Advanced computational fluid dynamics (CFD)–multi-body simulation (MBS) coupling to assess low-frequency emissions from wind turbines

Abstract. The low-frequency emissions from a generic 5 MW wind turbine are investigated numerically. In order to regard airborne noise and structure-borne noise simultaneously, a process chain is developed. It considers fluid–structure coupling (FSC) of a computational fluid dynamics (CFD) solver and a multi-body simulations (MBSs) solver as well as a Ffowcs-Williams–Hawkings (FW-H) acoustic solver. The approach is applied to a generic 5 MW turbine to get more insight into the sources and mechanisms of low-frequency emissions from wind turbines. For this purpose simulations with increasing complexity in terms of considered components in the CFD model, degrees of freedom in the structural model and inflow in the CFD model are conducted. Consistent with the literature, it is found that aeroacoustic low-frequency emission is dominated by the blade-passing frequency harmonics. In the spectra of the tower base loads, which excite seismic emission, the structural eigenfrequencies become more prominent with increasing complexity of the model. The main source of low-frequency aeroacoustic emissions is the blade–tower interaction, and the contribution of the tower as an acoustic emitter is stronger than the contribution of the rotor. Aerodynamic tower loads also significantly contribute to the external excitation acting on the structure of the wind turbine.