A Twin Unidirectional Impulse Turbine With Fluidic Diode for Wave Energy Conversion

As an air turbine equipped with oscillating water column (OWC) based wave energy plant, a rectification-valve system has been invented to date. However, this turbine system has problems with the durability of the valves and the complex mechanism. Moreover, it has a major fault in that the valves must be large for high output. Therefore, a twin unidirectional impulse turbine topology has been suggested in previous studies in order to use conventional unidirectional turbines without valves [1, 2]. The topology is composed of two unidirectional impulse turbines. However, the past study indicated that the mean efficiency of the topology was shown to be low, when the performance prediction of the topology in oscillating airflow was carried out by means of quasi-steady analysis [2]. Further, the cause of the low efficiency is because part of the air flow gets through the unidirectional impulse turbine in the direction of low efficiency [2]. In this study, a fluidic diode [3, 4] is adopted in order to suppress the air flow rate into the inefficient turbine in a twin unidirectional impulse turbine topology for wave energy plant, and the effect of the fluidic diodes on the performance of twin unidirectional impulse turbine topology is investigated by a wind tunnel test and computational fluid dynamics (CFD). Further, its usefulness is discussed from a view point of the turbine mean efficiency under unsteady flow condition.