Performance of improved savonius vertical axis marine current turbine rotor design

Abstract

Renewable energy resources are being explored as a respond to the diminishing fuel and fossil energy. One form of renewable energy is ocean current which requires horizontal and vertical axis turbines for its energy extraction. Savonius turbine is a vertical axis marine current turbine that has been found to suit the application in shallow water and low current speed of Malaysian seas. This turbine however has a very low mechanical efficiency. The purpose of this research is to improve the performance of the turbine. This research starts with a comparison of initial simulation data with previous work so that further simulation steps are reliable. The analysis was carried out using Computational Fluid Dynamic (CFD) ANSYS software. With its dimension limited to Malaysia sea characteristics and other consideration, a 1.67m height turbine was used for simulation and model construction for experiment. Parametric studies were carried out during the simulation steps focussing on the outer structure optimization of a plate or guide vane. The conventional shape of two stage Savonius rotor with overlap ratio of 0.21 and 90° phase angle difference was used. The effect of water speed to the incoming turbine was investigated. The used of a duct shows an improvement on the water speed, but it has very small effect to the rotor efficiency. However, the used of a plate at certain angle and distance from the turbine increase the rotor performance. It was also shown two plates are better than one, leading to a 25.6 percent increase of efficiency. For validation purpose, a 1:2.4 scale model was constructed from composite material and tested in Universiti Teknologi Malaysia Marine Technology Centre. This experimental work is to validate the simulation results of the two deflectors. The pattern of improvement is similar between numerical and experimental, although the quantitative differences of Coefficient of Performance range from 4 to 30%. This is sufficient to validate that the results of this project are acceptable, hence the Savonius rotor have been significantly improved.