Effects of length and maximum area of duct on the performance of bidirectional duct and turbine system for tidal energy conversion

Abstract

Tidal current energy is one of renewable ocean energies and the importance has been increasing recently. In this paper, a combination system of a bidirectional duct and a bidirectional turbine is examined by both an experiment and a Computational Fluid Dynamics (CFD). Before the experiment, in order to develop a design method for tidal turbine rotor with simplicity and reliability, a bidirectional turbine rotor is design by turbomachinery design method. In the experimental work, the power coefficient based on the maximum duct area is defined and the value takes maximum value when the value of the turbine efficiency is at its maximum. The performance of the turbine system such as the power coefficient and the thrust coefficient may be further improved by suppressing the flow separation around the bidirectional duct. Further, the effects of length and maximum area of duct on the performance of the turbine are investigated by using CFD. It is found that the duct efficiency increases when the maximum duct radius decreases, while the values such as the axial velocity ratio and the thrust coefficient do not change very much.