no simple correlations with surface tension or "time of travel" have 

 proved successful. And, as suggested, the subsequent theories based 

 largely on Parkin and Kermeen's 1953 observations have had difficulties. 

 As the final example of Table 1, we may cite again, that of Holl and 

 Kornhauser (1970). They, like van der Walle (1962), used the conceptual 

 idea of nuclei stabilization on the body by pressure gradient in a region 

 of tension, thereby, permitting growth through the Plesset-Zwick bubble 

 mechanics to explain the thermal effects experienced in hot water and some 

 non-aqueous fluids. Unlike many coworkers, they carried out many experi- 

 ments, only to find a negative correlation for the proposed mechanism. 

 All of these theories, and others, are summarized by Holl in his 

 exhaustive review article in "Cavitation State of Knowledge," (Robertson 

 and Wislicenus 1969). At that time, the International Towing Tank 

 Conference (ITTC) round robin tests were, regrettably, not very widely 

 known. 



The ITTC Tests 



Under the auspices of the ITTC, tests on a flat-faced ellipsoidal body 



were carried out in many different laboratories throughout the world, with 



the apparently chaotic results seen in Figure 5. There was no doubt that 



these tests were extremely thought-provoking, even if they did show a 



potentially embarrassing lack of uniformity in a standard test. Some of 



the oddities of these results, namely O. » -c were shown by Holl to 



i p . 

 mm 



be due to attached cavities in more-or-less equilibrium with the dissolved 



air in the tunnel water. Then p . = p . , where p is the gas satu- 



mm sat sat 



ration pressure, so that O. - p /q and as q decreases the cavitation 

 v l sat 



index may become quite large. At about this time it was suggested by 

 Johnsson (1969) that perhaps these differences were due to a laminar 

 separation. Peterson (1969), had, in fact, already observed a laminar 

 separation on a similar type of ellipsoidal body, but at tunnel speeds 

 less than those of his subsequent inception tests. A most graphic and 

 telling comparison was made by Johnsson (ibid) who showed a photograph of 

 the cavitation actually seen on some of the ITTC test bodies. Then part 



12 



