ABSTRACT 



A research program was conducted to investigate both the 

 fundamental aspects of, and techniques for delaying, tip vortex 

 cavitation on a three-dimensional hydrofoil. The specific con- 

 cepts considered for delaying tip vortex cavitation included: a 

 bulbous tip, an artificially roughened tip, and a mass injected tip. 

 The experiments were conducted in the David W. Taylor Naval Ship 

 Research and Development Center 24-inch cavitation tunnel, where 

 the effects of the various concepts on both foil tip vortex cavi- 

 tation inception and performance were established. These measure- 

 ments were made at a Reynolds number R , based on root chord length, 



fi 

 of approximately 5 x 10 . 



Some of the more fundamental aspects of the tip vortex rollup 

 proccess have been documented through the use of flow visualization 

 techniques. The results for the tip vortex cavitation delay con- 

 cepts indicate substantial increases in the tip vortex cavitation 

 inception speed relative to the unaltered tip; i.e., a 94 percent 

 increase for the roughened tip, 38 percent for the bulbous tip, and 

 54 percent and 33 percent for the active and passive mass injected 

 tips respectively. These results were obtained over a wide range 

 of foil angle of attack and with little or no measurable loss in 

 foil performance; i.e., no measurable lift decrease or drag increase. 



ADMINISTRATIVE INFORMATION 

 The research reported in this paper was sponsored by the Naval Material Command 

 Exploratory Development Program which is administered by the Ship Performance Depart- 

 ment of the David W. Taylor Naval Ship Research and Development Center (DTNSRDC) . 

 Funding was provided under Program Element 62543N, Task Area ZF 43-421-001 and Work 

 Unit 1500-104. 



INTRODUCTION 

 On a lifting surface of finite span, pressure gradients of opposite signs exist 

 on the pressure and suction sides. The span-wise velocity components at the tip 

 are similarly of opposite sign, -creating a vortex located at the foil tip, as shown 

 in Figure 1. This tip vortex phenomenon presents special problems in practically 

 all applications of winglike bodies; e.g., the noise and vibration caused by the 

 interaction of the concentrated tip vortex trailed from the tip of a helicopter 

 rotor with a following blade and the potential hazard associated with the loss of 

 control of light aircraft which follow in the trailing tip vortex wake of heavier 

 aircraft. Additionally, in the case of marine lifting surfaces, this phenomemon 



