Wind tunnels and their uses to study variables affecting precision applications of agricultural sprays

Authors: WOMAC, ALVIN - University Of Tennessee; OZKAN, ERDAL - The Ohio State University; Zhu, Heping; KOCHENDORFER, JOHN - National Oceanic & Atmospheric Administration (NOAA); Jeon, Hongyoung; ESWARACHANDRA, NATARAJ - University Of Tennessee

Submitted to: Journal of the ASABE
Publication Type: Review Article
Publication Acceptance Date: 7/20/2023
Publication Date: 10/9/2023
Citation: Womac, A., Ozkan, E., Zhu, H., Kochendorfer, J., Jeon, H., Eswarachandra, N. 2023. Wind tunnels and their uses to study variables affecting precision applications of agricultural sprays. Journal of the ASABE. 66(5):1135-1151. https://doi.org/10.13031/ja.15622.
DOI: https://doi.org/10.13031/ja.15622

Interpretive Summary: Precision pesticide spray applications are necessary to increase agricultural production while minimizing adverse effects to the environment. Extensive methodologies have been used to test application variables for their impacts in precision spray applications under uncontrolled environment; however, results between these tests were often inconsistent due to complex interactions of local microclimate and airflow, and their influences on the applications. This paper reviewed and documented representative publications studying the application variables including spray atomization, adjuvant effects, spray drift, spray, air movement, crop foliage interactions, unmanned aerial vehicle applications, airflow around sprayers, and spray test methods and collections in wind tunnels. In addition, available wind tunnel capabilities for studying application variables were researched and a comprehensive summary of the research was documented in this paper. The information in this paper will provide a guideline to engineers and researchers for studying application variables of precision pesticide spray applications in wind tunnels for modern spray application practices and research directions.

Technical Abstract: The objective of this study was to review publications that were representative of wind tunnels and their uses to study variables affecting precision applications of agricultural sprays. Precision application involved the very critical aspect of precision application involved the deliberate engineering of sprayers for accurate formation and dispersal of droplets and sprays to enhance spray deposits on targeted crop, foliage, or pest for increased agricultural production with reduced adverse effects to neighboring ecology and the environment Categorical themes of wind tunnel uses were (i) spray atomization, (ii) adjuvant effects, (iii) spray drift, (iv) spray, air movement, crop foliage interactions, (v) UAV applications, (vi) airflow around sprayer, and (vii) spray test methods and collections. A discovery was that nozzle design had more impact on droplet size than spray formulation which emphasized the importance of spray nozzle selection for atomization, and that air induction (AI) venturi nozzles consistently provided reduced spray drift potential. On occasion, some adjuvants marketed as drift reduction agents acted in an opposite manner and decreased droplet size. Wind tunnel use for spray drift represented to broadest range of variables studied among conceptual applications and included various nozzles, boom height, product active ingredients, adjuvants, and other variables. Deposits decreased in foliage from upper, middle, to lower foliage heights and decreased with increased wind speed. Low wind turbulence in the canopy did not contribute to deposition. Foliage deposition depended more on droplet size and local ambient winds. Canopy porosity limited the droplet size to 100 µm for contribution to deposits internal to the foliage. Wind tunnel use for UAV applications was spray drift centric for UAV variables such as rotor configurations and payload for mounted or tethered UAV. An ultimate recommendation was to use AI nozzles, reduce application speed, and to use a suitable adjuvant – which was similar other applications. Contrasting results for the impact of airflow around sprays was reported for vortices around fan spray discharge of a nozzle versus a 4-nozzle boom study that found no differences in velocity and turbulence fields due to the presence or no presence of spray discharge. Spray test methods and collections determined in wind tunnels primarily focused on collection efficiencies for a wide range of spray collectors. Collection efficiencies varied with collector and droplet size.