vertical shock tube using both schlieren photography and fog visualization diagnostics. The nonplanar incident shock wave is produced by a planar shock diffracting around a rigid cylinder, and the flat interface is created by a membraneless technique. Three different distances η (the ratio of spacing from cylinder to interface over cylinder diameter) are considered. Schlieren images indicate that the nonplanar incident shock can be divided into three different segments separated by two triple points. Fog visualization pictures show the formation of overall "Λ" shaped interface structures and a N_{2} cavity at the center and two interface steps at both sides. With the increase of the dimensionless time, the dimensionless interface amplitude increases as well as the penetration depth of the cavity, and both curves exhibit reasonable collapse for different η numbers. Through equating the preinterface perturbation of the rippled shock with a preshock perturbation of a corrugated interface, the growth rate of this instability is found to be noticeably smaller than that of the standard RM instability.