An integrated approach to investigate the orchard spraying process: towards a CFD model incorporating tree architecture

Drift is of more concern for air-assisted orchard sprayers than for field sprayers due to the high air jet velocity involved and the horizontal application direction. Orchard sprays are applied sideways to the trees, with a high risk for aerial drift by wind. Air-assistance has also been shown to be non-uniform, but the consequences for deposition uniformity in the canopy have yet to be demonstrated. Off-target deposition can be minimized and uniformity can be improved with the use of proper equipment and methods under favourable weather conditions depending on the nature of the target canopy and the level of infection. To this end knowledge of the canopy flow conditions of both the air and the spray are needed. It has been difficult to obtain such information experimentally. A Computational Fluid Dynamics (CFD) model that allows the simulation of spraying process for different machines including environmental and canopy conditions is presented. This comprehensive model considers the effects of wind velocity and turbulence, and the nature of the canopy on air assistance distribution. Orchard experiments were conducted on airflow profile from three air assisted orchard sprayers in leafless and fully leafed pear tree (Pyrus communis L.) orchards. The model results compared well to the measured profiles of airflow distribution, with average accuracies as high as 80%. The model is used to study effects of sprayer and nozzle design and operational parameters, weather conditions, and for different planting systems and development stages.