Abstract
Winglets have been employed in the aviation industry to reduce vortices generated at aircraft wings, decreasing drag, and hence increasing fuel economy. For rotating applications previous experimental and numerical studies addressed the application for wind turbines and suggested winglets facing backwards on the suction side of a blade could increase the power capture. This paper presents experimental work using a scale 3-bladed horizontal axis tidal turbine. An oil-based paint flow visualisation coupled to blade thrust and torque measurements helped to identify the mechanism behind the phenomenon affecting the performance of winglets facing the suction side of a turbine blade. The results show that on average a winglet facing downstream decreases the power coefficient 1–2% and increases the thrust coefficient up to 6% for tip speed ratios 5.0–7.0. On the other hand, a symmetrically mirrored winglet facing upstream increased the power coefficient by 1–2%, and the thrust coefficient by 3–4%. Further, increased bending moments at the root of the blade were estimated to be in the range 4.5–6.0%. Winglets have the potential to provide a meaningful increase to power capture at minimal additional capital cost without increasing rotor diameters. Further work to optimize pressure‐side winglets should be conducted.