Wind Energy

7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
3 Time Domain Comparison Using Constrained Wind Fields 19
flap
11 12 17
0
1
2
3
4
7
11
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
flap - hub
11 14 19
Fig. 3.4. COV of the blade equivalent flap moment range (left; generic turbine)
and the flap moment range at the hub (right; NM80/2750). Mean wind speeds are
indicated at bottom; legend indicates number of anemometers/constraints
Measured power [kW]
3000
2500
2000
measured
calculated
3000
1500
300 350 400 450 500 550
2000
600
Time [s]
Calculated power [kW]
Measured pitch angle [deg]
20
measured
15
10
5
calculated
0
5
100 150 200 250 300 350 400
Time [s]
Fig. 3.5. Comparison between measurement and calculations (constrained wind
in 1 point: rotor centre). Left: electrical power at 14.7 ms −1 ; right: pitch angle at
19.5 ms −1
In Fig. 3.4 (left) no clear trend can be observed; the reduction of the COV
by constrained simulation is limited. Noticeable improvement is obtained however
for the hub flap bending moment (right).
3.5 Comparison between Measured Loads
and Calculated Ones Based on Constrained Wind Fields
Whether it is useful to use constrained wind in load verification can only be
determined from a practical test. To this end we use the NEG Micon NM80
turbine in Tjæreborg (flat, open coastal terrain). The met-mast is located
200 m upwind of the turbine and has anemometers at 25, 41 and 60 m. Because
the wind must come from a direction where the rotor sees the wind measured
by the anemometer, only few measuring records could be used.
Two characteristic pictures are given in Fig. 3.5. It is clear that in both
cases the low frequency behaviour is well captured (once the time delay from
anemometer tower to wind turbine rotor has been incorporated, applying
Taylor’s frozen turbulence hypothesis), but that it is difficult to reproduce
25
20
15
10
0
1
2
3
4
7
Calculated pitch angle [deg]