The Influence of Periodic Wind Turbine Noise on Infrasound Array Measurements

Significance Statement

Wind turbine noise is a combination of audible acoustic and infrasonic components. Low infrasonic background noise is a prerequisite for infrasound detections of conceivable nuclear explosions in the atmosphere in the context of monitoring compliance with the Comprehensive Nuclear Test-Ban Treaty (CTBT). Aerodynamic noise emitted from the endlessly growing number of wind turbines in Germany is increasingly creating problems for the infrasound recording systems. During each revolution, the wind turbine blades encounter much variation in the air flow generated by changes in intensity and wind direction when flowing around the structural tower. As the wind turbine blade revolution process is repetitive, impulsive sound signals consisting of pure tones which are integer multiples of the fundamental blade-passing harmonic are generated. Consequently, studies on the intensity and frequency of the aerodynamic infrasonic noise signals produced have gained much interest.

In a recent paper published in Journal of Sound and Vibration Christoph Pilger and Lars Ceranna from The Federal Institute for Geosciences and Natural Resources (BGR) in Germany studied the influence of periodic wind turbine noise on infrasound array measurements. Their aim was solely focused on the effects of the infrasonic component of wind turbine noise on infrasound measurements by microbarometer arrays.

For the researchers to determine the emission of the infrasound signals by the wind turbines, a field campaign was carried out near a single 200kW horizontal axis turbine north of Hanover. Additionally, ten years of infrasound data recorded at the German infrasound array IGADE, were analyzed with respect to influences of nearby wind turbines. Theoretical models were then derived and validated by the field measurements using mobile microbarometer stations. Model computations on the influence of single versus multiple wind turbines and the effect of ducting and propagation on the sound pressure levels of infrasound observations were included and presented. Discussions and conclusions on least distances between wind turbines and infrasound arrays were derived from the model calculations of sound pressure levels in the infrasonic frequency range and verified by infrasound observations.

It was observed that at certain frequencies and during nearly all years and seasons, the aerodynamic sound waves of the BPH increased the SPL detected and quantified by the sensors. Blade-passing harmonics with multiples of 1 to 1.4Hz frequency were observed to occur during most of the observations and had the highest spectral increase compared to neighboring frequencies. From the model the researchers were able to estimate the generated sound pressure level of wind turbines and thus making it possible for specification of the minimum allowable distance between wind turbines and infrasound stations for undisturbed recording.

study demonstrated that a minimum distance of 20 km should be maintained between an infrasound station and a single wind turbine so as to guarantee unhindered recording and detection conditions. In the case of multi element wind farm, the distance would need to be increased to 50 km. However, if only occasional tropospheric ducts increasing the surface-near sound levels are considered, 5-10 km and 10-15 km would be adequate and sufficient to allow unhindered recording and detection conditions for a single turbine and a wind farm respectively.

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About The Author

Dr. Lars Ceranna, Diploma in Geophysics at the Ruhr-University Bochum in 1997. PhD in Seismology at the Ruhr-University Bochum in 2002. Research fellow at the Federal Institute for Geosciences and Natural Resources (BGR) in Hannover from 2002 to 2008. Since 2009 unit head for “Monitoring and Verification” and deputy chief of the sub-department for “Seismological Central Observatory, Nuclear Test Ban”.

Previous scientific activities include studies on numerical simulations of seismic wave-propagation in inhomogeneous media, as well as simulations and analyses of infrasound propagation in the atmosphere generated by natural and anthropogenic sources. Moreover, activities include contributions to the Atmospheric dynamics Research InfraStructure in Europe (ARISE), and to compliances with the verification of the Comprehensive Nuclear-Test-Ban Treaty (CTBT). Results have been published in Bulletin of the Seismological Society of America, Seismological Research Letters, Geophysical Journal International, Geophysical Research Letters, Natural Hazards and Earth System Sciences, Journal of Seismology, Journal of Geophysical Research, Pure and Applied Geophysics, InfraMatics, Journal of Sound and Vibration, and Nature.

Latest scientific studies include evaluations of the CTBT infrasound network performance to detect the 2013 Russian fireball event, as well as to monitor active volcanoes, and characterization of the influence of periodic wind turbine noise on infrasound array measurements.

About The Author

Dr. Christoph Pilger, Diploma in Mathematics at the University of Bonn in 2005. PhD in Atmospheric Physics at the University of Augsburg in 2011. Project scientist at the German Aerospace Center (DLR) in Oberpfaffenhofen from 2006 to 2012 and Research Associate at the German Federal Institute for Geosciences and Natural Resources (BGR) in Hannover since 2012.

Previous scientific activities include contributions to the German-Indonesian Tsunami Early Warning System (GITEWS), to the Network for the Detection of Mesosphere Change (NDMC) and to the Atmospheric dynamics Research InfraStructure in Europe (ARISE), as well as publications in the Journal of Atmospheric and Solar-Terrestrial Physics, Natural Hazards and Earth System Sciences, InfraMatics, Geophysical Research Letters, Journal of Geophysical Research and Journal of Sound and Vibration.

Current assignment at the German National Data Center of the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) situated in BGR’s sub-department “Central Seismological Observatory, Nuclear Test Ban”. Research topics are infrasound data processing, acoustic noise characterization, detection capability estimation and seismo-acoustic studies. More than ten years of experience in infrasound, atmospheric wave dynamics and wave propagation modeling.

Latest scientific studies include quantifications of the CTBT infrasound network performance to detect the 2013 Russian fireball event and of the influence of periodic wind turbine noise on infrasound array measurements.

Reference

Christoph Pilger, Lars Ceranna. The influence of periodic wind turbine noise on infrasound array measurements. Journal of Sound and Vibration. volume 388 (2017) pages 188–200

Bundesanstalt für Geowissenschaften und Rohstoffe (BGR), Stilleweg 2, 30655 Hannover, Germany.

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