ENOVAL is a EU-funded project aiming at developping novel aircraft engines architectures (geared and ungeared) achieving breakthrough performances in terms of environmental pollution (carbon dioxyde emission efficiency, noise reduction). A direction towards CO2 reduction lies in shortening the engine nacelle, thus leaving less space for acoustic lining (conventional sound absorbers). In that frame, the development of surface acoustic absorbers concepts with subwavelength dimensions is targeted.
In this project, EPFL is a subcontractor of the French nacelle manufacturer AIRCELLE, and collaborates with FEMTO-ST (Besançon, France) to develop novel acoustic liners concepts with distributed active acoustic impedance control features. The technology is based on the Electroacoustic Absorber concept developped at EPFL, combined with distributed acoustic impedance control strategies developped at FEMTO-ST.
The main objective of the project is the development of a novel active acoustic liner, composed of a periodic arrangement of unit-cells owing to the concept of electroacoustic resonator (the acoustic impedance of which can be adjusted with dedicated electronic control). The individual unit-cell should then allow to adapt the absorption in the middle-high frequency range, whereas the periodic arrangement should allow to extend the performances down to the low-frequency bound of the noise spectrum, owing to subwavelength phenomena.
- develop a numerical model of a small-scale duct with arrays of active unit-cells, accounting for a flow and multimodal acoustic field
- optimize the prototype of distributed active impedance control (loudspeaker, electronic control strategy, optimal acoustic impedance, global performances in terms of Insertion Losses)
- build a prototype
- test the prototype in a laboratory small-scale model, and in an industrial test-bench
Lissek, H., Boulandet, R., and Fleury, R., Electroacoustic Absorbers: bridging the gap between shunt loudspeakers and active sound absorption, The Journal of the Acoustical Society of America, 129(5), p. 2968, 2011.