Experimental Verification of the Implementation of Bend-Twist Coupling in a Wind Turbine Blade
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Experimental Verification of the Implementation of Bend-Twist Coupling in a Wind Turbine Blade
Authors: Marcin Luczak (LMS), Kim Branner (Risø DTU), Simone Manzato (LMS), Philipp Haselbach (Risø DTU), Bart Peeters (LMS), Peter Berring (Risø DTU)
EWEA Annual Event 14-17 March 2011, Brussels, Belgium
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Outline
1. Introduction
2. Goal and scope of the investigation
3. Object of an investigation
4. Static investigations
5. Dynamic investigations6. Assessment
7. Conclusions and further research
8. Acknowledgements
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IntroductionIntroduction1
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Introduction
Passive blade load reduction sudden wind changes, anisotropic composite material can introduce the bend-twist
coupling aero-elastic tailoring of the blades extend the fatigue life
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Goal and scopeGoal and scope2
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Main goal :experimentally confirm the numerical predictionof modification of the dynamic and staticproperties of the original and modified wind turbine blade.
SCOPE:
Objective
Original blade Modified blade
STATIC FEM / TEST FEM / TEST
DYNAMIC FEM / TEST FEM / TEST
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ObjectObject3
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Object: original composite material wind turbine blade
Blade section provided by Vestas Wind Systems A/S. 8m section was selected from the 23m blade. The 8m blade
section goes approximately from R11m to R19m
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Object: modified wind turbine blade section
Blade modification Introduction of bend-twist coupling into 8 meter blade section
Extra UD lamination
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Static investigationsStatic investigations4
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2 “clamps” in the wide end, which gives the clamped boundary Max horizontal force of 500 kN and moment of 50 kNm.
Static ExperimentsTest rig & setup: static boundary conditions and load configurations
Bending flapwise
Bending edgewise
Pure torsion
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ARAMIS system camera setup and measuring pattern
Static ExperimentsTest rig & setup: static measurement techniques
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Bend and twist definition
LENGTH OF THE BLADE
Bend
Angle
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Bend and twist definition
ORIGINAL MODIFIED
Twist AngleTwist
Angle
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Static Results - TESTOriginal and modified blade section static measurement
The z-rotation for the original blade section is almost equal to zeroThe z-rotation for the modified blade section indicates that the section
now has a measurable bend-twist coupling
Flapwise bending load
Bend
Twist
-0,03
-0,025
-0,02
-0,015
-0,01
-0,005
0
0,005
0 1000 2000 3000 4000 5000
Spanwise distance [mm]
Ro
tatio
n x
[ra
d]
-0,03
-0,025
-0,02
-0,015
-0,01
-0,005
0
0,005
0 1000 2000 3000 4000 5000
Spanwise distance [mm]
Ro
tatio
n z
[ra
d]
-0,03
-0,025
-0,02
-0,015
-0,01
-0,005
0
0,005
0 1000 2000 3000 4000 5000
Spanwise distance [mm]
Ro
tatio
n z
[ra
d]
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Dynamic investigationsDynamic investigations5
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Dynamic TEST and FEM Results– original blade section1st flap bending mode @ 4.47 Hz
MSc Thesis Mark Capellaro 2007
Bend and Twis angles for FEM and test were estimated
Good consistency of natural frequencies
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2 “clamps” in the wide end, which gives the clamped boundary
Dynamic ExperimentsTest rig & setup: dynamic boundary conditions & exctitation
Blade excited by 2 electromagnetic shakers in normal direction
Burst random excitation
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Dynamic ExperimentsTest rig & setup: modified blade section geometry
1st set of measurement performed on 25 sections along pitch axis (every 250 mm) 5 points measured on each section X and Y acceleration measured, with respect to the blade surface orientation
1=> Trailing edge
3 => Max height
5 => Leading edge
2-4 => Mid points
ORIENTATIONS:X => NORMAL TO BLADE SURFACEY => TANGENT TO BLADE SURFACE
1
23 4 5
X
Y
Z
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Support structure, XYZ direction accelerations measured
Dynamic ExperimentsTest rig & setup: geometry
C1C2L
C1C2R
C2U
C1U
C2D
C1D
M2L
M2R
M1L
M1R
ST
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Measurement points
Dynamic ExperimentsTest rig & setup: geometry
130 measurement points + 2 driving points
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0.00 130.00Hz
-25.12
74.88
dBg/N
0.00
1.00
Am
plitu
de
F FRF Drvp:2:-Y/Drvp:1:+XF FRF Drvp:1:+X/Drvp:2:-Y
0.00 130.00Hz
-50.00
50.00
dBg/N
F FRF Drvp:1:+Y/Drvp:1:+Y linearity_check_05VF FRF Drvp:1:+Y/Drvp:1:+Y linearity_check_10VF FRF Drvp:1:+Y/Drvp:1:+Y linearity_check_15VF FRF Drvp:1:+Y/Drvp:1:+Y linearity_check_20V
Dynamic ResultsLinearity, reciprocity & coherence for modified blade section
Linearity
Coherence
Reciprocity
Linearity & reciprocity check to verify if the structure meets the modal analysis assumptions
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Dynamic ResultsLinearity, reciprocity & coherence
