Effects of inward and outward overlap ratios on the two-blade Savonius type of vertical axis wind turbine performance

Abstract

ABSTRACTIn this paper, using numerical simulation, the effects of inward and outward overlaps on the performance of a conventional two-blade Savonius wind turbine and the complete analysis of the events caused by the rotation of the blades have been investigated. Computations have been carried out at several nondimensional overlap ratios such as G/d = 0, ±0.1, ±0.2, and ±0.3 for three wind speeds of 3, 5, and 7 m/s. On the other hand, in the present study, the values of the tip speed ratio (TSR) are considered in the range from 0.2 to 1.2. The obtained results are validated against the available data in the open literature and found excellent agreements between them. Several results such as the instantaneous velocity and pressure fields in the rotating zone, variation of torque coefficients in one complete cycle of the rotor, and mean power coefficient distributions as a function of TSR and wind speed have been presented in this numerical investigation. The results show that, regardless of the overlap ratio, the maximum power coefficient occurs at a tip speed ratio (TSR) of 0.8. Additionally, the maximum power coefficient is observed in the inwards overlap ratio of 0.2 and an increasing or decreasing the overlap ratio reduces the maximum value of the power coefficient in all wind speeds under consideration. Finally, it was concluded that at each TSR and G/D value, increasing the wind speed enhances the power coefficient of two-blade Savonius VAWT. It was hoped the obtained results arouse interest among the VAWT designers.