Gas -Turbine Powerplants for Two-Phase Hydropropulsion 



It already appears from these remarks that the hydrojector at moderately low 

 speed seems to promise higher efficiency than the pumpjector and, by extrapo- 

 lation, than the water jet. 



(c) The functions k-,, M^, Mj;, M'J ', V^, M^, V^, /3^, A^/A„, and 

 A^,/Ao are independent of the actual conditions of the gas, which are expressed 

 by the chamber density Pg^ ; they depend just on the parameters v^, /Sp, and 

 Mu, besides on the gas thermodynamical nature. On the contrary, the mass 

 ratio e will depend on p^-^, that is, on the engine powerplant configuration. 



(d) The area ratios A A^ present a strong increase in proximity of 

 the discharge limits M^. It can often be AA^ > 1, depending on the "dilata- 

 tion" of the gas during the expansion, as was noted. 



4 DEFINITION OF THE PERFORMANCE PARAMETERS 

 4.1 Thrust . •' 



For an adapted nozzle, the net thrust S will be . , 



S = m^CV^- V„) + m^V^ = ^^^y J ^ - 1 ] . (24) 



Let us define a specific thrust as 



s 



V. 



'^H^o, phA„ vj(i- 4>) 



1/2 V 



(25) 



This is a fundamental figure of merit for comparison among propulsors of same 

 design and advance velocity. On the other hand, the thrust coefficient c 



1 



2c7(l-^)i'2 



^hAoV, 



(26) 



depends on the frontal diameter of the propulsor instead of the overall design 

 coefficient A^(l - s^)^ '^; it will be especially useful in comparisons among pro- 

 pulsors of different shapes. 



If the nozzle is truncated during supersonic flow (under expanded nozzle), 

 the thrust s^ will be 



S, = VV^-V„) + A^(p^-p„) . (24') 



In the present work we will take into consideration the case of nozzles which 

 have been truncated at throat, that is, at the critical pressure p^. The corre- 

 sponding thrust is 



Sc -- '^h(Vc-V») + A^(p^-p„) , (24") 



1127 



