| In order to absorb more energy from the wind and reduce the cost of wind power generation,the size of wind turbine increases day by day,the blades of wind turbine become more slender,and the flexibility of blade structure increases.The aerodynamic load,gravity,inertia load and handling load rise sharply with the increase of blade length,and the aeroelastic problems caused by it become more and more prominent.The mechanism of passive load reduction through bending torsion coupling of swept back blade due to its stacking line bending has attracted extensive attention of researchers.The vibration of components such as blades makes the air flow through the blades produce complex unsteady flow,which will significantly affect the fatigue load and aeroelastic stability of the wind turbine.It is necessary to build an effective and accurate aeroelastic coupling model to predict the complex interaction between the unsteady aerodynamic load and the elastic deformation of swept blades.The stack line of swept blade is curved,and its directional flow is more significant than that of straight blade.In this study,the aerodynamic model of swept blades was established by using the helical tail vortex lift line model.Dynamic stall effect of airfoil is an important factor for vibration of wind turbine components.In this thesis,a modified Beddoes-Leishman dynamic stall model is used to simulate the dynamic aerodynamic coefficients of oscillating airfoils and to reveal the unsteady characteristics of the airfoil aerodynamic coefficients varying with the angle of attack.B-L dynamic stall model is introduced into lift line model to build dynamic aerodynamic load analysis model.Using the“super element” model,the swept blade and the whole machine are discretized into a multi-body system composed of a pair of motion,a spring and a damper.Based on the multi-body dynamics theory and the aerodynamic model,the non-linear aeroelastic coupling equation of the blade and the whole machine is established and the simulation program is compiled.The bending-torsion coupling of swept blades results in a change in the critical flutter speed relative to the straight blades,and the flutter characteristics of the blades are closely related to their aeroelastic mode damping.Based on the analysis of the aeroelastic time-domain response of swept blades,an aeroelastic mode damping analysis method and simulation program for swept blades are developed based on the combination of time-domain response and blade vibration mode analysis.Aiming at the unsteady complex working conditions of wind turbine,the unsteady wind conditions are simulated by random wind,wind shear and gust,and the aeroelastic coupling analysis of wind turbine is carried out.By comparing and analyzing the aeroelastic response of swept blades under different wind conditions,it is shown that dynamic stall will increase the frequency and amplitude of dynamic aerodynamic load fluctuation of swept blades.Through the aeroelastic coupling analysis of the unit under certain conditions,it is shown that the vibration of each component of the unit significantly affects the angle of attack of the blade and increases the amplitude of the aeroelastic load fluctuation of the blade roots.Through the static and dynamic aerodynamic analysis model,it is shown that the dynamic stall of blade affects the fluctuation of aeroelastic loads at the blade roots and tower bottom to varying degrees.The research work has reference value for fatigue life design,structural optimization design and safe and stable operation of large sweep wind turbine. |
