31 



Figure 20 - Air-Pilled Cavity Formed Behind a Disc 



Figure 21a - a = 0, 



S, Exposure Time: 2 Seconds 



Figure 21b - a = 0.188, Exposure Time: 1/10,000 

 Second 



Figure 21 - Cavity Behind a Disc 



It is possible to define the limits of the flow configuration that 

 behaves as a steady-state cavity on the basis of the correlation between av- 

 erage cavity shape and cavitation number and of results showing that cavity 

 shape is a single-valued function of the cavitation number. 54 The relation 

 between the maximum ordinate of bubbles formed behind a disc and the cavita- 

 tion number is shown in Figure 23- It is seen that above a certain cavita- 

 tion number, the data show a large scatter with no apparent correlation, while 

 below this region the data fall on a single curve. It is difficult to deter- 

 mine the process that takes place during the transition. However, it appears 

 from an examination of photographs of the region titled "vortex cavitation" 

 in Figure 23, that cavitation in this region is intermittent as a result of 

 the shedding process. In the region of the lower cavitation numbers, however, 

 there is evidence that the zone of cavitation is more or less continuous al- 

 though violent oscillations may still be observed. 



