Structure, penetration, and mixing of pulsed jets in crossflow

Effects of periodic disturbances on the structure and mixing of a transverse jet have been investigated through chemically reactive laser-induced fluorescence experiments in a water model. Flow visualization experiments with a steady, round jet in crossflow revealed a distinct vortex loop merging pattern among the vortices that make up the curved shear layer around the jet. As the vortex loops are stretched and distorted, certain parts of the neighboring loops with the opposite or the same sign of vorticity merge, resulting in cancellation or intensification of the vorticity in the corresponding regions of the jet. When the flow rate of this jet was periodically modulated by a square wave, however, distinct vortex rings were created whose spacing and strength were dictated by the pulsing frequency for a given jet and crossflow combination. At low pulsing rates, these rings penetrated into the crossflow significantly deeper than the steady jet. An optimum pulsing frequency was found at which closely spaced vortex rings were observed, which penetrated as discrete vortices into the crossflow in the near field. Strong interactions among neighboring rings were observed farther downstream