Study On The Aerodynamic Performance Optimization Of The Straight-bladed VAWT

With the global shortage of fossil fuels and the increasingly severe environmental problems,wind energy has received wide attention as renewable clean energy.Compared with the widely used and researched horizontal axis wind turbines(HAWTs),the vertical axis wind turbines(VAWTs)have advantages of low installation cost,no yaw device,low noise and convenient maintenance except for the low wind energy utilization rate.Therefore,improving the power coefficient(Cp)based on aerodynamic performance analysis for H-VAWT is very important.(1)Firstly,based on the motion law of the vertical bladed vertical axis wind turbine during the rotation process,the angle of attack of the blade at different tip speed ratios was analyzed;Secondly,the aerodynamic theory is used to reason about the aerodynamic forces during service of the wind turbine,and the aerodynamic torque acquisition is analyzed theoretically using the pressure distribution on the surface of the blades to provide a theoretical basis for the subsequent calculation and simulation of the vertical axis wind turbine.Finally,a wind tunnel experimental test platform for vertical axis wind turbines with straight blades was built to test the aerodynamic performance of wind turbines under various operating conditions.(2)The general laws of the operation of the straight-bladed VAWT are analyzed in detail by using three-dimensional CFD numerical simulation methods.The variation of the instantaneous power coefficient of a single blade and the entire rotor with the azimuth angle is analyzed,and the influence of the tip speed ratio and the wind speed on the power coefficient of the single blade of the vertical axis wind turbine and the entire rotor is analyzed.Comparing the three-dimensional CFD numerical simulation results with experimental test results,the accuracy of three-dimensional CFD numerical simulation is verified.(3)The fixed-pitch vertical axis wind turbine cannot ensure that angle of attack of the blade is always at an optimal value during the rotation process,resulting in a lower wind energy utilization efficiency of the wind turbine.Therefore,the aerodynamic performance optimization scheme for independent pitch is proposed in this paper.Based on the principle of tangential torque maximization,the optimal pitch angle of vertical axis wind turbine under different azimuth angles is obtained by using genetic algorithm and neural network prediction model.Through pitching,the angle of attack of the blade under different azimuth angles is optimized to maximize the absorption of wind energy,and verified by three-dimensional CFD numerical simulation method.(4)The numerical simulation results of two-dimensional CFD and three-dimensional CFD for vertical axis wind turbines are compared.Based on the torque coefficient curve of single blade,it is found that when the blade is in range of 0°~50° and 130°~180°,the attack angle is small so that the efficiency of wind energy obsorded by blade is lower.Therefore,a performance improvement scheme for adding upstream deflector of vertical axis wind turbine is proposed.Two counter-rotating vertical axis wind turbines with upstream deflector and a single vertical axis wind turbine with two upstream deflectors are simulated through two-dimensional CFD.The maximum wind energy utilization rate of the wind turbine has been increased by 16.4% and 29.1% compared with that without deflector respectively,which provides new ideas for the performance improvement of vertical axis wind turbine.