Johnson and Hsieh 



0.01 0.02 0.04 0.06 0.1 0.2 0.4 0.6 1.0 2.0 



HALF ULTIMATE BODY WIDTH - h, INCHES 



4.0 6.0 10.0 



Fig, 10 - Effect of body size on the inception of cavitation as a 

 function of the minimum radius of the gas nuclei (U = 25 fps) 



1. For a given size and speed, a unique entrained nuclei size exists whose 

 instability defines the maximum possible incipient cavitation number. This 

 maximum possible incipient cavitation number is always less than -C j^. 



2. The difference between the maximum possible incipient cavitation num- 

 ber and -C increases with decrease in body size. This difference also in- 



p mi n •' 



creases with decrease in speed if the free stream contains all sizes of bubbles. 



3. If the free stream does not contain the unique nuclei size associated 

 with the maximum possible incipient cavitation number, the difference between 

 the measured incipient cavitation number and -Cp ^^^ is, of course, further in- 

 creased. For a specific case of half body total width = 0.2 inch, speed = 50 fps, 

 the critical or unique nuclei size is R*. = 0.0021 inch, and the maximum possi- 

 ble value of the incipient cavitation number is 0.585, compared with -Cp^.^ = 

 0.587. If there is an absence of all entrained nuclei with R^ ^ 0.004 inch, the 

 measured incipient cavitation number will be 0.47, or 80 percent of -Cp^-^. 

 However, if the same body is operated at a speed of 25 fps, the maximum possi- 

 ble value of the incipient cavitation number is 0.578; and if there is an absence 

 of all entrained nuclei with Rq s 0.004 inch the measured incipient cavitation 

 number will be 0.517, or 88.3 percent of -c 



' -^ D mi n 



178 



