1) The document describes several inflow turbulence models available in the TurbSim code developed by NREL, including models based on standard IEC conditions, smooth homogeneous terrain, specific wind farm sites, complex mountainous terrain, and a North American high plains site. 2) Comparisons of simulation results using the IEC, Great Plains, and NWTC models show differences in predicted blade loads, rotor torque, bending moments and tip deflections when applied to the NREL 5 MW reference turbine. 3) In particular, the Great Plains model including a low-level jet produced significantly higher loads and deflections compared to the standard IEC model, demonstrating the importance of using site-specific models.

1. NREL is a national laboratory of the U.S. Department of Energy Office of Energy Efficiency and Renewable Energy operated by Midwest Research Institute • Battelle
National Wind
Technology Center
Neil Kelley
September 22-24, 2008
TurbSim Workshop: Site-Specific Models

2. National Renewable Energy Laboratory Innovation for Our Energy Future
TurbSim Models
• The TurbSim Code provides the designer with a
choice of five inflow turbulence environments
– The IEC NTM (Eds 2 & 3)
– Smooth, homogenous terrain
– Wind Farm
• Upwind of Row 1
• Upwind of Row 37 with 7D Row-to-Row Turbine Spacing
• Downwind of Row 41 with 14D Row-to-Row Turbine Spacing
– The NWTC (downwind of very complex mountainous terrain)
– A North American High Plains Site
• With the exception of the IEC and the Smooth
Models, the simulations are based on direct
measurements from each site.

3. National Renewable Energy Laboratory Innovation for Our Energy Future
IEC NTM
• TurbSim implements the IEC Kaimal NTM.
• It provides many options including the current (Ed.3) and earlier
versions (Ed.2) of the standard.
• This model runs very fast and provides a reasonable facsimile of
a turbulent inflow that may be encountered in neutral flow
conditions
• The approach assumes that the elevated turbulence levels will
induce the same amount of response and fatigue damage as
more site-specific models
• Many of the flow subtleties present in much more complex flows
and which may have some significance for specific turbine
designs are ignored.

4. National Renewable Energy Laboratory Innovation for Our Energy Future
Smooth Model
• The Smooth Model implements the diabatic spectral models
developed by Højstrup, Olesen, and Larsen
• They are based on the reference Kansas Experiment dataset
but with improvements from Kaimal’s original model the neutral
version of which forms the basis of the IEC Kaimal NTM.
• The Kansas Experiment was performed in very flat and
homogeneous terrain to exclude the effects of topography as
much as possible.
• This model extends many features of the IEC NTM since it can
simulate non-neutral flows but with more realistic scaling. It is
useful for matching observed data when available.

5. National Renewable Energy Laboratory Innovation for Our Energy Future
Wind Farm Models
• The TurbSim Wind Farm models are a legacy
development based on a limited set of measurements
upwind, within, and downwind of a 41-row wind farm
in San Gorgonio Pass California.
• Data was collected for a six week period at the height
of the 1989 wind season (July-August) from two 50-m
micrometeorological towers upwind and downwind of
the wind farm. They employed multiple levels of very
sensitive cups/vanes, a single three-axis sonic
anemometer at nominal hub height, and temperature,
temperature difference, humidity, and pressure
measurements.

6. National Renewable Energy Laboratory Innovation for Our Energy Future
Wind Farm Models – cont’d
• In 1990 data was collected from a 35-m met tower
located upwind of two Micon 65 turbines on Row 37
of the wind farm. The tower was similarly
instrumented with a single sonic
anemometer/thermometer near hub height but with
propeller-type anemometry. The nearest turbines
were located 7 rotor diameters upstream.
• The two turbines were heavily instrumented and
offered a detailed look at the effects of inflow
turbulence on two different rotor designs. Data
system malfunctions limited the useful of the data
collected but what is available covers a wide range of
conditions.

7. National Renewable Energy Laboratory Innovation for Our Energy Future
Wind Farm Models – cont’d
• Models based on measurements at the three
locations are offered in TurbSim. They include
conditions seen upwind of Row 1, at Row 37 with the
7D spacing, and downwind of Row 41 with a 14D
spacing to the nearest upwind turbines.
• We believe the data supports simulations up to about
50 m based on the scaling derived from the
measurements taken in 1989.

8. National Renewable Energy Laboratory Innovation for Our Energy Future
NWTC Model
• The NWTC Model simulates a range of turbulent inflows derived
from the measurements from an planar array of five sonic
anemometer/thermometers upstream of the NWTC ART
Turbine. The data was collected for the 1999-2000 NWTC wind
season (Oct-May) and represents a wide range of flow
conditions.
• The NWTC Site is very turbulent and produces some very
unique flow situations that are commonly seen in more complex
local terrain. It offers a distinct complement to the simulations
based on the measurements in the High Plains of Colorado.
• We believe the simulations are reasonably realistic up to a
height of 100 m.

