The identification of noise sources in the duct plays a crucial part in designing quiet turbines and aircrafts, which conventional methods using wall-flush mounted microphone arrays met difficulties in some engineering applications because of its needing of drilling holes on the duct wall to mount microphones. In this paper, an identification method using an out-duct placed microphone array is proposed to identify in-duct sources, by which the spatial distribution of in-duct sources can be reconstructed. The forward model between out-duct measured sound pressures and desired sources in-duct is established. This model includes acoustic emission propagating a cylindrical duct and acoustic radiation at the duct termination. The acoustic emission propagating in duct can be expressed as the superposition of spinning modes. Furthermore, the acoustic radiation at the duct termination can be obtained based on Tyler and Sofrin's model. A numerical simulation for sound imaging is obtained to verify the proposed in-duct source location approach. The DAMAS deconvolution is used to remove the influence of the side-lobes and the resolution effects, thereby more accurately quantifying the position. It is shown that sound sources inside the duct can be precisely localized.
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