The Darrieus turbine is a suitable power generation in free stream flow because it is simple in construction, but it has the disadvantage of its small starting torque. The Savonius turbine has a high starting torque but the efficiency is smaller than that of Darrieus turbine. To improve the starting torque of Darrieus turbine, the Savonius buckets are introduced into the Darrieus turbine and the combined turbine is called Darrieus-Savonius turbine. In this study, three semielliptic sections of aspect ratio 0.8 were used for Savonius bucket while the Darrieus blade used three wings of airfoil NACA 0015. The Darrieus-Savonius turbine’s performances were studied experimentally in an irrigation canal of South Sumatera, Indonesia. The results show that the distance of Savonius buckets from the shaft centre influences performance of combined turbine, and the attachment angle of Savonius rotor made important variation of turbine performance. 1. Introduction Free stream flow of a river can be used to generate electricity by installing a suitable water turbine. Wide sources of stream flow like tides, marine current, irrigation canal, and industrial flows can make a source of electricity generation by installing water turbine rotor. Turbines for free stream flow are mainly aimed for rural region at sites remote from existing electricity grids, and they are useful machines to improve quality of life of people and increase the economic activities. In its installations, the turbine’s rotors are fixed to a structure on the riverside or on floating pontoons. Different designs of water turbine are available for the extraction of kinetic energy of free stream flow. Gorlov, Darrieus, and Savonius turbines are suitable for this purpose. The commonly uses of these turbines are vertical axis types. The Gorlov turbine has helically shaped blades which are of more complicated nature of the blade’s construction. This could make Gorlov turbines at a serious disadvantage while the Darrieus turbine has straight bladed types, which are easy to be constructed. The Savonius turbine uses commonly a semicircular section which can be constructed by a semicircular pipe. The efficiency of a helical turbine for free flow condition as reported analytically by Gorban et al. is about 35% [1]. For Savonius turbine, most of the previous researchers used two buckets of semicircular section in exploring the performance. Kyozuka [2] gave an increase of value of coefficient of power of Savonius turbine by combination of Darrieus turbine having two wings and two Savonius buckets. Besides that the
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