Flow Around a Circular Cylinder with a Free End A Thesis Submitted to the College of Graduate Studies and Research in Partial Fulfillment of the Requirements for the Degree of Master of Science In the Department of Mechanical Engineering University of Saskatchewan Saskatoon, Saskatchewan Canada By Jonathan Lucas Heseltine © Copyright Jonathan Lucas Heseltine, August 2003. All rights reserved.
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Abstract A circular cylinder with a free end is one of the simplest possible three- dimensional structures, yet flow around such a body is complex and not well understood. Numerous previous studies have examined this flow situation; however there is disagreement within the literature about the exact nature of the flow behaviour. The primary dispute is whether a pair of counter-rotating trailing vortices exists near the free end or whether the Karman vortices are inclined near the cylinder free end and attach onto the body. There is a distinct lack of quantitative wake velocity results from previous work. Therefore, the focus of this study is to obtain such results in order to determine the structure of the wake. Velocity measurements were made in the wake of various circular cylinders mounted vertically perpendicular to a horizontal ground plane. Experiments were conducted in the subcritical ReYnolds number regime at ReD = 6x10 4 using a seven-hole pressure probe capable of determining the time-averaged velocity vector. From the literature, there is evidence that the flow pattern is sensitive to the cylinder aspect ratio and boundary layer thickness relative to the cylinder height. Therefore, the aspect ratio . was varied from 3 to 9 by changing the cylinder height while keeping the boundary layer height to cylinder diameter ratio constant at 2.5. For the higher aspect ratio cylinders, results indicate that there are streamwise vortical structures near both ends of the circular cylinder with the vortex pair near the tip of the cylinder much stronger than near the base. As well, thermal anemometry measurements show that the periodicity
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