Recent Advances in Modeling Thermal and Chemical Nonequilibrium in Continuum-Rarefied Gas Flows

Abstract

The modeling of the thermodynamic nonequilibrium state of the gas in continuum and rarefied regimes for hypervelocity flight requires appropriate modeling of translational and internal energy modes of molecules in the gas. Assumptions of equilibrium in the energy states along with simplified relaxation and dissociation models are restricted to certain flow regimes and conditions. In others it is necessary to model the translational nonequilibrium using higher moments of the Boltzmann equation and the internal energy modes modeled with state‐kinetic rates. The internal energy mode addressed in this paper are the transitions between the quantum levels in the vibrational energy mode and state‐specific dissociation from the vibrational quantum levels. The paper describes recent advances made in solving the Boltzmann equation in the rarefied regime and a gas kinetic scheme in the continuum regime, thus facilitating coupling by the use of the distribution function. The paper also describes recent advances in the modeling of internal energy relaxation involving multiquantum transitions in vibrational mode and state‐to‐state kinetics of dissociation. The methodology allows the analysis of flowfields around earth entry vehicles flying in mixed regions of continuum‐rarefied gas that are in thermodynamic nonequilibrium.