VELOCITY-FIELD IMAGING IN SUPERSONIC REACTING FLOWS NEAR ATMOSPHERIC-PRESSURE

A combined experimental and analytical effort was conducted to demonstrate the applicability of OH Doppler-shifted fluorescence imaging of velocity distributions in supersonic combustion gases near and above atmospheric pressure. The experiments were conducted in the underexpanded exhaust flow from a 6.8-atm, 2400-K, H2-O2-N2 burner exhausting into the atmosphere. The effects of pulse-to-pulse variations in the dye laser band shape and in-plane variations in temperature and pressure were examined in detail. A modification was developed to increase the single-pulse laser bandwidth, thereby increasing the intra-image velocity dynamic range as well as reducing the sensitivity of the velocity measurement to the gas property variations. Single-point and imaging measurements of the velocity field in the exhaust flowfield were compared with two-dimensional, finite-rate kinetics simulations of the flowfield. Relative velocity accuracies of +/-50 m/s out of 1600 m/s were achieved in time-averaged imaging measurements of the flow over an order of magnitude variation in pressure and a factor of 2 variation in temperature.