Measurements of fluctuating temperatures in a supersonic turbulent flow using laser-induced fluorescence

A laser-induced fluorescence technique that provides a practical means of nonintrusively measuring the instantaneous temperatures in low-temperature turbulent flows has been developed. It relies on the fluorescence from small concentrations of NO in a flow of N2. The technique has been demonstrated in a two-dimensional turbulent boundary layer at Mach 2. Both one and two-photon excitation methods were used, but limits imposed on the two-photon method by Stark effects rendered it less accurate. Single-pulse measurements, in flows with 100 ppm NO, were obtained in the range from 150 to 295 K with an uncertainty of 1% rms. Fluctuations up to 6% rms were observed, owing to the turbulent flow. The average temperature distribution through the boundary layer agreed well with temperatures implied by pitot-probe data.