CFD sample

In this article, we hypothesize that droplet transport in air-assisted spraying systems is related to the different diameter-dependent regime change, when aerodynamic drag, particle inertia, and canopy resistance interact. We also hypothesize that this porous canopy substantially affects how droplets fly and how they are made, so how they dispersed, transported and deposited.

To verify this hypothesis, a 3D transient CFD model has been developed based on dynamic mesh strategy and a Lagrangian Discrete Phase model (DPM). The model is an air-assisted sprayer, based on a real fruit orchard setup with open-field and porous canopy for example. The canopy was modeled as porous to account for vegetation resistance and droplet injection was performed with air-blast atomization, and droplet movement dynamics, for example with their diameter distribution, velocity and turbulence was studied.

Diameter and movement regimes of a droplet. The thin droplets (d < 80 µm) have strong air coupling and a high transport potential and drive the spray drift. Intermediate droplets, with 80-120 µm (Dv50) in diameter represent a critical phase in its transport. Droplets with large diameters are influenced more by inertia and present a good quality of deposition in the canopy.

The porous canopy greatly reduces the flow of air and distorts turbulence patterns thus leading to reduced transport of droplets and hence reduced deposition efficiency. The effect of porous canopy is even more pronounced for intermediate droplet sizes which is where canopy resistance reduces acceleration and interception of jet-driven droplets.

In general, our results show that droplet transport and deposition depend upon the aerodynamic composition of the droplets and canopy interaction. These results are useful for the development of spray application plans to control droplet distribution and airflow during orchard applications to ensure that the number of droplets does not increase while still delivering high deposition and drift results.