The Impact of Active Aerodynamic Load Control on Wind Energy Capture at Low

Wind Speed Sites

Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company,for the United States Department of Energy’s National Nuclear Security Administration

under contract DE-AC04-94AL85000.

Jose ZayasManager, Wind Energy Technology Dept.

Sandia National Laboratories

www.sandia.gov/windjrzayas@sandia.gov

SNL: Dale Berg, David Wilson, Brian Resor, Jonathan Berg, and Joshua PaquetteFexSys: Sridhar Kota, Gregory Ervin, and Dragan Maric

Authors:

Outline

Background & Motivation External Conditions and Opportunity Sandia’s SMART Research Approach Grow the Rotor Technique Morphing Technology (FlexSYS) Results Summary & Future Work

C:\Documents and Settings\sburge\Desktop\3-6-turbine.gif

Justification for Load Control Efforts

Increase in size results in decrease in COE• Leads to increase tower-top weight• Leads to increased gravity-induced stresses

at blade root Weight must be minimized Technology innovation is needed

Need to minimize blade weight => reduce loads => load control (Passive or Active)

Sandia Effort is Focused on Blades

Why are Blades a Key Research Opportunity?

• 20% of turbine cost, but 100% of energy capture

• Incremental improvements yield large system benefits

• Source of loads for the entire turbine

Turbines Experience Complex External Conditions

Large turbine size means loads vary along blade and change quickly (wind gusts)• Quickly changing loads cause fatigue damage• Active pitch control can only control “average” load on blade• Passive load control cannot respond to local load variations• Fatigue loads can drive the lifetime of all turbine components

Turbine Power Basics & Opportunity

Regions of the Power Curve

Region I – not enough power to overcome friction

Region II – Operate at maximum efficiency at all times

Region III – Fixed power operationGOAL!

Goal:Develop advanced rotors which incorporate passive and/or active aerodynamics

to address system loads, increase turbine efficiency, and energy capture.

Wind Turbine Power Curve

Power =½ρACpV∞3

Wind Speed Distribution

Future Design Needs

•Advanced Control Strategies

•Advanced Embedded Sensors•Structural Health Monitoring

Sandia Strategy for Enabling Advanced Blades

Aerodynamics

Sensors Controls

Enabling New TechnologyDevelop small, light-weight control devices & systems to attenuate fatigue loads on turbine blades and increase turbine efficiency

•Novel Concepts•Aeroacoustics

Also Need:•Structural analysis•Active aero device•Manufacturing (integration)

Active Aerodynamic Blade Load Control is One Promising Option

Consider Active Aerodynamic Load Control (AALC)• Sensors distributed along blade

sense local conditions current ongoing project (SNL-SBlade)

• Load control devices distributed along blade respond quickly alleviate local loads

• Control architecture and implementation

S818_2703 S825_2103 S826_1603

Outer 25%

1.5 MW Turbine Blade Model

Apply devices near the blade tip (initial focus)• Maximum loads• Maximum control impact

Previous AALC Work

Previous work (Risø & TU Delft) shows AALC has potential to significantly reduce blade loads• Approximately 50%

Successful AALC presents challenges• Integrate devices and sensors into blades• Maintain reliability• Minimize additional cost• Potential design and manufacturing impact

AALC may also increase energy capture

Sandia effort is referred to as Structural and Mechanical Adaptive Rotor Technology (SMART)

Grow the Rotor (GTR) Concept

Usual approach•Design new machine to withstand design loads (limit fatigue loads)•Determine component costs (subject to large errors)•Determine energy capture•Evaluate economics

Alternative approach•Examine existing machine•Determine reduction in fatigue loads due to active aero load control•Determine allowable increase in blade length•Determine additional rotor costs•Evaluate increase in energy capture•Evaluate economics

Estimate Cost of Energy:

FlexSys Morphing Trailing Edge Technology

Comparison of Flap GeometriesFlexSys Demonstration

Unit

1990-era Zond Flap Technology

Continuous deformation of upper & lower surfaces• Higher deflection without separation• Less drag for given deflection• No gap through which air can leak (noise)• Fast response (100 degrees/sec)

Fatigue Load Reduction Approach

Simulate turbine operation over operating wind-speed range

Evaluate fatigue damage at each wind speed• Rain-flow cycle counting • Linear damage accumulation

Combine with wind speed distribution to determine overall fatigue damage

Investigate baseline rotor, baseline with AALC (FlexSys Morphing Trailing Edge or FMTE) and 10% longer blades with AALC• Compare fatigue accumulation ratios• Normalize large fatigue calculation errors

