Aeroacoustic radiation from a vertical-axis wind turbine resolved by lattice Boltzmann simulations with body-fitted overset grids

Abstract. Blade number affects both the power performance and aerodynamic noise of vertical-axis wind turbines, but their phase relationships remain insufficiently understood. This study compares one- and two-bladed straight-bladed Darrieus rotors at a tip-speed ratio of 4.5 using three-dimensional direct aeroacoustic simulations. A hybrid lattice Boltzmann method with body-fitted overset grids resolves flow, sound generation, and propagation. Compared with standard lattice Boltzmann simulations, the hybrid method predicts mean streamwise wake velocities closer to measurements, although this agreement does not validate the acoustic predictions. For both blade counts, the principal radiation peaks occur near phases of rapid change in the power coefficient rather than at maximum power. The single-blade rotor radiates most strongly during upstream passage, consistent with a contribution from rapid aerodynamic load changes at high tip-speed ratio. Adding an opposed blade increases the pressure-based radiation indicator substantially more than the mean power coefficient. Reinforcement of waves from the opposed blades may contribute, but its contribution is not separated from changes in blade loading. These findings connect blade-count effects on power performance with phase-dependent pressure radiation. The indicator includes hydrodynamic pressure fluctuations; short, unequal records and a spanwise-periodic rotor model limit generalization to turbine noise.