Ducted Propellers 



Propulsion later, we shortened this discussion somewhat. However, related ma- 

 terial which had been submitted in prepared communications was presented by 

 G. Rosen from Hamilton Standard and J. Duport and J. Renard from Sogreah. 

 This included a short description of the very extensive study recently completed 

 by Hamilton Standard and the numerical programs used by Sogreah for high- 

 speed inlet conditions. A new 1200 m. towing tank under construction in France 

 with a fast gas-turbine-driven carriage was also mentioned. Several other par- 

 ticipants made supporting remarks and clearly indicated the wealth of data avail- 

 able from NSMB to NPL, from Skipsmodeltanken of Norway to the Sao Paulo 

 Towing Tank, for most ship applications, if ". . .we can find an owner prepared 

 to fit one." 



We finally addressed ourselves to the third and last objective, namely, to 

 recommend the future work required in general ducted-propeller technology. 

 Without order or preference, the following possibilities were suggested: 



Refine the mathematical model(s) for conditions at or near 

 zero forward speed and lower rotational speeds. 



Incorporate more exact analyses for the effect of the hub, 

 with special attention to larger hub-to- shroud-diameter 

 ratios. 



Improve the existing analyses for the case of angle of attack 

 and nonuniform or angular variations in inflow. 



Study ways and means to avoid separation/cavitation on duct 

 and center body. 



Complete the analytical efforts to formulate an optimum 

 ducted-propeller design, analogous to the Goldstein optimum 

 for the free propeller, cf., J. A. Sparenberg, and confirm the 

 design by experiment. 



Develop test facilities suitable for large-scale (10 m.) cavita- 

 tion tests. Such facilities would also fulfill many other needs. 



Work on application of lateral thrusters to large ships at 

 cruise speeds. 



Investigate the use of lifting- surface theory for the propeller in 

 the calculation of propeller- shroud interaction. Also, include 

 propeller thickness. 



Continue to refine the state of the art of ducted-propeller de- 

 sign procedures and narrow the differences between these pro- 

 cedures and measurements. 



These recommendations were by no means unanimous. Some felt, in particular, 

 that with respect to the first three recommendations, emphasis should be placed 

 on the nonlinear but potential flow aspects. Others felt that, when linear theory 



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