2011 International Conference on Alternative Energy in Developing Countries and Emerging Economies
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Fig. 20. Operating turbine: effects of roughness on NTF for escarpments
of (a) 11% and (b) 20%.
Fig. 21. Effects of hub height on nacelle transfer function of the J48 for
(a) non-operating turbine and (b) operating turbine.
VI. C
ONCLUSIONS
The effects of escarpment and terrain roughness on
nacelle anemometry were evaluated by simulating 3D
turbulent flow through a Nordex wind turbine in a neutral
atmospheric boundary layer. The rotor was modeled by
the actuator-disk concept, and the nacelle was entirely
represented in the mesh. The flat terrain and two
escarpment slopes (11% and 20%) were considered.
Analysis of the roughness effect was carried out by
considering two roughness heights (2.5cm and 5cm).
Numerical site calibrations on the various escarpments
(simulations with no turbine) were also necessary in order
to construct the nacelle transfer function.
The increase in the slope of the ground was
accompanied by two phenomena that significantly
influenced flow at the nacelle anemometer location. The
speed-up was positive only when the turbine was placed
far from the beginning of the escarpment. The second
phenomenon was the vertical flow angle, which increased
significantly with terrain slope. The complexity of the
nacelle's near wake was accentuated by this inclination of
the flow, and resulted in a slowdown of flow at the
anemometer's location due to the movement of the top
vortex towards that location. This tendency remained
significant up to the 11% slope. Beyond this value, the
top vortex no longer moved, and its associated slowdown
weakened.
More markedly rugged ground on an escarpment
tended to increase the speed at the nacelle anemometer,
along with a slight decrease in the vertical angle of the
flow. This effect was significantly reduced, however,
when the rotor was in operation.
Lastly, hub-height effect was evaluated for the
Jeumont turbine by raising the nacelle from 0.75
D
to
1.25
D
. No significant impact was noted on the NTF.
A
CKNOWLEDGMENT
We would like to thank Peter Eecen, of the Energy
research Centre of the Netherlands, for providing us with
experimental results.
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