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Aero-Elastic Optimization of a 10 MW Wind Turbine
Frederik Zahle, Carlo Tibaldi
David Verelst, Christian Bak
Robert Bitsche, José Pedro Albergaria Amaral Blasques
Wind Energy Department
Technical University of Denmark
IQPC Workshop for Advances in Rotor Blades
for Wind Turbines
24-26 February 2015
Bremen, Germany
Introduction
This Talk
Design Challenge
What are the multidisciplinary trade-offs between rotor mass and AEP for a
10 MW rotor mounted on the DTU 10MW RWT platform?
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F Zahle et al.
Wind Energy Department · DTU
Aero-Elastic Optimization of a 10 MW Wind Turbine
Introduction
This Talk
Design Challenge
DTU 10MW Reference Wind Turbine,
Optimization cases:
What are the multidisciplinary trade-offs between rotor mass and AEP for a
10 MW rotor mounted on the DTU 10MW RWT platform?
Structural optimization of the rotor,
Aero-structural optimization of the rotor,
Fatigue constrained aero-structural optimization of the rotor,
Frequency constrained aero-structural optimization of the rotor.
Conclusions.
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F Zahle et al.
Wind Energy Department · DTU
Aero-Elastic Optimization of a 10 MW Wind Turbine
Fully open source, available at
http://dtu-10mwrwt.vindenergi.dtu.dk,
Detailed geometry,
Previous Work
The DTU 10MW Reference Wind Turbine
300+ users,
Aeroelastic model,
3D rotor CFD mesh,
Detailed structural description,
ABAQUS model,
Used as reference turbine in the
EU projects INNWIND.eu,
MarWint, and IRPWIND, among
others.
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F Zahle et al.
Wind Energy Department · DTU
Aero-Elastic Optimization of a 10 MW Wind Turbine
Previous Work
The DTU 10MW Reference Wind Turbine
Parameter
Wind Regime
Rotor Orientation
Control
Cut in wind speed
Cut out wind speed
Rated wind speed
Rated power
Number of blades
Rotor Diameter
Hub Diameter
Hub Height
Drivetrain
Minimum Rotor Speed
Maximum Rotor Speed
Maximum Generator Speed
Gearbox Ratio
Maximum Tip Speed
Hub Overhang
Shaft Tilt Angle
Rotor Precone Angle
Blade Prebend
Rotor Mass
Nacelle Mass
Tower Mass
Airfoils
Value
IEC Class 1A
Clockwise rotation - Upwind
Variable Speed
Collective Pitch
4 m/s
25 m/s
11.4 m/s
10 MW
3
178.3 m
5.6 m
119.0 m
Medium Speed, Multiple-Stage Gearbox
6.0 rpm
9.6 rpm
480.0 rpm
50
90.0 m/s
7.1 m
5.0 deg.
-2.5 deg.
3.332 m
227,962 kg
446,036 kg
628,442 kg
FFA-W3
Table: Key parameters of the DTU 10 MW Reference Wind Turbine.
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F Zahle et al.
Wind Energy Department · DTU
Aero-Elastic Optimization of a 10 MW Wind Turbine
Results
Case 1: Pure Structural Optimization with Fixed Outer
Shape
Minimise (Case 1a)
Minimise (Case 1b)
Mblade−ref
Mblade
Mmomblade−ref
− Mmom
blade
−
with respect to
x = {tmat , DPcaps } (47 dvs)
subject to
Constraints on:
Tip deflection at rated power,
Tip torsion at rated,
Extreme wind tip deflection,
Ultimate strength,
Basic spar cap buckling: tcap /wcap > 0.08,
Pmek
> 1.
P
mek −ref
Tmax
Tmax −ref
< 1.
HAWCStab2 load cases: 7 operational cases, 1 extreme 70 m/s 15 deg yaw error
5 pre-computed extreme load cases for stress analysis.
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F Zahle et al.
Wind Energy Department · DTU
Aero-Elastic Optimization of a 10 MW Wind Turbine
Minimization of either mass or mass moment results in drastically
different designs.
