Pressure swirl nozzles with different discharge orifice shapes injecting into transverse airflow

In this study, the influence of the discharge orifice shape of swirl liquid jets injected in transverse gas flow was investigated by high-speed photography and shadowgraphy techniques. Three shapes of discharge orifice, including circular, square, and elliptical were tested at different flow conditions. Due to the cross-sectional asymmetry in the ellipse, it is important to place it horizontally or vertically in airflow, and these two states are considered in this study. The main characteristics of liquid jets in transverse air, including trajectory, breakup point, jet width, breakup length, drop size distribution, and Sauter mean diameter, were obtained by image processing. Visualization of flow development revealed that the asymmetry of the swirl hollow cone in the transverse air causes an expanded new structure that cannot be seen in the circular cross section. This structure was called the conical bag and the inflated sheet in elliptical and square cross sections, respectively. The results indicate that the variations of momentum ratio are more effective in the path of non-circular swirl jets. The ellipse in the horizontal direction and square cross section have the breakup point's lowest transverse and longitudinal coordinates, respectively. Theoretical models for predicting swirl liquid jet trajectory and its breakup point were developed and presented. Gamma probability distribution function was fitted on the drop size according to the discrete distribution of the drop size. The results indicated that the distribution of elliptical shapes in the horizontal direction produces the smallest droplets among them while square cross section has a wider distribution.