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Turbulent miscible fountains - height, rhythm and scales.
If you have a question about this talk, please contact ROBERTA TRUPIANO.
Sandwiches provided at 13:00, seminar begins 13:15.
Miscible turbulent fountains dilute the concentration of any contaminants present in the vertical release of fluid, including for example the buoyancy scalar (temperature or solute concentration). This process occurs through the action of turbulent entrainment and is similarly present in positively buoyant plumes. Unlike plumes, however, fountains describe a vertical release of fluid such that the density difference, between the source fluid and the environment, gives rise to a buoyancy force which opposes the source momentum. As such, fountains travel vertically within the environment before the buoyancy acts to reverse the flow, which then turns back towards the source. In this way, fountains dilute the properties of the source fluid over a limited, and known, vertical extent; thereby offering the potential to assist in any situation where localised mixing is required. Fountain-induced mixing has previously been applied in low-energy ventilation schemes but, with better understanding, offers scope to contribute in a number of applications.
Results will be presented from an experimental study in which fountains were generated by ejecting dense saline solution vertically upwards into a freshwater environment. An investigation into fountain rise height proposes a new classification of fountains. Analysis of the turbulent fluctuations in fountain height identifies dominant a time scale within each fountain class, these time scales are consistent with the dominant length (height) scales and physically apparent velocity scales. On dimensional grounds, we develop expressions for the fluxes of volume, momentum and buoyancy within the fountain outflow (the reverse-flow in the plane of the source) and show these fluxes attain a constant ratio which is invariant with the fountain’s source conditions.
This talk is part of the Fluid Mechanics (CUED) series.
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