Smart Acoustic Lining for UHBR Technologies Engine Part 1: design of an electroacoustic liner and experimental characterization under flow in rectangular cross-section ducts

TL;DR

This paper introduces an electroacoustic liner for UHBR engines that can be programmed to control acoustic impedance, with experimental validation in rectangular ducts demonstrating its potential for noise reduction in constrained engine nacelles.

Contribution

It presents the design and experimental characterization of an electroacoustic liner with programmable boundary laws for noise control in UHBR engine nacelles.

Findings

Achieved stable and robust scattering performance in rectangular waveguides.

Demonstrated the ability to program surface impedance for noise isolation.

Progressed the technology readiness level to TRL 3-4.

Abstract

The new generation of Ultra-High-By-Pass-Ratio (UHBR) turbofan engine while considerably reducing fuel consumption, threatens higher noise levels at low frequencies because of its larger diameter, lower number of blades and rotational speed. This is accompanied by a shorter nacelle, leaving less available space for acoustic treatments. In this context, a progress in the liner technology is highly demanded, prospecting alternative solutions to classic liners. The SALUTE H2020 project has taken up this challenge, proposing electro-active acoustic liners, made up of loudspeakers (actuators) and microphones (sensors). The electro-active means allow to program the surface impedance on the electroacoustic liner, but also to conceive alternative boundary laws. Test-rigs of gradually increasing complexities have allowed to raise the Technology Readiness Level (TRL) up to 3-4. In this first part, we describe the control laws employed in the experimental campaigns, and present the scattering performances in rectangular waveguides with monomodal guided propagation. These results have assessed the isolation capabilities, stability and robustness of such programmable boundary technology, allowing to gain confidence for the successive implementation in a scaled turbofan test-rig.