Experimental study of initial condition dependence on turbulent mixing in shock-accelerated Richtmyer–Meshkov fluid layers

Abstract

Experimental evidence is needed to verify the hypothesis that the memory of initial conditions is retained at late times in variable density flows. If true, this presents an opportunity to “design” and “control” late-time turbulence, with an improved understanding in the prediction of inertial confinement fusion and other general fluid mixing processes. In this communication, an experimental and theoretical study on the effects of initial condition parameters, namely, the amplitude δ₀ and wavenumber κ₀ , where λ₀ is the initial wavelength) of perturbations, on late-time turbulence and mixing in shock-driven Richtmyer–Meshkov (R-M) unstable fluid layers in a 2D plane is presented. Single and multi-mode membrane-free initial conditions in the form of a gas curtain having a light-heavy-light configuration (air-SF₆-air) with an Atwood number of A= 0.57 were used in our experiments. A planar shock wave with a shock Mach number M= 1.21 drives the R-M instability, and the evolution of this instability after incident shock is captured using high resolution simultaneous planar laser induced fluorescence (PLIF) and particle image velocimetry (PIV) diagnostics. Time evolution of statistics such as amplitude of the mixing layer, 2D turbulent kinetic energy, Reynolds number, rms of velocity fluctuations, probability density functions, and density-specific volume correlation were observed to quantify the amount of mixing and understand the nature of turbulence in this flow. Based on these results, it was found that the R-M mixing layer is asymmetric and non-Boussinesq. There is a correlation between initial condition parameters and large-scale, and small-scale mixing at late times, indicating an initial condition dependence on R-M mixing.

Keywords:

• initial conditions
• Richtmyer–Meshkov instability
• turbulent mixing

Acknowledgments

[Acknowledgements] This research work was supported by Los Alamos Laboratory Directed Research & Development program through Directed Research (LDRD-DR) on “Turbulence by Design,” research project number 20090058DR. The authors would like to acknowledge the help rendered by a former member of our team, Dr B.J. Balakumar, with data analysis and valuable discussions. We also thank our collaborators F.F. Grinstein, A.A. Gowardhan, J.R. Ristorcelli, M.J. Andrews, R.A. Gore, and D. Livescu for useful insights and discussions toward this research.