Experimental Investigation of the Wakes behind Cylinders and Plates at Low Reynolds Numbers

Wakes behind cylinders and plates were photographically investigated at Reynolds numbers from 0.1 to 2,000. Main results are as follows. In the case of a circular cylinder, the rear twin-vortices begin to form at R =5 ( R is U d /ν), then become more and more enlarged as R increases, and finally become asymmetrical at about R =45. The laminar wake, on the other hand, begins to oscillate sinusoidally some distance downstream at R =30. In the case of a flat plate parallel to the flow, the wake begins to oscillate sinusoidally some distance downstream at about R =700 ( R is U l /ν, where l is the length of the plate). Lastly, some detailed knowledges about the structure and the nature of the Kármán vortex street are obtained by a new method.