Further Studies of Tip Vortex Cavitation

Abstract

Cavitation in vertical flows is an important problem. In particular, cavitation in the vortices trailing from lifting surfaces such as propellers and hydrofoils has been studied extensively in the past few years. Factors which affect tip vortex cavitation include water quality (which relates to the amount of tension that can be supported before cavitation occurs), the details of vortex roll-up close to the tip, and flow unsteadiness. An experimental and numerical investigation has been conducted to examine these effects. The experimental phase reported herein includes lift and drag measurements, oil flow visualization of the boundary layer flow on lifting surfaces, and observation of cavitation inception in strong and weak water. An improved photographic technique has been developed to study the complex bubble dynamics inherent in the inception process. Preliminary results indicate that the growth process is strongly dependent on the size and number of nuclei in the free stream.

[missing text] vortices that occur at the tips of lifting surfaces and at the hubs of propellers and Francis turbines. Intermediate between turbulent eddies and tip and hub vortices are a variety of secondary flow phenomena such as the horseshoe vortices that form around bridge piers, chute blocks and struts, and the secondary vortices that are found in the clearance passages of turbomachinery.

The focus of this paper is on tip vortex cavitation. Recent research on tip vortex cavitation is discussed. This problem was first studied in detail by McCormick (1954, 1962). Subsequently, little further attention was given to this topic until recently, when there has been a resurgence of interest in the problem. Our understanding of the physics has been considerably enhanced in the past decade (1983-1993). The emphasis of this paper is on the details of the inception process. Developed cavitation is also briefly described.