Metamateriales aeroacústicos para sistemas de transporte más silenciosos y energéticamente eficientes

Low frequency noise sources are increasingly present in guided flows, particularly in aeronautics where new engine architectures are driven by the reduction of energy consumption. Current acoustic treatments present a conflict between achieving both high acoustic and aerodynamic performance while respecting the constraints of reduced lined surface, low thickness and low embarked weight. This problematic is also present in automotive transports for the aero-acoustic optimisation of exhaust silencers, in heat and ventilation systems in buildings for low-frequency noise reduction with minimal air pressure losses and in wind-turbines. Emergence of acoustic metamaterials (AM) allowed the development of compact sub-wavelength absorbers that can provide solutions in terms of the required wideband low-frequency sound dissipation. AMs derive their unconventional properties from their anisotropic cellular architecture that can be translated into unusual effective density and bulk modulus parameters. However, despite the tremendous growth of AM studies during the last decade, the potential of AMs in presence of a low-speed flow has still not yet been fully explored. Previous results from the applicants have shown that even though the AM produce high noise attenuation in the no-flow case, their aeroacoustic performance are highly sensitive to interactions between the flow and the AM interface. For a micro-perforated interface, it was found that extra-noise generation may appear due to efficient back-scattering of the turbulent energy into sound. Moreover, the presence of flow in direct contact with a flush-mounted porous surface generates drag, flow-induced noise and aeroacoustic instabilities, as observed for micro-perforated liners or interferential helicoid metamaterials. To overcome these difficulties, the AEROSMEET project addresses two challenges. First, it aims at developing new generations of AM-flow compliant interfaces, with micro-grooved and micro-channelled structures, able to achieve low frictional losses in presence of a sheared or turbulent flow, but without hindering the metasilencer acoustic performance. Moreover, augmented metasilencers will be designed to achieve full broadband noise reduction down to low frequencies both in reflection and transmission in presence of a low-speed sheared flow, thereby achieving an Aeroacoustic Black Hole (ABH) effect. The AEROSMEET outcomes will contribute to the national strategic actions on Climate, Energy and Mobility 2021-23. Indeed, the newly designed metasilencers will comply with energy-saving requirements in contrast to other silencing solutions prone to high fluid pressure discharge that should be compensated by more powerful flow turbines. They will also provide solutions to the challenging tasks of lowering low-frequency noise emissions in aeronautical and surface transports as well as improving the combustion efficiency of hydrogen engines through the ABH effect.