Aeroelastic Coupling Analysis And Optimization Of Wind Turbine Blade

With the development of wind power technology,the blade length increases and the flexibility of the blade enhances.The large deformation and multidimensional freedom coupling effect of the blade make the aeroelastic effect more obvious,which the bending and torsional deformation of the blade would be coupling.This coupling character will affect the aeroelastic twist and load distribution along the blade spanwise,which further impact the power output and stable operation of wind turbine.Therefore,studying the blade aeroelastic characteristic and seeking the influence law of aeroelastic effect on the blade performance are very important for the blade design and operating.The aeroelastic coupling model as the basis of this research work,in order to improve the calculation accuracy of aeroelastic coupling model,a quasi-three-dimensional aeroelastic coupling mathematical model is established in this study.In the respect of structural model,three-dimensional static and dynamic analysis models are built by the Ansys Parametric Design Language(APDL)based on the three-dimensional ply structure and material properties to increase the degree of freedom for blade structure analysis,which considering geometric nonlinearity and coupling load characteristics of flexible blades.The simulation results are compared with the full-scale static test of 100 kW blades to verify its accuracy.In the respect of aerodynamic model,combining with dynamic stall correction theory and improving the BEM,a corresponding aerodynamic analysis model is eatablished with programming based on Matlab platform,which considering the effect caused by blade deformation and vibration velocity.Similarly,comparing the simulation results with Bladed software results and experimental results to verify its accuracy.In addition,the weak coupling method appropriate balancing the calculation accuracy and time will be chose to solve the model,that is to say,the aerodynamic module and the structural module are solved independently,and the linear interpolation is used to transmit the information at the coupling interface.Based on the aeroelastic model,the following studies were carried out:(1)For the steady operation process of wind turbine,the static aeroelastic calculation is carried out with uniform air flow to compare the characteristics of deformation,power output and load distribution of 100kW wind turbine blades under coupling and uncoupling conditions respectively.The aeroelastic effect on the blade characteristics is obtained in different wind speed:the aeroelastic effect increases with the rising of wind speed,and maximum is reached near the rated wind speed.When the wind speed continues to rise,the influence of the aeroelastic effect decreases due to pitching of the blade.This is mainly because aeroelastic twist angle increase first and then decrease caused by aeroelastic effect,further leading to the changing of attack angle.However,the blade airfoil runs below the stall attack angle most of the time,in this case,the lift coefficient is proportional to attack angle and much higher than the drag coefficient.(2)For the unsteady factors in the practical operation of the wind turbine,considering the geometrical nonlinear influence,the dynamic aeroelastic characteristics calculation of 100 kW wind turbine blades is carried out to compare the blade characteristics variation under coupling and uncoupling conditions.It is found that tip deformation and load show cosine trend over time under wind shear.The aerodynamic performance of airfoil changes in circle round with the attack angle caused by dynamic stall effect,and the fluctuation of blade characteristics much larger than that without considering dynamic stall effect,besides,the relative error fluctuation of tip deformation caused by the aeroelastic effect also becomes larger.When the geometric nonlinearity is taken into consideration,the load and deformation of blade are no longer conformed to linear relationship,which are lower than the case of ignoring geometric nonlinearity,and the relative error of tip deformation caused by the aeroelastic effect becomes larger.In addition,when the aeroelastic effect is taken into consideration,the torsional deformation increases results in attack angle decreases,and then leads to the decline of aerodynamic load along the blade surface,which above are beneficial to the reliable operation of the wind turbine.But the torque of the rotor is also decreasing,which results in the reduction of power output,it is unfavorable for the operating costs of the wind turbine.(3)In order to compensate the power loss caused by the aeroelastic effect,a new aeroelastic optimization design model is established based on the above-mentioned aeroelastic coupling mathematical model.In this model,the annual energy production(AEP)is used as the objective function.The aeroelastic twist angles along the blade are the free variable.Under considering the influence of the aeroelastic effect on the power output,particle swarm optimization(PSO)algorithm is used to search the optimal value.Then this model was used to compensate the power loss of the 100 kW wind turbine and compared with the pre-twist coupling algorithm proposed by the Technical University of Denmark(DTU).The results show that the output power of this model is better than that of the pretwist coupling algorithm in most wind speeds.Moreover,the thrust coefficients are lower than that of the pre-twist coupling algorithm in all the wind speeds.All of those show the superiority of the aerodynamic design model.