Long-range downwind propagation of low-frequency noise

Willshire, William L.

doi:10.1121/1.2022591

Cited by 7 publications

(5 citation statements)

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“…When downwind of a turbine the sound refracts downwards and reflects off of the ground. This refraction is pronounced at low frequencies, with 8Hz sound levels at 5000m reaching up to 20dB higher than expected for spherical spreading (Willshire 1985). A temperature inversion, where the temperature at ground level is lower that the temperature higher in the atmosphere, also causes downward refraction of sound and will lead to similar effects.…”

Section: Possible Noise Mechanismsmentioning

confidence: 94%

A discussion of wind turbine interaction and stall contributions to wind farm noise

Laratro

Arjomandi

Kelso

et al. 2014

Journal of Wind Engineering and Industrial Aerodynamics

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Elsevier's Policy: An author may use the preprint for personal use, internal institutional use and for permitted scholarly posting. ... Elsevier's AAM Policy: Authors retain the right to use the accepted author manuscript for personal use, internal institutional use and for permitted scholarly posting provided that these are not for purposes of commercial use or systematic distribution. Elsevier believes that individual authors should be able to distribute their AAMs for their personal voluntary needs and interests, e.g. posting to their websites or their institution's repository, e-mailing to colleagues. However, our policies differ regarding the systematic aggregation or distribution of AAMs to ensure the sustainability of the journals to which AAMs are submitted. Therefore, deposit in, or posting to, subject-oriented or centralized repositories (such as PubMed Central), or institutional repositories with systematic posting mandates is permitted only under specific agreements between Elsevier and the repository, agency or institution, and only consistent with the publisher's policies concerning such repositories. Voluntary posting of AAMs in the arXiv subject repository is permitted. ... Highlights-Rotor-wake interaction plays a role in wind farm noise -More wake data needs to be collected -Dynamic stall noise needs to be characterised AbstractWind farms have recently been reported to produce a noise signature that is described as possessing a "thumping" quality. Measurements of these signatures are limited and their effects are debated but their effect on public opinion and complaints make them a concern for researchers in this field. Proposed reasons for these noise signatures include amplitude modulation, interference patterns and wake-rotor interaction. This paper discusses these effects and concludes that wake-rotor interaction plays a role by causing variations in turbulent-inflow noise and dynamic stall. The current state of research into stall noise and wind turbine wake structure is also reviewed and it is concluded that the available information and collected data on wind turbine wake are insufficient to determine how strong this role is. More information on the velocity and turbulence fields in the wake of horizontal-axis wind turbines as well as a characterisation of the noise produced by an airfoil experiencing dynamic stall is required in order to make a full assessment of rotor-wake contributions to wind farm noise.2

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Section: Possible Noise Mechanismsmentioning

confidence: 94%

A discussion of wind turbine interaction and stall contributions to wind farm noise

Laratro

Arjomandi

Kelso

et al. 2014

Journal of Wind Engineering and Industrial Aerodynamics

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“…We cannot distinguish with the present instrumentation if the signal is TS and/or amplitude modulation of other high-frequency WT-sound types (with sufficiently low frequency to support long-distance propagation) with similar spectral characteristics (peaks at the blade-passing frequency). Previous studies [Willshire, 1985;Son et al, 2010;Ohlund and Larsson, 2015] have reported and modeled the propagation of WT sound to distances from few hundreds of meters to several kilometers. This study shows that WT noise can be detected at distances of several tens of kilometers.…”

Section: Discussionmentioning

confidence: 99%

On infrasound generated by wind farms and its propagation in low‐altitude tropospheric waveguides

et al. 2015

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Infrasound from a 60‐turbine wind farm was found to propagate to distances up to 90 km under nighttime atmospheric conditions. Four infrasound sensor arrays were deployed in central New Mexico in February 2014; three of these arrays captured infrasound from a large wind farm. The arrays were in a linear configuration oriented southeast with 13, 54, 90, and 126 km radial distances and azimuths of 166°, 119°, 113°, and 111° from the 60 1.6 MW turbine Red Mesa Wind Farm, Laguna Pueblo, New Mexico, USA. Peaks at a fundamental frequency slightly below 0.9 Hz and its harmonics characterize the spectrum of the detected infrasound. The generation of this signal is linked to the interaction of the blades, flow gradients, and the supporting tower. The production of wind‐farm sound, its propagation, and detection at long distances can be related to the characteristics of the atmospheric boundary layer. First, under stable conditions, mostly occurring at night, winds are highly stratified, which enhances the production of thickness sound and the modulation of other higher‐frequency wind turbine sounds. Second, nocturnal atmospheric conditions can create low‐altitude waveguides (with altitudes on the order of hundreds of meters) allowing long‐distance propagation. Third, night and early morning hours are characterized by reduced background atmospheric noise that enhances signal detectability. This work describes the characteristics of the infrasound from a quasi‐continuous source with the potential for long‐range propagation that could be used to monitor the lower part of the atmospheric boundary layer.

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“…The emphasis is on the environmental parameters that must be specified and the assumptions that must be made in order to apply ray theory to the experiment. Much of the material in this section is drawn from reports by Willshire [5] and Shepherd and Hubbard [16].…”

Section: Scope Of Topics and Resultsmentioning

confidence: 99%

“…Upon further investigation, he concluded that the predicted sound levels based solely on the contribution of the ground wave fell far below the measured levels [5]. Following Willshire's experiments, other investigations were undertaken, the purpose of which was to explain…”

Section: Possible Approachesmentioning

confidence: 99%

Application of ray theory to propagation of low-frequency noise from wind turbines

Hawkins

1987

The Journal of the Acoustical Society of America

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Ray theory has been used to attempt to explain the propagation of very low-frequency (1–20 Hz) noise generated by downwind wind turbines. Two NASA field experiments with a large downwind machine at Medicine Bow, Wyoming, show that the downwind sound decays by spherical spreading near the source, but by cylindrical spreading downrange. Ray theory calculations explain this behavior. The favorable wind gradient downwind causes rays to refract downward and bounce along the ground. A sound channel is built up by repeated jumps in the number of ray arrivals at the receiver as downwind range is increased. Near the source, where no multiply reflected rays arrive, the sound field spreads spherically. The first jump (onset of multiple arrivals) is predicted to occur at about 2 km for the conditions of the NASA experiments. The second NASA experiment confirms this prediction. For the upwind sound, a shadow zone is predicted because of the unfavorable wind gradient. The NASA measurements show only that the upwind SPL in the predicted shadow zone is of order 7–15 dB less than the downwind SPL at comparable ranges. [Work supported by NASA.]

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Long-range downwind propagation of low-frequency noise

Cited by 7 publications

References 0 publications

A discussion of wind turbine interaction and stall contributions to wind farm noise

A discussion of wind turbine interaction and stall contributions to wind farm noise

On infrasound generated by wind farms and its propagation in low‐altitude tropospheric waveguides

Application of ray theory to propagation of low-frequency noise from wind turbines

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