风送喷雾农药雾滴在果树冠层中穿透机理研究

The canopy of fruit tree with it's unique tridimensional features that makes pesticide droplets can't to deposit and distribute uniformly in canopy. The pests and disease in the centre of fruit tree canopy can't be controlled thoroughly, that lead more and more pesticide have to be spayed again and again, which causing most problems such as excessive pesticide residues in fruit, environmental pollution, and so on. Therefore, this project mainly study on the influence of fruit tree canopy characteristics on pesticide droplet penetration, spread and deposition, under air-assisted spray conditions. The spindle-shaped and small fun-shaped pear tree canopy will be as the representative target, and a 3-D computational fluid dynamics (CFD) turbulence model of airflow from a air-assisted orchard sprayer and a CFD model of the canopy will be developed to model air flow and droplets penetrating and transporting in canopy. Using the computational fluid dynamics (CFD),uneven porous medium theory, and the κ-ε two-equation turbulence model with source/sink terms, to simulate the pear tree canopy flows, and to reveal the motion of airflow carrying droplets in canopy. And then, the structure of target canopy, the nature of turbulent airflow of the sprayers, the scope of droplet size, and spraying technical parameters will be studied thoroughly, to find the most effective treatment for air-assisted spray in orchard that the factors above are well matched to the target tree canopy, and to establish the pesticide applied simulation model finally. Further more, a theoretical basis will be provided for the later research about precise and variable spray technology based on the canopy structure .

果树以其特有的立体冠层特性使得农药雾滴在冠层中无法均匀沉积，冠层内病虫害的防治不彻底迫使农药大容量多次数喷洒，造成果品农药残留超标、环境污染等问题。因此本项目以纺锤形与小冠开心形梨树冠层为靶标，应用流体动力学（CFD）理论，以κ-ε两方程湍流模型为基础，采用不均匀多孔介质理论，在标准模型中κ方程和ε方程中添加源项，建立一套三维树冠流计算模型，揭示风送气流携带农药雾滴在梨树冠层中穿透机理。研究梨树冠层叶面积密度分布、雾滴尺寸范围、风送强度、施药技术参数等变化对梨树冠层内气流与雾滴运行轨迹的影响规律，构建果树仿真施药模型，确定纺锤形与小冠开心形梨树冠层特征与农药雾滴、风送流场及施药参数的最佳匹配关系，增加雾滴在梨树冠层内的沉积量和分布均匀性，构建仿真施药模型，为下一步果树的精准变量施药技术奠定理论基础。

果树的立体冠层特性使得农药雾滴无法均匀沉积，冠层内病虫害的防治不彻底迫使农药大容量多次数喷洒，造成果品与环境污染问题。本项目以纺锤形梨树冠层为靶标，研究风送气流携带农药雾滴在梨树冠层中穿透机理，确定纺锤形梨树冠层特征施药参数的最佳匹配关系，增加雾滴在梨树冠层内的沉积量和分布均匀性，具体开展了如下工作：（1）采用CFD模拟计算与实测相结合的方式，对果园风送喷雾机外部气流场三维分布进行了研究，通过调整上下导流板角度、不同风送强度、田间自然风速及风向等技术参数，形成了果园风送喷雾机外部气流场合理区域的调整方法，用于制订相关标准。（2）实测了纺锤形梨树树冠枝叶密度分布，采用激光雷达构建了果树冠层精准探测系统，以三维点云的数据直观反应了果树冠层的三维结构，为精准变量施药奠定了基础。（3）通过简化纺锤形果树树冠成四棱锥、圆锥、长方体形状，进行了风洞试验，发现果树冠层前有下降流，树冠上部为上升流，经过树冠后有下坠流，三股气流直接引起空中飘失、地面流失，以及飘失距离远近。湍流能量最大值出现在树冠顶部，随着向树冠上方的扩展，湍流能量逐渐减小；湍流能量最大值出现在距离树冠后边界5倍树高处，树冠顶部偏上方位置。 （4）结合基础理论研究内容和田间试验结果，初步确定了梨树冠层特性与农药雾滴特性、风送流场特性的最佳匹配关系，确定了依据果树冠层调整果园风送喷雾机有效气流场与雾流场区域；依据果树冠层枝叶量调整施药量和风送量最佳区间，使得果园风送喷雾机在最佳技术参数下作业，确保施药质量。. 果园精准施药是精准农业的重要组成部分，目前研究难点问题集中在了果树冠层信息准确提取与喷雾量、风送量的精量控制等方面，本项目在果树冠层三维信息的提取、CFD模拟分析、精准变量系统的研发等方面取得了初步成果，为进一步的深入研究奠定了基础，在精准施药技术领域具有较大的应用前景。