2011 International Conference on Alternative Energy in Developing Countries and Emerging Economies
- 318 -
Fig. 7. Description of the flow at the anemometer position: profile of
axial velocity for (a) non-operating turbine and (b) operating turbine.
Fig. 8. Description of the flow at the anemometer position: vertical flow
angle for (a) non-operating turbine and (b) operating turbine.
Fig. 9 describes the complex nature of the flow near
the nacelle and particularly in its immediate wake.
Streamlines and iso-velocities are plotted for various
escarpment slopes for the non-operating turbine.
For all terrain slopes, reversed flow was observed at the
rear of the nacelle, along with the development of two
opposite vortices, typical of flow behind a bluff body.
Fig. 9. Distribution of axial velocity and streamlines in the vicinity of
the nacelle for non-operating turbine.
Although these two vortices were relatively weak over
the flat terrain (Fig. 9a) they became more noticeable
with increasing escarpment slope. Due to nacelle
geometry and vertical flow angle, each of these vortices
was completely asymmetric. For the lesser escarpment
slope, the anemometer was in an accelerated-flow region
which slowed down gradually as the angle of flow
increased along with terrain slope. Another acceleration
zone, located at the lowest rear portion of the nacelle,
grew steadily larger as the escarpment slope increased.
Consequently, both of the wake vortices moved and
intensified with increasing escarpment slope. For the
rotor in operation (Fig. 10), the same trend was observed
as for the non-operating rotor, but with slightly lower
flow velocities. The wake also contained the two
vortices, with the upper vortex disturbing flow at the
anemometer position to a greater degree than the lower
vortex; upward movement of the upper vortex, observed
