Wind turbine noise

Wind turbines are large machines that generate a significant amount of noise. The type of noise depends on the design of the turbine, but generally speaking a wind turbine is a broadband source with a tilt towards the lower frequencies. It has been repeatedly shown in scientific studies that the highest noise levels from modern wind turbines are found in the infrasound region (frequencies below 20 Hz), and especially at 1 Hz and below. Based on measurements done together with acoustic experts, we have calibrated the 1 Hz source strength of modern wind turbines to be in the range of approximately 153-173 dB.

The atmospheric attenuation of infrasound is very small, for 1 Hz sound signals in normal weather the attenuation is less than 0.00003 dB/km. The small attenuation, together with the large source strengths of wind turbines in the infrasound region, leads to high infrasound noise levels in vast areas around wind farms. 

The noise levels of a wind farm is also hugely influenced by the atmosphere. Not only does a stronger wind lead to more noise being generated by the turbines, it also helps transports the noise in the wind direction. A refracting atmosphere (an atmosphere where the speed of sound increases with altitude) also bends the sound waves in the atmosphere downwards, increasing the noise levels at the ground. These conditions typically occur at night time.

In SoundSim360 a fully 3D atmosphere is used, incorporating physical properties such as temperature, pressure, density, relative humidity etc. We also take into account the topography and ground type in the specific simulation domain.

In the animation at the top of the page, we used SoundSim360 to simulate the infrasound propagation from the Lervik wind farm in southern Sweden, which consists of seven wind turbines. We have performed multiple measurements on Lervik and Målarberget wind farms to validate SoundSim360 and determine the source strength of modern wind turbines. In the figure below, the noise map from one such measurement is shown. 

Sound pressure levels in 1 Hz from Lervik wind farm (x marks the location of the seven wind turbines, + marks the measurement point). The simulation is done with SoundSim360, which incorporates accurate weather data and ground conditions at the time of the measurement.