Drift Predictions in the Near Nozzle Region of a Flat Fan Spray

Abstract

Previous work concerned with modelling spray drift from agricultural flat fan nozzles has used random-walk approaches to predict individual droplet trajectories in the region close to the nozzle and further downwind. Work reported here has extended this approach such that droplets are tracked in three dimensions in the near nozzle region and then a two-dimensional random-walk is used to predict trajectories further downwind. Model predictions were validated against wind tunnel drift experiments. Measurements in a wind tunnel with a 110° flat fan nozzle operating with a flow rate of 0·61 min -1 at a pressure of 3·0 bar, gave volumes of airborne spray 2·0 m downwind of the nozzle of 5·2% of the nozzle output with the spray fan oriented at right angles to the direction of airflow at a speed of 2-0 m s -1 and 0·6% when the spray fan was aligned with the direction of the airflow at a speed of 2·0 m s -1. The model gave drift percentages of 7·5% and 2·8% for the same conditions, and also over-predicted drift for all remaining angles of nozzle orientation. These results suggest that further work is required to: (1) account for the air interactions associated with spray formation processes from a flat fan nozzle; (2) examine the interactions between wind speed and the forward motion of the sprayer.