Spheres settling in an Oldroyd-B fluid*

In this talk we present a numerical study of two balls settling in a vertical channel  with a square cross-section filled with an Oldroyd-B fluid. Two initial configurations have been studied: two balls released side by side and one atop the other. For the side by side initial configuration, two balls may stay apart and interact periodically or form a vertical chain. For the initial configuration with one ball atop the other, we have obtained that either  the trailing ball catches up the leading one to form a  vertical chain or two balls separate with a stable final distance as observed experimentally  in Boger fluid.