Modelling pesticide flow and deposition from air-assisted orchard spraying in orchards: A new integrated CFD approach

Abstract

Pesticide spray flow from air-assisted orchard sprayer through pear orchard and deposition on different environmental systems were estimated using a new integrated computational fluid dynamics (CFD) approach. The model simulated the complex interactions between wind, air and spray flow from the sprayer with target orchard canopy and the neighbouring environment. The new CFD approach involves the incorporation of the actual 3D canopy architecture into the model to simulate its effect on air and spray flow and deposition of droplets on the branches. Source–sink terms were added to the basic momentum and turbulence equations in a detailed sub-domain created around the branches to represent the effect of leaves. The spray droplets were generated from atomization model and tracked using a Lagrangian particle transport model. A new stochastic deposition model was developed and used to calculate deposition on leaves. The deposition model is a function of leaf optical porosity of the trees, leaf area density, leaf drag coefficient and droplet interception coefficient of the leaves. Two distinct nozzle setups, orchard and boom sprayer setups with ATR brown and TT blue nozzles, respectively, were compared to assess the effect of droplet size distribution on spray flow and deposition. The model results were compared with results from field measurements. For both sprayer setups, the simulation results agreed well with the measurements. The spray proportion above the tree height and behind the trees for the boom sprayer setup was 57.2% and 69.6% more than the orchard sprayer setup according to the simulations and the measurements, respectively. Such a model can be used to improve design features and the calibration of operational parameters of sprayers for better spraying efficiency and reduced environmental impact.