Vibration analysis and system identification for a vertical-axis wind turbine installation in built environment

This study deals with the analysis and identification of the dynamic response of a vertical-axis wind turbine (VAWT) for residential use. The VAWT has been installed on a free standing steel tower and the system has been equipped of a decoupling device: vibrations are measured before and after the damper and the spectra in the frequency domain are interpreted. The decoupler is shown to mitigate the frequency contribution which is the third multiple (3P) of the fundamental shaft rotation frequency, but a resonance with the free beam oscillations arise: this indicates that the structural design of the device should be carefully tuned, in order to avoid that the damping interferes with the operation of the wind turbine. The transfer function between the pre and post-decoupler accelerations has been estimated numerically in the Laplace domain. This analysis reveals as well the vibration components (in term of orders) which are difficult to be damped by the decoupler: this gives interesting hints on the possible mechanical improvement of the system design.