9. National Renewable Energy Laboratory Innovation for Our Energy Future
Great Plains Model
• The Great Plains Low-Level Jet Model simulates
conditions based on extensive measurements from a
120-m tower and sodar for over one year at a site on
the High Plains of SE Colorado. The tower was
instrumented to make measurements for a GE wind
turbine with a 70-m rotor and an 85-m hub height.
• Of prime importance in this experiment and the
model it is based on is to include the turbulence
characteristics associated with the presence of a
nocturnal low-level jet stream of varying height and
strength. Coherent turbulent structures are an
integral part of the stable atmosphere and jet
presence and are modeled as accurately as possible.

10. National Renewable Energy Laboratory Innovation for Our Energy Future
Great Plains Model – cont’d
• The Great Plains Model is unique in that it provides
vertical profiles of wind direction in addition to wind
speed and turbulence. This feature is important
when simulations of a low-level jet at turbine hub
height are made which is a common situation at this
location.
• This model also provides the user with the option of
including or not including coherent structures to
reflect the observation that jets do not always break
down into organized turbulence but remain stable
with intense vertical wind shears.

11. National Renewable Energy Laboratory Innovation for Our Energy Future
120m Tower
(1357 m – 4451 ft)
Arkansas River
Pikes Peak
(4302 m - 14110 ft) Great Plains
Location of Great Plains Data Collection

12. National Renewable Energy Laboratory Innovation for Our Energy Future
US287
120m Tower
(1357 m – 4451 ft)
Local Topography Surrounding Measurement Site

13. National Renewable Energy Laboratory Innovation for Our Energy Future
Some Comparative Examples
• We discuss the some results when exciting the
NWTC 5 MW virtual turbine model with inflows
generated by the IEC NTM (Class C), Great Plains
(GP-LLJ), and the NWTC (NWTCUP) TurbSim
Models.

14. National Renewable Energy Laboratory Innovation for Our Energy Future
Example Boundary Conditions
Case Jet Height
(m)
Ujet
(m/s)
Ri Rotor
Disk
u* (m/s)
C-3 80 11.64 0.216 0.213
C-10 460 27.68 0.020 0.450
NREL 5 MW Virtual Turbine

15. National Renewable Energy Laboratory Innovation for Our Energy Future
Adjustments
• Hub height mean wind speeds for IEC and NWTC
models set to same as GP-LLJ to insure accurate
comparisons

16. National Renewable Energy Laboratory Innovation for Our Energy Future
Blade Root Bending Moments
Edgewise
IEC GP-LLJ NWTC
kNm
5600
5800
6000
6200
Flapwise
Inflow Excitation
IEC GP-LLJ NWTC
2000
3000
4000
5000
6000 Pitching
IEC GP-LLJ NWTC
90
100
110
120
130
Blade Root Bending Moments
Edgewise
IEC GP-LLJ NWTC
kNm
5600
5800
6000
6200
Flapwise
Inflow Excitation
IEC GP-LLJ NWTC
2000
3000
4000
5000
6000 Pitching
IEC GP-LLJ NWTC
80
90
100
110
120
130
Case 3
Case 10

17. National Renewable Energy Laboratory Innovation for Our Energy Future
Rotor
Generator Torque
IEC GP-LLJ NWTC
kNm
0.0
0.4
0.8
1.2
1.6
2.0 Rotor Thrust
Inflow Excitation
IEC GP-LLJ NWTC
kN
40
60
80
100
RotorTorque
IEC GP-LLJ NWTC
kNm
100
200
300
400
Generator Torque
IEC GP-LLJ NWTC
kNm
0.0
0.4
0.8
1.2
1.6
2.0 Rotor Thrust
Inflow Excitation
IEC GP-LLJ NWTC
kN
40
60
80
100
120
Rotor Torque
IEC GP-LLJ NWTC
kNm
100
200
300
400
Case 3
Case 10

18. National Renewable Energy Laboratory Innovation for Our Energy Future
Low-Speed Shaft Tip Bending
Low-Speed Shaft Tip Bending Moment
My
IEC GP-LLJ NWTC
kNm
800
1200
1600
2000
2400
2800
3200
Mz
Inflow Excitation
IEC GP-LLJ NWTC
Low-Speed Shaft Tip Bending Moment
My
IEC GP-LLJ NWTC
kNm 800
1200
1600
2000
2400
2800
3200
Mz
Inflow Excitation
IEC GP-LLJ NWTC
Case 3 Case 10

19. National Renewable Energy Laboratory Innovation for Our Energy Future
Tip Deflections
Axial
IEC GP-LLJ NWTC
15
30
45
60
Out-of-Plane
IEC GP-LLJ NWTC
cm
20
30
40
50
60
70 In-Plane
Inflow Excitation
IEC GP-LLJ NWTC
8
9
10
11
12
Blade Tip Deflections
Out-of-Plane
IEC GP-LLJ NWTC
cm
10
15
20
25
30
In-Plane
Inflow Excitation
IEC GP-LLJ NWTC
8
9
10
11
12
Axial
IEC GP-LLJ NWTC
15
30
45
60
Case 3
Case 10