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Published December 2021 | Published
Journal Article Open

Measurements of Reflected Shock Tunnel Freestream Nitric Oxide Temperatures and Partial Pressure


This paper reports on measurements of freestream nitric oxide (NO) rotational and vibrational temperatures and partial pressures, collected in the Caltech T5 reflected shock tunnel. Quantum cascade lasers, emitting mid-infrared light resonant with fundamental rovibrational NO transitions, were directed through the supersonic (Mach ∼5) freestream flow. Tunable diode laser absorption spectroscopy (TDLAS) was used to measure the path-averaged rotational and vibrational temperatures of NO in the flow, in addition to the NO partial pressure. The temperature measurements demonstrate strong evidence of NO rotational and vibrational equilibrium during the 1 ms test period. Agreement between vibrational and rotational temperatures was observed in all experiments, including one h₀,∞≈8  MJ/kg and four h₀,∞≍18 MJ/kg experiments, during and after the nominal test time. Absorption from CO and H₂O was also observed in the TDLAS measurements, though their concentrations cannot be accurately estimated. The goal of these and future experiments is to develop and demonstrate TDLAS experimental strategies for high-enthalpy impulse facilities and to help to inform improvements of existing models and solvers used for prediction of freestream conditions.

Additional Information

© 2021 by Julian Girard. Published by the American Institute of Aeronautics and Astronautics, Inc. Presented as Paper 2020-3714 at the AIAA Propulsion and Energy 2020 Forum, Virtual Event, August 24–28, 2020; received 29 January 2021; revision received 7May 2021; accepted for publication 20May 2021; published online 6 August 2021. This work was supported by the Air Force Office of Scientific Research (AFOSR) through grant number FA9550-19-1-0219, with Ivett Leyva and Sarah Popkin as contract monitors. We would like to acknowledge the help of Bahram Valiferdowsi in running the experiments.

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