VORTEX SHEDDING FROM A CIRCULAR-CYLINDER OF FINITE LENGTH PLACED ON A GROUND PLANE

This paper describes a study of changes in the vortex formation and the turbulent wake from a circular cylinder with a finite aspect ratio, placed on a ground plane. The experiment was carried out in an N.P.L. blow down type wind-tunnel with a working section of 500 mm x 500 mm x 2,000 mm, and between the Reynolds number 2.5 x 10(4) and 4.7 x 10(4). The surface-pressure distributions on the circular cylinder were measured and the drag coefficient was determined from these measurements. Vortices of two kinds generated in the flow-field around the cylinder were observed. The power spectrum, auto-correlation, space-correlation, velocity defects, and turbulent intensities in the turbulent wake behind a circular cylinder were also measured. It was found that the flow pattern changed rapidly above aspect ratio H/D = 4, with vortex shedding changing from symmetric ''arch '' type to antisymmetric ''Karman'' type.