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.

1.
Lobitz
,
D. W.
, and
Veers
,
P. S.
, 1998, “
Aeroelastic Behavior of Twist-Coupled HAWT Blades
,”
Proc. of the 1998 ASME/AIAA Wind Energy Symposium
, Reno, pp.
75
83
.
2.
Carbon-Hybrid Blade Developments: With and Without Twist-Coupling
,” TPI Composites/Global Energy Concepts,
Sandia National Laboratories
(contractor report to be published).
3.
Design and Analysis of 9 m Carbon Hybrid Wind Turbine Rotor Blades
,” Wichita State University/Wetzel Engineering, Inc., Principal Investigator: James Locke,
Sandia National Laboratories
(contractor report to be published).
4.
Lobitz
,
D. W.
, 2004, “
Aeroelastic Stability Predictions for a MW-Sized Blade
,”
Wind Energy
1095-4244
7
(
3
), pp.
211
224
.
5.
Hansen
,
M. H.
, 2004, “
Stability Analysis of Three-Bladed Turbines Using an Eigenvalue Approach
,”
Proc. of the 2004 ASME/AIAA Wind Energy Symposium
, Reno, pp.
192
202
.
6.
Bisplinghoff
,
R. L.
, and
Ashley
,
H.
, 1962,
Principles of Aeroelasticity
,
John Wiley and Sons, Inc.
, New York, Chap. 6.
7.
Dowell
,
E. E.
(Editor), 1995,
A Modern Course in Aeroelasticity
,
3rd ed.
,
Kluwer Academic Publishers
, Dordrecht, The Netherlands, Chaps. 3, 4.
8.
Fung
,
Y. C.
, 1969,
An Introduction to the Theory of Aeroelasticity
.
Dover Publications Inc.
, New York, Chap. 6.
9.
Bisplinghoff
,
R. L.
,
Ashley
,
H.
, and
Halfman
,
R. L.
, 1955,
Aeroelasticity
,
Addison-Wesley Publishing Company Inc.
, Menlo Park, CA, Chaps. 1, 5.
10.
Theodorsen
,
T.
, 1935, “
General Theory of Aerodynamic Instability and the Mechanism of Flutter
,” NACA, Rept. 496.
11.
MSC Software Corporation
, NASTRAN product (www.mscsoftware.comwww.mscsoftware.com), accessed November 18, 2003.
12.
Malcolm
,
D. J.
, and
Hansen
,
A. C.
, 2002, “
WindPACT Rotor Turbine Design Study
,”
National Renewable Energy Laboratory
, Rept. NREL/SR-500-32495.
13.
Lobitz
,
D. W.
, and
Veers
,
P. S.
, 2003, “
Load Mitigation with Bending/Twist-Coupled Blades on Rotors Using Modern Control Stategies
,”
Wind Energy
1095-4244
6
(
2
), pp.
105
117
.
You do not currently have access to this content.