NUMERICAL RESULTS AND DISCUSSIONS 



The preliminary design program is fully implemented when it is used with the final lifting-surface 

 design program' 22 '. These programs although tested for existing supercavitating propellers, have not 

 been used for designing a new supercavitating propeller. Experimental evaluations of propellers 

 designed by the new theory are planned for the near future. Among many propeller models tested 

 at DTNSRDC, two propellers, "DTNSRDC Models 3770 and 3870, were chosen for comparison. The 

 former propeller has three blades and a low advance coefficient and the latter has four blades and a 

 high advance coefficient. Experiments showed that both propellers had smooth cavities. The 

 experimental results and the previous design calculations are reported in Reference 3. 



The design and performance characteristics of the two propellers are listed in Table 1. The 

 predicted efficiencies of the lifting-line designs are very close to the measured efficiencies, although 

 they are related to the distribution of the leading-edge cavity thickness which is determined from the 

 cavity length predicted by cascade theory and a blade strength analysis. When the design leading-edge 

 cavity thickness is given, there are two design approaches used here in the preliminary design process 

 to meet the lift and the leading-edge conditions: Case 1 - specify the camber factor per unit C L 



Table 1 — Design and Performance Characteristics of Supercavitating Propellers 





Propeller 



3770 



3870 





Z 



3 



4 





P/D (0.7) 



0.786 



1.243 





EAR 



0.508 



0.727 





C/D (0.7) 



0.351 



0.344 



Experiment 



J 



0.44 



0.834 





a 



0.617 



0.45 





kt 



0.075 



0.115 





V 



52.0 



59.4 





by Venning & Haberman 3 



0.1004 



0.1402 





Preliminary Design 







kt 



(Lifting-Line Theory) 



0.075 



0.115 



Lifting-Surface Design 









Case 1 



0.073 



0.114 





Case 2 



0.073 



0.114 





by Venning & Haberman 3 



54.1 



64.0 





Preliminary Design 









Case 1 



50.1 



58.2 



V 



Case 2 

 Lifting-Surface Design 



50.5 



56.7 





Case 1 



47.8 



58.7 





Case 2 



50.4 



58.9 



