Acoustic liner test of DGEN 380 turbofan engine

Acoustic liner is one of the most effective devices for aero-engine noise suppression, especially for fan noise suppression. Its fundamental characteristics can be obtained by impedance tube measurements or by impedance eduction with grazing flow duct facilities, however in the product development stages it is necessary to evaluate its performance on large scale models, such as rotating fan rigs or real aero-engines. Japan Aerospace Exploration Agency (JAXA) introduced a small turbofan engine called DGEN380 for engine noise studies and has carried out outdoor tests since 2016. In this study, to achieve the fan noise reduction, the acoustic liners are designed. Then curved acoustic liner panels are fabricated by 3D printer and installed in an intake duct upstream of the fan blades. The acoustic performance of the liners is evaluated by two measurements. First, in-duct acoustic mode propagation is measured by the microphone array uniformly distributed both azimuthally and axially inside the duct surface at the upstream of the liner. In the other, sound radiation pattern from the engine is obtained by 20-meter arc microphone array measurement. From the results of both measurements, the noise reduction at the designed frequency bands is confirmed.