TYPES OF CAVITATION 



In Reference 3, brief discussions were given and several illustrations shown of the 

 types of multiphase, single or multi component flows which can be considered cavitational 

 flows from either a hydrodynamical or thermodynamical point of view or both. For the present 

 wort, it will only be necessary to define the terms preferred by the writer in referring to the 

 various types of cavitation: 



1. TRANSIENT CAVITIES. This term will be applied to the small, individual cavitation 

 bubbles which grow, sometimes oscillate, and eventually collapse and disappear. This type 

 has been characterized as "burbling" or "bubble" cavitation by naval architects working on 

 problems of cavitation of propellers and other ships' appendages. 



The following types may be considered in the general class of free streamline flows 

 and characterized as Kirchhoff flows or Helmholtz motions: 



2. STEADY-STATE CAVITIES. This term is applied to the large, stationary cavities 

 observed behind blunt bodies and very often on hydrofoil profiles having relatively sharp 

 leading edges. The analytic description is not a function of time.* Such cavitation is re- 

 ferred to among naval architects as "laminar" and, more recently, as "sheet" cavitation. 

 It should be noted that stationary vortex cavitation may be included here, being a time- 

 independent flow with circulation. 



3. NONSTATIONARY CAVITIES. This term is applied to cavities resembling the steady- 

 state cavity but varying with time as in the air-water entry of an air-dropped missile or of an 

 initially submerged but accelerating body. The term "unsteady" is also often used for this 

 type of flow. 



These terms provide a nonambiguous set both for physical descriptions and for the 

 associated mathematical formulations. Although all three are free-boundary flows, in the 

 first, the pressure at the boundary varies with time; in the second, the boundaries are free 

 streamlines (^ constant velocity magnitude and, therefore, pressure); and in the third, the 

 boundaries are such that the material lines are not necessarily free streamlines. 



THE INCEPTION OF CAVITATION 



INTRODUCTORY REMARKS 



Although it is usual to assume, in most engineering applications, that cavitation will 

 begin when the local pressure reaches the vapor pressure corresponding to the temperature of 

 the liquid, the actual conditions are much more complex and very often the errors resulting 



*It must be recognized here that when applying the term "steady-state" to cavities in real liquids reference is 

 made to the average description taken over a relatively long time interval. When examined in detail, such cavi- 

 ties are very often observed to oscillate both in the streamwise direction and locally in the cavity surface. 



