Investigations On Robust Aerodynamic Optimization Methods For Wind Turbine Airfoil

With the world’s demand for energy consumption and environmental protection,wind energy has developed rapidly in the world.Wind turbine is the main equipment of wind energy utilization.Improving the aerodynamic performance of wind turbine blades is the basis of improving the utilization rate of wind energy.Airfoil is basic element of the blade.Improving the aerodynamic performance of the airfoil is the key to improve the aerodynamic performance of the blade.Therefore,the design of airfoil with better aerodynamic performance is of great significance to improve the aerodynamic performance of the blade and increase the utilization rate of wind energy.Comprehensive research have been carried out on aerodynamic optimization design method of wind turbine airfoil.However,most of these aerodynamic optimization design methods are deterministic.The robustness of the optimization result is relatively poor.The practical operating environment of wind turbines is relatively complex with many uncertain factors.Thus the deterministic optimization result usually has optimal performance at design point and poor performance at off-design points.Therefore,the influence of uncertain parameters on the aerodynamic performance of airfoil should be considered in the airfoil optimization model to carry out robust optimization design.The main research contents are as follows:(1)The airfoil optimization design method is build based on CST parameterization method,CFD calculation,surrogate model and genetic algorithm method.Deterministic optimization design of NACA0012 and S809 airfoil are performed.The objective function is the maximum lift coefficient,the geometric constraint is maximum thickness and the position of the maximum thickness,and aerodynamic constraint is drag coefficient of optimized airfoil smaller than that of the original air foil.The geometrical and aerodynamic performance of the final optimized airfoil a recompared with that of the optimized airfoil without constraint.Result shows the lift coefficients of the airfoil obtained by both optimization methods are all imp roved.However,the drag coefficient of the airfoil obtained only by the constraine d optimization method is reduced.The maximum thickness of the optimized airfoi 1 with constraints is similar to that of the original airfoil,but less than that of the optimized airfoil without constraints.(2)The effect of coarse-to-fine training strategy to the surrogate model is perf ormed.Focusing on the relationship between the number of initial samples and the number of refining iterations in the coarse-to-fine strategy,the validity of coarse-to-fine strategy for improving the prediction accuracy of the surrogate model and is verified.S809 airfoil is used to verify the method and show the optimization results.Result shows that the aerodynamic performance of the optimized airfoil si gnificantly improves compared with the original S809 airfoil.The lift coefficient increases,and the drag coefficient reduces.The prediction accuracy of the surrogate model improves by using the coarse-to-fine iterations,and the total number of training samples is reduced.(3)Robust aerodynamic optimization method and multiple point optimization method are built through adding the non-intrusive probabilistic collocation method to deterministic optimization method.The robust aerodynamic optimization S809 airf oil is carried out under the condition of stochastic wind speed and the angle of attack,and non-intrusive probabilistic allocation point method is used for the uncert ain method.The results show that the aerodynamic performance of the multiple point design has a wide range of points,and the aerodynamic performance of the non-evenly distributed weight is improved more than that of the evenly distributed weight.However,the airfoil is thicker and more sensitive to uncertain changes in wind speed and angle of attack.The aerodynamic performance of the robust optimization under design conditions is improved steadily,and the sensitivity to rand om wind conditions is lower.However,aerodynamic performance may deteriorate beyond the design point.How to combine the advantages of the two optimization methods will be the main direction of the following research.The airfoil aerodynamic optimization and robust aerodynamic optimization met hods developed in the current studies provide technical support for the design of wind turbine blades with high performance and high reliability.