Research On The Influence Of Wind Turbine Operation Conditions On The Wake Effects

With the large-scale development and utilization of wind energy resources,wind power turbines are developing towards the large-scale development of high tower and long blade,and wind farm wake effect is increasingly prominent.The wake of one wind turbine affects the power generation and life of others in the wake area.Due to the complex and variable wind conditions,the wake area vary with the dynamic operation of the corresponding turbine at all time.Research on the variation law of wind farm wake under different operation conditions is not only of great significance to the actual problems of wind turbine output,fatigue load analysis,wind measurement near nacelle,but also can provide theoretical support for the field optimization scheduling of large wind farms based on wake.In this paper,the 1.5MW large-scale pitch wind turbine operating in the wind farm actually is taken as the research object,and a full-scale structured grid numerical model is established.Based on the Reynolds-averaged method,the wake numerical simulation is carried out under multiple operation conditions.Then turbine operation is divided to constant tip speed ratio control,constant rotate-speed control and constant power control.The velocity and pressure distribution in the blade surface are analyzed under the three phases.The law of flow field varying around the nacelle and the velocity distribution in the wake area are obtained.The main work of the paper is introduced below:(1)Establish the numerical model of 1.5MW large-scale wind turbine structure grid,and numerical simulation in the wake area under various operation conditions.The multi-block structured grid topology is applied to mesh the calculational domain of the large-scale wind turbine full-scale model.Under the three phases of optimal tip speed ratio,constant speed control and constant power control,7 examples of steady numerical simulation and 4 examples of unsteady numerical simulation are designed to calculate results in wake area according to actual operation conditions.And the thrust coefficient of steady simulation is compared with the results of Bladed,providing reference for the subsequent wake field analysis.(2)The law of wake varying under three phases in various operation conditions is revealed.The pressure and velocity distribution in turbine surface,the velocity distribution in wake area and the velocity distribution around nacelle are analyzed.The following conclusions are drawn:1)In the phase of constant tip speed ratio control,the velocity distribution is similar to pressure distribution in the blade surface.The normalized velocity is same at the same position of the wake area under the different wind speed.2)In the constant rotate-speed control phase,as the angle of attack increases,the pressure surface stagnation moves backward,the low pressure zone decreases,and the airfoil leading edge high pressure zone and the suction surface low pressure zone increase,resulting in the normalization speed around wake area inconsistent.3)In the constant power control phase,as the angle of attack decreases,the stagnation point of the pressure surface moves forward,and the separation point of the suction surface moves backward.The absolute speed and normalization speed of the flow field after the wind wheel increase simultaneously.(3)The velocity distribution near nacelle under different operation conditions is obtained.The fluctuation of speed on the upper surface of the engine room is periodic,but the fluctuation of wind velocity at different positions in horizontal direction,flow direction and vertical direction has obvious phase and amplitude difference.The wind speed fluctuation period near the nacelle varies due to the change of wind wheel speed,and the fluctuation amplitude rises due to the increased inflow wind speed.The change of pitch angle has little influence on the wind speed of nacelle,and the wind speed fluctuation law is similar to the stage of constant rotation rate.