Plumes in uniform flow with two-layer stratification

ABSTRACT Plumes occur when a fluid is discharged into another fluid with different density, such as pollutants in the atmosphere. In this work, an experimental study was carried out in a water tank and a mathematical modelling using the integral approach was performed to investigate the flow generated by saline plumes in uniform flow with two-layer stratification. The results indicated that the upper layer’s height (less dense) increased with the outflow from the lower layer, and decreased with the buoyancy flux of the plume, confirming the results available in the literature for systems supplied by point sources (non-uniform sources). After fitting the parameters of the classical theory for turbulent plumes, it was possible to predict the interface’s height with a maximum deviation of ±8%, and a Nash-Sutcliffe coefficient of 0.98. This indicates that the uniform flow did not affect significantly the plumes’ hydrodynamics compared to previous studies. On the other hand, unlike the systems supplied by point sources, the streamlines obtained through the injection of dye into the uniform flow followed a potential flow pattern, with all the flow being directed to the plume, therefore not mixing at the interface between the two layers. Thus, based on the principle of mass conservation, equations were proposed to generate the streamlines around the plumes, which were validated with the experimental data. Finally, practical applications of the proposed model in natural ventilation in buildings and pollutant discharges in the atmosphere were presented.