POLItecnico
di MIlano
WT2:
the Wind Turbine
in a Wind Tunnel Project
C.L. Bottasso, F. Campagnolo
Politecnico di Milano, Italy
Spring 2010
WT2: Wind Turbine in a Wind Tunnel
Outline
• 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
POLITECNICO di MILANO
Poli-Wind Research Lab
WT2: Wind Turbine in a Wind Tunnel
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
-…
POLITECNICO di MILANO
Poli-Wind Research Lab
WT2: Wind Turbine in a 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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Poli-Wind Research Lab
The Politecnico di Milano Wind Tunnel
WT2: Wind Turbine in a 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-β curves)
POLITECNICO di MILANO
Poli-Wind Research Lab
WT2: Wind Turbine in a Wind Tunnel
Outline
• 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
POLITECNICO di MILANO
Poli-Wind Research Lab
Model Scaling
WT2: Wind Turbine in a Wind Tunnel
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
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]
11.6
Nominal Torque
5.06 [Nm]
1790 [KNm]
1/1.97
Average Reynolds
 5÷6 e4
 4÷5 e6
Quantity
Scaling 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
Mach Ratio
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
POLITECNICO di MILANO
Poli-Wind Research Lab
WT2: Wind Turbine in a Wind Tunnel
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)
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Poli-Wind Research Lab
V2 Model Configuration
Pitch actuator control units:
• Faulhaber MCDC-3003 C
• 30 V – 10 A Max
• Position and speed
WT2: Wind Turbine in a Wind Tunnel
Cone = 4 deg
Main shaft with
torque meter
Slip ring Moog AC6355:
• 36 Channels
• 250 V – 2 A Max
Conical spiral gears
Pitch actuator:
• Faulhaber 1524
• Zero backlash gearhead
• Built-in encoder IE 512
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Torque actuator:
• Portescap Brushless B1515-150
• Pn = 340 W
• Planetary gearhead
• Torque and speed control
Poli-Wind Research Lab
WT2: Wind Turbine in a Wind Tunnel
V2 Model Configuration
POLITECNICO di MILANO
Poli-Wind Research Lab
WT2: Wind Turbine in a Wind Tunnel
V2 Model Configuration
Wind turbine model shown without
nacelle and tower covers, for clarity
POLITECNICO di MILANO
Poli-Wind Research Lab
WT2: Wind Turbine in a Wind Tunnel
Outline
• 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
POLITECNICO di MILANO
Poli-Wind Research Lab
• Good agreement in full load region III
• Poorer agreement in partial load regions II
and II1/2, due to higher drag of V2 airfoils
Region II1/2
P<Pr
Ω=Ωr
CP
WT2: Wind Turbine in a Wind Tunnel
BEM Predicted Aerodynamic Performance
Region II
CPopt
λopt
βopt
Region III
P=Pr
Ω=Ωr
TSR
POLITECNICO di MILANO
Poli-Wind Research Lab
Good agreement between thrust coefficients
in the entire working region, due to good lift
characteristics of V2 airfoils
CF
WT2: Wind Turbine in a Wind Tunnel
BEM Predicted Aerodynamic Performance
Region II1/2
P<Pr
Ω=Ωr
Region II
CPopt
λopt
βopt
Region III
P=Pr
Ω=Ωr
TSR
POLITECNICO di MILANO
Filippo Campagnolo
Poli-Wind Research Lab
Aerodynamic Identification
WT2: Wind Turbine in a Wind Tunnel
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)
POLITECNICO di MILANO
Poli-Wind Research Lab
WT2: Wind Turbine in a Wind Tunnel
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
CL
Design data
Identified data
a
CD
a
POLITECNICO di MILANO
Poli-Wind Research Lab
WT2: Wind Turbine in a Wind Tunnel
Outline
• 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
POLITECNICO di MILANO
Poli-Wind Research Lab
Blade Manufacturing
WT2: Wind Turbine in a Wind Tunnel
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)
CAD model for CNC
machining, with support tabs
(+resin support)
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FEM verification of strain gage
sensitivity
Poli-Wind Research Lab
WT2: Wind Turbine in a Wind Tunnel
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)
POLITECNICO di MILANO
Poli-Wind Research Lab
WT2: Wind Turbine in a Wind Tunnel
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
Chordwise Position
Width
Rohacell core with grooves
for the housing of carbon
fiber spars
Thickness
Thermo-retractable film
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ANBA (ANisotropic Beam Analysis) FEM
cross sectional model:
• Evaluation of cross sectional stiffness
(6 by 6 fully populated matrix)
Poli-Wind Research Lab
WT2: Wind Turbine in a Wind Tunnel
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
POLITECNICO di MILANO
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
Poli-Wind Research Lab
Design of the V2 Aero-elastically Scaled
Composite Blade
WT2: Wind Turbine in a Wind Tunnel
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
1. 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)
POLITECNICO di MILANO
Filippo Campagnolo
Poli-Wind Research Lab
Demonstration of Technology on Simple
Specimen
Characterization of material properties:
WT2: Wind Turbine in a Wind Tunnel
Dynamic testing
Static testing
Temperature–dependent characterization
Carbon fiber spars
Specimen of uniform properties:
Airfoil cross section
Results:
•
Good matching of lowest natural frequencies
•
Acceptable repeatability
•
Good shape and finishing
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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 %
Poli-Wind Research Lab
WT2: Wind Turbine in a Wind Tunnel
Outline
• 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
POLITECNICO di MILANO
Poli-Wind Research Lab
WT2: Wind Turbine in a Wind Tunnel
Simulation Environment
Comprehensive aero-elastic simulation environment:
supports all phases of the wind turbine model design
(loads, aero-elasticity, and control)
Measurement
noise
POLITECNICO di MILANO
Wind
Poli-Wind Research Lab
Simulation Models
Cp-Lambda highlights:
WT2: Wind Turbine in a Wind Tunnel
• 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)
Compute
sectional
stiffness
• Rigid body
ANBA (ANisotropic Beam Analysis)
cross sectional model
• Geometrically exact beam
Recover cross
sectional
stresses/strains
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• Revolute joint
• Flexible joint
• ActuatorPoli-Wind Research Lab
Simulation Environment
WT2: Wind Turbine in a Wind Tunnel
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
Example: LQR controller
outperforms PID by similar
amount on V2 and V90
• Simulate response of scaled and full-scale models
• Compare responses upon back-scaling
• Draw conclusions
Aeroelastic
Simulation
Model
Parameters
Performance
Scaling
Laws
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Aeroelastic
Simulation
Inverse
Scaling Laws
Poli-Wind Research Lab
WT2: Wind Turbine in a Wind Tunnel
Outline
• 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
POLITECNICO di MILANO
Poli-Wind Research Lab
WT2: Wind Turbine in a Wind Tunnel
Data Acquisition, Control and Model
Management System
Wind tunnel
control panel
• Pitch demand
• Torque demand
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
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Remote Control Unit:
• Management of experiment
(choice of control logic, choice
of trim points, etc.)
• Data logging, post-processing
and visualization
• Emergency shut-down
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
Poli-Wind Research Lab
WT2: Wind Turbine in a Wind Tunnel
Outline
• 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
POLITECNICO di MILANO
Poli-Wind Research Lab
WT2: Wind Turbine in a Wind Tunnel
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 C P-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
POLITECNICO di MILANO
Poli-Wind Research Lab
WT2: Wind Turbine in a Wind Tunnel
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 Politecnico di Milano
POLITECNICO di MILANO
Poli-Wind Research Lab