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DISCUSSION 



S. K. F. Karlsson 



Brown University 

 Providence, Rhode Island 



The following comments refer to the effects on a fluid flow by a non- 

 Newtonian additive, which have been discussed to some extent by Professor 

 Lumley and which appear to offer possibilities for considerable reduction in 

 skin friction in turbulent boimdary layers. 



For a visco-inelastic, shear thinning (Reiner -Rivlin) fluid, Lumley con- 

 cluded (Phys. Fluids, Vol. 7, No. 3, March 1964) that turbulent transport effects 

 in an existing turbulent flow would be no different from that in Newtonian fluids. 

 However, it seems that this does not exclude the possibility that even in such a 

 simple non-Newtonian fluid the development of instabilities both in the laminar 

 and turbulent boundary layers may well be substantially altered, resulting in 

 considerable changes of the overall boundary layer skin friction. 



We have started some laminar stability experiments with such a non- 

 Newtonian fluid in rotating Couette motion at Brown University recently, and 

 although our geometry is different from that of the boundary layer, the results 

 may still be of some interest here. Our fluid is a suspension of Milling Yellow, 

 a dye stuff, in distilled water. Peebles and co-workers at the University of 

 Tennessee have studied its properties extensively (e.g., A. E. Hirsch and F. N. 



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