Noise attenuation and aerosol agglomeration by rib-designed silencers under a low-speed particle-laden flow

Reducing the emissions of ultrafine and fine particles by thermal engines in the atmosphere or indoor by air-conditioning ventilation systems would have a beneficial impact on cardiovascular and respiratory health issues. A proposal is to design low-drag silencers able to provide both noise attenuation in presence of a low-speed flow while agglomerating fine particles into coarser aerosols that can be efficiently filtered out. This study explores under which conditions the effective slow sound properties of rib-designed silencers can trigger the coalescence of micrometric aerosols convected by a low-speed flow, while ensuring high transmission loss values over a broad bandwidth. The analysis considers which parameters of the silencer, such as the rate of increase of the cavity depths or their density subject to volume constraints, produce slow sound conditions at low Mach number. It is also examined how the mean flow velocity, as well as the frequency and intensity of the incident sound wave, enhance the coalescence of the micrometric particles. These results are expected to open up perspectives on the multi-functionality of aeroacoustic metamaterials.