NUMERICAL MODELLING OF A PHASE-GRADIENT LINING USING A METAFLUID MODEL

This contribution presents the modelling of a phase-gradient metamaterial for the surface treatment of the internal walls of a turbofan nacelle intake. The metamaterial is modelled through a metafluid, whose bulk modulus and inertia tensor are determined by a simulation-based numerical optimization, minimizing the acoustic emission from the duct inlet. The flow and its interaction with both the nacelle and lining are modelled in a simplified way using a potential flow over smooth surfaces. The parameters of the metafluid are tailored to tackle the incident field expressed in terms of duct modes propagating from the fan section for the blade passage frequency. Numerical results show the encouraging capabilities of a phase-gradient device to change the directivity of the noise radiated by an aeronautic turbofan nacelle, abating the propagation of a duct mode linked to a relevant noise generation mechanism.