Mass minimization: 17% reduction in mass, 0.6% increase in mass
moment,
Mass moment minimization: 9% reduction in mass, 13% reduction in
mass moment.
Mass minimization tends to remove mass primarily from the inner 50%
span.
Mass moment minimization removes mass more evenly, which will
contribute to a reduction in fatigue.
Blade mass
1400
1000
dm [kg/m]
0.09
Mass
Mass moment
DTU 10MW RWT
1200
0.08
0.07
Spar cap uniax thickness [m]
Results
Case 1: Mass Distribution
0.06
800
0.05
0.04
600
0.03
400
0.02
200
0
0.0
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DTU 10MW RWT
Mass
Mass moment
0.01
0.2
0.4
r/R [-]
0.6
0.8
F Zahle et al.
Wind Energy Department · DTU
1.0
0.000.0
0.2
0.4
r/R [-]
0.6
0.8
1.0
Aero-Elastic Optimization of a 10 MW Wind Turbine
Results
Case 2: Shape and structural Optimization for Mass and
AEP
Minimise
For cases
M
AEP
− wpow ∗ AEP
+ (1 − wpow ) ∗ blade−ref
Mblade
ref
wpow = [0.8, 0.85, 0.9, 0.925, 0.95, 0.975]
with respect to
x = {c, θ, tblade , tmat , DPcaps } (56 dvs)
subject to
Constraints on:
Tip deflection at rated power,
Tip torsion at rated,
Extreme wind tip deflection,
Ultimate strength,
Basic spar cap buckling: tcap /wcap > 0.08,
Trated < Trated −ref ,
Textreme < Textreme−ref ,
Extreme blade flapwise load < ref value
Extreme blade edgewise load < ref value
HAWCStab2 load cases: 7 operational cases, 1 extreme 70 m/s 15 deg yaw error
5 pre-computed extreme load cases for stress analysis.
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F Zahle et al.
Wind Energy Department · DTU
Aero-Elastic Optimization of a 10 MW Wind Turbine
Results
Case 2: Pareto Optimal Designs
1.20
AEP0.8
AEP0.85
AEP0.9
AEP0.925
AEP0.95
AEP0.975
1.15
Mass ratio [-]
1.10
1.05DTU 10MW RWT
1.00
0.95
0.90
0.85
0.80
0.75
0.995
1.000
1.005
1.010
AEP ratio [-]
1.015
1.020
Figure: Pareto optimal designs for the massAEP cases.
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F Zahle et al.
Wind Energy Department · DTU
Aero-Elastic Optimization of a 10 MW Wind Turbine
Results
Case 2: Blade Planform
0.08
DTU 10MW RWT
AEP0.8
AEP0.85
AEP0.9
AEP0.925
AEP0.95
AEP0.975
All designs tend towards a more
slender chord distribution, and a
significant reduction in root
diameter.
Maximum chord constraint is
active.
Normalized Chord [-]
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0.00
0.0
5
0.2
0.4
DTU 10MW RWT
AEP0.8
AEP0.85
r/R [-]
0.6
AEP0.9
AEP0.925
0.8
1.0
AEP0.95
AEP0.975
Twist [deg]
0
−5
−10
−15
−20
0.0
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Wind Energy Department · DTU
0.2
0.4
r/R [-]
0.6
0.8
1.0
Aero-Elastic Optimization of a 10 MW Wind Turbine
Results
Case 2: Blade Planform
1.0
DTU 10MW RWT
AEP0.8
AEP0.85
AEP0.9
AEP0.925
AEP0.95
AEP0.975
Significant increases in relative
thickness mid-span in particular
for the mass-biased designs.
Absolute thickness lower in root
and higher midspan.
Relative thickness [-]
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.0
0.07
Normalized absolute thickness [-]
Maximum chord constraint is
active.
All designs tend towards a more
slender chord distribution, and a
significant reduction in root
diameter.
0.9
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0.4
DTU 10MW RWT
AEP0.8
AEP0.85
r/R [-]
0.6
AEP0.9
AEP0.925
0.8
1.0
AEP0.95
AEP0.975
0.06
0.05
0.04
0.03
0.02
0.01
0.00
0.0
F Zahle et al.
