Optimization of camberline and thickness distribution in an outflow radial turbine for twin-OWC applications

Abstract

Oscillating Water Column (OWC) systems are among the most extensively investigated Wave Energy Converters, owing to their operational reliability and structural simplicity. Their functioning relies on exploiting the bidirectional and periodic airflow induced by the wave-driven piston effect within the chamber. Over the past decades, multiple turbine typologies have been examined for OWC applications, with the twin-turbine system emerging as a notable alternative. This configuration incorporates two unidirectional turbines that alternate between distinct operational modes depending on the direction of the airflow: functioning either as an energy-extracting turbine or as a flow-blocking device. In the present study, a radial turbomachine is employed within such a system, operating as a turbine during the outflow phase and serving as a flow preventer during the inflow phase. Starting from a previously developed baseline geometry, an optimization procedure was carried out to identify the blade configuration that delivers optimal performance under the imposed operating conditions. Unlike earlier designs, the current optimization simultaneously considers modifications in both the camberline and the thickness distribution, with the objective of satisfying performance requirements in both flow directions: maximizing efficiency during outflow operation and enhancing blocking capability during inflow operation. Following the optimization stage, the aerodynamic characteristics of the optimized outflow turbine were analytically coupled with those of the complementary inflow turbine to evaluate their combined contribution to the bidirectional performance of the twin-turbine system. The results indicate that targeted geometric refinement of the outflow turbine leads to a substantial improvement in centrifugal efficiency while preserving a controlled aerodynamic response under reverse-flow conditions.