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Buoyant jets in shallow water with a crossflow Labridis, Christodoulos


A common way to dispose of sewage or heated waste water is to discharge it through a submerged outfall located at the bottom of the receiving water. Such outfalls are usually situated in shallow coastal water. The dispersion and dilution of these buoyant jets depends greatly both on the shallowness of the ambient water and the presence of any current. A series of experiments with vertical buoyant jets in shallow water with a crossflow, were conducted in order to understand better the effect of the various parameters. Flow visualization and temperature probes were used. The results were compared to theoretical equations and previous results. The basic parameters of the problem are the ratio of the ambient to the jet velocity (less than 0.5), the ratio of the ambient depth to the jet diameter (less than 10) and the jet Froude number. It is shown that for shallow water jets the buoyancy of the jet doesn't have time to affect its dilution. The use of the densimetric Froude number is, therefore, not necessary and often misleading. Three flow regimes were identified according to these parameters. A crossflow dominated flow (maximum surface dilution), a typical shallow water flow with an upstream recirculation zone and a fountain-like flow (minimum surface dilution). It is, thus, possible to predict the flow regime of an outfall (and, therefore, the minimum surface dilution), for given ambient conditions. It is also possible to study the effect that a change of a basic parameter, will have on the flow regime.

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