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

TL;DR

This study investigates turbulent fountains in stratified media, identifying coherent structures and transport barriers using Lyapunov exponents, and applies findings to improve a technological device by understanding turbulence effects.

Contribution

It introduces a novel analysis of flow organization and transport barriers in turbulent fountains using finite-time Lyapunov exponents, and links turbulence to device efficiency.

Findings

Identification of self-similar coherent structures in turbulent fountains

A criterion for delimiting the fountain boundary surface

Turbulence enhances efficiency in the Selective Inverted Sink

Abstract

We analyse the flow organization of turbulent fountains in stratified media under different conditions, using three-dimensional 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.