Massachusetts Research Study on Wind Turbine Acoustics: Overview and Conclusions

Over the course of two years, the Commonwealth of Massachusetts (USA) undertook an extensive measurement and analysis campaign of five operating community-scale wind projects, collecting over 300 observed and calculated variables pertaining to acoustical, meteorological, and turbine SCADA data. Over 100 million time-series data records were recorded and synchronized, allowing for detailed analysis and comparisons. Acoustical measurements were conducted at a high sampling rate and included frequencies in the low infrasonic range. Meteorological measurements utilized on-site LIDAR systems, 10-meter meteorological towers, and nacelle anemometry. Turbine data were collected, including variables such as rotor rotational velocity, blade pitch, yaw angle, and power output. Regular shutdowns of turbines were coordinated in order to measure background conditions without the turbines operating. The results focus on the interrelation of meteorology, turbine operating parameters, and associated acoustical conditions. Factors related to amplitude modulation and its statistical distribution are discussed. Infrasound and tonality measurements are presented and compared to background levels. Two sound models and a variety of parameters are used to estimate sound levels and are compared to actual measurements. Lastly, different acoustical metrics are applied to the acoustical data and a statistical comparison is used to assess their applicability to compliance standards.