Optimized metamaterials for enhanced noise shielding of innovative aircraft configurations

Metasurfaces that exploit the so-called generalized Snell's law are suitable for the manipulation of acoustic waves in the subwavelength regime, exhibiting extraordinary refracting and reflecting behaviours. This attracted the interest of the aeroacoustic community for their potential as a disruptive technology for noise abatement and acoustic field control. New acoustic treatments have, hence, been imagined for highly innovative aircraft configurations, to be placed also in unconventional positions over the airframe, fully exploiting their characteristics. However, the direct simulation of metamaterials and metasurfaces in the aeroacoustic context can be computationally very expensive, even when involved geometries are not particularly complex, limiting the possibility to include metamaterial effects into multidisciplinary design process for applications of aeronautical interest. In this paper a generalized Snell law-based lining installed on the upper side of an airfoil is explored as a way to enhance its shielding of the noise emitted by a point source. This shall be seen as a 2 dimensional schematization of the center body of a Blended Wing Body configuration with the propulsion system mounted on top of it. A model of metafluid is used to reduce the computational burden, allowing a simulation-based optimization process to be conducted, maximizing the shielding factor of the airfoil.