Gas Nuclei Trajectories and Cavitation Inception 



DISCUSSION 



L. van Wijngaarden 

 Netherlands Ship Model Basin 

 Wageningen, The Netherlands 



The paper shows very clearly the effects of body size and bubble population 

 on cavitation inception. 



At the Netherlands Ship Model Basin, experiments have been conducted with 

 cylindrical bodies with a hemispherical head. The value of Cp ^.^ is equal to 

 -0.74 for these bodies. 



The results of the cavitation inception measurements show a bubble radius 

 at incipient cavitation of about 10"^ m. Very roughly speaking this is an order 

 of magnitude smaller than those occurring in the report (Figs. 7 and 9) under 

 discussion for comparable sizes. 



Can the authors tell us in what direction r^^ varies if, other conditions 

 being held constant, Ic I is increased. 



° ' ' p mi n ' 



Secondly, can the authors give on the basis of the present work any sugges- 

 tion as to how cavitation inception results from different water tunnels may be 

 compared ? 



REPLY TO DISCUSSION 



Virgil E. Johnson, Jr., and Tsuying Hsieh 



With regard to Mr. Johnsson's remarks concerning the necessity for larger 

 models to minimize scale effects when only very small nuclei are present (as in 

 tunnels with resorbers), our study certainly indicates this to be true. A similar 

 conclusion is that higher speeds are also necessary to minimize scale effects 

 when only very small nuclei are present. 



Concerning Professor van Wijngaarden's comments relative to the effect of 

 magnitude of Cp ^. 

 following information. 



the magnitude of C . ^ on the phenomena discussed in our paper, we submit the 



The nuclei screening process described is most pronounced for bodies with 

 strong -stagnation regions followed by a short axial extent of low-pressure 

 region. The effect is probably negligible for bodies with small-stagnation 

 regions followed by low-pressure regions of long-axial extent, such as thin 



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