Numerical Analysis on Effects of Wall Structures on Bubble Groups
doi: 10.21656/1000-0887.420041
壁面结构对三维可压缩气泡群影响的数值模拟研究
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摘要:
With the volume of fluid (VOF) method for a dam-break problem, the effects of wall structures on compressible bubble groups were studied through measurement of the spatial average pressure on the wall. An obstacle was set up at the bottom of the tank, which helps create air bubbles in the collapsing water impacting on it. Three kinds of structures were set up on the left wall, namely, a cuboidal structure, an ellipsoidal structure and a conical structure. It is found that when water hits the left wall, the topology of the bubble wrapped in the water will be changed by the wall structure, which leads to the change of pressure on the wall. The example analysis shows that, the cuboidal structure has the maximum effect in reducing the average pressure amplitude on the wall among those three kinds of wall structures. Especially, a proper adjustment of the position and the size of the cuboidal structure can eliminate the oscillation of the wall pressure.
Abstract:基于流体体积(VOF)法追踪自由液面，研究了壁面结构对三维可压缩气泡群流动的影响。通过在待测壁面上设置不同形状的壁面结构（长方体、椭球体和圆锥体）并改变它们各自的几何参数（位置和长度），来研究壁面结构对壁面附近的气泡群流动的影响，该影响表现为气泡群对壁面的空间平均压力。研究发现，壁面结构对气泡群的拓扑结构的影响会造成壁面压力的变化，其中长方体壁面结构降低壁面平均压力的效果最好，且通过适当调整该结构的位置和长度，能使壁面的压力脉动现象消失。
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Key words:
- 可压缩两相流 /
- 气泡与壁面结构间耦合作用 /
- 流体体积法
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Figure 1. Geometry and mesh of the computational domain with ellipsoids, cuboids and cones: (a) ellipsoidal wall structures; (b) cuboidal wall structures; (c) conical wall structures
Figure 2. Initial configuration of the static water column (ellipsoidal wall structures)
Figure 3. Comparison between the results of the codes used in this study and the experimental data[23]
Figure 4. Comparison of the results from cases where grid numbers are 65 536, 524 388 and 1 769 472, respectively: (a) 0~5 s; (b) 0.4~1.5 s
Figure 5. The impact process of wall structures, water and bubbles: (a) initial state; (b) before generation of bubbles; (c) generation of bubbles
Figure 7. Pressure and density distributions along the sample line at 0.5 s: (a) the sample line (white); (b) the pressure along the sample line; (c) the density along the sample line
Figure 8. Pressure and density distributions along the sample line at 0.57 s: (a) the sample line (white); (b) the pressure along the sample line;(c) the density along the sample line
Figure 9. Wall pressure evolutions: (a) the cases with ellipsoid height Lz = 0.2~0.8 m; (b) the case with Lz = 0.4 m and the no-ellipsoid case
Figure 10. Wall pressure evolutions and flow fields in the cases with ellipsoid height Lz = 0.1~0.3 m
Figure 11. Wall pressure evolutions and flow fields in the cases with ellipsoid height Lz = 0.5~0.7 m
Figure 13. The flow field in the ellipsoid wall structure case with ellipsoid height Ls = 0.4 m
Figure 18. The flow field in the cuboidal wall structure cases with cuboid heights Lz = 0.2 m and Ly = 0.5 m: (a) the flow profile; (b) the bubble contour
Table 1. Boundary conditions of each variable
wall boundary condition outlet boundary condition liquid phase fractional zero gradient inlet outlet pressure buoyant pressure total pressure velocity fixed value pressure inlet outlet velocity 
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