Determination of aerodynamic damping and vortex-shedding correlation length of wind turbine towers based on wind tunnel experiments with high frequency force balance (HFFB) and forced-oscillations methods

Abstract eng:
The presented investigations aim to suggest more realistic models to predict the dynamic behavior of wind turbine structures. Two key issues are addressed: the aerodynamic damping and the cross-wind vibrations. Based on experimental studies in the boundary layer wind tunnel, aerodynamic information for both effects has been obtained. Cylindrical models derived from a scaled model of a wind energy tower (1:150) have been tested in a test bench designed to carry out HFBB, dynamic wind pressures and forced-oscillation experiments. Reynolds number based scale effects on the tower model have been studied previously. In the predictions of cross-wind vibrations, the vortex shedding correlation length plays an important role. Therefore, wind dynamic pressures were measured along static cylinder models using pressure taps to determine realistic values of this magnitude. Motion-induced wind vibrations can be significantly influenced by the aerodynamic damping. Using the forced-oscillations method, experiments have been performed under controlled system oscillation with varying wind speed in cylinder models. The measured base model forces were correlated with the model motion using spectral methods to obtain the aerodynamic stiffness and damping coefficients. Both aerodynamic studies will allow more detailed models for the design of new wind tower structures. The acquired information will be applicable in MB-simulations to obtain more realistic and accurate wind turbine performances

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