Acoustic black hole effect due to variation in duct wall impedance

This presentation explores the acoustic black hole (ABH) effect achieved through variation of duct wall impedance. Unlike the method of Mironov and Pislyakov, which utilizes tapered annular rings within the duct to achieve the ABH effect, this approach leverages mechanical impedance variation to create the desired acoustic behavior. By engineering the impedance profile along the duct wall, an axially decreasing local phase speed results that mimics the event horizon of a black hole, causing sound waves to be significantly attenuated and trapped. Governing equations are derived and solved using both the WKB approximation and numerical methods. The solutions reveal that specific impedance profiles can effectively decelerate and absorb acoustic waves, resulting in substantial reduction in sound transmission. Verification is performed using the fully coupled structural acoustic finite element algorithm Sierra/SD. This research further paves the way for the development of innovative acoustic materials and devices which utilize ABH principles to achieve enhanced noise control and acoustic wave manipulation. [Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy's National Nuclear Security Administration under Contract DE-NA-0003525.]