Hypersonic Real-Gas Effects on Transition

Some of the results of an extensive research program into the effects on transition of the vibrational and chemical relaxation processes that occur in high-enthalpy flows are presented. Relaxation effects are found to influence transition significantly, with increases of the transition Reynolds number by up to a factor of five. The mechanism responsible for this transition delay is shown to be the damping of the acoustic second mode instability by relaxation processes. Transition is also found to be further delayed by up to a factor of two by suitable wall porosity.