| The structural characteristics of the unit and the outfield wind conditions make the wind turbine power show strong fluctuation characteristics,and the power fluctuation will lead to the increase of wind turbine load,voltage fluctuation,flicker and harmonics,which is not conducive to the healthy development of wind power,so through the analysis of power fluctuation characteristics,to optimize the design and control of wind turbines and enhance the competitiveness of wind power.The structural characteristics of the unit take into account elevation and tower,the outfield wind condition is usually yaw flow and wind shear flow,and the wind turbine power is formed by the superposition of many blade aerodynamic forces on the blade,but when the wind wheel has elevation angle,the influence of a single periodic pulsation source(yaw,wind shear,tower shadow effect)and its coupling on the aerodynamic fluctuation characteristics of blades is not clear.Therefore,quantitative analysis is made under 7 working conditions(elevation angle,yaw plus elevation angle,wind shear plus elevation angle,tower shadow effect plus elevation angle,yaw plus tower shadow effect plus elevation angle,wind shear plus tower shadow effect plus elevation angle,yaw plus wind shear plus tower shadow effect plus elevation angle).Fluctuation characteristics of wind turbine power,blade surface pressure and cross-section airfoils(0.335 R,0.462 R,0.588 R,0.715 R,0.905R).And explore the internal relationship between them.The main contents are as follows:(1)Based on the large eddy simulation,the fluctuation characteristics and power loss of wind turbine power under seven working conditions are studied,and the periodic pulsation source which leads to the maximum power fluctuation is explored.The results show that yaw is the main cause of power loss,followed by tower shadow effect,followed by wind shear,tower shadow effect is the main cause of power fluctuation,wind shear is the second,and yaw effect is less.the more coupled pulsation sources,the greater the fluctuation and loss of power.(2)The fluctuation characteristics of surface pressure of wind turbine blade under 7 working conditions are studied based on large eddy simulation.The results show that the pressure fluctuation law of the cross-section airfoil surface is similar to the power fluctuation law,and the characteristic area is the corresponding pressure surface at the chord length of 10% to 20% and the suction surface at the chord length0.5% to 6%,and from the root to the tip of the blade.The characteristic area increases gradually.And the characteristic area increases gradually from the root to the tip of the blade.The more the coupled pulsation source,the greater the pressure fluctuation,the influence of the tower shadow effect is the greatest at the root of the blade,followed by the yaw,the wind shear at the tip is the greatest,and the tower shadow effect is the second,and the interaction of the tower shadow effect with elevation and yaw reduces the amplitude of pressure fluctuation at the blade tip.Where the pressure fluctuation is large,the corresponding pressure surface at 0 to 1% of the chord length of the cross-section airfoil,and the suction surface at 0.5% to 6%,40% and 90% of the chord length,and the amplitude of pressure fluctuation at the tip is greater than that at the root of the blade.The amplitude of pressure fluctuation on the suction surface is larger than that on the pressure surface,which provides an effective position for the flow control of pressure fluctuation on the blade surface.(3)Based on the blade element momentum theory and the inverse blade element momentum theory,the fluctuation characteristics of the angle of attack and aerodynamic coefficient of the cross-section airfoil under seven working conditions are studied.The results show that after the range of normalized angle of attack,lift-drag coefficient,normal force coefficient and tangential force coefficient,it is found that the fluctuation law is similar,so the fluctuation characteristic of aerodynamic coefficient can be analyzed by analyzing the fluctuation characteristic of angle of attack;by analyzing the fluctuation law of angle of attack with azimuth angle,it is found that the interaction of multiple pulsating sources is superimposed on each other,and the main influencing factors are dominant,which is similar to the fluctuation law of power in one cycle.Based on the analysis of the law after the normalization of the angle of attack,it is found that the more the coupling pulsation source is,the greater the fluctuation is,the greater the influence of the tower shadow effect is at the root of the blade,the second is the influence of wind shear at the tip of the blade,and the second is the tower shadow effect,which is consistent with the law of pressure fluctuation,which provides a reference for flow control to reduce the fluctuation of airfoil angle of attack and aerodynamic coefficient,so as to achieve the goal of smoothing the power fluctuation of wind turbine. |
