Impact of dimpled surfaces on the hydrodynamic flow patterns of circular cylinders

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.