I am interested in how the Herschel-Bulkley model works in CFX. When I do the calculations by hand, I have to explicitly find the yield surface in the fluid then divide my region into two pieces for the velocity calculations. How does CFX calculate the yield surface, if at all? The Herschel-Bulkley equation gives an infinite viscosity for parts of the flow. Having an infinite viscosity would give numerical problems, so what modifications to the Herschel-Bulkley equations have been made to make the numerical solution tractable? How are the material parameters, yield stress and min/max shear strain rate values, used?