In this paper, a RANS/lifting line model interaction method is proposed to consider the duct geometry in the design of propellers and tidal turbines. In the lifting line model, the Lerbs-Wrench formulas are used for the wake alignment procedure. In the RANS solver, the blade is represented by a pressure jump profile. The blade loading is determined via a previously developed optimization algorithm which takes into consideration the effect of the duct via a simplified image model. An iterative procedure is developed in which the advance ratio (based on the ship speed) and the total thrust in the propeller case and the tip speed ratio (based on the inflow velocity far upstream) are kept constant. The procedure is tested for different cambers and thicknesses of the duct shape. The efficiency, inflow velocity and thrust on the blade and duct are obtained and analyzed. The influence of different factors, including the blade number, drag-to-lift ratio, advance ratio, thrust coefficient and tip speed ratio, are studied. This method is proved to be reliable and efficient in designing ducted propellers and tidal turbines.

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