Effects of Wingtip Vortices on Agricultural Spray Dispersion

Fixed-wing agricultural unmanned aerial vehicles (UAVs) provide efficient crop protection but generate coherent vortical structures, such as wingtip vortices that can significantly affect spray transport and deposition. This study investigates the effects of wingtip vortices on agricultural spray dispersion using a computational fluid dynamics (CFD) framework coupled with a discrete phase model (DPM). Idealized Lamb–Oseen vortex pairs were introduced to isolate vortex effects from aircraft geometry. Various vortex strengths, vortex-pair arrangements, and droplet sizes were examined. The results show that the spray plume generates a counter-rotating droplet-induced vortex pair under freestream conditions. Wingtip vortices modify the evolution of these structures and the resulting spray distributions. Vertically aligned and spanwise-offset vortex pairs produce distinct spatial evolution of the droplet-induced vortices, corresponding to suppression-type and merging-type interaction behaviors, respectively. However, these interaction modes do not result in a universal increase or decrease in plume width, concentration localization, or deposition non-uniformity. The resulting spray redistribution depends jointly on vortex configuration, circulation strength, droplet size, and evaluation location. Vortex-pair configuration primarily influences the spatial organization and interaction mode of the droplet-induced vortical structures, while circulation strength mainly modulates the magnitude of the local spray response. These findings demonstrate that wingtip vortices influence spray dispersion primarily through their interaction with droplet-induced vortices and provide guidance for the aerodynamic optimization of fixed-wing UAV spraying systems.