Effects of AALC on Turbine Components

Increase in Energy Capture

Turbulent Wind Input100 120 140 160 1808

10

12

14

16

18

20

22

24

26

Time (sec)

Win

d In

put V x [m

/s]

18.0 [m/s] MWS NTM IEC Type A Turbulence

Rain Flow CountingGrow the Rotor

FAST/Aerodyn/Simulink Simulation

Increase in Yearly Energy Capture

0

1000000

2000000

3000000

4000000

5000000

6000000

7000000

5.5 6 6.5 7 7.5 8

Annual Average Wind Speed, m/s

Annu

al E

nerg

y Ca

ptur

e, k

WH

Original Rotor

Longer Blades

Turbine

Blade Root Flap Moment for GTR is Comparable to Baseline Rotor

0 500 1000 1500 2000 2500 3000-2

-1

0

1

2

3

4

5

Blade Root Flap Moment (12m/s)RootMyb1

Moment (kN-m)*Active Aerodynamic Load Control (AALC)

20% chord length, +/- 10o max. actuation, PD blade tip displacement control

Cyc

le R

ate,

log 10

(100

0*cy

c/s)

BaselineBaseline w/AALC*10% Increased Rotor w/AALC*

Fatigue Damage Summary

All results are % increase or decrease relative to baseline rotorFlexSys Morphing Trailing Edge. 20%c, +/-10° Configuration

One-million Cycle Damage Equivalent Load

(Baseline-AALC/Baseline Rotor)

9m/s 11m/s 18m/sRayleigh

Wind5.5m/s

Rayleigh Wind7m/s

Low Speed Shaft Torque -1.7 -4.9 -33.5 -3.1 -7.3Blade Root Edge Moment 1.7 1.9 -2.5 0.8 0.8Blade Root Flap Moment -31.2 -27.1 -30.4 -23.1 -26.3Blade Root Pitch Moment -11.4 -4.5 -14.1 -7.1 -7

Tower Base Side-Side Moment -0.1 -8 -7.2 -0.9 -2.9Tower Base Fore-Aft Moment -18.6 -16.5 -13.8 -5 -8

Tower Top Yaw Moment -53.2 -42.9 -43.4 -25.1 -32.2

Fatigue Damage Summary

All results are % increase or decrease relative to baseline rotorFlexSys Morphing Trailing Edge. 20%c, +/-10° Configuration

One-million Cycle Damage Equivalent Load

(10% GTR-AALC/Baseline Rotor)

9m/s 11m/s 18m/sRayleigh

Wind5.5m/s

Rayleigh Wind7m/s

Low Speed Shaft Torque -12 -40.6 -39.1 2.5 -6.7

Blade Root Edge Moment 46.9 49.5 44 46.1 46.4

Blade Root Flap Moment -5 20.9 -1.5 6.5 4.3

Blade Root Pitch Moment 28.6 33 24.8 33.2 33.3

Tower Base Side-Side Moment 20.4 8.3 2.8 43.2 31.3

Tower Base Fore-Aft Moment -0.7 17.2 7.1 22.2 18.6

Tower Top Yaw Moment -37.6 -17.9 -16.1 -0.9 -8.2

GTR Energy Capture is Increased for Comparable Blade Flap Fatigue Damage

Blade Length Increase 10%Increase in energy capture is approximately 13% at 5.5 m/s, 12% at 6 m/s and 9% at 8

m/s

5.5 m/s Rayleigh Wind Speed Distribution

FMTE 20%c, +/-10° Configuration

Increase in Yearly Energy Capture

0

1

2

3

4

5

6

7

5.5 6 6.5 7 7.5 8

Annual Average Wind Speed, m/s

Annu

al E

nerg

y Ca

ptur

e, G

Wh Original Rotor

10% Longer Blades

Trailing Edge Demo

Use of AALC can achieve significant reductions in blade flap root fatigue damage

GTR concept results in significant additional energy capture at lower wind speed and provides a transition for the technology

Additional work remains•Control optimization (sensor/actuator optimization)•Analysis of impact on blade torsional compliance•Evaluate true “distributed” sensing & control

Summary and Future Work

Thank You!

Jose ZayasProgram Manager,

Wind Energy Technology Dept.

Sandia National Laboratories

jrzayas@sandia.gov(505) 284-9446

www.sandia.gov/wind