1. 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.

2. March 01, 2006EWEC 2006 – Aerodynamics, Aero-Elasticity, Aero-Acoustics, Loads2 Outline  Problem Statement and Goal  Active Control Background  Microtab Motivation  CFD work  Wind tunnel results  Modeling & Tools  Future Work  Conclusion

3. March 01, 2006EWEC 2006 – Aerodynamics, Aero-Elasticity, Aero-Acoustics, Loads3 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

4. March 01, 2006EWEC 2006 – Aerodynamics, Aero-Elasticity, Aero-Acoustics, Loads4 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 (VG’s, surface heating, plasma)

5. March 01, 2006EWEC 2006 – Aerodynamics, Aero-Elasticity, Aero-Acoustics, Loads5 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)

6. March 01, 2006EWEC 2006 – Aerodynamics, Aero-Elasticity, Aero-Acoustics, Loads6 Active Flow/Load Control Microtab Concept being Proposed Active Aileron on a Zond 750 Blade Courtesy: NREL

7. March 01, 2006EWEC 2006 – Aerodynamics, Aero-Elasticity, Aero-Acoustics, Loads7 Gurney Flap (Passive) Gurney Flap (Liebeck, 1978) –Significant increases in C L –Relatively small increases in C D –Properly sized Gurney flaps  increases in L/D

8. March 01, 2006EWEC 2006 – Aerodynamics, Aero-Elasticity, Aero-Acoustics, Loads8 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)

9. March 01, 2006EWEC 2006 – Aerodynamics, Aero-Elasticity, Aero-Acoustics, Loads9 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)

10. March 01, 2006EWEC 2006 – Aerodynamics, Aero-Elasticity, Aero-Acoustics, Loads10 Microtab Research Approach  Wind-Tunnel Based Physical Simulations:  Pro’s  Proof that concept works as “advertised”  Con’s  Requires extensive experimental resources  Can be expensive and time consuming  Limited to modest chord Reynolds numbers  CFD-Based Numerical Simulations:  Pro’s  Relatively fast and inexpensive to study a large number of geometric variations  Provides detailed insight to the flow-field phenomena  Con’s  Requires extensive computational resources (software & hardware)  Learning curve for CFD is steep

11. March 01, 2006EWEC 2006 – Aerodynamics, Aero-Elasticity, Aero-Acoustics, Loads11 Microtab Research Approach  Current Study uses a Closely-Coupled Collaboration Between Computational Fluid Dynamics (CFD) and Wind Tunnel Experimentation  Wind Turbine Dynamic Simulation  Pro’s  Gives understanding on the effects to the entire system  Cost effective in comparison to field testing  Mature codes  Con’s  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

12. March 01, 2006EWEC 2006 – Aerodynamics, Aero-Elasticity, Aero-Acoustics, Loads12 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  Menter’s k-  SST model

13. March 01, 2006EWEC 2006 – Aerodynamics, Aero-Elasticity, Aero-Acoustics, Loads13 CFD Methods  Grid Generation  Chimera Grid Tools 1.9  Structured O- and C-type grids  350 to 400 surface grid points  y + < 1.0 for all viscous surfaces

14. March 01, 2006EWEC 2006 – Aerodynamics, Aero-Elasticity, Aero-Acoustics, Loads14 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 < 0.1% FS for 80% of test section

15. March 01, 2006EWEC 2006 – Aerodynamics, Aero-Elasticity, Aero-Acoustics, Loads15 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

16. March 01, 2006EWEC 2006 – Aerodynamics, Aero-Elasticity, Aero-Acoustics, Loads16 Wind Tunnel -vs- CFD Results Repeatedly Show Excellent Agreement Between Computations and Experiment S809 Baseline Airfoil 1.1% chord tab 95% x/c lower surface Re = 1×10 6 Ma = 0.17

17. March 01, 2006EWEC 2006 – Aerodynamics, Aero-Elasticity, Aero-Acoustics, Loads17 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

18. March 01, 2006EWEC 2006 – Aerodynamics, Aero-Elasticity, Aero-Acoustics, Loads18 FAST –vs- ADAMS Codes Provide Virtually Identical Results

19. March 01, 2006EWEC 2006 – Aerodynamics, Aero-Elasticity, Aero-Acoustics, Loads19 Determining Blade Solidity Outboard Portion of the Blades is Analyzed

20. March 01, 2006EWEC 2006 – Aerodynamics, Aero-Elasticity, Aero-Acoustics, Loads20 Dynamic Effect of Microtabs (no control) Microtabs Deployed for the Entire Simulation

21. March 01, 2006EWEC 2006 – Aerodynamics, Aero-Elasticity, Aero-Acoustics, Loads21 Controlled Microtab Results Microtabs Response Using Simple Controller

22. March 01, 2006EWEC 2006 – Aerodynamics, Aero-Elasticity, Aero-Acoustics, Loads22 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

23. March 01, 2006EWEC 2006 – Aerodynamics, Aero-Elasticity, Aero-Acoustics, Loads23 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

24. March 01, 2006EWEC 2006 – Aerodynamics, Aero-Elasticity, Aero-Acoustics, Loads24 Thank You!!