Gas-Turbine Powerplants For Two-Phase Hydropropulsion 



Q2C 



(c) T^ig, for some values of a^ and for: \^ = 0.9 ..j f 

 ^ = 0.7 (p = IZ, a. p.) 



Fig. 29 - IR-(Z) powerplant performances (Continued) 



This efficiency appears to be surprisingly high when compared 

 with the water jet's, which does not reach 0.16. An improvement of 35% is 

 sufficiently large to include a margin for the inaccuracy due to the higher un- 

 foreseeability of two-phase flow with respect to water flow; that is, a hot-gas 

 hydrojector can be expected as actually competitive with water jets as for ef- 

 ficiency. On the other hand, the observation of the propulsive performances 

 allows control if the efficiency peaks are reached at values of discharge cross 

 sections not higher than 1, especially when truncated nozzles are adopted. 



Another advantage as regards to water jets is obtained in terms 

 of y (that is, in terms of turbine flow rate for given water flow rate), since 

 the values of y which correspond to the efficiency peaks for the hydrojector 

 are considerably lower than for the water jet. For example, at a^ = 0.6, 

 V^ = 35 m/s, M^, = 1.72 for the IR-(2) system we find v^ = 0.18, y = 5.7x 

 lO"-^, and cr = 0.96; the water jet which could provide the same value of a at 

 the same speed has /3p = 19, where it is y = 1.3 x 10" ^ and v^ = 0.15. The 

 advantages in terms of y are higher when the operating range is very close 

 to the limits at A = 0; also, however, far from this condition lower advantages 

 can be always obtained. 



Figures (29), (30) and (33) show the effect of changing the flow 

 rate fractions: An increase of a^ causes an increase of efficiency peak speed. 

 Since ai are independent of M^^, a change of their distribution does not change 

 cr, but (Fig. 30) it changes the inflow ratio y; therefore, as was obvious, a 

 change in the turbine air flow rate m^ as well in the flow rate fractions a-^ will 

 be required to change the advance speed. 



1149 



