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Numerical investigation of the effect of inflow non-uniformity on the noise radiated by a vertical axis wind turbine

AIAA 2021-2216
Session: General Acoustics III
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A simulation chain for noise prediction of a model vertical axis wind turbine (VAWT) is developed in order to investigate the effect of incoming flow non-uniformity on noise generation. A two-dimensional Unsteady Reynolds-Averaged Navier-Stokes (URANS) model is achieved using ANSYS CFX with the k-ω SST turbulence model. The flow solution is then coupled to an aeroacoustic solver, SherFWH, based on the Ffowcs Williams and Hawkings analogy for the prediction of tonal noise. A first validation case from literature with uniform inflow has been simulated. The flow appears as highly chaotic with the formation of a complex vortex system shed by the blades along their trajectory and interacting with them. The sound pressure level at the blade passing frequencies are compared with published experimental data on the same model turbine. Azimuthal directivity patterns have been computed as well, and are consistent with the fact that the blades experience varying loads along their rotation. Blade vortex interaction and dynamic stall play a key role in noise radiation in the upwind and downwind phases of rotation of the VAWT. The directivity of the overall sound pressure level is shifted towards the downwind phase of rotation of the turbine. A mean sheared inflow is used as an input to mimic the flow conditions typically encountered by a VAWT placed on a building or urban environment. The influence of sheared flow on the dynamic stall and blade vortex interaction phenomenon is analyzed indicating a strong gradient is required to observe significant changes in the tonal peaks, with a shift in directivity of the overall sound pressure level towards the direction of wind shear.