Assessing the wakes of unconventional marine propellers

A conventional propeller sheds vortices and other flow structures in its wake that cause cavitation, noise, and unsteady interactions with downstream structures. In the water, these can damage rudders and produce additional vibrations and noise that negatively impact ocean life. Unlike conventional ship propellers, rim-driven thrusters do not require a rotating hub to move their blades. Instead, the blades are installed on a rotating rim, which reduces the intensity of the flow structures in their wake.

Posa et al. compared the wake features of rim-driven thrusters with configurations ranging from three to six blades. The Large Eddy Simulation methodology allowed them to analyze the fluid dynamics of the wakes with high fidelity.

Their simulations showed that less intense vortices, known as inner tip vortices, dominated the wakes of the rim-driven thrusters. The onset of outer tip vortices, strong flow structures typical of conventional propellers, was completely avoided.

In conventional propellers, the vortices in the wake of each blade undergo strong interactions. In the authors’ simulations, this did not occur for the rim-driven thrusters, suggesting that more blades experiencing lower loads than in conventional propellers may be beneficial to the wake properties.

“The work we reported is the first to exploit high-fidelity simulations to demonstrate the benefits of rim-driven thrusters in mitigating the wake signature, providing reference data for lower-order computational models and discussing the influence of the number of blades on the wake features of this special class of propellers,” said author Antonio Posa. “The data generated in this project may be useful to the assessment of the advantages of rim-driven thrusters in terms of intensity of the radiated sound.”

Source: “Influence of the number of blades on the wake development of rim-driven thrusters,” by Antonio Posa, Stefano Gaggero, and Riccardo Broglia, Physics of Fluids (2026). The article can be accessed at https://doi.org/10.1063/5.0314358 .