A new base of wind turbine noise measurement data and its application for a systematic validation of sound propagation models

Abstract. Extensive measurements in the area of wind turbines were performed in order to validate a sound propagation model which is based on the Crank-Nicolson Parabolic Equations method. The measurements were carried out over a flat grass-covered landscape and under various environmental conditions. During the measurements, meteorological and wind turbine performance data were acquired and acoustical data sets were recorded in distances of 178, 535, and 845 m to the wind turbine. By processing and analyzing the measurement data, validation cases and input parameters for the propagation model were derived. The validation includes five groups that are characterized by different propagation directions, i.e. down-, cross- and upwind conditions in varying strength. Comparing measured and modeled propagation losses, a general good agreement is observed for all groups. Considering all groups and distances, the absolute averaged difference of the measured and modeled losses in total sound pressure level is 0.9 dB. At large distances, the propagation losses are slightly underestimated by the model. The model represents the measured propagation losses in the 1/3 octave spectra well. As in the measurements, frequency-dependent maxima and minima are identified and losses generally increase with increasing distance and frequency. For good results in upwind situations, turbulence has been considered in the model. The data sets used in the validation are available for further research.