2.04 64.00Linear
Hz
0.02
116.59
Log
g/N
2.04 64.00LinearHz
2.04 64.00Hz
-180.00
180.00
°
2.04 64.00Linear
Hz
1.98e-3
26.84
Log
g/N
2.04 64.00LinearHz
2.04 64.00Hz
-180.00
180.00
°
Modal synthesis
PolyMAX modal parameter estimation
Good modal synthesis
Well-separated modes
AutoMAC: blade
AutoMAC: blade+support
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Dynamic Results – modified blade section1st flap bending mode @ 4.48 Hz
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Dynamic Results – modified blade section 1st edge bending mode @ 12.08 Hz
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Dynamic Results – modified blade section 2nd flap bending mode @ 19.24 Hz
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Dynamic Results – modified blade section1st torsion mode @ 40.92 Hz
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AssessmentAssessment6
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FEM and Test geometries correlated and the FE nodes are paired with measurement points
Correlation analysis FEM model – TEST modelFinite Element Method model of modified blade section
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Correlation analysis FEM model – TEST modelFinite Element Method model of modified blade section
Modal Assurance Criterion matrix for test and simulation modal vectors of modified blade
Original blade
FE
Original blade Test
Modified blade
FE
Modified blade Test
4.7 Hz 4.5 Hz 5.01 Hz 4.48 Hz 1st bend flap
10.85 Hz 8.7 Hz 12.9 Hz 12.08 Hz 1st bend edge
18.56 Hz 18.9 Hz 20.03 Hz 19.24 Hz 2nd bend flap
42.99 Hz 39.5 Hz 43.75 Hz 40.92 Hz 1st torsion
Comparison of the natural frequencies for the experimental and numerical results obtained for the original and modified blade
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Numerical and experimental twist and bend angles1st flap bending mode original and modified blade section
Original blade - Finite Element Modified blade - Finite Element
Original blade - Test Modified blade - Test
4,7 [Hz] 1st Flap mode
-0,20
0,20,40,60,8
11,2
2 3 4 5 6 7 8 9
Blade Length [m]
Mod
al D
efle
ctio
n an
d T
wis
t [-
]
Y Defelction
Z rotation (rad)
5.01 [Hz] 1st Flap mode
-13,8
-8,8
-3,8
1,2
2 3 4 5 6 7 8 9
Blade Length [m]
Mod
al A
ngle
[-]
Bending Angle
Twisting Angle
4,47 [Hz] 1st Flap mode
-0,3
0,2
0,7
1,2
2 3 4 5 6 7 8 9
Blade Length [m]
Modal D
eflection a
nd
Tw
ist
[-] Y Defelction
Z rotation (rad)
4.48 [Hz] 1st Flap mode
-23,8
-18,8
-13,8
-8,8
-3,8
1,2
2 3 4 5 6 7 8 9
Blade Length [m]
Mod
al A
ngle
[-]
Bending Angle
Twisting Angle
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Numerical and experimental twist and bend angles2nd flap bending mode original and modified blade section
Original blade - Finite Element Modified blade - Finite Element
Original blade - Test Modified blade - Test
18,56 [Hz] 2nd Flap mode
-0,2
0
0,2
0,4
0,6
2 3 4 5 6 7 8 9
Blade Length [m]
Modal D
efle
ctio
n a
nd
Tw
ist
[-] Y Defelction
Z rotation (rad)
20.03 [Hz] 2nd Flap mode
-10
-5
0
5
10
2 3 4 5 6 7 8 9
Blade Length [m]
Mod
al A
ngle
[-]
Bending Angle
Twisting Angle
18,9 [Hz] 2nd Flap mode
-0,5
0
0,5
1
2 3 4 5 6 7 8 9
Blade Length [m]
Mod
al D
efle
ctio
n an
d T
wis
t [-
]
Y Defelction
Z rotation (rad)
19.24 [Hz] 2nd Flap mode
-4
-2
0
2
4
6
2 3 4 5 6 7 8 9
Blade Length [m]
Mod
al A
ngle
[-]
Bending Angle
Twisting Angle
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Bend-twist coupling index for 1st and 2nd flapwise mode
•For each considered blade cross-section, the ratio between the computed relative twisting and bending angles is evaluated.•Coupling index value close to zero means that the twisting is negligible with respect to the bending for the considered mode•High coupling index value means that twisting is dominant. •Coupling index value close to one, means twisting and bending are of the same order of magnitude
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Conclusions & further researchConclusions & further research7
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Conclusions
Multidisciplinary and interdisciplinary research oriented for the
experimental and numerical study in static and dynamic
domains on the bend-twist coupling in the original and modified full scale section of the wind turbine blade structure
Good correspondance between modal models (natural frequencies, damping ratios & mode shapes) in frequency range 0 - 100 Hz
Support structure influence on the FE-Test correlation is significant
Introduction of the bend-twist coupling was confirmed in static and dynamic experiments and simulations
Next step – Fluid-Structure Interaction model incorporating Computational Fluid Dynamics
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AcknowledgementsAcknowledgements8
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Acknowledgements
Vestas Wind Systems A/S has provided and modified the blade sections presented in this study. The work is partly supported by the Danish Energy Authority through the 2007 Energy Research Programme (EFP 2007). The
supported EFP-project is titled “Anisotropic beam model for analysis and design of passive controlled wind turbine blades” and has journal no. 33033-0075. The support is gratefully acknowledged and highly appreciated.
Research presented in section 5 was conducted in the context of the FP7 project PROND Ref No. 239191. Computations were performed on a 50Tflop cluster in TASK Academic Computer Centre in Gdansk, Poland.
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Thank you