Aerodynamic Response Analysis Of Swept Wind Turbine Blade Based On Geometrically Exact Beam Model

As a key component of wind turbine,wind turbine blade has significant nonlinear characteristics because of its complex structure and variable load.At the same time,in order to improve the utilization rate of wind power and wind power capacity,and reduce the cost of power generation,wind turbine upsizing has become an inevitable trend of wind turbine development,so the size of wind turbine blade also increases and its flexibility increases sharply.Therefore,the previous assumption of small deformation has been difficult to accurately describe the nonlinear large deformation of large blades,and the nonlinear problem of large blades has become one of the key research directions in the field of wind power.As a slender structure,wind turbine blades are usually approximated as beam models to study the structure.The most commonly used nonlinear beam models include finite element model,multi-body dynamic model,absolute node coordinate model and geometrically exact beam model.Compared with the finite element model and the absolute node coordinate model with more degrees of freedom,which leads to lower solving efficiency,and the multi-body dynamic model with partial structural information loss,the geometrically exact beam model can obtain higher computational accuracy with fewer degrees of freedom of nodes,and can be accurately used in the nonlinear dynamic analysis of blade.Swept wind turbine blade is designed by bending the airfoil at the blade spread direction to the trailing edge.It has the characteristics of adaptive passive load reduction,which can reduce the load on the blade and the production cost of wind turbine while maintaining a certain power output.It is a new development direction to improve the competitiveness of wind power.Based on the geometrically exact beam theory and blade element momentum theory,the nonlinear aerodynamic coupling dynamics model of swept blade is established in this thesis.The specific research work is as follows:（1）In this thesis,based on the geometrically exact beam theory,a geometrically exact beam dynamic model is established by using quaternion to express the cross section rotation,using Gauss-Lobatto integral rule,combined with the generalized-α time prediction iterative algorithm with second-order accuracy,and the accuracy of geometrically exact beam model to express the dynamic and static characteristics of nonlinear beams is verified by examples.（2）In Technical University of Denmark provides a level 10 MW wind turbine blade as the research object,combined with airfoil section and composite layer characteristics,combined with swept-back blade fold line of the cross section of offset,straight blade and sweep amount is built respectively for 4,6,8 m swept blade dynamic model,and calculate the deflection of the four blades,The effects of blade rotation speed and sweep amount on its characteristics of mode were studied.（3）With blade element momentum theory as the aerodynamic load,on the basis of the operational parameters of the wind turbine,in the case of the same output power,the aerodynamic response analysis results of straight blade and swept blade at 12m/s wind speed were calculated,and the influence of sweep amount on blade aerodynamic characteristics is analyzed and compared,for the later after blade shape design and the load reduction mechanism research to provide the reference data.