An Evaluation Testbed for Wind Turbine Blade Tip Designs — Winglet Results

Abstract

A 3.3 m diameter variable speed wind turbine and rotor has been designed, fabricated and tested with exchangeable blade tip capability. This rotor was custom designed utilizing the National Renewable Energy Laboratory's S83X series airfoils for the University of Waterloo Wind Energy research facility with blades that allow the outer 10% of the blade to be exchanged.

Turbine power production measurements were completed in the controlled wind facility covering a range of mean wind speeds, 3.6 m/s to 11 m/s, and turbine rotor shaft rotational rates, 100 rpm to 240 rpm. Power produced by the blades was determined as a function of input wind speed. The coefficient of power, C_P, was determined as a function of the tip speed ratio λ and peak C_P was found to approach 0.42 at the design λ of 6.7. At the design shaft speed of 200 rpm, the maximum power produced was 1.45 kW at 11 m/s.

Prior winglet designs are discussed and two winglet designs are evaluated. The effects of two different winglets, the Maniaci and Gertz designs, were evaluated with surface oil flow visualization and quantified by repeating the test that was executed with the standard tip for each winglet. Both winglets were found to have a bell-shaped power augmentation profile, with a broad peak between 6.5 m/s and 9.5 m/s where power was increased by 5% to 7%. These power augmentation figures matched closely with the findings in the literature that suggested increases of 2% to 8% are possible. It is noted, however, that these designs are certainly not optimal and it is possible that an optimized winglet design through further modeling and testing could be attained.