Thermoacoustic instability, also known as combustion instability, arises due to a two-way coupling between acoustic waves and unsteady heat release rate. The mechanism by which this occurs varies. A simple example would be a perturbed flame exhibiting unsteady heat release rate; this generates acoustic waves which propagate within the combustor, partially reflecting from boundaries to arrive back at the flame, further perturbing it. This sets up a cycle with the potential for successively increasing amplitudes. In practice, the mechanisms are more complex, and often involve advective flow disturbances, which are transported at the local fluid velocity rather than propagating at the speed of sound relative to the flow, as is the case for acoustic waves. Advective disturbances include temperature, entropy, vortical, hydrodynamic, equivalence ratio and compositional variations. For example, flame unsteadiness may generate temperature (entropy) perturbations as well as acoustic waves, which when accelerated leads to a further source of acoustic waves.^1,2 Furthermore, acoustic waves arriving back at the flame do not perturb the flame directly; rather, they excite hydrodynamic disturbances, which the flame subsequently responds to.³

中文翻译：

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燃烧室热声中的正向干扰

由于声波与不稳定的放热率之间存在双向耦合，因此会产生热声不稳定性（也称为燃烧不稳定性）。发生这种情况的机制各不相同。一个简单的例子是表现出不稳定的放热速率的扰动的火焰。这会产生在燃烧器内传播的声波，部分声波会从边界反射回火焰，从而进一步干扰火焰。这建立了一个具有连续增加振幅的潜力的循环。在实践中，机制更复杂，并且通常涉及对流流动扰动，对流流动扰动是以局部流体速度传输的，而不是像声波那样以相对于流的声速传播。显性干扰包括温度，熵，涡旋，流体动力，当量比和组成变化。例如，火焰不稳定可能会产生温度（熵）扰动以及声波，这在加速时会导致声波的另一个来源。^1,2此外，回到火焰的声波不会直接干扰火焰；相反，它们激发了流体动力扰动，火焰随后对其做出响应。³