Flow pattern analysis of an outflow radial turbine for twin-turbines-OWC wave energy converters

摘要

OutFlow Radial (OFR) Turbines have been recently proposed for Oscillating Water Column (OWC) devices based on a Twin Turbine Configuration (TTC). Previous experimental studies showed that these turbines are a feasible alternative to axial unidirectional turbines without rectifying systems. In this paper, a validated CFD model is employed to achieve a better understanding on how the OFR turbine is working in an OWC energy converter for both direct and reverse modes. The turbine geometry corresponds to a second prototype proposed in a previous publication, with a total-to-static peak efficiency of 54%. The key of the performance in reverse mode is the vortical structure created within the blade-to-blade passage, almost choking the flow rate through the rotor. It is also concluded that increasing the outer blade angle leads to a worse performance in reverse mode, although the global performance is improved due to the rotor efficiency gain in direct mode. Finally, it has been also observed that the kinetic energy at the outlet during direct mode still remains as the major source of loss, penalizing the attainable maximum efficiency. Future work should be focused on the reduction of this residual energy to boost the application of these OFR turbines for TTCs.