A PRELIMINARY DESIGN THEORY FOR POLYPHASE 

 IMPELLERS IN UNBOUNDED FLOW 



B. Yim 



David W. Taylor Naval Ship Research and Development Center 

 Bethesda, Maryland 



ABSTRACT 



The main role of preliminary design for supercavitating propellers is to supply the basic data for 

 the final design, such as: the hydrodynamic pitch angle, the radial load distributions, the approximate 

 cavity length and the distribution of cavity-source strengths which will help determine the three- 

 dimensional cavity-source distribution. For this purpose, the effective use of supercavitating cascade 

 theory with lifting-line theory is discussed together with influences of neighboring cavities on cavity 

 drag, the hydrodynamic pitch angle, inflow retardation and the optimum pitch distribution of the 

 propeller. 



The computer program developed here is applied to several existing propeller models. The results 

 show that propeller efficiency is predicted well but pitch distribution is a little larger than for the 

 model. The results are analyzed and compared with the results of a lifting-surface design method 

 which has been developed recently for use with the present preliminary design method. 



NOMENCLATURE 



c Chord length of blade section 



c Camber factor 



C, Design lift coefficient of blade section 



C, Lift coefficient of a foil in an infinite medium 



C T Thrust coefficient of propeller 



C_ Power coefficient 



D Diameter of propeller 



d Distance between the leading edges of neighboring blades at each section 



G Circulation distribution 



J Advance coefficient, V/(DN) 



N Rotation per unit time 



R Propeller radius 



r Radial coordinate divided by propeller radius 



r H Hub radius divided by propeller radius 



V Ship speed 



w Wake fraction 



