Performance Analysis of a Savonius Rotor for Wave Energy Conversion

Abstract

Ocean wave energy is rapidly becoming a field of great interest in the world of renewable energy. Significant advancements in design and technology are being made to make wave energy a viable alternative for our growing energy demands. Ocean waves are a significant resource of inexhaustible, non-polluting energy. Wave energy converters (WEC) provide a means of transforming wave energy into usable electrical energy. The development of these devices is undergoing rapid change. An overview of the various operating WEC is presented, classifying them according to shoreline, near shore and offshore applications. The prior concept of using an oscillating water column (OWC) with a savonius rotor at the bottom of the rear chamber as a potential WEC is of interest. (Under certain conditions and water depth, wave action in the OWC induces a reverse flow. As proposed, this reverse current could generate electric power by rotating the blades of a savonius rotor turbine).

A numerical study of the savonius type direct drive turbine in typical chamber geometry of an oscillating water column chamber for wave energy conversion was carried out. The research deals with a numerical modeling devoted to predict the turbine efficiency in the components of an oscillating water column system used for the wave energy capture, the flow behavior is modeled by using the commercial code ANSYS CFX (11). Several numerical flow models have been elaborated and tested independently in the geometries of a water chamber with a savonius type wave turbines

Constant periodic wave flow calculations were performed to investigate the flow distribution at the turbines inlet section, as well as the properties of the savonius type turbine. The flow is assumed to be two-dimensional (2D), viscous, turbulent and unsteady. The commercial CFD code is used with a solver of the coupled conservation equations of mass, momentum and energy, with an implicit time scheme and with the adoption of the hexahedral mesh and the moving mesh techniques in areas of moving surfaces. Turbulence is modeled with the k？e model. The obtained results indicate that the developed models are well suitable to analyze the water flows both in the chamber and in the turbine. For the turbine, the numerical results of pressure and torque were compared with each other.

The primary stages of the research effort can be described as follows

Firstly, a comprehensive literature survey was done to find those articles that deal specifically with wave energy conversion. Gleaned from this is the effect, that variances in technology, location, developments and etc (Appendix).

Secondly, development of a 3D numerical wave tank using CFD that can represent the physical model to an appropriate order of accuracy whilst maintaining realistic computational effort. Furthermore, extend the numerical wave tank to include a detailed OWC to determine energy capture efficiencies.

Thirdly, determine the effect of various 3 bladed savonius geometric parameters on efficiency

Fourthly, A mitigation technique that involves altering the geometry of the OWC chamber inlet section was studied.

Finally, the best geometric models were combined to obtain the highest efficiency for 5 bladed savonius rotor

The results obtained show that with careful consideration of key modeling parameters as well as ensuring sufficient data resolution. The results of the testing have also illustrated that simple changes to the front wall aperture shape can provide marked improvements in the efficiency of energy capture for OWC type devices.