Hydrodynamic aspects on three-dimensional effects were investigated in this study for simple and convenient conversion of tidal stream energy using a Vertical-Axis Turbine (VAT). Numerical approach was made to reveal the differences of flow physics between 2–D estimation and rigorous 3–D simulation. It was shown that the 3–D effects were dominant mainly due to the variation of tip vortices around the tip region of rotor blade, causing the loss of lift for the reduction of torque for rotating turbine blade. A VAT with supporting circular discs at both ends spanwisely was then proposed to reduce the three-dimensionality and increase the structural strength as well as the power coefficient.

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