Investigation of vortex flow fields around a circular cylinder using particle image velocimetry. I. Suppression of vortex shedding by helical strakes

The vortex-induced vibrations (VIVs) caused by a fluid flowing over a cylindrical structure present a significant challenge in engineering applications, often leading to structural fatigue and failure. This study investigates the effectiveness of three-start spiral helical strakes in suppressing vortex shedding around a cylindrical body. Flow fields are analyzed for semielliptical strake shapes using particle image velocimetry, and experiments are conducted at Reynolds numbers ranging from 0.97 × 105 to 1.32 × 105 to determine how helical strakes suppress vortex shedding. The analysis focuses on four distinct planes (0°, 30°, 60°, and 90°), corresponding to different alignments of the strake with the cylinder centerline. By comparing the velocity components in both the parallel (X) and transverse (Y) directions, the mechanisms behind vortex-shedding suppression are identified through examinations of the vorticity, averaged streamlines, Q-criterion, and turbulent kinetic energy. The results show that the helical strakes significantly reduce vortex shedding, effectively altering the flow dynamics and improving the efficiency of vortex suppression. The semielliptical helical strakes substantially weaken the von Kármán vortex street, broaden and stabilize the wake, and reduce peak in-plane turbulent kinetic energy by 30%–40% at the highest Reynolds number. These findings provide valuable insights into passive flow-control strategies, offering a practical approach to mitigating sources of VIV in cylindrical structures across various engineering applications. Because the influences of helical strakes and Reynolds-number effects had to be thoroughly established (in Paper I) before geometry-dependent behavior could be meaningfully interpreted (in Paper II), the study was separated into two coordinated parts to present each component with the clarity and depth it requires. Paper I established a physical base for further exploring the role of strake geometry, which is systematically addressed in Paper II.