cavitating flow

One of the biggest problems faced by designers of underwater propellers and turbines is cavitation. At the surface of moving edges, large pressure drops can result in sudden vaporization of the fluid, which leads to a loss of efficiency and structural damage. Cavitation is also a leading cause of underwater noise pollution hurting wildlife and damaging ecosystems. We tested an alternative hydrofoil design inspired by humpback whale fins. By adding protuberances to the leading edge of the hydrofoil, they sought to minimize cavitation effects and uncover how the design affects fluid flow. In particular, they sought to understand the development of sheet cavities and the shedding of cloud cavities, two forms of partial cavitation common in hydrofoils.

In this work, the effect of tip fins on vortex flow in non-cavitating and cavitating conditions is investigated experimentally. Rectangular hydrofoils with and without fin tips are considered. Velocity field is measured using laser Doppler velocimetry (LDV) at several plane sections. A high-speed camera is used to visualize the tip vortex cavitation (TVC), and pressure transducers are employed for acoustic measurements. The non-cavitating flow results reveal that Re has no discernible effect on the tip vortex characteristics, although the axial velocity at the tip vortex core is significantly affected.

In many practical submerged objects, various types of cavitation such as bubble, sheet, and cloud cavitation occur according to flow conditions. In this work, the series process consisting of inception, growth, and desinence of the partial cavity was investigated, and also noise generated during the process was measured. The results show that the periodic behavior of cavitation clouds is directly reflected in the noise characteristics. In addition, the visualization of coherent structures within the sheet and cloud cavity provides a qualitative understanding of hairpin vortices and their packets, which play a dominant role in turbulent cavitating flows.