An Efficient Method for Rotor Aeroacoustic Calculation Accounting for Rotor Downwash Influence

Based on the Ffowcs Williams–Hawkings equations and the computational fluid dynamics method, the rotor’s aeroacoustic characteristics, considering the influence of the downwash flowfield on the sound propagation process, are calculated and analyzed. First, a set of analysis methods for the aeroacoustic characteristics is developed, and a convection-based propagation time model is developed, where acoustic group velocity along source–observer lines quantifies flowfield effects. Then, the rotor’s aerodynamic and aeroacoustic characteristics are calculated, and the employed numerical analysis method is validated through the comparisons with experimental data. Finally, the aeroacoustic characteristics of the rotor in hover are analyzed, and the sound pressure positive peak point with/without the influence of the flowfield of downwash on the propagation time is discussed in detail. In addition, parameters, such as the rotor’s collective pitch and the azimuthal angle of the sound source, are quantified, and some conclusions are obtained. For those observers below the rotor rotation plane, the downwash flowfield will influence the sound propagation time, resulting in the increase in the sound pressure and the advance of the arrival time.