Study On Aerodynamic Damping Analysis Of Swept Blades Based On Dynamic Response Analysis

As the blade size and flexibility of modern wind turbines continue are increasing,the mass,aerodynamic load and inertial load also increase,and flexible blades undergo large elastic deformation and vibration under complex loads,which w ill greatly affect the blade’s aerodynamic performance and operational stability.As a new type of aerodynamic layout,the swept blade is widely concerned by scholars due to its mechanism of load-alleviating through bend-twist coupling.In this paper,based on the numerical analysis of the aeroelastic coupling response of the swept blade,combined with the mechanical vibration theory,the numerical analysis method of the modal aerodynamic damping of the large swept blade is studied.The research work has important theoretical significance and engineering application value for exploring the mechanism of load-alleviating and efficiency and aeroelastic instability of the swept blade.Taking a straight blade of a 5 MW wind turbine as a reference,a quadratic curve is used as a stacking line to design a swept blade.The helicoidal wake vortex lift line theory is selected to establish the blade aerodynamic load analysis model.This model has good three-dimensional flow field analysis capabilities and is suitable for the three-dimensional flow field analysis of the swept blades.The " superelement" method is used to discretize the swept blades into a multi-body system connected by a kinematic joint(universal joint,rotating joint),spring and damper,applying multi-body dynamics theory,combined with the developed aerodynamic model of the lift line,established the aeroelastic coupling equation of the swept blade,and developed the corresponding solver.The effectiveness and accuracy of the established aeroelastic coupling model are verified by comparison with the aeroelastic coupling response of straight blades under steady-state wind conditions.Aiming at the characteristics of wind speed varying with height,as well as the prominent geometric nonlinearity and bend-twist coupling characteristic of the swept blade,aeroelastic coupling numerical simulation of the blade under wind shear was carried out to study the effect of bend-twist coupling characteristic of the swept blade onaerodynamic performance.Quantitative results of the influence of torsional deformation of the swept blade on aerodynamic performance and structural response are obtained.The energy loss method is used to study the numerical analysis method of the modal aerodynamic damping of the swept blade.Extract the natural frequency and vibration mode of the blade through modal analysis,and calculate the time-domain response of the main coordinates of each mode of modal vibration.According to the work done by the aerodynamic damping force in one rotation period is equivalent to the energy consumed by the aerodynamic damping,the calculation formula of the modal aerodynamic damping is derived and the corresponding analysis program is developed.Using this program,the dynamic aeroelastic coupling modal damping of the swept blade was analyzed and compared with the results of the straight blade.In this paper,the multi-body dynamics theory and the aerodynamic model of the lift line are used to establish the aeroelastic coupling model of the swept blade,and the corresponding algorithm and simulation program are developed.Using modal analysis and energy loss method,a modal aerodynamic damping analysis method based on blade dynamic response is established.The research work puts forward a feasible numerical analysis method for the modal analysis and aeroelastic instability of large-scale wind turbine swept blades.