An investigation of the near-wake flow structure of a cylinder with guiding plates

Firat Ekinci,Erhan Firat,Göktürk M Özkan,Hüseyin Akilli,P Dančová

doi:10.1051/epjconf/201818002024

Firat Ekinci, Erhan Firat + Show 3 more

Open Access

https://doi.org/10.1051/epjconf/201818002024

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Abstract

In this study, the flow behind a circular cylinder with a pair of outer identical guiding plates was investigated using particle image velocimetry (PIV) for various angular positions of the plates (i.e. α=±70°, ±100°, and ±130°). The gaps between these plates and cylinder are equal and are 0.3D. Experiments were carried out at a subcritical Reynolds (Re=ρ·U∞·D/μ) number of 7500, based on the cylinder diameter (D) and the flow velocity (U∞). The features of the near-wake with and without the guiding plates were interpreted in terms of patterns of time-averaged vorticity and streamlines, time-averaged and fluctuating velocity components. The spectral analysis was also carried out to determine the time-dependent variation of the transverse velocity at given locations in the near-wake. Two-dimensional computations of flow around circular cylinders with and without guiding plates have also been performed to predict the timeaveraged and root-mean-square of force coefficients of the various models. It was seen that the guiding plates at an appropriate angular position can lead to substantial attenuation, or retardation, of the process of large-scale vortex formation in the near-wake, thus can lead to vortex-induced vibration (VIV) suppression without any increase in drag.

Highlights

When two-dimensional bodies that are not streamlined with respect to the free-stream direction subjected to a fluid flow at adequately large Reynolds numbers (Re), each of the shear layers from this body roll up in an alternating, periodic fashion, into large-scale vortices (Kármán vortices) behind these bodies
The shear stress transport (SST) k-ω turbulence model which is developed by Menter and provided in FLUENT was chosen since it shows a better performance in complex flows with boundary layer separation when compared to Reynolds-averaged Navier-Stokes (RANS) based one- and two-equations turbulence models [13, 14]
All positions and lengths were normalized by diameter of the circular cylinder (D) and all time-averaged velocity components and root-mean-square (RMS) values of the fluctuating velocity components were normalized by freestream velocity (U∞)

Summary

Introduction

When two-dimensional bodies that are not streamlined with respect to the free-stream direction (high-rise structural systems, bridge piers, some parts of onshore/ offshore systems, etc) subjected to a fluid flow at adequately large Reynolds numbers (Re), each of the shear layers from this body roll up in an alternating, periodic fashion, into large-scale vortices (Kármán vortices) behind these bodies (near-wake). High aerodynamic/hydrodynamic drag and fluctuating forces on the body are several natural consequences of the Kármán vortex formation. The aim of this study is firstly to alter the near-wake structure of the cylinder using guiding plates, and to interpret the foregoing physics of the near-wake in terms of patterns of time-averaged vorticity and streamlines, timeaveraged and fluctuating velocity components, and spectral analysis; secondly to predict the trend of timeaveraged drag coefficient and root-mean-square of the fluctuating lift coefficient numerically in the absence of the direct force measurements

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