Aerodynamic Characteristics And Reliability Computation Of Wind Turbine Blades

Blade is the main component of wind turbine which converts kinetic energy into mechanical energy.The cross section of blade is different along the span direction.As a basic performance of blade,its aerodynamic characteristics affect the operation of the whole wind turbine.When the wind turbine runs,the blades are subject to many uncertain loads,including aerodynamic loads,gravity loads,mechanical vibration loads,etc.These loads are highly random and non-linear,so the aerodynamic characteristics and reliability analysis of the wind turbine blades is particularly important.The main research contents and conclusions are summarized as follows:(1)The Reynolds number effect on aerodynamic performance of wind turbine blade airfoil is studied by Xfoil simulation program.The calculation shows that when the angle of attack is the same and the Reynolds number is increa sing,the lift and drag of the airfoil are increasing,and the lift-drag ratio is also increasing.Generally speaking,the larger of the lift-drag ratio represents the better of the aerodynamic performance of the airfoil.(2)The results calculated by several different turbulence models of Fluent and the Xfoil of aerodynamic parameters of wind turbine blade airfoil are compared.The calculation shows that the lift curve and drag curve calculated with Transition k-w SST model,k-epsilon model,S-A model and Xfoil program are in good agreement with experimental data at small angle of attack.The slope of the rise curve is basically the same.When the stall angle of attack is reached,the deviation between the calculated results and the experimental data increases gradually.In fact,when the airfoil reaches the stall zone,the flow becomes more complex,and the boundary layer separation exhibits obvious three-dimensional unsteadiness.The two-dimensional calculation results can not reflect the real flow situation.It is necessary to use more accurate large eddy simulation for three-dimensional calculation,but the two-dimensional calculation results still have reference significance.(3)Two-dimensional static wind tunnel tests were carried out on a special blade airfoil of a wind turbine.It shows that the results of Fluent and wind tunnel tests agree well with the angle of attack ranges from 0°to 15°.The pressure changes of airfoil are also in good agreement.When the angle of attack increases gradually,the pressure of the suction surface of the airfoil becomes negative,the pressure of the pressure surface of the airfoil becomes positive,the CFD calculation and measurement values of the suction surface of the airfoil are in good agreement.The upper airflow of the airfoil becomes separated,and the airflow of suction surface changes from uniform laminar flow to irregular turbulence.The three-dimensional effect is aggravated.In the simulation process,we use two-dimensional calculation method,which cannot simulate the airflow well after stall zone.(4)In this paper,subset simulation method is used to calculate relia bility of blades.When the failure probability of the structure is small,the traditional calculation method is time-consuming and labor-consuming,sometimes even impossible to complete.Subset simulation method has many advantages.Subset simulation method transforms the small probability failure events int o big probability events through conditional failure probability,which greatly reduces the amount of computation.The results show that the smaller the failure probability of the structure under random excitation,the smaller the number of samples require d by subset simulation method,and the subset simulation has higher efficiency compared with Monte Carlo simulation method.It provides a new idea for the reliability calculation of wind turbine blades.