C = C (sin a + cos a tan 3) (lib) 



where 3 is the angle between the direction of the wall friction vector and 

 the inviscid streamline. The angle 3 is precisely defined by 



3v 

 tan 3 = limit — = limit -;r— (12) 



where the boundary-layer velocity components u and v are in the direction 

 of the inviscid streamline and its normal, respectively. By assuming that 

 the component of the boundary layer flow in the inviscid streamline direc- 

 tion satisfies the two-dimensional velocity similarity laws, the skin 

 friction coefficient C, can be evaluated using a two-dimensional skin 



friction formula. The following skin friction formula given by Head and 



,10 . 

 Patel IS 



C = exp(aH+b) (13) 



where a = 0.019521 - 0.386768 c + 0.028345 c^ - 0.000701 c"^ 



b = 0.191511 - 0.83489 c + 0.062588 c^ - 0.001953 c 



c = In Rq 



^11 



and where 



\^n^i"^ii ^^'^ 



is the local streamline momentum thickness Reynolds number. Recall that U 

 is the dimensionless (scaled by U ) magnitude of the local inviscid velocity 



