B • TURBULENT FLOW 



pressure flow. Constant pressure flows are then just one member of a 

 family of flows developed under specific kinds of pressure distributions. 

 With regard to the kind of pressure distribution required to produce 

 an equilibrium flow, Clauser points out that a gradient parameter like 

 {8'/T^)dp/dx, where d' represents some effective face area over which the 

 pressure acts, represents the ratio of forces acting on the layer ; and if this 

 is held constant, the flow should have a constant history and therefore be 

 in equilibrium. The choice of the proper quantity, 5', was not known 

 when the experiments were performed, and the attainment of equilibrium 



Fig. B,20a. Equilibrium boundary layer profiles on the 

 basis of the velocity-defect law, after Clauser [73]. 



conditions proceeded on a cut-and-try basis. In a later article [72] Clauser 

 concluded that the proper parameter was (8*/r^)dp/dx. Studies were con- 

 ducted for two pressure distributions, designated as pressure distribu- 

 tion 1, corresponding to a mild adverse gradient, and pressure distribu- 

 tion 2, corresponding to a considerably stronger adverse gradient but not 

 sufficient to cause separation. The resulting mean velocity profiles are 

 shown in Fig. B,20a compared to a constant pressure profile. 



Due to the uncertainty in defining 5, Clauser sought a more suitable 

 thickness parameter. Obviously it was required that this be proportional 

 to 8, since equilibrium profiles correlate on the basis of y/8. The customary 

 8* and 6 were not suitable because their ratio to 8 could be shown to 



< 136 ) 



