  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).
