Influence Of Wind Turbine Wake On Aerodynamic Characteristics Of Downstream Wind Turbine

As the increasingly serious problems of environmental pollutions and energy shortage,the scale of wind farm is growing,and the number of wind turbines in the wind farm is increasing.The fatigue load of downstream wind turbines has increased and the power defect of wind farms has become increasingly prominent caused by the upstream wind turbine wake effect.Therefore,in this paper,NREL 5 MW wind turbine controlled by variable speed was used as research objects,and a large-eddy simulation with an actuator line technique was integrated as a numerical method on OpenFOAM open source software.Study the influence of the upstream wind turbine wake on the aerodynamics of the downstream wind turbine in the wind farm.The main research contents and results include the following three parts.It was found that the law of the two parameters satisfies the relatio nship ε=k·η,When the value of η is larger,the value of k should be smaller.For the problem studied in this paper,we determine the values of η and ε.When the calculated region is small,η takes 2.5m and ε takes 1.6η.When the calculation region is relatively large,η takes 5m and ε takes 1.2η;and based on the above conclusions,the numerical method is verified with the wind turbine power error and wind turbine speed error as evaluation criteria;In the second part,under the ideal inflow condition,the aerodynamic characteristics of the wind turbine wake under different tip speed ratios are studied.It is found that the wind turbine wake velocity loss is mainly concentrated in the corresponding position in the middle of the blade;as the tip speed ratio increases,the wake velocity recovers slowly,the wake expansion caused by the wind turbine block effect decreases,and the flow field vortex The amount of dissipation is slowed down,and the distance to the backward is longer.In the wake field of the wi nd turbine,the position of the vorticity is large,the large eddy viscosity and the subgrid kinetic energy are relatively large,and the subgrid stress is relatively large.Secondly,the study A strategy to increase the power output of a wind farm by cont rolling the wake of the upstream wind turbine to tilt or offset it.It is found that there is a yaw angle of the upstream wind turbine or a difference in the height of the hub between the two wind turbines,which can increase the total power output of the two wind turbines.Finally,the inclined wake or offset wake is studied at the rated wind speed for the downstream wind turbine.Thrust,torque and the effects of axial and tangential forces on the blade.It is found that the amplitude of the downstream wi nd turbine load increases significantly after the wake of the upstream wind turbine is changed.By analyzing the axial force and rotational tangential force of the blades at 0.3R,0.6R and 0.9R under different yaw angles,it is found that the axial force a nd tangential force increase with the increase of the yaw angle of the upstream wind turbine.Large,after increasing to a certain value,it remains constant,the azimuth interval corresponding to the maximum value increases,and the azimuth interval corresponding to the minimum value decreases.And in the azimuth interval corresponding to the minimum value,there is a phenomenon that the axial force and the rotational tangential force abruptly become large;when analyzing the height difference of different hubs,the blades are received at positions of 0°,60°,120° and 180°.The axial force and the tangential force are found to decrease with the influence of the wake of the upstream wind turbine as the height difference of the hub increases.When the blades are in the wake and non-wake regions,the axial and tangential forces vary greatly.In the third part,under the condition of complex inflow,the atmospheric buoyancy,Coriolis force and surface heat flux are first considered,and the atmospheric boundary layer of 3000*3000*1000 m3 is simulated.Below the inversion temperature layer,the bit temperature does not change in the height direction,and the average wind speed exhibits shear characteristics in the vertical direction;the wind speed and wind direction at each point in the atmospheric boundary layer exhibit a pulsating orientation.The pulsating wind speed satisfies the turbulence spectrum characteristics,and satisfies the-5/3 energy diminishing law in the inertia sub-region.Secondly,two wind turbines with a distance of 6D are arranged in the atmospheric boundary layer,and the wind turbines in the wind field are found to change with time.The power,thrust and torque are randomly changed,but the overall trend satisfies the sinusoidal distribution,and the average wind power,thrust and torque of the downstream wind turbine are smaller than that of the upstream wind turbine,but the variation amplitude is greater than that of the upstream wind turbine.The spectrum analysis of the aerodynamic loads of the upstream and downstream wind turbines is carried out.When the energy of the aerodynamic loads of the wind turbines is concentrated,the corresponding frequencies are related to the blades.Finally,8 wind turbines are arranged in the wind farm,and the flow fields of the wind farms and The aerodynamic characteristics of the wind turbine were studied.Before the rated wind speed,as the wind speed increases,the power loss of the wind farm is also increasing.The power,thrust and torque of each wind turbine change in the form of sine waves,and the amplitude of the power of the rear wind turbine is significantly higher than that of the first row of wind turbines.From the second row,the amplitude of the wind turbine has a tendency to decrease.The research content,methods and results involved in this topic have a reference role in the micro-site selection of wind farms.