Numerical simulation and experimental study of jet breakup using a water dispersal needle in irrigation sprinklers

Abstract

Introducing a water dispersal needle has been shown to be an effective way of improving the uniformity of water distribution from irrigation sprinklers. However, the jet breakup mechanism remains unknown. Here, the impacts of key parameters, including the insertion jet depth (h), cone angle (θ), and distance from the nozzle outlet (L), on jet breakup phenomena were investigated by simulation. A comprehensive computational approach was used, which integrated the Volume-of-Fluid method with the SST k-ω model, overset grids, and adaptive mesh refinement technique. The results showed distinct jet field zones characterised by stable velocity, descent, rebound, and fluctuation zones, which were delineated by the axial average velocity profile. It was found that increasing h, θ, or reducing L results in a significant reduction of 7.73%, 5.04%, and 5.54% respectively in axial average velocity within the fluctuation zone. Augmentation of large-scale eddies, vortex bands, wave-like eddies, and vortex ring structures intensified the local entropy production rates, increased energy dissipation. The findings showed how this greatly influenced the throw radius of the sprinkler. Moreover, increasing h, θ, or decreasing L also increased air entrainment rates within the velocity decrement zone. This phenomenon was significant in the rebound and fluctuation zones, heightening the jet breakup and increasing the number of detached water droplets. Such dynamic interaction significantly influences the predicted water application rate within a 6-m radius of the sprinkler. Thus, this simulation study serves as a reference for comprehending the intricate jet breakup characteristics and the consequent sprinkler system hydraulic performance.