Modification of an open-circuit, push-through, low-speed wind tunnel to assist pesticide spray application advancements

Authors: Zhu, Heping; OZKAN, ERDAL - The Ohio State University; CASTILLO THEODORO, JOSE - The Ohio State University; Jeon, Hongyoung; ZHAO, LINGYING - The Ohio State University

Submitted to: Journal of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/10/2025
Publication Date: 12/23/2025
Citation: Zhu, H., Ozkan, E., Castillo Theodoro, J.G., Jeon, H., Zhao, L. 2025. Modification of an open-circuit, push-through, low-speed wind tunnel to assist pesticide spray application advancements. Journal of the ASABE. 68(6):1029–1039. https://doi.org/10.13031/ja.16423.
DOI: https://doi.org/10.13031/ja.16423

Interpretive Summary: Pesticide spray application is one of the most complicated processes in crop production because spray quality and effectiveness are affected by many uncontrollable variables such as weather conditions. Wind tunnels are commonly used to simulate field tests under controlled environmental conditions to determine optimal controllable spray parameters such as nozzles, operating pressures, flow rates, and spray formulations. In this research, an 18-m long open-circuit wind tunnel was constructed and modified to achieve uniform laminar airflows. The modification of the wind tunnel included attaching a 15° permeable airflow deflector and 2.5 layers of 252-mesh fiberglass screens downwind the fan exit. With the modification, the wind tunnel was able to produce constant air velocities ranging from 0 to 10 m/s with turbulence intensities below 5%. In addition, the wind tunnel test section was renovated to include a 6.1 m long linear travelling boom to simulate field sprayers and a position-adjustable device to measure droplet sizes. This low-speed wind tunnel has enhanced our research capabilities and will have wide applications in simulation of field investigations under a controlled environment to advance pesticide spray technologies.

Technical Abstract: A centrifugal fan-driven wind tunnel, designed with standard instructions and computational fluid dynamics (CFD) models, was modified to produce uniform laminar airflows ranging from 0 to 10 m s-1. The primary components of the wind tunnel included a centrifugal fan, a fan housing assembly with a variable speed motor, a wide-angle diffusion and contraction chamber, a honeycomb settling chamber, and a detachable test section. The total length of the wind tunnel was 18 m, which included a 7.3 m long test section with a cross-sectional area of 1.83×1.83 m. Air velocities were measured with two different hot-film anemometry systems at 16 points evenly distributed across each of the four cross-sections in the test section. After initial measurements revealed that air velocities were not uniform, the wind tunnel was modified by attaching a 15° permeable deflector and 2.5-layer fiberglass screens to the exit of the fan housing assembly. The attachments redirected the airflows discharged from the centrifugal fan to the diffusion and contraction chamber before entering the test section. After the modification, uniform airflows with turbulence intensities below 5% were achieved for air velocities up to 10 m s-1 across the entire test section. Additionally, the test section was integrated with a position-adjustable droplet size measurement device and a linear traveling boom with nozzle flow rates controlled by a PWM solenoid valve to obtain the desired application rates. This low-speed wind tunnel would be a sophisticated tool to simulate field investigations in a controlled environment to advance pesticide spray application technologies.