Round plumes at plane surfaces

Plume models are widely used to support regulatory discharge permitting decisions and to help design outfalls. With thousands of projects worldwide, these models must be as accurate as possible. However, recent studies show that these models are subject to inaccuracies arising from the round plume assumption. For example, use of this assumption inadequately describes processes ranging from gravitational collapse to plumesurface interaction. In sharply-bending plumes, it also inadvertently introduces negative mass into the formulation. The onset of this condition is reported by EPA’s PLUMES UM model (a statement that dilution is over-estimated), but is not corrected. The round plume assumption can be modified to remove the negative mass anomaly, and to include the center-of-mass correction. Predictions strongly suggest the overlap condition is a criterion for plume lateral spreading. The successful modification reported here suggests the round plume assumption is viable for modeling behavior at unconstrained boundaries.