Development of a FW-H tool coupled with CFD for infrasound noise emissions from wind turbines

Noise remains an obstacle to the advancement of onshore wind energy. Despite the ongoing debate on the effects of infrasound on human health, especially from wind turbines, there is consensus that the blade passing frequency (BPF) in the infrasound range modulates the audible higher-frequency sound and creates a rhythmic "swishing"sound at farther distances. This paper presents a simulation framework for assessing infrasound noise (<20 Hz) from wind turbines, which was designed to capture the relevant physics without incurring in overwhelming computational costs. The flow is modelled using large eddy simulation (LES) and is coupled through an actuator line method (ALM) to the aeroelastic model of a wind turbine. The use of an ALM significantly reduces the computation effort compared to blade-resolved CFD approaches. Moreover, the Ffowcs Williams-Hawkings (FW-H) acoustic analogy is applied on a permeable integration surface that surrounds the entire wind turbine, thereby capturing the coupled effects of rotor, tower, and the near-wake turbulence shed by the turbine. The present approach is shown to be capable of resolving rotor-tower interactions as tonal peaks at BPF and its harmonics, enabling the evaluation of design and control measures to mitigate infrasound noise emissions from wind turbines.