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.

Rovibrational grouping for N2(1Σ+ g)-N2(1Σ+ g) energy transfer using state-to-state model

“…The degeneracy (or statistical weight) and the energy of a given state i ∈ I are denoted by the symbols g i and E i , respectively. Alternatively, the rovibrational states of N 2 ( 1 Σ + g ) can be sorted according to their rotational (J) and vibrational (v) quantum numbers via the mapping functions [19,20]:…”

Assessment of Vibrational Non-Equilibrium Effect on Detonation Cell Size

“…The distance between the shock front and the position at which H 2 is half consumed is defined as the half-reaction thickness, δ. At 0.1 atm, when the collision frequency is low, the two-temperature model seems to overestimate the vibrational relaxation, as mentioned by Bender et al (2015) and Panesi et al (2014). These halfreaction thickness features are further demonstrated in Figure 3.…”

Vibrational and electronic collisional-radiative model in air for Earth entry problems

“…In addition, a collisional model has been elaborated by Panesi et al 15,16 and the assessment of the time required to reach a Boltzmanian distribution for the rotational distribution has been derived. The conditions n 0 ¼ 7.2 Â 10 22 m À3 , T 0 A ¼ 10 000 K have been studied for the total density and the kinetic temperature, respectively.…”

“…(16). Finally, the rate coefficient of each backward elementary process is derived from the one of the forward elementary process using the detailed balance principle involving the Boltzmann, Guldberg and Waage and Saha equilibrium constants.…”