Velocity measurement by H2O photolysis and laser-induced fluorescence of OH.

Experimental results in a uniform, supersonic, free-jet flow containing water vapor show that enhancement of OH concentration by focused UV photodissociation of H(2)O at 248 nm is an excellent tagging mechanism for velocity measurements. Two-dimensional images of OH fluorescence with a vidicon show a narrow initial enhanced OH zone along a straight line limited by the jet diameter. Fluorescence induced by a time-delayed pulsed dye laser documents the convection of this enhanced OH by the uniform core flow and reveals sharply stretched edge regions due to the shear layer with ambient air. The core flow velocity measurements are in agreement with predicted values.