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Smart Acoustic Lining for UHBR Technologies Engines

Periodic Reporting for period 3 - SALUTE (Smart Acoustic Lining for UHBR Technologies Engines)

Reporting period: 2021-03-01 to 2022-11-30

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 has tackled these challenges by developing a new acoustic liner technology based on arrays of small loudspeakers or passive membranes. This innovative approach is proved to be able to deliver excellent sound absorption at low frequencies while remaining sufficiently small to fit into thin nacelle geometries. This development has been carried out on three different concepts, which has been compared and down-selected in the course of the project.
According to the project flow, these acoustic treatments were first tested using 2D (i.e. flat) prototypes at TRL 3, which constituted the baseline configuration of the project. The SALUTE project went further by testing 3D prototypes with a geometry corresponding to a small-scale fan at the PHARE test facility. This allows us to validate TRL4 of the proposed system and the associated manufacturing processing. Secondly, gaining more insight into the physical interaction between the transducers, the control system and the high-speed flow has been studied and results published for future developments. This has been achieved through multi-physics simulations coupling the adaptive liner and aero-acoustic flow validated by experimental confrontation.
The SALUTE project belongs to the Clean Sky 2 program.
The first period of SALUTE project was dedicated to design of the set of planar 2D prototypes for aero-acoustic testing that has been carried out in July 2020. Requirements and associated advanced components screening lead us to define the first design of the planar 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 works carried out on the second period of SALUTE project was dedicated to the fabrication and first experimental characterizations of the planar liners and the development of the associated numerical tools. The most important deliverable of this period is the electro-active liners with all functional cells that has been characterized on dedicated tube with flow. The second defined technology has also been validated by CDR and it will be ready for NLR test in the next few days. In parallel a strong effort was devoted to numerical developments in order to furnish tools for future 3D implementation.
The last period allowed us to build and test the inlet prototypes in PHARE bench that validates our technology TRL at 4. We also updated and finalized numerical tools allowing to explain the experimental measurements and optimized the setup and the control strategy in a complex architecture. Based on these very important results, one proposed new process and technologies for preparing TRL 5 demonstration. One tested 3 new lightweight transducers and plastronic assembly. The obtained results give new way for improving the propose active acoustic liner technology for future implementation.
To sum up, SALUTE project produced :
• 2D demonstrators validating TRL 3
• 3D demonstrators validating TRL 4
• Propositions of different solutions tackling blocking challenges toward TRL 5 : new transducers, integration process, control strategies…
• Designing numerical tools form the component to the full coupled aeroelastic system

The main project dissemination and exploitation performed were :
• Participation to 6 conferences and 5 workshops (and 3 expected in 2023)
• Publication of 6 journal papers (and 4 expected in 2023)
• 1 film and 2 exhibitions
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 planar large sample 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.
The last tests of the final inlet prototype is a real breakthrough in noise treatment technologies opening the path of new compact, efficient and adaptive smart liners. The lasts obtained results demonstrates that TRL 5 and 6 can be achieved by using lighter and integrated new technologies that have been proposed and identified in the project.
Detailed view of the P1 unit cell
3D system mounted on the engine nacelle
Left: Titanium plate with the laser-cut piston and arms. Right: Cavity forming the Helmholtz resonat
3D system assembly
2D Numerical Results with active liners
View of the prototype cells P1 with top foam as protective liner
picture of the electronics for one unit-cell (left: back of the actuator with the flexible connectio
Unit cell with electronics and transducers and 3D-printed prototype picture.
Examples of pressure and velocity calculated by the numerical model.
Plasma Based acoustic transducer
Picture of the compact P2 prototype flush mounted into a Helmholtz resonator (left) – Plain metal (u
View of the 39-cells panel (P1L/P1D) in the multimodal duct at FEMTO-ST