On the Vibrational State-Specific Modeling of Radiating Normal Shocks in Air

Abstract

A comprehensive state-to-state (StS) model for air was formed -including vibrationvibration-translation (VVT) reactions. The generated VVT reaction rates were compared to available first principles calculations and reasonable agreement was obtained. The influence of multi-quantum transitions revealed that the possible reduction on the number of VVT transitions depends on the application. The influence of VV transitions revealed that the vibrational excitation becomes too fast if VVT transitions are reduced to VT transitions, invalidating this approximation. Comparisons were made with existing NO emission measurements in the UV and mid-IR spectrum. At velocities of 3 -4 km/s, some of the current O2 dissociation rates may be inaccurate. At a higher velocity of 6.81 km/s, the NO mole fraction predicted by the StS model is around an order of magnitude greater than that predicted by

State-Specific Study of Air in the Expansion Tunnel Nozzle and Test Section

“…In fact, the E1 results are close to the L10 results despite considering much more VVT transitions (L10 only has 6.7 x 10 4 transitions). The same finding has been made for pure N2 and air in excitation heat bath and normal shock conditions respectively [49,53]. Regarding the energy-based criteria, due to anharmonicity, there is a bias where more reactions (out of the total number of VVT reactions) involve the higher vibrational levels and less reactions involve the lower vibrational levels.…”

“…involve the lower levels and less involve the higher energy levels, as discussed by Ref. [53,75], which is the opposite of what we get when using the energy-based criteria.…”

“…However, the current nozzle flow is immune to this problem because O2 maintains close to equilibrium with the translational mode. The previous studies also showed a slight increase in the N2 vibrational excitation rate when VVT transitions were reduced to VT transitions [53]. However, the current nozzle flow is immune to this problem as well because the N2 vibrational mode is almost frozen.…”

“…Previous studies for normal shocks have shown equation 9 to be a poor approximation as the O2 vibrational excitation rate was significantly increased when VVT transitions were reduced to VT transitions [48,53]. However, the current nozzle flow is immune to this problem because O2 maintains close to equilibrium with the translational mode.…”

“…Reactions 1-3 are the VVT reactions with rates generated in a previous work by the current authors [53] using the Forced Harmonic Oscillator (FHO) theory [54,55]. Comparisons with quasi-classical trajectory (QCT) and semi-classical (SC) calculations as well as experimental measurements were made, and varying degrees of agreements were observed -ranging from within 10 % to within an order of magnitude, depending on the temperature [53]. The remaining FHO rates in this tablereactions 4 and 5are obtained from the STELLAR database [56].…”