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Abstract: We present direct numerical simulations of turbulent channel flow withpassive Lagrangian polymers. To understand the polymer behavior we investigatethe behavior of infinitesimal line elements and calculate the probabilitydistribution function PDF of finite-time Lyapunov exponents and from them thecorresponding Cramer-s function for the channel flow. We study the statisticsof 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-sfunction to define the Weissenberg number precisely such that we observecoil-stretch transition at $\Wi\approx1$. We find agreement with earlieranalytical predictions for PDF of polymer extensions made by Balkovsky, Fouxonand Lebedev Phys. Rev. Lett., 84, 4765 2000. for linear polymers Oldroyd-Bmodel with $\Wi<1$ and by Chertkov Phys. Rev. Lett., 84, 4761 2000. fornonlinear FENE-P model of polymers. For $\Wi>1$ FENE model the polymer aresignificantly more stretched near the wall than at the center of the channelwhere the flow is closer to homogenous isotropic turbulence. Furthermore nearthe wall the polymers show a strong tendency to orient along the stream-wisedirection of the flow but near the centerline the statistics of orientation ofthe polymers is consistent with analogous results obtained recently inhomogeneous and isotropic flows.



Autor: Faranggis Bagheri KTH, mechanics, Dhrubaditya Mitra NORDITA, Prasad Perlekar Eindhoven University of Technology, Luca Brandt KTH,

Fuente: https://arxiv.org/



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