Auralization of Wind Turbine Noise: Propagation Filtering and Vegetation Noise Synthesis

An auralizator for wind turbine noise consists of an emission synthesizer, a propagation filter, a vegetation noise synthesizer and a suitable reproduction system. This article describes the propagation filtering, considering the specific geometry of a highly elevated source and distant receivers, and the vegetation noise synthesizer. It is shown that the propagation filtering can be implemented efficiently as a series of finite impulse response filters (FIR) with a relative small number of taps. Measurements have revealed that a wind turbine has to be modeled as largely extended source in order to correctly simulate the ground effect. Based on numerical simulations, a model to incorporate energy neutral short-time level fluctuation effects was derived. Due to the source extension, the fluctuations are significantly smaller than expected for a concentrated point source. The vegetation noise synthesizer uses an emission model that predicts a wind speed dependent volume-specific sound power spectrum for different tree species. The model is steered by a time varying wind speed function that is generated by a random process with a predefined power density spectrum.