90 



SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 62 



turbulence into the translational motion that is finally realized. The 

 turbulence of the wind may make the flow about the model turbulent 

 at all speeds used. Hence no critical velocity would be found. 



Stanton's tests were made with a Pitot tube placed i foot up stream 

 from the model. The tube was made up of two ^-inch tubes. The 

 disks were then placed in the wake of these tubes and we might expect 

 the critical velocity to be affected. That the effect of such an arrange- 

 ment is appreciable was determined from a simple test. In the course 

 of our test on the 5-inch disk above, a glass tube 3/16 inch in diameter 

 was run across the tunnel i foot up stream from the disk. The resist- 

 ance of the disk was found to be reduced by about 6 per cent. Increas- 

 ing Stanton's value of iv by 6 per cent brings it into agreement with 

 our mean value of K. The following table summarizes the values of 

 K for flat plates normal to the wind given by the several experi- 

 menters. The notation and units used are as as above. 



Authority 



Diameter 

 Plate 

 Inches 



Eiffel 



Riabouchinski 



Foppl 



Author 



Stanton 



4 



6 



10 



15 

 20 

 28 

 39 



0.5 



I 



2 



7-9 

 2 



3 

 4 

 5 

 6 



5 

 I 



1-5 

 2 



3 



Velocity | 

 Miles 



25 • 



25 



25 



40-90 



40-90 



40-90 



40-90 

 3-15 

 3-15 

 3-15 



15-30 



35 



35 



35 



35 



35 



13 

 13 

 13 

 13 

 13 



. 000240 

 . 000243 

 .000247 

 . 000263 

 .000275 

 . 000284 

 . 000290 

 .000255 

 . 000252 

 .000252 

 .000255 

 . 000265 

 . 000265 

 . 000265 

 . 000265 

 . 000268 



. 000243 

 . 000250 

 . 000248 

 . 000246 

 . 000268 



Remarks 



4.9 ft. wind tunnel. 

 4.9 ft. " 

 4.9 ft. " 

 Open air. 



3.9 ft. wind tunnel. 



3.9 ft. " 



3.9 ft. " 



6.7 ft. " 



4.0 ft. " 



4.0 ft. " 



4.0 ft. " 



4.0 ft. " 



4.0 ft. " " 



corrected for influence of walls. 

 2.0 ft. wind tunnel. 

 2.0 ft. " 

 2.0 ft. " 

 2.0 ft 

 2.0 ft. " 



It has been suggested that the critical velocity found by us is not 

 that of the disks but a critical velocity for the tunnel. It is well known 

 that there is a marked critical velocity for the flow of air or water 

 in pipes where the fluid becomes suddenly turbulent. 



From the experiments of Stanton and Panner on the flow of air, 

 oil, and water through pipes, it was concluded that turbulence began 



Phil. Trans. Roy. Soc, 1914, p. 200. 



