The effect of an ambient flow on the spreading of a viscous gravity current

The influence of an external laminar flow on the spreading of a viscous gravity current moving over a horizontal floor is studied theoretically and experimentally. The viscous stress exerted by the ambient flow drives the viscous gravity current streamwise with a velocity proportional to the local height of the current. The one-way coupling between the ambient flow and the spread of the current is examined. Similarity and numerical solutions are developed to describe viscous gravity currents spreading from line and point sources. An experimental study of the spreading of viscous gravity currents issuing from a point source in a channel flow, for both constant-flux and instantaneous releases, confirms the essential character of this description.