RECIRCULATING FLOW GENERATED BY LINE-SOURCE BUBBLE PLUMES

The flow structure in the far field of line-source bubble plumes in sh allow water is investigated. Recirculating cells form at both sides of the plume. Cell lengths, as given by other investigators, vary betwee n 2.5 and 7 times the water depth. The variations are caused in part b y different definitions of cell length and by the different geometries of the experimental setups. In the present study the influence of the cross-sectional geometry of the channel on the cell structure is inve stigated experimentally. Experiments have been made in a tank with dim ensions 1 x 1 x 40 m. A dividing wall has been used to vary the width of the channel. Flow velocities in the plane of symmetry have been mea sured by use of a propeller anemometer. These results have been supple mented by measurements with an acoustic Doppler velocimeter, Different criteria for the definition of the cell length have been examined, su ch as the surface flow rate, the surface velocity, and surface flow pa tterns. The velocity distributions show a strong influence of the cros s-sectional geometry. For values of the depth-to-width ratio higher th an unity the cell length is rather short. In a very wide channel three -dimensional effects occur. The aspect ratio is found to be a characte ristic parameter for the flow. For an analysis of the flow in the far field, a model based on an analogy of the surface flow with a free (ha lf) jet with counterflow is proposed.