Entrainment by adhered two-dimensional plumes

Measurements are presented of the variation with height of the mass flux of two-dimensional, adhered smoke plumes created by horizontal smoke layers that flow below a ceiling and spill into a hall near one of its walls, and of the effect of the Froude number (Fr) of these horizontal layers on the shape of the rising plumes in the hall. The measurements suggest that such smoke layers would usually rise vertically; either adhered to the wall, when Fr is roughly <1, or as a free plume, when Fr is roughly >1, and that the entrainment of ambient air to these plumes is approximately proportional to their free perimeter. It is also shown that in both cases, the variation at large heights of the mass flux of these plumes varies approximately as that of a similar, weak plume from a virtual line source, whose location can be estimated by a previously suggested simple model. Possible effects of downstands in the ceiling and of boundary conditions in the hall are also discussed.