Experimental study of initial condition dependence on Richtmyer-Meshkov instability in the presence of reshock

We present an experimental study on the dependence of initial condition parameters, namely, the amplitude delta and wavenumber kappa (kappa = 2 pi/lambda, where lambda is the wavelength) of perturbations, on turbulence and mixing in shock-accelerated Richtmyer-Meshkov (R-M) unstable fluid layers. A single mode, membrane-free varicose heavy gas curtain (air-SF6-air) at a shock Mach number M = 1.2 was used in our experiments. The density (concentration) and velocity fields for this initial configuration were measured using planar laser-induced fluorescence (PLIF) and particle image velocimetry (PIV). In order to understand the effects of multi-mode initial conditions on shock-accelerated mixing, the evolving fluid interface formed during the incident shock (M = 1.2) was shocked again by a reflected shock wave at various times using a movable wall, thus enabling us to change both delta and kappa simultaneously. A dimensionless length-scale defined as eta = kappa delta is proposed to parametrically link the initial condition dependence to late-time mixing. It was observed experimentally that high wavenumber (short wavelength) modes enhance the mixing and transition to turbulence in these flows. Statistics such as power spectral density, density self-correlation, turbulent kinetic energy, and the rms of velocity fluctuations were measured using simultaneous PLIF-PIV to quantify the amount of mixing for varying values of eta. The results indicate a dependence of initial condition parameters on mixing at late times. The results of this study present an opportunity to predict and design late-time turbulent mixing that has applications in inertial confinement fusion and general fluid mixing processes. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3693152]