  We study the impact of the Peterlin approximation on the statistics of the
end-to-end separation of poly- mers in a turbulent flow. The FENE and FENE-P
models are numerically integrated along a large number of Lagrangian
trajectories resulting from a direct numerical simulation of three-dimensional
homogeneous isotropic turbulence. Although the FENE-P model yields results in
qualitative agreement with those of the FENE model, quantitative differences
emerge. The steady-state probability of large extensions is overesti- mated by
the FENE-P model. The alignment of polymers with the eigenvectors of the
rate-of-strain tensor and with the direction of vorticity is weaker when the
Peterlin approximation is used. At large Weissenberg numbers, both the
correlation times of the extension and of the orientation of polymers are
underestimated by the FENE-P model.
