Measurements of the electric output of wind turbines have shown power oscillations with a 3p frequency which are caused by the interaction of the rotor with the supporting structure (tower). Potentially more troublesome than the power variations are the load pulses acting on the blades, the main shaft, the support bearings, the power transmission system, and the tower. These pulses are one factor among many causing the complex state of loading to which a wind energy converter is subjected. Simple aerodynamic modelling of this interaction is not capable of capturing all the effects present such as tower wake meandering, stall delay on the blades, lateral tower loads, and break-up of the rotor wake and trailing tip vorticity. This paper shows a method for estimating the magnitude of these effects based on fully turbulent CFD computations and discusses their importance for the design of structural components. Several turbulence models are used and their advantages and drawbacks are discussed. A better understanding of the aerodynamic and aeroelastic interaction between the rotor and the tower influences design parameters such as the tilt and overhang of the main shaft and should also be considered in the selection of the gear box and in possible modelling of blade damage. It is also shown that the near wake aerodynamics of the rotor has an influence on the far wake behavior making this an important factor for wind park simulations.

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