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针对旋流数为0.25,0.45和0.79三种工况下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尺度的湍流模型,研究旋流强度对钝体回流区、涡旋破碎和进动特征的影响.模拟结果与实验结果符合得较好.模拟结果表明:3个旋流数下钝体回流区的大小没有明显改变,轴向长度都约为20mm.Q准则用来显示涡旋结构,结果表明螺旋涡产生于旋流剪切层的Kelvin-Helmholtz不稳定性;增大旋流强度,涡旋破碎发生的位置向上游移动.功率谱密度(PSD)表明流场出现进动特征,进动运动沿流向逐渐衰减;旋流数为0.45和0.79时,钝体回流区末端出现进动特征;3个旋流数下,进动频率都约为78Hz.
A large eddy simulation (LES) was carried out for the cold flow field of a stratified swirl burner with a central bluff body under the three rotational flow regimes of 0.25, 0.45 and 0.79. The dynamic Smagorinsky eddy viscosity model was selected as the sub-lattice Scale turbulence model to study the influence of swirling intensity on bluff body backwash area, vortex breaking and precession characteristics.The simulation results are in good agreement with the experimental results.The simulation results show that: The size did not change significantly, the axial length is about 20mm.Q criterion is used to show the vortex structure, the results show that the spiral vortex is generated in the swirling shear layer Kelvin-Helmholtz instability; increase the swirling intensity, vortex broken (PSD) indicates that precession features appear in the flow field and the precession motion gradually attenuates along the flow direction. When the swirl number is 0.45 and 0.79, the precession features appear at the end of the bluff body reflow zone. Three Swirl number, precession frequency is about 78Hz.