Resource Documents: Noise (513 items)
Documents presented here are not the product of nor are they necessarily endorsed by National Wind Watch. These resource documents are provided to assist anyone wishing to research the issue of industrial wind power and the impacts of its development. The information should be evaluated by each reader to come to their own conclusions about the many areas of debate.
Author: Wiser, Ryan; Yang, Zhenbin; et al.
[section 126.96.36.199 (pp. 575-576), “Wind Energy,” IPCC Special Report on Renewable Energy Sources and Climate Change Mitigation, 2011]
A variety of proximal ‘nuisance’ effects are also sometimes raised with respect to wind energy development, the most prominent of which is noise. Noise from wind turbines can be a problem, especially for those living within close range. Possible impacts can be characterized as both audible and sub-audible (i.e., infrasound). There are claims that sub-audible sound, that is, below the nominal audible frequency range, may cause health effects (Alves-Pereira and Branco, 2007), but a variety of studies (Jakobsen, 2005; Leventhall, 2006) and government reports (e.g., FANM, 2005; MDOH, 2009; CMOH, 2010; NHMRC, 2010) have not found sufficient evidence to support those claims to this point. Regarding audible noise from turbines, environmental noise guidelines (EPA, 1974, 1978; WHO, 1999, 2009) are generally believed to be sufficient to ensure that direct physiological health effects (e.g., hearing loss) are avoided (McCunney and Meyer, 2007). Some nearby residents, however, do experience annoyance from wind turbine sound (Pedersen and Waye, 2007, 2008; Pedersen et al., 2010), which can impact sleep patterns and well-being. This annoyance is correlated with acoustic factors (e.g., sound levels and characteristics) and also with non-acoustic factors (e.g., visibility of, or attitudes towards, the turbines) (Pedersen and Waye, 2007, 2008; Pedersen et al., 2010). Concerns about noise emissions may be especially great when hub-height wind speeds are high, but ground-level speeds are low (i.e., conditions of high wind shear). Under such conditions, the lack of wind-induced background noise at ground level coupled with higher sound levels from the turbines has been linked to increased audibility and in some cases annoyance (van den Berg, 2004, 2005, 2008; Prospathopoulos and Voutsinas, 2005).
Significant efforts have been made to reduce the sound levels emitted by wind turbines. As a result, mechanical sounds from modern turbines (e.g., gearboxes and generators) have been substantially reduced. Aeroacoustic noise is now the dominant concern (Wagner et al., 1996), and some of the specific aeroacoustic characteristics of wind turbines (e.g., van den Berg, 2005) have been found to be particularly detectable (Fastl and Zwicker, 2007) and annoying (Bradley, 1994; Bengtsson et al., 2009). Reducing aeroacoustic noise can be most easily accomplished by reducing blade speed, but different tip shapes and airfoil designs have also been explored (Migliore and Oerlemans, 2004; Lutz et al., 2007). In addition, the predictive models and environmental regulations used to manage these impacts have improved to some degree. Specifically, in some jurisdictions, both the wind shear and maximum sound power levels under all operating conditions are taken into account when establishing regulations (Bastasch et al., 2006). Absolute maximum sound levels during the day (e.g., 55 A-weighted decibels, dBA) and night (e.g., 45 dBA) can also be coupled with maximum levels that are set relative to pre-existing background sound levels (Bastasch et al., 2006). In other jurisdictions, simpler and cruder setbacks mandate a minimum distance between turbines and other structures (MOE, 2009). Despite these efforts, concerns about noise impacts remain a barrier to wind energy deployment in some areas.
In addition to sound impacts, rotating turbine blades can also cast moving shadows (i.e., shadow flicker), which may be annoying to residents living close to wind turbines. Turbines can be sited to minimize these concerns, or the operation of wind turbines can be stopped during acute periods (Hohmeyer et al., 2005). Finally, wind turbines can shed parts of or whole blades as a result of an accident or icing (or more broadly, blades can shed built-up ice, or turbines could collapse entirely). Wind energy technology certification standards are aimed at reducing such accidents (see Section 7.3.2), and setback requirements further reduce the remaining risks. In practice, fatalities and injuries have been rare (see Chapter 9 for a comparison of accident risks among energy generation technologies).
Significant infrasound levels a previously unrecognized contaminant in landmark motion sickness studies
Author: Dooley, Kevin
Abstract. Airborne Infrasound at any given point can be accurately described as fluctuations or cyclic changes in the local barometric pressure. Variations in a motion sickness test subject’s elevation, result in fluctuations in the surrounding barometric pressure by a similar amount to that experienced on a ship in high seas. Cyclic variation in the lateral or linear velocity of a subject in a vehicle or platform in atmospheric air may also be subject to infrasonic pressure fluctuations due to the Bernoulli principle and associated with vortex shedding effects. Calculations presented demonstrate that in at least one landmark study (McCauley et al 1976) test subjects were exposed to infrasonic sound pressure levels in excess of 105 dB at discrete frequencies between 0.063 Hz and 0.7Hz. The infrasonic sound pressure level necessarily present in cyclic motion in free atmospheric air does not appear to have been accounted for as a nausea influencing factor in the McCauley et al (1976) motion sickness studies.
Proceedings of Meetings on Acoustics, Vol. 20, 040007 (2014)
Acoustic interaction as a primary cause of infrasonic spinning mode generation and propagation from wind turbines
Author: Dooley, Kevin; and Metelka, Andy
Abstract. Relatively balanced load related pressure waves from the rear surface of each rotor blade, are at a frequency of 1 per revolution of the turbine and are phase shifted by 120 degrees from each other. The superpositions of these infrasonic waves destructively interfere. This action results in a non-propagating rotor locked mode, however, the shielding (reflecting) effect of the tower as each blade passes, interrupts the balanced destructive interference for a small portion of rotor angle three times per revolution. The momentary un-balance between the destructive interfering waves, results in the generation of Tyler-Sofrin spinning mode series, which propagate into the far field. The spinning mode radiation angles, coupled with the low decay rate of infrasound, result in higher far field sound pressure levels than would be predicted for a point source. An analysis approach partially derived from Tyler-Sofrin (1962) is presented. Field microphone data including phase measurements identifying the spinning modes are also presented.
Kevin A. Dooley, Kevin Allan Dooley Inc., Toronto, Ontario, Canada.
Andy Metelka, Sound and Vibrations Solutions Inc., Acton, Ontario, Canada.
The Journal of the Acoustical Society of America 2013; 134: 4097.
Author: Vanderkooy, John; and Mann, Richard
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
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