A lifting surface panel model of a prototype tip-driven propeller has been developed. The model includes the propeller, surrounding duct, stators and bearing casings. It was used to predict the likely performance of the prototype thruster under various advance speeds, propeller speeds and duct profiles, and the results have been compared with the experimental data. The paper presents the development of the computational model comparison of predictions with experimental results, and the future use of the model to optimise the hydrodynamic characteristics of the propeller and duct.
Ducted propellers have been used for many years in the marine industry to both protect the propeller from damage, and to improve upon the propeller efficiency under certain load conditions, Consequently a wide range of tests have been carried out on the units and much performancee data has been published. One reason for losses in a dueted propeller system is the small clearance gap between the blade tips and the inner surface of the duet. In this region tip vortices occur and subsequently reduce propeller performance. In an attempt to eliminate tip vortices, the use of ring-propellers was studied (Oosterveld, 1972) whereby the propeller blades were attached to a profiled ring which rotated with the propeller. This did overcome the clearance gap problems, however, any gains were offset by the increased frictional resistance of the rotating ring. Further developments of the ring-propeller led to the ducted ringpropeller in which the propeller was attached to a thin ring, which sat flush within an external duct. This did offer an improvament in efficiency over the open ring-propeller, but not to the extent of matching that of a standard ductad propeller, which still remained the most efficient.
