A study of nonlinear aeroelastic response of a long flexible blade for the horizontal axis wind turbine

Abstract

As long flexible blades in large wind turbines are prone to excessive bending deformations, there are failures in dynamic analyses under linear (small deflection) conditions. Thus, a large deflection blade model is developed here to study the dynamic response. The updated Lagrangian equation is used to derive the large deflection blade model from the Euler–Bernoulli beam. Then, the nonlinear aeroelastic dynamics equations of the blade are established using blade element momentum (BEM) theory, and time-domain simulations are performed using the nonlinear Newmark and Newton–Raphson methods. The effects of structural vibrations and aerodynamic damping are considered throughout the process. Finally, the nonlinear model is applied to the DTU 10 MW wind turbine. The results show that under steady and below-rated wind speeds, the flapwise deflection of the nonlinear blade is smaller than that of the linear blade. However, this phenomenon is the opposite for above-rated wind speeds. Under a step wind, the model responds quickly to the blade’s flexible deformation. Under turbulence, the linear results are consistent with the DNVGL Bladed 4.3 results, indicating that the nonlinear blade based on the linear Euler–Bernoulli beam is reliable. Meanwhile, the flapwise deflection for both blades fluctuates slightly when turbulent speeds are lower than the rated speed (0–5 s and 41–50 s), which is distinct from the steady-state analysis. In the aeroelastic coupling analysis, responses that consider vibration feedback are significantly smaller than those without feedback, and a nonlinear blade is significantly more affected in the flapping direction than a linear blade. Finally, the aerodynamic performance of large wind turbines is negatively affected by certain turbulent wind speeds.