An experimental investigation of Richtmyer-Meshkov instability

In this study, the interaction of a shock wave with an interface between two gases is studied experimentally. The basic mechanism for the initial growth of perturbations on the interface is the baroclinic generation of vorticity which results from the misalignment of the pressure gradient in the shock and the density gradient at the interface. The growth of perturbations soon enters into a nonlinear regime with the appearance of bubbles of light fluid rising into heavy fluid and spikes of heavy fluid falling into light fluid. In the nonlinear regime, interaction between various scales and the appearance of other instabilities, such as Kelvin-Helmholtz instability, along the boundaries of the spikes occur, which results in the breakup of the interface. These processes lead to a turbulent mixing zone (TMZ) which grows with time. The main focus of this study is to understand the growth of TMZ with time in a cylindrical geometry with square cross section and for the first time study the effect of area convergence in a conical geometry on its growth rate. The present set of experiments is done in the GALCIT 17 in. shock tube with air and SF₆ as light and heavy gases. The growth of the TMZ is studied in a straight test section for single-mode initial perturbation consisting of two different wavelength and amplitude combinations at incident shock Mach number of M_S = 1.55. The multimode initial perturbation growth at late times is studied in a conical geometry to study the effect of area convergence at incident Mach numbers of M_S = 1.55 and 1.39. The results are compared with the experiments of Vetter [74] which were done in the same shock tube with a straight test section with no area convergence and at the same Mach number.; In the study of the Richtmyer-Meshkov (RM) instability of single-scale perturbations on air/SF₆ interface in a straight test section, the initially sinusoidal interface is formed by a polymeric membrane of thickness 1.5 μm and the flow visualization is done using schlieren imaging technique. The interface thickness is measured visually from the photographs. It is found that the growth rate decreases rapidly with time with a small dependence on the initial wavelength persisting until late times. (Abstract shortened by UMI.)...