Outline

1. WT2:the Wind Turbine in a Wind Tunnel ProjectC.L. Bottasso, F. CampagnoloPolitecnicodi Milano, ItalySpring 2010

2. Outline • Project goals • The wind tunnel at the Politecnicodi Milano • Wind turbine model scaling and configuration • Aerodynamics • Blade manufacturing • Simulation environment • Data acquisition, control and model management system • Conclusions and outlook

3. Project Goals • Goals: design, manufacture and test an aeroelastically-scaled model of the Vestas V90 wind turbine • Applications: • Testing and comparison of advanced control laws and supporting technologies (e.g. wind and state observers) • Testing of extreme operating conditions (e.g. high speed high yawed flow, shut-down in high winds, etc.) • Tuning of mathematical models • Testing of system identification techniques • Aeroelasticity of wind turbines • … • Possible extensions: • Multiple wind turbine interactions • Aeroelasticity of off-shore wind turbines (with prescribed motion of wind turbine base) • Effects of terrain orography on wind turbines • …

4. The Politecnicodi Milano Wind Tunnel • 1.4MW Civil-Aeronautical Wind Tunnel (CAWT): • 13.8x3.8m, 14m/s, civil section: • turbulence < 2% • with turbulence generators = 25% • - 13m turntable • 4x3.8m, 55m/s, aeronautical section: • turbulence <0.1% • open-closed test section

5. The Politecnicodi Milano Wind Tunnel • Turn-table 13 m • Turbulence (boundary layer) generators • Low speed testing in the presence of vertical wind profile • Multiple wind turbine testing (wake-machine interaction) • High speed testing • Aerodynamic characterization (Cp-TSR-β & CF-TSR-βcurves)

6. Outline • Project goals • The wind tunnel at the Politecnicodi Milano • Wind turbine model scaling and configuration • Aerodynamics • Blade manufacturing • Simulation environment • Data acquisition, control and model management system • Conclusions and outlook

7. Model Scaling • Criteria for definition of scaling (using Buckingham ΠTheorem): • Best compromise between: • Reynolds mismatch (quality of aerodynamics) • Speed-up of scaled time (avoid excessive increase of control bandwith) • Aeroelastic effects: correct relative placement of frequencies wrt rev harmonics, correct Lock number • Reynolds mismatch: • Use low-Re airfoils (AH79 & WM006) to minimize aerodynamic differences • Keep same chord distribution as original V90 blade, but • Adjust blade twist to optimize axial induction factor

8. V2 Model Configuration CONICAL SPIRAL TOOTHED GEARS • Electronic board for blade strain gages • Rotor radius = 1m • Height = 2.8 m • Up-tilt = 6 deg • Balance • (6 force/moment components)

9. V2 Model Configuration • Pitch actuator control units: • Faulhaber MCDC-3003 C • 30 V – 10 A Max • Position and speed • Cone = 4 deg • Main shaft with torque meter • Slip ring Moog AC6355: • 36 Channels • 250 V – 2 A Max • Conical spiral gears • Torque actuator: • Portescap Brushless B1515-150 • Pn = 340 W • Planetary gearhead • Torque and speed control • Pitch actuator: • Faulhaber 1524 • Zero backlash gearhead • Built-in encoder IE 512

10. V2 Model Configuration

11. V2 Model Configuration Wind turbine model shown without nacelle and tower covers, for clarity

12. Outline • Project goals • The wind tunnel at the Politecnicodi Milano • Wind turbine model scaling and configuration • Aerodynamics • Blade manufacturing • Simulation environment • Data acquisition, control and model management system • Conclusions and outlook

13. BEM Predicted Aerodynamic Performance • Goodagreement in full load region III • Pooreragreement in partial load regions II and II1/2, due to higher drag of V2 airfoils • Region II • CPopt • λopt • βopt Region II1/2 P<Pr Ω=Ωr CP RegionIII P=Pr Ω=Ωr TSR

