Geoscience Reference
In-Depth Information
Chapter 6
Physics of Wind Parks
Wind parks need special treatment, because here the flow conditions approaching
most of the turbines in the park interior are no longer undisturbed. Wakes pro-
duced by upwind turbines can massively influence downwind turbines. This
includes reduced wind speeds and enhanced levels of turbulence which will lead to
reduced yields and enhanced loads. For a given land or sea area, it is desirable to
place the wind turbines as close together as possible to maximize energy pro-
duction. However, if wind turbines are too closely spaced, wake interference
effects could result in a considerable reduction in the efficiency of the wind park's
energy production. Some wind parks with tightly spaced turbines have produced
substantially less energy than expected based on wind resource assessments. In
some densely packed parks where turbines have failed prematurely, it has been
suspected that these failures might have been caused by excessive turbulence
associated with wake effects (Elliot
1991
).
A special spatial arrangement of the turbines in smaller wind parks with regard
to the mean wind direction may help to minimize wake-turbine interactions. But
for larger wind parks, wake-turbine interactions are unavoidable in the park
interior and the ratio between mean turbine distance and rotor diameter becomes
the main parameter that governs the park efficiency. Before we consider such large
wind parks in
Sect. 6.2
, we will shortly describe the characteristics of single
turbine wakes.
6.1 Turbine Wakes
We distinguish between near wake and far wake when looking at turbine wakes.
The near wake is taken as the area just behind the rotor, where the special prop-
erties of the rotor itself can still be discriminated, so approximately up to a few
rotor diameters downstream. We find features such as 3D vortices and tip vortices
from single blades in the near wake. The presence of the rotor is apparent by the
Search WWH ::
Custom Search