| Rotating wind turbine blades are the core component of wind turbines.Influenced by changes in the incoming wind direction and wind speed,the complex stress and different operation conditions lead to the stress concentration and fatigue damage,which are the main causes of blade damage and fracture.The dynamic stress distribution of wind turbine blades under dynamic wind direction of wind shear inflow wind condition are not clear.Therefore,the research on the stress characteristics of wind turbine blades under different inflow conditions can provide reference for the safety design and yaw operation control of wind turbine blades.In this paper,the basic material properties of elastic modulus and Poisson's ratio of blade model are obtained by material mechanical properties experiments.Carried out the wind tunnel experimental study of blade stress and strain under different wind direction and yaw angles,and the numerical simulation of coupling solid and fluid.The reliability of the numerical simulation method was verified by wind tunnel experiment results.And the dynamic stress characteristics of blade under aerodynamic load,centrifugal load and coupling load were further studied.The dynamic change of wind direction and the dynamic stress characteristics of wind turbine blades under the condition of wind shear inflow based on the actual wind field data fitting are studied.The load on the wind turbine blade in operation is decomposed,and explored the sensitivity and difference of single aerodynamic load,centrifugal load and coupling load on blade stress.The results showed that the stress concentration of blades is different under different loads.The coupled load is greater than the stress under the action of a single pneumatic and a single centrifugal load.The maximum increment of stress under coupling load is 106.86% compared with that under aerodynamic load,and 262.42% compared with that under centrifugal load.It is quantitatively revealed that the single load which has great influence on the stress of wind turbine blades is aerodynamic load.It is found that aerodynamic load has great influence on the stress from blade root to blade middle and blade leading edge,and centrifugal load has great influence on the stress at blade tip and blade trailing edge.In addition,by studying the distribution of the maximum stress point,it is clarified that the maximum stress point is at the position of the maximum chord length of the blade root under centrifugal load and coupling load,the maximum stress point extends outward along the wingspan and near the leading edge of the blade with the increase of tip velocity ratio.Based on wind tunnel experiments and numerical simulation of coupling solid and fluid to explore the influence of dynamic change of wind direction on blade dynamic stress characteristics.There is a trend that the maximum principal stress direction of the maximum chord length and the aerodynamic center of the airfoil in the middle of the NACA4415 and SD2030 blade points to the blade root with the increase of tip speed ratio.The change of wind direction has greater influence on the blade strain of NACA4415 airfoil.The results showed that the dynamic change of wind direction is consistent with the stress concentration area and change trend under the action of fixed wind angle.And the maximum stress of blades decreases less than 1%.The stress distribution of the three blades is asymmetric under the action of the rapid dynamic change of wind direction,and the stress difference is large under the positive and negative wind directions.The maximum stress increases under the different wind direction yaw angles,and the maximum increment can reach up to 48.67%.The dynamic change of wind direction can increase the axial force,and it increases with the increase of wind direction change rate.The output power is cosine distribution with the change of wind direction,and it has the minimum output power at the maximum wind direction yaw angle.The shear inflow wind profile of the actual wind field is fitted as the dynamic inflow condition to explore the influence of wind shear on the stress distribution characteristics of wind turbine blades.At the same wind speed of the hub,the shear inflow can increase the maximum dynamic stress of the wind turbine blade,and make the azimuth of the maximum dynamic stress ahead of the uniform inflow condition,lag behind the highest wind speed point.The dynamic stress is minimum when all the blades are vertical and toward the ground.The dynamic stress of SD2030 is greater than that of NACA4415 airfoil at different azimuths.From root to tip spanwise direction,NACA4415 airfoil has the maximum dynamic stress in the middle of blade,SD2030 has the maximum dynamic stress at the maximum chord length,and the maximum dynamic stress at the position of dimensionless chord length x/C = 0.4from leading edge to trailing edge at the maximum chord length.The shear inflow has a great influence on the dynamic stress of SD2030 blade with high power.When the wind speed at the hub of the wind turbine is the same,the shear inflow increases the axial force of the blade and reduces the output power of the wind turbine,and the shear inflow has a great influence on the axial force of the single blade of the wind turbine.This study not only improves the research of blade stress characteristics under single and coupled loads,dynamic changes of wind direction and wind shear inflow in theory,but also provides a theoretical basis for yaw control strategy.At the same time,it has positive significance for guiding the safe and stable operation of wind turbines and prolonging the life of blades in engineering practice. |
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