Acoustic measurements

One of the most influential factors affecting the general public’s acceptance of wind turbines is the noise they emit. In heavily populated areas noise emissions from wind turbines can dictate the size of the project and the turbine selected. Since a turbine’s blades, gearbox and tower all generate noise, reducing emission levels is critical to the commercial viability of a wind farm – for manufacturers and owners alike. Besides such environmental considerations, noise evaluations of turbines and wind farms are required for compliance and certification reasons.

For the past two decades, GL Garrad Hassan’s WINDTEST Competence Centre has been carrying out noise measurements on wind turbines for clients all over the world. Noise measurements are conducted during a prototype test programme to reduce a turbine’s noise emission levels and are also part of the type certification process.

Since background noise would falsify the readings, effective type test noise measurements are only possible if ambient noise levels are low and neighbouring wind turbines are not running. Reference wind speed measurements are taken upwind of the turbine since wind speeds from cut-in to 10-11 m/s (95% of rated power) are required for valid measurements. Sound levels downwind of the turbine are recorded as a time series to calculate the tonality of the turbine noise emissions. These sound levels are then correlated to the normalised output power of the turbine. An analysis of sound pressure levels against power and tonality rounds off the evaluation process.

Noise impact measurements are carried out at commercial sites. If the source noise levels from a single turbine are required, the procedure is essentially the same as for type testing. If sound levels are required at a specific point, e.g. a house, the cumulative noise from all turbines nearby is the key parameter. The measurement procedure is again similar to the type testing method. Whatever your acoustic measurement needs, GL Garrad Hassan has the expertise and experience to provide you with a sound, all-round service.