Modelling of Serrated Trailing Edges to Reduce Aerodynamic Noise in Wind Turbines using Computational Fluid Dynamics

Abstract: An analysis is pursued on how serrations fitted on a section of a wind turbine blade affect noise generation and properties, seeking to ultimately verify its noise mitigation effects. The research is conducted using computational fluid dynamics with aid from a basic acoustic model following the theory developed by Proudman and Lilley, coupled with an analysis of sound properties by the characterization of turbulence length scales present in the flow. An outline of the numerical methods, aeroacoustic principles and the theory behind trailing edge noise generation is presented in order to achieve a more complete understanding of why noise is generated, with what means it can be studied and how it can ultimately be modified. It is found that, for the case at hand, turbulent structures become complex and anisotropic due to the presence of the serrations, thus cutting down on the effectiveness of the chosen acoustic model. The turbulence length scale analysis is used to compliment this method and, by coupling the results from both methods, a conclusion is reached on that noise can be mitigated by using serrated trailing edges since they extend the presence of a more varied range of turbulence length scales, thus reducing the effect of constructive interference from pressure fluctuations generated by eddies shed from the trailing edge of the blade.