Simulated polymer stretch in a turbulent flow using Brownian dynamics
|V. E. TERRAPON a1, Y. DUBIEF a2, P. MOIN a1a2, E. S. G. SHAQFEH a1a3 and S. K. LELE a1|
a1 Mechanical Engineering Department, Stanford University, Stanford, CA 94305, USA
a2 Center for Turbulence Research, Stanford University, Stanford, CA 94305, USA
a3 Department of Chemical Engineering, Stanford University, Stanford, CA 94305, USA
We examine the phenomenon of polymer drag reduction in a turbulent flow through Brownian dynamics simulations. The dynamics of a large number of single polymer chains along their trajectories is investigated in a Newtonian turbulent channel flow. In particular, the FENE, FENE-P and multimode FENE models with realistic parameters are used to investigate the mechanisms of polymer stretching. A topological methodology is applied to characterize the ability of the flow to stretch the polymers. It is found using conditional statistics that at moderate Weissenberg number Wi the polymers, that are stretched to a large fraction of their maximum extensibility, have experienced a strong biaxial extensional flow. When Wi is increased other flow types can stretch the polymers but the few highly extended molecules again have, on average, experienced a biaxial extensional flow. Moreover, highly extended polymers are found in the near-wall regions around the quasi-streamwise vortices, essentially in regions of strong biaxial extensional flow.
(Received August 23 2003)
(Revised January 16 2004)