The present discussion will, in general, proceed according to the 

 following outline: Description of "types" of cavitation ordinarily encountered 

 in technical applications, the effects of cavitation in such applications, 

 ideas relating to inception of cavitation, dynamics of "transient" cavitation 

 bubbles, mechanism of "steady-state" cavities, the mechanism of collapse of 

 cavities and associated damage, some remarks on scaling of cavitating systems, 

 and some methods available in design for prevention of cavitation and cavita- 

 tion damage. 



TYPES OP CAVITATION 



It is clear that cavitation will occur in a liquid when the pressure 

 is reduced to a certain critical value without change in the ambient tempera- 

 ture, or, conversely, when the temperature is raised above a critical value at 

 constant pressure. Thus, from a purely physical-chemical point of view, there 

 is no difference between boiling of a liquid and cavitation in a flowing liq- 

 uid, at least in so far as the question of inception is concerned. However, 

 a certain distinction must be made depending upon whether the cavitation is a 

 purely two-phase, one -component, phenomenon with a vapor cavity or whether the 

 cavity is formed by outgassing of dissolved or entrained gases at pressures 

 well above the pressure of the vapor phase of the liquid. Although the thermo- 

 dynamical conditions for the formation and maintenance of such types of cavi- 

 ties may differ considerably, from a hydrodynamical point of view no distinc- 

 tions need be made. Thus, for cavitation in a flowing liquid, it is of inter- 

 est to point out the conditions under which low pressures may occur. 



It will be sufficient- for illustrating the "types" of cavitation to 

 consider the phenomena from an elementary point of view. In steady, irrota- 

 tional flow of an incompressible fluid, the pressure equation may be written 

 (neglecting effects of gravitational acceleration): 



P = P + >(U 2 - u 2 ) [1] 



where p is the local pressure, 



P is a reference pressure, usually taken as the pressure in 

 the undisturbed fluid, 



u is the local velocity, 



U is a reference velocity taken in the undisturbed fluid, and 



p is the mass density of the fluid. 



In dealing with cavitating flows, the pressures must, of course, be referred 

 to the absolute scale. It is clear from Equation [l ] that the pressure p may 

 drop to very small values depending upon the velocity u. The liquid of par- 

 ticular interest to the present discussion is water; the difference in air 



