The influence of chemical models on hypersonic nonequilibrium flow field characteristics in numerical simulations

Hypersonic vehicles generate significant thermochemical nonequilibrium phenomena during reentry into the Earth's atmosphere, accompanied by complex physical processes, which pose challenges for accurate numerical prediction. Several chemical models have been developed to predict nonequilibrium flow fields, but research on the discrepancies among models at extremely high Mach is currently limited and it is essential to conduct further research, as the nonequilibrium phenomena intensify and these discrepancies become more significant under such conditions. To investigate the computational differences among the Park (1993) [9], Dunn and Kang (1973) [5], and Gupta et al. (1990) [10] chemical models, numerical simulations of hypersonic reentry nonequilibrium flow fields were conducted at an altitude of 60 km and within a Mach range from 15 to 30. The findings reveal that those three chemical models primarily alter the distribution difference of the NO component. The Park model has a significantly higher NO dissociation rate, resulting in a notably lower NO mass fraction. In terms of heat flux distribution, as the shock distance exceeds the thermochemical relaxation distance, allowing the nonequilibrium state behind the shock to transition to an equilibrium state, the aerodynamic heat flux calculated by the Park model is the maximum, while the minimum for the Dunn-Kang model. Finally, by comparing to the experimental data from Mars Pathfinder and Radio Attenuation Measurement (RAM-C II), the Park model shows better performance in predicting aerodynamic heating, with the calculation error maintained within 16.2%.