if .3 N.A.C.A. Technical Memorandum No. 567 Figs. 7 & 8 Fig.7 The opposite spiral vortex rings of the"trade circulations produced by the rotation of a cylinder in still water. … Fig.8 A cylinder provided with end disks develops by rotation in still water four pairs of opposite "trade"vortices. The vortex pairs at the end disks are much stronger than those around the cylinder.
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