The Brazier effect in wind turbine blades and its influence on design

Critical failure was observed in the shear web of a wind turbine blade during a full‐scale testing. This failure occurred immediately before the ultimate failure and was partly caused by buckling and non‐linear cross‐sectional strain. Experimental values had been used to compare and validate both numerical and semi‐analytical results in the analysis of the shear webs in the reinforced wind turbine blade. Only elastic material behaviour was analysed, and attention was primarily focused on the Brazier effect. The complex, geometrically non‐linear and elastic stress–strain behaviour of the shear webs and the cap in compression were analysed using a balance of experimental, numerical and analytical approaches. It was noted that the non‐linear distortion was caused by the crushing pressure derived from the Brazier effect. This Brazier pressure may have a significant impact on the design of new blades, and an optimized box girder had been studied to show the importance of including Brazier pressure in the design process for future wind turbine blades. Copyright © 2011 John Wiley & Sons, Ltd.     

Full‐scale test of trailing edge flaps on a Vestas V27 wind turbine: active load reduction and system identification

A full‐scale test was performed on a Vestas V27 wind turbine equipped with one active 70 cm long trailing edge flap on one of its 13 m long blades. Active load reduction could be observed in spite of the limited spanwise coverage of the single active trailing edge flap. A frequency‐weighted model predictive control was tested successfully on this demonstrator turbine. An average flapwise blade root load reduction of 14% was achieved during a 38 minute test, and a reduction of 20% of the amplitude of the 1P loads was measured. A system identification test was also performed, and an identified linear model, from trailing edge flap angle to flapwise blade root moment, was derived and compared with the linear analytical model used in the model predictive control design model. Flex5 simulations run with the same model predictive control showed a good correlation between the simulations and the measurements in terms of flapwise blade root moment spectral densities, in spite of significant differences between the identified linear model and the model predictive control design model. Copyright © 2013 John Wiley & Sons, Ltd.