Energetic Bubble Plumes in Arbitrary Stratification

Abstract

Field and laboratory experiments were performed to investigate the mixing induced by energetic point‐source bubble plumes in water columns of arbitrary stable stratification. Published data from various sources were also used in the present study to increase the parameter range. It was found that the bubble‐plume surface signatures were marked by a central unsteady core consisting of an air‐water mixture, surrounded by an annular up‐thrusting flow consisting of water only. Outside this, the rising plume water spread radially, plunged below the surface, and then flowed outward as an intrusive gravity current at a level of neutral buoyancy. By equating the observed arbitrary stratification to a linear profile of equal potential energy, the radial extent of the plunge point and the net detrainment rate could be parameterized using natural scales of the problem. These formulas were verified using field and laboratory data, and may thus be used in air‐diffuser design procedures.