基于球体模型的苹果接触点局部处理方式研究  

Local Processing Mode of Contact Points for Apples Based on Sphere Models

作　　者：韩佳伟[1] 赵春江[2] 钱建平[2] 张翔[3] 范蓓蕾[2] 

机构地区：[1]北京工业大学计算机学院,北京100124 [2]国家农业信息化工程技术研究中心,北京100097 [3]天津科技大学电子信息与自动化学院,天津300222

出　　处：《农业机械学报》2016年第11期8-17,共10页Transactions of the Chinese Society for Agricultural Machinery

基　　金："十二五"国家科技支撑计划项目(2013BAD19B04);欧盟FP7项目(PIRSES-GA-2013-612659)

摘　　要：为实现新鲜果蔬采后预冷CFD数值模拟研究,以单个富士苹果为研究对象,构建果品近真实3D模型,在雷诺数为10~30 000的范围内对比真实果形与等直径球体壁面切应力、壁面阻力系数、边界层分离角度以及尾流回流区长度之间的不同,验证在CFD模拟研究中是否可直接利用等直径球体替代苹果真实形状。为实现果品与果品（或箱体壁面）接触点局部位置的最佳CFD建模,充分考虑果品之间局部传热性对温度变化的影响,本文以彼此接触的两果模型为研究对象,从壁面阻力系数、两果中心线上的温度模拟结果准确性角度确定4种不同的局部处理方式（缩小法、膨胀法、消平法和桥梁法）在不同雷诺数范围内各自最佳的局部处理尺寸范围。研究结果表明,在研究中可直接利用等直径苹果替代苹果真实形状,在整个雷诺数范围内两者之间的各种边界层物理量最大相对偏差在15%左右,桥梁法在4种接触点局部处理方式中模拟准确性最高,通过对比实验验证,温度模拟值与实测值具有较好的一致性,其最大均方根误差为1.514℃,平均相对误差在20%左右。CFD simulations have been widely used in the study of precooling process of fresh fruits and vegetables. This work established a quasi real three-dimensional model of Fuji apples, by comparing the wall shear stress, drag coefficient, separation angle and recirculation length of an apple with those of an equal-diameter sphere over a large Reynolds number range （10 ~ 30 000） , and whether an apple can be directly replaced by an equal-diameter sphere in the study of CFD models was verifed. Moreover, to achieve the optimal CFD model of contact points between apple and apple （or the wall of boxes） and fully consider heat transferring by contact among apples, two apples contacting with each other were studied. From the accuracy of simulation results of the drag coefficient and temperature distribution along a line from the center of an apple to the center of another apple, the optimal size range of four different ways of the contact point modifications （e. g. , reduction, expansion, smoothing, bridge） for different Reynolds number range was determined. The results showed that an apple can be replaced by an equal-diameter sphere in academic research, and the maximum relative deviation was about 15% for all the physical parameters in the whole range of Reynolds number; the accuracy of bridge methods was the best in four different ways of the contact point modifications. The predicted results were consistent with the measured results by comparing simulation results with those of experiments, and the maximum root-mean-square error and average relative error for produce temperature were 1. 514% and 21.07% , respectively.

关 键 词：苹果 冷链物流 球体模型 接触点局部处理方式 计算流体力学 数值分析 

分 类 号：U469.66[机械工程—车辆工程] S229.3[交通运输工程—载运工具运用工程]