Wind Model for Simulation of Thrust Variations on a Wind Turbine

Abstract

The aerodynamic thrust induced by the air passing through the wind turbine rotor is transferred on to the tower and support structure, causing vibrations with increased fatigue as a consequence. To support the development of control strategies with the aim of reducing structural wear this paper provides a computationally efficient simulation model for the aerodynamic thrust on a wind turbine. The model is based on an equivalent wind formulation accounting for the effect of wind shear, tower shadow, turbulence and rotational sampling. Wind shear is shown to have a depleting effect on the mean rotor thrust. Both wind shear and tower shadow cause thrust variations oscillating with the blade passing frequency, the effect of wind shear is however small compared to the effect of tower shadow in this regard. The model accounting for turbulence and rotational sampling is verified by comparison with results obtained using the software code HAWC2 by DTU Wind Energy. The model shows good agreement although thrust variations are slighlty overestimated due to the lack of unsteady aerodynamics in the model.