基于DEM-CFD耦合的三七精密排种机构供种吸种数值模拟和试验研究

Panax is a unique valuable herb in Yunnan Province, cultivating acre is increasing year by year, sowing has been done by labor, the requirements of Panax seeding can't been satisfied by the existing mechanizing seed technology, precision seed-metering technology will been carried out urgently. Aiming at difficulty of achieving precision seeding by weak supplying-seed and poor flowability due to irregular shape of Panax seed, experiment and numerical simulation of supplying and sucking seed of Panax precision seed-metering device based on uniform feeding in vibration and supply seed in blowing will be carried out. On the basis of research on the particulate material characteristic and parametric design of seed-metering device, many techologies will applied comprehensively, such as discrete element, computational fluid dynamics, coupling DEM-CFD, high-speed imaging, X-ray photography, and so on. Model of forming uniform seed layer favoring supply-seed in vibration and gas-solid coupling model of supplying and sucking seed will be established by the technologies, process of supplying and sucking seed will be visually simulated by numerical simulation, movement orbit and discipline of seed in flow field will be analyzed, effect of many parameters on supplying, sucking and metering seed will be verified, parameter combinations of optimal seeding quality will be obtained. Design theory and method of Panax precision seed-metering device based on uniform feeding in vibration and supply seed in blowing will be put forward aiming at seed of poor flowability. The prototype of Panax precision seed-metering device will be designed and researched, it will provide basis and key technology for the research of precison seeding-metering in thoery field in China and Panax seeding mechanization.

三七是云南省特有的名贵中草药，种植面积逐年增大，播种全部采用人工点播，现有机械化播种技术不能满足三七精播要求，急需开展精密排种技术研究。针对三七种子流动性差形状不规则充种差，难于实现精密播种的问题，拟开展"振动均匀喂入和气吹供种"三七精密排种机构供种吸种数值模拟和试验研究。在研究种子颗粒物料性质和参数化设计排种机构的基础上，综合运用离散元法、计算流体力学、DEM-CFD耦合、高速摄像、X-射线摄影等技术方法，建立种子在振动作用下形成适宜供种的均匀种层模型和气力供种吸种气固耦合模型，数值模拟可视化仿真供种吸种过程，分析种子在流场中运动轨迹和规律，探明各参数对供种、吸种和排种的影响规律，优化得到最佳播种质量的参数组合；提出针对流动性差种子的"振动均匀喂入和气吹供种"的精密排种机构的设计理论和方法；研制三七精密排种器原型样机；为我国精密播种理论的研究及三七播种机械化提供基础和关键技术。

三七是驰名中外的名贵中药材，是400多种药物的主要成分，自古就有“止血神药”的美称。三七是云南省特色经济作物，被誉为云南农业璀璨的“明珠”，2015年三七种植面积已达70万亩。由于三七种子流动性差，精密排种器充种效果差，导致机械化精密播种难以实现。针对此现状，开展了振动气吹供种气吸滚筒式排种器以及DEM-CFD耦合数值模拟供种吸种过程的研究。.在三七种子物理特性测定方面，测定了不同含水率下的三七种子的三轴尺寸圆球度、密度、悬浮速度，并测定了不同含水率下种子与橡胶、有机玻璃、塑料、不锈钢板等材料间的休止角、内摩擦角；为排种器设计提供了依据。.在参数化设计和气固耦合两相流的数值模拟和仿真方面，利用三维设计软件参数化设计了排种器结构；采用Eulerian模型，利用EDEM软件获取时时颗粒体的位置与接触信息，将获取的信息传递到Fluent软件中，根据获取的信息模拟计算颗粒体对流场的影响情况，再将流场信息反馈到EDEM软件中，实现双向流固耦合的数值模拟和仿真；采用DEM-CFD耦合的方法模拟预测不同体积分数下三七种子悬浮速度；模拟振动气吹相结合的方法对充种性能的影响情况，结果显示在振频为105Hz，风压为2.25kPa，振动角度为45°时种群间瞬态的内摩擦力最小，充种效果最佳。.在排种器试验研究方面，以振频、振动角度、风压为因素，以播种的合格指数、重播指数以及漏播指数为目标函数，采用三因素五水平正交试验方法进行台架试验，并采用Design Expert软件进行数据分析与优化，结果显示振频、风压为极显著因素，振动角度为显著因素，优化结果为在振频为85Hz，风压为3kPa，振动角度为45°时合格指数为92.68，漏播指数为1.56，重播指数为5.76，与模拟结果一致。.该项目的科学意义在于实现了双向流固耦合的数值模拟和仿真，并将这种方法应用于振动气吹供种气吸式滚筒排种器的仿真模拟中；提出了一种振动气吹供种方法，研制了振动气吹供种气吸式滚筒排种器，优化得到了最佳参数，有效地解决了流动性差种子播种充种差的难题；并验证得到了仿真模拟结果与试验结果一致。