Dupovt 3 Viscont'i , and Merle 



the external flow upon the internal flow is relatively low and can be 

 approximately taken into account in the "separate flow" approach. 



For instance the transversal distribution of approach velocity 

 into the pump may be simulated by properly adjusting the profile of 

 the intake bell-mouth of the model. This adjustment is based upon 

 calculation (perfect fluid and boundary layer) and upon smaller scale 

 tests of the complete propulsion unit in a hydrodynamic tunnel. 



As regards the discharge nozzle, the absence of external flow 

 in the test rig described below, slightly modifies the jet contraction 

 compared with the prototype nozzle. Therefore we carried out model 

 tests of the pump with various nozzle diameters and finalised the 

 nozzle diameter adjustment during the prototype tests in the 

 TOULOUSE high-speed towing -tank. 



5. 2. Methods of approach applied to the design studies of jet propel- 

 lers 



The methods mentionned hereafter are the ones we applied for 

 finalising the hydraulic design of the straight flow 50 knots jet propel- 

 ler dealt with in § 7. However the same general way could be follow- 

 ed for Z flow jet propeller design, with some adaptation. 



a) Intake mouth of the nacelle 



Analysis of flow in this part of the machine requires the con- 

 sideration of both internal and external flow. Two main methods 

 have been used : 



_ potential flow axisymmetric computation with a special at- 

 tention towards the cavitation limits of the circular leading 

 edge area. 



_ experimental study on a hydrodynamic tunnel where the in- 

 ternal flow was separately controlled (see fig. 3). 



These approaches could well be adapted to the design studies 

 of intake scoop of a % flow jet propeller. 



b) Driving pump 



A special test rig had to be developped for that purpose as will 

 be explained in § 6. 



16 



