Isolating the specific contribution of boundary-layer edge chemical nonequilibrium to stagnation-point heating

This study, for the first time, systematically quantifies the specific impact of stagnation point boundary layer (BL) edge nonequilibrium on surface heating for arbitrary BLs by decoupling the problem. Stagnation point heat flux theory is used in conjunction with a quasi-one-dimensional stagnation streamline model, in which the BL edge state is precisely controlled: pressure, enthalpy, and velocity gradient are held constant while chemical composition is varied between the frozen and equilibrium limits. It is found that nonequilibrium at the edge has no effect on heat flux when the wall is super-catalytic, the flow is equilibrated, or the recombination rate is sufficiently fast to maintain the atomic mass fraction at the wall unchanged despite variations at the BL edge. If the Lewis number (Le) is not equal to 1 in these scenarios, edge nonequilibrium may moderately influence the heat flux by up to approximately ±20%, although Le≈1 is likely a good approximation. In contrast, edge nonequilibrium can significantly affect the heat flux if the wall is non-catalytic and chemistry in the BL is slow, regardless of Le. These results contribute significantly to theoretical understanding of high-enthalpy stagnation-point heating and enable clearer interpretation of full-fidelity simulations under various scenarios.