The Effect of Blade Aeroelasticity and Turbine Parameters on Wind Turbine Noise
In recent years, the demand for wind energy has dramatically increased as well as the number and size of commercial wind turbines. These large turbines are loud and can cause annoyance to nearby communities. Therefore, the prediction of large wind turbine noise over long distances is critical. The wind turbine noise prediction is a very complex problem since it has to account for atmospheric conditions (wind and temperature), ground absorption, un-even terrain, turbine wake, and blade deformation. In these large turbines, the blade deflection is significant and it can potentially influence the noise emissions. However, the effects of blade flexibility on turbine noise predictions have not been addressed yet, i.e. all previous research efforts have assumed rigid blades. To address this shortcoming, the present work merges a wind turbine aeroelastic code, FAST (Fatigue, Aerodynamics, Structures, and Turbulence) to a wind turbine noise code, WTNoise, to compute turbine noise accounting for blade aeroelasticity. Using the newly developed simulation tool, the effects flexible blades on wind turbine noise are investigated, as well as the effects of turbine parameters, e.g. wind conditions, rotor size, tilt, yaw, and pre-cone angles. The acoustic results are shown as long term average overall sound power level distribution over the rotor, ground noise map over a large flat terrain, and noise spectrum at selected locations downwind. To this end, two large wind turbines are modeled. The first one is the NREL 5MW turbine that has a rotor diameter of 126 m. The second wind turbine, the Sandia 13.2MW, has a rotor diameter of 206 m. The results show that the wind condition has strong effects on the noise propagation over long distances, primarily in the upwind direction. In general, the turbine parameters have no significant effects on the average noise level. However, the turbine yaw impacts significantly the turbine noise footprint by affecting the noise propagation paths. The rotor size is also a dominating factor in the turbine noise level. Finally, the blade aeroelasticity has minor effects on the turbine noise. In summary, a comprehensive tool for wind turbine noise prediction including blade aeroelasticity was developed and it was used to address its impact on modern large turbine noise emissions.