Numerical simulation of air inlets sound insulation

Breathing healthy air at home requires efficient ventilation which is generally achieved by mechanically controlled ventilation systems. However, the installation of air inlets, at the top of windows, reduces sound insulation. Actually, laboratory tests must be processed by manufacturers to measure the SRI (sound reduction index), which is calculated from the difference between the source and receiving sound power levels in the one-third octave band. The addition of melamine, a widely used porous material with interesting acoustic properties, slightly decreases the transmitted noise through air inlets, but the sound reduction remains far from that of a window without any inlet at all. Moreover, experimental settings induce uncertainties, particularly when low frequencies are involved. Numerical simulation is thus an interesting alternative for studying air inlets' vibro-acoustic behaviour. Many parameters can be considered without the need to carry out new experiments, thus greatly reducing financial costs. Calculations must be computationally efficient to enable an optimization approach. To this end, the proposed numerical model is based on the patch transfer function method which is a substructuring approach. Here, each subsystem of complex geometries is discretized by finite elements while porous materials are modelled using an equivalent fluid or localized impedance.