for Low Mechanical Noise from Wind Turbines
Sound emissions from wind turbines may have two different origins:
Mechanical noise which we deal with on this page, and aerodynamic
noise which we deal with on the next page.
Sources of Sound Emission
Mechanical noise, i.e. metal components moving or knocking against
each other may originate in the gearbox, in the drive train (the
shafts), and in the generator of a wind turbine.
Machines from the early 1980s or before do
emit some mechanical noise, which may be heard in the immediate
surroundings of the turbine, in the worst cases even up to a
distance of 200 m (600 ft.)
A survey on research and development priorities
of Danish wind turbine manufacturers conducted in 1995, however,
showed that no manufacturer considered mechanical noise as a
problem any longer, and therefore no further research in the
area was considered necessary. The reason was, that within three
years noise emissions had dropped to half their previous level
due to better engineering practices.
Wind Turbine Gearboxes
Gearboxes for wind turbines are no longer standard industrial
gearboxes, but they have been adapted specifically for quiet
operation of wind turbines. One way of doing this is to ensure
that the steel wheels of the gearbox have a semi-soft, flexible
core, but a hard surface to ensure strength and long time wear.
The way this is done is basically to heat
the gear wheels after their teeth have been ground, and then
let them cool off slowly while they are packed in a special high
carbon-content powder. The carbon will then migrate into the
surface of the metal. This ensures a high carbon content and
high durability in the surface of the metal, while the steel
alloy in the interior remains softer and more flexible.
When going by car, plane, or train, you may have experienced
how resonance of different components, e.g. in the dashboard
of a car or a window of a train may amplify noise.
An important consideration, which enters
into the turbine design process today, is the fact that the rotor
blades may act as membranes that may retransmit noise
vibrations from the nacelle and tower.
As explained in the tour section on Research
and Development, the turbine manufacturers nowadays make
computer models of their machines before building them, to ensure
that the vibrations of different components do not interact to
If you look at the chassis frame of the nacelle
on some of the large wind turbines on the market today, you may
discover some odd holes which were drilled into the chassis frame
for no apparent reason. These holes were precisely made to ensure
that the frame will not vibrate in step with the other components
in the turbine.
Sound insulation plays a minor role in most wind modern turbines
on the market today, although it can be useful to minimise some
medium- and high-frequency noise. In general, however, it seems
to be more efficient to attack noise problems at the source,
in the structure of the machine itself.