| Cavitation in vortical flows is an important problem since it is common in engineering practice. Of particular interest is cavitation in the vortex produced by a lifting surface. The study of tip vortex cavitation covers a wide array of topics. These include tip vortex formation near the tip, water quality effects (the amount of tension which can be supported before cavitation occurs), flow unsteadiness, bubble dynamics and noise production. This research was conducted using elliptic planform hydrofoils of different NACA cross-sections to examine three aspects of cavitation: (1) Viscous effects on tip vortex cavitation, (2) Bubble dynamics, and (3) Noise produced during inception and developed cavitation.;Bubble growth characteristics of cavitation inception were studied using high speed videos and movies, as well as with a new still photographic technique. Nuclei captured by the vortex were observed to grow cylindrically with elongation rates as high as high as 5 times the free stream velocity. Noise produced during inception was found to correlate well with the acoustical model for a compact source. This study shows that bubble growth characteristics are a complex function of vortex strength and water quality not easily modeled by a closed form analytical solution.;An interesting phenomenon occurs for developed tip vortex cavitation. Under certain conditions of lift coefficient and cavitation number, a standing wave pattern develops on the surface of the hollow core vortex which radiates significant noise at a discrete tone. Trends of measured frequency qualitatively agree with a dispersion relation developed by Lord Kelvin for waves on a hollow core vortex. Kelvin's derivation reveals that singing should occur at only one cavitation number. Observations suggest that an optimum condition exists at which singing occurs.;Viscous effects of tip vortex formation were studied using a sprayed oil droplet technique. Each hydrofoil was found to have dramatically different flow separation characteristics on both the pressure and suction sides. Careful examination of the tip region reveals a complex interaction of the vortex with the suction side boundary layer. The degree of vortex/boundary layer interaction was found to correlate with observed differences in tip vortex cavitation characteristics. |
