CFD Simulation of Circulating-Airflow Distribution Inside Canopy From Novel Air-Assisted Sprayer in Orchard

HIGHLIGHTS A CFD model was developed to simulate airflow movements from circulating air-assisted sprayer. The CFD model can simulate airflow distribution inside the pear canopy with good accuracy. Simulation identifies the preferred parameters for circulating air-assisted spraying. An excessive adjustment of the airflow angle resulted in the formation of an eddy. ABSTRACT. Circulating air-assisted (CAA) spraying involves a negative pressure suction (NPS) created by a fan placed over the top of a canopy to change the airflow direction twice, i.e., first from the outside of the canopy to its inside and then from the bottom up, which can increase the airflow velocity inside the canopy. However, this new pesticide application technology has not been adequately investigated. In particular, the effects of the inlet and outlet airflow parameters of CAA spraying technology on the airflow distribution inside a canopy are yet to be determined. In this study, a computational fluid dynamics (CFD) model is developed and validated to simulate the interactions between the airflow ejected by a CAA sprayer and the canopy of a fruit tree. In the computational domain, the fruit tree is considered a porous medium. The model is validated based on three fruit trees of different sizes, leaf-area densities (LAD). The root mean square error and the mean relative square error are 1.44, 1.43, 2.22 m/s, and 24.9%, 24.7%, and 36.4%, respectively. This suggests that the CFD model can predict the interactions between the airflow field generated by a CAA sprayer and the canopy of a fruit tree. The validated CFD model is employed to analyze the airflow distribution patterns inside a canopy under different combinations of inlet and outlet airflow parameters. A reasonable combination of inlet and airflow parameters is obtained for CAA spraying technology. For example, the suitable outlet airflow velocity, top NPS, and bottom outlet angle for seven-year-old crown pear trees (average height: 2.0 m; average canopy diameter: 1.2 m; average trunk height: 0.62 m; average LAD: 2.96) selected in this study from a farm in southern China are 15 m/s, 200 Pa, and 10°, respectively. The results of this study can facilitate the parametric adjustment of CAA sprayers and enhance plant protection in orchards. Keywords: Circulating air-assisted spraying, Fruit-tree canopy, Inlet and outlet airflow parameters, Simulation.