A Parametric Investigation of the Jet Breakup Patterns of a Rotary Sprinkler

ABSTRACT The spraying uniformity of a sprinkler is a key hydraulic performance indicator that is closely linked to the jet breakup pattern. The current research has focused mainly on the spraying performance of sprinklers, neglecting the exploration of the breakup morphology of spray jets from sprinklers. High‐speed photography technology is adopted to investigate the entire process of the water jet breaking into droplets in the air under different operating conditions. The jet breakup patterns and their corresponding breakup processes and droplet size distributions are analysed. Through multiple‐condition experimental observations, the jet breakup patterns, including split, column and liquid‐film jets, are identified according to their ejection morphology. The breakup processes differ significantly among the three patterns. Both split and column jets form droplets via continuous ligament rupture under inertia and surface tension, whereas the liquid‐film jet first breaks into ligaments and small droplets under aerodynamic shear, which then coalesce into larger ones. The droplet volume mean diameter follows a nonlinear power function with both working pressure and nozzle diameter. Increasing pressure leads to more complete breakup and a more concentrated size distribution, whereas a larger nozzle diameter flattens the peak of the droplet size distribution, resulting in greater nonuniformity.