The signature of a propeller-rudder system: Acoustic analogy based on LES data

The acoustic analogy is utilized to analyze the sound from a propeller-rudder system, exploiting data from high-fidelity Large-Eddy Simulations, performed on a cylindrical grid consisting of 3.8 billion points. Simulations were conducted with the downstream hydrofoil at incidence angles of 0°, 5°, 10° and 15°. The analysis demonstrates the significant effect of the downstream hydrofoil in increasing the sound pressure levels, especially due to the loading noise from its surface, but also as a result of the enhanced complexity of the wake topology. For increasing angles of incidence, the wake experiences a growing elongation in the direction of the span of the hydrofoil and higher values of cross-stream velocity, reinforcing the shear between the wakes shed by the propeller and the hydrofoil, respectively. A very complex directivity of the acoustic signature develops, whose dependence on the orientation of the hydrofoil is variable across both the azimuthal and the streamwise directions. Separation on the suction side of the hydrofoil for large incidence angles has the effect of reducing the loading component of noise from its surface, which is the leading one, with the exception of the radial coordinates within a few diameters from the axis of the propeller and its wake.