Abstract
It is shown, in a novel experimental study using a sub-scale model of a 5MW downwind turbine, that individual pitch control based on a sinusoidal pitching scheme that is locked to the phase of the rotor rotation further improves the yaw stability of a downwind turbine. The optimum pitching amplitude is observed to be insensitive to yaw angle. Furthermore, a positive pitching amplitude improves yaw stability at negative yaw angles, while at positive yaw angles, negative pitching amplitude improves yaw stability. Thus, individual pitch control further improves the superior yaw characteristics of downwind turbines compared to upwind configurations.
Highlights
As the size of wind turbines becomes increasingly larger, downwind turbines, which have less constraints than upwind turbines as regards tower to blade tip clearance [1,2], allow for lighter and more slender rotor blade designs
In a novel experimental study using a sub-scale model of a 5MW downwind turbine, that individual pitch control based on a sinusoidal pitching scheme that is locked to the phase of the rotor rotation further improves the yaw stability of a downwind turbine
Individual pitch control further improves the superior yaw characteristics of downwind turbines compared to upwind configurations
Summary
As the size of wind turbines becomes increasingly larger, downwind turbines, which have less constraints than upwind turbines as regards tower to blade tip clearance [1,2], allow for lighter and more slender rotor blade designs. Rotor tilt and blade cone can reduce the impact of the tower wake and allow for an increased blade length because of higher allowable deflection [3]. Rotor tilt causes a periodic variation in the velocity seen by each blade [4] since each blade section translates into/out of the wind during a revolution of the rotor. Rotor tilt causes a component of the turbine torque to be transmitted into the tower since the tower is no longer perpendicular to the drive train. Transmission of a torque component into the tower can reduce yaw stability [5,6,7], promoting further divergence of the rotor away from the zero yaw position; rotor tilt is absent in “free-yawing” wind turbine designs [8]. Notwithstanding the above, downwind rotors have improved yaw stability compared to upwind rotors [9, 10]
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