Elucidating coherent structures, transport barriers and entrainment in turbulent fountains in stratified media

Abstract

We analyse the flow organization of turbulent fountains in stratified media under different conditions, using threedimensional finite-time Lyapunov exponents. The dominant Lagrangian coherent structures responsible for the transport barriers in three different configurations suggest a self-similarity behaviour. After proposing a criterion for delimiting the boundary surface of the uprising fountain, we quantify the entrainment and re-entrainment rates under fully developed flow conditions using the proper coefficients. Finally, our analysis was applied to the Selective Inverted Sink, a technological application of turbulent fountains, identifying turbulence as the primary mechanism favouring the device’s efficiency.