| How to use energy effectively is the core problem that every country in the world needs to solve.Renewable energy has been paid more and more attention from all over the world,especially the wind energy,which is developing very rapidly.Due to the increasing demand for energy,along with the development of wind energy utilization technology,the large-scale trend of wind turbines is obvious.Yaw condition is a typical dynamic condition in horizontal axis wind turbine operation.Further research on the dynamic aerodynamic performance of large wind turbines under yaw condition is important for improving the prediction accuracy of wind power and the safe operation.The main contents of this paper are as follows:The conception of the yaw,dynamic stall,flow control and vortex generator is introduced,and the basic principles of the numerical method are expounded.Validity of the numerical method is verified and credibility of the subsequent analysis is ensured before analysis.The aerodynamic characteristics of Tjaereborg 2MW wind turbine and NREL 5MW wind turbine under yaw are analyzed.Compared with the axial flow condition,the mean power under yaw condition is not decreased by the rule of cos3β,and the thrust of wind wheel basically decreases with the rule of cosβ.During the yaw operation,the characteristics of the wind wheel(such as power and thrust)show 3P fluctuation characteristic,the larger the yaw angle,the greater the amplitude of the fluctuation.The second flow produced by the velocity yaw component in the plane of wind wheel will affect the main flow of the blade,which is related to yaw angle and azimuth angle.The dynamic change of aerodynamic performance is caused by the second flow at different azimuth angles.When large wind turbine is under yaw condition,the angle of attack in the root is large,and the dynamic stall phenomenon is prone to occur.Due to the mixing of shedding vortex and separation vortex,aerodynamic parameter of clean airfoil does not reduce monotonically with the decreasing of angle of attack,while with fluctuation and periodicity.Through the vortex generator,the dynamic aerodynamic performance of the airfoil can be improved,VG can effectively control the flow separation in the process of angle of attack reducing. |
