Kinetic energy budget in turbulent flows of dilute polymer solutions

Direct numerical simulation of a turbulent pipe flow of a realistic solution of 10(8) polymers, modelled as finitely extensible nonlinear elastic (FENE) dumbbells, and directly momen-tum coupled with the incompressible Navier-Stokes equations, are performed by means of an Eulerian-Lagrangian approach. Besides the drag reduction, the polymers significantly modify mean and turbulent kinetic energy budgets. The polymer backreaction to the sol-vent reduces the Reynolds stress and thus decreases the turbulent production and, at large Weissenberg number, the polymers act as a source of turbulent kinetic energy for y(+) > 40, leading to an increase in the dissipation. This effect is peculiar to large Weissenberg poly-mers and it is particularly apparent at a small Reynolds number. At a smaller Weissenberg number, the effect of the polymers remains confined in the buffer layer, with the kinetic energy budget not significantly altered elsewhere.