Resistance and propulsion performance of a twin skeg ship with different rudder angle

Abstract Rudder angle will change the flow field, resulting in different loads and interactions on the hull-propeller-rudder, which will affect the resistance and self-propulsion performance of the ship, and this effect will be amplified on the twin skeg ship. Resistance of the ship-rudder at the rudder angle of 0 ° -8 °, lift, moment, axial wake, the rudder profile velocity vector at the propeller shaft height, and the dynamic pressure distribution on the inner and outer surfaces of the rudder were simulated by CFD(Computational Fluid Dynamics) method, and verified by the EFD(Experimental Fluid Dynamics) method. Self-propulsion factors of the hull-propeller-rudder with rudder angle of 0 ° -6 ° were calculated by CFD method, and compared with the EFD results. Axial wake, dynamic pressure on the surface of the propeller and rudder and the velocity vector near the rudder, and the flow field and vorticity field of the hull-propeller-rudder were analyzed. The results showed that : 1 ) The CFD results had the same trend as the EFD results. When the rudder angle was 6 °, the total resistance of the ship-rudder was the smallest, and the resistance decreased by about 1%. 2 ) The change of rudder angle had little effect on the wake field in front, but it had a great influence on the flow field around the rudder, which in turn affected the resistance, lift and moment. 3 ) Self-propulsion performance was the best when the rudder angle was 4 °, and the self-propulsion power can decrease by about 4%, mainly due to the beneficial interaction between the propeller and the rudder. 4 ) Rudder angle had little effect on the surface pressure of the propeller, but it will slightly change the axial wake behind the propeller, and the dynamic pressure of the rudder was quite different. 5 ) When the rudder angle exceeded the optimal rudder angle of 4 °, the interaction between the hull-propeller-rudder became unfavorable, resulting in the chaos of the vorticity field and the overall performance degradation. For twin skeg ships, proper arrangement of rudder angle can effectively improve ship performance and achieve energy saving purpose.