Toward a generalized theory for convective acoustic metacontinua design

This thesis proposes a generalized theoretical framework for designing convective acoustic metacontinua. Its definition could represent a promising strategy for sustainable air transport systems, particularly in the context of increasing air traffic and drone integration in low-altitude airspace. Acoustic metamaterials are indeed an innovative technology that could lead to the control of acoustic noise emissions in aeronautics. However, traditional designs lose effectiveness when operating within a non-quiescent medium due to the coupling of the fluid dynamics and acoustics. Therefore, the main core of the thesis tries to addresses this challenge by validating a spacetime framework that act inducing a convective-like propagation pattern within a region occupied by an acoustic metacontinuum. The analytical adaptation of traditional designs is performed through spacetime transformations that can be introduces exploiting the formal invariance of the governing equation when rewritten into the spacetime. The research discloses potentialities and limits of the framework through accurate numerical simulations involving sensitivity analyses of the adapted designs to the variation of key aeronautical parameters such as the background flow intensity, the source location, and the acoustic source emission frequency. The work seeks the integration of this design framework into the already existing methodologies for aeroacoustic analyses. To this aim, the activity culminates with three ongoing strands of research involving the development of a unified wave equation enclosing conventional and unconventional propagating media, the definition of a BEM formulation associated with an anisotropic free-space Green function, and with the outline of a cost-efficient inverse design procedure.