Abstract: To reduce the flow separation with the ducted turbine and reduce its axial force, this paper presents a new type of combined ducted horizontal axis turbine with ducted flow paths and an analysis on its hydrodynamic performance using computational fluid dynamics (CFD) and towing tank experiments. The influence of the number, width and shape of the ducted flow paths is examined. Results show that compared with the original ducted turbine, the combined ducted turbine can significantly reduce the axial force on the duct and improve the wake flow condition and stability of a turbine system at low tip speed ratios while keeping a nearly fixed power output. And within a certain range, such an effect will become more obvious with the increase in the number or width of flow paths. Of the flow paths in different shapes, a straight passage produces the best effect. The study provides a new ducted turbine design helping reduce flow separation and optimize the turbine and its supporting devices.

Key words: combined ducted turbine, CFD, hydrodynamic performance, flow path, flow separation