F,ll • HEAT TRANSFER 



valid for 0.7 ^ Pn ^ 1. This formula reduces to von Karman's formula 

 when it is assumed that Pn = 1. For Pn^^ = Pn = 1, then s = 1, which 

 gives the basic Reynolds analogy, viz. St = c//2. 



The turbulent Prandtl number of 0.86, obtained above by making 

 Eq. 11-19 compatible with experiment, should be used in Eq. 11-19. 



0.84 



0.83 



0.82 



0.81 



0.80 



0.79 



0.78 



0.77 



1 2 cJ 4 5 



Me 



Fig. F,llg. Reynolds analogy factor for a turbulent boundary layer on a flat 

 plate in free flight in air as a function of Mach number. Te = 400°R. 



Fig. F,lle shows the effect of Reynolds number on s for air at low 

 speed (incompressible flow) , using Prt = 0.86 and Pn^ni = 0.71. Colburn's 

 [32] Pri is also plotted in this figure. 



Fig. F,llf and F,llg indicate that the effect of compressibility on s 

 for moderate heating or cooUng of flat plates (or cones) in a wind tunnel 

 and in free flight is small. 



It appears that for air a reasonable value for s is 0.825. 



Local skin friction coefficient. Analytically, it would be desirable to 

 obtain from Eq. 10-8 a shear distribution across the turbulent boundary 



(381 ) 



