Flow Above the Free End of a Surface-Mounted Finite-Height Cylinder
The flow above the free end of a surface-mounted finite-height circular cylinder was studied experimentally in a low-speed wind tunnel using particle image velocimetry. Velocity measurements were taken in horizontal and vertical planes above the free end
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Abstract The flow above the free end of a surface-mounted finite-height circular cylinder was studied experimentally in a low-speed wind tunnel using particle image velocimetry. Velocity measurements were taken in horizontal and vertical planes above the free end at a Reynolds number of Re = 4.2 9 104. Four cylinder aspect ratios, of AR = 9, 7, 5, and 3, were examined. The turbulent boundary layer on the ground plane had a thickness of d/D = 1.6. The results revealed details of the mean recirculation zone, reattachment position, critical points, and vortex patterns in the flow field above the free end. The sensitivity of the free-end flow field to changes in AR was much less pronounced than what is observed for the near-wake region. Keywords Finite circular cylinder PIV
Separated flow Vortex patterns Wake
1 Introduction The flow around surface-mounted finite-height circular cylinders [e.g., Sumner et al. (2004), Rostamy et al. (2012)] is more complex than the well-studied case of the ‘‘infinite’’ cylinder. In many engineering applications, such as high-rise buildings, oil storage tanks, and chimneys, the flow fields of these cylindrical structures are strongly three-dimensional owing to the flow around the free end and the flow around the body’s junction with the ground plane. On the free-end surfaces of these structures [e.g., Kawamura et al. (1984), Roh and Park (2003), Pattenden et al. (2005), Hain et al. (2008), Krajnovic´ (2011)], regions of N. Rostamy D. Sumner (&) D. J. Bergstrom J. D. Bugg Department of Mechanical Engineering, University of Saskatchewan, Saskatoon, SK, S7N 5A9, Canada e-mail: [email protected]
Y. Zhou et al. (eds.), Fluid-Structure-Sound Interactions and Control, Lecture Notes in Mechanical Engineering, DOI: 10.1007/978-3-642-40371-2_24, Springer-Verlag Berlin Heidelberg 2014
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recirculating flow, vortex patterns, and the flow separating from the curved leading edge act to influence the flow in the near-wake region. Although the near wake of a surface-mounted finite-height cylinder has been reasonably well-studied, comparably less attention has been focused on the flow over the free end and its relationship to the rest of the local flow field. How the cylinder aspect ratio and the boundary layer thickness on the ground plane influence the free-end flow field is not yet well understood. Furthermore, there are different interpretations of the free-end flow patterns in the literature [e.g., Kawamura et al. (1984), Roh and Park (2003), Pattenden et al. (2005), Hain et al. (2008), Krajnovic´ (2011)] which have yet to be fully resolved. In the present study, the flow field above the free end of a surface-mounted finite-height circular cylinder (Fig. 1) is investigated experimentally using particle image velocimetry (PIV). Of particular interest is the effect of aspect ratio (AR = H/D, where H and D are the cylinder’s height and diameter, respectively).
2 Experimental Approach The experiments were conducted in a low-speed wind tunnel at a Reynol
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