Planar laser-induced fluorescence imaging of shock-tube flows with vibrational nonequilibrium

Single-shot planar laser-induced fluorescence images of nitric oxide in shock-heated flows with vibrational nonequilibrium are reported. The results demonstrate that planar laser-induced fluorescence imaging is a promising diagnostic technique for multidimensional high-speed flows because of its ability to examine shock structure and to visualize and measure vibrational nonequilibrium. The flows studied were generated within a shock tube and were composed of dilute mixtures of NO in argon. A narrow-band ArF laser tuned to the D +- X (0,1) R2 (28.5) transition of NO at 193.346 nm was used as the excitation source. The broadband fluorescence was collected at 90 deg to the path of excitation using an intensified, two-dimensional photodiode array. Images presented include a normal incident shock, a normal reflected shock, and a four-image sequence of the development of high-temperat ure supersonic flow over a two-dimensiona l blunt body. The vibrational relaxation in the downstream region of the normal shocks is analyzed and compared with calculations based on known relaxation rates.