American Journal of Mechanical Engineering, 2015, Vol. 3, No. 3A, 15-21 Available online at http://pubs.sciepub.com/ajme/3/3A/3 © Science and Education Publishing DOI:10.12691/ajme-3-3A-3 Numerical Study of an Unconventional Savonius Wind Rotor with a 75° Bucket Arc Angle Zied Driss * , Olfa Mlayeh, Slah Driss, Makram Maaloul, Mohamed Salah Abid Laboratory of Electro-Mechanic Systems (LASEM), National School of Engineers of Sfax (ENIS), University of Sfax (US), B.P. 1173, Road Soukra km 3.5, 3038 Sfax, TUNISIA *Corresponding author: Zied.Driss@enis.rnu.tn Received May 20, 2015; Revised June 22, 2015; Accepted July 13, 2015 Abstract In this paper, computer simulation has been conducted to study the aerodynamic structure around an unconventional Savonius wind rotor with a 75° bucket arc angle. The numerical model is based on the resolution of the Navier-Stokes equations in conjunction with the standard k-ε turbulence model. These equations were solved by a finite volume discretization method. The software "Solidworks Flow simulation" has been used to characterise the flow characteristics in different transverse and longitudinal planes. The good comparison between numerical and experimental results confirms the validity of the numerical method. Keywords: unconventional Savonius wind rotor, bucket arc angle, wind tunnel, aerodynamic structure, CFD Cite This Article: Zied Driss, Olfa Mlayeh, Slah Driss, Makram Maaloul, and Mohamed Salah Abid, “Numerical Study of an Unconventional Savonius Wind Rotor with a 75° Bucket Arc Angle.” American Journal of Mechanical Engineering, vol. 3, no. 3A (2015): 15-21. doi: 10.12691/ajme-3-3A-3. 1. Introduction The Savonius wind rotor has aroused a large credit, not only in research and academic communities but also in industrial appliances. In comparison to that of other kinds, the efficiency of Savonius rotor is lower. The reason of low efficiency mainly rests on the fact that one bucket moves against wind when another one moves in the direction of wind [2,3]. In this context, numerical and experimental investigations have been conducted to improve the Savonius wind rotor performance. For example, Khan et al. [4] tested Savonius rotor both in tunnel and natural wind conditions with the provision of variation of overlap. Research conducted by Grinspan et al. [5] in this direction led to the development of a new blade shape with a twist for the Savonius rotor. They obtained a maximum power coefficient of 0.5 for its model. Saha and Rajkumar [6] performed work on twist bladed metallic Savonius rotor and compared the performance with conventional semi-circular blades having no twist. They obtained an efficiency of 0.14. Their rotor also produced good starting torque and larger rotational speeds. Saha et al. [7] conducted wind tunnel tests to assess the aerodynamic performance of single, two and three-stage Savonius rotor systems. Both semicircular and twisted blades have been used. Aldos [8] studied power augmentation of Savonius rotor by allowing the rotor blades to swing back when on the upwind side. He reported a power augmentation of the order of 11.25% with the increase in Cp. He further concluded that different basic rotors configuration might produce different power augmentation. Sabzevari [9] examined the effects of several ducting, concentrators and diffusers on the performance improvements of a split Savonius rotor. A circularly ducted Savonius rotor equipped with a number of identical wind concentrators and diffusers along the periphery of circular housing produced efficiency of the order of 40%. In order to eliminate the low aerodynamic performance of Savonius wind rotors, Mohamed et al. [10] studied several shapes of obstacles and deflectors placed in front of two and three blades Savonius turbine. A rounded deflector structure was placed in front of two counter-rotating turbines. An experimental investigation was carried out by Golecha et al. [11] to identify the position of the deflector plate to yield higher coefficient of power for single stage modified Savonius rotor. Akwa et al. [13] discussed the influence of the buckets overlap ratio of a Savonius wind rotor on the averaged moment and power coefficients, over complete cycles of operation. Kamoji et al. [14] compared the helical Savonius rotor with the conventional Savonius rotor. The results indicate that the helical Savonius rotors have positive coefficient of static torque. D’Alessandro et al. [15] developed a mathematical model of the interaction between the flow field and the rotor blades. The aim of their research was to gain an insight into the complex flow field developed around a Savonius wind rotor and to evaluate its performance. Irabu and Roy [16] improved and adjusted the output power of Savonius rotor under various wind power and suggests the method of prevention the rotor from strong wind disaster. On the basis of the previous studies, it appears important to propose a new design to improve the performance of the conventional Savonius wind rotor. For this purpose, computer simulations have been conducted to study the aerodynamic structure around an