Towards species turbulent scaling for chemically-reacting hypersonic boundary layers

Vehicles traveling at hypersonic speeds experience extreme mechanical and thermal loads, that increase significantly as the flow transitions to turbulence. The complexity of experimentally studying these phenomena makes numerical simulations of high speed turbulent flows a crucial part of this endeavor. At high Mach numbers, thermochemical non-equilibrium phenomena are triggered by the high temperatures and chemical dissociations must be taken into account as well (Di Renzo & Urzay 2021, Passiatore et al. 2021). In numerical simulations of high-temperature wall-bounded turbulence, it is necessary to extend the existing knowledge on turbulent scaling to chemically reacting flows. In this work, we use direct numerical simulation results of several flat plate turbulent boundary layers with a simplified dissociation-recombination mechanism in a two-species gas mixture. Different levels of chemical activity are considered by varying the activation energy and reaction rates of the mechanism. First results from laminar boundary layers show the loss of wall-normal monotonicity in species molar fractions when chemical activity becomes intense and history effects are evident in the streamwise evolution of the flow. After transition to turbulence, the effect of wall-normal turbulent mixing on chemical variables is studied and the dependence of turbulent profiles on Damkohler number is assessed.