Turbulent pipe flows of dilute polymer solutions

Direct numerical simulation of the Navier-Stokes equation with Lagrangian transport, and back-reaction, of millions of polymer molecules is employed to investigate the dynamics of a turbulent pipe flow of dilute polymer solutions. The drag-reducing capability of the polymers increases with the Weissenberg number (ratio of polymer to fluid time scale) and is not significantly affected by the Reynolds number. A new parameter, namely the polymer Reynolds number is defined as the ratio of the solvent inertial forces and the polymer viscous induced forces. Turbulence dynamics is significantly affected by slight changes in this parameter, with a transition from a Newtonian-like wall-bounded turbulence to a different state with large velocity fluctuations and turbulent kinetic energy in the bulk.