Acoustic Liner Drag: Further Measurements on Novel Facesheet Perforate Geometries

Over the past several years, the NASA Langley Liner Physics Team has worked to develop methods capable of characterizing the aerodynamic drag of acoustic liners in addition to their acoustic performance. For a given liner, one can compute its resistance factor, λ, based on static pressure drop measurements. The current study details experiments in the NASA Langley Grazing Flow Impedance Tube to quantify the relative drag of several perforate-over-honeycomb liner configurations at flow speeds of Mach 0.3 and 0.5. The liner facesheets incorporate novel perforate geometries rather than the conventional, round hole designs typically used. Measurements of the resistance factor for each liner are made with and without acoustic excitation. A tonal acoustic source is used at sound pressure levels of 140 and 150 dB over a frequency range of 400 to 3000 Hz when performing acoustic measurements. Educed impedance spectra are calculated to determine the impact of variations in perforate geometry on acoustic performance and the relationship between acoustic and drag performance.