Performance of fluidic diode for a twin unidirectional impulse turbine

Abstract

The rectification-valve system has been invented to drive an air turbine equipped with the oscillating water column (OWC) based wave energy plant. However, this flow rectification system has widely regarded as impractical, except possibly in small devices like navigation buoys, due to the lack of durability of the valves and its complex mechanism. Moreover, as the valve size must be large for a high output, that makes the system practically infeasible. Therefore, a twin unidirectional impulse turbine topology has been suggested in previous studies to make the system valueless; the conventional unidirectional air turbines can be used. In this topology, the bidirectional airflow is rectified by the pressure difference between two unidirectional impulse turbines, and the most of airflow should get through the forward turbine. However, our previous study suggested that the mean efficiency of the twin turbine system would be lower than that of the unidirectional impulse turbine, since a portion of airflow gets through the reverse turbine whose efficiency is very low. In this study, a fluidic diode was adopted in the twin unidirectional impulse turbine system in order to reduce the air flow through the reverse turbine. The wind tunnel test and computational fluid dynamics (CFD) analysis were conducted to investigate the effect of fluidic diodes on the turbine performance. Further, the usefulness of a fluidic diode in the twin unidirectional impulse turbine topology to be discussed from the view point of mean efficiency under an unsteady flow condition.