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Aeroelastic stability analysis and passive instability suppression

Aeroelastic stability analysis and passive instability suppression. EWEC 2006 – Athens Thomas Buhl*, Helena Markou, Morten H. Hansen, Kenneth Thomsen and Flemming Rasmussen. *Speaker. Stability Mechanisms. Effect of flap/edgewise frequency coincidence

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Aeroelastic stability analysis and passive instability suppression

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  1. Aeroelastic stability analysis andpassive instability suppression EWEC 2006 – Athens Thomas Buhl*, Helena Markou, Morten H. Hansen, Kenneth Thomsen and Flemming Rasmussen *Speaker

  2. Stability Mechanisms • Effect of flap/edgewise frequency coincidence • Effect of flap/edgewise whirling coupling on damping • Effect of torsional stiffness on damping • Can whirl-flutter happen on a wind turbine? 27. Feb. – 2. Mar. 2006 Athens

  3. Effect of flap/edgewise frequency coincidence

  4. Effect of flap/edgewise frequency coincidence • ASR turbine • Isolated blade analysis • Edge frequency lowered towards the flap frequency • Four intervals; • 25% • 50% • 75% • 100% 27. Feb. – 2. Mar. 2006 Athens

  5. Effect of flap/edgewise frequency coincidence Flapwise mode • Intermediate stiffness reductions gives virtually no change • Full coincidence: • Decreases damping below 21 m/s 27. Feb. – 2. Mar. 2006 Athens

  6. Effect of flap/edgewise frequency coincidence Flapwise mode • Intermediate stiffness reductions gives virtually no change • Full coincidence: • Decreases damping below 21 m/s • Increases damping above 21 m/s 27. Feb. – 2. Mar. 2006 Athens

  7. Effect of flap/edgewise frequency coincidence Edgewise mode • Intermediate stiffness reductions gives virtually no change • Full coincidence: • Increases damping below 19 m/s 27. Feb. – 2. Mar. 2006 Athens

  8. Effect of flap/edgewise frequency coincidence Edgewise mode • Intermediate stiffness reductions gives virtually no change • Full coincidence: • Increases damping below 19 m/s • Decreases damping above 19 m/s 27. Feb. – 2. Mar. 2006 Athens

  9. Effect of flap/edgewise frequency coincidence Sectional work 27. Feb. – 2. Mar. 2006 Athens

  10. Effect of flap/edgewise frequency coincidence Mode shape at 22 m/s 27. Feb. – 2. Mar. 2006 Athens

  11. Effect of flap/edgewise whirling coupling on damping

  12. Effect of flap/edgewise whirling coupling on damping Edgewise mode • ASR turbine • Full turbine analysis • 100% coincidence increases edgewise damping 27. Feb. – 2. Mar. 2006 Athens

  13. Effect of flap/edgewise whirling coupling on damping Flapwise mode • 100% coincidence decreases flapwise damping • Negative damped above 22 m/s 27. Feb. – 2. Mar. 2006 Athens

  14. Effect of flap/edgewise whirling coupling on damping Original ASR Shaft reduced to 2% of ori. 27. Feb. – 2. Mar. 2006 Athens

  15. Effect of flap/edgewise whirling coupling on damping 1st flapwise 1st edgewise 27. Feb. – 2. Mar. 2006 Athens

  16. Effect of flap/edgewise whirling coupling on damping Bladetip trace 1st edgewise 27. Feb. – 2. Mar. 2006 Athens

  17. Effect of torsional stiffness on damping

  18. Effect of torsional stiffness on damping PRVS turbine Torsional frequency reduced from 10.3 Hz to 3.8 Hz 27. Feb. – 2. Mar. 2006 Athens

  19. Effect of torsional stiffness on damping 27. Feb. – 2. Mar. 2006 Athens

  20. Effect of torsional stiffness on damping 27. Feb. – 2. Mar. 2006 Athens

  21. Effect of torsional stiffness on damping Tip speed 130 m/s (31 rpm) Torsion Flap modes 27. Feb. – 2. Mar. 2006 Athens

  22. Effect of torsional stiffness on damping 1st edge Sectional work 27. Feb. – 2. Mar. 2006 Athens

  23. Can whirl-flutter happen on a wind turbine?

  24. Can whirl-flutter happen on a wind turbine? PRVS - Tower top element reduced in stiffness 27. Feb. – 2. Mar. 2006 Athens

  25. Conclusions • ASR: An isolated blade analysis of flap-edgewise frequency coincidence showed that the damping could be decreased and result in instabilities. • ASR: The coupling of the flap/edgewise whirling modes can lead to increased damping of the edgewise mode when the modes couple at standstill. • PRVS: The critical relative wind speed for which flutter occurs is 130.75m/s when the torsional stiffness is reduced to 20% of the original. • PRVS: The reduction in torsional stiffness leads to negative damping of the first edgewise mode • PRVS: Whirl flutter was found when the tower top stiffness in the yaw and tilt directions was reduced to 1.5% of the original or less. 27. Feb. – 2. Mar. 2006 Athens

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