Figure 2 - Cavitation Number K for Incipient 

 Cavitation as a Function of Reynolds 

 Number for Bodies with Hemis- 

 pherical Noses 



These results were reported by R. W. Kermeen, 

 California Institute of Technology, Reference 11. 















































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are of some interest in connection with the remarks made in the subsequent section of this 

 report. The curves shown were obtained by first allowing cavitation to become fully develop- 

 ed at cavitation numbers well below the inception value and then raising the ambient pressure 

 until cavitation just disappeared. This point was defined as the "inception point." Attempts 

 to observe inception by the direct procedure of approaching the critical point starting with a 

 noncavitating system evidently resulted in so large a scatter that it was difficult to obtain 

 accurate correlation of the results. Kermeen remarks that a so-called "hysteresis" could 

 often be observed, i.e., when approaching the inception point from a noncavitating condition, 

 much lower critical cavitation numbers were observed than those at which cavitation disap- 

 peared. Nevertheless, the results evidently indicated the trends clearly shown in Figure 2. 

 These results are of further importance in that they tend to substantiate the physical picture 

 of the role of nuclei in cavitation inception since the observed trends coincide with the ex- 

 pected consequences of this concept. 



Although the results obtained by Kermeen and Parkin are consistent with the present 

 ideas of the role of nuclei, there still remains the anomaly of the results obtained by Crump 

 in which simultaneously increasing time of exposure to low pressures and decreasing pres- 

 sure resulted in decreasing critical cavitation numbers.* On the other hand, it will be ob- 

 served that in Crump's experiments, the inception point was obtained by approaching, from a 

 noncavitating condition, and that the same effect characterized as "hysteresis" was obtained 

 when approaching from the fully cavitating condition, (The latter method was not considered 

 as a criterion for inception in his experiments and no quantitative results were recorded.) 



♦whether Crump's results can be reconciled 

 vestigated. 



terms of the effects of the pressure gradients remains to be in- 



