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.

Blade Testing at NREL’s 

National Wind Technology Center

2010 Sandia 

National 

Laboratory

Blade 

Workshop

Scott Hughes

July 20, 2010

PIX 17536 NREL/PR-500-48898
Innovation for Our Energy Future

NREL Turbine Test Capabilities

• Field testing

– Demonstrates advances in control 

systems, load alleviation, innovative 

technology

• MW-scale turbines

• Small and mid-size turbines

• Drive train testing

– 225 kW dynamometer

– 2.5 MW dynamometer

– 5 MW dynamometer by 9/2012

– Grid integration upgrade

• Blade testing – Wind and Water

– 3 test labs at NWTC, up to 50m 

blades

– 90-m blades at Massachusetts blade 

test facility

PIX 17398

PIX 17244
Innovation for Our Energy Future

Why Test Blades?

• Blade reliability identified as significant O&M cost

• Minimize risk of field failures

• Testing is a certification requirement

– Withstand the design/test loads

– Identify manufacturing weaknesses

• Validate model data with empirical values

– Proof of concept and prototype testing

– Stress and strain

– Stiffness / deflection

– Ultimate static strength

– Design life verification

PIX 16392
Innovation for Our Energy Future

Advancing Blade Test Methodology

• Goal 

– Attain high levels of blade and rotor system reliability through advanced 

test methods

– Reduce the cost and time of testing

• Approach basis 

– 30 years of blade testing experience at the NWTC

• Design innovative test system hardware

• Advanced test methods with fast, low-cost deployment

• Collaborations with federal labs, industry, and academia

PIX 14707 PIX 11073 PIX 16269
Innovation for Our Energy Future

NWTC Blade Test Capabilities

• Testing facilities

– IUF – Blades to 50 m 

– Building A60 – Blades to 19 m

– Building 251 – Blades to 19 m 

• Typical test sequence

– Static testing

– Fatigue testing

– Property testing (modal, mass 

distribution)

• ISO/IEC 17025, A2LA accredited 

for full-scale blade testing

• Subcomponent Testing

PIX 14706

PIX 12894
Innovation for Our Energy Future

Certification Testing

• Tests the ability of the blade to 

withstand design load cases

• Typically applied in 4-6 load vectors

• Load application through quasi- static methods

– Cranes

– Ballast Weights

– Winches

– Hydraulic actuators

135 Full-scale blade tests have been 

conducted at the NWTC

• Lifetime verifications

– 20-year blade life on the order of 1x109 in-field 

cycles

– Laboratory testing accelerates loading through 

increasing load magnitude

• Methods 

– Single-axis

– Dual-axis

– Forced Displacement 

– Resonant Static Testing

Fatigue Testing

PIX 16270

PIX 14708
Innovation for Our Energy Future

Test Method Development

• Limitations of current test methods

– Blade failures continue despite current testing practices

– Complete testing time increases as blades get longer

– Current test practices not representative of in-field loading

• Research and Development to improve test efficiency

– Dual-Axis Resonant Testing (UREX)

– Phased-Locked Dual-Axis Testing (PhLEX)

– Base Excitation Testing (BETS)

• Assessment of test methods with field experience
Innovation for Our Energy Future

Test Method Development

Continual improvement in test 

characteristics

Courtesy: MTS

PIX 16270

PIX 17639

PIX 12894

PIX 17641
Innovation for Our Energy Future

Universal Resonant Excitation (UREX)

• Applies dual-axis fatigue loads at multiple resonant frequencies

• Prototype demonstrated on a 9-meter blade at NREL

• Commercialized version has been developed with MTS

• Modular, scalable

• Up to 2000-kg of oscillating mass at 0.15-meters of stroke

• Multi-station capability

• Developed for use at the WTTC facility

• Demonstration on MW-scale blades Fall 2010

• Technology deployed to testing facilities worldwide

MTS UREX. Courtesy: MTS UREX on blade. Courtesy: MTS

PIX 17637
Innovation for Our Energy Future

Phase-Locked Excitation (PhLEX)

