Environmental Engineering Reference
In-Depth Information
Flow slope
Terrain slope
Figure 21: Example of speed-up and infl ow angle across a mountain.
design standard IEC [25] assumes a maximum level of total turbulence of 18% for
a wind turbine designed for high turbulence.
5.3 Flow inclination
A layout should aim for a high energy yield. Since the fl ow is accelerated across
hills one idea could be to place the wind turbines at the point with the highest
acceleration which is typically at the location of greatest curvature of the slope of
the terrain. The unwanted side effect of such a location is that the fl ow might not
be horizontal as it follows the shape of the mountain, thus the infl ow angle is not
zero. The askew wind vector leads to lower production as the angular response of
the wind turbine can be simplifi ed as a cosine and thus the horizontal component
of the wind mainly contributes to the energy generation.
Additionally the wind turbine will be subject to higher loads when being exposed
to large infl ow angles. The fatigue loads on the blades will increase since the angle
of attack changes during one rotation. Furthermore, the bending loads of the rotat-
ing parts of the drive train are increased, and fi nally the yaw drive will be subject
to extra loads due to the uneven loading of the rotor. Thus a good layout avoids
these locations. Figure 21 shows an example where the turbine position has been
moved back from the edge of the cliff to a position with a much lower infl ow angle
(and slightly lower wind speed).
Information about the fl ow inclination can be obtained using ultrasonic or pro-
peller anemometers with the restrictions described earlier. However, the obtained
data only refl ects a single location. Only fl ow models are capable to evaluate the
fl ow inclination for each wind turbine location.
Care has to be taken, though when moving too far back from cliff edges, as this
area is prone to separation leading not only to increased turbulence but in the worst
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