The Effect of Tail Fin Size on the Yaw Performance of Small Wind Turbines Operating in Unsteady Flow

Abstract

This paper presents measurements and predictions of the yaw performance of a small 5 kW horizontal-axis wind turbine operating in unsteady flow fitted with a delta wing tail fin of two different sizes. Measurements show the smaller of the two tail fins causes the turbine to operate at a higher mean yaw error than the larger tail fin and to respond at a higher yaw rate than the larger tail fin, over most of the operating wind speed range for the turbine. Unsteady slender body theory was used to predict the dynamic performance of the tail fin. The dominant steady lift term in this theory assumes lift is linear with flow angle of attack, α, a valid assumption for α < 40°. Experimentally determined coefficient of lift and drag data and an analytical non-linear relationship for the coefficient of lift and drag as a function of α for the delta wing were also used in steady lift term. The relative motion of the yawing tail fin and the effects of the reduced wake velocity on the tail fin performance were also considered. Unsteady slender body theory incorporating experimentally determined data, with the inclusion of relative motion and reduced wake velocity gave the highest correlation with experimental results.