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Contribution à la modélisation de la pulvérisation d'un liquide phytosanitaire en vue de réduire les pollutions

Abstract : Viticulture is a very pesticides intensive crop (20% of overall French consumption). Therefore, optimizing spraying process is the key to reduce the amount of pesticides applied. Spray application most often consists in the spraying of a liquid mush composed of water, adjuvants and active ingredients. Recent research has shown that droplet size and velocity have a strong influence on the spraying efficiency. The purpose of the present work is to model the atomization process in order to characterize the flow in terms of droplet size and velocity distributions as well as liquid dispersion. These data would be used later as inlet conditions for transport or deposit models. For the numerical prediction of these quantities, an Eulerian model based on studies developed in the automotive industry was used. It assumed atomization as turbulent mixing in a flow with variable density. Dispersion of the liquid in the gas phase was computed by an equation for the mean liquid mass fraction. We calculated the mean size of liquid fragments through the modelling of the mean surface area of the liquid-gas interface per unit of volume. The equation related to the last variable was composed of various terms that took into account the physical phenomena responsible for interface stretching and collapse. Turbulence was modelled using a Reynolds Stress Model. These equations were implemented into the commercial CFD code, Fluent and were applied to an agricultural swirl nozzle. Numerical three-dimensional calculations of the flow inside the nozzle and in the dense spray region were conducted up to 1 cm of the exit. Results concerning the liquid dispersion are in good agreement with experimental shadowgraph images ; they show the same morphological behaviour of the jet : we obtain a hollow conical liquid sheet and the presence of a recirculation area that indicates the formation of an air core is underlined. Moreover, the break-up length and drop sizes calculated are also consistent with experimental results. They show that spray break-up occurs very close to the nozzle exit.
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Contributor : Magali de Luca <>
Submitted on : Monday, December 10, 2007 - 7:03:35 PM
Last modification on : Tuesday, October 20, 2020 - 9:16:28 AM
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  • HAL Id : tel-00195424, version 1

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Magali de Luca. Contribution à la modélisation de la pulvérisation d'un liquide phytosanitaire en vue de réduire les pollutions. Mécanique [physics.med-ph]. Université de la Méditerranée - Aix-Marseille II, 2007. Français. ⟨tel-00195424⟩

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