Implementation of new multi-temperature nonequilibrium air chemistry model for CFD based on first-principles calculations

Abstract

In this paper we present recent updates to the Modified Marrone-Treanor thermochemical nonequilibrium model for five-species air, originally developed for computational fluid dynamics calculations of hypersonic flows. The updated (2023) version of the chemistry model used here employs new high-fidelity kinetic rate data for all air reactions (including oxygen/nitrogen/nitric oxide dissociation and Zeldovich exchange reactions) derived from quasi-classical trajectory calculations on \emph{ab initio} potential energy surfaces. We first verify the updated chemistry model against first-principles Direct Molecular Simulations by studying nonequilibrium reacting air mixtures in space-homogeneous heat baths representative of high-temperature post-shock conditions. Once validated in these simple scenarios, we employ the model in larger-scale computational fluid dynamics studies of hypersonic flow around a geometry representing a generic flight vehicle. There we compare the Modified Marrone-Treanor predictions against the standard nonequilibrium model by Park. This research demonstrates how complex nonequilibrium chemistry induced by hypersonic flight can be incorporated into accurate and efficient models for large-scale computational fluid dynamics simulations.