B,21 • LAW OF THE WAKE ACCORDING TO COLES 

 21-5, using the normalizing condition co(l) = 2, that 



where 



(21-6) 



Thus Eq. 21-6 is an expression for 7r(x) in terms of the skin friction 

 coefficient c/. For other relationships and a tabulation of oi{yfh) and 

 related functions the reader is referred to Coles' original paper [85], 



Ci> 1 



0.6 



y/5 



Fig. B,21a. The law of the wake, after Coles [85]. 



Coles found that in most cases (Eq. 21-5) fitted available experimental 

 data on velocity distributions well and concluded, for unseparated flows 

 at least, that the wake hypothesis appeared to be a useful concept. The 

 analytic character of the method enabled him to express also the distribu- 

 tion of shear stress across the boundary layer. Computed distributions 

 represented observations, except where the adverse pressure gradients 

 were large. Here there were large discrepancies, reminiscent of those ob- 

 tained by using the momentum equation. 



The general success of the method led Coles to suggest that yawed or 

 three-dimensional flows might be usefully represented by universal func- 

 tions considered as vector rather than scalar quantities. For further dis- 

 cussions along these fines the reader is again referred to the original paper. 



< 141 ) 



