Sound absorption characteristics of a compact meta-structure under grazing flow

This study proposes a compact meta-structure for broadband and low-frequency sound absorption under grazing flow. It comprises a microperforated panel (MPP) and resonators with embedded tunable orifices and C-shaped cavities. The sound absorption characteristics of the proposed absorber are investigated via theoretical model (acoustic impedance circuit) and numerical model (finite element method). Consistent predicted results from both models manifest that the proposed meta-structure possesses good absorption capacity under a deep-subwavelength scale, compared to the conventional MPP absorber. To simultaneously achieve better low-frequency and broadband noise damping, a parallel configuration of the meta-structure and an MPP absorber is studied numerically and experimentally. Besides, notable variation on the acoustic performance of the proposed absorber is observed in case of grazing flow, which leads to the decline of the absorption peak and makes the peak wider than that without flow. The practical significance of this study is that it proposes a promising meta-structure for wide frequency sound attenuation applications; furthermore, it elucidates the flow effects on the acoustic performance of the meta-structure, providing a route to reduce flow-related noise in a broad frequency range.