A study on the near-surface flow and acoustic emissions of trailing edge serrations: For the purpose of noise reduction of wind turbine blades

The flow near the surface, and the acoustic emissions of trailing edge serrations are investigated in this work. The use of this family of aerodynamic devices on airfoils is intended for the reduction of turbulent boundary layer-trailing edge noise (TBL-TE noise). This purpose has been well demonstrated in wind tunnel and numerical experiments. Particularly, their use in the wind turbine industry has been of great interest in recent years. A growing number of field measurements have shown that a noticeable noise reduction of TBL-TE noise in state-of-the-art blades is also obtained. A full explanation on the mechanism of how noise is reduced is nevertheless lacking. Existing experimental research on serrations offers only a limited characterization of the relevant flow parameters. Fundamental concerns pertaining to the conditions at which that data has been previously gathered are furthermore recurrent. The persistent use of flow-misaligned serrations creates a situation in which flow structures may be observed and misinterpreted as necessary for the attainment of noise reduction. This circumstance complicates the discussion and isolation of the relevant noise reduction mechanism...