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Dependence of growth patterns and mixing width on initial conditions in Richtmyer–Meshkov unstable fluid layers

A preliminary investigation of the impact of initial modal composition on the mixing of a shocked, membraneless fluid layer is performed. The growth patterns that emerge upon the impulsive acceleration of three different initial conditions (varicose, sinuous and large-wavelength sinuous) by a Mach 1.2 shock wave are investigated using planar laser induced fluorescence (PLIF) in an air–SF6–air fluid layer. Time-series images of the flow evolution in each of these cases indicate the presence of concentrated regions of vorticity, with the intensity and stability of the resulting vortex configurations dictating the post-shock evolution. In the sinuous case, self advection of the nonuniformly spaced vortices generates a pattern of two streamwise separated regions of material concentration after first shock. However, upon reshock, substantial mixing occurs and results in a structure where the separated regions merge to create a density distribution with a single, broad plateau. This profile contrasts with the varicose case, in which the streamwise density profile is characterized by a narrow peak.