14. Filippo Campagnolo BEM Predicted Aerodynamic Performance • Goodagreement between thrust coefficients in the entire working region, due to good lift characteristics of V2 airfoils CF • Region II • CPopt • λopt • βopt Region II1/2 P<Pr Ω=Ωr RegionIII P=Pr Ω=Ωr TSR

15. Aerodynamic Identification • Goal: identification of airfoil aerodynamic characteristics • Application: blade redesign, choice of airfoils, understanding of rotor aerodynamics • Approach: use wind tunnel measurements of the wind turbine response • Pros: • Avoid testing of individual airfoils • Include 3D and rotational effects • Procedure: • Measure power and thrust coefficients • Parameterize airfoil lift and drag coefficients • Identify airfoil aerodynamic parameters that best match wind turbine performance, using a BEM model of the rotor • (Work in progress, results expected summer 2010)

16. Constrained optimization: • Goal: match CP & CF at tested TSR & β • Unknowns: parameters describing airfoil CL & CD characteristics • Rotor model: BEM • Experimental CP & CF coefficients • Trim at varying pitch βand TSR • Measure power CP and thrust CF CL Design data Identified data a CD a

17. Outline • Project goals • The wind tunnel at the Politecnicodi Milano • Wind turbine model scaling and configuration • Aerodynamics • Blade manufacturing • Simulation environment • Data acquisition, control and model management system • Conclusions and outlook

18. Blade Manufacturing • Rigid blades: • Easier and faster to manufacture than aero-elastically scaled blades • Used for initial testing and verification of suitable aerodynamic performance • Implemented two manufacturing solutions: • 1. CNC machining of light aluminum alloy 2. UD carbon fiber • Carbon blades (will include blade-root strain gage in 2nd blade set – May 2010) • FEM verification of strain gage sensitivity • CAD model for CNC machining, with support tabs (+resin support)

19. Blade Manufacturing • Aero-elastically scaled blades: • Need accurate aerodynamic shape: classical segmented solution is unsuitable • Structural requirements: match at least lower three modes • Very challenging problem: only 70g of weight for 1m of span! • Solution: • Rohacell core with carbon fiber spars and film coating • Sizing using constrained optimization • (Work in progress, expected completion of blade set by end of 2010)

20. Design of the V2 Aero-elastically Scaled Composite Blade • Objective: size spars (width, chordwise position & thickness) for desired sectional stiffness within mass budget • Cost function: sectional stiffness error wrt target (scaled stiffness) • Constraints: lowest 3 frequencies • Carbon fiber spars for desired stiffness Sectional optimization variables (position, width, thickness) Span-wise shape function interpolation • Rohacell core with grooves for the housing of carbon fiber spars Width Chordwise Position • ANBA(ANisotropicBeam Analysis) FEM cross sectional model: • Evaluation of cross sectional stiffness (6 by 6 fully populated matrix) Thickness • Thermo-retractable film

21. Design of the V2 Aero-elastically Scaled Composite Blade • Solid line: scaled reference values • Mass gap can be corrected with weights • Dash-dotted line: optimal sizing Filippo Campagnolo

22. Design of the V2 Aero-elastically Scaled Composite Blade • Approach: • Demonstration of technology on simple specimen: • Design specimen (uniform cross section, untwisted) of typical properties (mass, stiffness) • Characterize material properties • Manufacture specimen • Characterize specimen (mass, stiffness, frequencies, shape) • Verify accuracy wrt design • Status: completed • Demonstration of technology on blade-like specimen (twist, variable chord) • Status: in progress • Manufacture wind turbine model blade • Status: to be done (expected end 2010) Filippo Campagnolo

23. Demonstration of Technology on Simple Specimen • Characterizationof material properties: • Specimen of uniform properties: • Results: • Good matching of lowest natural frequencies • Acceptable repeatability • Good shape and finishing Static testing Temperature–dependent characterization Dynamic testing • Carbon fiber spars • Airfoil cross section

