A radial inflow air turbine design for a vented oscillating water column

The oscillating-water-column (OWC) is a ubiquitous style of wave-energy-converter for harnessing significant power from ocean waves. A new configuration of OWC described here as a vented-OWC provides opportunity to simplify air-turbine design by limiting the power extraction to inhalation mode. The asymmetric airflow profile of the vented-OWC requires a unidirectional-turbine configuration to be adopted.

The focus of this study is to analyse a unidirectional radial air-inflow-turbine design using Computational-Fluid-Dynamics (CFD) suitable for application with a vented-OWC. It is found that downstream of the rotor can cause significant energy losses due to its narrow flow passage. Two configurations of an inward-flow radial turbine were also compared, the first by keeping the casing height constant throughout the turbine domain and the second by increasing the casing height in a way to keep a constant sectional area from inlet to the outlet of the turbine domain. The latter configuration obtained a ten percent gain in peak efficiency compared to the first. The difference is identified as fewer energy losses at the downstream section and comparably higher torque for the same flow-coefficient. Introduction of downstream-guide-vanes was found to retard the chocking phenomenon, which offers a wider operational range for the radial-inflow design.