ABSTRACT:

In this paper, the unsteady hydrodynamic analysis of marine propellers and horizontal-axis tidal current turbines is performed by using a vortex lattice method (MPUF-3A) and a boundary element method (PROPCAV). A fully unsteady wake alignment algorithm is implemented into MPUF-3A to satisfy the force-free condition on the propeller and turbine wake surfaces. It was found that the position of the trailing wake is very important in predicting the performance of propellers or turbines in steady or unsteady flow. The effects of a non-linear interaction between uniform inflow and propeller/turbine blades have been taken into account by using a hybrid viscous/potential flow method, which couples the potential flow solver (PROPCAV/MPUF-3A) for the unsteady analysis of the propeller/turbine and a viscous flow solver for the prediction of the viscous flow field around them. The present method is then applied to predict unsteady hydrodynamic performance of a propeller and a horizontal-axis tidal current turbine. The predicted unsteady forces of a propeller subject to an inclined inflow are compared with those from experiment. The numerical results are compared with existing experimental data.

INTRODUCTION

Tidal energy, like wind and solar energies, is distributed across large areas and regarded as a potential renewable energy for the near future. The marine current turbines extract tidal energy from tidal flow by converting the sea water kinetic energy directly to mechanical power; hence avoid the environmental impact caused by the conventional tidal power plant. Furthermore, the tidal turbines become more and more economically competitive with conventional fossil fuels due to the improvements of turbine technology. An experimental study on a 3-blade horizontal tidal turbine was performed in a cavitation tunnel and also in a towing tank (Bahaj, Molland, Chaplin, Batten, 2007), and the corresponding power and thrust coefficients were presented for a range of tip speed ratios.

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