Passive control of turbulent flow around a circular cylinder using slots at separation points

Flow control is essential in various engineering applications and environmental contexts to ensure safety, improve efficiency, and enhance overall performance. This study examines the influence of slot configurations at turbulent flow separation points on a circular cylinder and their ability to passively control vortex shedding at a high Reynolds number (Re) = 3.6 × 10⁶. An unsteady Reynolds-Averaged Navier–Stokes (URANS) simulation using a realizable k–ε turbulence model with standard wall treatment was employed to evaluate the aerodynamic behavior of two slot geometries, straight and curved, under identical flow conditions. The results reveal that the introduction of slots substantially modifies the wake structure and aerodynamic loading, increasing the mean drag coefficient from 0.379 for the smooth cylinder to 0.99 and 1.5 for the straight and curved slot configurations, respectively. Similarly, the lift coefficient amplitude increased nearly tenfold, from ±0.1 to approximately ±1 for the curved-slotted cylinder. These findings confirm that slot-induced flow reattachment and momentum exchange enhance vortex coherence and wake stability, providing a robust passive flow-control mechanism. The proposed configuration demonstrates strong potential for integration into bluff-body-based systems such as bladeless wind turbines and tidal energy harvesters, where enhanced lift and controlled drag can improve energy capture efficiency and structural performance.