关键词: 茶树, 雾滴, 虚拟叶片, 数值模拟, 流场特性

Abstract: Leaf surface characteristics are an important variable for the deposition and retention of pesticide droplets on the surface of tea leaves. Incorporating the surface of the leaves into the study of droplet deposition characteristics is of great significance for a comprehensive understanding of the impact mechanism and movement rules of droplets on the surface of tea leaves. In the spray scene, the surface of the tea leaves is impacted by droplets in different directions. In order to explore the influence of impact angle, leaf curvature, and gravity on the droplet flow field and to visually display the flow field characteristics of the droplets during the movement, the tea tree leaves were reconstructed from the point cloud, and the droplet impact simulation was performed on the virtual leaf surface. Numerical simulation of drop impact was verified by theoretical models and laboratory experiments. Numerical simulation results showed that the smaller the impact angle was, the tangential velocity component of the droplet along the direction of movement on the leaf surface was greater than the normal velocity component, and the greater the difference between the two. When the droplet impacted obliquely, there was a slip phenomenon. The smaller the impact angle, the greater the droplet slip distance. Due to the slippage of the droplets, it was easy to cause the droplets to slip off the leaf, so it was recommended to use a 90° impact angle when spraying. When small and medium droplets with a particle size of 100-400 μm impacted the leaf surface, the initial spreading and contraction were mainly affected by the inertial force and surface tension. With the energy consumption, the speed decreased, and the curvature of the leaf had a greater influence on the droplet movement, which together with the droplet inertia and surface tension determined the stable form of the droplet. When the small and medium droplets were in contact with other droplets, coalescence would occur. Because the size of the small and medium droplets was small, the influence of gravity on the droplets was relatively small. For large droplets above 400 μm, the initial spreading and retraction were mainly driven by inertial force, surface tension and leaf curvature. As the droplets gradually condensed and became larger, the influence of gravity on the movement of droplets gradually became dominant. The verification found that the flow field characteristics of the droplets on the virtual leaves of tea trees were consistent with the theoretical analysis and experimental rules of the droplets impacting the surface of the tea leaves, and this simulation method was feasible. This research provided a new way to further improve the impact mechanism and motion law of droplets on the leaf.

Key words: tea tree, droplets, virtual leaf, numerical simulation, flow field characteristics