Rans and les simulation of a mach 7 axisymmetric flare interaction

Reynolds-averaged Navier-Stokes (RANS) and Hybrid Large-Eddy Simulation / Reynolds-averaged Navier-Stokes (LES/RANS) simulations of a Mach 7.05 flow over an axisymmetric cylinder / flare configuration are reported in this work. A RANS-LES hybridization strategy developed at NCSU is modified to enable wall-resolved LES upstream of the flare apex while shifting to a hybrid closure on the flare surface. RANS predictions using Menter BSL and SST models show significant deviations from experiment, with BSL failing to predict axial separation and SST generally over-predicting the degree of separation. The LES-type methods improve upon these results, predicting the level of upstream influence more correctly for the stronger interactions (30 and 32.5 degree flare angles) while accurately capturing the structure of the flow away from the flare surface for the 20 degree flare angle. The LES strategies under-predict measured heat transfer levels on the flare surfaces for all cases, a possible consequence of insufficient mesh resolution. Analysis of the LES results shows that the Boussinesq hypothesis for the Reynolds shear stress and the gradient-diffusion assumption for the turbulent heat flux do not hold very well in the region of strong shock / boundary layer interaction but improve as the boundary layer reaches more of an equilibrium state. Analysis of extracted turbulent momentum and thermal diffusivities reveals that the turbulent Prandtl number is not constant, reaching sub-unity values through much of the shock / boundary layer interaction region. The shear-stress structure factor is also not constant within the interaction region, rising above its equilibrium level near shock waves.