poli di mi tecnicolanotecnicolano wt 2 : the wind turbine in a wind tunnel project c.l. bottasso, f....
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PO
LI
di M
Itecn
ico
lano
WT2:the Wind Turbine in a Wind Tunnel
Project
C.L. Bottasso, F. CampagnoloPolitecnico di Milano, Italy
Spring 2010
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POLITECNICO di MILANO Poli-Wind Research Lab
OutlineOutline
• Project goals
• The wind tunnel at the Politecnico di Milano
• Wind turbine model scaling and configuration
• Aerodynamics
• Blade manufacturing
• Simulation environment
• Data acquisition, control and model management system
• Conclusions and outlook
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POLITECNICO di MILANO Poli-Wind Research Lab
Project GoalsProject 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 - …
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POLITECNICO di MILANO Poli-Wind Research Lab
The Politecnico di Milano Wind Tunnel
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
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POLITECNICO di MILANO Poli-Wind Research Lab
Turbulence (boundary layer) generators
The Politecnico di Milano Wind Tunnel
The Politecnico di Milano Wind Tunnel
Turn-table
13 m
• 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-β curves)
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POLITECNICO di MILANO Poli-Wind Research Lab
OutlineOutline
• Project goals
• The wind tunnel at the Politecnico di Milano
• Wind turbine model scaling and configuration
• Aerodynamics
• Blade manufacturing
• Simulation environment
• Data acquisition, control and model management system
• Conclusions and outlook
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POLITECNICO di MILANO Poli-Wind Research Lab
Model ScalingModel Scaling
V2 V90
Rotor Diameter 2 [m] 90 [m]
Blade Length 977.8 [mm] 44 [m]
Rotor Overhang 75.1 [mm] 3.38 [m]
Hub Height 1.78 [m] 79.94 [m]
Rotor Speed 367 [rpm] 16 [rpm]
Nominal Power 193.8 [W] 3 [MW]
Nominal Torque 5.06 [Nm] 1790 [KNm]
Average Reynolds 5÷6 e4 4÷5 e6
QuantityScaling factor
Length Ratio 1/45
Time Ratio 1/22.84
Velocity Ratio 1/1.97
Power Ratio 1/15477
Rotor Speed Ratio 22.84
Torque Ratio 1/353574
Reynolds Ratio 1/88.64
Froude Ratio 11.6
Mach Ratio 1/1.97
Criteria for definition of scaling (using Buckingham Π Theorem):• 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
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POLITECNICO di MILANO Poli-Wind Research Lab
CONICAL SPIRAL TOOTHED GEARS
Rotor radius = 1m
Balance (6 force/moment
components)
Height = 2.8 m
Up-tilt = 6 deg
Electronic board for blade strain
gages
V2 Model ConfigurationV2 Model Configuration
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Conical spiral gears
Main shaft with torque meter
Pitch actuator control units:• Faulhaber MCDC-
3003 C• 30 V – 10 A Max• Position and speed
Slip ring Moog AC6355:• 36 Channels• 250 V – 2 A Max
Torque actuator:• Portescap Brushless
B1515-150 • Pn = 340 W• Planetary gearhead • Torque and speed control
Cone = 4 deg
V2 Model ConfigurationV2 Model Configuration
Pitch actuator:• Faulhaber 1524• Zero backlash
gearhead• Built-in encoder IE
512
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V2 Model ConfigurationV2 Model Configuration
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POLITECNICO di MILANO Poli-Wind Research Lab
V2 Model ConfigurationV2 Model Configuration
Wind turbine model shown without nacelle and tower covers, for clarity
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OutlineOutline
• Project goals
• The wind tunnel at the Politecnico di Milano
• Wind turbine model scaling and configuration
• Aerodynamics
• Blade manufacturing
• Simulation environment
• Data acquisition, control and model management system
• Conclusions and outlook
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CP
TSR
Region II1/2P<Pr
Ω=Ωr
Region III
P=Pr
Ω=Ωr
BEM Predicted Aerodynamic Performance
BEM Predicted Aerodynamic Performance
Region IICPopt
λopt
βopt
• Good agreement in full load region III
• Poorer agreement in partial load regions II and II1/2, due to higher drag of V2 airfoils
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POLITECNICO di MILANO Poli-Wind Research Lab Filippo Campagnolo
BEM Predicted Aerodynamic Performance
BEM Predicted Aerodynamic Performance
CF
TSR
Region II1/2P<Pr
Ω=Ωr
Region III
P=Pr
Ω=Ωr
Region IICPopt
λopt
βopt
Good agreement between thrust coefficients in the entire working region, due to good lift characteristics of V2 airfoils
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Aerodynamic IdentificationAerodynamic 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:
1. Measure power and thrust coefficients
2. Parameterize airfoil lift and drag coefficients
3. Identify airfoil aerodynamic parameters that best match wind turbine performance, using a BEM model of the rotor
(Work in progress, results expected summer 2010)
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Aerodynamic identification
2.Experimental power CP and thrust
CF coefficients
3. Maximum Likelihood
identification
4. Identified aerodynamic coefficients of
airfoils
5. Redesign blade to improve matching
wrt V90
1. Wind tunnel testing
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 β and TSR
• Measure power CP and thrust CF
CD
a
a
Design dataIdentified data
CL
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POLITECNICO di MILANO Poli-Wind Research Lab
OutlineOutline
• Project goals
• The wind tunnel at the Politecnico di Milano
• Wind turbine model scaling and configuration
• Aerodynamics
• Blade manufacturing
• Simulation environment
• Data acquisition, control and model management system
• Conclusions and outlook
