the stable atmospheric boundary layer a challenge for wind turbine operations, agu fall meeting,...
DESCRIPTION
An overview presentation of the impact and challenge of the stable atmospheric boundary layer on wind turbine dynamics presented to AGU Fall Meeting 2008TRANSCRIPT
NREL is a national laboratory of the U.S. Department of Energy Office of Energy Efficiency and Renewable Energy operated by the Alliance for Sustainable Energy, LLC
American Geophysical Union Fall Meeting San Francisco Neil D. Kelley Bonnie J. Jonkman National Wind Technology Center December 15, 2008
The Stable Atmospheric Boundary Layer: A Challenge for Wind Turbine Operations
AGU Fall Meeting, San Francisco December 15, 2008 2 National Renewable Energy Laboratory Innovation for Our Energy Future
Outline • Background
• Field experiments using full-size wind turbines to provide an understanding of the role of atmospheric turbulence in inducing damaging fatigue loads on modern wind turbines
• Turbulence characteristics associated with increased turbine dynamic loads and component wear and tear (fatigue)
• Stable atmospheric boundary layer structures that are responsible for these characteristics
• Conclusions
• What are we doing about this?
AGU Fall Meeting, San Francisco December 15, 2008 3 National Renewable Energy Laboratory Innovation for Our Energy Future
Background • More than 21,000 MW of wind energy
will be installed in the US by the end of 2008 with over 1300 MW added from January to September alone
• Turbine capacities now being installed generally exceed 2 MW with hub heights in the 80-120 m range and rotor diameters of 100 m or more
• Large capacity turbines are critical in meeting the national goal of 20% of electrical power from wind by 2030
• An industry-wide systemic power underproduction in the range of 10-15% now exists as well as incurring much higher than expected maintenance and repair costs
Source: American Wind Energy Association
AGU Fall Meeting, San Francisco December 15, 2008 4 National Renewable Energy Laboratory Innovation for Our Energy Future
Wind Turbines and Turbulence • Wind turbine structures have
become much more flexible as the power generating capacity has steadily increased into the multi-megawatt range
• This has resulted in a greater number of high frequency vibrations becoming active under the dynamic loading induced by atmospheric turbulent structures embedded in the turbine inflow
• Like aircraft, wind turbines are considered fatigue critical structures
• The service lifetime of a typical wind turbine component is heavily influenced by the rate at which cumulative fatigue damage occurs
AGU Fall Meeting, San Francisco December 15, 2008 5 National Renewable Energy Laboratory Innovation for Our Energy Future
Determining the Effects of Turbulence
• Experiments have been performed within a multi-row wind farm in California’s San Gorgonio Pass and at NREL’s National Wind Technology Center in Colorado
• Detailed, simultaneous measurements were made of both the turbulent inflow characteristics and the resulting aeroelastic response of the wind turbine(s)
• A range of analysis techniques including time-frequency (wavelets) and statistical correlation have been used to establish the turbulence characteristics that have the greatest influence on turbine fatigue loads
AGU Fall Meeting, San Francisco December 15, 2008 6 National Renewable Energy Laboratory Innovation for Our Energy Future
The San Gorgonio Pass Experiment
Pacific Ocean Salton
Sea
wind farms (152 m, 500 ft)
(−65 m, −220 ft)
(793 m, 2600 ft) Mt. Jacinto (
row 37
(3166 m, 10834 ft)
Wind Farm
AGU Fall Meeting, San Francisco December 15, 2008 7 National Renewable Energy Laboratory Innovation for Our Energy Future
The Experiment at Row 37 of San Gorgonio Pass Wind Farm
Hub-height sonic
anemometer
AeroStar Rotor
SERI S-Series Rotor
30 m turbine inflow Tower
AGU Fall Meeting, San Francisco December 15, 2008 8 National Renewable Energy Laboratory Innovation for Our Energy Future
The Experiment at the NWTC
NWTC (1841 m – 6040 ft)
NWTC
Great Plains
Terrain Profile Near NWTC in Direction of Prevailing Wind Direction
Denver
Boulder
AGU Fall Meeting, San Francisco December 15, 2008 9 National Renewable Energy Laboratory Innovation for Our Energy Future
Measuring the Spatial Effects of Turbulence on Turbine Response
Continental Divide3960 m
EldoradoCanyon
EldoradoCanyon
1765 m1765 m
NWTC600 KW ART
Turbine
NWTC600 KW ART
Turbine43-m diameterplanar sonicanemometer
array
43-m diameterplanar sonicanemometer
array
NCARMesa Lab
1885 m
AGU Fall Meeting, San Francisco December 15, 2008 10 National Renewable Energy Laboratory Innovation for Our Energy Future
Diurnal Variation of High Blade Fatigue Loads
Local standard time (h)2 4 6 8 10 12 14 16 18 20 22 24
Prob
abili
ty (%
)
0
2
4
6
8
10
12
14sunrise sunrset
Local standard time (h)
0 2 4 6 8 10 12 14 16 18 20 22 24Pr
obab
ility
(%)
0
2
4
6
8OctMay Oct May
San Gorgonio Wind Farm NWTC
Missing data: Turbine not able to run due to very turbulent conditions
Diurnal periods that favor encountering high blade loads
AGU Fall Meeting, San Francisco December 15, 2008 11 National Renewable Energy Laboratory Innovation for Our Energy Future
Variation of High Blade Fatigue Loads with Vertical Stability
Turbine Layer Vertical Stability, Ri-0.06 -0.04 -0.02 0.00 0.02 0.04 0.06 0.08 0.10
Prob
abili
ty (%
)
0
10
20
30
40
50
60
Turbine Layer Vertical Stability, Ri
-0.08 -0.06 -0.04 -0.02 0.00 0.02 0.04
Prob
abili
ty (%
)
0
5
10
15
20
25
Both peaks occur in weakly or slightly stable conditions!
