Computation methods of vibrational non-equilibrium flows in nozzles

The computation methods of the steady vibrational non-equilibrium pure gas flow in a nozzle are compared. The first one (classical method) assumes that the fluid may be in a strong vibrational non-equilibrium state, but with the translational and rotational modes in equilibrium. The second one assumes a small non-equilibrium for all modes. The principal results concerning nitrogen flows in nozzles having different divergence angles show, for the total vibrational energy, either the expected rapid freezing (first method) or an asymptotic behavior to equilibrium values after a quasi-freezing phase (second method).