A modified savonius turbine with moveable blades for higher efficiency

Abstract

Previous research works have proposed Savonius vertical axis marine current turbine as appropriate for low current velocity applications such as in the Malaysian sea. The numerous benefits of Savonius turbine such as its simple structure, self-start ability, relatively low operating velocity, independence from flow direction and low environmental impact have generated interests among researchers. Despite these advantages, it suffers from low efficiency. Savonius turbine is composed of multiple physical parts; in which in this study, certain important parameters including blades, end plate, aspect ratio and overlap ratio had been investigated. This thesis proposes a newly modified Savonius turbine, designated ReT (Reza Turbine), for low speed marine currents to enhance the efficiency. The ReT consists of two blades, each blade divided into two parts which are joined by hinge. This makes ReT considerable as a turbine with movable blades. The blades, being movable, necessitates a specific design of endplates to ensure the blades to function properly. This research explored the nonlinear two-dimensional flow numerically over the novel type rotor. Simulations were conducted using Computational Fluid Dynamics (CFD) software, by applying the SIMPLE (Semi-Implicit Method for Pressure Linked Equations) algorithm. The unsteady Reynolds Averaged Navier-Stokes (RANS) equations were solved for velocity and pressure coupling with a code, based on the programming Language C through the User Defined Functions (UDF) at variation of marine current velocities. Dynamic Mesh Method (DMM) was used for solving the movement of the blades and adjusting the mesh according to the position of the blades on the surface. The numerical simulation using turbulence model Shear Stress Transport (SST k-ω) produced satisfactory results when compared with experimental results of the modified turbine and classical Savonius turbine. For validation purpose, the modified model was tested in Universiti Teknologi Malaysia’s low speed wind tunnel at different flow velocities. Important parameters such as torque, power and performance as well as the pressure distribution on the blades surfaces were measured at different angles of attack. Parametric study was conducted in six subsections, in which the modified turbine had been investigated and analysed. The maximum coefficient of power of ReT was found to be 0.34 at tip speed ratio (λ) of 0.9. This is 52% improvement in efficiency (power coefficient) compared to classical Savonius turbine without any extra accessories. The use of ReT will enable power to be extracted more efficiently from low speed marine currents.