Wind turbine acoustics - Wind Power Generation and Wind Turbine Design - page 181

even low sound pressure levels (below the admissible limits) can be experienced
as annoying. Björkman [34] carried out longtime measurements at several wind
turbine sites in southern Sweden. At the site located next to Lund low correla-
tion was observed by the wind speed and the registered noise levels which were
explained by the fact that the wind turbine noise was masked by other noise
sources.

8 Future perspective

Recently, van den Berg [15] showed that even if the noise limitation standards
were taken into account already in the design phase, the inhabitants living in the
surrounding of a new wind park were still annoyed by the emitted noise levels.
The two main reasons for the annoyance were found to be the inaccurate predic-
tion of the equivalent noise levels and the impulsive character of the sound. Thus
there is a need for improved models. First, there is need of improving the Category
III models to achieve detailed knowledge about the generated sound fi eld already
in the design phase. The infl uence of atmospheric stability and turbulence level,
landscape shape, type of vegetation or the presence of sea waves have to be evalu-
ated. Also, the impacts of the interaction of wind turbine wakes in wind turbine
farms are not well understood. Another important issue related to wind turbines
operating in cold areas is the ice accretion on the wind turbine blades. Since the
deposition of the ice affects the blade cross section it affects also the character of
the emitted noise. Thus acoustic measurements might be used to detect ice deposi-
tion. Recently, Fuchs and Szasz used a coupled Lagrangian

Eulerian approach to
model ice accretion [36]. From a legislative point of view there is a need for more
accurate and fl exible, but at the same time not too complicated models. Such mod-
els will lead to noise regulations which will increase the power production of the
wind turbines without impairing the well-being of the nearby residents.

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References

[1] van den Berg, G.P., The beat is getting stronger: the effect of atmospheric
stability on low frequency modulated sound of wind turbines. Journal of Low
Frequency Noise, Vibration and Active Control , 24(1) , pp. 1

− 24, 2005.

[2] Pedersen, E. & Persson Waye, K., Wind turbines low level noise sources

interfering with restoration? Environmental Research Letters , 3 , pp. 1

−

− 5,

2008.
[3] Andersson, J.D., Modern Compressible Flow with Historical Perspective ,
McGraw-Hill, 1990.
[4] Wagner, S., Bareiss, R. & Guidati, G., Wind Turbine Noise , Springer, 1996.
[5] Pinder, J.N., Mechanical noise from wind turbines. Wind Engineering , 16(3) ,
pp. 158 167, 1992.

[6] Pedersen, E., Noise annoyance from wind turbines

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− a review. Naturvårdsverket ,

Report 5308, 2003.