Duportj Visconti, and Merle 



velocity distribution at the nozzle outlet, i-e the momentum commu- 

 nicated to the jet. For these reasons we have found it necessary to 

 construct a specialized test-rig in which the momentum transmitted 

 to the propulsive flux is measured directly and not solely the incre- 

 ment of energy transmitted to the said flux. The design of this 

 test-rig also allowed for the necessity of simulating head (captation 

 energy) due to the forward drive speed of the ship. Thus a circula- 

 tory pump had to be used. 



The simulation of cavitation conditions is achieved by the con- 

 trol of absolute pressure on both sides of the model pump. 



The figures 5 and 6 show the basic arrangement of the test 

 rig. 



Maximum impeller diameter is 300 mm. The model, placed 

 between two tanks, allows visualisation of the impeller, distributor 

 and diffuse r. 



Water circulation is ensured by a 520 l/s pump with 9 metre 

 head at 835 rpm driven by a DC thyristorised motor at variable 

 speed between and 2 500 rpm. A l/3 reduction unit is mounted 

 between the pump and the motor. Motor speed stability is controlled 

 to within 1/100. 



The 500 mm diameter piping is fitted with two vaned elbows, 

 a manually controlled 500 mm diameter valve, a 3 50 mm diameter 

 vertical turbine flowmeter with calibrating piping. 



The 2. 2. metre diameter upstream tank was specially design- 

 ed to ensure correct feed to the pump : uniform flow distribution, 

 absence of vortex, etc. 



The water level is regulated by a capacitance sensor acting 

 upon rotation velocity of the circulation pump. The water level is 

 Zp =1,8 metres above the plane of the impeller. Absolute air pres- 

 sure above the water surface may vary between 0, 05 and 1, 7 

 atmospheres. The upper tank also supports the two water -floating 

 bearings - diameter 360 mm and 160 mm of the stator casing. 

 Internal stiffeners avoid displacement between these bearings. The 

 tank also supports the thrust-balance and the torque balance. 



The lower tank, diameter 2, 5 metres, was specially design- 

 ed to dampen jet energy without sucking unwanted air to the pump 

 while ensuring a stable level. The facility may be operated with the 

 nozzle either drowned or not. Absolute pressure above the water 



18 



