Investigations Of Dynamic Aerodynamic Characteristics Of Wind Turbine Based On The Multi-Axis Angular Motion Simulations

Energy shortage and restructuring have contributed to the rapid development of the renewable energy.As the most widely used clean and renewable energy,wind power has good develop prospects and reseach significance.During the operation of wnd turbine,there exists motions in which different components rotate simultaneously with multiple rotation axis.For example,under dynamic yaw,the wind turbine has a rotational motion while the rotational plane of wind turbine rotates with the yawing axis.The angle of attack of airfoil along the spanwise will change continuously,resulting in dynamic changes of the rotor overall performance,which presents complex three-dimensional unsteady characteristics.Another example is the motion of the platform for offshore wind turbine.So,in addition to the rotation and yaw motion,the rotor also moves with the platform,and aerodynamic characteristics presents more complicated phenomena.It is great significance to analyze and understand the variation mechanism of aerodynamic load for wind turbine under these dynamic motions,to improve the design leve of wind turbine and optimize the control strategy of the wind turbine.Taking NREL Phase VI wind turbine as test case,the flow variation law under yawed and yawing is studied.The experimental and momentum element theory methods are used to confirm the results,and the rationality of the new method is verified and confirmed.The effects under different yaw angles on the overall performance,circumferential and span aerodynamic loads and flow characteristics of the wind turbine are studied.It is found that under fixed yaw,with the increase of fixed yaw angle,the azimuthal load of the blade load is larger and the wake is skewed.During the yawing dynamic process,the circumferential load fluctuation of the blade load is increased than that in the fixed yaw,and the larger wake expansion is also oberseved Through the above comparison verification and confirmation,a numerical simulation method based on multi-axis angular motion is established.Taking NREL 5MW wind turbine as the research object,the aerodynamic loads and flow field details of large utility-scale wind turbine during fixed and different start-stop dynamic yaw are studied.Numerical simulations of the yaw dynamics of five different yaw steady states and two different start-stop changes cases were carried out.It is found that under yaw,as the yaw angle increases,the spanwise angle of attack in the retreating side of the wind rotor increases,the amplitude of the aerodynamic load is larger,and the amplitude of the circumferential fluctuation increases,The law of change in the advancing side is reversed.During dynamic yaw,the fluctuations in power and section aerodynamic loads increase than that of the fixed yaw angle.The aerodynamic load during the dynamic process of starting to constant yaw rotation speed during 2s is higher than the aerodynamic load during the 4s start-stop dynamic process.The fluctuation characteristics of the spanwise load are affected by the yaw dynamic rotational speed,and the maximum amplitude and fluctuation of the load are higher than the fixed yaw.Taking the NREL5MW wind turbine as test case,the angular motion models of four sinusoidal variations are used to study the effects of platform pitching and rolling on the aerodynamic characteristics and flow field details of the wint turbine with different amplitudes and frequencies.Under the coupling of the platform pitching axis and the rotating axis of the wind rotor,the increase of amplitude and frequency will lead to an increase in power and load fluctuations,the flow is more complicated,and the load characteristics of the spanwise section and the overall performance change are consistent with the change of angular velocity of the platform motion.Under the coupling of the platform rolling axis and the rotating axis of the wind rotor,the load of the wind rotor shows a tendency of fluctuation,and the variation law of thrust and power is the same with the variation law of the platform angular velocity.As the amplitude increases,the platform roll motion also causes the velocity vortex streets to alternately oscillate on the inner side of the wake,and the wake boundary also has a certain regular swing,and the intermittent action between the wake region and the mainstream region is more obvious.In summary,in this paper,a simulation method for unsteady aerodynamic characteristics of wind turbines based on multi-axis angular motion simulation is proposed.The single-rotation axis motion under yaw and the more complex multi-rotation axis coupling motion,including dynamic yaw,dynamic platform rolling and dynamic platform pitching,are studied.The research results provide a theoretical support for understanding the aerodynamic characteristics of the yaw process of the wind turbine and the aerodynamic characteristics of the platform coupled motion of the offshore wind turbine to ensure stable and safe operation of the wind turbine.