Temperature Profiles in a Blowdown Hypersonic Wind Tunnel via Femtosecond Coherent Anti-Stokes Raman Spectroscopy

Gas temperature profiles are performed using a femtosecond coherent anti-Stokes Raman scattering (fs-CARS) instrument in a blowdown hypersonic wind tunnel at Mach 8. Data were acquired in the boundary layer of a simple cone model and the separation region of a three-dimensional expansion-compression geometry. The laser instrument included a 100 fs pulse from a 1-kHz Ti:Sapphire laser at 800 nm, and a 7 picosecond pulse from a second-harmonic bandwidth-compressor at 400 nm. Single-laser-shot pure-rotational CARS spectra were compared to a theoretical model to extract quantitative gas temperature data. The CARS signal was split in a dual-channel detection scheme to enhance the dynamic range of the instrument for regions of hypersonic flow with vastly different gas densities and signal levels. Temperature profiles recorded in laminar, transitional, and turbulent hypersonic flows will be presented.