Effects of free-end corner shape on flow structure around a finite cylinder

Abstract

The flow structure around the free end of a finite circular cylinder embedded in an atmospheric boundary layer (ABL) over open terrain was investigated experimentally by modifying the free-end corner shape. The experiments were carried out in a closed-return subsonic wind tunnel. A finite cylinder (FC) with an aspect ratio (height/diameter) of 6 was mounted vertically on a long flat plate. The velocity fields near the FC free end were measured using the single-frame double-exposure PIV (particle image velocimetry) method. The Reynolds number based on cylinder diameter for the PIV measurements was about Re=7500. A hot-wire anemometer was employed to analyze the spectral characteristics of the wake structure. As a result, for the FC with a right-angled flat-tip free end, there is a strong vortical structure showing counter-rotating twin vortices near the FC free end. It is caused by the interaction between the entrained ambient fluids from both sides of the FC and the downwash flow from the FC free end. Due to the descending separated shear flow from the FC free end, regular vortex shedding from the cylinder seems to be suppressed and the vortex formation region is barely noticeable in the region near the FC free end, irrespective of free-end edge shape. For the case of the flat-tip free-end FC, the separated shear flow has a stronger downwash compared to the radiussed-tip free-end FC, reducing the size of the recirculation bubble in the near-wake region.