Hydroxyl-Tagging-Velocimetry Measurements of a Supersonic Flow over a Cavity

Hydroxyl-tagging-velocimetry measurements were made throughout the compressible flowfield of a Mach 2 air flow over a cavity. The supersonic flowfield simulates the pilot region of scramjet combustion under nonreacting conditions. In the hydroxyl-tagging-velocimetry method, ArF excimer laser (193 nm) beams pass through a humid gas flow, dissociating water to form a tagging grid of hydroxyl molecules. The hydroxyl-tagging-velocimetry grid density has been increased to 11 x 11 to yield up to 120 velocity vectors of the two-dimensional flow over a fixed time delay of 2-3 mu s. Instantaneous single-shot measurements of two-dimensional How patterns were made in the nonreacting Mach 2 flow over a wall cavity under low- and high-backpressure conditions. Single-shot profiles were analyzed to yield mean and rms deviation velocity profiles in the Mach 2 nonreacting flow. Compressibility greatly reduces the growth rate of the supersonic shear layer formed at the edge of the cavity. A set of velocity data (spanning the entire length of the cavity) for an open wall cavity in a supersonic flow under low- and high-backpressure conditions was compiled for validation of computational fluid dynamics models.