Buoyant slot jets into stagnant or flowing environments

Abstract

The diffusion following the release of a buoyant slot jet into a confined, uniformly flowing environment has been studied. A dimensionless analysis reveals the complexity of the problem; there are in general four governing dimensionless numbers. However, if the overall mixing and not the details of the process of diffusion is of importance, we can define basic flow regimes using a reduced number of parameters. Experiments were conducted first with a horizontal, buoyant slot jet into stagnant, ambient fluid. Observed trajectories and centerline dilutions were in good agreement with existing theories. In addition, two sets of experiments were perform ed with a vertical and a horizontal buoyant slot jet issuing into a uniformly flowing stream. A two-layer flow analysis provided the rationale for a classification of flow regimes. It was found that the mechanism of upstream intrusion of jet effluent is characterized primarily by a gross densimetric Froude number based on the ambient flow velocity and the buoyancy flux from the source. However, the formation of an upstream wedge may be hampered due to the effect of initial flux of momentum in the downstream direction. When the buoyant slot jet cannot entrain all the oncoming flow, while maintaining the typical jet or plume behavior, then the jet flow pattern breaks up and there is efficient mixing close to the source.