Numerical and experimental analysis of a counter-rotating type horizontal-axis tidal turbine

In order to exploit renewable energies form tidal currents, a unique counter-rotating type horizontal-axis tidal turbine was proposed in this paper. Although a counter-rotating type horizontal-axis wind turbine can be taken as a reference in designing the proposed counterrotating tidal turbine, there are some different characteristics such as the effects of the free surface and the occurrence of cavitation. The unique tidal turbine in this paper was preliminarily designed on the basis of the in-house wind turbine, and then CFD analysis and experimental test were carried out to evaluate its performance. For the extreme conditions where severe flow separation and vortex exist, the comparison of the power coefficients generated by the turbine between the CFD predictions and the experimental data shows not so good. However, good agreement has been obtained for the comfortable blade pitch setting angles and over a range of tip speed ratios, which provides an evidence of validation of CFD analysis. Such results give sufficient confidence that the CFD model set up here is suitable for the further works.