Quantification of aeroacoustic noise sources from wind turbines

One of the major environmental concerns regarding wind energy is an increase in noise levels, both in the atmosphere and the ocean. In this study, the generation and propagation of aeroacoustic noise from wind turbines were studied using available measurements together with several signal processing tools, as well as some well-known models within the field. The thesis starts by introducing some general and more advanced concepts regarding wind energy and aeroacoustics. Observational measurements conducted in a gust wind tunnel on a scaled wind turbine model were used to quantify noise characteristics from wind turbines. The experiment was conducted using 48 microphones in a ring array, with a known distance from the source. Then, a simple beamforming algorithm based on delay-and-sum in both 1D and 2D has been applied to identify the distribution of acoustic source strength on the turbine blade and subregions. An open-source program for the Amiet model was adjusted for studying the turbulence interaction and noise generation on the same NACA4412-airfoil, with some simplifications applied. Next, the low-frequency Parabolic Equation model (PE-model) for an inhomogeneous atmosphere was used to study the effect of different atmospheric stability conditions on noise propagation from a wind turbine. Tests for three stability conditions (stable, neutral, and unstable) for variations of source frequencies, as well as for different topography were presented and discussed. The studies conducted in this thesis illustrate the complexity of aeroacoustic noise and the different parts that need to be accounted for in the development of new wind farms, both onshore and offshore.Masteroppgåve i energiENERGI399