Evolution of jets generated by noncircular nozzles with varying aspect ratios

Two types of non-circular nozzles (NCNs) with diamond and elliptical shapes are designed, and the jet breakup characteristics of NCNs with different aspect ratios are investigated via high-speed photography. By capturing the jet breakup process and flow characteristics of low-pressure water jets, the effects of different nozzle shapes and aspect ratios on the jet breakup length and spread angle are analyzed. The results show that jet condensation and liquid film occur at the maximum curvature section of the NCN jets. The liquid film is more likely to be generated at the minor axis of jets with higher aspect ratio and lower jet velocities. For elliptical nozzles with different aspect ratios under the same pressure, the smaller the aspect ratio, the less the jet surface wave disturbance and the longer the jet break-up length. The VOF-LES method is used to study the axis-switching phenomenon in jet flows from NCNs with different aspect ratios. The jet flow process of NCNs is divided into four stages, i.e., incomplete axis-switching, complete axis-switching, jet instability, and jet breakup stages, according to the jet characteristics. It has been found that the aspect ratio and curvature of the nozzle affect the number and position of the binary vortices, respectively, which in turn affect the axis-switching times, instability length, and breakup length of the jet, resulting in changing the wetted radius and other hydraulic performance characteristics. In addition to the axis transformation phenomenon, the non-circular nozzle also affects hydraulic performance such as droplet diameter, droplet velocity, kinetic energy per unit volume of droplets, and coefficient of variation in water volume.