Influence of an upstream hydrofoil on the acoustic signature of a propeller

The acoustic analogy is adopted to reconstruct the sound generated by a system consisting of a hydrofoil and a downstream propeller. The data from high-fidelity large-eddy simulations with the hydrofoil at angles of incidence of 0 °, 10 °, and 20 ° were generated using a cylindrical grid consisting of 1.7 × 109 points. The results of the analysis demonstrate the following: (i) the strong influence by the incidence of the hydrofoil on the acoustic signature of the system; (ii) the leading role of the non-linear component of sound at small radial coordinates in the vicinity of the wake, especially moving away from the propeller plane; (iii) the leading role of the linear component of sound from the surface of the propeller moving away along the radial direction; (iv) the importance of the shear between the wakes shed by the hydrofoil and the propeller in accelerating the process of instability of the coherent structures and reinforcing the non-linear sources of sound; and (v) the strong, complex directivity of sound at small radial coordinates, as a consequence of the interaction between the wakes from the hydrofoil and the propeller.