Wind Energy Department · DTU
0.2
0.2
0.4
r/R [-]
0.6
0.8
1.0
Aero-Elastic Optimization of a 10 MW Wind Turbine
Results
Case 2: Aerodynamic Performance at 10 m/s
10000
Slender design requires higher
operational lift coefficients
Normal force [N/m]
8000
Mass biased designs tend
towards unloading the tip.
6000
AEP0.8
AEP0.85
AEP0.9
AEP0.925
AEP0.95
AEP0.975
DTU 10MW RWT
4000
2000
Cl − max constraint active for
all designs.
0
0.0
0.2
0.4
r/R [-]
0.6
0.8
1.0
1.8
1.6
Lift Coefficient [-]
1.4
1.2
AEP0.8
AEP0.85
AEP0.9
AEP0.925
AEP0.95
AEP0.975
DTU 10MW RWT
1.0
0.8
0.6
0.4
0.2
0.0
0.0
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F Zahle et al.
Wind Energy Department · DTU
0.2
0.4
r/R [-]
0.6
0.8
1.0
Aero-Elastic Optimization of a 10 MW Wind Turbine
Results
Case 2: Aerodynamic Performance at 10 m/s
1000
600
200
0
−200
0.0
Increase in thickness
compromises performance
mid-span.
Increase in performance on
inner part of blade due to
reduction in thickness.
AEP0.8
AEP0.85
AEP0.9
AEP0.925
AEP0.95
AEP0.975
DTU 10MW RWT
400
0.2
0.4
r/R [-]
0.6
80
AEP0.8
AEP0.85
AEP0.9
AEP0.925
AEP0.95
AEP0.975
DTU 10MW RWT
60
40
0
0.0
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1.0
100
20
F Zahle et al.
Wind Energy Department · DTU
0.8
120
Lift to drag ratio [-]
Tangential force [N/ ]
Cl − max constraint active for
all designs.
Slender design requires higher
operational lift coefficients
800
Mass biased designs tend
towards unloading the tip.
0.2
0.4
r/R [-]
0.6
0.8
1.0
Aero-Elastic Optimization of a 10 MW Wind Turbine
Results
Case 2: Structural Characteristics
EIx/EIx0 [-]
2.5
2.0
1.5
2.5
AEP0.8
AEP0.85
AEP0.9
AEP0.925
AEP0.95
AEP0.975
2.0
EIy/EIy0 [-]
3.5
3.0
1.5
AEP0.8
AEP0.85
AEP0.9
AEP0.925
AEP0.95
AEP0.975
1.0
1.0
0.5
0.5
2.0
1.8
1.6
GK/GK0 [-]
1.4
1.2
1.0
0.2
0.4
r/R [-]
0.6
0.8
1.0
0.4
r/R [-]
0.6
0.8
1.0
Mass per meter
AEP0.8
AEP0.85
AEP0.9
AEP0.925
AEP0.95
AEP0.975
DTU 10MW RWT
1200
1000
800
600
400
0.6
200
0.4
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0.2
1400
AEP0.8
AEP0.85
AEP0.9
AEP0.925
AEP0.95
AEP0.975
0.8
0.2
0.0
0.0
0.0
dm [kg]
0.0
0.0
0.2
0.4
r/R [-]
0.6
0.8
F Zahle et al.
Wind Energy Department · DTU
1.0
0
0.0
0.2
0.4
r/R [-]
0.6
0.8
1.0
Aero-Elastic Optimization of a 10 MW Wind Turbine
Results
Case 2: Structural Characteristics
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F Zahle et al.
Wind Energy Department · DTU
Aero-Elastic Optimization of a 10 MW Wind Turbine
Results
Case 2: Structural Characteristics
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F Zahle et al.
Wind Energy Department · DTU
Aero-Elastic Optimization of a 10 MW Wind Turbine
Results
Case 2: Structural Characteristics
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F Zahle et al.
Wind Energy Department · DTU
Aero-Elastic Optimization of a 10 MW Wind Turbine
Results
Case 2: Structural Characteristics
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F Zahle et al.
