Large Eddy Simulation of a Tip-Loaded Propeller (LESTLP)

Propellers are by far the most widespread device for marine propulsion. Their efficiency and silent operation are critical in defining both the economic and environmental impact of shipping. Higher levels of efficiency result in lower fuel consumption, which means lower costs and fewer emissions of pollutants and greenhouse gasses into the atmosphere. In addition, a milder acoustic signature allows improving the comfort of passengers and crew members and decreasing noise pollution, which is a rapidly increasing issue and seriously harmful to the life of marine species. Therefore, marine propellers are typically designed to place the location of their maximum load at about 75% of the radial extent of their blades. Decreasing the level of load at the tip of their blades is aimed at producing milder cavitation phenomena within the core of the vortices they shed. Cavitation is highly problematic, being source of noise, vibrations and erosion, damaging the propeller blades and the bodies placed in their wake, typically rudders. In this project, Large Eddy Simulation (LES) is proposed to study the dynamics of the tip vortices generated by a winglets propeller, including also computations dealing with a similar, baseline geometry without winglets, representing a conventional design. In addition, their process of instability will be investigated, also taking into account their interaction with the hub vortex, which is the other major coherent structure shed by marine propellers. Due to the purpose of the present study, a high-fidelity, eddy-resolving approach, as LES, is required. LES is able to capture the onset, evolution and instability phenomena of the large structures shed by propellers, including their tip vortices, having a major role in defining the acoustic signature of marine propulsion. The computational effort of LES, relying on very fine levels of resolution in both space and time, orders of magnitude beyond those typically adopted in both industry and academia, is at the forefront of the current computing capabilities and requires access to Tier-0 supercomputers.