Bindel 



aj, ttj Maximum variations of the angle of attack 



y Oscillation amplitude 



Q Inclination of the flow on the propeller shaft 



cp Longitude of a blade element 



^i> Phase of the oscillation relative to the incidence variation 



a- Cavitation parameter (based on the velocity V). 



INTRODUCTION 



The flow coming to a ship propeller is often inclined on the shaft, particu- 

 larly in the case of multiscrew fast ships such as destroyers or torpedo boats. 

 As a consequence, the relative flow is unsteady, even if the wake of the hull is 

 uniform, with the corresponding drawbacks: vibrations and premature 

 cavitation. 



There may also be severe erosion near the propeller hub. In some cases 

 it is possible to prevent this erosion by modifying the shape of the blade sections 

 [l], but in other cases this procedure seems to be insufficient [2j. 



Thus, among the solutions that may be considered, one consists in adjusting 

 the pitch of each blade to the local conditions encountered, so that the variations 

 of the relative flow become as small as possible: this would constitute an 

 oscillating-bladed propeller. This solution may be also considered for a pro- 

 peller operating in the wake of the hull (the case of a single- screw ship, for ex- 

 ample), but the law of pitch variation is here generally less simple. 



It was initially planned to evaluate this idea by experiments on several pro- 

 peller models, but, due to a lack of time, it was not possible to test more than 

 one model. The present paper gives the results of this experiment and the ten- 

 tative conclusions that can be drawn concerning oscillating-bladed propellers. 



VARIATION OF THE INCIDENCE ON THE BLADE ELEMENT 

 DUE TO THE INCLINATION OF THE SHAFT 



Let V be the velocity of the flow and 6 the angle of inclination of the flow 

 on the propeller shaft (Fig. 1). The axial flow component is then V cos 6 and 

 the transverse component V sin d. 



Assume that the hub is an infinite cylinder of radius Tj^; the transverse flow 

 is then the well-known two-dimensional potential flow around a circle (at least 

 out of the viscous wake of the shaft). At a given point of radius r and longitude 

 cp (the angle between the radius and the velocity at infinity), the component of 

 the relative velocity normal to the radius (the transverse component v^) is 

 given by the formula: 



1498 



