Blade materials, testing methods and structural design - Wind Power Generation and Wind Turbine Design - page 420

Although there are a variety of wind turbine designs (refl ecting different manufacturing
processes, material selection and design philosophy), the functionality of wind
turbine blades from a structural viewpoint can be understood by considering the
blade as a load-carrying beam (spar) enclosed by a shell. The primary purpose
of the shell is to give the blade an aerodynamic shape, creating the aerodynamic
forces that make the wind turbine blade to rotate and thus extracts energy from the
wind to make electrical power. The aerodynamic forces are transmitted to the wind
turbine hub through a load-carrying beam within the blade. The load-carrying
beam can be made as a box girder, sometimes called the main spar, or as laminates
in the aeroshell supported by webs. Figure 2 shows a sketch of the cross section of
a typical wind turbine blade. Steel bolts are present at the root, where the blade is
to be attached to the hub of a wind turbine.
Most blade manufacturing techniques involves making the blades in several
parts that are eventually joined by adhesive bonds. Figure 3 shows two common
design approaches. The one design involves the use of load-carrying laminates in
the aeroshells and webs for providing shear stiffness and buckling resistance. The
other design constitutes of two aeroshells bonded to a load-carrying box girder.
Sandwich structures are used extensively in the aeroshells and are also often used
in the webs (or correspondingly, in the sides of the box girder).

Downwind side

To w a r d s t i p

Trailing edge

Aerodynamic
shell Leading edge

Upwind side

Main spar
(load carrying box)

Sandwich panel

Adhesive layer
Flange
(load-carrying laminate - compression)

Face

Core

Adhesive joint

Adhesive joint

Adhesive layer

Web
(sandwich)

Flange
(load-carrying laminate - tension)

Figure 2: Terminology and defi nitions of coordinate system and structural parts of
a wind turbine blade [2].