Identification of flame transfer functions in the presence of intrinsic thermoacoustic feedback and noise
Identification of flame transfer functions in the presence of intrinsic thermoacoustic feedback and noise
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DOI：
10.1080/13647830.2018.1443517
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发表时间：
2018-01-01
影响因子：
1.3
通讯作者：
Polifke, Wolfgang
中科院分区：
文献类型：
--
作者：
Jaensch, Stefan;Merk, Malte;Polifke, Wolfgang
大涡模拟/系统识别（LES/SI）方法是一种从湍流反应流的大涡模拟中推导火焰传递函数（FTF）的通用、高效的数值方法。该方法可以概括如下：用宽带激励信号强制模拟火焰。通过SI技术对参考速度和整体热释放率的波动进行后处理，以估计火焰动力学的低阶模型。从低阶模型可以很容易地推导出FTF。在航空声学和热声学中最常用的SI方法是Wiener-Hopf反演（WHI）。众所周知，这种方法在有反馈的情况下会产生有偏差的估计，因此假设需要非反射边界条件才能使用LES/SI方法产生准确的结果。最近的研究表明，FTF是所谓的固有热声（ITA）反馈回路的一部分。因此，从可压缩LES中识别FTF始终是一个闭环问题，因此人们应该期望WHI会产生有偏差的结果。然而，一些研究证明WHI结果与验证数据比较有利。为了解决这一明显的矛盾，对各种识别方法进行了比较，包括为闭环识别设计的模型。与理论一致，我们证明了WHI给出的估计不收敛于实际的FTF。幸运的是，如果可以设置激励幅值，使信噪比大，但又不至于大到触发非线性火焰动力学，则产生的误差很小。此外，我们得出结论，非反射边界条件不是应用LES/SI方法所必需的。
The Large Eddy Simulation/System Identification (LES/SI) approach is a general and efficient numerical method for deducing a Flame Transfer Function (FTF) from the LES of turbulent reacting flow. The method may be summarised as follows: a simulated flame is forced with a broadband excitation signal. The resulting fluctuations of the reference velocity and of the global heat release rate are post-processed via SI techniques in order to estimate a low-order model of the flame dynamics. The FTF is readily deduced from the low-order model. The SI method most frequently applied in aero- and thermo-acoustics has been Wiener-Hopf Inversion (WHI). This method is known to yield biased estimates in situations with feedback, thus it was assumed that non-reflective boundary conditions are required to generate accurate results with the LES/SI approach. Recent research has shown that the FTF is part of the so-called Intrinsic ThermoAcoustic (ITA) feedback loop. Hence, identifying an FTF from a compressible LES is always a closed-loop problem, and consequently one should expect that the WHI would yield biased results. However, several studies proved that WHI results compare favourably with validation data. To resolve this apparent contradiction, a variety of identification methods are compared against each other, including models designed for closed-loop identification. In agreement with theory, we show that the estimate given by WHI does not converge to the actual FTF. Fortunately, the error made is small if excitation amplitudes can be set such that the signal-to-noise ratio is large, but not large enough to trigger nonlinear flame dynamics. Furthermore, we conclude that non-reflective boundary conditions are not essentially necessary to apply the LES/SI approach.