Within the European research project DAMPBLADE investigations were performed
into wind turbine rotor blade structures with enhanced material- and
aeroelastic damping properties. Within task 3.4 of this project 'Design
application, sensitivity analysis and aeroelastic tailoring', investigations
were performed into the influence of structural modifications of a rotor
blade that improve the aeroelastic stability and fatigue loading.
These investigations were performed by CRES, ECN, and by Riso and focussed
on the influence of Strutural Pitch on the aerodynamic damping.
Basis for these investigations was the RB70 rotor blade of Polymarin
B.V., that was designed for a variable-speed pitch-to-vane wind turbine.
The RB70 blade was modelled on basis of descriptions of several blade
cross sections that were provided by WMC. Because the aerodynamic damping
for the flatwise blade vibrations of pitch-to-vane controlled wind turbine
is inherently positive, only the influence of Structural Pitch on the
damping of the edgewise vibrations is reported.
From the calculations with BLADMODE, HAWCBladeStab, PHATAS, and Stab-Blade
it follows that Structural Pitch can be used effectively to improve
the aeroelastic response of rotor blade vibrations. The results from
the time-domain code PHATAS did not show such a strong influence, while
the results from the other aeroelastic analysis tools show quite similar
trends for Structural Pitch. It was also shown that modelling of the
steady deformed state does have an effect on the aerodynamic damping
of the edgewise vibrations.