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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20mm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。
Large-eddy simulation (LES) is performed on the cold flow field of a stratified swirl burner with a bluff body. The dynamic Smagorinsky eddy viscosity model is selected as the sub-lattice model to study the large swirling flow field when the swirl number is 0.45 Scaling structure. The simulation results show that both the internal and external spiral vortices and the precessional vortex nuclei (PVC) displayed by the instantaneous pressure isosceles are spatially orthogonal to the average velocity field flow line, indicating that both vortex structures are controlled by the Kelvin-Helmholtz Instability arises. The isosurfaces of the Q criterion show that the internal and external spiral vortexes begin to crumble about 20mm downstream. PVC originates from the downstream region of the annular swirl and annular jet shear. Power spectral density (PSD) of instantaneous circumferential velocity showed obvious characteristic peaks, indicating that PVC affected the fluid in the vicinity and made the precession feature appear. The turbulent pulsation velocity field was reconstructed by POD. The results of power spectral density under different modalities show that the large-scale structures of the first two modes have precession features. Using the pulse velocities of the first two modes, The isosurface shows the large scale vortex structure of the fluid around the PVC.