cavitation in internal flows. These are the flows that take place in 

 water tunnels, fluid machinery, and the duct flows of various types that 

 arise in large hydraulic systems and the propulsion systems of ships (see, 

 e.g., Narita and Kunitake 1977, Yamaguchi 1977). As in cavitation in- 

 ception, different forms of developed cavitation occur, and for internal 

 flows it is convenient to lump them into three types, as in Table 5: 



TABLE 5 - TYPES OF INTERNAL FLOW CAVITATION 



1. Attached two- and three-dimensional 

 surface cavities. 



2. Tip-vortex and tip-clearance flow 

 cavitation. 



3. "Bubbly" cavitation and two-phase flow. 



Although all of these forms are commonly seen in water tunnel tests, type 2 

 is most often associated with flow in fluid machines, such as a propeller 

 or pump. Often the tip-clearance flow in a pump is sufficiently strong to 

 cause a significant "backflow" resulting, thereby, in a very complex inflow 

 to the pump. 



Attached cavity flows have, of course, received much attention because 

 of the powerful analytic tools that can be brought to bear, as well as the 

 intrinsic importance of these flows (see, e.g., Wu 1972). These same 

 techniques may be used to explain tunnel-caused effects in steady flow 

 which may be termed "wall effects" (see, e.g., the review by Baker 1977). 

 When the void fraction of liquid-gas-vapor flows is appreciable it is 

 customary to call these "two-phase flows" (see, e.g., the text by Wallis). 

 Indeed, much effort has been, and is being, expended on this subject as it 

 is a key issue in the understanding of the thermo-hydraulics processes in 

 nuclear power plants. But many cavitating flows in naval hydrodynamics 

 consist of dispersed cavitation bubbles in which the void fraction is well 

 below one percent and these flows we may term bubbly cavitation. This 

 kind of cavitation is common, even dominant, in cavitating pumps and, as we 

 have seen, is also a highly visible feature of some water-tunnel flows. 



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