Large-scale structures in the wake behind a circular cylinder.

Abstract

The authors have reported that the two-dimensional Karman vortices behind a cicular cylinder are broken into lengths of about 8d and form chains of spoon-shaped vortex couples. In the present experiment disks were attatched to the cylinder so that the Karman vortices were artificially cut at fixed positions with fixed lengths of 4d, 4d, 8d and 10d. The structures with 8d were most stable, forming the vortex chains with least irregularities, and the wake was much wider than that without the disks, while the neighbouring vortices with a length 4d were merged to the scale of about 8d. There results show that the length 8d is a unique scale in the deformation of the Karman vortices to the three-dimensional large-scale structure.