Aeroelastic tailoring in wind-turbine blade applications Page: 1 of 15
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AEROELASTIC TAILORING IN WIND-TURBINE BLADE APPLICATIONS'
Paul Veers Gunjit Bir COAF-7
Sandia National Laboratories National Renewable Energy Laboratory
nd Energy Technology Department National Wind Technology Center
Iquerque, New Mexico, 87185-0708 Golden, Colorado, 80401-3 3
Donald Lobitz KEC E V ED
Sandia National Laboratories
Structural Dynamics Department
Albuquerque, New Mexico, 87185-0439
JUN 08 1998
This paper reviews issues related to the use of aeroelastic tailoring as a cost-effective, passive means to
shape the power curve and reduce loads. Wind turbine blades bend and twist during operation,
effectively altering the angle of attack, which in turn affects loads and energy production. There are
blades now in use that have significant aeroelastic couplings, either on purpose or because of flexible and
light-weight designs. Since aeroelastic effects are almost unavoidable in flexible blade designs, it may be
desirable to tailor these effects to our advantage. Efforts have been directed at adding flexible devices to
a blade, or blade tip, to passively regulate power (or speed) in high winds. It is also possible to build a
small amount of desirable twisting into the load response of a blade with proper asymmetric fiber lay up
in the blade skin. (Such coupling is akin to distributed 83 without mechanical hinges.) The tailored
twisting can create an aeroelastic effect that has payoff in either better power production or in vibration
alleviation, or both. Several research efforts have addressed different parts of this issue. Research and
development in the use of aeroelastic tailoring on helicopter rotors is reviewed. Potential energy gains as
a function of twist coupling are reviewed. The effects of such coupling on rotor stability have been
studied and are presented here. The ability to design in twist coupling with either stretching or bending
loads is examined also.
Whenever wind turbine blades twist, there is a direct influence on the angle of attack, changing loads and
affecting output power. This is directly exploited in classic pitch control used in not only wind turbines
but in rotors of all types. When the pitch changes are rapid enough, they can affect not only average
loads and power, but vibratory loads as well, influencing fatigue life throughout the system. Even quite
small angles of twist can have significant impact.
The concept of building blades that passively adapt to the incident wind loading is not new. Mechanisms
that adjusted blade angle of attack in response to the thrust loading were quite popular in the early days of
the modern wind energy push. Approaches and objectives were quite varied. Cheney and Speirings
(1978) regulated power with a centrifugally loaded mass on an elastic arm. Bottrell (1981) has a system
for cyclically adjusting pitch for per rev load balancing. The North Wind 4KW (Currin, 1981) had a
system for passively adjusting pitch for both power and load control. Hohenemser and Swift (1981)
studied alleviating yaw loads with cyclic pitch adjustments.
A Garrad-Hassan report (Corbet and Morgan, 1992) evaluates the use of all available blade loads to
effect pitch changes that would regulate the power output of a turbine, aiming at a flat power curve in
' This work was supported by the United States Department of Energy under Contract DE-AC04-94AL85000. Sandia is a
multiprogram laboratory operated by Sandia Corp., a Lockheed Martin Company, for the United States Department of Energy.
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Veers, P.; Lobitz, D. & Bir, G. Aeroelastic tailoring in wind-turbine blade applications, article, April 1, 1998; Albuquerque, New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc712371/m1/1/: accessed April 20, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.