Active Aerodynamic Load Control for Wind Turbine Blades

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. Outline • Problem Statement and Goal • Active Control Background • Microtab Motivation • CFD work • Wind tunnel results • Modeling & Tools • Future Work • Conclusion EWEC 2006 – Aerodynamics, Aero-Elasticity, Aero-Acoustics, Loads

3. 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 EWEC 2006 – Aerodynamics, Aero-Elasticity, Aero-Acoustics, Loads

4. 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) EWEC 2006 – Aerodynamics, Aero-Elasticity, Aero-Acoustics, Loads

5. 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) EWEC 2006 – Aerodynamics, Aero-Elasticity, Aero-Acoustics, Loads

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

7. Gurney Flap (Passive) • Gurney Flap (Liebeck, 1978) • Significant increases in CL • Relatively small increases in CD • Properly sized Gurney flaps  increases in L/D EWEC 2006 – Aerodynamics, Aero-Elasticity, Aero-Acoustics, Loads

8. 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) EWEC 2006 – Aerodynamics, Aero-Elasticity, Aero-Acoustics, Loads

9. 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) EWEC 2006 – Aerodynamics, Aero-Elasticity, Aero-Acoustics, Loads

10. 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 EWEC 2006 – Aerodynamics, Aero-Elasticity, Aero-Acoustics, Loads

11. 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 EWEC 2006 – Aerodynamics, Aero-Elasticity, Aero-Acoustics, Loads

12. 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 EWEC 2006 – Aerodynamics, Aero-Elasticity, Aero-Acoustics, Loads

13. 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 EWEC 2006 – Aerodynamics, Aero-Elasticity, Aero-Acoustics, Loads

14. 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 EWEC 2006 – Aerodynamics, Aero-Elasticity, Aero-Acoustics, Loads

15. 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 EWEC 2006 – Aerodynamics, Aero-Elasticity, Aero-Acoustics, Loads

16. Wind Tunnel -vs- CFD S809 Baseline Airfoil 1.1% chord tab 95% x/c lower surface Re = 1×106 Ma = 0.17 Results Repeatedly Show Excellent Agreement Between Computations and Experiment EWEC 2006 – Aerodynamics, Aero-Elasticity, Aero-Acoustics, Loads

17. 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 EWEC 2006 – Aerodynamics, Aero-Elasticity, Aero-Acoustics, Loads

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

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

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

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

22. 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 EWEC 2006 – Aerodynamics, Aero-Elasticity, Aero-Acoustics, Loads

23. 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 EWEC 2006 – Aerodynamics, Aero-Elasticity, Aero-Acoustics, Loads

24. Thank You!! EWEC 2006 – Aerodynamics, Aero-Elasticity, Aero-Acoustics, Loads