Aeroacoustic scattering of rotating sources using a frequency-domain acoustic pressure gradient formulation

In this paper, a frequency-domain methodology for acoustic scattering prediction from rotating sources is suggested. Frequency-domain acoustic analogy formulations are used for incident field prediction of acoustic pressure and the acoustic pressure gradient. The latter is required for evaluation of the hardwall boundary condition on the scattering surface. The boundary value problem is solved by the equivalent source method. The overall scattering approach is validated by an analytical case of scattering by a monopole point source rotating around a rigid sphere and by a hovering non-lifting helicopter rotor operating above an infinite flat plate. The implemented acoustic pressure gradient formulation can be coupled to any boundary method which requires a solution of the incident field on the hardwall scattering surface, for acoustic scattering computation from rotating sources. This scattering methodology is applicable to acoustic scattering prediction from rotating machines, allowing computation of specific tones of interest, thus being particularly efficient.