Dynamic Subgrid-Scale Modeling of Turbulent Reacting Hypersonic Flow in Chemical Non-equilibrium

Hypersonic flight vehicles are subject to significant aerodynamic heating due to the presence of several hydrodynamic phenomena, including the formation of leading-edge shock waves, viscous dissipation in compressible boundary layers, shock-interference heating, and shock-boundary layer interactions. The dissipation of bulk kinetic energy in high-Mach shock and boundary layers gives rise to a number of finite-rate thermochemical processes, including not only internal-energy excitation but also the activation of dissociation/recombination processes and nitric-oxide production via the Zel'dovich mechanism. With breakdown to turbulence enhancing radical-species mixing, the presence of small-scale thermodynamic fluctuations also modulates the effective rates of the reactive processes themselves. To enable predictive coarse-grained numerical simulations of turbulent reacting hypersonic flows, here we present novel subgrid-scale closure models for both species diffusion and turbulence-chemistry interaction. In particular, subgrid species transport is modeled with a generalized eddy diffusivity model, while the subgrid chemical production rates are closed with a multi-coefficient dynamic procedure leveraging Morkovin's hypothesis and the scale invariance of the thermodynamic fluctuations. Analysis of the closure models' performance is provided via comparison of a-posteriori wall-resolved large-eddy simulations with high-fidelity direct numerical simulation of a high-enthalpy Mach-7 turbulent hypersonic boundary layer undergoing significant dissociation/recombination activity.