Energy transfer mechanisms in hypersonic shocks

Abstract

This paper surveys the overall mechanisms of energy transfer between translational, rotational, vibrational, chemical and electronic degrees of freedom in a hypersonic shock wave in air. Particular stress is placed on those aspects of the problem which are not well understood; thus, one can write down a set of reaction rate constants for the major chemical reactions in dissociating and ionizing air, but some rather basic aspects underlying these rates are not understood. Thus at the elevated temperatures of interest here (to 8000°K), the mechanisms for vibrational excitation and dissociation by vibrational ladder-climbing, which apply at room temperature, break down. Further, we have very little knowledge and understanding about the mechanisms and rates leading to the excitation of electronic degrees of freedom which produce radiation in high-temperature air. For comparison, the case of a shock wave in argon is also reviewed.