Drag Reduction by Suction 



6r 



K LIMIT Cq = 0.0 and O-OOOI 



10 



20 



30 



40 50 



X (in) 



60 



70 



80 



90 



Fig. 7 - Calculated boundary — layer thickness and stability limits for TRI-B 

 according to Karman-Pohlhausen method for low Reynolds number 



CONCLUSIONS 



It is concluded from the results of the Karman-Pohlhausen method that the 

 probable reason why TRI-B has not yet achieved full-length laminar flow at 50 

 fps is due to transition occurring before the first suction slot. Wind tunnel 

 experiments at low Reynolds number and predictions based on the Karman- 

 Pohlhausen method were found to be in close agreement. This method assumes 

 the suction to be continuously distributed over the surface. A method, based on 

 calculating the decrease in S across a slot, did not prove fruitful. 



It was found experimentally that, even at low Reynolds number, continuous 

 suction in the circumferential direction was necessary to the maintenance of a 

 laminar layer. Interruption of the slots probably results in secondary flows or 

 streamwise vortices which cause instabilities. 



This paper would not be complete without pointing out the experience which 

 has been gained in handling a body of this type in the field. It is very important 

 to provide for proper handling equipment in the planning of such a program. All 

 dollies and packaging equipment must be lined with soft coverings. Field per- 

 sonnel, particular ordinary seamen, must be impressed with the importance of 

 not allowing the slightest scratch on the surface. This is not as easy as it may 

 sound. A navy diver bobbing up and down with the body along side the ship is 

 naturally more concerned with his own skin than with the skin of the body. It 



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