Effect of initial conditions on transition in Rayleigh-Taylor and Richtmyer-Meshkov instabilities

Rayleigh-Taylor (RT) instability is a type of flow consisting of a layer of heavy fluid over light fluid. Small perturbations along the interface separating the two layers cause the unstable system to begin mixing and eventually break down into turbulence. Richtmyer-Meshkov (RM) instability, while otherwise similar to RT, has the additional complexity of a shockwave disrupting the interface. These two variable-density flow instabilities are relevant to a variety of applications such as climate and combustion. Existing research suggests that the transition process in both RT and RM is strongly influenced by initial conditions. We explore this dependence using direct numerical simulation and implicit large eddy simulation in a variety of natural transition scenarios initialized with different combinations of perturbation modes and amplitudes. For analysis, we consider various quantities of interest including mixing layer height, mixture fraction, vorticity, turbulent length scale, and turbulent kinetic energy of the flow. Specifically, we use these metrics to track the amount of time required for transition to occur and to describe the state of the resulting turbulence. Lastly, we discuss the results of this sensitivity analysis on initial conditions and its importance for understanding variability in instability-driven turbulence.