Semi-collapse of turbulent fountains in stratified media and the mechanisms to control their dynamics

Turbulent fountains are widespread natural phenomena with numerous industrial applications. Extensive research has focused on the temporal evolution and maximum height of these fountains, as well as their dependence on Reynolds and Froude numbers. However, the minimum height of the surrounding ambient fluid, which is removed by the fountain due to the entrainment effect, has received little attention. In this study, we investigate the dependence of this minimum height on the characteristics of the fountain and demonstrate how to control it. Our findings present important implications for technological applications of turbulent fountains, particularly in contaminant withdrawal. We discuss the potential of our results to improve the efficiency of such applications.Comment: 16 pages, 10 figure

The interaction between two spheres falling in a viscoelastic fluid

The time evolution of the distance between two identical spheres falling in a viscoelastic fluid has been analyzed exper- imentally. The working fluid was a dilute solution of polyacry- lamide in an aqueous solution of glycerin. Several concentra- tions of polyacrylamide and glycerin have been used in order to analyze fluids with different viscoelastic properties. Two experi- mental configuration allow analyzing the effect of the boundary conditions. A CCD camera was used to record the movement of the spheres allowing the computation of evolution of the space separation between them. It has been found that beyond cer- tain critical initial elapsed time (tdc) the distance between the spheres grows in time, while the distance decrease for elapsed times smaller than the tdc. Reduction of the shear-thinning ef- fect tends to eliminate the repulsion interaction.Papers presented to the 12th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Costa de Sol, Spain on 11-13 July 2016

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

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