Negatively buoyant vertical jets

When a continuous jet of dense fluid is ejected vertically upwards into less dense surroundings it proceeds initially upwards, increasing in size and slowing down. The buoyancy force then becomes important, causing the plume to slow down even more and then, aRer reaching its maximum height, it falls down as an annular plume around the inner rising jet. This flow structure has been modelled both as a “double plume” (an inner rising circular forced plume and an outer sinking annular plume) on a computer and also in a laboratory experiment. This type of double plume structure has been invoked in the past to model the flow of dense salty water from the sea-bed (Turner and Gustafson (1978)), plumes driven by a source of bubbles in a stratified environment (McDougall (1978)) and cumulonimbus convection in the atmosphere (Berson and Baird (1975)).