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Wind turbine noise: papers from Inter-Noise 2014 conference  

Author:  | Noise, Technology

Inter-Noise 2014: 43rd International Congress on Noise Control Engineering
Melbourne, Australia, 16-19 November 2014

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The noise characteristics of ‘compliant’ wind farms that adversely affect its neighbours
Sarah Large, Mike Stigwood
MAS Environmental, UK
In the UK many wind farms cause complaints of noise despite complying with control limits. Problems relate to reliance on the LA90 index, failure to consider or apply ratings on the context of the sound characteristics and actual human responses due to complex characteristics. In general in the UK low frequency and very low frequency sound effects are either ignored or denied. The complex interrelationship of features within this noise and difficulties in quantifying and qualifying noise impact and inappropriate comparison with other sources of noise renders the effects difficult to investigate or quantify with contradictory outcomes possible using the same data sets. Claim and counterclaim of health and adverse effects complicate the analysis. This paper explores some of the interrelating characteristics of wind farm noise measured and observed in the field that appear to influence complaints made by communities. Cumulative effects occurring in environments normally dominated by natural sounds and both audible and inaudible elements remain alien sounds which are not habituated to. It appears that sensitisation arises. The physical reason for the failure to appropriately identify modulating noise effects and in particular low frequency modulating noise problems are explored.

Initial findings of the UK Cotton Farm Wind Farm long term community noise monitoring project
Mike Stigwood, Duncan Stigwood, Sarah Large
MAS Environmental, UK
This paper provides early results of a long term study of community impact from wind farm noise and uses of the data obtained. A continuously recorded database of noise collected under different meteorological conditions has allowed detailed analysis of particular characteristics such as amplitude modulation and also the reliability of assessment methodologies for predicting and quantifying impact. Surprising outcomes are explored including upwind impact. In 2013 MAS Environmental established a permanent monitoring station to record and publish data online located 600m from the nearest turbine to correlate the impact upon the community and provide an extensive database. This paper maps the evolution of the project. Online data enables a wider study of the effect of meteorological change on noise immission in a flat eastern area of the UK. Anyone can independently observe and listen to the audible elements of the noise that people complain about. This tool aids understanding as well as predicting times of likely adverse impact. The database has enabled testing of proposed controls, particularly in relation to audible amplitude modulation and demonstrated the recent Renewables UK proposed control mechanism fails. Data obtained challenges blade stall research claims as the primary cause of far field AM and wind farm noise prediction methodologies.

Investigating the impacts of wind turbine noise on quality of life in the Australian context: A case study approach
David Mcbride, Daniel Shepherd, Robert Thorne
University of Otago, New Zealand; Auckland University of Technology, New Zealand; Noise Measurement Services, Australia
The WHO considers noise pollution to be of sufficient threat to public health to justify the publication of guidelines on noise effects and mitigation. ‘Community noise’ has largely been studied in the context of transportation and general neighbourhood noise, with exposure to wind turbine noise relatively understudied for historical, methodological, and political reasons. There also appears to be a general uncoupling of wind turbine noise from the other sources, which endows upon it an exclusivity that excuses it from the methods, guidelines, and critique used for other noise sources. This study aimed to advance understanding of wind turbine noise impacts by adopting a case study approach based on detailed information from 25 individuals, Australian adults residing rurally and within 1000-3500m of three or more wind turbines. Participants were selected on the basis of health concerns evidenced through statutory declarations or submissions to hearings. The 25 respondents compeleted a face-to-face survey measuring health-related quality of life (HRQOL) questionnaire as developed by the World Health Organisation (WHO), the ‘WHOQOL-BREF’. The results were compared to normative population data and showed clinically significant reduction in HRQOL.

Outcome of systematic research on wind turbine noise in Japan
Hideki Tachibana
Professor Emeritus, The University of Tokyo
In Japan, serious complaints about wind turbine noise have arisen from nearby residents since the commencement of large-scale construction of wind generation plants in about 2000. Regarding this new type of environmental noise problem, scientific knowledge is insufficient and no standard methods for measuring and assessing the noise have been established in Japan. To improve this situation, a research project entitled “Research on the evaluation of human impact of low frequency noise from wind turbine generators” has been conducted over the three years from fiscal year 2010, funded by a grant from the Ministry of the Environment, Japan. This project consisted of three main subjects: (1) physical research on wind turbine noise by field measurement, (2) a social survey on the response of nearby residents, and (3) auditory experiments on the human response to noises containing low frequency components. In this paper, the outcome of the research project is reviewed and standard methods for measuring and assessing the wind turbine noise are discussed.

