Simultaneous Multi-Component Velocity Measurement in a Closed-Circuit Wind Tunnel via Coherent Rayleigh-Brillouin Scattering

We report on the use of coherent Rayleigh Brillouin scattering (CRBS) for simultaneous measurement of ux and uy velocity components of the gas flow with different gas mixtures in a custom built closed circuit wind tunnel. Single shot CRBS and coherent Brillouin scattering (COBRA) are used to probe and characterize the boundary layer over a airfoil in air and then in CO2. CRBS/COBRA are non-resonant techniques and therefore does not require any change in laser parameters such as wavelength or phase matching conditions while probing different gas media. The velocity of the flow is estimated by measuring the Doppler shift in the spectrum when compared to a calibrated spectrum in stagnant condition. All of these measurements are validated with Pitot probe measurements in the test section of the wind tunnel; in addition, this is verified with CFD simulations.