A laboratory study of buoyant plumes in laminar and turbulent crossflows

The results of laboratory experiments of buoyant plumes in crossflows are presented. Specific comparisons are made of plume evolution for laminar and weakly turbulent crossflows for otherwise identical flow parameters to establish that plume dilution rates differ significantly even for weakly turbulent crossflows. Decaying, grid-generated turbulence constituted the flow field of the weakly turbulent crossflow. Measurements comprised analyses of flow visualization, hot-film anemometry and conductivity probe data. Plume thicknesses and widths are found to be greater for turbulent crossflows, although they both grow as χ2/3 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 dilution for buoyant plumes in a laminar crossflow, that dilutions of plumes 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 integral model with a modified β, the entrainment coefficient, which relates the ratio of dissipation rates within and outside the plume.