Development of a standard approach for wind turbine measurements with an Acoustic Camera for optimization purposes
Résumé
The air flow at the rotor blades causes turbulence which generates sound at the trailing edge of the blade. So-called serrations at the end edge of rotor blades break the turbulence into smaller structures, reducing the strength of the end edge sound. Simple sound level measurements can be performed to check the effectiveness of these serrations. However, sound pressure measurements with single microphones provide only integral values about the overall sound emission. In contrast, beamforming methods allow to determine the location of sound sources on the blade and an estimation of the amplitude of these sources. Therefore, the acoustic camera is an interesting analysing tool in the optimisation process of wind turbines, for example to determine the best position for the serrations. So far, no standard approach exists for measurements on wind turbines with acoustic cameras. To develop such an approach, a measurement compaign with two different microphone arrays was carried out on two different wind turbines over a period of three days on several positions. The goal was to analyse the amplitude of the blade noise regarding to the distance and the azimuth between the acoustic camera and the wind turbine. Also the influence of downstream and upstream was analysed. The results of these investigations will be discussed in order to establish a standard protocol for wind turbine measurements with acoustic cameras.
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