An experimental investigation of the turbulent mixing transition in the Richtmyer–Meshkov instability

Abstract

AbstractThe Richtmyer–Meshkov instability (RMI) is experimentally investigated in a vertical shock tube using a broadband initial condition imposed on an interface between a helium–acetone mixture and argon ($A\approx 0.7$). The interface is created without the use of a membrane by first setting up a flat, gravitationally stable stagnation plane, where the gases are injected from the ends of the shock tube and exit through horizontal slots at the interface location. Following this, the interface is perturbed by injecting gas within the plane of the interface. Perturbations form in the lower portion of this layer due to the shear between this injected stream and the surrounding gas. This shear layer serves as a statistically repeatable broadband initial condition to the RMI. The interface is accelerated by either a$M= 1.6 $or$M= 2.2 $planar shock wave, and the development of the ensuing mixing layer is investigated using planar laser-induced fluorescence (PLIF). The PLIF images are processed to reveal the light-gas mole fraction by accounting for laser absorption and laser-steering effects. The images suggest a transition to turbulent mixing occurring during the experiment. An analysis of the mole-fraction distribution confirms this transition, showing the gases begin to homogenize at later times. The scalar variance energy spectra exhibits a near$k^{-5/3}$inertial range, providing further evidence for turbulent mixing. Measurements of the Batchelor and Taylor microscales are made from the mole-fraction images, giving${\sim }150\ \mu \mathrm{m}$and 4 mm, respectively, by the latest times. The ratio of these scales implies an outer-scale Reynolds number of$6\text {--}7\times 10^4$.