2.2 



- 



1 1 



1 1 1 1 



Rg = 5 (10)^, ROUGHNESS GRAIN SIZE-400 fi _ 

 — PARENT 



2.0 



- 





A SUCTION SIDE a=10.8C^ _ 







\ 



O PRESSURE SIDE a= 8.8 C^ (A 



1.8 



" 



\ 

 \ 

 \ 



□ BOTH SIDES a= 6.3C^ ^ '-' 



<= 1.6 

 X 



LU 



- 



/ .° °- 



Z 1.4 





\ 



/ 



t NOIl 





\ 

 \ 



/ /aO □ 



< 



1- 





\ 



/ / Q D 



% 1.0 



_ 



\ 



/ / / - 



o 





^ \ 



/ ry n 



0.8 







D 



/ J Y / 



0.6 



- 



on A 



//^/ 



0.4 



'" 





/^//^ 



0.2 





1 1 



_^i^^^ , , 



-0.1 



0.1 



LIFT COEFFICIENT C, 



0.2 



0.4 



Figure 22 - Cavitation Inception as a Function of Lift Coefficient — 



Roughened Foil Tip Pressure Side, Suction Side, and Both 



Pressure and Suction Sides — 400 Micron 



The foil force data indicated that only the 800 micron roughness size introduced a 

 significant performance penalty — a 5 percent increase in foil drag at design a. 



The TVC inception data for the various roughness sizes are shown in Figure 23. 

 These data indicate, for each roughness, substantial improvement in TVC performance 

 over a wide range of C . In general, TVC performance improves — lower a — as the 

 roughness size increases. Also, the differences between the 600- and 800-micron 

 data are small, which could represent a limiting roughness size for these particular 

 experimental conditions. In order to make a better comparison of foil performance 

 in terms of TVC due to variations in roughness, per se, the grain size data are 



32 



