Figure 1 - Tip-Vortex Rollup Process 



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can lead to the situation where the local pressure in the tip vortex core reduces 

 to the vapor pressure of the liquid, resulting in cavitation and its attendant 

 problems. 



Several years ago, a research program was initiated to develop techniques for 

 designing marine lifting surfaces with delayed/ improved tip vortex cavitation 

 (TVC) performance. The first phase of this program was devoted to a study of the 

 pertinent literature and the establishment of a technology base. In this survey," 

 over 150 tip-vortex-related documents were identified and cataloged. In addition, 

 those concepts which held promise for the delay of TVC on marine lifting surfaces 

 were given close attention and appropriate experimental investigations were recom- 

 mended. The second phase of the program involved carrying out the recommended ex- 

 perimental investigation. 



This report presents the results of the TVC experimental program. The specific 

 concepts recommended for evaluation included: a bulbous tip having a selective in- 

 crease in the foil tip thickness, an artifically roughened tip, and a mass injected 

 tip with the introduction of fluid directly into the tip vortex core. A detailed 

 description of these devices is presented in the following sections. The experiment 

 was conducted in the DTNSRDC 24-inch cavitation tunnel using a three-dimensional 

 hydrofoil model. Initially, efforts were directed toward gaining some fundamental 

 insight into both the tip vortex rollup and cavitation process. The results from 

 this initial work guided the design of the specific concepts discussed above and in- 

 cluded flow visualization techniques; e.g., tufts, photography and paint flow. 



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*A complete listing of references is given on page 53. 



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