Attività di ricerca nel campo dell energia eolica presso il Dipartimento di Scienze e Tecnologie Aerospaziali del Politecnico di Milano

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Aerospaziali del Politecnico di Milano C.L. Bottasso, A.

1 POLI di MI lano tecnico Attività di ricerca nel campo dell energia eolica presso il Dipartimento di Scienze e Tecnologie Aerospaziali del Politecnico di Milano C.L. Bottasso, A. Croce Politecnico di Milano, Italy 26 Aprile 2013 In collaborazione con:

2 POLI-Wind Research Activities at a Glance

3 Wind Energy at the Department of Aerospace Science and Technology Numerical Experimental In collaboration with Dept. Mechanical Engineering

Holistic Design of Wind Turbines - Annual Energy Production (AEP) - Noise - - Generator (RPM, weight, torque, drive-train, ) - Pitch and yaw actuators - Brakes - Pitch-torque control laws: -

transients: run-up, normal and emergency shutdown procedures - GE wind turbine (from inhabitat.

4 Holistic Design of Wind Turbines - Annual Energy Production (AEP) - Noise - - Generator (RPM, weight, torque, drive-train, ) - Pitch and yaw actuators - Brakes - Pitch-torque control laws: - Regulating the machine at different set points depending on wind conditions - Reacting to gusts - Reacting to wind turbulence - Keeping actuator duty-cycles within admissible limits - Handling transients: run-up, normal and emergency shutdown procedures - GE wind turbine (from inhabitat.com) - Loads: envelope computed from large number of Design Load Cases (DLCs, IEC-61400) - Fatigue (25 year life), Damage Equivalent Loads (DELs) - Maximum blade tip deflections - Placement of natural frequencies wrt rev harmonics - Stability: flutter, LCOs, low damping of certain modes, local buckling - Complex couplings among rotor/drivetrain/tower/foundations (off-shore: hydro loads, floating & moored platforms) - Weight: massive size, composite materials (but shear quantity is an issue, fiberglass, wood, clever use of carbon fiber) - Manufacturing technology, constraints

5 Aerodynamics Maximum theoretical aerodynamic efficiency = 16/ (Betz limit) Aerodynamic efficiency in practice < 0.50 (plus mechanical and electrical losses)

6 Aerodynamics

7 Structures LM Glasfiber LM kg (1-1.5MW) LM Glasfiber LM kg (5MW)

8 Structures

turbulence Keeping actuator duty-cycles within admissible

9 Controls Regulating the machine at different set points depending on wind conditions Reacting to gusts Reacting to wind turbulence Keeping actuator duty-cycles within admissible limits Handling transients: run-up, normal and emergency shut-down procedures

10 Systems

Holistic Design of Wind Turbines Current approach to design: discipline-oriented specialist groups Lengthy loops to satisfy all requirements/constraints (months) Different simulation models Data

11 Holistic Design of Wind Turbines Current approach to design: discipline-oriented specialist groups Lengthy loops to satisfy all requirements/constraints (months) Different simulation models Data transfer/compatibility among groups There is a need for multi-disciplinary optimization tools, which must: Be fast (hours/days) (on standard desktop hardware!) Provide workable solutions in all areas (aerodynamics, structures, controls) for specialists to refine/verify Account ab-initio for all complex couplings (no fixes a posteriori) Use fully-integrated tools (no manual intervention) They will never replace the experienced designer! but would greatly speed-up design, improve exploration/knowledge of design space

12 Multi-level analysis Multi-level analysis: captures effects missed at the aeroelastic model level Fully automated links Only weak up link (e.g. 3D root corrections) Up-down fully automated links

structural dofs and load computation section Load computation

13 Structural Blade Modeling Cross section types Sectional structural dofs Spanwise shape functions Location of structural dofs and load computation section Load computation section Twisted shear webs Straight webs Caps extend to embrace full root circle

14 Cp-Lambda highlights: Geometrically exact composite-ready 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 compliant (DLCs, wind models) Rigid body Geometrically exact beam Revolute joint Flexible joint Actuator

15 ANBA (Anisotropic Beam Analysis) cross sectional model (Giavotto et al., 1983): Evaluation of cross sectional stiffness (6 by 6 fully populated) Recovery of sectional stresses and strains Compute sectional stiffness of equivalent beam model Compute cross sectional stresses and strains Rigid body Geometrically exact beam Revolute joint Flexible joint Actuator

16 Multi-Level Optimization

data: Webs + Web core + Spar caps + LE & TE reinforcements

17 3D FEM Blade Modeling 3D CAD with solid and shell (with or without offsets) meshing directly from coarse-level model data: Webs + Web core + Spar caps + LE & TE reinforcements Internal skin + Skin core + External skin = Complete model Analyses

18 Physics-based Cost Function Cost model (Fingersh at al., 2006): CoE = FixedChangeRate InitialCapitalCost p AEP p + AnnualOperatingExpenses p where p = design parameters (at the moment for rotor and tower) When possible, avoid scaling relationships and compute cost item directly from model information Example: Detailed blade geometry bill of materials blade material cost Detailed tower geometry bill of materials tower material cost Torque Gear-box mass (from mass scaling model) Etc. Ideally this should be done for all major components (when not possible, use scaling relationships)

19 2MW 45m Wind Turbine Blade CNC machined model of aluminum alloy for visual inspection of blade shape Design developed in partnership with Gurit (UK)

