Overall performances of a propeller operating near the free surface

Abstract

Abstract The paper describes a numerical study on the effects of the interaction of the free surface with a marine propeller operating close to it, including the effects of the immersion on the cross flow. Extensive simulations using the ISIS-CFD naval hydrodynamics computational fluid dynamics solver are conducted to study the open water characteristics (POW hereafter), transient blade loads, and flow behavior around the DTMB 4119 three-bladed propeller, with comparisons to the fully submerged experimental data at two different immersions in respect to the undisturbed free-surface. Computations and experiments for the deeply submerged case show that the cross flow results in an increase of the energy spent and lower efficiency relative to the uniform inflow. Near the water surface, numerical solutions show that effects on thrust and torque increase significantly as the propeller load increases. Furthermore, the presence of the free surface breaks the symmetry resulting in highest blade force losses when the blade is near top dead center. As the propeller approaches the surface, not only the amplitude of the blade higher harmonics increases, but also the efficiency drops down.