Electron-vibration energy exchange models in nitrogen plasma flows
Résumé
This work presents an examination of the validity of the simple linear Landau-Teller-type model proposed by Lee for the electron-vibration energy exchange term in nitrogen ͓in Thermal Design of Aeroassisted Orbital Transfer Vehicles, edited by H. flow conditions encountered in high enthalpy wind tunnels are considered. The time-dependent relaxation of the vibrational energy of nitrogen due to electron inelastic collisions is calculated. The influence of the anharmonicity of the molecule and of the initial vibrational temperature T v is studied. With a harmonic oscillator approximation, it is found that a linear Landau-Teller-type model is accurate to describe the vibra-tional energy relaxation rate for electron temperatures T e in the range 3000 KрT e р20 000 K. When T v ϽT e , our results show that the initial model proposed by Lee overestimates by a mean factor of 3 the electron-vibration (e-V) relaxation time. When T v ϾT e , the relaxation time appears to depend on the initial vibrational distribution. When the anharmonicity of nitrogen is taken into account, generally the relaxation rate of the vibrational energy deviates from a linear rate equation. In this case, it appears much more difficult to model accurately the e-V energy exchange term.
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