The wake of an orbiting cylinder

Preliminary results are presented for the flow behind a circular cylinder orbiting about a vertical axis inside a tank. The wake was investigated experimentally using image de-rotation and particle image velocimetry (PTV). It was found that the vortex shedding was perturbed by its own wake and, as a result, showed characteristics distinctively different from the normal vortex shedding behind a stationary cylinder. The vortex structures formed behind the orbiting cylinder include the classical Karman vortices and regular/irregular small-scale shear layer vortices. The former are frequently overwhelmed by the latter. The formation length of the Karman vortices is shown to be substantially smaller than in the wake of a stationary cylinder. PIV measurement shows that there is a reduction in the circulation of the vortices in the near wake. (C) 1997 Academic Press Limited.