果园风送喷雾机出风口风场CFD建模与试验

doi:10.12133/j.smartag.2021.3.3.202106-SA007

摘要/Abstract

摘要：

塔式果园风送喷雾机是目前普遍使用的果园喷雾机，塔式结构易产生旋转和不规则的垂直气流，导致喷雾机出风口两侧风场分布不对称，且分布规律不易预测。为探究适用塔式果园风送喷雾机出风口风场建模方法，本研究基于喷雾机出风口风场计算流体动力学（Computational Fluid Dynamics，CFD）建模方法，提出了用户定义函数（User-Defined Function，UDF）分段式三维风速入口边界条件设置方法，并研究了湍流模型和计算域尺寸对喷雾机CFD风场模拟结果的影响特性。采用Fluent软件，建立了三种CFD模型：模型一以11个区域的平均风速作为边界条件；模型二采用UDF分段式三维风速入口作为边界条件；为进一步研究计算域尺寸对风场模拟的影响，建立了小计算域尺寸的模型三。三种模型均采用基于雷诺时均控制（Reynolds-Averaged Navier-Stokes，RANS）方程的 $k - ε$ 湍流模型和 $k - ω$ 湍流模型进行风场计算。为了验证模型的可靠性，设计了空间风场立体测量系统，实现了精确快速空间风速测量。验证结果表明，Standard $k - ε$ 、Realizable $k - ε$ 、BSL $k - ω$ 和SST $k - ω$ 湍流模型较适合风场CFD建模，其中Standard $? k - ε$ 湍流模型运算结果最优，模型决定系数R²为0.81。基于UDF分段式三维风速入口边界条件设置方法不仅提高了仿真结果的准确性（提高了5%），而且降低了计算的复杂性。在其他参数设置相同的情况下，大尺寸计算域模型的性能略优于小尺寸计算域。实际建模过程中建议根据计算机计算能力、仿真的实际要求设置合适的计算域尺寸。本研究结果可为喷雾机出风口风场CFD建模方法提供参考。

关键词: CFD, 边界条件, UDF, 湍流模型, 计算域

Abstract:

The tower-type sprayer produces swirling and irregular vertical airstream. The complex swirling results in airflow asymmetry between sides of the sprayer, and the vertical air velocity profile can be unpredictable when the rotational speed of the fan changes. The spray deposition is directly linked to the airflow pattern obtained from the sprayers. In order to study airflow field of this type of air-assisted sprayer, a CFD (Computational Fluid Dynamics) model for the tower-type sprayer was developed. A boundary condition setting method of UDF (User-Defined Function) sectional 3D air velocity was proposed. And the influences of turbulence models and the size of computational domain on CFD airflow simulation were studied. Using Fluent software, three different CFD models were established. The Model 1 took the average air velocity of 11 regions as the velocity inlet. The Model 2 used UDF segmented three-dimension air velocity line as the boundary condition. In order to further study the influence of the computational domain size on simulation, the Model 3 with a smaller computational domain was established. The turbulence model based on reynolds-averaged navier-stokes (RANS) control equation was used to calculate the airflow field in all models. In order to verify the reliability of the model, a three-dimensional measurement system of airflow field was designed, which was used for accurate and fast velocity measurement. The results showed that the Standard k-ε turbulence model, Realizable k-ε turbulence model, BSL k-w turbulence model, SST k-w turbulence model were suitable, and the Standard k-ε turbulence model was the best one. The CFD boundary condition setting method of UDF sectional three-dimension air velocity could improve the accuracy of simulation, and reduce the calculation complexity. With the same settings of other parameters, the performance of the CFD model with larger scale calculation domain was slightly better than that with smaller computational domain. The size of computational domain should be set to the appropriate extent, considering the calculation capacity and practical requirements of modelling. The research results could provide an important reference for CFD modeling of spray airflow field.

Key words: CFD, boundary condition, UDF, turbulence model, computational domain

中图分类号:

S224.3

翟长远, 张燕妮, 窦汉杰, 王秀, 陈立平. 果园风送喷雾机出风口风场CFD建模与试验[J]. 智慧农业(中英文), 2021, 3(3): 70-81.

ZHAI Changyuan, ZHANG Yanni, DOU Hanjie, WANG Xiu, CHEN Liping. CFD Modeling and Experiment of Airflow at the Air Outlet of Orchard Air-Assisted Sprayer[J]. Smart Agriculture, 2021, 3(3): 70-81.

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