A,8 • SHEAR LAYERS WITH REATTACHMENT 



Fig. A,8b. Further studies on the same airfoil and on a modified NACA 

 0010 airfoil were made by Gault [32]. 



Similar separation bubbles have been observed in the vicinity of the 

 leading edge of airfoils at relatively high angles of attack [33], and on an 

 elliptic cyUnder [34]- 



Attempts to correlate the observations into a unified scheme have 

 been unsuccessful, the data for bubbles near the leading edge exhibiting 

 different relationships than the data for bubbles near or behind the mid- 

 chord position. 



Jacobs and von Doenhoff [35, p. 311] suggested that transition oc- 

 curred when the Reynolds number i^gx-s formed from the local free stream 

 speed and the distance along the shear layer from the separation point 

 attained the critical value of 50,000, according to their fragmentary 



2.0 



1.6 



^\ 1.2 



(^) 



0.8 



0.4 



1.0 



0.2 0.4 0.6 0.8 



Chordwise station x/c 



Fig. A,8b. Pressure distribution over airfoil with separation bubble. 



measurements. Gault [32,33] obtained values for the shear layer in sepa- 

 ration bubbles near the leading edge of 13,000 to 103,000 for the NACA 

 663-OI8, to 171,000 for the modified NACA 0010, and 20,000 to 60,000 

 for the NACA 63-009 airfoil. Schiller and Linke's values [2J^,25\ of Re^^, for 

 the shear layer from a circular cylinder vary from 4000 to 5000, and 

 J?et_s was reduced to about 2000 by a turbulence-producing wire. Schu- 

 bauer's value [54] for the shear layer in a separation bubble on an elUptic 

 cylinder is about 28,000 in an air stream of turbulence 0.85 per cent. 

 Maekawa and Atsumi [36] obtained a value of 25,000 for the shear layer 

 in a separation bubble from the ridge of a model consisting of two flat 

 plates making an angle of nearly 180° at the ridge. These authors infer 

 that this value is independent of air stream turbulence from indirect 

 evidence based on observations of the point of reattachment and a theory 

 which is not too well established. Bursnall and Lof tin's data [31] give 



(25) 



