Turbulent gravity currents are produced when a finite volume of dense fluid is rapidly released from a source above a horizontal boundary into an environment of lower density. The dense fluid propagates horizontally under gravity along the lower boundary of the flow domain by displacing the original fluid in place. Owing to the considerable importance of gravity currents in many geophysical and environmental flows, their dynamics have been studied in some detail, using a combination of laboratory experiments and mathematical models. Important applications have been described by many authors (Simpson 1997) and, amongst other phenomena, include: the dynamics of cold fronts; the spread of dense gas following release from a vessel, for example in an explosion; the dynamics of submarine turbidites, which are dilute particle-laden flows (Buckee & Kneller 2000); and volcanic ash flows (Sparks et al. 1997). In the context of many of the above flows, the propagation speed and the density structure of the flow as it spreads from the source are of considerable interest. The key advance in this work is a quantitative assessment of the dilution of a two-dimensional gravity current by mixing of the fluid originally ahead of the current and displaced by the current: to this end, we combine new laboratory experiments with a new theoretical model.

Diana Sher and Andrew W. Woods, Journal of Fluid Mechanics, Volume 784, pp 130-162 (2015)