Special noise character in noise from wind farms
Valeri V. Lenchine, Jonathan Song
SA Environment Protection Authority, Australia
Noise produced by wind farms may exhibit a multitude of different noise characters, ranging from amplitude modulation, tonality and low frequency noise. The presence of the noise characters is able to increase the annoyance factor caused by a noise source significantly. A penalty to the noise levels is applied in accordance with some regulations when a noise character is detected. This paper discusses a noise character that can be described as “rumbling” that was detected during a long term monitoring program which was conducted in an area adjacent to a wind farm. The objective assessment of the data and subjective assessment of relevant audio records were performed to analyze the effect. The frequency spectra of the rumbling events indicate connection of the effect with low frequency noise and one of the low frequency components. The character was detected at low noise levels and might not be audible to a typical listener, however it is possible the character may cause an increased annoyance to people who have a higher sensitivity to the lower frequencies. Environmental conditions were also considered when discussing the occurrence of this noise character. The possible mechanism of the rumbling effect is suggested in the paper. The wind farm manufacturers may have to consider potential for low frequency impact of wind turbines and presence of prominent components at the design stage.

Correlation of amplitude modulation to inflow characteristics
Helge Aa. Madsen, Franck Bertagnolio, Andreas Fischer, Christian Bak
DTU Wind Energy, Technical University of Denmark
Amplitude modulation (AM) of noise from wind turbines and its more extreme version named “other amplitude modulation” OAM have been investigated intensively during the last few years due to the additional annoyance impact this type of noise has compared to broad band noise. In a recent published research by RenewableUK the hypothesis has been that one of the causes of OAM is transient stall on the blade due to non uniform inflow such as shear. Part of the RenewableUK research work was a contribution by DTU on analysis of data from the DANAERO MW experiment from 2009. In the DANAERO experiment a new 38.8m test blade for a 2MW NM80 turbine was manufactured and equipped with a massive instrumentation comprising flush mounted surface microphones, pressure taps and five hole pitot tubes. The correlation of the spectra from the surface microphones and the measured inflow angle (IA) confirmed the strong increase in the noise source for high IA. As only few 10min data sets were measured in the DANAERO project a data set with measured inflow angle from 2003 on the same turbine has been used to explore the statistical properties of AM and OAM based on assumed correlation to IA.

Wind turbine noise measurements – How are results influenced by different methods of deriving wind speed?
Sylvia Broneske
Hayes McKenzie Partnership Ltd, United Kingdom
With the increasing number of operational wind farms/turbines, the requirement for noise measurements required to demonstrate compliance with planning conditions is increasing as well. The British ETSU-R-97 noise limits are often set relative to measured or standardised 10 m height wind speeds and therefore the assessment of noise from wind turbines requires simultaneous noise and wind speed/direction measurements. For financial reasons, smaller and single turbine sites are often not equipped with a meteorological mast. If no independent hub height wind measurements are available, wind speed is either taken from nacelle anemometers or derived from power measurements combined with the power curve for the respective wind turbine type. Noise measurements referenced to nacelle anemometer data will be compared with the same measurements but correlated with derived power curve wind speed, and measured wind data from separate met mast or other remote sensing devices. The influence of incorrect filtering of wind data for shadow effects (mast and/or nearby wind turbines) on the noise assessment may be presented, depending on how much time is available. The advantages and disadvantages of the various methods will be discussed.

Using wind farm noise auralisations for effective community consultation
Frank Butera, Kym Burgemeister, Kai Fisher, David Mounter
Arup, Melbourne, Australia, and Singapore; Hydro Tasmania, Hobart, Australia
Two of the most common questions that wind farm developers face during community consultation are ‘what will the wind farm look like’ and ‘what noise will it make?’ A lot of work has been undertaken recently to develop ‘visualisations’ or ‘photomontages’ to answer the first question. However, there has not been an equivalent tool available to enable local communities to understand what a wind farm actually sounds like. Arup and Hydro Tasmania have jointly developed a tool that will accurately and effectively communicate what a wind farm sounds like under different wind conditions and from a range of distances and orientations. This auralisation tool provides a practical and affordable means for the industry to effectively communicate what a wind farm will sound like to the community. This paper looks at how auralisation techniques used in other sectors (such as transport and aviation) have been adapted for the renewable wind energy sector and serve as a valuable tool for increasing transparency, minimising risk and building trust within local communities early in the wind farm development process. It shows how a comprehensive field measurement program at Studland Bay Wind Farm, Tasmania has enabled a wind turbine sound library to be developed for future use in wind farm acoustic models and how calibrated auralisations can be presented at community settings.

