Wind pressure characteristics and flow mechanisms of three-dimensional square cylinder considering fluid–structure interaction

Highly flexible bluff-body structures are susceptible to nonlinear wind-induced vibrations, which may cause serviceability loss. Fluid–structure interaction (FSI) is central to this process. However, most existing studies focus on the aerodynamics of rigid structures, and the evolution of structural flow fields and underlying mechanisms under FSI remains insufficiently clarified. To address this gap, this study examines a finite-length square cylinder with a large height-to-width aspect ratio (18:1). Using a moving-mesh large-eddy simulation framework, we systematically investigate the effects of uniform inflow at reduced velocities Vr = 10, 26, 30 on pressure distribution, mean pressure coefficients, time-averaged flow, time-averaged vorticity, and coherent vortical structures. The results indicate that FSI markedly alters both the surface pressure distribution and the surrounding flow features. On the leeward face, the negative-pressure zones near the top and bottom edges expand, and the suction intensity is weakened by structural vibrations. At the fixed end, the compression of the windward recirculation bubble is significantly reduced. The downstream recirculation region elongates and becomes less sensitive to wind speed, and the upwash within the wake weakens appreciably. Away from the base region, vibration shifts the flow's topological focus, leading to reduced negative pressure at mid-height on the leeward face and near top of the side face. Vibration also modifies the periodic spatial pattern of the wake. This study systematically elucidates the coupled effects of structural motion and inflow conditions, overcoming the limitations of previous studies that mainly focused on the aerodynamic response of rigid structures, and further deepening the understanding of the overall FSI response mechanism.