Assessment of the sound quality of wind turbine noise reduction measures

Noise emissions from wind turbines are one of the main issues that the wind energy industry must deal with nowadays. Strict noise regulations often prevent wind turbines to operate at maximum power conditions, causing large losses of power production and, hence, of revenue. Several noise reduction measures have been proposed so far, but the use of trailing-edge serrations and permeable inserts seem to be the two most promising approaches, showing broadband noise reductions of several decibels. This paper considers the noise reductions (with respect to the baseline blade) observed in previous wind-tunnel measurements featuring these two measures, and scales and synthetically applies them to an experimental recording of a full-scale Vestas V90-2.0 MW wind turbine in operational conditions. The calculated results are then auralized for the observer location used for noise certification in the IEC 61400-11 standard. State-of-the-art sound quality metrics (loudness, tonality, sharpness, roughness and fluctuating strength) are then applied to these simulated sound signals to better understand the achieved reduction in noise annoyance experienced by humans. Reductions in the maximum A-weighted sound pressure level (L_p,A,max) of about 2.4 and 1.2 dBA are observed for the serrations and permeable inserts, respectively. In general, trailing-edge serrations seem to reduce the calculated annoyance experienced (17% lower than the baseline) more efficiently than the permeable inserts (just 2% lower)