Abstract:
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A linear microphone array is shown to be a simple tool to locate aerodynamic sound sources on a horizontal axis wind
turbine. This paper discusses the capabilities and limitations of a linear microphone array to locate sound sources and
measure aerodynamic noise on the blades of a horizontal axis wind turbine rotor. Compared with a planar microphone
array, a linear array requires fewer microphones to achieve the same resolution, a simpler structure to support it and a
simpler signal processing algorithm. For a linear array, areas exist in the rotor plane where the sources cannot be located
unambiguously. For certain applications, it is not necessary to map the whole rotor plane. This paper also shows the result
of an experimental test aimed at locating and measuring aerodynamic sound sources on the three blades of a wind turbine.
Each blade received a different surface treatment, with the goal of comparing their relative sound emission levels. The
test was carried out with a 10.32 m linear microphone array, placed horizontally near the ground, extending parallel to the
rotor plane. The results show that for all three blades, most of the noise is generated in the outer 25% of the blade span,
with a maximum occurring just after the blade has passed the horizontal position going downwards. Results also show that
tripped blade is the noisiest of the three, whereas the smoothest, polished blade is clearly the quietest. Copyright © 2012
John Wiley & Sons, Ltd. |