Effect of Back Cavity Configuration on Performance of Elastic Panel Acoustic Liner with Grazing Flow

Abstract This paper reports a comprehensive numerical study of noise mitigation performance of elastic panel liner comprising an elastic panel and a cavity beneath exposed to low Mach number grazing flow. A time-domain direct aeroacoustic simulation (DAS) seamlessly coupled with panel dynamics is adopted for its least assumptions taken on duct flow unsteadiness and acoustical behaviors so that both linear and nonlinear aeroacoustic-structural interactions of the problem can be fully explored. The numerical method is well validated with theoretical and experimental works on a liner with thick cavity reported in literature. The noise mitigation of liner with various combinations of cavity depth, panel length and cavity shape, are explored and the present numerical results show that back cavity configuration plays an important role in the liner problem. A decomposition method is applied to DAS acoustic solutions for uncovering the role of aeroacoustically induced panel vibration. The nonlinear effect due to aeroacoustic-structural interaction is found to be of secondary importance. Extensive cross spectral analyses between duct aeroacoustics and panel vibration reveal that the overall liner performance is largely determined by the liner elastic panel whose aeroacoustic and vibration responses are greatly modified by the variations of back cavity acoustics of the back cavity with different shapes. Based on these understandings a new configuration with acoustic absorption materials placed on a cavity wall is proposed. Detailed analysis of its numerical results shows that the introduction of acoustic absorption effectively relieves the cavity acoustics and modifies the panel responses in such a way that an enhanced liner mitigation performance over a broadband can be achieved.