Development and testing of tip devices for horizontal axis wind turbines

Abstract

A theoretical and field experimental program has been carried out to investigate the use of tip devices on horizontal axis wind turbine rotors. Objective was to improve performance by the reduction of tip losses. A vortex lattice computer model was used to optimize three basic tip configuration types for a 25 kW stall limited commercial wind turbines. The types were a change in tip planform, and a single-element and double-element nonplannar tip extension (winglets). Approximately 270 h of performance data were collected over a three-month period. The sampling interval was 2.4 s; thus over 400,000 raw data points were logged. Results for each of the three new tip devices, compared with the original tip, showed a small decrease (of the order of 1 kW) in power output over the measured range of wind speeds from cut-in at about 4 m/s to over 20 m/s, well into the stall limiting region. For aircraft wing tip devices, favorable tip shapes have been reported and it is likely that the tip devices tested in this program did not improve rotor performance because they were not optimally adjusted. The computer model used does not have adequate lifting surface resolution or accuracy to design thesemore » small winglet extensions. « less

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