or for X = c = 2 in. (0.051 m) 



6 ~ 0.044 in. (0.0011 m) 

 s 



and for the 600-inicron grain size k , this gives 



k /6 ~ 0.54 

 s s 



The corresponding boundary layer thickness for the roughened tip 6 can be esti- 

 mated as follows. In the completely rough regime, the local coefficient of skin 

 friction C. is related to the roughness height k according to the equation 



C^ = [2.87 + 1.58 log (x/k )]"^"^ 



which, for x = c = 2.0 in. (0.051 m) and k = 0.024 in. (600 y) gives 



C^ = 0.0118 



24 

 The boundary layer thickness 6 follows from the relation 



C^"-*"^^ = 3.96 log (6 /k ) + 7.55 

 f r s 



and for C^ = 0.0118 and k = 0.024 in. (600 y) 

 r s 



k /6 ~ 0.38 

 s r 



52 



