Blade materials, testing methods and structural design - Wind Power Generation and Wind Turbine Design - page 443

Branner et al . [58] recently investigated how well different FE modeling
techniques can predict bending and torsion behavior of a wind turbine blade. The
results from the numerical investigations were directly compared with measure-
ments obtained from experimental testing of a section of a full-scale wind turbine
blade. Torsional testing was performed by locking the tip cross section in a point
directly over the center of the box girder (see Fig. 18). This point is fi xed, but the
cross section can rotate around the z -axis and translate in the horizontal ( x - z ) plane,
since the vertical bar, indicated in Fig. 18, is able to rotate in both ends. The move-
ment in the horizontal plane is not entirely free since the movement is restricted to a
circular arc. The numerical and experimental results are in shown in Fig. 19.

y

z

x

T

Figure 18: Locked torsion of blade section. The vertical bar is able to rotate in
both ends. The cross section can rotate and is restricted to move along
a circular arc.

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

0

-0.005

-0.01

-0.015

Experimental data
Outer surface model
Mid thickness model
Shell solid model

-0.02

-0.025

-0.03

Spanwise distance (z-direction) [m]

Figure 19: The twist angle of the blade section (see Fig. 18) is shown as a function of
the distance from the root, z . The experimental results are shown as points
and the model predictions for various FE models are shown as lines [58].