Acoustic performance of a meta-liner based on an extended slit-neck resonator and a perforated panel under grazing flow

This study proposes a low-frequency broadband meta-liner (extended-slit resonator meta-liner, ERML) based on an extended slit-neck resonator and a perforated panel. A theoretical impedance model under grazing flow and a semi-analytical numerical model with equivalent impedance boundary conditions were established. The noise reduction performance and sound absorption characteristics under different typical low Mach number grazing flow conditions were comprehensively investigated. The ERML achieves broadband noise reduction below 500 Hz at grazing flow velocities ranging from 0 to 0.15 Ma, achieving the thickness-to-wavelength ratio of 1/24. Under static conditions, the measured average transmission loss within 150–500 Hz reaches 7 dB, while at Ma = 0.15, the corresponding value is 6.2 dB, suggesting that the presence of grazing flow reduces the sound attenuation performance of ERML. This reduction in sound attenuation can be attributed to the interaction between the grazing flow and the meta-surface, which affects the acoustic energy dissipation capability of ERML, leading to a slight decline in overall efficiency. Comparative analysis confirms that the integration of a perforated panel stabilizes the acoustic performance of ERML under grazing flow, enhancing its adaptability to complex flow fields. Finally, experimental samples were fabricated and tested in a flow duct to evaluate acoustic performance under grazing flow, validating the effectiveness of the theoretical model and numerical method. The ERML demonstrates outstanding low-frequency broadband noise suppression, strong adaptability to actual flow environments, along with advantages in structural simplicity and manufacturability, exhibiting promising prospects for noise control applications.