Abstract
Numerous methodologies have been developed to characterize sprinkler irrigation drops with the purpose of improving irrigation efficiency and controlling soil erosion and compaction. This paper presents the laboratory characterization of the morphology and velocity of drops in their free-falling trajectory as influenced by drop diameter and wind speed. For this purpose, a particle tracking velocimetry technique with in-line volumetric illumination was implemented. Hypodermic needles were used to produce droplets of uniform size. Two needle diameters resulted in drops with average diameters of 1.94 and 2.94 mm. Drops were illuminated with a double-pulsed laser beam or an LED lamp. Drop characterization reached an elevation of 4.28 m and occasionally attained terminal velocity. Motion blur was suppressed using a deconvolution filter. Drop equivalent diameter, velocity, chord ratio, canting angle and trajectory angle were determined using an ad-hoc software. The experimental approach led to the measurement of real drop size by illuminating a volume in the capture zone; drop shape ranged from quasi-sphere to ellipsoid. Drop deformation was more intense under high wind speeds. Ballistic simulations of drop fall were performed using sphere and ellipsoid drag force models. Both models resulted in excellent agreement with measured drop velocity, with the ellipsoid model performing marginally better. The robustness of the experimental equipment, particularly in combination with the developed LED lamp, announces future outdoor applications in real sprinkler irrigated fields. Such applications will provide insight on the governing processes, and data sets for the improvement of sprinkler simulation models.
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