San Gorgonio Wind Farm NWTC
AGU Fall Meeting, San Francisco December 15, 2008 12 National Renewable Energy Laboratory Innovation for Our Energy Future
Example of Turbine Rotor Encountering a Coherent Turbulent Structure – Aeroelastic Response
In-plane root bending moment (kNm)
AeroStar rotor out-of-plane (flapping) root bending moment (kNm)
SERI blade AeroStar blade
Blade 1 Blade 2
Blade 3
Significant stress reversals = fatigue cycles
AGU Fall Meeting, San Francisco December 15, 2008 13 National Renewable Energy Laboratory Innovation for Our Energy Future
Stable Boundary Layer 3-D Coherent Turbulent Structure at Hub Height Responsible for Observed Rotor Dynamic Response
Instantaneous local Reynolds stresses (m/s)2
Estimated local vorticity components (sec-1)
ωy
ωz
v’w’
u’v’
u’v’ v’w’
ωx ωy ωz
AGU Fall Meeting, San Francisco December 15, 2008 14 National Renewable Energy Laboratory Innovation for Our Energy Future
SBL Coherent Structures: Important Source of Turbine Fatigue Loading
• We have defined a fluid dynamics parameter that correlates well with observed turbine fatigue loads: Coherent TKE
• Ingesting coherent turbulent structure can induce strong oscillatory responses (stress reversals) in turbine components
Upwind arrayinflow CTKE
m2 /s
2
0
20
40
60
80
100
120
0
20
40
60
80
100
120rotor top (58m)rotor hub (37m)rotor left (37m)rotor right (37m)rotor bottom (15m)
IMU velocity components
0 2 4 6 8 10 12
mm
/s
-20
-10
0
10
20
-20
-10
0
10
20
Time (s)
492 494 496 498 500 502 504
vertical (Z)side-to-side (Y)fore-aft (X)
zero-meanroot flapbendingmoment
kNm
-400
-300
-200
-100
0
100
200
300
400
-400
-300
-200
-100
0
100
200
300
400
Blade 1Blade 2
Loads at Blade Roots
Drivetrain X,Y,Z velocities
ART Turbine Coherent Turbulence Response
Coherent TKE from Array
2 2 2 1 21 2 // [( ' ') ( ' ') ( ' ') ]= + +CTKE u w u v v w
AGU Fall Meeting, San Francisco December 15, 2008 15 National Renewable Energy Laboratory Innovation for Our Energy Future
Coherent Structures in Sub-jet Shear Layer
NOAA LIDAR TKE
Tower Sonics CTKE
SBL Vertical Structures: Low-Level Jets
• The West and Central Great Plains contain the best wind resource in the US
• Nocturnal low-level jets and the accompanying strong shear layers are ubiquitous during the warmer months (Apr-Sep)
• Kelvin-Helmholtz Instability (KHI) frequently occurs in these layers and is responsible for generating coherent structures such as KH billows that form, break, and decay
June 16-17, 2002
10-min mean wind speed (m/s)
2 4 6 8 10 12 14 16 18 20 22
Hei
ght a
bove
gro
und
leve
l (m
)
0
50
100
150
200
250
300
350
400
450
0
50
100
150
200
250
300
350
400
450
17:0019:0023:0000:0001:0002:0003:0004:00
Evolution of Low-Level Jet at Lamar Site
AGU Fall Meeting, San Francisco December 15, 2008 16 National Renewable Energy Laboratory Innovation for Our Energy Future
Conclusions
• Turbulent processes associated with shear flow instabilities in the stable boundary layer are likely one of the major sources of fatigue damage and the less than design lifetimes being observed of components used with modern, multi-megawatt wind turbines
• At most locations with a usable wind resource, the boundary layer is typically stable about 2/3 of the time an thus increasing the exposure to the turbulent structures generated under such conditions
• Evaluations of potential wind energy sites should identify any regional and local conditions that enhance the development of organized, nocturnal turbulence and match the design of the turbine to be installed accordingly
AGU Fall Meeting, San Francisco December 15, 2008 17 National Renewable Energy Laboratory Innovation for Our Energy Future
What Are We Doing About This?
• We have developed a stochastic turbulence inflow simulator (TurbSim) that replicates flow fields experienced at the NWTC, in the western Great Plains, and in and near a multi-row wind farm
• This simulator is used to drive the dynamics of numerical simulations of wind turbine designs and is used as a critical element of the design process
• We are studying methods employing remote-sensing technology to support the development of real-time turbine control schemes to reduce fatigue loads and to increase turbine production efficiency