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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - AERIALIST (AdvancEd aicRaft-noIse-AlLeviation devIceS using meTamaterials)

Teaser

Summary

AERIALIST is a fundamental research project whose primary goal is to contribute to the full disclosure of the potential of metamaterials in aeroacoustics. The target engineering application is the mitigation of community noise of commercial aircraft. The need of such a research stems from the urgent need of breakthrough technologies and disruptive concepts to guarantee the sustainable development of the civil aviation. Indeed, the constantly growing market demand can be satisfied in an environment-friendly way only imposing strict constraints on noise and chemical emissions (see, e.g., ACARE Flightpath 2050). The substantial development saturation of current technologies makes any further incremental improvement extremely difficult to achieve. In such a context, the fundamental research on highly innovative concepts and methods assumes a key role, and AERIALIST\'s ambition is to contribute to this process. The project approach is built on four technological pillars addressed by four technical work packages:
1. Consolidate the theory of metamaterials and metacontinua in the aeroacoustic context and enhance and adapt suitable numerical tools for the prediction of their acoustic response in presence of flow (WP2);
2. Develop and assess the methodology for the additive manufacturing of devices based on metamaterials (WP3);
3. Perform the experimental analysis of the manufactured devices in the aeroacoustic wind tunnel (WP4);
4. Establish and assess the toolchain involving theoretical modelling, numerical simulations, realisation, and experimental validation and eventually provide recommendations for the development roadmap towards TRL of industrial relevance (WP5).
These objectives require, for their own nature, a comprehensive multidisciplinary approach covering the entire conceptual workflow of fundamental research, from the theoretical development to the practical realisation and experimental assessment. The entire workflow is developed In AERIALIST aiming at its effective future exploitation, keeping in mind the industrial requirements and the expected design constraints and targeting at an easy integration in the conceptual design of the future aeronautical concepts, also through the connection to other H2020 projects focused on higher TRLs.

Work performed

The activity completed during the first 18 months of AERIALIST covers essentially three aspects: 1) the development of a consistent theory for the modelling of a metamaterials in the aeroacoustic context, capable to be completely integrated into the tools and the methods used in the aeroacoustic research and industrial community. Indeed, such a theoretical background is still missing, mainly due to the fact that the structure of equations governing the propagation of an acoustic disturbance changes substantially in presence of a background flow, thus making all the approaches to the design of a static acoustic metamaterial almost useless in aeroacoustics; 2) the assessment of the Design For Additive Manufacturing (DFAM) process to establish a reliable link between the theoretical and numerical modelling and the realisation of the experimental samples; 3) the preliminary experimental campaign to assess in the aeroacoustic wind tunnel the developed concepts and validate the simulation methodologies. These three parallel work-paths have been coordinated by the WP1 and WP5 activities to eventually close the toolchain loop on a first set of benchmarks.
The choice of the basic benchmarks followed two complementary criteria: on one side, a simple one-degree-of-freedom liner has been chosen as a widely-assessed reference, whereas, on the other side, a Kelvin-cell-based periodic structure
has been selected as fundamental brick to connect the theoretical model and the DFAM process for its lightness and compactness (i.e., shape that fill the space with minimal surface area). A summary of the specific results achieved within each technical WP is the following.

WP2
1) Theoretical development of a general method for the convective correction of existing metamaterials.
2) Development of a general approach for the spacetime design of a metacontinuum with arbitrary constitutive equations.
3) Development and validation of the Inverse Estimation Method (IEM) for the modelling of arbitrary constitutive equation.
4) Definition of a dynamic model of non-local boundary effects integrated in suited BEM and FEM codes and application to the concept of metamaterial pseudo-impedance.
5) Optimisation of metasurfaces for the broadband steering of the reflection.

WP3
1) Development and assessment of the six-stage design loop for DFAM using polymers (low-cost) and metals.
2) Realisation and test of a normal- and grazing-incidence impedance tubes.
3) Design and manufacturing of the wind tunnel models and the MM samples.

WP4
1) Design, manufacturing and testing of the bespoke contraction nozzle.
2) Experimental campaign on the benchmark models.

WP5
1) Classification and selection of concepts of relevance to the project objectives.
2) Identification of the target behaviours for shielding enhancement, virtual scarfing and noise trapping.

Final results

\"The progress beyond the state of the art produced by the results achieved so far can be divided in two main contributions. On one side, the development of a consistent theory for arbitrary metacontinua in aeroacoustics, where the existing approaches are all limited to static acoustics. AERIALIST approach integrates an unconstrained general continuum modelling at conservation laws level with a versatile homogenisation method to attain the target constitutive equations. The latters can either include significant shear effects or be associated to a purely spherical stress tensor (\"\"meta-solids\"\" or viscous/inviscid \"\"meta-fluids\"\"), allowing for the widest possible exploration of the design space. The approach integrates the modelling of the boundary response, which is a critical aspect in aeronautical applications.
The second innovative aspect is related to the establishment and assessment of a comprehensive toolchain that integrates theoretical and numerical modelling, executive design, manufacturing and experimental testing. Such an approach is still missing in the acoustic metamaterial context. The underlying rationale is connected to the need of a rapid enhancemnt of the technology readiness to levels of industrial interest. Indeed, one of the final outcomes of the project will be a development roadmap to rapidly achieve higher TRLs and allows for the integration of the AERIALIST toolchain in the conceptual design of the future generation of noise-abatement devices. The expected benefit is to contribute to the accomplishment of the noise abatement targets foreseen in the 2050 horizon.

The evolution of the project in the second period will pursue the final objectives through the application of the developed methodology in the design, manufacturing and testing of the selected concepts. The latters are currently being defined through a joint activity between WP2 and WP3 to identify the most promising concepts and layouts. In addition, the theoretical development will be completed by finalising the revisit of the acoustic analogy approach within the meta-fluids framework and its integration into existing computational tools, and by tuning the procedure of inverse identification of the metacontinuum constitutive equations from the desired target response.
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