High sensitivity boundary layer transition detector

A high sensitivity differential interferometer has been developed to locate the region where the boundary layer flow changes from laminar to turbulent. Two experimental configurations have been used to evaluate the performance of the interferometer, open shear layer configuration and wind tunnel turbulent spot configuration. In each experiment small temperature fluctuations were introduced as the signal source. Simultaneous cold wire measurements have been compared with the interferometer data. The comparison shows that the interferometer is sensitive to very weak phase variations in the order of .001 the laser wavelength.