Wind Tunnels and Their Uses to Study Variables Affecting Precision Applications of Agricultural Sprays

Highlights Wind tunnels were extensively used to study precision applications of agricultural sprays. Use of wind tunnels significantly contributed to the broad-reaching impact of precision applications. Wind tunnels provide controlled conditions to study a plethora of wide ranging spray variables. 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 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 (1) spray atomization, (2) adjuvant effects, (3) spray drift, (4) spray, air movement, crop foliage interactions, (5) UAV applications, (6) airflow around sprayer, and (7) 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 had the 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 less than 100 µm for contribution to deposits internal to the foliage. Wind tunnel use for UAV applications was mostly focused on spray drift 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 to other applications. Contrasting results for the impact of airflow around sprays were 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. Keywords: Keywords.,Boom sprayer,Droplet size,Droplet trajectory,Nozzle classification,Spray deposit,Spray drift,Spray nozzles.