experimental verification of the implementation of bend-twist coupling in a wind turbine blade

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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