A new approach to wind turbine noise measurement

Currently available wind turbine noise measurements are not sufficiently detailed to enable the sources of such noise to be fully characterised. This is because published noise data, prepared to IEA or equivalent standards, is based on averages over one or two minutes. Since wind turbine noise is a function of the wind speed, it is necessary to take measurements at fixed wind speeds in order to determine the noise source characteristics. It has been observed that short periods of stable wind up to 30s in length occur naturally. An experiment has been performed to capture these naturally occurring periods of steady wind conditions, in order properly to characterise wind turbine noise sources with respect to the controlling parameters, particularly the wind speed and electrical power output. Forty hours' multi-channel data was recorded for Vestas' Windane 34, and post processed to find desired test conditions. Periods of steady wind lasting more than 20 seconds were found to constitute approximately 25% of the total records. A high level of repeatability has been demonstrated for data captured in this way. (author)