Shouting for silent wind turbines
Large wind turbines generate trailing-edge noise and it is this factor that has impeded their implementation in Europe, despite the fact that the pressures for their use have increased. What was therefore needed was a means by which noise source could be localised and then quantified. Noise monitoring was conducted using a planar microphone array placed on the ground of about eight metres in diameter and carrying approximately 150 microphones. Using a standard directional signal transmission or reception process known as beamforming, the array is capable of localising the noise source in the rotor plane. By doing so, it could be determined whether a noise occurs in the nacelle or in the blades, for example. Furthermore, an alternative processing technique was utilised that measured the revolutions per minute through a trigger signal. By doing so the processing method can identify the noise of individual blades by localising and quantifying the dedopplerised signal of the rotating blades. These techniques have already produced improved signal to noise ratios and, with further research and development support, it might be possible to further silence these rotors.
