Thermochemical Relaxation in Shock Tunnels

Abstract

Thermochemical relaxation phenomena in the shock tunnel nozzle and behind a normal shock wave formed in its test section are investigated theoretically in one dimension using a state-to-state description. Test gas is assumed to be air containing hydrogen as an impurity. The state-to-state rate coefficients calculated by the forced harmonic oscillator model of Adamovich, Macheret, Rich, and Treanor (Vibrational Energy Transfer Rates Using a Forced Harmonic Oscillator Model, Journal of Thermophysics and Heat Transfer, Vol. 12, No. 1, January-March 1998, pages 57-65) are multiplied by correction factors to numerically reproduce the existing experimental data on vibrational relaxation times and dissociation rates. The calculations show that freezing in the nozzle causes the relaxation behind a normal shock wave to be generally different from that in free flight. In a shock tunnel with a nozzle length of 5 meters operating at a reflected-shock pressure of 1000 atmosphere, standard, free-flight conditions are simulated fairly closely in its test section.