Gas-Turbine Powerplants For Two-Phase Hydropropulsion 



DISCUSSION 



Earl Quandt 

 - Naval Ship Research and Development Center 



; Annapolis, Maryland 



Professor Pallabazzer has, in my opinion, presented commendable ideal 

 component and system analysis of several liquid-phase, continuous air-water 

 jet -propulsion arrangements. However, because of the assumptions concerning 



(a) Isentropic gas expansion in the presence of large amounts of 

 cold liquid, and 



(b) No relative slip between the gas and liquid phases, 



I would caution those who might interpret these results with too much 

 optimism. • ' 



REPLY TO THE DISCUSSION 



Rodolfo Pallabazzer 



I wish very much to thank Mr. Van Gent because his intervention allows me 

 to clear up a passage which appears to be questionable. The question arises 

 from the expressions mentioned by Mr. Van Gent about a quasi-constant pres- 

 sure mixing and a constant- section chamber, which obviously are inconsistent. 

 As a matter of fact, the first expression was never an assumption, that is, the 

 pressure was never set as a constant in the chamber; the expression about a 

 quasi -constant pressure mixing is purely qualitative and arises from the fact 

 that some quick checks showed only small pressure decreases. Therefore, the 

 equations appear not to be influenced by the constant-pressure assumption, be- 

 cause this assumption was never made. 



As regards the constant-cross-section chamber, this also has not the 

 meaning of a statement but just of a reference; indeed, as Mr. Van Gent kindly 

 emphasizes, only an experimental analysis can suggest the shape of the cham- 

 ber. In a purely theoretical analysis like the present one, there is no effect of 

 the shape of the chamber; therefore, it can be supposed cylindrical without any 

 difference in the discharge results. A difference appears if the discharge data 

 are referred to the chamber cross section, which happens here for the thrust 

 coefficient only. Since its expression [Eq. (26)] depends on the diffusion coeffi- 

 cient 0, the reference cross section is that where the flow velocity is v„ 

 (1 - 4>)'^'"^; this can be not the largest cross section if the chamber is actually 

 divergent. In practice one must pay for this inaccuracy until the shape of the 

 chamber cannot be specified. For this reason in this paper a large emphasis 



1170 



