CFD simulation of pesticide spray from air-assisted sprayers in an apple orchard: tree deposition and off-target losses

Authors: HONG, SEWOON - The Ohio State University; ZHAO, LINGYING - The Ohio State University; Zhu, Heping

Submitted to: Atmospheric Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/25/2018
Publication Date: 5/7/2018
Publication URL: https://handle.nal.usda.gov/10113/5912818
Citation: Hong, S., Zhao, L., Zhu, H. 2018. CFD simulation of pesticide spray from air-assisted sprayers in an apple orchard: tree deposition and off-target losses. Atmospheric Environment. 175:109-119.

Interpretive Summary: Although spray technologies for pesticide applications have been advanced significantly for the past decades, the efficiency of existing application practices still needs improvement. Assessing the spray deposition quantity on target trees in orchards can assist to configure sprayer settings and guide application practices to increase spray efficiency and minimize drift mitigation. However, full-scale field experiments are usually expensive and difficult to perform under uncontrollably environmental conditions. In this research, a comprehensive computational fluid dynamics (CFD) model was developed to simulate the movements of spray droplet clouds discharged from air-assisted sprayers through multiple rows of tree canopies in apple orchards. The CFD model accuracy was validated with experimental measurements of spray deposits inside canopies and off-target losses to the ground and air at three different growth stages. Fate and transport of spray droplets and mass balance of pesticide spray were analyzed under regular and worse scenarios of weather conditions. Consequently, this CFD simulation will provide a new economic approach to predict spray deposition and off-target losses including spray drift for crops with complex architectures and leaf densities in orchards when measurements are difficult, and will provide a new approach to improve sprayer operation performance.

Technical Abstract: The ultimate goal of a pesticide spraying system is to provide adequate coverage on intended canopies with a minimum amount of spray materials and off-target waste. Better spray coverage requires an understanding of the fate and transport of spray droplets carried by turbulent airflows in orchards. In this study, an integrated computational fluid dynamics (CFD) model was developed to predict displacement of pesticide spray droplets discharged from an air-assisted sprayer, depositions onto tree canopies, and off-target deposition and airborne drift in an apple orchard. Pesticide droplets discharged from a moving sprayer were tracked using the Lagrangian particle transport model, and the deposition model was applied to droplets entering porous canopy zones. Measurements of the droplet deposition and drift in the same orchard were used to validate the model simulations. Good agreement was found between the measured and simulated spray concentrations inside tree canopies and off-target losses (ground deposition and airborne drifts) with the overall relative errors of 22.1% and 40.6%, respectively, under three growth stages. The CFD model was able to estimate the mass balance of pesticide droplets in the orchard, which was practically difficult to investigate by measurements in field conditions. As the foliage of trees became denser, spray deposition inside canopies increased from 8.5% to 65.8% and airborne drift and ground deposition decreased from 25.8% to 7.0% and 47.8% to 21.2%, respectively. Higher wind speed also increased the spray airborne drift on the downwind side of the orchard. This study demonstrates that CFD model can be used to evaluate spray application performance and design and operate sprayers with a better spray efficiency and a reduced drift potential.