Design optimization of a purely radial turbine for operation in the inhalation mode of an oscillating water column

Abstract 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.