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VIBRATIONS OF A THREE-BLADED WIND TURBINE ROTOR DUE TO CLASSICAL FLUTTER

VIBRATIONS OF A THREE-BLADED WIND TURBINE ROTOR DUE TO CLASSICAL FLUTTER. Morten Hartvig Hansen Wind Energy Department Risø National Laboratory morten.hansen@risoe.dk. Outline. Motivation Stall-induced vibrations versus classical flutter Turbine Model

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VIBRATIONS OF A THREE-BLADED WIND TURBINE ROTOR DUE TO CLASSICAL FLUTTER

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  1. VIBRATIONS OF A THREE-BLADED WIND TURBINE ROTOR DUE TO CLASSICAL FLUTTER Morten Hartvig Hansen Wind Energy Department Risø National Laboratory morten.hansen@risoe.dk ASME 2002, Reno, 14-17 January

  2. Outline • Motivation • Stall-induced vibrations versus classical flutter • Turbine Model • Description and structural analysis • Blade Flutter • Stability limits • Effect of flapwise discretization • Turbine Flutter • Stability limits • Comparison with blade flutter • Visualization of flutter mode ASME 2002, Reno, 14-17 January

  3. Motivation • Post-design solution to stall-induced vibrations • Softening of stall • Primary design solution to classical flutter • Center of mass towards the leading edge • High torsional stiffness • Improved turbine design?? ASME 2002, Reno, 14-17 January

  4. Turbine model • 3N blade DOFs and 7 tower/nacelle DOFs • Center of mass and elastic axis at mid-chord • Blade Element Momentum theory • Quasi-steady aerodynamics, and no turbulence or shear ASME 2002, Reno, 14-17 January

  5. Campbell diagrams Basic model configuration: 1 flap (1.14 Hz), 1 lag (1.46 Hz), and 1 torsion (16.0 Hz) mode. low range high range ASME 2002, Reno, 14-17 January

  6. Operation conditions Variable speed and pitch turbine ASME 2002, Reno, 14-17 January

  7. Aerodynamic conditions in steady state = Attached flow conditions ASME 2002, Reno, 14-17 January

  8. Single blade flutter Aeroelastic damping of torsion mode in basic model configuration: 1 flap, 1 lag, and 1 torsion mode. ASME 2002, Reno, 14-17 January

  9. Single blade flutter Pitching and flapping motion at 75 % radius, wind speed 20 m/s, and torsion frequency 8.5 Hz. ASME 2002, Reno, 14-17 January

  10. Stability limits for blade flutter Effect of the discretization of flapwise blade motion ASME 2002, Reno, 14-17 January

  11. Damping of blade torsion on turbine Basic model configuration with original torsion frequency of 16 Hz ASME 2002, Reno, 14-17 January

  12. Comparison of flutter limits The critical torsion frequency is higher for turbine flutter! ASME 2002, Reno, 14-17 January

  13. Flutter motion Pitching and flapping motion at 75 % radius, wind speed 20 m/s, and torsion frequency 8.5 Hz. ASME 2002, Reno, 14-17 January

  14. Flutter whirling amplitudes ASME 2002, Reno, 14-17 January

  15. Conclusion • Structural dynamics of turbines is important • Affects the risk of flutter (and stall-induced vibrations) • Flutter analysis must include these effects • Blade-only analysis is not conservative • Flutter may become a problem for large turbines Future • Inclusion of unsteady aerodynamics • Optimization of turbine dynamics • Complete stability and optimization tool ASME 2002, Reno, 14-17 January

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