CFD Based Analysis of the Effect of Wind in Orchard Spraying

Abstract

The high velocity air jet generated from air assisted orchard sprayers offsets the effect of wind on the spray flow pattern in front of the tree and within the vicinity of the tree height. This combined with the small wind magnitude at lower heights of the boundary layer results in insignificant wind effect within this zone. Once the spray droplets pass through the trees, the velocity of the air jet is significantly reduced by the resistance of the trees increasing the chance of deflection by wind. The projection of the spray droplets also affects the extent of the wind effect and strongly depends on the outlet design of the sprayer. The classical single axial fan sprayer used in this analysis projects part of the spray beyond the tree height resulting in a higher risk of deflection by wind. The CFD modeling approach used in this work allowed studying these wind effects of spray applications in a comprehensive way. It was observed that wind blowing opposite to the spraying direction significantly deflected the spray back to the sprayer. The effect is increased with wind velocity magnitude. Wind blowing in the direction of spraying increased the amount of spray passing through the trees (resulting in increased drift potential), but also increased on-target deposition for this type of sprayer that blows a significant amount of spray over the trees. In this case, wind helps to contain the air assistance of the axial sprayer within the canopy height to some extent.