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The fast development of Urban-Air-Mobility as well as the constant growth of the air transport have made the acoustic pollution abatement a crucial requirement for the aviation industries in order to comply with the increasingly demanding constraints for the community acceptance. The aeroacoustic characterization of arrays of electrically-powered propellers is one of the most challenging issues. The vast majority of the UAM concepts under development adopt propulsion systems based on multiple propellers, for which reliable and cost-efficient aeroacoustic models are still lacking. The present paper proposes the development of surrogate models for the description of acoustic emission of multi-propeller configurations. The numerical investigation focuses on surrogate models able to take into account the effects of the propeller blade geometry (e.g., chord and twist distributions) and global propeller-array geometric parameters (e.g., propellers clearance) on acoustic performances of the whole system. An innovative Artificial Neural Network adaptive metamodelling technique is applied on a numerical database obtained through a boundary integral formulation for the solution of incompressible potential flows around lifting/thrusting bodies, followed by the application of the Farassat 1A boundary integral formulation for the noise field evaluation.

The project AERIALIST (AdvancEd aicRaft-noIse-AlLeviation devIceS using meTamaterials), funded within the Breakthrough Innovation topic of the H2020 program, has closed its activity on May 2020. The objective of the project was the disclosure of the potential of metamaterials in developing disruptive devices for the mitigation of aircraft noise, in order to contribute to the identification of the breakthrough technologies targeted at the achievement of the noise reduction targets foreseen by the ACARE Flightpath 2050. Although targeted to low TRL, AERIALIST has been focused on the development of an integrated toolchain capable to address the entire design loop, from the early conception to the numerical and experimental proof of concept, up to the final design and manufacturing. The toolchain was founded onto four pillars: i) the extension of the acoustic metamaterial theory to aeroacoustics; ii) the exploitation of the latest additive manufacturing technologies; iii) the wind-tunnel assessment of the selected concepts; iv) the identification of a development roadmap towards higher TRL. After three years of activity, the project has attained all its objectives. The present paper is a review of the main outcomes of the project, their application potential and relevance to the ACARE objectives.