Tonal Noise Mitigation On Wind Turbines

Xi Engineering

Tones are very easily perceived by human hearing, so that tonal noise from wind turbines seems to increase the annoyance of receivers and has been identified as the primary cause for complaint [1]. Consequently, legislation has been put into place to regulate tonal noise emitted from wind tur-bines, which, if not adhered to can lead to financial penalties, curtailment and even closure of a tur-bine site. The risk of such economic losses has highly motivated the wind turbine industry to de-velop solutions to tonal noise.

A tonal noise mitigation solution has been developed based on free layer damping of the wind turbine tower. This paper presents a case study where vibration measurement combined with finite element (FE) modelling showed that the principal radiation source of tonal noise was the tower wall. Polymer tiles were adhered to the walls of the wind turbine tower, thereby increasing their damping characteristics. This free layer damping solution reduced the amplitude of resonant vibrations responsible for amplifying tonal noise. A validation IEC 61400 measurement showed that the audibility of the tone was significantly reduced, and that the installation also lead to a broadband sound power level reduction.

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