ASME 2002, Reno, 14-17 January
VIBRATIONS OF A THREE-BLADED WIND TURBINE ROTOR
DUE TO CLASSICAL FLUTTER
Morten Hartvig HansenWind Energy DepartmentRisø National [email protected]
ASME 2002, Reno, 14-17 January
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
MotivationPost-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
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
Campbell diagramsBasic 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
Operation conditionsVariable speed and pitch turbine
ASME 2002, Reno, 14-17 January
Aerodynamic conditions in steady state
= Attached flow conditions
ASME 2002, Reno, 14-17 January
Single blade flutterAeroelastic damping of torsion mode in basic model configuration: 1 flap, 1 lag, and 1 torsion mode.
ASME 2002, Reno, 14-17 January
Single blade flutter
Pitching and flapping motion at 75 % radius, wind speed 20 m/s, andtorsion frequency 8.5 Hz.
ASME 2002, Reno, 14-17 January
Stability limits for blade flutter
Effect of the discretization of flapwise blade motion
ASME 2002, Reno, 14-17 January
Damping of blade torsion on turbine
Basic model configuration with original torsion frequency of 16 Hz
ASME 2002, Reno, 14-17 January
Comparison of flutter limitsThe critical torsion frequency is higher for turbine flutter!
ASME 2002, Reno, 14-17 January
Flutter motion
Pitching and flapping motion at 75 % radius, wind speed 20 m/s, andtorsion frequency 8.5 Hz.
ASME 2002, Reno, 14-17 January
Flutter whirling amplitudes
ASME 2002, Reno, 14-17 January
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
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