Modeling of Jet Noise Sources and their Diffraction with Uniform Flow

A methodology is presented for treating the propagation of elementary jet noise sources in the presence of a uniform mean flow. The sources include wavepacket and point sources, and the propagation includes the diffraction around solid boundaries. The governing equations are reduced to the canonical wave equation through established transformations. The impact of the transformations on the wavepacket and point sources is discussed, with attention on the distinction between sources of pressure and sources of volume. The coupling of the transformations with the boundary element method, for the prediction of diffraction, is outlined. The impact of uniform flow on the emission of an acoustic monopole produces a complicated pressure field with different nearand and far-field scaling laws. The principal effect of flight speed on the wavepacket emission is to shift the range of radiating axial wavenumbers, resulting in attenuation and re-direction of the acoustic emission. For both the wavepacket and monopole, the flight Mach number causes a compaction of the acoustic field downstream of the source, a trend that benefits the shielding of those sources.