2.2 

 2.1 

 2.0 



O 1.8 



I- 

 < 



1.7 



Ui 



w 1.6 



Z 



g 



£ 1.5 



o 



1.4 

 1.3 

 1.2 - 

 1.1 - 

 1.0 



5 dor 



□ 800 ju 



O 600/11 



^ 400 ju 



O 90m 



STANDARD 



ROUGHNESS 



PATTERN 



0.16 



0.20 



0.24 



0.40 



0.44 



0.52 



LIFT COEFFICIENT C, 



Figure 24 - Tip Vortex Cavitation Inception Speed Ratio as a Function of Lift 

 Coefficient for Varying Roughness Grain Size — 

 Standard Roughness Pattern 



where the subscripts 3 and p refer to the altered and parent foils, respectively. 

 The data in Figure 24 exhibit the following trends: 



(a) . Each of the roughness grain sizes produces significant increases in the 

 TVC inception speed; e.g., for C ~ 0.28, 53 percent for 90 micron, 71 percent for 

 400 micron, 92 percent for 600 micron, and 74 percent for 800 micron. 



(b) . In general for a fixed roughness size, the effectiveness of roughness is 



reduced for the higher a; i.e., for each grain size, U„/U decreases as C increases. 



p P ^ 



Apparently the ability of the roughness to dissipate or destablize the tip vortex 

 core energy is reduced as the tip vortex vorticity is increased, i.e., increased C . 



34 



