On the application of semicircular and Bach-type blades in the internal Savonius rotor of a hybrid wind turbine system

Abstract

In the present study, a comparison has been performed numerically to explore the impact of internal rotor type on power characteristics of a two-bladed hybrid vertical axis wind turbine (VAWT). For this purpose, the internal rotor of a hybrid wind turbine built with the conventional semicircle and Bach-type blades is considered under two free-wind speeds (U∞) of 5 and 10 m/s. Computations are conducted at three tip speed ratios (TSRs) of 1.5, 2.5, and 3.5. Effects of different relative positions between the external and internal rotors, called attachment angle, (φ) such as 0°, 45°, and 90° are studied in detail and the obtained results are validated against the available data for Darrieus and Savonius rotors, separately. The results illustrate that the internal rotor type, attachment angle, and TSR have considerable impacts on the hybrid rotor performance. Moreover, it is demonstrated that the Bach-type Savonius rotor has better performance than the conventional semicircle one in a two-bladed hybrid wind turbine regardless of φ, TSR, and U∞. The maximum improvement of 20% is reported for hybrid wind turbine equipped with Bach-type rotor under φ = 90°, TSR = 1.5, and U∞ = 5 m/s.