机械-气流组合作用下水稻冠层的扰动机理及雾滴穿透和沉积特性研究

Available sprayers could hardly transport pesticide droplets to the middle and bottom parts of dense rice canopy, where suffered severe diseases and insect pests. In order to solve this problem, this project proposes a spraying method, using mechanical equipment to split the rice canopy in top part, and droplets were transported to interior part of the canopy through the clearance by airflow. This proposal based on the good application efficiency of a combined air-assisted sprayer in cotton field with mechanical splitting and air blowing functions, developed by our project group. In order to optimize the construction and parameters of the system, considering the rice canopy characteristics and dynamic turbulence process, the project studies its inner airflow and droplets field with the combination application of theoretical analysis, numerical simulation and experiment test methods. Viscoelasticity porous medium model of rice canopy were created based on mechanical dynamics characteristics obtained by the mechanical properties test, creep test and vibration test and aerodynamic characteristics obtained by the pneumatic experiment. It studied turbulence characteristics with theoretical analysis and motion analysis through high-speed photography. Taking rice canopy as an unsteady viscoelasticity porous medium, it reveals the influence of rice canopy on airflow field based on segmentation of computation domains and modification of governing equations. Based on modification of Lagrangian stochastic model and Brown motion parameters of droplets movement and introduction of the concept of droplet collection efficiency factors, the effects of canopy and air flow on the droplet motion and deposition characteristics were described. On the basis of the above, it constructs a comprehensive CFD model of airflow and droplets in paddy field in the condition of mechanical-airflow combined disturbance. The effects on droplets penetration and deposition characteristics generated by working speed, push rod position, airflow parameters and canopy characteristics were revealed. Thus a theoretical basis for the mechanical-airflow combined disturbance optimization design and work parameters adjustment has been provided to improve the efficiency of target oriented spraying and to reduce the dose of pesticide and environmental pollution.

针对现有水稻施药机雾滴难以到达病虫害严重的中下部冠层的现状，受前期开发的棉田组合风送式喷雾机“机械分行+行内风送”良好施药效果的启示，本项目提出稻田机械-气流组合扰动施药方式，推杆推开上部冠层，气流携带雾滴从缝隙内直入内部冠层。为优化系统结构和工作参数，项目采用理论分析、数值模拟和试验测试相结合的方法，考虑冠层特性及扰动过程，对其内部气流雾滴场进行研究。通过蠕变、振动和风洞试验确定其机械、空气动力学特性，建立冠层粘弹性多孔介质模型。通过理论分析和高速摄影，揭示其扰动规律。基于计算域分割和控制方程修正表达冠层对气流场的影响，基于雾滴群随机运动模型和雾滴收集效率，描述冠层和气流场对雾滴运动的影响，建立气流雾滴场综合CFD模型，揭示作业速度、推杆位置、气流参数、雾化特性和冠层特性对雾滴穿透及沉积行为的影响规律，从而为系统优化和工作参数调整提供理论依据，实现高效对靶施药，减少农药用量和环境污染。

机械-气流组合扰动是实现水稻开冠式风送施药，解决水稻中下部冠层施药难题的有效方式。但在机械-气流组合扰动下，冠层运动以及冠层、气流和雾滴之间的相互作用更加复杂，施药机的优化设计更加困难。本课题即以机械-气流组合扰动下水稻冠层的运动规律和内部气流雾滴场分布为研究对象，通过建立水稻冠层的粘弹性多孔介质模型，实现其运动规律和内部气流雾滴场分布的仿真分析，从而解析各参数对施药效果的影响规律。. 通过对不同生长时期水稻株高、叶片数、叶面积和茎秆力学特性等参数的测试和统计分析，建立了水稻植株的三维模型。多株水稻组成一簇，多簇水稻组成冠层，建立了水稻冠层的机械动力学模型。. 在不同气流扰动风速下，对不同叶面积密度水稻冠层的气流阻力系数进行了测试。结果表明：冠层密度对气流阻力系数影响较小，而气流扰动风速影响较为显著，当风速≥2.83m/s时，气流阻力系数稳定在0.51左右。. 将水稻冠层视为各向异性的粘弹性多孔介质，综合其机械动力学和空气动力学特性，建立了水稻冠层的粘弹性多孔介质模型。设置不同的推杆离地高度，对平推扰动下冠层的运动规律进行仿真分析，结果表明：推杆高度对冠层位移量（即开冠缝隙的大小）有显著影响。利用高速摄影对推杆平推扰动下水稻冠层的运动过程进行记录，提取标志点的运动轨迹，所得实际位移量与仿真结果基本一致，验证了仿真结果和仿真模型的正确性。在不同气流扰动风速下，对水稻冠层内部气流场进行CFD仿真分析，结果表明：随着向冠层内部的深入，风速逐渐衰弱，且越来越不稳定，直到气流扰动风速≥4m/s时，冠层内部气流才逐渐平稳。实际测试结果也验证了仿真结果和仿真模型的正确性。. 以上研究成果为机械-气流组合扰动施药系统的优化设计奠定了理论基础，对于解决水稻中下部冠层施药技术难题具有重要意义，并可为其他风送式施药机和机械分行/开冠类施药机的优化设计提供借鉴，对于全面提升我国植保机械的技术水平也具有重要意义。