Kurtulmus N.Ispir M.Aksoy M.H.Goktepeli I.2025-12-242025-12-2420260955-5986https://doi.org/10.1016/j.flowmeasinst.2025.103109This 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 β = 15° and β = 60°. 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 β = 45° exhibited the most notable improvements in wake recovery and reduction in cross-stream 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. © 2025 Elsevier Ltd. All rights are reserved, including those for text and data mining, AI training, and similar technologies.eninfo:eu-repo/semantics/closedAccessCircular CylinderDimpled/Protruded Surface ModificationsFlow ControlPIVReynolds NumberArticle10.1016/j.flowmeasinst.2025.1031092-s2.0-105030095074