Characteristics of a Cavitating Hydrofoil in Separation Region.

Abstract

Cavity breakdown on a hydrofoil in the transient region between subcavitation and supercavitation causes violent vibrations which are serious obstacles to the reliability and strength design of hydraulic machinery. By the use of high-speed photographs and three-component load cells, this paper clarifies the cavity aspects and the characteristics of fluid forces from noncavitation to supercavitation in the nonseparation, separation and stall regions. The following three results were obtained at cavity breakdown. (i) In the separation or the stall region, several vortex-cavity strings stretched from the end of still-existent sheet cavity on the hydrofoil to the downstream direction and encircled the breakdown cavity cluster. (ii) The fluctuating lift coefficient reached up to about 15% and the fluctuating drag coefficient up to 20% compared with the time mean lift and drag coefficient, respectively. (iii) The center of pressure shifted toward the trailing edge from about 30% chord during noncavitation or subcavitation to 40% chord.