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Vibrational State-to-State Modeling of a Recombining Nitrogen/Argon Plasma

Abstract : A vibrational state-to-state kinetic model is developed and compared with recent measurements performed in a nitrogen/argon recombining plasma at atmospheric pressure. It is shown that the flow experiences high vibrational non-equilibrium, which slows down the recombination process of nitrogen atoms. The present state-to-state model overpredicts the experimental atomic nitrogen densities. I. Introduction During atmospheric reentry, spacecraft experience high convective and radiative heat fluxes. Reliable kinetics models are required to predict both quantities, because they influence the energy balance and the population of radiating levels. Computational fluid dynamics (CFD) codes [1]-[4] generally use chemical models based on empirical fits of shock tube data [5]-[7]. These models describe non-equilibrium effect only crudely, because internal energy levels are assumed to follow Boltzmann distributions (typically for a 2-temperature model, electronic-vibrational levels and rotational-translational levels follows Boltzmann distributions at = and = respectively). Recent advances in computational chemistry enable to reconsider these models from ab initio methods [8]-[10] and to develop state-to-state models (StS). The StS models can account for non-equilibrium chemistry, where internal energy levels can depart from Boltzmann distributions. Vibrational levels can be treated as pseudo-species, with populations obtained by solving the master equation. Recently, experiments were performed to provide well-defined test cases to validate CFD codes and reactions mechanisms for recombining flows. In particular, the recombination of an / plasma was studied experimentally at Stanford [11]-[13], and the same facility was used recently in CentraleSupélec to confirm and extend the Stanford results [14], [15]. Chemical reactions mechanisms from Park, Gupta and Dunn have been compared against experimental data in [11]-[13]. It was shown that the limiting recombination reaction is + ⇌ + + with = , , and. The authors concluded that Park's model was closest to their experimental results but that there were still discrepancies. In the present paper, we repeat the same analysis as in [11], [12] with the new set of measurements obtained at CentraleSupélec and reported in [15]. Then we extend the study by comparing chemical and StS models on this updated test case.
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Pierre Mariotto, A Tibère-Inglesse, S Mcguire, Marie-Yvonne Perrin, Christophe Laux, et al.. Vibrational State-to-State Modeling of a Recombining Nitrogen/Argon Plasma. AIAA Scitech 2019 Forum, 2019, San Diego, France. ⟨10.2514/6.2019-0796⟩. ⟨hal-02494090⟩

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