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”
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