Reduced-order modeling of non-equilibrium kinetics and radiation for CO₂ axisymmetric wake flows

This paper presents a physics-based reduced-order model for describing vibrational non-equilibrium in CO₂ flows. The use of the coarse grain approach, which entails grouping individual internal states together into macroscopic bins, allows a dramatic reduction in computational costs while retaining key information from the full state-to-state model. The accuracy of the current model reduction methodology is further improved by utilizing state-specific kinetics to determine an optimal strategy for dividing states into bins. The time-evolution of CO₂ under strong thermal and chemical non-equilibrium in an ideal chemical reactor is studied using both the full vibrational state-to-state model and the resultant coarse grain-based reduced-order models. The developed reduced-order model successfully reproduces the internal population distribution and other macroscopic quantities of interest while providing a nearly three order of magnitude speedup. The new modeling framework is used to investigate the flowfield and radiative heating during atmo-spheric entry for the Mars 2020 mission. Predictions for the forebody region match results obtained using conventional multi-temperature models. However, the two approaches yield significantly different estimates for the CO₂ vibrational state distribution and infrared radiation in the backshell region.