Different sound source setups in the simulation of wind turbine sound propagation

Kurzfassung

During the development phase of a windfarm project, assumptions are made as to the acoustic propagation conditions of the wind farm noise. During the operation phase, the results of a wind farm noise measurement can only be compared to the prediction as far as the effective operating conditions match the assumptions made for the acoustic propagation calculation. The micrometeorology at the wind farm site and at the dwellers locations has a large impact on the acoustic propagation. Practical and effective methods of collecting information on the micrometeorology have yet to be developed for the specific needs of wind farm acoustics. Hints on possible methods can be derived from the experience gained in the realm of the acoustic assessment of ground-based noise sources. The height profile of the speed of sound must be considered. It is related to the vertical wind profile and the temperature gradient, which depends on the cloud cover and the solar radiation but the question arises how to collect detailed site-specific information. After many years using for wind farms, and their noise sources at high height, the same methods which have been developed for ground-based noise sources, some discrepancies have appeared which called for justifications or for more specific assessment methods. In several countries, detailed investigations have been performed which show how the results of an acoustic propagation calculation depends on the assumptions on the properties of the atmosphere as a propagation medium. Collecting detailed information especially about the vertical temperature gradients and the wind shear is recommended during wind farm noise measurements.