Design and validation of a 2D CFD model of the airflow produced by an airblast sprayer during pesticide treatments of citrus

Abstract

During plant protection treatments using airblast sprayers, part of the chemical is lost in the atmosphere (spray drift), ground, surface water, etc., causing risks to the environment. Although there is a growing interest in quantifying these losses, field measurements are extraordinarily complex and expensive. Computational Fluid Dynamics (CFD) generates mathematical models of this phenomenon that may help to understand and quantify it. The air flow produced by the fan is affected by the tree canopies, which modify the trajectories of spray droplets. Current state of the art in CFD considers canopies as porous bodies and uses the k-epsilon turbulence model. In a first step, this work proposes and validates a two dimensional CFD model to be applied in citrus tree applications from experimental data. This new CFD model considers canopies as solid bodies. Four different geometries for the first tree are compared using three different turbulence models: k-epsilon, SST k-omega and Reynolds Stress Model. Air velocities measured in front of a canopy in a previous field test are introduced as boundary conditions. We used the experimental data to adjust the model and select the geometry and the turbulence model. In order to test the validity of the model, air velocities obtained with the model are compared with the experimental data obtained in other experiment. The final CFD model was able to reproduce the airflow behaviour around the tree canopy, with the same turbulent structures. The solid body with the new turbulence model (SST k-omega) was considered as a good approximation to the real life.