TIP VORTEX ABATEMENT CONCEPTS 

 SCHEMES PROPOSED IN THE LITERATURE 



The literature identifies approximately twenty concepts for allevi- 

 ating tip vortex. These concepts, some of which are shown in Figure 4, 

 generally involve wing tip modifications. Table 1 identifies the biblio- 

 graphy listing with the particular concept considered. Comparison of the 

 relative merits between concepts is difficult due to differences in the 

 experimental procedures, the recorded data, and the operational Reynolds 



number R . 

 n 



Figure 5 shows the range of investigative Reynolds number R and angle 

 of attack a for the various concepts shown in Figure 4. The majority of 

 these investigations were performed in low-speed wind tunnels and involved 

 far-field wake surveys of vorticity generated by planar wings. Approxi- 

 mately one-half of the investigations include some force data to determine 

 the efficiency of the concept. Only a small percentage of the studies were 

 performed in water and recorded cavitation data. 



In light of the above findings, it is apparent that the results of the 

 literature offer very limited guidance when considering the problems of 

 delaying tip vortex cavitation on a marine propeller. The crucial cavita- 

 tion inception data and the wing near-field wake data are generally not 

 available. In addition, for application to marine propellers, any concept 

 must be evaluated with regard to certain practical aspects, e.g., structural 

 suitability, reliability, and operational environment. Also, the concept 

 should not be a source of any additional local cavitation and should not 

 introduce prohibitive performance penalties. These requirements should 

 be kept in mind as the details of the various concepts are discussed. 



SPANWISE LOAD DISTRIBUTION 



The strength of the tip vortex is strongly dependent on the magnitude 

 of the spanwise load distribution near the tip. As the loading shifts in- 

 board, away from the tip, the tip vortex strength decreases. This is 

 accomplished for aircraft through the use of wing flaps, which effectively 

 change the wing aspect ratio, and for propeller blades through appropriate 



