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

摘要： 叶片表面特性是农药雾滴在茶树叶面沉积持留的重要变量，将叶片表面特性纳入雾滴沉积特性研究中对全面了解雾滴在茶树叶面撞击机理和运动规律具有重要意义。喷雾场景中茶树叶面受到不同方向雾滴撞击，为探究撞击角、叶片曲率及重力对雾滴流场的影响，同时直观显示运动过程中雾滴的流场特性，文中对茶树叶片进行点云重构，在虚拟叶面上进行雾滴撞击模拟，并借助理论模型和室内试验进行验证。结果表明：撞击角越小，雾滴在叶面上沿运动方向的切向速度分量越大于法向速度分量，且两者差值越大；雾滴斜撞击时，存在滑移现象，撞击角越小，雾滴滑移距离越大，因雾滴滑移易造成雾滴从叶片滑落，建议喷雾时采用90°撞击角；粒径为100~400 μm的中小雾滴撞击叶面时，其初始铺展收缩主要受惯性力及表面张力影响，随能量消耗其速度减小，叶片曲率对雾滴运动影响变大，其与雾滴惯性力及表面张力一起决定雾滴的稳定形态；当中小雾滴接触时会发生聚结，因其体积较小，重力对雾滴影响比较小；对于400 μm以上大雾滴，其初始铺展收缩主要由惯性力、表面张力和叶片曲率驱动，随雾滴逐渐凝聚变大，重力对雾滴运动的影响逐渐成主导作用。验证发现，雾滴在茶树虚拟叶片上的流场特性与雾滴撞击茶树叶面的理论和试验规律具有一致性，此模拟方法可行。本研究为完善雾滴在茶树叶片上的撞击机理及运动规律提供新的途径。

关键词: 茶树, 雾滴, 虚拟叶片, 数值模拟, 流场特性