Small scale characteristics of turbulent/non-turbulent interfaces of viscoelastic fluids

New direct numerical simulations (DNS) of turbulent fronts bounded by irrotational regions in viscoelastic fluids are carried out in order to investigate the characteristics of the turbulent/non-turbulent interface (TNTI) layer. The viscoelastic fluid analysed here consists of a Newtonian solvent carrying a very small fraction of long chained polymer molecules, which is described using the finitely extensible nonlinear elastic constitutive equation closed with the Peterlin approximation (FENE-P), and the new simulations attain the highest Reynolds numbers yet observed for this fluid, in simulations or experiments. The work focusses on the small scale aspects associated with the entrainment mechanism that exists at the edges of wakes, jets, mixing layers and boundary layers. Specifically, we analyse the enstrophy and kinetic energy dynamics and the behaviour of the invariants of the velocity gradient tensor and their role in the turbulent entrainment mechanism in TNTI layers from viscoelastic fluids.