Viability of unidirectional radial turbines for twin-turbine configuration of OWC wave energy converters

Oscillating Water Column devices are the most widespread among Wave Energy converters, with an efficiency that is closely related to the performance of its Power Take-Off element, usually a turbine. Using unidirectional turbines requires a system of valves to rectify the bidirectional flow, so self-rectifying turbines are more convenient for an OWC device. Another recent proposal is the use of a twin turbine configuration, where an arrangement of two unidirectional turbines could perform this task, with each turbine extracting the flow energy alternately. To date, all the twin turbine configurations studied in the open literature consider unidirectional axial turbines. In this paper, the use of a radial turbine to improve the system's efficiency by enhancing flow rectification is presented for the first time. An experimentally validated numerical model has been used to analyse the flow field of the radial turbine when working in both direct and reverse modes. Interesting conclusions are extracted. Finally, a performance comparison of the twin turbine configuration using axial or radial turbines has been carried out. It is concluded that the good performance of the radial turbine working as a flow preventer makes this kind of turbine an interesting option for twin systems.