Dispersion and transport near shear interfaces

Shear fronts and vorticity interfaces persist in turbulent flows over relatively long time scales and may locally block the transfer, whereas when present in a coherent structure, they may transport fluid over large distances. These structures are generally characterised by a local region of intense vorticity, they play an important role for transport and mixing properties in turbulence and have attracted an increasing attention over the past decades. Though their exact form and shape may differ from one flow to another, they are now often referred to as Turbulence/ Non-Turbulent Interfaces, (TNTI’s) and Turbulence/ Turbulence interfaces (TTi’s).

In this project we are interested in the dynamics of these vorticity interfaces and the role they play for dispersion and transport of active particles in a turbulent fluid. Observations in geophysical as well as industrial flows have shown that particles can be captured within monopolar or dipolar vortex structures, and accumulate near stagnation points that are often present at shear fronts. Though these structures have been observed in turbulent jets as part of a turbulent flow, a systematic study on these structures in isolation, and their interaction with a turbulent environment, as well as their relevance for particle dispersion, is still lacking.

The aim of the present collaboration is to investigate the behaviour of an artificially generated and well-controlled vorticity interface (or coherent structure) in a turbulent environment. This will allow for a better modelling of its dynamics and its influence on the dispersion of particles, and is therefore relevant for the knowledge about the dispersion of pollutants in general. In a more recent context, it applies to the dispersion of viruses, the prediction of recirculation pockets, and the longevity of filaments that may contain a relatively high concentration of pollutants.