Vehicle-scale simulations of hypersonic flows using the MMT chemical kinetics model

The Modified Marrone-Treanor (MMT) chemical kinetics model has recently been developed for and implemented in CFD codes suitable for vehicle-scale simulation. The MMT model is based on ab-initio quantum chemistry data and it is designed for hypersonic flows in air. This work investigates the effect of chemical kinetics model on a simple geometry for a range of altitudes. A 10 cm sphere-cone geometry at 5000 m/s is considered, with an isothermal non-catalytic wall. The difference in stagnationpoint heat flux between the MMT and Park models is found to be up to 31 % for the recombination-dominated regime and up to 12 % for the dissociation-dominated regime. Qualitatively similar differences are also observed on the cone portion of the body, with up to a 18 % difference in area-averaged heat flux. Next, several modifications to the MMT model are tested, based on uncertainties and physical phenomena. Maximum differences in stagnation-point heat flux of about 5 % are observed when modifying the O₂ + O dissociation rate, the rate of NO dissociation, and the approximate treatment of non-Boltzmann distributions. However, none of these realistic modifications approach the differences observed between the Park and MMT models, confirming these differences as significant. These results help to clarify the MMT model and decrease uncertainties by targeting future investigations.