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Title:
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Stall Flexteeter: computations
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Author(s):
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Published by:
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Publication date:
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ECN
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1995
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ECN report number:
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Document type:
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ECN-C--95-010
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ECN publication
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Number of pages:
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Full text:
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116
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Download PDF
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Abstract:
In order to establish the applicability of aero-elastic codes PHATAS-2(ECN) and FLEXLAST (SPE)) for the design of flexible rotors, the results of a
set of load and motion measurements were compared to computed loads and
motions. The evaluation took into consideration 6 signals: the flap moment on
the flexbeam, the lead/lag moment on the flexbeam, the torsional motion on
the flexbeam, the flap angle, the teeter angle and the rotor shaft torque.
Computations for rotor operation at a small yaw misalignment included 24
cases representing 8 different wind intervals, whereas the computations at a
large yaw misalignment included 4 cases representing 4 different yaw
intervals. This involved an evaluation of the aerodynamic modelling, the
pitch mechanism, the blade mass and stiffness distribution, the teeter hinge,
the generator and the drive train, and the tower. The rotor model was
verified by comparing computed and measured rotor characteristics : the
aerodynamic performance, the mechanical characteristics, and the teeter
motion. It appeared that although the teeter motion is adequately modelled,
there is no exact correspondence between the computed and the measured
characteristics. The results of the two computations are mutually consistent.
The results indicate up to the experimental uncertainty the average computed
quantities agree with the corresponding measured quantities. The variation in
the computed quantities, on the other hand, is smaller than the measured
variation. For the yawed cases the same picture appeared although here large
differences between the computed results were found. An evaluation of the
power spectra of the computed and the measured quantities revealed these
spectra have corresponding natural frequencies but different spectral
densities. In particular, the computed magnitude of the second symmetric flap
frequency is smaller than the measured magnitude of this frequency. This
suggests the difference between the computed and the measured variations
originates from large symmetric flap motions during turbine operation, which
motions were not included in the input to the design codes. 40 figs., 21
tabs., 4 appendices, 24 refs.
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