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
Outline 1. Introduction 2. Goal and scope of the investigation 3. Object of an investigation 4. Static investigations 5. Dynamic investigations 6. Assessment 7. Conclusions and further research 8. Acknowledgements 2 copyright LMS International - 2011
3 copyright LMS International - 2011 Introduction
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 4 copyright LMS International - 2011
5 copyright LMS International - 2011 Goal and scope
Objective Main goal : experimentally confirm the numerical prediction of modification of the dynamic and static properties of the original and modified wind turbine blade. SCOPE: Original blade Modified blade STATIC FEM / TEST FEM / TEST DYNAMIC FEM / TEST FEM / TEST 6 copyright LMS International - 2011
7 copyright LMS International - 2011 Object
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 8 copyright LMS International - 2011
Object: modified wind turbine blade section Blade modification Introduction of bend-twist coupling into 8 meter blade section Extra UD lamination 9 copyright LMS International - 2011
10 copyright LMS International - 2011 Static investigations
Static Experiments Test rig & setup: static boundary conditions and load configurations 2 clamps in the wide end, which gives the clamped boundary Max horizontal force of 500 kn and moment of 50 knm. Bending flapwise Bending edgewise Pure torsion 11 copyright LMS International - 2011
Static Experiments Test rig & setup: static measurement techniques ARAMIS system camera setup and measuring pattern 12 copyright LMS International - 2011
Bend and twist definition LENGTH OF THE BLADE Bend Angle 13 copyright LMS International - 2011
Bend and twist definition ORIGINAL MODIFIED Twist Angle Twist Angle 14 copyright LMS International - 2011
Static Results - TEST Original and modified blade section static measurement Flapwise bending load Rotation x [rad] 0,005 0-0,005-0,01-0,015-0,02-0,025-0,03 0 1000 2000 3000 4000 5000 Spanwise distance [mm] Bend Rotation z [rad] 0,005 0-0,005-0,01-0,015-0,02-0,025-0,03 0 1000 2000 3000 4000 5000 Spanwise distance [mm] Rotation z [rad] 0,005 0-0,005-0,01-0,015-0,02-0,025-0,03 0 1000 2000 3000 4000 5000 Spanwise distance [mm] Twist The z-rotation for the original blade section is almost equal to zero The z-rotation for the modified blade section indicates that the section now has a measurable bend-twist coupling 15 copyright LMS International - 2011
16 copyright LMS International - 2011 Dynamic investigations
Dynamic TEST and FEM Results original blade section 1st flap bending mode @ 4.47 Hz Bend and Twis angles for FEM and test were estimated Good consistency of natural frequencies 17 copyright LMS International - 2011 MSc Thesis Mark Capellaro 2007
Dynamic Experiments Test rig & setup: dynamic boundary conditions & exctitation 2 clamps in the wide end, which gives the clamped boundary Blade excited by 2 electromagnetic shakers in normal direction Burst random excitation 18 copyright LMS International - 2011
Dynamic Experiments Test 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 2 3 4 5 1=> Trailing edge 3 => Max height 5 => Leading edge 2-4 => Mid points X 1 Z Y ORIENTATIONS: X => NORMAL TO BLADE SURFACE Y => TANGENT TO BLADE SURFACE 19 copyright LMS International - 2011
Dynamic Experiments Test rig & setup: geometry Support structure, XYZ direction accelerations measured M2R M1R C2U C1C2R C1U M2L C2D ST C1C2L C1D M1L 20 copyright LMS International - 2011
Dynamic Experiments Test rig & setup: geometry Measurement points 130 measurement points + 2 driving points 21 copyright LMS International - 2011
