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Tuesday, 11 March 2014
16:30 - 18:00 Wind turbine noise: How to avoid disturbing the neighbours
Resource Assessment  


Room: Ponent
Session description

With a new version of IEC 61400-11 published this year, it may be thought that wind turbine noise emission is well understood. However, wind farm developers still receive complaints from residents about 'amplitude modulation' (AM) noise, a subject not covered by the IEC standard. Amplitude modulation will therefore be one of the main topics in this session. This session will also explore different sound propagation models and the impact of environmental conditions on propagation. Another topic for this session is how to optimise wind turbines and wind farms for sites with noise restrictions.

Learning objectives

  • Understand why it is important to consider noise for resource assessment
  • Understand how a wind farm as a whole can be optimised to maximise performance with noise constraints
  • Understand what amplitude modulation is and why it is a concern for residents near wind farms
  • Understand the role that propagation modelling plays in the prediction of far field noise
Lead Session Chair:
Saskia Honhoff, GE Energy, Germany
Joachim Gabriel DEWI GmbH, Germany
Co-authors:
Joachim Gabriel (1) F P
(1) DEWI GmbH, Wilhelmshaven, Germany (2) University, Halle-Wittenberg, Germany

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Presenter's biography

Biographies are supplied directly by presenters at EWEA 2014 and are published here unedited

Dipl.-Ing. Joachim Gabriel is the head of DEWI noise immission control. He studied electrical engineering at the University of Braunschweig and Physics at the University of Oldenburg. Working since 1990 at DEWI, his background comprises more than 20 years’ experience in measurement and standardisation of acoustic noise from wind turbines. He is convenor for the “German Technical Guideline for Wind Turbines Part 1, Acoustic Noise”, for more than 20 years member of the German wind turbine noise working group and works in IEC and, MEASNET committees.

Abstract

Time series of amplitude modulation of wind farm noise at noise receptor locations

Introduction

Installations of wind turbines are accompanied by an increasing number of complaints about noise from wind farms. But what makes residents complain? Amplitude modulated aerodynamic noise (AM) turned out to be the common ground of complaints documented within a research project about acceptance of noise from wind turbines. The project combined psychology and acoustic noise measurements.

Approach

As interdisciplinary approach the project combined interviews with residents of a wind farm with physical measurements. Temporary acoustic noise measurements according to accredited standards were performed. In addition audio recorders had been handed out to residents to record annoying noise situations by themselves, as it is difficult to perform a temporary measurement just at the time of annoyance and complains.

Main body of abstract

In order to get an idea of frequency, duration and intensity of AM in wind turbine noise, the audio files have been listened to and analysed by a numerical evaluation tool. Within the tool the modulation depth ΔL was used as a parameter for AM. The modulation depth ΔL is defined as the difference between the maximum and minimum sound pressure level. In addition a second parameter for AM quantification - fluctuation strength F* - was used. F* is a psycho acoustically motivated measure, representing the perceived AM. The origin of F* is the fluctuation strength, developed by Zwicker, which was slightly modified for the analysis of wind turbine noise.
An AM assessment tool for the quantification of AM-perception has been developed and applied to the sound recordings. A clearly perceptible AM occurred only sporadically and mostly for short time periods, but it might trigger the attention and focus it on the sound of the wind farm.


Conclusion

If AM as an attention trigger is a temporary phenomenon investigations of the causes of far field AM are worth to be carried out. An improved version of the AM assessment tool - featuring long term data analysis - will help to identify AM critical operational conditions. Standardization of AM assessment is aimed in order to be able to quantify the specific AM-annoyance and the efficiency of AM mitigation.


Learning objectives
The presentation helps to a better understanding of amplitude modulation in wind turbine noise and points out a way to objectify annoyance caused by AM.