WTDISP – adapting a Lagrangian ground sprayer model using wind tunnel data

Abstract

The ground boom model (AGriculture DISPersion) or AGDISP calculates the deposition of agrichemicals both in the area sprayed and more importantly downwind on neighbouring properties. However modelling the breakup and evaporation of the spray droplet cloud over the first few metres is very difficult. Wind Tunnel Dispersion or WTDISP arose to overcome this difficulty. Measurements of droplet spectra and fluxes were made 2 m downwind of several nozzles in a wind tunnel. WTDISP originated as this source was input into the frame work of the ground boom model AGDISP. AGDISP calculates the deposition by ensemble averaging the droplet paths to the ground and uses a statistical distribution of the likely paths about these averages to calculate the deposition on the ground. The paper below also outlines possible ways to improve the technique to model field and wind tunnel measurements, including turbulence scaling effects, the orientation of the nozzle fan to the wind direction and field measurements. It also discusses the drop size distribution from both models at 2 m downwind leading to improvements to the evaporation/breakup algorithms used in AGDISP and gives recommendations for experiments to improve the model results.