CFD prototyping of an air-assisted orchard sprayer aimed at drift reduction

The environmental contamination due to off-target deposition of pesticide droplets can be minimized by using optimum design and operating parameters of sprayers. A three-dimensional computational fluid dynamics (CFD) model was developed and used to evaluate concepts of boom sprayer setup to orchard spraying to reduce drift without a decrease in biological efficacy. To track the path of the droplets, a Lagrangian particle tracking multiphase flow model was used, combined with spray atomization models and taking into account the velocity variation at the fan outlet. The studied sprayer settings included: sprayer ground speed, fan speed (air jet velocity), number, type, size, position and orientation of nozzles and liquid pressure. To account for the speed of the tractor, a moving coordinate system was implemented. For the boom sprayer setup, nozzles were employed that produce a flat fan spray pattern (110° Turbo Teejet and 85° Teejet off-centre air induction nozzles). Boom-type spraying was compared to conventional orchard spraying using 80° hollow cone nozzles. There was a good similarity between the vertical spray distribution profile patterns produced from the boom and orchard sprayer setups; however, the boom sprayer setup produced lower droplet concentration to the highest positions and could therefore offer possibilities for drift reduction at long distance, while providing good coverage at a short range. There was a good agreement between measured and predicted vertical spray distribution patterns.