Application of infrared diode laser absorption spectroscopy to the F4 high enthalpy wind tunnel

Abstract A tunable diode laser spectrometer has been used to probe the ONERA-F4 arc-driven high-enthalpy wind tunnel. By fast wave number tuning of the laser beam passing through the flow, free-stream measurements from NO or H 2 O absorption lines can be made at high repetition rates (1 kHz) in the infrared domain near 5 μm. Temperature and density measurements are obtained from the absorption line shapes, and the flow velocity is deduced from the Doppler shift at the line centre position. This line-of-sight technique gives averaged values over the absorption path through the flow. Herein we report results concerning medium and high enthalpy runs, where velocities inferred from the Doppler shifts range between 2500 and 4500 m/s. The results are also compared to calculations from heat flux probes measurements and flow models.