Transpiration Cooled Stagnation Point in Nonequilibrium Hypersonic Flows

Extreme heat loads during flight constrain the design of hypersonic vehicles. Further, certain missions necessitate the use of sharp leading edges, which enhance aerodynamic performance. Sharp leading edges decrease the shock standoff distance, which increases temperature gradient and thus surface heat flux. Additionally, reduced standoff distance introduces non-equilibrium phenomena into the near-surface gas mixture, which may result in high catalytic heating. Transpiration cooling is a method for reducing surface heat loads, preventing oxidative damage, and maintaining leading-edge geometry during flight, while also providing reusability. This paper investigates the application of transpiration cooling to stagnation points in hypersonic flight, across a wide parameter space. Results are generated from a stagnation line solver, applying Park two-temperature nonequilibrium thermochemistry and rigorous multicomponent evaluations for transport properties. This study explores a range of freestream altitudes and velocities, leading-edge radii, injectants, and surface properties. Correlations for both heat and mass Stanton numbers are presented and compared to existing correlations. Injectants similar to the shock-layer gas align with correlations established with equilibrium assumptions and mixture definitions for transport properties. However, wall catalycity, wall temperature, and dissimilar injectants modify the cooling behavior. These effects are due to alterations in near-wall mixing that can only be captured with nonequilibrium thermochemistry and multicomponent transport properties.