Comparison between the acoustic signatures of a conventional propeller and a tip-loaded propeller with winglets

The Ffowcs-Williams and Hawkings acoustic analogy is utilized to reconstruct the acoustic signature of two marine propellers with and without winglets at the tip of their blades. The database from a large-eddy simulation study is exploited and conducted on a computational grid consisting of about 5 × 10^9 points. The results of this study demonstrate that tip-loading of the propeller with winglets successfully improves its performance in terms of thrust and efficiency of propulsion. Meanwhile, despite the use of winglets at the tip of the propeller blades, its acoustic signature is reinforced. This result is mainly found attributable to the loading component of sound, originating from the fluctuations of hydrodynamic pressure on the surface of the propellers, in particular at their outer radii: they are significantly higher in the tip-loaded case. In contrast, the non-linear component of sound is similar between the two cases, as a result of the similarity between wake developments and instability behaviors of the structures shed by the conventional and tip-loaded propellers. However, also in this case, the sound coming from the latter is slightly higher, due to the acoustic signature of its stronger tip vortices.