Dynamic Results Linearity, reciprocity & coherence for modified blade section 50.00 74.88 1.00 F F F F FRF Drvp:1:+Y/Drvp:1:+Y linearity_check_05v FRF Drvp:1:+Y/Drvp:1:+Y linearity_check_10v FRF Drvp:1:+Y/Drvp:1:+Y linearity_check_15v FRF Drvp:1:+Y/Drvp:1:+Y linearity_check_20v F F FRF Drvp:2:-Y/Drvp:1:+X FRF Drvp:1:+X/Drvp:2:-Y g/n db g/n db Amplitude Linearity Reciprocity -50.00 0.00 Hz 130.00-25.12 0.00 Hz 130.00 0.00 Linearity & reciprocity check to verify if the structure meets the modal analysis assumptions Coherence 22 copyright LMS International - 2011
Dynamic Results Linearity, reciprocity & coherence 116.59 Modal synthesis g/n Log 0.02 180.00-180.00 26.84 2.04 Hz 64.00 AutoMAC: blade g/n Log 1.98e-3 180.00-180.00 2.04 Hz 64.00 23 copyright LMS International - 2011 AutoMAC: blade+support PolyMAX modal parameter estimation Good modal synthesis Well-separated modes
Dynamic Results modified blade section 1st flap bending mode @ 4.48 Hz 24 copyright LMS International - 2011
Dynamic Results modified blade section 1st edge bending mode @ 12.08 Hz 25 copyright LMS International - 2011
Dynamic Results modified blade section 2nd flap bending mode @ 19.24 Hz 26 copyright LMS International - 2011
Dynamic Results modified blade section 1st torsion mode @ 40.92 Hz 27 copyright LMS International - 2011
28 copyright LMS International - 2011 Assessment
Correlation analysis FEM model TEST model Finite Element Method model of modified blade section FEM and Test geometries correlated and the FE nodes are paired with measurement points 29 copyright LMS International - 2011
Correlation analysis FEM model TEST model Finite Element Method model of modified blade section Original blade FE Original blade Test Modified blade FE Modified blade Test 4.7 Hz 4.5 Hz 5.01 Hz 4.48 Hz 1 st bend flap 10.85 Hz 8.7 Hz 12.9 Hz 12.08 Hz 1 st bend edge 18.56 Hz 18.9 Hz 20.03 Hz 19.24 Hz 2 nd bend flap 42.99 Hz 39.5 Hz 43.75 Hz 40.92 Hz 1 st torsion Modal Assurance Criterion matrix for test and simulation modal vectors of modified blade Comparison of the natural frequencies for the experimental and numerical results obtained for the original and modified blade 30 copyright LMS International - 2011
Numerical and experimental twist and bend angles 1st flap bending mode original and modified blade section Modal Deflection and Twist [-] 1,2 1 0,8 0,6 0,4 0,2 0-0,2 4,7 [Hz] 1st Flap mode Y Defelction Z rotation (rad) 2 3 4 5 6 7 8 9 Modal Angle [-] 1,2-3,8-8,8-13,8 5.01 [Hz] 1st Flap mode Bending Angle Twisting Angle 2 3 4 5 6 7 8 9 Blade Length [m] Blade Length [m] Original blade - Finite Element Modified blade - Finite Element Modal Deflection and Twist [-] 1,2 0,7 0,2-0,3 4,47 [Hz] 1st Flap mode Y Defelction Z rotation (rad) 2 3 4 5 6 7 8 9 Modal Angle [-] 1,2-3,8-8,8-13,8-18,8-23,8 4.48 [Hz] 1st Flap mode Bending Angle Twisting Angle 2 3 4 5 6 7 8 9 Blade Length [m] Blade Length [m] Original blade - Test Modified blade - Test 31 copyright LMS International - 2011
Numerical and experimental twist and bend angles 2nd flap bending mode original and modified blade section Modal Deflection and Twist [-] 0,6 0,4 0,2 0-0,2 18,56 [Hz] 2nd Flap mode Y Defelction Z rotation (rad) 2 3 4 5 6 7 8 9 Modal Angle [-] 10 5 0-5 -10 20.03 [Hz] 2nd Flap mode Bending Angle Twisting Angle 2 3 4 5 6 7 8 9 Blade Length [m] Blade Length [m] Original blade - Finite Element Modified blade - Finite Element Modal Deflection and Twist [-] 1 0,5 0-0,5 18,9 [Hz] 2nd Flap mode Y Defelction Z rotation (rad) 2 3 4 5 6 7 8 9 Blade Length [m] Modal Angle [-] 6 4 2 0-2 -4 19.24 [Hz] 2nd Flap mode Bending Angle Twisting Angle 2 3 4 5 6 7 8 9 Blade Length [m] Original blade - Test Modified blade - Test 32 copyright LMS International - 2011
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 33 copyright LMS International - 2011
Conclusions & further research 34 copyright LMS International - 2011
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 35 copyright LMS International - 2011
36 copyright LMS International - 2011 Acknowledgements
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. 37 copyright LMS International - 2011
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