APPENDIX 

 HYDROFOIL TIP BOUNDARY LAYER THICKNESS AND ROUGHNESS HEIGHT 



To compare the foil tip boundary layer thickness 6 with the corresponding rough- 

 ness height (grain size) k , assume that the tip flow is similar to fully turbulent 

 flat plate flow with zero pressure gradient shown below. 



^^ 



p 





', 





.7 



u = U 



^ 



^c:^C^ 



8 



r 



/:5<J--S^ 





t 





















Figure 34 - Schematic Diagram of a Turbulent Boundary Layer on a Rough Wall 



The Reynolds number, based on a representative tip chord length c of 2 in. (0.051 m) 

 and a free stream velocity U of 43 ft/sec (13.1 m/sec) is 



R = Uc/v = 8.3 X 10 



The corresponding boundary layer thickness for the smooth tip 6 is given as 



23 



_£ = 0.0598 



X log R - 3.17 



= 2.2 X 10 



-2 



51 



