Nucleation and cavitation number effects on tip vortex cavitation dynamics and noise

The spatial and acoustic characteristics of tip vortex cavitation (TVC) inception were measured in a cavitation tunnel. Numerous cavitation events were recorded to reveal the influence of different nuclei populations and cavitation numbers on nuclei capture and activation physics, and the role of the streamwise pressure distribution in a vortex. Synchronised high speed video and hydrophone measurements of cavitation events were taken in the trailing vortex of an elliptical hydrofoil at an incidence of 6° and a Reynolds number of 1.5 × 10⁶. The injected nuclei population in the tunnel test section was varied by using different microbubble generators mounted upstream of the test section. Both the nuclei population and cavitation number have a significant effect on the inception location distribution along the trailing vortex, and in particular, inception event rates. The cavitation number alters the flow volume subjected to tension, thereby also affecting the shape of the inception location distribution. Once the nuclei are activated, cavity kinematic and acoustic properties are influenced by the local pressure (i.e. inception location and cavitation number) more so than initial nucleus size, at least in the ∼50–100 μm diameter range considered in this study. Inception events that occur near the tip generate stronger acoustic pulses. At these inception locations, the frequency of the tonal peak associated with inception remains relatively constant for the two nuclei populations, but increases with cavitation number. This study provides insights into the roles of nucleation and cavitation number in TVC and informs future measurements and predictions of TVC dynamics and noise.