Passive wake control of a square cylinder using a detached flexible splitter plate: Force reduction and vortex-interaction regimes

Passive control of vortex shedding behind a square cylinder is numerically investigated using a detached flexible splitter plate at a Reynolds number of 150. The effects of the plate-length ratio 𝐿 * = 𝐿 / 𝐷 and the gap ratio 𝐺 * = 𝐺 ⁡ / 𝐷 where D is the side length of the square cylinder, on the wake characteristics, hydrodynamic forces, and plate-tip oscillation amplitude are examined. The mean drag coefficient, root-mean-square lift coefficient, and Strouhal number vary non-monotonically with the gap ratio and plate-length ratio, indicating the existence of favorable parameter combinations for different control objectives. Across the investigated cases, the maximum reductions in the mean drag coefficient, root-mean-square lift coefficient, and Strouhal number reach 16.7%, 97.6%, and 55.5%, respectively, although these maxima occur at different parameter combinations. Three vortex-interaction regimes are identified: destructive interaction, constructive interaction type A, and constructive interaction type B. Constructive interactions generally produce larger plate oscillations, whereas destructive interactions are associated with comparatively small plate responses. These findings provide insight into passive wake control, hydrodynamic-load reduction, and the potential use of flexible-plate oscillations in future energy-harvesting studies.