Optimised Design of Acoustic Black Hole for Broadband Noise Attenuation in Ducts

Abstract Broadband noise attenuation remains a challenging problem in ducts. The development of acoustic metamaterials in recent times has made it possible to control and manipulate sound waves in novel ways. Acoustic black holes (ABH) are passive type absorbers. The two major parameters affecting the sound absorption characteristics of ABH are known as power-law decay of duct radius and tailored wall admittance. In theory, the tailored geometry induces power-law decay of wave propagation velocity, and the incident wave gets trapped inside the geometry without any reflections. The current study aims to develop an optimised ABH design targeting broadband frequency. The transfer matrix method (TMM) approach is used to characterise the reflection coefficient and validated using numerical approach considering thermoviscous effect along the thin walls. The developed basic design is further optimised for the influencing parameters and validated using numerical analysis. The result shows a broadband noise attenuation for the optimised design of the black hole.