Particle Image Velocimetry in a Nonreacting and Reacting High-Speed Cavity

Particle image velocimetry measurements were taken at the center plane of a high-speed cavity combustor in nonreacting and reacting conditions at fuel flows corresponding to medium, medium-high, and high fuel-loading conditions with supersonic core flow velocities. Calculation of the instantaneous and averaged pathlines, vorticity, swirling strength, and divergence of the velocity field revealed a highly unsteady three-dimensional flow with coherent eddy structures formed at the stagnation zone of the shear layer against the downstream ramp of the cavity, which appear to be convected upstream in the cavity. Comparison of the shear layer location, thickness, and impingement stagnation zone revealed a number of changes in the mean and unsteady velocity behavior that were dependent on the heat release in the cavity and shear layer. As combustion shifted from the cavity at medium fuel loading into the shear layer at high fuel loading, the volumetric expansion compressed the primary recirculation zone and thickened the downstream boundary layer at the cavity exit. Combustion in the cavity tended to attenuate cavity and shear layer unsteadiness. When the combustion shifted to the shear layer, velocity unsteadiness increased, though not to the amplitudes measured without combustion.