Experimental investigation of water droplet deformation and the effect on its drag characteristic
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摘要: 为了探索飞机结冰研究中水滴撞击过程的变形行为发生机理和本质特征，提高结冰数值模拟的精准度，利用高速相机对水滴加速运动过程的变形现象进行了实验研究。通过研究，定义了水滴变形过程的4个典型形态，分析了水滴变形与各无量纲量的关系，拟合了水滴变形后的阻力系数曲线和计算式。研究表明：水滴在气动力作用下会发生显著的变形现象，依次历经圆球形、椭球形、半球形、圆盘形4种典型形状；水滴的纵横比随韦伯数(We)的增大呈线性减小，随邦德数(Bo)的增大呈双曲线减小；水滴变形会导致其阻力系数增大，在Re=500左右时，水滴阻力系数曲线开始脱离球形阻力系数曲线，逐渐增大至接近圆盘形阻力系数曲线，这与其变形过程一致。Abstract: In order to explore the dynamic behavior mechanism and essential feature for water droplets in the process of impact in aircraft icing, and improve the precision of numerical simulation of icing, an experimental investigation of the water droplet deformation and its effect on the drag coefficient in the acceleration was conducted by high-speed camera. Four typical forms of the droplet deformation were defined. The relationship between the deformation water and the dimensionless was also analyzed. The coefficient curve and calculation formula of the deformation droplet were also fitted. The results show that the droplet will distort under aerodynamic force, and the shape of the droplet changes from sphere, ellipsoid and saucer to disc. The aspect ratio of the water droplet linearly decreases with the increase of Weber number(We), and hyperbola decreases along with the increase of Bond number(Bo). The deformation of the water droplet will cause the increase of the drag coefficient, and the increase of the drag coefficient is consistent with the deformation process of the droplet.
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图 5 收缩段和实验段中心线气流速度
Figure 5. Velocity at the center line of contraction section and experimental section
图 6 收缩段出口气流速度计算值与实测值对比图
Figure 6. Comparison between the calculated value and the measured value of the air velocity at the outlet of the contraction section
图 10 水滴纵横比与We的关系
Figure 10. The relationship between the droplet′s aspect ratio and We
图 11 水滴纵横比与Bo的关系
Figure 11. The relationship between the droplet′s aspect ratio and Bo
图 12 水滴纵横比与Sn的关系
Figure 12. The relationship between the droplet′s aspect ratio and Sn
图 13 水滴纵横比的实验测量值与计算值对比
Figure 13. Comparison of the measured results and calculated values of the droplet′s aspect ratio
图 15 水滴阻力系数与圆球形、圆盘形阻力系数对比
Figure 15. Comparison of the drag coefficient among the droplets, spheres and disks
表 1 不同转速下收缩段入口与出口气流速度
Table 1. The air velocity at the inlet and outlet of the contraction section at different rotating speeds
Case n/(r·min-1) vin/(m·s-1) vout/(m·s-1) Case1-1 1100 3.47 13.90 Case1-2 1400 4.28 17.70 Case1-3 1700 5.36 21.70 Case1-4 2000 6.31 25.40 Case1-5 2300 7.17 29.40 Case1-6 2600 8.13 33.40 Case1-7 2800 8.84 35.90 
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