Numerical simulations of a fully submerged propeller subject to ventilation

Numerical simulations aimed at modeling the phenomenon of ventilation on a fully submerged propeller were performed. Ventilation occurs on thruster propellers operating at high loadings and heavy sea states, experiencing continuous cycles in and out-of water. This leads to sudden thrust losses and violent impact loads, which can damage shaft bearings and gears of azimuth and tunnel thrusters. Damages in rough seas were reported also during transit operations.In the simulated configuration the propeller is fully submerged (h/R=1.4) and working at high loading (J=0.1), where the blade becomes surface-piercing only after ventilation occurs.The dynamic loads computed with the numerical model are in satisfactory agreement with the experimental data at the upright position where the blade is piercing the free-surface, whereas thrust is over-estimated at all the other angular positions. A thorough analysis of the causes of this deviation was performed, identifying the inability of the numerical simulation to properly resolve the tip vortex at some distance from the propeller blades as the most likely responsible factor. Unlike ventilation of surface-piercing propellers with super-cavitating profile, it was found that the tip vortex plays an important role in ventilation of conventional propellers, which is the object of the present study.

► RANS simulations were performed on a fully submerged propeller at high loading, subject to intermittent ventilation.
► The computed dynamic loads agree with experiments at the blade's upright position.
► Thrust is over-estimated at all the other angular positions.
► This deviation is explained by the inability of the numerics to resolve the tip vortex.