Performance evaluation of acoustic liners combined with Fine-Perforated-Film and visualization test of acoustic liner models

Abstract

It is known that the sound absorption performance of resonant type acoustic liners is affected by glazing flow, which interferes with the motion of fluid particles. In order to prevent the effects of glazing flow, we propose new design concepts, which apply with a special thin film called Fine-Perforated-Film (FPF) to the surface of the acoustic liners. We made two types of liners. Typical resonant type acoustic liners are “Baseline” which has round holes and “V-Slit” which has slit holes. New resonant type acoustic liners have a gap fixed between the FPF and “Baseline” liner surface. Each liner was tested using the flow duct rig of Japan aerospace exploration agency (JAXA). From the data obtained, the sound absorption coefficient Δ and the drag coefficient were calculated. The results show that the drag coefficient can be reduced without changing the sound absorption coefficient by changing the hole shape of the FPF. It is suggested that small hole size of FPF reduces the peak value of the sound absorption coefficient and the drag coefficient. These results show that acoustic liners combined with FPF can be superior to conventional acoustic liners in both acoustic and aerodynamic performance. To find the mechanism of drag reduction due to hole shape change, we performed visualization tests using PIV on acoustic liner models. It was found that shortening the length of the hole in the flow direction suppresses the flow into and out of the cavity and reduces the occurrence of turbulence.