Polymer stress statistics in the near-wall turbulent flow of a drag-reducing solution

The direct numerical simulation of the turbulent flow of a dilute polymer solution in a plane channel at low Reynolds number has been performed in order to investigate tye reduction in friction drag. The polymer solution has been represented as a continuum fluid whose constitutive equations have been derived on the basis of a modified FENE-P dumbbell model. The mean polymer dynamics in the turbulent flow have been studied through statistical moments of the configuration tensor. The analysis of the results obtained suggests that polymers can be effective in terms of drag reduction only if their relaxation time is comparable to the charachteristic time of their convection in the normal-to-the-wall dicerction within near-wall turbulent structures. The energy budget of the normal components of the Reynolds stress tensor suggests that elongated polymers inhibit turbulence regeneration by opposing pressure redistribution from streamwise to cross-flow velocity fluctuations.