Numerical analysis of wake field and unsteady forces on submarine propeller with twisted rudders

A twisted submarine rudder was designed to reduce the unsteady force on and improve the propulsion efficiency of the propeller. The twisted rudder not only switches the wake in the pre-rotation state in the direction opposite to the propeller rotation but also increases the mismatch between the circumferential phase-angle distribution characteristics of the wake peak and propeller profile at each radius. To investigate the influence of this rudder on the submarine's flow field and the propeller's hydrodynamic performance, the shear stress transport (SST) k omega turbulence model was used to calculate and compare the resistance characteristics and flow field at the aft of the submarine without a propeller when the ordinary and twisted rudders were installed, as well as the wake field of and unsteady force on the propeller with the propeller. The circumferential velocity in the propeller wake was significantly reduced, and the propulsion efficiency was improved by approximately 7.31%. In addition, the pulsation amplitude of the unsteady force was significantly reduced. The main blade-passing frequency (1BPF) amplitudes of the force and torque decreased by more than 40% and 35%, respectively, which significantly reduced the hull vibration caused by the unsteady force on the propeller.