Cavitation Inception on Rough Bodies 



0.60 



0.40 



0.10 

 O.OB 



0.06 



0.04 



0.02 



0.01 



0.02 



0.04 0.06 0.08 0.1 0.2 0.4 0.6 



BOUNDARY LAYE R THICKNESS IN INCHES 



0.8 1.0 



2.0 



Fig. 11 - Effect of the pressure coefficient and the boundary layer 

 thickness on cavitation inception on a two-dimensional roughness 

 (U„ = 22 knots, H^ = 15 ft, m = 7, T = 54° F) 



layers and on those areas of the body where the pressure coefficient is 

 a minimum. 



Figure 11 shows that the height of a triangular roughness needed to give 

 cavitation inception at any particular point on a parent body increases with the 

 boundary layer thickness. There are no breaks in the curves when the rough- 

 ness element protrudes through the boundary layer. Figure 12 shows similar 

 curves for the cylindrical roughness element. When the roughness height be- 

 comes greater than the boundary layer thickness, cavitation inception is no 

 longer dependent on the boundary layer thickness. This follows from the orig- 

 inal assumption that cavitation inception on a three-dimensional element is a 

 function of the local velocity at the height of the roughness in the oncoming flow. 

 Although the sharp discontinuities in the curves show a deficiency in the anal- 

 ysis, there are insufficient data for a suitable formulation of the local flow in 

 the vicinity of the cavity on these three-dimensional roughness elements. 



197 



