Small scale aspects of flows in proximity of the turbulent/non-turbulent interface

TL;DR

This study investigates small-scale flow properties near the turbulent/non-turbulent interface in Newtonian fluids, using advanced particle tracking and simulations to understand entrainment mechanisms without strong mean shear.

Contribution

It provides the first detailed analysis of small-scale turbulence characteristics near the interface using combined 3D-PTV and DNS methods.

Findings

Striking differences between small-scale strain and enstrophy.

Entrainment primarily driven by viscous forces originating in strain.

Distinct flow behaviors identified in turbulent, intermediate, and non-turbulent regions.

Abstract

The work reported below is a first of its kind study of the properties of turbulent flow without strong mean shear in a Newtonian fluid in proximity of the turbulent/non-turbulent interface, with emphasis on the small scale aspects. The main tools used are a three-dimensional particle tracking system (3D-PTV) allowing to measure and follow in a Lagrangian manner the field of velocity derivatives and direct numerical simulations (DNS). The comparison of flow properties in the turbulent (A), intermediate (B) and non-turbulent (C) regions in the proximity of the interface allows for direct observation of the key physical processes underlying the entrainment phenomenon. The differences between small scale strain and enstrophy are striking and point to the definite scenario of turbulent entrainment via the viscous forces originating in strain.