F,16 • STATUS OF EXPERIMENTAL KNOWLEDGE 



F,14. Effects of Variable Free Stream Pressure, Wall Tempera- 

 ture, Etc. The effects of variable free stream pressure and variable 

 wall temperature are generally qualitatively the same but relatively less 

 for turbulent than for laminar boundary layers. Two references are 

 Rubesin [38] for surface temperature variation and Clauser [39] for 

 pressure gradients. 



Fluid injection in the stream through the wall is effective in reducing 

 heat transfer to the surface from the boundary layer. For example, 

 Rubesin [40] has developed a theory for gas injection into a high speed 

 turbulent boundary layer; comparison of the theory at Mach number 

 zero with data of Mickley, et al. [41] shows good agreement. (For detailed 

 discussion see Sec. G.) 



F,15. Rough Walls. All of the aforementioned analyses had to do 

 with smooth walls. However, the following formula, derived in the same 

 manner as Eq. 11-28, will be indicative of local skin friction (and there- 

 fore heat transfer) on rough plates [37] : 



0.242 



where e is the plate roughness and x is the distance from the plate leading 

 edge. It is assumed, of course, that the roughness projections are great 

 enough to disrupt the viscous influence of the wall and that the projec- 

 tions do not reach the sonic line. As with skin friction, heat transfer rates 

 for rough plates should be significantly greater than for smooth plates. 



F,16. Status of Experimental Knowledge. 



Skin friction. Since heat transfer is proportional to skin friction, and 

 since friction is apparently easier to measure than heat transfer, it is 

 proper to glean first the experimental data on skin friction so that more 

 data may be made available to verify the theory. 



The data of Coles [31] and Korkegi [42] for local friction on insulated 

 plates is plotted in Fig. F,16a, The data were obtained by direct force 

 measurements. Also plotted are Eq. 11-28 and 11-29 for n = 0.76. Ap- 

 parently both Eq. 11-28 and 11-29 are adequate for engineering purposes. 

 However, for more precision when more definitive data are available, and 

 assuming that Eq. 11-28 and 11-29 have the proper form, it may be sug- 

 gested that an equation be written as follows: 



242 Ty, 



(sin-^ a + sin-i 13) = 0.41 -\- log (Re ■ c/) — (p -{- n) log 



(16-1) 

 where p is an arbitrary constant to be adjusted to the data. 



< 391 > 



