Gas-Turbine Powerplants For Two-Phase Hydropropulsion 



Fig. 1 - The Hydrojector: schematic cutway 



owing to the free- stream velocity, is accelerated by a high-energy low-rate pri- 

 mary gas jet (supposed in the figure as injected from the chamber walls). The 

 chamber can present a rectangular [8] or a circular [7] cross section. In an 

 ideal propulsor there is no dissipation, since the water enters the chamber at 

 same (high) pressure and (low) velocity of the gas. The basic effect consists 

 in the production of a high-density two-phase compressible fluid, which can be 

 accelerated in the nozzle to high speed. The drag effect is important just be- 

 cause it avoids slip, not because it accelerates water. In the hypothesis of no 

 slip effect there will be no momentum exchange between water and gas, and the 

 only phenomena in which we will be interested are the total amount of energy 

 and the direct energy exchange. The slip effect can be very low in a two-phase 

 mixture when operating at high-flow-rate ratios of water to gas (that is, in 

 "bubble" flow). However, the slip effect can be differently strong, depending 

 on the jet shattering into the water and on the bubble diameter, that is, on in- 

 jection technique and on chamber design. An injection coaxial with the water 

 stream (see, e.g., Ref. [9]) will provide a gas axial momentum recovery but 

 also a strong slip effect with large bubbles mean diameter, while a radial in- 

 jection [7j will destroy the axial momentum, producing small bubbles mean 

 diameter and lower slip effect. 



It is beyond the purpose of this work to investigate the methods of opti- 

 mizing the ejector performances, and later an idealization will be done about 

 its behavior. 



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