EVALUATION OF AN AIR-ASSISTED BOOM SPRAYING SYSTEM UNDER A NO-CANOPY CONDITION USING CFD SIMULATION

Abstract

Air-assisted spraying is one recommended strategy for reducing spray drift. Even though many studies pertaining to air-assisted spraying have shown its advantages in reducing spray drift, little information about optimal operating parameters and effects of wind velocity, sprayer travel speed, and sprayer travel direction on reducing spray drift for air-assisted spraying was available. In this study, an air-assisted spraying system with various operating parameters under a no-canopy condition was evaluated by using a computational fluid dynamics software package (FLUENT) and response surface methods to optimize operating parameters and evaluate spray drift characteristics. Selected operating parameters (air jet velocities of 45 and 24.7 m s-1, air jet angles of 16° and 4.3°, and the same air jet-nozzle angle of 30° for upwind and downwind spraying, respectively) were used to investigate effects of wind velocity and sprayer travel speed on reducing spray drift. Results of this study for the air-assisted sprayer with an air jet outlet of 1.5 cm in width at a wind velocity of 4 m s-1 and a sprayer travel speed of 0.9 m s-1 indicate that the air jet-nozzle angle of air-assisted spraying has no significant influence on reducing spray drift. For the air-assisted sprayer, air velocities from 20 to 30 m s-1 appear to be acceptable in reducing spray drift for downwind spraying, as the related relative drift indexes range from -50% to -80%. However, for upwind spraying with the same air velocities, relative drift indexes range from -5% to -22%, indicating greater drift potential. This implies that the air-jet velocity must be increased to provide the same drift indexes as achieved with downwind spraying. After excluding the exceptional cases that resulted from spray drift subject to an excessive air jet velocity, the effect of local relative wind velocity on drift potential could be used to explain variations of relative drift indexes of air-assisted spraying under various wind velocities, sprayer travel speeds, and sprayer travel directions. The relative drift index increases as the local relative wind velocity increases. Results of this study provide air-assisted spraying operations with valuable information, which is beneficial for reducing spray drift from air-assisted sprayers.