A • TRANSITION FROM LAMINAR TO TURBULENT FLOW 



two screens and the scatter of points is about the same whether Re^ is 

 plotted against w'/we or the modified Taylor parameter {u' /u^){x/M)^ 

 where M is the mesh of the screen. Nevertheless, the results are not 

 inconsistent with Taylor's theory. 



Experiments on airfoils were made by Drougge [45] and the results 

 were analyzed to show that the effect of turbulence is related to inter- 

 mittent separation. Another analysis of this type has been made by 

 Dorodnitsein and Loitsianskii [44] and applied to published data. 



A,12. Schlichting's Procedure for Computing Transition on an 

 Airfoil. In 1940 Schlichting published a theoretical method [45] for 

 the computation of the transition position on an airfoil based on compu- 

 tations of the stability of boundary layers in accelerated and retarded 



i-6r 



1.2 



u° 



0.4 



0.2 



0.4 0.6 



s/c' 



0.8 



1.0 



Fig. A, 12a. Velocity distribution around elliptic cylinder of fineness ratio 4. s = 

 distance along surface, c' = distance from leading to trailing edge measured along 

 surface. 



flows. The method was further refined in 1942 [46]. On the basis of the 

 experimental data available to him at the time, SchHchting assumed that 

 transition always occurred ahead of the separation of the laminar bound- 

 ary layer; in other words he did not consider separation bubbles with tran- 

 sition in the separated layer and subsequent reattachment. Schlichting 

 also observed that for Reynolds numbers up to 3 milHon, transition never 

 occurred ahead of the position of minimum pressure on the airfoil. Experi- 

 ments available to Schlichting showed values of Re^, for a flat plate with 

 zero pressure gradient lying within the range 350,000 to 500,000 whereas 

 now values between 90,000 and 2,800,000 have been observed. 



As a prehminary to his airfoil computations, Schhchting computed 

 the stabihty characteristics of a boundary layer subjected to uniform 

 pressure gradients (Art. 3 and IV,F). Schhchting then assumes that tran- 

 sition depends only on the local boundary layer Reynolds number Re^*; 



{ 32 ) 



