Dynamics of Hydrofoils as Applied to Naval Propellers 



The tolerances of the models resulted as follows: s 



1 



mean pitch . ± 0.3% ,. 



thickness on inner radii ± 1.8% _•; 



thickness on outer radii ±0.9% 



3.2 Experimental Results ." ' . . .; 



The final results of the tests carried out in a cavitation tunnel, at constant 

 velocity and variable revolutions, are reported in Table 8. Experimental data 

 have been corrected for wall effect according to the formula 



V . a 

 Tr= ^ " 2 



f/l +Cj.- 



in which ^ • . - ;; 



V = velocity of the water in the tunnel, measured by a venturimeter; 



v^ = advance velocity of the propeller in open water at the same thrust 

 constant C^; i . : 



a = propeller disk area/tunnel test section area. • 



3.3 Comments and Conclusions 



An examination of the results presented in Table 8 gives rise to the follow- 

 ing comments and conclusions: 



(a) The actual performance of propellers with a low expanded blade 

 area ratio (equal to or less than 0.45) matches the expected data very well 

 when the mean lines a = 0.8 and NASA 65 are adopted (propeller models 

 E.1066, E.997, E.998 and E.999), and when the hydrofoil coefficients sug- 

 gested in Sec. 2. are used. 



When the mean line a = l is employed, performance is about 10% 

 lower. This reconfirms the advisability, already mentioned in previous 

 pages, of adopting a reduction coefficient equal to 0.675 for viscous flow 

 (instead of 0.75 as used in designing the models in question) when employ- 

 ing the mean line a = l. 



(b) Propellers with a high expanded blade area ratio are subject to a 

 further drop in performance (valuable at 10% when 4^4^ > 1.00). Such a 

 conclusion has been reached by other authors, and the problem has given 

 rise to many thorough, theoretical and experimental investigations (8), (9), 

 (10), (11). 



1039 



