Aeroacoustic Performance of Multiple Complaint Panel Liner in Grazing Duct Flow

Broadband noise mitigation in flow ducts remains a crucial research topic, especially in the low-frequency regime where conventional liner technologies such as dissipative liners, micro-perforated panels, and Helmholtz resonators are ineffective. To address this, we investigate a novel approach using multiple complaint units, which are elastic panels backed by air-filled cavities, arranged along the duct walls. These compliant units, when properly tuned, leverage fluid-structure interactions to create low-frequency stopbands. By tuning the resonant frequency of each unit to introduce a spatial resonant frequency gradient, we create overlapping stopbands that enhance low-frequency sound suppression. In this study, we utilize the perturbation evolution method. First, a steady base flow is obtained by solving the normalized compressible Navier–Stokes equations in a two-dimensional duct flow. A weak broadband disturbance is then introduced, comprising uniform incremental frequencies with random phase angles. This forcing simulates a realistic aeroacoustic duct flow environment. In parametric analysis, we compare two compliant liner configurations: (1) compliant liner system with uniform resonance distribution and (2) compliant liner system with increasing resonance distribution along the streamwise direction. The study results confirmed that even the compliant system with uniform resonance distribution yields broadband noise reduction with a noticeable wide stopband in the low-frequency regime. More importantly, the compliance system with increasing resonance distribution further broadens these stopbands, achieving enhanced noise attenuation and greater overall transmission loss than the uniform resonance compliant system. Furthermore, we analyze the underlying aeroacoustic mechanisms by examining acoustic pressure spectra, panel vibration, and reflection/transmission coefficients. These findings show that strategically distributing fluid-loaded resonant frequencies in multi-compliant unit arrangements can significantly improve broadband noise suppression, offering promising directions for next-generation aeroacoustic liners in demanding low-frequency environments.