Small scale dynamics of a shearless turbulent/non-turbulent interface in dilute polymer solutions

TL;DR

This study investigates how dilute polymer solutions influence the small-scale dynamics of turbulent/non-turbulent interfaces, revealing mechanisms that reduce vorticity stretching and entrainment in shearless turbulent flows.

Contribution

It demonstrates the effects of polymers on small-scale turbulence dynamics and validates a FENE-P model with experimental data in shearless conditions.

Findings

Polymers reduce vorticity stretching near the interface.

Polymer alignment alters strain and vorticity interactions.

Enstrophy production and entrainment are decreased by polymers.

Abstract

We study the physics of turbulent/non-turbulent interface of an isolated turbulent region in dilute polymer solutions and Newtonian fluid. The performance of a FENE-P model with a localized homogeneous forcing is verified using the specially designed experimental setup of a turbulent patch growing in water/dilute polymer solution, without mean shear and far from the walls. The results of the small scale dynamics of vorticity and strain help to reveal the key mechanism of polymer action in turbulent flows without mean shear. Modified degrees of alignment between vorticity, the polymer conformation and the rate-of-strain tensors found especially near the interface explain the reduced vorticity stretching and increased vorticity compression terms. These small scale alignments in the non-Newtonian turbulent flow thus lead to a reduced production of enstrophy and consequently to a reduced entrainment (seen as propagation or dispersion).