Effects of configuration and stiffness of flexible splitter plates on the aerodynamic characteristics of stationary rectangular cylinder

Numerical simulations based on the bidirectional CFD/CSM fluid-structure coupling algorithm are performed to investigate the flow characteristics of flexible splitter plates mounted on the leeward side of a fixed rectangular cylinder. The effects of the installation position and bending stiffness of the flexible plate on the evolution of flow structures around the cylinder are analyzed. The Reynolds number is 2.4 × 10 4 , and the length ratio of the splitter plate to the cylinder height L / D ranges from 1 to 3.54. The simulation results reveal that the tip amplitude and mean displacement of the flexible plate generally decrease with the increase of bending stiffness K B . The plate exhibits intense vibration under low stiffness and gradually becomes static at high stiffness. In the low-stiffness range, the flexible plate installed at the middle position S middle produces the maximum fluctuating lift coefficient, while the dual-position configuration D yields the minimum value. The lift fluctuation of the rectangular cylinder is dominated by the plate vibration. When the first-order natural frequency of the plate f t1 rises to 1.5 f n , the lift fluctuations for all installation positions drop to nearly zero, and the aerodynamic forces become stable. For long plates with L / D ≥ 1.41, the flexible splitter plate exhibits a weaker vortex shedding suppression capability compared with the rigid counterpart of the same length, accompanied by larger lift fluctuations and a higher dominant lift frequency. In contrast, short flexible plates with L / D ≤ 1.15 perform better than rigid plates in suppressing vortex shedding, which effectively reduces the dominant lift frequency and lift fluctuations. Under low stiffness, the dominant lift frequency first increases and then declines as the stiffness rises. The low-stiffness flexible plate vibrates severely accompanied by intense vortex shedding and shear layer oscillation, which acts as the dominant source of lift fluctuations. For the high-stiffness flexible plate, the wake flow presents a stable shear layer regime without periodic vortex shedding, and the dominant frequency of the lift coefficient is significantly reduced or even completely eliminated. The findings of this study provide in-depth insights for the engineering applications of flexible splitter plates in vibration suppression and flow-induced energy harvesting.