Mastering Wind Turbine Tonalities with Active Vibration Control

When considering wind turbines in relation to noise, tonal components are critical. Their removal can be very complex, especially if a speed dependency of the tonalities is present. One approach to mitigate emerging tonalities is the use of distributed active vibration absorbers. The active absorbers discussed here generate dynamic forces up to 5 kN each at a system mass of about 100 kg.The positioning of the absorbers requires the knowledge of the sound radiating components. This can be determined by structure-borne and airborne sound measurements, ideally together with finite-element-simulations. With a structural dynamic model of the wind turbine first the structure-borne noise of potentially radiating components is calculated. By means of the transfer of structure-borne noise to an appropriate airborne noise model and subsequent extrapolation to the reference point the contributions of the individual components to the tonality level can be determined. The next step is the integration of the active vibration absorber in the simulation model. A comparison of the calculated sound level with and without absorbers allows a quantification of the achievable noise reduction.The active control approach has been developed to a series solution with more than 800 active vibration absorbers in the field.