Location: Application Technology Research Unit
2013 Annual Report
Computer simulation programs will be developed for the prediction of spray droplet deposition discharged from air-assisted sprayers under different microclimatic conditions. The programs will use the mathematical models and algorithms based on simulation results from a computational fluid dynamics program (FLUENT). Two-phase flow models with stochastic process under turbulent conditions will be developed and used in the computer simulation. Evaporation of droplet dispersal will be included in the models. A CAD program (Pro/ENGINEER) will be used to establish geometries of nozzles, sprayers and trees. The join-mapping technique will be used to incorporate the geometrics of sprayers and field targets into FLUENT for simulation. Variables in the models include wind velocity, turbulence intensity, canopy structure, ambient temperature, relative humidity, spray droplet size distribution, space ratios between droplets and air, sprayer structure and travel speed. The accuracy of the computer simulation models for air-assisted sprayers will be verified under controlled conditions in a wind tunnel and in orchard and nursery fields.
Air velocity distributions discharged from axial fans commonly used in air-assisted sprayers were simulated with a computational fluid dynamics program. The simulation included two fan inlet designs and three outlet designs constructed with a computer-aided design program program. In the simulation, the outlet was divided into one, two and three ports. A cluster of droplets were also released into the air flows to investigate droplet dispersions and flight distances. The computer simulation demonstrated the discharged air speed varied with the fan inlet and outlet shapes. With a conical frame in the inlet, the outlet air speed increased from 19 to 26 m/s. Droplet cloud distributions varied with the fan outlet shape. The droplet distribution in the air from three ports had much less variation than that from a single port. Second atomization of droplets in high air streams was also observed with the computer simulation.
This project addresses critical elements for increasing pest control efficiency with less pesticide use envisioned in ARS parent project Objective 2.1 “Determine how water droplets amended with spray additives, relative humidity and the morphological surfaces of leaves affect the droplet evaporation time, spread factor and residual pattern on leaves”, and Objective 1 “Develop precision sprayers that can continuously match canopy characteristics to deliver agrichemicals and bio-products accurately to nursery and fruit crops”.