Spatio-temporal aeroacoustic–structural responses of cavity-backed elastic panel liner exposed to grazing duct flow

Abstract

An in-duct device laid with acoustic liner is a popular noise control option for extensive ductworks carrying unsteady flow in various engineering applications. Besides the conventional absorptive liner, elastic panel liner backed by a cavity emerges as a promising alternative concept that has advantages in providing effective broadband reduction at low frequencies yet with significantly low fluid dynamic pressure loss. The present paper reports a numerical study of aeroacoustic–structural interaction of elastic panel liner exposed to subsonic duct boundary layer flow in time domain and explores its role in liner mitigation of plane wave broadband acoustic excitation. The aeroacoustics of the duct flow and panel dynamics are respectively modeled by the two-dimensional compressible Navier–Stokes equations that solved by the conservation element and solution element (CE/SE) method, and one-dimensional elastic panel equation that is solved with finite difference method. The interaction between aeroacoustics and panel dynamics is resolved with a monolithic coupling scheme that is well validated down to acoustic scales. Special attention is placed on the sensitivity of liner acoustic performance to duct flow Mach number (M≤0.3) and the relative directions between duct flow and acoustic excitation. Extensive cross-spectral analyses of acoustic results reveal that the transmission loss of the elastic panel liner is primarily a result of the destructive interference of the incident wave with the scattered wave as well as the dissipation of non-planar waves radiated by the panel vibration. The contribution of interference and dissipation to liner reflection and absorption are particularly pronounced at low and high frequencies respectively. In addition, the effect of flow is not strong for M≤0.1. The presence of flow with the incident wave in the flow direction mainly weakens the reflection. However, the effect of flow with incident waves against the flow largely enhances the absorption. Overall, the elastic panel liner is much more effective when the noise source radiates against the flow.