Spectroscopic Measurements in the Shock Relaxation Region of a Hypervelocity Mach Reflection

We examine the spatial temperature profile in the non-equilibrium relaxation region behind a stationary shock wave. The normal shock wave is established through a Mach reflection configuration from an opposing wedge arrangement for a hypervelocity air Mach 7.42 freestream. Schlieren images confirm that the shock configuration is steady and the location is repeatable. Emission spectroscopy is used to identify dissociated species and to obtain vibrational temperature measurements using the NO and OH A-X band sequences. Temperature measurements are presented at selected locations behind the normal shock. LIFBASE is used as the simulation spectrum software for OH temperature-fitting, however the need to access higher vibrational and rotational levels for NO leads to the use of an in-house developed algorithm. For NO, results demonstrate the contribution of higher vibrational and rotational levels to the spectra at the conditions of this study. Very good agreement is achieved between the experimentally measured NO vibrational temperatures and calculations performed using a state-resolved, one-dimensional forced harmonic oscillator thermochemical model.