All images are taken in our laboratory. Click each images to see enlarged pictures. (JPEG, 12--34KB)
Links with this icon will show you movies (animations).
Flow direction is from left to right.
This old monocrome picture shows typical "bubble" cavitation. Bubble cavities collapse very violently so that this cavitation is noisy, erosive and bad. (EN foil)
Such cavitation is called "sheet cavitation" because it looks like a clear valor sheet. As variation of its volume is small, it does not cause large noise or vibration.
(NACA 0015, 8.36deg, 8m/s, cavitation number: 1.96)
If the surrounding pressure decreases from sheet-cavitating condition, sheet cavity grows and causes such phenomena. Whole/Part of sheet cavity breaks off into cavity clusters which looks like a cloud. This cavitation also causes serious noise, vibration and erosion.
Note that such unstable and cyclic phenomena will appear even the foil is fixed and uniform flow velosity is kept constant (static condition).
(NACA 0015, 8.36deg, 8m/s, cavitation number: 1.54)
Side view (EN foil)
A movie of cloud cavitation(QuickTime Movie with sound, 2.1MB)
NACA 0012 hydrofoil of 150mm×150mm. about 8m/s, Reynolds number: 1,400,000.
This is not a high-speed image but a continual pictures taken syncronized with a storobe.
A movie taken from above.(mpeg movie, 88KB)
Imaging speed: 4,500fps.
Other movies are here.
The pictures above show "partial cavitation" which length is shorter than the chord length of the foil. On the other hand we sometimes see "supercavitation" which is longer than the foil and surrounds the foil. Supercavitation is almost stable and steady.
This figure shows "supercavitating foil" which is optimized for a certain supercavitating condition.
Above pictures show cavitating "two-dimentional" hydrofoils. However it is needless to say that cavitation will occur on three-dimentional hydrofoils and/or propellers.
Three-dimentional hydrofoils and propeller brades cause vortices from their tips and as the pressures of the center of vortices are very low, there you can see cavitation phenomena.
Finite span hydrofoil with no swept-back angle Finite span hydrofoil with swept-back angle = 30deg.
You can see that a tip-vortex cavitation is made with two vortices interwined each other so that it looks like a twisted ribbon.
Flow direction is from right before to left away. The propeller rotates counter-clockwise.
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Dept. of Environmental & Ocean Eng.
Univ. of Tokyo
Last modified: Mon Apr 10 10:53:04 JST 2000