## 3 Results and Discussion
### Motion Patterns of Droplets  
In order to further understand the different dynamic behaviors of droplets on an inclined surface in the airflow, this section summarizes different motion patterns of droplets  
Figure 11: Schematic diagrams of droplets moving in different directions: (**a**) Upward; (**b**) Downward. Figure 10: Force diagram of droplets in the airflow of downward motion in the windshield. by analyzing the changes in droplet contours. The experimental results in the previous section indicate that the droplet's direction will change as airflow velocity increases. To better capture and analyze this change in droplet morphology and movement pattern in an airflow environment, this study reproduces the movement of the surface droplet through planarization, and the direction of the droplet's movement is indicated by the arrows in the picture. The changes in droplet contours at different times on a 30\({}^{\circ}\) windshield for droplets with a spherical diameter \(D\) of 3 mm, 3.5 mm, and 4 mm in air velocities U of 3-7 m/s are illustrated in Figure 12. \(t=0\) corresponds to the beginning of droplet motion. The initial state of the droplet is a spherical cap shape. As time increases, the droplet profiles begin to change. From the overall view of Figure 12, the droplet motion direction is all downward along the windshield. In the states of air velocity U of 3 m/s and 4 m/s, the influence of airflow is smaller, and the droplet still shows a tendency to accelerate downward. With the increase in droplet size, the inertia force of droplet motion is enhanced, resulting in the increasing speed of droplet motion. The deformation effects of the droplet are also more obvious, which are manifested by a larger advancing contact angle \(\theta_{adv}\) and a smaller receding contact angle \(\theta_{nc}\). When the droplets are the same size, with the increase in wind speed, the droplets slide down the inclined surface with a decreasing distance, the wetting length \(L_{d}\) decreases with the increase of the droplet height \(H\), the advancing contact angle \(\theta_{adv}\) decreases and the receding contact angle \(\theta_{nc}\) increases. However, when the wind speed is increased to 7 m/s, it can be seen from the schematic diagrams of the droplet contours that the sliding distance of the droplet decreases for the same time span. The profiles of 3 mm droplets at t = 100 ms and t = 150 ms are approximately coincident, and there is also a tendency for the profiles of 3.5 mm and 4 mm droplets to coincide. This means that, when the wind speed increases to a certain value, the movement speed of the droplets shows an increase and then decreases, and may even have a stationary tendency. To obtain the motion of droplets on the windshield at higher air speeds, Figure 13 illustrates the variation of the profiles of \(D\) = 3 mm, 3.5 mm, and 4 mm droplets at different times on a 30\({}^{\circ}\) windshield in air velocity U of 8-12 m/s. It can be seen from Figure 13 that the direction of the droplets is upwards along the inclined plane. At wind speed of 8 m/s, the 3 mm droplet accelerated to climb along the inclined surface, the droplet contours of 3.5 mm and 4 mm overlapped after climbing for a certain distance, and the velocity first increased and then decreased. With increasing air velocity, which makes the wind traction force \(F_{wind}\) dominant, the phenomenon of accelerated droplet climbing is more obvious, and the degree of droplet profile changes is more drastic. With the increase in droplet sizes, the inertia force of the droplet increases, and the increase in droplet velocity in the same time is greater. Even the rear part of the 3.5 mm and 4 mm droplets formed a \"tail\" at higher wind speeds, in which case the receding contact angle \(\theta_{nc}\) of the droplets decreased significantly and the wetting length \(L_{d}\) increased significantly.