is the fact that even though the shadowgraph technique responds to the second 

 derivative of the index of refraction field, thus giving heavy emphasis on the fine 

 structure, there is still detectable structure of a size comparable with the wake diameter. 

 For a quantitative display, we look at the comparison between mean velocity 

 profiles and transverse correlation functions of turbulent velocities in representative 

 shear flows. Figures 2 and 3 show that in channel, boundary layer, wake and jet [5, 

 6, 7, 1, 8, 9], there is measurable correlation over distances comparable with the shear 



.2 



"Yd (x-x.) 



Extent of Turbulent Correlation Across Shear Flow 



Fig. 3 



376 



