Richtmyer-Meshkov Flow Simulation: Ensemble-Averaged or Instantaneous Interfaces?

This work investigates the impact of the interface characterization in the simulation of an Air-SF6 Richtmyer-Meshkov (RM) flow. Toward this end, two-dimensional instantaneous and ensemble-averaged density fields defining diffusive interfaces measured experimentally are used as initial condition of high-fidelity RM computations. Three-dimensionality is added through density perturbations of distinct amplitudes and modes. Among others, quantities of interest comprise the density field, mixing layer width and mixedness, kinetic energy, and vorticity production mechanisms. The study demonstrates the critical role of mimicking the initial material interface, especially its instantaneous features. Their replication enables a deeper understanding of the RM flow physics and higher-fidelity simulations. Compared to the case based on the instantaneous initial condition, it is shown that the mixing layer height and mixedness can vary 50% when the initial density field of the interface is ensemble averaged (with or without added perturbations). Such variations are more pronounced for higher-order quantities of interest. In summary, this study clearly highlights the role of the diffusive interface characterization level in predicting and understanding RM material mixing flows.