INFLUENCE OF WIND SHEAR ON AERODYNAMIC CHARACTERISTICS AND WAKE SHAPE OF WIND TURBINE BLADES

A wind turbine usually operates in unsteady conditions, and the aerodynamic performance and wake of the rotor will change with the change of working conditions. Wind shear is the most common and long-term environment of wind turbine. It often affects the aerodynamic load, the shape of the wake and the overall performance of the wind turbine. So it is important to analyze the aerodynamic performance of blade of the wind turbine under the wind shear condition. In this paper, a time-marching free vortex wake method, which coupled with the wind shear model, is used to calculate the aerodynamic coefficient, thrust and wake shape change under different wind shear factors. At the same time, the influence of the wake shape variation on the induced velocity of the rotor rotating plane and the aerodynamic performance of the wind turbine blade are studied. The results show that: under the condition of wind shear inflow, with the increase of the wind shear factor, the fluctuation amplitude of aerodynamic coefficient of the wind turbine, which fluctuates periodically with time is increased, the average thrust decreases gradually, the tilted degree of wake increases and the tilted degree of wake under the center of hub is more obvious. The distortion of wake shape makes the distribution of the axial induced velocity factor in the rotational plane uneven, and makes the overall performance of wind turbine decrease and deviate greatly. There is a distinct difference of the induced effect on the rotational plane between the tilted wake and the symmetrical wake. The fluctuation amplitude of the aerodynamic coefficient induced by the tilted wake is larger than that induced by the symmetrical wake, and the deviation of the wave trough is more obvious than the wave crest. The more tilted the wake is, the more obvious the load asymmetry in the rotating plane is.