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

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The Impact of Active Aerodynamic Load Control on
Wind Energy Capture at Low Wind Speed Sites
Jose Zayas Manager, Wind Energy Technology
Dept. Sandia National Laboratories www.sandia.gov
/wind jrzayas_at_sandia.gov
Authors
SNL Dale Berg, David Wilson, Brian Resor,
Jonathan Berg, and Joshua Paquette FexSys
Sridhar Kota, Gregory Ervin, and Dragan Maric
Sandia is a multiprogram laboratory operated by
Sandia Corporation, a Lockheed Martin
Company,for the United States Department of
Energys National Nuclear Security
Administration under contract DE-AC04-94AL85000.
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Outline

• Background Motivation
• External Conditions and Opportunity
• Sandias SMART Research Approach
• Grow the Rotor Technique
• Morphing Technology (FlexSYS)
• Results
• Summary Future Work

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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 gt reduce loads gt
  load control (Passive or Active)

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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

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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

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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 operation
Goal Develop advanced rotors which incorporate
passive and/or active aerodynamics to address
system loads, increase turbine efficiency, and
energy capture.
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Sandia Strategy for Enabling Advanced Blades
Enabling New Technology Develop small,
light-weight control devices systems to
attenuate fatigue loads on turbine blades and
increase turbine efficiency

• Novel Concepts
• Aeroacoustics

Aerodynamics
Controls
Sensors

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

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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

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

1.5 MW Turbine Blade Model
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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)
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Grow the Rotor (GTR) Concept
Estimate Cost of Energy

• 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

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FlexSys Morphing Trailing Edge 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)

1990-era Zond Flap Technology
FlexSys Demonstration Unit
Comparison of Flap Geometries
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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

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Effects of AALC on Turbine Components
FAST/Aerodyn/Simulink Simulation
Turbine
Turbulent Wind Input
Increase in Energy Capture
Grow the Rotor
Rain Flow Counting
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Blade Root Flap Moment for GTR is Comparable to
Baseline Rotor
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Fatigue Damage Summary
One-million Cycle Damage Equivalent
Load (Baseline-AALC/Baseline Rotor)
9m/s 11m/s 18m/s Rayleigh Wind 5.5m/s Rayleigh Wind 7m/s
Low Speed Shaft Torque -1.7 -4.9 -33.5 -3.1 -7.3
Blade Root Edge Moment 1.7 1.9 -2.5 0.8 0.8
Blade Root Flap Moment -31.2 -27.1 -30.4 -23.1 -26.3
Blade Root Pitch Moment -11.4 -4.5 -14.1 -7.1 -7
Tower Base Side-Side Moment -0.1 -8 -7.2 -0.9 -2.9
Tower 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
All results are increase or decrease relative
to baseline rotor
FlexSys Morphing Trailing Edge. 20c, /-10
Configuration
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Fatigue Damage Summary
One-million Cycle Damage Equivalent Load (10
GTR-AALC/Baseline Rotor)
9m/s 11m/s 18m/s Rayleigh Wind 5.5m/s Rayleigh Wind 7m/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
All results are increase or decrease relative
to baseline rotor
FlexSys Morphing Trailing Edge. 20c, /-10
Configuration
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GTR Energy Capture is Increased for Comparable
Blade Flap Fatigue Damage
FMTE 20c, /-10 Configuration
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
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Trailing Edge Demo
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Summary and Future Work

• 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

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Thank You!
Jose Zayas Program Manager, Wind Energy
Technology Dept. Sandia National
Laboratories jrzayas_at_sandia.gov [phone]
www.sandia.gov/wind