This paper explores the source mechanism which cause amplitude modulation of the emitted sound of a wind turbine at large distances from the turbine, named as other amplitude modulation. Measurements of the fluctuating surface pressure on a 2.3MW wind turbine showed a considerable variation over a blade revolution in the presence of angle of attack variations. If the blade undergoes transient stall, the variation of the surface pressure spectrum was enhanced and shifted to frequencies below 200Hz. The surface pressure spectra could be directly related to the emitted far eld sound. These ndings give further evidence that transient stall is a main mechanism to cause other amplitude modulation. Wind shear was identified as a critical condition to cause angle of attack variations. Dierent control strategies to mitigate other amplitude modulation were proposed.
Proceedings of Ewea 2014, 2014
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European Wind Energy Conference & Exhibition 2014