MECHANISTIC STUDY OF LASER-DRIVEN DROPLET MIGRATION
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摘要: 液滴热毛细迁移是微重力流体科学中的典型科学问题, 微重力液滴动力学研究不仅具有流体力学的理论意义, 而且具有重要的实际应用价值. 建立了二维轴对称激光驱动液滴迁移模型, 通过仿真计算研究微重力环境下激光驱动液滴迁移的过程, 研究了液滴直径、母液参数等对液滴迁移速度及行为的影响. 首先研究了母液和液滴对激光系数均较小, 液滴初始位置不同时液滴的迁移行为; 然后研究了母液对激光吸收系数较小, 液滴对激光吸收系数较大时, 不同液滴直径与母液宽度比条件下液滴的迁移行为. 仿真结果表明: 当母液和液滴对激光的吸收系数都很小时, 液滴迁移的方向主要受到液滴初始位置的影响; 当母液对激光的吸收系数较小, 液滴对激光的吸收系数较大时, 液滴会朝激光方向迁移, 液滴初始位置对迁移方向影响较小, 但液滴直径与母液宽度之比会影响液滴迁移行为. 将模拟结果与YGB理论对比, 仿真结果与理论结果趋势一致. 研究激光驱动液滴迁移的物理机制, 探索界面张力作用机理, 得到激光驱动液滴迁移的规律, 探索对液滴的驱动控制方法.Abstract: Droplet thermocapillary migration is a typical scientific problem in microgravity fluid science, and the study of microgravity droplet dynamics not only has the theoretical significance of fluid mechanics, but also has important practical value. A two-dimensional axisymmetric laser-driven droplet migration model was established. The laser-driven droplet migration process in microgravity environment is studied by simulation calculations, and the effects of droplet diameter and mother liquor parameters on droplet migration speed and behavior are investigated. Firstly, the migration of the droplets was studied when the mother liquor and the droplets have smaller laser coefficients and the initial positions of the droplets are different; then the migration of the droplets was studied the mother liquor has a smaller laser absorption coefficient and the droplets have a larger laser absorption coefficient and the ratios of the diameter to the width of the mother liquor are different. Simulation results show that when the absorption coefficients of both mother liquor and droplet for laser are small, the direction of droplet migration is mainly influenced by the initial position of the droplet. When the absorption coefficient of the mother liquor to the laser is small and the absorption coefficient of the droplet to the laser is large, the droplet will move toward the laser. The initial position of the droplet has less influence on the migration direction, but the ratio of the droplet diameter to the width of the mother liquor will affect the droplet migration behavior. By comparing with the YGB theory, the simulation results are consistent with the trend of the theoretical results. The physical mechanism of laser-driven droplet migration is studied, the mechanism of interfacial tension effect is explored, the law of laser-driven droplet migration is obtained, and the driving control method for droplets is explored.
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Key words:
- laser-driven /
- droplet /
- thermocapillary /
- microgravity
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图 4 不同时间步长下同一工况液滴界面附近母液流速及液滴速度图
Figure 4. Velocity of droplet and mother liquor around droplet interface for the same working condition at different time steps
图 5 液滴初始位置在母液上部时的流线图
Figure 5. Streamline when the initial droplet position droplet is in the upper part of the mother liquor
图 6 液滴初始位置在母液上部液滴界面附近母液流速及液滴速度图
Figure 6. Velocity of droplet and mother liquor around droplet interface when initial droplet position is in the upper part of the mother liquor
图 7 液滴初始位置在母液上部液滴界面附近压力图
Figure 7. Pressure variation around droplet interface when initial droplet position is in the upper part of the mother liquor
图 8 液滴初始位置在母液正中时的流线图
Figure 8. Streamline when the initial droplet position droplet is in the middle of the mother liquor
图 9 液滴初始位置在母液正中液滴界面附近母液流速图
Figure 9. Velocity of droplet and mother liquor around droplet interface when initial droplet position is in the middle of the mother liquor
图 10 液滴初始位置在母液正中液滴界面附近压力图
Figure 10. Pressure variation around droplet interface when initial droplet position is in the middle of the mother liquor
图 11 液滴初始位置在母液下部时的流线图
Figure 11. Streamline when the initial droplet position droplet is in the lower part of the mother liquor
图 12 液滴初始位置在母液下部液滴界面附近母液 流速及液滴速度图
Figure 12. Velocity of droplet and mother liquor around droplet interface when initial droplet position is in the lower part of the mother liquor
图 13 液滴初始位置在母液下部液滴界面附近压力
Figure 13. Pressure variation around droplet interface when initial droplet position is in the lower part of the mother liquor
图 14 液滴初始位置在母液下部时的流线图
Figure 14. Streamline when the initial droplet position droplet is in the lower part of the mother liquor
图 15 液滴初始位置在母液下部液滴界面附近母液流速及液滴速度图
Figure 15. Velocity of droplet and mother liquor around droplet interface when initial droplet position is in the lower part of the mother liquor
图 16 不同Ar时液滴球心距母液底端距离
Figure 16. Distance variation from the center of the droplet sphere to the bottom of the mother liquor with different Ar
图 17 液滴初始位置在母液下部液滴界面附近母液流速及液滴速度图
Figure 17. Velocity of droplet and mother liquor around droplet interface when initial droplet position is in the lower part of the mother liquor
图 18 不同Ar时液滴球心距母液底端距离
Figure 18. Distance variation from the center of the droplet sphere to the bottom of the mother liquor with different Ar
图 19 液滴初始位置在母液下部液滴界面附近母液流速及液滴速度图
Figure 19. Velocity of droplet and mother liquor around droplet interface when initial droplet position is in the lower part of the mother liquor
表 1 物性参数
Table 1. Physical property parameters
ν/
(µm2·s−1)ρ/
( kg·m−3)Λ/
(W·m−1·K−1)σT/
(µN·m−1·K−1)mother liquor 30.0 955 0.151 droplet 2.8 955 0.410 −86.3 
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表 2 不同直径不同温度梯度液滴迁移仿真计算速度与YGB理论迁移速度及Re, Ma对照表
Table 2. Size of droplets, simulation calculation migration velocity, YGB model velocity, Re and Ma
R/mm Г/(K·mm−1) Vmax/(mm·s−1) VYGB/(mm·s−1) Re Ma/103 2.50 0.03 0.145 2.921 0.002 0.016 2.50
1.50
2.00
2.25
2.50
3.000.12
13.30
25.00
33.33
20.00
30.000.162
4.124
11.046
14.900
13.677
13.54110.629
34.713
87.000
130.370
87.000
156.6000.009
0.344
1.150
1.939
1.438
3.1050.057
2.255
7.536
12.704
9.420
20.347
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