Aeroacoustic design of metafluid devices

The present paper examines different methods for the design of acoustic metamaterial devices required to operate in presence of an aerodynamic flow. The ultimate goal of the research is the exploitation of the acoustic properties of acoustic metafluids in the aeronautical context. Particular attention is paid to the development of innovative devices capable to modify the propagation pattern of aviation noise to mitigate its effect on the population. Possible applications are a new generation of liners to achieve the virtual scarfing of nacelle intakes or special surface treatments to enhance the shielding of engine noise by wings and fuselage. The paper is focused on aerodynamic flows at Mach number not higher than 0.3, which is compatible with the take-off and landing conditions of commercial aircraft. Different approaches are used to define appropriate corrections of static metamaterial designs to recover, partially or completely, the efficiency of the meta-response lost as a consequence of the aerodynamic convection. All the approaches are based on classic aeroacoustic coordinate transformations, suitably revisited and adapted to specific application at hand. All the corrections presented are independent on the technique used in the static design of the device. Preliminary numerical results are obtained in the scattering abatement (cloaking) of obstacle with simple geometries. The numerical simulations are obtained using an original, general integral formulation of the problem, solved using an extended boundary element method.