Water-Jet Propulsion for High-Speed Surface Ships 



flow analysis". This does not mean that each flow can be considered 

 as independent from the other ; particularly the circulation around the 

 duct and the negative thrust on this part of the propeller are properly 

 taken into account. 



The authors were probably wrong not to explain clearly enough 

 that the so-called "separate flow approach" is preceded by a "complete 

 flow approach (i. e. dealing with both flows together) which serves the 

 purpose of determining the respective "limit conditions" (i. e. bound- 

 ary conditions) of each flow. 



Before coming back to this "complete flow approach "which, 

 in the case of the "I sere" design studies, was a simplified one - we 

 feel it advisable to emphasize : 



(i) that either internal or external flow is entirely determined 



as soon as the "limit conditions" are fixed. For the internal flow, 

 these conditions are (see Figure 10) : 



the "flow tube" separating both flows, upstream as well as 

 downstream of the propeller, and the internal solid boundaries ; 



pressure (which is equal to poo) at each remote cross- 

 section SI and Sj ; 



velocity distribution in each of these sections. Each flow 

 can then be analysed from these limit conditions (as soon as they are 

 known) without further reference to the other part of the complete 

 flow. 



(ii) predetermination of the "complete flow" need presetting of 



- the circulation around the duct (or equivalently the intern- 

 al rate of flow) 



- the radial load distribution of the impeller (or equivalent- 

 ly the normal velocity distribution in section Sj . 



Once these figures are preset, the profiles (and r.p.m.) of 

 the impeller (stator and rotor) have to be designed in accordance with 

 them ; it is enough for that to apply to the impeller design the limit 

 conditions proper to the internal flow. 



(iii) in a "inviscid flow approach" as the one considered present- 



ly, the thrust of the propeller (including the duct) can be derived from 

 the internal flow description alone. This is an obvious result of the 

 momentum equation applied to the complete flow. 



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