分层旋流燃烧器冷态流场的大涡模拟

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.

Large eddy simulation of non-reacting flow fields in stratified swirl combustor

The non-reacting flow fields of the stratified swirl combustor with a central bluff-body were studied through large eddy simulation (LES) under three swirl numbers 0.25, 0.45 and 0.79. Smagorinsky eddy viscosity model with dynamic procedure was selected as the sub-grid scale turbulence model. Influence of swirl intensity on the bluff-body recirculation zone, vortex breakdown and precessing motion was investigated. The LES results showed overall good agreement with experimental data. The axial lengths of bluff-body recirculation zone approximately 20mm showed no obvious variation under three swirl numbers. Q-criterion was used to visualize vortices structures, the spiral vortices were formed as the result of the Kelvin-Helmholtz instability of swirl shear layers; the vortex breakdown occurred upstream with the increase of swirl intensity. Power spectrum density (PSD) indicates the existence of precession motion, which decays along the flow direction. And precession motion appears at the terminal of bluff-body recirculation zone under higher swirl numbers 0.45 and 0.79. The precession frequencies are approximately 78Hz under three swirl numbers.