• Control actuator stiffens system in the flapwise direction until the

natural frequencies in both flapwise and edgewise directions are

approximately equal

• Minimize point-load forces introduced by actuators

• Faster, more efficient resonant testing with ideal cycle-to-cycle load

and phase control

• Prototype demonstration on a 9-meter blade fall of 2010
Innovation for Our Energy Future

Base Excitation Test System (BETS)

• Design for applying dual-axis fatigue loads at multiple resonant

frequencies

• Design for scaling to large blades

• Incorporate a flexible link at the root of the blade, which can be

adaptable to existing test stand designs

• Prototype demonstration on a 9-meter blade at NREL in the Fall of

2010
Innovation for Our Energy Future

Static Testing Development

• Specification and development 

WTTC equipment

– MTS UREX specifications

– MTS static loading equipment 

specifications

• $2M of MTS test equipment 

supplied to WTTC by January 2011

• NREL contact Dave Snowberg, 

david.snowberg@nrel.gov

Hydraulic Winches

Hydraulic Actuators

Pull-down

Floor Sheaves (Typ)

Steel Floor

Embedment Plates

Force Sensor

(Typ)

Winch module

Courtesy: MTS

Static test setup

Courtesy: MTS

PIX 17636
Innovation for Our Energy Future

Analog 

Sensors

Multiple 

EtherCAT

Chassis

Blade Test Data Acquisition Development

DAS Host PC 

(recording & 

visualization)

Data Acquisition 

Controller (RealTime Operating 

System)

Other Sensor 

Networks (CAN, 

DeviceNet, etc)

• Advanced NI distributed hardware

– Short analog wires for reduced noise

– Simplified test setup

• Records hundreds of channels at high 

sample rates (up to 5 kHz each)

– Eigenfrequency analysis

– Capture transient events

Multiple 

EtherCAT

Chassis

Analog 

Sensors

Multiple 

EtherCAT

Chassis

Analog 

Sensors

• NWTC customized software

– Real-time monitoring of 

equivalent fatigue damage

– Automated event detection

– Virtual channels for quality 

control and display

PIX 17638
Innovation for Our Energy Future

Test Design Code: BladeFS

• Modules for both static and fatigue tests

– Test load calculation

– Deflection prediction (discrete beam 

analysis)

– Layout optimization for load introduction

• Graphical user interface

• Excel input file

• Word and Excel output files

http://wind.nrel.gov/designcodes/simulators/BladeFS/

Contact Michael Desmond: 

michael.desmond@nrel.gov

Developed to analyze and optimize blade test setup
Innovation for Our Energy Future

Sandia Sensor Blade Testing

• Collaborative test with SNL to demonstrate 

internal accelerometers and CM systems

• Blade tested in fatigue to failure, test 

collaborators to provide summary of results

• CM/NDE test collaborators

– Los Alamos National Labs -Macro Fiber 

Composite actuator/sensor waveform

– UMASS – Lowell – Digital Image 

Correlation

– Luna Innovations – Fiber Optic Strain

– Micron Optics – FBG fiber optic strain

– Intelligent Fiber Optic Systems- fiber 

optic strain

– NASA – Piezoelectric actuator/sensor 

waveform measurement

– Laser Technology Inc - Shearography PIX 17640
Innovation for Our Energy Future

WTTC Commissioning

•Objective

– Demonstrate new facility capabilities with a MW-scale blade test

– Optimize and validate test methods

•NREL solicits feedback from blade manufacturers and suppliers 

on effective means to conduct initial test to commission facility

•Approaches under consideration

– Competitive CRADA solicitation

– WTTC/NREL cost-shared demonstration blade test

– Purchase of test blade

Technical contact is Derek Berry: derek.berry@nrel.gov

Business contact is Rahul Yarala: ryarala@masscec.com