Influence of UAV rotor wash on spray droplet atomization: Implications for pesticide application and environmental risk

Authors: Fritz, Bradley - Brad; BUTTS, THOMAS - University Of Arkansas

Submitted to: Journal of ASTM International
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/21/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: Spray droplet size is a key factor impacting the effectiveness and environmental consequences of any spray application. A wind tunnel was utilized to determine how rotor wash affects spray droplet formation in unmanned aerial vehicle (UAV) pesticide applications. The work found that the rotor wash can cause more spray break-up, leading to smaller droplets that are more likely to move off-target. These findings can help improve UAV design standards, pesticide application rules, and spray drift modeling, resulting in more precise environmental risk assessments in the pesticide approval process.

Technical Abstract: This research explores a critical aspect of Unmanned Aerial Vehicle (UAV) pesticide application: the effect of rotor wash on spray droplet atomization. Field deposition data indicate that rotor wash may induce additional breakup of the spray, resulting in finer droplets than those anticipated by nozzle catalogs or conventional wind tunnel droplet sizing tests. The objective of this study was to quantify this impact and explore potential boundaries on spray size data that might exist due to the supplementary forces introduced by rotor wash. To isolate the effects of rotor wash, a series of experiments were conducted within a controlled wind tunnel environment. These experiments compared droplet sizes from a spray nozzle under standard wind tunnel conditions with those exposed to simulated rotor wash. Measurement techniques, including laser diffraction and high-speed imagery, were adapted to account for potential biases arising from the varying velocities of different-sized droplets. Furthermore, the stationary UAV rotor and nozzle setup in the wind tunnel necessitated either traversing the measurement system or using multiple sampling locations throughout the spray plume. An averaging scheme was developed and applied to weight data from multiple locations appropriately, ensuring that representative volume-weighted distributions resulted. Developing a better understanding of the potential influence of rotor wash on droplet atomization can inform improvements in UAV design standards, pesticide application guidelines, and spray drift modeling, contributing to more accurate environmental risk assessments in the pesticide registration process.