A numerical study on the aerodynamics and aeroacoustics of a ducted propeller in the presence of oblique flow

The aerodynamic performance and noise generation of a ducted propeller in oblique flow have been evaluated with numerical simulations. The results of steady simulations quantify the reduction in thrust when the incoming flow angle is increased. Higher flow angles induce a larger flow separation on the side of the duct facing the flow. The unsteady flow features of the ducted propeller and the acoustic properties are obtained with delayed detached eddy simulations. The far-field noise is predicted by solving the Ffowcs-Williams and Hawkings equation. The case with axial flow is also considered as a reference. When the flow angle is larger, the broadband noise generation is increased, and additional tones appear at the blade-passing frequency (BPF) harmonics, with directivity changes. The results with a flow angle of 60° are compared with the unducted propeller configuration. The results show that the duct can reduce the tonal noise from the system at the harmonics of the BPF. The rotor tonal noise is also estimated using the frequency-domain method, which considers the contribution of the unsteady modes at different flow angles. The results show that the amplitude of the noise unsteady modes can increase with the incoming flow angle, but it can be reduced when the propeller is ducted, reducing the noise at the harmonics of the BPF.