Vibration responses and mechanisms of operating wind turbine blades: Effects of yaw and tip speed ratio variations in a sheared inflow field

This study investigates the vibration responses and underlying mechanisms of a full-scale National Renewable Energy Laboratory (NREL) 5 MW wind turbine blade under sheared inflow conditions, employing the Reynolds-Averaged Navier-Stokes (RANS) methodology coupled with the Shear Stress Transport (SST) k-ω turbulence model. The results reveal that flapwise vibration is amplified at a larger yaw angle (γ), primarily due to enhanced fluctuations in flapwise force (Ff). These fluctuations in Ff originate from stall-induced elevated negative pressure in high wind speed regions and diminished negative pressure caused by reduced attack angles in low wind speed regions. In contrast, edgewise vibration remains largely insensitive to γ, as it is dominated by the gravity component (Feg), peaking at azimuth angles near θ = 90° and 270°. Torsional vibration exhibits minimal variation due to the counteracting effects of Ff and spanwise bending moments (Ms), which induce positive and negative torsion, respectively. Furthermore, a higher tip speed ratio (TSR) strongly intensifies flapwise vibration, driven by increases in both the mean and fluctuation components of Ff. Concurrently, torsional vibration shifts from negative to positive displacement, a trend governed by the combined growth of Ff and Ms, with Ms becoming dominant at higher TSR. Edgewise vibration, however, remains stable due to the continued dominance of Feg. Finally, centrifugal effects markedly increase the blade's natural frequencies. Ignoring this effect will lead to substantial overestimations of both mean displacement and vibration amplitude, especially for flapwise vibration.