Aerodynamic properties of Wind Turbine Towers based on Wind Tunnel Experiments

Abstract 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. A scaled model of a wind energy tower (1:150) in combination with complementary models have been tested in a test bench designed to carry out HFFB, dynamic wind pressure 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 length related correlation of vortices shedding from cylindrical structures plays an important role. Therefore, wind dynamic pressures were measured along static tower and cylinder models using pressure taps to determine realistic values of the vortex shedding correlation length. 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 prism models and tower model. The measured base model forces were correlated with the model motion using spectral methods to obtain the corresponding 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