Aerodynamic performance test and flow visualization for reducing acoustic liner drag in grazing flow

We aim to reduce aerodynamic drag over an acoustic liner, which comprises of a perforated plate, a honeycomb core, and a rigid backplate, for aero-engine applications through both performance testing and flow visualization. Whereas the acoustic liner can attenuate engine noise, the structural characteristic of the liner surface causes the additional drag in grazing flow, resulting in deterioration of engine fuel efficiency. In this work, acoustic liner test pieces with various hole geometries are tested in the flow duct rig capable of generating sound wave and grazing air flow inside the duct. The static pressure drop measurement reveals that the perforation in the grazing flow direction wound increase the drag despite the same overall perforation for all test pieces. We further conduct the flow visualization using the test rig designed for water flow to be analogous to the air flow of the flow duct rig, and the analogy is based on Reynolds number defined with the friction velocity and the representative size of an acoustic liner. The result via particle image velocimetry represents the flow patterns causing the drag.