CAVITATION INCEPTION AND INTERNAL FLOWS 

 WITH CAVITATION 



INTRODUCTION 



Cavitation has been a topic of unique importance in naval hydro- 

 dynamics since the introduction of high speed propellers. The interesting 

 historical survey by Johnson (1972)* shows that the principal features of 

 cavitation as a source of noise, vibration, damage, and reduced performance 

 were experienced at the outset in ship propulsion in a pattern that has 

 continued to be repeated in the most current applications. These un- 

 desirable features of cavitation were highlighted in Knapp's well-known 

 Clayton Lecture before the Institute of Mechanical Engineers (Knapp 1952) 

 and is echoed in the summary volume on cavitation (Knapp et al. 1970). 

 The inception of cavitation announces the start of the phase change that 

 may lead, in turn, to these unwanted effects and is therefore a boundary 

 between fully wetted and cavitating modes of flow that is very desirable 

 to know. But the onset of cavitation, when it does occur, does so in a 

 variety of forms which may differ from facility to facility on similar 

 bodies. Even on one test body, the various appearances of cavitation may 

 change with flow speed and liquid environment. 



Thus, this inception process does not appear to be a well-defined, 

 unique kind of physical event for which there are clear-cut simple govern- 

 ing relations. Indeed, as in all fluid mechanics the presence of cavita- 

 tion requires appeal to all three of the basic conservation laws (mass, 

 momentum, energy) . Cavitation inception appears to be one of those physical 

 problems which does not yet seem well posed for the laboratory; experi- 

 mental results on supposedly similar tests show wide variability and, even 

 for one specific test condition, a wide "scatter" is often observed. This 

 state of affairs was not helped much, in early years, by the absence of a 

 detailed scientific description of the flow (with some exceptions) at the 

 moment of cavitation inception. It was then not surprising that many of 

 the theoretical attempts to explain the "scaling laws" fell short. 



*A bibliographic listing of references is given on page 93. 



