Unstable jets generated by a sphere descending in a very strongly stratified fluid

The flow around a sphere descending at constant speed in a very strongly stratified fluid ( $Fr\lesssim 0.2$ ) is investigated by the shadowgraph method and particle image velocimetry. Unlike the flow under moderately strong stratification ( $Fr\gtrsim 0.2$ ), which supports a thin cylindrical jet, the flow generates an unstable jet, which often develops into turbulence. The transition from a stable jet to an unstable jet occurs for a sufficiently low Froude number $Fr$ that satisfies $Fr/Re