Kang Gao

In acoustic testing for aircraft engines, duct-mounted microphone arrays are widely used for sound source localization, mode identification, and acoustic liner experiments. Phase calibration of arrays is considered equally critical as amplitude calibration; however, such calibration is often constrained by duct geometry and necessitates repeated disassembly, which poses a risk of mechanical damage. An in-situ microphone array calibration method based on a rotating sound source has been proposed in this paper. Because a rotating source enables frequency-shift of distinct azimuthal modes, the resulting mode-resolved sound fields can be used to distinguish positional phase differences from inter-channel phase errors in single-ring microphone arrays. By combining the proposed axial and single-ring phase calibration techniques, calibration of arrays with a large number of microphones is achieved and validated through Monte Carlo simulations and test rig experiments. Results demonstrate that the proposed method offers the advantages of in-situ calibration within acoustic ducts, compatibility with high-channel-count arrays, and robust, efficient operation.

Beamforming and inverse methods are widely applied to the localization and reconstruction of acoustical sources inside ducts. Identification of in-duct sources using the conventional beamforming method would lead to poor spatial resolution and even fail at some specific frequencies with multiple virtual sources. Employing the inverse method would improve the accuracy of inner duct source localization, however, severe deviation of source intensity results calculated by the inverse method from actual results would occur due to tremendous dimensions of inversion and regulation process of the transfer function matrix. To reduce the dimensions of inversion and further improve the accuracy of source identification, a combined imaging methodology is proposed. The beamforming method is firstly applied to locate regions containing sound sources preliminarily, then an inverse method is applied to regions contributed by beamforming to remove ghosts and side lobes. Numerical simulations are implemented to validate the method. Azimuthal and radial localization results indicate that the combined imaging method is with better spatial resolution than beamforming or inverse methods. Reconstructed results of the source's volumetric velocity demonstrate that the proposed method has a lower deviation of source intensity than the inverse method.