Tip Vortex Cavitation Suppression by Active Mass Injection

Injection of water and aqueous polymer solutions in to the core of a trailing vortex was found to delay the inception of tip vortex cavitation (TVC). Optimal levels of mass injection reduced the inception cavitation number from 3.5 to 1.9, or a reduction of 45%. At the optimal fluxes, injection of water alone produced a reduction of 35%, and the addition of polymer solution led to a reduction of 45%. Stereo particle image velocimetry was employed to examine the flow fields in the region of TVC inception and infer the average core pressure, and planar PIV was used to examine the flow unsteadiness in this region. The time-averaged pressure coefficients for the vortex core pressure were estimated and compared to the pressure needed for TVC inception and full development. Measurement of flow variability in the TVC inception region indicated that relatively low fluxes of mass injection in the TVC roll-up region led to a substantial decrease in flow unsteadiness in the core region near the observed location of inception, and this corresponded to a substantial decrease in the inception pressure. Increased injection of water or polymer solutions led to a modest increase in the average vortex core radius, which was discernable in the measured pressure needed for developed cavitation.