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A vented Oscillating-Water-Column (OWC) simplifies the pneumatic energy conversion problem by rectifying air flow and enabling a unidirectional-air-turbine to be employed. It shifts power-extraction to the inhalation phase of the cycle and provides equivalent pneumatic power to a full-wave-cycle. Conventional Radial-air-turbines feature a low global-efficiency in OWC applications, however they offer simpler designs and lower thrust loads. The aim of this study is to modify the design of a centripetal-radial-turbine for optimum efficiency in steady-state using CFD methods for application with the pressure/flow profile experienced by the vented-OWC. Nine design variables were used to control the shape of the rotor and its adjustment to the inward-flow direction. The optimized rotor was found to achieve significant efficiency and output power by using asymmetric and non-zero-staggered blades. The downstream section was optimized for an efficient matching with the optimized-inflow-rotor and four parameters were used to control the shape of the downstream section. A diffuser with a 7-degree diffusion-angle was found to be the optimal connection between the turbine and the chamber. The inflow radial turbine obtained 81% peak efficiency in the steady-state, and its average efficiency over the expected flow coefficients is comparable to the axial-turbines used with OWCs. • Optimization studies were used to optimize the rotor of a radial inflow turbine. • Angles of the blades and guide vanes were found to have the highest sensitivity. • The losses in all sections of the optimized inflow turbine are highly reduced. • The optimized inflow turbine was found to obtain 81% peak efficiency in steady-state. [ABSTRACT FROM AUTHOR]

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. • Unidirectional radial turbines are investigated for inflow and outflow directions. • The outflow radial turbine is less affected by backflow in a bidirectional OWC. • Compared to the outflow design, inflow turbine has lower RPM and larger size. • The outflow turbine is less sensitive to RPM variations than the inflow turbine. • The inflow turbine in vented-OWC obtains comparable power with a bidirectional OWC. [ABSTRACT FROM AUTHOR]

Research on employing unidirectional air turbines for oscillating water columns (OWC) has received much attention in the last few years. Most unidirectional turbine topologies considered to date use axial flow unidirectional turbines. The radial turbine offers an alternative with increased resistance to backflow. However, in general, the efficiency of radial turbines is lower than axial turbines. This study describes a computational fluid dynamics (CFD)-based design optimisation of an outflow radial turbine for the intended application in an OWC system configured to enable primarily unidirectional flow through the turbine. The rotor blade geometry is parametrically described in addition to other turbine components. The central composite design (CCD) and genetic algorithm were used to explore an optimum design of a centrifugal radial turbine for a maximum total-to-static efficiency. Seven computer aided design (CAD) parameters were investigated as the design variables, and the optimum turbine design was identified in a population of 79 design points. The optimum outflow turbine was found to have a peak steady-state efficiency of 72%, and the leading-edge angle, guide vane angle, trailing edge angle, and the chord length were found to have the highest sensitivity. Compared to an inflow radial turbine, the geometrical features of the outflow turbine permit higher absolute velocities of the flow at the rotor entrance and increase the dynamic pressure changes across the rotor. Therefore, the optimised outflow radial turbine can obtain acceptable rotor energy transfer despite having a negative centrifugal energy transfer term. [ABSTRACT FROM AUTHOR]