Direct Measurements of Aerodynamic Drag of Acoustic Liners

Recently, the aerodynamic performance of acoustic liners has become a research focus. It is necessary to study the influencing factors of the acoustic liner drag to further reduce engine fuel consumption and emission. In this paper, a drag balance is designed to directly measure the liner drag in a grazing flow tube. The test samples include conventional acoustic liners, multi-slot acoustic liners, and a smooth wall set as a reference for comparison. All the test samples are under the fully developed grazing flow with variable bulk Mach number (M) from 0.1 to 0.6. The effects of the configuration characteristics of the acoustic liner on the flow drag are studied. Experimental results show that the design parameters of the acoustic liner have considerable influence on the flow drag, including the perforation size, plate thickness, porosity, perforation layout, and fabric mesh. Besides, a conventional liner is tested to evaluate the effects of acoustic tonal excitation with the sound pressure level up to 150 dB between 500 Hz and 1700 Hz. The extra drag induced by the incoming sound waves can increase by 137% at M = 0.1. But the increasing flow speed will suppress this extra drag penalty in this study.