Wind Energy Department · DTU
Aero-Elastic Optimization of a 10 MW Wind Turbine
Results
Case 2: Structural Characteristics
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F Zahle et al.
Wind Energy Department · DTU
Aero-Elastic Optimization of a 10 MW Wind Turbine
Results
Case 2: Structural Characteristics
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F Zahle et al.
Wind Energy Department · DTU
Aero-Elastic Optimization of a 10 MW Wind Turbine
Results
Case 2: Structural Characteristics
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F Zahle et al.
Wind Energy Department · DTU
Aero-Elastic Optimization of a 10 MW Wind Turbine
Results
Case 2: Structural Characteristics
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F Zahle et al.
Wind Energy Department · DTU
Aero-Elastic Optimization of a 10 MW Wind Turbine
Results
Case 2: Structural Characteristics
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F Zahle et al.
Wind Energy Department · DTU
Aero-Elastic Optimization of a 10 MW Wind Turbine
Results
Case 2: Structural Characteristics
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F Zahle et al.
Wind Energy Department · DTU
Aero-Elastic Optimization of a 10 MW Wind Turbine
Results
Case 2: Structural Characteristics
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F Zahle et al.
Wind Energy Department · DTU
Aero-Elastic Optimization of a 10 MW Wind Turbine
Results
Case 2: Structural Characteristics
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F Zahle et al.
Wind Energy Department · DTU
Aero-Elastic Optimization of a 10 MW Wind Turbine
Results
Case 2: Extreme Loads Computed Using HAWC2
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F Zahle et al.
Wind Energy Department · DTU
Aero-Elastic Optimization of a 10 MW Wind Turbine
Results
Case 2: Extreme Loads Computed Using HAWC2
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F Zahle et al.
Wind Energy Department · DTU
Aero-Elastic Optimization of a 10 MW Wind Turbine
Results
Case 2: Extreme Loads Computed Using HAWC2
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F Zahle et al.
Wind Energy Department · DTU
Aero-Elastic Optimization of a 10 MW Wind Turbine
Results
Case 3: Shape and structural Optimization with Fatigue
Constraints
Mblade−ref
Mblade
Minimise
with
AEP
+ (1 − wpow ) ∗
− wpow ∗ AEP
ref
wpow = 0.9
with respect to
x = {c, θ, tblade , tmat , DPcaps } (56 dvs)
subject to
Constraints on:
Tip deflection at rated power,
Tip torsion at rated,
Extreme wind tip deflection,
Ultimate strength,
Basic spar cap buckling: tcap /wcap > 0.08,
Trated < Trated −ref ,
Textreme < Textreme−ref ,
Extreme blade flapwise load < ref value
Extreme blade edgewise load < ref value
Tower bottom long. fatigue < [5%, 10%]
Blade rotor speed fatigue < ref value
HAWCStab2 load cases: 7 operational cases, 1 extreme 70 m/s 15 deg yaw error
5 pre-computed extreme load cases for stress analysis.
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F Zahle et al.
Wind Energy Department · DTU
Aero-Elastic Optimization of a 10 MW Wind Turbine
Fatigue constrained designs lie inside the pareto front of the massAEP
designs.
Results
Case 3: Pareto Front
Both the 5% and 10% fatigue constraint almost met.
Optimizations not fully converged.
AEP0.925
Fatigue 5%
Fatigue 10%
Pareto front
Mass ratio [-]
0.95
0.90
0.85
Longitudinal tower
base fatigue damage variation [%]
100
1.00
98
97
96
95
94
93
92
91
0.80
1.000
1.002
1.004
1.006
AEP ratio [-]
1.008
1.010
a) AEP and blade mass in the Pareto front.
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F Zahle et al.
Wind Energy Department · DTU
Fatigue 5%
Fatigue 10%
99
0
5
10
15
20
Iteration number
25
30
b) Tower base longitudinal bending
moment fatigue damage variation.
Aero-Elastic Optimization of a 10 MW Wind Turbine
Fatigue damage equivalent load reduction of tower base longitudinal
bending moment and rotor speed with respect to the reference design.
Results
Case 3: Validation of Results With Time Domain
Simulations
Values evaluated with nonlinear time domain simulations.
