ECN publication
Insects cause double stall
Corten, G.P.; Veldkamp, H.F.
Published by: Publication date:
ECN Wind Energy 1-9-2001
ECN report number: Document type:
ECN-RX--01-052 Conference Paper
Number of pages: Full text:
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Presented at: European Wind Energy Conference and Exhibition, Copenhagen, Denmark, 2-6 juli 2001.

Several large commercial wind turbines demonstrate drops in maximum power levels up to 45%, under apparently equal conditions. Earlier studies attempting to explain this effect by technical malfunctioning, aerodynamic instabilities and blade contamination effects estimated with computational fluid dynamics, have not yet yielded a plausible explanation.A number of hypotheses was formulated, three of which were useful. By performing stall flag measurements, as well as two other experiments, one of the three hypotheses was confirmed: the Insect Hypothesis. Insects only fly in low wind, impacting near the leading edge of the blade. In low wind conditions, the 'insect roughness' has little influence on profile performance and power is not affected. In high winds, however, the flow pattern around the blade has changed, and contamination on the leading edge now has a market affect, resulting in power drop. In conclusion: the level of contamination changes only in low wind when insects fly and influences the power level in high winds when insects do not fly. As a consequence the power curve displays distinct levels as high wind speeds.

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