Flow of viscoplastic fluids in eccentric annular geometries

A classification of flowfields for the flow of a Bingham fluid in general eccentric annular geometries is presented. Simple arguments show that a singularity can exist in the stress gradient on boundaries between zones with yielded and un-yielded fluid respectively. A Finite Element code is used to verify this property of the Bingham fluid. An analytical solution for the flowfield in case of small eccentricities is derived.