24. Outline • Project goals • The wind tunnel at the Politecnicodi Milano • Wind turbine model scaling and configuration • Aerodynamics • Blade manufacturing • Simulation environment • Data acquisition, control and model management system • Conclusions and outlook

25. Simulation Environment Comprehensive aero-elastic simulation environment: supports all phases of the wind turbine model design (loads, aero-elasticity, and control) Measurement noise Wind

26. Simulation Models • Cp-Lambda highlights: • Geometrically exact composite-ready FEM beam models • Generic topology (Cartesian coordinates+Lagrange multipliers) • Dynamic wake model (Peters-He, yawed flow conditions) • Efficient large-scale DAE solver • Non-linearly stable time integrator • Fully IEC 61400 compliant (DLCs, wind models) Cp-Lambda (Code for Performance, Loads, Aero-elasticity by Multi-Body Dynamic Analysis): Global aero-servo-elastic FEM model Compute sectional stiffness • Rigid body • Geometrically exact beam • Revolute joint • Flexible joint • Actuator ANBA (ANisotropicBeam Analysis) cross sectional model Recover cross sectional stresses/strains

27. Simulation Environment • Example: verify adequacy of model for the testing of control laws • Question: does testing of control laws on V2 lead to similar conclusions than V90 testing, notwithstanding differences in aerodynamics (Reynolds)? • Approach: • Choose comparison metrics • Simulate response of scaled and full-scale models • Compare responses upon back-scaling • Draw conclusions • Example: LQR controller outperforms PID by similar amount on V2 and V90 Aeroelastic Simulation Performance Model Parameters Scaling Laws Aeroelastic Simulation Inverse Scaling Laws

28. Outline • Project goals • The wind tunnel at the Politecnicodi Milano • Wind turbine model scaling and configuration • Aerodynamics • Blade manufacturing • Simulation environment • Data acquisition, control and model management system • Conclusions and outlook

29. Data Acquisition, Control and Model Management System • Wind tunnel control panel • Pitch demand • Torque demand • Remote Control Unit: • Management of experiment (choice of control logic, choice of trim points, etc.) • Data logging, post-processing and visualization • Emergency shut-down • Wind turbine sensor readings: • Shaft torque-meter • Balance strain gages • Blade strain gages (May 2010) • Rotor RPM and azimuth • Blade pitch • Nacelle accelerometer • Wind tunnel sensor readings: • Wind speed • Temperature, humidity Ethernet • Control PC: • Real time Linux OS (RTAI) • Supervisory control • Control logic: • - Normal mode: pitch-torque control law • - Trimming mode: RPM regulation and pitch setting

30. Outline • Project goals • The wind tunnel at the Politecnicodi Milano • Wind turbine model scaling and configuration • Aerodynamics • Blade manufacturing • Simulation environment • Data acquisition, control and model management system • Conclusions and outlook

31. Conclusions and Outlook • Work is in progress on many fronts, no meaningful conclusions can be drawn at the moment • Work plan: • Initial entry in the wind tunnel by April 2010 (rigid blades, trimming control mode) • - Verification of functionality of all systems, troubleshooting, software debugging • - Verification of aerodynamic performance (measurement of CP-TSR-β & CF-TSR-βcurves) • Second entry in May 2010 after fixes/improvements (rigid blades with root strain gages, trimming and normal control modes) • Aerodynamic identification: possible redesign of rotor blades to improve aerodynamic model fidelity (airfoils, transition strips, flaps, etc.) • Blade design and manufacturing: • Implement strain gages in composite rigid blades • Continue development of flexible composite blades • Add strain gages and/or fiber optics to flexible composite blades • Control and management system: complete and improve GUI and functionalities • Full model capabilities: expected end 2010

32. Acknowledgements Research funded by Vestas Wind Systems A/S The authors gratefully acknowledge the contribution of S. Calovi and S. Cacciola, G. Galetto, L. Maffenini, P. Marrone, M. Mauri, M. Monguzzi, D. Rocchi, S. Rota, G. Sala of the Politecnicodi Milano