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

Abstract

The work reported below is the first of its kind to study the properties of turbulent flow without strong mean shear in a Newtonian fluid in proximity of the turbulent/nonturbulent interface, with emphasis on the small-scale aspects. The main tools used are a three-dimensional particle tracking system allowing one to measure and follow in a Lagrangian manner the field of velocity derivatives and direct numerical simulations. The comparison of flow properties in the turbulent (A), intermediate (B), and nonturbulent (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.