B • TURBULENT FLOW 



without equilibrium a family of curves instead of a single curve would be 

 obtained for any one pressure distribution. The parameters for these 

 curves are: 



We shall return to Fig. B,20b in Art. 23 in connection with the universal 

 skin friction law proposed by Clauser for equilibrium flows. 



Another interesting fact brought out by Clauser's investigation is that 

 equilibrium profiles do not conform to the iif -parameter family of profiles 

 shown in Fig. B,19a. Comparisons at two values of H are shown in Fig. 

 B,20c. It will be seen that nonequilibrium profiles are considerably more 



Fig. B,20c. Comparison of equilibrium profiles and von Doenhoff- 

 Tetervin one-parameter profiles, after Clauser [83], 



rounded than equilibrium profiles. Furthermore H remained nearly con- 

 stant with downstream distance for equilibrium profiles, whereas H in- 

 creases progressively for nonequilibrium profiles. This suggests that the 

 increase in 6* is slower and therefore that mixing is more thorough when 

 equilibrium exists. This may merely mean that the imposed changes from 

 section to section are now slow enough for the turbulent mixing to better 

 keep pace. It may also mean that the mixing rates are higher for equi- 

 librium than for nonequilibrium flow. In this connection information on 

 turbulent structure is needed. A start in this direction was made by 

 Ruetenik and Corrsin [90] who investigated equilibrium turbulent flow 

 in a channel with a 1-degree half angle of divergence. Even for this small 

 divergence, the average turbulent energy was found to be greater than 

 that for a parallel channel by a factor of about 3. However, what is 

 still needed is information of this sort to compare equilibrium and non- 

 equihbrium flows. 



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