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8
10
AEP0.925
Rotor speed
fatigue damage reduction [%]
Longitudinal tower base bending
moment fatigue damage reduction [%]
Dashed vertical lines indicate the wind speed where the constraint is
present in the optimization.
6
4
2
AEP0.925
0
−2
10
Fatigue 5%
Fatigue 10%
12
14
16
18
20
Wind speed [m/s]
22
F Zahle et al.
Wind Energy Department · DTU
24
26
Fatigue 5%
Fatigue 10%
5
0
−5
−10
−15
10
12
14
16
18
20
Wind speed [m/s]
22
24
26
Aero-Elastic Optimization of a 10 MW Wind Turbine
Results
Case 4: Shape and structural Optimization with Frequency
Constraint
Mblade−ref
Mblade
Minimise
with
AEP
+ (1 − wpow ) ∗
− wpow ∗ AEP
ref
wpow = 0.9
with respect to
x = {c, θ, tblade , tmat , DPcaps } (56 dvs)
subject to
Constraints on:
Tip deflection at rated power,
Tip torsion at rated,
Extreme wind tip deflection,
Ultimate strength,
Basic spar cap buckling: tcap /wcap > 0.08,
Trated < Trated −ref ,
Textreme < Textreme−ref ,
Extreme blade flapwise load < ref value
Extreme blade edgewise load < ref value
abs((Edgewise FW mode frequency)/6P) > 7%
min(Edgewise BW mode damping) > 1%
HAWCStab2 load cases: 7 operational cases, 1 extreme 70 m/s 15 deg yaw error
5 pre-computed extreme load cases for stress analysis.
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F Zahle et al.
Wind Energy Department · DTU
Aero-Elastic Optimization of a 10 MW Wind Turbine
Results
Case 4: Pareto Front
The frequency constrained design lies significantly inside the pareto
front of the massAEP designs.
1.00
AEP0.8
AEP0.925
Freq. constr.
Pareto front
Mass ratio [-]
0.95
0.90
0.85
0.80
0.998
1.000
1.002
1.004
1.006
AEP ratio [-]
1.008
1.010
Figure: Iterations of Test case 4 optimizations.
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F Zahle et al.
Wind Energy Department · DTU
Aero-Elastic Optimization of a 10 MW Wind Turbine
All aeroelastic frequencies of the optimized designs are reduced.
Results
Case 4: Aeroelastic Frequencies
The frequency constrained design hits the upper frequency constraint at
25 m/s.
The FW edgewise mode of the AEP0.8 design overlaps the 6P
frequency, while the AEP0.925 is sufficiently below.
DTU 10MW RWT
AEP0.8
AEP0.925
Freq. constr.
1.1
6P constraint
9P
Aeroelastic frequency [Hz]
1.0 FW edge
0.9
0.8 BW edge
FW flap
0.7
Coll. flap
0.6
BW flap
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6P
5
F Zahle et al. 0
Wind Energy Department · DTU
10
15
Wind speed [m/s]
20
25
Aero-Elastic Optimization of a 10 MW Wind Turbine
Multi-disciplinary trade-offs between mass reduction and AEP
successfully captured by the fully coupled MDO approach,
Significant reductions in mass and increase in AEP, depending on the
weighting of the cost function.
New frequency based model for fatigue showed promising results with
up to 8% reduction in tower bottom longitudinal fatigue.
Conclusions
Frequency placement was demonstrated, although the constraint
formulation resulted in less improvements in the design than the
unconstrained designs.
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F Zahle et al.
Wind Energy Department · DTU
Aero-Elastic Optimization of a 10 MW Wind Turbine
In progress: Further design of 10 MW rotors with the Risø airfoil series,
Ongoing/Future Work
Bend twist coupled blades,
Additional extreme load cases?
Further tuning of necessary constraints.
Buckling: Buckling loads are not computed, which is an important design
driver. Low fidelity methods suitable for optimization need to be
implemented.
Blades with trailing edge flaps.
Implementation of CoE models based on FUSED-Wind.
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F Zahle et al.
Wind Energy Department · DTU
Aero-Elastic Optimization of a 10 MW Wind Turbine