Optimal shape and position of a thick deflector plate in front of a hydraulic Savonius turbine Emeel Kerikous a, b, * , Dominique Th  evenin a a Lab. of Fluid Dynamics & Technical Flows, Univ. of Magdeburg “Otto von Guericke”, 39106, Magdeburg, Germany b Mechanical Power Engineering Department, Faculty of Engineering-Mattaria, Helwan University,11718, Cairo, Egypt article info Article history: Received 13 May 2019 Received in revised form 12 September 2019 Accepted 17 September 2019 Available online 21 September 2019 Keywords: Hydraulic turbine Savonius Blade shape Optimization CFD Deflector plate abstract This paper describes an optimization procedure for the shape and position of a thick deflector plate in front of a hydraulic Savonius turbine to improve the output power of the system for a constant frontal area. Seven geometrical parameters are taken into account during the optimization process. The simu- lation code Star-CCMþ is used to investigate the flow field around numerous structures to obtain the optimal configuration. This code is driven by OPALþþ (in-house code optimization). During the opti- mization procedure, maximizing the average power coefficient (C p ) is the main objective function. The optimal configuration improves the C p by almost 11% for a tip speed ratio l ¼ 1:1 in comparison with the traditional Savonius turbine. The hydrodynamic features of the turbine with the optimal deflector plate are discussed in detail and compared with the standard turbine, explaining that the increase in the turbine performance was obtained by an improved pressure distribution and enhanced flow configu- ration around the turbine blades. The performance of the turbine with optimal deflector plate is finally compared with the standard design for the whole operation range by varying the tip speed ratio. This comparison reveals that the power coefficient C p is increased by nearly 15% for l ¼ 1:2. Finally, it has been checked that the turbine with the deflector plate is still self-starting. The obtained design should not only be very useful to considerably improve the power of the turbine at a constant frontal area but also effective to protect the returning blade from collisions with suspended objects thanks to the deflector plate. © 2019 Elsevier Ltd. All rights reserved. 1. Introduction The ever-growing energy demand in the world is one of the most important problems to be solved today, coupled to a contin- uous growth of population. Obviously, renewable energy sources should be preferred as far as possible to fulfill this purpose. Considering that water covers 71% of the earth surface, hydropower appears as a particularly attractive source of green energy. Water energy can be mainly extracted by two different techniques. The first, currently mostly used one, relies on the potential energy of water, using a hydraulic head difference and needing some kind of dam [1,2]. The other approach converts directly the kinetic energy of water to useful mechanical power, relying on hydro-kinetic turbines [3]. Both processes can be combined in practical systems [4]. While using a head allows employing much larger systems with a very high efficiency, the associated dam typically leads to a major impact on landscape, population, fauna and flora, resulting into very complex political decisions. It is clear that there are many advantages regarding environmental issues in case of using only hydro-kinetic turbines; besides, they are commonly very simple and cost-efficient. Unfortunately, their efficiency is very low, explaining why many projects are running to improve this point in various countries [5e8]. Prototype hydro-kinetic turbines have been already tested by various companies such as Electric Energy Limited (UK), Alternative Hydro solutions Limited (Canada), Lucid Energy Technology (USA), Throptom Energy services (UK), and Seabell Int. Co., Ltd. (Japan) [9]. However, hydrokinetic turbines generate very restricted energy. Moreover, their power coefficient is generally extremely low compared with the theoretical power coefficient ð59:3%) defined by Betz limit [10]. Hydro-kinetic turbines are a recent research topic but the literature regarding wind turbines can be surely used to obtain the main concepts for this field. Water turbines working at water speed * Corresponding author. Lab. of Fluid Dynamics & Technical Flows, Univ. of Magdeburg “Otto von Guericke”, 39106, Magdeburg, Germany. E-mail address: emeel.kerikous@ovgu.de (E. Kerikous). Contents lists available at ScienceDirect Energy journal homepage: www.elsevier.com/locate/energy https://doi.org/10.1016/j.energy.2019.116157 0360-5442/© 2019 Elsevier Ltd. All rights reserved. Energy 189 (2019) 116157