Thermochemical Nonequilibrium Processes in Weakly Ionized Air Using Three-Temperature Models

Abstract

Two three-temperature thermochemical nonequilibrium models were used to simulate the relaxation processes in weakly ionized air in compression and expansion regions. The three energy equations were the total energy, vibrational energy, and electron energy. The partition of electronic energy was investigated by considering it to be in equilibrium with the vibrational energy (free-electron model) or electron energy (electron–electronic model). Several zero-dimensional simulations were completed that demonstrated the potential of a three-temperature model to capture additional physics of the nonequilibrium processes above that of the legacy two-temperature model. The electron–electronic model consistently predicted, as expected, the electron temperature to be the last to equilibrate and for there to be significant electron nonequilibrium in all cases considered. However, the utility of the free-electron model to increase the fidelity of a simulation above that predicted by the two-temperature model was shown to be limited. Additionally, two vibrational–electron energy exchange relaxation times for the molecule were investigated; the resulting nonequilibrium processes were relatively insensitive to the use of a particular model.