The Impact of Liquid Properties on Spray Drift from Fixed-Wing Aerial Application Aircraft

Highlights Small variations in liquid properties can increase the spray volume contained in drift-prone droplets by over 40%. Dynamic surface tension, shear viscosity, and extensional viscosity affect drift by altering droplet size. The degree to which liquid properties affect droplet size and drift is dependent on the sprayer configuration. Changing liquid properties can increase spray drift by over 100% compared to baseline mixtures for select cases. Abstract. Two experimental datasets are analyzed to quantify the impact of various spray mixtures and their associated nominal liquid physical properties on spray drift at conditions relevant to aerial application. Droplet size distributions measured in wind tunnels were used as inputs in AgDRIFT, a commercially available software package that simulates drift from various spray vehicles. Near-field drift metrics were extracted from the simulation results and subsequently analyzed, showing that even relatively small changes in nominal liquid physical properties can significantly impact spray drift. For some low-drift cases, these drift metrics increased from 100% to over 250% relative to a baseline formulation, water with a non-ionic surfactant solution typically used as a test surrogate. However, a large majority of the tested cases resulted in a decrease of between 13.5% and a 47.6% increase in drift relative to the baseline formulation. These results demonstrate that the typical practice of using a single blank spray solution to represent a broad range of spray materials may lead to a significant underestimation of near-field drift.