Initial conditions and modeling for simulations of shock driven turbulent material mixing

Abstract

Abstract We focus on the simulation of shock-driven material mixing driven by flow instabilities and initial conditions (IC). Beyond complex multi-scale resolution issues of shocks and variable density turbulence, me must address the equally difficult problem of predicting flow transition promoted by energy deposited at the material interfacial layer during the shock interface interactions. Transition involves unsteady large-scale coherent-structure dynamics capturable by a large eddy simulation (LES) strategy, but not by an unsteady Reynolds-Averaged Navier–Stokes (URANS) approach based on developed equilibrium turbulence assumptions and single-point-closure modeling. On the engineering end of computations, such URANS with reduced 1D/2D dimensionality and coarser grids, tend to be preferred for faster turnaround in full-scale configurations. With suitable initialization around each transition – e.g., reshock, URANS can be used to simulate the subsequent near-equilibrium weakly turbulent flow. We demonstrate 3D state-of-the-art URANS performance in one such flow regime, in the context of a sequential LES/URANS hybrid simulation strategy. We first simulate canonical shock-tube (AWE and CEA) experiments with an implicit LES (ILES) strategy. We report new validation studies benchmarking ILES with the available turbulence velocity and mixing data from the CEA laboratory studies. In turn, the ILES generated flow data is then used to initialize and as reference to assess the 3D URANS. We find that by prescribing (ILES generated) physics-based 3D IC and allowing for 3D convection with just enough resolution, the computed dissipation in 3D URANS blends effectively with the modeled dissipation to yield significantly improved statistical predictions.