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摘要:
在大推力液体火箭发动机燃烧过程中，推进剂射流失稳与雾化是起始环节，会对后续蒸发与燃烧等过程产生显著影响。尽管前人做过很多研究，但对湍流射流雾化机理的认知还存在盲区。基于此通过流动拓扑理论来揭示湍流液体平面射流的雾化机理。采用直接数值模拟方法对静止空气环境下的液体平面射流雾化过程进行了高分辨率数值模拟，分析了流场中不同拓扑结构与气液界面曲率的相互影响，阐明了流动拓扑对液体平面射流雾化的影响机制。研究发现，所有流动拓扑结构都有助于产生压缩应变率和拉伸应变率，其中不稳定焦点结构(UFC)拓扑结构对流场应变率的影响最大；在流动拓扑结构影响下，液体体积分数等值面的曲率与应变呈现负相关关系。另外，UFC主要产生拉伸应变率，而其余流动拓扑结构主要产生压缩应变率。研究结果表明: 射流雾化过程主要受到UFC拓扑结构的影响，UFC会促进气液界面产生较大的拉伸应变率，进而促进片状或管状结构液体结构生成，从而引起液体射流破碎。
Abstract:In the combustion process of liquid fuels, jet instabilities and atomization are the starting points, which can have significant effects on following processes such as evaporation and combustion. There remain gaps in our under standing of the turbulent jet atomization mechanism despite the extensive prior research. This work aims to reveal the atomization mechanism of turbulent liquid planar jets through the use of flow topology. A high-resolution direct numerical simulation method is used to solve the atomization process of a liquid plane jet in a still air environment. In order to clarify the process by which flow topology affects the atomization of liquid plane jets, the interaction between various topologies in the flow field and the curvature of the gas-liquid interface is analyzed. It is found that all flow topologies contribute to the generation of compressive and extensive strain rate, among which the UFC topology has the greatest effect on the flow field strain rate; the curvature of the liquid volume fraction iso-surface shows a negative correlation with the strain rate under the influence of the flow topology. In addition, the UFC structure mainly generates extensive strain, while the remaining flow topologies mainly generate compressive strain. These results suggest that the jet atomization process is mainly influenced by the UFC topology, which facilitates a large extensive strain at the gas-liquid interface, which in turn promotes the generation of sheet or saddle structures, thus causing liquid jet fragmentation.
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Key words:
- jet atomization /
- plane jet /
- flow topology /
- curvature /
- strain rate
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图 5 第2、第3张量不变量的联合概率密度分布
Figure 5. Joint probability density function of the second and the third tensor invariance
图 7 不同时刻下应变率在Q-R平面内的条件平均分布
Figure 7. Conditional average distribution of strain rate in Q-R plane in different moments
图 8 不同等值面应变率在Q-R平面内的条件平均分布
Figure 8. Conditional average distribution of strain rate in Q-R plane on different iso-surfaces
图 9 不同等值面上的κg-κm联合概率密度分布
Figure 9. Joint probability density distribution of κg-κm on different equivalence sufales
图 10 不同时刻下整个流场的κg-κm联合概率密度分布
Figure 10. Joint probability density distribution of κg-κm for whole flow field at different moments
图 11 不同拓扑区域内的应变率概率密度分布
Figure 11. Probability density distribution of strain rate in different topological regions
图 12 不同拓扑区域内的平均曲率概率密度分布
Figure 12. Mean curvature probability density distribution in different topological regions
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