Study on the Deformation and Breakup Process of Jet Falling Film in Crossflow
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摘要: 为探究横流作用下射流降膜变形与破碎过程，基于计算流体动力学（CFD）软件进行两相数值模拟。研究发现，降膜流动惯性和初始开尔文-亥姆霍兹（K-H）不稳定波的横向发展导致降膜在流动初期发生横向断裂，从而形成若干干涸处，降膜迎风侧相比背风侧更早出现干涸处。横流作用下的降膜主要存在两种破碎模式：液膜破碎和表面破碎，其中液膜破碎是指瑞利-泰勒（R-T）不稳定波主导下降膜发生的沿流向的断裂破碎，表面破碎则是指K-H不稳定波主导下降膜迎风侧液丝和液滴的剥离。液气动量比对横流作用下射流降膜的变形与破碎过程有重要影响，当液气动量比大于13.16时，降膜以表面破碎为主；随着液气动量比的减小，降膜的表面破碎和液膜破碎同时增强，降膜破碎显著增加。射流降膜的连续流动长度和展向宽度均随液气动量比的增大而增大，降膜的偏移距离随液气动量比的增大而减小。Abstract: To investigate the deformation and breakup process of jet falling film in crossflow, a two-phase numerical simulation based on CFD software is conducted in this study. It is found that the inertia of the falling film flow and the lateral development of the initial Kelvin-Helmholtz (K-H) instability wave lead to the lateral fracture of the falling film in the initial stage of flow, resulting in the formation of several dry spots, while the dry spot occurs earlier on the windward side of the falling film than on the leeward side. The results show that there are two main breakup modes of falling film in crossflow: liquid film breakup and surface breakup. Liquid film breakup refers to the fracture and breakup along the flow direction of the falling film dominated by the Rayleigh-Taylor (R-T) unstable wave, while surface breakup refers to the peeling of liquid filaments and droplets on the windward side of the falling film dominated by the K-H unstable wave. The liquid to gas momentum ratio plays a significant role on the deformation and breakup process of jet falling film in crossflow. When the liquid to gas momentum ratio is greater than 13.16, surface breakup is the main breakup form of falling film. As the liquid to gas momentum ratio decreases, both surface breakup and liquid film breakup of the falling film increase simultaneously, leading to a significant increase of the falling film breakup. The continuous flow length and spanwise width of the jet falling film increase with the increase of the liquid to gas momentum ratio, while the offset distance of the falling film decreases with the increase of the liquid to gas momentum ratio.
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Key words:
- Jet falling film /
- Crossflow /
- Surface wave /
- Deformation and breakup /
- Liquid to gas momentum ratio
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图 3 不同网格数量下的射流降膜流动形状
Figure 3. Flow Shape of Jet Falling Film under Different Mesh Numbers
图 4 Z=−0.115 m平面上液膜厚度分布比较
Figure 4. Comparison of Liquid Film Thickness Distribution on the Plane of Z=−0.115 m
图 5 射流降膜在横流作用下的宏观流动特性
Figure 5. Macroscopic Flow Characteristics of Jet Falling Film under Cross-flow
图 7 Z=−3.588d平面降膜的流动特性
Figure 7. Flow Characteristics of Falling Film on the Plane of Z=−3.588d
图 8 流动初始阶段降膜的横向断裂过程
Figure 8. Transverse Fracture Process of Falling Film in the Initial Stage of Flow
图 9 距冲击壁面0.002 m平面及Z=−7.523d 平面处的压力云图
Figure 9. Pressure Contour at 0.002 m from the Impact Wall and at Z=−7.523d
图 11 Z=−15.741d平面处降膜的流场信息
Figure 11. Flow Field Information of Falling Film on the Plane of Z=−15.741d
图 12 迎风侧液丝的生长及破碎过程
Figure 12. Growth and Breakup Process of Liquid Filament on the Windward Side
图 13 不同液气动量比下射流降膜的变形与破碎过程
Figure 13. Deformation and Breakup Process of Jet Falling Film under Different Liquid to Gas Momentum Ratios
图 14 降膜连续流动长度随液气动量比的变化
Figure 14. Variation of Continuous Flow Length of Falling Film with Liquid to Gas Momentum Ratio
图 15 降膜迎风侧轮廓线和降膜偏移距离随液气动量比的变化
Figure 15. Variation of Windward Profile and Offset Distance of Falling Film with Liquid to Gas Momentum Ratio
图 16 降膜展向宽度随液气动量比变化
Figure 16. Variation of Falling Film Spanwise Width with Liquid to Gas Momentum Ratio
表 1 工质的物性
Table 1. Physical Properties of Working Fluids
液体密度ρl/(kg·m−3) 气体密度ρg/(kg·m−3) 液体粘度μl/(Pa·s) 气体粘度μg/(Pa·s) 表面张力系数σ/(N·m−1) 998.2 1.204 1.0×10−3 1.82×10−5 0.073 
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