Acoustic attenuation of side-branched Helmholtz resonator with embedded apertures in grazing flow ducts

Refrigeration equipment is widely used on a daily basis in residential, commercial and industrial applications, but the aerodynamic performance and noise problems remain a tragic problem. Acoustic duct silencers as an effective noise elimination solution have received great and continuing interest in noise control engineering to mitigate acoustic instability. In the presence of grazing flow, acoustic-attenuation performances of duct silencers decrease greatly due to the vortices and flow oscillations generated in the duct. In this work, the acoustic-attenuation performances of side-branched metasurfaces composed of Helmholtz resonators with embedded apertures (HREAs) in a flow duct were systematically investigated. HREAs are capable of efficiently weakening the flow-induced noise by damping the vortices and flow oscillations with an improved acoustic impedance design, which leads to better acoustic-attenuation performance. Furthermore, the optimal attenuation performance of the proposed HREAs under grazing flow was demonstrated by tuning the diameter and extending the length of the embedded apertures. The proposed structures, with double HREAs separated at a distance or arranged at the same location, can realize a higher efficient and broadband acoustic attenuation performance. The results show outstanding noise-attenuation performance and may inspire the development of highly efficient, thin and tunable acoustic mufflers for refrigeration equipment.