High-performance Beihang grazing flow duct for acoustic liner research

• The BGFD generates grazing flows up to Mach 0.65 and incident tones of 140–150 dB. • The BGFD includes microphone arrays for educing impedance up to 6 kHz and decomposing acoustic modes up to 10 kHz. • An uncertainty analysis was used to confirm the accuracy and repeatability of the measurements. Beihang Grazing Flow Duct (BGFD) is a high-performance facility designed to mimic the aeroacoustic environment in aeroengine nacelles for assessing the liner impedance and propagation characteristics. A grazing flow of utmost cross-section average Mach 0.65 and incident tones of 140 to 150 dB from 500 to 6000 Hz can be achieved within its test section measuring 51 by 63 mm 2 in the inner cross section, while the background noise is maintained below 100 dB across most frequencies, guaranteeing high signal-to-noise ratios. In this facility, the original and the Mirror-based Multimodal StraightForward Methods (MMSFM) are employed to educe the impedance. An uncertainty analysis confirms not only the eduction accuracy but also the repeatability, with 95 % confidence intervals of both the educed and predicted impedances falling within acceptable ranges. Results of the MMSFM further demonstrate that the impedance can be measured in the BGFD at Mach 0.5 and frequencies up to 6000 Hz. Moreover, the BGFD adopts two optimized arrays to decompose all acoustic modes at utmost 10 kHz in the up/downstream rigid-wall sections, and thus enables the quantitative assessment of the transmission loss, whose accuracy is validated from good consistencies between the experiment and a simulation using the predicted impedance as the input.