Study On The Effect Of Trailing Edge Flaps On The Aerodynamic Performance And Wake Characteristics Of Large Wind Turbine

In the process of continuous development of wind turbines,in order to obtain more wind energy to a greater extent,the single-machine power and blade size of wind turbines are increasing.The large-scale wind turbines aggravate the ultimate load and fatigue load of wind turbines.The trailing edge flap can reduce the fatigue load of wind turbines.However,large-scale wind turbines operate at the bottom of the atmospheric boundary layer,which is affected by the wind shear effect and will change the aerodynamic performance and wake of wind turbines.In this paper,based on the NREL5 MW reference wind turbine,a wind turbine model with trailing edge flap deflection angles of 0°,±2°,±4°,±6°,±8°,and ±10° is established.The large wind turbine with trailing edge flap is simulated under uniform inflow and shear inflow.The influence of trailing edge flap on the aerodynamic performance and wake characteristics of wind turbine is studied.The main contents are as follows:(1)Under the rated wind speed,the steady-state numerical simulation of the wind turbine with the trailing edge flap angle of 0°,±2°,±4 °,± 6°,±8° and ±10° is carried out,and the wind turbine with the trailing edge flap deflecting to the pressure surface under the wind speed of 7m/s,11.4m/s and 15m/s is simulated.The results show that under the rated wind speed,the deflection of the trailing edge flap to the pressure surface increases the pressure difference and load on the blade surface,increases the output power,and the deflection of +6° is the largest,increasing by 6.6%.The deflection to the suction surface reduces the pressure difference and load on the blade surface,suppresses the power output,and is the lowest when the deflection is-10°,which is reduced by 12.7%.The deflection of the trailing edge flap causes a high-speed zone near the edge of the wake region,the wake v elocity deficit increases,the wake becomes more complex,the trailing edge flap deflects to the pressure surface,the angle increases,the velocity deficit increases,and the turbulent kinetic energy intensity increases;the trailing edge flap deflects to the suction surface,the angle increases,the velocity loss decreases,and the turbulent kinetic energy intensity decreases.When the wind speed is 15m/s,the deflection of the trailing edge flap to the pressure surface has little effect on the wake.(2)Under the shear flow,the unsteady numerical simulation of the wind turbine with the trailing edge flap angle of 0°,±2°,±4°,±6°,±8° and ±10° is carried out.The results show that the trailing edge flap deflects the positive angle,the deflection angle increases,the blade surface load and the surface pressure difference increase,the aerodynamic force of the wind turbine increases,and the output power increases.The maximum deflection +6°,the output power increase is 7.39%;when the deflection angle is negative,the deflection angle increases,the blade surface load and surface pressure difference decrease,the output power decreases,and the blade section load near the trailing edge flap section is affected.The trailing edge flap can increase the output power of the wind turbine under low wind speed shear flow.The larger the wind speed,the more significant the effect.Compared with the case without flaps,in the core area of the wake,the negative angle of the trailing edge flap deflection has a velocity deficit,and the turbulent kinetic energy intensity of the tip vortex is low.The trailing edge flap deflects at a positive angle.As the deflection angle increases,the turbulent kinetic energy intensity of the tip vortex and the central vortex incr eases.The deflection of the trailing edge flap to a positive angle has a greater impact on the downstream wake of the wind turbine.(3)The transient simulation of the wind turbine with trailing edge flap deflection+6° is carried out under the rated wind speed of 11.4m/s and the shear index of0.12,0.20,0.30 inflow.The results show that the change of shear index has a great influence on the pressure of suction surface of blade section.The spanwise distribution of blade load increases with the increase o f shear index at 0° azimuth,and decreases with the increase of shear index at 180° azimuth.As the shear index increases,the root mean square of the blade torque increases,the thrust decreases,the root mean square of the torque and thrust of the wind wheel decreases,and the relative variation amplitude increases.When the shear index changes from 0.12 to 0.30,the root mean square of the output power of the wind turbine decreases by 0.32%,and the relative variation increases by 20%.Under the wind she ar flow,the wake of the wind turbine is inclined spiral.The larger the shear index is,the more obvious the inclination is.In the area above the rotor shaft,the larger the shear index is,the larger the axial velocity is,the smaller the wake depth is,the smaller the velocity loss is,and the greater the turbulent kinetic energy intensity of the tip vortex is.In the area below the rotor shaft,the larger the shear index,the smaller the axial velocity,the greater the wake depth,and the greater the velocity loss.In this paper,the effects of trailing edge flap deflection on the aerodynamic performance and wake characteristics of large wind turbines under uniform flow and shear flow are studied.The influence mechanism of trailing edge flap deflection on the output characteristics of wind turbines is revealed.The influence of different angles of trailing edge flap deflection on the wake velocity distribution provides a reference for the application of trailing edge flap in large wind turbines.