Jet Formation in a Tube

A vertical cylinder is partially immersed in a water-filled container and pressurized to lower the fluid level inside the tube. A sudden release of the pressure in the tube creates a singularity on top of the rising free surface: At the very beginning of the process a jet emerges at the center of the surface, the strength of which strongly depends on the initial shape of the meniscus. Here we study the jet formation process. The time-evolution of the complex shape of the free surface and the flow around the cylinder are analyzed using high-speed imaging, velocimetry and numerical simulations.