Acoustic scattering mechanism and noise attenuation of circumferentially non-uniform liner with spectral-wave guide method

In this paper, a model is established with application of the spectral-wave guide method, which has higher accuracy and can serve as a rapid calculation tool for sound transmission calculations. Based on this calculation model, some numerical results of circumferentially non-uniform lined annular/circular ducts are carried out, and some physical mechanisms can be discovered. The numerical results show that periodical impedance distributions along the circumferential direction will lead to discontinuous scattered modes with regular spacing; and mirror-symmetric structure liner will converge the energy of opposite modes. Relying on this mechanism, the potential of acoustic scattering can be further developed by suppressing lower or enhancing higher order modes with expressly designed segmented liner configurations. In particular, the intrinsic mechanism of mode redistribution brought about by the non-uniform liner can be subtly utilized to attenuate broadband noise. The present work indeed shows that circumferentially non-uniform liner is conducive to the reduction of the practical broadband sound source. Furthermore, the effects of non-uniform flow are considered in the model, then distinction of noise attenuation and scattered modes energy in different flows is shown. A possible mechanism is proposed that refraction effects in complex flows lead to the distinction. These works show that the current model has profound potential and availability for the research and designs of circumferentially non-uniform liner.