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RESEARCH PAPERS

Parameter Sensitivities Affecting the Flutter Speed of a MW-Sized Blade

[+] Author and Article Information
Don W. Lobitz

 Sandia National Laboratories,1 P. O. Box 5800, MS0708, Albuquerque, NM 87185-0708dwlobit@sandia.gov

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Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract DE-AC04-94AL85000.

J. Sol. Energy Eng 127(4), 538-543 (Jul 12, 2005) (6 pages) doi:10.1115/1.2037091 History: Received February 28, 2005; Revised July 06, 2005; Accepted July 12, 2005

With the current trend toward larger and larger horizontal axis wind turbines, classical flutter is becoming a more critical issue. Recent studies have indicated that for a single blade turning in still air the flutter speed for a modern 35 m blade occurs at approximately twice its operating speed (2 per rev), whereas for smaller blades (5–9 m), both modern and early designs, the flutter speeds are in the range of 3.5–6 per rev. Scaling studies demonstrate that the per rev flutter speed should not change with scale. Thus, design requirements that change with increasing blade size are producing the concurrent reduction in per rev flutter speeds. In comparison with an early small blade design (5 m blade), flutter computations indicate that the non rotating modes which combine to create the flutter mode change as the blade becomes larger (i.e., for the larger blade the second flapwise mode, as opposed to the first flapwise mode for the smaller blade, combines with the first torsional mode to produce the flutter mode). For the more modern smaller blade design (9 m blade), results show that the non rotating modes that couple are similar to those of the larger blade. For the wings of fixed-wing aircraft, it is common knowledge that judicious selection of certain design parameters can increase the airspeed associated with the onset of flutter. Two parameters, the chordwise location of the center of mass and the ratio of the flapwise natural frequency to the torsional natural frequency, are especially significant. In this paper studies are performed to determine the sensitivity of the per rev flutter speed to these parameters for a 35 m wind turbine blade. Additional studies are performed to determine which structural characteristics of the blade are most significant in explaining the previously mentioned per rev flutter speed differences. As a point of interest, flutter results are also reported for two recently designed 9 m twist/coupled blades.

FIGURES IN THIS ARTICLE
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Copyright © 2005 by American Society of Mechanical Engineers
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Figures

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Figure 1

Planforms of the scaled WindPACT and GX-100 blades

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Figure 2

Chordwise CG and shear center axis locations for the scaled WindPACT and GX-100 blades

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Figure 3

Structural and mass properties for the scaled WindPACT and GX-100 blades

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Figure 4

Second flapwise and first torsional stationary (non rotating) mode shapes for the scaled WindPACT and GX-100 blades

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Figure 5

Classical flutter complex-mode shapes for the scaled WindPACT and GX-100 blades

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Figure 6

Per rev flutter speed variation with frequency ratio for the WinPACT blade

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Figure 7

Per rev flutter speed variation with average chordwise CG and shear center axis separation

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Figure 8

WindPACT flutter speed variations resulting from the selective substitution of scaled GX-100 properties

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