The wake of a wind turbine and its influence on sound propagation

The wake of a single wind turbine was measured with a Doppler wind lidar system during a night with a well developed low-level jet. Two meteorological microscale models with different model assumptions were applied to the same situation to generate consistent three-dimensional fields of wind components, turbulent kinetic energy and temperature. A three-dimensional ray-based sound particle model was used to simulate the propagation of the wind turbine noise into the downwind area. Two-dimensional sound propagation simulations were performed on the basis of the lidar measurements and three-dimensional simulations were based on the results of the meteorological models. Both meteorological models are capable of reproducing the main features of the measured wake flow. However, the results differ in many details from each other as well as from the lidar measurements. The acoustical model results show that the wake flow favours the sound propagation from the upper sources (aerodynamic noise at the wing tips near the crest of the rotor plane) towards the ground. The acoustical simulations also suggest a high sensitivity of the noise impact near the ground to differences between the simulated meteorological fields.