Flows wtth Drag Reductton (Veloetty and Friction) 
DISCUSSION 
Jaroslav J. Voitkounsky 
Shtpbutldtng Instttute 
Lentngrad U.S.S.R. 
The problem being discussed is of great interest, of course, 
but it is very difficult for us. It is important to describe the pheno- 
mena in the turbulent flow and in my opinion it is especially useful to 
try to apply for it Prandtl's ideas about the ''Mischungsweg"' (mixing 
lengths), Such a method was used by the author and some years ago it 
was used in the Soviet Union too, In particular the van Driest idea 
about the construction of formulae for the mixing length was used. I 
think it is a very useful method and the results obtained by the authors 
are also very interesting. 
I should be grateful if the author who presented the paper 
could answer one question. What, in his opinion, is the prospect of 
applying that method to the case of the rough surfaces because from 
the application point of view it is a very interesting problem. Some 
years ago in England these natural experiments were carried out with 
a natural ship and it is clear that the roughness of the surface of that 
ship was of a high degree, and it would be very interesting to apply 
this theory to a description of that phenomena. 
DISCUSSION 
Edmund V. Telfer 
lia sba Merl 
Ewell, Surrey, U.K. 
This is quite a fascinating paper and whilst it has many di- 
verse applications I would like to ask the author for his opinion on 
only one point. We have all been attracted by the possibilities of drag 
reduction, but I would like to suggest that there are also immense ad- 
vantages to be got by going in the opposite direction so far as ship 
model experiments are concerned. When one considers the terrific 
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