Laser Doppler anemometer for boundary layer measurements in high velocity, high temperature MHD channel flows

A laser Doppler anemometer has been developed for measurements in the boundary layer of MHD channel flows. Because of the high velocities, the frequency shift is determined by direct optical spectral analysis using a scanning confocal Fabry-Perot interferometer. A coaxial backscatter configuration is employed to facilitate scanning the velocity profile in the presence of refractive index inhomogeneities in the hot turbulent boundary layer. The Ar(+) laser beam is expanded to 50 mm diam. and focused to give a beam waist of 25 microns at the measurement point. The flow is seeded with ZrO2 powder. The rate of detected scattered-signals is displayed as a function of velocity as the Fabry-Perot is slowly swept.