The relevance of the precautionary principle to wind farm noise planning
Bob Thorne
Noise Measurement Services Pty Ltd, Australia
Wind farms consist of clusters of industrial wind turbines which, when placed in rural areas, are associated with intrusive and unwanted sound. Wind turbine noise has characteristics sufficiently different from other, more extensively studied, noise sources to suggest that standard industrial noise standards are not appropriate for measurement and assessment purposes. A seven year study is reported and, although limited in population size, it is clear that there are definite adverse health effects related to wind farm noise. Time-aggregated noise metrics have limited utility in assessing individual human health and well-being, and a cluster of metrics are needed to describe and estimate potential effects on individuals and communities. Sleep deprivation is a widely reported occurrence by people in the vicinity of a wind farm. At this time, however, the quantity and quality of research are insufficient to effectively describe the relationship between wind turbine noise and health, and until such time that a definitive relationship is obtained, legislation should apply the precautionary principle and conservative criteria when assessing proposed wind farm developments.

Wind turbine sound – metric and guidelines
Conny Larsson, Olof Öhlund
Uppsala University, Sweden
The meteorological conditions vary over the globe but also change over the day and the year and vary a lot depending on the terrain for a certain location. The meteorological parameters govern both the wind turbine emission sound levels and the sound propagation conditions and therefore gives rise to different sound immission levels. Long-time measurements of meteorological effects on sound propagation from wind turbines over forest areas have been performed at two sites in Sweden for more than two years. One site is located in the southern part with flat terrain and the other site is located in the northern part of Sweden with more hilly terrain. The aim of the project is to improve the knowledge of sound propagation from wind turbines and especially over varying terrain and weather conditions. Control measurements of wind turbine immission sound levels will be needed to see that they fulfill the noise regulations. It is therefore of most importance to be able to make representative measurements. Discussions about under what meteorological conditions the immission measurements have to be carried out, the sound metric and the impact of the guidelines are presented in this paper.

An investigation of different secondary noise wind screen designs for wind turbine noise applications
Colin Novak, Anders Sjöström, Helen Ule, Delphine Bard, Göran Sandberg
University of Windsor, Canada; Lund University, Sweden; Akoustik Engineering Limited, Canada
The use of diaphragm type microphones with the typical foam windscreen ball for outdoor noise measurement applications are mostly restricted to wind speeds below 4 to 6 m/s. This is due to the extra noise induced into the microphone, particularly at low and infrasonic frequencies, as a result of the wind excitation on the diaphragm. For wind turbine noise measurement applications, it is often necessary to measure the turbine noise under the typical operating conditions with wind speeds up to 12 m/s. This introduces a problem in the measurement system, as the normal microphone setup and windscreen are not adequate at these elevated wind speeds. Secondary windscreens, such as for example that prescribed by IEC 64100-11, “Acoustic noise measurement techniques” imparts their own problems including ridged body motion of the windscreen structure due to turbulence. Also, ground plane secondary windscreen measures the noise at ground level, instead of at ear level. This study investigates the use of several secondary windscreens with microphones capable of measuring at infrasonic frequencies for measuring wind turbine noise at elevated wind speeds. The result was that no windscreen provided a full solution to the problem. Specific recommendations for additional windscreen design and investigation are included.

Noise and low frequency noise from wind turbines
Bo Søndergaard
Grontmij, Department of Acoustics, Acoustica, Denmark
Noise is a key issue when planning wind farms. The presentation will look into details in noise from wind turbines, noise measurements, noise assessment, including the Danish noise limits for low frequency wind turbine noise, and noise propagation. Development of noise and low frequency noise with the size of the turbines will be discussed. Questions like how far does low frequency noise propagate will be addressed.

This article is the work of the author(s) indicated. Any opinions expressed in it are not necessarily those of National Wind Watch.

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