Numerical study on the influence of chemical kinetic models on high-speed non-equilibrium flow and radiative characteristics

Hypersonic vehicles bear more pronounced aerothermal effects due to the increase in flight altitudes and speed, underscoring the need for accurate chemical kinetic models that reflect realistic physicochemical processes to reliably predict complex flow fields, surface heat, and radiation properties. In this study, a simplified air chemistry model, self-consistently derived from a collisional-radiative model, is applied for the first time to multi-dimensional hypersonic flow simulations. Our model results show good agreement with ground experimental data for shock standoff distance and flight data on wall heat flux. Meanwhile, a comparative analysis is conducted to study the influence of different chemical models on the non-equilibrium characteristics, surface heating, and radiative properties of spherical nose models with varying radii. The results indicate that non-equilibrium effects are most pronounced at a smaller radius. Our model predicts the highest post-shock temperature, lower ionization levels, and notable differences in species composition compared to the Park, Gupta, and Dunn-Kang models. The thermochemical non-equilibrium effect significantly affects radiation mechanisms and spectral characteristics. Our model results suggest that radiation in the shock layer is dominated by molecular band emissions in the ultraviolet (UV) and vacuum ultraviolet (VUV) ranges for a flow with a Mach number of 20 at an altitude of 40 km. The radiation intensity differs considerably from that of other chemical models, highlighting that an appropriate choice of chemical reaction model is crucial for predicting non-equilibrium flow fields and radiation characteristics.