Flow Investigation and Acoustic Measurements of an Unconfined Turbulent Premixed Jet Flame
Flow Investigation and Acoustic Measurements of an Unconfined Turbulent Premixed Jet Flame
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无侧限湍流预混射流火焰的流动研究和声学测量
DOI：
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发表时间：
2013
期刊：
影响因子：
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通讯作者：
H. Bockhorn
中科院分区：
文献类型：
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作者：
H. Nawroth;C. Paschereit;Feichi Zhang;P. Habisreuther;H. Bockhorn
利用大涡模拟（LES）和直接数值模拟（DNS），以及光学（OH*化学发光）、声学（麦克风）和激光光学测量技术（粒子图像测速）的实验手段，研究了从无约束预混燃烧器中发出的湍流射流。通过实验、LES和DNS得到的结果进行了比较，结果一致。为了分析网格细化对分辨火焰特性和声辐射的影响，采用了不同分辨率的计算网格。由于所考虑的流动情况下存在较大的相干流动运动，由于过度预测扩散，用LES计算的火焰长度被低估。另一方面，DNS显示出与实验相似的OH*强度分布，因此，DNS可以准确地预测火焰长度。对于非反应流，发射的噪声频谱具有音调形状，峰值位于燃烧器共振频率处，而对于反应流，发射的噪声频谱变为宽带噪声，并且通常振幅升高。此外，研究表明，雷诺数、预热温度的增加或当量比接近化学计量比的降低会产生更多的噪声。后者表明直接燃烧噪声与湍流波动与火焰锋面的相互作用有关。当使用更接近化学计量比的当量比时，预期反应区更薄，火焰与湍流之间的内在相互作用更明显。
A turbulent jet emanating from an unconfined, premixed burner is investigated by using large eddy simulation (LES) and direct numerical simulation (DNS) as well as experimentally by means of optical (OH* chemiluminescence), acoustic (microphone), and laser-optical measurement techniques (Particle Image Velocimetry). Comparison of the results obtained through experiments, LES, and DNS indicate a reasonable agreement. In order to analyze the impact of mesh refinement on the resolved flame properties and acoustic radiations, computational grids with varying resolutions are used for the LES. As large coherent flow motion exists in the considered flow case, due to an over-predicted diffusion the flame length calculated with LES is underestimated. On the other hand, DNS exhibits a similar intensity distribution for OH* as the experiment and, hence, the flame length is predicted accurately by DNS. The emitted noise spectrum has a tonal shape with peaks at the burner’s resonance frequency for the non-reacting flow which changes to broadband noise and, in general, is raised in amplitude for reacting flows. In addition, it is shown that an increase in Reynolds number, preheat temperature, or a decrease in equivalence ratio close to stoichiometric ratios yields more noise being emanated from the burner. The latter indicates the fact that direct combustion noise is linked to interactions of turbulent fluctuations with the flame front. When using an equivalence ratio closer to stoichiometric ratio, a thinner reaction zone is expected and the intrinsic interaction between the flame and turbulent flow is more pronounced.