Catalysis and Dissociation Effects on Hypersonic Boundary Layers Structure over Small Defects

Nonequilibrium aerodynamics can significantly impact flow field characteristics and gas-surface interactions, particularly in relation to material ablation for Hypersonic flows. Defects on ablative surfaces pose a significant challenge in Hypersonic flows due to the mixed hyperbolic-elliptic characteristics of the viscous-inviscid interaction. Modeling their effect on separation and catalytic recombination is necessary to improve the understanding of flow-reaction coupling over damaged ablators. This study aims to compare the dissociation effects of air in nonequilibrium on surface geometry with a defect present in representative hypersonic flow field conditions. Both the boundary layer impact and the ablation thermo-chemistry changes are taken into account. An analytical approach based on the Triple Deck Theory (TDT) of boundary layer response to localized defects was used, and the results are compared to numerical methods and schemes modeled in SU2. A custom-configured Carbon-air mixture was created using Mutation++ that includes Catalytic recombination and gas surface interaction models. Results show that separation in high Mach number flows is a complex phenomenon with a single separation region transitioning to multiple bubbles before supporting unsteady breathing. The recirculation significantly affects the transport of atomic species from the dissociation layer to the surface.