Research Article Investigations on the Effect of Radius Rotor in Combined Darrieus-Savonius Wind Turbine Kaprawi Sahim , Dyos Santoso, and Dewi Puspitasari Mechanical Engineering Department, Sriwijaya University, Sumatera Selatan, Indonesia Correspondence should be addressed to Kaprawi Sahim; kaprawis@yahoo.com Received 23 October 2017; Accepted 10 January 2018; Published 1 March 2018 Academic Editor: Tariq Iqbal Copyright © 2018 Kaprawi Sahim et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Renewable sources of energy, abundant in availability, are needed to be exploited with adaptable technology. For wind energy, the wind turbine is very well adapted to generate electricity. Among the diferent typologies, small scale Vertical Axis Wind Turbines (VAWT) present the greatest potential for of-grid power generation at low wind speeds. Te combined Darrieus-Savonius wind turbine is intended to enhance the performance of the Darrieus rotor in low speed. In combined turbine, the Savonius buckets are always attached at the rotor shaf and the Darrieus blades are installed far from the shaf which have arm attaching to the shaf. A simple combined turbine ofers two rotors on the same shaf. Te combined turbine that consists of two Darrieus and Savonius blades was tested in wind tunnel test section with constant wind velocity and its performance was assessed in terms of power and torque coefcients. Te study gives the efect of the radius ratio between Savonius and Darrieus rotor on the performance of the turbine. Te results show that there is a signifcant infuence on the turbine performance if the radius ratio was changed. 1. Introduction Darrieus and Savonius wind turbines are the most common VAWTs. Te Savonius wind turbine is an aerodynamically drag based, self-starting turbine with low cut in speed, but its inefciency curtails it to fewer applications, whereas Darrieus wind turbines are aerodynamically lifing based turbines having higher cut in speed with higher coefcients of performance. Tus, it can rotate faster than the wind veloc- ity. Combined rotors are the combination of Darrieus and Savonius rotors mounted on the same shaf. Mostly combined wind turbines are available in the vertical axis confguration. Figure 1 gives a performance comparison of the various types of all conventional turbines that have been constructed [1]. As can be seen in the fgure, turbines with horizontal axis have high power coefcient among other turbines which reach 49% in ≈7. All turbines with vertical shaf have low power coefcient and the smallest power coefcient is Savonius turbine having maximum power coefcient 0.15 on  ≈ 0.8. 1.1. Darrieus Turbine. Various types of Darrieus turbine rotor confguration exist; among them are: egg beater type, straight blade type, and helical blade rotor. To increase the Darrieus turbine performance, Takao et al. [2] placed a guide vane row upstream of the rotor in order to enhance its torque, so the power coefcient of the turbine is 1.5 times higher than that of the original turbine which has no guide vane. Te micro Darrieus turbine consists of usually two or three pairs of airfoils of NACA type and each pair has a single blade. Confguration of each pair consists of two blades, where one of them is auxiliary blade and gives a higher static torque [3]. Te number of Darrieus blades infuences the turbine performance. Te fewer the number of blades, the higher the performance of the rotor [4]. Te use of double blades of solo Darrieus rotor makes the turbine lower in performance [5]. Te efect of an upstream fat defector on the power output of two counterrotating straight-bladed Darrieus wind turbines was investigated experimentally [6, 7]. Te result shows that the power output of a turbine increases signif- cantly. Te efect of solidity will increase the torque of H- Darrieus turbine, but increasing solidity alone does not improve the performance of the rotor since there is an efect of blockage and interaction [8]. Te new model of Darrieus blade is introduced by Zamani et al. [9] in using J-shaped profle; the wind turbine performance and self-starting of Hindawi International Journal of Rotating Machinery Volume 2018, Article ID 3568542, 7 pages https://doi.org/10.1155/2018/3568542