Thermochemical kinetic model for high altitude and low altitude high-speed flow and radiation prediction based on the State-to-State model

The reasonable thermochemical kinetic model is a key prerequisite for accurately predicting the non-equilibrium flow field and radiation of high-speed atmospheric reentry vehicles. A vibrational and electronic specific State-to-State kinetic model is first established to couple with post-shock flow equations to analyze the thermochemical non-equilibrium flow characteristics. It is found that the vibrational and electronic energy levels non-Boltzmann metric are large at the flight altitude higher than 50 km, which is thus considered a demarcation line for constructing the low- and high-altitude models. Therefore, in this study, two new physics-based thermochemical kinetic models are constructed from the State-to-State model using the multi-group maximum entropy method for low-altitude and high-altitude regions, respectively, across the entire flight velocity domains. By analyzing the differences in post-shock flow physical characteristics under various flight altitudes, single-group and multi-group functions are, respectively, adopted to reconstruct the internal energy levels distributions within the flow field for the low-altitude and high-altitude chemical models. Compared to the State-to-State model, the low-altitude and high-altitude models significantly reduce the number of solved species and chemical reactions, while maintaining computational accuracy of post-shock non-equilibrium flow, with calculated thermodynamic parameters error less than 5% and chemical parameters error below 10%. Finally, the low-altitude and high-altitude chemical models constructed in this study exhibit better predictive capability in reproducing ground experimentally measured electron number density and predicting reentry flight heat flux and radiation compared with the classical Park's and Gupta's models, demonstrating the promising applicability of developed models. This study provides a new, reasonable chemical model for the entire flight altitude and velocity domain that can be used in computational fluid dynamics simulations to predict non-equilibrium flow and radiation in high-speed reentry vehicles.