Direct numerical simulation of turbulent intermediate Froude number fountain flow

Nicholas John Williamson, S. W. Armfield, W. Lin


Fountains are an important flow in many industrial and geophysical problems but the understanding of this flow at low Froude numbers is limited. In this study we use direct numerical simulation to examine two regimes of turbulent fountain flow, weak flow at Fr=2.2 and very weak flow at Fr=0.45. At Fr=0.45 buoyancy stabilises the flow and there is little entrainment of ambient fluid. Kelvin--Helmholtz instabilities are generated at the interface between the upwelling flow and the ambient fluid. At Fr= 2.2 the shear interaction between the rising and falling flow streams becomes important as it drives both large and small scale vortex structures. Large scale structures draw ambient fluid into the fountain while small scale structures exchange mass between the upflow and downflow. Periodic ejection of mass from the top of the fountain is shown to be an important dynamic in the flow. The results provided here can assist in analytical model development.

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