AEROACOUSTIC DESIGN OF METAFLUID DEVICES

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