Abstract
The understanding and quantitative prediction of velocity and pressure fluctuations in turbulent flows around such bluff bodies have been evolving over the years. The main aim of the present work is to investigate experimentally and numerically the flow field in the wake region of different bluff bodies such as circular, square and triangle cross section cylinders placed horizontally perpendicular to the uniform flow. The experimental studies were performed by Particle Image Velocimetry (PIV) method in an open water channel at Reynolds numbers 5000 and 10000 defined according to the characteristic lengths of the cylinders in the facilities of Selcuk University of Advanced Technology Research and Application Center in Turkey. The experimental results are compared to the numerical results obtained by means of transient simulation with LES turbulence model of ANSYS-Fluent Software. It is shown that the numerical and experimental results have a good agreement in respect of the instantaneous and time-averaged flow field patterns of vorticity, velocity component streamwise direction and streamline topology. In addition, drag coefficient of the geometries were also numerically calculated. For all geometries the wake length in x and y directions and size of the foci of the streamlines are decreasing by increasing Reynolds numbers in time-averaged results. The time-averaged flow patterns of both experimental and numerical results have considerable symmetry with respect to the centerline of each cylinder. Contours of the time-averaged stream wise velocity for Re=10000 demonstrate that the stagnation point around the symmetry plane moves further upstream for all cylinders in accordance with Re=5000. The maximum drag coefficient value was yielded for the square cross-section cylinder as 1.78 due to the sharp-edged geometry.
Highlights
The motion of fluid passing through different crosssection cylinders is encountered in several industrial applications, as well as offshore and environmental settings, including tall buildings and structures such as bridges, chimneys, trash racks, cooling towers, heat exchangers, vortex flow meters etc
The main aim of the present study is to investigate experimentally and numerically the flow field in the wake region of different bluff bodies such as circular, square and triangle cross section cylinders placed at horizontal position under the uniform flow condition (Figure 1)
While the numerical results show that the length of wake region was longer at low Reynolds number with 2.0
Summary
The motion of fluid passing through different crosssection cylinders is encountered in several industrial applications, as well as offshore and environmental settings, including tall buildings and structures such as bridges, chimneys, trash racks, cooling towers, heat exchangers, vortex flow meters etc. When fluid flows around any bluff body, the vortices are alternatively shed and a well-known Karman vortex street is formed in the wake of the cylinder, which can cause structural damage as a result of regular and irregular surface loading [1]. Vortex-shedding frequencies and surface pressures of the square, circular and rectangular cylinders in a wind tunnel were investigated experimentally using hot-film measurement techniques. They determined the dominant peak location of the vortex shedding frequency and obtained Strouhal numbers in the range of various Reynolds numbers for the circular cylinder, square cylinder and oriented square cylinder [6]
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