content and particle content of fresh and sea water is of importance, however. 

 For most applications, in which the water contains a fairly high air-content, 

 cavitation in the form of air bubbles may begin at pressures well above the 

 vapor pressure. In general, however, cavitation will occur at or near the 

 vapor pressure with the cavities containing primarily vapor, some initial air 

 and possibly some gas diffused from the liquid into the cavity during the life 

 of the cavity. Although these statements are approximately correct for engi- 

 neering applications, the role of gas or solid nuclei in inception is of a 

 very complicated nature and is discussed in somewhat more detail in subsequent 

 sections. 



Familiar examples of cavitation in flows which obey Equation [1 ] on 

 individual streamlines are shown in Figures 1 , 2, 3, and 4. Figure 1, from 



Figure 1 - Cavitation in a Venturi Section — After Fottinger, 



Reference 8 



Reference 8, shows the cavitation developed in a venturi section. Figures 2 

 and 3 show cavitation on the backs of propeller models. Cavitation on a body 

 of revolution is shown in Figure 4. The latter three photographs were taken 

 during tests of models in the TMB variable-pressure water tunnels. It will 

 be noted that the character of the cavities in the venturi section and near 

 the top of the uppermost blade in Figure 2 is different from that of the cav- 

 ities in Figures 3 and k. The first type has been characterized as "sheet" 

 cavitation and the second as "bubble" cavitation by naval architects working 

 on the problems of cavitation of propellers and other ships' appendages. As 

 will be shown in the subsequent discussion, however, the first type behaves, 

 on a time-average, as a steady cavity and the second type behaves as a tran- 

 sient oscillating system. The writer therefore prefers the terms "steady- 

 state" and "transient" cavities, respectively. 



Another type of flow in which low pressures may occur is the vorti- 

 cal flow which may be approximated in a real fluid by a rectilinear vortex. 

 The equation of motion for such flows is 



.L2E.-ui r?l 



P 9r r UJ 



