Dynamic evaluation of airflow stream generated by a reverse system of an axial fan sprayer using 3D-ultrasonic anemometers. Effect of canopy structure

Air assisted sprayers are currently used for the applications of plant protection products in fruit trees and vineyards. However, the use of these equipment carries a high environmental risk, mainly owing to the generation of airborne spray drift in the lower boundary layer above crop canopy. Hence, many tests are currently focused on investigating several factors that affect the efficiency of the spray process, in which air assistance and air behaviour are two of the most difficult parameters to evaluate. This present work proposes a first approach on the characterization of the airflow generated by an orchard sprayer equipped with an axial fan and an air reverse system in the outlet plane of the air, while circulated through two artificial rows of canopy representing vineyard trellis, using 3D-ultrasonic anemometers to measure the experimental data. A first series of static field tests measured the air velocity at different heights on both sides of the sprayer and at both sides of every row of artificial canopy and evaluated the effect of the canopy on the sprayer airflow passing through. A second set of experiments were carried out with the sprayer moving at 4.1 km h(-1) between canopy rows to simulate the normal spray process. Finally, velocity vectors and turbulent intensities were calculated. The resistance of the vegetation was also characterized by using a drag coefficient, both when the sprayer was stationary and moving. The results between the static and dynamic tests were compared. Although there were similarities between the two tests, the results indicated that when the equipment moves along the canopy rows, the axial fan asymmetry on air velocities is more noticeable and turbulence intensity increased. In addition, the vegetation received direct airflow at different times. This could affect the trajectory of the droplets. On the other hand, the resistance of the vegetation on each side was similar. The air reverse system could be affecting the airflow direction to the driving direction. Ultrasonic anemometers were successful in characterizing sprayer fan airflows but it is necessary to continue working on the descriptive analysis of the airflow in other planes different from the air outlet only and with other vineyard systems.