Experimental and numerical analyses of the hydrodynamic performance of propeller boss cap fins in a propeller-rudder system

This paper presents the simulated and experimental results of propeller-rudder systems with propeller boss cap fins (PBCFs) and analyzes the hydrodynamic performance of PBCFs in propeller-rudder systems. The purpose is to study the impact of PBCFs on the hydrodynamic performance of rudders. Hydrodynamic experiments were carried out on propeller-rudder systems with PBCFs in a cavitation tunnel. The experimental energy-saving effect of the PBCF without a rudder was 1.47% at the design advance coefficient J = 0.8. The numerical simulation was based on the Navier-Stokes equations solved with a sliding mesh and the SST (Shear Stress Transfer) k-. turbulence model. After the grid independence analysis, the flow fields of an open-water propeller with and without a PBCF were compared, then the efficiencies of the propulsion systems including different rudders and the thrust coefficient Kr of rudders were analyzed. The results indicate that the installation of a PBCF increases the resistance of the rudder, which results in a reduction in the energy-saving effect of the PBCF. At the design advance coefficient, the energy-saving effect of the PBCF with an ordinary rudder and a twisted rudder decreases from 1.47% to 1.08% and 1.16%, respectively; thus, it is important to factor in the rudder of a propulsion system when evaluating the energy-saving effects of PBCFs.