Mechanism and Control of Cloud Cavitation

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.

Observations of shock waves in cloud cavitation

“…These profile and planform images are not unlike the descriptions of cloud cavitation in the two-dimensional hydrofoil experiments of de Lange et al (1994) Kawanami et al (1996). The most important difference in the present case is the substantial spanwise variation in the cavitation and its evoiution caused by the finite-span configuration of the hydrofoil.…”

“…This re-entrant jet mechanism was described by Knapp (1955) Kawanami et al (1996). The re-entrant jet does not, however, progress uniformly toward the leading edge.…”

“…Detailed descriptions of cavity growth, collapse and cloud formation on hydrofoils have been given by many authors including Knapp (1955), Wade & Acosta (19661, Bark (1985, McKenney & Brennen (1994), Shen & Peterson (1978, 19801, Blake et al (19771, Franc & Michel (19881, Hart et al (1990, Kubota et al (1989, 19921, Le et al (1993), de Larige et al (1994 and Kawanami et al (1996). By viewing the high-speed motion pictures taken during the current experiments, a series of stages in the cloud cavitation process were identified.…”

Experimental and numerical investigation on cloud cavitating flow around an axisymmetric projectile near the wall with emphasis on the analysis of local cavity shedding

“…They showed that shed cloud is a large-scale vortex structure containing various small cavitation bubbles. Kawanami et al (1997) investigated the generation mechanism of cloud cavitation in details. Callenaere et al (2001) investigated the instability of a partial cavity induced by the development of a re-entrant jet using experiments.…”

Cavitation regime detection through Proper Orthogonal Decomposition: Dynamics analysis of the sheet cavity on a grooved convergent–divergent nozzle

“…The role of surface condition has also been studied in a fully developed cavitating flow. Most of works about random distributed, transversal distributed, or local roughness show that it is possible to decrease sheet cavity length, in order to increase oscillation frequency of the cavity or even to change cavitation regime (Kawanami et al (1997); Stutz (2003); Coutier-Delgosha et al (2005); Yongjian et al (2009)). But, to the best of our knowledge, there is no study about the effect of organized longitudinal roughness like grooves on the cavitation regime.…”