OH LASER-INDUCED FLUORESCENCE VELOCIMETRY TECHNIQUE FOR STEADY, HIGH-SPEED, REACTING FLOWS

A high-resolution OH laser-induced fluorescence velocity measurement technique was developed for use in steady, high-speed, reacting flows. A narrow-linewidth laser source was tuned through an isolated OH absorption line to measure the Doppler-shifted line center frequency relative to an iodine reference line. A counterpropagating-beam approach was used to eliminate the collisional impact shift and minimize systematic errors. Results from pointwise measurements of velocity in a unique reacting underexpanded jet facility are compared to an axisymmetric Navier-Stokes calculation with finite-rate chemical kinetics as a test of the technique over a wide range of flow conditions. The measured and calculated velocities in the supersonic jet core agree on average to within 1.3%. The uncertainty in the velocity measurement in the jet core was on average +/-6.0% for a single measurement and +/-3.5% for the average value of three scans. Potential errors caused by absorption effects were not detected in these measurements.