Brockett (1972). This body, termed the NSRDC body, like the ITTC body, 



possesses a laminar separation up to a critical Reynolds number based on a 



diameter of about 0.46 x 10 at which both the e method (n = 7) and 



observations show transition to occur, thereby forestalling the presence 



of separation. 



For Reynolds numbers less than this critical one the appearance of 



cavitation on this body is very similar to that on the ITTC body, i.e., a 



smooth band cavity is seen (in the Caltech HSWT) . At greater Reynolds 



numbers this band type gives way to patchy regions of foamy cavitation 



bubbles, intermittently spaced around the periphery with the smooth sheet 



cavity. Finally, at greater Reynolds numbers of say 7 x 10 , spots or 



wedges of cavitation are seen. The inception index on one such body has 



been determined in two different facilities with quite different results 



(Arakeri and Acosta 1976). In the Caltech facility the correlation 



a. - c was found to be valid for Reynolds numbers less than the critical 



1 P s 

 one. A natural transition, precluding the separation, existed for Reynolds 



numbers greater than about 5 x 10 . The observed inception index remained 



quite close to the pressure coefficient at the site of the predicted 



transition location (Figure 21) though there was hardly any change in the 



pressure coefficient from the separation value. 



Spot or wedge cavitation was also observed to occur at the greatest 



values of Reynolds number originating from positions near c . These 



min 

 indices are quite different from the attached cavitation associated with 



the presumed location of transition. 



However, more recent studies, by Huang and Santelli (1977), show that 



on one body not subject to a laminar separation, travelling-bubble inception 



was, in fact, observed at the estimated position of transition. From these 



observations, they deduce an inception index behavior of the form of 



Equation (11) with the local pressure coefficient being that of transition 



as in Figure 17 and with the unsteady term being about -0.06. This latter 



is, however, air content sensitive, which is a subject we shall return to 



later. 



38 



