Wavepacket Modeling of the Jet Noise Source

This research is motivated by the need for physical models for the jet noise source to be used in practical noise prediction schemes for propulsion-airframe integration concepts. The emphasis is on jets with high-subsonic velocities typical of modern turbofan engines. The basis for the source model is an amplitude-modulated traveling wave the wavepacket. Its parameters are determined by minimizing the difference between the modeled and experimental sound intensity distributions in the far field. Even though the pressure signal that reaches the far field is highly filtered, sufficient information is available to construct a wavepacket with reasonable physical characteristics. A simple stochastic extension of this concept shows a connection between the shape of the far-field sound pressure level spectrum and the emission polar angle. It suggests that the broadening of the spectrum with increasing polar angle can be explained on the basis of a single noise source (the wavepacket), rather than the prevailing model of two disparate noise sources, one coherent and the other incoherent.