Hypersonic Boundary Layer Transition and Heat Loading

Abstract

Hypersonic boundary layer transition using high-order methods for direct numerical simulations (DNS) is largely unexplored, although a few references exist in the literature. Experimental data in the hypersonic regime are scarce, while almost all existing hypersonic codes have low-order accuracy, which could lead to erroneous results in long-time integration and at high Reynolds numbers. Here, we focus on the transition from laminar to turbulent flow, where the Nusselt number may be five times or higher than the Nusselt number in the turbulent regime. The hypersonic flow regime must be modeled accurately using realistic chemistry to predict heat flux on the surface correctly. In this study, we simulate hypersonic boundary layer transition on a flat plate to compute the thermal and shear stresses on the wall. The domain is initialized with a laminar Blasius solution of compressible boundary layer equations. The transition to turbulence is induced using suction and blowing from a thin strip on the wall. Sponge regions are defined at the inflow and outflow boundaries to eliminate the solution contamination due to the reflections of the boundary conditions. In the spanwise direction, periodic boundary conditions are imposed. The numerical method applied here is a sixth-order compact finite difference in the interior of the domain coupled with a fourth-order Runge-Kutta time-stepping scheme for a structured Cartesian grid using staggered variables. The base finite difference code can perform simulations of non-equilibrium hypersonic flows. The numerical scheme is stabilized using the approximate deconvolution model (ADM) and artificial diffusion coefficients. We investigated the effect of non-equilibrium chemistry on the non-linear instability growth with hypersonic boundary layers. We also quantify thermal loads during the boundary layer laminar to turbulent transition for Mach number 10.