Effect of nozzle inlet swirl and air column shape in nozzle on water jet occurring periodic droplets splashing

Abstract

Water with free surface inside the water tank was pressurized and ejected as a water jet from nozzle with abrupt contraction flow path attached to the bottom of the tank. When the height of the free surface of water makes low into some height from the bottom of the tank, a peculiar air column is generated in the nozzle, a phenomenon occurs in which the droplets are periodically aligned outward in the radial direction and are rapidly splashed from the jet due to the pressure difference from the atmospheric pressure. In order to investigate how water swirling near the nozzle inlet affects this droplet splashing phenomenon, The bottom of the tank was designed to affect the flow of water, and the flow of water was analyzed using visualization photography. As a result, it was found that the circumferential velocity has a great influence on the droplet splashing phenomenon under low pressure. When the circumferential velocity increases, it affects the shape of the air column in the large tube of nozzle, and the shape makes it easier for air bubbles to be generated in the small tube of nozzle. It was found that these processes facilitated the occurrence of the droplet splashing phenomenon.