CFD Modeling and Experiment of Airflow at the Air Outlet of Orchard Air-Assisted Sprayer

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.

Keywords

• cfd
• boundary condition
• udf
• turbulence model
• computational domain