Giacomo Rismondo

In the coming decades, wind energy will become increasingly popular, with an anticipated increase in power rate, rotor size and energy capacity (Bovsnjakovic (2022) and Njiri (2016)). However, this growth will be accompanied by a concurrent increase in the potential for acoustic pollution from wind turbines, which could have a significant impact on wildlife species. It is of pivotal importance to gain an understanding of the generation mechanism and noise propagation in order to address environmental pollution, as highlighted by Teff et al. (2022). The noise emitted by a wind turbine is the superposition of different fluid dynamic phenomena. Tonal noise and sub-harmonics are associated with blade passage and the presence of helicoidal coherent structures, namely tip and hub vortices. The pressure fluctuations on the blade surface and the turbulent structures that make up the turbine wake generate a very complex broadband noise. For many years, experimental analysis has been the most appropriate technique for studying the noise generated by wind turbines. However, the experimental facilities are affected by reflection phenomena (Tani et al. (2020)). Recently, the numerical method based on the acoustic analogy (Lightill (1952)) has been used to characterize the noise generated by marine propellers (see, for example, Cianferra et al. (2019), Posa et al. (2022), Rocca et al. (2022)). In particular they demonstrated the efficacy of this method. However, to the best of our knowledge, this method has not yet been widely adopted in the field of wind turbines.

The near wake instability, the tip and hub vortex breakdown, and the turbulence generation mechanism along the wake of the wind turbine are fundamental aspects that influence the acoustic field and are analyzed here.

The numerical technique is used to achieve our goal. An eddy resolving technique, such as Large Eddy Simulation (LES), is required to give an accurate characterization of the wind turbine wake and acoustic signature. We considered the incompressible Navier-Stokes equation to individuate the fluid motion, while the Ffowcs-Williams and Hawkings (1969) equation was used to individuate the acoustic pressure. We considered a model wind turbine, the same as used by Gambuzza et al. (2023) in their experimental analysis, for comparison purposes.

We are still running the numerical simulation on the Galileo100 HPC cluster (Cineca). Preliminary results confirmed the reliability of the numerical setup, in particular, we compared the thrust and power coefficients with the results obtained by Gambuzza et al. (2023), and a good agreement was found. Finally, we expected to better understand the near wake instability and the turbulence generation mechanism in the wind turbine wake and its influence on the acoustic signature.