development on the ITTC body. This body, however, has a much smaller 

 laminar-separation region and in the Caltech HSWT the progress from 

 initial inception to the macroscopic cavitation seen in Figure 7 is 

 practically instantaneous. But, again, careful study shows that the ter- 

 minus of the laminar region is the location of the most intense cavitation, 

 and it is this location where cavitation is seen to disappear as pressure 

 is raised. 



We can see that a laminar-separation region has an important role in 

 cavitation inception. At the very least, the static pressure there pro- 

 vides the reference pressure at which inception occurs. It would then seem 

 most plausible that 



a. = -c (6) 



1 P„ 



(7) 

 P i 

 reattach 



i.e., we identify the inception index with the pressure coefficient at 

 separation or reattachment, the latter being Reynolds number dependent. 

 In fact, this suggestion had previously been made by Bailey (1970) based on 

 hydrofoil tests. Here we exhibit tests on the two bodies, hemisphere and 

 ITTC, made in the Caltech HSWT in Figures 13 and 14, respectively, in which 

 it may be seen that the rule is better than 



a. - -c (8) 



1 P • 

 min 



and that the inception index approaches -c as speed increases. But, 



s 

 there are differences in the two sets of results: namely, 



24 