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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
Blade ManufacturingBlade Manufacturing
CAD model for CNC machining, with support tabs (+resin support)
Carbon blades (will include blade-root strain gage in 2nd blade set – May 2010)
FEM verification of strain gage sensitivity
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POLITECNICO di MILANO Poli-Wind Research Lab
Blade ManufacturingBlade 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)
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POLITECNICO di MILANO Poli-Wind Research Lab
Structuraloptimization
Design of the V2 Aero-elastically Scaled Composite Blade
WidthChordwise Position
Thickness
Sectional optimization variables (position, width, thickness)Span-wise shape function interpolation
Optimization
Cross sectional analysis
Equivalent beam model
ANBA (ANisotropic Beam Analysis) FEM cross sectional model:• Evaluation of cross sectional
stiffness (6 by 6 fully populated matrix)
Objective: size spars (width, chordwise position & thickness) for desired sectional stiffness within mass budgetCost function: sectional stiffness error wrt target (scaled stiffness)Constraints: lowest 3 frequencies
Rohacell core with grooves for the housing of carbon fiber spars
Thermo-retractable film
Carbon fiber spars for desired stiffness
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POLITECNICO di MILANO Poli-Wind Research Lab
Design of the V2 Aero-elastically Scaled Composite Blade
Filippo Campagnolo
Modes Reference [Hz]Optimization
procedure [Hz]
1st Flap-wise
23.2 23.1
2nd Flap-wise
59.4 59.1
1st Edge-wise
33.1 33.1
Mass gap can be corrected with weights
Solid line: scaled reference values
Dash-dotted line: optimal sizing
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POLITECNICO di MILANO Poli-Wind Research Lab
Design of the V2 Aero-elastically Scaled Composite Blade
Filippo Campagnolo
Approach:
1. 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
2. Demonstration of technology on blade-like specimen (twist, variable chord)
Status: in progress
3. Manufacture wind turbine model blade
Status: to be done (expected end 2010)
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Characterization of material properties:
Specimen of uniform properties:
Results:
• Good matching of lowest natural frequencies
• Acceptable repeatability
• Good shape and finishing
Demonstration of Technology on Simple Specimen
Demonstration of Technology on Simple Specimen
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 %
Dynamic testing Static testing Temperature–dependent characterization
Carbon fiber spars
Airfoil cross section
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POLITECNICO di MILANO Poli-Wind Research Lab
OutlineOutline
• Project goals
• The wind tunnel at the Politecnico di Milano
• Wind turbine model scaling and configuration
• Aerodynamics
• Blade manufacturing
• Simulation environment
• Data acquisition, control and model management system
• Conclusions and outlook
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POLITECNICO di MILANO Poli-Wind Research Lab
Controller
Sensor modelsVirtual plant
Cp-Lambda model
WindMeasureme
nt noise
SupervisorStart-up, power production,
normal shut-down, emergency shut-down, …
Pitch-torque controller
Simulation EnvironmentSimulation Environment
Comprehensive aero-elastic simulation environment: supports all phases of the wind turbine model design (loads, aero-elasticity, and control)
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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
• Rigid body
• Geometrically exact beam
• Revolute joint
• Flexible joint
• Actuator
ANBA (ANisotropic Beam Analysis) cross sectional model
Compute sectional stiffness
Recover cross sectional
stresses/strains
Simulation ModelsSimulation Models
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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
Simulation EnvironmentSimulation Environment
ModelParameters
AeroelasticSimulation
AeroelasticSimulation
ScalingLaws
InverseScaling Laws
Performance
Example: LQR controller outperforms PID by similar amount on V2 and V90
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POLITECNICO di MILANO Poli-Wind Research Lab
OutlineOutline
• Project goals
• The wind tunnel at the Politecnico di Milano
• Wind turbine model scaling and configuration
• Aerodynamics
• Blade manufacturing
• Simulation environment
• Data acquisition, control and model management system
• Conclusions and outlook
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Data Acquisition, Control and Model Management System
Data Acquisition, Control and Model Management System
Control PC:• Real time Linux OS (RTAI)• Supervisory control• Control logic:- Normal mode: pitch-torque control law- Trimming mode: RPM regulation and pitch setting
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 tunnel control panel
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
• Pitch demand• Torque
demand
Ethernet
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POLITECNICO di MILANO Poli-Wind Research Lab
OutlineOutline
• Project goals
• The wind tunnel at the Politecnico di Milano
• Wind turbine model scaling and configuration
• Aerodynamics
• Blade manufacturing
• Simulation environment
• Data acquisition, control and model management system
• Conclusions and outlook
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Conclusions and OutlookConclusions 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-β curves)• 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
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AcknowledgementsAcknowledgements
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 Politecnico di Milano