Abstract The role that acoustic reflections from duct boundaries play in aeroengine fan flutter is theoretically investigated. To make a systematic parametric study attainable, a three-dimensional semi-analytical approach is employed. Based on the transfer element method combined with a boundary integral equation method, this approach effectively captures the acoustic coupling effect of an annular rotor undergoing incipient oscillation and a finite-length non-rigid duct in subsonic flow. For a given vibration mode, the disturbances generated both inside and outside the duct are determined by a simultaneous solution. The flutter likelihood is subsequently evaluated through the energy method. Results reveal that near the flutter boundary, the aeroelastic impact of duct boundary reflections becomes evident and critical when propagating (cut-on or weakly damped) acoustic modes exist in the flow duct. Under such condition the aerodynamic interaction between both duct openings strongly affects the sound field distribution, thus contributing to the notable installation effect on aeroelastic stability. Moreover, the flutter-driven acoustic field is also susceptible to the sound reflection effect of the partially lined duct wall. It is found that the variation of the blade aerodynamic damping with the liner impedance is markedly different when the duct end reflections come into play. Under appropriate conditions the mutual effect of the lined wall and the duct openings significantly strengthens their acoustic couplings with the ducted fan, where a reasonable estimate of aeroelastic stability can only be provided with an adequate consideration of the realistic acoustic boundary conditions for the entire duct.

中文翻译：

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风道边界声反射在风机颤振中的作用

摘要 从理论上研究了管道边界声反射在航空发动机风扇颤振中的作用。为了使系统参数研究成为可能，采用了三维半分析方法。该方法基于传递元法与边界积分方程法相结合，有效地捕捉了在亚音速流动中经历初始振荡的环形转子和有限长度的非刚性管道的声耦合效应。对于给定的振动模式，管道内外产生的扰动由同时解确定。随后通过能量方法评估颤振可能性。结果表明，在颤振边界附近，当流动管道中存在传播（截止或弱阻尼）声学模式时，管道边界反射的气动弹性影响变得明显和关键。在这种情况下，两个管道开口之间的空气动力学相互作用强烈影响声场分布，从而对气动弹性稳定性产生显着的安装效果。此外，颤振驱动的声场也容易受到部分衬里的管道壁的声音反射效应的影响。发现当导管端部反射起作用时，叶片气动阻尼随衬管阻抗的变化显着不同。在适当的条件下，内衬墙和管道开口的相互影响显着加强了它们与管道风扇的声学耦合，