Borden 



head H^, and the temperature or vapor pressure H^. It now remains to examine 

 the local flow conditions in the boundary layer and to determine the roughness 



height which is compatible with the Reynolds number condition. This can be 



done by a method of trial and error. For example, select a value of u^^ (or uj^ ). 

 Then obtain a^ from Eq. (4) or (10). Find the local Reynolds number from Eq. 

 (6), compute h, and compare h b with y/S of the velocity profile. When the two 

 are equal, the problem is solved. 



COMPUTED CAVITATION PARAMETERS 



A computer program was written for calculating the minimum or critical 

 roughness heights which would produce cavitation inception on a particular 

 roughness geometry as functions of flow -elocity, submergence depth, water 

 temperature, boundary layer thickness ^^id profile, and the pressure distribution 

 of the parent body. Calculations have been made for each of the roughness 

 geometries investigated. The trends of these calculations are shown in Figs. 4 

 through 12. The pressure coefficients and boundary parameters selected for 



26 28 30 



FLOW VELOCITY IN KNOTS 



Fig. 4 - Effect of geometry of isolated roughness elements on 

 cavitation inception (C = -0.5, S = 0.4 in., m = 7, T = 54*^) 



190 



