大涡模拟研究钝体有旋流流场的拟序结构
收稿日期: 2013-10-22
修回日期: 2014-01-27
网络出版日期: 2014-02-21
基金资助
国家自然科学基金（51176178）
Coherent Structures of Flow Fields in Swirling Flow Around a Bluff-body Using Large Eddy Simulation
Received date: 2013-10-22
Revised date: 2014-01-27
Online published: 2014-02-21
Supported by
National Natural Science Foundation of China (51176178)
对带有中心钝体的分层旋流燃烧器的冷态流场进行了大涡模拟（LES），选取动态Smagorinsky涡黏模型作为亚格子模型，研究旋流数为0.45时旋流场的大尺度拟序结构。模拟结果表明：瞬时压强等值面显示的内外螺旋涡及进动涡核（PVC）均与平均速度场流线在空间上呈正交关系，表明两种涡结构均由剪切层Kelvin-Helmholtz不稳定性产生。Q准则等值面显示内外螺旋涡在下游20 mm左右开始发生破碎。PVC发源于环形旋流与环形射流剪切层附近的下游区域。瞬时周向速度的功率谱密度（PSD）出现明显的特征峰，表明PVC影响附近的流体，使之出现进动特征。采用本征正交分解（POD）重构湍流脉动速度场，不同模态下功率谱密度结果表明前两个模态的大尺度结构具有进动特征，使用前两个模态的周向脉动速度等值面显示了PVC周围流体的大尺度涡旋结构。
张宏达 , 张济民 , 韩超 , 叶桃红 . 大涡模拟研究钝体有旋流流场的拟序结构[J]. 航空学报, 2014 , 35(7) : 1854 -1864 . DOI: 10.7527/S1000-6893.2013.0535
Large eddy simulation (LES) is performed to study the non-reacting flow fields of a stratified swirl burner with a central bluff-body. A dynamic Smagorinsky sub-grid scale eddy viscosity model is used. Large scale coherent structures are investigated in the flow fields with a swirling number of 0.45. The results show that the inner and outer helical vortices and precessing vortex core (PVC), displayed by the iso-surface of instantaneous pressure, are orthogonal to the streamlines of mean velocity. This fact supports the idea that the helical vortex and PVC are generated by the Kelvin-Helmholtz shear layer instability. The helical vortex structures, visualized by the iso-surface of Q-criterion, begin to break down at about 20 mm downstream of the burner exit. PVC originates from the downstream shear layer between the annular swirl and jet flow. The power spectral density (PSD) of instantaneous circumferential velocity exhibits an obvious characteristic peak which indicates that PVC leads to the precession motion of the adjacent flow fields. Fluctuating velocity fields are reconstructed using a proper orthogonal decomposition (POD) method. The PSD results of different modes indicate that large scale vortex structures of the first two modes are related to the precession motion. Large scale vortex structures around the PVC can also be clearly visualized by the iso-surfaces of circumferential velocity fluctuations in the first two modes.
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