A HETEROGENEOUS ALTERNATING-DIRECTION METHOD FOR A MICRO-MACRO DILUTE POLYMERIC FLUID MODEL

We examine a heterogeneous alternating-direction method for the approximate solution of the FENE Fokker-Planck equation from polymer fluid dynamics and we use this method to solve a coupled (macro-micro) Navier-Stokes-Fokker-Planck system for dilute polymeric fluids. In this context the Fokker-Planck equation is posed on a high-dimensional domain and is therefore challenging from a computational point of view. The heterogeneous alternating-direction scheme combines a spectral Galerkin method for the Fokker-Planck equation in configuration space with a finite element method in physical space to obtain a scheme for the high-dimensional Fokker-Planck equation. Alternating-direction methods have been considered previously in the literature for this problem (e.g. in the work of Lozinski, Chauviere and collaborators [J. Non-Newtonian Fluid Mech. 122 (2004) 201 214; Comput. Fluids 33 ( 2004) 687-696; CRM Proc. Lect. Notes 41 (2007) 73-89; Ph. D. Thesis (2003); J. Computat. Phys. 189 (2003) 607-625]), but this approach has not previously been subject to rigorous numerical analysis. The numerical methods we develop are fully-practical, and we present a range of numerical results demonstrating their accuracy and efficiency. We also examine an advantageous superconvergence property related to the polymeric extra-stress tensor. The heterogeneous alternating-direction method is well suited to implementation on a parallel computer, and we exploit this fact to make large-scale computations feasible.