Wind Turbine Trailing Edge Noise

Posted in the Fairhaven Forum

Jack Kelly

Jamestown, RI

#1 Jun 21, 2013
Wind Turbine Trailing Edge Noise Page 7

http://prod.sandia.gov/techlib/access-control...

Recent work in Europe has shed more light on the aeroacoustic noise mechanisms for utilityscale
wind turbines. Detailed blade noise measurements were made for an 850 kW Gamesa G58
turbine [8] and for a 2.3 MW GE prototype turbine [10]. Both of these turbines are three-bladed
upwind machines that can be considered representative of the current fleet of wind turbines in terms
of aerodynamic and aeracoustic characteristics. The measurements were made with a microphone
array that was able to resolve the amplitude and location of noise sources in the rotor plane and
along the blade span. Important observations were made on the character of the blade noise, some
of which shed light on the nature of the noise sources:
• Blade noise sources were much louder than mechanical noise sources located within the
nacelle for both turbines.
• Blade noise sources were loudest near, but not at, the blade tips, indicating that tip vortex
noise is not the dominant blade noise mechanism.
• The measured noise for an upwind observer on the ground varies with blade azimuth, and
was 15 dB louder for a downward traveling blade (approximately the 3 o’clock position)
than for an upward traveling blade (approximately the 9 o’clock position). This variation is
consistent with predictions given by aeroacoustic theory for trailing edge noise. The noise
directed towards the ground is louder during downward blade passage due to the combined
effects of Doppler amplification and the directivity of the noise source.
• The blade noise intensity scales with the fifth power of the flow velocity relative to the blade
at the source location. This matches the scaling that has been observed in trailing edge noise
experiments and predicted by theory.

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