苜蓿种子收获机采集装置流场分析与结构参数优化

发布时间：2018-06-08 16:01

  本文选题：采集头 + CFD模拟　； 参考：《中国农业机械化科学研究院》2017年硕士论文

【摘要】：我国苜蓿种植面积、总产量均居世界前列,随着畜牧业的发展,苜蓿种植规模仍在持续、快速地增长,但由于苜蓿植株的特殊结构,苜蓿种子采集难度大、机械化收获技术水平不高。本文在分析苜蓿植株与种荚生长特性及物理特性的基础上,对9ZQ-2.7型苜蓿种子采集机采集头内部结构进行了理论分析和试验研究,完成了采集头CFD模拟及结构改进优化方案设计,最终实现采集头进口速度分布均匀性的提高。主要研究内容和结论如下:1、本文对苜蓿植株及种荚的物理特性与空气动力学特性进行了试验研究。利用统计学原理建立了具有北方代表性品种的紫花苜蓿的物理力学特性与空气动力学特性的基础数据,苜蓿植株的高度、种荚上部高度、种荚下部高度、种荚高度幅差、植株上部直径、植株中部直径、植株底部直径的分布结果分别为796～1184mm、741～1123 mm、490～610mm、181～559mm、1.08～1.52 mm、2.20～3.32 mm、2.46～3.58 mm,苜蓿种子与种荚的悬浮速度分别为:5.06±0.15 m/s、6.95±0.14m/s,茎秆的悬浮速度为8.26±0.15m/s,为采集头的改进提供数据支撑。2、对9ZQ-2.7型苜蓿种子采集机的工作原理及采集头的结构进行了系统研究。根据采集头的结构建立了三维CAD模型,利用前处理软件对模型进行了简化,并采用四面体单元进行了网格的划分;设置了 25个压力进口及1个压力出口,建立了k-ε 标准湍流模型,采用速度压力耦合SIMPLE算法;进口处的压力为标准大气压101325 Pa,出口处的压力为101085 Pa,来模拟采集头内气流场的分布。对仿真结果进行分析,得到原结构的进口速度由左侧区域Ⅰ往右侧区域Ⅲ逐渐减小,而在调风板处的速度出现波动;最左侧的速度能达到15.7 m/s,右侧的速度最小值为3.61 m/s,从而确定原结构的速度分布均匀性差。3、在原有结构的基础上进行了仿真分析与试验,发现进口处速度分布均匀性差。针对存在的问题对原结构进行改进,设计了 20种改进方案;对改进方案依次进行仿真分析,然后从中选择三种速度分布均匀性比较好的方案进行试验验证;对选择的三种方案试验结果进行比较分析,确定最优方案为方案12,改方案的结构为d1=198mm,d2=175 mm,α1=15°,α2=20°。
[Abstract]:With the development of animal husbandry, alfalfa planting scale is still increasing rapidly in China. However, because of the special structure of alfalfa plants, it is difficult to collect alfalfa seeds. Mechanized harvesting technology is not high. Based on the analysis of the growth characteristics and physical characteristics of alfalfa plants and pods, the internal structure of the collecting head of 9ZQ-2.7 alfalfa seed collector was analyzed theoretically and experimentally, and the CFD simulation of the collecting head and the design of structural improvement optimization scheme were completed. Finally, the velocity distribution uniformity of the inlet of the acquisition head is improved. The main contents and conclusions are as follows: 1. The physical and aerodynamic characteristics of alfalfa plants and pods were studied in this paper. Based on the principle of statistics, the basic data of physical, mechanical and aerodynamics characteristics of alfalfa with representative northern varieties were established. The height of alfalfa plant, the upper height of seed pod, the lower height of seed pod, the amplitude difference of seed pod height were obtained. The upper diameter of the plant, the diameter of the middle part of the plant, The distribution of the bottom diameters of alfalfa seeds and pods were 796 卤1184 mm / 741 1 123 mm ~ 490 ~ 610 mm ~ (-1) ~ (59) mm ~ (-1) 1.52 mm ~ 2.20 ~ 3.32 mm ~ 3.46 ~ 3.58 mm, respectively. The suspension velocity of alfalfa seeds and pods was 5.06 卤0.15 mm / s (6.95 卤0.14 m / s), respectively. The suspension velocity of stem was 8.26 卤0.15 m / s, which provided data support for the improvement of collecting head, and provided data support for 9ZQ-2.7 type alfalfa seed collector. The working principle and the structure of the collecting head are studied systematically. According to the structure of the collecting head, the 3D CAD model is established, the model is simplified by pre-processing software, the mesh is divided by tetrahedron element, 25 pressure inlet and 1 pressure outlet are set up. The k- 蔚 standard turbulence model is established, and the velocity and pressure coupled simple algorithm is used. The pressure at the inlet is 101325 Paa and the pressure at the exit is 101085 Pa. to simulate the distribution of the air flow field in the head. The simulation results show that the inlet velocity of the original structure decreases gradually from the left region I to the right region 鈪，

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