Vibrationally Relaxing Flow of N2 past an Infinite Cylinder

The results of a numerical study aimed to verify the accuracy of the thermodynamic models based on the Boltzmann distribution in the hypersonic regime and to detect discrepancies, if any, with the analysis based on the more rigorous method of vibrational kinetics are presented and discussed. The test case considered in the study is the steady, two-dimensional, chemically inert, inviscid flow of diatomic nitrogen past an infinite cylinder in a uniform stream at M_inf=6.5. The vibrational relaxation has been calculated from the standard vibrational energy rate equation, assuming a harmonic-oscillator behavior of N2, and from a set of vibrational master equations that account for the first 10 vibrational energy levels of the N2 molecule, assumed as an anharmonic oscillator. The flow patterns produced by the two calculation methods are thoroughly discussed and the critical influence of the vibrational relaxation time, associated with the harmonic-oscillator models, in determining agreement or disagreement with the results from the vibrational kinetics method is evidenced.