Vibration-dissociation coupling using master equations in nonequilibrium hypersonic blunt-body flow

Numerical simulations are presented of a steady-state hypersonic flow past a hemisphere cylinder. Two types of models, one a lumped Landau-Teller vibr ational relaxation model (Landau, L., and Teller, E., "Zur Theorie der Scha lldispersion," Physikalalische Zeitschrift der Sowjetunion, Vol. 10, No. 1, 1936, pp. 34-43) and the other a discrete state kinetic relaxation model ( DSKR), were used to study effects of vibration-dissociation coupling on the flow physics. The widely used Park's dissociation model was used as baseli ne for coupling vibration and dissociation processes (Park, C., Nonequilibr ium Hypersonic Aerothermodynamics, Wiley, New York, 1990, p. 114). For a Ma ch 8.6 flow both relaxation models matched experimental data. At Mach 11.18 , however, the underprediction of shock-standoff distance by both relaxatio n models using Park's model for dissociation coupling provided the motivati on to implement a new master equation-based (DSKR) depletion model. The new model was used to study the effect of dissociation on population depletion in the vibrational states of the nitrogen molecule. The new model helps ex plain the restricted success of Park's dissociation model in certain temper ature ranges of hypersonic how past a blunt body. In the range of 5000-15,0 00 K, the new model yielded a substantial rate reduction relative to Park's equilibrium rate at lower temperatures and a consistent value at the high end. Application of the new model to a Mach 19.83 flow at reentry condition s resulted in an increase in the shock-standoff distance.