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Aeroelastic Stability Analysis and Passive Instability Suppression for Wind Turbines

This paper presents an in-depth analysis of aeroelastic stability mechanisms and their implications for wind turbine design, specifically focusing on flap-edgewise frequency coincidence and damping effects. Results from isolated blade analysis of the ASR turbine show that full coincidence can decrease damping below critical wind speeds, potentially leading to instabilities like whirl-flutter. Additionally, the impact of torsional stiffness on damping characteristics is explored. The findings aim to enhance understanding and mitigation strategies for aeroelastic instabilities in wind turbine systems.

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Aeroelastic Stability Analysis and Passive Instability Suppression for Wind Turbines

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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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