Evolutionary Characteristics of Jet Vortex Structure in Grid Flocculation Tank
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摘要:
为探究网格絮凝池涡流中场射流涡结构的演化特征，采用大涡模拟（LES）对网格絮凝池涡流场进行瞬态模拟，从二维和三维的角度对网格涡流场进行研究. 结果表明：水流经过网格板后，立即在网孔后形成射流涡流场；在射流与背景流体间的剪切、卷吸和掺混作用下，格挡后方区域形成回流涡旋区，边壁处生成不断发展的涡环结构；这些涡环结构导致射流前端发生不同程度的变形与偏移，并抑其向前推进；涡旋主要分布在射流的边界层，其中射流前沿的涡结构聚集变化最快，其面积和强度最大，而靠近边壁处的涡结构强度变化最为显著，每一股射流的涡结构均关于射流轴心线呈镜像对称；此外，三维涡结构的前端形似一冠状结构，随射流向前发展，冠状结构会不断延伸、膨胀、变大，并最终离散和脱落；各时刻的涡结构分布与变化均表现出关于流场平分线的镜像对称性，且流场形态变化过程呈现出从边壁向流场中心发展的趋势.
Abstract:The large eddy simulation (LES) was employed to make a transient simulation of the flow field within the grid flocculation tank to investigate the evolutionary characteristics of the jet vortex flow structure of flow field within the grid flocculation tank. The grid flow field was analyzed from both two-dimensional and three-dimensional perspectives. The results indicate that a jet vortex flow field is formed immediately behind mesh holes as fluid flows through a grid plate. Due to shear, entrainment, and mixing between jet and background fluid, a backflow vortex zone is formed in the region behind the grid, accompanied by a continuously developing vortex ring structure along the side wall. The vortex ring structure causes varying degrees of deformation and displacement at the front of the jet, while also suppressing its forward movement. The vortices are mainly located within the boundary layer of the jet, with rapid changes occurring in their structure at its forefront. This area exhibits both maximum size and intensity. The most significant variations in vortex structure intensity are observed near the side wall, where the vortex structures of each jet display mirror symmetry about its axis. Additionally, the front of the three-dimensional vortex structure resembles a coronal formation. As the jet develops forward, the coronal structure will extend and swell to become larger and then will eventually discrete and detach. The distribution of vortex structure at each moment exhibits mirror symmetry with respect to the bisector of the flow field, while the variation process of the flow field morphology demonstrates a trend from the side wall towards the center of the flow field.
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图 2 特征截面及特征线位置示意
Figure 2. Schematic diagrams of characteristic cross-sections and characteristic lines
图 3 PIV与LES测量射流中心截面速度矢量图对比
Figure 3. Comparison of PIV and LES measurements of velocity vector graphics on center cross-section of jet
图 4 特征截面上不同时刻的速度矢量图
Figure 4. Velocity vector graphics at different moments on characteristic cross-sections
图 6 特征截面上不同时刻的涡旋分布云图
Figure 6. Cloud atlases of vortex distributions at different moments on characteristic cross-sections
图 7 特征截面上不同时刻射流涡流场
Figure 7. Jet vortex flow fields at different moments on characteristic cross-sections
图 10 边壁到流场中心三维射流涡结构的变化情况
Figure 10. Variation of 3D jet vortex structure from side wall to center of flow filed
表 1 网格板尺寸参数
Table 1. Size parameters of
mm 编号 网格板长 × 宽 网孔边长 格挡宽度 网格板厚度 1 200×160 8 4 5 2 200×160 8 6 5 3 200×160 8 8 5 4 200×160 8 10 5 5 200×160 8 12 5 
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