20 660kW 24m Wind Turbine Blade Manufactured in Italy (ETA) Design developed in partnership with ECN (NL) and Gurit (UK)

21 POLI-Wind Research Activities

22 The Politecnico di Milano Wind Tunnel

23 The Politecnico di 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

24 The Politecnico di Milano Wind Tunnel Turn-table 13 m Turbulence (boundary layer) generators Low speed testing with vertical wind profile Multiple wind turbine testing (wake-machine interaction) High speed testing Aerodynamic characterization (C p -TSR-β & C F -TSR-β curves)

25 Wind Turbine Wind Tunnel Models Turbulence (boundary layer) generators Height = 1.78 m Wind tunnel model of the Vestas V90 wind turbine Aeroelastically-scaled Real-time individual blade pitch and torque control Radius = 1m

Design of V2 Aero-elastically Scaled Composite Blade Carbon fiber spars Objective: size spars (width, chordwise position & thickness) for desired sectional stiffness within mass budget Cost function:

Carbon fiber spars for desired stiffness Sectional optimization variables (position, width, thickness) Span-wise shape function interpolation Chordwise Position Width Rohacell core with grooves for

26 Design of V2 Aero-elastically Scaled Composite Blade Carbon fiber spars 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 POLI-Wind Research Activities Airfoil cross section 1m, 70g! Carbon fiber spars for desired stiffness Sectional optimization variables (position, width, thickness) Span-wise shape function interpolation Chordwise Position Width Rohacell core with grooves for the housing of carbon fiber spars Thickness Film of glue to close pores and ensure smooth finish Modes (specimen A/B) Percent Error (specimen A/B) 236/246 Hz 4.5/0.3 % 329/339 Hz 3.1/6.1 % 545/570 Hz 1.9/6.3 % 604/627 Hz 5.1/1.2 % ANBA (ANisotropic Beam Analysis) FEM cross sectional model: Evaluation of cross sectional stiffness (6 by 6 fully populated matrix)

V2 Model Configuration Wind turbine model shown without nacelle and tower covers, for clarity Configuration as of April 2011, non-aeroelastic carbon fiber

87 m Radius = 1m Pitch actuator housed in blade root, with zero-backlash gearhead and built-in encoder Control and conditioning board for blade (not shown)

27 V2 Model Configuration Wind turbine model shown without nacelle and tower covers, for clarity Configuration as of April 2011, non-aeroelastic carbon fiber blades Height = 1.87 m Radius = 1m Pitch actuator housed in blade root, with zero-backlash gearhead and built-in encoder Control and conditioning board for blade (not shown) and shaft strain gages Conical spiral gears 6 dof balance Cone = 4 deg Pitch actuator control units, with position and speed control Main shaft with torque/bending meter Up-tilt = 6 deg Torque actuator housed in tower top, with planetary gearhead, and torque/speed control 36 channel slip ring

28 V2 Model Configuration Torque motor heating: Air flow for adequate cooling Back-to-back test bench for testing of control laws

Validation/Calibration of Modeling Tools by Wind Tunnel Testing Field (full-scale) testing Validated mathematical models Wind tunnel (scaled) testing Upscaling Wind tunnel testing: - Cons: Usually

29 Validation/Calibration of Modeling Tools by Wind Tunnel Testing Field (full-scale) testing Validated mathematical models Wind tunnel (scaled) testing Upscaling Wind tunnel testing: - Cons: Usually impossible to exactly match all relevant physics due to scaling + Pros: Better control/knowledge of conditions/errors/disturbances Much lower costs Does not replace simulation nor field testing, but works in synergy with them Wind tunnel role is not limited to aerodynamics

(Schito & Zasso 2012) Emergency shutdown Floating wind

30 Applications: Aerodynamics and Beyond Aerodynamics Wake interference conditions WT 1 WT 2 4D LES+lifting line (Schito & Zasso 2012) Emergency shutdown Floating wind turbine Individual blade pitch control Wind direction observer φ

31 Aerodynamic Performance High speed test section data Wake characterization for LES validation (in progress) Testing in yawed flow (for validation of observer)

32 Wake Interference Conditions 2 wind turbines: Wake and load measurements Control ( mini wind farm ) WT 1 WT 2 4D

33 VAWT Performance

34 POLI-Wind Research Activities at a Glance

35 Acknowledgements Thanks to the POLI-Wind team! Special thanks to M. Bassetti, P. Bettini, M. Biava, F. Campagnolo, S. Calovi, S. Cacciola, F. Cadei, G. Campanardi, M. Capponi, G. Galetto, L. Maffenini, P. Marrone, M. Mauri, S. Rota, G. Sala, A. Zasso of the Politecnico di Milano Funding provided by Vestas Wind Systems A/S, Clipper Windpower, Alstom Wind, DOE National Renewable Energy Laboratory, Italian Ministry of Education University and Research Thank you for your attention!

36 Contact Alessandro Croce Dipartimento di Scienze e Tecnologie Aerospaziali Politecnico di Milano Via G. La Masa, Milano alessandro.croce@polimi.it Tel:

tecnico lano POLI di MI tecnico Short Course on Wind Energy - Multidisciplinary Design of Wind Turbine Blades -

tecnico lano POLI di MI tecnico Short Course on Wind Energy - Multidisciplinary Design of Wind Turbine Blades - di MI tecnico POLI tecnico lano Short Course on Wind Energy - Multidisciplinary Design of Wind Turbine Blades - Carlo L. Bottasso Politecnico di Milano, Italy November 2011 Presentation Outline Holistic