of the problem became immediately clear. We see in Figure 6 a reproduction 

 of this photograph in which it can be seen that quite different kinds of 

 cavitation are present on those test bodies and a closeup photograph taken 

 in the High Speed Water Tunnel (HSWT) at Caltech (Figure 7), reveals an 

 attached, smooth form of cavitation with no travelling bubbles whatever! 



Forms of Cavitation 



The photograph of Figure 7 is certainly far removed from the concept 

 of travelling-bubble cavitation, and although it is quite different from 

 many contemporary photographs in other facilities, it is by no means 

 unique. Eventually, by observation on this and other bodies, such as the 

 hydrofoil of Figure 8, we, together with other workers, became convinced 

 that three more-or-less different kinds of cavitation could usually be 

 distinguished. These are:* 



1. Travelling-bubble cavitation. 



2. Sheet or band cavitation. 



3. Attached spots, "fingers" or "wedges" of 

 cavitation. 



All of these forms can be seen in Figure 6. In the light of all these 



observations and suggestions it seemed an appropriate time to consider, in 



more detail, the actual viscous flow about these various bodies that had 



previously been studied. 



VISCOUS EFFECTS ON CAVITATION INCEPTION 

 Experimental Methods 



As in aerodynamic flows, we expect, in hydrodynamic applications, 

 changes to be brought about by viscosity in surface boundary layers. We 

 expect to be wary of laminar separation in adverse pressure gradients and 

 to anticipate laminar-to-turbulent-flow transition of attached boundary 

 layers at sufficiently high Reynolds numbers. Also we know, in a general 

 way, that although transition is a complex process, a precise knowledge of 

 its location is rarely required except for drag calculations. But to know, 



*Vortex cavitation also occurs on lifting surfaces but is not included 

 in the present discussion. 



14 



