A LABORATORY STUDY OF BUOYANT PLUMES IN LAMINAR AND TURBULENT CROSS-FLOWS

The results of laboratory experiments of buoyant plumes in crossflows are presented. Specific comparisons are made of plume evolution for la minar and weakly turbulent crossflows for otherwise identical flow par ameters to establish that plume dilution rates differ significantly ev en for weakly turbulent crossflows. Decaying, grid-generated turbulenc e constituted the flow held of the weakly turbulent crossflow. Measure ments comprised analyses of flow visualization, hot-film anemometry an d conductivity probe data. Plume thicknesses and widths are found to b e greater for turbulent crossflows, although they both grow as x(2/3) for laminar and turbulent crossflows. The effect of turbulence in the crossflow is to increase entrainment and dilution with the consequence of lower plume trajectories. It is found, relative to the values of d ilution for buoyant plumes in a laminar crossflow, that dilutions of p lumes in a weakly turbulent crossflow (with kinetic energy dissipation rates two orders of magnitude smaller than internal plume dissipation rates) were greater by 33%. Trajectories can be predicted by an integ ral model with a modified beta, the entrainment coefficient, which rel ates the ratio of dissipation rates within and outside the plume.