Resource Documents: Technology (139 items)
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Author: Thorsson, Pontus
In most countries there are regulations of wind turbine sound level outdoors at dwellings. Often there are also regulations of the sound levels inside the dwelling, however not often directly aiming at wind turbine sound. The sound level indoors from wind turbines has attracted more interest in the latest years, and then especially in the low frequency region (up to 200 Hz). Studies on the in situ sound level difference between outside and inside of dwellings are however scarce. This paper presents the in situ measured sound level difference for two Swedish houses in rural locations, both using a loudspeaker and using the wind turbine sound as exciting signal. This is possible due to a 2 month long measurement series with simultaneous sound recordings outside and inside. The sound pressure level differences from the two methods are shown to differ substantially.
Pontus THORSSON, Akustikverkstan, Lidköping, Sweden
Proceedings of the 23rd International Congress on Acoustics, 9–13 September 2019, Aachen, Germany: pages 3826-3830
Download original document: “In situ measured facade sound insulation of wind turbine sound”
Denmark, Europe, Germany, Italy, Netherlands, Noise, Regulations, Technology •
Author: Marini, Martino; et al.
The enduring energy scenario leads to further promote the development of the exploitation of renewable energy sources. Recent European standards have been defining a path to reach in 2050 a level of decarbonization lower of 80% compared to 1990. Wind farms have been growing quickly for [the] last decade with individual wind turbines getting larger and larger. In addition to the benefits of containing greenhouse gas emissions and restraining the use of depletable resources, drawbacks have also appeared due to noise generation from wind turbines and adverse reaction of some nearby residents. The noise generated by wind turbines has a broad spectrum character but the low frequency noise causes special problems. It is a fact that in different European countries special laws have been adopted to impose noise limits and evaluation methods for the assessment of environmental low frequency noise from this kind of sound source. Other countries are still lacking specific rules but in the authorization procedure such analysis is required by environmental control agencies. The purpose of this study consists of comparing the assessment procedures currently used in different European countries for the prediction of low frequency noise from wind turbines and its propagation. The comparison of procedures gives a chance to put forward progressions in low frequency noise emission and reception.
Martino MARINI, DADU University of Sassari, Italy
Costantino Carlo MASTINO, Roberto BACCOLI, Andrea FRATTOLILLO, DICAAR University of Cagliari, Italy
Antonino DI BELLA5, DII University of Padova, Italy
Proceedings of the 23rd International Congress on Acoustics, 9–13 September 2019, Aachen, Germany: pages 1441–1446
Download original document: “Implementation of the issue of noise from wind turbines at low frequencies”
Author: Sedaghatizadeh, Nima
«The results of this study show that underlying mechanism associated with the perceived noise in the far-field of the turbine blades is amplitude modulation due to partial stall on the blades or interaction of the blades with incoming turbulent structures. This is in contrast with the common belief of trailing edge noise to be the dominant source for the perceived noise and its amplitude modulation due to rotation of the blades. Moreover, it is observed that the majority of the locations in which the noise from whole turbines is perceived by the community, are in close proximity of the wake region. … Results revealed that, the highest noise level in the vicinity of a wind turbine corresponds to blade pass frequency and is due to amplitude modulation of the trailing edge noise caused by the rotation of the blade, as well as blade tower interaction. Results also showed that the emitted noise is refracted due to the wind shear in atmospheric boundary layer, as well as the wake and associated turbulent structures. The [computational fluid dynamics] outcomes showed that the wake breakdown occurs at a distance of 12 diameters downstream of the turbine with a strong downwash due to longitudinal vortices. Contours of sound pressure level at the breakdown location of the wake of the wind turbine showed refraction and modulation of the sound at this location. Results also revealed refraction of the noise towards the ground and wider areas due to existence of the longitudinal vortices.»
School of Mechanical Engineering, University of Adelaide, Australia
Thesis submitted in fulfilment of the requirements for the degree of Ph.D. in Mechanical Engineering
Download original document: “The effect of unsteady flow on wind turbine wake development and noise generation”
Author: Hansen, Kristy; Zajamšek, Branko; and Hansen, Colin
In the measurement of wind farm noise, it is standard practice to mount outdoor microphones at a height of 1.5 m. On the other hand, measurements at this height can be affected by wind-induced noise, which has the potential to mask the noise of interest, particularly at low and infrasonic frequencies. Therefore, to minimise wind-induced noise, it is advantageous to measure on or below the ground, where the wind speed is close to zero. However, results from measurements taken at any height other than 1.5 m must be interpreted with caution, due to different interference effects between direct and ground-reflected waves at each location. This investigation explores the feasibility of using a prediction model based on Nord2000 algorithms to correct the 1/3-octave sound pressure level measured at ground level to obtain a representative value for a height of 1.5 m. The model takes into account phase changes due to the difference in travel-time for the direct and reflected rays and finite ground impedance, multiple source contributions and incoherence due to turbulence. The focus is on propagation distances greater than 2 km, where limited validation of existing propagation models has been attempted previously. Comparison is made between the model and measurement results obtained at four locations near a wind farm, where microphones were mounted at a height of 1.5 m and at ground level. A lack of agreement between measurements and the model indicates that the efficient and practical correction method considered here is not feasible for long-range wind farm measurements. Thus, it is recommended that wind farm noise is measured at both 1.5 m (for mid- to high-frequency noise) and at ground level (for low-frequency noise, which is more affected by wind).
Kristy L. Hansen, Branko Zajamšek, College of Science and Engineering, Flinders University, Tonsley, Australia
Colin H. Hansen, School of Mechanical Engineering, University of Adelaide, Adelaide, Australia
Volume 155, 1 December 2019, Pages 97-110