Modelling of Ice Throw and Noise from Wind Turbines

To assess the impact of the issues related to ice throw and noise from the wind turbine two independent mathematical models were developed. A model of the trajectories of ice fragments thrown from a rotating wind turbine blade is used to estimate the ground impact locations that could occur under different scenarios. Wind speed, ejection position on the blade and turbine rotation rate play a role in determining the impact point, as well as mass, density and drag coefficient of the ice fragment. For 'compact' ice fragments, the trajectory depends on the combination CDA/M where CD is the drag coefficient, A is the frontal area and M the mass of the ice fragment. Sensitivity tests show that ice fragments can travel further laterally for low CD and further downwind for high CD. For plate-like fragments, aerodynamic lift can increase the distance travelled if the plate maintains an orientation to maximize lift. Although this may be a relatively rare event, but result from the simulation shows a case, where a 1 kg plate-like fragment could travel up to 350 m from the base of the turbine. Another model based on the ray theory is developed to simulate propagation of sound from a point source. The model incorporates propagation loss, loss due to refraction, ground interaction and atmospheric absorption. Sound pressure level at a specific distance from the sound source can be calculated using the model. Variation in the terrain feature is included to investigate its impact on the ray trajectory.