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Published April 2023 | public
Journal Article

Measurements of T5 Shock Tunnel Freestream Temperature, Velocity, and Composition


We report on measurements of rotational and vibrational temperature, velocity, and concentrations of nitric oxide (NO) in freestream flows at the T5 reflected shock tunnel at California Instistute of Technology. Quantities were measured at 50 kHz by tunable diode laser absorption spectroscopy using five lasers simultaneously to sample 27 quantum state-specific transitions. To isolate core flow measurements from the shear flow surrounding it, optical flow-cutter arms were designed. Two sets of arms with differing optical path lengths were used to assess freestream spatial uniformity. This study consists of nine total experiments ("shots") spanning four nominal conditions with reservoir enthalpy 8–21 MJ/kg and flow velocity 3.5–5.5 km/s. Freestream measurements generally imply thermal equilibrium of the rotational and vibrational temperatures except at lower-enthalpy conditions. We compare temperature measurements with predictions from five species air simulations and find reasonable agreement at lower-enthalpy conditions but underprediction of NO concentrations. At higher-enthalpy conditions, we observed transitory agreement in temperature but overprediction of NO concentrations. Measured and simulated velocity generally agree well across all conditions. Carbon monoxide, water, and potassium were also detected in the T5 flow, and their concentrations are reported where relevant.

Additional Information

© 2023 by the American Institute of Aeronautics and Astronautics, Inc. We would like to acknowledge the help of Bahram Valiferdowsi in running the experiments. This work was supported by the Air Force Office of Scientific Research through grant number FA9550-19-1-0219, with Ivett Leyva and Sarah Popkin as contract monitors. The development of the diagnostic was also supported by the Office of Naval Research through award number N00014-20-1-2322, with Eric Marineau as contract monitor. Fundamental NO spectroscopy research which underlaid this work was supported by Air Force Office of Scientific Research grant number FA9550-18-1-0282, with Brett Pokines as program manager.

Additional details

August 22, 2023
October 23, 2023