An inverse method for source identification in rectangular waveguides with reverberation

Closed-section wind tunnels represent a typical reverberant environment where microphone arrays are frequently used to identify noise sources. However, wall reflections can be a serious problem for source localization, especially at lower frequencies or when a source locates close to reflecting walls. To address this problem, a novel inverse method is developed for source localization in a hard walled rectangular duct, which incorporates wall reflections into the proposed algorithm by using an appropriate rectangular waveguide Green’s function. No flow is considered in this study, focusing solely on wall reflection effects. Numerical and experimental results obtained with the conventional beamforming (CBF), the image source model (ISM) and the present inverse method (IM) are presented and analyzed. Pronounced spurious sidelobes appear on the CBF maps, causing reduced resolution or erroneous source location at low frequencies. The ISM can remove most of the spurious side lobes, but it still suffers from low resolution at low frequencies and its spatial resolution is direction dependent. By comparison, the IM shows considerably improved performance in terms of mainlobe width, localization accuracy and sidelobe level, with its resolution close to omnidirectional similar to that obtained under anechoic conditions. It is effective for both coherent and incoherent sound sources. At the low frequency of 500 Hz, it achieves subwavelength resolution by exploiting evanescent modes. Furthermore, the robustness of the IM to noise is examined through both simulations and experiments, showing that it outperforms the other two methods at an SNR of 10 dB.