Implicit Large Eddy Simulation of high-speed non-reacting and reacting air/H2 jets with a 5th order WENO scheme

This work reports the results of Large Eddy Simulation based on a dissipative 5th order finite-difference WENO scheme, with explicit subgrid model (LES) and without (ILES), in the specific case of multi-component high speed free shear flows. Transonic non-reacting and supersonic reacting H2 jets in coflowing air, typical of scramjet engines, are chosen to be the flow prototypes for this study. Numerical simulations are performed at resolutions ranging from 32×32×128 to 256×256×1024. Explicit subgrid models are the Smagorinsky and the Selective Structure Function models, associated to molecular diffusion. Implicit LES are performed with and without molecular diffusion, by solving either the Navier–Stokes or the Euler equations. In the non-reacting case, the Smagorinsky model is too dissipative, even with a low value of the constant, Cs=0.1. The Selective Structure Function leads to better results, but does not show any superiority compared to ILES, whatever the grid resolution. In the reacting case, a molecular viscous cut-off in the simulation is mandatory to set a physical width for the reaction zone in the ILES Euler, hence to achieve grid-convergence.