Numerical study on liquid jet breakup characteristics of rectangular nozzles in crossflow
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摘要:
通过数值模拟研究了矩形喷嘴在横向流场中的液体射流。着重分析了喷嘴的纵横比对液柱初次破碎过程中破碎行为及变形特征的影响。纵横比的范围为1～8。结果表明：在较低风速下，表面破碎几乎不受矩形喷嘴纵横比的影响，柱破碎模式由袋状破碎逐渐向着“两条纹一膜”（two-streak-one-membrane）结构转变。在较高风速下，表面破碎较为强烈。随着纵横比增加，表面破碎先减弱后增强，柱破碎模式由“两条纹一膜”（two-streak-one-membrane）结构向着“三条纹两膜”（three-streak-two-membrane）结构转变。随着射流的延伸，液柱宽度逐渐增加。矩形喷嘴的纵横比越大，表面张力越大，横流对液柱变形的促进作用越弱，液柱宽度增加的趋势也就越缓。液柱厚度的变化不仅与喷嘴纵横比有关，还受到射流过程中柱破碎模式的影响。此外，随着风速的增加，矩形喷嘴的纵横比对表面破碎和柱破碎起始点的影响逐渐减弱。
Abstract:Liquid jet in crossflow of rectangular nozzle was investigated by numerical simulation. The influences of the aspect ratio of nozzles on the breakup behavior and deformation characteristics of liquid column in the primary breakup were emphatically analyzed. The aspect ratio ranged from 1 to 8. The results showed that at low velocity of crossflow, the surface breakup was almost unaffected by the aspect ratio of rectangular nozzles, and the column breakup mode gradually changed from bag breakup to “two-streak-one-membrane” structure. At higher velocity, surface breakup was more intense. With the increase of aspect ratio, the surface breakup first weakened and then strengthened, and the column breakup mode changed from “two-streak-one-membrane” structure to “three-streak-two-membrane” structure. With the extension of liquid jet, the width of liquid column increased gradually. The larger aspect ratio of rectangular nozzles indicated the greater surface tension, and the weaker promoting influence of crossflow on the deformation of liquid column. Thus, the trend of increasing the width of liquid column was slower. The change of liquid column thickness was not only related to the aspect ratio of nozzles, but also affected by column breakup mode in the liquid jet process. In addition, with the increase of velocity of crossflow, the influence of aspect ratio on the onset of surface breakup and column breakup gradually decreased.
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Key words:
- rectangular nozzle /
- aspect ratio /
- liquid jet in crossflow /
- surface breakup /
- column breakup
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图 4 不同网格参数下迎风轨迹的比较
Figure 4. Comparison of the windward trajectory with different mesh parameters
图 11 表面破碎和柱状破碎起始点示意图
Figure 11. Schematic of onset of surface breakup and column breakup
图 14 不同射流高度下液柱截面形状
Figure 14. Cross section shape of liquid column at different penetration height
表 1 喷嘴的几何参数
Table 1. Geometrical parameters of nozzles
L/mm W/mm R Dh/mm An/mm2 0.300 0.300 1 0.300 0.09 0.212 0.424 2 0.283 0.150 0.600 4 0.240 0.122 0.735 6 0.210 0.106 0.849 8 0.189 
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表 2 物性参数及边界条件
Table 2. Physical parameters and boundary conditions
参数 数值 ρl/（kg/m3） 998 ρg/（kg/m3） 1.2 ul/（m/s） 10 ug/（m/s） 40, 60, 80 σl/（N/m） 0.072 pout/Pa 0
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表 3 网格参数
Table 3. Mesh parameters
网格序列
编号初始网格
尺寸/mm自适应
加密等级加密后网格
尺寸/μmM1 0.10 1 50.00 M2 0.10 2 25.00 M3 0.10 3 12.50 M4 0.08 3 10.00
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