THE REDUCTION OF SKIN 

 FRICTION DRAG 



J. L. Lumley 



The Pennsylvania State University 

 University Park, Pennsylvania 



ABSTRACT 



A survey and analysis is presented of the various principles which have 

 been suggested to reduce the skin friction drag; a description of some 

 of the techniques for the application of these principles and experimen- 

 tal results are given. 



INTRODUCTION 



The majority of the drag of a properly streamlined underwater vehicle is 

 skin friction drag resulting from the excessive momentum transport of the tur- 

 bulent boundary layer. All techniques which have been suggested for the reduc- 

 tion of skin friction drag act to reduce this transport by altering, or preventing 

 the formation of, the turbulent boundary layer. Few of the techniques which we 

 will describe are supported by complimentary experimental and theoretical in- 

 formation; for some, only theory exists; for others only experiment; for a few, 

 there is both, but in conflict. I will try to present here the principles so far as 

 they are known, the results where they are available, and attempt to explain the 

 discrepancies. 



CONVENTIONAL TECHNIQUES 



General Considerations 



Most of the drag reduction techniques which have been suggested involve the 

 stabilization of the laminar boundary layer, and these will be referred to as con- 

 ventional techniques. The boundary layers in question are always thin relative to 

 some relevant length, and are usually considered, for an examination of stability, 

 as plane parallel flows without inflection points. 



In the discussion of the various stabilization techniques which follows, sev- 

 eral things must be borne in mind. First, from the work of Klebanoff, Tidstrom 

 and Sargent (1962) it is clear that transition can be caused in a laminar boundary 

 layer at any Reynolds number by a sufficiently violent disturbance— of the order 



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