Cavitation inception as a separate topic of study has seemed then to 

 be a somewhat "messy" subject. Yet, it is an important one in fluid 

 engineering, and recently there has been some substantial progress by the 

 combined efforts of workers in several countries including this Center, 

 both in understanding the basic flows involved, and in laboratory tech- 

 niques. In the remaining sections, we will review, briefly, some of these 

 findings and recent experimental work. To appreciate the point of view of 

 many of the workers in cavitation we need to survey the highlights of 

 bubble mechanics, the most common denominator in cavitation-inception 

 scaling theories. At the root of all phase change processes in cavitation 

 is a "nucleating source" — or simply a cavitation nucleus — since technical 

 fluids do not exhibit the large tensions required of pure liquids prior to 

 cavitation. These nuclei, long the subject of speculation, are now be- 

 coming accessible to measurement, although there is still an observational 

 gap connecting these sources of cavitation and the macroscopic cavitation 

 ultimately seen on bodies. Some of these findings are reviewed in light 

 of current laboratory practice. Finally, we discuss, in a preliminary way, 

 some of the special problems nosed by developed cavitation when this occurs 

 in confined flows. 



CAVITATION INCEPTION 

 Preliminaries 



It is common to express the ambient pressure at which cavitation occurs 

 in a coefficient form called the "cavitation number" 



P -P (T ) 

 a = (1) 



q 



2 

 where q is the freestream dynamic pressure, 1/2 pU , p^ is the ambient 



static pressure and p (T ) is the vapor pressure of the pure liquid at 

 ambient (i.e., freestream) temperature. At the same time the static pres- 

 sure, p, on a body is put into dimensionless form 



