Thermochemical nonequilibrium effects on the aero-optics in high-enthalpy flow over a double wedge

This paper aims to analyze the impact of thermochemical nonequilibrium effects on the aero-optics in high-enthalpy multidimensional complex flows. The nitrogen flow is simulated over a 15^∘−48^∘ double wedge with a total enthalpy of 26.1 MJ/kg. High-fidelity state-to-state (StS) model and conventional Park’s two-temperature (2T) model are adopted to characterize thermochemical nonequilibrium. For high-enthalpy conditions, a formulation method for the refractive index of a multi-component gas mixture with vibrational nonequilibrium in Boltzmann or non-Boltzmann distributions of molecules is developed for 2T and StS models, respectively. It is indicated that the distribution trends of refractive index obtained by the two thermochemical models exhibit an overall consistency. However, marked discrepancies in the values of refractive index exist in regions of typical shock structures, which are mainly caused by the differences in the density distributions due to different positions of the shocks. Moreover, the species mass fractions and N₂ polarizability show a certain degree of difference, which has a relatively minor influence on refractive index. The optical distortions exhibit distinct disparities on the aft wedge due to complex shock structures. The specific thermochemical nonequilibrium mechanism inherent in the StS model can lead to considerable discrepancies in the refractive index and optical propagation.