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Numerical Study of Savonius Wind Turbine Start-up Considering the Rotor moment of Inertia in Sinusoidal Unsteady Wind Conditions

Savonius rotor is considered as a class of vertical axis wind turbines (VAWTs), which has attracted more attention since the early 70's regarding the potential advantages such as start-up without the requirement for initial torque and simplicity in design. Despite the great influence of dynamic characteristics on start-up and stability of these rotors, as well as working in areas subjected to highly turbulent atmospheric boundary layer, dynamic characteristics and unsteady wind condition were neglected in most of the previous research. In this study, the turbine start-up characteristics have been investigated numerically considering the dynamic characteristics of the traditional Savonius rotor and unsteady sinusoidal upstream flow, using user-defined functions in Fluent software. The simulation results are highly consistent with the existing experimental results and hence, relatively accurate prediction of the start-up behavior of the Savonius turbine can be achieved. According to the obtained results, increasing the mean velocity leads to an increase in the growth rate of tip speed ratio. In addition, reducing the period in the upstream, hastens the rotor acceleration process. Moreover, by increasing the tip speed ratio up to 0.7, an increase in the torque coefficient can be seen, which is followed by a decreasing trend with further increase in tip speed ratio.