An analytical model for deformation analysis of wind turbine adaptive blades

Abstract

Abstract An analytical model capable of predicting the induced deformation due to the presence of bend-twist and stretch-twist elastic couplings in multi-cell closed thin walled beams with arbitrary cross-sections is presented. For various structural and material configurations, the results obtained by the developed model are compared with the results of the finite element analysis. It is shown that the developed analytical model provides reasonable accuracy in predicting induced twist. The developed model is implemented in an aero-structure simulation environment for simulation of wind turbines utilising adaptive blades. Keywords: thin-walled beam, multi-cell closed thin walled beams, adaptive blades, elastic coupling, bending-twist coupling, wind turbine composite blade 1 Introduction Fibrous composite materials have been broadly used in aeronautical and aerospace structures due to their proven advantages, such as high strength-weight ratios. One particular application of these materials is in fabricating smart and adaptive aerodynamic lifting surfaces such as wind turbine adaptive blades and aircraft smart wings. An adaptive blade acts as an open-loop controller that senses the wind velocity or rotor speed variations and adjusts its aerodynamic characteristics accordingly to improve the wind turbine performance. This self-control system can be achieved by implementing elastic coupling in the structure of the blade. In order to determine the aerodynamic performance of adaptive blades at various loading conditions, a structural analyser is required to calculate the induced deformation of the blade. Figure (1) shows the simulation environment for wind turbines utilising this type of blades. Torsional deformation of an adaptive blade is the key parameter influencing the wind turbine aerodynamic performance. The accuracy of the predicted torsional deformation is crucial in simulation and design of adaptive blades [1, 2]. A number of analytical models of anisotropic thin-walled beams have been proposed for box beams. Most of researchers employed strain energy and virtual work methods to study the static and dynamic characteristic of thin- and thick-walled beams. Chandra et al. [3] and Kim and White [4] developed analytical models for circumferentially asymmetric stiffness (CAS) and circumferentially uniform stiffness (CUS) for single-cell box beams. They considered the bending, torsional and extensional loads and included shear and warping effects. Their model was, however, limited to rectangular cross-sections. Wu et al. [5]