Environmental Engineering Reference
In-Depth Information
Flutter Analysis Results
Aeroelastic stability predictions with the rotor turning in still air were made for this base-
line model. Results indicate that the onset of flutter occurs at a rotational speed of 43.4 rpm
(0.723 Hz) which is 2.14 times the maximum design operating speed of the rotor. As shown
in Figure 11-18, the mode shape associated with the onset of flutter contains significant
amounts of edgewise (motion in the direction of the chord), flapping, and pitching motion.
Its frequency of oscillation is 6.234 Hz, which is significantly lower than the 1
st
torsional
frequency of 9.289 Hz.
1
1
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Distance from rotor center (m)
Distance from rotor center (m)
Distance from rotor center (m)
Distance from rotor center (m)
Amplitude
Amplitude
Phase (deg)
Phase (deg)
Figure 11-18. Mode shape at the onset of flutter for the 1.5 MW baseline WindPACT
uncoupled blade.
In classical flutter, motion in the edgewise direction is generally minimal, and the large
amount predicted here is thought to be due to the fact that the blade is twisted, and that the
frequency of the second edgewise mode (6.153 Hz) is close to the flutter frequency of 6.234
Hz. The amount of twist in the blade appears to have an important influence on the flutter
mode shape. In fact, when flutter predictions are made for an entirely similar blade that is not
twisted, edgewise motion in the associated flutter mode is minimal.
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