DRIFT PREDICTIONS IN THE NEAR NOZZLE REGION OF A FLAT FAN SPRAY

Previous work concerned with modelling spray drift from agricultural f lat fan nozzles has used random-walk approaches to predict individual droplet trajectories in the region close to the nozzle and further dow nwind. Work reported here has extended this approach such that droplet s are tracked in three dimensions in the near nozzle region and then a two-dimensional random-walk is used trajectories further downwind. Mo del were validated against wind tunnel drift experiments. Measurements in a wind tunnel with a 110 degrees flat fan nozzle operating with a flow rate of 0.61 min(-1) at a pressure of 3.0 bar, gave volumes of ai rborne 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 airfl ow at a speed of 2.0 m s(-1) and 0.6% when the spray fan was aligned w ith 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 a lso over-predicted drift for all remaining angles of nozzle orientatio n. These results suggest that further work is required to: (1) account for the air interactions associated with spray formation processes fr om a flat fan nozzle; (2) examine the interactions between wind speed and the forward motion of the sprayer.