Broadband low-frequency sound absorption under grazing flow: a dual-layer embedded metamaterial with a flow-resistive acoustic mesh

Abstract To resolve the inherent trade-off between low-frequency absorption bandwidth and deep-subwavelength component thickness in dynamic ventilation systems, this study proposes a compact Dual-Layer Multi-Tube acoustic meta-absorber integrated with a precision flow-resistive wire mesh. The proposed topology leverages structural mode coupling and geometric boundary-layer scaling to simultaneously flatten the acoustic reactance slope and amplify thermoviscous dissipation. This synergistic ‘low-Q’ mechanism inherently overcomes single-resonance limitations by generating a significantly broadened, dual-peak absorption profile. To globally optimize the impedance matching while explicitly enforcing bandwidth flatness, the geometric parameters of a 16-unit supercell are tailored for the 250–900 Hz target regime by a hybrid Genetic-Algorithm / Sequential-Quadratic-Programming (GA-SQP) inverse-design framework that combines physically-grounded initialization, two-stage global–local search and a hard-constraint flatness penalty. Comprehensive experimental validation, conducted via an impedance tube and a custom acoustic wind tunnel, confirms the superior performance of the design. Specifically, the fabricated device achieves an exceptional, experimentally measured average sound absorption coefficient of 0.938. Furthermore, the structurally integrated wire mesh completely suppresses flow-induced pseudo-sound and severs shear-layer feedback loops, guaranteeing true acoustic-flow decoupling. Dynamic in-duct aeroacoustic measurements demonstrate a peak noise reduction of 24.63 dB and a robust average broadband attenuation of 8.28 dB under a high-speed grazing flow of 9.8 m s −1 . Ultimately, this work presents a highly efficient, aerodynamically stable solution for broadband noise mitigation in space-constrained fluid-conveying environments.