Vibrational Nonequilibrium Quantification for State-Resolved Simulation of a Hypersonic Flow

Abstract

Recent developments in internal energy nonequilibrium modeling for hypersonic gas flow simulations indicate a strong need for improved fidelity. Research efforts have consequently focused on discrete state kinetic relaxation techniques which independently model quantum state populations, although computational requirements for discrete state kinetic relaxation modeling of large-scale flows have to date limited the applicability of this type of model. With an ultimate goal of improving discrete state kinetic relaxation calculation efficiency through the use of locally adaptive model fidelity, in the present work various means of quantifying and predicting vibrational nonequilibrium for a representative hypersonic flow are investigated. A series of nonequilibrium metrics is assessed both for individual states and for the overall vibrational energy distribution, based on quantities including the normalized difference between translational and vibrational temperatures, deviation from equilibrium state populations, time scale ratios, and entropy generation. As a test case, an inviscid Mach 6.5 flow of over a cylindrical forebody geometry is considered. In observing trends among various metrics, areas of agreement as well as significant discrepancies are found. In a demonstration of local model adaptation, an additional simulation is performed, for which near-equilibrium regions are automatically assigned simplified discrete state kinetic relaxation procedures, and good agreement is observed with baseline simulation results.