Breakthrough technology helps aircraft achieve noise reduction targets
The EU-funded AERIALIST project identified and developed breakthrough technologies based on metamaterials to achieve noise reduction targets outlined in the ACARE Flightpath 2050 strategy, Europe’s vision for aviation. Metamaterials can be defined as materials engineered to attain a response not available in nature and are typically characterised by a recurring structure at the macro or micro scale. Consortium members built on current acoustic metamaterial theory by studying the effect of realistic aerodynamic flows to develop numerical methods that simulate the behaviour of acoustic metamaterials under aircraft operating conditions. AERIALIST also assessed the technical feasibility of noise reduction devices based on the concepts developed, proposing a roadmap towards their practical realisation.
New design tool developed
Project partners focused on the reduction of noise propagating outside the turbofan housings (nacelles), exploiting the unconventional properties of acoustic metamaterials to modify noise scattering patterns. “Scattering cancellation, hyper-focusing and noise trapping techniques were investigated to achieve virtual scarfing of intakes, suitable treatment of outflow ducts and enhancement of shielding effects,” comments project coordinator Umberto Iemma. This approach combined theoretical modelling, development of numerical methods, design, additive manufacturing and experimental validation into an integrated design toolchain. “The development of this design tool has been successfully applied to the target meta-behaviours identified as relevant to aircraft noise mitigation,” Iemma explains. Researchers developed a theory for the modelling of metamaterials in the aeroacoustic context that can be completely integrated into the tools and the methods used in the aeroacoustic research and industrial community. Aeroacoustics involves noise generation through turbulent fluid motion or aerodynamic forces interacting with surfaces. State-of-the-art additive manufacturing processes were then used to realise a 3D object from the digital 3D model and link the modelling activity with the experimental samples. Wind tunnel experiments were then conducted to assess the developed concepts and validate the simulation methodologies.
Applications in multiple sectors
The new technologies developed, including new theoretical models and analysis techniques are capable of mimicking the acoustic response of a moving medium and the inverse identification method. “Innovative aspects have also been introduced in the development of numerical models. These take account of non-uniform convection and reduced-order models to include visco-thermal losses in the design of multi-cells periodic structures,” notes Iemma. “Furthermore, the application of state-of-the-art optimisation techniques in the design of reflection-steering metasurfaces substantially widened the effective frequency range.” The metamaterials design toolchain will contribute to future integration in the industrial design process, benefiting both research establishments and industry. The concepts identified and assessed in AERIALIST up to technology readiness level (TRL) 3 are ready to be enhanced and further developed to TRLs of industrial relevance. Part of this activity will be performed by the EU-funded ARTEM project. AERIALIST therefore successfully developed an approach for exploiting the potential of acoustic metamaterials in aeronautics and for all those engineering applications where an acoustic disturbance produced by moving sources propagates in a moving medium. “Hence, the project’s results can also be readily applied to the automotive, railway and naval sectors,” Iemma points out.
Keywords
AERIALIST, design, noise, metamaterials, aircraft, aeroacoustic, aviation, modelling, toolchain
