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

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 blown by 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 measurement 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 distribution inside canopies with various canopy dimensions and densities. The complex airflow patterns obtained by the CFD model offered advantages of analyzing effects of various factors on sprayer performance.