Computational Aeroacoustic Simulations of Small Vertical Axis Wind Turbine

Reducing the noise of wind turbines, which are installed in the vicinity of urban areas, is one major issue for social acceptance. In general, horizontal wind turbines are the most common configuration for using wind energy. However, the interest of small wind turbines are grown in the last years because of the future demand for decentralized power generation. The present work deals with two different numerical schemes of noise prediction of small vertical axis wind turbines using hybrid methods. For both schemes the time-dependent turbulent flow field is solved with Scale-Adaptive Simulation. The two schemes then differ in how the location of the acoustic sources and their propagation is calculated. In the first scheme the acoustic source terms are computed according to Lighthill's acoustic analogy which gives source terms located on the original CFD grid. These source terms are projected onto a coarser acoustic grid on which the propagation is calculated by solving the wave equation. In the second scheme the Ffowcs-Williams Hawkings method is used which is based on a free field Green's function. The far field acoustic radiation is calculated by extrapolation of the acoustic waves. Both methodologies are compared with each other and validated with experimental data.