Study on cavitation flow around a hydrofoil

Hydrofoil is widely used in studies for hydrodynamic machinery. Cavitation in pumps or turbines will result in problems such as vibration and cavitation erosion. In order to avoid cavitation, it´s necessary to develop methods for the cavitation generation mechanism because cavitation may lead to serious damage. In this paper, experimental methods were used to study the development, flow structures and characteristics of the cavitation regimes around different hydrofoils with different surface roughness, respectively. Experiments are conducted to get details of the cavitation flow. Cavitation around the Clark-V hydrofoil is observed in a cavitation tunnel using a high speed visualization system. The foils are processed by a numerical control machine and the surface roughness height is examined. The results show that three cavitation regimes are observed accompanying with decreasing the cavitation number: the incipient cavitation, attached cavitation and cloudy cavitation. When cloudy cavitation exists, the cavitation is periodic with shedding of large scale of vapor bubbles. The wall irregularities have great effects on the cavitation flow. The cavitation is more serious under the same cavitation number within the region having irregulars. Its cavitation flow consists of many small attached spot cavities independently. The cavitation around the foil is consisted of attached spot cavities which generate great influence on the developing process of cloudy cavitation. And the reentrant jets within the attached spot cavity result in the shedding of bubble clouds from the attached spot cavity.