Singular behavior of a clear attached cavity accompanied by cavitation-violent vibrations around a hydrofoil.

Abstract

In order to improve the high-speed performance of outboard engines, we carefully observed cavitation aspects, especially those of clear attached cavities around a thick symmetric hydrofoil conforming to the profile of the engine strut. in a two-dimensional water flow when violent cavitation vibrations take place. The behavior and the associated vibrational accelerations were measured through stereo-high-speed photography, high-speed movies and an accelerometer. Such an attached cavity appears periodically on the foil back-surface, resulting in very unstable, abrupt cavity breakdown accompanied by periodical shedding of bubble clouds into the downstream. A reentrant jet appearing at the cavity trail plays an important role both in the breakdown and in the vibrations. Such vibrations usually result in a drastic change of flow pattern, so that highly erosive types of cavitation and/or a marked size change in many bubbles flowing into the wake often arise.