A numerical analysis of the propulsion efficiency improvement effect of pre-swirl flow control fins (FCF)

• A novel energy-saving device (ESD) to improve propulsive efficiency of marine vessels • Asymmetric flow control fin (FCF) attached to port side only, generating vorticity opposite the propeller rotation • Propulsion efficiency is improved by reducing energy losses caused by the propeller rotation • Pre-Swirl FCF combining the benefits of the conventional FCF and pre-swirl stator (PSS) • ESD with simpler structure applicable both to newbuilds and retrofitting existing vessels The International Maritime Organization (IMO) has established regulations that impose penalties on not only newly built ships but also existing vessels in operation if they fail to reduce carbon emissions, and these regulations are being implemented in stages. In response, shipyards are making various efforts, such as developing energy-saving devices (ESDs). Among various ESDs, the widely used flow control fin is a device attached to the hull that generates vortices in the flow along the hull. This study introduces the pre-swirl flow control fin (FCF), a newly developed and effective energy-saving device derived from the conventional flow-control fin concept. When installed on the port side of the stern, the pre-swirl FCF generates a vortex whose tangential velocity produces a downwash opposite to the propeller’s rotational direction. As this vortex reaches the propeller plane, it counteracts part of the propeller-induced swirl, thereby reducing rotational energy losses. To assess the performance of the pre-swirl FCF, a model-scale CFD analysis was conducted using the commercial software STAR-CCM+ and the KRISO Container Ship (KCS) hull. After performing resistance analysis, the circulation (Γ) of the in-plane velocity at the wake plane was used as an indicator to quantitatively assess the intensity of the generated rotational flow. Finally, a self-propulsion analysis was carried out to verify the improvement in propulsion efficiency. As a result, it was confirmed that the increase in resistance due to the installation of the ESD was less than 1%, while the power delivered ( 2 π n Q ) was reduced by approximately 3%.