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Measuring Wind Turbine Coherent Infrasound  

Author:  | Noise, Technology

Abstract. To extract the optimum coherent infrasound signal from a wind turbine whose rotation is not precisely periodic, we use an optical telescope fitted with a photodetector to obtain reference blade passage periods, recording these together with the microphone infrasound signal. Signal processing of the quasi-periodic microphone signal is then used to obtain periodic data, which are analyzed by an appropriate length DFT [discrete Fourier transform] to extract optimum values for the fundamental and harmonics of the coherent signal. The general procedure is similar to order domain analysis for rotating machines and is thoroughly explained and illustrated with measurements and analysis from a number of different wind farms. If several turbines are measured by a single microphone with blade passage periods obtained from several separate reference tracks, it may be possible to retrieve separate useful coherent signals from multiple turbines by appropriate processing. … Our analysis reveals a characteristic infrasonic pulse. We conjecture that the pulse from a single WT is caused by the interaction of the blades against the pylon, while the rather more complex background signal relates to the radiation of the Tyler-Sofrin spinning modes.

John Vanderkooy, Department of Physics and Astronomy
Richard Mann, Department of Computer Science
University of Waterloo, Waterloo, Ontario, Canada
2 October, 2014

Download original document: “Measuring Wind Turbine Coherent Infrasound

Some references:

Aeroacoustics of large wind turbines. Harvey H. Hubbard and Kevin P. Shepherd. J Acoust Soc Am 1991; 89: 2495. http://dx.doi.org/10.1121/1.401021

Acoustic interaction as a primary cause of infrasonic spinning mode generation and propagation from wind turbines. Kevin A. Dooley and Andy Metelka. J Acoust Soc Am 2013; 134: 4097. http://dx.doi.org/10.1121/1.4830965

Responses of the ear to low frequency sounds, infrasound and wind turbines. Alec N. Salt and Timothy E. Hullar. Hear Res 2010 Sep 1; 268(1-2): 12-21. http://dx.doi.org/10.1016/j.heares.2010.06.007

Approximately 20 Hz plus harmonics amplitude modulated acoustic emissions from a 1.6 MW wind turbine, measurements versus predictions. Kevin A. Dooley and Andy Metelka. J Acoust Soc Am 2014; 135: 2272. http://dx.doi.org/10.1121/1.4877444

Significant infrasound levels a previously unrecognized contaminant in landmark motion sickness studies. Kevin A. Dooley. POMA 2014; 20: 040007. http://dx.doi.org/10.1121/1.4868716

This article is the work of the author(s) indicated. Any opinions expressed in it are not necessarily those of National Wind Watch.

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