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    Behaviour of flow at the junction of cylinder and base plate in deep water
    (Elsevier Sci Ltd, 2009) Sahin, Besir; Ozturk, N. Adil
    The present study aims at looking into the nature of the horseshoe vortex system and its interaction with the wake-flow region in the base of circular cylinder mounted on a base plate in deep water. These kinds of flows have been attracting considerable attention due to its importance in engineering applications. Flow fields in plan and side-view planes were visualized using a laser based particle image velocimetry to examine the flow structure quantitatively for the range of Reynolds number 1500 <= Re-d <= 9600. The analysis of the cinema of instantaneous flow data, time-averaged velocity vectors map, streamlines, vorticity patterns, Reynolds stress correlations and fluctuations of the velocity components clearly demonstrate that the flow structure occurred in the base of the cylinder is three dimensional. The area of flow field occupied and affected by the horseshoe vortex system around the cylinder varies as a function of Reynolds number. This horseshoe vortex system emanating from the upstream of the cylinder swirls while travelling in the main flow direction. Counter-clockwise rotating vortices take place downstream of the cylinder in vertical plan-view plane. These swirling and rotating vortices in the junction region of the plate and cylinder cause scour mechanisms. Horseshoe vortices magnify the entrainment process and circulatory motions between the main and wake-flow regions downstream of the cylinder which stimulate the scour mechanisms. (C) 2008 Elsevier Ltd. All rights reserved.
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    Horseshoe vortex system in the vicinity of the vertical cylinder mounted on a flat plate
    (Elsevier Sci Ltd, 2007) Sahin, Besir; Ozturk, N. Adil; Akilli, Huseyin
    The present investigation concentrates on the flow structure around the base of the vertical cylinder mounted on a flat plate for the Reynolds number of Re = 4000. The technique of high-image density particle image velocimetry (PIV) is employed in order to obtain instantaneous representations of the unsteady flow for a specified flow field. The time history of velocity and time-averaging of PIV data, particularly near the juncture, reveal valuable information about the behaviour of the horseshoe vortex system. In the forward face of the cylinder base, three different stagnation points occur, indicating the development of three different horseshoe vortices. These vortices occasionally roll up to combine a single primary vortex. Four different measuring planes were taken across the boundary layer in order to observe the effect of these three-dimensional junction flows arising from the base of the cylinder on the flow structures downstream of the cylinder. (C) 2007 Elsevier Ltd. All rights reserved.
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    PIV measurements of flow past a confined cylinder
    (2008) Ozturk, N. Adil; Akkoca, Azize; Sahin, Besir
    This study investigates the flow past a confined circular cylinder built into a narrow rectangular duct with a Reynolds number range of 1,500 ? Re d ? 6,150, by employing the particle image velocimetry technique. In order to better explain the 3-D flow behaviour in the juncture regions of the lower and upper plates and the cylinder, respectively, as well as the dynamics of the horseshoe vortex system, both time-averaged and instantaneous flow data are presented for regions upstream and downstream of the cylinder. The size, intensity and interaction of the vortex systems vary substantially with the Reynolds number. Although the narrow rectangular duct with a single built-in cylinder is a geometrically symmetrical arrrangement, instantaneous flow data have revealed that the flow structures in both the lower and upper plate-cylinder junction regions are not symmetrical with respect to the centreline of the flow passage. The vortical flow structures obtained in side-view planes become dominant sometimes in the lower juncture region and sometimes in the upper juncture region in unsteady mode. © 2008 Springer-Verlag.
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    PIV measurements of flow through normal triangular cylinder arrays in the passage of a model plate-tube heat exchanger
    (Elsevier Science Inc, 2016) Ozturk, N. Adil; Ozalp, Coskun; Canpolat, Cetin; Sahin, Besir
    In this work, the flow behaviors of multiple circular cylinders in a staggered arrangement, located in a rectangular duct with a narrow gap are studied experimentally using laser particle image velocimetry (PIV). Each cylinder is positioned at the corner of an equilateral triangle with a pitch ratio of 2d. It is known that multiple cylinders in staggered arrangements are more efficient than in-line tube arrangements in the case of heat transfer. With this in mind, this study examines the effect of a combination of multiple cylinders on flow characteristics. The staggered arrangement of the multiple cylinders guides the flow to be in a mode of repeated growth-and-destruction of the boundary-layer. This flow phenomenon increases the disorder of the vortical flow characteristics profoundly. Since the efficiency of heat exchangers depends mainly on the hydrodynamic, this investigation focuses on the flow characterization particularly on the development of horseshoe vortices. In this regard, distributions of velocity vectors, streamlines, vorticity and Reynolds stress, turbulent kinetic energy and single point spectral analysis are used to analyze the flow characteristics in detail. (C) 2016 Elsevier Inc. All rights reserved.