title: Nonequilibrium shock-heated nitrogen flows using a rovibrational state-to-state method.
abstract: A rovibrational collisional model is developed to study the internal energy excitation and dissociation processes behind a strong shock wave in a nitrogen flow. The reaction rate coefficients are obtained from the ab initio database of the NASA Ames Research Center. The master equation is coupled with a one-dimensional flow solver to study the nonequilibrium phenomena encountered in the gas during a hyperbolic reentry into Earth's atmosphere. The analysis of the populations of the rovibrational levels demonstrates how rotational and vibrational relaxation proceed at the same rate. This contrasts with the common misconception that translational and rotational relaxation occur concurrently. A significant part of the relaxation process occurs in non-quasi-steady-state conditions. Exchange processes are found to have a significant impact on the relaxation of the gas, while predissociation has a negligible effect. The results obtained by means of the full rovibrational collisional model are used to assess the validity of reduced order models (vibrational collisional and multitemperature) which are based on the same kinetic database. It is found that thermalization and dissociation are drastically overestimated by the reduced order models. The reasons of the failure differ in the two cases. In the vibrational collisional model the overestimation of the dissociation is a consequence of the assumption of equilibrium between the rotational energy and the translational energy. The multitemperature model fails to predict the correct thermochemical relaxation due to the failure of the quasi-steady-state assumption, used to derive the phenomenological rate coefficient for dissociation.
authors.affiliation: University of Illinois at Urbana-Champaign, Urbana, 104 S. Wright street, Champaign, Illinois 61801, USA.
authors.forename: M
authors.initials: M
authors.lastname: Panesi
authors.affiliation: von Karman Institute for Fluid Dynamics, chaussée de Waterloo 72, 1640 Rhode-Saint-Genèse, Belgium.
authors.forename: A
authors.initials: A
authors.lastname: Munafò
authors.affiliation: von Karman Institute for Fluid Dynamics, chaussée de Waterloo 72, 1640 Rhode-Saint-Genèse, Belgium.
authors.forename: T E
authors.initials: TE
authors.lastname: Magin
authors.affiliation: NASA Ames Research Center, Moffett Field, Mountain View, California 94035, USA.
authors.forename: R L
authors.initials: RL
authors.lastname: Jaffe
mesh_terms: D006358:Hot Temperature; D008962:Models, Theoretical; D009584:Nitrogen / Q000737:chemistry*; D012399:Rotation; D014732:Vibration
chemical_list: D009584:Nitrogen