Comparative CFD analysis of the hydrodynamic performance of a ship propulsion system using pre-swirl ducts

An energy-saving device (ESD) fitted upstream of marine propellers can increase propulsion efficiency by improving wake quality in the stern region and reducing adverse rotational losses. In this paper, the hydrodynamic performance of a propulsion system, under the influence of upstream ESDs including the Mewis duct, Becker Twisted Fin, semi-circular duct, and SILD duct, is investigated using computational fluid dynamics (CFD). The study is conducted on a scaled model of the KRISO Container Ship equipped with a DTMB 4119 propeller. Numerical simulations were conducted at several ship speeds utilizing the unsteady Reynolds-Averaged Navier-Stokes solver with SST k-ω turbulence model, Volume-of-Fluid method, and Overset Mesh approach. It was found that all devices investigated provide improved wake quality by changing axial, radial and tangential wake properties in relation to the case without devices. The baseline self-propulsion case, defined as the KCS hull–DTMB 4119 propeller system without any upstream ESD, was used as the reference configuration. The Becker Twisted Fin provided the most effective wake conditioning, increasing the mean axial wake near the propeller plane by up to 16% relative to the baseline case. As far as propulsive performance is concerned, the highest one is provided by the Becker Twisted Fin, followed by Mewis duct. Propulsion performance improvement was demonstrated by reduction of shaft torque and increase of propulsion power for all investigated devices at high operational speed. The pressure field and wake vortex analyses confirmed influence of geometrical shape on blade loading and wake structure.