Wind Turbine Acoustics - Wind Turbine Technology: Fundamental Concepts of Wind Turbine Engineering - page 459

The scale of the reduction in sound power that can be achieved by altering the shape
of a rotor blade is indicated by the diamond symbols in Figure 7-43. The open diamonds
show the sound power of the rotor with blades of the original design that was found to be
quite noisy in higher winds. The closed diamonds indicate the much lower sound power
coming from the redesigned blades on the same wind turbine. At wind speeds from 10 to
15 m/s, sound power was reduced 12 to 15 dB by the blade design change.
Sound Sources on Wind Turbines
Acoustic tests have been conducted on an operating intermediate-scale wind turbine
to determine the specific locations from which sound power is emitted. Oerlemans et al.
[2005] conducted a detailed series of noise measurements on a pitch-controlled, three-
bladed GAMESA G58 wind turbine, which has a rotor diameter of 58 m, a tower height of
53.5 m, and a rated power of 850 kW. Using an elliptical array of 152 microphones
mounted on a wooden platform on the ground, these researchers were able to obtain a profile
of the noise sources on the operating turbine.
Figure 7-44. Noise sources measured on a Gamesa G58 850 kW wind turbine by
means of a microphone array on the platform in the foreground. The downward-moving
blades emit the majority of the noise, as indicated by the sound power contours whose range is
12 dB. [Oerlemnes 2005]