CFD SIMULATION OF MECHANICAL SPRAY SHIELDS

Abstract

In this study, we used a computational fluid dynamics software package (FLUENT) to investigate the aerodynamics of six mechanical spray shields that partially cover the spray boom. Effectiveness of mechanical spray shields was compared based on spray–drift reduction. Results of this study indicate that use of solid bluff–plate shields inevitably results in a low–velocity zone, which plays an important role in the movement of small droplets immediately behind the shield or within the shielded area. However, a double–foil shield induces a high–velocity airflow immediately behind the spray nozzle and may force droplets downward, reducing interference of the low–velocity zone on droplet trajectories. As compared with conventional straight–down spraying, all shields simulated in this research, except one, reduced drift potential from 8% to 50% when droplets were released straight down and from 2% to 45% when droplets were released against the wind with an angle of 20³ to the vertical. Among these shields, the double–foil shield provided the best performance for drift reduction due to the assistance of shield–induced airflow. Optimization of droplet–release position and angle for the double–foil shield, with a response–surface method, showed that placing the nozzle closer to the shield, reducing nozzle height, and decreasing droplet release angle significantly lowered drift potential.