Flapping line fountains

Results of an experimental study are presented on a turbulent line fountain formed when a dense saline solution is ejected steadily upwards from a slender rectangular slot into a lighter aqueous environment. A combination of flow visualisations and measurements reveal the complex three-dimensional structure of these fountains. The flow is interrogated by simultaneously viewing it from above and from the side. These views reveal that the fountain flaps about the slot in distinct patterns. Insights into the mechanism causing the flapping were acquired by examining the internal structure of the fountain along vertical sections cutting across the slot. Measurements of rise height and lateral excursion of flapping events, alongside their associated spatial and temporal statistics, are discussed to show that a single driving mechanism underlies the motion.