A comparison of line-sources of buoyancy placed near and far from a wall

Experiments are presented on turbulent buoyant free-line and wall plumes, whereby the buoyancy source is emitted from a horizontal line source, in one case free of the presence of a wall and in the other placed immediately adjacent to a wall. The dynamics of turbulent entrainment, whereby ambient fluid is mixed in to the plume, are explored. The velocity field and scalar edge of the plumes are measured. From this the time-averaged plume-width and volume flux are compared. The spreading rate, and therefore the entrainment, of the wall plume is found to be half that of the free-line plume, indicating that the wall has a significant effect on the entrainment process. Further, the volume flux of the wall plume is found to be half that of the free-line plume, indicating that larger maximum scalar concentrations are present in the wall plume. The effect that the reduced entrainment rate has on a typical heated room, via a line source of buoyancy, is demonstrated by comparing a numerical model of the developing temperature stratification within a sealed enclosure in the case of the line source near a wall and away from a wall, where in particular it is found that higher maximum temperatures are present for the case of the line source near a wall.