Design and Performance Testing of a Ducted Savonius Turbine for Marine Current Energy Extraction

Abstract

Marine current energy is a reliable and clean source of energy. Several marine current turbines have been developed over the years, most of the turbines perform well at velocities over 2 m/s and need to be installed at depths of 20–40 m. Placing an appropriately designed duct or shroud around the turbine significantly improves the turbine’s performance. Ducted Savonius turbines can operate at low depths, since large clearance is not required because turbulent flow has little effect on the performance of the Savonius rotor. Ducted Savonius turbine has simple components and can be easily fabricated in Pacific Island Countries (PIC) and other places that do not have advanced manufacturing industries. A ducted Savonius turbine was designed for a location in Fiji, to operate at a rated marine current speed of 1.15 m/s and cut in speed of 0.2 m/s. The model of ducted Savonius turbine, scaled down to 1/20, was fabricated and tested in a water stream with a velocity of 0.6 m/s and was validated with commercial Computational Fluid Dynamics (CFD) code ANSYS-CFX. Finally, a full scale numerical model was constructed to study the flow characteristics and compute the performance. The area ratio of the duct of 2.5:1 (inlet to turbine section) shows significant increase in kinetic energy and an improved turbine performance. The maximum efficiency of the turbine is around 50% at a tip speed ratio (TSR) of 3.5 and the maximum power produced is 10 kW at the rated speed of 1.15 m/s and 63.4 kW at a free-stream velocity of 2.15 m/s.