Propellers are by far the major device for marine propulsion. The improvement of their efficiency is critical for reducing fuel consumption, resulting in beneficial effects on the economic and environmental costs of shipping. In addition, developing a better control of the wake features is also a priority.
The wake of marine propellers is dominated by strong tip vortices, where cavitation phenomena usually occur. They are detrimental to the structural integrity of the propeller blades and any device placed downstream of them, as rudders. In addition, their are a very important source of noise, negatively affecting marine life.
In this project a winglet propeller will be simulated across its operational range using high-fidelity, turbulence-resolving simulations on a computational grid consisting of 5 billion points, orders of magnitudes finer than in the typical approaches utilized by both industrial and academic research. The particular propeller geometry is characterized by a winglet at the tip of its blades. It is known that this design solution is able to decrease the intensity of the tip vortices.
This way, the propeller blades can be designed exploiting tip loading, having a beneficial outcome on the efficiency of propulsion. In addition, weaker tip vortices cause less damage and lower levels of noise. Currently a significant limitation to the optimal exploitation of winglets and tip-loading is represented by the lack of a complete understanding of the flow physics. Experiments can provide useful visualizations, but numerical simulations are critical for achieving a deeper insight, making available the full three-dimensional flow field with finer levels of resolution. However, conventional methods, relying on turbulence-modeling on grids consisting of a few million points, are unsuitable to this purpose.
Therefore, in this project we are going to conduct turbulence-resolving simulations on a grid at least two orders of magnitude finer to produce high-fidelity results on the process of onset of the tip vortices, their streamwise evolution and eventual instability. Turbulence in the wake and its acoustic signature will be analyzed as functions of the rotational speed of the propeller.
These results will serve as a benchmark for engineers to devise better propeller geometries and more accurate turbulence models, better suited to this class of propellers, with the purpose of improving the predictive capabilities of lower-fidelity methodologies.