Wind tunnel investigation of pressure distribution and unsteady aerodynamics for a 3:2 rectangular prism in accelerating flow

Accelerating flow is one of the typical characteristics of non-synoptic winds and acts as a key factor leading to sudden increases in wind velocity and pronounced unsteady aerodynamic responses that may cause severe structural damage and property loss. However, the underlying unsteady aerodynamic mechanisms governing these flow-structure interactions remain insufficiently understood. In this study, aerodynamic pressures on a sectional model with a 3:2 rectangular cross section were directly measured under various accelerating flow conditions. Surface pressures were compared with quasi-steady predictions based on steady coefficients at representative wind attack angles of α = 0°, 10°, and 50°. These results reveal that at α = 0°, acceleration suppresses shear-layer instability and vortex shedding, causing near-in-phase pressure variations on both side faces and a reduced lift amplitude relative to quasi-steady estimates. At α = 10°, acceleration amplifies the steady-flow asymmetry between the upper and lower side faces, producing a transient positive mean lift deviation due to vortex reattachment and intensified shedding. At α = 50°, enhanced suction fluctuations on leeward faces significantly increase lift variance while the mean value remains quasi-steady. These findings clarify the mechanisms of unsteady aerodynamic responses under accelerating flows and provide insights for transient wind-load modeling.