Question:
Are wind turbines noisy?
...Wind Turbines whisper quietly, now...
Large, modern wind
turbines have become very quiet. At distances above 200 metres,
the swishing sound of rotor blades is usually masked completely
by wind noise in the leaves of trees or shrubs.
There are two potential
sources of noise from a wind turbine: Mechanical noise from
the gearbox or generator , and aerodynamic noise from the rotor
blades.
Mechanical noise
has virtually disappeared from modern wind turbines. This is
due to better engineering with more concern about avoiding vibrations.
Other technical improvements include elastically dampened fastenings
and couplings of the major components in the nacelle, and to
a certain extent sound insulation. Finally, the basic components
themselves, including gearboxes , have developed considerably
over the years. Modern wind turbine gearboxes use "soft" gearwheels,
i.e. toothed wheels with hardened surfaces and relatively elastic
interiors.
Aerodynamic noise
i.e. the "swish" sound of the rotor blades passing the tower
of a wind turbine primarily arises at the tip and the back edge
of the rotor blade. The higher the rotational speed, the louder
the sound. Aerodynamic noise has been cut dramatically during
the past ten years due to better design of rotor blades (particularly
blade tips and back edges).
Pure tones can
be very annoying to a listener, while "white noise" is hardly
noticed at all. Rotor blade manufacturers take extreme care
to ensure a smooth surface which is important to avoid pure
tones. Likewise, manufacturers who install wind turbines take
great care to ensure that the rotor blades are not damaged when
a wind turbine is being installed.
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