Physics – Fluid Dynamics
Scientific paper
2010-11-16
Physics
Fluid Dynamics
to be submitted to Phys. Rev. E
Scientific paper
We present direct numerical simulations~(DNSs) of turbulent channel flow with passive Lagrangian polymers. To understand the polymer behavior we investigate the behavior of infinitesimal line elements and calculate, for the first time, the PDF of finite-time Lyapunov exponents and from them the corresponding Cramer's function for the channel flow. We study the statistics of polymer elongation for both the Oldroyd-B model (for Weissenberg number Wi <1) and the FENE model. We use the location of the minima of the Cramer's function to define the Weissenberg number precisely such that we observe coil-stretch transition at Wi \approx 1. For linear polymers (Oldroyd-B model), with Wi <1, we find that the PDF of polymer extensions shows power-law behavior with an exponent consistents with earlier analytical results [1]. For Wi>1 (FENE model) the polymer are significantly more stretched near the wall than at the centre of the flow. Furthermore near the wall the polymers show a strong tendency to orient along the stream-wise direction of the flow but near the centerline the statistics of orientation of the polymers is consistent with analogous results obtained recently in homogeneous and isotropic flows [2].
Bagheri Faranggis
Brandt Luca
Mitra Dhrubaditya
Perlekar Prasad
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