Comparison of inflow and outflow radial air turbines in vented and bidirectional OWC wave energy converters

Abstract

This study analyses the aerodynamic performance of two unidirectional-radial-air-turbine configurations; inflow and outflow. These turbines were studied as the Power-Take-Off unit for application on a vented-OWC and a conventional-bidirectional-OWC with a twin-turbine topology, forming four different turbine-OWC configurations. These configurations were evaluated in terms of full-scale power extraction using extrapolated hydrodynamic experimental data of irregular waves for a King Island test site. The power extraction capacity was evaluated by defining a lower and upper bound of power generation under fixed and controlled-RPM schemes and the energy produced in each configuration was then compared against a state-of-the-art twin-rotor turbine. It was found that the difference between these power extraction bounds was lower in case of the outflow turbine, which shows this turbine is less sensitive to RPM variations than the inflow turbine. In addition, due to its lower resistance to the flow in direct mode, the outflow turbine has a smaller full-scale size than the inflow turbine. It was concluded that the outflow turbine provides better efficiency in a twin-turbine-OWC system, while the inflow turbine yields higher conversion efficiency in a vented-OWC system. The vented OWC equipped with a radial inflow turbine can obtain comparable power to the bidirectional OWC system.