Experimental observations of the mixing transition in a shock-accelerated gas curtain

Richtmyer–Meshkov instability of a thin curtain of heavy gas (SF6) embedded in air and accelerated by a planar shock wave (Mach 1.2) leads to the growth of interfacial perturbations in the curtain and to mixing. Our experiments produce a phenomenological description of the mixing transition and incipient turbulence during the first millisecond after the shock interaction. Growth of scales both larger and smaller than that of initial perturbations is visually observed and quantified by applying a wavelet transform to laser-sheet images of the evolving gas curtain. Histogram and wavelet analyses show an abrupt mixing transition for a multimode initial perturbation that is not apparent for single-mode perturbations.