A • TRANSITION FROM LAMINAR TO TURBULENT FLOW 



values of RCi for the smooth plate from 700,000 to 2.6 million correspond- 

 ing to free stream turbulence levels (according to Fig. A, 2b) ranging from 

 0.92 per cent to 0.14 per cent. The effects of roughness are present at all 

 turbulence levels. At k/b* = there is a large variation of Re^ with tur- 

 bulence level. However, for values of k/b* greater than 0.6, the effect of 

 turbulence is small. A roughness element for which k/b* is 0.5 has about 

 the same effect on transition as a turbulence level of 0.6 per cent. 



2.4 



I 

 o 



'- 2.0 

 X 



1.6 



1.2 



0.8 



0.2 



0.6 



1.0 



k/5,* 



1.4 



1.8 



Fig. A,5d. Effect of single roughness elements on the transition Reynolds number of 

 a plate. Measurements of Fage [13]. X = pressure gradient parameter (8^/v){due/dx). 

 B = chord of roughness element. 



Dryden suggested that the ratio of Re^ for the rough plate to the 

 transition Reynolds number (J^ejo for the smooth plate was a universal 

 function of /c/5* independent of air stream turbulence. The data shown in 

 Fig. A,5g, in particular the measurements by Tani, luchi, and Yamamoto 

 [22] and by Feindt [9] disprove this hypothesis. Fig. A,5h is a plot of 

 ReJ{Re^Q vs. k/bf for presently available data. At high turbulence levels 

 the ratio falls off more slowly than at low turbulence levels ; thus transition 



< 12 > 



