ECN publication
Smart rotor: feasibility study for a passive pitch regulation of a windturbine rotor blade
Published by: Publication date:
ECN 1996
ECN report number: Document type:
ECN-I--96-011 Other
Number of pages: Full text:
65 Download PDF  

In October 1995 the section Wind Energy of the Netherlands EnergyResearch Foundation ECN initiated a study on the feasibility of a passive pitch regulation on a wind turbine rotor blade; a so called 'Smart Rotor'. By means of an isotropic tailoring (choosing specific fiber orientations in the rotor blade root) a defined coupling is created between strains and torsional deformation. Chapter 2 describes the basic principles of power control for wind turbines and limitations of this study. Chapter 3 outlines the computer model of the applied rotor test facility of ECN: the 25m HAWT with AERPAC 25WPX blades. Also the possible improvements in the power curve by altering the pitch angle are discussed. In chapter 4 the loads in the rotor blade are calculated. In chapter 5 the qualitative deformation of the pitch bearing is defined by combining the required pitch angles with the calculated loads. The anisotropic mechanical behaviour of fibre reinforced plastic laminae can be used to give structural members a coupling between longitudinal strain and shear deformation (aero-elastic tailoring). Specific tailoring of the wind turbine rotor blades, couples flap bending with torsional or pitch deformation as a power regulating principle. This study investigates the possibility to use a relatively small part of the rotor (only the shanks between rotor centre and largest chord) to function as a passive pitch bearing. Main conclusions are that: a continuous relation between wind speed and pitch angle is feasible; torsional deformation due to normal force and flap bending moment can be designed independently, without coupling lag bending; there is a quasi linear relation between flap bending moment and required pitch angle variation to stall above rated wind speed; a passive pitch bearing has considerable lower inspection and maintenance costs. Further research should be carried out on a more realistic rotor, designed with pitch angle variation. Also the required material properties to reach the amount of coupling within the constraints for fatigue resistance, should be further investigated. 21 figs., 4 tabs., 10 refs., 3 appendices

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