Neck-embedded acoustic meta-liner for the broadband sound-absorbing under the grazing flow with a wide speed range

Acoustic liners are the most commonly used dissipative muffler for aero-engines but remain a challenge to design a broadband acoustic liner under the grazing flow. In this work, a novel neck-embedded meta-liner is proposed for the broadband sound-absorbing under the grazing flow with a wide speed range. The meta-liner is composed of many neck-embedded Helmholtz Resonators, and the idea of bending the subsequent cavity is introduced to improve low-frequency sound absorption performance. The acoustic impedance model of the meta-liner with neck-embedded slit is first detailly established by analyzing the acoustic characteristics of the equivalent elliptical pipe and using the matrix transfer method. Then by designing the local coupling between channels, efficient broadband impedance modulation and broadband matching with air impedance under grazing flow conditions are realized. The proposed meta-liner exhibits the excellent sound attenuation capacity in the frequency domain of 500–3000 Hz under the grazing flow speeds from 0 m s−1 to 98 m s−1 and the sound absorption performance is greatly boosted compared with the traditional Double- Degree-Of-Freedom liner. Features mentioned above have been verified numerically and in a series of comparative experiments. Besides, the thickness of the meta-liner is only 50 mm. Our work provides a possible design reference for the new generation of acoustic liners and has potential applications in noise reduction engineering.