Borden 



5,0 

 4.0 



3.0 — 



h _ 



103 



\ 



48 Inch Tunnel 

 Circular Arc 

 Triangle 



5 = 0.293" 



Circular Arc 

 Tiiangle 



S = 0.453" 



12 Inch Tunnel 

 • Circular Arc 1 ^ 

 k Triangle ) 



1^ Circular Afc \ 

 A Triangle 



S = 0.147" 



Fig. 



3 - Local cavitation number as a function of the local Reynolds 

 number (ORL two-dimensional data based on Uj^) 



Table 2 



Values of A and B for Two-Dimensional 



Roughness Elements 



with local Reynolds number implies that cavitation inception on circular-arc 

 roughness elements is not occurring in a separated region but is produced 

 when the pressure on the element is reduced to a value close to the vapor 

 pressure. 



The same averaging process did not seem appropriate for finding the local 

 flow conditions over three-dimensional roughness elements. Here the flow lines 

 are displaced to the side as well as over the tip of the element. Figure 1 in- 

 cludes a single datum point obtained for cavitation inception on a much larger 

 cylinder in a uniform flow. These measurements were made on a cylinder, 8 in. 

 in diameter and 6 in, high, mounted on a flat plate, and towed at a depth of 6.5 ft 

 in the towing basin. Cavitation occurred at the tip of the cylinder at a towing 

 speed of 16 knots. The boundary layer on the plate was a small fraction of the 

 cylinder height, so that the oncoming flow over the tip was essentially uniform. 

 Despite the different scale and flow conditions, the cavitation inception number 

 falls on the same curve with the other cylinder data. Therefore the velocity w^ 

 of the oncoming flow at the height of cavitation inception on the roughness 



188 



