Study of A Twisted Savonius Water Current Turbine M. Imtiaj Hassan, Nahidul Khan, Michael Hinchey, Tariq Iqbal, Vlastimil Masek Memorial University of Newfoundland St. John’s, NL, A1B 3X5, Canada Abstract-Savonius Turbine is a drag type device; having good starting torque and operating at low speed. For better performance Savonius turbine has been studied with twist angle along its vertical axis. This work presents Computational Fluid Dynamics (CFD) analysis as well as experiments on the twisted Savonius turbine. Flow-3D, developed by Flow Science, has been used as a CFD software package. 180 0 twisted Savonius rotor has been proposed, having two endplates and zero overlap ratio. Experiments have been done on the turbine at Flume tank in Marine Institute. CFD results show an efficiency of 12% of the turbine. Experimental results validate the CFD results. Index Terms—Twisted Savonius, Computational Fluid Dynamics, Flow 3D, Power co efficient, Tip Speed Ratio I. INTRODUCTION The twisted Savonius is a vertical axis machine with high starting torque and reasonable peak power output [1]. The twisted Savonius rotor has an ‘‘S-shaped’’ cross-section. It can be constructed by two semi circular buckets. The concept of the Savonius rotor is based on the principle developed by Flettner [2]. The power from the rotor is based on the difference in pressure across the blade retreating from the wind and that advancing into the wind. This is in turn related to the difference in the drag coefficients associated with the convex and the concave side of the blades [3]. The Savonius rotor has a simple structure. Though it has good starting characteristics, it can also operate at relatively low speeds and has the ability to accept fluid from any direction. The twisted Savonius rotor is a drag type device. This means that the main driving force is drag force of fluid acting on its blade. However, at low angles of attacks, lift force also contributes to torque production. The twisted Savonius design is very consistent in operation and also has a much higher average power output compared to conventional ones [4]. Therefore, the twisted Savonius is one of the best rotors for a turbulent fluid flow to generate small scale power. The problem is that the process of constructing a twisted Savonius wind turbine is currently extremely complex, requiring expensive materials and machinery to build and, therefore, making the cost very high. This work investigates the performance of a twisted Savonius turbine. The turbine has been studied from fluid dynamics point of view as well as the performance of the turbine has been studied by doing experimental set up. In this work Flow-3D, developed by Flow Science [5], has been used as the Computational Fluid Dynamics (CFD) software. By investigating the dynamic behavior of liquids and gases Flow- 3D provides flow simulation solutions. It also specializes in the solution of time-dependent (transient), free-surface problems in one, two and three dimensions and models confined flows and steady-state problems. No special additional modules for meshing or post-processing are needed. An integrated graphical user interface ties everything together, from problem setup to post-processing. It gives a magnificent visualization of the simulation results. Experiments on the turbine have been done in Flume Tank for a set of variable current speed. The experimental results validate the Flow-3D simulation results. II. TWISTED SAVONIUS The cross section of twisted Savonius resembles like two half circle but it moves a certain degree in every step for certain cross sectional width. In this work Savonius rotor has a twist of half pitch along its vertical axis. Figure 1 shows the top view of the twisted Savonius turbine. Figure 1. Top view of twisted Savonius rotor The power coefficient Cp of a turbine is: Cp =P/ (2 AρV 3 ) (1) Where, P is the output power (W) ρ is the density of water (kg/m 3 ) A is the swept area of rotor (m 2 ) V is the speed of water (m/s)