Fountains in industry and nature

Abstract

Turbulent fountains arise when a localized flow, free to entrain fluid from its surroundings, is opposed by a buoyancy force. This review cites numerous examples to highlight their wide occurrence in nature and in industry. The breadth of the literature reviewed is significant, drawing from over half a century of progress, and we initially focus on axisymmetric, small density difference fountains in uniform environments. Many aspects of their rich dynamical behavior, including that of their rise heights and fluctuations in height, are described and encapsulated within the fountain classification presented. Drawing from detailed experimental data sets, dimensional considerations, recent numerical studies, and numerous successful extensions to the original theoretical model for a fountain, we implicitly highlight the current predictive capability offered. The turbulent entrainment of ambient fluid, the effects of environmental stratification, and the role of confinement on a fountain are all discussed. Finally, we suggest future avenues of research.