Experimental assessment of a programmable Electroacoustic Liner in a representative turbofan facility

The Flightpath 2050 European Union stringent regulations for aviation noise reduction, along with the new generation of Ultra-High-Bypass-Ratio turbofans to reduce fuel consumption, significantly challenge the scientific community to find unprecedented acoustic liner designs. The SALUTE H2020 project has taken up this challenge, by designing and testing a programmable metasurface made up of electroacoustic resonators. Each electroacoustic resonator is composed by a loudspeaker and four microphones in a compact design, allowing to synthesize tunable local impedance behaviours thanks to a current-driven control strategy. A steel wiremesh mounted onto a perforated plate allows to protect the elctromechanical devices from the aerodynamic disturbances. For the first time, such advanced liner concept has been tested in a scaled turbofan rig: the ECL-B3 PHARE-2 in the Laboratory of Fluid Mechanics and Acoustics of the Ecole Centrale of Lyon. The performances of the electroacoustic liner reported in this paper, correspond to three different regimes: 30%, 40% and 100% of the nominal engine speed. The electroacoustic technology demonstrated robustness faced with a realistic reproduction of actual turbofan conditions, as well as its tunability to target different frequency bandwidth, attaining good radiated noise reduction. The results reported in this experimental campaign open the doors for unprecedented liner designs, by exploiting the huge potentialities of programmable surfaces.