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    Active and passive wake control of a circular cylinder using rotation and surface texturing
    (Pergamon-Elsevier Science Ltd, 2026) Aksoy, Muharrem Hilmi; Kurtulmus, Nazim; Ispir, Murat; Goktepeli, Ilker
    Flow structures over circular cylinders have been widely investigated due to their practical importance and the complexity of wake interactions. In this study, combined passive and active flow control strategies have been examined for rotating cylinders with surfaces having dimples/protrusions at a Reynolds number as Re = 2 x 103. Particle Image Velocimetry (PIV) measurements have been conducted for rotation rates ranging from alpha = 0 to alpha = 1.26 to explore modifications in wake topology for different circumferential angles ((3) between 15 degrees and 60 degrees. For the stationary bare cylinders, symmetric recirculation regions including counter-rotating eddies have been observed, whereas rotation caused the separated region to contract, shifted and lost its symmetry. Dimples/ protrusions, even without rotation, altered shear layer development with effects varying according to the circumferential angle. When rotation was applied, the modified surfaces produced notable changes compared with that of the bare cylinder, including reduced negative-velocity regions and more rapid momentum recovery. The time-averaged vorticity distributions indicated the diminished vortex intensity, while the periodic organization of the shedding became less distinct at higher rotation rates. Turbulence kinetic energy and Reynolds stress correlations presented that surface modifications, particularly at (3 = 30 degrees, 45 degrees and 60 degrees, enhanced shear layer energization, delayed flow separation and disrupted wake symmetry at alpha >= 0.84. The combination of rotation and surface texturing is therefore effective in reshaping wake dynamics and attenuating large scale vortex structures, offering practical implications for flow control applications.
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    Öğe
    Experimental investigation of flow past circular cylinders with dimpled and protruded surface modifications using PIV
    (Elsevier Sci Ltd, 2026) Kurtulmus, Nazim; Ispir, Murat; Aksoy, Muharrem Hilmi; Goktepeli, Ilker
    This study examines the impact of surface modifications, including dimpled/protruded formations, on the flow characteristics of circular cylinders in free-stream flow, aiming to enhance passive flow control. Experiments have been conducted in an open-water channel using a Particle Image Velocimetry (PIV) system to obtain detailed velocity field data and turbulent statistics. Circular cylinders with in-line dimple/protrusion arrangements have been fabricated via 3D printing and their performance was evaluated at Reynolds numbers of Re = 4000 and Re = 6000. Furthermore, the angle of dimple/protrusion configured in an in-line arrangement around the circumference of the cylinder varied between beta = 15 degrees and beta = 60 degrees. The results indicate that the formation of dimples/protrusions on the cylinder surface is an efficient tool that substantially alters wake characteristics, including reduced backflow intensity and delayed vortex interactions. Compared to that of the bare cylinder, configurations with beta = 45 degrees exhibited the most notable improvements in wake recovery and reduction in crossstream velocity fluctuations. Furthermore, normalized Reynolds shear stress distributions revealed a marked decrease in magnitude and a reduced affected region for modified cylinders, contributing to potential drag reduction and lowering the forces influencing the body.
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    Öğe
    Impact of dimpled surfaces on the hydrodynamic flow patterns of circular cylinders
    (Springer, 2026) Kurtulmus, Nazim; Ispir, Murat; Aksoy, Muharrem Hilmi; Goktepeli, Ilker
    The motivation of this study is the evaluation of the dimpled patterns on a cylinder surface in terms of controlling the turbulent flow structures. To reach this goal, the cylinders with dimples have been manufactured by utilizing a high-resolution 3D printer and these cylinders have been subjected to cross-flow in a water tunnel and the flow data have been acquired by Particle Image Velocimetry (PIV) at Reynolds number (Re) values of 4000 and 6000. The dimple formation angle (beta) on the cylinder surface texture varied between 15 degrees and 60 degrees, with the dimples arranged to be in-line formation around the entire cylinder circumference. Vortex formation length for bare cylinder was nearly Lf = 2.75 at Re = 4000. Its slight decrement has been obtained by increasing beta. However, it suddenly reached 3.15 at beta = 45 degrees. Its trend at Re = 4000 was not obvious at Re = 6000. It was 2.4 and remained approximately constant as beta increased. The results revealed that dimpled surfaces could become an effective tool to control the flow characteristics over the cylinders, resulting in reducing the undesired dynamic forces. The vortices shed from the sides of the cylinders with dimple surfaces interact to a lesser extent, leading to an elongation of the shear layer compared to that of a bare cylinder. Moreover, the severity of Reynolds shear stress attenuated and the high-intensity cluster formations have been delayed in a particular case, such as beta = 45 degrees at Re = 4000.
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    Öğe
    PIV Investigation of Flow Structures Around Rotating Circular Cylinders with Dimpled Surfaces
    (Springer, 2026) Goktepeli, Ilker; Ispir, Murat; Kurtulmus, Nazim; Aksoy, Muharrem Hilmi
    Flow around rotating cylinders with dimples has been evaluated at a Reynolds number of Re = 2000. It has been determined since the rotational influence was more effective for lower Re values. Angular dimple distributions have been considered as 15 degrees <= beta <= 60 degrees. Different rotation rates have also been evaluated from alpha = 0 to alpha = 1.26 as lower rotation rates for the current Re were significant to suppress the vortex shedding. Particle Image Velocimetry (PIV) results have been compared by those of a bare cylinder. The wake regions have been shrunk due to dimpled surfaces. Excluding the case of alpha = 0.42 for a bare cylinder (4.5%), the regions had tendency to approach the bodies. The highest displacement (-78.9%) to the cylinder has been attained for beta = 15 degrees with alpha = 1.26 as observed. The lowest value (-5.6%) has been obtained by alpha = 0.42 for beta = 45 degrees by approaching the cylinder. For the influence of passive flow control, the cases without rotation have been regarded and beta = 60 degrees was more dominant. For the wake lengths, the changes for F and S locations have also been exhibited in the wake regions as these points affecting the length of recirculation bubble were substantial. As interpreted from the vorticity results, peak values were more dominant in the cylinder wakes. Since the rotation rates were increased, these regions tended to shrink. It is related to the presence of fluctuations in the wake regions. The displacements of maximum turbulence kinetic energy values have been shown for the level of turbulence intensity. Turbulent intensity has been enhanced in the regions closer to the bodies except the stationary cases of beta = 30 degrees and beta = 45 degrees. Nevertheless, the forced rotation was more effective.