Assessment of thermochemical models on nonequilibrium flowfield and radiation in shock-heated nitrogen

Abstract

Numerical simulations based on various physical models are performed to study thermochemical nonequilibrium flowfield and radiation in high enthalpy shock-heated nitrogen flows and compared against available experimental shock tube data. The physical models include both the two-temperature (2T) model and the four-temperature (4T) model, each integrated with different vibration-dissociation (VD) coupling models. For Sharma and Gillespie’s shock tube experiment, it is observed that the 4T model demonstrates satisfactory agreement with experimental rotational and vibrational temperatures, while the 2T results fall short of achieving comparable accuracy. When employing identical equilibrium dissociation rate coefficients and energy relaxation times, the modified Marrone–Treanor (MMT) model shows the lowest dissociation rate and the highest peak rotational temperature, which is closer to experimental data, in comparison to the Park and Marrone–Treanor (MT) models. For recent experiments conducted at the Electric-Arc Shock Tube facility (Shot 37 and Shot 40), our 4T-QSS results with the MMT model give the predictions for nonequilibrium radiative metrics closest to experimental data among the three VD models considered, although discrepancies compared to the experiments are still observed. Moreover, our investigation concludes that the influences of radiative cooling, rate coefficients of associative ionization and heavy-particle impact dissociation of N₂, and predissociation of the N₂(C) state on nonequilibrium radiative metrics are insignificant for these two shots. The discrepancies (persisted when incorporating various modeling options) in both nonequilibrium radiative metric and radiance versus position between the present calculations and experimental measurement indicate the necessity of employing a detailed state-to-state model and considering the shock tube-related phenomena to reproduce the experimental data.