Teresa Bravo, Cedric Maury, Daniel Mazzoni, Muriel Amielh
30thInternational Congress on Sound and Vibration. ICSV'30
Del 8 al 11 de julio de 2024, Amsterdam, Países Bajos
The Acoustic Black Hole (ABH) is a new technique that was proposed for passive vibration control but has been recently extended for broadband noise control in ducted geometries. For instance, in areas such as building and transportation industries, the control of low-frequency noise propagating in exhaust or air-conditioning waveguides constitutes an important issue and a very challenging problem. Although many studies have presented closed ABH geometries, the used of open-ended ABHs is compulsory in duct systems where a mean axial flow is present. In this case, the concept of sound trapping involves minimization of both sound reflection and transmission inside the retarding structures. This work is focused on the optimal determination of the ABH physical constituting parameters that mostly influence the metamuffler performance. The requirements on minimal volume impose a constraint for the total dissipation that has to be considered regarding low-frequency broadband operation and manufacturing constraints. An analytical formulation will be presented in terms of the Transfer Matrix Method to model a widely-opened silencer composed of a finite number of sidebranch cavities with an axial variation of their depth according to an exponential law. These cavities are separated by rigid rings of constant thickness. Assuming plane wave propagation along the main duct and within the annular cavities, viscothermal effects are considered to calculate the power dissipated by the ABH. Influence of several parameters is studied considering the optimal axial rate of cavity depth variation, the wall porosity and the ratio between the total silencer length and the duct radius. The simulated optimal results are verified against a set of measurements performed in a standing wave tube where the ABH is inserted. A good agreement is found between both values that validates the proposed metamuffler with near-unit dissipation over its efficiency broad bandwidth.
