Active Aerodynamic Load Control for Wind Turbine Blades

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Active Aerodynamic Load Control for Wind Turbine
Blades

• Jose R. Zayas
• Sandia National Laboratories
• C.P. van Dam, R. Chow, J.P. Baker, E.A. Mayda
• University of California - Davis

Sandia is a multiprogram laboratory operated by
Sandia Corporation, a Lockheed Martin
Company,for the United States Department of
Energy under contract DE-AC04-94AL85000.
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Outline

• Problem Statement and Goal
• Active Control Background
• Microtab Motivation
• CFD work
• Wind tunnel results
• Modeling Tools
• Future Work
• Conclusion

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Problem Statement Goal

• With Wind Turbines Blades Getting larger and
  Heavier, Can the Rotor Weight be Reduced by
  Adding Active Devices?
• Can Active Control be Used to Reduce Fatigue
  Loads?
• Can Energy Capture in Low Wind Conditions be
  Improved?
• Research Goal

Understand the Implications and Benefits of
Embedded Active Blade Control, Used to Alleviate
High Frequency Dynamics
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Active Flow/Load Control

• Blade Load Variations Due to Wind Gusts,
  Direction Changes, and Large Scale Turbulence
• Active Load Control on Blade/Turbine can be
  Achieved by Modifying
• Blade incidence angle (pitch)
• Flow velocity (modification in RPM)
• Blade length
• Blade aerodynamic characteristics through
• Changes in section shape (aileron, smart
  materials, microtab)
• Surface blowing/suction
• Other flow control techniques (VGs, surface
  heating, plasma)

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Active Flow/Load Control

• Active Load Control
• May remove fundamental design constraints
• These large benefits are feasible if active
  control technology is considered from the onset
• May allow for lighter more slender blades designs
• Active Load Control has Already been Implemented
  in Wind Turbine Design. e.g.
• Yaw control
• Blade pitch control
• Blade aileron (Zond 750)

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Active Flow/Load Control
Courtesy NREL
Active Aileron on a Zond 750 Blade
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Gurney Flap (Passive)

• Gurney Flap (Liebeck, 1978)
• Significant increases in CL
• Relatively small increases in CD
• Properly sized Gurney flaps ? increases in L/D

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Microtab Concept

• Evolutionary Development of Gurney flap
• Tab Near Trailing Edge Deploys Normal to Surface
• Deployment Height on the Order of the Boundary
  Layer Thickness
• Effectively Changes Sectional Camber and Modifies
  Trailing Edge Flow Development (so-called Kutta
  condition)

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Microtab Concept

• Small, Simple, Fast Response
• Retractable and Controllable
• Lightweight, Inexpensive
• Two-Position ON-OFF Actuation
• Low Power Consumption
• No Hinge Moments
• Expansion Possibilities (scalability)
• Do Not Require Significant Changes to
  Conventional Lifting Surface Design (i.e.,
  manufacturing or materials)

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Microtab Research Approach

• Wind-Tunnel Based Physical Simulations
• Pros
• Proof that concept works as advertised
• Cons
• Requires extensive experimental resources
• Can be expensive and time consuming
• Limited to modest chord Reynolds numbers
• CFD-Based Numerical Simulations
• Pros
• Relatively fast and inexpensive to study a large
  number of geometric variations
• Provides detailed insight to the flow-field
  phenomena
• Cons
• Requires extensive computational resources
  (software hardware)
• Learning curve for CFD is steep

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Microtab Research Approach

• Current Study uses a Closely-Coupled
  Collaboration Between Computational Fluid
  Dynamics (CFD) and Wind Tunnel Experimentation
• Wind Turbine Dynamic Simulation
• Pros
• Gives understanding on the effects to the entire
  system
• Cost effective in comparison to field testing
• Mature codes
• Cons
• Difficult to capture all of the physics in the
  model
• Requires insight and careful validation of the
  results

Final Goal is to Fly an Effective, Robust Active
Load Control System on a Wind Turbine
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CFD Methods

• ARC2D
• Compressible 2D RANS
• One-equation Spalart-Allmaras turbulence model
• OVERFLOW 2.0y
• Compressible 3D RANS
• Structured Chimera overset grids
• Multiple turbulence models
• Spalart-Allmaras
• Menters k-? SST model

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CFD Methods

• Grid Generation
• Chimera Grid Tools 1.9
• Structured O- and C-type grids
• 350 to 400 surface grid points
• y lt 1.0 for all viscous surfaces

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Wind Tunnel Methods

• Open Circuit, Low Subsonic
• Test Section Dimensions
• Cross section 0.86 m ? 1.22 m (2.8 ft ? 4.0 ft)
• Length 3.66 m (12 ft)
• Low Turbulence lt 0.1 FS for 80 of test section

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Wind Tunnel Methods

• Force Measurement
• Lift and moment determined using 6-component
  pyramidal balance
• Drag determined using wake measurements
• Pitot-static probe measurements
• Based on Jones Method

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Wind Tunnel -vs- CFD
S809 Baseline Airfoil 1.1 chord tab 95 x/c
lower surface Re 1106 Ma 0.17

• Results Repeatedly Show Excellent Agreement
  Between Computations and Experiment

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Full System Modeling - Background

• Wind Turbine Model
• Micon 65 Stall Regulated
• 3-bladed upwind
• Model results have been verified with field data
• Dynamic Simulation Tools
• NuMAD (Numerical Manufacturing and Design Tool)
• ANSYS FEA preprocessor
• Blade property extraction tool (BPE)
• FAST (Fatigue, Aerodynamics, Structures, and
  Turbulence)
• Modal representation
• Limited degrees of freedom
• Used as a preprocessor to ADAMS
• ADAMS (Automatic Dynamic Analysis of Mechanical
  Systems)
• Commercial multi body dynamic simulation software
• Virtually unlimited degrees of freedom

Micon 65 ADAMS Model
NuMAD FEA Model
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FAST vs- ADAMS
Codes Provide Virtually Identical Results
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Determining Blade Solidity

• Outboard Portion of the Blades is Analyzed

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Dynamic Effect of Microtabs(no control)
Microtabs Deployed for the Entire Simulation
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Controlled Microtab Results
Microtabs Response Using Simple Controller
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Future Work

• Develop and Analyze Active Control Microtab
  Airfoil Model for the Wind Tunnel Testing
• Quantify Potential Benefits of Microtabs for
  Increase Energy Capture
• Analyze other Potential Devices (flaps,
  spoilers,)
• Model Devices on a Variable Speed / Variable
  Pitch Machine (in progress)
• Develop a MATLAB Simulink Controller for Active
  Devices

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Conclusion

• Potential Advantages of Active Control have been
  Investigated
• Microtab Analysis has been Quantified both
  Computationally and Experimentally
• Potential Microtab Benefits have been
  Demonstrated on a Full System Model
• Active Devices may Provide Substantial Benefit
  for Future Wind Turbine Designs

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Thank You!!