Investigation of Low-Frequency Noise of Horizontal Axis Wind Turbines by a Hybrid Approach

Noise pollution is known as the biggest environmental problem of horizontal axis wind turbines. The main part of the noise is in the range of Low-Frequency Noise (LFN) since wind turbines rotate slowly. Several studies show that the LFN could have adverse effects on human health. In this study, the LFN generated by NREL VI wind turbine in wind speeds of 13 m/s is calculated by using a hybrid approach. In this approach, noise sources are defined on a data surface (DS), and then the noise propagating form the DS is calculated. The results show that a DS obtained by scaling the blade span with a size factor of 5 is appropriate for surrounding all main sources in this problem. It means, in addition to sources located on blade surface, a significant part of steady sources generating LFN is far from blades. On the other hand, the results show that tip vortices have no significant effect on the LFN.