Research On Aerodynamic Optimization Design And Wind Tunnel Test Of Wind Turbine Airfoils

Wind energy is a kind of clean, renewable energy, every country in the world is paying more and more attention to it. In the next 20 years, the world’s wind power market will increase 25% annually. Recently, wind turbines have been applied and developed widely, with the emphasis on wind power market.The blade is the core component of wind turbine for getting wind energy. The performance of the blade determines the wind energy utilization efficiency of wind turbines, load characteristics, noise levels and so on. An airfoil is the basis for blade design, which is the most important factor in determining the performance of the blade. Therefore, the airfoil design is the most important element of wind turbine design. The airfoils with excellent performance can dramatically improve the capability of energy capture, reducing structural weight to save cost of manufacturing and transportation, and lowering the loads. This paper carried out the aerodynamic analysis, optimization design method and wind tunnel test technique for wind turbine airfoil. The main research issues and contributions of this dissertation can be summarized as follows:1. The aerodynamic characteristics and wind tunnel wall interference effects of the flow around wind turbine airfoils at angle of attack ranging from-180 degree to 180 degree are numerically simulated.Based on overset grids, the aerodynamic characteristics of wind turbine airfoil at angle of attack ranging from-180 degree to 180 degree are predicted, using unsteady, preconditioned compressible Reynolds averaged Navier-Stokes equations with SST two-equation turbulence model. The qualitative laws of areodynamic performance changing with the angle of attack is gotten. For improving the accuracy of predicting the aerodynamic characteristics of wind turbine airfoil at angle of attack ranging from-180 degree to 180 degree, the Large Eddy Simulations(LES) method based-on the WALE subgrid model are used to simulate the aerodynamic characteristics of the wind turbine airfoils at angle of attack ranging from-180 degree to 180 degree. Compared with the experimental data, the LES method can provide accurate and reliable aerodynamic computational results. With the wind tunnel wall interference, the aerodynamic characteristics of wind turbine airfoil DU 93-W-210 at angle of attack ranging from-180 degree to 180 degree are calculated with LES method. The amounts of aerodynamic characteristics with wall interference are obtained, the instantaneous flow fields are shown.2. The multi-objective aerodynamic optimization design of wind turbine airfoil is carried out.Based-on the Pareto optimal sets, the multi-objective optimization design of wind turbine airfoils using the in-house optimization code, is carried out. The airfoils with the thickness ratio of 18%, 21%, 25%, 30%, 35% are obtained by the optimization, comparison with the baseline airfoils, the aerodynamic performances of the optimized airfoils are improved. Controlling the transition position of the suction side of the airfoil is to improve the lift-drag characteristics and insensitivity of roughness. Constraining the maximization of the thickness and their locations for airfoil is to ensure geometric compatibility. Comparison and analysis of aerodynamic properties for optimization airfoil with the original airfoil, shows that the optimization airfoil can can satisfy the demand of wind turbine blade.3. The adjoint-based aerodynamic optimization design method is studied.By introducing the Bracket line search method, the robustness of the adjoint-based airfoil optimization design method is improved. The line search method can obtain the optimal step. The results illustrate that it can automatically find the optimal step, and overcome the restriction imposed by the choice of user-defined constant step, which is used in the traditional adjointbased optimization method, thus improving the robustness of the adjoint-based airfoil optimization design method. According the requirement of the multi-point multi-objective aerodynamic optimization design of wind turbine airfoil, the code of the multi-objective adjoint-based aerodynamic optimization design is developed. The relevant examples of inverse design and optimization design are carried out. For the wind turbine airfoils of 18%, 21% relative thickness obtaining from the Pareto multi-objective optimization design, the drag reduction are performed with the improved adjoint method of optimized design.4. The wind tunnel tests of the airfoil, including the conventional angle of attack and the high angle of attack, are carried out.The NF-3 low-speed wind tunnel is introduced. The wall interference correction for wind tunnel test is described. For the conventional angle of attack of the airfoil, the consistent test data of the wind turbine airfoils are compared with that of TU Delft wind tunnel test. The result demonstrates the NF-3 wind tunnel test method and its equipment conditions can satisfy the requirements of wind tunnel test for wind turbine airfoils. The seven repetitive wind tunnel test about the DU 93-W-210 wind turbine airfoil at transition are carried out to verify the accuracy of wind tunnel test. Through the results from wind tunnel test, the aerodynamic characteristics of NPU-WA airfoils on the high Reynolds number are researched. For the airfoil test at the very high angle of attack, the compared agreed test results of the different chord of the NPU-WA-210 airfoil are obtained, which indicates the wall interference correction method of wind turbine airfoil test at very high angle of attack is right.