0-90 



0-85 



0-80 



0-5 



1-5 



Figure 8. Variation of modified drag coefficient with cavitation number for flow past disc. 



axi-symmetric problems. His basic technique is to relate the stream functions in plane 

 and axi-symmetrical flow by the partial differential equation 



+ = 



3a; 2 dy' 2 y dy 



(1) 



where £ - corresponds to the plane flow and 



e zz 1 corresponds to the flow with axial symmetry. 



He considers the flow in the later case to be a perturbation solution of the case of 

 plane flow, i.e. e = 0. Relationships connecting the boundary conditions on the free 

 streamlines are similarly derived. Garabedian's method offers attractive possibilities: 

 however, like all other techniques in this field, it entails considerable computation in 

 its actual application. It is interesting to note that Garabedian's computation of the 

 modified drag coefficient of a disc is in reasonably good agreement with the value 

 obtained by Armstrong and Dunham. 



b. Approximate methods using Principles of Similitude. The difficulties 

 involved in applying exact theory have led to attempts to solve certain axi-symmetric 

 problems by the use of similitude considerations linking the axi-symmetric flow with 

 the corresponding problems in two dimensional flow. It can be shown (Armstrong and 

 Tadman, 1954) that for the fully wetted flow past elliptical profiles, an exact similarity 

 exists between plane and axi-symmetric flow for different but specific values of the 



223 



