Stall-induced vibrations analysis and mitigation of a wind turbine rotor at idling state: Theory and experiment

With the development of wind turbine manufacturing technology, the wind turbine rotor is facing more design challenges for exposing to complex environmental conditions and severe wind loads. This paper investigates the stall-induced vibrations of a wind turbine rotor operating at idling state, and a strategy to mitigate the stall-induced vibrations is proposed. The equations of motion of the wind turbine rotor are established by Hamilton's principle and solved using the finite element method (FEM). The aerodynamic forces are evaluated based on the blade element theory, and the aero-damping is obtained by solving the eigenvalue problem of the rotor system. The stability of the wind turbine rotor is analyzed under different wind speeds, wind deviation angles, azimuth angles and pitch angles. The calculation results show that negative aero-damping exists in specific wind deviation angles, which leads to the divergence of edge-wise motions of the blades. An on-site experimental study validates the criteria of stability of the wind turbine rotor. The present work provides positive outlooks for aeroelastic analysis of the wind turbine blades at idling states, and it is significant for the design and safety improvement of large wind turbine blades.