Publishers version - DTU Orbit

Normalized C r = C r
P Q 2
W (r)
b
1
0.8
0.6
0.4
0.2
0
Blade Span (%)
0 10 20 30 40 40 50 60 60 70 80 90 100
U = 11.4 m/s
U = 13 m/s
U = 15 m/s
0 6.3 12.6 18.9 25.2 31.5 37.8 44.1 50.4 56.7 63
Spanwise Position, r (m)
Figure137:Aerodynamictorque-basedbladeeffectiveweightingfunctionWb(r) fortheNREL
5-MW turbine model at the rated wind speed 11.4 m/s and two above-rated wind speeds.
10.4.1 The Relative Importance of the u, v, and w Components
When a turbine is operating in above-rated wind speeds, variations in the u component of
the wind have a much greater effect than variations in the v and w components, in terms of
their effect on generatorspeed and structural loads. To illustrate this point, linearized transfer
functions from wind speed to variables of interest were generated for the 5-MW model using
NREL’s FAST software (Jonkman and Buhl, 2005).For example, in Fig. 138, which showsthe
magnitude frequency responses of several transfer functions, the effect of the u component
is generally about ten times (20 dB) greater than that of the v and w components, when
looking at the frequencies where the turbine speed and loads are most affected. There are
some frequencies at which v and w have a greater effect than u on the vertical and horizontal
components of blade root bending. However, all wind inputs shown are uniform over the
rotor plane, and shear was not included. It is expected that the magnitude of the transfer
functions from vertical and horizontal shear in the u component of the wind to the vertical
and horizontal components of blade root bending would be much higher than the magnitude
of the transfer functions from the v and w components.
The u component likely has a greater effect than v and w in part because the turbine
blades move quickly in the direction of the v and w components. In above-rated wind speeds,
a turbine’s tip speed is typically around 70 m/s, so the outboard half of the blade (which is
most influential in powercapture and loads) is moving through the v and w wind components
at 35 to 70 m/s. The angle of attack seen by a blade section is more influenced by a small
changeinthe13m/sucomponentthanasmallchangein the35to70m/sv orw component
it sees.
10.5 Lidar Measurements
The performance of lidar measurements is investigated using the hub-mounted, circularly
scanning lidar scenario shown in Fig. 133. The lidar model is based on the ZephIR 300
continuous-wave lidar (Slinger and Harris, 2012), which has a sampling rate of 50 Hz. Measurement
performance is assessed as a function of the two scan parameters: scan radius r and
preview distance d.
In general, measurement quality is described using the coherence between the lidar measurement
and the blade effective wind speed. The coherence calculations require a frequency
DTU Wind Energy-E-Report-0029(EN) 201