Theoretical modeling of chemical nonequilibrium stagnation point boundary layer heat transfer under rarefied conditions

This paper theoretically studies the recombination-dominated nonequilibrium reacting flow inside the stagnation point boundary layer (SPBL) and the heat transfer characteristics under rarefied conditions. A general model is intuitively proposed to describe the energy transfer and conversion along the stagnation streamline towards a slightly blunted nose with non-catalytic wall surface. It is found that the atoms recombination effects inside the SPBL could be equivalent to a modification on the degree of dissociation in the external flow. As a result, a recombination nonequilibrium criterion Dar, that is a specific Damköhler number, is introduced to characterize the nonequilibrium degree of the reacting flow in the SPBL, and then, based on the general model and Dar, a bridging function indicating the nonequilibrium chemical effects on the SPBL heat transfer is established. By using the explicitly analytical bridging function, the flow and heat transfer mechanisms, including the real gas flow similarity law and the nonequilibrium flow regimes classification, are discussed. In addition, the direct simulation Monte Carlo (DSMC) method has also been employed to systematically validate the analytical results.