旋流条件下复杂声模态的形成、传播与耗散研究

With the advancement of high-bypass-ratio turbofan engines, it is crucial to conduct a comprehensive investigation into the effects of swirling flows within their nacelles on acoustic propagation characteristics and the impedance design of perforated liners. Based on the linearized Euler equations, we established an eigenvalue equation to systematically analyze the acoustic propagation characteristics and acoustic transmission loss in an impedance duct under swirling flow conditions. The results show that an increase of frequency causes the acoustic wave to move away from the cut-off frequency, resulting in a reduction in acoustic transmission loss for both upstream and downstream waves. Additionally, the circumferential velocity component of the swirling flow suppresses the acoustic transmission loss of counter-propagating acoustic waves while amplifying the acoustic transmission loss of co-propagating acoustic waves. The presence of swirling flows also leads to a shift in the optimal acoustic resistance of the perforated liner; specifically, the optimal acoustic resistance decreases for modes propagating with the swirl and increases for modes propagating against it. This study elucidates the multidimensional mechanisms of swirling flows on duct acoustics, thereby providing a theoretical foundation for the design of perforated liners in advanced aero-engine nacelles.