Structural response to aeroelastic phenomena and cross-wind vibrations of large wind turbine towers

The large wind turbine tower is highly slender and susceptible to both turbulent wind-induced vibrations and aeroelastic phenomena. The present paper discusses and reports the recent findings on two aeroelastic phenomena: firstly, Vortex-Induced Vibration (VIV) on free-standing tower and fully-built parked wind turbine, and secondly, Interference Galloping on grouped configurations of wind turbine towers. VIV causes large periodic cross-wind vibrations, predominantly harmonic, due to vortex resonance with the structural motion. Full-scale measurements on large wind turbine towers in the Test Centre Østerild were performed as the main investigation tool on VIV response modelling, validation, and the applicability of correct-Reynolds number aerodynamic coefficients and vortex shedding parameters. Insights are provided into first-mode VIV, higher-mode VIV, and the potential superposition to cross-wind gust buffeting, causing sustained cross-wind oscillations in post-lock-in wind velocity. Interference galloping on grouped towers and its interaction with VIV are studied through wind tunnel tests on various group and Scruton number configurations. The effect of high Scruton number is found to reduce VIV amplitude and delay the onset velocity of interference galloping. The findings are summarized into recommendations for design that can be considered for the standards and design process of wind turbine tower.