Numerical Simulation of Aerodynamic Noise Radiated form Vertical Axis Wind Turbines

Vertical Axis Wind Turbines (hereafter VAWT) are one of the useful renewable energy systems. They have several advantages in comparison with the conventional, propeller-typed, horizontal axis wind turbines. VAWTs operate independently of the wind direction. Moreover, maximum power coefficient can be obtained at lower tip-speed ratio compared to the conventional wind turbines. Flow induced noise is therefore smaller than that of the conventional ones. In this paper, we attempt to simulate an unsteady flow filed and aerodynamic sound radiated from VAWT by using the discrete vortex method and Ffowcs Williams-Hawkings equation. The result shows that the power coefficient is almost the same as the conventional typed wind turbines. Moreover, the predicted noise level of the developed VAWT is about 70dB, which is 10 dB lower than that of the horizontal axis wind turbine. We also attempted to estimate sound spectrum by using three dimensional vortex methods. However, the applied vortex methods can not simulate turbulent eddy motions such as the combination process and vortex break down process. Aerodynamic sound simulation by using discrete vortex methods is therefore limited to overall noise level estimation. However, vortex methods are useful to estimate aerodynamic noise from VAWT with small-scale computers. 1