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    Flow details of a circular cylinder mounted on a flat plate
    (Int Assoc Hydraulic Research, 2008) Ozturk, Nurhan Adil; Akkoca, Azize; Sahin, Besir
    The main purpose of this study is to investigate the flow structure up- and downstream of a circular cylinder mounted on a flat surface in the boundary layer region using a Particle Image Velocimetry (PIV) technique for Reynolds numbers ranging from 750 to 9600. The interaction between the primary, incoming, and counter-clock-wise rotating vortices and the trail of the horseshoe vortices formed at the upstream base of the cylinder are quantitatively identified in terms of the instantaneous and time-averaged flow data. The entrainment is shown to be activated between the main and separated flow regions across the shear layer by interactions of opposite signed rotating vortices which are responsible for scour in the upstream region of the cylinder. The surface fluid bursts to create counter-clock-wise rotating vortices upstream of the cylinder to split the incoming clock-wise rotating vortex into an independent vortex. Since the counter-clock-wise rotating vortices are not fed continuously by the surface fluid, they gradually expand in size but lose the strength and later are swept away by the developing vortices.
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    Horseshoe vortex studies in the passage of a model plate-fin-and-tube heat exchanger
    (Elsevier Science Inc, 2008) Sahin, Besir; Ozturk, Nurhan Adil; Gurlek, Cahit
    An experimental investigation is reported using particle image velocimetry of the flow structure in the flow through a rectangular duct containing a circular cylinder with axis normal to the flow. A duct with a narrow gap was designed to simulate a fin-tube heat exchanger containing a single circular cylinder. The time-averaged velocity vectors map, < V >, patterns of streamlines, and corresponding vorticity contours, (omega) were obtained using 490 instantaneous images. Development of the entrainment process between the main flow and wake-flow regions is magnified by a helical horseshoe vortex system emerging upstream of the cylinder. The occurrence and development of boundary layer separation and the formation of horseshoe vortices upstream of the cylinder close to both upper and lower plate surfaces and the merging of these developing horseshoe vortices into a primary horseshoe vortex system were also observed in the side-view plane for the Reynolds number range of 1500 <= Re-d <= 6150. (c) 2007 Elsevier Inc. All rights reserved.