Mechanism and Control of Cloud Cavitation

TLDR

The authors examined cloud cavitation on a hydrofoil by high‑speed imaging, pressure and acoustic measurements, and by adding a surface obstacle to manipulate the phenomenon. They found that a re‑entrant jet from the trailing edge initiates sheet‑cavity collapse, producing cloud cavitation, and that a small surface obstacle can suppress this effect, lowering drag and cavitation noise.

Abstract

Generation mechanism of cloud cavitation on a hydrofoil section was investigated in a sequence of experiments through observation of cloud cavitation by high-speed video and high-speed photo as well as pressure measurements by pressure pick-ups and a hydrophone. The mechanism was also investigated by controlling cloud cavitation with an obstacle fitted on the foil surface. From the results of these experiments, it was found that the collapse of a sheet cavity is triggered by a re-entrant jet rushing from the trailing edge to the leading edge of the sheet cavity, and consequently, the sheet cavity is shed in the vicinity of its leading edge and thrown downstream as a cluster of bubbles called cloud cavity. In other words, the re-entrant jet gives rise to cloud cavitation. Moreover, cloud cavitation could be controlled effectively by a small obstacle placed on the foil. It resulted in reduction of foil drag and cavitation noise.