Aerodynamics of dual facesheet acoustic liners

Abstract

This thesis presents an in-depth investigation of the consequences of adding a second facesheet on the aerodynamic performance of acoustic liners. This is done by performing pore-resolved Direct Numerical Simulations (DNS) of a channel flow at Reτ = 500. Simulations are conducted for various dual facesheet configurations, exploring different facesheet layouts and relative positions of the second facesheet. Design considerations are constrained by preserving the attenuation properties of the multiple facesheet liner, achieved by maintaining adequate spacing between the facsheet. The study examines how the presence and staggering of the second facesheet affect the pressure drop and the wall-normal velocity fluctuations, both of which correlate with the added liner drag. The simulations reveal a relationship between the staggering distance of dual facesheet liners and added drag, demonstrating that increased shifting distance of regular facesheet configurations leads to reduced added drag compared to lesser shifting distances. Furthermore, the staggering diminishes wall-normal velocity fluctuations between the facesheets, aligning with observed trends in added drag. However, the study finds that while dual facesheet configurations offer some reduction in added drag compared to conventional single facesheet designs, the extent of drag reduction is limited. The study shows that the addition of a second facesheet to the liner causes additional wall parallel permeabilities not present in a single facesheet liner influencing the flow below the wall.