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Smart Acoustic Lining for UHBR Technologies Engines

Periodic Reporting for period 1 - SALUTE (Smart Acoustic Lining for UHBR Technologies Engines)

Reporting period: 2018-11-01 to 2019-12-31

Reducing noise emissions is one of the main design targets driving the development of new aircraft engines, and is therefore a key priority for the competitiveness of the aerospace sector. Ultra-high bypass ratios (UHBR) turbofan engines are expected to equip the next generation of aircraft to maximize efficiency. The noise generated by these engines will concern lower frequencies compared to existing engine technologies. Also, with a thinner nacelle, absorption performances are expected to drop at low frequencies. And with a shorter nacelle, less surface area will be available for acoustic treatments. UHBR engine technologies then represent significant challenges for the design of next-generation acoustic treatments.
The SALUTE project will tackle these challenges by developing a new acoustic liner technology based on arrays of small loudspeakers or passive membranes. This innovative approach is able to deliver excellent sound absorption at low frequencies while remaining sufficiently small to fit into thin nacelle geometries. This development will be carried out on three different concepts, which will be compared and down-selected in the course of the project.
Conventionally, these acoustic treatments were tested using 2D (i.e. flat) prototypes, which will constitute a baseline configuration of the project. The SALUTE project will go further by testing 3D prototypes with a geometry corresponding to a small-scale fan at the PHARE test facility. This is required to reach TRL4, but will present specific challenges in terms of manufacturing. Secondly, gaining more insight into the physical interaction between the transducers, the control system and the high-speed flow will be necessary. This will be achieved through multi-physics simulations coupling all these sub-systems.
The first period of SALUTE project was dedicated to design of the set of 2D prototypes for aero-acoustic testing that will be carried out in July 2020. Requirements and associated advanced components screening lead us to define the first design of the 2D innovative liner implementation. Associated numerical tools have also been developed for helping in designing and choosing the finally adopted systems. Two technologies have been defined and the first experimental validations underline the potential of the targeted liners for acoustic treatment.
The main objective of the Workpackage 2 is to write the UHBR innovative liners specifications under Safran Aircraft Engines leadership. All components will be directly design to be compatible to PHARE testing. 2D prototypes are only a step toward TRL 4 characterization. During the reporting period, the specifications of the 2D and 3D liners have been written, under the leadership of Safran Aircraft Engines (SAE, Topic Manager). The resulting requirements for the transducers have been expressed.

WP3 aims at performing a thorough examination of concepts and components allowing the construction of the active liner prototypes and identify the best components achieving the acoustics and environmental specifications from WP2. The component selection will address the following items:
• Actuators and sensors
• Control electronics (including cabling)
• Mechanical frame and mounting
The screening consisted in identifying transducers, electronics, and mechanical hardware complying with the specifications provided by the Topic Manager. It has been completed as regards both electromechanical, electronics, and mechanical frame components. Some adjustments are still possible depending on the final mounting constraints for the different experimental test-benches.

WP4 aims at designing 2 different 2D prototypes (P1 and P2) of innovative membrane liners including different categories of transducers and control technologies. The design will cover (i) the electro-mechanical specifications of the transducers, (ii) the electronic systems controlling these transducers, (iii) the assembly of the transducers to form a full-sized panel.
The PDR has been done in February and some first designed prototypes have been defined for processing and characterization to make the CDR by end of March. A key aspect will be the viability of the prototypes in the test rigs to sustain the high-speed flows.

WP5 is focused on the manufacturing of the tunable membrane liner panels complying with the 2D detailed definitions provided in WP4. This WP includes not only the manufacturing of the panels, but also the validation of the components at several levels, in order to guarantee the effectiveness of the panels that will be tested under grazing flow in WP6. On this period, first designed prototypes have been processed. Additional tests will be carried out for allowing final CDR.

WP7 aims at :
- Providing modelling tools to support the design and optimization of the innovative membrane liners.
- Developing a better understanding of the fluid-structure coupling between the membrane oscillations and the flow acoustics.
We have developed a numerical model for the simulation of the sound field in a duct equipped with a single, or several, transductor(s). Stability and efficiency margins can be evaluated using the first developed numerical tools.
The expected impacts of SALUTE project are socio-economic addressing the preservation of the acoustic environment in Europe and targeting the need to propose new technologies in view of developing UHBR while decreasing noise emission that constitutes a major industrial challenge. For SAFRAN, SALUTE aims at characterizing a TRL4 liner prototype tested on a ¼ full scale inlet and interstage mock-up and at giving the key of this new technology at TRL5. The associated numerical design tools will also be created in the project. This technological progress will also impact aeronautical industry and any industrial sector by paving the way to new efficient and integrated innovative noise treatments. In this first period, we progressed toward these goals by testing some first design prototypes demonstrating very promising capabilities for noise treatment. TRL 4 ascension is on the way and we plan to validate this readiness level by next summer. The first numerical developments allowed us to precise our design and integrate new industrial constraints for future realistic design tools.
The measures to maximize impact will really starts after the acoustic characterization of our 2D liner prototype especially with the aero acoustic test in July 2020. Some specific papers are already proposed for conference publication and workshop pointed out specific tools and results firstly obtained.
Detailed view of the P1 unit cell
2D Numerical Results with active liners
View of the prototype cells P1 with top foam as protective liner
Unit cell with electronics and transducers and 3D-printed prototype picture.
Picture of the compact P2 prototype flush mounted into a Helmholtz resonator (left) – Plain metal (u