Suppression of Tip Vortex Cavitation by Water and Polymer Injection

Tip vortex cavitation (TVC) is typically the first form of cavitation observed in propellers; therefore a delay of its inception is desirable. In this study, TVC inception was delayed via mass injection from the tip of a modified NACA-66 elliptic plan-form hydrofoil. The injected mass used were water and Polyox WSR 301 solutions with concentrations from 10 to 500 ppm. The free-stream nuclei content was measured using a Cavitation Susceptibility Meter, and the TVC inception event rate was quantified with a light scattering system. The vortical flow field in the region of inception was characterized using Stereo Particle Imaging and Velocimetry (SPIV), with measurements taken from 0.25 to 1 chord length at various concentrations and injection rates. It was observed that TVC inception was delayed with injection by a $\Delta \sigma $ of 0.03 to 1.8 from a baseline of $\sigma $ = 3.5. Injection with higher polymer concentrations and higher volume flux led to larger delays. A saturation effect for the TVC suppression was observed for both the polymer concentration (125ppm) and volume flux rate ($\dot {Q}_j $\textbf{/}$\dot {Q}_c $ = 0.48). These effects are related to the SPIV flow field.