Abstract
As the size of wind turbine blades increases, the influence of geometric nonlinearity on aerodynamic, structural and design of blades becomes more and more serious. In this work, the efficient aero-elastic calculation of large flexible blades is studied. In order to solve the problem of efficient aeroelastic caculation of large flexible blades, this work applied the geometrically exact beam theory based on Legendre spectral finite element and coupled with the blade element momentum theory to establish the aero-elastic analysis model of large flexible blades. This model can efficiently calculate the deformation and load on the blade under aerodynamic loading and fully consider the influence of geometric nonlinearity caused by deformation on aeroelastic ability. Taking NREL 5MW and IEA 15MW wind turbines as examples, the linear and nonlinear dynamic responses of these two wind turbine blades are calculated. The result shows that the neglect of nonlinear effect will bring error. From 5MW wind turbine to 15MW wind turbine, the numerical error increased by 27.88%. The influence of geometric nonlinearity of blades on dynamic responses is analysed, which is of great significance to improve the design level of large-scale wind turbines.
Highlights
With the increase of the size of composite blades, nonclassical effects, such as geometric nonlinearity, warpage in and out of the section, have significant effects on the dynamic response of blade structures
The geometrically exact beam theory based on the Legendre spectral finite element is applied, which is based on the classical Timoshenko beam theory and takes into account the section rotation
As for the 15MW blade, the diameter of the wind turbine is 240m, the hub height is 150m, and the total length of the blade is 117m. 3.1 Blade model comparison As shown in Fig.2, there are some differences in the twist distribution between 5MW and 15MW wind turbine blades
Summary
With the increase of the size of composite blades, nonclassical effects, such as geometric nonlinearity, warpage in and out of the section, have significant effects on the dynamic response of blade structures. For large-scale wind turbines, large deflections may occur under working conditions. At this time, the traditional linear method can no longer accurately predict the dynamic response of blades. Developing a geometrically nonlinear beam model for the pre-twisted and curved composite blade is a relatively new focus of the wind turbine community[2]. The geometric nonlinearity is mainly caused by the finite rotation of the blade section. The geometrically exact beam theory based on the Legendre spectral finite element is applied, which is based on the classical Timoshenko beam theory and takes into account the section rotation. The commonly used methods in the aerodynamic calculations are the actuator line – large-eddy simulation (AL-LES)
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