Abstract: To improve the power output of a tidal energy conversion turbine system, a new type of horizontal axis ducted turbines is studied using a Reynolds Averaged Navier Stokes (RANS)-CFD method, focusing on modeling power output, load, cavitation, flow unsteadiness, and the effect of attached ducts. A towing tank experiment is carried out to validate the numerical simulations. The results show that a ducted turbine has higher power output and larger axial thrust than those of the bare turbine and can maintain high power output within ±30° of the yaw angle. And it is featured with non-cavitation and satisfactory flow unsteadiness under design conditions. For a multi-ducted turbine, large attached ducts can improve its power and thrust in the full range of tip-to-speed ratio and further improvement can be achieved if the angles of attack of the ducts are increased, while small duct sizes are not conducive to the power output. Thus, this study demonstrates the advantages of the ducted turbine and its broad prospect of engineering application.

Key words: tidal energy, ducted turbine, RANS-CFD, hydrodynamic performance, multi-ducts