Computational aeroacoustic study of small three and four blade helical vertical axis wind turbines in turbulent flow

Aeroacoustic analysis of a small vertical-axis Darrieus wind turbine suitable for urban area applications is performed using numerical simulation and acoustic analogy. The analysis is performed for two helical wind turbine models with three- and four-blade configurations and under different operating conditions. Numerical simulations are performed using the unsteady Reynolds averaged Navier-Stokes method, along with the Ffowcs-Williams and Hawkings aeroacoustic analogy. Validation of the performance of the computational model against experimental data demonstrates its ability to accurately predict the aerodynamic and aeroacoustic behavior of the turbine. The influence of the number of turbine blades and their distance from the center of the turbine on the generated noise is analyzed. The analysis is further focused on the highest power coefficient, obtained at the tip speed ratio of 1.8, and the sound pressure level (SPL) curves recorded by the receivers are analyzed. Predictions show that while the four-blade turbine has a higher SPL than the three-blade one at a downstream position of about four turbine diameters, the situation is reversed at farther downstream positions. The aeroacoustic findings of this research have direct implications for the proper installation of small vertical-axis Darrieus wind turbines in urban areas, where wind turbine generated noise is important.