Flow Inhomogeneities in a Realistic Aeronautical Gas-Turbine Combustor: Formation, Evolution, and Indirect Noise
Flow Inhomogeneities in a Realistic Aeronautical Gas-Turbine Combustor: Formation, Evolution, and Indirect Noise
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DOI：
10.1115/1.4040810
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发表时间：
2019-01-01
影响因子：
1.5
通讯作者：
Zedda, Marco
中科院分区：
文献类型：
--
作者：
Giusti, Andrea;Magri, Luca;Zedda, Marco
燃烧不均匀加速产生的间接噪声是航空发动机设计中的一个重要方面，因为它对飞机排放的整体噪声产生影响，并可能导致燃烧不稳定。本文对一种实际的浓淡燃烧室进行了数值模拟，目的是定量分析喷管导叶内流动不均匀的形成和演化，并确定间接燃烧噪声的大小。在这项工作中，既计算了熵，又计算了成分噪声。基于大涡模拟(LES)方法和条件矩闭合(CMC)燃烧模型，对燃烧室进行了高保真数值模拟。不同气流对流动不均匀形成的贡献被固定下来，并用七个专用的被动标量进行分离。然后，LES-CMC结果被用来确定提供给NGV气动声学模型的声源，该模型输出由熵和成分不均匀产生的噪声。结果表明，燃烧室出口温度和成分的波动是不可忽略的。燃烧不均匀既源于有限速率的化学效应，也源于不完全混合。特别强调了掺混稀释剂和内衬气流对燃烧室出口燃烧不均匀程度的影响。确定了对间接噪声贡献最大的物种，并计算了实际NGV的传递函数。噪声水平表明，温度波动产生的间接噪声大于成分不均匀产生的间接噪声，尽管后者不可忽略，预计在超音速喷管中会变得更大。结果还表明，局部火焰结构的较小波动会导致喷嘴传递函数的显著变化，其增益随马赫数的增加而增大。这突出了由CMC执行的局部火焰结构的在线解的必要性，以准确地预测组成噪声的水平。这项研究为实际航空燃气轮机间接燃烧噪声源的识别、分离和计算提供了新的可能性。
Indirect noise generated by the acceleration of combustion inhomogeneities is an important aspect in the design of aero-engines because of its impact on the overall noise emitted by an aircraft and the possible contribution to combustion instabilities. In this study, a realistic rich-quench-lean (RQL) combustor is numerically investigated, with the objective of quantitatively analyzing the formation and evolution of flow inhomogeneities and determining the level of indirect combustion noise in the nozzle guide vane (NGV). Both entropy and compositional noise are calculated in this work. A high-fidelity numerical simulation of the combustion chamber, based on the large-eddy simulation (LES) approach with the conditional moment closure (CMC) combustion model, is performed. The contributions of the different air streams to the formation of flow inhomogeneities are pinned down and separated with seven dedicated passive scalars. LES-CMC results are then used to determine the acoustic sources to feed an NGV aeroacoustic model, which outputs the noise generated by entropy and compositional inhomogeneities. Results show that non-negligible fluctuations of temperature and composition reach the combustor's exit. Combustion inhomogeneities originate both from finite-rate chemistry effects and incomplete mixing. In particular, the role of mixing with dilution and liner air flows on the level of combustion inhomogeneities at the combustor's exit is highlighted. The species that most contribute to indirect noise are identified and the transfer functions of a realistic NGV are computed. The noise level indicates that indirect noise generated by temperature fluctuations is larger than the indirect noise generated by compositional inhomogeneities, although the latter is not negligible and is expected to become louder in supersonic nozzles. It is also shown that relatively small fluctuations of the local flame structure can lead to significant variations of the nozzle transfer function, whose gain increases with the Mach number. This highlights the necessity of an on-line solution of the local flame structure, which is performed in this paper by CMC, for an accurate prediction of the level of compositional noise. This study opens new possibilities for the identification, separation, and calculation of the sources of indirect combustion noise in realistic aeronautical gas turbines.