wind turbine blade testing at nrel - sandia...
TRANSCRIPT
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Wind Turbine Blade Testing at NREL
2008 Sandia Blade WorkshopScott Hughes
National Renewable Energy Laboratory
National Wind Technology Center
Golden, CO USA
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Outline
Background of the NWTC and wind turbine blade testing
Testing Capabilities at the NWTC Aggregate Blade Test Results Current Test Activities Test methodology development
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About the NWTC Testing Group
Perform Full-scale and subcomponent tests of wind turbine blades Perform research and prototype tests on DOE sponsored
programs Perform Certification tests for industry clients through
CRADAs and other work-for-other agreements NREL also has dedicated dynamometer test facility and
field testing capabilities Development of test methodologies
Improve accuracy and efficiency of testing Develop methods for testing advanced blade designs
Bend-twist Swept Soft structures
Demonstrate advanced NDE systems and structural health monitoring systems
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Why We Test Blades
Testing is a Certification Requirement Demonstrate blade can withstand the
design/test loads Minimize risk of field failures
Validate Blade Design Demonstrate as-built blade properties
consistent with design Stress and Strain Stiffness / Deflection Ultimate strength testing, buckling stability or
other failure mode
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Structural Testing Facilities
Three Testing Facilities IUF Blades to 50-m A60 and 251 Blades to 19-m
Typical Tests Static Testing Fatigue Testing Property Testing (modal, mass
distribution) ISO/IEC 17025, A2LA Accredited for
full-scale blade testing Subcomponent Testing
22-kip, 100-kip load frames
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Structural Testing Data Acquisition
Data Acquisition Common Sensors
Load Displacement Strain gages lots of them Accelerometers
Acquisition Systems BSTRAIN
NI based Chassis VDAS
Scalable Ethernet based system Distributed A/D layout minimizes
instrument cable lengths
NDE Capabilities Acoustic Emission Modal Testing Thermography Surface Profiling
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Static Testing Tests the ability of the blade to
withstand design load cases or ultimate strength as required
Typically applied in 4-6 load vectors representing worst case loading for standard design load cases
Load application through quasi- static methods
Cranes Ballast Weights Winches Hydraulic actuators
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Fatigue Testing Tests the ability of the blade to withstand operating-life
loads 20-year blade life on the order of 1x109 cycles Laboratory testing accelerates loading through increasing load
magnitude to manageable number of cycles, typically 1-million to as high as 10-million
Methods Single-axis Two-axis Forced Displacement Resonant Methodology development more on this later
smgershTypewritten Text(click image to play video)
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Structural Testing History
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Num
ber o
f Bla
des
Test
ed
AOC
15/5
0
AWT-
26/2
7
Berg
ey X
L50
GE
Win
d 1.
5-M
W
GE
Win
d 75
0-kW
GE
Win
d 55
0-kW
Foam
Mat
r ix 1
5-ft
KENE
TECH
16-
m
NedW
ind
25-m
NPS
NW-1
00-k
W
NPS
NW-2
50-k
W
Phoe
nix
7.9-
m
PSE-
85-k
W
TPI -
56-
100
TPI 3
0-m
m s
tuds
TPI/M
HI 1
000-
A
USW
56-
100
Win
dlite
SW W
indp
ower
MHI
/TPI
92
Clip
per C
93/C
96
WTC
-POC
Full Blade Fatigue - 56
Full Blade Static - 65
NDE - 15
Substructures - 39
Updated May ,07
NREL/NWTC USA
WMC / TU Delft Netherland
Blaest/Risoe DTU Denmark
NaREC United Kingdom
CENER Spain
Fraunhofer Institute Germany
Private Labs LM, Siemens, MHI, Tecsis
Blades Tested at NRELBlade Testing Labs
May 2008 125 full-scale blade tests
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Aggregate Test Blade Data
Megawatt-scale blades Designs representative of current in-
field designs Blade testing in accordance with IEC
61400 -23 Standard Loading above IEC envelop not included Fatigue testing above target damage
equivalent loading not included
Catastrophic Failure Breaking of primary blade structure Complete failure of structural elements,
internal or external bond lines, skins, shear webs, root fasteners
Major parts become separated from the main structure
Functional Failure Reduction in Stiffness (5 to 10%) Permanent deformation Substantial permanent change of cross-
sectional shape After unloading the blade, a mechanism is
no longer capable of performing its design objective
Superficial Failure Small cracks not causing significant strength
degradation or bond line weakening Gel coat cracking Paint flaking Surface bubbles Minor elastic panel buckling Small Delaminations
Definition of Failures (IEC 61400-23)Test Data Population
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Representative Failures
Bondline
Failures
Material Failures
Stability
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Aggregate Catastrophic or Functional Failure Modes
One Test Article may have multiple failure modes
Design / Material Inadequate Design Ply Drops Panel Stability
Laminate Defect Waves Voids Dry spots
Bondlines Shear Web Leading Edge Trailing Edge
Root Fixing T-bolts Barrel Nuts Flanges
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Design /Material
Laminate Defect Bondline Root Fixturing
Perc
ent o
f occ
uran
ce
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Static Fatigue
Perc
ent o
f occ
uran
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Observations and recommendations from a blade testers perspective
Majority of laboratory failure events are during fatigue testing Anecdotally this is the reverse of what European laboratories and manufacturers have observed
The results of lab tests and how they relate to in-field service of blades is difficult to determine due to IP.
