Classical aeroelastic stability analysis of large composite wind turbine blades

Abstract

To achieve higher energy production bigger wind turbine systems with very long blades are increasingly used in the wind turbine industry. As the length of the wind turbine blades is increased, blades become more flexible in bending and torsion. Increased bending and torsional flexibility of long wind turbine blades may cause torsional divergence and flapwise bending-torsion flutter at high speeds. Therefore, it is important that aeroelastic stability characteristics of the blades be investigated to ensure that wind turbine system is free of any aeroelastic instability. In this study, classical aeroelastic stability approach is applied to a simplified composite blade model. For the purpose of the study, the composite wind turbine blade is modeled as an elastic cantilevered rotating thin-walled composite box beam with the developed Circumferentially Asymmetric Stiffness (CAS) structural model. Circumferentially asymmetric stiffness structural model takes into account a group of non-classical effects such as the transverse shear, the material anisotropy and warping restraint. The aerodynamic strip method based on indicial function in unsteady incompressible flow is used to simulate incompressible unsteady aerodynamic effects. Hamilton’s principle and the extended Galerkin’s method are used to obtain the coupled linear governing system of dynamic equations. Preliminary results show that fiber angle of the CAS structural model affects the aeroelastic instability speed significantly and fiber angle also controls the aeroelastic instability mode.