Experimental and CFD-DPM Evaluation of Crosswind-Induced Spray Deposition from a Flat-Fan Nozzle

Crosswind can displace agricultural spray droplets from their intended target and alter both ground deposition and the vertical distribution of airborne droplets. This study developed a transient computational fluid dynamics-discrete phase model (CFD-DPM) for a single ST110-03 flat-fan nozzle and evaluated its deposition trends against controlled indoor experiments. Two nozzle heights (0.875 and 1.25 m), three crosswind speeds (2, 3, and 4 m s⁻¹), and a spray pressure of 0.4 MPa were investigated. Ground collectors quantified downwind deposition, while five cotton strings placed 2 m downstream at heights of 0.40-0.80 m characterized vertical interception. Ground-collector trials were conducted for 10 min per run, whereas cotton-string sampling used 60 s exposures; each tested experimental condition was independently repeated three times. The CFD domain was 7 m × 2 m × 2 m and contained approximately 1.98 million tetrahedral cells. A realizable k-ε model described the continuous phase, and the measured spray was represented by nine fan directions and three droplet groups (75.29, 206.23, and 336.57 μm). Droplets were injected for 20 s and tracked to 22 s. At a nozzle height of 1.25 m, the measured ground drift fraction increased from 25.57% to 43.31% as crosswind speed increased, while the simulated fraction increased from 42.04% to 51.73%. Across five matched ground cases, experimental and simulated fractions were strongly correlated (r = 0.922), although the mean absolute error was 16.39 percentage points. The model reproduced several vertical-distribution tendencies but substantially overpredicted cotton-string capture in selected cases. The model is therefore suitable for qualitative interpretation and relative trend analysis, but its simplified angular injection and ideal trapping boundaries require refinement before quantitative prediction.