Encourage open forum of manufacturers, certifying bodies, operators, and testing laboratories to enable a more accurate assessment of testing methods
Sometimes it is not possible to test every detail on blade Add expanded component testing requirements Full-scale tests necessary subcomponent testing will not capture design or manufacturing details of
as-built blades Normative NDE requirements should go beyond current requirements
Test articles are typically from the initial lot of production blades if not the first article produced Benefit of attention to detail during construction Test Article can be subject to defects due to lack of production experience
Laminate imperfections detected prior to testing could be used to gauge adequacy of test article
Damage Tolerant Design based testing could however incorporate or require using worst-case test blades
Effect of multiple assembly plants and lines should be evaluated this topic not rigorously defined in current IEC standards
Blade Design Standard?
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Recent and Current Tests TX-100 9-m blade
New resonant hardware (UREX) system development
Bend-twist test technology BSDS Testing
Fatigue test In progress Verdant Power
Marine Kinetic Hydropower System Blade and rotor system static testing
Other Commercial Projects 40-50-m blade static and fatigue
testing
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Knight and Carver STAR Blade Testing
26-m blade fatigue test Swept planform blade
testing using resonant technology
Moments and torque (twist) of the test loads ideally optimized to properly simulate in- field conditions
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NWTC Testing Capacity Current laboratory can test 50-m blades,
industry just keeps making bigger blades Need for new US test facilities
Accommodate blades larger than 50-m Accommodate demand of commercial
clients Detailed presentations to follow
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Testing methodology development Forced Displacement Testing
Dual-axis capability Accurate load replication High equipment and operating cost Longer test duration Prohibitive to test entire blade length Large test loads introduced to blade
Linear Resonant Testing Low(er) Equipment costs Relatively short test duration Can test entire blade span Method scales favorably for larger turbines Ability to ramp load at resonant frequency Currently for large blades, resonant/forced hydraulic dual-axis
testing is unavailable
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Blade Length (m)
Hyd
raul
ic A
ctua
tor F
low
Rat
e (lp
m)
Flow Rate for Forced Displacement is 0.25-Hz Cycle Frequency
Resonant Testing Flow Rate
Single-axis testing
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Dual Axis Resonant Testing
Employ linear actuators in both flap and edge directions
System operated at two distinct frequencies
Potential for single-frequency operation with tuning elements
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0.2
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0.8
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1.2
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Frequency [Hz]
FFT
Mag
Fundamental Flap Frequency
Fundamental Edge Frequency
From Dual AxisTime-series Data
Edge Actuator
Flap Actuators
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Dual-axis Resonance Movie
smgershTypewritten Text(click image to play video)
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Thank You
Slide Number 1OutlineAbout the NWTC Testing GroupWhy We Test BladesStructural Testing FacilitiesStructural Testing Data Acquisition Static TestingFatigue TestingStructural Testing HistoryAggregate Test Blade DataRepresentative FailuresAggregate Catastrophic or Functional Failure ModesObservations and recommendations from a blade testers perspectiveRecent and Current TestsKnight and Carver STAR Blade TestingNWTC Testing CapacityTesting methodology developmentDual Axis Resonant TestingDual-axis Resonance MovieThank You