Abstract: Thermo-acoustic instability results in large amplitude oscillations in pressure and heat release.These are a potential hazard to both aero-engines and ground-based gas turbines,which operate in fuel-lean combustion.Unsteady heat release generates sound waves that can resonate with the unsteady flame dynamics.Active control can be used to suppress instability,but engineers invariably favour passive solutions with simple designs.One passive design technique involves the addition of helmholtz resonators to absorb the sound energy at a few chosen frequencies,but the resonance frequency can shift significantly with the engine working conditions.A semi-active tuning of resonator geometry may be necessary and that complicates the design.In this study,we investigate the effectiveness of an acoustic valve that relieves the sound pressure like a small opening and its performance is not strongly frequency dependent.The proposed valve may be constructed as a side-branch helmholtz resonator with flexible cavity walls that lets out part of the sound wave but not the fluid flow.Eigen-value solution demonstrates that the addition of such a valve alters the fundamental standing wave structure inside the combustion chamber,and unstable operation conditions may be eliminated for arbitrary linear flame properties provided that a valve of reasonable size can be established.

Key words: Acoustic valve;Passive control;Combustion instability;Thermo-acoustic coupling

摘要： 为了对发动机燃烧不稳定性进行被动控制,利用亥姆赫兹声学共振器原理,设计一种声学阀门,当一个管道侧面安装的亥姆赫兹共振器的空腔壁面是柔软的时候,声学阀门的性能与频率就没有很强的关系,从而实现由于热声学不稳定带来的压力和热释放导致的不稳定燃烧进行被动控制。阀门的功能是让声音通过,但它必须阻止时间平均意义上的流动。本文对带有这种装置的热声学特征根问题给出数值解。结果显示声学阀门对燃烧室内的驻波结构造成很大改变,进而可以消除不稳定的特征根模态。只要阀门具备足够的尺寸,这种效果可以在任意的线性火焰声学特性中广泛实现。

关键词: 声学阀门;被动控制;燃烧不稳定性;热声藕合