CFD Online Discussion Forums - Initial yield stress for Hershel-Bulkley model

Hi All

I am attempting to simulate 2D channel flow of a Herschel-Bulkley fluid. It is a simple problem, but my results cannot match with literature values.
1. The initial yield stress leads to lower velocity comparing with theory values. Sometime, it also leads to continuity convergence problem.
2. The velocity profile cannot show slug-flow zone that is predicted by theory.

I have used the Herschel-Bulkley model in FLUENT and UDF to define the viscosity. Both of two methods have the same issues.

Any suggestions? Thanks in advance!:)