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Browsing by Author "Maines, Brant H."

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    Further Studies of Tip Vortex Cavitation
    (1994-04) Arndt, Roger E.A.; Maines, Brant H.
    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.
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    Viscous effects in tip vortex cavitation and nucleation
    (1994) Arndt, Roger E.A.; Maines, Brant H.
    This paper is concerned with the physics of cavitation in trailing vortices. The research was aimed at investigating the interrelated effects of the vortex structure and bubble dynamics. The experimental phase utilizes a series of hydrofoils and includes lift and drag measurements, oil flow visualization of the boundary layer flow, and observation of both cavitation inception and disinence in strong and weak water. The complex bubble dynamics inherent in the inception process have been studied using an improved photographic technique. The bubble growth process is strongly dependent on the size and number of nuclei in the free stream and on the strength of the vortex. Numerical simulations indicate that the minimum pressure in the vortex is very close to the tip of the lifting surface, in agreement with the observation that the inception process also occurs very close to the tip under most conditions.