Gas-Turbine Powerplants For Two-Phase Hydropropulsion 



QA 



1.2 0.4 



Fig. 38 - IB-(2) powerplant: y 

 for a few values of Pp (no solu- 

 tion above) {^i - 0.9, p = 12, a. p.) 



This limit is imposed if the gas injection must be made possible. On the other 

 hand, a pure water jet can offer higher limits, imposed by the condition of no 

 thrust (see Figs 17 and 41, dashed line) or by the condition of maximum effi- 

 ciency (Fig. 41). The last condition is actually comparable with the pumpjec- 

 tor's, since the limit of this corresponds roughly to maximum efficiency. 

 Therefore, it appears that a (/3 = 12)-pumpjector allows higher advance speeds 

 than the water jet up to /3p = 7, while above this /3p the water jet allows higher 

 speeds of maximum efficiency than the pumpjector. The inflow ratio y required 

 by a pumpjector is increased by /3^ and it approaches the water jet values. 



The previous considerations confirm the idea that a system of gas 

 injection as modification of the water jet either design or operation is possible, 

 and it accomplishes a large improvement of the performances. 



(e) For the hydrojector the condition of maximum efficiency does not 

 allow high thrust (Fig. 41); the a corresponding to ^g^ax is about 0.45, that is, 

 a somewhat low value. Higher thrust can be obtained at lower efficiency, but 

 the actual problem in the hydrojector design is the discharge cross section. In 

 Fig. 41 a line at A^j/A„ = 1 for a conventional nozzle is shown; the zone at its 

 right is not practicable if a discharge cross section higher than the chamber 

 one must be avoided. This limitation practically does not affect the efficiency 

 range, but it is very restrictive for the thrust, especially at high speed. 



Better results can be obtained with a triincated nozzle. In this 

 case, the condition A^/A^ = 1 provides a specific thrust which can be 0.64 at 

 v^ = 50 m/s. (It must be observed that the condition A^ A^ = 1 for a nozzle 

 truncated at throat means that the chamber mixture speed coincides with its 

 critical speed. Therefore, conditions at A^/A„ > 1 are physically not available, 

 because it would correspond to choking in the chamber.) 



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