Downwind wind turbine yaw stability and performance

Abstract

In this experimental work, the yaw stability and performance of three different downwind rotors are measured and compared to those of the corresponding upwind rotors. A modular scale-model wind turbine that allows for either upwind or downwind operation, with a range of rotor cone and yaw angles, is used. The measurements, at near full-scale Reynolds numbers, show all downwind rotor configurations have yaw stability. On the otherhand, upwind turbines are shown to be either unstable or to have significantly reduced yaw stability compared to the corresponding downwind rotor configurations. Downwind configurations with zero, 5° and 10° cone have higher shaft power and rotor thrust than the corresponding upwind configurations. For zero yaw, the 5° and 10° cone angle, the downwind configurations each yield 5% more power, and have only 3% higher thrust, than the upwind configurations, indicating a potential benefit in performance compared to upwind configurations. Overall, it is concluded that coned downwind configurations provide for easier yaw control and yield more power.