Effect of blade and tower interference on wind turbine tower vibration occurred before grid connection

Abstract

The towers of large-scale wind turbines often experience low-frequency oscillations in the months before grid connections, threatening the turbines safety. The NREL offshore 5 MW wind turbine is investigated using computational fluid dynamics, to investigate oscillation mechanisms involving blade-tower interference. The multibody dynamics method is used to study the vibration response induced by two vortices. The results reveal that the interaction of tower and blade trailing vortices forms a larger vortex street, increasing the size and deviation of the tower’s trailing vortex. The merging of wake vortices reduces the shedding frequency, intensifies the dynamic response of the overall structure, and results in a 6-fold pressure increase exerted on the tower surface, consequently the vortex-induced resonance effects are strengthened. The lift force induced by the blade and tower trailing vortice is substantially increased and larger than that conventionally induced by a single tower’s trailing vortex. At a wind speed of 6 m/s, the maximum lift coefficient amplitude is increased by six-fold. Two-vortices interference makes vibration particularly severe at yaw angles from 40° to 50°. At 50° yaw angle, the torque at tower bottom is seven times larger than that in the nonyaw case, with lateral displacement reaching 0.97 m and forward–backward displacement reaching 0.60 m.