Experimental and Numerical Study of Nonequilibrium in Unsteady Nonuniform Nozzle Flows

This study employs mid-infrared tunable diode laser absorption spectroscopy (TDLAS) combined with transient computational fluid dynamics (CFD) to characterize unsteady and nonuniform airflow at the nozzle exit of the detonation-driven JFX reflected shock tunnel at the Chinese Academy of Sciences. Three NO rovibrational transitions and two [Formula: see text] transitions were scanned by two quantum cascade lasers at 5.2 and [Formula: see text] to retrieve temperatures and partial pressures. Test gas purity and an annular gas-bleed arrangement were used to mitigate water contamination. Dehydrated synthetic air had an essentially imperceptible effect, while the gas-bleed device extended the contamination-free measurement window from 200 to [Formula: see text], during which the flow remains highly unsteady. The observed mismatch between translational and rotational temperatures is attributed to Doppler shift effects from strong expansion, with deviations of up to 56.9% of the rotational temperature. Simulated path-averaged rotational temperatures agreed closely with TDLAS results when NO exchange and [Formula: see text] dissociation rates were increased by an order of magnitude relative to Park’s model. In contrast, TDLAS-derived vibrational temperatures showed limited agreement with the simulated species-averaged vibrational temperature, and simulated NO partial pressures were roughly twice the measured values.