cavitating flow

The cavitation phenomenon reduces hydrodynamic performance and generates vibrations and noise, significantly compromising the operational stability of the system. In this study, we investigate the efficiency of air injection in controlling cavitation patterns and reducing noise on hydrofoil, both experimentally and numerically. The focus is to assess how the location of air injection on the hydrofoil's suction side, the air injection rate, and the cavitation number affect the cavitating flow. Noise reduction is primarily noticeable in the high-frequency region (over 2 kHz) at a high cavitation number of 2.22. 

Tip vortex cavitation (TVC) leads to several technical problems, such as efficiency loss and noise. This study explains the patterns of flow around the tip of an elliptical foil and the cavity shape deformations under different flow conditions through experimental analysis. There is good agreement between the vortex cavity shapes captured by this high-speed imaging and those derived in previous studies. Using laser Doppler velocimetry (LDV) measurements and analysis through image processing of high-speed images, we compare the vortex core trajectories in cavitating and non-cavitating conditions.

The influence of sweep angles on cavitation characteristics and mechanisms of a wedge-section hydrofoil is investigated experimentally and numerically. The wake vortex changes from eddy vortex shedding at the wake region of the straight hydrofoil into two root trailing-edge vortices as the sweep angle increases. The swept hydrofoil reduces the average cavity volume by more than 45% compared with the straight foil. The findings offer valuable insight into the design and optimization of foils for various applications where cavitation affects their performance and stability.

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.