Fuchs L., Moroianu D.

The aerodynamically produced noise by a wind turbine is computed using a hybrid method: Large Eddy Simulations (LES) and an acoustical analogy known in literature as the Ffowcs Williams and Hawkings equation. The underlying assumption of the approach is that for the far-field the acoustic analogy is rather accurate for describing the acoustic wave propagation. The boundary conditions are such that the acoustic waves are reflected from the ground and are allowed to leave the computational domain without being reflected. At the near field, the quality of the approach depends on the quality of the approximation of the acoustical sources. The acoustical sources include the contribution from the spatial variations in the flow field, the pressure that the blades exert on the air and the acoustical source due to the acceleration of the blades. To ensure an adequate quality of the source terms we use LES for the fully 4-D problem. The LES resolves all the scales that are responsible for the coherent structures generated by the rotating blades and the mast. Also, the spatial resolution is such that it resolves a portion of the inertial subrange. The dynamics of tip and hub vortices together with some coherent structures that appear in the downstream side of the wind turbine mast and blades are considered. The noise reflected by the ground surface and the noise produced by the interaction between nearby wind turbines has also been studied. The effects of these interactions lead to the cancellation or enhancement of (in particular low-frequency) noise at certain locations.