Winglet design for wind turbines using a free-wake vortex analysis method

A winglet was designed for a small-scale, stall regulated wind turbine using a free-wake vortex analysis method. The baseline planar blade (without winglet) was designed by a research group at the University of Waterloo for the purposes of testing the performance gains possible from a winglet. The winglet toe and twist angles were found by exploring a range of possible combinations. The PSU94-097 sailplane winglet airfoil was used as the wind turbine winglet airfoil. The effect of profile drag was only modeled on the winglet and stall was not modeled in the free-wake vortex method, limiting the analysis to only be valid for the range of wind speeds below the wind speed for rated power. The winglet was built as a modification to a small wind turbine, and tested in the small wind turbine testing facility at the University of Waterloo. The experimental test results showed a peak gain of 9.1% in power at a tip-speed ratio of 4.7, falling to a gain of 4% for a broad range of tip-speed ratios. The free-wake vortex model matched the peak performance gain of the experimental results, but predicted a broader range of operating speeds where the winglet showed the higher level of increased power, rather than the small peak region of the experimental results.