# Interactions between Two Deformable Droplets in Tandem Fixed in a Gas Flow Field of a Gas Well
## 3 Results and Discussion
### Interactions between Two Droplets in Tandem  
#### 3.3.1 For a Separating Space of 1.5D  
Figure 5 shows the simulation results for the two droplets in tandem with different Weber numbers and a separating spacing of 1.5D. It can be seen from Figure 5 that the deformation of the upstream droplet was similar to that of the single isolated droplet, but the deformation of the downstream droplet was obviously different from that of the single isolated droplet. Comparing Figure 5a-c, it can be found that the deformation degree of the upstream droplet increased with the Weber number. However, the downstream droplet  
Figure 4: The shape characteristics of a single droplet under different Weber numbers.  
deformed to a much lesser extent compared with the upstream droplet. The downstream droplet was gradually deform into a gyroscopic downward as the Weber number increased under the suction force of the low-pressure region behind the upstream droplet.  
Figure 5: Deformation and breakup of two droplets in tandem with different Weber numbers and a separating space between them of 1.5D.  
Comparing Figure 4d with Figure 5d, we would conclude that the critical Weber number for the breakup of the upstream droplet is 12, which is consistent with that of the single isolated droplet. However, it would be concluded from Figure 5d that the downstream droplet could deform further and break up when the breakup of the upstream droplet had finished and the flowing gas could blow on it.  
Figure 6 shows the drag coefficient of two droplets in tandem with a separating space between them of 1.5D. In order to analyze the influence of the droplet interaction on the drag coefficient, the drag coefficient of the single isolated droplet is also shown in Figure 6.  
For the upstream droplet, it can be seen from Figure 6a-d that the variations of the drag coefficient over time were similar to those of the single droplet; the drag coefficients of the upstream droplet and the isolated droplet increased as the droplet deformed, and finally stopped at a constant value of 0.55, 0.75, 0.95, and 1.0 for the Weber numbers of 1, 4, 6.8, and 12.1, respectively. The final drag coefficient of the upstream droplet increased as the Weber number increased. At beginning, the drag coefficient of the upstream droplet was smaller than that of the isolated droplet, but the difference became smaller and smaller, before its deformation reached a steady condition.  
However, for the downstream droplet, the drag coefficient was reduced sharply at beginning and then slowly decreased to a constant value of 0.05, \(-\)0.25, \(-\)0.35, and \(-\)0.42  
Figure 6: The drag coefficient of two droplets in tandem with different Weber numbers and a separating space between them of 1.5D.  
for the Weber numbers of 1, 4, 6.8, and 12.1, respectively. The final drag coefficient of the downstream droplet decreased dramatically as the Weber number increased. The difference in the drag coefficient between the upstream and the single isolated droplets became larger. With the increase of the Weber number, the upstream droplet became an ellipsoid, or pancake, which sheltered the downstream droplet from direct contact with the flowing gas, and the wake effects behind the upstream droplet increased.