Vibrational state-to-state and multiquantum effects for N2+ N2interactions at high temperatures for aerothermodynamic applications

Abstract

In this paper we study the vibrational energy transfer process and dissociation due to N$_2$ + N$_2$ collisions using the state-to-state method. We discuss vibrational state transition rates and vibrational state specific dissociation rates obtained from QCT using the PES developed at the University of Minnesota \cite{PES:TruhlarN4, PES:BenderN4}. We first simulate an isothermal heat bath without dissociation to study the vibrational energy transfer process in isolation and then investigate nonequilibrium dissociation under QSS conditions to examine the impact of state-transitions and state-specific dissociation rates in a coupled simulation. Lastly, this paper delineates the role of multiquantum effects on vibrational energy transfer and dissociation to establish an engineering criteria to limit multi quantum effects so as to make the state-to-state approach computationally feasible for realistic geometries. The analysis was carried out over a temperature range of $T = 8000$ K to $30000$ K. The multi quantum truncation criteria proposed can reduce state-to-state computational cost up to $\sim65\%$ at the low temperature end of $T = 8000$ K and up to $\sim12\%$ at the high temperature end of $T = 30000$ K while being within $10\%$ of the accuracy of the full vibrational state-to-state solution.