Micro-Perforated Panels for Silencers in Ducted Systems
Résumé
Classical porous materials are extensively used in ducted systems such as heating, ventilation and air conditioning, or in automotive exhaust systems. However, there are many difficulties in using such passive materials in these situations. The available space to install the control device is often limited and the surrounding environment can be hostile. In many applications, they are subject to high air flow velocities and temperatures that cause their deterioration and a lack of long-term security conditions. Micro-Perforated Panels (MPPs) are promising solutions in order to achievenoise reduction in such difficult environments. They consist of a thin panel with sub-millimetric perforations situated in front of an air cavity creating a resonance-type absorber. The attenuation of sound is due to friction losses through the holes at the Helmholtz-type cavity resonance. These absorbers are non-combustible, ecologically friendly, cleanable, and their efficiency bandwidth is tuneable. By a proper selection of the constitutive physical parameters, it is possible to obtain a relatively broadband attenuation partition without the introduction of fibrous materials. These devices were initially proposed by D. Y. Maa and were mainly conceived for applications in room acoustics. In this work, we present a theoretical model for the prediction of the acoustic propertiesof a cylindrical silencer based on the Multi-Modal Propagation Method, that calculates thepropagation of sound in ducts with varying cross-section and with either rigid, locally- or non-locally reacting boundary conditions. This method isadapted to analyse the absorbing propertiesof a circular duct lined with a MPP treatment.