Nonlinear Aeroelastic Modal Analysis of Large Wind Turbine Flexible Blades

Aiming at the increasing size of wind turbine and the enhancement of blade's rigid-flexible coupling and aeroelastic coupling characteristics, the aeroelastic mode and stability of the flexible blade bending and torsion coupling deformation of large wind turbines are studied. In order to exactly describe the nonlinear deformation characteristics of flexible blades, the super-element method is used to discretize the flexible blades into a number of rigid bodies. And the multi-body system is formed by connecting the motion pair and the force element, and then the blade's nonlinear dynamic equation is established by the Newton-Euler equation. The blade element momentum method combined with modified Beddoes-Leishman(B-L) dynamic stall model to calculate the unsteady aerodynamic loads. Based on the variational principle, the nonlinear dynamic equations of the blade are linearized, and the aeroelastic linearization state equation of the rotating blade is constructed. Finally, the influence of large geometric deflection of flexible blade and unsteady effect of blade aerodynamic loads on aeroelastic modal characteristics and the mechanism of flutter are investigated by flutter analsys of NREL 5 MW blade at a constant tip speed ratio.