Abstract
Abstract Droplet shear stress is the main cause of soil erosion under sprinkler irrigation, and the effect of droplet impact angle on the shear stress distribution cannot be ignored. In this study, a ball-driven sprinkler was selected to investigate the radial distributions of droplet impact angles under three operating pressures (0.25, 0.30, and 0.35 MPa) and two nozzle diameters (1.9 and 2.2 mm), which are commonly used in agricultural irrigation. The effect of droplet impact angles on the distances from the sprinkler, droplet impact velocities, and shear stresses were analyzed by a 2DVD instrument. Irrespective of the nozzle diameter or operating pressure, the droplet velocities and impact angles near the sprinkler were distributed at 1.0–5.5 m s−1 and 70–90°, respectively, and the droplet shear stress increased with the distance from the sprinkler. Suitable operating pressure and distance from the sprinkler significantly reduced the droplet shear stress. Although the nozzle diameter had a certain effect on the maximum shear stress, the overall effect was insignificant. We developed the models for the radial distribution of droplet shear stresses, which were in good agreement with the measurement. This study proposes a new method for accurately predicating the soil erosion under sprinkler irrigation.
Highlights
As a high-efficiency water-saving irrigation technique, sprinkler irrigation has been developed, promoted, and applied in China since the 1950s (Yan et al )
The effect of nozzle diameter on the droplet impact angle was not significant (P > 0.05, results not presented) at the same operating pressure and measuring point, which was in good agreement with the results reported by Chang & Hills ( a)
Regardless of the nozzle diameter and operating pressure, the droplet impact angles in the range of [70–90] basically occurred within 4 m of the sprinkler
Summary
As a high-efficiency water-saving irrigation technique, sprinkler irrigation has been developed, promoted, and applied in China since the 1950s (Yan et al ). By the end of 2018, China’s sprinkler irrigation area has reached 4.4 million hm, accounting for about 20% of the total area under high-efficiency water-saving irrigation. Soil surface sealing or crust formation caused by sprinkler irrigation is common (Chang & Hills a). It reduces the water infiltration rate, and leads to surface runoff. Previous studies have shown that soil particle detachment is the main reason for soil surface sealing (Assouline & Ben-Hur ) and generally related to droplet kinetic energy (Yan et al ; Caracciolo et al ). Some studies (Huang et al ; Ghadiri & Payne ) showed that from a mechanism perspective, the soil particle detachment from aggregates is caused by external shear stress rather than droplet kinetic energy
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