Early-stage deformation of liquid drop in shock induced high-speed flow
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摘要: 基于激波管平台和高速摄影方法对平面激波诱导高速气流中液滴的早期变形现象进行实验研究。研究发现在相近的We数或Re数下，实验参数的改变可导致液滴形态发展出现显著差异。这种差异主要体现在背风面的脊状环形突起、褶皱区以及后驻点区的凹凸形态。对刚性圆球外流的数值模拟显示，液滴变形早期形态与外流场结构和表面气动力分布之间存在鲜明的对应关系。最后采用简化理论推导出一组估测液滴早期变形的表达式。将数值模拟所得气动力数据代入计算发现：导致液滴变形的主要驱动力是液滴表面不均匀压力的挤压效应，而不是界面剪切摩擦所引起的切向流动堆积效应，前者高出后者约2个数量级；此外，采用压力作用理论计算所得液滴外形在主要变形特征和变形量级上均可与实验图像很好地吻合。Abstract: In the present study the early-stage deformation of a liquid drop in the high-speed flow induced by a planar shock wave was experimentally investigated using the shock tube facility and high-speed photography technique. It was found that the variation of the flow and drop conditions may cause significant divergences in the morphology of the drop deformation, even though such classical dominant parameters such as the Weber number or the Reynolds number are conserved. The divergences are mainly on the lee side of the drop, involving major characteristics of the circular ridges, the wrinkle band and the concave-plane convex profile of the lee side polar zone. Numerical simulations of the flow around a sphere show evident correspondence between the deformation patterns and the flow structures as well as the aerodynamic forces distributed along the sphere surface. For further evaluation and understanding of the detailed deformation features, a set of equations were deduced from hydrodynamic theories with necessary simplification. Feeding the equations with the aerodynamic data from numerical simulations, the calculation results indicate that, the main mechanism behind the deformation on the lee side of the drop is the squeezing effect of the uneven pressure distribution, rather than the accumulation effect of the surfacial flow induced by friction, with the former about two orders higher than the latter. Moreover, the drop profiles calculated following the pressure acting theory were found to agree quite well with the real drop patterns, not only in the deformation characteristics but also in the order of deformation magnitudes.
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Key words:
- drop /
- aero-breakup /
- early-stage deformation /
- high-speed photography /
- drop lee-surface
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图 3 工况A激波作用后液滴变形和破碎图像
Figure 3. Images of drop deformation and breakup subsequent to the interaction of a shock wave for Case A
图 4 工况B激波作用后液滴变形和破碎图像
Figure 4. Images of drop deformation and breakup subsequent to the interaction of a shock wave for Case B
图 5 工况C激波作用后液滴变形和破碎图像
Figure 5. Images of drop deformation and breakup subsequent to the interaction of a shock wave for Case C
图 7 工况B对应球面压力与剪切力分布
Figure 7. Pressure and friction distribution on surface of a sphere under condition of Case B
图 8 剪切力诱导表面液体堆积示意图
Figure 8. Schematic of friction induced surficial liquid accumulation
图 10 压力不均匀分布诱导液滴径向加速度
Figure 10. Radial acceleration induced by uneven pressure distribution
图 11 液滴初期变形理论计算结果与实验的比较
Figure 11. Comparison of early-stage drop deformation between theoretical calculation and experiment
表 1 实验参数
Table 1. Experiment parameters
工况 d/mm p0 /kPa Ma ug /(m·s-1) ρg /(kg·m-3) We Re/104 Oh/10-3 tf /μs tb /μs tshock/μs A 2.66 15.8 1.89 396.3 0.460 2670 1.9 2.3 6.7 312.9 4.04 B 3.76 69.1 1.37 186.2 1.312 2370 4.24 1.9 20.2 557.7 7.89 C 3.94 35.7 1.62 291.8 0.856 3990 4.1 1.9 13.5 461.4 6.99 
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