An experimental study of flow around a circular cylinder with and without end plates in ground effect

Nishino, Takafumi, Roberts, Graham T. and Zhang, Xin (2006) An experimental study of flow around a circular cylinder with and without end plates in ground effect. 36th AIAA Fluid Dynamics Conference, San Francisco, USA. 04 - 07 Jun 2006.

Abstract

Flow and force characteristics have been experimentally studied for a circular cylinder, with and without end plates, placed near and parallel to a moving ground, over which no boundary layer developed to interfere with the cylinder. Mean drag and lift measurements, surface oil-flow visualisation, and particle image velocimetry (PIV) measurements were carried out at two upper-subcritical Reynolds numbers of 0.4 and 1.0×10⁵ (based on the cylinder diameter d) to investigate the effects of the gap ratio h/d, where h is the gap between the cylinder and the ground. For the cylinder with end plates, the drag rapidly decreased ash/d decreased to less than 0.5, but became constant for h/d of less than 0.35. This distinctive drag behaviour was explained by a global change in the near wake: the Kármán-type vortex shedding was found to be intermittent at h/d = 0.4, and then totally ceased (and instead two nearly parallel shear layers were formed) at h/d = 0.3 and below. Meanwhile, for the cylinder without end plates, no such a critical change in drag was observed as the Kármán-type vortices were not generated in the near wake region for all h/d investigated.

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