Environmental Engineering Reference
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in design or for monitoring. For control purposes, measuring the structural response
is especially useful if the harmonics of the blade play a large role. If the blade is
excited close to a resonance peak, suppressing these dynamics already poses a
signifi cant load reduction potential. In this case, fl ow measurement might still be
needed, but primarily for controlling the performance of the aerodynamic load
control device, not for the load control itself.
This has also been shown in a load control experiment by the Delft University
of Technology's wind energy research institute DUWind. Here, a series of experi-
ments was conducted to research the (dynamic) load reduction potential of the
'smart' rotor concept. The primary goal of this experiment was showing the feasi-
bility of the concept and to have a test set-up to test new control algorithms and
actuator designs. Recently non-rotating experiments have been conducted and
plans on a scaled turbine are planned.
5.1 Load alleviation experiments
A fi rst approach these experiments were performed on a non-rotating blade. In these
experiments the blade operates as a cantilever beam with uniform cross-section - the
DU96 W180 aerofoil profi le. The blade is mounted onto a pitch system at the wind
tunnel's top wall and free to defl ect over a table at the bottom side. The pitch system
can be used to change the mean angle of attack, as well as inducing the dynamic
disturbances that are to be mitigated. This way rotational effects are not taken into
account and the blade has no twist or taper and constant thickness, unlike actual
HAWT rotor blades. The table ensures that there are no tip-effects, because only
2D aerodynamic analyses were made. Thus, quasi-2D fl ow would be obtained
in the static case. However, additionally experiments without table were also
performed. See Fig. 18 for a picture of the set-up.
For controlling the aerodynamic loads it was chosen to implement partial camber
control: the aft half of the cord at certain stations in the outboard section of the blade
was made deformable therefore allowing for a change in camber of that part of the
span. Such aerodynamic load control systems were also suggested for wind turbine
blades by Buhl et al . [12] and Joncas et al. [10] and intensively discussed before. The
actuator is based on a piezoelectric Thunder™ actuator, already elaborated on in sec-
tion 3.1.4. The actuator is covered with a soft polyether foam which in turn is covered
with a latex skin to provide a smooth surface. See Fig. 19 for the actuator design.
5.2 Control
In order to control the actuators and read the signals from the sensors, a dSpace™
system was employed for both feed forward as feedback experiments. With these
systems sensors signals are converted to a digital signal and sampled. These sig-
nals can be recorded as well as fed to a feedback control algorithm. The output
of the controller (whether it is feedforward or feedback) is converted to an ana-
logue signal and send to the different actuators. The system of processing signals
as well as the feedback controller is designed in Simulink™ and compiled onto
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