Large Eddy Simulation of Transitional and Turbulent Hypersonic Flow

Abstract

Large eddy simulation (LES) of transitional and turbulent hypersonic flow are carried out. We focus on two canonical flow systems: oblique shock impingement on a hypersonic boundary layer and hypersonic compression ramp flow. We employ the gradient based reconstruction method, monotonicity-preserving (MP) limiting, a novel discontinuity sensor, and the Harten-Lax-van Leer-Contact (HLLC) approximate Riemann solver to discretize the inviscid terms of the governing equations with excellent dissipation and dispersion properties. For the viscous terms, we employ a fourth-order alpha-damping scheme to avoid odd-even decoupling. The importance of low dissipation smooth flow numerical methods, sensitive discontinuity detecting, and wall stress modelling is emphasized. The first case undertaken is that of oblique shock impingement caused by a 4 degree deflection on a disturbed Mach 6 laminar boundary layer. The compressible equilibrium ODE wall model is used to reduce computational cost. The present wall modelled LES (WMLES) quantitatively matches previous experiments, direct numerical simulation (DNS), and previous WMLES. The second case carried out is Mach 7.7 transitional flow over a 15 degree compression ramp. The Reynolds number based on the flat plate length of 0.1 m is 4.2e5. The wall model is not used for this case as the flow does not fully transition to turbulence. The present implicit LES (ILES) is shown to quantitatively match previous experiment and DNS, albeit with some discrepancy due to coarse wall-normal grid spacing. The final case examined is a longer 15 degree compression ramp at a higher Reynolds number of 8.6e5. The third case becomes fully turbulent and as such, WMLES is used for this case. While some regions quantitatively match experiment and DNS, the separation bubble is not well captured by the equilibrium assuming wall model, the reattachment location heating is over-predicted, and the coarse grid under-predicts wall heating in the downstream portion of the domain where the flow is fully turbulent.