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Seventh International Symposium on Turbulence and Shear Flow Phenomena
July, 28-31, 2011, Ottawa Convention Centre, Ottawa, Canada

DOI: 10.1615/TSFP7

MODIFICATION OF HAIRPIN AUTO-GENERATION PROCESS IN TURBULENT CHANNEL FLOWS DUE TO POLYMER STRESS

pages 1-6
DOI: 10.1615/TSFP7.440
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ABSTRACT

To study the influence of dynamical interactions between turbulent vortical structures and polymer stress on turbulent friction drag reduction, a series of simulations were performed for channel flow at Reτ = 395. The initial eddy extracted by the conditional averages for the Q2 event from fully turbulent Newtonian flow is self-consistently evolved in the presence of polymer stresses by utilizing the FENE-P model (finitely extensible nonlinear elastic-Peterlin). The initial polymer conformation fields are given by the solutions of FENE- P model equations for the Newtonian mean shear. For a relatively low Weissenberg number, defined as the ratio of fluid relaxation time to the time scale of viscous diffusion, (Weτ = 50) the generation of new vortices is inhibited by polymer-induced counter torques, which results in fewer vortices in the buffer layer. However, the head of primary hairpin is unaffected by the polymer stress. For larger values of Weτ( ≥ 100), the hairpin head becomes weaker and vortex auto-generation and Reynolds stress growth are almost entirely suppressed.

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