Nonlinear Aeroelastic Modal Analysis Of Back-swept Wind Turbine

With the large-scale of wind turbine and the complexity of operating conditions.The aeroelastic stability of wind turbine has gradually become the focus of researchers at home and abroad;At the same time,as a new type of wind turbine which can realize passive load reduction under extreme wind conditions,back-swept wind turbine has attracted extensive attention.Its aeroelastic coupling model will have severe nonlinear characteristics.As a result,the wind turbine vibration intensifies,and even aeroelastic instability occurs,which brings damage and damage to the wind turbine.On the one hand,the structural nonlinearity of wind turbine is reflected in the nonlinear coupling relationship between bending deformation and torsional deformation,resulting in large flexible deformation.On the other hand,compared with the straight blade,the spanwise flow and dynamic stall of the back-swept blade flow field lead to obvious unsteady aerodynamic characteristics.Therefore,it is necessary to use an appropriate nonlinear dynamic model to express this nonlinear effect.In this thesis,a nonlinear aeroelastic coupling model of back-swept wind turbine is established based on the computational multi-body dynamics theory and the aerodynamic model of vortex lift line;Through the time domain and frequency domain response analysis of the wind turbine,the blade flutter characteristics and aeroelastic instability characteristics of the unit are studied.The specific research work is as follows:（1）In order to accurately describe the nonlinear deformation characteristics of back-swept blade and back-swept wind turbine,taking DTU 10 MW wind turbine as the prototype,this thesis uses the "super element" method to discretize the back-swept blade and back-swept wind turbine into multiple rigid bodies,which are connected with the moving pair through force elements,so as to form a multi-body system.（2）The nonlinear structural dynamic equations of back-swept blade and back-swept wind turbine are established by Newton Euler equation;In order to accurately calculate the aerodynamic load with three-dimensional characteristics flowing along the spanwise direction of the blade,this thesis uses the lift line theory to calculate the aerodynamic module.Through the combination of multi-body structure model and aerodynamic module,the aeroelastic coupling dynamic equations of back-swept and back-swept wind turbine can be formed respectively.（3）In order to linearize the aeroelastic coupling dynamic equations of back-swept blade and back-swept wind turbine,the variational principle is used in this thesis.In order to accurately describe the unsteady effect of aerodynamic parameters due to the dynamic stall of airfoil,the modified Beddoes Leishman dynamic stall model is introduced in the process of linearization.（4）Compare the deformation under no wind load（assembly position）and constant wind speed（steady-state deformation position）.By solving the linearized aeroelastic coupling dynamic equations of back-swept blade and back-swept wind turbine by eigenvalue method,the aeroelastic frequency and aeroelastic damping ratio of both can be obtained,so as to analyze their flutter.