Abstract: The upper bound of polymer drag reduction is identified as a unique transitional state between laminar and turbulent flow corresponding to the onset of the nonlinear breakdown of flow instabilities.
Abstract: A novel eddy viscosity model for predicting friction drag reduction induced by polymers in turbulent wall-bounded flows is presented. The approach is based on the elliptic relaxation model modified to account for the modified Reynolds-stress equilibrium established by the presence of elastic polymer chains in the fluid. The increased wall damping of the turbulent fluctuations is obtained by modifying the pressure–strain redistribution term. Polymer solutions are represented using the Finite Extensibility Non-linear elastic FENE-P dumbbell model; only one transport equation for the elongation of the polymer chains is considered. The model reproduces the level of drag reduction observed over a wide range of rheological parameters. In addition, both the mean velocity and the turbulent fluctuations are predicted with good accuracy. The approach is computationally attractive because of its limited increase in computational cost in comparison with its Newtonian counterpart.