Drag Reduction by Suction 

 REFERENCES 



1. Investigations Relating to the Extension of Laminar Flow by Means of 

 Boundary- Layer Suction Through Slots , Loftin, J. K. and Burrows, Dale L., 

 NACA TN 1961, Oct. 1949. 



2. Boundary Layer Theory , Schlichting, H., 4th edition, McGraw-Hill, 1960. 



3. Boundary Layer and Flow Control , Vol. 11, edited by Lachmann, G. V., 

 Pergamon Press, 1961. 



DISCUSSION 



T. G. Lang 



Naval Ordnance Test Station 



Pasadena, California 



I would like to compliment Dr. McCormick on developing a relatively sim- 

 ple system for testing bodies with boundary layer control in a variety of open- 

 water conditions. Using this system, such problems as clogging due to plankton 

 and transition caused by natural turbulence can be investigated. A few years 

 ago, we experimented on the susceptibility to clogging of several types of per- 

 meable materials. Samples of sea water, tap water, lake water with suspended 

 particles, and distilled water were used in a small water tunnel specially de- 

 signed to provide a high-speed laminar boundary layer over a small test plate 

 to which suction was applied. The results of our limited tests showed that slots 

 greater than 0.002 in. in width were relatively free from clogging, as were per- 

 forated plates with holes greater than 0.002 in. in diameter. Test plates made 

 of sintered spheres clogged very rapidly while samples of porous fibrous mate- 

 rial could be used for 5 to 10 minutes before clogging to the point where their 

 permeability was reduced by a factor of two. Also, it was found that backf lush- 

 ing for about one second cleared the material. Perhaps if Dr. McCormick en- 

 counters problems due to clogging that the backflush technique would be of help. 



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