Flow structure around a finite circular cylinder embedded in various atmospheric boundary layers

Abstract

The flow structure around the free end of a finite circular cylinder (FC) embedded in various atmospheric boundary layers (ABLs) was investigated experimentally. The experiments were carried out in a closed-return type subsonic wind tunnel with various oncoming ABLs. A finite circular cylinder with an aspect ratio (L/D) of 6 was mounted vertically on a flat plate. The Reynolds number based on the cylinder diameter is ∼Re = 20,000. The wake structure behind a cylinder located in a uniform flow condition was also measured for comparison. A hot-wire anemometer was employed to measure the wake velocity, and mean pressure distributions on the cylinder surface were also measured. The flow past the FC free end exhibits a complicated three-dimensional wake structure, and the flow structure is quite different from that of a two-dimensional cylinder. The three-dimensional flow structure seems to arise from the strong entrainment of irrotational fluids caused by the downwash counter-rotating vortices separated from the FC free end. The vortex-shedding frequency and vortex-formation length are lower for an FC immersed in ABLs compared with those in a uniform flow. Spectral analysis revealed that a peculiar flow structure with a 24 Hz frequency component closely related to the counter-rotating twin-vortex exists near the FC free end.