DESIGN ANALYSIS 



OF GAS-TURBINE POWERPLANTS 



FOR TWO-PHASE HYDROPROPULSION 



Rodolfo Pallabazzer 



Politecnico di Milano 



Milan, Italy 



INTRODUCTION 



Marine propulsion is probably one of the most contradictory fields of engi- 

 neering research. Many propulsive systems and problems are in fact developed 

 in detail, but we do not have an exact idea of what kind of system would be the 

 optimum beyond the speed range in which we now operate. There are no uncer- 

 tainties about hydrodynamic problems, because the hydrodynamic phenomena 

 are uniquely determined by the motion itself; besides, the solutions until now 

 proposed to delay hydrodynamic problems are hydrodynamically corrected and 

 can be easily shared; therefore, hydrodynamic problems are in a refinement 

 and improving phase for some time to come. 



This cannot come true for propulsive problems; any new speed field or en- 

 vironment yields special exigencies, related to the achievement of high propul- 

 sive performances, such as low fuel consumption, low weight, large range, 

 mechanical simplicity, reliability, governing, control stability, and low addi- 

 tional drag induced by the propulsor on the base vehicle. 



Such a collection of disparate and often contradictory problems needs not 

 only lengthy and specialized research but also a wide-ranging tentative activity, 

 by means of which one could evaluate the availability of new solutions and achieve 

 exact ideas about the real exigencies of the operative field one wants to penetrate. 



One must admit that this kind of lengthy research is very poor, in marine 

 propulsion, especially when compared to aerospace propulsion. Few solutions 

 have been proposed and developed as advanced propulsors, apart from the well- 

 known supercavitating propeller and the water jet, and no solution has been pro- 

 posed for the powerplant but the classical mechanical connection between a gas 

 turbine and the propulsor. [Since the only jet propulsor sufficiently developed 

 for marine propulsion is the water-jet (or pump-jet) system, in the following it 

 will be also the fundamental term of comparison for other jet devices.] 



A new kind of propulsor has been proposed by Foa [1,2,3,4] based on non- 

 steady (cryptosteady) energy exchange between two fluids; this idea has been not 

 sufficiently developed for underwater propulsion to approach the expected 



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