Velocity and Temperature Measurements in Mach 18 Nitrogen Flow at Tunnel 9
Arthur Dogariu, Laura E. Dogariu, Michael S. Smith, Brianne McManamen, John Lafferty, Richard B. Miles
Abstract
View Video Presentation: https://doi.org/10.2514/6.2021-0020.vid We report the first application of Femtosecond Laser Electronic Excitation Tagging (FLEET) and Coherent Anti-Stokes Raman Scattering (CARS) spectroscopy to measurement of velocity and, respectively temperature in Mach 18 nitrogen flow at the AEDC Hypervelocity Wind Tunnel 9. We have refined our measurement system used in previous testing campaigns at Mach 10 and Mach 14, to allow for simultaneous single-shot FLEET velocimetry and CARS rotational/vibrational thermometry at 1kHz repetition rate. Velocity measurements with a dynamic range of over 2 km/s have been obtained within the operational envelope of the tunnel, and the lowest measurement precision attained in freestream flow was 0.1-0.2%. We obtained estimates of the rotational temperature, Trot, and the vibrational temperature, Tvib, by fitting the experimental CARS spectra to theoretical nitrogen spectra. The results experimentally demonstrate the strong thermo-chemical non-equilibrium conditions of the freestream flow. These measurements are important in that they are used to quantify the slight changes in the freestream conditions due to the frozen vibrational energy in the Mach 18 flow.