Prediction of Jet Noise Shielding with Forward Flight Effects

Use of conventional scattering solvers for the problem of sound diffraction in the presence of a mean flow requires the use of variable transformations that reduce the wave equation to its canonical form. This enables the assessment of the mean-flow impact on the radiation of the isolated source as well as its diffraction by an object. Applications include the shielding of propulsion noise sources by the airframe. The focus of this study is the diffraction of a wavepacket noise source, simulating jet noise, from a surface having the general shape of the hybrid-wing-body (HWB) airplane. In addition, the canonical problem of monopole diffraction by a sphere is addressed. In both instances the potential solution for the mean flow is used in the transformations, and the boundary element method is used to compute the scattered fields. The study addresses the effect of the mean flow on the incident and total pressure fields and conducts a systematic assessment of the errors introduced by the transformations. The general trend is a compaction of the downstream influence of the noise source, leading to better shielding for the HWB problem. The overall error tends to be less than 5% for flight Mach number not exceeding 0.2.

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