Experiment on breakup processes and surface waves of round liquid jets in crossflows

An experiment was conducted to investigate the surface wave development and the breakup processes of round water jets in cross airflows at room temperature and pressure by high-speed photography. The jets were injected normal to the crossflow direction opposing gravitation forces from a plain orifice nozzle with the diameter of 0.3 mm and length-to-diameter ratio of 40. Successive images were recorded by a megapixel high-speed video camera with maximum frame rate frequency of 10000 Hz. The jet injection velocity varied from 3.8 m/s to 7.8 m/s. The crossflow velocity varied from 25.6 m/s to 35.1 m/s which resulted in the liquid-to-air momentum flux ratio varied from 10.2 to 80. The experimental results indicate that the surface of the liquid jet is smooth at first and then the initial surface wave appears a distance downstream along the jet column. The structure of the liquid jet would be successively deformed to a spiral wave in the cross airflow. When the amplitude grows large enough the liquid column is pinched into segments from the locations of wave troughs due to surface tension. With the increasing of the cross airflow velocity the aerodynamic forces, instead of the surface tension, begin to play an important role in the column breakup process. The liquid column is disintegrated by the cutting of the aerodynamic forces. The smooth length defined as the distance from where initial surface wave appears to the nozzle exit is correlated with the test operation parameters. The smooth length will be increased with the increasing of the jet injection velocity and decreased with the increasing of airflow velocity. The liquid jet column will bend and fluctuate in the crossflow and the normalized fluctuation displacement of the liquid column is correlated with the test operation parameters. The results depict that the increasing of jet injection velocity will diminish the jet column fluctuation whereas the increasing of airflow velocity will enhance it. The liquid column breakup points also fluctuate in the cross airflow. The coordinates of the time-averaged breakup locations are correlated with the liquid-to-air momentum ratio. The equation of the near-field liquid column trajectory curve before the column breakup point is concluded. The curves based on the equation agree well with the tested results.