Experimental examination of nozzle geometry on water jet in a subsonic crossflow

Abstract

The effect of a nozzle’s internal geometry was studied experimentally to determine the breakup of the emitted water jet when it was injected perpendicularly into a quiescent atmosphere or a subsonic air crossflow. The nozzle’s diameter, nominal surface roughness, length-to-diameter ratio and contraction angle were varied, together with the injection pressure, to find the water column’s breakup length. Photographs of the water jet at the nozzle’s exit, gave a clue as to identify the occurrence of cavitation and a hydraulic flip. On the other hand the water column’s breakup length and trajectory, in a subsonic crossflow, were measured by using a stroboscope in conjunction with a high speed CCD camera. Results agreed with previous literature that the breakup length grew with greater liquid/air momentum flux ratios for non-cavitating flows. This was true regardless of the injector nozzle. The rate of increase decreased at the inception of cavitation. On the other hand even shorter breakup lengths were observed at the inception of a hydraulic flip due to the detachment of the water jet from the internal surface of the nozzle. Increasing the nozzle’s length-to-diameter ratio eliminated the occurrence of hydraulic flip. The jet’s trajectory was correlated with the liquid/air momentum flux ratio and the nozzle’s exit diameter. The results showed that higher water jet trajectories were measured under non-cavitating conditions. Even shorter jet trajectories were measured at the inception of a hydraulic flip.