Advanced Models for Vibrational and Chemical Kinetics Applied to Mars Entry Aerothermodynamics

The paper presents a comparative study of vibrational-chemical kinetics and heat transfer in carbon dioxide flows under Mars entry conditions for two classes of models: the state-to-state and multitemperature models. The state-to-state approach treats each vibrational state of a molecule as a separate chemical species, thus providing a very detailed flow description. Reduced multitemperature models are based on nonequilibrium quasi-stationary Boltzmann distributions over vibrational energy with vibrational temperatures of different modes. Implementation of multitemperature models requires much less computational effort, making them rather attractive for engineering applications. Simulations have been performed for the upper part of the Mars Pathfinder entry trajectory. Comparisons between different models demonstrate a good agreement for the flowfield variables obtained using the state-to-state and multitemperature approaches, except some discrepancies for the species mole fractions prediction. This conclusion is encouraging for computational fluid dynamics, since it confirms that multitemperature models, while not being so much detailed as state to state, are still able to capture the main peculiarities of thermal and chemical nonequilibrium flows. The transport and thermochemical models have been validated using experimental data obtained in the NASA Hypersonic Pulse ground test facility. It is shown that both state-to-state and advanced multitemperature transport models used in the present simulations provide a better agreement for the heating predictions compared to traditional models.