CFD simulation of airflow inside tree canopies discharged from air-assisted sprayers

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

Submitted to: Computers and Electronics in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/21/2017
Publication Date: 6/11/2018
Publication URL: https://handle.nal.usda.gov/10113/5761389
Citation: Hong, S., Zhao, L., Zhu, H. 2018. CFD simulation of airflow inside tree canopies discharged from air-assisted sprayers. Computers and Electronics in Agriculture. 149: 121-132.

Interpretive Summary: Application of pesticides is essential for mass production of high-quality specialty crops. However, excessive pesticide use and unnecessary off-target waste from conventional air-assisted sprayers have considerably increased production costs. To improve pesticide application accuracy, it is essential to understand sprayer-induced airflow patterns that carry spray droplets in and around the target canopy as well as at locations far from the targets. In this research, an integrated computational fluid dynamics (CFD) model was developed to simulate air velocity distributions inside and around tree canopies discharged from a newly developed air-assisted sprayer. The CFD model calculated complex airflow patterns induced by the strong air jets from the sprayer, integrating the motion of the sprayer and the effect of tree canopies on air momentum and turbulence quantities. Validation of the CFD model was accomplished by comparing the calculated results with previous measurements. Simulated air velocities downwind from the sprayer agreed with the measurements when the sprayer was both stationary and in motion. Consequently, this CFD simulation will provide a new economic approach to predict airflows through tree canopies with complex architectures and leaf densities when measurements are difficult, and will be used to modify new sprayer designs and guide spray practices to increase pesticide application efficiency.

Technical Abstract: Effective pesticide application is not only essential for specialty crop industries but also very important for addressing increasing concerns about environmental contamination caused by pesticide spray drift. Numerical analysis using computational fluid dynamics (CFD) can contribute to better understanding of the transport of spray droplets carried by strong air jets from sprayers. In this research, an integrated CFD model was developed to predict air velocity distributions inside and around tree canopies from an air-assisted pesticide sprayer. The sprayer motion was simulated by the sliding mesh technique, and the tree canopies were defined in the computational domain as virtual porous media without their geometric modeling. Validation of the CFD model was accomplished in three steps by comparing the CFD results with previous measurements. Air velocities and airflow pressures downwind from the sprayer agreed well with the measurements when the sprayer was both stationary and in motion. The model was also able to predict accurately the peak air velocity and airflow pressure inside the canopies with average RMS errors of 1.68 m s-1 and 0.89 kg m-2, and relative errors of 29.2% and 20.2%, respectively. Although, discrepancy existed between the field experiment and CFD simulation this study can conclude that the simulation will give a reasonable prediction of air distributions discharged from air-assisted sprayers. The validated CFD model was applied to predict air penetration inside canopies according to various canopy dimensions, canopy densities, and simplification of tree modeling. The complex airflow patterns obtained by the CFD model offered advantages of analyzing effects of various factors on sprayer performance.